Influences on the Functional Behavior of Great Arteries during Orthostasis / Gravidade Influencia o Comportamento Funcional das Grandes Artérias Durante a Ortostase

Abstract Background: Arterial compliance reduction has been associated with aging and hypertension in supine position. However, the dynamic effects of orthostatism on aortic distensibility has not been defined. Objective: We sought to determine the orthostatic influence and the interference of age, blood pressure (BP) and heart rate (HR) on the great arteries during gravitational stress. Methods: Ninety-three healthy volunteers (age 42 ± 16 years). Carotid-femoral pulse wave velocity (PWV) assumed as aortic stiffness was assessed in supine position (basal phase), during tilt test (TT) (orthostatic phase) and after return to supine position (recovery phase). Simultaneously with PWV acquisition, measures of BP and HR rate were recorded. Results: PWV during TT increased significantly compared to the basal and recovery phases (11.7 ± 2.5 m/s vs. 10.1 ± 2.3 m/s and 9.5 ± 2.0 m/s). Systolic BP (r = 0.55, r = 0.46 and r = 0.39) and age (r = 0.59, r = 0.63 and r = 0.39) correlated with PWV in all phases. The significance level for all tests was established as α = 0.05. Conclusion: We conclude that there is a permanent increase in PWV during orthostatic position that was returned to basal level at the recovery phase. This dynamic pattern of PWV response, during postural changes, can be explained by an increase in hydrostatic pressure at the level of abdominal aorta which with smaller radius and an increased elastic modulus, propagates the pulse in a faster way. Considering that it could increase central pulse reflection during the orthostatic position, we speculate that this mechanism may play a role in the overall adaptation of humans to gravitational stress.

Resumo Fundamento: A redução da complacência arterial tem sido associada ao envelhecimento e à hipertensão na postura supina. Entretanto, os efeitos dinâmicos do ortostatismo na distensibilidade aórtica não foram definidos. Objetivo: Determinar a influência ortostática e a interferência da idade, pressão arterial (PA) e frequência cardíaca (FC) sobre as grandes artérias durante o estresse gravitacional. Métodos: Noventa e três voluntários saudáveis (idade de 42 ± 16 anos). A velocidade da onda de pulso carotídeo-femoral (VOP), assumida como rigidez aórtica, foi avaliada na posição supina (fase basal) durante o teste de inclinação (TT) (fase ortostática) e após o retorno à posição supina (fase de recuperação). Simultaneamente à aquisição da PWV, registrou-se as medidas de PA e FC. Resultados: A VOP durante o TT aumentou significativamente em comparação com as fases basal e de recuperação (11,7 ± 2,5 m/s vs. 10,1 ± 2,3 m/se 9,5 ± 2,0 m/s). PA sistólica (r = 0,55, r = 0,46 e r = 0,39) e idade (r = 0,59, r = 0,63 e r = 0,39) correlacionaram-se com a VOP em todas as fases. O nível de significância para todos os testes foi estabelecido como = 0,05. Conclusão: Observou-se um aumento permanente da VOP durante a postura ortostática, que retornou ao nível basal na fase de recuperação. Esse padrão dinâmico de resposta da VOP, durante as alterações posturais, pode ser explicado pelo aumento da pressão hidrostática no nível da aorta abdominal que, com raio menor e aumento do módulo de elasticidade, propaga o pulso de maneira mais rápida. Considerando-se que poderia aumentar a reflexão do pulso central durante a posição ortostática, podemos especular que esse mecanismo pode desempenhar um papel na adaptação global do humano ao estresse gravitacional.

Women with Polycystic Ovarian Syndrome Exhibit Reduced Baroreflex Sensitivity That May Be Associated with Increased Body Fat / Mulheres com Síndrome do Ovário Policístico Apresentam menor Sensibilidade Barorreflexa, a Qual Pode Estar Associada ao Aumento da Gordura Corporal

Abstract Background: Polycystic ovarian syndrome (PCOS) women have a high prevalence of obesity and alterations in cardiovascular autonomic control, mainly modifications in heart rate variability (HRV) autonomic modulation. However, there are few studies about other autonomic control parameters, such as blood pressure variability (BPV) and baroreflex sensitivity (BRS). In addition, there are still doubts about the obesity real contribution in altering autonomic control in these women. Objective: To investigate BPV and BRS autonomic modulation alterations in PCOS women, as well as, to evaluate whether these alterations are due PCOS or increased body fat. Methods: We studied 30 eutrophic volunteers [body mass index (BMI) < 25 kg/m2] without PCOS (control group) and 60 volunteers with PCOS divided into: eutrophic (BMI < 25 kg/m2, N = 30) and obese women (BMI > 30 kg/m2, N = 30). All volunteers were submitted to anthropometric evaluation, hemodynamic and cardiorespiratory parameters record at rest and during physical exercise, analysis of HRV, BPV and spontaneous BRS. The differences in p less than 5% (p < 0.05) were considered statistically significant. Results: Related to eutrophics groups, there were no differences in autonomic parameters evaluated. The comparison between the PCOS groups showed that both PCOS groups did not differ in the BPV analysis. Although, the obese PCOS group presented lower values of spontaneous BRS and HRV, in low frequency and high frequency oscillations in absolute units. Conclusion: Our results suggest that obesity did little to alter HRV in women with PCOS, but it may influence the spontaneous BRS.

Resumo Fundamento: As mulheres com síndrome do ovário policístico (SOP) apresentam alta prevalência de obesidade e alterações no controle autonômico cardiovascular, principalmente modificações na modulação autonômica da variabilidade da frequência cardíaca (VFC). No entanto, existem poucos estudos sobre outros parâmetros de controle autonômico, como a variabilidade da pressão arterial (VPA) e a sensibilidade barorreflexa (SBR). Além disso, ainda há dúvidas sobre a real contribuição da obesidade na alteração do controle autonômico dessas mulheres. Objetivo: Investigar as alterações da modulação autonômica da VPA e SBR em mulheres com SOP, bem como avaliar se essas alterações se devem à SOP ou ao aumento da gordura corporal. Métodos: Foram estudadas 30 voluntárias com peso normal [índice de massa corporal (IMC) < 25 kg/m2] sem SOP (grupo controle) e 60 voluntárias com SOP, divididas em: mulheres com peso normal (IMC < 25 kg/m2, N = 30) e mulheres obesas (IMC > 30 kg/m2, N = 30). Todas as voluntárias foram submetidas à avaliação antropométrica, com registro de parâmetros hemodinâmicos e cardiorrespiratórios em repouso e durante exercício físico, e análise da VFC, VPA e SBR espontânea. As diferenças de p < 5% (p < 0,05) foram consideradas estatisticamente significantes. Resultados: Em relação aos grupos com peso normal, não houve diferenças nos parâmetros autonômicos avaliados. A comparação entre os grupos SOP mostrou que ambos os grupos não diferiram na análise da VPA. No entanto, o grupo SOP obeso apresentou menores valores de SBR espontânea e VFC nas oscilações de baixa e alta frequências, em unidades absolutas. Conclusão: Nossos resultados sugerem que a obesidade pouco influenciou a VFC em mulheres com SOP, mas pode afetar a SBR espontânea.

Baroreflex sensitivity in frailty syndrome

Frailty is related to a decrease in the physiological reserves, which causes difficulties in maintaining homeostasis. An example of physiological mechanisms for cardiovascular homeostasis is the baroreflex. The aim of this study was to compare baroreflex among frail, prefrail, and nonfrail individuals, in supine and orthostatic positions. Community-dwelling older adults were evaluated and categorized into frail, prefrail, or nonfrail groups, according to frailty phenotype. The RR interval (RRi) and systolic blood pressure (SBP) series were recorded for 15 min in the supine and 15 min in the orthostatic positions. Mean and variance of RRi and SBP, and baroreflex evaluated by phase, gain (α), and coherence (K2) were determined. A two-way repeated measures ANOVA, with Tukey's post hoc, was applied for group, position, and their interaction effects. The significance level established was 5%. Prefrail and frail participants did not present a significant decrease in mean values of RRi after postural challenge (893.43 to 834.20 ms and 925.99 to 857.98 ms, respectively). Frail participants showed a reduction in RRi variance in supine to orthostatic (852.04 to 232.37 ms2). Prefrail and frail participants showed a decrease in K2 after postural change (0.69 to 0.52 and 0.54 to 0.34, respectively). Frail participants exhibited lower values of K2 (0.34) compared to nonfrail and prefrail participants (0.61 and 0.52, respectively). Baroreflex indicated the presence of decoupling between heart period and SBP in frail and prefrail. Thus, reduced K2 might be a marker of the frailty process.

Impaired baroreflex sensitivity and increased systolic blood pressure variability in chronic post-ischemic stroke

OBJECTIVES: Acute post-stroke patients present cardiovascular autonomic dysfunction, which manifests as lower heart rate variability and impaired baroreflex sensitivity. However, few studies performed to date have evaluated cardiovascular autonomic function in chronic post-stroke patients. The aim of this study was to evaluate cardiovascular autonomic modulation in chronic post-ischemic stroke patients. METHODS: The seventeen enrolled subjects were divided into a stroke group (SG, n=10, 5±1 years after stroke) and a control group (CG, n=7). Non-invasive curves for blood pressure were continuously recorded (Finometer®) for 15 minutes while the subject was in a supine position. Heart rate variability and blood pressure variability were analyzed in the time and frequency domains. RESULTS: No differences were observed in systolic and diastolic pressure and heart rate between post-stroke patients and healthy individuals. The SG group had lower indexes for heart rate variability in the time domain (standard deviation of normal to normal R-R intervals, SDNN; variance of normal to normal R-R intervals, VarNN; and root mean square differences of successive R-R intervals, RMSSD) and a lower high-frequency band for heart rate variability than was observed in the CG. Systolic blood pressure variability and the low-frequency band for systolic pressure were higher in post-stroke patients, while the alpha index was lower in the SG than in the CG. CONCLUSION: After ischemic stroke, affected patients present chronically reduced heart rate variability, impaired cardiac vagal modulation, increased systolic blood pressure variability and higher sympathetic vascular modulation along with impaired baroreflex sensitivity, which can increase the risk of cardiovascular events, despite adequate blood pressure control.

Resting spontaneous baroreflex sensitivity and cardiac autonomic control in anabolic androgenic steroid users

OBJECTIVES: Misuse of anabolic androgenic steroids in athletes is a strategy used to enhance strength and skeletal muscle hypertrophy. However, its abuse leads to an imbalance in muscle sympathetic nerve activity, increased vascular resistance, and increased blood pressure. However, the mechanisms underlying these alterations are still unknown. Therefore, we tested whether anabolic androgenic steroids could impair resting baroreflex sensitivity and cardiac sympathovagal control. In addition, we evaluate pulse wave velocity to ascertain the arterial stiffness of large vessels. METHODS: Fourteen male anabolic androgenic steroid users and 12 nonusers were studied. Heart rate, blood pressure, and respiratory rate were recorded. Baroreflex sensitivity was estimated by the sequence method, and cardiac autonomic control by analysis of the R-R interval. Pulse wave velocity was measured using a noninvasive automatic device. RESULTS: Mean spontaneous baroreflex sensitivity, baroreflex sensitivity to activation of the baroreceptors, and baroreflex sensitivity to deactivation of the baroreceptors were significantly lower in users than in nonusers. In the spectral analysis of heart rate variability, high frequency activity was lower, while low frequency activity was higher in users than in nonusers. Moreover, the sympathovagal balance was higher in users. Users showed higher pulse wave velocity than nonusers showing arterial stiffness of large vessels. Single linear regression analysis showed significant correlations between mean blood pressure and baroreflex sensitivity and pulse wave velocity. CONCLUSIONS: Our results provide evidence for lower baroreflex sensitivity and sympathovagal imbalance in anabolic androgenic steroid users. Moreover, anabolic androgenic steroid users showed arterial stiffness. Together, these alterations might be the mechanisms triggering the increased blood pressure in this population.

The Effect of Physical Resistance Training on Baroreflex Sensitivity of Hypertensive Rats / Efeito do Treinamento Físico Resistido na Sensibilidade Barorreflexa de Ratos Hipertensos

Abstract Background: Baroreceptors act as regulators of blood pressure (BP); however, its sensitivity is impaired in hypertensive patients. Among the recommendations for BP reduction, exercise training has become an important adjuvant therapy in this population. However, there are many doubts about the effects of resistance exercise training in this population. Objective: To evaluate the effect of resistance exercise training on BP and baroreceptor sensitivity in spontaneously hypertensive rats (SHR). Method: Rats SHR (n = 16) and Wistar (n = 16) at 8 weeks of age, at the beginning of the experiment, were randomly divided into 4 groups: sedentary control (CS, n = 8); trained control (CT, n = 8); sedentary SHR (HS, n = 8) and trained SHR (HT, n = 8). Resistance exercise training was performed in a stairmaster-type equipment (1.1 × 0.18 m, 2 cm between the steps, 80° incline) with weights attached to their tails, (5 days/week, 8 weeks). Baroreceptor reflex control of heart rate (HR) was tested by loading/unloading of baroreceptors with phenylephrine and sodium nitroprusside. Results: Resistance exercise training increased the soleus muscle mass in SHR when compared to HS (HS 0.027 ± 0.002 g/mm and HT 0.056 ± 0.003 g/mm). Resistance exercise training did not alter BP. On the other hand, in relation to baroreflex sensitivity, bradycardic response was improved in the TH group when compared to HS (HS -1.3 ± 0.1 bpm/mmHg and HT -2.6 ± 0.2 bpm/mmHg) although tachycardia response was not altered by resistance exercise (CS -3.3 ± 0.2 bpm/mmHg, CT -3.3 ± 0.1 bpm/mmHg, HS -1.47 ± 0.06 bpm/mmHg and HT -1.6 ± 0.1 bpm/mmHg). Conclusion: Resistance exercise training was able to promote improvements on baroreflex sensitivity of SHR rats, through the improvement of bradycardic response, despite not having reduced BP.

Resumo Fundamento: Os barorreceptores atuam como reguladores da pressão arterial (PA); no entanto, sua sensibilidade encontra-se prejudicada em pacientes hipertensos. Dentre as recomendações para a redução da PA, o treinamento físico tem se tornado um importante adjunto na terapia dessa população. Porém, ainda há diversos questionamentos sobre os efeitos de treinamento físico resistido nessa população. Objetivo: Avaliar o efeito do treinamento físico resistido na PA e na sensibilidade de barorreceptores em ratos espontaneamente hipertensos (SHR). Método: Ratos SHR (n = 16) e Wistar (n = 16) com 08 semanas de idade foram aleatoriamente divididos em 4 grupos: controle sedentário (CS, n = 8); controle treinado (CT, n = 8); SHR sedentário (HS, n = 8) e SHR treinado (HT, n = 8). O treinamento físico foi realizado em aparato com degraus (1,1 × 0,18 m, 2 cm entre os degraus, 80° inclinação) com peso fixado na cauda, (5 vezes por semana durante 8 semanas). O controle barorreflexo da frequência cardíaca (FC) foi testado com estímulos de fenilefrina e nitroprussiato de sódio. Resultados: O treinamento resistido foi capaz de aumentar a massa muscular do sóleo em ratos SHR (HS 0,027 ± 0,002 g/mm e HT 0,056 ± 0,003 g/mm). Não houve alteração da PA com o treinamento. Por outro lado, houve melhora na resposta bradicárdica da sensibilidade barorreflexa no grupo HT (HS -1,3 ± 0,1 bpm/mmHg e HT -2,6 ± 0,2 bpm/mmHg), no entanto, a resposta taquicárdica não foi alterada pelo exercício resistido (CS -3,3 ± 0,2 bpm/mmHg, CT -3,3 ± 0,1 bpm/mmHg, HS -1,47 ± 0,06 e HT -1,6 ± 0,1). Conclusão: O exercício físico resistido foi capaz de otimizar a sensibilidade barorreflexa dos ratos SHR por meio da melhora à resposta bradicárdica, apesar de não alterar a PA.

Serotoninergic Modulation of Basal Cardiovascular Responses and Responses Induced by Isotonic Extracellular Volume Expansion in Rats / Modulação Serotoninérgica de Respostas Cardiovasculares Basais e Induzidas pela Expansão Isotônica do Volume Extracelular em Ratos

Abstract Background: Isotonic blood volume expansion (BVE) induced alterations of sympathetic and parasympathetic activity in the heart and blood vessels, which can be modulated by serotonergic pathways. Objective: To evaluate the effect of saline or serotonergic agonist (DOI) administration in the hypothalamic paraventricular nucleus (PVN) on cardiovascular responses after BVE. Methods: We recorded pulsatile blood pressure through the femoral artery to obtain the mean arterial pressure (MAP), systolic (SBP) and diastolic blood pressure (DBP), heart rate (HR) and the sympathetic-vagal ratio (LF/HF) of Wistar rats before and after they received bilateral microinjections of saline or DOI into the PVN, followed by BVE. Results: No significant differences were observed in the values of the studied variables in the different treatments from the control group. However, when animals are treated with DOI followed by BVE there is a significant increase in relation to the BE control group in all the studied variables: MBP (114.42±7.85 vs 101.34±9.17); SBP (147.23±14.31 vs 129.39±10.70); DBP (98.01 ±4.91 vs 87.31±8.61); HR (421.02±43.32 vs 356.35±41.99); and LF/HF ratio (2.32±0.80 vs 0.27±0.32). Discussion: The present study showed that the induction of isotonic BVE did not promote alterations in MAP, HR and LF/HF ratio. On the other hand, the injection of DOI into PVN of the hypothalamus followed by isotonic BVE resulted in a significant increase of all variables. Conclusion: These results suggest that serotonin induced a neuromodulation in the PVN level, which promotes an inhibition of the baroreflex response to BVE. Therefore, the present study suggests the involvement of the serotonergic system in the modulation of vagal reflex response at PVN in the normotensive rats.

Resumo Fundamento: Expansão de volume extracelular (EVEC) promove alterações da atividade simpática e parassimpática no coração e vasos sanguíneos, os quais podem ser moduladas por vias serotoninérgicas. Objetivo: Avaliar o efeito da administração de salina ou agonista serotoninérgico (DOI) nos núcleos paraventriculares hipotalâmico (NPV) sobre respostas cardiovasculares após EVEC. Métodos: Foram obtidos registros da pressão arterial pulsátil, por meio da artéria femoral, para obtenção dos valores da pressão arterial média (PAM), sistólica (PAS), diastólica (PAD), frequência cardíaca (FC) e razão simpático-vagal (LF/HF) de ratos Wistar antes e após receberem microinjeções bilaterais no NPV de salina ou DOI seguida de EVEC. Resultados: Não foram observadas diferenças significativas dos valores das variáveis estudadas nos diferentes tratamentos do grupo controle. Entretanto, quando os animais são tratados com DOI seguida de EVEC ocorre aumento significativo em relação ao grupo controle com EVEC em todas as variáveis estudadas: PAM (114,42±7,85 vs 101,34±9,17), PAS (147,23±14,31 vs 129,39±10,70), PAD (98,01 ±4,91 vs 87,31±8,61), FC (421,02±43,32 vs 356,35±41,99) e LF/HF (2,32±0,80 vs 0,27±0,32). Discussão: O presente estudo mostrou que a indução de EVEC isotônica não promoveu alterações na PAM, PAD, PAS, FC e LF/HF. Por outro lado, os animais que receberam microinjeção de DOI no NPV seguida de EVEC apresentaram aumento significativo de todas as variáveis. Conclusão: Esses resultados sugerem que a serotonina exerce uma neuromodulação em nivel do NPV, e essa promove uma inibição da resposta barorreflexa frente à EVEC. Assim, o presente trabalho sugere o envolvimento serotoninérgico na neuromodulação no nivel do NPV na resposta reflexa vagal em ratos normotensos.

Time course of changes in heart rate and blood pressure variability in rats with myocardial infarction

Our aim was to determine the time course of changes in autonomic balance in the acute (1 and 3 days), sub-acute (7 days) and chronic (28 days) phases of myocardial infarction (MI) in rats. Autonomic balance was assessed by temporal and spectral analyses of blood pressure variability (BPV) and heart rate variability (HRV). Pulsatile blood pressure (BP) recordings (30 min) were obtained in awake and unrestrained male Wistar rats (N = 77; 8-10 weeks old) with MI (coronary ligature) or sham operation (SO). Data are reported as means±SE. The high frequency (HF) component (n.u.) of HRV was significantly lower in MI-1- (P<0.01) and MI-3-day rats (P<0.05) than in their time-control groups (SO-1=68±4 vs MI-1=35.3±4.3; SO-3=71±5.8 vs MI-3=45.2±3.8), without differences thereafter (SO-7=69.2±4.8 vs MI-7=56±5.8; SO-28=73±4 vs MI-28=66±6.6). A sharp reduction (P<0.05) of BPV (mmHg2) was observed in the first week after MI (SO-1=8.55±0.80; SO-3=9.11±1.08; SO-7=7.92±1.10 vs MI-1=5.63±0.73; MI-3=5.93±0.30; MI-7=5.30±0.25). Normal BPV, however, was observed 4 weeks after MI (SO-28=8.60±0.66 vs MI-28=8.43±0.56 mmHg2; P>0.05). This reduction was mainly due to attenuation of the low frequency (LF) band of BPV in absolute and normalized units (SO-1=39.3±7%; SO-3=55±4.5%; SO-7=46.8±4.5%; SO-28=45.7±5%; MI-1=13±3.5%; MI-3=35±4.7%; MI-7=25±2.8%; MI-28=21.4±2.8%). The results suggest that the reduction in HRV was associated with decrease of the HF component of HRV suggesting recovery of the vagal control of heartbeats along the post-infarction healing period. The depression of BPV was more dependent on the attenuation of the LF component, which is linked to the baroreflex modulation of the autonomic balance.

Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

ABSTRACT Background A joint symbolic analysis (JSA) is applied to assess the strength of the cardiovascular coupling from spontaneous beat-to-beat variability of the heart period (HP) and the systolic arterial pressure (SAP) during an experimental protocol inducing a gradual baroreflex unloading evoked by postural change (i.e. graded head-up tilt). Method: The adopted JSA can quantify the degree of association between the HP and SAP variabilities as a function of the time scale of the HP and SAP patterns. Traditional linear tools assessing the HP-SAP coupling strength, such as squared correlation coefficient, squared coherence function, and percentage of baroreflex sequences, were computed as well for comparison. Results: We found that: i) JSA indicated that the strength of the cardiovascular coupling at slow temporal scales gradually increased with the magnitude of the orthostatic challenge, while that at fast temporal scales gradually decreased; ii) the squared correlation coefficient and percentage of baroreflex sequences did not detect this behavior; iii) even though squared coherence function could measure the magnitude of the HP-SAP coupling as a function of the time scale, it was less powerful than JSA owing to the larger dispersion of the frequency domain indexes. Conclusion: Due to its peculiar features and high statistical power, JSA deserves applications to pathological groups in which the link between HP and SAP variabilities is lost or decreased due to the overall depression or impairment of the cardiovascular control.

Autonomic and Renal Alterations in the Offspring of Sleep-Restricted Mothers During Late Pregnancy

OBJECTIVES: Considering that changes in the maternal environment may result in changes in progeny, the aim of this study was to investigate the influence of sleep restriction during the last week of pregnancy on renal function and autonomic responses in male descendants at an adult age. METHODS: After confirmation of pregnancy, female Wistar rats were randomly assigned to either a control or a sleep restriction group. The sleep-restricted rats were subjected to sleep restriction using the multiple platforms method for over 20 hours per day between the 14th and 20th day of pregnancy. After delivery, the litters were limited to 6 offspring that were designated as offspring from control and offspring from sleep-restricted mothers. Indirect measurements of systolic blood pressure (BPi), renal plasma flow, glomerular filtration rate, glomerular area and number of glomeruli per field were evaluated at three months of age. Direct measurements of cardiovascular function (heart rate and mean arterial pressure), cardiac sympathetic tone, cardiac parasympathetic tone, and baroreflex sensitivity were evaluated at four months of age. RESULTS: The sleep-restricted offspring presented increases in BPi, glomerular filtration rate and glomerular area compared with the control offspring. The sleep-restricted offspring also showed higher basal heart rate, increased mean arterial pressure, increased sympathetic cardiac tone, decreased parasympathetic cardiac tone and reduced baroreflex sensitivity. CONCLUSIONS: Our data suggest that reductions in sleep during the last week of pregnancy lead to alterations in cardiovascular autonomic regulation and renal morpho-functional changes in offspring, triggering increases in blood pressure.

Cardiac Autonomic Adjustments During Baroreflex Test in Obese and Non-Obese Preadolescents / Ajustes Autonômicos Cardíacos Durante Teste Barorreflexo em Pré-Adolescentes Obesos e Não Obesos

Abstract Background: Recent studies have shown changes in cardiac autonomic control of obese preadolescents. Objective: To assess the heart rate responses and cardiac autonomic modulation of obese preadolescents during constant expiratory effort. Methods: This study assessed 10 obese and 10 non-obese preadolescents aged 9 to 12 years. The body mass index of the obese group was between the 95th and 97th percentiles of the CDC National Center for Health Statistics growth charts, while that of the non-obese group, between the 5th and 85th percentiles. Initially, they underwent anthropometric and clinical assessment, and their maximum expiratory pressures were obtained. Then, the preadolescents underwent a constant expiratory effort of 70% of their maximum expiratory pressure for 20 seconds, with heart rate measurement 5 minutes before, during and 5 minutes after it. Heart rate variability (HRV) and heart rate values were analyzed by use of a software. Results: The HRV did not differ when compared before and after the constant expiratory effort intra- and intergroup. The heart rate values differed (p < 0.05) during the effort, being the total variation in non-obese preadolescents of 18.5 ± 1.5 bpm, and in obese, of 12.2 ± 1.3 bpm. Conclusion: The cardiac autonomic modulation did not differ between the groups when comparing before and after the constant expiratory effort. However, the obese group showed lower cardiovascular response to baroreceptor stimuli during the effort, suggesting lower autonomic baroreflex sensitivity.

Resumo Fundamento: Estudos recentes revelaram alterações no controle autonômico cardíaco de pré-adolescentes obesos. Objetivo: Avaliar as respostas de frequência cardíaca e modulação autonômica cardíaca de pré-adolescentes obesos durante esforço expiratório constante. Métodos: Estudaram-se 10 pré-adolescentes obesos e 10 não obesos com idades entre 9 e 12 anos. O índice de massa corporal dos obesos esteve entre os percentis 95 e 97 das curvas do gráfico do National Center for Health Statistics, enquanto o de não obesos, entre os percentis 5 e 85. Inicialmente, realizaram-se avaliações antropométrica e clínica, e as pressões expiratórias máximas foram obtidas. A seguir, os pré-adolescentes foram submetidos a um esforço expiratório constante correspondendo a 70% das pressões expiratórias máximas por 20 segundos, com registro da frequência cardíaca 5 minutos antes e depois do esforço, e durante o mesmo. A variabilidade e os valores de frequência cardíaca foram analisados em um software. Resultados: Os índices da variabilidade da frequência cardíaca não diferiram ao serem comparados antes e depois do esforço expiratório constante intra- e intergrupos. Os valores da frequência cardíaca diferiram (p < 0,05) durante o esforço, sendo a variação total nos não obesos de 18,5 ± 1,5 bpm e nos obesos, 12,2 ± 1,3 bpm. Conclusão: A modulação autonômica cardíaca não diferiu entre os grupos antes e depois do esforço expiratório constante. No entanto, o grupo de obesos mostrou menor resposta cardiovascular ao estímulo barorreceptor durante o esforço, o que sugere menor sensibilidade autonômica barorreflexa.

Role of Baroreflex Sensitivity in Predicting Tilt Training Response in Patients with Neurally Mediated Syncope

PURPOSE: An association between baroreflex sensitivity (BRS) and the response to tilt training has not been reported in patients with neurally mediated syncope (NMS). This study sought to investigate the role of BRS in predicting the response to tilt training in patients with NMS. MATERIALS AND METHODS: We analyzed 57 patients who underwent tilt training at our hospital. A responder to tilt training was defined as a patient with three consecutive negative responses to the head-up tilt test (HUT) during tilt training. RESULTS: After tilt training, 52 patients (91.2%) achieved three consecutive negative responses to the HUT. In the supine position before upright posture during the first session of tilt training for responders and non-responders, the mean BRS was 18.17+/-10.09 ms/mm Hg and 7.99+/-5.84 ms/mm Hg (p=0.008), respectively, and the frequency of BRS > or =8.945 ms/mm Hg was 45 (86.5%) and 1 (20.0%; p=0.004), respectively. Age, male gender, frequency of syncopal events before HUT, type of NMS, phase of positive HUT, total number of tilt training sessions, and mean time of tilt training did not differ between the study groups. In the multivariate analysis, BRS <8.945 ms/mm Hg in the supine position (odds ratio 23.10; 95% CI 1.20-443.59; p=0.037) was significantly and independently associated with non-response to tilt training. CONCLUSION: The BRS value in the supine position could be a predictor for determining the response to tilt training in patients with NMS who are being considered for inpatient tilt training.

Time-course effects of aerobic exercise training on cardiovascular and renal parameters in 2K1C renovascular hypertensive rats

Exercise training (Ex) has been recommended for its beneficial effects in hypertensive states. The present study evaluated the time-course effects of Ex without workload on mean arterial pressure (MAP), reflex bradycardia, cardiac and renal histology, and oxidative stress in two-kidney, one-clip (2K1C) hypertensive rats. Male Fischer rats (10 weeks old; 150–180 g) underwent surgery (2K1C or SHAM) and were subsequently divided into a sedentary (SED) group and Ex group (swimming 1 h/day, 5 days/week for 2, 4, 6, 8, or 10 weeks). Until week 4, Ex decreased MAP, increased reflex bradycardia, prevented concentric hypertrophy, reduced collagen deposition in the myocardium and kidneys, decreased the level of thiobarbituric acid-reactive substances (TBARS) in the left ventricle, and increased the catalase (CAT) activity in the left ventricle and both kidneys. From week 6 to week 10, however, MAP and reflex bradycardia in 2K1C Ex rats became similar to those in 2K1C SED rats. Ex effectively reduced heart rate and prevented collagen deposition in the heart and both kidneys up to week 10, and restored the level of TBARS in the left ventricle and clipped kidney and the CAT activity in both kidneys until week 8. Ex without workload for 10 weeks in 2K1C rats provided distinct beneficial effects. The early effects of Ex on cardiovascular function included reversing MAP and reflex bradycardia. The later effects of Ex included preventing structural alterations in the heart and kidney by decreasing oxidative stress and reducing injuries in these organs during hypertension.

Heart Rate and Systolic Blood Pressure Variability on Recently Diagnosed Diabetics / Variabilidade da Frequência Cardíaca e da Pressão Arterial Sistólica em Diabéticos com Diagnóstico Recente

Background:Diabetes affects approximately 250 million people in the world. Cardiovascular autonomic neuropathy is a common complication of diabetes that leads to severe postural hypotension, exercise intolerance, and increased incidence of silent myocardial infarction.Objective:To determine the variability of heart rate (HR) and systolic blood pressure (SBP) in recently diagnosed diabetic patients.Methods:The study included 30 patients with a diagnosis of type 2 diabetes of less than 2 years and 30 healthy controls. We used a Finapres® device to measure during five minutes beat-to-beat HR and blood pressure in three experimental conditions: supine position, standing position, and rhythmic breathing at 0.1 Hz. The results were analyzed in the time and frequency domains.Results:In the HR analysis, statistically significant differences were found in the time domain, specifically on short-term values such as standard deviation of NN intervals (SDNN), root mean square of successive differences (RMSSD), and number of pairs of successive NNs that differ by more than 50 ms (pNN50). In the BP analysis, there were no significant differences, but there was a sympathetic dominance in all three conditions. The baroreflex sensitivity (BRS) decreased in patients with early diabetes compared with healthy subjects during the standing maneuver.Conclusions:There is a decrease in HR variability in patients with early type 2 diabetes. No changes were observed in the BP analysis in the supine position, but there were changes in BRS with the standing maneuver, probably due to sympathetic hyperactivity.

Fundamento:O diabetes afeta aproximadamente 250 milhões de pessoas no mundo. A neuropatia autonômica cardiovascular é uma complicação comum do diabetes que leva à hipotensão postural grave, intolerância ao exercício e aumento na incidência de infarto do miocárdio silencioso.Objetivo:Determinar a variabilidade da frequência cardíaca (FC) e da pressão arterial sistólica (PAS) em pacientes diabéticos com diagnóstico recente.Métodos:O estudo incluiu 30 pacientes com diabetes tipo 2 diagnosticado há menos de 2 anos e 30 controles saudáveis. Nós utilizamos o dispositivo Finapres® para medir durante cinco minutos a FC batimento-a-batimento e a pressão arterial (PA) em três condições experimentais: posição supina, em pé e durante respiração rítmica na frequência de 0,1 Hz. Os resultados foram analisados nos domínios do tempo e da frequência.Resultados:Em relação à FC, foram encontradas diferenças estatisticamente significativas nos valores da análise do domínio do tempo, especificamente em valores determinados a curto prazo, tais como o desvio-padrão dos intervalos NN (DPNN), a raiz quadrada da média das diferenças sucessivas (RQMDS) para a FC e o número de pares de NNs sucessivos que diferem em mais de 50 ms (pNN50). Não houve diferença significativa na análise da PA, mas houve uma dominância simpática nas três condições. A sensibilidade do barorreflexo (SBR) esteve diminuída em pacientes com diabetes de início recente, em comparação aos indivíduos saudáveis durante execução da manobra na posição ortostática.Conclusões:Há uma diminuição na variabilidade da FC em pacientes com diabetes tipo 2 de início recente. Não foram observadas alterações na análise da PA na posição supina, mas a SBR apresentou mudança com a manobra em pé provavelmente causada por hiperatividade simpática.

Portuguese version of the PTSD Checklist-Military Version (PCL-M) - II: diagnostic utility

Objective: War veterans are at high risk of developing posttraumatic stress disorder (PTSD), and the development of brief self-report instruments that enable screening for PTSD in this population is crucial. The PTSD Checklist-Military Version (PCL-M) is widely used for this purpose. This study sought to explore the diagnostic utility of the Portuguese version of the PCL-M. Methods: The participants were 86 Portuguese Colonial War veterans (42 with a PTSD diagnosis and 44 without PTSD). Participants completed a self-report instrument designed to collect sociodemographic data, the PCL-M, and the Clinician-Administered PTSD Scale (CAPS). Results: The area under the receiver operator characteristic (ROC) curve showed excellent discriminant ability between subjects with and without PTSD (AUC = 0.94). To achieve a positive PTSD diagnosis, an optimal cutoff point of 49 for the PCL-M total score and cutoff points for each of its 17 items are recommended. Conclusions: This work is a relevant contribution for research and clinical practice in the vast population of Portuguese Colonial War veterans. Use of the PCL-M as a screening tool for PTSD symptoms will allow easier, resource-aware targeting of subjects with a potential PTSD diagnosis, adding to the improvement of public health in Portugal. .

Resistance Training After Myocardial Infarction in Rats: Its Role on Cardiac and Autonomic Function / Treinamento Resistido Após Infarto do Miocárdio em Ratos: Papel na Função Cardíaca e Autonômica

Background: Although resistance exercise training is part of cardiovascular rehabilitation programs, little is known about its role on the cardiac and autonomic function after myocardial infarction. Objective: To evaluate the effects of resistance exercise training, started early after myocardial infarction, on cardiac function, hemodynamic profile, and autonomic modulation in rats. Methods: Male Wistar rats were divided into four groups: sedentary control, trained control, sedentary infarcted and trained infarcted rats. Each group with n = 9 rats. The animals underwent maximum load test and echocardiography at the beginning and at the end of the resistance exercise training (in an adapted ladder, 40% to 60% of the maximum load test, 3 months, 5 days/week). At the end, hemodynamic, baroreflex sensitivity and autonomic modulation assessments were made. Results: The maximum load test increased in groups trained control (+32%) and trained infarcted (+46%) in relation to groups sedentary control and sedentary infarcted. Although no change occurred regarding the myocardial infarction size and systolic function, the E/A ratio (-23%), myocardial performance index (-39%) and systolic blood pressure (+6%) improved with resistance exercise training in group trained infarcted. Concomitantly, the training provided additional benefits in the high frequency bands of the pulse interval (+45%), as well as in the low frequency band of systolic blood pressure (-46%) in rats from group trained infarcted in relation to group sedentary infarcted. Conclusion: Resistance exercise training alone may be an important and safe tool in the management of patients after myocardial infarction, considering that it does not lead to significant changes in the ventricular function, reduces the global cardiac stress, and significantly improves the vascular and cardiac autonomic modulation in infarcted rats. .

Fundamento: Embora o treinamento físico resistido esteja inserido nos programas de reabilitação cardiovascular, pouco se sabe sobre seu papel isolado na função cardíaca e autonômica após o infarto do miocárdio. Objetivo: Avaliar os efeitos do treinamento físico resistido iniciado precocemente após o infarto do miocárdio na função cardíaca, no perfil hemodinâmico e na modulação autonômica de ratos. Métodos: Ratos Wistar machos foram divididos em Grupos Controle Sedentário, Controle Treinado, Infartado Sedentário e Infartado Treinado. Cada grupo foi composto por 9 ratos. Os animais realizaram o teste de carga máxima e a ecocardiografia ao início e ao final do treinamento físico resistido (em escada adaptada, 40 a 60% do teste de carga máxima, 3 meses, 5 dias/semana). Ao final, foram realizadas avaliações hemodinâmicas, de sensibilidade barorreflexa e da modulação autonômica. Resultados: O teste de carga máxima aumentou nos Grupos Controle Treinado (+32%) e Infartado Treinado (+46%) em relação aos Grupos Controle Sedentário e Infartado Sedentário. Embora a área de infarto do miocárdio e a função sistólica não tenham sido alteradas, a relação E/A (-23%), o índice de desempenho miocárdico (-39%) e a pressão arterial sistólica (+6%) foram melhorados pelo treinamento físico resistido no Grupo Infartado Treinado. Paralelamente, o treinamento induziu os grupos a benefícios adicionais nas bandas de alta frequência do intervalo de pulso (+45%), bem como a banda de baixa frequência da pressão arterial sistólica (-46%) nos ratos do Grupo Infartado Treinado em relação aos do Infartado Sedentário. Conclusão: O treinamento físico resistido dinâmico ...

Baroreflex Sensitivity and its Association with Arrhythmic Events in Chagas Disease / A Sensibilidade do Barorreflexo e sua Associação com Eventos Arrítmicos na Doença de Chagas

Background: Sudden death is the leading cause of death in Chagas disease (CD), even in patients with preserved ejection fraction (EF), suggesting that destabilizing factors of the arrhythmogenic substrate (autonomic modulation) contribute to its occurrence. Objective: To determine baroreflex sensitivity (BRS) in patients with undetermined CD (GI), arrhythmogenic CD with nonsustained ventricular tachycardia (NSVT) (GII) and CD with spontaneous sustained ventricular tachycardia (STV) (GIII), to evaluate its association with the occurrence and complexity of arrhythmias. Method: Forty-two patients with CD underwent ECG and continuous and noninvasive BP monitoring (TASK force monitor). The following were determined: BRS (phenylephrine method); heart rate variability (HRV) on 24-h Holter; and EF (echocardiogram). Results: GIII had lower BRS (6.09 ms/mm Hg) as compared to GII (11.84) and GI (15.23). The difference was significant between GI and GIII (p = 0.01). Correlating BRS with the density of ventricular extrasystoles (VE), low VE density (<10/h) was associated with preserved BRS. Only 59% of the patients with high VE density (> 10/h) had preserved BRS (p = 0.003). Patients with depressed BRS had higher VE density (p = 0.01), regardless of the EF. The BRS was the only variable related to the occurrence of SVT (p = 0.028). Conclusion: The BRS is preserved in undetermined CD. The BRS impairment increases as disease progresses, being more severe in patients with more complex ventricular arrhythmias. The degree of autonomic dysfunction did not correlate with EF, but with the density and complexity of ventricular arrhythmias. .

Fundamento: Morte súbita é a principal causa de morte na doença de Chagas (DC), mesmo em pacientes com fração de ejeção (FE) preservada, sugerindo que fatores desestabilizadores do substrato arritmogênico (modulação autonômica) contribuam para a sua ocorrência. Objetivo: Determinar a sensibilidade do barorreflexo (SBR) em pacientes com DC na forma indeterminada (GI), arritmogênica com TVNS (GII) e com TVS (GIII) a fim de avaliar sua associação com a ocorrência e complexidade da arritmia. Método: Quarenta e dois pacientes chagásicos foram submetidos à monitorização do ECG e PA contínua e não invasiva (TASK force monitor). Foi determinada a SBR (método da fenilefrina), a variabilidade da frequência cardíaca (VFC) ao Holter 24 h. e FE (ecocardiograma). Resultados: O GIII apresentou menor SBR (6,09 ms/mmHg) quando comparado aos GII (11,84) e GI (15,23). A diferença foi significativa entre os GI e GIII (p = 0,01). Correlacionando SBR com densidade de extrassístoles ventriculares (EV), observou-se que a baixa densidade de EV (< 10/h.) associou-se com SBR preservada. Nos pacientes com alta densidade de EV (> 10/h.), somente 59% tinham SBR preservada (p = 0,003). Os pacientes com SBR deprimida apresentavam maior densidade de EV (p = 0,01), independente da FE. A SBR foi a única variável relacionada à ocorrência de TVS (p = 0,028). Conclusão: A SBR está preservada na forma indeterminada da DC. O comprometimento da SBR é progressivo e acompanha a evolução da doença, sendo mais intenso nos pacientes com arritmias ventriculares mais complexas. O grau de disfunção autonômica não se correlacionou com a FE, mas sim com a densidade e complexidade da arritmia ventricular. .

Avaliação da função autonômica em portadores de cardiomiopatia hipertrófica com e sem síncope / Evaluation of the autonomic function in patients with hypertrophic cardiomyopathy with and without syncope

FUNDAMENTO: Diversos mecanismos podem estar envolvidos no desencadeamento da síncope em pacientes com cardiomiopatia hipertrófica (CMH), incluindo colapsos hemodinâmicos que podem estar relacionados a um desequilíbrio autonômico. OBJETIVO: Avaliar e comparar a função autonômica de pacientes que apresentam CMH com síncope inexplicada (SI) com os que não apresentam síncope. MÉTODOS: Trinta e sete pacientes foram incluídos, sendo 16 com SI e 21 sem síncope. Sua função autonômica foi avaliada por sensibilidade barorreflexa (SB) espontânea e induzida por fenilefrina, pela variabilidade da frequência cardíaca (VFC) no domínio do tempo durante o Holter de 24 horas e no domínio da frequência (análise espectral), ambos em decúbito dorsal e no teste de inclinação (TI) a 70º. RESULTADOS: A SB espontânea mostrou-se semelhante em ambos os grupos (16,46 ± 12,99 vs. 18,31 ± 9,88 ms/mmHg, p = 0,464), assim como a SB induzida por fenilefrina (18,33 ± 9,31 vs. 15,83 ± 15,48 ms/mmHg, p = 0,521). Não foram observadas diferenças no SDNN (137,69 ± 36,62 vs . 145,95 ± 38,07 ms, p = 0,389). O grupo com síncope apresentou um RMSSD significativamente menor (24,88 ± 10,03 vs. 35,58 ± 16,43 ms, p = 0,042) e tendência a menor pNN50 (4,51 ± 3,78 vs . 8,83 ± 7,98%, p =0,085) e a menores valores do componente de alta frequência da análise espectral da VFC em repouso (637,59 ± 1.295,53 vs. 782,65 ± 1.264,14 ms2 , p = 0,075). Nenhuma diferença significativa foi observada em resposta ao TI (p = 0,053). A sensibilidade, especificidade e acurácia do TI na identificação da etiologia da SI em pacientes com CMH foram 6%, 66% e 40%, respectivamente. CONCLUSÃO: Observou-se tônus parassimpático mais baixo em pacientes com CMH e SI, mas a relevância clínica deste achado ainda não está clara. O TI não é uma ferramenta vantajosa para avaliar a origem da síncope em tais doentes, principalmente por causa da sua baixa especificidade.

BACKGROUND: Several mechanisms may be involved in the trigger of syncope in patients with hypertrophic cardiomyopathy (HCM), including hemodynamic collapses that might be related to an autonomic imbalance. OBJECTIVE: To evaluate and compare the autonomic function of patients presenting HCM with unexplained syncope (US) to those without syncope. METHODS: Thirty-seven patients were included, 16 with US and 21 without syncope. Their autonomic function was assessed by spontaneous and phenylephrine induced baroreflex sensitivity (BRS), by heart rate variability (HRV) in time domain during 24-hour Holter and in frequency domain (spectral analysis), both in supine position and at 70º head-up tilt (HUT). RESULTS: The spontaneous BRS was similar in both groups (16,46 ± 12,99 vs. 18,31 ± 9,88 ms/mmHg, p = 0,464), as was phenylephrine-induced BRS (18,33 ± 9,31 vs. 15,83 ± 15,48 ms/mmHg, p = 0,521). No differences were observed in SDNN (137,69 ± 36,62 vs . 145,95 ± 38,07 ms, p=0,389). The group presenting syncope had a significantly lower RMSSD (24,88±10,03 vs. 35,58 ± 16,43 ms, p = 0,042) and a tendency to lower pNN50 (4,51 ± 3,78 vs . 8,83 ± 7,98%, p =0,085) and lower values of the high frequency component of HRV spectral analysis at rest (637,59±1.295,53 vs. 782,65±1.264,14ms2, p=0,075). No significant difference was observed in response to HUT (p = 0,053). HUT sensitivity, specificity and accuracy in identifying the etiology of US in HCM patients were 6%, 66% and 40%, respectively. CONCLUSIONS: A lower parasympathetic tone was observed in HCM patients with US, but the clinical relevance of this finding remains unclear. HUT is not a valuable tool for evaluating the origin of syncope in these patients, mainly because of its poor specificity.

Reflexo dos barorreceptores e homeostase da pressão arterial / Baroreflexes and blood pressure homeostasis

A hipertensão arterial é considerada um dos principais fatores de risco para a morbidade e mortalidade cardiovascular. Os reflexos originados nos barorreceptores arteriais e nos receptores de estiramento da região cardiopulmonar são os principais mecanismos de controle efetivo da pressão arterial a curto prazo. O reflexo dos barorreceptores é considerado um sistema de controle de alto ganho, que mantém a pressão arterial dentro de limites normais em períodos de segundos a minutos. Dessa forma, esta revisão busca abordar os mecanismos desenvolvidos pelos barorreceptores na homeostase da pressão arterial. No presente artigo foram relatadas as alterações dos reflexos cardiovasculares na hipertensão arterial, focando a distribuição dos barorreceptores e seu funcionamento no restabelecimento da pressão arterial. Para realização desta pesquisa foi realizada uma revisão de artigos científicos utilizando as bases de dados Medline, Scielo e Lilacs. Adicionalmente foram consultados livros de fisiologia humana para complementação das informações sobre a fisiologia do barorreflexo na homeostase da pressão arterial. Estudos clínicos têm mostrado que uma reduzida sensibilidade do barorreflexo está associada com a morte súbita que se segue ao infarto agudo do miocárdio. O entendimento dos reflexos dos barorreceptores e a manutenção da hipertensão arterial em curto prazo são de grande importância para o entendimento da fisiopatogenia envolvidas no desenvolvimento e/ou evolução de determinadas alterações patológicas (AU)

Hypertension is considered one of the main risk factors for cardiovascular morbidity and mortality. The reflexes of arterial baroreceptors and stretch receptors in the cardiopulmonary region are the primary mechanisms for effectively controlling arterial blood pressure in the short term. Baroreflexes are a relatively high gain control system that regulates blood pressure during short time periods such as seconds or minutes. This literature review aims to discuss the mechanisms developed by baroreceptors in blood pressure homeostasis. We describe the effects of cardiovascular reflexes on blood pressure, with focus on the distribution of baroreceptors and on its role in controlling blood pressure. Our research was based on scientific articles from the Medline, Scielo, and Lilacs databases. We also researched books on human physiology in order to describe the physiology of baroreflexes in blood pressure homeostasis. Clinical studies have shown that decreased baroreflex sensitivity is associated with sudden death following myocardial infarction. Understanding baroreflexes and short-term blood pressure regulation is essential for understanding the physiopathogenesis involved in the development of certain pathological changes (AU)

Relation of the baroreflex mechanism with the photoplethysmographic volume in healthy humans during orthostatism / Relación del mecanismo barorreflejo con el volumen fotopletismográfico en humanos sanos durante ortostatismo

Objective: Our aim was to evaluate the effect of the baroreflex mechanism upon peripheral blood volume during sympathetic stimulation by orthostatism. Methods: Nineteen clinically healthy volunteers were included (12 men), 28.4 ± 6.2 years old. Blood pressure was monitored with a Finometer and blood volume with a photoplethysmo-graph during supine position and orthostatism (15 minutes each), in order to obtain systolic blood pressure (SBP), diastolic blood pressure (DBP), systolic volume (SysV), diastolic volume (DiaV), and inter beat intervals (IBI) measurements. Baroreflex sensitivity index (IBI/SBP) and baroreflex effect on blood volume (IBI/SysV) were estimated by the sequence method. The pertinence of using only systolic values was tested by linear regression analysis of systolic versus diastolic measurements. Results: More than 70% of DBP and DiaV variations can be explained by SBP and SysV, respectively (p<0.001), with coherence >0.5 in frequencies between 0.04 and 0.15 Hz. IBI/SBP and IBI/SysV were linearly correlated (R>0.4) and both decreased during orthostatism (p<0.05). Conclusion: The sequence method showed a strong baroreflex effect upon peripheral blood volume that became more apparent during sympathetic stimulation with orthostatism. This approach could be clinically useful for the evaluation of blood volume regulation for many diseases such as diabetes mellitus and heart failure, and during therapeutic interventions such as hemodialysis.

Objetivo: Evaluar el efecto del mecanismo barorreflejo sobre el volumen sanguíneo periférico durante estimulación inducida por ortostatismo. Métodos: Se incluyeron 19 voluntarios sanos (12 hombres), con edad de 28.4 ± 6.2 años. La presión arterial se midió con un Finometer y el volumen sanguíneo con un fotopletismógrafo, ambos durante posiciones supina y ortostatismo activo (15 minutos cada una), para obtener los valores de presión arterial sistólica (PAS), presión arterial diastólica (PAD), volumen sistólico (VS), volumen diastólico (VD) e intervalo inter pulso (IIP). Se estimó la sensibilidad barorrefleja (IIP/PAS) y el efecto barorreflejo sobre el volumen sanguíneo (IIP/VS) mediante el método de secuencias. La pertinencia de usar sólo variables sistólicas, se evaluó mediante análisis de regresión lineal de las mediciones sistólicas versus las diastólicas. Resultados: Más de 70% de las variaciones de presión arterial diastólica y volumen diastólico pueden ser explicadas mediante presión arterial sistólica y volumen sistólico, respectivamente (p<0.001), con coherencia >0.5 en frecuencias entre 0.04 y 0.15 Hz. IIP/PAS y IIP/VS tuvieron correlación positiva (R>0.4) y ambos disminuyeron durante ortostatismo (p<0.05). Conclusiones: El método de secuencias demostró un importante efecto barorreflejo sobre el volumen sanguíneo periférico que se hizo más notable durante estimulación simpática con ortostatismo. Este enfoque podría ser clínicamente útil en la evaluación de la regulación del volumen sanguíneo en distintas enfermedades como diabetes mellitus o falla cardiaca, y durante intervenciones terapéuticas como la hemodiálisis.