Postural dysautonomia in response to head-up tilt in a military pilot aspirant: Aeromedical considerations

Intolerance to orthostasis encompasses a group of responses on assumption of upright posture. One such response is postural dysautonomia. One of the types of postural dysautonomia is postural orthostatic tachycardia syndrome, which is characterised by an increase in heart rate of more than 30 bpm without hypotension along with other features of dysautonomia on attaining an erect posture, either actively or passively. This paper brings out a case of postural dysautonomia in a pilot aspirant in response to Head-up tilt (HUT) test. A 23-year-old female military pilot aspirant reported for evaluation of Syncope and Air Sickness. She gave a history of solitary episode of loss of consciousness on ground while preparing for an early morning sortie. She was diagnosed with a case of neurocardiogenic syncope and was put back to flying training. Subsequently, after about 2 months, she developed features of air sickness while flying and also could not tolerate preliminary motion sickness desensitisation at her unit. A thorough medical evaluation failed to reveal any neurocardiological abnormality. Before commencing the air sickness desensitisation protocol at the Institute of Aerospace Medicine, she was subjected to HUT during which she developed signs and symptoms suggestive of postural dysautonomia. A test retest assessment with repeat HUT and passive standing test revealed similar responses.

Measurement of baroreflex & sympathetic control of haemodynamics in mid pregnancy by orthostatic test.

Pregnancy induces changes in the endocrinal and neural regulatory mechanisms affecting the cardiovascular system. The endocrinal manifestations of increased steroid hormone causes volume overload, which ultimately puts stress on the autonomic activity. Orthostatic dysregulation leads to spontaneous abortion, low birth weight infant and still birth. In the orthostatic test, reloading of the baroreceptors causes an increase in the blood pressure along with a rapid decrease in the heart rate within 30 seconds of standing up, which stabilizes by the end of 3 minutes. The haemodynamic changes of increased blood volume, increased cardiac output, decreased peripheral resistance and manifestations of endocrinal functions causing volume overload are maximal in the mid term pregnancy. In our study comparison of 30 mid term pregnant women with an equal number of non pregnant (purposive) control subjects was made by measuring instantaneous increase in heart rate (IIHR); heart rate difference (HRDiff.); orthostatic blood pressure at 30 seconds (OSBP 30); orthostatic blood pressure at the end of 3 minutes (OSBP 3) and Maximum (Max.)/ Minimum (Min.) ratio. The statistical analysis was done by students unpaired ‘t’ test. The percentage difference of Max./Min. ratio among pregnant as compared to non pregnant was significant (p<0.017) though it remained within physiological limits.

Respostas cardiovasculares a mudança postural e capacidade aeróbia em homens e mulheres de meia-idade antes e após treinamento físico aeróbio / Cardiovascular responses to postural change and aerobic capacity among middle-aged men and women before and after aerobic physical training

OBJETIVO: Comparar respostas cardiovasculares a Manobra Postural Passiva (Tilt Test) e capacidade cardiorrespiratória em homens e mulheres de meia-idade antes e após treinamento físico aeróbio. MATERIAIS E MÉTODOS: Sete homens - GH (44,6±2,1 anos) e sete mulheres - GM (51,7±4,8 anos), participaram de treinamento físico aeróbio por 12 semanas. Foi realizado protocolo de Tilt Test (cinco minutos supino, dez minutos inclinado 70º, cinco minutos supino), com monitoração da pressão arterial e freqüência cardíaca. Para mensuração da capacidade cardiorrespiratória foi realizado protocolo em cicloergômetro. RESULTADOS: Na condição sedentária, GH mostrou maior influência parassimpática no controle da freqüência cardíaca evidenciada por maior intervalo RR (iRR) durante Tilt Test. Na condição treinada, os valores de iRR de ambos os grupos se assemelham, tendo as mulheres iRR maior em supino, mas na inclinação os homens mantêm iRR mais elevado. Para pressão arterial, as mulheres permanecem com valores superiores após treino, mas a freqüência cardíaca tende a se assemelhar em ambos. Já na capacidade cardiorrespiratória, homens e mulheres têm um padrão de comportamento semelhante após treino. Com exceção dos valores absolutos da freqüência cardíaca, sem diferenças entre os grupos, para todas as outras variáveis os homens obtiveram valores superiores aos das mulheres. Observa-se ainda que, após o treinamento, houve redução significativa dos valores de pressão arterial no GM, mesmo continuando superiores aos dos homens. CONCLUSÃO: O treinamento parece ter reduzido os níveis pressóricos nas mulheres, além de serem observadas melhorias na capacidade cardiorrespiratória de ambos os grupos, permanecendo os homens com melhor desempenho do que as mulheres.

OBJECTIVE: To compare the cardiovascular responses to passive postural maneuvers (tilt test) and the cardiorespiratory capacity in middle-aged men and women, before and after aerobic physical training. METHODS: Seven men (44.6±2.1 years old) and seven women (51.7±4.8 years old) participated in aerobic physical training for 12 weeks. The tilt test protocol (five minutes supine, ten minutes tilted at 70º and five minutes supine) was followed, with arterial blood pressure and heart rate monitoring. A cycle ergometer protocol was used to measure cardiorespiratory capacity. RESULTS: In the sedentary condition, men showed greater parasympathetic influence in heart rate control, as demonstrated by their higher RR interval (iRR) during the tilt test. After training, the iRR values became more similar in the two groups, although the women had higher iRR in the supine position and the men continued to present higher iRR under tilted conditions. The women's blood pressures continued to be higher after training, but heart rate tended to become similar in the two groups. The cardiorespiratory capacity patterns in the two groups were similar after training. Except for absolute heart rate values, for which there were no differences between the groups, the men's values were higher than those of the women for all other variables. It was also observed that, after the training, the women's blood pressures were significantly lower, even though their pressures remained higher than the men's. CONCLUSIONS: The training seemed to reduce the women's arterial blood pressure levels and improve both groups' cardiorespiratory capacity, but the men continued to present better performance than the women.

Studies on Safe Bathing Based on the Measurement of Cerebral Hemodynamics during Bathing / 日本温泉気候物理医学会雑誌

Frequently occurred sudden deaths in the bath have become to serious problem in Japan. Sudden death in the bath possibly concerned with neurally mediated syncope. During and after bathing, bather is possibly tended to occur orthostatic intolerance by thermal stress to the circulatory dynamics. The experiment was performed focused on changes in cerebral and cardiovascular hemodynamics by postural change in the bathing to discuss the safe way of bathing.<br>On 9 healthy young subjects, 41±1°C bathing was performed 15 minutes, change in oxidized hemoglobin (ΔOxyHb) on the forehead as an indicator of cerebral blood flow was monitored by near-infrared spectroscopy method at interval of 0.5s through the experiment. In sitting and upright position, blood pressure and heart rate were measured before bathing, at 5 minutes, 10 minutes and 15 minutes (upright with head down) after immersion and after bathing.<br>Some subjects felt dizziness at upright during and/or after bathing. It suggests that orthostatic stress under heat stress is implicative even for healthy young. ΔOxyHb for subjects with dizziness at upright during bathing is significant lower below the baseline than it for subject without dizziness.<br>Degrees of depression of systolic blood pressure, elevation of heart rate and depression of cerebral blood flow by standing at 10 minutes after starting immersion were significant larger than their values before bathing. Degree of elevation of heart rate and depression of cerebral blood flow by standing with head down were significant smaller than their value at standing without head down. It suggests that upright with head down reduce the orthostatic stress to the cerebral and cardiovascular hemodynamics.

Initial Drop of Blood Pressure during Head-up Tilt in Patients with Cerebrovascular Accidents

Objective: To investigate cardiovascular responses to orthostatic stress in patients with cerebrovascular accidents (CVA). Methods: Twelve male patients with CVA, 11 healthy elderly and 12 healthy young males participated in the present study. The CVA patients had suffered stroke with hemiplegia at least 11 months prior to the study, their medical conditions were stable, and no subjects were taking medications affecting the cardiovascular system. Heart rate (HR) was determined using RR intervals from the ECG. Stroke volume (SV) was estimated by an impedance method, and cardiac output (CO) was calculated by multiplying SV by HR. Blood pressure (BP) was determined by the auscultatory method. SV, HR, CO and BP were measured every 2 min before and during 7 min of 60-degree head-up tilt (HUT). Results: SV decreased and HR increased immediately after starting HUT in all groups. CO in healthy elderly and young subjects immediately decreased during HUT also, and the decrease was sustained throughout the head-up period. However, CO in CVA patients remained constant throughout the experiment. HUT immediately decreased SBP in all groups and the magnitude of initial SBP reduction in CVA patients was greater than that in the other groups. Conclusions: We identified an initial reduction of BP during HUT in CVA patients and the recovery of BP by 3 min of head-up tilt. We emphasize that adjustment to orthostatic stress in CVA patients should be practiced by HUT, as our findings showed that CVA patients maintained physiological orthostatic tolerance except for the initial fall in BP.

Initial drop of blood pressure during head-up tilt in patients with cerebrovascular accidents

<p><b>OBJECTIVE</b>To investigate cardiovascular responses to orthostatic stress in patients with cerebrovascular accidents (CVA).</p><p><b>METHODS</b>Twelve male patients with CVA, 11 healthy elderly and 12 healthy young males participated in the present study. The CVA patients had suffered stroke with hemiplegia at least 11 months prior to the study, their medical conditions were stable, and no subjects were taking medications affecting the cardiovascular system. Heart rate (HR) was determined using RR intervals from the ECG. Stroke volume (SV) was estimated by an impedance method, and cardiac output (CO) was calculated by multiplying SV by HR. Blood pressure (BP) was determined by the auscultatory method. SV, HR, CO and BP were measured every 2 min before and during 7 min of 60-degree head-up tilt (HUT).</p><p><b>RESULTS</b>SV decreased and HR increased immediately after starting HUT in all groups. CO in healthy elderly and young subjects immediately decreased during HUT also, and the decrease was sustained throughout the head-up period. However, CO in CVA patients remained constant throughout the experiment. HUT immediately decreased SBP in all groups and the magnitude of initial SBP reduction in CVA patients was greater than that in the other groups.</p><p><b>CONCLUSIONS</b>We identified an initial reduction of BP during HUT in CVA patients and the recovery of BP by 3 min of head-up tilt. We emphasize that adjustment to orthostatic stress in CVA patients should be practiced by HUT, as our findings showed that CVA patients maintained physiological orthostatic tolerance except for the initial fall in BP.</p>