ABSTRACT
Hypoxia increases inspiratory muscle work and consequently contributes to a reduction in exercise performance. We evaluate the effects of inspiratory muscle warm-up (IMW) on a 10 km cycling time trial in normoxia (NOR) and hypoxia (HYP). Eight cyclists performed four time trial sessions, two in HYP (FiO2: 0.145) and two in NOR (FiO2: 0.209), of which one was with IMW (set at 40% of maximal inspiratory pressure-MIP) and the other was with the placebo effect (PLA: set at 15% MIP). Time trials were unchanged by IMW (NORIMW: 893.8 ± 31.5 vs. NORPLA: 925.5 ± 51.0 s; HYPIMW: 976.8 ± 34.2 vs. HYPPLA: 1008.3 ± 56.0 s; p > 0.05), while ventilation was higher in HYPIMW (107.7 ± 18.3) than HYPPLA (100.1 ± 18.9 L.min-1; p ≤ 0.05), and SpO2 was lower (HYPIMW: 73 ± 6 vs. HYPPLA: 76 ± 6%; p ≤ 0.05). A post-exercise-induced reduction in inspiratory strength was correlated with exercise elapsed time during IMW sessions (HYPIMW: r = -0.79; p ≤ 0.05; NORIMW: r = -0.70; p ≤ 0.05). IMW did not improve the 10 km time trial performance under normoxia and hypoxia.
ABSTRACT
We tested the hypothesis that inspiratory resistive loading (IRL) increases vagal-mediated complexity of heart rate variability (HRV) in older women. We recorded heart rate continually during 30 breaths with Sham or IRL (30 % of maximal inspiratory pressure) in sitting position. The normalized spectral power in the low (LFn) and high (HFn) frequency bands and the symbolic dynamics measures for 0 V, 2UV and 2 L V were obtained. HFn was higher and LFn was lower during IRL than Sham (p < 0.05). During IRL, 2UV component increased more than Sham (p < 0.05) while 0 V index remained unchanged (p> 0.05). In conclusion, acute IRL improved vagal modulation index of both linear (spectral analysis) and non-linear analysis (symbolic dynamics) in older women.
Subject(s)
Aging/physiology , Autonomic Nervous System/physiology , Breathing Exercises , Heart Rate/physiology , Inhalation/physiology , Respiratory Muscles/physiology , Aged , Female , Humans , Middle Aged , Respiratory Rate/physiology , Vagus Nerve/physiologyABSTRACT
PURPOSE: Aging impairs the autonomic balance reducing the vagal and increasing the sympathetic components of heart rate variability (HRV) and this could be associated with a decline in physical capacity. Inspiratory muscle training (IMT) is a possible tool to attenuate this physical capacity decline in older women. The aim of this study was to investigate the influence of IMT in the older women on physical capacity and autonomic cardiac modulation at rest and post exercise. METHODS: 20 female participants 60-72 years old were randomly allocated in two groups. One group underwent IMT set at 50% of maximum inspiratory pressure (MIP), every day for 4 weeks (IMT-group). The placebo group performed the same training procedure but with a minimal resistance (5% MIP; PLA-group). Every week, the IMT load was readjusted and the HRV evaluated at rest. The six-minute walk test (6MWT) was performed once pre and post IMT-intervention. The IMT-group and PLA-group performed the same test and intervention procedures. RESULTS: After a 5 weeks intervention, the MIP had significantly improved in the IMT-group but not in the PLA-group (p < 0.01; es = 1.17). The high frequency power of the HRV spectrum had already improved by the second week (p < 0.01; es = 1.13) and remained elevated until the last week of intervention (p < 0.01; es = 1.43). The same positive results were described in 6MWT distance (p = 0.04; es = 0.39) and the change (∆) of heart rate recovery (HRR) from 1 min (p = 0.02; es = 0.68). CONCLUSION: IMT increases HRV, improves 6MWT distance and HRR.
Subject(s)
Autonomic Nervous System/physiology , Exercise Tolerance , Heart/physiology , Physical Conditioning, Human/methods , Respiratory Muscles/physiology , Aged , Female , Heart/innervation , Heart Rate , Humans , Middle Aged , Physical Conditioning, Human/adverse effectsABSTRACT
Fundamento: A hipóxia é uma condição fisiológica que pode influenciar a modulação autonômica cardíaca, qualpode ser avaliada pelas flutuações espontâneas da frequência cardíaca, chamada de variabilidade da frequência cardíaca (VFC). Estudos têm reportado reduções ou manutenção da VFC em situação de hipóxia apresentando efeitos controversos. Há uma lacuna no conhecimento em relação às modificações da VFC durante a hipóxia. Objetivo: Revisar sistematicamente estudos que investigaram os efeitos da hipóxia na VFC em adultos saudáveis e não aclimatados durante o repouso. Métodos: A presente revisão sistemática foi realizada a partir da diretriz PRISMA. Os termos utilizados para a busca nas bases MEDLINE, SCOPUS, LILACS e EUROPE PMC foram: "heart rate variability" OR "cardiac autonomic modulation" OR "cardiac autonomic regulation" AND (hypoxia OR altitude) NOT intermitente NOT sleep. Os registros foram filtrados por espécie, idade e idiomas. Resultados: Ao final da triagem e elegibilidade restaram 13 artigos para a síntese qualitativa. Discussão: Os estudos utilizam protocolos experimentais variados que envolvem diferença na pressão barométrica, no nível de oxigênio, no tempo de exposição à hipóxia e no controle da frequência respiratória. Possivelmente a influência desses fatores e também a variação interindividual à hipóxia podem justificar diferentes respostas na VFC. Conclusão: A partir dos estudos investigados, a hipóxia foi capaz de gerar uma queda na VFC, seja por retirada ou manutenção da modulação vagal, ou por predomínio simpático ou mesmo pela combinação dessas respostas em adultos saudáveis não aclimatados a hipóxia. Este efeito parece ser dependente do nível de altitude e da pressão barométrica
Background: Hypoxia is a physiological condition that may affect the cardiac autonomic modulation, which can be assessed by spontaneous fluctuations in heart rate, know as heart rate variability (HRV). Studies have reported reductions or maintenance of HRV in hypoxic situation presenting controversial effects. There is a knowledge gap in relation to changes in HRV during hypoxia. Objective: The aim of this study was to systematically review the effects of hypoxia on HRV in unacclimatized healthy adults at rest. Methods: This systematic review was performed according to PRISMA guidelines. Search terms used in MEDLINE, SCOPUS, LILACS and EUROPE PMC database were: "heart rate variability" OR "cardiac autonomic modulation" OR "cardiac autonomic regulation" AND NOT intermittent NOT sleep (hypoxia OR altitude). Records were filtered by species, age group and language. Results: At the end of the screening and eligibility, 13 manuscripts remained for qualitative synthesis. Discussion: The studies used different experimental protocols involving difference in barometric pressure, oxygen level, time of exposure to hypoxia and control of respiratory rate. Possibly the influence of these factors and also the interindividual variation to hypoxia may justify different responses in HRV. Conclusion: Based on the investigated studies, hypoxia has been capable of generating a decrease in HRV, either by reduction or maintenance of vagal modulation, or by sympathetic predominance or even the combination of these responses in healthy adults unacclimatized to hypoxia. This effect appears to be dependent on altitude level and barometric pressure
