Effects of Intermittent Hypoxia on Heart Rate Variability during Rest and Exercise

Abstract

Changes in heart rate variability induced by an intermittent exposure to hypoxia were evaluated in athletes unacclimatized to altitude. Twenty national elite athletes trained for 13 days at 1200 m and either lived and slept at 1200 m (live low, train low, LLTL) or between 2500 and 3000 m (live high, train low, LHTL). Subjects were investigated at 1200 m prior to and at the end of the 13-day training camp. Exposure to acute hypoxia (11.5% O(2)) during exercise resulted in a significant decrease in spectral components of heart rate variability in comparison with exercise in normoxia: total power (p < 0.001), low-frequency component. LF (p < 0.001), high-frequency component, HF (p < 0.05). Following acclimatization, the LHTL group increased its LF component (p < 0.01) and LF/HF ratio during exercise in hypoxia after the training period. In parallel, exposure to intermittent hypoxia caused an increased ventilatory response to hypoxia. Acclimatization modified the correlation between the ventilatory response to hypoxia at rest and the difference in total power between normoxia and hypoxia (r (2) = 0.65, p < 0.001). The increase in total power, LF component, and LF/HF ratio suggests that intermittent hypoxic training increased the response of the autonomic nervous system mainly through increased sympathetic activity.

Cardiorespiratory parameters during submaximal exercise under acute exposure to normobaric and hypobaric hypoxia

“…18 A similar behaviour for cardiorespiratory parameters has also been described for acute simulated altitude exposure. 19,20 Simulated altitude systems are now more frequently used than ''real'' high altitude exposure. In this sense there are two types of simulated altitude exposure: hypobaric hypoxia (low pressure chambers) and normobaric hypoxia (hypoxic gas mixtures).…”

Sample Entropy Analysis of Heart Rate Variability during Rest and Exercise in Hypoxia

“…The increase in total power suggests that intermittent hypoxic increased the response of the autonomic nervous system mainly through increased sympathetic activity. Exposure to acute hypoxia during exercise resulted in a significant decrease in spectral components of HRV in comparison with exercise in normoxia [14].…”

“…Frequency domain analysis of HRV dissects sympathetic and parasympathetic activity [6,14], but it is very sensitive to data point missing [16,17]. Loss of data point is irrelevant to the calculation of Sample Entropy, the research of [18] shown that Sample Entropy little affected by loss of more than one-third of the data.…”

Aclimatação em altitude simulada: efeitos sobre a frequência cardíaca e saturação de oxigênio da hemoglobina em jogadores de futebol

“…Resultado também confirmado por outros estudos (POVEA et al, 2005;ALARCÓN et al, 2012), tanto para o repouso quanto durante o exercício submáximo. A diminuição da SpO 2 e o aumento do débito cardíaco em repouso ou em exercício submáximo são considerados os fatores decisivos para a redução do VO 2MÁX em altitude (CALBET et al, 2003).…”

“…Beidleman et al, (2003) observaram que a SpO 2 de repouso aumentou de 82% para 90% e a FC diminuiu de 93 para 78 bpm após três semanas de aclimatação (4h/dia, 5 dias/semana, 4.300 m). Semelhantes tendências são relatadas em estudos com hipoxia normobárica (POVEA et al, 2005;VENTURA et al, 2003 De acordo com estudos anteriores (BENDER et al, 1989;BEIDLEMAN et al, 2003), a redução da FC de repouso reflete também na queda da FC durante exercício submáximo após aclimatação a altitude. Ambas as situações apresentam redução do débito cardíaco (GROVER; WEIL; REEVES, 1986) para a mesma intensidade de esforço, e isso implica em menor carga de trabalho ao coração.…”