Abstract
Understanding the mechanisms of oxygen supply regulation, which involves the respiratory and cardiovascular systems, during human adaptation to intense physical activity, accompanied by hypoxemia, is important for the management of a training process. The objectives of this study were to investigate the cardiorespiratory coherence (CRC) changes in the low-frequency band in response to hypoxic exposure and to verify a dependence of these changes upon sports qualification level in athletes. Twenty male runners aged 17–25 years were exposed to acute normobaric hypoxia (10% O2) for 10 min. Respiration, gas exchange, and heart rate were measured at baseline, during hypoxia, and after the exposure. To evaluate cardiorespiratory coupling, squared coherence was calculated based on 5-s averaged time series of heart and respiratory rhythms. Based on sports qualification level achieved over 4 years after the experimental testing, athletes were retrospectively divided into two groups, one high level (HLG, n = 10) and the other middle level (MLG, n = 10). No differences in anthropometric traits were observed between the groups. In the pooled group, acute hypoxia significantly increased CRC at frequencies 0.030–0.045 Hz and 0.075 Hz. In response to hypoxia, oxygen consumption decreased in HLG, and carbon dioxide production and ventilation increased in MLG. At 0.070–0.080 Hz frequencies in hypoxia, the CRC in HLG was higher than in MLG. Thus, highly qualified athletes enhance intersystem integration in response to hypoxia. This finding can be a physiological sign for the prognosis of qualification level in runners.
Highlights
At rest and during sleep, the coupling of the cardiovascular and respiratory systems manifests as respiratory sinus arrhythmia (RSA) and cardiorespiratory phase synchronization (Moser et al, 1995; Kralemann et al, 2013; Bartsch et al, 2014)
We have previously demonstrated that the magnitude of the relationship between the hypoxic responses of the systems depends on the kind of sport and the athlete’s qualification level (Divert et al, 2015, 2017)
Based on sports qualification level achieved over 4 years after the hypoxic experimental testing, athletes were retrospectively divided into two groups, one high level (HLG, n = 10) and the other middle level (MLG, n = 10)
Summary
At rest and during sleep, the coupling of the cardiovascular and respiratory systems manifests as respiratory sinus arrhythmia (RSA) and cardiorespiratory phase synchronization (clustering of heartbeats within each respiratory cycle) (Moser et al, 1995; Kralemann et al, 2013; Bartsch et al, 2014). Stress tests from a battery of Ewing tests (handgrip static load and tilt test) have been shown to lead to the disappearance of intersystem phase synchronization (Sobiech et al, 2017). Other work suggests that orthostatic challenge and cognitive load enhance the role of the baroreflex-mediated cardiorespiratory interaction (Krohova et al, 2018). Since the effect of baroreflex is demonstrated in the low-frequency (LF) band, it seems reasonable to suspect that stress induces a rise in cardiorespiratory coupling in a lower frequency range rather than in the range characterizing vagal tone
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