Vagal cardiac and pulmonary mechanisms are linked, and improvement in one vagal limb might spill over into the other. Baroreceptor sensitivity can be enhanced significantly by slow breathing (supported by a small reduction in the heart rate observed during slow breathing and by reduction in both systolic and diastolic pressure). Slow pace bhastrika pranayama (respiratory rate 6/min) exercise thus shows a strong tendency to improving the autonomic nervous system through enhanced activation of the parasympathetic system.
Introduction:
In the spaceflight, during launch and re-entry, the crew is exposed to acceleration ranging from +4Gx to +8Gx in nominal conditions. This study was conducted to assess the changes in cardiorespiratory parameters, namely, heart rate (HR), electrocardiogram (ECG), respiratory rate (RR), and SpO2 on exposure to simulated +Gx acceleration.
Material and Methods:
Fifteen randomly selected healthy male volunteers participated in the study. They were exposed to a simulated acceleration profile consisting of two peaks in the high-performance human centrifuge; first peak of +4Gx for 30 s and second peak of+8Gx for 30 s. The cardiorespiratory parameters were monitored and recorded during the acceleration exposure. The data were compiled and analyzed using one-way repeated measures ANOVA.
Results:
Significant increase in HR was observed on exposure to +4Gx (110.4 ± 16.7 bpm; P < 0.001) in comparison to the baseline value (80.5 ± 7.5 bpm). However, the changes in the HR at +8Gx were not significant in comparison to baseline as well as +4Gx values. On the other hand, RR indicated a significant increase on exposure to +8Gx (25.2 ± 5.8 breaths/min) in comparison to the baseline (15.1 ± 1.6 breaths/min; P = 0.001) and +4Gx (19.0 ± 6.1 breaths/min; P = 0.009) values. SpO2 showed a significant reduction at +8Gx (94.2 ± 3.8%) in comparison to baseline (98.9 ± 0.3%; P = 0.004) and +4Gx (96.9 ± 1.5%; P = 0.003). ECG did not show any evidence of arrhythmia during the exposure to +Gx acceleration.
Conclusion:
The insignificant changes in the HR at peak of +8Gx indicate less pronounced effects on the smaller hydrostatic gradient in +Gx acceleration unlike +Gz acceleration. However, the findings of the study point towards a significant increase in respiratory rate and reduction in SpO2 at +8Gx.
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