Reproducibility of cardiovascular and gas parameters in voluntary apnea related to apnea duration: A case study

The physiology and pathophysiology of voluntary apnea is an important issue not only for recreational and professional apnea diving, rescue and military diver, but also for the genesis of the involuntary sleep apnea. Numerous physiological mechanisms are involved to counteract the induced unbalance in the body´s homeostasis. Even though cardiovascular effects are qualitatively similar in humans (such as diving reflex) the extent and temporal course can strongly vary from person to person. The present work discloses for the first time the behaviour of vital cardiovascular and gas parameters (in blood and air) as a novel function of the apnea duration. Blood pressure and heart rate increased for increasing apnea durations while pulsatile amplitude of the pulse wave in the finger and in the ear decreased. It is shown that carbon dioxide production per minute was quite stable independently of the voluntary apnea duration, whereas oxygen consumption per minute increased with increasing duration. The estimated respiratory quotient declined for longer apneas since the produced carbon dioxide in the lungs tended to increase slower than the consumed oxygen in the lungs. The oxygen saturation in blood exhibited a non-linear behaviour over the apnea duration, whereas the estimated partial pressure of oxygen decreased almost linearly over the duration. In addition, the reproducibility of cardiovascular parameters for apneas of different durations was quantified, given standardized conditions before apnea. Reproducibility, i.e. variation of a signal, for heart rate, systolic blood pressure and oxygen saturation was 10.6%, 8% and 1.4%, respectively, attained over different days of apnea recording. Higher variability in the heart rate and the blood pressure indicates their relevance as a regulatory parameter to counteract the physiological imbalance due to apnea.