Physiological unbalance during dry static apneas: Effects of preceding preparations

The aim of the present study was to determine whether, and to what extent, breathing preparations right before a voluntary apnea influences the characteristics of the diving response. To validate the impact of such breathing exercise on the diving response, sixteen non-divers and three diving athletes performed short apneas of 45 seconds with alternating starting conditions. We found that while the diving response in non-divers was observed during apneas after normal inspiration (mean arterial pressure, MAP, increased by 12.3±12.8% and heart rate, HR, decreased by 10.4±9.6%), the effects of the response decreased during apneas after deep inspiration (MAP 3±8%, HR 7.4±10.3%) and were hardly noticeable during apneas following a short breathing exercise (MAP 0.7±10.3%, HR 3.5±9.7%). Similar effects could also be seen in professional divers with stronger expressed diving response. Apneas with larger load on the body were accompanied by a stronger diving response. We also found that apneas without any preceding preparation but one normal inspiratory breath were subjectively hard to sustain even for diving athletes. This was also displayed in a prominent drop of oxygen saturation in both groups of divers and non-divers.