Abstract
SummaryFace immersion breath‐holds were performed by five seated male subjects after normal breathing of room air, normal breathing of 100% oxygen for 15 minutes and hyperventilation of 100% oxygen for 15 minutes. Heart rate and forearm blood flow were determined in all three procedures and PO2,PCO2 and pH of brachial artery blood were measured in the oxygen breathing experiments.Simulated diving after breathing room air significantly reduced the heart rate and forearm blood flow. After normal breathing and hyperventilation of oxygen, PaO2 was elevated by three and five times, respectively. PaCO2 was unchanged by normal breathing but halved by hyperventilation. “Diving” after both oxygen breathing procedures still significantly reduced both heart rate and forearm blood flow below resting control levels and these responses were not significantly different from those after breathing room air.The fall in arterial oxygen tension during “diving” after hyperventilation of oxygen was inversely related to the fall in forearm blood flow (P < 0.001) which fits the concept that the diving response may serve an oxygen conserving function in man. Despite arterial hyperoxia with or without hypocapnia, a significant diving response was still evoked by face immersion breath‐holding, showing that the response is basically independent of asphyxial blood gas changes.
Published Version
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