Effect of lung volume on the diving response in man.

In an attempt to clarify the influence of lung volume on the cardiac component of the diving response in man, 10 subjects were studied while holding their breath for 20 s after inspiration or expiration, with or without immersion of the face in water. The electrocardiogram was recorded before and during each maneuver. After expiration, an increase in pulse interval was seen only on face immersion. After inspiration, an equal change in pulse interval was seen whether or not the face was immersed. Therefore the early bradycardia of face immersion is not apparent after inspiration.