RELIEF OF DISTRESS OF BREATHHOLDING - SEPARATE EFFECTS OF EXPIRATION AND INSPIRATION

It is well known that rebreathing relieves the respiratory distress of maximal breathholding despite worsening blood gases, and it has been suggested that vagal input has a role in ameliorating this sensation via activation of pulmonary stretch receptors (PSR). However, it is believed by divers that expiration can lead to partial relief of distress of breathholding at total lung capacity (TLC) allowing a prolongation of breathholding. We studied the independent effects of an expiration and an inspiration on relief of respiratory distress of breathholding. Subjects held their breath at TLC until distress became intolerable, then exhaled to FRC and performed a second breathhold. When distress again became intolerable, subjects inspired to TLC a gas that resembled their exhaled gas and performed a third breathhold. Subjects noted partial relief with both an expiration and an inspiration. However, relief of distress was greater and the subsequent breathhold longer after an inspiration than after an expiration. We suggest that relief of distress after an inspiration is compatible with the inhibitory effect of PSR input; the mechanism of relief that occurs after an expiration is as yet uncertain.