DIFFERENTIAL-EFFECTS OF DIGITALIS ON CHEMOREFLEX RESPONSES IN HUMANS

To investigate the effects of digitalis on chemoreflexes in humans, we measured muscle sympathetic nerve activity (microneurography), minute ventilation, oxygen saturation, end-tidal carbon dioxide, mean arteri al pressure, heart rate, and central venous pressure during stimulatio n of peripheral chemoreceptors with hypoxia, during stimulation of cen tral chemoreceptors with hypercapnia, and during a cold presser test b efore and after digitalis and placebo in 10 healthy volunteers on two different days (randomized, double-blind, crossover design). Digitalis did not affect baseline measurements significantly. Despite similar c hanges in oxygen saturation and end-tidal carbon dioxide during hypoxi a and hypercapnia with both placebo and digitalis, digitalis significa ntly potentiated overall ventilatory responses to hypoxia (+67+/-12% b efore versus +98+/-3% after digitalis; mean+/-SEM; P<.01) but did not affect the response to hypercapnia. Sympathetic nerve activity increas ed by 25+/-9% during hypoxia before digitalis and 30+/-10% during hypo xia after digitalis (P=NS) and increased by 38+/-18% during hypercapni a before digitalis and 26+/-11% during hypercapnia after digitalis (P= NS). Digitalis did not significantly change responses to the cold pres ser test. Placebo had no effect on ventilatory and sympathetic nerve a ctivity responses. We conclude that digitalis selectively augments ven tilatory responses to peripheral chemoreceptor stimulation by hypoxia.