Contrasting effects of hypoxia and hypercapnia on ventilation and sympathetic activity in humans

V. K. Somers, A. L. Mark, D. C. Zavala, F. M. Abboud

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415 Scopus citations


We compared the effects of isocapnic hypoxia (IHO) and hyperoxic hypercapnia (HC) on sympathetic nerve activity (SNA) recorded from a peroneal nerve in 13 normal subjects. HC caused greater increases in blood pressure (BP), minute ventilation (V̇E), and SNA [53 ± 14% (SE) during HC vs. 21 ± 7% during IHO; P < 0.05]. Even at equivalent levels of V̇E, HC still elicited greater SNA than IHO. However, apnea during HC caused a lesser (P < 0.05) increase in SNA (91 ± 26% compared with apnea on room air) than apnea during IHO (173 ± 50%). Hypercapnic hypoxia resulted in a greater absolute increase in V̇E (23.6 ± 2.8 l/min) than the additive increases due to HC alone plus IHO alone (18.0 ± 1.8 l/min, P < 0.05). SNA also increased synergistically by 108 ± 23% with the combined stimulus compared with the additive effect of HC alone plus IHO alone (68 ± 19%; P < 0.05). We conclude that 1) HC causes greater increases in V̇E and SNA than does hypoxia; 2) for the same increase in V̇E, hypercapnia still causes a greater increase in SNA than hypoxia; however, during apnea, hypoxia causes a much greater increase in SNA than hypercapnia; 3) the inhibitory influence of ventilation on SNA is greater during hypoxia (i.e., predominantly peripheral chemoreceptor stimulation) than hypercapnia (i.e., predominantly central chemoreceptor stimulation); and 4) combined hypoxia and hypercapnia have a synergistic effect on SNA as well as on V̇E.

Original languageEnglish (US)
Pages (from-to)2101-2106
Number of pages6
JournalJournal of applied physiology
Issue number5
StatePublished - 1989


  • Hypercapnic hypoxia

ASJC Scopus subject areas

  • General Medicine


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