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

J Appl Physiol (1985). 1989 Nov;67(5):2101-6. doi: 10.1152/jappl.1989.67.5.2101.

Abstract

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 (VE), and SNA [53 +/- 14% (SE) during HC vs. 21 +/- 7% during IHO; P less than 0.05]. Even at equivalent levels of VE, HC still elicited greater SNA than IHO. However, apnea during HC caused a lesser (P less than 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 VE (23.6 +/- 2.8 l/min) than the additive increases due to HC alone plus IHO alone (18.0 +/- 1.8 l/min, P less than 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 less than 0.05). We conclude that 1) HC causes greater increases in VE and SNA than does hypoxia; 2) for the same increase in VE, 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 VE.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Apnea
  • Carbon Dioxide / pharmacology*
  • Chemoreceptor Cells / physiology
  • Female
  • Hemodynamics
  • Humans
  • Hypoxia
  • Male
  • Membrane Potentials
  • Oxygen / pharmacology*
  • Respiration / physiology*
  • Respiratory Function Tests
  • Sympathetic Nervous System / physiology*

Substances

  • Carbon Dioxide
  • Oxygen