Effect of mild hypoxia on ventilation during exercise

¹ Laboratory of Thoracic Physiology, Department of Surgery; Division of Anesthesiology; and Department of Physiology, Washington University School of Medicine, St. Louis, Missouri

Hypoxia of mild degree (Pa_OO2 above 60 mm Hg) produces little or no ventilatory response in resting man during the steady state. To evaluate the possibility that the effectiveness of a hypoxic chemoreceptor drive might be enhanced by exercise, the ventilatory response to mild hypoxia was measured in two human subjects during rest and exercise. Though no significant increase in ventilation occurred at rest above a Pa_OO2 of 60 mm Hg, a decrease in Pa_OO2 from 100 to 94 mm Hg produced a statistically significant increase in steady state ventilation during moderate exercise. In addition, temporary block of the sympathetic innervation to the carotid and aortic bodies in one subject resulted in a diminution of work hyperpnea. This suggests that increased sympathetic tone during exercise, by reducing blood flow through the chemoreceptors, might result in increased neural discharge and hence increased ventilation even though arterial P_OO2 is the same as at rest. Thus, activity of the chemoreceptors as modified by sympathetic control of their blood supply may be an important determinant of the ventilatory response to exercise. Since work hyperpnea is enhanced by even mild hypoxia, this ventilatory response may be sufficient to initiate respiratory acclimatization to altitudes so low that resting ventilation on acute exposure is unaffected.

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				H. E. Wood, M. Fatemian, and P. A. Robbins Respiratory: Prior sustained hypoxia attenuates interaction between hypoxia and exercise as ventilatory stimuli in humans Exp Physiol, January 1, 2007; 92(1): 273 - 286. [Abstract] [Full Text] [PDF]