Selected contribution: chemoreflex responses to CO2 before and after an 8-h exposure to hypoxia in humans.
The ventilatory sensitivity to CO2, in hyperoxia, is increased after an 8-h exposure to hypoxia. The purpose of the present study was to determine whether this increase arises through an increase in peripheral or central chemosensitivity. Ten healthy volunteers each underwent 8-h exposures to 1) isocapnic hypoxia, with end-tidal PO2 (PET(O2)) = 55 Torr and end-tidal PCO2 (PET(CO2)) = eucapnia; 2) poikilocapnic hypoxia, with PET(O2) = 55 Torr and PET(CO2) = uncontrolled; and 3) air-breathing control. The ventilatory response to CO2 was measured before and after each exposure with the use of a multifrequency binary sequence with two levels of PET(CO2): 1.5 and 10 Torr above the normal resting value. PET(O2) was held at 250 Torr. The peripheral (Gp) and the central (Gc) sensitivities were calculated by fitting the ventilatory data to a two-compartment model. There were increases in combined Gp + Gc (26%, P < 0.05), Gp (33%, P < 0.01), and Gc (23%, P = not significant) after exposure to hypoxia. There were no significant differences between isocapnic and poikilocapnic hypoxia. We conclude that sustained hypoxia induces a significant increase in chemosensitivity to CO2 within the peripheral chemoreflex.
University Laboratory of Physiology, University of Oxford, Oxford OX1 3PT, United Kingdom.
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Fatemian
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Robbins
D000293:Adolescent; D000328:Adult; D000465:Algorithms; D001273:Atmosphere Exposure Chambers; D002245:Carbon Dioxide / Q000097:blood / Q000502:physiology*; D002490:Central Nervous System / Q000503:physiopathology; D002628:Chemoreceptor Cells / Q000502:physiology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017933:Peripheral Nervous System / Q000503:physiopathology; D015656:Respiratory Mechanics / Q000502:physiology
D002245:Carbon Dioxide