Identification of fast and slow ventilatory responses to carbon dioxide under hypoxic and hyperoxic conditions in humans

• Published in: The Journal of physiology Vol. 521; no. 1; pp. 273 - 287
• Main Authors: Pedersen, Michala E. F., Fatemian, Marzieh, Robbins, Peter A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 15.11.1999; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Adult; Carbon Dioxide - administration & dosage; Chemoreceptor Cells - physiology; Female; Humans; Hyperoxia - physiopathology; Hypoxia - physiopathology; Male; Models, Biological; Original; Respiratory Physiological Phenomena; Space life sciences
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1999.00273.x

Under conditions of both euoxia and hypoxia, it is generally accepted that the ventilatory response to CO 2 has both rapid (peripheral chemoreflex) and slow (central chemoreflex) components. However, under conditions of hyperoxia, it is unclear in humans whether the fast component is completely abolished or merely attenuated in magnitude. The present study develops a technique to determine whether or not a two-compartment model fits the ventilatory response to CO 2 significantly better than a one-compartment model. Data were collected under both hypoxic (end-tidal P O 2 = 50 Torr) conditions, when two components would be expected, and under hyperoxic (end-tidal P O 2 = 200 Torr) conditions, when the presence of the fast compartment is under question. Ten subjects were recruited, of whom nine completed the study. The end-tidal P CO 2 of each subject was varied according to a multi-frequency binary sequence that involved 13 steps into and 13 steps out of hypercapnia lasting altogether 1408 s. In four out of nine subjects in hypoxia, and six out of nine subjects in hyperoxia, the two-compartment model fitted the data significantly better than the one-compartment model ( F ratio test on residuals). This improvement in fit was significant for the pooled data in both hypoxia ( P < 0·05) and hyperoxia ( P < 0·005). Mean ventilatory sensitivities for the central chemoreflex were (mean ± s.e.m.) 1·69 ± 0·39 l min −1 Torr −1 in hypoxia and 2·00 ± 0·32 l min −1 Torr −1 in hyperoxia. Mean ventilatory sensitivities for the peripheral chemoreflex were 2·42 ± 0·36 l min −1 Torr −1 in hypoxia and 0·75 ± 0·16 l min −1 Torr −1 in hyperoxia. It is concluded that the rapid and slow components of the ventilatory response to CO 2 can be separately identified, and that a rapid component persists under conditions of hyperoxia.