Journal of Applied Physiology, Vol 72, Issue 1 242-250, Copyright © 1992 by American Physiological Society

ARTICLES

Long-lasting ventilatory response of humans to a single breath of hypercapnia in hyperoxia

M. Modarreszadeh and E. N. Bruce
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106.

It has often been assumed that under normoxia, closed-loop ventilatory responses to transient CO2 stimulation (i.e., lasting for 1-3 breaths) are less likely to be mediated by the slow-responding central (medullary) chemoreflex. This assumption, however, has not been quantitatively examined in humans. We hypothesized that in the closed-loop respiratory chemical feedback system [in which the centrally mediated ventilatory response to transient changes in the arterial PCO2 levels (PaCO2) will in turn affect the pulmonary CO2 and hence PaCO2], the contribution of the central chemoreflex pathways to brief disturbances in blood gases may be more important than considered previously. Using the technique of pseudorandom binary CO2 stimulation, we quantified the ventilatory response of normal humans to brief disturbances in arterial CO2 during hyperoxia. Tidal volume (VI), inspiratory ventilation (VI), inspiratory time (TI), expiratory time (TE), and end-tidal CO2 fraction (FETCO2) were measured in subjects who inhaled a mixture that was pseudorandomly switched between 95% O2-5% CO2 and 100% O2 (63 breath sequences). From these data, we calculated the responses of VI, VI, TI, TE, and FETCO2 to a single-breath inhalation of 1% CO2 in O2. Our results showed that in response to a brief increase of 0.75 Torr in alveolar CO2, VI showed a transient increase (average peak response of 0.12 1/min) that persisted for greater than or equal to 80 s in every subject. The response of VI was similar to that of VI, whereas TI and TE showed no consistent changes. Using these results we calculated that central chemoreflex pathways may contribute significantly to typical transient CO2 stimulation tests in hyperoxic and normoxic humans.

This article has been cited by other articles:

				S. Thomson, M. J. Morrell, J. J. Cordingley, and S. J. Semple Ventilation is unstable during drowsiness before sleep onset J Appl Physiol, November 1, 2005; 99(5): 2036 - 2044. [Abstract] [Full Text] [PDF]

				K. A. Waters and K. D. Tinworth Effect of stimulus cycle time on acute respiratory responses to intermittent hypercapnic hypoxia in unsedated piglets J Appl Physiol, June 1, 2003; 94(6): 2465 - 2474. [Abstract] [Full Text] [PDF]

				Z. L. Topor, L. Johannson, J. Kasprzyk, and J. E. Remmers Dynamic ventilatory response to CO2 in congestive heart failure patients with and without central sleep apnea J Appl Physiol, July 1, 2001; 91(1): 408 - 416. [Abstract] [Full Text] [PDF]

				D. W. HUDGEL, E. A. GORDON, S. THANAKITCHARU, and E. N. BRUCE Instability of Ventilatory Control in Patients with Obstructive Sleep Apnea Am. J. Respir. Crit. Care Med., October 1, 1998; 158(4): 1142 - 1149. [Abstract] [Full Text] [PDF]

				D. S. Pine, J. D. Coplan, L. A. Papp, R. G. Klein, J. M. Martinez, P. Kovalenko, N. Tancer, D. Moreau, E. S. Dummit III, D. Shaffer, et al. Ventilatory Physiology of Children and Adolescents With Anxiety Disorders Arch Gen Psychiatry, February 1, 1998; 55(2): 123 - 129. [Abstract] [Full Text] [PDF]

				J. Lai and E. N. Bruce Ventilatory stability to transient CO2 disturbances in hyperoxia and normoxia in awake humans J Appl Physiol, August 1, 1997; 83(2): 466 - 476. [Abstract] [Full Text] [PDF]