VOLUNTARY BREATHHOLDING. III. THE RELATION OF THE MAXIMUM TIME OF BREATHHOLDING TO THE OXYGEN AND CARBON DIOXIDE TENSIONS OF ARTERIAL BLOOD, WITH A NOTE ON ITS CLINICAL AND PHYSIOLOGICAL SIGNIFICANCE 1

Open Access
Publisher Website
Google Scholar
Abstract
The authors studied in men the arterial O2, CO2 and pH before, during and at the termination of maximum voluntary breathholding at tensions of O2 in the initially inspired air ranging from 85 to 740 mm. Hg and correlated these blood levels with pulmonary oxygen diffusion as measured by the technique of underwater weighing. It was demonstrated that during breathholding, O2 diffuses through the lungs much more readily than CO2[long dash]due, in part, to the higher diffusion coefficient of gaseous O2 and, in part, to the higher O2 diffusion gradient. Thereafter, under normal conditions, respiratory ventilation is adjusted to equilibrate CO2 rather than O2 because CO2 is the least diffusible gas. The arterial O2, CO2 and pH levels at the breaking point (termination of maximum breathholding) were analyzed to determine the relative importance of O2 and CO2 in forcing the subjects to take a breath. At normal or subnormal O2 tensions PO2 and pCO2 levels were of equal importance in forcing the subject to breathe. At higher O2 tensions, pO2 had little influence. However, there was a constant reciprocal interrelation of O2 content and.pCO2 to the breaking point at all tensions of O2 studied and O2 content and CO2 were equally important in stimulating the taking of breath. The lessening effect of added O2 increments at supranormal arterial and alveolar O2 tensions in lengthening the breadthholding time is not because O2 loses its effect on respiratory tissues, but because once the hemoglobin is saturated, the blood is less effective in delivering added increments of O2 to the tissues. O2 and CO2 are interrelated as factors which influence the breathholding time, regardless of the relative tensions of each of these gases in the blood. It is suggested that breathholding techniques may be usefully applied to the study of pulmonary diffusion and of factors related to respiratory control in man.