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REVIEW

HIGHLIGHTED TOPIC
The Physiology and Pathophysiology of the Hyperbaric and Diving Environments

Pulmonary gas exchange in diving

¹Department of Anesthesiology, Department of Medicine, and Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; and ²Department of Molecular Pharmacology and Physiology, University of South Florida, Tampa, Florida

ABSTRACT

Diving-related pulmonary effects are due mostly to increased gas density, immersion-related increase in pulmonary blood volume, and (usually) a higher inspired PO₂. Higher gas density produces an increase in airways resistance and work of breathing, and a reduced maximum breathing capacity. An additional mechanical load is due to immersion, which can impose a static transrespiratory pressure load as well as a decrease in pulmonary compliance. The combination of resistive and elastic loads is largely responsible for the reduction in ventilation during underwater exercise. Additionally, there is a density-related increase in dead space/tidal volume ratio (VD/VT), possibly due to impairment of intrapulmonary gas phase diffusion and distribution of ventilation. The net result of relative hypoventilation and increased VD/VT is hypercapnia. The effect of high inspired PO₂ and inert gas narcosis on respiratory drive appear to be minimal. Exchange of oxygen by the lung is not impaired, at least up to a gas density of 25 g/l. There are few effects of pressure per se, other than a reduction in the P50 of hemoglobin, probably due to either a conformational change or an effect of inert gas binding.

respiratory dead space; ventilation-perfusion ratio; respiratory mechanics

This article has been cited by other articles:

				D. R. Pendergast and C. E. G. Lundgren The physiology and pathophysiology of the hyperbaric and diving environments J Appl Physiol, January 1, 2009; 106(1): 274 - 275. [Full Text] [PDF]