Pulmonary gas exchange in diving

• Published in: Journal of applied physiology (1985) Vol. 106; no. 2; pp. 668 - 677
• Main Authors: Moon, R. E, Cherry, A. D, Stolp, B. W, Camporesi, E. M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-02-2009; American Physiological Society
• Subjects: Airway Resistance; Animals; Biological and medical sciences; Diffusion; Diving; Diving - adverse effects; Fundamental and applied biological sciences. Psychology; Hemoglobin; Hemoglobins - metabolism; Humans; Hypercapnia - etiology; Hypercapnia - metabolism; Hypercapnia - physiopathology; Hyperoxia - etiology; Hyperoxia - metabolism; Hyperoxia - physiopathology; Lung - blood supply; Lung - physiopathology; Lung Compliance; Oxygen; Oxygen - blood; Physiology; Pulmonary Circulation; Pulmonary Edema - etiology; Pulmonary Edema - physiopathology; Pulmonary Ventilation; Respiratory Dead Space; Respiratory Mechanics; Respiratory system; Tidal Volume; Ventilation-Perfusion Ratio; Work of Breathing; Lung; ventilation-perfusion ratio; Respiratory system; Dead space; Vertebrata; Mammalia; Perfusion; respiratory dead space; respiratory mechanics; Diving; Ratio; Gas exchange; Pulmonary ventilation; Respiration
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.91104.2008

1 Department of Anesthesiology, Department of Medicine, and Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; and 2 Department 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 P O 2 . 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 (V D /V T ), possibly due to impairment of intrapulmonary gas phase diffusion and distribution of ventilation. The net result of relative hypoventilation and increased V D /V T is hypercapnia. The effect of high inspired P O 2 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
Address for reprint requests and other correspondence: R. E. Moon, Dept. of Anesthesiology, Dept. of Medicine, and Center for Hyperbaric Medicine & Environmental Physiology, Duke Univ. Medical Center, Durham, NC 27710 (e-mail: richard.moon{at}duke.edu )