Pulmonary gas exchange in diving.
Diving-related pulmonary effects are due mostly to increased gas density, immersion-related increase in pulmonary blood volume, and (usually) a higher inspired Po(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 (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 Po(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.
Moon
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Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA. richard.moon@duke.edu
Cherry
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Stolp
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Camporesi
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D000403:Airway Resistance; D000818:Animals; D004058:Diffusion; D004242:Diving / Q000009:adverse effects*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D006935:Hypercapnia / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology*; D018496:Hyperoxia / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology*; D008168:Lung / Q000098:blood supply / Q000503:physiopathology*; D008170:Lung Compliance; D010100:Oxygen / Q000097:blood; D011652:Pulmonary Circulation; D011654:Pulmonary Edema / Q000209:etiology / Q000503:physiopathology; D012123:Pulmonary Ventilation; D012126:Respiratory Dead Space; D015656:Respiratory Mechanics; D013990:Tidal Volume; D014692:Ventilation-Perfusion Ratio; D014939:Work of Breathing
D006454:Hemoglobins; D010100:Oxygen