title: Lung compression effects on gas exchange in human breath-hold diving.
abstract: Lung compression during breath-hold diving reduces gas exchanging surface area. Beyond a critical depth, collapse of all alveoli should result in total pulmonary shunt and a drop in arterial oxygen partial pressure toward the mixed-venous level. The effect of lung collapse on human breath-hold diving capability is analysed using a computational model of the lungs and circulation that simulates oxygen, carbon dioxide, and nitrogen exchange between alveoli, blood, and tissues. Gas uptake during descent becomes limited by lung compression when the ratio of diffusing capacity to the product of perfusion and gas solubility in blood drops below one. An equation is derived for estimating collapse depth due to direct alveolar compression and time-dependent absorption atelectasis. Oxygen dissolved in blood during descent builds a limited capacitive store for supporting metabolism during the period of lung collapse. Hypoxemia with loss of consciousness prior to alveolar re-opening on ascent is predicted to occur on dives beyond 300 m, depending on initial lung volume.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, 5849 University Avenue, Halifax, N.S., Canada B3H 4H7. jfitzclarke@eastlink.ca
authors.forename: John R
authors.initials: JR
authors.lastname: Fitz-Clarke
mesh_terms: D001049:Apnea / Q000503:physiopathology; D002245:Carbon Dioxide / Q000378:metabolism; D004058:Diffusion; D004242:Diving / Q000502:physiology*; D006801:Humans; D008176:Lung Volume Measurements; D008954:Models, Biological; D008955:Models, Cardiovascular; D010100:Oxygen / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000098:blood supply / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D014109:Total Lung Capacity / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen