Subacute effects of inspiratory resistive loading and head-out water immersion on pulmonary function

Extrathoracic airways obstruction and scuba diving may induce pulmonary edema, probably because of increased hydrostatic transmural capillary pressure in the lung. This study was designed to examine the subacute pulmonary effects of the combined exposure to inspiratory resistive loading and immersion, as in scuba diving. Two groups each of eight healthy men were exposed to head-out water immersion in thermoneutral water for 40 min with or without an added inspiratory resistive load. At flows of 0.5 and 1.0 liter.s, the measured resistances were 4.4 and 9.0 hPa.s(-1).liter(-1), respectively. Pulmonary function, including a flow-volume loop and transfer factor of the lung for carbon monoxide (Tl-CO), was measured before and 60 min after the end of the exposures. Body fluid balance was restored in the first 15 min after exposure, and Tl-CO was always corrected to a hemoglobin concentration of 146 g.liter(-1). There was a significant reduction in Tl-CO of 7.3 +/- 5.5% (P < 0.01) after the combined exposure to head-out water immersion and inspiratory resistive load. No changes in pulmonary function were seen after exposure to head-out water immersion or inspiratory resistive loading alone. The change in Tl-CO was normalized within 24 h. Submersion and resistance in breathing apparatus may contribute to the changes in pulmonary function seen immediately after dives. The nature of the exposure in these experiments and the time for recovery indicate that these changes are mechanically induced, and may not contribute to the long-term effects of diving on the lung.