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

Extrathoracic airways obstruction and scuba diving may induce pulmonary ede ma, probably because of increased hydrostatic transmural capillary pressure in the lung. This study was designed to examine the subacute pulmonary eff ects of the combined exposure to inspiratory resistive loading and immersio n, 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. Pu lmonary function, including a flow-volume loop and transfer factor of the l ung for carbon monoxide (Tl-CO), was measured before and 60 min after the e nd of the exposures. Body fluid balance was restored in the first 15 min af ter 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 afte r exposure to head-out water immersion or inspiratory resistive loading alo ne. The change in Tl-CO was normalized within 24 h. Submersion and resistan ce in breathing apparatus may contribute to the changes in pulmonary functi on seen immediately after dives. The nature of the exposure in these experi ments and the time for recovery indicate that these changes are mechanicall y induced, and may not contribute to the long-term effects of diving on the lung.