FUNCTIONAL-CHARACTERISTICS OF THE LARGE LUNGS FOUND IN COMMERCIAL DIVERS

This paper describes the lung function of commercial divers with larger than normal lungs. We found that the ratio of the forced expired volume in the 1st s of the forced vital capacity (FEV(1.0)/FVC) decreased as the FVC increased above 100% of the predicted value. In addition, all the subdivisions of lung volume, except expiratory reserve volume, were greater than predicted, the gas transfer as shown by the single-breath carbon monoxide test (DL(CO)) was increased but the gas transfer per unit alveolar volume (DL/VA) was decreased. 4 of the 5 indices monitoring expiratory airflow (FEV(1.0)/FVC, FEV(3.0)/FVC, MMEF(25-75%) and MMEF(75-85%)) were reduced, suggesting that some airflow obstruction was present. Nevertheless these men could move large quantities of air in/out of their lungs in response to a progressive exercise load. They used exceptionally large tidal breaths and had reduced respiratory rates and slow heart rates when under exercise load. We also describe how years of diving experience increases the FVC up to about 30 yr of age, but thereafter the FVC declines despite continued underwater work. These findings suggest that as the muscles of respiration hypertrophy and the lungs enlarge the airways cannot dilate or the elastic recoil tissue cannot hypertrophy to match the alveolar enlargement, and with time there is an accelerated decline in lung size. Finally, we describe how divers with abnormal respiratory airflows and excess ventilation at high oxygen uptakes can be identified by routine spirometry.