Most divers tend towards an increase in vital capacity with age but the general conclusion, that divers tend to have larger vital capacities than nondivers, was not confirmed by a study of 126 saturation divers by Thorsem et al (1989). They suggest that the increase is transient and that there is a greater, but belated, diminution. Any change of vital capacity probably has little effect upon the divers general health though recent studies have shown that divers do develop some degree of air flow obstruction due to airway narrowing(Elliott et al, 1990).
Pulmonary diffusion capacity is another physiological function which deteriorates with age. At the present time the work to assess a possible acceleration in divers is incomplete. Early studies have been confined to deep diving, where a diminution of pulmonary diffusion post-dive from a particular dive may not be clinically significant and tends to improve during the next few weeks. This change is also associated with diminution of exercise tolerance (Thrones et al, 1990) but only to a degree that is functional rather than clinically significant.
In contrast, a study of 8 divers in a German deep dive (Lehnigk et al) showed no significant diminution of total lung carbon monoxide diffusion (TLCO) though there were a number of other variables, a conclusion also reached from a 450m dive at the National Hyperbaric Center in Aberdeen. However, there may be a possible cumulative effect and the most favored explanation is in association with a cumulative dose of oxygen at tensions greater than 0.3 bar.