Medical & Clinical Research

Author(s): Hua CHENG

Objective: Ventilation attenuation often happened in professional divers due to long-term cumulative effects in diving exercises. By case-control experiments, we observed the immediate effects of pulmonary ventilation before and after the exposure of 12m-depth underwater for 20 min to discuss the relationships between the short-term and long-time effects caused by diving environment.

Methods: Participants were randomly assigned into the Experimental Group (EG) who stayed for 20 min under 12-m water environment or the Control Group (CG) who stayed in hyperbaric chamber under the pressure of 2.2ATA. Pulmonary ventilation function parameters including VC, FVC, MVV and MV were detected respectively before and after hyperbaric exposure by the Spirometer. Immediate effects of pulmonary ventilation before and after diving were compared by paired t test to reveal the different influence caused by environmental pressure.

Results: The value of VC appears to rise while the MV, MVV were detected decreased after the exposure of 2.2ATA of environment pressure for 20min in the two groups. VC increased more significantly in the CG (t=-1.26, p=0.23) after hyperbaric exposure, that leads to the FEV1.0%t (=FEV1.0/VC %) increase in EG (t=-0.73, p=0.48) while decrease in CG (t=0.42, p=0.17). The same trend in VC, MV and MVV after high pressure exposure in the two groups mainly due to the effect of common factors –the pressure. In addition to the impact of the pressure itself, EG members also face diving related immersion effect, influence of diving equipment load and water under low temperature. The FVC is detected decreased in EG (t=1.21, P =0.25) while it increased in CG (t=-0.42, P =0.68) , but the differences are not significant and couldn’t affect the measured FEV1.0% (=FEV1.0/FVC %) values showed both increasing in EG (t=-1.48, P =0.16) and in CG (t=-0.23, P =0.82). The expiratory flow rate including PEF, FEF25-75, MEF75, MEF50 increased in EG (t are -0.72, -0.69, -0.87 and -0.36 respectively with P all greater than 0.05) while decreased in CG (t are 1.67, 0.50, 1.53 and 0.71 respectively with P all greater than 0.05). MEF25 is the expiratory flow index of not affected by respiratory muscle force and the measured values of MEF25 increased in the EG (t=-0.68, P =0.51) and in the CG (t=-0.36, P =0.72).

Conclusion: Water immersion and water temperature during diving exposure could cause and accelerate hemodynamic changes in pulmonary circulation induced pulmonary interstitial edema and led to the increase of external respiratory work. Instant effects of diving exposure in the study are quite consistent with the long-term cumulative effect of professional divers in previous research, which is FVC reduced because small airway become narrower. The results illustrate even the small depth of short-range diving exercise have definite influences on pulmonary ventilation, which mainly comes from the environmental factor but not the pressure increases.