PURPOSE: Dyspnea is common among divers who use oxygen-enriched breathing mixtures in semi-closed and closed-circuit diving apparatus and constitutes a major limiting factor in combat diving. When not related to mechanical dysfunction of the diving apparatus or reduced efficiency of the CO2 scrubber, the dyspnea may be secondary to exercise-related carbon dioxide accumulation, respiratory muscle fatigue or changes in the CNS control of respiration. CO2 pressures as low as 1-2 kPa can potentiate CNS oxygen toxicity underwater. Thus, although alleviate dyspnea may improve diver performance, it can lead to CO2 accumulation with increased risk of CNS oxygen toxicity. We investigated whether respiratory muscle training (RMT) in healthy, trained oxygen divers might improve respiratory muscle strength and endurance, change the perception of dyspnea, and affect their exercise-induced CO2 accumulation.
METHODS: Twelve oxygen divers were included in the study and 9 in the control group. We recorded spirometry, maximal inspiratory (PImax) and expiratory (PEmax) pressures as measures of inspiratory and expiratory muscle strength, perception of dyspnea according to Borg scale, respiratory muscle endurance by PMpeak, and the respiratory response to CO2 accumulation for both groups before and after 42 days of RMT. RMT was carried out using the Threshold Inspiratory Muscle Trainer up to 80% and 15% of PImax in the study and control groups respectively.
RESULTS: Respiratory muscle endurance was significantly improved in the study group (PMpeak 120±21, 150±34 cmH2O before and after RMT respectively; p<0.01, repeated measures ANOVA), and their perception of dyspnea was significantly reduced (p<0.0004). No significant changes were found in spirometry parameters and respiratory muscle strength. CO2 level was not increased in the trained group and their was no change in the respiratory response to CO2.
CONCLUSION: In oxygen divers RMT training improve respiratory muscle endurance and dyspnea perceptio without CO2 retention.
CLINICAL IMPLICATIONS: RMT may improve the performance of oxygen divers without accumulation of carbon dioxide and therefore not compromising their safety.
DISCLOSURE: Yochai Adir, None.