[abstract] RESPIRATORY MUSCLE TRAINING IN DIVERS: REDUCED DYSPNEA AND INCREASED ENDURANCE

Abstract

BACKGROUND: 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 carbon dioxide scrubber, the dyspnea may be secondary to exercise-related carbon dioxide accumulation, respiratory muscle fatigue or changes in the CNS control of respiration. Carbon dioxide pressures as low as 1-2 kPa can potentiate CNS oxygen toxicity underwater. Thus, although reducing dyspnea may improve diver performance, a major risk to diving safety may be anticipated if this is accompanied by a build-up of carbon dioxide. 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 carbon dioxide accumulation. MATERIALS AND 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 carbon dioxide accumulation for both groups before and after 42 days of RMT. RMT was carried out using the Threshold Inspiratory Muscle Trainer (PowerBreath, IMT Technologies Ltd., Birmingham, England) up to 80percent and 15percent 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 less than 0.01, repeated measures ANOVA), and their perception of dyspnea was significantly reduced (p less than 0.0004). No significant changes were found in spirometry parameters, respiratory muscle strength or the respiratory response to carbon dioxide. CONCLUSIONS: RMT may improve the performance of oxygen divers without compromising their safety.