Association between cardiorespiratory fitness and ventilatory efficiency in patients with coronary artery disease: effect of aerobic exercise training

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Background: Previous studies have demonstrated that patients with coronary artery disease (CAD) have lower ventilatory efficiency (VE) during graded exercise test. However, there is scarce information whether the level of cardiorespiratory fitness might have association with lower VE observed in CAD patients. Purpose: To test the hypothesis that: 1) CAD patients with lower CF demonstrate a lower VE; and 2) CAD patients with lower CF exhibit greater responsiveness on improving VE after aerobic exercise training. Methods: 78 patients with CAD matched for age (60.2 + 6.2 years) were divided according to CF into 3 groups: Group 1 (n = 20, VO2 peak <17.5 ml/kg/min), Group 2 (n = 41, VO2 peak > 17.5 and < 24.5 ml/kg/min) and Group 3 (n = 17, VO2 peak > 24.5 ml/kg/min). All patients performed a graded exercise test on treadmill to determine ventilatory anaerobic threshold (VAT), respiratory compensation point and peak oxygen consumption (VO2 peak) before and after interventions. The VE was determined by the relationship between minute ventilation and carbon dioxide production at VAT (VE/VCO2@VAT). The exercise program consisted of 12-week, 3 times a week supervised moderate-intensity aerobic exercise training program. Results: The group 1 demonstrated both lower CF and VE when compared to other groups: Group 1 (VO2peak = 14.8±2,4; VEVCO2@VAT = 34,5±3,7); Group 2 (VO2peak = 20,2±1,9; VEVCO2@VAT = 30,9±3,5); group 3 (VO2peak = 27,7±2,5; VEVCO2@LAV = 29,7±1,9 respectively, p <0.05). After the intervention period, only group 1 has shown an increase in VE (p <0.05). Furthermore, group 1 demonstrated greater responsiveness in increasing both the CF and VE compared to the other groups: Group 1 (Δ VO2peak = 5.1; Δ VEVCO2@ VAT = -3,6); Group 2 (ΔVO2peak = 4.2; Δ VEVCO2@VAT = -1.5); Group 3 (Δ VO2peak = 2.2; ΔVEVCO2@ LAV = -1.3 respectively, p <0.05). Conclusion: These findings suggest that different levels of cardiorespiratory fitness may be an important determinant on responsiveness of increased in ventilatory efficiency after a period of exercise training in patients with coronary artery disease. Collectively, these data suggest a clinical significance for aerobic exercise program, since the low VE observed in patients with CAD has an important prognostic value for cardiovascular mortality.