Limitação ventilatória e eficiência cardiorrespiratória de indivíduos após infarto do miocárdio recente e/ou insuficiência cardíaca crônica

Abstract

Myocardial infarction (MI) and chronic heart failure (CHF) are among the cardiovascular diseases with high morbidity and mortality and both conditions are characterized by reduced ability to perform dynamic exercise. In CHF, the mechanisms responsible for exercise intolerance has been most widely investigated. There is a complex interaction between central and peripheral factors, including changes in lung function, reduced respiratory muscle strength and impaired autonomic modulation. However, little is known about their capacity to exercise at high altitude. The responsible factors to the functional capacity reduction in IM are unclear, especially in the early phase of recovery after hospital discharge. In this sense, two studies were developed with the purpose of assessing ventilatory limitation and cardiorespiratory efficiency in subjects with recent myocardial infarction and chronic heart failure. The first was developed in two stages and involved eight men (49 ± 8 years) with uncomplicated recent MI (RMI) and ten men (48 ± 9 years) apparently healthy subjects (CG). All patients underwent pulmonary function (PF), cardiopulmonary exercise testing on a ramp (CPX) and constant load (TECC) protocol. TECC was applied at three intensities, identified in CPET, corresponding to ventilatory anaerobic threshold, plus 25% and minus 25%. At the initial step we investigated the ventilatory limitation, with exercise tidal flow-volume loop, the breathing strategy and ventilatory efficiency during exercise (VE/VCO2 slope and OUES). The RMI group presented lower expiratory reserve volume (0.9±0.3 vs. 1.8±0.5 L; p<0.05) and OUES (1836±470 vs. 2695±258; p<0.01) when compared to the CG. RMI group also demonstrated EFL during all three CWETs, whereas the CG presented EFL only during the higher intensity. In the second step we evaluated the heart rate (HR) and oxygen uptake (VO2) responses at the beginning of dynamic exercise at three intensities, through the kinetics analysis. The RMI time constants (_) of HR (_HR) and VO2 (_VO2) showed different response, because the _VO2 was slower than _HR. When compared to the CG, RMI presented slower _VO2 at moderate workload. In conclusion, recent uncomplicated MI is associated with reduction in oxygen uptake ventilatory efficiency, slowing of _VO2 and ventilatory limitation at dynamic exercise, even when there is no reduction in PF and respiratory muscle strength. In the second study, thirty CHF patients (NYHA I-III, 25M/5F; 59±10 years, LVEF=39.6±7.1%) treated with carvedilol were underwent to CPET and CWET. CWET was applied at 50% of the peak workload reached at CPET, in normoxia and hypoxia, to simulate a 2000 meters altitude. To identify the effect of carvedilol on the response to moderate exercise in hypoxia, we evaluated the kinetics of HR and VO2 at the initial stage of dynamic exercise and the response of these variables during the CWET. The VO2 was 20% higher in hypoxia, the _VO2 was faster in hypoxia and the _HR was faster in normoxia. Ten patients, who lowered _VO2 in hypoxia had greater HR increase during maximal CPET, suggesting lower functional betablockade. The faster _VO2 in hypoxia is likely due to a peripheral effect of carvedilol mediated either by _- or _-receptor.