Cardiopulmonary Exercise Response in Patients with Left Ventricular Dysfunction or Heart Failure: A Noninvasive Study by Gas Exchange and Impedance Cardiography Monitoring

Abstract

We investigated the upright bicycle exercise cardiopulmonary response in 20 patients with left ventricular dysfunction (LVD, secondary to previous myocardial infarction, left ventricular ejection fraction range 18-44%). Ten patients (48 ± 7 years) were asymptomatic (I NYHA class) without drug treatment (LVD group). The others (n = 10) (50 ± 1 years) complained of dyspnea and/or fatigue despite therapy (NYHA II–III). They represented the heart failure (HF) group. Eight sedentary men (40 ± 10 years) served as controls. Controls and patients performed stress testings under drug treatment, when administered. Anaerobic ventilatory threshold (ATge) was considered as an index of submaximal exercise while peak exercise VO₂ (PeakVO₂) was considered the maximal volitional exercise capacity. The ratio between minute ventilation (VE) to carbon dioxide release (VCO₂) (VE/VCO₂) was assessed to evaluate the ventilatory response during exercise. We coupled gas exchange assessment (2001, MGC) with noninvasive monitoring of stroke volume (SV) by impedance cardiography (NCCOM3, BOMED) and total systemic vascular resistances (TSVR; by auscultatory blood pressure measurement). In controls VO₂ increase during exercise was related to higher heart rate (HR) and SV both from resting to ATge and from this point to the peak. TSVR declined during both steps. In patients with HF VO₂ rose from resting to ATge (by faster HR and unchanged SV). VO₂ increased slightly from this point to PeakVO₂. This result was related to flat HR increase and unchanged SV as well as TSVR. In patients with LVD VO₂ increased similarly to controls from resting to ATge and less above the threshold. In these patients both HR and SV increased during submaximal exercise. From ATge to PeakVO₂ only HR increased. TSVR declined significantly similarly to controls. The VE/VCO₂ ratio was higher at peak exercise in patients with HF compared to controls. Different determinants were demonstrated in patients with left ventricular dysfunction with mild or symptomatic chronic heart failure (CHF). These findings and the increased ventilatory response in patients with CHF can explain different changes of VO₂ in these patients during submaximal and maximal voluntary exercise and contribute to explain exercise-induced exertion in these subjects.