Peak Oxygen Uptake is Limited by Oxygen Transport and not Peripheral Extraction in Congestive Heart Failure Patients

Patients with congestive heart failure (CHF) are characterized by low levels of aerobic fitness (peak oxygen consumption, VO2peak) that may be secondary to reductions in oxygen transport capacity and peripheral oxygen extraction (Belardinelli et al., 1995). Near infrared spectroscopy (NIRS) is a valid and reliable non-invasive technique for evaluating localized muscle oxygenation and blood volume during exercise in situ in CHF patients (Watanabe et al., 2005). PURPOSE: To investigative the relationship between VO2peak and selected cardiorespiratory responses and muscle oxygenatioin/blood volume changes in patients with CHF. METHODS: Twelve CHF patients (ischemic/non-ischemic:4/8, age (mean±SD): 63 ±11.5 yrs, VO2peak: 1.19±0.52 L/min, 14.3±5.2 ml/kg/min) gave written informed consent to participate in a step-wise symptom-limited incremental cycle exercise test to voluntary fatigue. Cardiorespiratory variables were recorded using a metabolic measurement cart. Localized muscle oxygenation and blood volume were recorded continuously from the right vastus lateralis using a dual wave NIRS device for 2 mins at rest (baseline) and throughout exercise. The difference between the baseline and the highest values recorded during exercise were used for statistical analysis. RESULTS: Oxygen uptake, heart rate and ventilation rate increased systematically during incremental exercise. In most patients, muscle blood volume increased up to 50% to 60% of VO2peak and then leveled off or decreased until the termination of exercise. Muscle oxygenation decreased (implying greater oxygen extraction) with increasing work rate and leveled off prior to the attainment of VO2peak. In a forward stepwise multiple regression analysis, only the peak exercise oxygen pulse and heart rate were selected into the regression equation to predict VO2peak. These two variables explained 71% and 28% of the variance respectively in VO2peak. The ventilation rate, muscle oxygenation and blood volume changes were not included into the predictive model. CONCUSIONS: The findings on this small sample of CHF patients suggest that VO2peak is determined primarily by the ability of the central circulation to transport oxygen and not by the capacity of the exercising muscles to extract oxygen.