Oxygen uptake during daily life domestic activities in patients with heart failure and reduced ejection fraction

Background Dyspnea is a pivotal symptom of chronic heart failure with reduced ejection fraction (HFrEF). It seriously compromises exercise performance, capability to perform standard activities of daily living (ADLs) and quality of life. Cardiopulmonary exercise test (CPET) is the gold standard in assessing functional capacity in HFrEF carrying an important diagnostic and prognostic role. However, exercise protocols don’t fully represent patients’ daily-life, with most of the symptoms arising with different activities like climbing the stairs or fastening the shoes (i.e. bendopnea). Task-related oxygen consumption in HFrEF patients are still lacking. The aim of the present study is to assess the differences in task-related oxygen uptake (maxVO2), both as absolute value and as % of the peakVO2 obtained at CPET (%peakVO2), ventilation (VE), and Borg symptom scores between pre-selected HFrEF sub-groups of patients (stratified according to their peakVO2) and healthy subjects during a standardized protocol of ADLs. Materials and Methods Subjects underwent a basal CPET and the following exercises (Fig. 1) wearing a full wearable device (Cosmed® K5): -ADL1: getting dressed; -ADL2: folding 8 towels; -ADL3: putting away 6 bottles; -ADL4: making a bed; -ADL5: sweeping the floor for 4-min; -ADL6: climbing 1 flight of stair carrying a load; -Six minutes walking test; -4-minutes 2Km/h treadmill; -4-minutes 3Km/h treadmill. The degree of dyspnea was recorded at the beginning and end of all exercises using a modified Borg symptom score. Results Sixty stable HFrEF patients with optimized medical treatment (age 65.2±12.1y; EF 30.4±6.7%), and 40 healthy volunteers (58.9±8.2y) were enrolled. As expected, at CPET, HFrEF patients showed significantly lower peak VO2 (14.2±4.0 vs. 28.1±7.4ml/min/kg, respectively) and higher VE/VCO2slope (36.8±9.1 vs. 27.2±4.0). For each exercise, patients showed higher VE/CO2 and %peakVO2 values compared to controls, while maxVO2 was significantly higher in all the exercises except treadmill (the only ones in which both execution time and velocity are fixed). As expected, patients experienced more dyspnea (Borg scale), lower heart rate and higher exercises duration. Table 1 shows differences in the main metabolic values recorded in HFrEF sub-groups for each exercise performed: in exercises with non-fixed execution velocity, patients with more severe HFrEF have lower maxVO2, higher %peakVO2 and higher VE/VCO2. In exercises with fixed execution time and velocity maxVO2 did not changed among groups. Conclusions. Oxygen consumption during ADLs worsens according to the severity of heart failure, with progressively increasing ventilatory inefficiency and erosion of the patients’ VO2 “reserve”. Our data suggest that HFrEF patients limit themselves during the exercise, whenever possible, by decreasing velocity and/or intensity of the exercise.