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. Aim The aim of the present study is to assess the differences in task-related oxygen uptake (both as absolute value [maxVO2] and as percent of 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 will undergo 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 will be recorded using a modified Borg symptom score. Inclusion criteria: Healthy subjects: age 18-80y both males and females, no history of cardiovascular diseases or therapy, normal clinical evaluation; Patients: age 18-80y both males and females, New York Heart Association Class (NYHA) II-III stable clinical conditions, reduced ejection fraction (<50%), capability to perform a cardiopulmonary exercise test (CPET). Exclusion criteria: Moderate-severe chronic obstructive pulmonary disease; chronic oxygen therapy; contraindication to CPET. Statistical analysis: Parametric data will be analyzed by ANOVA or Kruskal Wallis for parametric and non-parametric data respectively. A p value <0.05 will be considered for significance. Preliminary 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) have been currently enrolled. As expected, at CPET, HFrEF patients showed significantly lower peakVO2 (14.2±4.0 vs. 28.1±7.4ml/min/kg, respectively) and higher VE/VCO2 slope (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 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 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.