Body Mass Index and Cardiopulmonary Exercise Testing Variables in Patients with Heart Failure

Abstract

Background Obesity is often associated with reduced exercise capacity, but the impact of elevated body mass index (BMI) on CPET performance in patients with heart failure (HF) is incompletely understood. We sought to define the relationship between BMI, peak oxygen consumption (pkVO2) and minute ventilation/carbon dioxide production slope (VE/VCO2). A greater body mass should generate greater O2 consumption and CO2 production, but the interaction between BMI and minute ventilation is less clear, leaving uncertainty as to whether BMI has an independent relationship with VE/VCO2. Methods We retrospectively reviewed cardiopulmonary exercise tests (CPETs) from 4/2017 to 11/2018 at a tertiary center. Patients with congenital or valvular heart disease were excluded. Baseline demographics, BMI on the day of testing, and key CPET parameters were recorded. Pearson correlation coefficients were calculated between the BMI and key CPET parameters, and multivariable linear regression models constructed to identify independent relationships. Results There were 142 CPETs performed during the study period, of which 121 met inclusion criteria. The cohort (n=121) was 30% female, with median age 59 years and BMI 28.9 kg/m2. The primary cardiac condition was non-ischemic cardiomyopathy in 38%, ischemic cardiomyopathy in 40%, hypertrophic cardiomyopathy in 14% and HF with preserved ejection fraction in 8%. Median CPET parameters were exercise time 9.2 min, metabolic equivalents (METS) 5.4, respiratory exchange ratio (RER) 1.09, pkVO2 1.23 L/min, weight-adjusted pkVO2 14.6 mL/kg/min, VE/VCO2 34. There was a positive correlation between BMI and pkVO2 in L/min (r=0.40, p Conclusions Higher BMI was associated with greater pkVO2 (L/min) as expected, but this relationship was accounted for by using the weight-adjusted pkVO2 in mL/kg/min. Higher BMI was also independently associated with lower VE/VCO2, which is not routinely expressed in a weight-adjusted format. This highlights the importance of understanding interactions between BMI and CPET variables, including the finding that obesity may negatively bias the VE/VCO2 in patients with HF.