Ventilatory Efficiency Among Patients With Pulmonary Hypertension With Varying Levels Of Adaptation To Exercise Training

Abstract

The 6-minute walk test (6MWT) is universally accepted as a measure of functional capacity in patients with pulmonary hypertension (PH). While aerobic exercise training (AET) has generally been shown to improve exercise tolerance and 6MWT distance in patients with PH, some patients have been observed to adapt differently to AET, with minimal or even negative changes in 6MWT distance being reported. Differences in patient characteristics and peak ventilatory efficiency to AET have not been characterized and compared in these subset of patients. PURPOSE: To determine differences in ventilatory efficiency, defined as peak ventilatory equivalents for O2 uptake (VE/VO2), peak ventilatory equivalents for CO2 output (VE/VCO2), end-tidal CO2 (PETCO2) and tidal volume (TV), in patients with high (HI, >42 meters), low (LI, 0-42 meters) and negative (NEG, <0 meters) change in 6MWT distance after AET. METHODS: Subjects were 25 females (age 54±11 years; BMI 31±7 kg/m2) enrolled in the NIH Exercise Therapy for Advanced Lung Disease Trial. Participants completed 24-30 supervised treadmill walking exercise sessions, over 10 consecutive weeks, at a training intensity of 70% to 80% of heart rate reserve. The thrice-weekly sessions were 30-45 minutes in duration. A cardiopulmonary exercise test and 6MWT was completed before and after the 10-weeks of training. Ten of the 25 subjects were classified as HI (range = 47-143 meters), 11 were classified as LI (range = 4 - 37 meters) and 4 were classified as NEG (range = -17-53 meters). RESULTS: After AET, peak values in VE/VO2 (p=0.02), VE/VCO2 (p=0.002), PETCO2 (p=0.016) and TV (p=0.016) were improved for the HI versus NEG group. Peak values for VE/VCO2 (p=0.003) and TV (p=0.041) were improved for the LI versus NEG group. CONCLUSION: Previous studies suggest that reduced ventilatory efficiency (VE/VCO2) is associated with a poor prognostic outcome in patients with PH. To our knowledge this is the first study to look at changes in ventilatory efficiency after AET, specifically in HI, LI and NEG subsets. Findings from this study suggest that reduced ventilatory efficiency may also contribute to reduced functional capacity in patients with PH, contributing to the etiological basis for the association between 6MWD and mortality in these patients. Funding NIH IRP [1 Z01 CL060068-05 CC].