Post‐Exercise Oxygen Uptake and Muscle Oxygenation in Pediatric Heart Transplant Recipients

Abstract

Pediatric heart transplant recipients (HTR) have reduced exercise tolerance and peak oxygen uptake (VO2) values are 57–73% of age‐predicted norms. Slow post‐exercise VO2 and muscle oxygenation recovery are related to exercise intolerance. However, despite clear exercise tolerance limitations and post‐exercise fatigue, VO2 and muscle oxygenation during recovery responses are unknown in this population.PurposeWe tested the hypothesis that both post‐exercise VO2 recovery and muscle oxygenation recovery would be slower after peak exercise in pediatric HTR compared to controls.MethodsFive pediatric HTR (mean ± SD age = 10.6 ± 3.0 years) and six healthy controls (age = 11.7 ± 2.7 years) performed cycle ergometry to peak exercise followed by 5 minutes of 20‐W cycle recovery. Pulmonary VO2 and muscle oxygenation (vastus lateralis tissue oxygenation index, TOI using near infrared spectroscopy) were sampled continuously during exercise and recovery. Data were linearly interpolated to 1‐s intervals, and both VO2 and TOI data were averaged into 5‐s and 10‐s time bins, respectively. VO2 recovery data were mono‐exponentially curve‐fitted to yield a recovery time constant (tau). TOI recovery was normalized from 0% (end exercise) to 100% (5 min post‐exercise) and data analyzed at set time points to characterize TOI time course changes (0s, 15s, 30s, 60s, 90s, 120s, 180S, 240s, and 300s). Statistical analyses included independent t‐tests for VO2 data and a between‐within (2 × 9, group × time) factorial ANOVA for TOI time course changes. Significance was accepted at p< 0.05.ResultsRecovery VO2 tau was significantly slower in pediatric HTR compared to healthy controls (68 ± 17 vs. 47 ± 12 s, respectively; p=0.044). There was a significant group × time interaction for TOI recovery (p=0.003) where TOI in HTR was significantly lower compared to controls at 15s (8 ± 8 vs. 46 ± 19%; p=0.003), 30s (22 ± 13 vs. 91 ± 31%; p=0.001), and 60s (47 ± 23 vs. 117 ± 36%; p=0.005). TOI was not statistically different between groups by 90s onwards (all p>0.05).ConclusionsPost‐exercise VO2 and TOI recovery are prolonged in pediatric HTR compared to healthy controls. These findings suggest that non‐cardiac factors may contribute to the excessive recovery time following peak exercise in pediatric HTR.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.