Cardiovascular Responses to the Exercise Pressor Reflex in Pediatric Heart Transplant Recipients

Abstract

Pediatric heart transplant recipients (HTR) have reduced exercise tolerance despite normal systolic ventricular function. A slower heart rate adaptation to exercise in HTR due to cardiac denervation is commonly observed in HTR patients, which explains, in part, the exercise intolerance. We tested the hypothesis that the cardiovascular response to exercise pressor reflex activation from handgrip exercise would be blunted in HTR.MethodsSix pediatric HTR (3f/3m; mean±SD, 10±3 yrs) and five healthy‐matched controls (CTL; 3f/2m; 10±2 yrs) were studied. After 3 min of resting baseline, subjects performed 2 min of isometric handgrip (HG) exercise at 40% maximal voluntary contraction, followed by 3 min post‐exercise circulatory occlusion (PECO). Beat‐by‐beat mean arterial pressure, heart rate, and modelflow stroke volume and cardiac output were recorded. Data were analysed as the change (Δ) from rest using two‐way repeated measures ANOVA (2 × 3; group × condition) and Holm‐Sidak multiple comparisons analysis. Significance was accepted at P<0.05.ResultsMean arterial pressure increased in HTR (Δ17±15 mmHg) and CTL (Δ13±16 mL) during HG (P<0.001) and remained elevated above baseline during PECO (HTR: Δ10±10 mmHg; CTL: Δ11±9 mmHg; P<0.05), with no between group differences. Heart rate did not significantly increase during HG in HTR (Δ4±5 bpm, P=0.235) but did in CTL (Δ14±11 bpm, P<0.001), and was 9 bpm lower in HTR vs CTL (P=0.005). Heart rate was not different during PECO from rest in HTR and CTL. Stroke volume increased in HTR (Δ3±1 mL) and CTL (Δ3±3 mL) during HG (P<0.001) and remained elevated above baseline during PECO (HTR: Δ3±2 mL; CTL: Δ4±3 mL; P<0.001), with no between group differences. Cardiac output did not significantly increase during HG in HTR (Δ0.34±0.21 L/min, P=0.074) but did in CTL (Δ0.71±0.54 L/min, P<0.001), and was 0.37 L/min lower in HTR vs CTL (P=0.035). Cardiac output was not different during PECO from rest in HTR and CTL.ConclusionsOwing to the impaired heart rate response during handgrip exercise, cardiac output was lower in pediatric HTR compared to healthy‐matched controls in response to exercise pressor reflex activation.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.