Adolescent children born preterm have altered cardiac regulation during and immediately following maximal exercise

Abstract

IntroductionHeart rate recovery (HRR) after maximal exercise has been shown to be a marker of fitness and disease status. Individuals born prematurely exhibit increased left ventricular mass and reduced end systolic and end diastolic volume. It has been shown that slower HRR is correlated with a higher risk for cardiovascular disease. Oxygen (O2) pulse is defined as the total volume of oxygen consumed per heartbeat and a low O2 pulse has been associated with pulmonary hypertension (PH) and other cardiovascular (CV) diseases. It is correlated with stroke volume and overall cardiovascular efficiency during exercise. The purpose of our research was to investigate the long‐term effects of preterm birth on HRR immediately following maximal exercise, and we hypothesized that it would be slower in adolescents born preterm.MethodsFifteen children 12–13 years old, 8 born preterm (birthweight <1500 g, gestational age <32 weeks) and 7 children born full term (gestational age 38–40 weeks) underwent progressive maximal exercise testing on a cycle ergometer, with continuous measurement of O2 consumption (ml/kg/min) and heart rate (HR), as well as cardiac output (Q), stroke volume (SV) using thoracic bioimpedance. SV and Q were indexed to body surface area (BSA (m2), SVi and Qi). HR was recorded for 2 minutes of rest following maximal exercise and HRR was the absolute drop in HR at 2 minutes from maximal HR (HRR2min). Statistical analysis was done using multiple t‐tests and linear regression.ResultsHRR2min following maximal exercise was lower in preterms than controls (54.4 ± 4.2 v 63.5 ± 5.9, p=0.01, respectively). Preterm subjects had lower relative maximal oxygen consumption (VO2max) compared to control subjects (39.6 ± 9.3 v 52.8 ± 7.3 ml/kg/min, p=0.03). The increase in O2 pulse from rest to maximal exercise was greater in controls compared to the preterms (8.8 ± 1.1 v 4.8 ± 3.0 ml O2/beat, p=0.02). SVi did not increase significantly in preterms from rest to maximal exercise (51.7 ± 9.0 v 53.3 ± 8.3 ml/m2, p=0.77), but SV significantly increased in controls from rest to maximal exercise (47.4 ± 4.0 v 51.3 ± 8.4 ml/m2, p=0.01). Furthermore, the change in SVi (ΔSVi) from rest to maximal exercise was significantly smaller in preterms than in controls (0.0 ± 7.2 v 20.3 ± 17.0 ml/m2, p=0.012). A simple linear regression showed a positive relationship between ΔSV and HRR (p=0.03, r2=0.39).DiscussionWe found that multiple measurements associated with cardiac regulation were significantly different in preterms compared with controls. A slower HRR has been correlated with PH risk and CV disease that could lead to future complications. The inability to augment SV during exercise is uncommon, and has been noted in patients with CV disease. Finally, the positive relationship between ΔSVi and HRR after exercise indicates that there may be a direct relationship between the two variables. We have demonstrated that multiple cardiac parameters are altered in adolescent children born preterm during and immediately following exercise. There appears to be an altered cardiac regulation mechanism in adolescent children born preterm, and this will be an important area of study in the future.Support or Funding InformationNational Institutes of Health: 1R01 HL086897 (M.W.E.) and R01 HL38149 (M.P.).