Abstract
Hypoxic exposure increases right ventricular (RV) afterload by triggering pulmonary hypertension, with consequent effects on the structure and function of the RV. Improved myocardial contractility is a critical circulatory adaptation to exercise training. However, the types of exercise that enhance right cardiac mechanics during hypoxic stress have not yet been identified. This study investigated how high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) influence right cardiac mechanics during hypoxic exercise A total of 54 young and healthy sedentary males were randomly selected to engage in either HIIT (3-min intervals at 40% and 80% of oxygen uptake reserve, n = 18) or MICT (sustained 60% of oxygen uptake reserve, n = 18) for 30 min/day and 5 days/week for 6 weeks or were included in a control group (CTL, n = 18) that did not engage in any exercise. The primary outcome was the change in right cardiac mechanics during semiupright bicycle exercise under hypoxic conditions (i.e., 50 watts under 12% FiO2 for 3 min) as measured by two-dimensional speckle tracking echocardiography.: After 6 weeks of training, HIIT was superior to MICT in improving maximal oxygen consumption (VO2max). Furthermore, the HIIT group showed reduced pulmonary vascular resistance (PVR, pre-HIIT:1.16 ± 0.05 WU; post-HIIT:1.05 ± 0.05 WU, p < 0.05) as well as an elevated right ventricular ejection fraction (RVEF, pre-HIIT: 59.5 ± 6.0%; post-HIIT: 69.1 ± 2.8%, p < 0.05) during hypoxic exercise, coupled with a significant enhancement of the right atrial (RA) reservoir and conduit functions. HIIT is superior to MICT in dilating RV chamber and reducing radial strain but ameliorating radial strain rate in either systole (post-HIIT: 2.78 ± 0.14 s-1; post-MICT: 2.27 ± 0.12 s-1, p < 0.05) or diastole (post-HIIT: − 2.63 ± 0.12 s-1; post-MICT: − 2.36 ± 0.18 s-1, p < 0.05). In the correlation analysis, the changes in RVEF were directly associated with improved RA reservoir (r = 0.60, p < 0.05) and conduit functions (r = 0.64, p < 0.01) but inversely associated with the change in RV radial strain (r = − 0.70, p < 0.01) and PVR (r = − 0.70, p < 0.01) caused by HIIT. HIIT is superior to MICT in improving right cardiac mechanics by simultaneously increasing RA reservoir and conduit functions and decreasing PVR during hypoxic exercise.
Highlights
Hypoxic exposure increases right ventricular (RV) afterload by triggering pulmonary hypertension, with consequent effects on the structure and function of the RV
Right cardiac performance is assessed by echocardiography under normoxic environments, which only displays chamber size and wall motion by two-dimensional speckle-tracking echocardiography (2D-STE) with normal estimated P VR14
Right cardiac performance is assessed by echocardiography under normoxic environments, which displays only the chamber size and myocardial motion with a normal pulmonary vascular resistance (PVR)
Summary
Hypoxic exposure increases right ventricular (RV) afterload by triggering pulmonary hypertension, with consequent effects on the structure and function of the RV. HIIT is superior to MICT in improving right cardiac mechanics by simultaneously increasing RA reservoir and conduit functions and decreasing PVR during hypoxic exercise. CTL Control group FAC% Fractional area change FiO2 Fraction of inspiration oxygen HIIT High-intensity interval training LV Left ventricle MICT Moderate-intensity continuous training post- After the intervention pre- Before the intervention PVR Pulmonary vascular resistance RA Right atrial RV Right ventricular RVD1 RV basal cavity diameter RVD2 RV middle cavity diameter RVD3 RV longitudinal diameter RVEF Right ventricular ejection fraction RVOT Right ventricular outflow tract RVSP Right ventricular systolic pressure SR Strain rate SV Stroke volume TAPSE Tricuspid annular plane systolic excursion TPR Total peripheral resistance VCO2 Carbon dioxide production VE Respiratory minute volume VO2 Oxygen consumption VO2max Maximal oxygen consumption VTI Velocity time integral. Few studies have elucidated the distinct effects of different training regimens on radial or longitudinal RV mechanics
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