Lower-body dynamic exercise reduces wave reflection in healthy young adults

Abstract

New findings: What is the central question of this study? There is a paradoxical reduction in augmentation index during lower-body dynamic (LBD) exercise in the face of an increase in central pressure. To determine causality, the amplitudes of forward and backward pressure waves were assessed separately using wave separation analysis. What is the main finding and its importance? Reflection magnitude decreased during LBD exercise in healthy young adults and was attributable to an increased forward pressure wave amplitude and decreased backward pressure wave amplitude. This vasoactive response might limit the adverse effects of wave reflection during LBD exercise, optimizing ventricular-arterial interactions.

Abstract: Acute lower-body dynamic (LBD) exercise decreases surrogate measures of wave reflection, such as the augmentation index. However, the augmentation index is influenced by the combined effects of wave reflection timing, magnitude and other confounding factors external to wave reflection, which make it difficult to discern the origin of changes in surrogate measures. The relative contributions of forward (Pf) and backward (Pb) pressure wave amplitudes to central pressure can be determined by wave separation analysis. Reflection magnitude (RM = Pb/Pf) and the timing of apparent wave reflection return can also be determined. We tested the hypothesis that acute LBD exercise decreases RM and reflected wave transit time (RWTT). Applanation tonometry was used to record radial artery pressure waveforms in 25 adults (24 ± 4 years of age) at baseline and during light-, moderate- and vigorous-intensity exercise. Wave separation analysis was conducted offline using a personalized physiological flow wave to determine Pf, Pb, RM and RWTT. The RM decreased during all intensities of exercise compared with baseline (all P < 0.001; baseline, 43 ± 5%; light, 33 ± 6%; moderate, 23 ± 7%; vigorous, 17 ± 5%). The reduction in RM was attributable to the combined effect of increased Pf and decreased Pb during exercise. The RWTT decreased during all intensities of exercise compared with baseline (all P < 0.04; baseline, 156 ± 17 ms; light, 144 ± 15 ms; moderate, 129 ± 16 ms; vigorous, 121 ± 17 ms). Lastly, in a stepwise multilinear regression, Pf, but not Pb and RWTT, contributed to increased central pulse pressure during LBD exercise. These data show that wave reflection decreased and that central pulse pressure is most influenced by Pf during LBD exercise.

Keywords: central blood pressure; lower-body dynamic exercise; wave reflection; wave separation analysis.

Figure 1.. Example of Forward and Backward Pressure Waves.

(A) Pf and Pb at baseline; and during (B) light; C) moderate; and D) vigorous intensity exercise in one subject. Pf, forward pressure wave amplitude is traced in blue; Pb, backward pressure wave amplitude is traced in red; RM, reflection magnitude is defined as Pb/Pf and expressed as a percentage.

Figure 2.. Surrogate Measures of Wave Reflection During LBD Exercise.

(A) Augmentation index decreased during light, moderate, and vigorous intensity LBD exercise compared to baseline. (B) Time to inflection point decreased during light, moderate, and vigorous intensity LBD exercise compared to baseline. *P <0.05 vs. baseline; ^†P <0.05 vs. light; n = 25. Men (n=13) are in blue, women (n=12) are in red.

Figure 3.. Wave Separation Analysis Measures of Wave Reflection During Lower Body Dynamic Exercise.

(A) Forward pressure wave amplitude increased during light, moderate, and vigorous intensity LBD exercise compared to baseline. (B) Backward pressure wave amplitude and (C) reflection magnitude decreased during light, moderate, and vigorous intensity LBD exercise compared to baseline. (D) Reflected wave transit time decreased during light, moderate, and vigorous intensity LBD exercise compared to baseline. *P <0.05 vs. baseline; ^†P <0.05 vs. light; ^‡P<0.05 vs. moderate; n = 25. Men (n=13) are in blue, women (n=12) are in red.