Pulsatile load and wasted pressure effort are reduced following an acute bout of aerobic exercise

Abstract

Following aerobic exercise, sustained vasodilation and concomitant reductions in total peripheral resistance (TPR) result in a reduction in blood pressure that is maintained for two or more hours. However, the time course for postexercise changes in reflected wave amplitude and other indices of pulsatile load on the left ventricle have not been thoroughly described. Therefore, we tested the hypothesis that reflected wave amplitude is reduced beyond an hour after cycling at 60% V̇o_2peak for 60 min. Aortic pressure waveforms were derived in 14 healthy adults (7 men, 7 women; 26 ± 3 yr) from radial pulse waves acquired via high-fidelity applanation tonometry at baseline and every 20 min for 120 min postexercise. Concurrently, left ventricle outflow velocities were acquired via Doppler echocardiography and pressure-flow analyses were performed. Aortic characteristic impedance (Zc), forward (Pf) and backward (Pb) pulse wave amplitude, reflected wave travel time (RWTT), and wasted pressure effort (WPE) were derived. Reductions in aortic blood pressure, Zc, Pf, and Pb were all sustained postexercise whereas increases in RWTT emerged from 60 to 100 min post exercise (all P < 0.05). WPE was reduced by ∼40% from 40 to 100 min post exercise (all P < 0.02). Stepwise multiple regression analysis revealed that the peak ΔWPE was associated with ΔRWTT (β = -0.57, P = 0.003) and ΔPb (β = 0.52, P = 0.006), but not Δcardiac output, ΔTPR, ΔZc, or ΔPf. These results suggest that changes in pulsatile hemodynamics are sustained for ≥100 min following moderate intensity aerobic exercise. Moreover, decreased and delayed reflected pressure waves are associated with decreased left ventricular wasted effort after exercise.NEW & NOTEWORTHY We demonstrate that pulsatile load on the left ventricle is diminished following 60 min of moderate intensity aerobic exercise. During recovery from exercise, the amplitude of the forward and backward traveling pressure waves are attenuated and the arrival of reflected waves is delayed. Thus, the work imposed upon the left ventricle by reflected pressure waves, wasted pressure effort, is decreased after exercise.

Keywords: afterload; arterial load; left ventricle; postexercise hypotension.

Figure 1.

A: representation of the forward (Pf, blue) and backward traveling waves (Pb, red) derived from wave separation analysis. A pressure of 0 mmHg represents mean arterial pressure; therefore, positive values indicate augmentations to mean pressure by each respective wave at a given time. Reflected wave travel time (RWTT, time difference between the Pf and Pb) represents the length of time for forward traveling waves to reach peripheral reflection sites and return to the left ventricle as reflected waves. B: postexercise change in Pf amplitude. C: postexercise change in Pb amplitude (mixed effects model with Dunnett post hoc test). D: postexercise change in RWTT. Absolute values were used for all statistical analysis; however, Δvalues are displayed relative to baseline for clarity of individual responses. Thick black lines indicate group mean ± SD or median (IQR) and dashed gray lines are individual responses (all n = 14 subjects). B and C: mixed effects model with Dunnett’s post hoc tests. D: Friedman test with Dunn’s post hoc test. *P < 0.05, †P < 0.01, and ‡P < 0.001 vs. baseline. IQR, interquartile range.

Figure 2.

A: representation of an aortic pressure wave partitioned into the time integral of left ventricular outflow and aortic characteristic impedance (QZc, dark gray), wasted pressure effort (WPE, red), and diastole (light gray). All pressures are normalized so that 0 mmHg represents diastolic pressure. B: postexercise change in QZc. C: postexercise change in WPE. Data for B and C analyzed via mixed effects model with Dunnett’s post hoc tests using absolute values; however, Δvalues are displayed relative to baseline for clarity of individual responses. Thick black lines indicate group mean ± SD and dashed gray lines are individual responses (all n = 14 subjects). *P < 0.05, †P < 0.01, and ‡P < 0.001 vs. baseline.