Acute cardiac functional and mechanical responses to isometric exercise in prehypertensive males

Abstract

Isometric exercise (IE) training has been shown to reduce resting arterial blood pressure (ABP) in hypertensive, prehypertensive, and normotensive populations. However, the acute hemodynamic response of the heart to such exercise remains unclear. We therefore performed a comprehensive assessment of cardiac structure, function, and mechanics at rest and immediately post a single IE session in 26 male (age 44.8 ± 8.4 years) prehypertensive participants. Conventional echocardiography recorded standard and tissue Doppler measures of left ventricular (LV) structure and function. Speckle tracking echocardiography was used to measure LV global longitudinal, circumferential, and radial strain and strain rate. From this data, apical and basal rotation and rotational velocities, LV twist, systolic twist velocity, untwist velocity, and torsion were determined. IE led to a significant post exercise reduction in systolic (132.6 ± 5.6 vs. 109.4 ± 19.6 mmHg, P < 0.001) and diastolic (77.6 ± 9.4 vs. 58.8 ± 17.2 mmHg, P < 0.001) blood pressure, with no significant change in heart rate (62 ± 9.4 vs. 63 ± 7.5b·min−1, P = 0.63). There were significant reductions in LV end systolic diameter (3.4 ± 0.2 vs. 3.09 ± 0.3 cm, P = 0.002), LV posterior wall thickness (0.99 ± 0.1 vs. 0.9 ± 0.1 cm, P = 0.013), relative wall thickness (0.4 ± 0.06 vs. 0.36 ± 0.05, P = 0.027) estimated filling pressure (E/E' ratio 6.08 ± 1.87 vs. 5.01 ± 0.82, P = 0.006) and proportion of participants with LV concentric remodeling (30.8% vs. 7.8%, P = 0.035), and significant increases in LV ejection fraction (60.8 ± 3 vs. 68.3 ± 4%, P < 0.001), fractional shortening (31.6 ± 4.5 vs. 39.9 ± 5%, P < 0.001), cardiac output (4.3 ± 0.7 vs. 6.1 ± 1L·min−1, P < 0.001), and stroke volume (74.6 ± 11 vs. 96.3 ± 13.5 ml, P < 0.001). In this setting, there were significant increases in global longitudinal strain (−17.8 ± 2.4 vs. −20 ± 1.8%, P = 0.002) and strain rate (−0.88 ± 0.1 vs. −1.03 ± 0.1%, P < 0.001), basal rotation (−5 ± 3.5 vs. −7.22 ± 3.3°, P = 0.047), basal systolic rotational velocity (−51 ± 21.9 vs. −79.3 ± 41.3°·s−1, P = 0.01), basal diastolic rotational velocity (48.7 ± 18.9 vs. 62.3 ± 21.4°·s−1, P = 0.042), LV twist (10.4 ± 5.8 vs. 13.8 ± 5°, P = 0.049), systolic twist velocity (69.6 ± 27.5 vs. 98.8 ± 35.8°·s−1, P = 0.006), and untwist velocity (−64.2 ± 23 vs. −92.8 ± 38°·s−1, P = 0.007). These results suggest that IE improves LV function and mechanics acutely. This may in turn be partly responsible for the observed reductions in ABP following IE training programs and may have important implications for clinical populations.

The safety of isometric exercise

“…[ 46 ] Furthermore, the magnitude of dBP response observed in the present study, which as indicated earlier might also be representative of previous IE interventions using the same standard protocol, may even act as a specific stimulus for the BP adaptations reported. Indeed, the physiological benefits following a single IE session including improved cardiac autonomic modulation and baroreceptor reflex sensitivity [ 30 ] and cardiac mechanical responses [ 47 ] have been recently reported. However, despite the potential importance of the dBP rise seen during IE, it is suggested that there will still be an adverse dBP threshold specifically pertinent to participants with suboptimal BP and as such a safe limit needs to be ascertained when prescribing this type of exercise in higher risk populations.…”

Blood pressure and cardiac autonomic adaptations to isometric exercise training: A randomized sham‐controlled study

“…For the IET group, participants were required to complete a wall squat, consisting of resting their back against a fixed wall with their feet parallel, shoulder width aside, and their arms relaxed down by their side. As previously described (Goldring et al, 2014;O'Driscoll et al, 2017;Wiles et al, 2008), peak HR was determined via an incremental isometric wall squat test with beat-to-beat HR responses in accordance to the prescribed knee angle (Wiles et al, 2017). In line with previous evidence (Wiles et al, 2017), the intervention group was prescribed a 4-week IET program at a knee joint angle predicted to elicit 95% peak HR.…”

Cardiac autonomic and left ventricular mechanics following high intensity interval training: a randomized crossover controlled study

“…All images were examined to validate quality, and those that did not meet the required level of optimization and standardization were excluded. The sonographer's reproducibility of speckle-tracking indices have been previously reported (32). All echocardiography results were analyzed by an investigator blinded to participant order and condition.…”