High-tech isometrics helps persons on hypertension medication

Oct 5 2004

Don’t try this at home, but a high-tech version of the muscle crowd’s hand-grip has demonstrated the ability to lower blood pressure, improve the flexibility of the carotid artery and heighten vasoactive sensitivity in people taking medication for hypertension.

Two studies at the McMaster University Department of Kinesiology Exercise and Metabolism Research Group sought to confirm earlier findings related to risk factors for cardiovascular disease (CVD), as well as to uncover some of the underlying mechanisms. Both studies used similar methodology and isometric handgrip (IHG) exercise three times a week for eight weeks at 30% of maximal voluntary contraction.

Adrienne Visocchi led a group studying whether arterial distensibility (AD, or the ability of arteries to stretch) contributed to the reduction in resting blood pressure (RBP). They compared the impact of isometric arm and leg exercise on RBP as well as central (carotid) and peripheral (arm and leg arteries) AD in persons who were already taking medication for hypertension, or high blood pressure. Her group consisted of Cheri L.M. McGowan, Martha Faulkner, Robin Verduyn, Neil McCartney and Maureen J. MacDonald.

Results indicated that following IHG exercise systolic blood pressure decreased significantly, while carotid AD improved significantly. IHG didn’t affect either diastolic BP or peripheral AD. The study also tested isometric leg press exercise, but it had no effect on any of the parameters being studied.

Hypertension is associated with endothelial dysfunction and development of cardiovascular disease, noted Cheri L.M. McGowan, who led the other McMaster study. Her group studied endothelial function after IGH to see if it played a role in the reduction of blood pressure in people taking anti-hypertensive medication. Other group members included Adrienne Viscocchi, Martha Faulkner, Mark Rakobowchuk, Neil McCartney and Maureen J. MacDonald. Both McMaster studies were undertaken in Dr. MacDonald’s laboratory.

Prior to beginning the exercise regimen, vascular reactivity, which is a measure of an artery’s ability to dilate in response to an increase in blood flow, was measured in both arms using a technique called flow-mediated dilation (FMD). This technique involves stopping blood flow to the forearm for 5 minutes then measuring the artery’s internal diameter with ultrasound after blood flow is reintroduced. After training, systolic blood pressure decreased significantly, while FMD increased (both relative and normalized to average shear rate). Average resting diameter and resting flow remained unchanged.

The researchers also noted that following training there was a reduced reactive hyperemic flow (blood flow after cuff deflation). Although the amount of blood flowing through the artery was less than before training, the artery still dilated more. This suggests a heightened vasoactive sensitivity to the reactive hyperemic stimulus. These findings suggest that the reduction of blood pressure with IHG may be due to improvements of endothelial function.