Oct. 20, 2003 Mildly elevated blood pressure affecting millions of Americans could lead to heart pumping disorders if left untreated. A new Johns Hopkins study indicates that the amount of oxygen that can be circulated throughout the body during each heart beat while exercising could reveal to doctors early signs of heart trouble in this population.
The research, to be presented Oct. 17 at the annual meeting of the American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR) in Kansas City, should help physicians better follow patients with problems of the left ventricle, or main pumping chamber of the heart, by studying so-called oxygen pulse.
During exercise, lungs take in air and transfer oxygen to the blood, which is then pumped by the heart to the muscles that need it. Oxygen pulse is the amount of oxygen put through this process with each heart beat, and is a measure of cardiovascular efficiency.
Researchers studied 99 adults (44 men and 55 women) ages 55 to 75 who had mild hypertension but were otherwise healthy. The participants' blood pressures ranged from 130 mmHg to 159 mmHg systolic (the upper number) and 85 mmHg to 99 mmHg diastolic (the lower number). These levels are also known as "prehypertension" or "Stage I hypertension."
The Hopkins team measured the adults' heart size and performance at rest through traditional echocardiograms (or ultrasound), and tissue Doppler imaging, a newer ultrasound method that examines the functioning of the heart's walls. Next, they compared those results with the participants' heart performance during exercise while the adults walked on a treadmill. The scientists measured oxygen usage during the exercise portion by having the subject breathe through a mouthpiece attached to a valve that measures how much oxygen is used during the test.
Normally there is a sharp increase in oxygen pulse during the first few minutes of exercise. This rise continues with exercise, and the load on the heart also rises as it works harder to meet the body's increased needs for oxygen carried by the blood. However, researchers found that subjects who were delivering less oxygen to the body per beat after the first few minutes of exercise also had reduced levels of heart function during the Doppler tests of their hearts at rest.
"Our research shows that patients with mild hypertension have some reductions in heart function," says Kerry J. Stewart, Ed.D., director of clinical exercise physiology at Hopkins. "We found signs that their hearts were not operating efficiently during exercise, and this was matched with decreased heart function at rest as revealed by newer imaging methods. We need to get their blood pressure under control, even if it is only mildly elevated."
Further study should indicate whether oxygen pulse during exercise is a useful screening tool for identifying heart problems.
Study coauthors were Jimmy G. Lim, M.D.; Timothy J. McAveney, M.D.; Jerome L. Fleg, M.D.; and Edward P. Shapiro, M.D.
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