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, presented Oct. 17 at the annual meeting
of the American Association of Cardiovascular and Pulmonary
Rehabilitation in Kansas City, Mo., 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 Johns 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," said
Kerry J. Stewart, director of Clinical Exercise Physiology
at Johns 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 co-authors were Jimmy G. Lim, Timothy J.
McAveney, Jerome L. Fleg and Edward P. Shapiro.
Related Web sites:
Division of Cardiology — Johns Hopkins Bayview
Medical Center
American Association of Cardiovascular and Pulmonary
Rehabilitation
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