Inability
to pump oxygen
during exercise could
pinpoint
early heart problems
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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