SCI-TECH & AGRI

Oxygen pulse, a measure of cardiovascular efficiency

MILDLY ELEVATED blood pressure could lead to heart pumping disorders if left untreated. A new Johns Hopkins study indicates that the amount of oxygen that can be circulated in the body during each heart beat while exercising could reveal early signs of heart trouble.

The research, to be presented 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 adults who had mild hypertension but otherwise healthy. The participants' BP ranged from 130 mmHg to 159 mmHg systolic (upper number) and 85 mmHg to 99 mmHg diastolic (lower number). These levels are called `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.

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