Hypertensive smoking gun.

Smoking a couple of cigarettes can substantially raise blood pressure for at least 20 to 30 minutes. Yet when hypertensive patients visit their doctors, even those who smoke heavily tend to have blood pressure readings no higher than their nonsmoking counterparts.

This seeming paradox has furrowed many a researcher's brow. Now, a research team has verified the suspicions of many cardiologists: that among older smokers at least, reading taken in the doctor's office lead to underestimates of average daytime blood pressure.

At the New York Hospital-Cornell Medical Center in New York City, Samuel J. Mann and his co-workers fitted 177 people suffering from untreated hypertension with small blood-pressure monitors. The volunteers included 59 smokers and 118 nonsmokers matched to the smokers by age, sex, weight and race. The portable monitors assayed blood pressure every 15 to 30 minutes throughout one day.

Neither sleeping nor daytime blood pressures varied between smokers and nonsmokers under age 50. Indeed, the researchers report in the May 1 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, the only major difference they observed involved the older smokers' systolic blood pressure -- the larger of the two pressure values, reflecting pressure as the heart contracts. During the day, smokers 50 and older maintained a significantly higher systolic pressure (averaging 153 millimeters of mercury) than did nonsmokers the same age (142 mm Hg). Both groups averaged 143.5 mm Hg at the doctor's office.

Mann says these findings may reflect arteriosclerosis in the older smokers. "What I think I'm seeing is a stiffer arterial system -- [one] less able to buffer an increase in blood pressure during exercise," he says.