Blood pressure changes from hour to hour, sometimes minute to minute. Standing up from a chair, watching an exciting show, eating a meal, or being stressed -- perhaps because of a visit to the doctor -- all influence blood pressure.

Blood pressure readings jump around so much that people are more likely to get an accurate reading if they check it at home rather than in the doctor's office, reports the September 2008 issue of the Harvard Heart Letter.

The idea underlies a new recommendation from the American Heart Association urging individuals with high blood pressure or at high risk for developing it to become do-it-yourselfers, for a number of reasons:

Finding the real blood pressure: In some individuals, the doctor's office snapshot tells the whole story and is an excellent approximation of their usual pressure. In others, it isn't.

Tracking progress: Checking blood pressure at home lets people know whether their lifestyle changes and medications are having their desired effects.

Saving time and medications: Home measurement may mean fewer trips to the doctor's office. If people have "white-coat" hypertension -- a rise in blood pressure when they go to the doctor -- it may also mean taking fewer medications.

If people choose to measure their blood pressure at home, technique matters.

A free instructional video from Harvard Health Publications shows Harvard Heart Letter editor Patrick J. Skerrett demonstrating the right way to take a blood pressure reading at home.

It is available online at http://www.health.harvard.edu/newsletters/Heart-webextra-0908.htm