Measuring blood pressure seems so straightforward. Stick your arm in a cuff for a few seconds, and there they are: two simple numbers, all the information you need to know whether you are in a healthy range or high enough that you should be taking one of the many cheap generic drugs that can bring down your blood pressure.
But the reality is more confusing, as I discovered recently when I tested mine.
It turns out that blood pressure can jump around a lot — as much as 40 points in one day in my case — which raises the question of which reading to trust.
Ever since I wrote about a woman who was in denial about her high blood pressure until she had a stroke, I have been worried that my blood pressure might creep up without my knowing it. I became interested again when I reported that a large federal study of people at high risk for a heart attack or stroke found that bringing blood pressure well below the current national guidelines — a systolic blood pressure below 120 millimeters of mercury instead of 140, or instead of 150 for people older than 60 — significantly reduced the death rate and the rate of heart attacks, strokes and heart failure. The results were so compelling that guideline committees are expected to revise their recommendations.
A week after that study was published, I decided to check my blood pressure with a home monitor before a coming physical examination. The first night, I was startled to find that my systolic pressure was a scary 137. The next night, it was only 117. The next morning, before I saw my doctor, it was a terrifying 152. At the doctor's office, it was 150. I measured it again that night, and it had plummeted to 110. And my diastolic pressure, the lower number, was a rock-bottom 60 that evening.
It seemed unreal. Did I have hypertension because my pressure had hit 152 in the morning? But if I took a drug to bring it down, what would happen if my pressure was trying to go down to 110 in the evening?
I asked a few experts.
"Short answer is, you are normal," said Dr. David McCarron, a research associate at the University of California, Davis, adding that anyone whose pressure goes down to 120 or, in my case 110/60, does not have hypertension. His advice to patients is to abstain from obsessively monitoring their blood pressure.