Twenty-four hour ambulatory intra-arterial blood pressure in normotensive and borderline hypertensive subjects

A number of studies have shown that blood pressure values obtained by ambulatory monitoring are lower than those obtained in the doctor's office by cuff readings. However, there is still no suitable information on 'normal' 24-h ambulatory blood pressure values. In 19 normotensive and 13 borderline hypertensive subjects, defined by repeated office blood pressure measurements, we recorded intra-arterial blood pressure under ambulatory conditions for 24 h (Oxford method) in order (1) to assess the 24-h blood pressure values of normal subjects, and (2) to compare their 24-h blood pressure values with those of borderline hypertensive patients. In the normotensive subjects systolic, diastolic and mean ambulatory blood pressure values over 24 h were significantly lower than the corresponding office values, the differences being -15.0, -22.1 and -17.9 mmHg, respectively. In the borderline hypertensives 24-h ambulatory blood pressure was significantly lower than office readings. On average, the 24-h mean blood pressure of normotensive subjects was significantly lower than that of borderline patients (P less than 0.01). However, individual 24-h blood pressure values showed a considerable overlap. Thus, (1) ambulatory blood pressure values just below 140/90 mmHg do not necessarily mean that the blood pressure is in the normal range, the mean 24-h blood pressure of true normotensive subjects being much lower; (2) ambulatory blood pressure monitoring in patients with high office blood pressure readings may help to identify subjects whose 24-h mean values are indistinguishable from those of normotensives. However, the clinical relevance of these findings in the diagnosis of hypertension has to be validated by prospective clinical trials.