Sex difference in response of blood pressure to calcium antagonism in the treatment of moderate-to-severe hypertension

Background. The pressor response to examination in the clinic setting is called the 'white coat effect' (WCE). This response may be a confounder when investigators use clinic blood pressure as a measure of response to antihypertensive therapy. Objective. To study the effect of the pressor response by evaluating the sex-specific effect of treatment with calcium antagonism on blood pressure measured in the clinic and by ambulatory blood pressure monitoring (ABPM). Methods. Untreated hypertensive subjects (n = 39) with seated clinic diastolic blood pressures (DBP) ≥ 100 and ≤ 130 mmHg were studied. Same-day clinic systolic blood pressure (SBP) and ambulatory SBP were obtained after 1 week of placebo, and after 1 month of treatment with either nifedipine or verapamil in a randomized, blinded, parallel trial. Results. With placebo, women's average SBP was 18 ± 4 mmHg lower than clinic SBP. By contrast, men's average SBP with placebo was 4 ± 15 mmHg lower than clinic SBP. There was a significantly greater reduction in clinic SBP for women than there was for men after 1 month of treatment (by 33 ± 13 versus 18 ± 18 mmHg, P < 0.005). However, reduction in ambulatory SBP after 1 month was the same for both sexes (20 ± 11 versus 19 ± 12 mmHg). Conclusions. In this study of moderate-to-severe hypertensives, the large WCE measured for women, which markedly diminished with treatment, accounts for the observed sex difference in response of clinic SBP to calcium antagonism, By contrast, with ABPM there was an equivalent response to treatment for both sexes. Use of ABPM could be a valuable means of eliminating the WCE as a confounder in clinical research. (C) 1999 Lippincott Williams and Wilkins.