Effect of sex-related changes in blood pressure at entry to the MRC trial on prediction of cardiovascular risk.
1. Using the MRC trial placebo group as the data source, we examined relationships between cardiovascular risk, gender, and blood pressure (BP) at screening, on entry to the trial, and after 3 months of follow up. 2. Blood pressure on entry to the trial (162/98 mmHg) was significantly higher than at the second screening (154/95 mmHg) visit and at 3 months (144/91 mmHg). The entry BP was higher, and the changes from screening to entry and from entry to 3 months were greater in females. Females had a low cardiovascular risk, but because of the greater changes of BP at entry they were over-represented at the top of the entry BP distribution, whereas males were over-represented at the bottom. The result of these effects was that the relationship between cardiovascular risk and entry BP was shifted to the right and was flatter than the corresponding curves measured at screening or after 3 months of follow up. 3. In consequence, the severity of hypertension in the trial population was overestimated from measurement of BP at entry, and the capacity of trial entry BP to predict cardiovascular risk was weakened. 4. BP on entry to the MRC Trial was affected by a pressor effect that diminished the value of BP as a cardiovascular risk factor because it differentially affected sub-populations by gender.
Millar
J A
JA
Department of Internal Medicine, Royal Perth Hospital, Western Australia.
Lever
A F
AF
D001794:Blood Pressure / Q000502:physiology*; D002318:Cardiovascular Diseases / Q000209:etiology*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications / Q000453:epidemiology / Q000503:physiopathology*; D008297:Male; D012307:Risk Factors; D012727:Sex Characteristics