Objective: To determine reference values for ambulatory blood pressure in a random sample of Spanish elderly population, and their correlations with office blood pressure measurements.
Methods: A representative random sample was obtained, stratified by sex and age, of 1,227 elderly subjects aged > 65 years, residents in an urban district, Barrio de Salamanca, or Madrid, Spain. In a random subsample (n = 420), two different blood pressure measurement approaches were performed: Office blood pressure and twenty-four hour ambulatory blood pressure (spacelabs 90207) were recorded, and two periods were defined: awake and sleeping, on the basis of the daily activities. Hypertension was defined if the average of casual blood pressure was > or = 140/90 mmHg or if there was current use of antihypertensive drugs.
Results: Among the 420 participants, 333 ambulatory blood pressure monitorings were performed, 301 with valid registers, of whom 105 were receiving antihypertensive drug treatment. Office, 24 hour, awake and sleeping pressures averaged 147/84 mmHg, 128/72 mmHg, 132/77 mmHg and 122/66 mmHg respectively. Differences between whole sample and no treated group were not significant (p = 0.2), nor between the whole sample and the treated group (p = 0.7). Office blood pressure was markedly higher than 24 hour and awake averages (20 and 15 mmHg for systolic and 12 and 7 mmHg for diastolic, respectively). The differences between clinic and awake average blood pressures were significantly higher in females (p = 0.001) and increased, in both genders, as age (p = 0.001) and clinic blood pressure values (p < 0.000) increased. Correlation coefficients between office and the average awake period of the ambulatory blood pressures were of 0.60 and 0.48 for systolic and diastolic respectively. The ambulatory blood pressure value equivalent to 140/90 mmHg when obtained by causal measurement, was 15 mmHg lower when considering the 24 h average, or 10 mmHg lower when the awake averages.
Conclusion: Ambulatory systolic and diastolic blood pressure values in the elderly are markedly lower than office values, specially in the case of systolic blood pressure. Differences in results between the two methods increase with age and with clinic blood pressure values, and are bigger in females. The cut-off point for ambulatory blood pressure monitoring equivalent to 140/90 mmHg in the casual measurement is of 125/75 mmHg for the 24 hour average and of 130/80 mmHg for awake average.