Hypertension Diagnosis and Evaluation
Measurement Issues
In light of the greater variability in blood pressure among older individuals (due, in part, to the decrease in baroreceptor sensitivity), it s critically important to make an accurate diagnosis of hypertension in this population. To do so requires careful attention to correct measurement of blood pressure with respect to utilizing the proper cuff size, measuring the blood pressure in both arms, having the patient appropriately positioned (sitting comfortably following 5 min of quiet rest with the arm supported at heart level), palpating the systolic blood pressure level at the radial artery to avoid the auscultatory gap, and taking two blood pressure measurements separated by at least 2 min (more if there is greater than 5 mmHg difference between the first two readings) at each of three visits.
The average of these measurements is used to define an individual’s blood pressure, which determines the presence or absence of hypertension according to the classification scheme given in
Table 40.1
.The statement that “hypertension should not be diagnosed on the basis of a single measurement” is especially relevant to the older patient. It has been observed that, when antihypertensive medication is withdrawn from some older individuals, a significant number do not manifest a blood pressure high enough to be classified as hypertensive, suggesting that some older individuals are at risk for overtreatment of their blood pressure. Careful adherence to these measurement techniques will minimize the likelihood that older individuals are misdiagnosed as hypertensive and inappropriately placed on an antihypertensive medication.
Given the age-associated increase in arterial vascular stiffness, there have been concerns that indirect (cuff) blood pressure measurement may not accurately reflect actual intra-arterial blood pressure in older individuals. This overestimation of true blood pressure by the indirect method secondary to the incompressibility of the brachial artery is referred to as pseudohypertension. Despite these concerns, it has been demonstrated that indirect blood pressure measurement is as accurate among older (at least up to age 80 years) as it is in younger individuals; the indirect measurement tends to underestimate systolic and overestimate diastolic blood pressure to similar degrees in both age groups. Similar findings have been observed in a group of 26 subjects from age 50 to 80 years who had isolated systolic hypertension. There remains some uncertainty as to the true frequency of pseudohypertension in the elderly population; prevalence estimates vary from 2% to 70% among the published descriptions.
Some investigators have suggested that the presence of a positive Osler’s sign, the ability to palpate the radial artery when the radial pulse is obliterated by inflating an arm cuff to above the systolic blood pressure, increases the likelihood of pseudohypertension. The utility of identifying a positive Osler’s sign has been questioned, however, due to its poor reproducibility and low positive predictive value. The possibility of pseudohypertension should be entertained in the presence of a discrepancy between the severity of the blood pressure and evidence of target organ damage, a wide pulse pressure, or perhaps a positive Osler’s sign. In these situations, other measurement techniques, such as oscillometric or plethysmography of the digital blood pressure (Finapres) methods, or in some cases direct intra-arterial blood pressure monitoring, may be utilized to make the definitive diagnosis.
Another clinical situation in which overestimation of blood pressure may occur is office or “white coat” hypertension. Ambulatory home blood pressure monitoring or patient self-monitoring may provide additional information needed to evaluate the patient’s blood pressure when concern for white coat hypertension arises, in borderline situations where there is uncertainty about the diagnosis of hypertension, or when there is extreme variability in blood pressure readings. In a substudy reported from the Systolic Hypertension in Europe Trial, results from 24-h ambulatory blood pressure readings provided a better predictor of subsequent cardiovascular events than did the standard blood pressure readings, suggesting another potential benefit of ambulatory blood pressure monitoring.
Although not directly pertinent to the diagnosis of hypertension, another critically important aspect of blood pressure measurement in the older hypertensive patient is obtaining baseline postural or orthostatic blood pressure measurements. Orthostatic hypotension is usually defined as a decline in blood pressure from the supine baseline of greater than 20 mmHg systolic and/or 10 mmHg diastolic after 1 to 2 min of standing. This definition is supported by a careful study of the postural blood pressure response of normal individuals that determined that this extent of decline exceeded the 95% confidence limits for the postural change in blood pressure. Aging per se is not associated with an increased prevalence of orthostatic hypotension. The supine systolic blood pressure has been identified as the best predictor of the postural decrease in systolic blood pressure. Accordingly, the presence of supine hypertension is an important risk factor for orthostatic hypotension. Baseline orthostatic blood pressure readings are therefore required in every patient to avoid adverse events related to further declines in postural blood pressure that may result from antihypertensive therapy.