Bilateral Indirect and Direct Arterial Pressures
Authors: HARRISON EDGAR G. , ROTH GRACE M. , HINES EDGAR A. 
Published: June 2012

Bilateral determinations of the blood pressures were made nonsimultaneously and simultaneously by the indirect method under basal conditions on 447 patients. In this group 26.6 per cent of the paired measurements by the nonsimultaneous indirect method exhibited systolic differences of 10 mm. Hg or greater and 15 per cent exhibited diastolic differences of this magnitude, whereas only 5.3 per cent of the measurements by the simultaneous indirect method had systolic differences and only 4 per cent had diastolic differences of this degree. This indicates that bilateral determinations of blood pressure must be performed simultaneously on patients being examined for possible inequalities of blood pressure.
Bilateral differences in blood pressure obtained by the simultaneous indirect and simultaneous direct methods in 14 normal subjects and 53 selected patients were compared. In the normal subjects, 3 of the 42 paired indirect measurements and none of the paired direct measurements in either the radial or brachial arteries had systolic differences of 10 mm. Hg or greater, and none of the diastolic differences were of this level. In the 53 selected patients, 10 per cent of the indirect and 6 per cent of the direct measurements of systolic blood pressure differed by 10 mm. Hg or more and 8 per cent of the paired indirect measurements of diastolic blood pressure and less than 1 per cent of the paired direct measurements differed by this amount. These differences in bilateral blood pressures were characterized by their inconstancy and lack of agreement with subsequent measurements when studied by both the indirect and direct methods, which apparently separates them from those due to altered hemodynamics from pathologic conditions of the aortic arch or its tributaries.
Bilateral differences of blood pressure are of clinical importance when they are great and are reproducible by the direct as well as by the indirect methods, as illustrated by a patient encountered in this study.
In addition, 1 case of extreme obesity and 1 of advanced arteriosclerosis were reported. Both patients were found to have pseudohypertension, which was detected in this study.
A slight increase in the incidence of bilateral differences in indirect blood pressures was found in a group of patients whose blood pressures were measured while they were in the supine and then in the sitting position.
A slight increase in the incidence of bilateral differences was found at higher levels of blood pressure by comparing the blood pressures of nonhypertensive and hypertensive patients and of hypertensive patients before and during treatment with antihypertensive drugs.
Bilateral inequalities of blood pressure did not appear to be related to the age or sex of the subjects. Likewise, differences in circumferences of the arm or right or left-handedness did not appear to influence these inequalities, and there was no marked side dominance for differences found.
Bilaterally simultaneous, indirect measurements of blood pressure should be carried out on patients with hypertension who will be treated with antihypertensive drugs. Bilateral direct measurements may be used to verify the existence of inequality of blood pressures detected by the indirect method and to determine the correct pressure to be followed. This is particularly important in patients being screened for pheochromocytomas, since such differences may produce false-positive results.