Blood Pressure Changes in the Leg on Standing

Abstract

Normotensive and hypertensive patients develop peripheral arterial disease. The authors hypothesized that significant changes in lower extremity blood pressures occur upon standing, which could play a role in the pathogenesis of peripheral arterial disease. Forty‐one subjects had blood pressure measurements performed in the arm and ankle in the supine and standing positions. The data show a marked increase in leg blood pressure on assuming the standing position, with mean increases of 65 mm Hg in systolic and 62 mm Hg in diastolic blood pressure in the lower extremities, compared with the arm on standing. In addition, the changes in diastolic pressure in the leg on standing were significantly correlated to height (r=0.47; p<0.002). These data reveal a previously unappreciated aspect of blood pressure, namely a large increase in lower extremity blood pressure values on standing, which may predispose to peripheral arterial disease

The measurement of blood pressure in the arm is the standard approach to determining the presence of hypertension in an individual, and to staging blood pressure as a risk factor for cardiovascular diseases. ¹ Among the associated target organ effects of high blood pressure is symptomatic peripheral arterial disease (PAD). Several studies have shown hypertension to be an independent risk factor for PAD. ² , ³ , ⁴ The prevalence of PAD in hypertensive cohorts in the literature varies, in part because the criteria with which PAD is diagnosed ranges from symptomatic claudication ⁴ to an ankle‐brachial index (in which supine blood pressure measured at the level of the ankle is expressed as the percentage of the value measured in the arm) of less than 0.9. ⁵ In a recent study of PAD, more than one half of the subjects did not have hypertension ⁵ ; thus, both normotensive and hypertensive patients are at risk for PAD.

Despite the abundance of literature on hypertension as a risk factor for PAD, little is known about the level of blood pressure in the lower extremity compared with the arm as one changes from the supine to the standing position. Studies such as those of Hamilton et al. ⁶ compared the supine systolic and diastolic pressures in the upper and lower extremities and demonstrated that systolic pressures in the brachial arteries were up to 20 mm Hg less than in the foot and up to 55 mm Hg less than in the thigh. Hocken ⁷ showed that the supine diastolic pressures in the brachial and dorsalis pedis were similar to those of the femoral and brachial vessels. However, we are unable to find any studies of blood pressure measurements in the leg compared with the arm when measured in both extremities in both the supine and standing positions. Because the change in position from supine to standing likely exposes the arterial vessels in the lower extremities to much greater blood pressure compared with the upper extremities, we hypothesized that significant changes in lower extremity blood pressures upon standing, if present, may play a role in the pathogenesis of PAD.

METHODS

Subjects

All subjects were interviewed and studied in the Outpatient Hypertension Program Offices at the University of Pennsylvania. Eligible participants enrolled on a volunteer (nonpaying) basis after providing written informed consent. The studies were approved by the Committee on Studies Involving Human Subjects of the University of Pennsylvania (IRB).

Subjects were aged 18 years or older and included men and women without ethnic restriction. Subjects included those with normal blood pressures as well as those with hypertension. Hypertensive subjects, defined as those on drug therapy for high blood pressure, or having supine arm blood pressure >140/90 mm Hg, remained on their usual antihypertensive therapy (if so prescribed). A total of 41 subjects were evaluated.

Procedures

After 5 minutes of rest in the examination room, blood pressures were taken in the dominant arm with the participant supine. Three sets of systolic and diastolic blood pressures and heart rate at 1–2‐minute intervals were taken in the arm and averaged together to yield a single value. The cuff was then removed and placed approximately 1 inch above the ankle (medial malleolus) and another set of three recordings was obtained. With the blood pressure cuff still in the position over the ankle, the subjects were then asked to assume an upright (standing) position. After 5 minutes in the standing position, the same data were again obtained three times (with 1–2‐minute intervals between each recording). The blood pressure cuff was then removed and placed back on the arm and similar recordings made with the subject standing.

A Dinamap (Criticon, Hialeah, FL) automated blood pressure monitor was used for all measurements of blood pressure and heart rate, to minimize observer bias. The Dinamap has been validated in prior studies of ankle blood pressure measurement. ⁸

Data

The data were recorded on standardized case report forms and entered into an Excel database (version 7.0, Microsoft Corp, Redmond, WA). All data are expressed as means±SD. Data collection included age, gender, race, weight, height, and the averaged values of supine and standing systolic and diastolic blood pressure and heart rate. Data were then analyzed using Sigmastat (version 2.0, Jandel Scientific, San Rafael, CA) software to perform the appropriate statistical tests. Within‐group and betweengroup comparisons were performed using a paired t test. Correlations of height vs. systolic or diastolic blood pressures were analyzed using a Pearson correlation coefficient. Two‐tailed p values of <0.05 were considered statistically significant.

RESULTS

The demographic characteristics of our study population are shown in Table I. Of the 41 participants, 23 (56%) were males, 19 (46%) were hypertensives, and there were 16 African Americans, 22 Caucasians, and three Asians.

Table I.

Demographics of Study Subjects

Number of Subjects	41
Age (years)	52±14 (SD)
Gender (men/women)	23 (56%)/18 (44%)
Ethnicity (African American/Caucasian/Asian)	16/22/3
Brachial supine blood pressure (mm Hg)	132±23/77±12
Heart rate (beats per minute)	68±8
Hypertensive, n (% of total)	19 (46%)
Height (inches)	66±4
Weight (pounds)	156±30

Figure 1 graphically shows the changes in blood pressure, comparing supine with standing values, in the dominant arm and the same‐side leg in the entire group of participants. Supine systolic blood pressure in the leg was higher than in the arm (132±23 mm Hg vs. 157±26 mm Hg, arm vs. leg, respectively; p<0.001). However, the diastolic blood pressures in the arm and leg were similar (77±12 mm Hg vs. 80±12 mm Hg, arm vs. leg, respectively; p=NS). The standing systolic blood pressure showed no statistically significant change in the arm compared with the supine value (129±22 mm Hg vs. 132±23 mm Hg, standing vs. supine in the arm, respectively; p=NS). However, there was a large and statistically significant increase in the standing systolic blood pressure of the leg compared with either the standing systolic blood pressure in the arm (222±23 mm Hg vs. 129±22 mm Hg, leg vs. arm, respectively; p<0.001) or the supine systolic blood pressure in the leg (222±23 mm Hg vs. 157±26 mm Hg, standing leg vs. supine leg, respectively; p<0.001). Similarly, the standing diastolic blood pressure in the arm showed no statistically significant change when compared with the supine value in the arm (79±12 mm Hg vs. 77±12 mm Hg, supine vs. standing, respectively; p=NS). However, there was a large and statistically significant increase in the standing diastolic blood pressure of the leg compared with either the standing diastolic blood pressure in the arm (to 142±18 mm Hg vs. 79±12 mm Hg, leg vs. arm, respectively; p<0.001) or the supine diastolic blood pressure in the leg (142±18 mm Hg vs. 80±12 mm Hg, standing vs. supine leg, respectively; p<0.001). There was no significant change in heart rate after changing from the supine to the standing positions (data not shown).

Figure 1.

Changes in blood pressure, comparing supine with standing values, in the dominant arm and leg in the entire group (N=41) of subjects. Stick figure below each floating bar shows subject position.
 **The standing leg systolic and diastolic blood pressures are significantly different (p<0.001) from the systolic and diastolic pressures in the supine leg and significantly different (p<0.001) from the systolic and diastolic pressures in the arm on standing.

In a subset analysis, we compared the changes in the blood pressure of normotensive subjects in the leg on changing from the supine to the standing position with the changes in hypertensive subjects who were matched for age. The characteristics of this subset of subjects are presented in Table II.

Table II.

Demographics of Subset of Subjects

	Hypertensive	Normotensive
Number of Subjects	10	10
Age (years)	52.8±5.4	52.2±5.7
Gender (men/women)	6	6
Ethnicity (African American/Caucasian/Asian)	4/6/0	3/6/1
Brachial supine blood pressure (mm Hg)	149±25/88±10	119±11/73±7
Heart rate (beats per minute)	70±6	67±8
Height (inches)	67±4	67±3
Weight (pounds)	172±28	165±28

Figure 2 summarizes the results of this study. Supine systolic and diastolic blood pressures measured in the arm were higher, as expected, in the hypertensive compared with the normotensive subjects. The delta (mm Hg increase) in systolic pressure in the leg in the normotensive subjects, from supine to standing, was not significantly higher than the delta in systolic blood pressure in the hypertensive subjects (71±14 vs. 60±23 mm Hg, normotensive vs. hypertensive, respectively; p=NS). Similarly, the delta in diastolic pressure when going from supine to standing was also not significantly higher than the delta in diastolic blood pressure in the hypertensive subjects (62±15 vs. 62±13 mm Hg, normotensive vs. hypertensive, respectively; p=NS).

Figure 2.

Comparison of changes in leg blood pressure between age‐matched normotensive and hypertensive subjects on changing from the supine to the standing position. Stick figure below each floating bar shows subject position. Panel A depicts pressure readings in normotensive subjects in the arm, supine and standing. Panel B depicts normotensive pressure readings in normotensive subjects in the leg, supine and standing. Panel C depicts pressure readings in hypertensive subjects in the arm, supine and standing. Panel D depicts pressure readings in hypertensive subjects in the leg, supine and standing.
 **The standing leg systolic and diastolic blood pressures are significantly different (p<0.001) from the systolic and diastolic pressures in the supine leg and significantly different (p<0.001) from the systolic and diastolic pressures in the arm on standing within the normotensive and hypertensive groups.

Lastly, we conducted an analysis comparing the height of a subject to the delta in either systolic or diastolic blood pressure. We hypothesized that taller subjects would have greater increases (delta) in blood pressure. The results of this comparison are shown in Figure 3. There was a nonsignificant trend (r=0.26; p=0.10, NS) for height compared with the delta systolic blood pressure (upper panel); however, there was a statistically significant relationship comparing height with delta diastolic blood pressure (r=0.47; p<0.002).

Figure 3.

Scattergraphs with regression lines showing correlation of height with change (DELTA) in systolic blood pressure (SBP) in the leg (standing systolic‐supine systolic) in the upper panel (p=0.10, NS) and correlation of height with change (DELTA) in diastolic blood pressure (DBP) in the leg (standing diastolic‐supine diastolic) in the lower panel (p<0.002).

DISCUSSION

Our data show that normotensive and hypertensive subjects exhibit a marked increase in both systolic and diastolic blood pressure in the legs on assuming the standing position.

The change in systolic blood pressure in the legs from supine to standing was numerically larger in the normotensive subgroup than in the hypertensive group, perhaps because our hypertensive subjects were on antihypertensive drug therapy. These data show a significant mean increase of 65 mm Hg in the systolic and 62 mm Hg in the diastolic blood pressure in the lower extremities on standing in our combined group of 41 subjects. Although height showed only a statistically insignificant trend toward correlation with the change (delta) in systolic pressure, comparing the supine leg values with the standing leg values, there was a statistically significant correlation between the delta in diastolic pressure, comparing the supine leg values with the standing leg values, and height.

Our data confirm the common clinical finding that in the standing position the average systolic blood pressure in the arm is reduced slightly, while the average diastolic blood pressure in the arm rises slightly. In the standing position, both the normotensive and the hypertensive participants had blood pressures at the level of the ankle that would have been clearly classified as severe (stage 3) hypertension if these were measured in the arm. ¹ These data raise the question of whether PAD, which generally occurs first (and most severely) in the legs compared with the arms may result in part from the contribution of the pronounced elevation in blood pressures on standing. This study was not designed to address that particular question, and no subject in our group had a leg systolic pressure that was <90% of the arm value; thus, the role of the delta in systolic and diastolic blood pressure at the level of the ankle on standing remains speculative.

Data from the Atherosclerosis Risk in Communities (ARIC) study ⁹ have evaluated blood pressures in the arm in the supine and standing position, with changes noted that are similar to our findings. However, no study of which we are aware has evaluated the blood pressure in the ankle and its relationship to brachial blood pressure in the standing position.

Limitations

This is a small study, and we acknowledge that our data need to be validated in larger study populations. The particular blood pressure medications the patients were prescribed were not taken into account in the study population, and this could have played a role in our analysis of the hypertensive and normotensive subsets (Figure 2). We also combined the treated hypertensives (n=8) with the untreated hypertensives (n=2) in our subset analysis.

In summary, a large and consistent increase in systolic and diastolic blood pressure occurs at the level of the ankle on changing from the supine to the standing position. The magnitude of the change in blood pressure in the leg, particularly for the diastolic value, as position changes from supine to standing shows a significant correlation to height. Since blood pressure contributes to the development and progression of PAD in both hypertensive and normotensive patients, the large changes in blood pressure we demonstrated in our study may be a contributing factor in the development of PAD. Evaluation of positional blood pressure changes in the lower extremities of populations such as those with diabetes and/or prevalent PAD will further clarify the role of this phenomenon.

Acknowledgment: This work was supported by National Institute of Health (NIH) grant K24‐DK02684.