Date Published: June 8, 2015
Publisher: Public Library of Science
Author(s): Yi Gong, Kai-wu Cao, Jin-song Xu, Ju-xiang Li, Kui Hong, Xiao-shu Cheng, Hai Su, Tatsuo Shimosawa.
This study aimed to establish a normal range for ankle systolic blood pressure (SBP).
A total of 948 subjects who had normal brachial SBP (90-139 mmHg) at investigation were enrolled. Supine BP of four limbs was simultaneously measured using four automatic BP measurement devices. The ankle-arm difference (An-a) on SBP of both sides was calculated. Two methods were used for establishing normal range of ankle SBP: the 99% method was decided on the 99% reference range of actual ankle BP, and the An-a method was the sum of An-a and the low or up limits of normal arm SBP (90–139mmHg).
Whether in the right or left side, the ankle SBP was significantly higher than the arm SBP (right: 137.1±16.9 vs 119.7±11.4 mmHg, P<0.05). Based on the 99% method, the normal range of ankle SBP was 94~181 mmHg for the total population, 84~166 mmHg for the young (18–44 y), 107~176 mmHg for the middle-aged(45–59 y) and 113~179 mmHg for the elderly (≥60y) group. As the An-a on SBP was 13mmHg in the young group and 20mmHg in both middle-aged and elderly groups, the normal range of ankle SBP on the An-a method was 103–153 mmHg for young and 110–160 mmHg for middle-elderly subjects. A primary reference for normal ankle SBP was suggested as 100-165 mmHg in the young and 110-170 mmHg in the middle-elderly subjects.
Ankle blood pressure (BP) is used more frequently in clinical practice as it could be easily taken using an electronic BP device [1–4]. Previously, ankle BP was mainly used for calculating ankle-brachial index (ABI) [5, 6]. Although ankle BP has been demonstrated a predictor for subclinical atherosclerosis, cardio-cerebrovascular morbidity and mortality [2–4], the understanding on ankle BP per se is insufficient at present. For example, the normal range of ankle BP is still uncertain, although one study considered >175 mmHg as elevated ankle systolic BP (SBP) . Generally, arm SBP is used as the reference for identifying the abnormality of ankle SBP in most studies [7, 8].
The SBP of four limbs in three age groups are shown in Table 2. The ankle SBP was similar between two sides, although the right arm SBP was slightly higher than left arm in three age groups. As age increased, the ankle SBP of both sides increased as arm SBP did.
The present study showed that the ankle SBP was 18mmHg higher than arm SBP in 960 subjects with normal arm SBP. Previous studies in healthy volunteers also showed similar results, 22mmHg by Engvall et al.  and 17.8 mmHg by Swiet et al . Furthermore, our study showed that An-a on SBP is age-dependent, 13mmHg in the young group, but 20 mmHg in both middle-aged and elderly groups.
This study primarily suggests 100–165 mmHg in the young and 110–170 mmHg in the middle-elderly subjects as normal range of ankle SBP.