There is currently no consensus on appropriate rest time prior to undertaking an ankle pressure measurement to use in calculating an ABI. The results of this present study suggest that in a community‐based population the systolic ankle blood pressure falls by ≈5 mm Hg during the first 10 minutes of rest, but between 10 and 15 minutes further reductions are marginal. Only ankle systolic pressures were measured in this study to ensure that each measurement could be made exactly at each time point. Had brachial pressures also been included, the time taken to perform the measurements would mean that both measurements could not be taken at each specific time interval. However, our findings are consistent with literature relating to the effect of premeasurement rest time on systolic brachial pressures which have been demonstrated to drop over the first 10 minutes of rest in both seated and supine positions.15,20
The total drop in systolic ankle pressure between 5 and 10 minutes of 5 mm Hg is a relatively small change in pressure and similar drops have been reported in systolic brachial pressures over the same time, meaning a ratio measurement such as an ABI may be less affected by this change if both pressures are taken following a similar amount of premeasurement rest. However, given that the time implication of taking each measurement makes this difficult, the results of our study combined with previous investigations of brachial pressure15,20
suggest the most accurate method of performing the ABI is following a 10‐minute rest time.
Diabetes was demonstrated to have a significant effect on the amount of change between 5 and 15 minutes. The mean change in ankle pressure in this subset of the population was smaller than for the entire cohort. Potential presence of diabetes‐related autonomic neuropathy may account for this finding as this has been suggested to affect blood pressure regulation in the lower extremity due to sympathetic denervation.21–22
demonstrated reduced variability of blood flow to the feet of people with diabetes suggesting this may cause impairment of thermoregulation and contribute to the development of orthostatic hypotension. Impaired sympathetic activity has been demonstrated to cause subsequent lack of vascular resistance during standing, leading to decreases in blood pressure in the diabetic‐versus‐nondiabetic cohort,22
indicating altered sympathetic response to positional change. In this present study, altered sympathetic control in people with diabetes may have affected the amount of change seen in ankle pressures following a positional change (from standing to supine) when compared to the entire cohort. These findings suggest further investigation on the impact of specific diabetes‐ related comorbidities on ankle pressure regulation is required to determine their impact on current clinical testing procedures. It should also be considered that a number of other variables, including baseline ankle pressure, presence of hypertension, and significant PAD, may also affect systolic ankle blood pressure change with rest and are worthy of further investigation.
Reliability of the ankle pressure testing between test and retest was found to be excellent at 5, 10, and 15 minutes with only marginal increases in reliability following stabilization of systolic ankle pressure at 10 minutes (ICC range: 0.84 to 0.89) and greater precision of the measurement following 10 minutes of rest (SEM 3.05 mm Hg vs 2.22 mm Hg). The lack of significant change in mean systolic ankle pressure between test and retest at each time point indicated by the nonsignificant results of paired samples t
tests suggest that overall the response of systolic ankle pressure to supine positioning and duration of rest was replicated at the second testing session. The results of our study are consistent with previously reported test‐retest reliability of ankle systolic pressures taken with a 8 MHz Doppler probe 7 days apart following 15 minutes of rest (ICC range 0.85 to 0.99).11
High reliability may have been due to strict control of external factors such as caffeine and exercise, which are known to affect blood pressure measurements, the retest occurring at a similar time of day to the first test, and the experience level of the clinician taking the measurements. These findings indicate that measurement of systolic ankle pressure with a handheld 8 MHz Doppler and aneroid sphygmomanometer is a clinically reliable method of assessing peripheral arterial flow.
This study did not utilize a baseline measurement (taken at 0 minutes), therefore the total drop in systolic pressure between 0 and 15 minutes is unknown. The first measurement was taken at 5 minutes as this was the shortest duration of premeasurement rest time found to be reported in the literature.13
The overall change in pressure between 0 and 15 minutes may therefore have been >5 mm Hg or <5 mm Hg depending on the direction of the change in the first 5 minutes. Previous research assessing brachial pressures in the supine position suggests that this is likely to have been an additional reduction. However, this needs to be determined in relation to ankle pressures.
The results of this study are relevant to an older community‐based population which is likely to have higher rates of hypertension, diabetes, and PAD than the general population. This participant group was chosen for clinical relevance as all participants met the criteria to undergo routine screening with an ABI according to current guidelines. However, results from this study may not be reflective of changes occurring in a younger cohort free from risk factors for, or signs and symptoms of, PAD.