Effects of lower limb heating on the ankle-brachial index

Abstract

Background: Peripheral artery disease (PAD) is an atherosclerotic disease with luminal narrowing of blood vessels, leading to an obstruction of blood flow. It most commonly affects blood vessels of the lower extremities. The ankle-brachial index (ABI, the ratio of ankle pressure over brachial pressure) is a primary index in the diagnosis (ABI < 0.9) of PAD. However, resting ABI may not be sensitive enough to detect mild/moderate PAD in some patients. The ABI after a 5 -min exercise stress test is currently used to confirm a diagnosis of PAD in patients with classical symptoms of PAD, but with normal resting ABIs. However, not all of the patients can tolerate the treadmill test. The purpose of this study was to examine the effects of lower limb heating on the ABI measurement, since lower limb heating can also induce lower limb vasodilation as walking does. Hypothesis: We hypothesized that lower limb heating would specifically decrease ABI in PAD patients. Methods: In 10 PAD patients and 12 healthy control subjects, resting ABI was measured at first. Then, both feet and lower legs were immersed in warm water (~ 40 ºC) for 30 min. Thereafter, ABI was measured again. This study is associated with a registered clinical trial (NCT03900832). Data and a summary of the results: Lower limb heating did not significantly alter the hemodynamic variables in both groups. Lower limb heating significantly decreased the ABI of both legs in PAD patients (0.75 ± 0.03 to 0.67 ± 0.04, P = 0.003), and did not alter the ABI in healthy controls (1.01 ± 0.01 to 1.03 ± 0.01, P = 0.103). Discussion and Conclusion: The presented data show that lower limb heating decreases ABI in PAD patients, while it does not alter ABI in healthy individuals. The results suggest that lower limb heating can increase the sensitivity of the ABI measurement in PAD patients. Many patients with PAD can have comorbidities that are either absolute or relative contraindications to exercise treadmill testing. Moreover, many patients with intermittent claudication may not tolerate exercise treadmill testing. We speculate that the lower limb heating approach can be applied in these patients. Further studies on the mechanisms are warranted. This study was supported by National Institutes of Health Grants R01 HL141198 and R01 HL164571. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.