Autonomic Responses to Cold Pain: Effect of Type, Duration, and Habituation in Cryotherapy.

Purpose: Cold limb immersion, a form of cryotherapy, can cause cardiovascular changes due to cold-pain induced autonomic reflexes. This cryotherapy treatment side effect has received less attention but could have direct implications for physical rehabilitation of individuals with cardiovascular comorbidities.

Methods: To test hypotheses related to the pressor effects of varied limb sites and surface areas of cryotherapy, two common lower limb injury sites (ankle and knee) were immersed into cold water (15 min, 1-3°C) and then referenced to a standard cold pressor test (CPT). Beat-by-beat arterial blood pressure (finger photoplethysmography), heart rate (ECG), systemic vascular conductance (SVC; Modelflow), and calf vascular conductance (VC) (venous occlusion plethysmography) were measured in 14 healthy participants.

Results: At 2 min, CPT increased mean arterial pressure (21 ± 4 mm Hg) more than either ankle or leg immersion (15 ± 4 and 15 ± 5 mm Hg, respectively; P = 0.015). Systemic vascular conductance and calf VC decreased but were not different across treatments ( P = 0.417 and P = 0.086). Mean arterial pressure and SVC were not different from 2 to 15 min of immersion ( P = 0.164 and P = 0.522), but calf VC decreased further by the end of immersion (3.1 ± 0.5 to 2.8 ± 0.4 and 2.7 ± 3 to 1.7 ± 0.2 units; P = 0.028). Mean arterial pressure increases with CPT were similar with solely CPT and when CPT followed ankle or leg immersion (27 ± 5 and 23 ± 4 mm Hg, respectively; P = 0.199).

Conclusions: These data indicate robust pressor responses without autonomic reflex habituation and that cryotherapy immersion location but not surface area appears to mediate cardiovascular responses. This cryotherapy side effect may be an important consideration for patients with cardiovascular-related comorbidities.