Passive heat therapy to improve cardiometabolic health in persons with a spinal cord injury — a pilot study
Authors: Trbovich Michelle , Hoekstra Sven , Wu Yubo , Uhlig-Reche Hannah , Leicht Christof , Kellogg Dean 
Published: May 2024

Objective: To test the effect of repeated heat therapy on markers of inflammation, glucose metabolism and vascular health in persons with a spinal cord injury (SCI). It was hypothesized that the heat therapy intervention would lead to a reduction in the fasting concentration of inflammatory markers as well as an improvement in glucose tolerance and microvascular function.Methods: Five adults with thoracic SCI ((1 female, age: 43 (27 – 60) yrs, BMI: 29 (23 to 30) kg/m2, years since injury: 7 (1 – 11) yrs)) enrolled in an 8-week passive heat therapy intervention consisting of 24 session during which the oral temperature was elevated by 1°C by means of a water-perfused suit and heating blankets. The number of completed sessions, time to reach the desired oral temperature and adverse events were reported. Thermoregulatory and perceptual responses to a single passive heat therapy session were assessed during the first session of the intervention. Fasting interleukin-6 (IL-6), C-reactive protein (CRP) and glucose concentration were measured in plasma before and after the chronic intervention. Additionally, thermal hyperemia in sensate (i.e., arm) and insensate (i.e., leg) skin through laser Doppler flowmetry were determined at 39°C and 45°C pre- and post-intervention. Descriptive data are expressed as median (range).Results: The median time to reach a 1°C increase in oral temperature during passive heating was 53 (49 – 75) min, which was accompanied by a final mean skin temperature of 38.6 (36.5 – 38.9)°C, a thermal comfort of 2 (0 – 4) on a 0 to 5 ratings scale and a basic affect of +3 (+1 - +4) on a -5 to +5 rating scale. Four out of the five participants completed all prescribed passive heating sessions. However, in two participants a number of sessions (N = 10 and 2 out of 24 sessions) were stopped at 0.8°C due to thermal discomfort. There were no skin burns or signs of autonomic dysreflexia. All participants remained hemodynamically stable throughout the sessions. Resting IL-6 and CRP changed from 3.2 (2.7 – 10.5) pg/ml to 8.1 (7.6 – 11.1) pg/ml and 0.40 (0.14 – 1.16) to 1.11 (0.51 – 1.26) pg/ml, respectively. Fasting glucose concentration changed from 90.0 (85.5 – 206.0) mg/dl to 94.5 (69 – 266) mg/dl. Cutaneous vascular conductance at 39°C as a percentage of maximal vasodilation at the arm and leg changed from 23.2 (11.2 – 36.0)% to 30.4 (13.8 – 46.1)% and 34.3 (30.4 – 49.4)% to 47.4 (6.7 – 52.8)%, respectively. Conclusion: These preliminary findings suggest that it is feasible, well-tolerated and safe for persons with SCI to engage in repeated heat therapy. A full data set of this ongoing study is needed to provide more conclusive insight into its effects on cardiometabolic health outcomes. VA Rehabilitation R&D (I21RX003724-01A1). This is the full abstract presented at the American Physiology Summit 2024 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.