Passive Heating as an Accessible and Tolerable Strategy to Improve the Inflammatory Profile and Cardiometabolic Health in People With Spinal Cord Injury
Phase: NA
Conditions: Spinal Cord Injury, Chronic Inflammation, Glucose Metabolism, Endothelial Function
Sponsor: VA Office of Research and Development

3DVVLYHKHDWLQJDVDQDFFHVVLEOHDQG
WROHUDEOHVWUDWHJ\WRLPSURYHWKH
LQIODPPDWRU\SURILOHDQGFDUGLRPHWDEROLF
KHDOWKLQSHRSOHZLWKVSLQDOFRUGLQMXU\
1&7
1RYHPEHU

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
Significance 
Persons with spinal cord injury (SCI) are at an increased risk for T2DM and CVD compared to able-
bodied (AB) individuals. 3 This may be related to factors directly associated with the injury, such as 
the loss of muscle mass and autonomic dysfunction.2 It is, however, increasingly recognized that the 
physical inactivity among people with SCI is but one of several contributors to the increased risk of 
CVD compared to the AB population. 20 An increase in absolute21 and relative22 total body fat 
(visceral adipose tissue in particular),4 occurs as a result of a chronically positive energy balance and 
contributes to other disorders associated with poor glucose utilization and endothelial dysfunction.23 
Furthermore, structural adaptations of large conduit arteries occur as soon as 3-6 weeks after SCI.6,7 
Specifically, resting diameter of the common femoral artery is 30-50% smaller,7,24 limb blood flow is 
reduced by 30-40%25,26 and responses to reactive ischemia decreased.24,27 One year post-injury, 
arterial stiffening is documented,28,29 which is an independent risk factor for CVD.30,31 The etiology of 
such changes is yet to be elucidated but chronic inflammation has been proposed.15 
            Cardiometabolic disorders such as T2DM and CVD share a common and likely causative 
etiology; chronic low grade inflammation.4,32,33 Indeed, the increased concentration of 
circulating pro-inflammatory factors such as interleukin-6 (IL-6), C-reactive protein (CRP) and 
tumor necrosis factor-α (TNF- α) in persons with chronic low-grade inflammation can directly 
interfere with insulin signaling4, potentially through inhibition of C-Jun N-Terminal Kinase (JNK). 34 
Animal studies show that a reduction in markers of inflammation, such as c-Jun N-Terminal Kinase 
(JNK) activity as well as TNF-α expression, enhances insulin sensitivity.34-36 For CVD, these pro-
inflammatory cytokines, facilitate the infiltration of macrophages through the vascular wall to 
form atherosclerotic plaques,37,38 which compromises vascular integrity. In mice, gene knockout 
studies provide evidence that the actions of TNF-α lead to an increase of plaque formation.39 This 
aligns with observational epidemiological data that show a positive association between pro-
inflammatory markers and future CVD events.40  
Individuals with SCI have chronically elevated serum concentrations of pro-
inflammatory markers (e.g.; CRP, IL-6 and TNF-α) compared with able-bodied (AB) 
individuals.3,5,41-43 Reasons for this are not fully elucidated but two theories include 1) The increase in 
visceral fat that leads to an increased production of pro-inflammatory cytokines by adipose tissue and 
2) The decrease in sympathetic activity after SCI leads to an attenuation of lipolysis, dyslipidemia, 
and increased macrophage infiltration in adipose tissue, which contribute to chronic inflammation.23 In 
addition, after SCI, endothelial function15 of the brachial artery, an important risk factor for CVD, 
and glucose tolerance44 is impaired compared to AB individuals. As an intervention, exercise 
training can serve as a non-pharmacological, low-cost intervention to reduce chronic low-grade 
inflammation.10 Its positive effects may be related to the anti-inflammatory environment created in the 
circulation following each exercise session, characterized by an immediate increase in IL-6 
concentration that in turn stimulates the sustained elevation of anti-inflammatory cytokines, 
IL-1ra and IL-10.10  
It should be noted that IL-6 is a pleiotropic cytokine, having both pro-and anti-inflammatory 
properties as well as affecting metabolism. Chronic elevation of IL-6 concentration is associated 
with chronic diseases such as T2DM and inflammatory conditions such as rheumatoid arthritis.45 In 
contrast, the acute, transient increase in IL-6 concentration as observed following exercise has 
predominantly metabolic and anti-inflammatory effects, as evidenced by the accompanied 
increase in the concentration of anti-inflammatory cytokines IL-1ra and IL-10 in the absence of 
changes in pro-inflammatory cytokines TNF-α and IL-1β.14 Furthermore, transient elevations of 
IL-6 concentration have been shown to stimulate fat and glucose metabolism.46,47 
It should further be pointed out that, exercise in the heat results in a greater inflammatory (i.e.; 
acute IL-6 increase) response when compared with exercise in thermoneutral or cold conditions.48-52 
Moreover, clamping core temperature (Tcore) by cycling in cold water can abolish the acute IL-6 
response.51 The amplified acute cytokine response following exercise in the heat may be partly 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
mediated by the increased plasma catecholamine concentrations51 and carbohydrate utilization when 
compared with exercise in thermoneutral or cold conditions.53 In conclusion, the increase in body 
temperature plays a large role in the exercise-induced acute inflammatory response.  
Interestingly, similar to exercise, heat stress raises antegrade shear stress and, importantly, it 
also reduces retrograde shear stress.54,55  More specifically, in the femoral artery, passive heating 
can increase antegrade shear stress on the endothelium by a greater magnitude than can exercise.56 
Thus, the rise in Tcore alone (in absence of exercise) not only has anti-inflammatory, but also 
vascular health benefits.  
Despite the appeal of exercise to lower the risk for chronic disease, the reduced physical 
capacity of persons with SCI and their inability to achieve maximum workloads13 comparable 
to AB persons, often precludes or limits participation in regular exercise.57 Additionally, persons 
with SCI do not demonstrate the same positive acute and chronic physiologic responses to exercise. 
For example, the acute increase in IL-6 following exercise is dampened in people with a cervical 
SCI,12 (possibly due to decreased lean muscle mass) potentially interfering with its anti-inflammatory 
benefits. In addition, we have demonstrated that a seven-day exercise program in the heat does not 
lead to typical heat acclimation adaptations (i.e.; decreased core temperature and heart rate) in 
persons with SCI, possibly due to autonomic dysfunction.13 In conclusion, considering the limitations 
of the ability to exercise, the ability to achieve similar workloads to AB persons, and the lack of anti-
inflammatory and physiologic benefits of exercise in the SCI population, alternative interventions 
that increase body temperature and provide the same anti-inflammatory and cardiometabolic 
benefits are highly warranted.9 Passive heating, a practical and accessible intervention even for 
those at the lowest end of the physical capacity-spectrum, such as post-SCI,14 may be such a 
therapy. 
 
Innovation  
Several methods exist to passively elevate body temperature in humans. Most stem from ancient 
cultures worldwide, such as the Romans and ancient Scandinavian and Asian cultures. Sauna 
bathing and hot water immersion (HWI) are most widely studied. While both demonstrate 
improvements in vascular health in AB persons, emerging evidence is showing anti-inflammatory 
effects as well. A brief overview of evidence is presented in Table 1 however, for an exhaustive list of 
studies see Hoekstra et al. 2020.9 The current status of the field of passive heat therapy to improve 
inflammation and cardiometabolic health is now discussed followed by gaps in the SCI literature and 
how we intend to test its impact in persons with SCI. 
OUTCOMES 
Author 
Population Intervention 
Inflammation 
Glucose 
Metabolism 
Vascular Health 
ACUTE (one heat stress 
session) 
Laing et al.50 
AB (n=13) 2h HWI 
Acute increase in IL-6, 
IL-10, IL-1ra and 
Hsp72 
NT 
NT 
Oehler et al.58 
AB (n=12) 2h HWI 
Acute increase in IL-6, 
IL-10, IL-1ra and 
Hsp72 
NT 
NT 
Hoekstra et al.16  
AB (n=10) 60min HWI 
Acute increase in IL-6 
lower fasting 
glucose and 
insulin 
Increase NO bioavailability 
Table 1. Summary of a few passive heating studies in AB (see Hoekstra et al9 for exhaustive list of AB studies) and of 
all studies (n=3) in persons SCI (in grey shade) that report inflammatory, glucose metabolism and vascular health 
outcomes. Note, only 3 studies of acute responses to passive heating have been performed in persons with SCI and 
no studies have examined the chronic responses to repeated passive heating sessions over a longer term. 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
Hashizaki et al.59  
SCI (n=19) 
60min hot water 
perfused suit (lower 
body) 
Acute increase in IL-6 NT 
NT 
Leicht et al.14  
SCI (n=7) 60min HWI 
Acute increase in IL-6, 
IL-8 and IL-1ra 
NT 
NT 
Coombs et al.15  
SCI (n=15) 
60min HWI  
(lower limbs only) 
NT 
NT 
1.elevated CD62e+ 2.unchanged 
macrovasculature AND 
microvascular function 
CHRONIC (repeated) 
Brunt et al.17  
AB (n=12) 
8 wks. of 60min HWI 
(4-5x/wk.) 
increase in Hsp90 
NT 
improved microvascular function 
Ely et al.60  
AB (n=18) 
8-10 wks. of 60min 
HWI (3-4x/wk.) 
decrease in CRP 
NT 
1.improved FMD                         
2. decreased carotid and femoral 
artery thickness 
None to date in SCI  
SCI 
? 
? 
? 
? 
Acute responses to passive heating 
Important in the context of passive heating, the acute inflammatory response after exercise is greater 
when exercising in the heat compared with thermoneutral conditions.50 Recent studies have built on 
this notion by investigating whether passively elevating body temperature can also acutely induce the 
production and secretion of inflammatory markers. Laing et al50 and Oehler et al58 showed that 2h of 
HWI leads to an increased plasma concentration of IL-6, IL-10, IL-1ra and heat shock protein 72 
(Hsp72). In search for a more tolerable, shorter and applicable passive heating method, Hoekstra et 
al. showed that just 60 min HWI also increases plasma concentrations of these markers.16 Therefore, 
the acute responses to passive heating suggest that, in 
keeping with exercise, this strategy also has potential to 
reduce chronic low-grade inflammation when engaging 
in it on a regular basis.  
Additionally, elevation of core body temperature 
increases nitric oxide (NO) production through enhanced 
NO synthase activity (NOS),17,61 that is possibly mediated by 
increased expression of Hsp90.62 (Figure 1.) NO not only 
reflects endothelial function but also impacts glucose 
uptake within tissues.63-66 Furthermore, higher NO 
bioavailability has anti-inflammatory effects on human 
leukocytes64 and increases the expression of iHSP72 in 
monocytes.67 This suggests some signaling between NO 
and the immune system. Further, supporting the possible 
benefits of passive heating on blood vessel health, both 
sauna bathing and HWI can acutely increase blood flow in 
the brachial as well as femoral artery.8 Indeed, Hoekstra et 
al. demonstrated that HWI can acutely elevate NO 
bioavailability in AB individuals.16 
In 2015, Leicht, et al. published the first study in persons with SCI, showing that one 
episode of passive heating elicits an acute anti-
inflammatory response (increase in IL-6, IL-8 and IL-1ra) 
comparable to that of AB persons.14 Hashizaki et al later 
confirmed this finding of increase in IL-6 in persons with SCI 
using another method of passive heating, a water-perfused suit.59 Regarding vascular function effects 
of passive heating, Coombs et al15 showed that a single 60 minute session of hot water lower limb 
immersion at 40°C (rise in core temperature of 0.7°C) acutely increased arterial blood flow in the 
Figure 1. Potential mechanisms for the effect of 
heat stress on the vasculature 8 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
femoral and brachial artery in persons with SCI. Furthermore, one passive heating session reduced 
the circulating concentrations CD62+ microparticles to the levels found in healthy control 
participants. As elevated circulating CD62+ microparticles indicate endothelial activation and 
potentially inflammation and atherosclerosis at the vessel wall, repeated passive heating sessions 
may improve vascular health over the long-term. Importantly, these studies indicate that passive 
heating can be safely implemented in this population and may exert protective anti-
inflammatory and vascular health effects.  
Despite the short-term/transient changes after acute (one bout) passive heating in AB and SCI 
persons, it is unknown how long these benefits are sustained and if the same responses are seen 
with chronic (repeated bouts) passive heating.  Furthermore, acute changes in inflammation from one 
passive heating session are likely insufficient to decrease long-term risk of DM and CVD, and their 
associated morbidity and mortality in persons with SCI. Coombs et al concluded by suggesting the 
following: “the effects of long term controlled heating (in SCI persons) warrant further 
testing.”15  This proposal aims to pursue this recommendation. 
 
Chronic responses to passive heating 
There exist limited data on the effects of a chronic repeated (2-8 weeks) passive heating 
intervention on cardiometabolic health in AB individuals, let alone in persons with SCI, where there is 
none. Nonetheless, the available AB studies show promise. For instance, eight weeks of passive 
heating (HWI 4-5x/week to maintain rectal temperature >38.5°C for 60 min/session) in young, healthy 
participants elevates the expression of the anti-inflammatory protein Hsp72 in peripheral blood 
mononuclear cells, while also improving endothelial function (assessed via local thermal 
hyperaemia).17 Furthermore, in a pilot study to inform chronic interventions in persons with a 
disability, we showed that repeated passive heating (39°C for 1 h x 10 sessions over 2 weeks) 
improves glucose metabolism in sedentary, overweight AB males.16 This finding was later 
corroborated in obese women with polycystic ovary syndrome, where 30 one-hour sessions of heat 
stress over 10 weeks significantly improved flow mediated dilation (FMD) (i.e.; NO activity), 
decreased C reactive protein (CRP) and carotid and femoral wall thickness.68 Together, this 
provides tentative evidence that in AB individuals, chronic repeated bouts of passive heating has 
the potential to improve the inflammatory profile, blood vessel health as well as glucose 
metabolism. Whether persons with SCI experience these benefits is unknown. 
In summary, passive heat stress appears to be an easily feasible and practical preventative 
health intervention with evidence to potentially improve underlying pathophysiology that leads to 
T2DM and CVD in persons with SCI. Whether persons with SCI receive similar benefits to AB 
persons during an intervention of chronic repeated bouts of a heat stress is unknown. At present, no 
long-term/chronic intervention study investigating the effects of passive heating on 
immunological, metabolic and endothelial responses in people with SCI exists. This pilot 
proof-of-concept study is the first step addressing such issues.  
 
This study aims to address the current gaps in the literature and be the first to test the impact of 
chronic passive heat therapy in persons with SCI and the first to test its impact on glucose 
metabolism acutely and chronically.  We will test the hypothesis that 8 weeks of a chronic 
passive heating method of electrical heating blankets will 1) decrease chronic inflammation, 2) 
improve glucose utilization and 3) improve endothelial function in persons with SCI. This 
proposed research project aims to take the first step to address a gap in the literature by providing 
proof-of-concept and preliminary evidence of therapeutic benefit.  
Given HWI is more cumbersome and less feasible/practical for persons with paralysis from SCI, we 
will utilize a more practical and safe method of electrical heating blankets and water perfused suits, 
used extensively in our lab over the past 3 years for over 100 sessions of passive heat stress.11 If 
effective, these heating methods can be more easily implemented than HWI in clinical settings as well 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
as in the home setting. 
 
Significance to Veterans: The United States Veterans Health Administration (VA) provides primary 
and chronic care to over 27,000 patients with SCI and is the largest health care system in the world 
providing such persons` lifelong care. Medical care for the SCI population is improving and as such 
life expectancy of this population is slowly approaching that of persons without SCI, with 
cardiovascular disorders as the leading cause of mortality. Primary providers within the VA manage 
long-term sequela of chronic SCI such as CVD and type T2DM and would thus benefit from additional 
interventions to prevent such conditions.  Indeed, in a population with many of its members unable to 
engage in regular exercise due to barriers such as a low physical capacity, the creation of an 
evidence-based alternative to improve cardiometabolic health can have a major impact. As passive 
heating can be performed by a practical accessible intervention, such as heating blankets, if effective, 
it can be widely implemented in clinical settings as well as in the home setting. On an individual level, 
passive heat therapy may reduce disease-risk, enhancing mobility and ultimately quality of life.  
 
Preliminary Studies: This is a new study born out of mutual scientific interest and recently findings 
of studies conducted by the PIs and collaborators (Hoekstra and Leicht). Both of the involved labs 
have conducted studies related to heat therapy to promote health in non-injured individuals and 
persons with SCI, evidenced by multiple publications12-14,16,69,70 Over the past 3 years of Dr. 
Trbovich’s VA Career Development Award  entitled “Vasomotor and sudomotor activity during heat 
stress in persons with SCI” has studied 24 persons with SCI (10 with tetraplegia and 14 with 
paraplegia) with passive whole body heat stress (core temperature rise of up to 1.2°C) using electrical 
heating blankets over approximately 100 sessions total. The proposed heat stress protocol using 
electrical heating blankets has not only been perfected over this time, but also been shown to be safe 
(i.e.; no significant medical complications such as burns, autonomic dysreflexia, hypotension) and 
tolerable as has also been seen in HWI protocols in SCI persons.71   This proposed study is the first 
next step to evaluate the therapeutic impact of passive heat stress with Dr. Hoekstra who has 
expertise in studying the inflammatory outcome measures proposed.14 Furthermore, Drs. Kellogg and 
Trbovich have conducted local thermal hyperaemia studies on over 10 persons with chronic SCI and 
demonstrated this to be safe in persons with SCI, without risk of burns in the protocol proposed.72 The 
combination of experience with whole body passive heat stress protocols11 in persons with SCI 
coupled with clinical SCI expertise from Dr. Trbovich, expertise in local skin heating protocols of Dr. 
Kellogg 72-74 and expertise in inflammation changes with passive heat therapy (via HWI) of Dr. 
Hoekstra12 and Leicht,14 make this team well poised to carry out this proposal. The ultimate goal of 
the team is to determine if this non-invasive, practical therapy can ultimately impact the underlying 
pathophysiology of the leading causes of morbidity and mortality in persons with SCI. 
 
Research Design and Methods 
Participants: Ten adults with sensorimotor complete (AIS A) SCI levels C2-T6.  
Inclusion criteria:1) Spinal cord injury of >1 year of age; 2)18-60 years old and; 3) with a clinical 
history of sensorimotor complete (AIS A) SCI with level ranging from the C2 cervical level to the T10 
thoracic level. All subjects with SCI will have their neurological level of injury (LOI) established by 
Dr. Trbovich at the time of enrollment via the International Standards of Neurological Classification 
after SCI (ISNCSCI) exam.75,76 The “International Standards to document remaining Autonomic 
Function after Spinal Cord Injury (ISAFSCI)” form will also be filled out by Dr. Trbovich on all 
participants.76 
Exclusion criteria: 1) Subjects who smoke; 2) Daily administration of anti-inflammatory medications; 
3) Daily administration of vasoactive medications (e.g.; beta or alpha antagonists or agonists); 4) 
Current pressure ulcer or skin breakdown; 5) History of heat related illness (e.g.; heat stroke); and 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
6) Any active acute illness, 7) A resting haemoglobin concentration of less than 11 g/dl, as obtained 
from clinical records within 6 months of study enrolment or the baseline blood sample at Visit 1.  
A schematic of the study protocol is given in Fig. 3. Outcome measurements will be collected at three 
time points: at baseline (BL), after 8 weeks without intervention (control=CON) and following an 8-
week passive heating protocol (intervention=INT), allowing participants to serve as their own control. 
We will ask participants to not make any major changes in exercise frequency or intensity or dietary 
changes (e.g.; switching to vegan diet) during participation. If they do for medical reasons (ie: doctors’ 
recommendation) they need to inform us 
 
Baseline measurements 
Visit 1 (V1) 
(a). Inflammatory markers assessment: A resting blood sample will be collected to assess the 
expression of inflammatory markers in plasma (i.e. CRP, IL-6, IL-1β, TNF-α and IL-1ra) and 
circulating monocytes using flow cytometry (Hsp72 and TLR4), according to previously developed 
methods.16 This group of inflammatory markers are strongly associated with impaired glucose 
utilization and vascular disease; moreover, mechanistic animal studies support their direct detrimental 
effects on insulin signaling and vascular health. As previously mentioned, IL-6 can have anti-
inflammatory (transient increase after exercise/heat stress) and pro-inflammatory (chronic levels) 
effects. We will measure chronic inflammatory marker concentrations by measuring before initial (V1), 
after control period (V3) and 3 to 5 days after the final (V29) heat stress 
session (see figure 3). Flow cytometry is a powerful method to phenotype 
specific immune cells. Using the surface markers CD14 and CD16, the 
expression of Hsp72 and TLR4 in one of the major sources of circulating 
inflammatory markers, namely monocytes, will be investigated.  
(b). Glucose metabolism testing: An oral glucose tolerance test (OGTT) will be conducted to assess 
glucose metabolism. After a 10-12 hour fast overnight, the participants 
will consume a 75-g glucose drink, where after blood samples will be 
collected at -10, -5, +15, +30, +45, +60, +90, +120, +150 and +180 min 
to measure glucose, insulin, C-peptide and glucagon. This method has 
been validated against the more invasive insulinemic - and glycaemic 
clamp methods and is widely used to test glucose tolerance.77 BRU will 
be used for the OGTT and the blood draw for inflammatory and 
circulating vascular markers assessments. Together, a maximum of 200 
ml blood will be drawn at Visit 1 (and Visit 2,3 and 29) 
(c). Endothelial function testing: Human skin is an easily accessible 
tissue for studying both physiological and pathophysiological 
mechanisms of neural and endothelial control of blood vessels.18,74,78 
Changes in the skin circulation are similar to those of other vascular beds in hypertension, diabetes, 
and aging, thus making the skin an excellent model for human in vivo pathophysiological studies.78,79 
The application of skin-specific methods of study makes this vascular bed particularly useful as a safe 
model for in vivo studies. Endothelial function in this protocol will be assessed via nitric oxide (NO) 
dependent  cutaneous vasodilation responses (local thermal hyperaemia) over the right ventral 
forearm and right posterior calf with local skin heating to 39°C19 using laser Doppler flowmetry (LDF) 
to measure skin blood flow. The following equation will be used to measure cutaneous vascular 
conductance (CVC): CVC = LDF/mean arterial blood pressure). Values will be measured at 34°C 
(baseline), and 39°C (NO dependent vasodilation), then 42°C (maximum vasodilation) so the 39°C 
values can normalized to maximum CVC obtained at skin temperatures of 42°C.18 (Fig. 2) Persons 
with SCI have tolerated this well in our lab without adverse events (e.g.: burns).70,71 
(d) Evaluation of impact of PHS on mental health, general physical health, sleep, pain, mood and 
physical activity via 7 surveys as follows: 
Figure 2. Change in skin blood 
flow during local heating to 
42°C 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
1. 
The International Spinal Cord Injury Pain Extended Data Set (Version 1.0) 
2. 
5-item Mental Health Inventory 
3. 
Epworth Sleepiness (ESS)-Adult version 
(e) Participants will be asked to report the foods and drinks consumed in the 24 hours prior to the visit 
using a food diary, which they will then use to replicate their diet in the 24 hours prior to Visit 3 and 
29. 
 
 
 
 
 
 
 
 
 
Visit 2 (V2) (within 1 week of V1) 
Passive heat stress session 1: The acute thermo-physiological, perceptual and inflammatory 
response to passive heating will be assessed in this first passive heat stress session. To enhance the 
impact of the work and facilitate its implementation in practice, a highly accessible and tolerable 
method of passive heating (i.e. electrical heating blankets and water perfused suits) will be used. This 
method has been safely utilized on over twenty persons with SCI (~100 sessions) in our lab over the 
past three years. 11 During a one-hour passive heating session, participants will rest in a supine 
position while a warm fleece lined electrical blanket set at 43°C is placed over insensate skin areas 
while a water perfused suit (water temp 42°C ) is placed over sensate areas. 11 Area of ventral arm 
and post calf of endothelial function testing (Visit 1) will not have blanket or suit touching them during 
passive heat stress to enable the measurement of skin blood flow during the passive heat stress 
session, using laser Doppler flowmetry. Starch iodine test will be conducted over the arms, chest and 
lower limbs to measure the number of dermatomes with intact sweating as in our previous studies.11 
Previous studies found beneficial impact on inflammation, metabolism and vascular health with core 
temperature (Tcore) rise of 0.7-1°C. In our experience, induction of passive heat stress using electric 
heating blankets and water perfused suits, one hour is sufficient time period to elevate Tcore by 1°C. 
During passive heat stress, Tcore will be measured by an oral temperature probe that is placed under 
the tongue and Deep tissue temperature at the vastus lateralis will be measured using the validated 80 
non-zero heat flux method (Bair Hugger, 3M, Minnesota, US).81 Skin temperature (Tskin) will be 
measured by local thermocouples over the forehead, chest, upper arm, upper and lower leg; blood 
pressure (BP) and heart rate (HR) will be measured via Portapres; and perceived thermal strain 
responses will be measured on a 9 point Likert scale from 0-8.82If Tcore rises above 39°C (sufficient 
Tcore to obtain heat therapy CVD benefits,60 while a Tcore >39.6°C increases the risk for heat 
illness83,84), Tcore rises 1°C, or the participant becomes uncomfortable prior to one hour, heating will 
cease. 
 
Figure 3. Schematic of the 16-week chronic passive 
heating protocol. Participants are their own control for the 
first 8 wks, followed by 8-wk passive heating intervention. 

 
Protocol Trbovich clinicaltrials 
Protocol Trbovich clinicaltrials 
 
 
 
Control phase (CON): Visit 3 (8 weeks after V2) will repeat V1. BRU will be used for the OGTT and 
the blood draw for inflammatory and circulating vascular markers assessments. Visit 4 (within 1 week 
of V3) will be the same as V2 excluding the blood draw.  
Intervention phase (INT): Visits 5-29 
The passive heat stress protocol will be identical to V2; without blood collection and starch iodine test, 
but with cardiovascular (i.e.; HR and BP) and temperature monitoring (oral) for safety. This will occur 
3 times per week for 8 weeks. On the final passive heating session (V28), repeat measurements will 
be obtained using the procedures described for V2 (except there will be no blood draw). The V29 
procedures (within 2-7 days of V2817) will be identical to V1 (Fig. 3). BRU will be used for the OGTT 
and the blood draw for inflammatory and circulating vascular markers assessments.  
Statistical Analyses:  Hsp72 and TLR4 expression in monocytes will be assessed by subtracting the 
geometric mean fluorescence intensity of the appropriate isotype control from that of the antibody of 
interest. Inflammatory cytokine levels (CRP, IL-6, IL-1β, TNF-α and IL-1ra) will be compared between 
baseline, CON and INT values via repeated measures ANOVA. The same analysis will be conducted 
to test the acute change in inflammatory marker concentrations in response to a single passive heat 
stress session (Visit 2).Nitric oxide dependent vasodilation data will be analysed as follows: CVC at 
39°C will be normalized to maximum CVC at 42°C and expressed as % CVC 
max at the arm and the leg. Ten blood samples collected 
during the 2h OGTT will be used to calculate the glucose 
and insulin incremental area under the curve (iAUC) by 
the trapezoid method, where a lowered iAUC signifies 
improved glucose tolerance. To test for differences 
between BL (V1-2), CON (V3-4) and INT (V28-29) visits, 
repeated measures ANOVAs will be conducted on all 
normally distributed data; while their nonparametric counterparts will be used when the assumption of 
normality is violated. Effect of lesion level (i.e.: tetraplegia vs. paraplegia) on all outcome measures 
and effect of limb (arm vs. leg) on CVCs will be compared. Dermatomes with intact sweating on 
starch iodine test in V2 vs. V4 vs. V28 will be compared. 
Future directions: This study is the first step needed to determine if repeated bouts of heat stress has 
potential reduce inflammation in persons with SCI.  If this proof-of-concept study is deemed feasible 
and once power analysis provides a number of subjects needed for a larger trial, we will pursue a 
larger randomized control trial (via a funding mechanism such as an NIH RO1). Next steps would also 
include 1) Comparing the impact of passive heating with electrical blankets in the laboratory-
controlled setting vs. home setting (to evaluate feasibility and efficacy in the most practical setting) on 
the same outcome measures, to see if similar results are obtained and 2) Measuring impact of long 
term/chronic passive heat therapy on the incidence of DM and T2DM and its associated morbidity 
and mortality.  Finally, this work takes the first step towards evidence-based guidelines for the use of 
passive heat treatment to improve cardiometabolic health in individuals with SCI, comparable to the 
SCI-specific exercise guidelines as produced by international partners.85 
 
ACTIVITY
Year 1
Year 2
Quarter (Q)
Q1
Q2
Q3
Q4
Q1
Q2
Q3
Q4
Recruit and enroll 5 participants
Begin and complete protocol for 5 participants
Recruit and enroll 5 more participants
Begin and complete protocol for 5 more participants
Analyze preliminary data and start article writing
Submit abstract to national meeting and paper for 
publication
Table 2. Study timeline