Effect of a Cooling Vest on Core Temperature in Athletes With and Without Spinal Cord Injury

Background:

It is well accepted that persons with spinal cord injury (SCI) have impaired ability to regulate core temperature due to impaired vasomotor and sudomotor activity below their level of injury. Impaired heat dissipation puts SCI athletes at great risk of exercise-induced hyperthermia (EIH) (>37.8°C). There is minimal evidence for efficacy of any specific cooling method in SCI athletes in a thermoneutral sport-specific setting.

Objective:

To evaluate the extent of EIH in persons with and without SCI and subsequently examine the effect of a cooling vest to attenuate rise in core body temperature (T_c).

Methods:

SCI (n = 17) and able-bodied (AB; n = 19) athletes participated in a 60-minute intermittent sprinting exercise in a thermoneutral (21.1°C-23.9°C) environment. Participants were separated according to their level of injury: tetraplegia defined as above T1 (TP; n = 6), high paraplegia defined as T5 through T1 (HP; n = 5), low paraplegia defined as T6 and below (LP; n = 6), and AB (n = 19). T_c was recorded at 15-minute intervals using an ingestible thermometer pill. This protocol was completed with a cooling vest (V) and without a cooling vest (NV).

Results:

All SCI and most AB athletes experienced EIH. After 60 minutes, T_c of TP athletes was significantly increased compared to HP (P = .03) and AB athletes (P = .007). There was no significant effect of the vest on T_c over time for any group.

Conclusions:

TP athletes have the highest risk of exercise-induced hyperthermia. The cooling vest does not significantly attenuate rise in T_c in SCI or AB athletes.Key words: body temperature, hyperthermia, spinal cord injury, thermoregulationInjury to the spinal cord results in impairment of vasomotor and sudomotor function at and below the level of injury (LOI).¹ In non–spinal-cord-injured individuals, internal heat gain from metabolically active muscles (eg, during exercise) and external heat gain from the ambient air is mitigated through processes regulated by the hypothalamus. The afferent input of heat gain results in neurological efferent signals that regulate vasomotor tone (convective cooling) and sudomotor activation (evaporative cooling). In persons with spinal cord injury (SCI), the output from the hypothalamus is blocked due to lesions within the spinal cord. Furthermore, the loss of skeletal muscle pump activity from the paralyzed limbs further impairs blood circulation and thus core temperature regulation. As a result, persons with SCI have difficulty dissipating heat during exercise compared to their able-bodied (AB) counterparts.^1–3 The extent of such thermal impairment has been shown to be directly related to level and completeness of injury, with higher and complete lesions having more impairment than lower, incomplete lesions.^4,5 Specifically, the vessels of the face and neck are sympathetically mediated from levels T1-4, upper extremity vessels mediated from T5-7, and vessels of the lower extremity from T10 to L3.⁶ Therefore, persons with complete tetraplegia have essentially no vasomotor control, whereas persons with high paraplegia have vasomotor control of face and neck and persons with low paraplegia have control of upper limbs and potentially some control of lower limb vessels depending on the LOI.In the AB athlete, is it well accepted that elevated core temperature (T_c) due to internal and external heat gain during exercise can impair endurance and performance.^7,8 Extreme elevations in T_c can result in exercise-induced hyperthermia (EIH) (>37.8°C-38.3°C) that that can lead to heat exhaustion (<40°C) or heat stroke (>40°C) as defined by American College of Sports Medicine (ACSM).⁹ For this reason, cooling methods such as whole body cooling, cooling vests, and hand/foot cooling are utilized before and during exercise in AB athletes.^10–13 These devices have been shown to reduce thermal strain, increase endurance capacity, and improve performance.^14–17Due to the increased risk of EIH and heat-related illness from thermoregulatory dysfunction in persons with SCI, a number of commercially available cooling devices have been tested in a controlled laboratory setting in attempts to attenuate rise in T_c. Foot cooling garments, hand cooling garments, head and neck cooling garments, misting devices, and a cooling vest have been tested in SCI populations.^18–22 This study sought to test the efficacy of the cooling device in a sport-specific environment. The cooling vest interferes minimally with wheelchair propulsion during sporting activities and was thus chosen for this study.While the efficacy of the cooling vest in normalizing T_c in the AB population has been clearly documented, the efficacy of the vest in SCI populations has variable results from 3 small studies.^14,23,24 Armstrong et al¹⁸ found that cooling (ice) vests worn during 30 minutes of wheelchair roller exercise in a hot-humid environment (~33°C and ~75% relative humidity) did not significantly decrease T_c in an SCI group (4 with paraplegia, 1 with tetraplegia). Webborn et al evaluated the effect of cooling vests in 2 studies of 8 persons with tetraplegia during an arm crank ergometry intermittent sprint protocol (defined as 14 two-minute exercise periods each consisting of 10 seconds passive rest, 5 seconds maximum sprint, and 105 seconds of active recovery). The first study reported a significant decrease in T_c and rate of perceived exertion when vests were used before (pre-cooling) or during 28 minutes of exercise in the heat.¹⁹ The second study also reported a significant decrease in T_c and time to exhaustion during 60 minutes in the heat when wearing the vest.²⁵ Webborn recommended that tetraplegic athletes performing intermittent sprint exercise in hot conditions should wear a cooling vest before or during exercise to attenuate rise in T_c. This study tested Webborn’s recommendation to examine whether these findings translate to a nonlaboratory field-based environment of athletes engaging in intermittent sprint exercise during play of wheelchair basketball and rugby. This concept of testing has recently been recommended, as testing of athletes in their normal sports wheelchair and their natural environment may yield results that are more relevant than laboratory testing.²⁶The objectives of this study are 2-fold: (1) to evaluate the extent of EIH in persons with and without SCI, and (2) to examine the ability of a cooling vest to attenuate the rise in T_c of SCI and AB athletes during intermittent sprinting exercise.