Thermoregulation

The goal of this clinical trial is to determine if perfusion index (PI) can reliably predict changes in systolic blood pressure (SBP) in persons with spinal cord injury (SCI) during a cool temperature challenge. Participants with SCI can be 18-75 years of age, male or female, neurological level of injury C4-T12, ASIA Impairment Scale (AIS: A or B: motor complete) or gender and healthy age-matched able-bodied (AB) controls. The main question this study aims to answer is: can PI reliably predict change in SBP during a cool temperature challenge? We hypothesize that PI can be used as a biomarker of SBP in persons with SCI. Researchers will compare the relationship of 1) changes in PI and SBP and 2) relationship of changes in other vital signs to SBP, during the cool temperature challenge. The researchers aim to determine if PI can be used as a biomarker of SBP in persons with SCI during a cool temperature challenge (experimental group/arm). Able-bodied controls (control group/arm) will receive the same intervention (cool challenge) as the experimental group. During the study, participants will be asked to wear only shorts and a T-shirt so that their skin can be exposed to the warm and cool temperatures of the 2 rooms. We will put put on non-invasive sensors (taped or attached on the surface of your body) to measure PI, BP, and other vital signs. We will record these measurements while you are seated in a wheelchair for 10 minutes in a warm room and up to 90 minutes in a cool room.

Maintaining neonatal body temperature (thermoregulation), particularly during the first hour after birth, is critical for survival and successful adaptation to the extrauterine environment. Implementation of a thermoregulation bundle is expected to facilitate faster stabilization of physiological parameters and to positively influence the initiation of breastfeeding as well as overall breastfeeding success. The effects of a thermoregulation bundle applied at birth on neonatal physiological parameters-including body temperature, respiratory rate, heart rate, and oxygen saturation-and on breastfeeding outcomes will be evaluated.

Exertional heat stroke (EHS) affects \~500 Military Personnel and over 100 Soldiers every year, and it is believed that these numbers are underreported. EHS is the most severe form of exertional heat illness (EHI) and can result in substantial, long-lasting organ damage, and even death in severe cases. Based on current knowledge and training needs, it is impossible to prevent every EHS - which shifts the focus from exclusively prevention to a combination of prevention, treatment, and enhancing recovery as much as possible. While many risk factors have been identified and there are adequate treatments available, biomarkers associated with heat stroke risk, recovery, and return-to-duty (RTD) remain largely unclear. The purpose of the proposed study is to enhance knowledge surrounding biomarkers of EHS and long-term health consequences that result from EHS. The investigators will recruit research volunteers for a field study in order to collect pre-, post-, and follow-up measures from a high-risk EHS event (i.e. ruck marches, timed runs) this will allow us to have a basis for comparison between Soldiers who collapse with EHS (from previously collected data) and those that complete high-risk events, but do not collapse. This will allow for comparison between the groups to identify EHS-specific biomarkers that could aid in recovery and RTD decisions for Soldiers.

Maintaining a stable core temperature is vital for physiological function; yet, exercise in heat can be problematic, and there is risk of exertional heat-related illness (Flouris \& Schlader, 2015; Leyk et al., 2019; Périard et al., 2021; Tyler et al., 2016; Veltmeijer et al., 2015). While aerobic fitness improves heat tolerance (Alhadad et al., 2019), strategies like acclimation and pre-cooling also mitigate heat stress (Casadio et al., 2016; Lorenzo et al., 2010; Ross et al., 2013; Siegel et al., 2010). Caffeine, an ergogenic aid (Del Corso et al., 2011; John et al., 2024), is known to enhance performance via adenosine antagonism and increased catecholamines in normothermic environments (Fredholm et al., 1999; Graham \& Spriet, 1991). However, effects in heat are inconsistent (Ganio et al., 2009; Zhang et al., 2014), possibly due to caffeine reducing the ability to thermoregulate effectively. Therefore, the aim of this study is to investigate the effects of a moderate dose of caffeine (5 mg/kg) on thermoregulation during a 30-minute running time trial in 35°C heat.