Novel application of chemical cold packs for treatment of exercise-induced hyperthermia: a randomized controlled trial.

OBJECTIVE: Heat-related illness is a common disease with significant morbidity and mortality. Despite no proven efficacy, application of chemical cold packs (CCP) to the skin overlying the large vessels of the neck, groin, and axillae is a traditional recommended cooling modality. The study objective was to compare the cooling rates of CCP applied to these traditional areas vs the glabrous skin surfaces of the cheeks, palms, and soles in exercise-induced hyperthermia. METHODS: Ten healthy adult male volunteers walked on a treadmill in a heated room (40°±0.5°C) while wearing insulated military overgarments until their esophageal temperatures (Tes) reached 39.2°C. Each participant had three heat stress trials on separate days: no treatment followed by randomly ordered traditional (neck, groin, and axillae) cooling and glabrous skin cooling. RESULTS: With no treatment, Tes remained stable after the first 5 minutes of the heat trial (ΔTes=0.12°±0.07°C/10 min). Traditional cooling followed a linear decline (ΔTes=0.17°±0.04°C/10 min; P<.001). Glabrous cooling enhanced the treatment effect by a steeper decline (ΔTes=0.30°±0.06°C/10 min; P<.001), significantly different from traditional cooling by 2-way analysis of variance (P<.001). CONCLUSIONS: Application of CCP to glabrous skin surfaces was more effective for treating exercise-induced heat stress than the traditional CCP cooling intervention. This novel cooling technique may be beneficial as an adjunctive treatment for heat-related illness in the prehospital environment.

Chemical cold packs may provide insufficient enthalpy change for treatment of hyperthermia.

OBJECTIVE: Heat illness is a common ailment that, if left untreated, is associated with high morbidity and mortality. Chemical cold packs (CCPs) and ice packs are widely used in the pre-hospital setting and by those with limited resources, yet no controlled studies have compared the cooling of ice to that of CCPs. This study determined the theoretical cooling of CCPs on a benchtop model, comparing the results to similarly sized ice packs, and is the first known comparison of these hyperthermia treatments. METHODS: The CCPs used in Stanford University's Emergency Department were activated in an insulated volume of water (2 L), and temperature was recorded at 1-second intervals in a controlled environment (41°C at 20% humidity). The procedure was repeated with 1-quart ice packs. RESULTS: The CCPs resulted in a 5.25°C degree temperature drop, with a time constant (time to 63% of initial temperature--a common engineering characterization metric) of 1.72 minutes for the test volume. Ice packs resulted on average in a 19.8°C temperature change, with a time constant of 26.8 minutes. The CCPs provide less overall temperature change and were shorter lived. Application of 6 CCPs on a 50th percentile male (weight 86.6 kg, height 1.7 m), assuming ideal heat transfer, would result in less than 0.5°C temperature change. Similarly configured ice packs would result in a 2.5°C change. CONCLUSIONS: Experiments demonstrate that CCPs are inferior to similarly sized ice packs for thermal regulation, and lose their effectiveness more quickly. These findings support the consideration of ice packs as an alternative to chemical cold packs when cooling hyperthermic patients.

The three-dimensional micro- and nanostructure of the aortic medial lamellar unit measured using 3D confocal and electron microscopy imaging.

Changes in arterial wall composition and function underlie all forms of vascular disease. The fundamental structural and functional unit of the aortic wall is the medial lamellar unit (MLU). While the basic composition and organization of the MLU is known, three-dimensional (3D) microstructural details are tenuous, due (in part) to lack of three-dimensional data at micro- and nano-scales. We applied novel electron and confocal microscopy techniques to obtain 3D volumetric information of aortic medial microstructure at micro- and nano-scales with all constituents present. For the rat abdominal aorta, we show that medial elastin has three primary forms: with approximately 71% of total elastin as thick, continuous lamellar sheets, 27% as thin, protruding interlamellar elastin fibers (IEFs), and 2% as thick radial struts. Elastin pores are not simply holes in lamellar sheets, but are indented and gusseted openings in lamellae. Smooth muscle cells (SMCs) weave throughout the interlamellar elastin framework, with cytoplasmic extensions abutting IEFs, resulting in approximately 20 degrees radial tilt (relative to the lumen surface) of elliptical SMC nuclei. Collagen fibers are organized as large, parallel bundles tightly enveloping SMC nuclei. Quantification of the orientation of collagen bundles, SMC nuclei, and IEFs reveal that all three primary medial constituents have predominantly circumferential orientation, correlating with reported circumferentially dominant values of physiological stress, collagen fiber recruitment, and tissue stiffness. This high resolution three-dimensional view of the aortic media reveals MLU microstructure details that suggest a highly complex and integrated mural organization that correlates with aortic mechanical properties.