Amide proton transfer imaging in rats after heatstroke

Metabolic acidosis is the most common acid-base change following heatstroke. This study aimed to evaluate the internal environment changes caused by heatstroke using amide proton transfer (APT) imaging. Nineteen male Sprague-Dawley rats were randomly divided into the control group (CTRL, n  = 7) and the heatstroke group (HS, n  = 12). All the rats underwent a 7.0-T MRI, which included T2-weighted imaging (T2WI) and APT imaging. Subsequently, the surviving HS group rats repeated the same magnetic resonance scanning after 25 days and were designated as the follow-up group (FU, n  = 7). APT values were measured in the hippocampus, thalamus, and corpus callosum. The APT values of the three groups were statistically analyzed and found in the hippocampus (CTRL vs. HS, P  = 0.011; CTRL vs. FU, P  = 0.078; HS vs. FU, P  = 0.484; η ² = 0.276), left thalamus (CTRL vs. HS, P  = 0.004; CTRL vs. FU, P  = 0.014; HS vs. FU, P  = 0.822; η ² = 0.331), right thalamus (CTRL vs. HS, P  = 0.003; CTRL vs. FU, P  = 0.015; HS vs. FU P  = 0.769; η ² = 0.336), and corpus callosum (CTRL vs. HS, P  < 0.001; CTRL vs. FU, P  = 0.005; HS vs. FU, P  = 0.523; η ² = 0.437). APT imaging can be a viable and practical tool for diagnosing heatstroke and monitoring its progression.

Multiparametric cardiac magnetic resonance reveals persistent myocardial inflammation in patients with exertional heat illness

OBJECTIVES

To explore the clinical potential of multiparametric cardiac magnetic resonance (CMR) in evaluating myocardial inflammation in patients with exertional heat illness (EHI).

METHODS

This prospective study enrolled 28 males with EHI (18 patients with exertional heat exhaustion (EHE) and 10 with exertional heat stroke (EHS)) and 18 age-matched male healthy controls (HC). All subjects underwent multiparametric CMR, and 9 patients had follow-up CMR measurements 3 months after recovery from EHI. CMR-derived left ventricular geometry, function, strain, native T1, extracellular volume (ECV), T2, T2*, and late gadolinium enhancement (LGE) were obtained and compared among different groups.

RESULTS

Compared with HC, EHI patients showed increased global ECV, T2, and T2* values (22.6% ± 4.1 vs. 19.7% ± 1.7; 46.8 ms ± 3.4 vs. 45.1 ms ± 1.2; 25.5 ms ± 2.2 vs. 23.8 ms ± 1.7; all p < 0.05). Subgroup analysis showed that ECV was higher in the EHS patients than those in EHE and HC groups (24.7% ± 4.9 vs. 21.4% ± 3.2, 24.7% ± 4.9 vs. 19.7% ± 1.7; both p < 0.05). Repeated CMR measurements at 3 months after baseline CMR showed persistently higher ECV than HC (p = 0.042).

CONCLUSIONS

With multiparametric CMR, EHI patients demonstrated increased global ECV, T2, and persistent myocardial inflammation at 3-month follow-up after EHI episode. Therefore, multiparametric CMR might be an effective method in evaluating myocardial inflammation in patients with EHI.

CLINICAL RELEVANCE STATEMENT

This study showed persistent myocardial inflammation after an exertional heat illness (EHI) episode demonstrated by multiparametric CMR, which is a potential promising method to evaluate the severity of myocardial inflammation and guide return to work, play, or duty in EHI patients.

KEY POINTS

• EHI patients showed an increased global extracellular volume (ECV), late gadolinium enhancement, and T2 value, indicating myocardial edema and fibrosis. • ECV was higher in the exertional heat stroke patients than exertional heat exhaustion and healthy control groups (24.7% ± 4.9 vs. 21.4% ± 3.2, 24.7% ± 4.9 vs. 19.7% ± 1.7; both p < 0.05). • EHI patients showed persistent myocardial inflammation with higher ECV than healthy controls 3 months after index CMR (22.3% ± 2.4 vs. 19.7% ± 1.7, p = 0.042).

Metabolomic profiling identifies a novel mechanism for heat stroke‑related acute kidney injury

Heat stroke can induce a systemic inflammatory response, which may lead to multi‑organ dysfunction including acute kidney injury (AKI) and electrolyte disturbances. To investigate the pathogenesis of heat stroke (HS)‑related AKI, a mouse model of HS was induced by increasing the animal's core temperature to 41˚C. Blood samples obtained from the tail vein were used to measure plasma glucose and creatinine levels. Micro‑positron emission tomography‑computed tomography (micro‑PET/CT), H&E staining and transmission electron microscopy were conducted to examine metabolic and morphological changes in the mouse kidneys. Immunohistochemistry (IHC) and western blot analyses were performed to investigate the expression of apoptosis‑inducing factor mitochondria‑associated 2 (Aifm2), high‑mobility group box 1 (HMGB1) and receptor for advanced glycosylation end products (RAGE). Liquid chromatography‑mass spectrometry analysis was conducted to find differential metabolites and signaling pathways. The HS mouse model was built successfully, with significantly increased creatinine levels detected in the serum of HS mice compared with controls, whereas micro‑PET/CT revealed active metabolism in the whole body of HS mice. H&E and TUNEL staining revealed that the kidneys of HS mice exhibited signs of hemorrhage and apoptosis. IHC and western blotting demonstrated significant upregulation of Aifm2, HMGB1 and RAGE in response to HS. Finally, 136 differential metabolites were screened out, and enrichment of the 'biosynthesis of unsaturated fatty acids' pathway was detected. HS‑associated AKI is the renal manifestation of systemic inflammatory response syndrome, and may be triggered by the HMGB1/RAGE pathway. Metabolomics indicated increased adrenic acid, docosahexaenoic acid and eicosapentaenoic acid may serve as metabolic biomarkers for AKI in HS. The findings suggested that a correlation between the HMGB1/RAGE pathway and biosynthesis of unsaturated fatty acids may contribute to the progression of HS‑related AKI.

Dopamine overload visualized in the basal ganglia of rabbit brain during heatstroke can be suppressed by hypothermia

The present study assesses the changes of dopamine levels in the basal ganglia (BG) of rabbit brain during heatstroke with or without hypothermia therapy. The dopamine levels were determined by using 6(F18) fluoro-L-dopa (FDOPA) positron emission tomography (PET) scan. Heatstroke was induced by exposing the anesthetized rabbits to a high blanket temperature (T(blanket)) of 45 degrees C. Hypothermia therapy was accomplished by decreasing T(blanket) from 45 to 16 degrees C. Regions-of-interest were carefully selected on the BG and cerebellum (C). The uptake ratio of FDOPA was defined as the mean counts per pixel from BG divided by the mean counts from C. BG/C ratios represent the dopamine levels of BG. The results showed that the values of mean arterial pressure (MAP) in heatstroke rabbits without hypothermia therapy were significantly lower than those in normothermic controls. However, BG/C FDOPA ratios were greater. Both the arterial hypotension and the increased BG/C FDOPA ratios observed during heatstroke were all reduced after hypothermia therapy. Our data demonstrate that the dopamine overload visualized in the BG of rabbit brain during heatstroke can be suppressed by hypothermia therapy.

Gray-white matter discrimination--a possible marker for brain damage in heat stroke?

INTRODUCTION/OBJECTIVE

Heat stroke (HS) is a common medical emergency which carries high morbidity and morality. This study was designed to describe the pattern of central nervous system (CNS) changes as detected by brain CT scan in a case series of six patients suffering from classical and exertional HS.

METHODS AND PATIENTS

All the patients were admitted in critical condition during the heat wave in the summer of 1999 in Israel. Each was in deep coma with a measured core temperature of over 40 degrees C upon admission to the emergency department.

RESULTS

Aggressive cooling measures decreased the core temperature to <38 degrees C within 30 min following admission. Two patients (33.3%) died. One of the survivors remained in a vegetative state. Brain CT studies carried out within 4 days of admission in all the patients revealed severe loss of gray-white matter discrimination (GWMD) without signs of acute bleed or significant focal lesion, findings that persisted in repeated brain CTs in one patient who remained in a vegetative state.

DISCUSSION AND CONCLUSIONS

Loss of GWMD may represent an early and sensitive indication of severe brain damage in patients with severe HS. Further studies in larger groups of patients are warranted in order to determine whether the appearance of GWMD in brain CTs of patients with HS has prognostic value.

Echocardiographic and Doppler study of patients with heatstroke and heat exhaustion

This is a two-dimensional and Doppler echocardiographic study of the hemodynamic changes in patients with heatstroke and heat exhaustion. It demonstrates that the hemodynamic changes in severe heat exposure reflect a hyperdynamic circulation with tachycardia and high cardiac output states. Relative hypovolemia was more pronounced in patients with heatstroke compared to patients with heat exhaustion. Signs of peripheral vasoconstriction were more often present in patients with heatstroke, while patients with heat exhaustion more often demonstrated peripheral vasodilatation.