Sensitivity and specificity of using exercise heart rate in a thermoneutral environment to predict heat tolerance status

OBJECTIVES

Following heat illness, a return to activity may require passing a heat tolerance test (HTT). However, there are several logistical limitations to the widespread use of the HTT. Thus, it would be advantageous to develop a test that could be conducted in a thermoneutral (~22°C) environment to predict heat tolerance status. The purpose of the current study was to determine the sensitivity and specificity of using the criteria of a heart rate (HR) ≥130 bpm following 30 min of thermoneutral exercise in detecting heat-intolerant and heat-tolerant individuals.

MATERIAL AND METHODS

Sixty-five subjects visited the lab on 3 separate days. The first visit consisted of completing a maximal oxygen uptake (VO2 max) test to assess cardiovascular fitness. For lab visits 2 and 3, subjects randomly completed a 2-hour walking treadmill test in either a hot (40°C, 40% relative humidity [RH]) or thermoneutral (22°C, 40% RH) environment.

RESULTS

Forty-eight subjects were classified as heat-intolerant and 17 subjects as heat-tolerant. Using the criterion of a HR ≥130 bpm at 30 min of exercise in the thermoneutral environment, specificity (54%) and sensitivity (100%) of passing the HTT was calculated. Secondary analysis using multiple regression revealed 3 significant variables for predicting ending HR during the HTT. They were: 1) absolute VO2 max (l/min), 2) age, and 3) HR at 30 min of exercise during thermoneutral exercise.

CONCLUSIONS

Exercise in a thermoneutral environment had a positive predictive value of 100%, thus, if a subject has a HR ≥130 bpm at 30 min of exercise in a thermoneutral environment, they are very likely to fail a subsequent 2-hour HTT in the heat and be classified as heat-intolerant. Therefore, prior screening has the potential to save time and money, along with providing safety to a heat-intolerant subject. Int J Occup Med Environ Health. 2023;36(2):192-200.

[Life expectancy of mesocephalic, dolichocephalic and brachycephalic dog breeds in Switzerland]

INTRODUCTION

Lifespan and time of death of dogs died in Switzerland between 2016 and 2020 were evaluated in order to increase the awareness of the public to animal welfare-related consequences of extreme brachycephalic breeding and to clarify the torture breeding problem of dogs suffering from brachycephalic obstructive airway syndrome (BOAS). Skull shape, body size, country of origin and altitude of the registered place of residence at the time of death were analysed in a set of anonymized data from the national animal database Amicus as potential factors influencing the life expectancy. Death rate during summer months and the altitude of the reported place of residence at death were analysed in relation to the skull shape to demonstrate the heat intolerance of brachycephalic dog breeds. The final dataset included 137 469 dogs. The average age of death of the study population was 11,8 years, mixed breeds reaching a higher average age of 12,4 years than purebred dogs with 11,5 years. Bodyweight classification, skull shape and the origin of the dogs had a significant effect on the average lifespan. Giant breeds reached with 9,0 years the lowest mean age compared to the other bodyweight categories. The mean life expectancy of brachycephalic dogs was 9,8 years, i.e., 2,1 and 1,7 years less than mesocephalic and dolichocephalic dogs, respectively. Brachycephalic dogs and dogs imported from abroad showed increased mortality at a young age.

Current Clinical Concepts: Heat Tolerance Testing

Heat tolerance testing (HTT) has been developed to assess readiness for work or exercise in the heat based on thermoregulation during exertion. Although the Israeli Defense Forces protocol has been the most widely used and referenced, other protocols and variables considered in the interpretation of the testing are emerging. Our purpose was to summarize the role of HTT after exertional heat stroke; assess the validity of HTT; and provide a review of best-practice recommendations to guide clinicians, coaches, and researchers in the performance, interpretation, and future direction of HTT. We also offer the strength of evidence for these recommendations using the Strength of Recommendation Taxonomy system.

A Rare Case of Hypohidrotic Ectodermal Dysplasia in a Seven-Year-Old Child

Ectodermal dysplasias (EDs) encompass a large group of inherited disorders that affects two or more ectodermally derived structures. Hair, sweat glands, teeth, and nails are the most common ectodermal derivates affected. Other ectodermal structures that may be affected are ears, eyes, lips, and mucous membranes of the mouth or nose. During embryonic development, the ectoderm forms the outermost layer of the primary germ layers that give rise to the several structures that are commonly affected in ED. Therefore, ED manifests differently among patients, depending on the abnormality's combination and severity. Out of 150 distinctive syndromes, the most common syndromes within this group are hypohidrotic (defective sweat glands) and hidrotic (normal sweat glands). In addition, different types of inheritance patterns are found in ED; X-linked inheritance is by far the most common mode of inheritance. We present here the clinical case of hypohidrotic (anhidrotic) ED in a seven-year-old boy.

Pseudo-pheochromocytoma due to obstructive sleep apnea: a case report

SUMMARY

Obstructive sleep apnea (OSA) is a condition of intermittent nocturnal upper airway obstruction. OSA increases sympathetic drive which may result in clinical and biochemical features suggestive of pheochromocytoma. We present the case of a 65-year-old male with a 2.9-cm left adrenal incidentaloma on CT, hypertension, symptoms of headache, anxiety and diaphoresis, and persistently elevated 24-h urine norepinephrine (initially 818 nmol/day (89-470)) and normetanephrine (initially 11.2 µmol/day (0.6-2.7)). He was started on prazosin and underwent left adrenalectomy. Pathology revealed an adrenal corticoadenoma with no evidence of pheochromocytoma. Over the next 2 years, urine norepinephrine and normetanephrine remained significantly elevated with no MIBG avid disease. Years later, he was diagnosed with severe OSA and treated with continuous positive airway pressure. Urine testing done once OSA was well controlled revealed complete normalization of urine norepinephrine and normetanephrine with substantial symptom improvement. It was concluded that the patient never had a pheochromocytoma but rather an adrenal adenoma with biochemistry and symptoms suggestive of pheochromocytoma due to untreated severe OSA. Pseudo-pheochromocytoma is a rare presentation of OSA and should be considered on the differential of elevated urine catecholamines and metanephrines in the right clinical setting.

LEARNING POINTS

Obstructive sleep apnea (OSA) is a common condition among adults. OSA may rarely present as pseudo-pheochromocytoma with symptoms of pallor, palpitations, perspiration, headache, or anxiety. OSA should be considered on the differential of elevated urine catecholamines and metanephrines, especially in patients with negative metaiodobenzylguanidine (MIBG) scan results.

Clinical and histopathological studies on neurodegeneration and dysautonomia in buffalo calves during foot-and-mouth disease outbreaks in Egypt

Background and Aim

Signs of dysautonomia were frequently observed in calves that died during foot-and-mouth disease (FMD) virus (FMDV) outbreaks in Egypt from 2015 to 2018. This study aimed to describe the clinical and histopathological features of the central nervous system in malignant cases of FMD and excluding possible concurrent bacterial, and bovine herpes virus 4 (BHV4) infections or both.

Materials and Methods

In this study, 335 FMDV-infected buffalo calves aged 1-22 months were clinically examined and followed until recovery or death. Of the 335 calves, 134 died (malignant group) and 201 recovered after exhibiting classic symptoms of FMD (recover group). The calves were subjected to clinical examination. For the malignant group, several laboratory trials were conducted to assess the possible cause/s of dysautonomia-related viral, bacterial, or concurrent infections. Koch's postulates and polymerase chain reaction were employed. Postmortem and histopathological examinations of nervous tissue were performed.

Results

In the malignant group, signs of dysautonomia were observed before death, including partial or complete gut dysfunction, loss of anal sphincter tone, rapid breathing sounds, fluctuating body temperature, and cardiac arrhythmias. In the malignant group, histopathological examination of the spinal cord, pons, medulla oblongata, hypothalamus, cerebellum, and cerebrum revealed demyelination, neuronal degeneration, and focal areas of malacia and gliosis. The nervous tissue and heart samples from malignant cases were positive for serotype O FMDV.

Conclusion

Findings revealed in this study support the existence of neurodegeneration induced by FMDV infection in buffalo calves.

A basal heat stress test to detect military operational readiness after a 14-day operational heat acclimatization period

A basal heat stress test (HST) to predict the magnitude of adaptive responses during heat acclimatization (HA) would be highly useful for the armed forces. The aim was to identify physiological markers assessed during a HST (three 8-min running sets at 50% of the speed at VO_2max) performed just before a 14-day HA period that would identify participants still at "risk" at the end of HA. Individuals that responded poorly (large increases in rectal temperature [T_rec] and heart rate [HR]) during the initial HST were more likely to respond favorably to HA (large reductions in T_rec and HR). However, they were also more likely to exhibit lower tolerance to HST at D15. Basal T_rec was found to efficiently discriminate participants showing a T_rec > 38.5°C after HA, who are considered to be "at risk". Finally, participants were classified by quartiles based on basal T_rec and HR at the end of the HST and physiological strain index (PSI). Most of the participants "at risk" were among the upper quartile (i.e. the least tolerant) of T_rec and PSI (p = 0.011 for both). Overall, these results show that the individuals who are less tolerant to a basal HST are very likely to benefit the most from HA but they also remain less tolerant to heat at the end of HA than those who better tolerated the basal HST. A basal HST could therefore theoretically help the command to select the most-ready personnel in hot conditions while retaining those who are less tolerant 6.

When Should a Heat-Tolerance Test Be Scheduled After Clinical Recovery From an Exertional Heat Illness?

OBJECTIVE

Researchers have produced a hypothesis of transient heat intolerance (HI) after exertional heat stroke (EHS). Based on this hypothesis, heat-tolerance testing (HTT) has been postponed until weeks 6 to 8 after EHS and other types of exertional heat illness (EHI). We compared the HTT results of participants after either EHS or other EHI who were tested earlier (≤6-week group) versus those who were tested later (>6-week group) to verify the hypothesis.

DESIGN

Cohort study.

SETTING

Data obtained from records of military athletes who experienced EHS or EHI.

PATIENTS OR OTHER PARTICIPANTS

All participants who underwent HTT after EHI or EHS experienced between 2014 and 2018 and for whom complete data regarding the severity of the event (rectal temperature, neurologic symptoms, and laboratory results) and HTT results were available were included. Participants with suspected EHS and those with other EHIs were evaluated separately.

MAIN OUTCOME MEASURE(S)

The percentages of participants with HI and mean probability of heat tolerance were compared between those tested within 6 weeks of the event and those tested later.

RESULTS

A total of 186 participants were included in this study (EHS: 12 in the <6-week group, 9 in the >6-week group; EHI: 94 in the <6-week group, 71 in the >6-week group). In the EHS group, the percentages with HI (33% versus 44%, P = .67) and mean probability of heat tolerance (0.82 versus 0.82, P = .98) did not differ. In the EHI group, participants who were tested after 6 weeks had a greater chance of being diagnosed with HI (38% versus 21.3%, P < .02).

CONCLUSIONS

The HTT results were similar between participants with EHS who were tested early (<6 weeks) and those tested late (>6 weeks). Further investigation of heat-tolerance changes in larger cohorts of patients after EHS is required to verify the theory of transient HI.

Thermoregulatory dysfunction in multiple sclerosis

Multiple sclerosis (MS) is a progressive neurologic disorder that disrupts axonal myelin in the central nervous system. Demyelination produces alterations in saltatory conduction, slowed conduction velocity, and a predisposition to conduction block. An estimated 60-80% of MS patients experience temporary worsening of clinical signs and neurologic symptoms with heat exposure (Uhthoff's phenomenon). This heat intolerance in MS is related to the detrimental effects of increased temperature on action potential propagation in demyelinated axons, resulting in conduction slowing and/or block. Additionally, MS may produce impaired neural control of autonomic and endocrine functions. Isolating and interpreting mechanisms responsible for autonomic dysfunction due to MS can be difficult as it may involve sensory impairments, altered neural integration within the central nervous system, impaired effector responses, or combinations of all of these factors. MS lesions occur in areas of the brain responsible for the control and regulation of body temperature and thermoregulatory effector responses, resulting in impaired neural control of sudomotor pathways or neural-induced changes in eccrine sweat glands, as evidenced by observations of reduced sweating responses in MS patients. Although not comprehensive, some evidence exists concerning treatments (cooling, precooling, and pharmacologic) for the MS patient to preserve function and decrease symptom worsening during heat stress. This review focuses on four main themes influencing current understanding of thermoregulatory dysfunction in MS: (1) heat intolerance; (2) central regulation of body temperature; (3) thermoregulatory effector responses; and (4) countermeasures to improve or maintain function during thermal stress.