Histamine, mast cell tryptase and post-exercise hypotension in healthy and collapsed marathon runners

Improvements in Orthostatic Tolerance with Exercise Are Augmented by Heat Acclimation: A Randomized Controlled Trial

INTRODUCTION

Heat adaptation is protective against heat illness; however, its role in heat syncope, due to reflex mechanisms, has not been conclusively established. The aim of this study was to evaluate if heat acclimation (HA) was protective against heat syncope and to ascertain underlying physiological mechanisms.

METHODS

Twenty (15 males, 5 females) endurance-trained athletes were randomized to either 8 d of mixed active and passive HA (HEAT) or climatically temperate exercise (CONTROL). Before, and after, the interventions participants underwent a head up tilt (HUT) with graded lower body negative pressure (LBNP), in a thermal chamber (32.0 ± 0.3°C), continued until presyncope with measurement of cardiovascular parameters. Heat stress tests (HST) were performed to determine physiological and perceptual measures of HA.

RESULTS

There was a significant increase in orthostatic tolerance (OT), as measured by HUT/LBNP, in the HEAT group (preintervention; 28 ± 9 min, postintervention; 40 ± 7 min) compared with CONTROL (preintervention; 30 ± 8 mins, postintervention; 33 ± 5 min) ( P = 0.01). Heat acclimation resulted in a significantly reduced peak and mean rectal and skin temperature ( P < 0.01), peak heat rate ( P < 0.003), thermal comfort ( P < 0.04), and rating of perceived exertion ( P < 0.02) during HST. There was a significantly increased plasma volume (PV) in the HEAT group in comparison to CONTROL ( P = 0.03).

CONCLUSIONS

Heat acclimation causes improvements in OT and is likely to be beneficial in patients with heat exacerbated reflex syncope. Heat acclimation-mediated PV expansion is a potential physiological mechanism underlying improved OT.

Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation

Mast cells (MC) are ubiquitous in the body, and they are critical for not only in allergic diseases but also in immunity and inflammation, including having potential involvement in the pathophysiology of dysautonomias and neuroinflammatory disorders. MC are located perivascularly close to nerve endings and sites such as the carotid bodies, heart, hypothalamus, the pineal gland, and the adrenal gland that would allow them not only to regulate but also to be affected by the autonomic nervous system (ANS). MC are stimulated not only by allergens but also many other triggers including some from the ANS that can affect MC release of neurosensitizing, proinflammatory, and vasoactive mediators. Hence, MC may be able to regulate homeostatic functions that seem to be dysfunctional in many conditions, such as postural orthostatic tachycardia syndrome, autism spectrum disorder, myalgic encephalomyelitis/chronic fatigue syndrome, and Long-COVID syndrome. The evidence indicates that there is a possible association between these conditions and diseases associated with MC activation. There is no effective treatment for any form of these conditions other than minimizing symptoms. Given the many ways MC could be activated and the numerous mediators released, it would be important to develop ways to inhibit stimulation of MC and the release of ANS-relevant mediators.

What do environment-related illnesses tell us about the character of military medicine and future clinical requirements?

Extreme environments present medical and occupational challenges that extend beyond generic resuscitation, to formulating bespoke diagnoses and prognoses and embarking on management pathways rarely encountered in civilian practice. Pathophysiological complexity and clinical uncertainty call for military physicians of all kinds to balance intuition with pragmatism, adapting according to the predominant patterns of care required. In an era of smaller operational footprints and less concentrated clinical experience, proposals aimed at improving the systematic care of Service Personnel incapacitated at environmental extremes must not be lost to corporate memory. These general issues are explored in the particular context of thermal stress and metabolic disruption. Specific focus is given to the accounts of military physicians who served on large-scale deployments into the heat of Iraq and Kuwait (Operation TELIC) and Oman (Exercise SAIF SAREEA). Generalisable insights into the enduring character of military medicine and future clinical requirements result.

Effects of aerobic exercise on ambulatory blood pressure responses to acute partial sleep deprivation: impact of chronotype and sleep quality

Blood pressure (BP) follows a circadian rhythm intertwined with the sleep-wake cycle. Acute partial sleep deprivation (PSD; sleep ≤ 6 h) can increase BP, associated with increased cardiovascular risk. Acute exercise can reduce BP for up to 24 h, a phenomenon termed postexercise hypotension. The present study tested whether aerobic exercise could mitigate the augmented 24-h ambulatory BP caused by acute PSD. Twenty-four young otherwise healthy adults (22 ± 3 yr; 14 females; self-reported chronotypes: 6 early/10 intermediate/8 late; Pittsburgh sleep quality index: 17 good/7 poor sleepers) completed a randomized crossover trial in which, on different days, they slept normally (2300-0700), restricted sleep [0330-0700 (PSD)], and cycled for 50 min (70-80% predicted heart rate maximum) before PSD. Ambulatory BP was assessed every 30 min until 2100 the next day. Acute PSD increased 24-h systolic BP (control 117 ± 9 mmHg, PSD 122 ± 9 mmHg; P < 0.001) and prior exercise attenuated (exercise + PSD 120 ± 9 mmHg; P = 0.04 vs. PSD) but did not fully reverse this response (exercise + PSD, P = 0.02 vs. control). Subgroup analysis revealed that the 24-h systolic BP reduction following exercise was specific to late types (PSD 119 ± 7 vs. exercise + PSD 116 ± 6 mmHg; P < 0.05). Overall, habitual sleep quality was negatively correlated with the change in daytime systolic BP following PSD (r = -0.56, P < 0.01). These findings suggest that the ability of aerobic cycling exercise to counteract the hemodynamic effects of acute PSD in young adults may be dependent on chronotype and that habitual sleep quality can predict the daytime BP response to acute PSD.NEW & NOTEWORTHY We demonstrate that cycling exercise attenuates, but does not fully reverse, the augmented 24-h ambulatory blood pressure (BP) response caused by acute partial sleep deprivation (PSD). This response was primarily observed in late chronotypes. Furthermore, daytime BP after acute PSD is related to habitual sleep quality, with better sleepers being more prone to BP elevations. This suggests that habitual sleeping habits can influence BP responses to acute PSD and their interactions with prior cycling exercise.

Risk factors for reflex syncope in the British Army

INTRODUCTION

Reflex syncope in the UK Armed Forces is reportedly higher than comparable militaries and civilian populations and is significantly more common in soldiers who take part in State Ceremonial and Public Duties (SCPD) compared with other British Army service personnel (SP). This study aimed to investigate individual susceptibility factors for syncope in soldiers who regularly take part in SCPD.

METHODS

A retrospective cohort study was performed in 200 soldiers who perform SCPD. A questionnaire was undertaken reviewing soldiers' medical history and circumstances of any fainting episodes. A consented review of participants' electronic primary healthcare medical record was also performed. Participants were divided into two groups (syncope, n=80; control, n=120) based on whether they had previously fainted.

RESULTS

In the syncope group orthostasis (61%) and heat (35%) were the most common precipitating factors. The most common interventions used by soldiers were to maintain hydration (59%) and purposeful movements (predominantly 'toe wiggling'; 55%). 30% of participants who had previously fainted did not seek definitive medical attention. A history of migraines/headaches was found to increase the risk of reflex syncope (OR 8.880, 1.214-218.8), while a history of antihistamine prescription (OR 0.07144, 0.003671-0.4236), non-white ethnicity (OR 0.03401, 0.0007419-0.3972) and male sex (OR 0.2640, 0.08891-0.6915) were protective.

CONCLUSION

This is the first study, in the British Army, to describe, categorise and establish potential risk factors for reflex syncope. Orthostatic-mediated reflex syncope is the most common cause in soldiers who regularly perform SCPD and this is further exacerbated by heat exposure. Soldiers do not use evidence-based methods to avoid reflex syncope. These data could be used to target interventions for SP who have previously fainted or to prevent fainting during SCPD.

Are young military personnel at a disproportional risk of heat illness?

Heat illnesses (HI) define a continuum of conditions where patients become incapacitated due to uncompensable heat stress. In the military, HI has a significant health, financial and operational burden that requires vigilant management. Military training and operations regularly expose personnel to known HI risk factors, meaning that prevalence remains high despite stringent attempts to reduce risk to as low as reasonably practicable. While prepubertal children and elderly adults are widely demonstrated to be at greater risk of classic HI than young adults due to impaired physiological and/or behavioural thermoregulation, in military personnel, it is young recruit-age individuals (16-19 years) who consistently experience the highest prevalence of exertional HI. Mechanistically, controlled laboratory studies have never directly compared thermoregulation between young recruit-age individuals and other groups of adults, though research highlighting impaired thermoregulation in prepubertal children potentially has some relevance to late-developing young recruit-age personnel. Aside from potential age-related differences in thermoregulation, a major consideration must also be given to the increased prevalence of organisational risk factors for HI in younger military personnel (eg, education, physical load, rank, job roles), which is likely to be the primary explanation behind age-related trends in HI prevalence, at least in the military. The aims of this article are to review: (i) the epidemiology of HI between young recruit-age individuals and older military personnel; (ii) the theoretical basis for age-associated differences in thermoregulatory function and (iii) pertinent areas for future research.

Insult of Ultraendurance Events on Blood Pressure: A Systematic Review and Meta-Analysis

The rise of ultraendurance sports in the past two decades warrants evaluation of the impact on the heart and vessels of a growing number of athletes participating. Blood pressure is a simple, inexpensive method to evaluate one dimension of an athlete's cardiovascular health. No systematic review or meta-analysis to date has chronicled and delineated the effects of ultraendurance races, such as ultramarathons, marathons, half-marathons, and Ironman triathlon events, specifically on heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), and mean arterial pressure (MAP) measurements in supine and standing positions before and after the event. This meta-analysis reviews the effects of ultraendurance events on positional and calculated hemodynamic values. Data were extracted from 38 studies and analyzed using a random effects model with a total of 1,645 total blood pressure measurements. Of these, 326 values were obtained from a standing position, and 1,319 blood pressures were taken supine. Pre-race and post-race measurements were evaluated for clinical significance using established standards of hypotension and orthostasis. HR and calculated BP features, such as PP and MAP, were evaluated. Across all included studies, the mean supine post-race HR increased by 21±8 beats per minute (bpm) compared to pre-race values. The mean standing post-race HR increased by 23±14 bpm when compared with pre-race HR. Overall, there was a mean SBP decrease of 19±9 mmHg and a DBP decrease of 9±5 mmHg post-race versus pre-race values. MAP variations reflected SBP and DBP changes. The mean supine and standing pre-race blood pressures across studies were systolic (126±7; 124±14) and diastolic (76±6; 75±12), suggesting that some athletes may enter races with existing hypertension. The post-race increase in the mean HR and decline in mean blood pressure across examined studies suggest that during long-term events, ultramarathon athletes perform with relatively asymptomatic hypotension.

Heatstroke-induced acute kidney injury and the innate immune system

Heatstroke can cause multiple organ failure and systemic inflammatory response syndrome as the body temperature rises beyond the body's ability to regulate temperature in a hot environment. Previous studies have indicated that heatstroke-induced acute kidney injury (AKI) can lead to chronic kidney disease. Therefore, there is an urgent need to elucidate the mechanism of heatstroke-induced AKI and to establish methods for its prevention and treatment. Recent reports have revealed that innate immunity, including neutrophils, macrophages, lymphocytes, and mast cells, is deeply involved in heat-induced AKI. In this review, we will discuss the roles of each immune cell in heat-induced renal injury and their potential therapeutic use.

HIGH-INTENSITY INTERVAL TRAINING POSES NO RISK TO HYPERTENSIVE WOMEN

ABSTRACT Introduction: The aim of this study was to evaluate whether a single session of high-intensity interval training (HIIT) would promote a hypotensive effect and cardiovascular risk in hypertensive women, in addition to increasing the bioavailability of nitric oxide. Methods: The sample consisted of 10 hypertensive women (63.7 ± 10.34 years; 66 ± 7.67 kg and 153.7 ± 9.08 cm) and the training load was established at 60% of the maximum aerobic speed. Results: We observed a very high hypotensive effect between the interaction moments during the intervention (Int. Pre: 122.40 ± 18.58; Int. Post: 143.00 ± 24.90; Int. Post 60min: 121.40 ± 13.87; p<0.001, η2P = 0.569). No cardiovascular risk was observed during the intervention (DP = Int. Pre: 9138.20 ± 1805.34; Int. Post: 14849.70 ± 3387.94; Int. Post 60min: 9615.90 ± 1124.41, p< 0.001, η2P = 0.739) and there was no increase in the bioavailability of nitric oxide. Conclusion: In conclusion, this work reveals that an HIIT session is capable of generating a hypotensive effect while not posing cardiovascular risk in hypertensive women. Level of evidence I; High-quality randomized clinical trial with or without statistically significant difference, but with narrow confidence intervals .