Paroxysmal episodic central thermoregulatory failure

Be cool to be far: Exploiting hibernation for space exploration

In mammals, torpor/hibernation is a state that is characterized by an active reduction in metabolic rate followed by a progressive decrease in body temperature. Torpor was successfully mimicked in non-hibernators by inhibiting the activity of neurons within the brainstem region of the Raphe Pallidus, or by activating the adenosine A1 receptors in the brain. This state, called synthetic torpor, may be exploited for many medical applications, and for space exploration, providing many benefits for biological adaptation to the space environment, among which an enhanced protection from cosmic rays. As regards the use of synthetic torpor in space, to fully evaluate the degree of physiological advantage provided by this state, it is strongly advisable to move from Earth-based experiments to 'in the field' tests, possibly on board the International Space Station.

[Spontaneous periodic hypothermia syndrome: A systematic review of the literature]

INTRODUCTION

Periodic spontaneous hypothermia syndrome (PSHS), also known as hypersudation-hypothermia syndrome, is a rare condition characterised by the occurrence of paroxysmal attacks of spontaneous hypothermia occurring without age limit. Few studies have attempted to synthesise the available data on PSHS. The objective of this study was to summarize the literature on this condition.

METHODS

A literature review was conducted using the Pubmed and ScienceDirect databases. Cases from a registry of PSHS initiated at the CHU of Saint-Étienne were added to the analysis. For each clinical case, clinical, biological and morphological data as well as therapeutic management and evolution were collected.

RESULTS

Seventy-one cases of PSHS were collected. The median age at symptom onset was 21.5 years. The clinical sign most frequently associated with hypothermia was the presence of hyperhidrosis. The triad of hypothermia-hypersudation-agenesis of the corpus callosum was present in 35.7% of cases.

CONCLUSION

PSHS remains a poorly known cause of hypothermia, without consensual therapeutic options. The need to better describe cases and obtain more long-term data will allow a better definition and knowledge of this syndrome.

Dysautonomia secondary to third ventriculostomy successfully managed with midodrine

Hypothalamic lesions can compromise its essential regulatory roles resulting in critical disruption of temperature and blood pressure homoeostasis. We present the case of a 55-year-old woman who had been previously submitted to several neurosurgical procedures aimed at treating idiopathic hydrocephalus. She presented to our department with recurring episodes of hypothermia and wide blood pressure variations, which had been worsening over the last few years. After extensive complementary workup, which excluded new neurological lesions or endocrinological conditions, hypothalamic dysfunction was assumed to be the cause of this syndrome. She was successfully treated with midodrine and on-demand captopril, which resulted in adequate control of her blood pressure. This case highlights the rare and unpredictable consequences of damage to the hypothalamus, depicting the favourable result of a heretofore unpublished medical approach.

Is Adenosine Action Common Ground for NREM Sleep, Torpor, and Other Hypometabolic States?

This review compares two states that lower energy expenditure: non-rapid eye movement (NREM) sleep and torpor. Knowledge on mechanisms common to these states, and particularly on the role of adenosine in NREM sleep, may ultimately open the possibility of inducing a synthetic torpor-like state in humans for medical applications and long-term space travel. To achieve this goal, it will be important, in perspective, to extend the study to other hypometabolic states, which, unlike torpor, can also be experienced by humans.

Consciousness in hibernation and synthetic torpor

While human hibernation would provide many advantages for medical applications and space exploration, the intrinsic risks of the procedure itself, as well as those involved if the procedure were to be misused, need to be assessed. Moreover, the distinctive brain state that is present during a hibernation-like state raises questions regarding the state of consciousness of the subject. Since, in animal studies, the cortical activity of this state differs from that of sleep, coma, or even general anesthesia, and resembles a sort of "slowed wakefulness", it is uncertain whether residual consciousness may still be present. In this review, I will present a brief summary of the literature on hibernation and of the current state of the art in inducing a state of artificial hibernation (synthetic torpor); I will then focus on the brain changes that are observed during hibernation, on how these could modify the neural substrate of consciousness, and on the possible use of hibernation as a model for quantum biology. Finally, some ethical considerations on the use of synthetic torpor technology will be presented.

The Central Control of Energy Expenditure: Exploiting Torpor for Medical Applications

Autonomic thermoregulation is a recently acquired function, as it appears for the first time in mammals and provides the brain with the ability to control energy expenditure. The importance of such control can easily be highlighted by the ability of a heterogeneous group of mammals to actively reduce metabolic rate and enter a condition of regulated hypometabolism known as torpor. The central neural circuits of thermoregulatory cold defense have been recently unraveled and could in theory be exploited to reduce energy expenditure in species that do not normally use torpor, inducing a state called synthetic torpor. This approach may represent the first steps toward the development of a technology to induce a safe and reversible state of hypometabolism in humans, unlocking many applications ranging from new medical procedures to deep space travel.

The inhibition of neurons in the central nervous pathways for thermoregulatory cold defense induces a suspended animation state in the rat

The possibility of inducing a suspended animation state similar to natural torpor would be greatly beneficial in medical science, since it would avoid the adverse consequence of the powerful autonomic activation evoked by external cooling. Previous attempts to systemically inhibit metabolism were successful in mice, but practically ineffective in nonhibernators. Here we show that the selective pharmacological inhibition of key neurons in the central pathways for thermoregulatory cold defense is sufficient to induce a suspended animation state, resembling natural torpor, in a nonhibernator. In rats kept at an ambient temperature of 15°C and under continuous darkness, the prolonged inhibition (6 h) of the rostral ventromedial medulla, a key area of the central nervous pathways for thermoregulatory cold defense, by means of repeated microinjections (100 nl) of the GABA(A) agonist muscimol (1 mm), induced the following: (1) a massive cutaneous vasodilation; (2) drastic drops in deep brain temperature (reaching a nadir of 22.44 ± 0.74°C), heart rate (from 440 ± 13 to 207 ± 12 bpm), and electroencephalography (EEG) power; (3) a modest decrease in mean arterial pressure; and (4) a progressive shift of the EEG power spectrum toward slow frequencies. After the hypothermic bout, all animals showed a massive increase in NREM sleep Delta power, similarly to that occurring in natural torpor. No behavioral abnormalities were observed in the days following the treatment. Our results strengthen the potential role of the CNS in the induction of hibernation/torpor, since CNS-driven changes in organ physiology have been shown to be sufficient to induce and maintain a suspended animation state.

Paroxysmal episodic hypothalamic instability with hypothermia after traumatic brain injury

This case report describes a patient in vegetative state after severe traumatic brain injury (TBI) with hypothalamic damage and clinical manifestations of autonomic dysfunction. He also presented late onset paroxysmal hypothermia associated with mild bradycardia and hypotension. Hypothermia due to traumatic lesions of the hypothalamus is an uncommon clinical problem and few cases have been reported; no cases could be found in the literature which evidenced periodic hypothermia associated with clinical features of autonomic dysfunction after TBI. In the article, the main causes and the primary pathophysiology of hypothermia after TBI are discussed. The manifestations in this patient have been interpreted as possible consequences of autonomic dysfunction and considered atypical and rare clinical expression of acute post-traumatic hypothalamic instability.

Unnoticed dysautonomic syndrome of the face: Harlequin syndrome

Harlequin sign and harlequin syndrome, which are used interchangeably in the literature, are characterized by sudden onset of hemifacial sweating and flushing, induced by exercise and heat. Hemifacial sweating and flushing with normal ocular sympathetic innervation, known as harlequin syndrome, is rarely associated with tonic pupils, parasympathetic oculomotor lesion and pre- or postganglionic sudomotor sympathetic deficit. In the literature, hemifacial sweating and flushing in patients with apparently abnormal ocular sympathetic innervation has been defined as harlequin sign. To date, a few reports of excessive hemifacial sweating and flushing in structural lesion have been documented. Herein, we report five patients with excessive hemifacial sweating and flushing, two of whom had a syrinx. In presenting the patients, we have attempted to distinguish harlequin syndrome from harlequin sign. With this in mind, Case 1 can be described as harlequin syndrome resembling Ross syndrome, Case 2 as harlequin syndrome with normal ocular sympathetic innervation, Case 3 as harlequin sign with congenital Horner syndrome, Case 4 as harlequin sign with sympathetic and parasympathetic denervation sensitivity, and Case 5 as harlequin syndrome associated with occult sympathetic denervation sensitivity. These cases are discussed together with a review of the literature.

Hypothermies spontanées : dix observations, place du syndrome de Shapiro

SUBJECT

Hypothermia (defined as a core temperature lower than 35 degrees C) may result from accidental causes (exposure to cold, drug intoxications), from endocrine disorders (hypothyroidism), or from central or peripheral neurological disease. Among the causes of spontaneous hypothermia, the place of spontaneous periodic hypothermia or Shapiro's syndrome, of which less than 50 cases in children or adults have been reported, remains unclear.

METHODS

Case series of spontaneous hypothermia in adults, from a register of the French Society of Internal Medicine (SNFMI).

RESULTS

The ten collected cases of spontaneous hypothermia are heterogeneous. In half of the cases, an often ill-labeled psychiatric illness and/or epilepsy and/or anti-psychotic medication were found contributive. Only 5 cases at best seem to conform to the pattern of spontaneous periodic hypothermia or Shapiro's syndrome (in which agenesis of corpus callosum is typically found). In such cases, the episodes of hypothermia start with profuse hyperhidrosis suggesting a paroxystic reset of the hypothalamic thermostat with a lower temperature set point. In none of the cases was found a significant encephalic lesion. None of the treatment trials with anti-epileptics or cyproheptadine were found useful. Spontaneous hypothermia, whether periodic or not, seems to have an unpredictable course, with long periods of remission, and a benign long-term outcome.

CONCLUSIONS

Spontaneous hypothermia is a symptom of likely multifactorial etiology. Even in cases conforming to the definition of Shapiro's syndrome, central nervous system anomalies are not unequivocal. No specific treatment for spontaneous hypothermia, whether periodic or not, can be recommended in the current state of knowledge.