Heat Stroke And Dysautonomia: Exploring A Potential Link

could a heat stroke cause dysautonomia

Heat stroke is a medical emergency that can lead to organ damage or death. It occurs when the body fails to maintain its normal core temperature, resulting in a systemic inflammatory response and multi-organ dysfunction. Dysautonomia, on the other hand, is a condition that affects the autonomic nervous system, which regulates the body's response to heat. People with dysautonomia may experience heat intolerance, which can manifest as intense sweating or anxiety when exposed to heat. While the direct link between heat stroke and dysautonomia is unclear, it is known that heat exposure can lead to a range of complications, and those with dysautonomia may be particularly prone to these complications due to their impaired thermoregulatory abilities. Therefore, it is crucial for individuals with dysautonomia to be cautious in extreme heat and take preventive measures to manage their symptoms.

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Heat stroke and dysautonomia in young children

Heat-related illnesses are a serious concern, especially for young children who are more susceptible to the effects of heat. One condition that has been linked to heat stroke in children is dysautonomia, an autoimmune disorder that affects the autonomic nervous system.

Dysautonomia, also known as Riley-Day syndrome, is an uncommon condition that disrupts the body's ability to regulate functions such as temperature control, heart rate, and sweating. Children with dysautonomia may have difficulty maintaining a normal body temperature, particularly in hot environments, which can increase their risk of developing heat stroke.

Heat stroke is a life-threatening condition characterised by an elevated core body temperature above 40°C, along with central nervous system dysfunction. It can be triggered by exposure to high environmental temperatures or strenuous exercise. Young children, especially those with underlying medical conditions like dysautonomia, are at a higher risk of developing heat stroke due to their sensitive and still-developing physiological systems.

The case study of a 14-month-old female with dysautonomia referred to the pediatric department with a high fever of 41.6°C, watery diarrhoea, and vomiting illustrates this link. Within a few hours, the child also exhibited signs of encephalopathy, and laboratory tests revealed elevated liver enzyme levels. The diagnosis was heat stroke, and the impaired autonomic nervous system function was identified as a contributing factor.

To protect young children from heat stroke, it is crucial to recognise the early warning signs of heat-related illnesses, such as dizziness, lethargy, and hot or blistering skin. Taking preventive measures, such as staying hydrated, seeking shade, and wearing appropriate clothing, is essential for everyone, especially those at higher risk. Additionally, seeking prompt medical attention is vital if symptoms worsen or persist, as heat stroke is a medical emergency that can lead to permanent neurological damage or even death.

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Heat stroke and postural orthostatic tachycardia syndrome (POTS)

Heat-related illnesses affect a wide range of people and can vary in intensity and duration. Postural orthostatic tachycardia syndrome (POTS) is a blood circulation disorder that affects an estimated one to three million Americans. It is a type of orthostatic intolerance (OI), which is characterised by an excessively reduced volume of blood returning to the heart when standing up from a lying-down position. The primary symptom of OI is lightheadedness or fainting.

POTS is diagnosed when orthostatic hypotension is ruled out, and there is no acute dehydration or blood loss. It is identified by a specific group of symptoms that occur when standing upright and an increase in heart rate of at least 30 beats per minute in adults (or 40 in adolescents) within the first 10 minutes of standing. The symptoms of POTS include lightheadedness, difficulty concentrating, fatigue, exercise intolerance, palpitations, tremors, and nausea.

Heat stroke is a medical emergency and can be life-threatening. It is caused by prolonged exposure to extreme heat and results in a rapid increase in body temperature, often leading to organ damage. POTS can be triggered or worsened by exposure to warm environments, and heat stroke is a potential complication of prolonged heat exposure. Therefore, individuals with POTS are at an increased risk of developing heat-related illnesses, including heat stroke.

The autonomic nervous system regulates the body's response to heat, and in individuals with POTS, this system is disrupted. The body's inability to regulate blood flow and temperature effectively may increase the risk of heat stroke. Additionally, the symptoms of POTS, such as lightheadedness and fatigue, may be exacerbated by heat exposure, further increasing the risk of heat-related complications.

While the exact causes of POTS are not fully understood, it is believed to be associated with damage to the small fibre nerves, elevated levels of stress hormones, abnormally low blood volume, and other underlying conditions such as autoimmune disorders. The condition is more common in women than in men and typically affects individuals between the ages of 15 and 50.

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Heat stroke and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Splanchnic Vasoconstriction and Hypoxia

Heat stroke is associated with an increase in blood flow to the skin, which requires a reduction in blood flow to internal organs (splanchnic vasoconstriction). This results in hypoxia, which has important consequences for the gut and brain. Similarly, several hypotheses suggest that vasoconstriction and hypoxia are central to the pathology of ME/CFS. Postural orthostatic tachycardia syndrome (POTS) is a common comorbidity of ME/CFS, which is also associated with gastrointestinal dysfunction.

Gut Permeability and Endotoxemia

Animal models of heat stroke have shown that reduced blood flow to the gut causes mucosal damage and a weakening of the tight junctions in the gut, leading to a "leaky gut". This allows bacteria and toxins to enter the bloodstream, triggering a systemic inflammatory response. Research has also found gut hyper-permeability and gut inflammation in ME/CFS patients, as well as increased levels of antibodies to lipopolysaccharides (LPS).

Systemic Inflammatory Response

Heat stroke is associated with an increase in inflammatory cytokines, which can lead to fever, leukocytosis, increased synthesis of acute-phase proteins, muscle catabolism, and activation of leukocytes and endothelial cells. ME/CFS is also characterised by chronic inflammation, including inflammation of the brain (myalgic encephalomyelitis).

Central Nervous System Dysfunction

Delirium, convulsions, and coma are common symptoms of heat stroke, which are believed to be caused by a combination of ischemia, hypoxia, thermolysis, and hemorrhage. ME/CFS patients may experience brain fog and hypersensitivity to noise and light, although the underlying mechanisms are not well understood. However, brain imaging studies have revealed significant neuroinflammation and white matter abnormalities.

Coagulation Disorders and Endothelial-Cell Injury

Both heat stroke and ME/CFS have been associated with coagulation disorders and endothelial-cell injury. Intestine-derived endotoxins and cytokines activate vascular endothelial cells and coagulation factors, triggering a positive feedback loop that contributes to microvascular thrombosis.

Mitochondrial Dysfunction

There is limited research on mitochondrial function in heat stroke, but some studies have observed ATP depletion and mitochondrial swelling in animal models. Mitochondrial dysfunction is also believed to play a role in ME/CFS, potentially due to immuno-inflammatory pathways and oxidative and nitrosative stress.

Altered Gene Transcription

Initial transcriptomic studies suggest that similar gene expressions are altered in both heat stroke and ME/CFS, particularly genes related to mitochondrial and immune function.

Predisposing Factors

Young children, the elderly, and those with chronic diseases are most susceptible to classic heat stroke. Prior infection, inflammation, and a compromised immune system may also increase the risk of heat stroke and ME/CFS.

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Heat stroke and the autonomic nervous system

Heat stroke is a life-threatening condition that arises when the body fails to regulate its core temperature in response to high environmental temperatures or strenuous exercise. It is characterised by a body temperature that rises above 40°C, hot and dry skin, and central nervous system abnormalities such as delirium, convulsions, or coma. The condition can lead to organ damage or death, with a hospital mortality rate ranging from 3% to 65%.

Heat stroke is associated with a failure of the autonomic nervous system, which is responsible for regulating the body's automatic functions, including its response to heat. Dysautonomia refers to a group of conditions that affect the autonomic nervous system, and it is a known risk factor for heat stroke.

Heat Intolerance

Heat intolerance is an unusual sensitivity to heat, where a person may feel hot when others feel comfortable or cold. It is not a disease but can be a symptom of an underlying medical condition, such as dysautonomia. People with heat intolerance may have an unusual response to heat, such as intense sweating or anxiety, and are at a higher risk of heat-related illnesses like heat stroke.

Symptoms of Heat Intolerance

  • Feeling very hot in moderately warm temperatures
  • Not sweating enough in the heat
  • Exhaustion and fatigue during warm weather
  • Nausea, vomiting, or dizziness in response to heat
  • Changes in mood when too hot

Strategies for Managing Heat Intolerance

  • Avoid direct sunlight, especially during the hottest parts of the day (11 am to 3 pm)
  • Use air conditioning or a fan
  • Drink plenty of fluids to stay hydrated
  • Wear light-coloured, loose-fitting clothing
  • Avoid alcohol in hot weather
  • Take cool baths or swims
  • Wrap a towel soaked in cold water around the neck
  • Avoid strenuous activities during hot weather

Postural Orthostatic Tachycardia Syndrome (POTS)

POTS is a condition that often co-occurs with heat intolerance and heat-related illnesses. It is characterised by an abnormal increase in heart rate when moving from a lying down or sitting position to a standing position. People with POTS may experience fainting, nausea, and dehydration in response to heat.

Familial Dysautonomia

Familial dysautonomia, also known as Riley-Day syndrome, is a rare genetic disorder that affects the autonomic nervous system and can increase the risk of heat stroke in young children. It is characterised by high fever, watery diarrhoea, vomiting, and signs of encephalopathy.

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Heat stroke and the immune system

Heat stroke is a life-threatening condition that can be fatal if not appropriately managed. Hyperthermia, septicaemia, central nervous system impairment, and cardiovascular failure play important roles in the pathology of heat stroke. The current models of heat stroke suggest that it is triggered by hyperthermia but driven by endotoxaemia. Endotoxaemia triggers a systemic inflammatory response, which can lead to systemic coagulation, haemorrhage, necrosis, cell death, and multi-organ failure.

Research has shown that athletes undergoing intense training are subjected to a variety of immune and gastrointestinal disturbances. These disturbances include the suppression of immune cells and their functions, suppression of cell-mediated immunity, translocation of lipopolysaccharide (LPS), suppression of anti-LPS antibodies, increased macrophage activity due to muscle tissue damage, and increased concentration of circulating inflammatory and pyrogenic cytokines.

The dual pathway model of heat stroke suggests that prolonged intense exercise suppresses anti-LPS mechanisms and promotes inflammatory and pyrogenic activities. This model illustrates the existence of two pathways of heat stroke: endotoxaemia (heat sepsis), the primary pathway, and hyperthermia, the secondary pathway.

Cytokines are intracellular peptides that serve as immune mediators. Both pro- and anti-inflammatory cytokine levels rise in the event of heat stroke in both human and animal models. The strong inflammatory response to heat stroke increases after the cessation of heat stress and is involved in both damage-generating processes and repair mechanisms during the recovery phase. A greater magnitude of the inflammatory response is associated with poor prognosis and fatalities, suggesting an imbalance in the immune system.

Frequently asked questions

Heat stroke is a medical emergency that occurs when the body fails to maintain its normal core temperature when exposed to high environmental temperatures or strenuous exercise. It is characterised by a body temperature above 40°C, hot and dry skin, and central nervous system abnormalities such as delirium, convulsions, or coma.

Dysautonomia is a condition that affects the autonomic nervous system, which regulates automatic functions of the body, including the body's response to heat. It can cause heat intolerance, which is an unusual sensitivity to heat.

Heat stroke can be a trigger for dysautonomia. Impaired autonomic nervous system function may be a risk factor for the development of heat stroke in young children.

Symptoms of heat stroke include a high body temperature, dry and hot skin, delirium or confusion, and a rapid heart rate. It is a medical emergency, and 911 should be called immediately if it is suspected. While waiting for emergency services to arrive, the person should be moved to a cool and shaded area, and cool water or an electrolyte drink should be sipped. Cool towels or cloths should be placed on the person's body.

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