Pathpphysiology of body temperature regulation Prof J Hanek

Pathpphysiology of body temperature regulation Prof. J. Hanáček

Thermoregulation of human body

Normal body temperature regulation It is achieved by activities in 3 subsystems: 1) Thermoafferent system 2) Integrating system 3) Effector system 4) 1) Thermoafferent system: 5) Thermoreceptors – skin, hypothalamus, spinal cord. . . 6) afferent n. fibres rostral brain stem thalamic nuclei and 7) hypothalamus somatosensory cortex 8) Density of thermoreceptors: skin in face, neck and chest contain 5 times

2) Integrating system - it is present at several levels of the CNS (mesencephalon, medulla oblongata. . . ) - hypothalamus is the center for thermoregulation 3) Effector system - autonomic nerve system is involved – vasodilatation, sweating vasoconstriction, shivering - nerve pathways from dorsal hypothalamus: control shivering nerve tract emerges and connect to extrapyramidal motor tract shivering

Disturbancies of thermoregulatory sweating Generalized anhydrosis – resulting in hyperthermia – idiopathic – due to lesions in hypothalamus or in the spinal cord Segmental anhydrosis – only local disturbance of sweating – lesion of sympathetic trunk – anhydrosis in the area of sensory deficit – in nerve plexus lesions, – isolated or combined neuropathies

Central hyperthermia Causes: - hypothalamic lesions (infarction, hemorrhage, tumor, trauma, encephalitis) - intoxication(anticholinergic and sympatho mimetic drugs, salicylates, amphetamines, cocaine) - acute spinal cord transection above T 3 -4 - delirium, catatonia - malignant neuroleptic sy. (caused by skeletal muscle rigidity from treatment with neuroleptic medications (e. g. , antipsychotics, antidepressants, antiemetics). - malignant hyperhermia (rapid and massive skeletal muscle contraction from exposure to anesthesia) - dehydration, heat stroke, generaised tetanus

Another mechanisms involved in damage of tissue in hypethermia: - When blood flow is diverted to the skin, reduced perfusion of the intestines and other viscera can result in ischemia, endotoxemia, and oxidative stress - Excessively high tissue temperatures (heat shock >41° C, 105. 8° F) can produce direct tissue injury - Heat shock, ischemia, and systemic inflammatory responses can result in cellular dysfunction, disseminated intravascular coagulation, and multiorgan dysfunction syndrome - Reduced cerebral blood flow, combined with abnormal local metabolism and coagulopathy, can lead to dysfunction of the central nervous system

Sympoms and signs of heat illness (hyperthermia) Minor intensity of heat illness - symptoms and signs - Miliaria rubra (heat rash) - results from occlusion of eccrine sweat gland ducts - Heat syncope (fainting) - caused by temporary circulatory insufficienc as a result of pooling of blood in the peripheral veins - Heat cramps (skeletal muscles cramps) - occur during and after intense exercise and are believed to result from excessive loss of sodium in sweat

Serious heat illness – sympoms and signs - Heat exhaustion - a mild to moderate illness characterized by an inability to sustain cardiac output with moderate (>38. 5° C, 101° F) to high (>40° C, 104° F) body temperatures (hot skin and dehydration) - Heat injury - a moderate to severe illness characterized by organ (e. g. liver, renal) and tissue (e. g. gut, muscle) injury with high body temperatures, usually but not always greater than 40° C (104° F) - Heat stroke - a severe illness characterized by central nervous system dysfunction with high body temperatures, usually but not always greater than 40° C (104° F)

Cold injury Cold injuries are classified as hypothermia and peripheral cold injuries - Hypothermia - whole body cooling - Peripheral cold injuries - localized to the extremities and exposed skin: - nonfreezing (chilblain, trench foot) - freezing (frostbite) Both hypothermia and peripheral cold injuries often occur simultaneously

Cold exposure elicits: - peripheral vasoconstriction to reduce heat transfer between the body's core and shell (skin, subcutaneous fat) - underlying tissues (e. g. , muscle) constrict to thicken the isolative shell while reducing the body core area - this vasoconstrictor response defends core temperature, but at the expense of declining peripheral tissue temperatures, which contribute to peripheral cold injuries - hypothermia depresses enzymatic activity, interferes with physiologic functions (e. g. , clotting, respiration, cardiac conduction and rhythm), impairs expression of cytokines, and can induce cellular injury and death

Symptoms and signs of cold injury Hypothermia - a core temperature below 95° F (35° C), and clinical manifestations are related to the core temperature achieved. The classic J wave on ECG appears at a core temperature below about 93° F Chilblain - appears as localized inflammatory lesions of the skin that most often involve the dorsal surface of fingers, but the ears, face, and exposed shins are common areas “Trench foot”- caused by prolonged cold-wet (e. g. , wet socks or gloves) exposure, which can cause skin breakdown and nerve damage - trench foot is often accompanied by infection and increased sensitivity to pain

Frostbite - the freezing of tissues and can be categorized as: - first degree (superficial, “frostnip”) - second degree (full skin), - third degree (subcutaneous tissue) - fourth degree (extensive tissue and bone). - The severity of frostbite may take many days to weeks to determine - Frostbite requires early surgical consultation once the diagnosis is made

Hypothermic Syndromes Exercise-induced bronchospasm can be triggered by exercise in cold air, particularly in patients with asthma. Livedo reticularis is patchy mottling of the limbs with cold exposure. Cryoglobulinemia occurs when immunoglobulins (Ig. M, Ig. G) reversibly precipitate after being cooled and contribute to impaired capillary blood flow in hypothermic tissues. Cold urticaria is the development of localized and general erythema and wheals in skin exposed to cold. Paroxysmal hypothermia is periodic lowering of thermoregulatory set point and is often associated with hypothalamic abnormalities. Raynaud's phenomenon is intense vasoconstriction with sensitivity to pain in limbs exposed to cold