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Altitude, temperature, circadian rhythms and exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Henning Wackerhage, Kenneth A. Dyar, Martin Schönfelder
Humans have evolved a regulatory system that maintains the temperature of our body within a narrow range. In relation to temperature, our body has two parts. First, our shell includes our skin and extremities, and here the temperature can vary considerably, for example when we have cold hands or feet. Second, our core comprises the vital inner organs and here the temperature is on average close to ≈37°C. Maintaining our core body temperature is important, as temperature has profound effects on the molecules of life. For example, the activity of enzymes increases with temperature before a too hot temperature causes enzymes and other proteins to denature. If we become too hot then we can suffer a heat stroke which is hyperthermia (core body temperature of >40°C) accompanied by systemic inflammation which can cause defects of several organs and eventually death (35). In contrast, when our body cools down, then enzymes are less active, membranes are more rigid and ion fluxes are reduced. Hypothermia is a medical syndrome when the core body temperature falls to below 35°C. When we are hypothermic, we start to shiver and become lethargic and this can progress further to confusion, coma and death.
Selected topics
Published in Henry J. Woodford, Essential Geriatrics, 2022
Hypothermia is defined as core body temperature 35.0°C or below.56 Cardiac arrest becomes more likely with temperatures below 32.0°C (i.e. ventricular fibrillation). Ear wax can make tympanic membrane thermometers inaccurate.56 In people aged over 80, hypothermia is more likely to occur in their own homes and less likely to be associated with alcoholism, self-harm or immersion/drowning incidents. The risk is increased by cognitive impairment, living alone and social isolation. Mortality was found to be around 30% in a group of people aged over 80 (median age 87).57 Warmed intravenous fluids (38–42°C) and forced air blankets are the usual minimally-invasive management techniques.56
Heat, cold and electrical trauma
Published in Jason Payne-James, Richard Jones, Simpson's Forensic Medicine, 2019
Jason Payne-James, Richard Jones
Generally, the elderly, children and trauma patients are susceptible to hypothermia. Hypothermia can be classified into mild (core temperature 32°C–35°C compared with a normal of 37.5°C), moderate (30°C–32°C), or severe (<30°C). Below a core temperature of 32°C, shivering ceases and thus this extra muscle activity will no longer generate heat, worsening the situation. Unconsciousness may occur between core temperatures of 27°C and 30°C, while ventricular fibrillation and apnoea occur at core temperatures below 27°C. Those who may be prone to developing hypothermia are those in extreme weather conditions (e.g., climbers, walkers, skiers, sailors), homeless people who are unable to find shelter, heavy drug and/or alcohol users (collapsing in the open) and those who have been immersed in cold water. Those who have been subject to severe trauma (e.g., trapped in a motor vehicle requiring extrication) are prone to hypothermia whilst they are being recovered.
Heat distribution and the condition of hypothermia in the multi-layered human head: A mathematical model
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Ahsan Ul Haq Lone, M.A. Khanday, Saqib Mubarak, Feroze A. Reshi
Variation in the temperature of human head exposed to external cold temperature at different qm (metabolic heat generation) values was plotted against time, as shown in Figure 2. The resulting graph indicates decrease in the temperature of the human head with prolonged exposure to cold environment. This is in consonance with the clinical finding of hypothermia, where the body temperature lowers by about 1–2 degrees than the normal and emerges as a medical condition. The speedy decrease in temperature of head on exposure to cold environment reflects the vulnerability of head to the hypothermia-induced impairment in the body. The variation of temperature in the human head in relation to axial distance from the core of the head also shows decrease in the temperature (Figure 3). This result garners support from the biological organisation of the head, in which the core is insulated from the surrounding environment by multiple protections, with scalp rather directly interfacing with the external environs. As a result, the scalp experiences the temperature more severely than the inner tissues/compartments of the head. The insulating layers of the core head are likely to succumb to the continued exposure of head to cold atmospheric temperature. Continuous exposure of head surface to the cold temperature gradually results in decrease in the temperature of core head 2–3 degrees lower than the normal body temperature. Such a condition is clinically marked as the manifestation of hypothermia.
Measuring the Systemic Inflammatory Response to On- and Off-Pump Coronary Artery Bypass Graft (CABG) Surgeries Using the Tryptophan/Kynurenine Pathway
Published in Journal of Investigative Surgery, 2022
Ahmed Farouk, Rasha A. Hamed, Saeid Elsawy, Nashwa F. Abd El Hafez, Farag M. Moftah, Muammar A. Y. Nassar, Fify Alfy Gabra, Tahia H. Saleem
For coronary bypass, patients were approached via a median sternotomy approach. Standard aortic and bicaval cannulation were made. About 400 μg/kg of heparin was given as initial dose to obtain an activated clotting time. Blood pressure range was kept at 50–70 mmHg and blood flow was adjusted to 2–2.4 L/min. Mannitol and heparin containing priming solution were used. Hypothermia occurred for 25–30 min. After aortic cross clamping, cold crystalloid cardiologic (4 °C) arrest was adopted. The coronary bypass grafting was performed using venous and arterial conduits. ICU follow up was maintained for hemodynamic changes in the heart rate, arterial blood pressure and central venous pressure. Broad spectrum antibiotics and antipyretics were given. All patients had to meet the following criteria before discharge: awareness, impulsive breathing and endotracheal tube detached.
Pre-hospital mild therapeutic hypothermia for patients with severe traumatic brain injury
Published in Brain Injury, 2022
Wusi Qiu, Mingmin Chen, Xu Wang, Ws Qiu, Mm Chen, X Wang
The best effects of therapeutic hypothermia in our present study might lie in the following factors. We excluded the patients with GCS 3, and all patients in our study reached their target temperature. While in POLAR-RCT (The Prophylactic Hypothermia Trial to Lessen Traumatic Brain Injury-Randomized Clinical Trial) study (18), a significant number of patients in the hypothermia group never reached the target temperature of 33°C (19% had hypothermia withdrawn early and a further 13% did not reach 33°C), and enrollment of patients without sTBI in the out-of-hospital setting before full evaluation might be another factor for the incorrect application of prophylactic hypothermia rather than therapeutic hypothermia. Furthermore, the clinicians and patients’ families were not blinded to the intervention in the POLAR-RCT study.