Studies of Body Temperatures, Blood Lactate, Cortisol and Free Fatty Acid Levels During Exercise in Human Subjects Susceptible to Malignant Hyperpyrexia

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Abstract
Body temperature at a variety of sites (external auditory meatus, rectum, thigh, chest wall, pad of thumb), blood cortisol, lactate and free fatty acid levels and urinary adrenaline, noradrenaline and dopamine excretion were measured in five human subjects susceptible to malignant hyperpyrexia (MHS) and five normal subjects during a period of progressively severe exercise, starting at rest and going up to an exercise intensity producing heart rates in excess of 180 beats/min. In addition, results are reported of a further study of rectal temperature measurements made during a period of mild exercise in a different group of nine MH susceptible and nine non‐susceptible subjects. The results of the progressive exercise study indicated that as the exercise increased in severity, central (external auditory meatal) temperature rose more in the MHS subjects than it did in the controls. Thumb temperature in both groups rose with exercise but in the MHS subjects this rise was significantly delayed compared with the control subjects. It was thought that this was due to a delay in the onset of vasodilatation which usually accompanies high intensities of exercise. Serum free fatty acids and cortisol levels rose more in the MHS subjects than the controls and during the early stages of exercise blood lactate concentrations in the MHS subjects were higher than in the controls group. During mild exercise, rectal temperature in the MHS subjects was lower than in the controls. It was concluded that the pattern of temperature change was evidence of an abnormality of the heat dissipation mechanisms in the MHS subjects. This, together with the rise in the free fatty acids, could indicate an abnormality of sympathetic activity in individuals susceptible to malignant hyperpyrexia.