Skeletal muscle contraction characteristics in vivo in malignant hyperthermia susceptible subjects.

Ten malignant hyperthermia susceptible (MHS) subjects were investigated, all of them positive in in vitro tests. As a control group 12 healthy subjects were investigated. The investigation was done in a blind fashion during strictly standardized conditions. Electromechanical delay of contraction and half contraction time to tetanus were faster (P less than 0.05) while half relaxation time was shorter in the MHS subjects (P less than 0.05). Skin and intramuscular temperature were significantly higher in the MHS subjects (P less than 0.05). This indicates that MHS subjects differ in various skeletal muscle characteristics during "normal" conditions. Further studies to define the temperature level at which the test of muscle function is most discriminating are needed before it can be used for diagnostic purposes.