Examining the effects of age, sex, and body mass index on normative median motor nerve excitability measurements.
ABSTRACT The purpose of this study was to build a large reference database of excitability measures in normal subjects and to examine the effects of age, sex, and BMI.
One hundred and five healthy subjects had median motor nerve excitability testing performed at the wrist using the automated threshold-tracking program, QTRAC. Statistical linear regression was used to explore relationships between nerve excitability and the independent variables.
The main effect of age is a reduced superexcitability. Lesser effects are flattening of the normalized stimulus response curve and reduction in threshold change following strong hyperpolarizing currents. Females have lower thresholds than males and small but significant differences in voltage-gated potassium channel (KCNQ) mediated properties (late subexcitability, accommodation half time, and threshold undershoot following depolarizing electrotonus), as well as a small increase in superexcitability. BMI has no influence on nerve excitability data and does not explain sex-related differences in threshold.
Age and sex have few and small effects on excitability parameters.
The expression of nodal KCNQ channels appears to be greater in females. Age-related increases in subexcitability may be attributable to changes in the muscle fibre and not the nerve.
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ABSTRACT: To evaluate the possible effects of sex and age on strength-duration time constant (SDTC). The SDTC of 126 healthy volunteers was measured following stimulation of right median nerve at the wrist. Variations in values were evaluated according to sex and age. The SDTC was 438.6+/-114.5 micros in women and 396.2+/-90.3 in men (P=.023). In men, as age increased, so did SDTC. However, this was not true in women. Comparing the values of women and men, aged below 40, demonstrated a difference in excitability, confined to younger patients. As SDTC depends on the biophysical properties of the axonal membrane and can provide some information about Na(+) channel function, these data raise the possibility of a difference in Na(+) channel function between men and women and a difference in the conductance with age. The age- and sex-related differences shown in this study suggest a possible biochemical or hormonal influence on axonal excitability.Clinical Neurophysiology 10/2006; 117(9):2069-72. · 3.14 Impact Factor