Reliability of labial closure force measurements in normal subjects and patients with CNS disorders

This study determined the reliability of maximal upper and lower lip closing forces measured using a strain-gauged cantilever beam assembly. An intraclass correlation approach was used to explicitly partition the "error free" between-subject variance and measurement error variance across repeated days (2) and across repeated trials (5). Ten healthy adults served as controls and 30 patients with diagnoses of multiple sclerosis, cerebrovascular accident, or Parkinson's disease served as subjects. The intraclass correlation analyses revealed generally high reliability (R greater than .90) for upper and lower lip force measurements, for various combinations of control and/or patient groups, and within each individual patient group. There was moderate correspondence between the quantitative measures of lip force and the clinical assessment of combined upper (r = .67) and lower lip closure force (r = .62) but low correspondence between the quantitative measures of lip force and the presence of motor speech deficit. The lower lip force of patients with Parkinson's disease (M = 3.1 N) on Day 1 was markedly reduced from that of all other patient groups and controls (M = 10.1 N). These results yield helpful information for the design of investigations of oral-motor weakness and for the quantitative assessment of an individual's clinical status.