Reliable lip force measurement in healthy controls and in patients with stroke: a methodologic study.

ABSTRACT

A prefabricated oral screen has shown promising results as a muscle self-training device to improve the lip function of stroke patients affected by oropharyngeal dysphagia. However, a technique for the measurement of lip muscle force, whether in healthy individuals or in stroke patients, is lacking. The present study was designed to (1) test the intra- and interreliability of lip force measurements by means of a newly devised Lip Force Meter, LF100, (2) determine a normal lower limit for lip force in newtons (N), and (3) ascertain the instrument's sensitivity and specificity. LF100 is a modified strain gauge for recording the ability of lips to withstand pressure from a predentally placed oral screen. Forty-two healthy controls and 22 stroke patients agreed to participate in the trial. The controls and patients were examined three times with the LF100, with 2-min rest intervals, twice by investigator MH and once by investigator MO. Intrainvestigator reliability with the LF100 proved excellent in both controls and patients ICC was 0.83 and 0.90, respectively. Interinvestigator reliability was good or excellent in both groups ICC was 0.71 and 0.91. There was a significant difference in lip force between controls and stroke patients (mean = 24.7 +/- 6.3 N and 9.5 +/- 5.5 N, p < 0.001). The sensitivity of LF100 was 91% and the specificity 95%. The cutoff level for normal lip force was 15 N. The LF100 showed itself to be a suitable and reliable instrument for measuring lip force.