Novel characteristics of the temporal transition to maximum tongue pressure in Parkinson's disease: A pilot study

Abstract

Introduction: The reason why maximum tongue pressure (MTP) decreases in patients with Parkinson's disease (PD) remains unclear. Repeated measurements of isometric force and MTP may be useful for analyzing muscle wasting and force generation. The purpose of this pilot study was to evaluate the clinical characteristics and temporal transition of MTP in PD and normal control (NC) groups.

Methods: There were 18 participants in this study: 10 with PD and 8 NCs. The MTP was measured 20 times at regular intervals. The area under the curve of MTP temporal transitions, time to reach MTP, and total transition time of the tongue pressure (time to return to baseline) were compared between the groups.

Results: MTP decreased from baseline in PD subjects. Unlike NCs, PD subjects showed diverse and inconsistent temporal transitions. The decrease in MTP and delays in time to reach MTP and time to return to baseline were significantly greater in PD subjects (p < 0.05), while there was no group difference in area under the curve values. According to repeated-measures ANOVA, MTP was not different over time between PD subjects and NCs.

Conclusion: In this study, muscle fatigue did not affect the decrease in MTP seen in PD subjects, or the diversity and inconsistency of the temporal transition in MTP in that group. These findings indicate that the motor control needed for the repeated, identical movements associated with MTP generation may be impaired in PD patients.

Keywords: Bradykinesia; Isometric tongue pressure; Parkinson’s disease; Repeated measurements; Temporal transition.

Fig. 1

Schematic representation of maximum tongue pressure (MTP). The temporal transition of MTP was similar between some normal controls (NCs) and Parkinson’s disease (PD) subjects, while in other PD subjects (PD #1, #2, #3, #4, #5, #6, and #8) it showed multiple peaks and an irregular, inconsistent pattern that was considerably different from that of NCs (A). In contrast, all NCs showed a consistently monophasic and smooth pattern of MTP generation and temporal transition (B). MTPs were mainly distributed between 20 and 40 kPa, with a total transition time of the tongue pressure (TTT) of 1.0–4.0 s, in PD subjects. MTPs were mainly distributed between 30 and 50 kPa, with a TTT of 0.5–1.5 s, in NCs (C). Neither within- nor between-subject effects related to MTPs were statistically significant in either group (D).