Objective: Chest wall vibrations are commonly used techniques that remain largely unquantified. In order to understand their effects, it is essential to measure the forces applied and their repeatability over time. This study investigated the repeatability of vibrations within and between test occasions.
Design: Test-retest repeatability study.
Participants: Eight physiotherapists applied vibrations to two healthy female adults.
Intervention: Physiotherapists performed seven vibrations on each subject, and measurements were repeated after 24 hours and 6 months.
Outcome measures: A force-sensing mat placed over the subject's chest measured the amplitude, duration and force profile of each physiotherapist's vibrations.
Results: There were no significant differences in maximum force, duration, frequency of oscillation or amplitude of oscillation within each set of seven chest wall vibrations, confirmed by repeated measures analysis of variance (P=0.42). However, there were wide variations in vibrations between different physiotherapists. Maximum forces ranged from 71 to 258 N, with frequency and amplitude of oscillation ranging from 3 to 11 Hz and 2 to 66 N, respectively. Duration of vibration ranged from 2 to 5 seconds. While there was no systematic bias in forces applied between test occasions, limits of agreement were wide following an interval of 24 hours (-34 to 58 N) and wider still after 6 months (-84 to 76 N).
Conclusion: Physiotherapists exhibit fine control of techniques, delivering vibrations uniformly within single test occasions. However, the variation between therapists and test occasions precludes accurate prediction of applied forces when treating stable patients on consecutive occasions. Furthermore, this study raises important questions about factors influencing the pattern and magnitude of forces applied, and the clinical and physiological effects of such variations.