Assessment of respiratory muscle strength with two different methods in individuals with Mucopolysacchariosis type VI: a pilot study

Background: Mucopolysaccharidosis type VI (MPS VI) is a rare progressive disease presenting pulmonary function impairment. Maximum Inspiratory Pressure (PImax) is useful to detect respiratory muscle weakness and can be measured through different devices by volitional (depending on cooperation) or non-volitional (independent of cooperation by Mueller maneuver) methods. However, it is unknown if these methods have agreement in individuals with MPS VI. Aim: To evaluate the concordance between volitive and non-volitive tests in patients with MPS VI. Method: PImax was measured by POWERbreathe® inspiratory muscle trainer (volitive) and digital manuvacuometer (non-volitive) in seven patients with MPS VI with 18±15.8 years old (71.4% male). The both methods were measured three times and the highest values were analyzed. To assess the agreement between the PImax POWERbreathe® and PImax digital manuvacuometer, we used Bland-Altman plot for multiple measurements per subject. Results: the pool of 21 measurements analized by Bland-Altman scatter plot between volitive and non-volitive PImax presented agreement with bias= -1.1 and limits of agreement -25.7.8 to 27.8 cmH2O (CI=95%) (Figure1). Conclusion: The volitive PImax test using POWERbreathe® device could be used as a surrogative assessment of inspiratory muscle strength in individuals with Mucopolysaccharidosis VI. Figure1. Bland-Altman scatter plot for analysis of agreement between PImax POWERbreathe® and PImax mano. Pacient box: three measurements per pacient; Solid line: mean (bias) and dashed line; limits of agreement. Pimax: maximum inspiratory pressure. Mano: manovacuemeter digital.