Noninvasive determination of the tension-time index in Duchenne muscular dystrophy.
OBJECTIVE
Noninvasive determination of the tension-time index of the inspiratory muscles (TT MUS) can identify predisposition to respiratory muscle fatigue in neuromuscular disease. We correlated TT MUS with age and extent of need of ventilator use for patients with Duchenne muscular dystrophy.


METHODS
Maximal inspiratory pressure, inspiratory pressure 0.1 sec after the onset of inspiration (P 0.1), and the breathing pattern during spontaneous breathing were measured in 46 subjects with Duchenne muscular dystrophy and in 46 healthy males of the same age. TT MUS (TT MUS = T I/T TOT x P I/MIP) was determined by calculating P I from P 0.1 (P I = 5 x P 0.1 x T I). The data were compared with normal values and related to age and ventilator use.


RESULTS
TT MUS was significantly higher in the entire Duchenne muscular dystrophy group than in controls (0.21 +/- 0.11 vs. 0.06 +/- 0.02, P < 0.001) and increased with age in the patients (P < 0.001). TT MUS was significantly higher in subjects ventilated 8-20 hrs per day than in nocturnal-only users and in patients ventilated >20 hrs per day than in those ventilated 8-20 hrs per day (P < 0.001). TT MUS surpassed 0.23 in 95% of subjects ventilated 8-20 hrs. TT MUS exceeded 0.37 in 95% of individuals ventilated >20 hrs per day, whereas it was less than this value in 95% of patients ventilated 8-20 hrs.


CONCLUSIONS
TT MUS increases significantly with disease progression and is a sensitive indicator of risk of inspiratory muscle fatigue and ventilator use. Longitudinal determination of TT MUS in patients with Duchenne muscular dystrophy may help to justify the extent of need for mechanical ventilation.
Hahn
Andreas
A
Department of Neuropediatrics, University of Giessen, Giessen, Germany.
Duisberg
Barbara
B
Neubauer
Bernd A
BA
Stephani
Ulrich
U
Rideau
Yves
Y
D000293:Adolescent; D016022:Case-Control Studies; D018450:Disease Progression; D005541:Forced Expiratory Volume; D006801:Humans; D001239:Inhalation; D008176:Lung Volume Measurements; D008297:Male; D018763:Muscle Fatigue; D009129:Muscle Tonus; D020388:Muscular Dystrophy, Duchenne / Q000175:diagnosis / Q000503:physiopathology*; D012131:Respiratory Insufficiency; D012720:Severity of Illness Index; D013997:Time Factors; D014797:Vital Capacity