A novel clinical test of respiratory muscle endurance.
Impaired respiratory muscle endurance (RME) could reduce exercise tolerance and contribute to ventilatory failure. The aim of the present study was to develop a clinically-feasible method to measure RME using negative-pressure inspiratory-threshold loading. It was hypothesized that endurance time (tlim) could be predicted by normalizing oesophageal pressure-time product (PTP) per total breath cycle (PTPoes) for maximum oesophageal pressure (Poes,max); the load/capacity ratio. The corresponding mouth pressures, PTPmouth and Pmouth,max were also measured. The RME test was performed on 30 healthy subjects exposed to the same target pressure (70% of Poes,max). Eight patients with systemic sclerosis/interstitial lung disease were studied to assess the validity and acceptability of the technique. Normal subjects showed a wide intersubject variation in tlim (coefficient of variation, 69%), with a linear relationship demonstrated between log tlim and PTPoes/Poes,max (r=0.88). All patients with systemic sclerosis/interstitial lung disease had normal respiratory muscle strength, but six out of eight had a reduction in RME. In conclusion, endurance time can be predicted from the load/capacity ratio, over a range of breathing strategies; this relationship allows abnormal respiratory muscle endurance to be detected in patients. Oesophageal and mouth pressure showed a close correlation, thus suggesting that the test could be applied noninvasively.
Hart
N
N
Respiratory Muscle Laboratory, Royal Brompton Hospital, London, UK.
Hawkins
P
P
Hamnegård
C H
CH
Green
M
M
Moxham
J
J
Polkey
M I
MI
D000328:Adult; D000368:Aged; D003187:Compliance; D004947:Esophagus / Q000502:physiology; D005260:Female; D006801:Humans; D007320:Inspiratory Capacity; D017563:Lung Diseases, Interstitial / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance; D011312:Pressure; D015203:Reproducibility of Results; D012119:Respiration; D012132:Respiratory Muscles / Q000502:physiology* / Q000503:physiopathology