Normal range for transdiaphragmatic pressures during sniffs with catheter mounted transducers.

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Abstract
BACKGROUND--Transdiaphragmatic pressure (sniff PDI) during maximal sniffs is a useful clinical test of inspiratory muscle function. Although a normal range has been established for sniff PDI using air filled balloons, no comparable data are available for catheter mounted pressure transducers. METHODS--Using a single catheter with two pressure transducers 15 cm apart, oesophageal and gastric pressures were recorded in 50 normal volunteers (25 women), five of each sex from each decade between the third and seventh decades of life. Each subject performed 10 maximal sniffs at functional residual capacity. RESULTS--Mean (SD) sniff PDI was 149 (32) cm H2O in men and 127 (22) cm H2O in women. The lower limits of normal for sniff PDI (mean -1.96 x SD) after logarithmic transformation of the data were 95 and 78 cm H2O in men and women respectively. CONCLUSIONS--With this technique transdiaphragmatic pressure can be measured using a single catheter which can easily be cleaned and reused. The values for sniff PDI are similar to those recorded previously with air filled balloons, suggesting that the method of recording pressure does not significantly affect the values obtained.