Evaluation of inspiratory muscle function in a healthy austrian population--practical aspects

There is no clear evidence whether inspiratory muscle strength (Pi(max)) is closely linked to inspiratory muscle endurance (T(lim)). Moreover, normal values of T(lim), measured by flow-resistive loads, have not been established.

We tried to find answers to the following questions: Is it possible to establish normative values of T(lim) when using flow-dependent, resistive loads? Are Pi(max) and Borg scale values predictors of T(lim)? Are anthropometric and spirometric data closely related to T(lim)? Is it really necessary to measure T(lim) in addition to Pi(max) when evaluating inspiratory muscle function?

Sixty-eight healthy Austrian volunteers between 17 and 75 years of age and with a sedentary lifestyle participated in our study. Pi(max) was defined as the maximal inspiratory mouth pressure, measured with a differential pressure transducer. T(lim) was determined as the time span until exhaustion, while breathing against a resistive loading device.

Pi(max) values showed a low intra- and high interindividual variability for both sexes and were significantly age, weight and height dependent. For male subjects, Pi(max) was also significantly related to spirometric parameters. T(lim) values showed a very high interindividual variability, but a low intraindividual variability. Interestingly, no correlation was found between T(lim) and Pi(max), nor lung function parameters and age.

The results indicate that both Pi(max) and T(lim) have to be determined when inspiratory muscle function is measured. Normal values for T(lim), evaluated by flow-resistive loads, cannot be satisfactorily established due to the high interindividual variability.