New impedance spectrometer for scientific and clinical studies of the respiratory system

Abstract

The simple techniques generally used to investigate the biomechanical properties associated with the respiratory process are able to identify only basic characteristics, just supplying an initial representation of the complex behavior of the respiratory system. A much more detailed description can be obtained by the forced oscillation technique (FOT). Requiring very little cooperation of the subject, this technique allows a noninvasive evaluation of the mechanical impedance of the respiratory system. Although the FOT has a great scientific and clinical potential, this is attended by technical difficulties and has yet to be put to widespread use. In this context, this work describes a new flexible, open architecture, virtual-instrument-based impedance spectrometer for the FOT. After the design details are described, the system accuracy is evaluated investigating mechanical models simulating normal and individuals with restrictive disease. This analysis revealed errors smaller than 4% in modulus and 7° in phase. Experimental results obtained in a normal and an asthmatic subject, presented as examples, revealed mean resistance in asthmatic (5.72 cm H2O/l/s) higher than in normal (2.47 cm H2O/l/s). The mean-reactance curve revealed higher resonance frequency in the asthmatic subject (∼29 Hz) than in the normal one (∼9 Hz). A higher influence of the upper airways impedance of the asthmatic individual was also observed. These results are in close agreement with physiological fundamentals, supplying substantial evidence that this instrument can contribute to the production of more detailed biophysical respiratory descriptions and composes an improved basis for the fast and easy implementation of complex medical research projects.