Mechanical impedance of the canine diaphragm. Part 1. Experimental system and measurements.

A technique which does not require the measurement of strain has been developed for the investigation of the incremental dynamic properties of soft tissue sheets. Radially prestressed and circularly clamped canine diaphragm samples were exposed to small-amplitude pseudorandom pressure variations. From the measurement of these pressure variations and the volume flow caused by the vibration of the membrane the incremental mechanical impedance spectrum was computed in the 0.25-5 Hz frequency range at three different levels of initial stress. The diaphragm tissue was found to be basically elastic. However, the small viscous component showed a sharp negative frequency dependence between 0.25 and 2 Hz. The quasistatic elastances of the samples were in good agreement with the elastance values derived from the impedance data. The relationship between the elastance and the initial stress was close to linear. It was concluded that the method is applicable to the study of the incremental dynamic properties of planar soft tissue samples.