Passive mechanical properties of rat diaphragms: a new method for analyzing mechanical tissue properties

Introduction

During controlled mechanical ventilation the diaphragm's passive mechanical characteristics contribute to the respiratory system's impedance, reflecting predominantly a part of thorax compliance. We focus here on the passive mechanical properties of the diaphragm. We hypothesize that changes in diaphragm compliance can be quantitatively assessed with our new bioreactor setup [1].

Methods

Isolated diaphragms of wildtype rats were placed inside the bioreactor on an elastic membrane building the deformable wall of a pressure chamber of 5.5 ml volume. By increasing the pressure inside the chamber, the membrane and the diaphragms were deflected following the shape of a spherical cap. By analysis of the pressure–volume relationship inside the pressure chamber we calculated the mechanical properties (that is, compliance of the passive diaphragms) at certain points in time.

Results

Two diaphragms were investigated for 24 hours after explantation. Courses of compliance over time of the cultivated diaphragms showed characteristic courses reflecting relaxation, onset and end of rigor mortis and breakup of tissue structure (Figure 1).

Figure 1

Conclusion

We attribute the increase in compliance to time-dependent changes of mechanical tissue properties of the diaphragms after explantation. We conclude that our method allows investigation of changes in mechanical characteristics of biological tissue during application of strain. In combination with histological and molecular–biological examinations, our method could give new insights into processing of mechanically evoked development of inflammation, apoptosis, necrosis or physiological reactions (for example, muscle fatigue). To our knowledge, this is the fist setup that allows repeated measurement of mechanical tissue properties at the same sample. We therefore further conclude that with our method the number of animal experiments could be reduced.