Meeting Abstract
Insects breathe using a complex network of tracheal tubes, parts of which rhythmically compress in some species, facilitating active ventilation. Previous studies suggest that hemolymph pressures of 1-2 kPa may induce tracheal tube collapse in beetles. However, it is not known if pressure alone induces collapse, or if other physiological processes are at play. Considering the tracheal system as an isolated mechanical system, we ask, do tracheal tubes respond to fluid pressure as thin-walled cylinders? If so, their response can be predicted using an analytical thin-walled cylinder model, which assumes the tubes to be long, thin, and circular, with elastic and isotropic walls. We used atomic force microscopy (AFM) to measure elastic moduli and microtome sectioning to determine thicknesses of tracheal tubes throughout the tracheal system. To determine collapse pressures of tracheal tubes in sacrificed beetles (n =11), we manually increased hemolymph pressures to physiologically-relevant maxima (~2 kPa, in the thorax) while simultaneously recording tube collapse using synchrotron X-ray imaging at Argonne National Laboratory. We found that smaller tubes required greater collapse pressures than larger tubes, with values ranging from 0.3-0.6 kPa. Preliminary AFM results revealed an elastic modulus on the order of ~2 GPa, and sectioning showed that the thicknesses of the tracheae ranged between 4-25 μm for tubes with diameters of 10-200 μm. Using these values, the model predicts an inverse relationship between collapse pressure and diameter, with larger tubes requiring less pressure for collapse, congruent with the values obtained with X-ray imaging. These results support the hypothesis that tracheae collapse in response to hemolymph pressure during rhythmic compression. Supported by NSF 1558052.
