P1.226 Wednesday, Jan. 4 Collapse patterns of insect tracheal tubes under pressure PENDAR, H.*; BERINGER, D.; SOCHA, J.J.; Virginia Tech; Virginia Tech; Virginia Tech email@example.com
Rhythmic tracheal compression is a form of active ventilation known to occur in the respiratory system of some insects. During compression, segments of the tracheal system collapse and reinflate on the time scale of seconds. In-vivo x-ray imaging has demonstrated that tracheal compression occurs by the formation of local dimples, but the biomechanical mechanism of tube collapse is not known. One hypothesis suggests that an increase in hydrostatic pressure of the surrounding hemolymph induces tube collapse by buckling. To investigate the collapse properties of tracheae in the American cockroach (Periplaneta americana), sections of large (diameter, ~500μm) tracheal tube were excised and tested ex-vivo in a custom-made pressure chamber. Each tracheal section was sealed at one end and connected to ambient air via a microtube at the other end, and then was compressed by increasing the pressure in the surrounding fluid. Video and pressure data were recorded simultaneously and analyzed to characterize collapse patterns. In a typical trial, the tracheal tube remained fully inflated during the initial pressure ramp, but when a threshold pressure was reached (range, 0.15—0.55 kPa), instantaneous buckling occurred. The observed range of collapse pressures is congruent with the magnitude of in-vivo pressure pulsations previously measured in the hemolymph of a carabid beetle, suggesting that changes in pressure may play a prominent role in tube collapse in insects.