Mechanical properties of the isolated equine trachea

Abstract

In order to study the in vitro mechanical properties of the equine trachea submitted to the compressive pressures observed in vivo, the pressure-volume relationship was determined in intra- and extrathoracic tracheal segments taken post mortem from 29 healthy horses (one to 15 years old; 352 to 651 kg). At the same time, the cross-sectional lumen area (X- sa) at the mid-point of the segment was measured using a slit-lamp transillumination and photographic measurement by endoscopy. The tracheal specific compliance (Cs) as well as the relative changes in x- sa and in the sagittal and transverse diameters, for intraluminal pressures from 5 to − 5 k Pa, were calculated. The extrathoracic tracheal Cs was 0·060 ± 0·002 k Pa −1 and, at an intraluminal pressure of −5 k Pa, x- sa was reduced to about 73 per cent of its resting value. The intrathoracic segments were more compliant and, at similar compressive pressure, their x- sa was more reduced. These data show that the equine tracheal compliance is high and suggest that the increase in pulmonary resistance observed during strenuous exercise may be partly explained by a partial tracheal collapse.