Measurement of lung mechanics and FVC
Measurement of lung mechanics and FVC was performed with a
computer-controlled small-animal ventilator connected to a negative
pressure reservoir (FlexiVent; SCIREQ, Montreal, Canada), as previously
described (K. Tanaka, Azuma, Miyazaki, Sato, & Mizushima, 2012). Mice
were anaesthetised with three types of mixed anesthetic agents (0.75
mg/kg medetomidine, 4.0 mg/kg midazolam, and 5.0 mg/kg butorphanol), a
tracheotomy was performed, and an 8 mm-long section of metallic tube
(outer and inner diameters of 1.27 mm and 0.84 mm, respectively) was
inserted into the trachea. Mice were mechanically ventilated at a rate
of 150 breaths/min, using a tidal volume of 8.7 ml/kg and a positive
end-expiratory pressure of 2–3 cmH2O.
Total respiratory system elastance and tissue elastance were measured by
snap shot and forced oscillation techniques, respectively. For
determination of FVC, lungs were inflated to 30 cmH2O
over one second and held at this pressure. After 0.2 sec, the pinch
valve (connected to the ventilator) was closed, and after 0.3 sec, the
shutter valve (connected to the negative pressure reservoir) was opened,
exposing the lung to the negative pressure, which was held for 1.5 sec
to ensure complete expiration. All data were analysed using FlexiVent
software (version 5.3; SCIREQ, Montreal, Canada).