Mechanical ventilation
Ventilation necessitated a thoracotomy at the fifth intercostal space
as, in closed-chest rats, excessive contractions of the diaphragm and
intercostal muscles was found to prevent effective respiration. A
positive end-expiratory pressure was exerted and air ventilation
provided at 54 strokes min-1 (3-4.5 ml per stroke)
using a Harvard Bioscience small animal respirator. Rabbits were
ventilated with air at 38 strokes min-1 (13-18 ml per
stroke). A thoracotomy was not necessary in anaesthetized rabbits. Blood
gases were measured using a Corning 158 or 850 pH / blood gas analyser.
Stroke volumes were adjusted for pre-drug PO2>80 mmHg and PCO2 >30 mmHg.