Figure 1. Animal preparation. The animal's lungs are ventilated by tracheostomy. Transdiaphragmatic pressure is measured with esophageal and abdominal balloon-tipped catheters. Diaphragm is paced with bilateral phrenic nerve stimulation in the chest. Nuclear magnetic resonance (NMR) spectroscopy surface coil is adjacent to right abdominal diaphragm. Left ventricular and aortic catheters are used are used for microsphere injection and withdrawal, respectively. a = artery. (Reproduced with permission from Nichols et al. [7])