We studied the effects of neostigmine and salbutamol on the force generated by the fatigued diaphragm in anesthetized dogs. Mechanically ventilated animals were prepared with an open thorax. A thin-walled latex balloon was positioned beneath the diaphragm to measure transdiaphragmatic pressure (Pdi) and a rigid cast was fixed around the abdomen to limit changes in diaphragmatic length and geometry during contractions. Pdi was the index of force generated by the diaphragm. We measured Pdi during supramaximal phrenic stimulation at different frequencies and during spontaneous inspiratory effects. The diaphragm was fatigued by repeated phrenic stimulation. Fatigue sifnificantly reduced Pdi at all frequencies of stimulation and during spontaneous contractions (P < 0.05). The reduction in Pdi was associated with a decrease in peak twitch tension (PTT) to 50% of control (P < 0.05). Infusion of neostigmine restored PTT to values equivalent with or greater than control (P < 0.05) and improved Pdi at low stimulation frequencies (P < 0.05) and during spontaneous inspiratory efforts (P < 0.05). Infusion of salbutamol had no effect on PTT, but did significantly shortened twitch half relaxation time (P < 0.05). Salbutamol also had no effect on Pdi during stimulated and spontaneous contractions. We conclude that neostigmine improves force generated by the fatigued diaphragm by increasing twitch amplitude while salbutamol did not have a positive inotropic effect.
- Phrenic nerve
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine