Mechanical insufflation-exsufflation: pressure, volume, and flow relationships and the adequacy of the manufacturer's guidelines.

OBJECTIVE: Pulmonary complications of neuromuscular disease can be averted by increasing peak cough flows with the use of a forced exsufflation device. The purpose of this study was to examine the pressure, volume, and flow relationships for a range of settings generated by this device, and compare them with clinically efficacious values and the manufacturer's guidelines.
METHODS: The In-exsufflator was connected to a standard lung model. The resulting forced deflation volumes, flows, and pressures were averaged over 10 cycles at each setting.
RESULTS: The set insufflation pressures significantly correlated with the generated insufflation pressures and volumes and the exsufflation volumes and flows. Increasing set insufflation time significantly increased generated insufflation pressures, flows, and volumes and exsufflation volumes. Increasing set exsufflation time did not significantly increase generated exsufflation flows. At set pressures of 40 to -40 cm H2O, insufflation time of 3 sec, and exsufflation time of 2 sec, the exsufflation flow was 4.09 l/sec. A plateau insufflation volume of 3.8 l was reached after 4.9 sec of insufflation.
CONCLUSIONS: In-exsufflator performance was very consistent. Its clinical effectiveness can be explained by its generation of exsufflation flows >2.7 l/sec. Increasing insufflation times more than exsufflation times is more important for optimal function. Current manufacturer use guidelines may not yield optimal exsufflation flows.