Apparatus for monitoring respiratory muscle activity

Abstract

A respiratory muscle activity monitoring apparatus is provided with a pressure sensor for detecting pressure in an air passage connecting a lung ventilator and the airway system of a patient and a flow rate sensor for detecting flow rate in the air passage. An arithmetic constant detecting unit detects resistance Rrs and elastance Ers of the respiratory system including the airway and thorax beforehand by using detection signals from the pressure sensor and the flow rate sensor while the lung ventilator is supplying air to the patient whose spontaneous breathing is temporarily stopped. Using airway opening pressure Paw detected by the pressure sensor and flow rate dV/dt detected by the flow rate sensor, a developed pressure calculating unit calculates pressure Pmus developed by the respiratory muscles during mechanical ventilation as well as during spontaneous breathing from the expression: Pmus=-Paw+Rrs(dV/dt)+Ers .intg.(dV/dt)dt. An output unit displays and/or records the obtained Pmus together with waveform signal detected by the pressure sensor along a common time axis. Furthermore, by detecting a tidal volume VT from flow rate, work Wmus is calculated as follows: Wmus=-.intg.Paw(dV/dt)dt+.intg.Rrs(dV/dt).sup.2 dt+(1/2)Ers(VT).sup.2