A ventilator generating a positive or negative internal compliance

This paper describes technical details of a ventilator for altering the resistive and elastic load placed on respiratory muscles during spontaneous breathing in intubated infants. Positive or negative values for ventilator resistance and/or ventilator compliance can be chosen by superimposing the weighted sum of the flow and/or the volume signal over the input to a pressure controller within the pressure feedback control system of the ventilator. The aim of the study was to compare values of the ventilator's compliance (Cv), as measured with a ventilation mechanics calculator, with those Cv values set by the ventilator's Cv control knob on the front panel. Another aim was to compare measured values of total compliance of a combined ventilator-lung model system (Ct) with the values expected according to theory where 1/Ct = 1/Cv + 1/C1m (Eq. alpha; C1m is the lung model's compliance). The Cv values set on the front panel were nearly identical to those measured (Cvm = 0.97 * Cvs + 0.54) over the whole tested range from -20 to +20 ml/kPa. Similarly, the measured Ct values were almost equal to those expected according to Eq. alpha; the standard deviation of the relative residuals was 2.7% for elastic loading and 12.4% for elastic unloading. We conclude that the ventilator described in this study can effectively provide both elastic loading and elastic unloading of spontaneous breathing, as expected according to theory.