The effect of varying inspiratory flow waveforms on peak and mean airway pressures with a time-cycled volume ventilator: A bench study

We examined the effect of seven inspiratory flow waveforms on peak (PAP) and mean (MAP) airway pressures using a lung model. METHODS: The Hamilton Veolar ventilator was operated in assist-control mode with standardized settings. PAP and MAP were measured for each inspiratory flow waveform under three simulated lung conditions: (1) a baseline of low 'airway' resistance (R(aw)) and high compliance, (2) low compliance, and (3) increased airway resistance. RESULTS: With the baseline and low-compliance conditions, the inspiratory flow waveform resulted in PAP from 21.4 to 31.4 and 49.5 to 57.1 cm H₂O [2.1-3.08 and 4.85-5.6 kPa], respectively. PAP was lowest with the full decelerating waveform and increased in this order: modified-sine, sine, partial-decelerating, square, partial-accelerating, and full-accelerating waveforms. MAP was inversely related to PAP (r = -0.94, p = 0.0014 for baseline and r = -0.884, p = 0.0083 for low compliance). With increased R(aw), PAP increased from 33.5 to 67.8 cm H₂O [3.29-6.65 kPa]. R(aw) was lowest with the partial-decelerating waveform and increased in this order: square, modified-sine, partial-accelerating, sine, full-decelerating, full-accelerating waveforms. MAP was not related to PAP (r = -0.083, p = 0.8602). CONCLUSION: Under all three test-lung conditions, a form of decelerating flow produced the lowest PAP and the highest MAP; whereas, the full-accelerating waveform produced the highest PAP and the lowest MAP. Under the baseline and low-compliance conditions, as PAP increased MAP decreased. With elevated R(aw), PAP is a function of the peak flow value more than of the pattern of flow. Knowledge of the effects of inspiratory flow waveform on PAP and MAP may aid clinicians in selecting an appropriate flow pattern for a given condition.