Flow dynamics using high-frequency jet ventilation in a model of bronchopleural fistula†   M.J. Wood, E.S. Lin, J.P. Thompson  British Journal of Anaesthesia  Volume 112, Issue 2, Pages 355-366 (February 2014) DOI: 10.1093/bja/aet343 Copyright © 2014 The Author(s) Terms and Conditions

Fig 1 Schematic diagram of experimental set-up. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions

Fig 2 The effect of varying ventilator frequency on displayed and measured volumes in the intact artificial test lung (a) and cadaveric pig lung (b) models with inspiratory time (IT) 40% and driving pressure of 1.5 bar. All data presented as mean (sd). Each experiment repeated six times. Tidal volumes estimated by the jet ventilator, and directly measured entrained and expired volumes all decreased in an exponential manner as respiratory frequency increased in both artificial test lung (a) and cadaveric pig lung (b) models, with similar absolute values in both models. There was a marked difference between the measured expired volume and the tidal volume estimated by the HFJV ventilator over all the frequencies tested. In these intact lung models, there was no gas leak, which enables the injection pulse volume to be calculated (=VTE−ENT). The contribution of entrained volume becomes more important at lower frequencies and accounted for almost 50% of the measured expired tidal volume at frequencies <100 min−1. MACTV, tidal volume displayed by the high-frequency jet ventilator; ENT, measured entrained volume; VTE, measured expired volume; INJ PULSE, calculated injection pulse of HFJV; LEAK, measured leak volumes. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions

Fig 3 The effect of varying ventilator frequency on displayed and measured volumes in the porcine lung model, with a 2 and 10 mm BPF in proximal, middle, and distal positions. Data presented as mean (sd). Each experiment repeated six times. Tidal volumes estimated by the jet ventilator, and directly measured entrained and expired volumes all as respiratory frequency increased. Expired and displayed volumes were similar with a proximal, middle, and distal fistula (a–c). Entrained and leak volumes were relatively low with middle and distal fistulae (b and c), but comprised an increasing proportion of total tidal volume at low frequencies (a), despite expired volumes being similar to those with a middle and distal fistula, throughout the range of frequencies. With a 10 mm proximal fistula, no ventilation occurred and no measurements were possible. With middle and distal fistulae, there was a substantial decrease in expired tidal volume across all frequencies (d and e), with increasing leak volumes at low frequencies and entrained gas contributing an increasing proportion to total expired volume. Expired tidal volumes (VTE) were lower with a middle compared with a distal fistula. Note that the machine-displayed volumes are relatively constant irrespective of fistula size or position, and are much larger than the measured expired volumes, especially with a larger fistula at low frequencies. DP, driving pressure; MACTV, tidal volume displayed by the high-frequency jet ventilator; ENT, measured entrained volume; VTE, measured expired volume; INJ PULSE, calculated injection pulse of HFJV; LEAK, measured leak volumes. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions

Fig 4 The effect of altered driving pressure on 10 mm simulated distal (a–c) and proximal (d–f) fistula in the artificial test lung. Data presented as mean (sd). Each experiment repeated six times. Entrained, leak, and expired volumes all increased with increasing driving pressure in a distal fistula particularly at frequencies <150 min−1 (a–c). At a driving pressure of 2 bar with a distal fistula, expired volumes exceeded 400 ml at a frequency of <75 min−1 (c). With a proximal fistula (d–f), expired volumes increased at lower frequencies but were lower than with a distal fistula at lower frequencies. However, at a driving pressure >1.5 bar, leak volumes increased markedly and the entrained volumes exceeded the expired volumes for at 1.5 and 2.0 bar. Additional data for the middle fistula are available in Supplementary Figure S2. MACTV, tidal volume displayed by the high-frequency jet ventilator; ENT, measured entrained volume; VTE, measured expired volume; INJ PULSE, calculated injection pulse of HFJV; LEAK, measured leak volumes. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions

Fig 5 The effect of varying inspiratory time as a percentage of each cycle (IT %) on delivered and leak volumes in the artificial test lung with a 10 mm distal hole. Data presented as mean (sd). Each experiment repeated six times. There was little effect of alterations in IT on expired volumes at frequencies >200 min−1 with a 10 mm distal fistula (a–c). All volumes were increased at low frequencies with an IT of 40% compared with 20%. When IT was set at 60%, the proportion of entrained volume decreased compared with 20 and 40% IT, and the expired volumes were correspondingly reduced. At frequencies >250 min−1 and a 60% IT, the high airway pressures encountered caused the ventilator shut-off mechanism to halt ventilation and therefore no data were recorded. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions

Fig 6 The effect of varying IT (as a percentage of each cycle) on leak volumes in the artificial test lung at a proximal, middle, and distal sites, with a driving pressure of 1.5 bar. Data presented as mean (sd). Each experiment repeated six times. Changing IT had little effect on leak volumes with a distal fistula, particularly at frequencies >150 min−1 (a). However, leak volumes were highest with a 40% IT at frequencies <120 min−1 compared with 20 and 60% IT. A similar pattern occurred with a middle fistula, but the absolute leak volumes were greater, and increasing IT to 60% produced the highest leak volumes (b). With a proximal fistula (c), higher leak volumes occurred with all IT compared with middle and distal fistulae, but with an IT of 20% or 40%, remained relatively low at frequencies >200 min−1. British Journal of Anaesthesia 2014 112, 355-366DOI: (10.1093/bja/aet343) Copyright © 2014 The Author(s) Terms and Conditions