Session Item

Breathing motion causes substantial uncertainties in tumor position during radiotherapy. High frequency ventilation with small tidal volumes reduces the amplitude of breathing motion. The aim of this study was to quantify the motion of the right diaphragm dome in conscious healthy volunteers during non-invasive mechanical ventilation without percussion at various high frequency settings, using ultrasound.

Seven volunteers were mechanically ventilated with Positive End Expiratory Pressure (PEEP) at 60 breaths per minute (brpm) using a Hamilton-T1 ventilator, and at 60, 150, 250 and 400 brpm using a TwinStream jet-ventilator. During 40 s recordings, 900 consecutive sagittal images of the diaphragm were acquired using the bk3000 ultrasound system (BK Medical Benelux NV/SA, Mechelen, Belgium) with a convex ultrasound probe at 3.5 MHz and a temporal resolution of 23 frames per second. The same trained operator made all measurements. Measurements were undertaken in two separate sessions. The order of ventilation frequency settings for the TwinStream was randomized. The images from six volunteers of both measurement sessions and at all ventilation frequency settings were adequate and further analyzed semi-automatically in MATLAB (n=12). Excursions were determined based on a time motion image along the direction of movement near the anterior layer of the coronary ligament (Fig.1). From each time motion image, the diaphragm was segmented by thresh holding and the mean diaphragm excursion (peak – trough) for all inflations determined and analyzed with a Wilcoxon signed-rank test (Bonferroni adjusted α=0.05/4).

The mean diaphragm excursion (8mm) at 60 brpm using the TwinStream ventilator showed a significantly larger median excursion (p=0.002) than when using any other ventilation frequency setting (Fig. 2). The smallest diaphragm excursions, with a mean of 1 mm, were found using the TwinStream ventilator at 250 and 400 brpm. At all ventilation frequencies except using the TwinStream ventilator at 60 brpm the mean inter-session variability was <1 mm.