High Frequency Percussive Ventilation for Chest Wall Motion Immobilization

Abstract

High frequency percussive ventilation (HFPV) employs high frequency (100 to 400 bursts/min) low tidal volumes to provide respiration in awake patients while simultaneously eliminating respiratory motion. In this study, we evaluate each HFPV interface device for compliance, ease of use, comfort, geometric interference, minimal chest wall motion and prolonged percussive time. We recruited 15 healthy volunteers (age 30y-75y) and investigated three types of interfaces on an IRB approved study. The first interface was a soft plastic mouthpiece. The second interface was a silicon oral only mask with headgear straps for pressure adjustments. The third interface was a full-face mask that used gel pad with a silicon flap and CapStrap headgear for comfort. Rubber nose clips were utilized for all interfaces. The volunteers were evaluated supine on a flat treatment bed with their arms above their head. Their chest wall motion was monitored using an external respiratory motion laser system. The percussive ventilations were delivered via an air driven pneumatic system. All volunteers were monitored for PO2 and tc-CO2 with a pulse oximeter and CO2 system. After each interface device, the volunteers completed a questionnaire to provide their feedback on comfort, pain, dyspnea, anxiety etc. on a subjective rating scale ranging from one to five. The external respiratory motion signal was analyzed for length of percussive time, Duty Cycle (DC) (for 2mm and 5mm threshold band) and ripple magnitude (peak to peak) for both normal and percussive breathing. A total of N=62 percussive sessions were analyzed from the external respiratory motion laser system. Although all volunteers experienced a base-line drift in amplitude, the mean breath hold was 199.37sec (med: 115.50sec, range: 9.00sec to 16.83min). DC ranged from 14.00-100.00% (med: 52.09%, mean: 55.67%) for 2mm threshold band and 31.85-100.00% (med: 93.03%, mean: 87.24%) for 5mm. A temporal local chest wall ripple magnitude reduction was observed from mean 9.37mm (N=27, med: 9.71mm, range: 2.70-18.60mm) in normal breathing to mean 2.55mm (med: 2.29mm, range: 0.60- 6.51mm) in percussive. Most volunteers indicated that the third interface provided additional comfort and less dyspnea (mean subjective score: 4.03) compare to the other two interfaces (mean subjective score: 3.63 and 3.66 for first and second interface respectively); they were in percussive state longer with the second interface. Volunteers had an increase in percussive time by 66.61%, 63.16% and 5.65% from the total mean when using second interface vs. third and first respectively. During this study, we were able to conclude that the second interface can prolong the percussive sessions when compared to the other two. Chest-wall motion was well tolerated and drastically reduced using HFPV in each volunteer evaluated. As a result, we believe HFPV may provide thoracic immobilization during radiotherapy, particularly in the SBRT and scanning pencil beam Proton therapy setting.