Abstract
Background:
Electrical impedance tomography (EIT) noninvasively monitors the degree and distribution of ventilation. We examined the effects of 2 ventilators (Respironics V-60 (D1) and Dräger V-500 (D2)) at various pressure levels. We hypothesized that tidal distribution of ventilation (TID) and end-expiratory lung impedance (EELI) will not differ when NIV is applied via different devices. Also, with increasing pressures, the lung volume distribution will shift from ventral to dorsal regions.
Methods:
After IRB approval was obtained 20 healthy volunteers were studied. A Dräger Pulmovista EIT device was used. The thoracic electrode belt was placed at the 5th ICS level; subjects were placed in semi-fowlers. After a short stabilization period, an oro-nasal mask was applied. At each pressure setting a 5-minute period of analysis (3-minute stabilization; 2 minutes of analysis) was performed. The mask was removed to allow the subject to return to baseline between devices. The main measures were the global and regional (ventral, dorsal) TID and the global and regional EELI. TID values represent the percent of ventilation in that area. EELI baseline is assumed to be 0 and other measures represent a percent change relative to baseline. Repeated measure ANOVA was used to compare groups.
Results:
Global TID for D1 vs D2 at baseline: 100 + 0 vs 100 + 0, CPAP5: 102 + 16 vs 109 + 22, PS 5/CPAP5: 132 + 40 vs 118 + 33, PS5/CPAP 10: 129 + 47 vs 126 + 46. Ventral TID for D1 vs D2 baseline: 43 + 14 vs 43 + 13, CPAP5 43 + 13 vs 48 + 21, PS5/CPAP5: 62 + 22 vs 57 + 26, PS5/CPAP10: 67 + 33 vs 60 + 25. Dorsal TID for D1 vs D2 baseline: 57 + 14 vs 57 + 12, CPAP5: 59.0 + 19 vs 61 + 18, PS5/CPAP5: 69 + 31 vs 62 + 22, PS5/CPAP10: 71 + 40 vs 67 + 33. Global EELI for D1 vs D2 baseline: 0 + 0 vs 0 + 0, CPAP5: 47 + 28 vs 71 + 69, PS5/CPAP5: 54 + 33 vs 61 + 54, PS5/CPAP10: 135 + 63 vs 141 + 101. Regional TID device data was combined for ventral vs dorsal at baseline: 43 + 13 vs 57 + 13, CPAP5: 45 + 16 vs 60 + 17, PS5/CPAP5: 60 + 21 vs 65 + 23, PS5/CPAP10: 58 + 17 vs 69 + 33. Regional EELI device data was combined for ventral vs dorsal at baseline: 0 + 0 vs 0 + 0, CPAP5: 42 + 28 vs 17 + 18, PS5/CPAP5: 42 + 25 vs 15 + 16, PS5/CPAP10: 97 + 53 vs 41 + 31.
Conclusions:
When using EIT to monitor lung volume distribution there was no statistical difference between devices. As pressure increased, the lung volume distribution did not shift from ventral to dorsal but rather increased in both areas to a similar degree.
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