Postural Influence on Ventilation Efficiency and Relationship With Oxygen-Enhanced MRI in Cystic Fibrosis.

BACKGROUND

Pulmonary function tests (PFTs) and medical imaging in cystic fibrosis (CF) occasionally show discrepancies in severity levels, potentially due to different postures during testing (seated PFTs and supine imaging). To assess this, we utilised multiple breath washout with Short extension (MBWShX) and oxygen-enhanced MRI (OE-MRI). MBWShX is a more sensitive PFT and offers novel insights into global ventilation efficiency by incorporating signal from under-ventilated lung units (UVLU). We hypothesised there would be a significant difference in MBWShX parameters between seated and supine postures and aimed to compare the relationship between MBWShX obtained in both posture and OE-MRI.

METHODS

Twenty three CF patients performed two seated and at least 1onesupine MBW, along with same day OE-MRI. MBWShX outcome measures included conventional lung clearance index (LCI2.5), and two novel parameters: LCIShX and UVLU. The primary OE-MRI parameter was the ventilation defect percentage (VDP%).

RESULTS

We demonstrated a significant increase in LCIShX (median difference [IQR]:2.00[0.16; 2.61]; p < 0.01) and UVLU (0.66[0.11; 2.22]; p < 0.05) from seated to supine posture, but no significant change in LCI2.5 (0.27 [-0.21; 0.89]; p = 0.06). Moreover, we showed strong correlation between MBW and VDP% of OE-MRI parameters across postures (ρ > 0.8). However, no differences were detected between seated and supine MBW correlations with OE-MRI (LCI2.5, p = 0.77; LCIShX, p = 0.90; UVLU, p = 0.29).

CONCLUSION

We found significant postural differences in MBWShX parameters, with reduced global ventilation efficiency (increased LCIShX) and increased UVLU in supine posture. However, the relationship between MBW and OE-MRI remained unaffected by posture. In conclusion, supine MBW may offer novel clinical insights but does not enhance sensitivity for comparisons with medical imaging.