Introduction: IPF causes lung restriction and impaired gas diffusion but these measures may be discordant. Understanding of discordant physiology and the implications for interpretation of physiology and clinical management are limited. 

Aims: To compare groups of IPF patients with discordant lung function. 

Methods: IPF patients with discordant FVC and KCO values were allocated into 2 groups: Volume Impaired, VI (FVC:KCO ?1.3) and Diffusion Impaired, DI (FVC:KCO ?4). Visual assessment of HRCT provided quantification of honeycombing and reticulation/ground glass change¹, presence of emphysema and pulmonary hypertension (diameter main pulmonary artery (PA) and PA/aorta(A) ratio²). Comparison was by independent t-test.  

Results: Data are shown in Table 1 and illustrated via Box plot (Figure 1). Mortality was greater in those with emphysema, p=0.024.

Conclusions: Significant physiological differences can be seen in patients with comparable TLCO and extent of fibrosis.  Coexisting emphysema rather than pulmonary hypertension may account for DI phenotype.

¹Sverzellati et al. doi:10.10007/s11547-007-0213-x

²Konstantinides et al. doi:10.1093/eurheartj/ehz405