Background/Purpose: Pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD) are the leading causes of mortality in systemic sclerosis (SSc).  Many SSc patients have both pulmonary hypertension (PH) and ILD and it can be difficult to distinguish PAH from PH secondary to chronic ILD (PH-ILD).  In addition, it is not known to what degree the extent of ILD or pulmonary physiology impact cardiac hemodynamic parameters of PAH. The purpose of this study was to determine the impact that extent of ILD and degree of pulmonary physiologic restriction have on specific cardiac hemodynamic parameters within a subset of the PHAROS cohort. 

Methods: We identified PHAROS subjects with right-heart catheter-proven PH that had a forced vital capacity (FVC) < 70% predicted or that had ILD reported on computed tomography (CT) scans. Subjects with pulmonary venous hypertension (wedge pressure >15mmHg) were excluded.  Baseline CT scans were scored by the investigator at each site by a standardized system that graded severity of ILD as none (0), mild (1), moderate (2), or severe (3) at 5 specific zones distributed throughout the lungs.  A cumulative score based on summation of the score for all 5 zones was generated from each CT scan and defined as none-mild (sum=0-5), moderate (sum=6-10), or severe (sum=11-15). 

Results: Sixty subjects met the inclusion criteria and had CT scoring performed:  19 had none-mild, 26 had moderate, and 15 had severe ILD.  There were no differences between groups with respect to age (mean 57+/-11) or SSc type (43% diffuse).  None-mild ILD was associated with higher mean pulmonary artery pressures (mPAP) (41.8+/-10.7) than moderate (32.7+/-8.4;p=0.002) and severe ILD (mPAP 34.3+/-8.1;p=0.03) or the combination of moderate and severe ILD (33.3+/-8.2;p=0.001).  None-mild ILD was also associated with higher pulmonary vascular resistance (PVR) (623+/-340) than seen with combined moderate and severe ILD (361+/-227;p=0.001).  There were no differences in mPAP or PVR between moderate and severe ILD or between the combinations of none-mild-moderate ILD compared with severe ILD.  In contrast, when stratified by FVC, no differences in mean PAP or PVR were identified.  FVC was not a reliable predictor of the extent of ILD in this cohort:  29% of those with FVC% less than 70 had none-mild ILD, and in those with FVC% greater than 70, 54% had moderate and 16% had severe ILD. 

Conclusion: Within this PHAROS subset, significant differences in cardiac hemodynamics were associated with varied extent of ILD but not with degree of restriction estimated by FVC.  Furthermore, FVC alone was not a reliable predictor of degree of ILD.   Further studies, incorporating CT extent of ILD along with pulmonary physiology, are needed to help determine ways to distinguish PAH from PH-ILD.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/pulmonary-hypertension-and-interstitial-lung-disease-within-pharos-impact-of-extent-of-fibrosis-and-pulmonary-physiology-on-cardiac-hemodynamic-parameters/