Treating Pulmonary Hypertension in Interstitial Lung Disease: Severity, Not Route
Louise's pulmonary hypertension is more severe than her lung disease alone would predict. Whether a pulmonary vasodilator helps her turns on where her resistance sits against a specific trial threshold, not on delivery route.
Louise K., a 71-year-old woman, spent thirty years as a public librarian and has kept an ambitious backyard vegetable garden since retiring — work she has had to hand off in pieces to a granddaughter over the past year as idiopathic pulmonary fibrosis, diagnosed two years ago, has slowly taken more of her breath than her lungs alone can explain. She is on 4 liters of supplemental oxygen at rest, more with exertion, and her most recent pulmonary function tests show an FVC of 58% predicted — a real decline from 68% a year ago, but her breathlessness has outpaced even that drop, and it was that mismatch that prompted a right heart catheterization. The result: mean pulmonary artery pressure 42mmHg, pulmonary vascular resistance 6.8 Wood units — pulmonary hypertension disproportionate to what her FVC alone would predict, and severe enough by current thresholds that the team is now discussing pharmacologic treatment of the pulmonary vasculature itself, not just the fibrosis. Beyond the fibrosis and now the pulmonary hypertension it has produced, her only other chronic condition is well-controlled hypothyroidism on a stable levothyroxine dose.
Two trials are cited whenever this comes up, and both are routinely misremembered. STEP-IPF (Zisman and colleagues, 2010) tested oral sildenafil in advanced IPF with no pulmonary-hypertension entry requirement and missed its primary endpoint. It is often invoked as evidence that systemic vasodilation blunts hypoxic pulmonary vasoconstriction and worsens gas exchange in a fibrotic lung — a real mechanistic concern, but not one STEP-IPF found. The trial measured gas exchange directly and sildenafil improved it: arterial oxygen tension by 3.02mmHg, saturation by 1.21%, diffusing capacity by 1.55 percentage points, alongside less dyspnea. The honest reading of STEP-IPF is that the drug did not improve walk distance, not that it harmed oxygenation. INCREASE (Waxman and colleagues, 2021) is likewise not the severity-selected trial it is described as — it enrolled at a mean pulmonary artery pressure of 25mmHg with resistance of only 3 Wood units, a permissive floor. What makes it apply to Louise is buried one layer down, in its prespecified subgroup analysis: patients entering below 4 Wood units showed no significant walk-distance benefit. At 6.8, she is not merely inside INCREASE's door. She is inside the part of it where the drug actually worked, and that narrower claim is what has to be acted on or declined this afternoon.
Pulmonary hypertension conference, ILD-PH case review
STEP-IPF is the largest randomized trial we have of a PAH-specific vasodilator in this exact underlying disease, and it was negative on its primary endpoint. I'll say plainly what I don't think it showed, because we all repeat this wrong: it did not demonstrate gas-exchange harm. Sildenafil actually improved her equivalents of oxygen tension and diffusing capacity there. My objection is narrower and I think harder to answer — a trial of this drug class in this disease didn't move the thing patients notice, which is how far they can walk. She's on oxygen and antifibrotic therapy. Adding a pulmonary vasodilator to a lung whose problem is mostly parenchymal buys us a hemodynamic number and, on the randomized evidence in IPF, not much else.
Accepted on both counts, and I'd rather we argue from what the trials enrolled than what we remember them proving. STEP-IPF took IPF patients broadly, with no pulmonary-hypertension entry requirement at all — most of that population had nothing like Louise's resistance of 6.8.
But I won't overclaim INCREASE either, because its floor was 3 Wood units, which is barely a threshold. The trial isn't severity-selected the way we all describe it. What it does have is a prespecified subgroup finding that patients below 4 Wood units got no significant walk-distance benefit — and that cuts my way for her specifically while cutting against giving this to the next mild-PH-on-a-fibrosis-workup patient who walks in. Her 6.8 isn't a technicality clearing an entry criterion. It's the difference between the slice of INCREASE where the drug worked and the slice where it didn't.
Then let's stop leaning on the route argument, because it's doing less work than either of you thinks. Inhaled delivery to ventilated regions is a good mechanistic story, but STEP-IPF is the wrong evidence to contrast it against — that trial's oxygenation went the right way. The distinction that actually survives scrutiny is the severity one, and it's the pharmacology I'd stake the decision on: at 6.8 Wood units her limitation has become substantially vascular rather than purely parenchymal, and a vascular problem is the only kind this drug class can address. Start inhaled treprostinil today, check oximetry at initiation and through titration because monitoring costs nothing, and be clear with her that we are treating the vascular component of her breathlessness and not the fibrosis. If her resistance had come back at 3.5, I would be telling her the opposite, and I'd want that on the chart so the next person reading it knows which number decided this.
Agreed: start inhaled treprostinil, with close oximetry monitoring at initiation and through titration.
Not agreed: where the PVR threshold should sit for future ILD-PH patients seen at this conference. The pulmonologist wants a higher bar reserved for cases this severe; the pulmonary hypertension specialist thinks the threshold should be set closer to INCREASE's actual, more permissive entry criteria. Louise's own plan wasn't affected by the disagreement, but the group didn't settle it for the next case.