# Diffusing capacity of the lung for carbon monoxide, transfer coefficient of the lung for carbon monoxide and forced vital capacity/diffusing capacity of the lung for carbon monoxide in suspected systemic sclerosis-associated pulmonary hypertension: insights from the ASPIRE registry

## TL;DR

The study finds that DLCO is as effective as other gas transfer measures in predicting pulmonary hypertension in systemic sclerosis patients, with changes in prediction equations affecting results.

## Contribution

The study evaluates the impact of transitioning to GLI-predicted values on gas transfer parameters in systemic sclerosis-associated pulmonary hypertension.

## Key findings

- DLCO% showed the strongest correlation with pulmonary arterial pressure compared to KCO% and FVC%/DLCO%.
- Transitioning to GLI equations resulted in lower predicted spirometric volumes and higher DLCO% values.
- DLCO is non-inferior to other measures in predicting PH presence in systemic sclerosis patients.

## Abstract

There are limited data comparing parameters reflecting gas transfer used to assess the likelihood of pulmonary hypertension (PH) in patients with systemic sclerosis (SSc) and regarding the impact of transitioning to Global Lung Initiative (GLI)-predicted values.

632 patients with suspected SSc-associated PH were identified from the ASPIRE registry. Spirometry and computed tomography reports were reviewed to identify significant lung disease. Receiver operating characteristic curve analysis and correlations of the three markers of gas transfer with pulmonary arterial pressure were performed.

Correlations of GLI-derived values with mean pulmonary arterial pressure were diffusing capacity of the lung for carbon monoxide (DLCO)% r= −0.45, transfer coefficient of the lung for carbon monoxide (KCO)% r= −0.42 and forced vital capacity (FVC)%/DLCO% r=0.37. Correlations in patients without lung disease were DLCO% r= −0.51, KCO% r= −0.44, FVC%/DLCO% r=0.38, compared with patients with lung disease: DLCO% r= −0.41, KCO% r= −0.39, FVC%/DLCO% r=0.39. Area under the curve for the presence of PH in the overall study cohort was significantly superior for DLCO% at 0.84 (optimal threshold 53%), compared with KCO% 0.74 (60%) and FVC%/DLCO% was 0.74 (1.91), p<0.001 for both. Compared with European Coal and Steel Community-derived data, GLI-derived % predicted lung volumes were lower, DLCO% and KCO% were higher and consequently FVC%/DLCO% lower (p<0.001, all).

DLCO performed as least as strongly as KCO or FVC%/ DLCO% in terms of correlations with mean pulmonary arterial pressure and diagnostic utility, regardless of the presence or absence of lung disease. Transitioning to GLI equations led to lower predicted spirometric volumes and higher DLCO%. This should be considered when interpreting changes in values over time and when using screening algorithms.

DLCO is non-inferior to other measures of gas transfer in predicting the presence of PH in patients with systemic sclerosis. Changing from ECSC to GLI prediction equations results in lower FVC%/DLCO%: this should be considered when using prediction tools.
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