The Roughton-Forster equation for pulmonary diffusion: how it happened

Pulmonary function tests: an integrated approach to interpreting results in the search for treatable traits

INTRODUCTION

Technological advances have led to the proliferation of lung function assessment techniques beyond spirometry in most countries. At the same time, new knowledge of respiratory physiology has allowed an expansion of lung function parameters, requiring an integrated approach to interpreting results.

AREAS COVERED

This review addresses the major pulmonary function tests (PFTs) used in clinical practice, new concepts regarding reference values, and reformulations of terminology for defining standards of lung function impairment. It highlights the complexities and nuances inherent in the interpretation of PFT parameters, particularly in light of recent updates from the European Respiratory Society/American Thoracic Society.

EXPERT OPINION

In a new paradigm, PFTs should be used to classify the pathophysiology of treatable traits rather than to diagnose respiratory disease, given the considerable variation in the clinical patterns of PFTs. It is necessary to look not only at lung mechanics but also at lung volume, gas transfer, and small airway involvement to capture as much information as possible. In this context, it is also important to understand that racial/ethnic differences in lung function are not due to biological differences but may reflect socioeconomic status and represent health disparities.

Adjusting diffusing capacity for anemia in patients undergoing allogeneic HCT: a comparison of two methodologies

BACKGROUND

Diffusing capacity (DLCO) measurements are affected by hemoglobin. Two adjustment equations are used: Cotes (recommended by ATS/ERS) and Dinakara (used in the hematopoietic stem cell transplantation comorbidity index [HCT-CI]). It is unknown how these methods compare, and which is better from a prognostication standpoint.

STUDY DESIGN

This is a retrospective cohort of 1273 adult patients who underwent allogeneic HCT, completed a pre-transplant DLCO and had a concurrent hemoglobin measurement. Non-relapse mortality was measured using competing risk analysis.

RESULTS

Patients had normal spirometry (FEV1 99.7% [IQR: 89.4-109.8%; FVC 100.1% [IQR: 91.0-109.6%] predicted), left ventricular ejection fraction (57.2[6.7]%) and right ventricular systolic pressure (30.1[7.0] mmHg). Cotes-DLCO was 85.6% (IQR: 76.5-95.7%) and Dinakara-DLCO was 103.6% (IQR: 90.7-117.2%) predicted. For anemic patients (Hb<10g/dL), Cotes-DLCO was 84.2% (IQR: 73.9-94.1%) while Dinakara-DLCO 111.0% (97.3-124.7%) predicted. Cotes-DLCO increased HCT-CI score for 323 (25.4%) and decreased for 4 (0.3%) patients. Cotes-DLCO was superior for predicting non-relapse mortality: for both mild (66-80% predicted, HR 1.55 [95%CI: 1.26-1.92, p < 0.001]) and moderate (<65% predicted, HR 2.11 [95%CI: 1.55-2.87, p<0.001]) impairment. In contrast, for Dinakara-DLCO, only mild impairment (HR 1.69 [95%CI 1.26-2.27, p < 0.001]) was associated with lower survival while moderate impairment was not (HR 1.44 [95%CI: 0.64-3.21, p = 0.4]). In multivariable analyses, after adjusting for demographics, hematologic variables, cardiac function and FEV1, Cotes-DLCO was predictive of overall survival at 1-year (OR 0.98 [95%CI: 0.97-1.00], p = 0.01), but Dinakara-DLCO was not (OR 1.00 [95%CI: 0.98-1.00], p = 0.20).

CONCLUSION

The ERS/ATS recommended Cotes method likely underestimates DLCO in patients with anemia, whereas the Dinakara (used in the HCT-CI score) overestimates DLCO. The Cotes method is superior to the Dinakara method score in predicting overall survival and relapse-free survival in patients undergoing allogeneic HCT.