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Open Access Research

Loss of alveolar membrane diffusing capacity and pulmonary capillary blood volume in pulmonary arterial hypertension

Samar Farha1*, Daniel Laskowski12, Deepa George2, Margaret M Park23, WH Wilson Tang3, Raed A Dweik12 and Serpil C Erzurum12

Author Affiliations

1 Respiratory Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH, 44195, USA

2 Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH, 44195, USA

3 Heart and Vascular Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH, 44195, USA

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Respiratory Research 2013, 14:6  doi:10.1186/1465-9921-14-6

Published: 22 January 2013

Abstract

Background

Reduced gas transfer in patients with pulmonary arterial hypertension (PAH) is traditionally attributed to remodeling and progressive loss of pulmonary arterial vasculature that results in decreased capillary blood volume available for gas exchange.

Methods

We tested this hypothesis by determination of lung diffusing capacity (DL) and its components, the alveolar capillary membrane diffusing capacity (Dm) and lung capillary blood volume (Vc) in 28 individuals with PAH in comparison to 41 healthy individuals, and in 19 PAH patients over time. Using single breath simultaneous measure of diffusion of carbon monoxide (DLCO) and nitric oxide (DLNO), DL and Dm were respectively determined, and Vc calculated. Dm and Vc were evaluated over time in relation to standard clinical indicators of disease severity, including brain natriuretic peptide (BNP), 6-minute walk distance (6MWD) and right ventricular systolic pressure (RVSP) by echocardiography.

Results

Both DLCO and DLNO were reduced in PAH as compared to controls and the lower DL in PAH was due to loss of both Dm and Vc (all pā€‰<ā€‰0.01). While DLCO of PAH patients did not change over time, DLNO decreased by 24 ml/min/mmHg/year (pā€‰=ā€‰0.01). Consequently, Dm decreased and Vc tended to increase over time, which led to deterioration of the Dm/Vc ratio, a measure of alveolar-capillary membrane functional efficiency without changes in clinical markers.

Conclusions

The findings indicate that lower than normal gas transfer in PAH is due to loss of both Dm and Vc, but that deterioration of Dm/Vc over time is related to worsening membrane diffusion.

Keywords:
Membrane diffusion; Pulmonary arterial hypertension; Lung capillary blood volume