Study objectives: Systemic rheumatic diseases impair the vasculature in lungs. The aim of this study was to visualize vascular impairment and determine its consequence on lung function.
Patients and measurements: Seventy-two patients with rheumatic diseases were evaluated by pulmonary function tests, ventilation-perfusion scintigraphy, and thermography of the hands. The ventilation-perfusion mismatch of the lungs was visualized and quantified by calculating the ventilation-perfusion ratio (V̇/Q̇) at each pixel. The microvascular impairment in fingers was assessed by the temperature difference between the nail fold and the dorsal hand.
Results: Patients with rheumatic diseases exhibited an increased V̇/Q̇ that distributed at the periphery of the lungs. The diffusing capacity of the lung for carbon monoxide (Dlco) decreased (mean [± SD], 76.4 ± 27.4% of predicted) relative to the vital capacity (VC) [mean, 88.4 ± 21.8% of predicted; p < 0.01] regardless of the presence or absence of interstitial lung disease (ILD). The distal-dorsal temperature difference showed colder fingers in patients with Raynaud phenomenon (mean temperature, − 0.6 ± 2.1°C) than in those without it (mean temperature, 0.3 ± 1.5°C) and significantly correlated with the ventilation-perfusion mismatch of the lungs both in patients with ILD (p = 0.04) and in those without ILD (p = 0.02). The ventilation-perfusion mismatch of the lungs significantly correlated with the relative reduction in Dlco evaluated by the percent Dlco/percent VC ratio both in patients with ILD (p < 0.01) and in those without ILD (p = 0.02).
Conclusions: These results suggest that the periphery-distributed microvascular impairment in the lungs leads to ventilation-perfusion mismatch that functionally causes a relative reduction in Dlco in patients with rheumatic diseases. The reduction in Dlco relative to VC represents the vascular impairment in the lungs both in patients with ILD and in those without.