Anatomical lung shunting in pulmonary fibrosis.

Abstract

Eleven patients with cryptogenic fibrosing alveolitis were evaluated for the presence of pulmonary shunting by injection of radiolabelled particles of macroaggregated albumin larger than lO 4um in diameter and by body scanning with a gamma camera. The mean shunt of 9% (SD 2%) in the patients was not significantly different from the mean shunt of 7% (2%) measured in 10 normal controls. These findings suggest that shunting is not an important part of the gas exchange abnormalities noted in such patients.Arteriovenous channels larger than normal pulmonary capillaries have been found in the lung in patients with hepatic cirrhosis and with chronic obstructive lung disease.'`3 This abnormal vasculature has been evaluated by quantitative radionuclide techniques. These enlarged vessels are believed to play a part in the genesis of hypoxaemia in these disorders. In cirrhosis a constellation of disturbances may occur, including decreased lung diffusing capacity, aggravation of hypoxaemia by exercise, and an apparent shunt like mechanism.4 The findings are similar in chronic obstructive lung disease, and the magnitude of the radionuclide shunt is correlated with the decrement in diffusing capacity.3 In chronic obstructive lung disease aggravation of hypoxaemia by exercise is correlated with loss of diffusing capacity.5 Decreased diffusing capacity and aggravation of hypoxaemia with exercise are also characteristic of pulmonary fibrosis,6 and these findings are themselves correlated in pulmonary fibrosis.7 A common underlying mechanism in the form of enlarged alveolar vessels might be present in all these disorders. We have studied patients with pulmonary fibrosis for evidence of the presence of abnormal pulmonary vasculature. MethodsMacroaggregated albumin particles tagged with 3mCi of technetium 99m were injected intravenously with the patient in the supine position. The radioactivity distributed to the brain, kidneys, and lungs was measured with a gamma camera. Acquisition of counts was begun dorsally 10 minutes after injection with Address for reprint requests: Dr Warren C Miller, Humana Pulmonary Center, 500 Medical Center Boulevard, Webster, Texas 77598, USA. Accepted 23 July 1985 sequential two minute intervals each for lungs, kidneys and brain, so that counting was completed 16 minutes after injection. The particles were measured by light microscopy, with an eye piece micrometer; the longest diameter was noted. Particles were found to be 1 1-60 gm in diameter with a typical size distribution of: 11-20 gm 54%; 21-30gm 26%; 31-40 gm 16% (they were rarely greater than 40 pm). Any particles traversing the lungs to the systemic circulation would necessarily pass through vessels larger than 10pm. The amount of radioactivity in the distribution of the systemic circulation was calculated on the assumption that at rest 32% of the cardiac output goes to brain and kidneys.8 The fractional amount of blood shunted is therefore the radioactivity in the systemic circulation divided by the sum of that radioactivity and tha...

Single Cell Transcriptomics of Fibrotic Lungs Unveils Aging-associated Alterations in Endothelial and Epithelial Cell Regeneration

“…Inflammatory and hypoxic stimuli originating from the fibrotic intima may have stimulated angiogenic sprouting of ACKR1 + venous ECs from the outer arterial layer into the media. Vascular malformations involving arteries and veins, such as arteriovenous shunts, have been previously described in IPF lungs (79, 80), however, the endothelial origin and the mechanisms implicated in these vascular aberrations have remained largely unexplored. Altogether, our findings demonstrated that vascular endothelial turnover is compromised in IPF lungs favoring the expansion of venous ECs while restricting that of alveolar capillaries.…”

Mortality prediction in idiopathic pulmonary fibrosis: evaluation of computer-based CT analysis with conventional severity measures

“…A third possible mechanism relates to pleuroparenchymal and/or bronchial-pulmonary artery anastomoses described histopathologically in patients with fibrosing lung disease [30]. While the clinical importance of shunting within the lungs is yet to be established [31], the development of shunts could theoretically increase the PVV as fibrosis progresses.…”

Pulmonary vessel volume can help to differentiate fibrotic lung diseases

“…Jacob et al [10] postulated that increased PVV in IPF patients can be related to the following reasons : i) Diversion of the blood flow from fibrotic areas to relatively spared lung regions, resulting in dilation of vessels and therefore an increased PVV, ii) Increased negative pressure during inspiration, due to increased lung stiffness in IPF patients, that result in the dilation effect on blood vessels, iii) Increased pleuro-parenchymal and bronchial-pulmonary arterial anastomosis that was previously described in histological lung specimens of IPF patients [23,24].…”