Objective To quantitatively assess the distribution heterogeneity of lung ventilation/perfusion (V/Q) in patients with chronic thromboembolic pulmonary hypertension (CTEPH) and to evaluate the correlation between distribution heterogeneity parameters and pulmonary artery pressure.

Methods Twenty CTEPH patients, comprising twelve males and eight females (age, 48.75±14.07 years old), who were hospitalized in Fuwai Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College from February 2018 to December 2018, were confirmed to have CTEPH by means of right heart catheterization and pulmonary angiography. Thirteen controls, comprising seven males and six females (age, 54.46±8.56 years old), were also enrolled. Patients and controls underwent V/Q san and low-dose CT, and echocardiography was performed within 1 week to estimate pulmonary artery systolic pressure (PASP). The heterogeneity indexes of lung V/Q distribution include LogSD_V, LogSD_Q, and LogSD_VQR (V and Q and V/Q are the radioactivity count of ventilation and perfusionand, and its ratio). SD is the standard deviation. The abovementioned indexes were obtained by image reconstruction and analysis. Then, on CT images, the lung CT threshold was used to automatically delineate the boundary of the left lung, the right lung, and the whole lung as the volume of interest, and it was replicated on the pulmonary perfusion images to acquire the standardized uptake value (SUV), including peak of SUV (SUV_peak), maximum of SUV (SUV_max), minimum of SUV (SUV_min), mean of SUV (SUV_mean), and standard deviation of SUV (SUV_SD). SUV_SD represents the heterogeneity of perfusion distribution. The comparation of two groups by utilising t-test. Using Pearson correlation to analyse distribution heterogeneity parameters and PASP correlation.

Results The distribution of lung V/Q in the healthy control patients presented a symmetrical unimodal distribution, whereas the distribution curve of lung V/Q in patients with CTEPH presented an asymmetric multi-peak distribution. Compared with the control group, LogSD_V, LogSD_VQR, total pulmonary perfusion SUV_peak, SUV_max, and SUV_SD significantly increased in the CTEPH group. The differences were statistically significant (LogSD_V: 0.56±0.16 vs. 0.31±0.11, t=4.91, P=0.000; LogSD_VQR: 0.61±0.15 vs. 0.40±0.14, t=3.89, P=0.001; SUV_peak: 19.12±7.94 vs. 10.81±4.05, t=3.48, P=0.002; SUV_max: 20.19±8.30 vs. 11.44±4.33, t=3.49, P=0.001; SUV_SD: 3.54±1.44 vs. 2.42±0.91, t=2.50, P=0.018). The differences of LogSD_Q, SUV_mean, and SUV_min were not statistically significant between the two groups. PASP of CTEPH patients was (72.80±0.15) mmHg. The LogSD_VQR was moderately correlated with PASP in patients with CTEPH (R=0.544, P=0.013).

Conclusion The lung V/Q scan can quantitatively assess the distribution heterogeneity and reflect the pulmonary artery pressure status of the patients with CTEPH.