Pulmonary Perfusion Research Articles

Dual-input tracer kinetic modeling of dynamic contrast-enhanced MRI in thoracic malignancies.

Pulmonary perfusion with dynamic contrast‐enhanced (DCE‐) MRI is typically assessed using a single‐input tracer kinetic model. Preliminary studies based on perfusion CT are indicating that dual‐input perfusion modeling of lung tumors may be clinically valuable as lung tumors have a dual blood supply from the pulmonary and aortic system. This study aimed to investigate the feasibility of fitting dual‐input tracer kinetic models to DCE‐MRI datasets of thoracic malignancies, including malignant pleural mesothelioma (MPM) and nonsmall cell lung cancer (NSCLC), by comparing them to single‐input (pulmonary or systemic arterial input) tracer kinetic models for the voxel‐level analysis within the tumor with respect to goodness‐of‐fit statistics. Fifteen patients (five MPM, ten NSCLC) underwent DCE‐MRI prior to radiotherapy. DCE‐MRI data were analyzed using five different single‐ or dual‐input tracer kinetic models: Tofts‐Kety (TK), extended TK (ETK), two compartment exchange (2CX), adiabatic approximation to the tissue homogeneity (AATH) and distributed parameter (DP) models. The pulmonary blood flow (BF), blood volume (BV), mean transit time (MTT), permeability‐surface area product (PS), fractional interstitial volume (v I), and volume transfer constant (K Trans) were calculated for both single‐ and dual‐input models. The pulmonary arterial flow fraction (γ), pulmonary arterial blood flow (BFPA) and systemic arterial blood flow (BFA) were additionally calculated for only dual‐input models. The competing models were ranked and their Akaike weights were calculated for each voxel according to corrected Akaike information criterion (cAIC). The optimal model was chosen based on the lowest cAIC value. In both types of tumors, all five dual‐input models yielded lower cAIC values than their corresponding single‐input models. The 2CX model was the best‐fitted model and most optimal in describing tracer kinetic behavior to assess microvascular properties in both MPM and NSCLC. The dual‐input 2CX‐model‐derived BFA was the most significant parameter in differentiating adenocarcinoma from squamous cell carcinoma histology for NSCLC patients.

P2742Right ventricular stroke volume during dobutamine stress magnetic resonance compared to lung perfusion and peak oxygen uptake after arterial switch operation for transposition of the great arteries

Abstract Objectives Abnormal pulmonary perfusion due to stenosis of the central pulmonary arteries is common after neonatal arterial switch operation (ASO) for transposition of the great arteries (TGA). We conducted a monocentric prospective study in young adults after neonatal ASO for TGA to evaluate the effects of abnormal pulmonary perfusion on the increase of the right ventricular stroke volume (RVSV) during dobutamine stress magnetic resonance (DSMR) and on cardiopulmonary exercise capacity. Methods 68 unselected patients (age 18–29 years) underwent CMR at rest and under dobutamine stress (10 to 40 μg/kg/min). RVSV, pulmonary blood flow distribution (PBFD) and peak flow velocity were derived from phase contrast mapping in the main, right and left pulmonary artery (PA) at rest and each stress level. A cardiopulmonary exercise test (CPET) was performed at the same day. All patients reached maximal exercise effort according to heart rate and respiratory exchange rate. Results PBFD at rest: 9/68 patients (13%, ASO-S) had abnormal pulmonary perfusion at rest, defined as PBFD >2:1 (right/left or left/right) and/or relevant stenosis of the main PA (Vmax >2.5 m/s). 59/68 patients (87%, ASO-N) had normal pulmonary perfusion. PBFD under DSMR: (1) In the whole patient group, there was no increase of PBFD under stress compared to PBFD at rest. On an individual patient level, no relevant worsening of abnormal PBFD was found. (2) Under low dose dobutamine, ASO-S had a significantly lower RVSV-increase (RVSVstress/RVSVrest) compared to ASO-N (see figure). However, under high dose dobutamine, this effect was no longer significant (see figure). (3) The RVSV-increase under low and high dose dobutamine did not correlate with peak oxygen uptake during CPET, neither in the total group nor in the subgroups (see table). Peak oxygen uptake was not significantly different between ASO-N and ASO-S (p=0,72). RVSV-increase compared to CPET peak VO2% ASO-total ASO-S ASO-N RVSV-increase/peak VO2% RVSV-increase/peak VO2% RVSV-increase/peak VO2% low dose dobu high dose dobu low dose dobu high dose dobu low dose dobu high dose dobu Pearson correlation coefficient −0.02 −0.05 0.01 −0.22 −0.05 −0.04 p-value 0.90 0.71 0.98 0.56 0.71 0.78 Figure 1 Conclusion (1) Patients with relevant stenosis of main PA and/or abnormal peripheral blood flow distribution (ASO-S) exhibit a reduced RVSV-increase under low dose dobutamine compared to patients without stenosis (ASO-N). This effect was not present under high dose dobutamine stress. (2) These findings did not correlate with peak oxygen uptake during CPET, an objective parameter of cardiopulmonary exercise capacity. (3) Therefore, a conservative proceeding rather than surgery or catheter intervention should be considered, especially in asymptomatic adult patients. Acknowledgement/Funding Supported by Kinderherzen, Fördergemeinschaft Deutsche Kinderherzzentren e.V.

P6161The evaluation of the effectiveness of the treatment of patients with chronic thromboembolic pulmonary hypertension using subtraction CT pulmonary angiography

Abstract Introduction Chronic thromboembolic pulmonary hypertension (CTEPH) is a life-threatening delayed complication of acute pulmonary embolism. It is characterized by chronic obstruction of the branches of the pulmonary artery, arteriopathy and vasoconstriction of small vessels, that ultimately leading to right ventricular failure. Subtraction CT pulmonary angiography (CTPA) allows to perform a comprehensive the assessment of the state of the vascular bed and pulmonary perfusion, it is especially important for pathological changes in the distal branches of the pulmonary artery. Analysis of perfusion defects in combination with the standard protocol of CTPA can increase the diagnostic value of the method in examining patients with CTEPH that will select the optimal treatment strategy with the possibility of an objective assessment of its effectiveness. Purpose The aim of this work was to determine the possibilities of the method of subtraction CTPA in the evaluation of the effectiveness of the treatment of patients with CTEPH. Methods and materials Primary and repeated subtraction CTPA was performed 36 patients with the diagnosis of CTEPH (10 patients after surgical treatment, 13 patients after endovascular treatment and 13 patients after initiation of PAH-specific therapy) (figure).All patients were examined on 320-detector row CT scanner using the standard protocol Lung subtraction. Using subtraction CTPA was calculated of CT-scores of obstruction and perfusion defect. The data of primary and repeated CT studies were compared with the clinical and hemodynamic status of patients. CT color-coded iodine images were produced by subtraction of non-contrast from contrast images. Results According to repeated CTPA a decrease of the degree of obstruction was observed in 18 out of 36 (50%) patients: in 10 (100%) patients from the surgical treatment group and 8 (61.5%) patients from the endovascular treatment group. Subtraction CTPA was a good quality for interpreting perfusion maps in 28 of 36 (77.8%) patients.Evaluation of the dynamics of perfusion disorders was not performed in 8 patients: in 3 patients from the surgical treatment group and 5 patients from the endovascular treatment group. Improvement of lung perfusion according to perfusion maps was determined in 18 out of 28 (64.3%) patients: 7 (100%) patients from the surgical treatment group, 5 (62.5%) patients from the endovascular treatment group, and 6 (46.2%) patients from the group of drug treatment. Improvement of clinical and hemodynamic parameters was observed in all patients in the surgical and endovascular treatment groups. There was no statistically significant improvement in clinical and hemodynamic parameters in the drug treatment group. Conclusion The results of the study demonstrated the possibility of using subtraction CTPA for an objective assessment of the effectiveness of the treatment of patients with CTEPH.

P5733IABP use in patients with STEMI complicated by cardiogenic shock: time for rehabilitation?

Abstract Background Evidence from a large randomized clinical trial has led international guidelines to downgrade to Class III the recommendation level for the routine use of intra-aortic balloon pump (IABP) in patients with STEMI complicated by cardiogenic shock (CS). Despite this, its use in clinical practice remains high. Purpose The aim of our study was to evaluate whether IABP use could provide a prognostic benefit in a large real-world population of STEMI patients undergoing primary PCI (pPCI). Methods Our registry included 2958 consecutive patients undergoing primary pPCI for STEMI in our department from 2005 to 2017. The presence of a persistent (>30 min) systolic blood pressure <90 mmHg and signs of pulmonary congestion or impaired end organ perfusion needing catecholamine infusion qualified for CS. Among patients with CS we compared mortality between those with and those without IABP in the whole population and in the pre-specified subgroup with anterior STEMI. Univariate (cross-tables and Kaplan-Meier curves with log-rank test) and multivariate mortality analysis (Cox regressions) were performed. Results CS occurred in 246 patients (8.3%); among these patients, 145 (60%) had anterior AMI. Mortality at 30 days was 3.7 in inferior vs 7.1% in anterior STEMI (p<0.001). In these two groups of patients, IABP was used in 32% and 66.7% of cases, respectively. In the whole CS group, IABP use was associated with a lower 30-day mortality (39% vs 53%, p=0.020 – see figure panel A); this figure was confirmed at multivariable analysis (HR 0.49, 95% CI 0.27–0.87, p=0.016) after adjusting for age, CK peak, triple-vessel disease, eGFR and all-TIMI bleeding during hospital stay. IABP use in CS patients was not associated with major complications or an increased rate of Hb drop (>3 mg/dL) during hospital stay. In the subgroup of patients with anterior STEMI, there was a marked survival benefit at univariate analysis (30-day mortality 41% vs 61%, p=0.013 – see figure panel B), confirmed at multivariable analysis (HR 0.40, 95% CI 0.19–0.88, p=0.023) after adjusting for the same variables of the previous model. In the subgroup of patients with inferior STEMI, IABP use was not significantly associated with a lower 30-day mortality (32% vs 41%, p=0.380). Figure 1 Conclusion In the present large real-world cohort of unselected patients with STEMI, the use of IABP in case of CS was found to improve survival. This finding suggests that IABP could still play a role in patient with STEMI complicated by CS, especially when additional risk features are present, such as anterior MI. We suggest that additional careful prospective studies are needed before abandoning or markedly limiting the use of IABP in this clinical setting.

Hemodynamic management in chronically ventilated infants

Positive pressure ventilation can significantly alter hemodynamics. The reduction in systemic venous return and increase in right ventricular afterload in response to an inappropriately high mean airway pressure can decrease pulmonary blood flow and compromise systemic perfusion as a result. In addition to ventilator parameters, the degree of hemodynamic effects depends on the baseline cardiac function and lung compliance. Furthermore, the chronically ventilated infants often have a multitude of comorbidities which may also impact hemodynamics. These include pulmonary and systemic hypertension which can lead to myocardial dysfunction as a result of the increase in the right and left ventricular afterload, respectively. In this section, we aim to outline the hemodynamic changes associated with chronic lung disease and mechanical ventilation and discuss management options.

Research on the method of controlling the 99mTc-Technegas inhaled during 1-day pulmonary ventilation/perfusion imaging.

Our purpose was to establish a simple and feasible method for monitoring and controlling the Tc-Technegas inhaled to improve the success ratio of imaging and ensure the imaging quality. The relationship between the success ratio and the pulmonary ventilation counting rate (VCR) of 113 cases, the activity of perfusion imaging agents injected and the pulmonary perfusion counting rate (PCR) of another 114 cases were analysed retrospectively. And combined with the relationship between the surface radioactivity monitoring value and the SPECT probe counting rate of a pulmonary model, the effective range of the VCR and the surface radioactivity monitoring value were determined. Two hundred fifty cases with Tc-Technegas inhaled monitored and controlled were used to verify the reliability and practicability of this method. The VCR of the ventilation/perfusion imaging with deep venous thrombosis imaging and the ventilation/perfusion imaging without deep venous thrombosis imaging was in 1.0-3.0 kct/s and 1.0-2.0 kct/s when the monitoring values of handheld radiation monitor was within the range of 60-170 µSv/h and 60-110 µSv/h, respectively. The success ratio of the V/Q-Only increased from 48.9% (43/88) of the control group to 80.8% (122/151) of the experimental group. The VCR in the two groups was examined by the non-parametric Mann-Whitney U test (P < 0.001), which indicated that there was a significant difference between the experimental group and the control group. The external monitoring method established in this study was of great significance in improving the success ratio of 1-day pulmonary ventilation/perfusion imaging and ensuring the image quality.

Dynamic susceptibility contrast 19 F-MRI of inhaled perfluoropropane: a novel approach to combined pulmonary ventilation and perfusion imaging.

PurposeTo assess alveolar perfusion by applying dynamic susceptibility contrast MRI to 19F‐MRI of inhaled perfluoropropane (PFP). We hypothesized that passage of gadolinium‐based contrast agent (GBCA) through the pulmonary microvasculature would reduce magnetic susceptibility differences between water and gas components of the lung, elevating the T2∗ of PFP.MethodsLung‐representative phantoms were constructed of aqueous PFP‐filled foams to characterize the impact of aqueous/gas phase magnetic susceptibility differences on PFP T2∗. Aqueous phase magnetic susceptibility was modulated by addition of different concentrations of GBCA. In vivo studies were performed to measure the impact of intravenously administered GBCA on the T2∗ of inhaled PFP in mice (7.0 Tesla) and in healthy volunteers (3.0 Tesla).ResultsPerfluoropropane T2∗ was sensitive to modulation of magnetic susceptibility difference between gas and water components of the lung, both in phantom models and in vivo. Negation of aqueous/gas phase magnetic susceptibility difference was achieved in lung‐representative phantoms and in mice, resulting in a ~2 to 3× elevation in PFP T2∗ (3.7 to 8.5 ms and 0.7 to 2.6 ms, respectively). Human studies demonstrated a transient elevation of inhaled PFP T2∗ (1.50 to 1.64 ms) during passage of GBCA bolus through the lung circulation, demonstrating sensitivity to lung perfusion.ConclusionWe demonstrate indirect detection of a GBCA in the pulmonary microvasculature via changes to the T2∗ of gas phase PFP within directly adjacent alveoli. This approach holds potential for assessing alveolar perfusion by dynamic susceptibility contrast 19F‐MRI of inhaled PFP, with concurrent assessment of lung ventilation properties, relevant to lung physiology and disease.

Effectiveness of balloon pulmonary angioplasty in patients with inoperable chronic thromboembolic pulmonary hypertension despite having lesion types suitable for surgical treatment

BackgroundBalloon pulmonary angioplasty (BPA) has been performed in patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). However, some patients have inoperable CTEPH despite having lesions suitable for surgical treatment. The effectiveness of BPA in such cases is unclear. The aim of this study was to clarify the effectiveness of BPA in these cases. MethodsWe retrospectively investigated patients with inoperable CTEPH and divided them into two groups: BPA-suitable and BPA-unsuitable groups based on the findings of pulmonary angiography, computed tomography, and perfusion scintigraphy. The BPA-unsuitable group included patients whose lesions are suitable for surgical treatment but who did not undergo the procedure for any specified reason. We analyzed the hemodynamic, respiratory, and functional status of the patients before and after BPA. ResultsForty-three consecutive patients with inoperable CTEPH (age, 62.6 ± 13.5 years; 31 women) were included; all of them underwent BPA. There were 10 patients in the BPA-unsuitable group. In all patients, the mean pulmonary artery pressure, pulmonary vascular resistance, arterial oxygen saturation level, and 6-min walking distance significantly improved after BPA (mean pulmonary artery pressure, from 43.3 ± 7.8 mmHg to 23.9 ± 4.7 mmHg; pulmonary vascular resistance, from 924.1 ± 462.2 dynes/s/cm−5 to 319.7 ± 163.8 dynes/s/cm−5; arterial oxygen saturation level, from 89.3 ± 4.3% to 93.4 ± 3.3%; 6-min walking distance, from 370.0 ± 107.4 m to 443.8 ± 101.4 m). Notably, none of the parameters significantly differed between the groups after BPA. Importantly, the amount of lung bleeding did not differ between them. However, several sessions were required in the BPA-unsuitable group (BPA-unsuitable group: six sessions vs. BPA-suitable group: four sessions). ConclusionsBPA safely improved the hemodynamic and functional statuses of the patients with CTEPH who are judged as inoperable for any reason despite lesion being suitable for surgical treatment. However, numerous BPA sessions were required in these patients.

Comparison of image quality and radiation doses between rapid kV-switching and dual-source DECT techniques in the chest

PurposeTo compare image quality and radiation doses for chest DECT acquired with dual-source and rapid-kV switching techniques. Materials and methodsOur institutional Review Board approved retrospective study included 97 patients (54 men, 43 women; 63 ± 14 years) who underwent contrast-enhanced chest DECT with both single source, rapid kV-switching (SS-DECT) and dual source (DS-DECT) techniques per standard of care departmental protocols. Reconstructed images from both scanners had identical section thickness and section interval for virtual monoenergetic and material decomposition iodine (MDI) images. Two thoracic radiologists independently evaluated all DECT for findings, quality of images, perfusion defects (MDI), and presence of artifacts. Radiation dose descriptor, size-specific dose estimates (SSDE), was recorded. Data were analyzed with Wilcoxon Signed Rank and Cohen’s Kappa tests. ResultsThere were no significant differences in patient weight or SSDE for the two DECT techniques (p > 0.06). Both radiologists reported no difference in lesion and artifact evaluation on the virtual monoenergetic images from either technique (p > 0.05). However, SS-DECT (in 63–71/97 patients) had substantial artifactual heterogeneity in pulmonary perfusion on MDI images compared to none on DS-DECT (p < 0.001). ConclusionDespite identical patients and associated radiation doses, there were substantial differences in material decomposition iodine images generated from SS-DECT and DS-DECT techniques. Pulmonary heterogeneity on MDI images from SS-DECT leads to artifactual areas of low perfusion and can confound interpretation of true pulmonary perfusion.

A comparison of ventilation perfusion combined with pulmonary perfusion fusion tomography imaging and CT pulmonary angiography for diagnosis of pulmonary embolism

Objective To compare the diagnostic value of ventilation/perfusion (V/Q) combined with pulmonary perfusion single photon emission computed tomography combined with CT (SPECT/CT) fusion tomography imaging and computed tomographic pulmonary angiography (CTPA) in evaluation of pulmonary embolism. Methods We retrospectively analyzed 60 patients with clinically suspected pulmonary embolism diagnosed in Shanxi Dayi Hospital from May 2015 to May 2017. All patients underwent pulmonary V/Q imaging and lung perfusion SPECT/CT fusion tomography, and CTPA inspections were completed within 3 days. The final clinical diagnosis and follow-up confirmed the presence or absence of pulmonary embolism. The diagnostic efficacy of two imaging methods for pulmonary embolism were calculated and compared. Results Of the 60 cases of patients, 33 cases were diagnosed with pulmonary embolism; the sensitivity, specificity, and accuracy of V/Q combined with pulmonary perfusion SPECT/CT fusion tomography were 96.97% (32/33), 92.59% (25/27) and 95% (57/60), respectively; the sensitivity, specificity, and accuracy of CTPA were 81.82% (27/33), 92.59% (25/27) and 86.67% (52/60), respectively; both have no diagnostic uncertainty, there was no significant difference in the qualitative diagnosis of pulmonary embolism between the two examination methods (P>0.05). V/Q combined with pulmonary perfusion SPECT/CT fusion tomography found 253 lung segment and 50 unmatched sub-pulmonary segments, including 15 V/Q mismatch lung segment and 5 sub-segment caused by lung lesions which were confirmed by lung perfusion SPECT/CT fusion image (5 interlobular or pleural effusion, 4 local emphysema and pulmonary bulla, 3 interlobular hypertrophy, 8 pulmonary parenchymal inflammation); CTPA found 3 sub-segmental pulmonary filling defects, 6 cases of false-negative cases were multiple sub-pulmonary segment pulmonary embolism. Conclusions V/Q combined with pulmonary perfusion SPECT/CT fusion tomography is similar to CTPA in diagnosing pulmonary embolism, and both of them have better diagnostic efficacy; the former has advantages in the diagnosis of sub-pulmonary segment pulmonary embolism, and can exclude false-positive diagnoses due to other lung lesions and provide additional diagnostic information for lung disease. Key words: Pulmonary embolism; Tomography, emission-computed, single-photon; Radionuclide imaging; Angiography; Tomography, spiral computed

Deep semantic lung segmentation for tracking potential pulmonary perfusion biomarkers in chronic obstructive pulmonary disease (COPD): The multi-ethnic study of atherosclerosis COPD study.

Chronic obstructive pulmonary disease (COPD) is associated with high morbidity and mortality. Identification of imaging biomarkers for phenotyping is necessary for future treatment and therapy monitoring. However, translation of visual analytic pipelines into clinics or their use in large-scale studies is significantly slowed by time-consuming postprocessing steps. To implement an automated tool chain for regional quantification of pulmonary microvascular blood flow in order to reduce analysis time and user variability. Prospective. In all, 90 MRI scans of 63 patients, of which 31 had a COPD with a mean Global Initiative for Chronic Obstructive Lung Disease status of 1.9 ± 0.64 (μ ± σ). 1.5T dynamic gadolinium-enhanced MRI measurement using 4D dynamic contrast material-enhanced (DCE) time-resolved angiography acquired in a single breath-hold in inspiration. [Correction added on August 20, 2019, after first online publication: The field strength in the preceding sentence was corrected.] ASSESSMENT: We built a 3D convolutional neural network for semantic segmentation using 29 manually segmented perfusion maps. All five lobes of the lung are denoted, including the middle lobe. Evaluation was performed on 61 independent cases from two sites of the Multi-Ethnic Study of Arteriosclerosis (MESA)-COPD study. We publish our implementation of a model-free deconvolution filter according to Sourbron et al for 4D DCE MRI scans as open source. Cross-validation 29/61 (# training / # testing), intraclass correlation coefficient (ICC), Spearman ρ, Pearson r, Sørensen-Dice coefficient, and overlap. Segmentations and derived clinical parameters were processed in ~90 seconds per case on a Xeon E5-2637v4 workstation with Tesla P40 GPUs. Clinical parameters and predicted segmentations exhibit high concordance with the ground truth regarding median perfusion for all lobes with an ICC of 0.99 and a Sørensen-Dice coefficient of 93.4 ± 2.8 (μ ± σ). We present a robust end-to-end pipeline that allows for the extraction of perfusion-based biomarkers for all lung lobes in 4D DCE MRI scans by combining model-free deconvolution with deep learning. 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:571-579.

Influence of background lung tissue conductivity on the cardiosynchronous EIT signal components: a sensitivity study.

Electrical impedance tomography is an accepted and validated tool to analyze and support mechanical ventilation at the bedside. In the future it could furthermore clinically provide information of the pulmonary perfusion and other blood volume changes within the thorax by exploiting a cardiosynchronous EIT component. In the presented study, the spatial forward sensitivity against different background lung tissue distributions was analyzed. Spheres with a 10% change of the background conductivity were introduced in the lungs and in the heart. The cranio-caudal distribution of sensitivity had a bell shape and was similar between all simulated scenarios, varying only in magnitude. If the background tissue conductivity within the lungs was chosen to be the one of deflated tissue, the overall sensitivity was 46% smaller compared to the overall sensitivity against inflated lung tissue conductivity. Within the heart region, the sensitivity was increased for fully deflated lung tissue conductivity (23% relative to the sensitivity in the lungs) compared to a homogeneous distribution of inflated lung tissue conductivity (10% relative to the sensitivity in the lungs).

Update on Thrombolytic Therapy in Acute Pulmonary Thromboembolism.

Thrombolytic treatment accelerates the dissolution of thrombus in acute pulmonary thromboembolism (PTE) and is potentially a lifesaving treatment. High-risk PTE is the clearest indication for this therapy, and its use in intermediate-risk cases is still controversial. A PTE response team may enable a rapid and effective determination of risk and treatment in these controversial clinical cases. Approved thrombolytic agents for the PTE treatment are streptokinase, urokinase, and alteplase. Currently, the most widely used agent is alteplase. It has a short infusion time (2 h) and a rapid effect. Newer, unapproved agents for the PTE treatment are tenecteplase and reteplase. The active resolution of thrombus via thrombolytic agents improves rapidly pulmonary perfusion, hemodynamic defect, gas exchange, and right ventricular dysfunction. However, it is important to determine appropriate candidates carefully, to prevent hemorrhage, which is the most important side effect of these drugs. Catheter-directed thrombolysis seems to be an alternative in patients not eligible for systemic thrombolytic therapy.

Pulmonary Vascular Dynamics.

The pulmonary circulation carries deoxygenated blood from the systemic veins through the pulmonary arteries to be oxygenated in the capillaries that line the walls of the pulmonary alveoli. The pulmonary circulation carries the cardiac output with a relatively low driving pressure, and so differs considerably in structure and function from the systemic circulation to maintain a low-resistance vascular system. The pulmonary circulation is often considered to be a quasi-static system in both experimental and computational studies of pulmonary perfusion and its matching to ventilation (air flow) for exchange. However, the system is highly dynamic, with cardiac output and regional perfusion changing with posture, exercise, and over time. Here we review this dynamic system, with a focus on understanding the physiology of pulmonary vascular dynamics across spatial and temporal scales, and the changes to these dynamics that are reflective of disease. © 2019 American Physiological Society. Compr Physiol 9:1081-1100, 2019.

Regional pulmonary perfusion patterns in humans are not significantly altered by inspiratory hypercapnia.

Pulmonary vascular tone is known to be sensitive to both local alveolar Po2 and Pco2. Although the effects of hypoxia are well studied, the hypercapnic response is relatively less understood. We assessed changes in regional pulmonary blood flow in humans in response to hypercapnia using previously developed MRI techniques. Dynamic measures of blood flow were made in a single slice of the right lung of seven healthy volunteers following a block-stimulus paradigm (baseline, challenge, recovery), with CO2 added to inspired gas during the challenge block to effect a 7-Torr increase in end-tidal CO2. Effects of hypercapnia on blood flow were evaluated based on changes in spatiotemporal variability (fluctuation dispersion, FD) and in regional perfusion patterns in comparison to hypoxic effects previously studied. Hypercapnia increased FD 2.5% from baseline (relative to control), which was not statistically significant (P = 0.07). Regional perfusion patterns were not significantly changed as a result of increased (P = 0.90). Reanalysis of previously collected data using a similar protocol but with the physiological challenge replaced by decreased ( = 0.125) showed marked flow redistribution (P = 0.01) with the suggestion of a gravitational pattern, demonstrating hypoxia has the ability to affect regional change with a global stimulus. Taken together, these data indicate that hypercapnia of this magnitude does not lead to appreciable changes in the distribution of pulmonary perfusion, and that this may represent an interesting distinction between the hypoxic and hypercapnic regulatory response.NEW & NOTEWORTHY Although it is well known that the pulmonary circulation responds to local alveolar hypoxia, and that this mechanism may facilitate ventilation-perfusion matching, the relative role of CO2 is not well appreciated. This study demonstrates that an inspiratory hypercapnic stimulus is significantly less effective at inducing changes in pulmonary perfusion patterns than inspiratory hypoxia, suggesting that in these circumstances hypercapnia is not sufficient to induce substantial integrated feedback control of ventilation-perfusion mismatch across the lung.

Optimizing human pulmonary perfusion measurement using an in silico model of arterial spin labeling magnetic resonance imaging.

Arterial spin labeling (ASL) magnetic resonance imaging (MRI) is an imaging methodology that uses blood as an endogenous contrast agent to quantify flow. One limitation of this method of capillary blood quantification when applied in the lung is the contribution of signals from non‐capillary blood. Intensity thresholding is one approach that has been proposed for minimizing the non‐capillary blood signal. This method has been tested in previous in silico modeling studies; however, it has only been tested under a restricted set of physiological conditions (supine posture and a cardiac output of 5 L/min). This study presents an in silico approach that extends previous intensity thresholding analysis to estimate the optimal “per‐slice” intensity threshold value using the individual components of the simulated ASL signal (signal arising independently from capillary blood as well as pulmonary arterial and pulmonary venous blood). The aim of this study was to assess whether the threshold value should vary with slice location, posture, or cardiac output. We applied an in silico modeling approach to predict the blood flow distribution and the corresponding ASL quantification of pulmonary perfusion in multiple sagittal imaging slices. There was a significant increase in ASL signal and heterogeneity (COV = 0.90 to COV = 1.65) of ASL signals when slice location changed from lateral to medial. Heterogeneity of the ASL signal within a slice was significantly lower (P = 0.03) in prone (COV = 1.08) compared to in the supine posture (COV = 1.17). Increasing stroke volume resulted in an increase in ASL signal and conversely an increase in heart rate resulted in a decrease in ASL signal. However, when cardiac output was increased via an increase in both stroke volume and heart rate, ASL signal remained relatively constant. Despite these differences, we conclude that a threshold value of 35% provides optimal removal of large vessel signal independent of slice location, posture, and cardiac output.

Measurement of relative lung perfusion with electrical impedance and positron emission tomography: an experimental comparative study in pigs

BackgroundElectrical impedance tomography (EIT) with indicator dilution may be clinically useful to measure relative lung perfusion, but there is limited information on the performance of this technique. MethodsThirteen pigs (50–66 kg) were anaesthetised and mechanically ventilated. Sequential changes in ventilation were made: (i) right-lung ventilation with left-lung collapse, (ii) two-lung ventilation with optimised PEEP, (iii) two-lung ventilation with zero PEEP after saline lung lavage, (iv) two-lung ventilation with maximum PEEP (20/25 cm H2O to achieve peak airway pressure 45 cm H2O), and (v) two-lung ventilation under unilateral pulmonary artery occlusion. Relative lung perfusion was assessed with EIT and central venous injection of saline 3%, 5%, and 10% (10 ml) during breath holds. Relative perfusion was determined by positron emission tomography (PET) using 68Gallium-labelled microspheres. EIT and PET were compared in eight regions of equal ventro-dorsal height (right, left, ventral, mid-ventral, mid-dorsal, and dorsal), and directional changes in regional perfusion were determined. ResultsDifferences between methods were relatively small (95% of values differed by less than 8.7%, 8.9%, and 9.5% for saline 10%, 5%, and 3%, respectively). Compared with PET, EIT underestimated relative perfusion in dependent, and overestimated it in non-dependent, regions. EIT and PET detected the same direction of change in relative lung perfusion in 68.9–95.9% of measurements. ConclusionsThe agreement between EIT and PET for measuring and tracking changes of relative lung perfusion was satisfactory for clinical purposes. Indicator-based EIT may prove useful for measuring pulmonary perfusion at bedside.

Should Perfusion Scintigraphy Be Performed to Follow Patients with Acute Pulmonary Embolism? If So, When?

This investigation evaluated the changes of pulmonary perfusion at 4 different points of follow-up within 1 y in patients with pulmonary embolism (PE) and the factors predictive of complete or incomplete recovery of pulmonary perfusion. Methods: Patients with symptomatic PE underwent perfusion lung scintigraphy and blood gas analysis within 48 h from clinical presentation, after 1 wk, and after 1, 6, and 12 mo; echocardiography was performed at baseline and after 6 and 12 mo. All perfusion lung scintigraphy scans were examined by 2 expert nuclear medicine physicians with a scoring method that attributed a score of 0, 0.5, or 1 for extension (maximum score, 18) to the presence of perfusion defects (PD), both at baseline and on each follow-up scan. Results: Among 183 patients who completed 1 y of follow-up, the median baseline PD score was 8.2; it decreased significantly at each follow-up time point until 6 mo (P < 0.001). Median baseline alveolar-arterial difference in oxygen partial pressure (PA-aO2) was 50.9 and decreased significantly up to 1 mo (P < 0.001); median pulmonary artery systolic pressure (PAsP) was 45.9 mm Hg and decreased significantly until 12 mo (P < 0.001). A correlation was found between PD and both PA-aO2 (P < 0.05) and PAsP (P < 0.05). We found a correlation between PD ≠ 0 and PAsP ≥ 40 mm Hg at 12 mo (P < 0.05); in 6 (3.3%) of these patients such a correlation was still present after 24 mo, suggesting they could develop chronic thromboembolic pulmonary hypertension. Low baseline PD (odds ratio, 0.80; P < 0.0001) and high 1-wk percent recovery (odds ratio, 1.04; P < 0.0001) were predictive factors of complete 6-mo recovery. Conclusion: Perfusion scintigraphy may be useful to follow patients with PE. The follow-up should consist of 3 steps: the baseline examination, which reflects the severity of PE; the scan at 1 wk, which indicates the early amount of reperfusion; and the scan at 6 mo, which demonstrates the maximum attainable recovery. Patients with incomplete recovery and persistence of pulmonary hypertension on the 24-mo control should be further studied for possible development of chronic thromboembolic pulmonary hypertension.

Features of pulmonary circulation in children with congenital pulmonary venolobar syndrom

Introduction. Despite the continuous improvement of methods for prenatal diagnosis of fetal malformations, at present, the limitations of intrauterine verifcation of vascular lung anomalies and relevance in postnatal typing of all components of pathological pulmonary hemodynamic, especially in the case of complex, combined vascular malformations, remain. Detailed and expert assessment of the anatomy of the pulmonary vessels, intrapulmonary hemodynamic is necessary to minimize the time for the surgical correction of the defect in order to avoid the development of irreversible pulmonary hypertension. One of the most rare and diffcult to diagnose forms of a combination of vascular abnormalities is congenital pulmonary venolobar syndrome (CPVS), which combines venous, arterial, pulmonary and cardiac pathology, to one degree or another coexisting in one patient.Objective – analysis of clinical material and data of different diagnostic methods in children with CPVS. This everything will help to optimize diagnostics and choose the most safe and informative method to visualize combination of pulmonary and cardiovascular diseases and to determine the specifcity of pulmonary circulation. Furthermore, it will allow to minimize all risks and negative consequences for patient’s body.Material and methods. We reviewed the records of 11 children (age from 14 days to 17 years old) with intraoperative verifcation of CPVS. We systematized all variants of vascular anomalies of lungs in children with CPVS, its possible combinationswith other abnormalities. We performed the comparison of capability and diagnostic signifcance of plain radiography, echocardiography, selective angiography and CT­scan in determining the specifcity of pulmonary circulation in children with CPVS and assessment of combination of the malformation components. Results. Antenatal echocardiography and postnatal diagnostics using echocardiography, plain radiography and selective angiography is extremely limited. We suggested the diagnostic algorithm using CT­scan with the proof of the great representativeness. Obligatory components of CPVS were identifed: reduction of the right lung volume, anomalous pulmonary venous drainage (scimitar syndrome) and non­obligate components of malformation: aplasia or hypoplasia of the right pulmonary artery, systemic pulmonary arterial supply with differential pulmonary perfusion, pulmonary sequestration, other congenital heart abnormalities.Conclusion. CPVS is a rare congenital malformation. Antenatal diagnosis of all components of CVLS is impossible. MDCTAG is the most effective diagnostic method that allows to identify all components of CPVS in postnatal period. This method does not require additional radiodiagnostics and invasive diagnostic procedures.

State of the art: utility of multi-energy CT in the evaluation of pulmonary vasculature.

Multi-energy computed tomography (MECT) refers to acquisition of CT data at multiple energy levels (typically two levels) using different technologies such as dual-source, dual-layer and rapid tube voltage switching. In addition to conventional/routine diagnostic images, MECT provides additional image sets including iodine maps, virtual non-contrast images, and virtual monoenergetic images. These image sets provide tissue/material characterization beyond what is possible with conventional CT. MECT provides invaluable additional information in the evaluation of pulmonary vasculature, primarily by the assessment of pulmonary perfusion. This functional information provided by the MECT is complementary to the morphological information from a conventional CT angiography. In this article, we review the technique and applications of MECT in the evaluation of pulmonary vasculature.