Pulmonary Blood Flow Values Research Articles

Improving pulmonary perfusion assessment by dynamic contrast-enhanced computed tomography in an experimental lung injury model.

Pulmonary perfusion has been poorly characterized in acute respiratory distress syndrome (ARDS). Optimizing protocols to measure pulmonary blood flow (PBF) via dynamic contrast-enhanced (DCE) computed tomography (CT) could improve understanding of how ARDS alters pulmonary perfusion. In this study, comparative evaluations of injection protocols and tracer-kinetic analysis models were performed based on DCE-CT data measured in ventilated pigs with and without lung injury. Ten Yorkshire pigs (five with lung injury, five healthy) were anesthetized, intubated, and mechanically ventilated; lung injury was induced by bronchial hydrochloric acid instillation. Each DCE-CT scan was obtained during a 30-s end-expiratory breath-hold. Reproducibility of PBF measurements was evaluated in three pigs. In eight pigs, undiluted and diluted Isovue-370 were separately injected to evaluate the effect of contrast viscosity on estimated PBF values. PBF was estimated with the peak-enhancement and the steepest-slope approach. Total-lung PBF was estimated in two healthy pigs to compare with cardiac output measured invasively by thermodilution in the pulmonary artery. Repeated measurements in the same animals yielded a good reproducibility of computed PBF maps. Injecting diluted isovue-370 resulted in smaller contrast-time curves in the pulmonary artery (P < 0.01) and vein (P < 0.01) without substantially diminishing peak signal intensity (P = 0.46 in the pulmonary artery) compared with the pure contrast agent since its viscosity is closer to that of blood. As compared with the peak-enhancement model, PBF values estimated by the steepest-slope model with diluted contrast were much closer to the cardiac output (R2 = 0.82) as compared with the peak-enhancement model. DCE-CT using the steepest-slope model and diluted contrast agent provided reliable quantitative estimates of PBF.NEW & NOTEWORTHY Dynamic contrast-enhanced CT using a lower-viscosity contrast agent in combination with tracer-kinetic analysis by the steepest-slope model improves pulmonary blood flow measurements and assessment of regional distributions of lung perfusion.

Quantitative assessment of regional pulmonary perfusion using three-dimensional ultrafast dynamic contrast-enhanced magnetic resonance imaging: pilot study results in 10 patients

Background. Currently there is a high demand in reliable noninvasive diagnostic technique assessing the physiological parameters of the lungs. We are exploring the three-dimensional ultrafast MRI sequence as a novel diagnostic modality allowing the assessment of regional quantitative perfusion parameters in pulmonary tissue.&#x0D; Aim. To assess regional differences in quantitative pulmonary perfusion parameters in 10 volunteers with no evidence of interstitial lung disease by computed tomography, clinical, and laboratory data.&#x0D; Materials and methods. 10 volunteers with no signs of interstitial lung disease were examined by three-dimensional ultrafast dynamic contrast-enhanced MR imaging using 3D T1-weighted images. The values of pulmonary blood flow (PBF), mean transit time (MTT), and pulmonary blood volume (PBV) for the targeted regions of interest were calculated based on the dynamic image series. For calculations, arterial input function (AIF) was used, as well as the time-intensity curves.&#x0D; Results. The values of PBF, MTT, and PBV showed statistically significant differences between central and peripheral sections of lungs. Provided model can be implemented for quantitative assessment of regional pulmonary perfusion allows it to be used to determine the reliability of PBF, MTT and PBV values.&#x0D; Conclusions. Three-dimensional ultrafast MRI sequence is a novel diagnostic modality allowing the assessment of regional quantitative pulmonary perfusion parameters in pulmonary tissue, regardless of physiological features of blood supply mechanisms in different lung regions.

Quantitative Dual-Energy Computed Tomography Predicts Regional Perfusion Heterogeneity in a Model of Acute Lung Injury.

ObjectiveThe aims of this study were to investigate the ability of contrast-enhanced dual-energy computed tomography (DECT) for assessing regional perfusion in a model of acute lung injury, using dynamic first-pass perfusion CT (DynCT) as the criterion standard and to evaluate if changes in lung perfusion caused by prone ventilation are similarly demonstrated by DECT and DynCT.MethodsThis was an institutional review board–approved study, compliant with guidelines for humane care of laboratory animals. A ventilator-induced lung injury protocol was applied to 6 landrace pigs. Perfused blood volume (PBV) and pulmonary blood flow (PBF) were respectively quantified by DECT and DynCT, in supine and prone positions. The lungs were segmented in equally sized regions of interest, namely, dorsal, middle, and ventral. Perfused blood volume and PBF values were normalized by lung density. Regional air fraction (AF) was assessed by triple-material decomposition DECT. Per-animal correlation between PBV and PBF was assessed with Pearson R. Regional differences in PBV, PBF, and AF were evaluated with 1-way analysis of variance and post hoc linear trend analysis (α = 5%).ResultsMean correlation coefficient between PBV and PBF was 0.70 (range, 0.55–0.98). Higher PBV and PBF values were observed in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −10.24 mL/100 g per zone for PBV (P < 0.001) and −223.0 mL/100 g per minute per zone for PBF (P < 0.001). Prone ventilation also revealed higher PBV and PBF in dorsal versus ventral regions. Dorsal-to-ventral linear trend slopes were −16.16 mL/100 g per zone for PBV (P < 0.001) and −108.2 mL/100 g per minute per zone for PBF (P < 0.001). By contrast, AF was lower in dorsal versus ventral regions in supine position, with dorsal-to-ventral linear trend slope of +5.77%/zone (P < 0.05). Prone ventilation was associated with homogenization of AF distribution among different regions (P = 0.74).ConclusionsDual-energy computed tomography PBV is correlated with DynCT-PBF in a model of acute lung injury, and able to demonstrate regional differences in pulmonary perfusion. Perfusion was higher in the dorsal regions, irrespectively to decubitus, with more homogeneous lung aeration in prone position.

Quantitative pulmonary blood flow measurement using 15O-H2O PET with and without tissue fraction correction: a comparison study

BackgroundPhysiological measures per lung parenchyma, rather than per lung volume, sometimes reflect the disease status. PET images of the lung, which are usually expressed per lung volume, could confound the interpretation of the disease status, especially in cases with a prominent heterogeneity in aeration. The aim of the present study was to develop a method for measuring pulmonary blood flow (PBF) with aeration correction using 15O-H2O PET and to compare the results with those obtained using a conventional method. We obtained the voxel-based tissue fraction (TF) derived from density images converted from transmission images obtained using an external 137Cs point source. Quantitative PBF values with and without the TF were calculated using 15O-H2O PET to examine contralateral lung tissue in 9 patients with unilateral lung cancer. The heterogeneity in PBF before and after TF correction was then evaluated and compared. As a measure of PBF heterogeneity, we used the skewness and kurtosis of the PBF distribution.ResultsThe mean PBF of contralateral lung was 1.4 ± 0.3 mL/min per mL of lung. The TF-corrected PBF was 5.0 ± 0.6 mL/min per mL of lung parenchyma. After TF correction, the skewness and kurtosis of the PBF decreased significantly.ConclusionsThe present PBF calculation method using TF correction demonstrated that the normal PBF increased significantly and the PBF distribution became uniform. The proposed TF correction method is a promising technique to account for variations in density when interpreting PBF in PET studies.

Lung Perfusion MRI After Congenital Diaphragmatic Hernia Repair in 2-Year-Old Children With and Without Extracorporeal Membrane Oxygenation Therapy.

In severe cases of congenital diaphragmatic hernia (CDH), extracorporeal membrane oxygenation (ECMO) therapy improves survival. Later on, lung morbidity mainly defines development. The purpose of this study was to investigate whether 2-year-old children who need ECMO therapy after delivery have reduced perfusion MRI values as a sign of more severe lung hypoplasia than do children who do not need ECMO. After CDH repair, 38 children underwent dynamic contrast-enhanced MRI with a 3D time-resolved angiography with stochastic trajectories sequence. Fifteen (39%) of the children had received ECMO therapy in the neonatal period. Pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time were calculated for both lungs. In addition, the ratio of ipsilateral to contralateral lung was calculated for all parameters. In all children, those with and those without ECMO requirement, PBF and PBV were significantly reduced on the ipsilateral side (p < 0.05). Children who had received ECMO therapy had significantly reduced PBF and PBV values on the ipsilateral side (p < 0.05) compared with children who had not needed ECMO therapy. The ratios of ipsilateral to contralateral lung for PBF and PBV were also significantly reduced after ECMO. Two-year-old children undergoing CDH repair who had needed neonatal ECMO had significantly reduced perfusion MRI values in the ipsilateral lung in comparison with children who had not needed ECMO. Perfusion MRI measurements are associated with the severity of lung hypoplasia and may therefore be helpful in follow-up investigations.

Arterial input function placement effect on computed tomography lung perfusion maps.

A critical source of variability in dynamic perfusion computed tomography (DPCT) is the arterial input function (AIF). However, the impact of the AIF location in lung DPCT has not been investigated yet. The purpose of this study is to determine whether the location of the AIF within the central pulmonary arteries influences the accuracy of lung DPCT maps. A total of 54 lung DPCT scans were performed in three pigs using different rates and volumes of iodinated contrast media. Pulmonary blood flow (PBF) perfusion maps were generated using first-pass kinetics in three different AIF locations: the main pulmonary trunk (PT), the right main (RM) and the left main (LM) pulmonary arteries. A total of 162 time density curves (TDCs) and corresponding PBF perfusion maps were generated. Linear regression and Spearman's rank correlation coefficient were used to compare the TDCs. PBF perfusion maps were compared quantitatively by taking twenty six regions of interest throughout the lung parenchyma. Analysis of variance (ANOVA) was used to compare the mean PBF values among the three AIF locations. Two chest radiologists performed qualitative assessment of the perfusion maps using a 3-point scale to determine regions of perfusion mismatch. The linear regression of the TDCs from the RM and LM compared to the PT had a median (range) of 1.01 (0.98-1.03). The Spearman rank correlation between the TDCs was 0.88 (P<0.05). ANOVA analysis of the perfusion maps demonstrated no statistical difference (P>0.05). Qualitative comparison of the perfusion maps resulted in scores of 1 and 2, demonstrating either identical or comparable maps with no significant difference in perfusion defects between the different AIF locations. Accurate PBF perfusion maps can be generated with the AIF located either at the PT, RM or LM pulmonary arteries.

Noninvasive Quantitative Assessment of Pulmonary Blood Flow with 18F-FDG PET

Pulmonary blood flow (PBF) is a critical determinant of oxygenation during acute lung injury (ALI). PET/CT with (18)F-FDG allows the assessment of both lung aeration and neutrophil inflammation as well as an estimation of the regional fraction of blood (FB) if compartmental modeling is used to quantify (18)F-FDG pulmonary uptake. The aim of this study was to validate the use of FB to assess PBF, with PET and compartmental modeling of (15)O-H2O kinetics as a reference method, in both control animals and animals with ALI. For the purpose of studying a wide range of PBF values, supine and prone positions and various positive end-expiratory pressures (PEEPs) and tidal volumes (V(T)s) were selected. Pigs were randomized into 3 groups in which ALI was induced by HCl inhalation: pigs studied in the supine position with a low PEEP (5 ± 3 [mean ± SD] cm of H2O; n = 9) or a high PEEP (12 ± 1 cm of H2O; n = 8) and pigs studied in the prone position with a low PEEP (6 ± 3 cm of H2O; n = 9). Also included were a control group that did not have ALI (n = 6) and 2 additional groups (n = 6 each) that had a high V(T) to maintain a transpulmonary pressure of greater than or equal to 35 cm of H2O and that either received HCl inhalation or did not receive HCl inhalation. PBF and FB were measured with PET and compartmental modeling of (15)O-H2O and (18)F-FDG kinetics in 10 lung regions along the anterior-to-posterior lung dimension, and both were expressed in each region as a fraction of their values in the whole lung. PBF and FB were strongly correlated (R(2) = 0.9), with a slope of the regression line close to unity and a negligible intercept. The mean difference between PBF and FB was 0, and the 95% limits of agreement were -0.035 to 0.035. This good agreement between methods was obtained in both normal and injured lungs and under a wide range of V(T), PEEP, and regional PBF values (7-71 mL/kg, 0-15 cm of H2O, and 24-603 mL·min(-1)·100 mL of lung(-1), respectively). FB assessed with (18)F-FDG is a good surrogate for PBF in both normal animals and animals with ALI. PET/CT has the potential to be used to study ventilation, perfusion, and lung inflammation with a single tracer.

Quantitative pulmonary perfusion imaging at 3.0 T of 2-year-old children after congenital diaphragmatic hernia repair: initial results

To investigate whether dynamic contrast-enhanced MR imaging of the lung following congenital diaphragmatic hernia repair is feasible at 3.0 T in 2-year-old children and whether associated lung hypoplasia (reflected in reduced pulmonary microcirculation) can be demonstrated in MRI. Twelve children with a mean age 2.0 ± 0.2 years after hernia repair underwent DCE-MRI at 3.0 T using a time-resolved angiography with stochastic trajectories sequence. Quantification of lung perfusion was performed using a pixel-by-pixel deconvolution approach. Six regions of interest were placed (upper, middle and lower parts of right and left lung) to assess differences in pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) while avoiding the inclusion of larger pulmonary arteries and veins. The difference in PBF and PBV between ipsilateral and contralateral lung was significant (P < 0.5). No significant differences could be detected for the MTT (P = 0.5). DCE-MRI in 2-year-old patients is feasible at 3.0 T. Reduced perfusion in the ipsilateral lung is reflected by significantly lower PBF values compared with the contralateral lung. DCE-MRI of the lung in congenital diaphragmatic hernia can help to characterise lung hypoplasia initially and in the long-term follow-up of children after diaphragmatic repair. Congenital diaphragmatic hernia often leads to lung hypoplasia and secondary pulmonary hypertension. Dynamic contrast-enhanced 3-T magnetic resonance can assess these complications in 2-year-olds. The affected ipsilateral lung shows reduced perfusion and lower pulmonary blood flow. Thoracic DCE-MRI helps characterise lung hypoplasia in children after hernia repair.

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Non-invasive determination of effective pulmonary blood flow: Evaluation of a simplified rebreathing method

Primary objective : To evaluate a new technical approach to measuring effective pulmonary blood flow (PBF) in mechanically ventilated patients. Research design : Prospective clinical study; evaluation of accuracy and reproducibility. Methods : Effective pulmonary blood flow was determined non-invasively in 32 mechanically ventilated patients by using a new rebreathing system (PBF rb ). Cardiac output corrected for intrapulmonary shunt was taken as reference value (PBF thd ). Bias, precision and reproducibility of the rebreathing method were calculated from duplicate measurements in each patient. Main results : The mean difference between PBF rb and PBF thd was m v 0.67 v - v 0.83 l min m 1. The mean difference between duplicate measurements with the rebreathing system was 0.16 v - v 0.36 l min m 1. However, the accuracy of the rebreathing system tended to decrease in patients with PBF levels greater than 6 l min m 1. Conclusions : The new device appears to be reliable for determination of PBF values below 6 l min m 1. With this limitation, the present method may be used as a trend-indicator of PBF in mechanically ventilated patients.

Gas Exchange in the Loggerhead Sea Turtle Caretta Caretta

ABSTRACT Pulmonary CO diffusion capacity (DLCO), lung volume (VL), oxygen uptake and pulmonary blood flow (Q̇L) were measured simultaneously in the loggerhead sea turtle Caretta caretta (Linnaeus) (8-11 kg) using a gas rebreathing technique (syringe pump ventilation). Calculated DLCO and values in the loggerhead turtle are approximately twice those of non-varanid reptiles and about 25 % of values for resting mammals. Evidence based on an estimated lung-capillary O2 gradient, , shows that only a small driving gradient is required for O2 conductance across the loggerhead turtle lung. Pulmonary blood flow values are high compared to those for other reptiles; on the basis of the Fick principle, this implies a substantial blood convection requirement. Differences in oxygen transport mechanisms between the loggerhead sea turtle and other highly aerobic but terrestrial reptiles may result from divergent lung structures and breathing patterns. In sea turtles, the coupling of respiration with locomotory behaviour is one factor that may limit aerobic performance. Since sea turtles have only intermittent access to air, they are required to load both arterial and venous blood with O2 before submerging.