Distribution of blood flow and ventilation in the lung: gravity is not the only factor

A model of mechanical loading of the lungs including gravity and a balancing heterogeneous pleural pressure

Recent years have seen the development of multiple in silico lung models, notably with the aim of improving patient care for pulmonary diseases. These models vary in complexity and typically only consider the implementation of pleural pressure, a depression that keeps the lungs inflated. Gravity, often considered negligible compared to pleural pressure, has been largely overlooked, also due to the complexity of formulating physiological boundary conditions to counterbalance it. However, gravity is known to affect pulmonary functions, such as ventilation. In this study, we incorporated gravity into a recent lung poromechanical model. To do so, in addition to the gravitational body force, we proposed novel boundary conditions consisting in a heterogeneous pleural pressure field constrained to counterbalance gravity to reach global equilibrium of applied forces. We assessed the impact of gravity on the global and local behavior of the model, including the pressure-volume response and porosity field. Our findings reveal that gravity, despite being small, influences lung response. Specifically, the inclusion of gravity in our model led to the emergence of heterogeneities in deformation and stress distribution, compatible with in vivo imaging data. This could provide valuable insights for predicting the progression of certain pulmonary diseases by correlating areas subjected to higher deformation and stresses with disease evolution patterns.

Regional distribution of mechanical strain and macrophage-associated lung inflammation after ventilator-induced lung injury: an experimental study

BACKGROUND

Alveolar macrophages activation to the pro-inflammatory phenotype M1 is pivotal in the pathophysiology of Ventilator-Induced Lung Injury (VILI). Increased lung strain is a known determinant of VILI, but a direct correspondence between regional lung strain and macrophagic activation remains unestablished. [68Ga]Ga-DOTA-TATE is a Positron Emission Tomography (PET) radiopharmaceutical with a high affinity for somatostatin receptor subtype 2 (SSTR2), which is overexpressed by pro-inflammatory-activated macrophages. Aim of the study was to determine, in a porcine model of VILI, whether mechanical strain correlates topographically with distribution of activated macrophages detected by [68Ga]Ga-DOTA-TATE uptake.

METHODS

Seven anesthetized pigs underwent VILI, while three served as control. Lung CT scans were acquired at incremental tidal volumes, simultaneously recording lung mechanics. [68Ga]Ga-DOTA-TATE was administered, followed by dynamic PET scans. Custom MatLab scripts generated voxel-by-voxel gas volume and strain maps from CT slices at para-diaphragmatic (Para-D) and mid-thoracic (Mid-T) levels. Analysis of regional Voxel-associated Normal Strain (VoStrain) and [68Ga]Ga-DOTA-TATE uptake was performed and a measure of the statistical correlation between these two variables was quantified using the linear mutual information (LMI) method.

RESULTS

Compared to controls, the VILI group exhibited statistically significant higher VoStrain and Standardized Uptake Value Ratios (SUVR) both at Para-D and Mid-T levels. Both VoStrain and SUVR increased along the gravitational axis with an increment described by statistically different regression lines between VILI and healthy controls and reaching the peak in the dependent regions of the lung (for strain in VILI vs. control was at Para-D: 760 ± 210 vs. 449 ± 106; at Mid-T level 497 ± 373 vs. 193 ± 160; for SUVR, in VILI vs. control was at Para-D: 2.2 ± 1.3 vs. 1.3 ± 0.1; at Mid-T level 1.3 ± 1.0 vs. 0.6 ± 0.03). LMI in both Para-D and Mid-T was statistically significantly higher in VILI than in controls.

CONCLUSIONS

In this porcine model of VILI, we found a topographical correlation between lung strain and [68Ga]Ga-DOTA-TATE uptake at voxel level, suggesting that mechanical alteration and specific activation of inflammatory cells are strongly linked in VILI. This study represents the first voxel-by-voxel examination of this relationship in a multi-modal imaging analysis.

Inhaled iloprost in off-pump coronary artery bypass surgery: a randomized controlled trial

PURPOSE

Mechanical cardiac constraint during off-pump coronary artery bypass surgery (OPCAB) causes right ventricle (RV) compression and increased pulmonary artery pressure (PAP), which may further compromise RV dysfunction. We aimed to assess the effect of inhaled iloprost, a potent selective pulmonary vasodilator, on the cardiac index (CI) during mechanical constraint. The secondary aim was to determine the resultant changes in the hemodynamic and respiratory parameters.

METHODS

A total of 100 adult patients with three-vessel coronary artery disease who had known risk factors for hemodynamic instability (congestive heart failure, mean PAP ≥ 25 mm Hg, RV systolic pressure ≥ 50 mm Hg on preoperative echocardiography, left ventricular ejection fraction < 50%, myocardial infarction within one month of surgery, redo surgery, and left main disease) were enrolled in a randomized controlled trial. The patients were randomly allocated to the control or iloprost groups at a 1:1 ratio, in which saline and iloprost (20 μg) were inhaled for 15 min after internal mammary artery harvesting, respectively. Cardiac index was measured by pulmonary artery catheterization.

RESULTS

There were no significant intergroup differences in CI during grafting (P = 0.36). The mean PAP had a significant group-time interaction (P = 0.04) and was significantly lower in the iloprost group at circumflex grafting (mean [standard deviation], 26 [3] mm Hg vs 24 [3] mm Hg; P = 0.01). The remaining hemodynamic parameters were similar between the groups.

CONCLUSION

Inhaled iloprost showed a neutral effect on hemodynamic parameters, including the CI and pulmonary vascular resistance index, during OPCAB.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT04598191); first submitted 12 October 2020.

Clinical implications of dose to functional lung volumes in the trimodality treatment of esophageal cancer

BACKGROUND

Trimodality treatment, i.e., neoadjuvant chemoradiotherapy (nCRT) followed by surgery, for locally advanced esophageal cancer (EC) improves overall survival but also increases the risk of postoperative pulmonary complications. Here, we tried to identify a relation between dose to functional lung volumes (FLV) as determined by 4D-CT scans in EC patients and treatment-related lung toxicity.

MATERIALS AND METHODS

All patients with EC undergoing trimodality treatment between 2017 and 2022 in UZ Leuven and scanned with 4D-CT-simulation were selected. FLVs were determined based on Jacobian determinants of deformable image registration between maximum inspiration and expiration phases. Dose/volume parameters of the anatomical lung volume (ALV) and FLV were compared between patients with versus without postoperative pulmonary complications. Results of pre- and post-nCRT pulmonary function tests (PFTs) were collected and compared in relation to radiation dose.

RESULTS

Twelve out of 51 EC patients developed postoperative pulmonary complications. ALV was smaller while FLV10Gy and FLV20Gy were larger in patients with complications (respectively 3141 ± 858mL vs 3601 ± 635mL, p = 0.025; 360 ± 216mL vs 264 ± 139mL, p = 0.038; 166 ± 106mL vs 118 ± 63mL, p = 0.030). No differences in ALV dose-volume parameters were detected. Baseline FEV1 and TLC were significantly lower in patients with complications (respectively 90 ± 17%pred vs 102 ± 20%pred, p = 0.033 and 93 ± 17%pred vs 110 ± 13%pred, p = 0.001), though no other PFTs were significantly different between both groups. DLCO was the only PFT that had a meaningful decrease after nCRT (85 ± 17%pred vs 68 ± 15%pred, p < 0.001) but was not related to dose to ALV/FLV.

CONCLUSION

Small ALV and increasing FLV exposed to intermediate (10 to 20 Gy) dose are associated to postoperative pulmonary complications. Changes of DLCO occur during nCRT but do not seem to be related to radiation dose to ALV or FLV. This information could attribute towards toxicity risk prediction and reduction strategies for EC.

The Pulmonary Vasculature

The pulmonary circulation is a low-pressure, low-resistance circuit whose primary function is to deliver deoxygenated blood to, and oxygenated blood from, the pulmonary capillary bed enabling gas exchange. The distribution of pulmonary blood flow is regulated by several factors including effects of vascular branching structure, large-scale forces related to gravity, and finer scale factors related to local control. Hypoxic pulmonary vasoconstriction is one such important regulatory mechanism. In the face of local hypoxia, vascular smooth muscle constriction of precapillary arterioles increases local resistance by up to 250%. This has the effect of diverting blood toward better oxygenated regions of the lung and optimizing ventilation-perfusion matching. However, in the face of global hypoxia, the net effect is an increase in pulmonary arterial pressure and vascular resistance. Pulmonary vascular resistance describes the flow-resistive properties of the pulmonary circulation and arises from both precapillary and postcapillary resistances. The pulmonary circulation is also distensible in response to an increase in transmural pressure and this distention, in addition to recruitment, moderates pulmonary arterial pressure and vascular resistance. This article reviews the physiology of the pulmonary vasculature and briefly discusses how this physiology is altered by common circumstances.

High-Temporal-Resolution Lung Kinetic Modeling Using Total-Body Dynamic PET with Time-Delay and Dispersion Corrections

Tracer kinetic modeling in dynamic PET has the potential to improve the diagnosis, prognosis, and research of lung diseases. The advent of total-body PET systems with much greater detection sensitivity enables high-temporal-resolution (HTR) dynamic PET imaging of the lungs. However, existing models may become insufficient for modeling the HTR data. In this paper, we investigate the necessity of additional corrections to the input function for HTR lung kinetic modeling. Methods: Dynamic scans with HTR frames of as short as 1 s were performed on 13 healthy subjects with a bolus injection of about [Formula: see text] of 18F-FDG using the uEXPLORER total-body PET/CT system. Three kinetic models with and without time-delay and dispersion corrections were compared for the quality of lung time-activity curve fitting using the Akaike information criterion. The impact on quantification of 18F-FDG delivery rate [Formula: see text], net influx rate [Formula: see text] and fractional blood volume [Formula: see text] was assessed. Parameter identifiability analysis was also performed to evaluate the reliability of kinetic quantification with respect to noise. Correlation of kinetic parameters with age was investigated. Results: HTR dynamic imaging clearly revealed the rapid change in tracer concentration in the lungs and blood supply (i.e., the right ventricle). The uncorrected input function led to poor time-activity curve fitting and biased quantification in HTR kinetic modeling. The fitting was improved by time-delay and dispersion corrections. The proposed model resulted in an approximately 85% decrease in [Formula: see text], an approximately 75% increase in [Formula: see text], and a more reasonable [Formula: see text] (∼0.14) than the uncorrected model (∼0.04). The identifiability analysis showed that the proposed models had good quantification stability for [Formula: see text], [Formula: see text], and [Formula: see text] The [Formula: see text] estimated by the proposed model with simultaneous time-delay and dispersion corrections correlated inversely with age, as would be expected. Conclusion: Corrections to the input function are important for accurate lung kinetic analysis of HTR dynamic PET data. The modeling of both delay and dispersion can improve model fitting and significantly impact quantification of [Formula: see text], [Formula: see text], and [Formula: see text].

The effect of posture on airflow distribution, airway geometry and air velocity in healthy subjects

BACKGROUND

Gravity, and thus body position, can affect the regional distribution of lung ventilation and blood flow. Therefore, body positioning is a potential tool to improve regional ventilation, thereby possibly enhancing the effect of respiratory physiotherapy interventions. In this proof-of-concept study, functional respiratory imaging (FRI) was used to objectively assess effects of body position on regional airflow distribution in the lungs.

METHODS

Five healthy volunteers were recruited. The participants were asked during FRI first to lie in supine position, afterwards in standardized right lateral position.

RESULTS

In right lateral position there was significantly more regional ventilation also described as Imaging Airflow Distribution in the right lung than in the left lung (P < 0.001). Air velocity was significantly higher in the left lung (P < 0.05). In right lateral position there was significantly more airflow distribution in the right lung than in the left lung (P < 0.001). Significant changes were observed in airway geometry resulting in a decrease in imaged airway volume (P = 0.024) and a higher imaged airway resistance (P = 0.029) in the dependent lung. In general, the effect of right lateral position caused a significant increase in regional ventilation (P < 0.001) in the dependent lung when compared with the supine position.

CONCLUSIONS

Changing body position leads to significant changes in regional lung ventilation, objectively assessed by FRI The volume based on the imaging parameters in the dependent lung is smaller in the lateral position than in the supine position. In right lateral decubitus position, airflow distribution is greater in dependent lung compared to the nondependent lung.

TRIAL REGISTRATION

The trial has been submitted to www.

CLINICALTRIALS

gov with identification number NCT01893697 on 07/02/2013.

Effects of airway pressure release ventilation on multi-organ injuries in severe acute respiratory distress syndrome pig models

BACKGROUND

Extra-pulmonary multi-organ failure in patients with severe acute respiratory distress syndrome (ARDS) is a major cause of high mortality. Our purpose is to assess whether airway pressure release ventilation (APRV) causes more multi-organ damage than low tidal volume ventilation (LTV).

METHODS

Twenty one pigs were randomized into control group (n = 3), ARDS group (n = 3), LTV group (n = 8) and APRV group (n = 7). Severe ARDS model was induced by repeated bronchial saline lavages. Pigs were ventilated and monitored continuously for 48 h. Respiratory data, hemodynamic data, serum inflammatory cytokines were collected throughout the study. Histological injury and apoptosis were assessed by two pathologists.

RESULTS

After severe ARDS modeling, pigs in ARDS, LTV and APRV groups experienced significant hypoxemia and reduced lung static compliance (C_stat). Oxygenation recovered progressively after 16 h mechanical ventilation (MV) in LTV and APRV group. The results of the repeated measures ANOVA showed no statistical difference in the PaO₂/FiO₂ ratio between the APRV and LTV groups (p = 0.54). The C_stat showed a considerable improvement in APRV group with statistical significance (p < 0.01), which was significantly higher than in the LTV group since 16 h (p = 0.04). Histological injury scores showed a significantly lower injury score in the middle and lower lobes of the right lung in the APRV group compared to LTV (p_middle = 0.04, p_lower = 0.01), and no significant increase in injury scores for extra-pulmonary organs, including kidney (p = 0.10), small intestine (p = 1.0), liver (p = 0.14, p = 0.13) and heart (p = 0.20). There were no significant differences in serum inflammatory cytokines between the two groups.

CONCLUSION

In conclusion, in the experimental pig models of severe ARDS induced by repetitive saline lavage, APRV improved lung compliance with reduced lung injury of middle and lower lobes, and did not demonstrate more extra-pulmonary organ injuries as compared with LTV.

Quantification of lung function on CT images based on pulmonary radiomic filtering

PURPOSE

To develop a radiomics filtering technique for characterizing spatial-encoded regional pulmonary ventilation information on lung computed tomography (CT).

METHODS

The lung volume was segmented on 46 CT images, and a 3D sliding window kernel was implemented across the lung volume to capture the spatial-encoded image information. Fifty-three radiomic features were extracted within the kernel, resulting in a fourth-order tensor object. As such, each voxel coordinate of the original lung was represented as a 53-dimensional feature vector, such that radiomic features could be viewed as feature maps within the lungs. To test the technique as a potential pulmonary ventilation biomarker, the radiomic feature maps were compared to paired functional images (Galligas PET or DTPA-SPECT) based on the Spearman correlation (ρ) analysis.

RESULTS

The radiomic feature maps GLRLM-based Run-Length Non-Uniformity and GLCOM-based Sum Average are found to be highly correlated with the functional imaging. The achieved ρ (median [range]) for the two features are 0.46 [0.05, 0.67] and 0.45 [0.21, 0.65] across 46 patients and 2 functional imaging modalities, respectively.

CONCLUSIONS

The results provide evidence that local regions of sparsely encoded heterogeneous lung parenchyma on CT are associated with diminished radiotracer uptake and measured lung ventilation defects on PET/SPECT imaging. These findings demonstrate the potential of radiomics to serve as a complementary tool to the current lung quantification techniques and provide hypothesis-generating data for future studies.

Changes in infant porcine pulmonary tissue oxylipins induced by cardiopulmonary bypass

BACKGROUND

Oxylipins are metabolites derived from fatty acids such as arachidonic acid (AA) and are key mediators in inflammation, host defense, and tissue injury. Serum oxylipins increase in adults after cardiopulmonary bypass (CPB) but tissue-level changes are poorly defined. The objective of this study was to characterize pulmonary tissue oxylipins in an infant porcine model of CPB with deep hypothermic circulatory arrest (DHCA).

METHODS

Infant pigs underwent CPB with DHCA. Controls received anesthesia only. Right upper and lower lobes of the lung underwent oxylipin analysis via liquid chromatography-tandem mass spectrometry. One-way ANOVA was utilized to assess differences in oxylipin concentrations across groups, followed by pairwise comparisons.

RESULTS

AA and multiple AA metabolites via cytochrome P450 (CYP450), lipoxygenase (LOX), and cyclooxygenase (COX) pathways were significantly increased in the upper and lower lobe of pigs exposed to CPB/DHCA as compared to controls. Multiple prostaglandin metabolites produced via COX were also significantly elevated in the lower lobes of control animals.

CONCLUSIONS

CPB/DHCA induces a significant increase in pulmonary tissue AA, with subsequent metabolism via COX, LOX, and CYP450 pathways. Interestingly, prostaglandins were also elevated in the lower lobes of the controls, suggesting a mechanism separate from CPB/DHCA. Future oxylipin studies are needed to better understand CPB-induced acute lung injury.

IMPACT

CPB/DHCA and, to a lesser extent, lung region influence pulmonary tissue-level AA metabolite production. Inflammatory mediator AA metabolites have been noted in previous studies to increase following CPB; however, this is the first study to look at pulmonary tissue-level differences following CPB/DHCA. Increases in many AA metabolites, including LOX- and CYP450-derived products, were seen in both upper and lower lobe of piglets following CPB/DHCA. COX-derived prostaglandin metabolites were increased not only in CPB upper and lower lobe but also in mechanically ventilated control lower lobe, suggesting an additional, separate mechanism from CPB/DCHA.

Amyloidogenesis via interfacial shear in a containerless biochemical reactor aboard the International Space Station

Fluid interfaces significantly influence the dynamics of protein solutions, effects that can be isolated by performing experiments in microgravity, greatly reducing the amount of solid boundaries present, allowing air-liquid interfaces to become dominant. This investigation examined the effects of protein concentration on interfacial shear-induced fibrillization of insulin in microgravity within a containerless biochemical reactor, the ring-sheared drop (RSD), aboard the international space station (ISS). Human insulin was used as a model amyloidogenic protein for studying protein kinetics with applications to in situ pharmaceutical production, tissue engineering, and diseases such as Alzheimer’s, Parkinson’s, infectious prions, and type 2 diabetes. Experiments investigated three main stages of amyloidogenesis: nucleation studied by seeding native solutions with fibril aggregates, fibrillization quantified using intrinsic fibrillization rate after fitting measured solution intensity to a sigmoidal function, and gelation observed by detection of solidification fronts. Results demonstrated that in surface-dominated amyloidogenic protein solutions: seeding with fibrils induces fibrillization of native protein, intrinsic fibrillization rate is independent of concentration, and that there is a minimum fibril concentration for gelation with gelation rate and rapidity of onset increasing monotonically with increasing protein concentration. These findings matched well with results of previous studies within ground-based analogs.

Bias field correction in hyperpolarized 129 Xe ventilation MRI using templates derived by RF-depolarization mapping

PURPOSE

To correct for RF inhomogeneity for in vivo 129 Xe ventilation MRI using flip-angle mapping enabled by randomized 3D radial acquisitions. To extend this RF-depolarization mapping approach to create a flip-angle map template applicable to arbitrary acquisition strategies, and to compare these approaches to conventional bias field correction.

METHODS

RF-depolarization mapping was evaluated first in digital simulations and then in 51 subjects who had undergone radial 129 Xe ventilation MRI in the supine position at 3T (views = 3600; samples/view = 128; TR/TE = 4.5/0.45 ms; flip angle = 1.5; FOV = 40 cm). The images were corrected using newly developed RF-depolarization and templated-based methods and the resulting quantitative ventilation metrics (mean, coefficient of variation, and gradient) were compared to those resulting from N4ITK correction.

RESULTS

RF-depolarization and template-based mapping methods yielded a pattern of RF-inhomogeneity consistent with the expected variation based on coil architecture. The resulting corrected images were visually similar, but meaningfully distinct from those generated using standard N4ITK correction. The N4ITK algorithm eliminated the physiologically expected anterior-posterior gradient (-0.04 ± 1.56%/cm, P < 0.001). These 2 newly introduced methods of RF-depolarization and template correction retained the physiologically expected anterior-posterior ventilation gradient in healthy subjects (2.77 ± 2.09%/cm and 2.01 ± 2.73%/cm, respectively).

CONCLUSIONS

Randomized 3D 129 Xe MRI ventilation acquisitions can inherently be corrected for bias field, and this technique can be extended to create flip angle templates capable of correcting images from a given coil regardless of acquisition strategy. These methods may be more favorable than the de facto standard N4ITK because they can remove undesirable heterogeneity caused by RF effects while retaining results from known physiology.

Lung thermography during the initial reperfusion period to assess pulmonary function in cellular ex vivo lung perfusion

BACKGROUND

Thermography is a non-invasive technology to detect low temperatures in poorly circulated areas. In ex vivo lung perfusion (EVLP), lungs are rewarmed to body temperature during the initial 1 h. Currently, the effect of graft thermal changes during the rewarming phase on pulmonary function is unknown. In this study, we evaluated the correlation of lung surface temperature with physiological parameters, wet/dry ratio, and transplant suitability in Lund-type EVLP.

METHODS

Fifteen pigs were divided into three groups: control group (no warm ischemia) or donation after circulatory death groups with 60 or 90 min of warm ischemia (n = 5, each). Thermal images of the lower lobes were continuously collected from the bottom of organ chamber using infrared thermography throughout EVLP.

RESULTS

At 8 min, lung surface temperatures of non-suitable cases were significantly lower than in suitable cases (25.1 ± 0.6 vs. 27.8 ± 1.2°C, P < 0.001), while there was no difference in lung surface temperature between the two groups at 0-4 min and 12-120 min. There was a significant negative correlation between lung surface temperature at 8 min and wet/dry ratio at 2 h in the lower lobes (R = -0.769, P < 0.001, cut-off = 26°C, Area under the curve = 1.0). A lung surface temperature of < 26°C was significantly correlated with poor pulmonary function and transplant non-suitability.

CONCLUSION

A lung surface temperature of ≥ 26°C at 8 min is a good early predictor of transplant suitability in cellular EVLP and might be applicable in clinical EVLP.

Correlation of Serum Albumin Level to Lung Ultrasound Score and Its Role as Predictors of Outcome in Acute Respiratory Distress Syndrome Patients: A Prospective Observational Study

Background

There is ambiguity in the literature regarding hypoalbuminemia as a cause of extravascular lung water and acute respiratory distress syndrome (ARDS) outcomes. The aim of the study was to determine if low serum albumin on admission leads to lung deaeration and higher lung ultrasound score (LUSS) in ARDS patients. Patients and Methods. It was a prospective observational study in which 110 ARDS patients aged between 18 and 70 years were recruited. Serum albumin level and lung ultrasound score were assessed on the day of ICU admission. Length of ICU stay and hospital mortality were recorded.

Results

The mean and standard deviation of serum albumin level in mild, moderate, and severe ARDS was 2.92 ± 0.65 g/dL, 2.91 ± 0.77 g/dL, and 3.21 ± 0.85 g/dL, respectively. Albumin level was not correlated to the global LUSS (Pearson correlation r −0.006, p=0.949) and basal LUSS (r −0.066, p=0.513). The cut-off value of albumin for predicting a prolonged length of ICU stay (≥10 days) in ARDS patients was <3.25 g/dL with AUC 0.623, p < 0.05, sensitivity of 86.67%, specificity of 45.45%, and 95% confidence interval (CI) [0.513–0.732], and on multivariate analysis it increased the odds of prolonged ICU stay by 8.9 times (Hosmer and Lemeshow p value 0.810, 95% CI [2.760–28.72]). Serum albumin at admission was not a predictor of mortality. LUSS on the day of admission was not useful to predict either a prolonged length of ICU stay or mortality. Basal LUSS contributed about 56% of the global LUSS in mild and moderate ARDS, and 53% in severe ARDS.

Conclusion

Serum albumin level was unrelated to LUSS on admission in ARDS patients. Albumin level <3.25 g/dL increased the chances of a prolonged length of ICU stay (≥10 days) but was not associated with an increase in mortality. LUSS on the day of admission could not predict either a prolonged length of ICU stay or mortality. This trial is registered with CTRI/2019/11/021857.

Reappraisal of lung manifestations in the setting of Fontan circulation

Fontan circulation is a well-established palliation in patients with functional single ventricles. Absence of a sub-pulmonary pumping chamber creates a unique physiology in which blood flow is mainly guided by negative intrathoracic and elevated central venous pressures. Various pulmonary anatomic or pathophysiologic changes can jeopardize optimal Fontan circulation. Long-term survival of patients who have undergone the contemporary total cavopulmonary connection is satisfactory. Thorough literature review in conjunction with accumulated clinical experience can lead clinicians to extract conclusions regarding Fontan and lung interactions indicating the purpose of this review.

Oh G: The x, y and z of human physiological responses to acceleration

NEW FINDINGS

What is the topic of this review? This review focuses on the main physiological challenges associated with exposure to acceleration in the Gx, Gy and Gz directions and to microgravity. What advances does it highlight? Our current understanding of the physiology of these environments and latest strategies to protect against them are discussed in light of the limited knowledge we have in some of these areas.

ABSTRACT

The desire to go higher, faster and further has taken us to environments where the accelerations placed on our bodies far exceed or are much lower than that attributable to Earth's gravity. While on the ground, racing drivers of the fastest cars are exposed to high degrees of lateral acceleration (Gy) during cornering. In the air, while within the confines of the lower reaches of Earth's atmosphere, fast jet pilots are routinely exposed to high levels of acceleration in the head-foot direction (Gz). During launch and re-entry of suborbital and orbital spacecraft, astronauts and spaceflight participants are exposed to high levels of chest-back acceleration (Gx), whereas once in space the effects of gravity are all but removed (termed microgravity, μG). Each of these environments has profound effects on the homeostatic mechanisms within the body and can have a serious impact, not only for those with underlying pathology but also for healthy individuals. This review provides an overview of the main challenges associated with these environments and our current understanding of the physiological and pathophysiological adaptations to them. Where relevant, protection strategies are discussed, with the implications of our future exposure to these environments also being considered.

Supine vs upright exercise in patients with hepatopulmonary syndrome and orthodeoxia: study protocol for a randomized controlled crossover trial

BACKGROUND

The hepatopulmonary syndrome (HPS) is a pulmonary complication of liver disease found in 10 to 32% of patients with cirrhosis and is characterized by intrapulmonary vascular dilatations and abnormal oxygenation. Liver transplantation is the only effective therapy for this disease. Patients with HPS have significant exercise limitations, impacting their quality of life and associated with poor liver transplant outcomes. Many patients with HPS exhibit orthodeoxia-an improvement in oxygenation in the supine compared to the upright position. We hypothesize that exercise capacity will be superior in the supine compared to the upright position in such patients.

METHODS

We propose a randomized controlled crossover trial in patients with moderate HPS (PaO₂ < 80 mmHg) and orthodeoxia (supine to upright PaO₂ decrease > 4 mmHg) comparing the effect of supine vs upright position on exercise. Patients with pulmonary hypertension, FEV1/FVC ratio < 0.65, significant coronary artery disease, disorders preventing or contraindicating use of a cycle ergometer, and/or moderate or severe ascites will be excluded. Participants will be randomized to cycle ergometry in either the supine or upright position. After a short washout period (a minimum of 1 day to a maximum of 4 weeks), participants will crossover and perform an exercise in the alternate position. Exercise will be performed at a constant work rate of 70-85% of the predicted peak work rate until the "stopping time" is reached, defined by exhaustion, profound desaturation, or safety concerns (drop in systolic blood pressure or life-threatening arrhythmia). The primary outcome will be the difference in the stopping time between exercise positions, compared with a repeated measures analysis of variance method with a mixed effects model approach. The model will be adjusted for period effects. P < 0.05 will be considered statistically significant.

DISCUSSION

HPS patients have hypoxemia leading to significant exercise limitations. If our study is positive, a supine exercise regimen could become a routine prescription for patients with HPS and orthodeoxia, enabling them to exercise more effectively. Future studies could explore the corresponding effects of a supine exercise training regimen on physiologic variables such as long-term exercise capacity, quality of life, dyspnea, and liver transplantation outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov Protocol Registration and Results System (PRS) NCT04004104 . Registered on 1 July 2019.

Modelling the effects of environmental heterogeneity within the lung on the tuberculosis life-cycle

•

In silico model of TB in the lung incorporating environmental heterogeneity.

•

Preferential conditions at the apex of lung localise post-primary disease there.

•

Analysis of the key influences driving disease at different regions of the lung.

Progress in shortening the duration of tuberculosis (TB) treatment is hampered by the lack of a predictive model that accurately reflects the diverse environment within the lung. This is important as TB has been shown to produce distinct localisations to different areas of the lung during different disease stages, with the environmental heterogeneity within the lung of factors such as air ventilation, blood perfusion and oxygen tension believed to contribute to the apical localisation witnessed during the post-primary form of the disease.

Building upon our previous model of environmental lung heterogeneity, we present a networked metapopulation model that simulates TB across the whole lung, incorporating these notions of environmental heterogeneity across the whole TB life-cycle to show how different stages of the disease are influenced by different environmental and immunological factors. The alveolar tissue in the lung is divided into distinct patches, with each patch representing a portion of the total tissue and containing environmental attributes that reflect the internal conditions at that location. We include populations of bacteria and immune cells in various states, and events are included which determine how the members of the model interact with each other and the environment. By allowing some of these events to be dependent on environmental attributes, we create a set of heterogeneous dynamics, whereby the location of the tissue within the lung determines the disease pathological events that occur there.

Our results show that the environmental heterogeneity within the lung is a plausible driving force behind the apical localisation during post-primary disease. After initial infection, bacterial levels will grow in the initial infection location at the base of the lung until an adaptive immune response is initiated. During this period, bacteria are able to disseminate and create new lesions throughout the lung. During the latent stage, the lesions that are situated towards the apex are the largest in size, and once a post-primary immune-suppressing event occurs, it is the uppermost lesions that reach the highest levels of bacterial proliferation. Our sensitivity analysis also shows that it is the differential in blood perfusion, causing reduced immune activity towards the apex, which has the biggest influence of disease outputs.

Lung lobe torsion in 15 dogs: Peripheral band sign on ultrasound

The diagnosis of lung lobe torsion in dogs is usually based on radiological, endoscopic, and CT features. Few ultrasonographic descriptions have been published. The purpose of this multicenter, retrospective, and prospective observational study was to investigate the presence of a hypoechoic area forming a pulmonary band or line at the periphery of the twisted lobe on ultrasonography and assess its significance by comparing it to CT and histological findings. Fifteen dogs with lung lobe torsion confirmed surgically or postmortem were included. All had received ultrasonography and CT examinations; 13 had additional histopathological examination performed. In 14 cases, thoracic ultrasonography revealed a peripheral hypoechoic band, overlying areas of scattered, hyperreflecting interfaces in the affected lobe. On CT, central emphysema was surrounded by a peripheral, soft tissue attenuation band, affecting the periphery in 14 cases. No band was observed in one case, in which the lobe was entirely consolidated. Histological examination yielded a comparable peripheral band, consisting of a thickened visceral pleura with or without hemorrhagic necrosis of the underlying pulmonary parenchyma. This peripheral band may be related to the specific fractal organization of airways and vessels, which plays an important role in lung perfusion and ventilation and makes the lung periphery more prone to ischemia. Our findings suggest that the presence of a peripheral hypoechoic band, associated with central emphysema in a noncollapsed lung lobe on ultrasonography, is suggestive of compromised blood supply and air flow, and lung lobe torsion should therefore be suspected.

The quantitative assessment of interstitial lung disease with positron emission tomography scanning in systemic sclerosis patients

Objectives

The reversibility of interstitial lung disease (ILD) in SSc is difficult to assess by current diagnostic modalities and there is clinical need for imaging techniques that allow for treatment stratification and monitoring. ¹⁸F-Fluorodeoxyglucose (FDG) PET/CT scanning may be of interest for this purpose by detection of metabolic activity in lung tissue. This study aimed to investigate the potential role of ¹⁸F-FDG PET/CT scanning for the quantitative assessment of SSc-related active ILD.

Methods

¹⁸F-FDG PET/CT scans and high resolution CT scans of eight SSc patients, including five with ILD, were analysed. For comparison, reference groups were included: eight SLE patients and four primary Sjögren’s syndrome (pSS) patients, all without ILD. A total of 22 regions of interest were drawn in each patient at apical, medial and dorsobasal lung levels. ¹⁸F-FDG uptake was measured as mean standardized uptake value (SUVmean) in each region of interest. Subsequently, basal/apical (B/A) and medial/apical (M/A) ratios were calculated at patient level (B/A-p and M/A-p) and at tissue level (B/A-t and M/A-t).

Results

SUVmean values in dorsobasal ROIs and B/A-p ratios were increased in SSc with ILD compared with SSc without ILD (P = 0.04 and P = 0.07, respectively), SLE (P = 0.003 and P = 0.002, respectively) and pSS (P = 0.03 and P = 0.02, respectively). Increased uptake in the dorsobasal lungs and increased B/A-t ratios corresponded to both ground glass and reticulation on high resolution CT.

Conclusion

Semi-quantitative assessment of ¹⁸F-FDG PET/CT is able to distinguish ILD from non-affected lung tissue in SSc, suggesting that it may be used as a new biomarker for SSc-ILD disease activity.

Normal Dual Isotope V/Q SPECT Model for Monte-Carlo Studies

Background: There is currently no reliable or validated tool to delineate and quantify functional lung volumes with ventilation/perfusion (V/Q) SPECT/CT. The main challenges encountered include the physiological non-uniformity of lung function, such as the anterior-to-posterior gradient on perfusion images, and the lack of ground truth to assess the accuracy of delineation algorithms. In that respect, Monte-Carlo simulations would be an interesting tool. Thus, the aim of this study was to develop a realistic model of dual-isotope lung V/Q SPECT-CT Monte-Carlo simulations, integrating the anterior to posterior gradient on perfusion. Methods: Acquisitions and simulations parameters were set in accordance to nuclear medicine guidelines for V/Q lung SPECT-CT. Projections were acquired and simulated, then the reconstructions [with and without attenuation correction (AC)] were compared. A model was built from a patient's CT scan. To model the anterior to posterior gradient, the lungs were divided into sixteen coronal planes, where a rising radioactivity concentration was set. To assess the realism of simulations, they were compared to a normal co-registered normal cases database in terms of pixelwize Z-score map. Results: For ventilation images, mean (SD) Zscores on Zscore maps were -0.2 (0.7) and -0.2 (0.7) for AC and noAC images, respectively. For perfusion images, mean (SD) Zscores were -0.2 (0.6) and -0.1 (0.6) for AC and noAC images, respectively. Conclusion: We developed a model for dual isotopes lung V/Q SPECT-CT, integrating the anterior-to-posterior gradient on perfusion images. This model could be used to build a catalog of clinical scenarios, in order to test delineation methods of functional lung volumes.

Respiratory Physiology for the Anesthesiologist

Respiratory function is fundamental in the practice of anesthesia. Knowledge of basic physiologic principles of respiration assists in the proper implementation of daily actions of induction and maintenance of general anesthesia, delivery of mechanical ventilation, discontinuation of mechanical and pharmacologic support, and return to the preoperative state. The current work provides a review of classic physiology and emphasizes features important to the anesthesiologist. The material is divided in two main sections, gas exchange and respiratory mechanics; each section presents the physiology as the basis of abnormal states. We review the path of oxygen from air to the artery and of carbon dioxide the opposite way, and we have the causes of hypoxemia and of hypercarbia based on these very footpaths. We present the actions of pressure, flow, and volume as the normal determinants of ventilation, and we review the resulting abnormalities in terms of changes of resistance and compliance.

Impact of Body Position on Lung Deposition of Nebulized Surfactant in Newborn Piglets on Nasal Continuous Positive Airway Pressure

INTRODUCTION

The ideal body position during surfactant nebulization is not known.

OBJECTIVE

The aim of this study was to determine whether body positioning during surfactant nebulization influences surfactant distribution and deposition in the lungs.

METHODS

Twenty-four 12- to 36-h-old full-termpiglets (1.3-2.2 kg) on nasal continuous positive airway pressure (nCPAP) were randomized into four groups: lateral decubitus with right or left side up, prone or supine positions (n = 6 each). All animals received 200 mg kg-1 of poractant alfa mixed with 200 MBq of 99mtechnetium-nanocolloid via a customized eFlow-Neos investigational vibrating-membrane nebulizer. Surfactant deposition (percentage of the administered dose) was measured by gamma scintigraphy.

RESULTS

Comparing all groups, the mean total lung surfactant deposition was significantly higher in the prone position (32.4 ± 7.7%, p = 0.03). The deposition in this group was higher in the right lung (21.0 ± 8.6 vs. 11.3 ± 5.7%, p = 0.04). When nebulization was performed in the lateral decubitus, most of the surfactant was found in the dependent lung, regardless of which side the piglet lay on (right side up 15.3 ± 1.0 vs. 3.4 ± 1.0%, p = 0.06, and left side up 11.2 ± 9.8 vs. 1.8 ± 0.7%, p = 0.04).

CONCLUSIONS

In spontaneously breathing animals on nCPAP, the prone position yielded the highest lung dose. Higher deposition rates in the dependent lung while on lateral decubitus indicates that deposition was also influenced by gravity.

Supine, prone, right and left gravitational effects on human pulmonary circulation

BACKGROUND

Body position can be optimized for pulmonary ventilation/perfusion matching during surgery and intensive care. However, positional effects upon distribution of pulmonary blood flow and vascular distensibility measured as the pulmonary blood volume variation have not been quantitatively characterized. In order to explore the potential clinical utility of body position as a modulator of pulmonary hemodynamics, we aimed to characterize gravitational effects upon distribution of pulmonary blood flow, pulmonary vascular distension, and pulmonary vascular distensibility.

METHODS

Healthy subjects (n = 10) underwent phase contrast cardiovascular magnetic resonance (CMR) pulmonary artery and vein flow measurements in the supine, prone, and right/left lateral decubitus positions. For each lung, blood volume variation was calculated by subtracting venous from arterial flow per time frame.

RESULTS

Body position did not change cardiac output (p = 0.84). There was no difference in blood flow between the superior and inferior pulmonary veins in the supine (p = 0.92) or prone body positions (p = 0.43). Compared to supine, pulmonary blood flow increased to the dependent lung in the lateral positions (16-33%, p = 0.002 for both). Venous but not arterial cross-sectional vessel area increased in both lungs when dependent compared to when non-dependent in the lateral positions (22-27%, p ≤ 0.01 for both). In contrast, compared to supine, distensibility increased in the non-dependent lung in the lateral positions (68-113%, p = 0.002 for both).

CONCLUSIONS

CMR demonstrates that in the lateral position, there is a shift in blood flow distribution, and venous but not arterial blood volume, from the non-dependent to the dependent lung. The non-dependent lung has a sizable pulmonary vascular distensibility reserve, possibly related to left atrial pressure. These results support the physiological basis for positioning patients with unilateral pulmonary pathology with the "good lung down" in the context of intensive care. Future studies are warranted to evaluate the diagnostic potential of these physiological insights into pulmonary hemodynamics, particularly in the context of non-invasively characterizing pulmonary hypertension.

Changes in lung volume parameters regarding the received dose in the lobes of the lungs after locoregional radiotherapy of breast cancer

Aim

The purpose of this study was to evaluate ΔLVP and correlate them with MLD and V20 in the lobes of the lung.

Background

Radiation-induced lung injury after breast irradiation is controversial. The incidence of such an injury could have negative consequences on breast cancer patients.

Materials and Methods

Twenty-three women treated with Breast-conserving surgery, chemotherapy, and locoregional RT underwent body plethysmography pre-RT and 3 and 6 months post-RT. Statistical analysis was used to evaluate ΔLVP over time and relate them with MLD, V20, age, and concurrent hormonal therapy.

Results

LVP decreased after 3 months and then showed a slight improvement by returning partially to their pre-RT values after 6 months. The mean ΔLVP was -0.64% for one Gy increase of MLD and -0.34% for one percent increase of V20 after 3 months. After 6 months, only ΔVC showed 0.45% reduction with MLD in the upper lobe. Finally, there was no significant correlation between ΔLVP with respect to age and concurrent hormonal therapy.

Conclusions

The results of this study showed that lung volume changes were not a cause for concern in breast cancer patients. There are three reasons to support this conclusion. Lung volume changes and percentage reductions in LVP for each Gy increase of MLD and each percentage increase of V20 in each lobe were small; patients were asymptomatic during the follow-up period; and LVP showed partial improvements after 6 months.

Functional CT imaging for identification of the spatial determinants of small-airways disease in adults with asthma

BACKGROUND

Asthma is a disease characterized by ventilation heterogeneity (VH). A number of studies have demonstrated that VH markers derived by using impulse oscillometry (IOS) or multiple-breath washout (MBW) are associated with key asthmatic patient-related outcome measures and airways hyperresponsiveness. However, the topographical mechanisms of VH in the lung remain poorly understood.

OBJECTIVES

We hypothesized that specific regionalization of topographical small-airway disease would best account for IOS- and MBW-measured indices in patients.

METHODS

We evaluated the results of paired expiratory/inspiratory computed tomography in a cohort of asthmatic (n = 41) and healthy (n = 11) volunteers to understand the determinants of clinical VH indices commonly reported by using IOS and MBW. Parametric response mapping (PRM) was used to calculate the functional small-airways disease marker PRMfSAD and Hounsfield unit (HU)-based density changes from total lung capacity to functional residual capacity (ΔHU); gradients of ΔHU in gravitationally perpendicular (parallel) inferior-superior (anterior-posterior) axes were quantified.

RESULTS

The ΔHU gradient in the inferior-superior axis provided the highest level of discrimination of both acinar VH (measured by using phase 3 slope analysis of multiple-breath washout data) and resistance at 5 Hz minus resistance at 20 Hz measured by using impulse oscillometry (R5-R20) values. Patients with a high inferior-superior ΔHU gradient demonstrated evidence of reduced specific ventilation in the lower lobes of the lungs and high levels of PRMfSAD. A computational small-airway tree model confirmed that constriction of gravitationally dependent, lower-zone, small-airway branches would promote the largest increases in R5-R20 values. Ventilation gradients correlated with asthma control and quality of life but not with exacerbation frequency.

CONCLUSIONS

Lower lobe-predominant small-airways disease is a major driver of clinically measured VH in adults with asthma.

Do pulmonary cavity shapes influence lung function?

Distribution of lung tissue within the chest cavity is a key contributor to delivery of both blood and air to the gas exchange regions of the lung. This distribution is multifactorial with influences from parenchyma, gravity and level of inflation. We hypothesize that the manner in which lung inflates, for example, the primarily diaphragmatic nature of normal breathing, is an important contributor to regional lung tissue distribution. To investigate this hypothesis, we present an organ-level model of lung tissue mechanics which incorporates pleural cavity change due to change in lung volume or posture. We quantify the changes using shape and density metrics in ten healthy subjects scanned supine at end-inspiratory and end-expiratory volumes and ten subjects scanned at both supine and prone end-inspiratory volumes. Comparing end-expiratory to end-inspiratory volume, we see primarily a change in the cranial-caudal dimension of the lung, reflective of movement of diaphragm. In the diaphragmatic region there is greater regional lung expansion than in the cranial aspect, which is restricted by the chest wall. When moving from supine to prone, a restriction of lung was observed anteriorly, resulting in a generally reduced lung volume and a redistribution of air volume posteriorly. In general, we see the highest in lung tissue density heterogeneity in regions of the lung that are most inflated. Using our computational model, we quantify the impact of pleural cavity shape change on regional lung distribution, and predict the impact on regional elastic recoil pressure.

Pulmonary Artery Compression Facilitates Intersegmental Border Visualization

Intravenous indocyanine green injection is useful for the identification of the intersegmental border by infrared thoracoscopy during anatomic segmentectomy. However, surgeons encounter cases in which visualization of the intersegmental border is difficult. In particular, intravenous indocyanine green fluorescence in the upper lobe is occasionally obscured by to the relatively lesser blood flow in the upper lobe pulmonary arteries. This report describes an interlobar pulmonary artery compression method that is a simple and effective technique for clearly visualizing the intersegmental border through infrared thoracoscopy with intravenous indocyanine green during upper lobe segmentectomy.

Significant increases in the density and number of lymphatic vessels in pleuroparenchymal fibroelastosis

AIMS

Some investigators have detected fibrinous exudate or immature organisation in the alveolar spaces prior to the development of subpleural elastofibrosis in patients with pleuroparenchymal fibroelastosis (PPFE). We hypothesised that PPFE progress is associated with an impaired lymphatic drainage system, resulting in the failed resolution of intra-alveolar exudate. The aim of this study is to investigate the pulmonary lymphatic vessels in PPFE, histologically.

METHODS AND RESULTS

We retrospectively reviewed our medical records from 1995 to 2017, and selected autopsied or surgically biopsied patients with PPFE (n = 18), pulmonary apical cap (n = 18), and IPF (n = 26). We detected lymphatic endothelial cells by using immunostained specimens, calculating the percentage of lymphatic vessel area in the non-aerated area (lymphatic vessel density) and the number of lymphatic vessels per non-aerated area (per mm² ) (lymphatic vessel number). These parameters in PPFE were compared with those in apical cap, IPF, and normal lung tissue. The lymphatic vessel density in PPFE patients [2.97%; interquartile range (IQR) 2.61-3.86] was significantly higher than that in normal lung (0.91%; IQR 0.84-1.07), pulmonary apical cap (0.67%; IQR 0.58-0.83), and IPF (0.91%; IQR 0.68-1.25) (P < 0.01 in any comparison). The lymphatic vessel number in PPFE was also significantly higher than that in normal lung, pulmonary apical cap, and IPF. Among PPFE patients, the increase in lymphatic vessel density was found to be correlated with the characteristic physiology of PPFE, such as a flattened chest cage on computed tomography and high residual volume/total lung capacity ratio on spirometry.

CONCLUSIONS

Significant increase in the density and number of lymphatic vessels is a supportive characteristic that enables the differentiation of PPFE from IPF and apical cap.

Pulmonary Circulation Transvascular Fluid Fluxes Do Not Change during General Anesthesia in Dogs

General anesthesia (GA) can cause abnormal lung fluid redistribution. Pulmonary circulation transvascular fluid fluxes (J_VA) are attributed to changes in hydrostatic forces and erythrocyte volume (EV) regulation. Despite the very low hydraulic conductance of pulmonary microvasculature it is possible that GA may affect hydrostatic forces through changes in pulmonary vascular resistance (PVR), and EV through alteration of erythrocyte transmembrane ion fluxes (_ionJ_VA). Furosemide (Fur) was also used because of its potential to affect pulmonary hydrostatic forces and _ionJ_VA. A hypothesis was tested that J_VA, with or without furosemide treatment, will not change with time during GA. Twenty dogs that underwent castration/ovariectomy were randomly assigned to Fur (n = 10) (4 mg/kg IV) or placebo treated group (Con, n = 10). Baseline arterial (BL) and mixed venous blood were sampled during GA just before treatment with Fur or placebo and then at 15, 30 and 45 min post-treatment. Cardiac output (Q) and pulmonary artery pressure (P_AP) were measured. J_VA and _ionJ_VA were calculated from changes in plasma protein, hemoglobin, hematocrit, plasma and whole blood ions, and Q. Variables were analyzed using random intercept mixed model (P < 0.05). Data are expressed as means ± SE. Furosemide caused a significant volume depletion as evident from changes in plasma protein and hematocrit (P < 0.001). However; Q, P_AP, and J_VA were not affected by time or Fur, whereas erythrocyte fluid flux was affected by Fur (P = 0.03). Furosemide also affected erythrocyte transmembrane K⁺ and Cl⁻, and transvascular Cl⁻ metabolism (P ≤ 0.05). No other erythrocyte transmembrane or transvascular ion fluxes were affected by time of GA or Fur. Our hypothesis was verified as J_VA was not affected by GA or ion metabolism changes due to Fur treatment. Furosemide and 45 min of GA did not cause significant hydrostatic changes based on Q and P_AP. Inhibition of Na⁺/K⁺/2Cl⁻ cotransport caused by Fur treatment, which can alter EV regulation and J_VA, was offset by the Jacobs Stewart cycle. The results of this study indicate that the Jacobs Stewart cycle/erythrocyte Cl⁻ metabolism can also act as a safety factor for the stability of lung fluid redistribution preserving optimal diffusion distance across the blood gas barrier.

Deregulated angiogenesis in chronic lung diseases: a possible role for lung mesenchymal progenitor cells (2017 Grover Conference Series)

Chronic lung disease (CLD), including pulmonary fibrosis (PF) and chronic obstructive pulmonary disease (COPD), is the fourth leading cause of mortality worldwide. Both are debilitating pathologies that impede overall tissue function. A common co-morbidity in CLD is vasculopathy, characterized by deregulated angiogenesis, remodeling, and loss of microvessels. This substantially worsens prognosis and limits survival, with most current therapeutic strategies being largely palliative. The relevance of angiogenesis, both capillary and lymph, to the pathophysiology of CLD has not been resolved as conflicting evidence depicts angiogenesis as both reparative or pathologic. Therefore, we must begin to understand and model the underlying pathobiology of pulmonary vascular deregulation, alone and in response to injury induced disease, to define cell interactions necessary to maintain normal function and promote repair. Capillary and lymphangiogenesis are deregulated in both PF and COPD, although the mechanisms by which they co-regulate and underlie early pathogenesis of disease are unknown. The cell-specific mechanisms that regulate lung vascular homeostasis, repair, and remodeling represent a significant gap in knowledge, which presents an opportunity to develop targeted therapies. We have shown that that ABCG2^pos multipotent adult mesenchymal stem or progenitor cells (MPC) influence the function of the capillary microvasculature as well as lymphangiogenesis. A balance of both is required for normal tissue homeostasis and repair. Our current models suggest that when lymph and capillary angiogenesis are out of balance, the non-equivalence appears to support the progression of disease and tissue remodeling. The angiogenic regulatory mechanisms underlying CLD likely impact other interstitial lung diseases, tuberous sclerosis, and lymphangioleiomyomatosis.

Image-based computational fluid dynamics in the lung: virtual reality or new clinical practice?

The development and implementation of personalized medicine is paramount to improving the efficiency and efficacy of patient care. In the respiratory system, function is largely dictated by the choreographed movement of air and blood to the gas exchange surface. The passage of air begins in the upper airways, either via the mouth or nose, and terminates at the alveolar interface, while blood flows from the heart to the alveoli and back again. Computational fluid dynamics (CFD) is a well-established tool for predicting fluid flows and pressure distributions within complex systems. Traditionally CFD has been used to aid in the effective or improved design of a system or device; however, it has become increasingly exploited in biological and medical-based applications further broadening the scope of this computational technique. In this review, we discuss the advancement in application of CFD to the respiratory system and the contributions CFD is currently making toward improving precision medicine. The key areas CFD has been applied to in the pulmonary system are in predicting fluid transport and aerosol distribution within the airways. Here we focus our discussion on fluid flows and in particular on image-based clinically focused CFD in the ventilatory system. We discuss studies spanning from the paranasal sinuses through the conducting airways down to the level of the alveolar airways. The combination of imaging and CFD is enabling improved device design in aerosol transport, improved biomarkers of lung function in clinical trials, and improved predictions and assessment of surgical interventions in the nasal sinuses. WIREs Syst Biol Med 2017, 9:e1392. doi: 10.1002/wsbm.1392 For further resources related to this article, please visit the WIREs website.

Hypoxic Pulmonary Vasoconstriction in Humans: Tale or Myth

Hypoxic Pulmonary vasoconstriction (HPV) describes the physiological adaptive process of lungs to preserves systemic oxygenation. It has clinical implications in the development of pulmonary hypertension which impacts on outcomes of patients undergoing cardiothoracic surgery. This review examines both acute and chronic hypoxic vasoconstriction focusing on the distinct clinical implications and highlights the role of calcium and mitochondria in acute versus the role of reactive oxygen species and Rho GTPases in chronic HPV. Furthermore it identifies gaps of knowledge and need for further research in humans to clearly define this phenomenon and the underlying mechanism.

Platypnea-orthodeoxia Syndrome Induced by an Infected Giant Hepatic Cyst

An 83-year-old man was admitted with a chief complaint of exacerbation of dyspnea. His blood oxygen saturation was 90% in the recumbent position despite oxygen therapy, and it dropped to less than 80% when the patient attempted to sit upright. A computed tomography scan revealed a giant hepatic cyst compressing the right atrium and the inferior vena cava. After percutaneous drainage, the oxygen saturation improved and did not change with alteration of the patient's positions from recumbent to sitting or standing. This case report describes a patient with the platypnea-orthodeoxia syndrome due to a giant hepatic cyst successfully managed by percutaneous drainage.

Effect of time and body position on ventilation in premature infants

BACKGROUND

Infants with respiratory dysfunction undergo regular position changes to improve lung function however it is not known how often a position change should occur. This study measured changes in lung function occurring over time after repositioning in preterm infants.

METHODS

Changes in end-expiratory level (EEL) and ventilation distribution were measured 30 mins, 2 h, and 4 h after repositioning into either prone, quarter turn from prone, or supine using Electrical Impedance Tomography (EIT). Physiological measurements were also taken.

RESULTS

Sixty preterm infants were included in the study. Infants receiving respiratory support (mechanical ventilation or continuous positive airway pressure (CPAP)) had improved ventilation homogeneity after 2 h (P < 0.01), maintained at 4 h. Spontaneously breathing infants had improved homogeneity at 2 h (P < 0.01) and improved global EEL after 4 h (P < 0.01) whereas infants receiving CPAP demonstrated an improved global EEL at 2 h (P < 0.01).

CONCLUSION

Regional ventilation distribution is influenced by time independent of changes due to body position. Differences exist between infants on ventilatory support compared with those who are spontaneously breathing. Infants receiving ventilatory support have a physiological peak in lung function after 2 h which remains above baseline at 4 h. A change in body position facilitates an improvement in lung function in infants on ventilatory support.

Hypoxia-induced pulmonary arterial hypertension augments lung injury and airway reactivity caused by ozone exposure

Ozone (O3)-related cardiorespiratory effects are a growing public health concern. Ground level O3 can exacerbate pre-existing respiratory conditions; however, research regarding therapeutic interventions to reduce O3-induced lung injury is limited. In patients with chronic obstructive pulmonary disease, hypoxia-associated pulmonary hypertension (HPH) is a frequent comorbidity that is difficult to treat clinically, yet associated with increased mortality and frequency of exacerbations. In this study, we hypothesized that established HPH would confer vulnerability to acute O3 pulmonary toxicity. Additionally, we tested whether improvement of pulmonary endothelial barrier integrity via rho-kinase inhibition could mitigate pulmonary inflammation and injury. To determine if O3 exacerbated HPH, male C57BL/6 mice were subject to either 3 weeks continuous normoxia (20.9% O2) or hypoxia (10.0% O2), followed by a 4-h exposure to either 1ppm O3 or filtered air (FA). As an additional experimental intervention fasudil (20mg/kg) was administered intraperitoneally prior to and after O3 exposures. As expected, hypoxia significantly increased right ventricular pressure and hypertrophy. O3 exposure in normoxic mice caused lung inflammation but not injury, as indicated by increased cellularity and edema in the lung. However, in hypoxic mice, O3 exposure led to increased inflammation and edema, along with a profound increase in airway hyperresponsiveness to methacholine. Fasudil administration resulted in reduced O3-induced lung injury via the enhancement of pulmonary endothelial barrier integrity. These results indicate that increased pulmonary vascular pressure may enhance lung injury, inflammation and edema when exposed to pollutants, and that enhancement of pulmonary endothelial barrier integrity may alleviate such vulnerability.

Effect of Electrode Belt and Body Positions on Regional Pulmonary Ventilation- and Perfusion-Related Impedance Changes Measured by Electric Impedance Tomography

Ventilator-induced or ventilator-associated lung injury (VILI/VALI) is common and there is an increasing demand for a tool that can optimize ventilator settings. Electrical impedance tomography (EIT) can detect changes in impedance caused by pulmonary ventilation and perfusion, but the effect of changes in the position of the body and in the placing of the electrode belt on the impedance signal have not to our knowledge been thoroughly evaluated. We therefore studied ventilation-related and perfusion-related changes in impedance during spontaneous breathing in 10 healthy subjects in five different body positions and with the electrode belt placed at three different thoracic positions using a 32-electrode EIT system. We found differences between regions of interest that could be attributed to changes in the position of the body, and differences in impedance amplitudes when the position of the electrode belt was changed. Ventilation-related changes in impedance could therefore be related to changes in the position of both the body and the electrode belt. Perfusion-related changes in impedance were probably related to the interference of major vessels. While these findings give us some insight into the sources of variation in impedance signals as a result of changes in the positions of both the body and the electrode belt, further studies on the origin of the perfusion-related impedance signal are needed to improve EIT further as a tool for the monitoring of pulmonary ventilation and perfusion.

Effects of a 1:1 inspiratory to expiratory ratio on respiratory mechanics and oxygenation during one-lung ventilation in patients with low diffusion capacity of lung for carbon monoxide: a crossover study

STUDY OBJECTIVE

To investigate the effects of a 1:1 inspiratory-to-expiratory (I:E) ventilation ratio on oxygenation and respiratory mechanics during one-lung ventilation (OLV) in patients with low diffusion capacity of lung for carbon monoxide (DLCO).

DESIGN

Prospective, randomized, crossover study.

SETTING

Operating room, university hospital.

PATIENTS

Twenty-six patients with a preoperative DLCO less than 80% who were scheduled for lung lobectomy requiring OLV under general anesthesia.

INTERVENTIONS

In the first group (n = 13), OLV was begun with a 1:1 I:E ratio, which was switched to a 1:2 I:E ratio after 30 minutes. In the second group (n = 13), the modes of ventilation were performed in the opposite order. Pressure-controlled ventilation with 5 cm H2O of positive end-expiratory pressure and a tidal volume of 5 to 8 mL/kg was applied during OLV.

MEASUREMENTS

Arterial and central venous blood gas analyses were recorded and used to calculate intrapulmonary shunt fraction and physiologic dead space. These measurements were taken at 4 time points: 10 minutes after two-lung ventilation in the lateral decubitus position, 30 minutes after initiation of OLV, 30 minutes after switching the I:E ratio, and 10 minutes after two-lung ventilation was resumed.

MAIN RESULTS

There was no difference in arterial oxygen tension during OLV between the 2 groups (P = .429). Arterial carbon dioxide tension and peak airway pressure were lower in the 1:1 group than in the 1:2 group (P = .003; P = .008). Physiologic dead space was also decreased in the 1:1 I:E ratio group (P = .003). Mean airway pressure and dynamic compliance were higher in the 1:1 group (P = .003; P = .007).

CONCLUSIONS

Pressure-controlled ventilation with a 1:1 I:E ventilation ratio did not improve oxygenation in patients with low DLCO during OLV compared with a 1:2 I:E ventilation ratio. However, it did provide benefits in terms of respiratory mechanics and increased the efficiency of alveolar ventilation during OLV.

Mechanical ventilation of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) has been intensively and continuously studied in various settings, but its mortality is still as high as 30-40 %. For the last 20 years, lung protective strategy has become a standard care for ARDS, but we still do not know the best way to ventilate patients with ARDS. Tidal volume itself does not seem to have an important role to develop ventilator-induced lung injury (VILI), but the driving pressure, which is inspiratory plateau pressure-PEEP, is the most important to predict and affect the outcome of ARDS, though there is no safe limit for the driving pressure. There is so much controversy regarding what the best PEEP is, whether collapsed lung should be recruited, and what parameters should be measured and evaluated to improve the outcome of ARDS. Since the mechanical ventilation for patients with respiratory failure, including ARDS, is a standard care, we need more dynamic and regional information of ventilation and pulmonary circulation in the injured lungs to evaluate the efficacy of new type of treatment strategy. In addition to the CT scanning of the lung as the gold standard of evaluation, the electrical impedance tomography (EIT) of the lung has been clinically available to provide such information non-invasively and at the bedside. Various parameters have been tested to evaluate the homogeneity of regional ventilation, and EIT could provide us with the information of ventilator settings to minimize VILI.

Quantitative Assessment of Global and Regional Air Trappings Using Non-Rigid Registration and Regional Specific Volume Change of Inspiratory/Expiratory CT Scans: Studies on Healthy Volunteers and Asthmatics

Objective

The purpose of this study was to compare air trapping in healthy volunteers with asthmatics using pulmonary function test and quantitative data, such as specific volume change from paired inspiratory CT and registered expiratory CT.

Materials and Methods

Sixteen healthy volunteers and 9 asthmatics underwent paired inspiratory/expiratory CT. ΔSV, which represents the ratio of air fraction released after exhalation, was measured with paired inspiratory and anatomically registered expiratory CT scans. Air trapping indexes, ΔSV_0.4 and ΔSV_0.5, were defined as volume fraction of lung below 0.4 and 0.5 ΔSV, respectively. To assess the gravity effect of air-trapping, ΔSV values of anterior and posterior lung at three different levels were measured and ΔSV ratio of anterior lung to posterior lung was calculated. Color-coded ΔSV map of the whole lung was generated and visually assessed. Mean ΔSV, ΔSV_0.4, and ΔSV_0.5 were compared between healthy volunteers and asthmatics. In asthmatics, correlation between air trapping indexes and clinical parameters were assessed.

Results

Mean ΔSV, ΔSV_0.4, and ΔSV_0.5 in asthmatics were significantly higher than those in healthy volunteer group (all p < 0.05). ΔSV values in posterior lung in asthmatics were significantly higher than those in healthy volunteer group (p = 0.049). In asthmatics, air trapping indexes, such as ΔSV_0.5 and ΔSV_0.4, showed negative strong correlation with FEF_25-75, FEV₁, and FEV₁/FVC. ΔSV map of asthmatics showed abnormal geographic pattern in 5 patients (55.6%) and disappearance of anterior-posterior gradient in 3 patients (33.3%).

Conclusion

Quantitative assessment of ΔSV (the ratio of air fraction released after exhalation) shows the difference in extent of air trapping between health volunteers and asthmatics.

A new quantitative index of lobar air trapping in chronic obstructive pulmonary disease (COPD): comparison with conventional methods

PURPOSE

To determine the usefulness of newly-proposed index (attenuation-volume index, AVI: increase in mean value of lung attenuation (MVLA) divided by volume decrease ratio (VDR)) for quantitative assessment of lobar air trapping (LAT) using expiratory/inspiratory (E/I) computed tomography (CT) by minimizing influence of respiratory level.

MATERIALS AND METHODS

Institutional review board approved study protocol. Twenty-one moderate or severe COPD (group A), 16 mild COPD (group B) and 26 normal volunteers (group C) underwent both E/I scans via 320-row CT and pulmonary functional test (PFT). Volume image data were automatically segmented into six lung lobes with minimal manual intervention. AVI, pixel index (PI), air trapping ratio (ATR) and relative volume change (RVC860-950) were calculated in total lung (TL) and each lobe. Four indices in TL were correlated with both PFT result and VDR and those in TL and each lobe were compared between three groups.

RESULTS

Similar to ATR, AVI correlated with both FEV1/FVC (r=0.772, p<0.01) and RV/TLC (r=-0.726, p<0.01) and demonstrated a significant difference between three groups in both TL (group A: 1.69±0.45, group B: 2.21±0.45 and group C: 2.80±0.44) and five lobes except for left lingular segment. In a lobe-based analysis regarding relationship with VDR, AVI was much less dependent than ATR, although regression lines of groups A and C were separated for AVI as well as ATR. Coefficient of variation of either PI or RVC860-950 was significantly larger than that of AVI.

CONCLUSION

AVI can be a more suitable CT index for quantitative evaluation of LAT, minimizing influence of respiratory level.

Computational modeling of the obstructive lung diseases asthma and COPD

Asthma and chronic obstructive pulmonary disease (COPD) are characterized by airway obstruction and airflow limitation and pose a huge burden to society. These obstructive lung diseases impact the lung physiology across multiple biological scales. Environmental stimuli are introduced via inhalation at the organ scale, and consequently impact upon the tissue, cellular and sub-cellular scale by triggering signaling pathways. These changes are propagated upwards to the organ level again and vice versa. In order to understand the pathophysiology behind these diseases we need to integrate and understand changes occurring across these scales and this is the driving force for multiscale computational modeling.

There is an urgent need for improved diagnosis and assessment of obstructive lung diseases. Standard clinical measures are based on global function tests which ignore the highly heterogeneous regional changes that are characteristic of obstructive lung disease pathophysiology. Advances in scanning technology such as hyperpolarized gas MRI has led to new regional measurements of ventilation, perfusion and gas diffusion in the lungs, while new image processing techniques allow these measures to be combined with information from structural imaging such as Computed Tomography (CT). However, it is not yet known how to derive clinical measures for obstructive diseases from this wealth of new data. Computational modeling offers a powerful approach for investigating this relationship between imaging measurements and disease severity, and understanding the effects of different disease subtypes, which is key to developing improved diagnostic methods.

Gaining an understanding of a system as complex as the respiratory system is difficult if not impossible via experimental methods alone. Computational models offer a complementary method to unravel the structure-function relationships occurring within a multiscale, multiphysics system such as this. Here we review the current state-of-the-art in techniques developed for pulmonary image analysis, development of structural models of the respiratory system and predictions of function within these models. We discuss application of modeling techniques to obstructive lung diseases, namely asthma and emphysema and the use of models to predict response to therapy. Finally we introduce a large European project, AirPROM that is developing multiscale models to investigate structure-function relationships in asthma and COPD.

Acute and delayed toxicity of gemcitabine administered during isolated lung perfusion: a preclinical dose-escalation study in pigs

OBJECTIVES

Colorectal cancer is the third most commonly diagnosed cancer worldwide, with up to 25% of patients presenting with metastases at the time of diagnosis. Despite pulmonary metastasectomy many patients go on to develop pulmonary recurrence, which might be linked to the presence of lung micrometastases. In this setting, the adjuvant administration of high-dose chemotherapy by isolated lung perfusion (ILP) has shown encouraging results. However, the tolerance to and efficacy of modern gemcitabine (GEM)-based chemotherapy regimens during adjuvant ILP remain unknown. We conducted a dose-escalating preclinical study to evaluate the immediate and delayed toxicity of GEM in a pig model to define dose-limiting toxicity (DLT) and maximum tolerated concentration.

METHODS

Twenty-three pigs were given increasing concentrations of GEM during ILP, and were awakened at the end of the procedure. The concentrations of GEM were 40, 80, 160, 320, 640 and 1280 µg/ml. Serum and lung samples were taken to measure GEM concentrations. Pulmonary damage was evaluated by histological examination and cleaved caspase-3 detection. Immediate and delayed (1 month) toxicity were recorded.

RESULTS

All of the animals underwent successful ILP with GEM. No systemic leak was observed. The three pigs that received a concentration of GEM of 1280 µg/ml died of hypoxia after lung recirculation at the end of the procedure. Eleven pigs survived for 1 month. Major lung toxicity was observed for the concentration of GEM of 640 µg/ml, both at the end of the procedure and after 1 month. DLT was defined at the concentration of 640 µg/ml and the maximum tolerated dose (MTD) was defined at the concentration of 320 µg/ml.

CONCLUSIONS

ILP with GEM is a safe and reproducible technique in this large-animal model, which includes 1 month of survival. The MTD in this pig model was a concentration of GEM of 320 µg/ml.

Increase in relative deposition of fine particles in the rat lung periphery in the absence of gravity

While it is well recognized that pulmonary deposition of inhaled particles is lowered in microgravity (μG) compared with gravity on the ground (1G), the absence of sedimentation causes fine particles to penetrate deeper in the lung in μG. Using quantitative magnetic resonance imaging (MRI), we determined the effect of gravity on peripheral deposition (DEPperipheral) of fine particles. Aerosolized 0.95-μm-diameter ferric oxide particles were delivered to spontaneously breathing rats placed in plethysmographic chambers both in μG aboard the NASA Microgravity Research Aircraft and at 1G. Following exposure, lungs were perfusion fixed, fluid filled, and imaged in a 3T MR scanner. The MR signal decay rate, R2*, was measured in each voxel of the left lung from which particle deposition (DEP) was determined based on a calibration curve. Regional deposition was assessed by comparing DEP between the outer (DEPperipheral) and inner (DEPcentral) areas on each slice, and expressed as the central-to-peripheral ratio. Total lung deposition tended to be lower in μG compared with 1G (1.01 ± 0.52 vs. 1.43 ± 0.52 μg/ml, P = 0.1). In μG, DEPperipheral was larger than DEPcentral (P < 0.03), while, in 1G, DEPperipheral was not significantly different from DEPcentral. Finally, central-to-peripheral ratio was significantly less in μG than in 1G (P ≤ 0.05). These data show a larger fraction of fine particles depositing peripherally in μG than in 1G, likely beyond the large- and medium-sized airways. Although not measured, the difference in the spatial distribution of deposited particles between μG and 1G could also affect particle retention rates, with an increase in retention for particles deposited more peripherally.

Challenging a paradigm: positional changes in ventilation distribution are highly variable in healthy infants and children

RATIONALE

Current understanding is that infants and children preferentially ventilate non-dependent lungs, a reversal of that of adults, based on studies using krypton-81m ventilation scanning. Participants in these studies had lung disease and were either sedated or ventilated. There is little understanding of the distribution of ventilation in spontaneous breathing healthy infants and children.

OBJECTIVES

This study aimed to determine the effects of side lying on the distribution of ventilation in healthy, spontaneously breathing infants and children between the ages of 6 months and 9 years.

METHODS AND MEASUREMENTS

Measurements were taken using electrical impedance tomography (EIT) in supine, left and right side lying. Distribution of ventilation was described using end-expiratory to end-inspiratory relative impedance change.

RESULTS

Fifty-six (31, 55% male) participants were studied. Nineteen (35%) participants consistently showed greater ventilation in the non-dependent lung, eight (15%) consistently showed greater ventilation in the dependent lung and 28 (51%) showed a varied pattern between left and right side lying. Overall, left side lying resulted in significantly better mean ventilation of the right (non-dependent) lung (P < 0.01). Distribution of ventilation in right side lying was relatively equal between left and right lungs.

CONCLUSIONS

This study demonstrates that the distribution of ventilation in spontaneously breathing infants and children is not as straightforward as previously described. The distribution of ventilation was variably affected by body position with no clear reversal of the adult pattern evident.

Aerosol deposition in the human lung in reduced gravity

The deposition of aerosol in the human lung occurs mainly through a combination of inertial impaction, gravitational sedimentation, and diffusion. For 0.5- to 5-μm-diameter particles and resting breathing conditions, the primary mechanism of deposition in the intrathoracic airways is sedimentation, and therefore the fate of these particles is markedly affected by gravity. Studies of aerosol deposition in altered gravity have mostly been performed in humans during parabolic flights in both microgravity (μG) and hypergravity (~1.6G), where both total deposition during continuous aerosol mouth breathing and regional deposition using aerosol bolus inhalations were performed with 0.5- to 3-μm particles. Although total deposition increased with increasing gravity level, only peripheral deposition as measured by aerosol bolus inhalations was strongly dependent on gravity, with central deposition (lung depth<200 mL) being similar between gravity levels. More recently, the spatial distribution of coarse particles (mass median aerodynamic diameter≈5 μm) deposited in the human lung was assessed using planar gamma scintigraphy. The absence of gravity caused a smaller portion of 5-μm particles to deposit in the lung periphery than in the central region, where deposition occurred mainly in the airways. Indeed, 5-μm-diameter particles deposit either by inertial impaction, a mechanism most efficient in the large and medium-sized airways, or by gravitational sedimentation, which is most efficient in the distal lung. On the contrary, for fine particles (~1 μm), both aerosol bolus inhalations and studies in small animals suggest that particles deposit more peripherally in μG than in 1G, beyond the reach of the mucociliary clearance system.

Positive end-expiratory pressure attenuates positional effect after thoracotomy

CONTEXT:

Thoracotomy is a common procedure. However, thoracotomy leads to lung atelectasis and deteriorates pulmonary gas exchange in operated side. Therefore, different positions with operated side lowermost or uppermost may lead to different gas exchange after thoracotomy. Besides, PEEP (positive end-expiratory pressure) influence lung atelectasis and should influence gas exchange.

AIMS:

The purpose of this study was to determine the physiological changes in different positions after thoracotomy. In addition, we also studied the influence of PEEP to positional effects after thoracotomy.

MATERIALS AND METHODS:

There were eight pigs in each group. Group I received left thoracotomy with zero end-expiratory pressure (ZEEP), and group II with PEEP; group III received right thoracotomy with ZEEP and group IV with PEEP. We changed positions to supine, LLD (left lateral decubitus) and RLD (right lateral decubitus) in random order after thoracotomy.

RESULTS:

PaO₂ was decreased after thoracotomy and higher in RLD after left thoracotomy and in LLD after right thoracotomy. PaO₂ in groups II and IV was higher than in groups I and III if with the same position. In group I and III, PaCO₂ was increased after thoracotomy and was higher in LLD after left thoracotomy and in RLD after right thoracotomy. In groups II and IV, there were no PaCO₂ changes in different positions after thoracotomy. Lung compliance (C_rs) was decreased after thoracotomy in groups I and III and highest in RLD after left thoracotomy and in LLD after right thoracotomy. In groups II and IV, there were no changes in C_rs regardless of the different positions.

CONCLUSION:

There were significant changes with regards to pulmonary gas exchange, hemodynamics and C_rs after thoracotomy. The best position was non-operated lung lowermost Applying PEEP attenuates the positional effects.