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Janowski AM, Ravellette KS, Insel M, Garcia JGN, Rischard FP, Vanderpool RR. Advanced hemodynamic and cluster analysis for identifying novel RV function subphenotypes in patients with pulmonary hypertension. J Heart Lung Transplant 2024; 43:755-770. [PMID: 38141893 DOI: 10.1016/j.healun.2023.12.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Revised: 12/18/2023] [Accepted: 12/18/2023] [Indexed: 12/25/2023] Open
Abstract
BACKGROUND Quantifying right ventricular (RV) function is important to describe the pathophysiology of in pulmonary hypertension (PH). Current phenotyping strategies in PH rely on few invasive hemodynamic parameters to quantify RV dysfunction severity. The aim of this study was to identify novel RV phenotypes using unsupervised clustering methods on advanced hemodynamic features of RV function. METHODS Participants were identified from the University of Arizona Pulmonary Hypertension Registry (n = 190). RV-pulmonary artery coupling (Ees/Ea), RV systolic (Ees), and diastolic function (Eed) were quantified from stored RV pressure waveforms. Consensus clustering analysis with bootstrapping was used to identify the optimal clustering method. Pearson correlation analysis was used to reduce collinearity between variables. RV cluster subphenotypes were characterized using clinical data and compared to pulmonary vascular resistance (PVR) quintiles. RESULTS Five distinct RV clusters (C1-C5) with distinct RV subphenotypes were identified using k-medoids with a Pearson distance matrix. Clusters 1 and 2 both have low diastolic stiffness (Eed) and afterload (Ea) but RV-PA coupling (Ees/Ea) is decreased in C2. Intermediate cluster (C3) has a similar Ees/Ea as C2 but with higher PA pressure and afterload. Clusters C4 and C5 have increased Eed and Ea but C5 has a significant decrease in Ees/Ea. Cardiac output was high in C3 distinct from the other clusters. In the PVR quintiles, contractility increased and stroke volume decreased as a function of increased afterload. World Symposium PH classifications were distributed across clusters and PVR quintiles. CONCLUSIONS RV-centric phenotyping offers an opportunity for a more precise-medicine-based management approach.
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Affiliation(s)
- Alexandra M Janowski
- Division of Cardiovascular Medicine, The Ohio State University, Columbus, Ohio; Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio
| | - Keeley S Ravellette
- Division of Translational and Regenerative Medicine, The University of Arizona, Tucson, Arizona
| | - Michael Insel
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, The University of Arizona, Tucson, Arizona
| | - Joe G N Garcia
- Center for Inflammation Science and Systems Medicine, University of Florida, Jupiter, Florida
| | - Franz P Rischard
- Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, The University of Arizona, Tucson, Arizona
| | - Rebecca R Vanderpool
- Division of Cardiovascular Medicine, The Ohio State University, Columbus, Ohio; Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio.
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Kianzad A, Baccelli A, Braams NJ, Andersen S, van Wezenbeek J, Wessels JN, Celant LR, Vos AE, Davies R, Lo Giudice F, Haji G, Rinaldo RF, Vigo B, Gopalan D, Symersky P, Winkelman JA, Boonstra A, Nossent EJ, Tim Marcus J, Vonk Noordegraaf A, Meijboom LJ, de Man FS, Andersen A, Howard LS, Bogaard HJ. Long-term effects of pulmonary endarterectomy on pulmonary hemodynamics, cardiac function, and exercise capacity in chronic thromboembolic pulmonary hypertension. J Heart Lung Transplant 2024; 43:580-593. [PMID: 38000764 DOI: 10.1016/j.healun.2023.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Revised: 11/06/2023] [Accepted: 11/17/2023] [Indexed: 11/26/2023] Open
Abstract
BACKGROUND Long-term changes in exercise capacity and cardiopulmonary hemodynamics after pulmonary endarterectomy (PEA) for chronic thromboembolic pulmonary hypertension (CTEPH) have been poorly described. METHODS We analyzed the data from 2 prospective surgical CTEPH cohorts in Hammersmith Hospital, London, and Amsterdam UMC. A structured multimodal follow-up was adopted, consisting of right heart catheterization, cardiac magnetic resonance imaging, and cardiopulmonary exercise testing before and after PEA. Preoperative predictors of residual pulmonary hypertension (PH; mean pulmonary artery pressure >20 mm Hg and pulmonary vascular resistance ≥2 WU) and long-term exercise intolerance (VO2max <80%) at 18 months were analyzed. RESULTS A total of 118 patients (61 from London and 57 from Amsterdam) were included in the analysis. Both cohorts displayed a significant improvement of pulmonary hemodynamics, right ventricular (RV) function, and exercise capacity 6 months after PEA. Between 6 and 18 months after PEA, there were no further improvements in hemodynamics and RV function, but the proportion of patients with impaired exercise capacity was high and slightly increased over time (52%-59% from 6 to 18 months). Long-term exercise intolerance was common and associated with preoperative diffusion capacity for carbon monoxide (DLCO), preoperative mixed venous oxygen saturation, and postoperative PH and right ventricular ejection fraction (RVEF). Clinically significant RV deterioration (RVEF decline >3%; 5 [9%] of 57 patients) and recurrent PH (5 [14%] of 36 patients) rarely occurred beyond 6 months after PEA. Age and preoperative DLCO were predictors of residual PH post-PEA. CONCLUSIONS Restoration in exercise tolerance, cardiopulmonary hemodynamics, and RV function occurs within 6 months. No substantial changes occurred between 6 and 18 months after PEA in the Amsterdam cohort. Nevertheless, long-term exercise intolerance is common and associated with postoperative RV function.
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Affiliation(s)
- Azar Kianzad
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Andrea Baccelli
- National Heart and Lung Institute, Imperial College London, London, United Kingdom; Respiratory Unit, ASST Santi Paolo e Carlo, San Paolo Hospital, Department of Health Sciences, University of Milan, Milan, Italy
| | - Natalia J Braams
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Stine Andersen
- Aarhus University Hospital, Department of Cardiology, Aarhus, Denmark
| | - Jessie van Wezenbeek
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Jeroen N Wessels
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Lucas R Celant
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Anna E Vos
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands
| | - Rachel Davies
- National Pulmonary Hypertension Service, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Francesco Lo Giudice
- National Pulmonary Hypertension Service, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Gulammehdi Haji
- National Pulmonary Hypertension Service, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Rocco F Rinaldo
- Respiratory Unit, ASST Santi Paolo e Carlo, San Paolo Hospital, Department of Health Sciences, University of Milan, Milan, Italy
| | - Beatrice Vigo
- Respiratory Unit, ASST Santi Paolo e Carlo, San Carlo Hospital, Department of Health Sciences, University of Milan, Milan, Italy
| | - Deepa Gopalan
- Department of Radiology, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Petr Symersky
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Cardiothoracic Surgery, Amsterdam, the Netherlands
| | - Jacobus A Winkelman
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Cardiothoracic Surgery, Amsterdam, the Netherlands
| | - Anco Boonstra
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Esther J Nossent
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - J Tim Marcus
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands; Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Radiology and Nuclear Medicine, Amsterdam, the Netherlands
| | - Anton Vonk Noordegraaf
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Lilian J Meijboom
- Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands; Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Radiology and Nuclear Medicine, Amsterdam, the Netherlands
| | - Frances S de Man
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands
| | - Asger Andersen
- Aarhus University Hospital, Department of Cardiology, Aarhus, Denmark
| | - Luke S Howard
- National Heart and Lung Institute, Imperial College London, London, United Kingdom; National Pulmonary Hypertension Service, Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Harm Jan Bogaard
- Amsterdam UMC, location Vrije Universiteit Amsterdam, Department of Pulmonary Medicine, Amsterdam, the Netherlands; Amsterdam Cardiovascular Sciences, Pulmonary Hypertension and Thrombosis, Amsterdam, the Netherlands.
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Schreier DA, Hacker TA, Tabima DM, Platt MO, Chesler NC. Effects of Red Blood Cell Sickling on Right Ventricular Afterload in vivo. Exp Mech 2021; 61:229-235. [PMID: 33776073 PMCID: PMC7992815 DOI: 10.1007/s11340-020-00669-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 09/28/2020] [Indexed: 06/12/2023]
Abstract
BACKGROUND Hemolysis in sickle cell disease (SCD) releases cell free hemoglobin, which scavenges nitric oxide (NO), leading to pulmonary vascular vasoconstriction, increased pulmonary vascular resistance (PVR), and the development of PH. However, PVR is only one component of right ventricular (RV) afterload. Whether sickled red blood cells increase the total RV afterload, including compliance and wave reflections, is unclear. OBJECTIVE Patients with SCD and pulmonary hypertension (PH) have a significantly increased risk of sudden death compared to patients with SCD alone. Sickled red blood cells (RBCs) are fragile and lyse easily. Here, we sought to determine the acute effects of SCD RBCs and increased cell free hemoglobin on RV afterload. METHODS Main pulmonary artery pressures and flows were measured in C57BL6 mice before and after exchanges of whole blood (~200 uL, Hct=45%) with an equal volume of SCD RBCs in plasma (Hct=45%) or cell free hemoglobin (Hb+) in solution. After transfusions, animals were additionally stressed with acute hypoxia (AH; 10% O2). RESULTS SCD RBCs increased PVR only compared to control RBCs; cell free hemoglobin increased PVR and wave reflections. These increases in RV afterload increased further with AH. CONCLUSIONS The release of cell free hemoglobin from fragile SCD RBCs in vivo increases the total RV afterload and may impair RV function more than the SCD RBCs themselves.
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Affiliation(s)
- D A Schreier
- Department of Biomedical Engineering University of Wisconsin, 2146 ECB, 1550 Engineering Dr., Madison, WI 53706
| | - T A Hacker
- Department of Medicine 1685 Highland Avenue, 5158 Medical Foundation Centennial Building, Madison, WI 53705-2281
| | - D M Tabima
- Department of Biomedical Engineering University of Wisconsin, 2146 ECB, 1550 Engineering Dr., Madison, WI 53706
| | - M O Platt
- Department of Biomedical Engineering University of Georgia Tech, Engineered Biosystems Building, 950 Atlantic Drive, Suite 3015, Atlanta, GA 30332
| | - N C Chesler
- Department of Biomedical Engineering University of Wisconsin, 2146 ECB, 1550 Engineering Dr., Madison, WI 53706
- Department of Medicine 1685 Highland Avenue, 5158 Medical Foundation Centennial Building, Madison, WI 53705-2281
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Schreier DA, Hacker TA, Hunter K, Eickoff J, Liu A, Song G, Chesler N. Impact of increased hematocrit on right ventricular afterload in response to chronic hypoxia. J Appl Physiol (1985) 2014; 117:833-9. [PMID: 25170068 DOI: 10.1152/japplphysiol.00059.2014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic hypoxia causes chronic mountain sickness through hypoxia-induced pulmonary hypertension (HPH) and increased hematocrit. Here, we investigated the impact of increased hematocrit and HPH on right ventricular (RV) afterload via pulmonary vascular impedance. Mice were exposed to chronic normobaric hypoxia (10% oxygen) for 10 (10H) or 21 days (21H). After baseline hemodynamic measurements, ∼500 μl of blood were extracted and replaced with an equal volume of hydroxyethylstarch to normalize hematocrit and all hemodynamic measurements were repeated. In addition, ∼500 μl of blood were extracted and replaced in control mice with an equal volume of 90% hematocrit blood. Chronic hypoxia increased input resistance (Z0 increased 82% in 10H and 138% in 21H vs. CTL; P < 0.05) and characteristic impedance (ZC increased 76% in 10H and 109% in 21H vs. CTL; P < 0.05). Hematocrit normalization did not decrease mean pulmonary artery pressure but did increase cardiac output such that both Z0 and ZC decreased toward control levels. Increased hematocrit in control mice did not increase pressure but did decrease cardiac output such that Z0 increased. The paradoxical decrease in ZC with an acute drop in hematocrit and no change in pressure are likely due to inertial effects secondary to the increase in cardiac output. A novel finding of this study is that an increase in hematocrit affects the pulsatile RV afterload in addition to the steady RV afterload (Z0). Furthermore, our results highlight that the conventional interpretation of ZC as a measure of proximal artery stiffness is not valid in all physiological and pathological states.
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Affiliation(s)
- David A Schreier
- Department of Biomedical Engineering University of Wisconsin, Madison, Wisconson
| | - Timothy A Hacker
- Department of Medicine Medical Science Center, Madison, Wisconsin; and
| | - Kendall Hunter
- Department of Bioengineering University of Colorado, Aurora, Colorado
| | - Jens Eickoff
- Department of Medicine Medical Science Center, Madison, Wisconsin; and
| | - Aiping Liu
- Department of Biomedical Engineering University of Wisconsin, Madison, Wisconson
| | - Gouqing Song
- Department of Medicine Medical Science Center, Madison, Wisconsin; and
| | - Naomi Chesler
- Department of Biomedical Engineering University of Wisconsin, Madison, Wisconson; Department of Medicine Medical Science Center, Madison, Wisconsin; and
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Liu A, Schreier D, Tian L, Eickhoff JC, Wang Z, Hacker TA, Chesler NC. Direct and indirect protection of right ventricular function by estrogen in an experimental model of pulmonary arterial hypertension. Am J Physiol Heart Circ Physiol 2014; 307:H273-83. [PMID: 24906919 DOI: 10.1152/ajpheart.00758.2013] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pulmonary arterial hypertension (PAH) results in right ventricular (RV) dysfunction and failure. Paradoxically, women are more frequently diagnosed with PAH but have better RV systolic function and survival rates than men. The mechanisms by which sex differences alter PAH outcomes remain unknown. Here, we sought to study the role of estrogen in RV functional remodeling in response to PAH. The SU5416-hypoxia (SuHx) mouse model of PAH was used. To study the role of estrogen, female mice were ovariectomized and then treated with estrogen or placebo. SuHx significantly increased RV afterload and resulted in RV hypertrophy. Estrogen treatment attenuated the increase in RV afterload compared with the untreated group (effective arterial elastance: 2.3 ± 0.1 mmHg/μl vs. 3.2 ± 0.3 mmHg/μl), and this was linked to preserved pulmonary arterial compliance (compliance: 0.013 ± 0.001 mm(2)/mmHg vs. 0.010 ± 0.001 mm(2)/mmHg; P < 0.05) and decreased distal muscularization. Despite lower RV afterload in the estrogen-treated SuHx group, RV contractility increased to a similar level as the placebo-treated SuHx group, suggesting an inotropic effect of estrogen on RV myocardium. Consequently, when compared with the placebo-treated SuHx group, estrogen improved RV ejection fraction and cardiac output (ejection fraction: 57 ± 2% vs. 44 ± 2% and cardiac output: 9.7 ± 0.4 ml/min vs. 7.6 ± 0.6 ml/min; P < 0.05). Our study demonstrates for the first time that estrogen protects RV function in the SuHx model of PAH in mice directly by stimulating RV contractility and indirectly by protecting against pulmonary vascular remodeling. These results underscore the therapeutic potential of estrogen in PAH.
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Affiliation(s)
- Aiping Liu
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - David Schreier
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - Lian Tian
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - Jens C Eickhoff
- Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison, Madison, Wisconsin
| | - Zhijie Wang
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin
| | - Timothy A Hacker
- Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin
| | - Naomi C Chesler
- Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin; Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin
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Linguraru MG, Pura JA, Gladwin MT, Koroulakis AI, Minniti C, Machado RF, Kato GJ, Wood BJ. Computed tomography correlates with cardiopulmonary hemodynamics in pulmonary hypertension in adults with sickle cell disease. Pulm Circ 2014; 4:319-29. [PMID: 25006451 PMCID: PMC4070777 DOI: 10.1086/675997] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Accepted: 02/17/2014] [Indexed: 01/18/2023] Open
Abstract
Our objective was to determine whether computed tomography angiography (CTA) measurements of pulmonary artery size can noninvasively assess hemodynamics and diagnose pulmonary hypertension (PH) secondary to sickle cell disease (SCD). Twenty SCD patients with confirmed PH were compared with 20 matched controls. Diameters of the pulmonary artery trunk and branches were measured with CTA and a semiautomatic segmentation algorithm. Measurements were normalized by body size and correlated (Spearman rank) with hemodynamic markers from right-heart catheterization. Receiver operating characteristic (ROC) curves were used to investigate the role of pulmonary artery sizes in diagnosing PH. Analysis of pulmonary artery sizes adjusted for body surface area (BSA) resulted in the most significant discrimination between subjects with PH secondary to SCD and controls (P < 0.001); PH was diagnosed accurately with an area under the ROC curve of 0.99. There was significant correlation between pulmonary artery sizes and body mass index (BMI) and BSA only in controls (r = 0.46-0.68, P < 0.04 for all). The most significant correlations with hemodynamic markers were found between BMI-adjusted pulmonary artery sizes and high systolic pulmonary arterial pressure, high pulmonary vascular resistance, high systemic vascular resistance, and low cardiac output (r = 0.47, 0.62, 0.61, and 0.66, respectively; P < 0.04 for all). BMI-adjusted CTA measures of the pulmonary artery relate to high pulmonary vascular resistance and reduced cardiac output in patients with SCD and PH. CTA with quantitative image analysis is a powerful noninvasive diagnostic tool for PH in SCD and shows promise as estimator of hemodynamic markers.
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Affiliation(s)
- Marius George Linguraru
- Sheikh Zayed Institute for Pediatric Surgical Innovation, Children’s National Healthcare System, Washington, DC, USA
- Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, Maryland, USA
- School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - John A. Pura
- Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, Maryland, USA
- Department of Biostatistics and Bioinformatics, Duke University, Durham, North Carolina, USA
| | - Mark T. Gladwin
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Antony I. Koroulakis
- Sheikh Zayed Institute for Pediatric Surgical Innovation, Children’s National Healthcare System, Washington, DC, USA
- School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | - Caterina Minniti
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Roberto F. Machado
- Section of Pulmonary/Critical Care, Department of Medicine, University of Illinois at Chicago, Chicago, Illinois, USA
| | - Gregory J. Kato
- Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Bradford J. Wood
- Radiology and Imaging Sciences, National Institutes of Health Clinical Center, Bethesda, Maryland, USA
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