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Hopkins SR, Stickland MK. The Pulmonary Vasculature. Semin Respir Crit Care Med 2023; 44:538-554. [PMID: 37816344 DOI: 10.1055/s-0043-1770059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/12/2023]
Abstract
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.
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Affiliation(s)
- Susan R Hopkins
- Department of Radiology, University of California, San Diego, California
| | - Michael K Stickland
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta
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2
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Hsia CCW. Tissue Perfusion and Diffusion and Cellular Respiration: Transport and Utilization of Oxygen. Semin Respir Crit Care Med 2023; 44:594-611. [PMID: 37541315 DOI: 10.1055/s-0043-1770061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/06/2023]
Abstract
This article provides an overview of the journey of inspired oxygen after its uptake across the alveolar-capillary interface, and the interplay among tissue perfusion, diffusion, and cellular respiration in the transport and utilization of oxygen. The critical interactions between oxygen and its facilitative carriers (hemoglobin in red blood cells and myoglobin in muscle cells), and with other respiratory and vasoactive molecules (carbon dioxide, nitric oxide, and carbon monoxide), are emphasized to illustrate how this versatile system dynamically optimizes regional convective transport and diffusive gas exchange. The rates of reciprocal gas exchange in the lung and the periphery must be well-matched and sufficient for meeting the range of energy demands from rest to maximal stress but not excessive as to become toxic. The mobile red blood cells play a vital role in matching tissue perfusion and gas exchange by dynamically regulating the controlled uptake of oxygen and communicating regional metabolic signals across different organs. Intracellular oxygen diffusion and facilitation via myoglobin into the mitochondria, and utilization via electron transport chain and oxidative phosphorylation, are summarized. Physiological and pathophysiological adaptations are briefly described. Dysfunction of any component across this integrated system affects all other components and elicits corresponding structural and functional adaptation aimed at matching the capacities across the entire system and restoring equilibrium under normal and pathological conditions.
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Affiliation(s)
- Connie C W Hsia
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas
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3
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Hsia CCW, Bates JHT, Driehuys B, Fain SB, Goldin JG, Hoffman EA, Hogg JC, Levin DL, Lynch DA, Ochs M, Parraga G, Prisk GK, Smith BM, Tawhai M, Vidal Melo MF, Woods JC, Hopkins SR. Quantitative Imaging Metrics for the Assessment of Pulmonary Pathophysiology: An Official American Thoracic Society and Fleischner Society Joint Workshop Report. Ann Am Thorac Soc 2023; 20:161-195. [PMID: 36723475 PMCID: PMC9989862 DOI: 10.1513/annalsats.202211-915st] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Multiple thoracic imaging modalities have been developed to link structure to function in the diagnosis and monitoring of lung disease. Volumetric computed tomography (CT) renders three-dimensional maps of lung structures and may be combined with positron emission tomography (PET) to obtain dynamic physiological data. Magnetic resonance imaging (MRI) using ultrashort-echo time (UTE) sequences has improved signal detection from lung parenchyma; contrast agents are used to deduce airway function, ventilation-perfusion-diffusion, and mechanics. Proton MRI can measure regional ventilation-perfusion ratio. Quantitative imaging (QI)-derived endpoints have been developed to identify structure-function phenotypes, including air-blood-tissue volume partition, bronchovascular remodeling, emphysema, fibrosis, and textural patterns indicating architectural alteration. Coregistered landmarks on paired images obtained at different lung volumes are used to infer airway caliber, air trapping, gas and blood transport, compliance, and deformation. This document summarizes fundamental "good practice" stereological principles in QI study design and analysis; evaluates technical capabilities and limitations of common imaging modalities; and assesses major QI endpoints regarding underlying assumptions and limitations, ability to detect and stratify heterogeneous, overlapping pathophysiology, and monitor disease progression and therapeutic response, correlated with and complementary to, functional indices. The goal is to promote unbiased quantification and interpretation of in vivo imaging data, compare metrics obtained using different QI modalities to ensure accurate and reproducible metric derivation, and avoid misrepresentation of inferred physiological processes. The role of imaging-based computational modeling in advancing these goals is emphasized. Fundamental principles outlined herein are critical for all forms of QI irrespective of acquisition modality or disease entity.
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Kizhakke Puliyakote AS, Elliott AR, Sá RC, Anderson KM, Crotty Alexander LE, Hopkins SR. Vaping disrupts ventilation-perfusion matching in asymptomatic users. J Appl Physiol (1985) 2020; 130:308-317. [PMID: 33180648 DOI: 10.1152/japplphysiol.00709.2020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Inhalation of e-cigarette's aerosols (vaping) has the potential to disrupt pulmonary gas exchange, but the effects in asymptomatic users are unknown. We assessed ventilation-perfusion (V̇A/Q̇) mismatch in asymptomatic e-cigarette users, using magnetic resonance imaging (MRI). We hypothesized that vaping induces V̇A/Q̇ mismatch through alterations in both ventilation and perfusion distributions. Nine young, asymptomatic "Vapers" with >1-yr vaping history, and no history of cardiopulmonary disease, were imaged supine using proton MRI, to assess the right lung at baseline and immediately after vaping. Seven young "Controls" were imaged at baseline only. Relative dispersion (SD/means) was used to quantify the heterogeneity of the individual ventilation and perfusion distributions. V̇A/Q̇ mismatch was quantified using the second moments of the ventilation and perfusion versus V̇A/Q̇ ratio distributions, log scale, LogSDV̇, and LogSDQ̇, respectively, analogous to the multiple inert gas elimination technique. Spirometry was normal in both groups. Ventilation heterogeneity was similar between groups at baseline (Vapers, 0.43 ± 0.13; Controls, 0.51 ± 0.11; P = 0.13) but increased after vaping (to 0.57 ± 0.17; P = 0.03). Perfusion heterogeneity was greater (P = 0.04) in Vapers at baseline (0.53 ± 0.06) compared with Controls (0.44 ± 0.10) but decreased after vaping (to 0.42 ± 0.07; P = 0.005). Vapers had greater (P = 0.01) V̇A/Q̇ mismatch at baseline compared with Controls (LogSDQ̇ = 0.61 ± 0.12 vs. 0.43 ± 0.12), which was increased after vaping (LogSDQ̇ = 0.73 ± 0.16; P = 0.03). V̇A/Q̇ mismatch is greater in Vapers and worsens after vaping. This suggests subclinical alterations in lung function not detected by spirometry.NEW & NOTEWORTHY This research provides evidence of vaping-induced disruptions in ventilation-perfusion matching in young, healthy, asymptomatic adults with normal spirometry who habitually vape. The changes in ventilation and perfusion distributions, both at baseline and acutely after vaping, and the potential implications on hypoxic vasoconstriction are particularly relevant in understanding the pathogenesis of vaping-induced dysfunction. Our imaging-based approach provides evidence of potential subclinical alterations in lung function below thresholds of detection using spirometry.
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Affiliation(s)
- Abhilash S Kizhakke Puliyakote
- Pulmonary Imaging Laboratory, Department of Radiology, UC San Diego Health Sciences, San Diego, California.,Department of Radiology, University of California, San Diego, California
| | - Ann R Elliott
- Pulmonary Imaging Laboratory, Department of Radiology, UC San Diego Health Sciences, San Diego, California.,Department of Medicine, University of California, San Diego, California
| | - Rui C Sá
- Pulmonary Imaging Laboratory, Department of Radiology, UC San Diego Health Sciences, San Diego, California.,Department of Medicine, University of California, San Diego, California
| | - Kevin M Anderson
- Pulmonary Imaging Laboratory, Department of Radiology, UC San Diego Health Sciences, San Diego, California.,Department of Radiology, University of California, San Diego, California
| | | | - Susan R Hopkins
- Pulmonary Imaging Laboratory, Department of Radiology, UC San Diego Health Sciences, San Diego, California.,Department of Radiology, University of California, San Diego, California.,Department of Medicine, University of California, San Diego, California
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Hopkins SR, Sá RC, Prisk GK, Elliott AR, Kim NH, Pazar BJ, Printz BF, El-Said HG, Davis CK, Theilmann RJ. Abnormal pulmonary perfusion heterogeneity in patients with Fontan circulation and pulmonary arterial hypertension. J Physiol 2020; 599:343-356. [PMID: 33026102 DOI: 10.1113/jp280348] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Accepted: 10/06/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The distribution of pulmonary perfusion is affected by gravity, vascular branching structure and active regulatory mechanisms, which may be disrupted by cardiopulmonary disease, but this is not well studied, particularly in rare conditions. We evaluated pulmonary perfusion in patients who had undergone Fontan procedure, patients with pulmonary arterial hypertension (PAH) and two groups of controls using a proton magnetic resonance imaging technique, arterial spin labelling to measure perfusion. Heterogeneity was assessed by the relative dispersion (SD/mean) and gravitational gradients. Gravitational gradients were similar between all groups, but heterogeneity was significantly increased in both patient groups compared to controls and persisted after removing contributions from large blood vessels and gravitational gradients. Patients with Fontan physiology and patients with PAH have increased pulmonary perfusion heterogeneity that is not explainable by differences in mean perfusion, gravitational gradients, or large vessel anatomy. This probably reflects vascular remodelling in PAH and possibly in Fontan physiology. ABSTRACT Many factors affect the distribution of pulmonary perfusion, which may be disrupted by cardiopulmonary disease, but this is not well studied, particularly in rare conditions. An example is following the Fontan procedure, where pulmonary perfusion is passive, and heterogeneity may be increased because of the underlying pathophysiology leading to Fontan palliation, remodelling, or increased gravitational gradients from low flow. Another is pulmonary arterial hypertension (PAH), where gravitational gradients may be reduced secondary to high pressures, but remodelling may increase perfusion heterogeneity. We evaluated regional pulmonary perfusion in Fontan patients (n = 5), healthy young controls (Fontan control, n = 5), patients with PAH (n = 6) and healthy older controls (PAH control) using proton magnetic resonance imaging. Regional perfusion was measured using arterial spin labelling. Heterogeneity was assessed by the relative dispersion (SD/mean) and gravitational gradients. Mean perfusion was similar (Fontan = 2.50 ± 1.02 ml min-1 ml-1 ; Fontan control = 3.09 ± 0.58, PAH = 3.63 ± 1.95; PAH control = 3.98 ± 0.91, P = 0.26), and the slopes of gravitational gradients were not different (Fontan = -0.23 ± 0.09 ml min-1 ml-1 cm-1 ; Fontan control = -0.29 ± 0.23, PAH = -0.27 ± 0.09, PAH control = -0.25 ± 0.18, P = 0.91) between groups. Perfusion relative dispersion was greater in both Fontan and PAH than controls (Fontan = 1.46 ± 0.18; Fontan control = 0.99 ± 0.21, P = 0.005; PAH = 1.22 ± 0.27, PAH control = 0.91 ± 0.12, P = 0.02) but similar between patient groups (P = 0.13). These findings persisted after removing contributions from large blood vessels and gravitational gradients (all P < 0.05). We conclude that patients with Fontan physiology and PAH have increased pulmonary perfusion heterogeneity that is not explained by differences in mean perfusion, gravitational gradients, or large vessel anatomy. This probably reflects the effects of remodelling in PAH and possibly in Fontan physiology.
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Affiliation(s)
- Susan R Hopkins
- Department of Radiology, University of California, San Diego, CA, USA.,Department of Medicine, University of California, San Diego, CA, USA
| | - Rui C Sá
- Department of Medicine, University of California, San Diego, CA, USA
| | - G Kim Prisk
- Department of Radiology, University of California, San Diego, CA, USA.,Department of Medicine, University of California, San Diego, CA, USA
| | - Ann R Elliott
- Department of Medicine, University of California, San Diego, CA, USA
| | - Nick H Kim
- Department of Medicine, University of California, San Diego, CA, USA
| | - Beni J Pazar
- Department of Radiology, University of California, San Diego, CA, USA
| | - Beth F Printz
- Department of Radiology, University of California, San Diego, CA, USA.,Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
| | - Howaida G El-Said
- Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
| | - Christopher K Davis
- Rady Children's Hospital-San Diego, San Diego, CA, USA.,Department of Pediatrics, University of California, San Diego, CA, USA
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6
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Ross BA, Brotto AR, Fuhr DP, Phillips DB, van Diepen S, Bryan TL, Stickland MK. The supine position improves but does not normalize the blunted pulmonary capillary blood volume response to exercise in mild COPD. J Appl Physiol (1985) 2020; 128:925-933. [PMID: 32163328 DOI: 10.1152/japplphysiol.00890.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Patients with mild chronic obstructive pulmonary disease (COPD) demonstrate resting pulmonary vascular dysfunction as well as a blunted pulmonary diffusing capacity (DLCO) and pulmonary capillary blood volume (VC) response to exercise. The transition from the upright to supine position increases central blood volume and perfusion pressure, which may overcome microvascular dysfunction in an otherwise intact alveolar-capillary interface. The present study examined whether the supine position normalized DLCO and VC responses to exercise in mild COPD. Sixteen mild COPD participants and 13 age-, gender-, and height-matched controls completed DLCO maneuvers at rest and during exercise in the upright and supine position. The multiple FIO2-DLCO method was used to determine DLCO, VC, and membrane diffusion capacity (DM). All three variables were adjusted for alveolar volume (DLCOAdj, VCAdj, and DMAdj). The supine position reduced alveolar volume similarly in both groups, but oxygen consumption and cardiac output were unaffected. DLCOAdj, DMAdj, and VCAdj were all lower in COPD. These same variables all increased with upright and supine exercise in both groups. DLCOAdj was unaffected by the supine position. VCAdj increased in the supine position similarly in both groups. DMAdj was reduced in the supine position in both groups. While the supine position increased exercise VCAdj in COPD, the increase was of similar magnitude to healthy controls; therefore, exercise VC remained blunted in COPD. The persistent reduction in exercise DLCO and VC when supine suggests that pulmonary vascular destruction is a contributing factor to the blunted DLCO and VC response to exercise in mild COPD.NEW & NOTEWORTHY Patients with mild chronic obstructive pulmonary disease demonstrate a combination of reversible pulmonary microvascular dysfunction and irreversible pulmonary microvascular destruction.
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Affiliation(s)
- Bryan A Ross
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada
| | - Andrew R Brotto
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada.,Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Desi P Fuhr
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada
| | - Devin B Phillips
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada.,Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Sean van Diepen
- Faculty of Medicine and Dentistry, Division of Cardiology, Department of Critical Care, University of Alberta, Edmonton, Alberta, Canada
| | - Tracey L Bryan
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada
| | - Michael K Stickland
- Faculty of Medicine and Dentistry, Division of Pulmonary Medicine, University of Alberta, Edmonton, Alberta, Canada.,G.F. MacDonald Centre for Lung Health, Covenant Health, Edmonton, Alberta, Canada
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Geier ET, Theilmann RJ, Darquenne C, Prisk GK, Sá RC. Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent. J Vis Exp 2019. [PMID: 31233033 DOI: 10.3791/59579] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Specific ventilation imaging (SVI) is a functional magnetic resonance imaging technique capable of quantifying specific ventilation - the ratio of the fresh gas entering a lung region divided by the region's end-expiratory volume - in the human lung, using only inhaled oxygen as a contrast agent. Regional quantification of specific ventilation has the potential to help identify areas of pathologic lung function. Oxygen in solution in tissue shortens the tissue's longitudinal relaxation time (T1), and thus a change in tissue oxygenation can be detected as a change in T1-weighted signal with an inversion recovery acquired image. Following an abrupt change between two concentrations of inspired oxygen, the rate at which lung tissue within a voxel equilibrates to a new steady-state reflects the rate at which resident gas is being replaced by inhaled gas. This rate is determined by specific ventilation. To elicit this sudden change in oxygenation, subjects alternately breathe 20-breath blocks of air (21% oxygen) and 100% oxygen while in the MRI scanner. A stepwise change in inspired oxygen fraction is achieved through use of a custom three-dimensional (3D)-printed flow bypass system with a manual switch during a short end-expiratory breath hold. To detect the corresponding change in T1, a global inversion pulse followed by a single shot fast spin echo sequence was used to acquire two-dimensional T1-weighted images in a 1.5 T MRI scanner, using an eight-element torso coil. Both single slice and multi-slice imaging are possible, with slightly different imaging parameters. Quantification of specific ventilation is achieved by correlating the time-course of signal intensity for each lung voxel with a library of simulated responses to the air/oxygen stimulus. SVI estimations of specific ventilation heterogeneity have been validated against multiple breath washout and proved to accurately determine the heterogeneity of the specific ventilation distribution.
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Affiliation(s)
- Eric T Geier
- Pulmonary Imaging Laboratory, Department of Medicine, University of California, San Diego
| | - Rebecca J Theilmann
- Pulmonary Imaging Laboratory, Department of Radiology, University of California, San Diego
| | - Chantal Darquenne
- Pulmonary Imaging Laboratory, Department of Medicine, University of California, San Diego
| | - G Kim Prisk
- Pulmonary Imaging Laboratory, Department of Medicine, University of California, San Diego
| | - Rui Carlos Sá
- Pulmonary Imaging Laboratory, Department of Medicine, University of California, San Diego;
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Patz MD, Sá RC, Darquenne C, Elliott AR, Asadi AK, Theilmann RJ, Dubowitz DJ, Swenson ER, Prisk GK, Hopkins SR. Susceptibility to high-altitude pulmonary edema is associated with a more uniform distribution of regional specific ventilation. J Appl Physiol (1985) 2017; 122:844-852. [PMID: 28057815 DOI: 10.1152/japplphysiol.00494.2016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Revised: 12/29/2016] [Accepted: 01/03/2017] [Indexed: 01/09/2023] Open
Abstract
High-altitude pulmonary edema (HAPE) is a potentially fatal condition affecting high-altitude sojourners. The biggest predictor of HAPE development is a history of prior HAPE. Magnetic resonance imaging (MRI) shows that HAPE-susceptible (with a history of HAPE), but not HAPE-resistant (with a history of repeated ascents without illness) individuals develop greater heterogeneity of regional pulmonary perfusion breathing hypoxic gas (O2 = 12.5%), consistent with uneven hypoxic pulmonary vasoconstriction (HPV). Why HPV is uneven in HAPE-susceptible individuals is unknown but may arise from regionally heterogeneous ventilation resulting in an uneven stimulus to HPV. We tested the hypothesis that ventilation is more heterogeneous in HAPE-susceptible subjects (n = 6) compared with HAPE-resistant controls (n = 7). MRI specific ventilation imaging (SVI) was used to measure regional specific ventilation and the relative dispersion (SD/mean) of SVI used to quantify baseline heterogeneity. Ventilation heterogeneity from conductive and respiratory airways was measured in normoxia and hypoxia (O2 = 12.5%) using multiple-breath washout and heterogeneity quantified from the indexes Scond and Sacin, respectively. Contrary to our hypothesis, HAPE-susceptible subjects had significantly lower relative dispersion of specific ventilation than the HAPE-resistant controls [susceptible = 1.33 ± 0.67 (SD), resistant = 2.36 ± 0.98, P = 0.05], and Sacin tended to be more uniform (susceptible = 0.085 ± 0.009, resistant = 0.113 ± 0.030, P = 0.07). Scond was not significantly different between groups (susceptible = 0.019 ± 0.007, resistant = 0.020 ± 0.004, P = 0.67). Sacin and Scond did not change significantly in hypoxia (P = 0.56 and 0.19, respectively). In conclusion, ventilation heterogeneity does not change with short-term hypoxia irrespective of HAPE susceptibility, and lesser rather than greater ventilation heterogeneity is observed in HAPE-susceptible subjects. This suggests that the basis for uneven HPV in HAPE involves vascular phenomena.NEW & NOTEWORTHY Uneven hypoxic pulmonary vasoconstriction (HPV) is thought to incite high-altitude pulmonary edema (HAPE). We evaluated whether greater heterogeneity of ventilation is also a feature of HAPE-susceptible subjects compared with HAPE-resistant subjects. Contrary to our hypothesis, ventilation heterogeneity was less in HAPE-susceptible subjects and unaffected by hypoxia, suggesting a vascular basis for uneven HPV.
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Affiliation(s)
- Michael D Patz
- Department of Anesthesiology, University of Washington, Seattle, Washington
| | - Rui C Sá
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Chantal Darquenne
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Ann R Elliott
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Amran K Asadi
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Rebecca J Theilmann
- Department of Radiology, University of California, San Diego, La Jolla, California; and
| | - David J Dubowitz
- Department of Radiology, University of California, San Diego, La Jolla, California; and
| | - Erik R Swenson
- Medical Service, Veterans Affairs Puget Sound Health Care System, University of Washington, Seattle, Washington
| | - G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California.,Department of Radiology, University of California, San Diego, La Jolla, California; and
| | - Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California; .,Department of Radiology, University of California, San Diego, La Jolla, California; and
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