Effect of tidal volume on distribution of ventilation assessed by synchrotron radiation CT in rabbit

Porra, Liisa; Monfraix, Sylvie; Berruyer, G.; Duc, Géraldine Le; Némoz, Christian; Thomlinson, W.; Suortti, P.; Sovijärvi, Anssi; Bayat, Sam

doi:10.1152/japplphysiol.00866.2003

Cited by 49 publications

(63 citation statements)

References 49 publications

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“…More recently, similar conclusions were reached using reconstructed images of inhaled fluorescent microsphere content recovered from lung cubes of the order of a cubic centimeter in sheep and pigs (123,124). Using synchrotron radiation computed tomography in rabbits and stable Xe as the inhaled contrast agent, extremely high-resolution images can now be obtained to reveal ventilation distribution of lung units as small as 1.5 mm 3 (125). These more invasive studies are necessarily performed in animal models, and are in support of ventilation heterogeneity potentially occurring at small length scales in various animal species.…”

Section: Inter-and Intraregional Ventilation Heterogeneity Experimentmentioning

confidence: 59%

Gas Mixing in the Airways and Airspaces

Verbanck¹,

Paiva

2011

Comprehensive Physiology

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Basic physical concepts of diffusion, convection, and dispersion pertaining to gas transport in the human airways are reviewed. Their incorporation into quantitative models of gas mixing is presented, also illustrating the crucial interaction of gas transport equations with the model geometry. Model simulations are confronted with the available experimental gas mixing indices such as the phase III slope obtained in normal human lungs, with some pertinent examples in laboratory animals and in human lung disease. The use of inert gases with differing diffusion coefficients and their associated phase III slope provides invaluable experimental information on gas mixing in the lungs, with the concept of the diffusion front playing a central role. Sources of inter- and intraregional ventilation heterogeneity can be related to the location of the diffusion front, which offers the possibility to distinguish between ventilation heterogeneity proximal to the diffusion front (driven by convection between lung units larger than acini) and more peripheral ventilation heterogeneity (driven by diffusion-convection interaction mainly within the acinus). While specific ventilation distribution and flow asynchrony co-act to generate convection-dependent ventilation heterogeneity, local structural asymmetry of the acinar air spaces is sufficient to generate diffusion-convection-dependent ventilation heterogeneity. The remaining hiatus in our understanding of ventilation heterogeneity in the human lung is described, together with some potential perspectives for its investigation.

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Section: Inter-and Intraregional Ventilation Heterogeneity Experimentmentioning

confidence: 59%

Gas Mixing in the Airways and Airspaces

Verbanck¹,

Paiva

2011

Comprehensive Physiology

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“…9 yields sV ϭ 7.5 min Ϫ1 . The latter value can be compared with sV Ϸ 4.6 min Ϫ1 reported for a rabbit study with VT ϭ 12.7 ml/kg (32).…”

mentioning

confidence: 66%

³He MRI-based assessment of posture-dependent regional ventilation gradients in rats

Månsson¹,

Deninger²,

Magnusson³

et al. 2005

Journal of Applied Physiology

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A recently developed method for quantitative assessment of regional lung ventilation was employed for the study of posture-dependent ventilation differences in rats. The measurement employed hyperpolarized 3 He MRI to detect the build-up of the signal intensity after increasing numbers of 3 He breaths, which allowed for computation of a regional ventilation parameter. A group of six anesthetized rats was studied in both supine and prone postures. Three-dimensional maps of the ventilation parameter were obtained with high spatial resolution (voxel volume ϳ2 mm 3 ). Vertical (dorsal-ventral) gradients of the ventilation index, defined as the regional ventilation normalized by the average ventilation within the whole lung, were investigated. Variations in the regional distribution of the ventilation parameter, as well as of the ventilation index, could be detected, depending on the posture of the rats. In supine posture, ventilation was elevated in the dependent parts of the lungs, with a linear gradient of the ventilation index of Ϫ0.11 Ϯ 0.03 cm Ϫ1 . In prone posture, the distribution of ventilation was more uniform, with a significantly (P Ͻ 0.001) smaller gradient of the ventilation index of Ϫ0.01 Ϯ 0.02 cm Ϫ1 . It is concluded that the 3 He MRI-based method can detect and quantify regional ventilation gradients in animals as small as the rat and that these gradients depend on prone or supine posture of the animal.hyperpolarized gas magnetic resonance imaging; helium-3; lung function; posture dependence IT IS WELL KNOWN THAT THE distribution of regional pulmonary ventilation depends on the posture of an air-breathing animal or human (27). This has classically been attributed to effects of gravity on pleural pressure and alveolar expansion (24). Regional ventilation values change dramatically between prone and supine body postures, with predominantly dorsal ventilation in supine posture and a more uniform distribution of ventilation in prone posture (15,16,20,31,40,41). Oxygenation and gas exchange improve in prone posture, but the exact mechanism remains unclear (27). This is not fully explained by effects of gravity, and other important factors have been suggested, e.g., dorsoventral differences in lung structure balancing out the gravitational forces in the prone posture (37). Various studies on the influence of posture on the regional distribution of ventilation have been conducted on humans and large animals like dogs, sheep, and pigs (28), but no data are available for small species like the rat.In the past, quantitative measurements of regional lung ventilation have been obtained with invasive techniques or with radioisotope imaging (2, 3, 5), but these methods have been limited in their spatial and temporal resolution. Improved spatial resolution has been realized with xenon-enhanced computed tomography, where the ventilation is determined from the wash-in and wash-out rates of stable xenon (13,14,18,20). Using a MRI-based method, regional ventilation has been evaluated qualitatively from the variations ...

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“…The same process was applied to three different Xe gas image data sets to measure the magnitude of the contrast enhancement. To test the robustness or sensitivity to noise of the time constant with the 30% Xe/30% Kr mixture compared with that with Xe-only studies (30,40, and 55% [Xe]), the mean time constant and the CV* (half 95% CI/mean), obtained by MC simulation, were calculated (see Fig. 7).…”

Section: Discussionmentioning

confidence: 99%

“…Further investigation will be needed to verify the measurement of pulmonary regional ventilation using a Xe and Kr mixture in humans. Recent work by Porra et al (30) has shown that dual-energy imaging at either side of the K-edge of Xe gas yields exquisitely detailed images of the gas distribution in the lung. It is of great interest to determine whether dual-energy imaging about the K-edge of Kr may make imaging via Kr alone practical.…”

Section: Comparison Of 30% Xe/30% Kr Mixture With Xementioning

confidence: 99%

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

Chon¹,

Beck²,

Simon³

et al. 2007

Journal of Applied Physiology

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EA. Effect of low-xenon and krypton supplementation on signal/ noise of regional CT-based ventilation measurements. J Appl Physiol 102: [1535][1536][1537][1538][1539][1540][1541][1542][1543][1544] 2007. First published November 22, 2006; doi:10.1152/japplphysiol.01235.2005.-Xenon computed tomography (Xe-CT) is used to estimate regional ventilation by measuring regional attenuation changes over multiple breaths while rebreathing a constant Xe concentration ([Xe]). Xe-CT has potential human applications, although anesthetic properties limit [Xe] to Յ35%. We investigate effects of lower [Xe], including a low [Xe]-krypton (Kr) combination, on time constant (TC) determination. Six anesthetized sheep were scanned prone and supine using multidetector row CT. Lungs were imaged by respiratory gating during washin of a 30%, 40%, 55% Xe, and a 30% Xe/30% Kr mixture. Using Kr avoids unwanted effects of Xe. Mean TCs, coefficients of variation (CV), and half confidence intervals (CI)/ mean served as indexes of sensitivity to noise. Mean supine and prone TCs of three [Xe] values were not significantly different. Average CVs of TCs increased from 57% (55% Xe), 58% (40% Xe), and 73% (30% Xe) (P Ͻ 0.05: paired t-tests; 30% Xe vs. higher [Xe]). Monte Carlo simulation indicated a CV based on inherent image noise was 8% for 55% Xe and 17% for 30% Xe (P Ͻ 0.05). Adding 30% Kr to 30% Xe gave a washin signal equivalent to 40% Xe. Half CI/mean using the 30% Xe/30% Kr mixture was not significantly different from 55 and 40% Xe. Although average TCs were not affected by changes in [Xe], the higher CV and half CI/mean suggested reduced signal-to-noise ratio at the 30% [Xe]. The 30% Xe/30% Kr mixture was comparable to that of 40% Xe, providing an important agent for CT-based assessment of regional ventilation in humans.washin; regional ventilation measurements; computed tomography; pulmonary imaging; multidetector computed tomography; Monte Carlo simulation; regional lung function SINCE XENON (XE) GAS WAS FIRST introduced by Knipping and coworkers (21) as a contrast material applicable to the assessment of pulmonary function, it has been used extensively in scintigraphy (2, 3, 26), MRI (36), single-photon emission computed tomography (CT) (1), and X-ray CT (10,25,28). Stable (nonradioactive) Xe gas has a K-edge similar to that of iodine and is a potent X-ray attenuator, providing good contrast enhancement when used in conjunction with CT scanning (42). When imaged in a conventional CT scanner, lung attenuation varies linearly with the Xe concentration ([Xe]) in the air spaces (9), and the time course of Xe accumulation in the lung periphery during breathing, measured with serial CT images, is the basis for the Xe-CT measurement of regional ventilation (4, 33).Although Xe is an inert gas, it is moderately soluble in blood and tissue (18) and has been used clinically (7) as an inhaled anesthetic, ϳ30% more potent than nitrous oxide (5, 12, 25).[Xe] values of 30 -50% have been used to measure cerebral blood flow in human studies, but with repo...

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Effect of tidal volume on distribution of ventilation assessed by synchrotron radiation CT in rabbit

Cited by 49 publications

References 49 publications

Gas Mixing in the Airways and Airspaces

Gas Mixing in the Airways and Airspaces

³He MRI-based assessment of posture-dependent regional ventilation gradients in rats

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

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Effect of tidal volume on distribution of ventilation assessed by synchrotron radiation CT in rabbit

Cited by 49 publications

References 49 publications

Gas Mixing in the Airways and Airspaces

Gas Mixing in the Airways and Airspaces

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

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Product

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³He MRI-based assessment of posture-dependent regional ventilation gradients in rats