Contributions of pulmonary perfusion and ventilation to heterogeneity in V˙<scp>a</scp>/Q˙measured by PET

Treppo, Steven; Mijailovich, Srboljub M.; Venegas, José G.

doi:10.1152/jappl.1997.82.4.1163

Cited by 100 publications

(130 citation statements)

References 32 publications

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“…These results can be explained by considering both the vertical distribution of the time constant and the interaction of noise level and absolute value of the time constant on the half CI/mean of the time constant. The time constants are longer in the nondependent regions than in the middle and dependent regions, which means that middle and dependent regions are better ventilated than the nondependent region, in agreement with many previous studies of regional ventilation distribution (17,25,38). According to the result of MC simulation performed by Simon et al (33), as the level of noise increases, the half CI/mean of the time constant increases to a greater degree for longer compared with shorter time Fig.…”

Section: Comparison Of 55 40 and 30% Xesupporting

confidence: 90%

“…Hoffman and colleague (14,15) found a significant vertical gradient of air content (3.3% air/cm at functional residual capacity) in the supine position, but a minimal gradient (Ϫ0.36% air/cm) in the prone position. Other studies found similar gradients of subpleural alveolar size (44), pleural pressure (41), and alveolar volume by PET (38) in the supine position, but no or minimal gradient in the prone position.…”

Section: Repeatability Of Xe-ct Methodsmentioning

confidence: 64%

“…5). In addition, the CVs at all three [Xe] values were smaller in the prone position than in the supine position, reflecting the fact that the prone position is less heterogeneous in the distribution of ventilation than the supine position due to gravity and lung geometry (17,31,38). CVs of time constants in the nondependent, middle, and dependent regions when using three different [Xe] values were calculated for the supine (Table 3) and prone (Table 4) positions.…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Comparison Of 55 40 and 30% Xesupporting

confidence: 90%

Section: Repeatability Of Xe-ct Methodsmentioning

confidence: 64%

Section: Resultsmentioning

confidence: 99%

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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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“…PaO 2 in the supine position when ventilated without PEEP. This is in accordance with measurements of V/Q heterogeneity in dogs using PET (Treppo et al, 1997).…”

Section: Effects Of Peep and Positionsupporting

confidence: 91%

Gas Exchange in the Normal Lung : Experimental studies on the effects of positive end-expiratory pressure and body position

Johansson¹

2014

Linköping University Medical Dissertations

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BACKGROUND:The principal function of the lung is gas exchange requiring adequate ventilation and perfusion at the level of the alveoli. The efficiency of gas exchange is depending on the distributions of regional ventilation (V) and pulmonary blood flow (Q) and their correlation. AIMS:To validate a high-resolution method to quantify regional V and to investigate the Radioactive microspheres, 15 m in diameter, were used for determining regional Q. Nitric oxide synthase (NOS) was inhibited with Nω-nitro-L-arginine methyl ester (L-NAME) to evaluate the role of NO on regional V/Q matching. The right lung was dried at total lung capacity and diced in approx. 1000 regions tracking the spatial location of each region. CONCLUSION: There were marked differences in redistribution of regional ventilation and regional pulmonary blood flow between prone and supine position when PEEP was applied. RESULTS:NO was not an active mechanism for V/Q matching in normal sheep lungs. VII List of original papershis thesis is based on the following four papers, which will be referred to by their Roman numerals: I.Positive end-expiratory pressure affects regional redistribution of ventilation differently in prone and supine sheep.

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“…Ao melhorar a relação V/Q, houve também redução da fração de shunt (Qs/Qt). As áreas pouco aeradas na região dorsal são recrutadas com pouca ou nenhuma mudança na ventilação na região ventral do pulmão, provocando, assim, maior homogeneidade na relação V/Q (pela diminuição da proporção de áreas com reduzida V/Q) 11,[26][27][28][29][30] . A melhora da distribuição da relação V/Q na posição prona também pode ser comprovada em seres humanos, observando-se o recrutamento de áreas previamente atelectasiadas, mas sem doença 31 .…”

Section: Discussionunclassified

Efeito a curto prazo da posição prona na oxigenação de crianças em ventilação mecânica

Bruno¹,

Piva²,

García³

et al. 2001

J. Pediatr. (Rio J.)

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Objective: to analyze the short-term effects of prone positioning on the oxygenation of mechanically-ventilated children suffering from severe hypoxemia.Materials and Methods: a prospective, nonrandomized trial (each patient as his/her own control) was conducted between July 1998 and July 1999. Mechanically-ventilated children with peak inspiratory pressure (PIP) greater than or equal to 30 cm H 2 O, FiO 2 greater than or equal to 0.5, and PaO 2 /FiO 2 ratio less than or equal to 200 were included in the study. Each patient was kept in the prone position for two hours, returning to the supine position after this period. Oxygenation was assessed by means of PaO 2 /FiO 2 in the supine position (one hour before prone positioning), one hour after prone positioning, and one hour after returning to the supine position. Patients who presented an increase of at least 20 in PaO 2 /FiO 2 were considered responsive. The results were compared by Student t-test, Friedman test, chi-square test, Fisher's exact test, and confidence interval (CI).Results: eighteen children (10 males), whose mean age was 11.5 +11.5 months, with initial PaO 2 /FiO 2 of 96.06 + 41.78, participated in the study. After one hour in the prone position, 27.7% of the patients (5/18) improved their PaO 2 /FiO 2 ratio (P=0.045). Six of these patients presented reduced lung compliance (four of them had acute respiratory distress syndrome); and twelve patients showed increased airway resistance (six of them presented bronchiolitis). No significant difference was observed between these two groups (reduced lung compliance x increased airway resistance) in terms of age, sex, duration of ventilation prior to change in position, peak inspiratory pressure, FiO 2 , severity of hypoxemia, and outcome.Conclusion: prone positioning during mechanical ventilation of children with severe hypoxemia may improve the PaO 2 /FiO 2 ratio in the first hour.J Pediatr (Rio J) 2001; 77 (5): 361-8: pronation, oxygenation, acute respiratory distress syndrome, pediatric intensive care unit, children, artificial respiration. ResumoObjetivos: analisar o efeito a curto prazo da posição prona na oxigenação de pacientes pediátricos com hipoxemia severa e submetidos a ventilação mecânica.Material e Métodos: ensaio clínico prospectivo, não randomizado, sendo cada paciente o seu próprio controle, realizado no período de julho de 1998 a julho de 1999. Incluídas todas as crianças com diagnóstico de insuficiência respiratória aguda, em ventilação mecânica, com pressão inspiratória positiva (PIP) > 30cm H 2 O e fração de oxigênio inspirada (FiO 2 ) > 0,5, que apresentassem paO 2 / FiO 2 < 200. Os pacientes foram mantidos duas horas na posição prona, retornando, a seguir, à posição supina. Avaliou-se a oxigenação, através da paO 2 /FiO 2 , na posição supina (1 hora antes da mudança de posição), com 1 hora de posição prona e 1 hora após retornar à posição supina. Considerou-se responsivo todo o paciente que apresentasse um aumento de, no mínimo, 20 na paO 2 /FiO 2 . Os resultados foram com...

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Contributions of pulmonary perfusion and ventilation to heterogeneity in V˙a/Q˙measured by PET

Cited by 100 publications

References 32 publications

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

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

Gas Exchange in the Normal Lung : Experimental studies on the effects of positive end-expiratory pressure and body position

Efeito a curto prazo da posição prona na oxigenação de crianças em ventilação mecânica

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