Relationship of end-expiratory pressure, lung volume, and 99mTc-DTPA clearance

Abstract

We investigated the dose-response effect of positive end-expiratory pressure (PEEP) and increased lung volume on the pulmonary clearance rate of aerosolized technetium-99m-labeled diethylenetriaminepentaacetic acid (99mTc-DTPA). Clearance of lung radioactivity was expressed as percent decrease per minute. Base-line clearance was measured while anesthetized sheep (n = 20) were ventilated with 0 cmH2O end-expiratory pressure. Clearance was remeasured during ventilation at 2.5, 5, 10, 15, or 20 cmH2O PEEP. Further studies showed stepwise increases in functional residual capacity (FRC) (P less than 0.05) measured at 0, 2.5, 5, 10, 15, and 20 cmH2O PEEP. At 2.5 cmH2O PEEP, the clearance rate was not different from that at base line (P less than 0.05), although FRC was increased from base line. Clearance rate increased progressively with increasing PEEP at 5, 10, and 15 cmH2O (P less than 0.05). Between 15 and 20 cmH2O PEEP, clearance rate was again unchanged, despite an increase in FRC. The pulmonary clearance of aerosolized 99mTc-DTPA shows a sigmoidal response to increasing FRC and PEEP, having both threshold and maximal effects. This relationship is most consistent with the hypothesis that alveolar epithelial permeability is increased by lung inflation.

Efeito De Diferentes Níveis De Pressão Positiva Continua Sobre a Depuração Pulmonar Do 99mtc-Dtpa

“…Tais autores demonstraram que a depuração do aerossol de DTPA é dependente do nível de pressão positiva aplicado. 8,[17][18][19] O mecanismo pelo qual o aumento do volume pulmonar aumenta a taxa de depuração pulmonar do 99m Tc--DTPA ainda permanece em discussão. É sugerido que essa aceleração no processo de depuração ocorra devido a um aumento da área de superfície alveolar, atenuando a espessura da parede alveolar ou devido ao aumento da permeabilidade da membrana epitelial pelo alargamento das junções intercelulares, considerando essa última alternativa mais consistente.…”

“…Coates e O'Brodovich (1986) hipotetizam que esse aumento possa ocorrer devido ao aumento do volume pulmonar, ao aumento da permeabilidade do epitélio ou devido à lesão transitória no epitélio pulmonar, o que ocasionaria redução do tempo de meia-vida (T ½ ) do radioaerossol de 99m Tc-DTPA, que é o tempo requerido até que a atividade decaia para 50% do valor de pico. [8][9][10] Assim, devido à importância do uso da CPAP na prá-tica clínica, avaliou-se diferentes níveis de pressão positiva altera o padrão da depuração pulmonar do radioaerossol 99m Tc-DTPA. O delineamento de cada região foi feito criando-se um retângulo próximo dos limites de atividade radioativa em cada pulmão; a largura foi determinada pelos pontos mais craniais e mais caudais de cada pulmão e para cada região de interesse delineada foi gerada uma curva tempo--atividade.…”

Chronic Sidestream Cigarette Smoke Exposure Causes Lung Injury in Rabbits

“…Additionally, changes in lung volume and surfactant concentration have been shown to alter 99mTcDTPA up take [21][22][23], but lung surfactant concentration was not measured. Another possibility is that intact eosinophils can induce alveolar epithelial cell injury by the release of granule-associated products, possibly lysosomal enzymes [24].…”

Real Time Lung Imaging for the Detection of Lung Injury and Alveolar Fluid Movement During Mechanical Ventilation

“…Imaging techniques providing a gross estimation of the epithelial and the endothelial layer permeability to proteins have been developed for more than 40 years and have had, physiological, pharmacological and clinical applications [6]. Depending of its route of administration, via the airways [7][8][9] or intravenously [10][11][12], a radiolabeled protein can be used for estimating epithelial or microvascular permeability, respectively.…”

“…*Address correspondence to this author at the Department of Anesthesia and Critical Care, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114, USA; Tel: (617) 726-8980; Fax: (617) 726-5985; E-mail: nicoladeprost@gmail.com Ventilation at high peak airway pressures produces a lung edema of the permeability type if enough protracted [13], because lung inflation, and thus tissue stretch, increases alveolar epithelial [7,9] and microvascular permeability [7,9,14]. Continuously and noninvasively monitoring the changes in lung alveolar and microvascular permeability during mechanical ventilation with scintigraphic methods helped to better understand the pathophysiology of the lung injury consecutive to lung tissue overstretch, which is called ventilator-induced lung injury (VILI).…”