Surfactant deficiency is a major cause of respiratory failure in newborns. We have investigated the roles of surfactant and positive end-expiratory pressure (PEEP) in the development of a functional residual capacity (FRC) and the distribution of ventilation at birth. Preterm rabbit pups (28 d GA) were delivered and received either saline or surfactant and then ventilated with (3PEEP) or without (0PEEP) 3 cm H 2 O PEEP (groups: saline/0PEEP, surfactant/ 0PEEP, saline/3PEEP, surfactant/3PEEP). Lung gas volumes were measured using plethysmography, and the uniformity of ventilation was analyzed using phase contrast (PC) x-ray imaging. Surfactant/ 0PEEP pups had greater FRCs and the lungs were more uniformly ventilated than saline/0PEEP pups; FRC at inflation 19 -21 was 2.46 Ϯ 0.52 mL/kg versus 0.91 Ϯ 0.95 mL/kg (p Ͻ 0.05). Saline/ 3PEEP pups developed an FRC of 7.54 Ϯ 1.68 mL/kg at inflation 19 -21 (p Ͻ 0.05), but the distribution of ventilation was initially nonuniform. Surfactant/3PEEP pups had an FRC of 8.50 Ϯ 0.80 mL/kg (at inflation 19 -21), and the distribution of ventilation was more uniform than with saline/3PEEP (p Ͻ 0.05). In ventilated preterm newborn rabbits, PEEP has a greater effect on FRC than surfactant, although the two are additive. Surfactant, administered at birth, markedly improved the uniformity of ventilation irrespective of whether PEEP was applied.
Background: Recent phase-contrast X-ray imaging studies suggest that inspiration primarily drives lung aeration and airway liquid clearance at birth, which questions the role of adrenaline-induced activation of epithelial sodium channels (eNacs). We hypothesized that pressures generated by inspiration have a greater role in airway liquid clearance than do eNacs after birth. Methods: Rabbit pups (30 d of gestation) were delivered and sedated, and 0.1 ml of saline (s) or amiloride (Am; an eNac inhibitor) was instilled into the lungs before mechanical ventilation. Two other groups (30 d of gestation) were treated similarly but were also given adrenaline (s/Ad and Am/Ad) before mechanical ventilation. results: Amiloride and adrenaline did not affect functional residual capacity (FRc) recruitment (P > 0.05). Amiloride increased the rate of FRc loss between inflations (Am: −5.2 ± 0.6 ml/kg/s), whereas adrenaline reduced the rate of FRc loss (s/Ad: −1.9 ± 0.3 ml/kg/s) as compared with saline-treated controls (s: −3.5 ± −0.6 ml/kg/s; P < 0.05). conclusion: These data indicate that inspiration is a major determinant of airway liquid clearance and FRc development during positive pressure ventilation. Although eNac inhibition and adrenaline administration had no detectable effect on FRc development, eNac may help to prevent liquid from re-entering the airways during expiration. a t birth, airway liquid clearance and lung aeration initiate cardiopulmonary changes, and together they underpin the transition to newborn life. Airway liquid clearance is accomplished by a variety of mechanisms (1-3), depending on the mode and timing of delivery. However, cell culture (4,5), animal (6-8), and human (9,10) studies imply that adrenaline-induced activation of pulmonary epithelial sodium channels (ENaCs) is the primary mechanism. This predicts that increased Na + reabsorption from the lung lumen reverses the osmotic gradient across the pulmonary epithelium, favoring liquid movement from the airways into the interstitial tissue (11-13). However, no studies have assessed the independent effects of ENaC inhibition vs. other factors such as increased transpulmonary hydrostatic pressures generated by inspiration. These transpulmonary pressures refer to the pressure difference across the pulmonary epithelium between the distal airways and the surrounding interstitial tissue.Phase-contrast (PC) X-ray imaging exploits the refractive index difference between air and water to generate high-resolution images of the aerating lung after birth. As X-rays pass through the aerated lung, they are refracted at each air-liquid interface, which generates a characteristic "speckle" pattern from which lung gas volumes can be determined (14-16). Together with plethysmography, PC X-ray imaging has demonstrated the dependence of lung aeration on inspiratory activity after birth (17,18). These data have questioned the role of Na + reabsorption and suggest that inspiration may be the primary force promoting airway liquid clearance after birth. However, because ...
Background:We investigated the effects of positive endexpiratory pressure (PEEP) and tidal volume (V T ) on lung aeration, pulmonary mechanics, and the distribution of ventilation immediately after birth using a preterm rabbit model. Methods: Sixty preterm rabbits (27 d) received volumetargeted positive pressure ventilation from birth, with one of the 12 combinations of PEEP (0, 5, 8, or 10 cmH 2 O) and V T (4, 8, or 12 ml/kg). Outcomes included functional residual capacity (FRC), peak inflating pressure (PIP), dynamic compliance (Cd), and distribution of ventilation. results: Increasing PEEP from 0 to 10 cmH 2 O increased FRC by 4 ml/kg, increased Cd by 0.2 ml/kg/cmH 2 O, and reduced PIP by 5 cmH 2 O. Increasing V T from 4 to 12 ml/kg increased FRC by 2 ml/kg, increased Cd by 0.3 ml/kg/cmH 2 O, and increased PIP by 4 cmH 2 O. No effect of V T on FRC occurred at 0 or 5 PEEP, and no effect of PEEP occurred at V T = 4 ml/kg. At 0 PEEP, increasing V T increased the proportion of gas entering the smaller apical regions, whereas at 10 PEEP, increasing V T increased the proportion of gas entering basal regions, from 47% to 63%. conclusion: Both PEEP and V T have independent, additive effects on FRC, lung mechanics, and the distribution of ventilation during the immediate newborn period.
This paper presents an image segmentation technique based on temporal subtraction that has successfully been used to isolate the lungs from PBI chest images, allowing the change in lung air volume to be measured over regions as small as the pixel size. Using this technique, it is possible to measure changes in regional lung volume at high spatial and temporal resolution during breathing at much lower x-ray dose than would be required using computed tomography.
The mechanisms of controlling residual volume and lung emptying in different ages have been examined. Elastic bandage was wrapped around the abdomen, chest and shoulder (chest strapping). The measurements of various lung volumes and airway resistance were performed with and without chest strapping. Reduction in all lung volumes including residual volume (-12%) and light increase in airway resistance were obtained in subjects below 25 years with chest strapping, whereas residual volumes were higher (+ 17%, + 12%) under chest strapping in subjects between 35 and 50 years and > 60 years of age, respectively. The airway resistance was also considerably higher in these two groups, A decrease in residual volume points to the fact that the major controlling mechanism of residual volume lies in the chest wall. Chest strapping removes the outward force on the airways, enhances their closure, and traps more air, which increases residual volume. This means that the limitation of emptying lies in the airways in advanced age ( > 34 years)
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