Deformation of the dog lung in the chest wall

Data on the shape of the chest wall at total lung capacity (TLC) and functional residual capacity (FRC) were used as boundary conditions in an analysis of the deformation of the dog lung. The lung was modeled as an elastic body, and the deformation of the lung from TLC to FRC caused by the change in chest wall shape and gravity were calculated. Parenchymal distortions, distributions of regional volume at FRC as a fraction of the volume at TLC, and distributions of surface pressure at FRC are reported. In the prone dog there are minor variations in fractional volume along the cephalocaudal axis. In transverse planes opposing deformations are caused by the change of shape of the transverse section and the gravitational force on the lung, and the resultant fractional volume and pleural pressure distributions are nearly uniform. In the supine dog, there is a small cephalocaudal gradient in fractional volume, with lower fractional volume caudally. In transverse sections the heart and abdomen extend farther dorsally at FRC, squeezing the lung beneath them. The gradients in fractional volume and pleural pressure caused by shape changes are in the same direction as the gradients caused by the direct gravitational force on the lung, and these two factors contribute about equally to the large resultant vertical gradients in fractional volume and pleural pressure. In the prone position the heart and upper abdomen rest on the rib cage. In the supine posture much of their weight is carried by the lung.(ABSTRACT TRUNCATED AT 250 WORDS)     

Shape of the chest wall in the prone and supine anesthetized dog

The shape of the passive chest wall of six anesthetized dogs was determined at total lung capacity (TLC) and functional residual capacity (FRC) in the prone and supine body positions by use of volumetric-computed tomographic images. The transverse cross-sectional areas of the rib cage, mediastinum, and diaphragm were calculated every 1.6 mm along the length of the thorax. The changes in the volume and the axial distribution of transverse area of the three chest wall components with lung volume and body position were evaluated. The decrease of the transverse area within the rib cage between TLC and FRC, as a fraction of the area at TLC, was uniform from the apex of the thorax to the base. The volume of the mediastinum increased slightly between TLC and FRC (14% of its TLC volume supine and 20% prone), squeezing the lung between it and the rib cage. In the transverse plane, the heart was positioned in the midthorax and moved little between TLC and FRC. The shape, position, and displacement of the diaphragm were described by contour plots. In both postures, the diaphragm was flatter at FRC than at TLC, because of larger displacements in the dorsal than in the ventral region of the diaphragm. Rotation from the prone to supine body position produced a lever motion of the diaphragm, displacing the dorsal portion of the diaphragm cephalad and the ventral portion caudad. In five of the six dogs, bilateral isovolume pneumothorax was induced in the supine body position while intrathoracic gas volume was held constant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of chest strapping on regional lung function.

We studied lung mechanics and regional lung function in five young men during restrictive chest strapping. The effects on lung mechanics were similar to those noted by others in that lung elastic recoil increased as did maximum expiratory flow at low lung volumes. Chest strapping reduced the maximum expiratory flow observed at a given elastic recoil pressure. Breathing helium increased maximum expiratory flow less when subjects were strapped than when they were not. These findings indicated that strapping decreased the caliber of airways upstream from the equal pressure point. Regional lung volumes from apex to base were measured with xenon 133 while subjects were seated. The distribution of regional volumes was measured at RV, and at volumes equal to strapped FRC and strapped TLC; no change due to chest strapping was observed. Similarly, the regional distribution of 133Xe boluses inhaled at RV and strapped TLC was unaffected by chest strapping. Closing capacity decreased with chest strapping. We concluded that airway closure decreased during chest strapping and that airway closure was not the cause of the observed increase in elastic recoil of the lung. The combination of decreased slope of the static pressure-volume curve and unchanged regional volumes suggested that strapping increased the apex-to-base pleural pressure gradient.     

Lung elastic recoil during breathing at increased lung volume.

During dynamic hyperinflation with induced bronchoconstriction, there is a reduction in lung elastic recoil at constant lung volume (R. Pellegrino, O. Wilson, G. Jenouri, and J. R. Rodarte. J. Appl. Physiol. 81: 964-975, 1996). In the present study, lung elastic recoil at control end inspiration was measured in normal subjects in a volume displacement plethysmograph before and after voluntary increases in mean lung volume, which were achieved by one tidal volume increase in functional residual capacity (FRC) with constant tidal volume and by doubling tidal volume with constant FRC. Lung elastic recoil at control end inspiration was significantly decreased by approximately 10% within four breaths of increasing FRC. When tidal volume was doubled, the decrease in computed lung recoil at control end inspiration was not significant. Because voluntary increases of lung volume should not produce airway closure, we conclude that stress relaxation was responsible for the decrease in lung recoil.     

Effects of chest wall on volume and strain patterns in canine lungs

Lobar functional residual capacity-to-total lung capacity ratios (FRC/TLC) and strains in five supine anesthetized dogs were determined from volumes and side lengths of tetrahedra formed by multiple intraparenchymal markers whose positions were determined roentgenographically. Strain is related to fractional changes in length of elements in a Cartesian coordinate system and was used to describe parenchymal distortion. Volumes and strain patterns were compared in three states: intact dogs, after transection of forelimb structures to relieve traction on the chest wall, and in dogs' excised lungs. Removing traction (NT) decreased the plethysmographically determined FRC and the upper-to-lower lobe ratio (UL/LL) for FRC/TLC. The ratio in the NT state was more like the ratio in the excised lungs (UL/LL approximately equal to 1) than in the intact dog (UL/LL greater than 1). Strain patterns were similar between the intact and the NT states, indicating no lobar shape change at FRC between these two states. Strain in the excised lungs differed greatly from strains in the intact and NT states. We conclude that forelimb traction alters volume distribution between lobes and that lung-chest wall interactions are important in determining volume and strain patterns.     

Regional lung strain in dogs during deflation from total lung capacity

Regional lung distortion during deflation from total lung capacity to functional residual capacity (FRC) in intact supine and prone anesthetized dogs was determined from the displacement of multiple metallic markers embedded in the lung parenchyma. Distortion was expressed as strain (epsilon), which is related to fractional length changes. In the supine position, transverse strain (epsilon yy) was larger than vertical strain (epsilon xx) and cephalocaudal strain (epsilon zz) in the upper lobe. The FRC of the lower lobe was smaller than FRC of the upper lobe and all strains were larger, but epsilon zz increased most and became equal to epsilon yy. In the prone position, epsilon yy was largest in all upper lobes and in three of four lower lobes. Strains and volumes of the upper and lower lobes were similar. The upper and lower lobes rotated slightly around different axes, indicating that interpleural fissures allow additional degrees of freedom for the lungs to conform to the thoracic cavity. In the prone position, there were no consistent gradients of strain or volume. These results indicate that, in determining the regional distribution of FRC in the recumbent dog, in addition to the effect of gravity on the lung, there are important interactions between lung and thoracic cavity shapes.     

Influence of the heart on the vertical gradient of transpulmonary pressure in dogs

Estimations were made of the vertical gradient of transpulmonary pressure (VGTP) from measurements of esophageal pressure in nine head-up dogs at functional residual capacity (FRC) when alive, when dead, and after total bilateral pneumothorax. The VGTP of 0.4 cmH2O/cm height in the alive state was abolished by pneumothorax, and roentgenograms showed that the heart moved in a caudal-dorsal direction. There was a small but significant increase in the VGTP on going from FRC to near total lung capacity (TLC) in alive head-up dogs. In eight dead head-up dogs heart weight was increased by replacing various amounts of heart blood with Hg. The VGTP was significantly increased from 0.28 to 0.51 cmH2O/cm height. The fractional increase in the VGTP was similar to the fractional increase in heart weight. In five dogs extrapolation to zero heart weight gave an average VGTP of 0.14 cmH2O/cm height. We conclude that the lungs help support the heart in the head-up dog and that the VGTP is in part determined by the pressure distribution required for this support.     

Effect of a hydrostatic pleural pressure gradient on mechanical behavior of lung lobes

Using 133Xe, the vertical distribution of regional volume (Vr) was measured in three regions of excised canine lobes both in air and when completely submerged in saline at 40, 60, 70, and 80% lobar vital capacity (VC). The estimated pleural pressure gradient, derived from values of Vr, distance between regions, and the lobar pressure-volume (PV) curve, underestimated the true gradient by 45%. Conversely, the gradient of Vr was substantially less than predicted. From the mean depth of each region below the waterline, pleural, and hence transpulmonary, pressure (PL) was computed. The values of Vr-PL for each region at 40, 60, and 80% lung volume (VL) were related to the lobar PV curve. Slopes of lines joining initial VL-PL points on the lobar PV curve to corresponding Vr-PL points in submerged lobes represent an effective regional compliance of a lobe undergoing deformation. With one exception this was less than the corresponding homogeneous compliance, indicating a stiffening of the lobe during deformation. Slopes of lines joining Vr-PL points of each region at the three lobar volumes represent effective regional compliance of a deformed lobe undergoing volume change. This was not significantly different from the homogeneous compliance. However, effective compliance can only be an approximate indicator of the forces required for a given volume change due to the inadequacy of PL to represent the unequal stress components induced by lobe deformation.     

Effect of body position on regional diaphragm function in dogs

The in situ lengths of muscle bundles of the crural and three regions of the costal diaphragm between origin and insertion were determined with a video roentgenographic technique in dogs. At total lung capacity (TLC) in both the prone and supine positions, the length of the diaphragm is not significantly different from the unstressed excised length, suggesting that the diaphragm is not under tension at TLC and that there is a hydrostatic gradient of pleural pressure on the diaphragmatic surface. Except for the ventral region of the costal diaphragm, which does not change length at lung volumes greater than 70% TLC, all other regions are stretched during passive deflations from TLC. Therefore below TLC the diaphragm is under passive tension and supports a transdiaphragmatic pressure (Pdi). The length of the diaphragm relative to its unstressed length is not uniform at functional residual capacity (FRC) and does not follow a strict vertical gradient that reverses when the animal is changed from the supine to the prone position. By inference, the length of muscle bundles is determined by factors other than the vertical gradient of Pdi. During mechanical ventilation, regional shortening is identical to the passive deflation length-volume relationship near FRC. Prone and supine FRC is the same, but the diaphragm is slightly shorter in the prone position. In both positions, during spontaneous ventilation there are no consistent differences in regional fractional shortening, despite regional differences in initial length relative to unstressed length.     

Mechanical role of expiratory muscles during breathing in upright dogs

To examine the mechanical effects of the abdominal and triangularis sterni expiratory recruitment that occurs when anesthetized dogs are tilted head up, we measured both before and after cervical vagotomy the end-expiratory length of the costal and crural diaphragmatic segments and the end-expiratory lung volume (FRC) in eight spontaneously breathing animals during postural changes from supine (0 degree) to 80 degrees head up. Tilting the animals from 0 degree to 80 degrees head up in both conditions was associated with a gradual decrease in end-expiratory costal and crural diaphragmatic length and with a progressive increase in FRC. All these changes, however, were considerably larger (P less than 0.005 or less) postvagotomy when the expiratory muscles were no longer recruited with tilting. Alterations in the elastic properties of the lung could not account for the effects of vagotomy on the postural changes. We conclude therefore that 1) by contracting during expiration, the canine expiratory muscles minimize the shortening of the diaphragm and the increase in FRC that the action of gravity would otherwise introduce, and 2) the end-expiratory diaphragmatic length and FRC in upright dogs are thus actively determined. The present data also indicate that by relaxing at end expiration, the expiratory muscles make a substantial contribution to tidal volume in upright dogs; in the 80 degrees head-up posture, this contribution would amount to approximately 60% of tidal volume.     

Static lung-lung interactions in unilateral emphysema.

Motivated by the introduction of single-lung transplantation into clinical practice, we compared the static mechanical properties of the respiratory system in six supine dogs before (at baseline) with those after the induction of unilateral emphysema. Relaxation volume (Vrel), total lung capacity (TLC), and static compliance of the emphysematous lung increased to 214 +/- 68, 186 +/- 39, and 253 +/- 95% (SD) of baseline, respectively. Vrel of the nonemphysematous lung fell to 81 +/- 28% of baseline, with no significant change in TLC of the nonemphysematous lung or its pressure-volume relationship, indicating that unilateral hyperinflation does not cause dropout of contralateral lung units. After unilateral emphysema, the chest wall shifted to a higher unstressed or neutral volume (when pleural pressure equals atmospheric pressure) in three of six animals, minimizing the anticipated decrease in lung recoil pressure at the higher respiratory system Vrel. The pattern of relative lung emptying in the intact dog and in the excised lungs was similar during stepwise deflations from TLC, suggesting that mean pleural pressure of the hemithoraces is equal. We conclude that in the dog the static volume distribution between emphysematous and nonemphysematous lungs is determined only by differences in lung recoil and compliance.     

Hyperinflation: control of functional residual lung capacity

Hyperinflation is the consequence of a dysbalance of static forces (determining the relaxation volume) and/or of the dynamic components. The relaxation volume is determined by an equilibrium between the elastic recoil of the lungs and of the chest walls. The dynamic components include the pattern of breathing, upper airway resistance and postinspiratory activity of inspiratory muscles. The respiratory and laryngeal muscles are under control and thus both static and dynamic hyperinflation can be secured. Our knowledge of the mechanism of increased FRC is based on clinical observations and on experiments. The most frequent stimuli leading to a dynamic increase of functional residual lung capacity (FRC) include hypoxia and vagus afferentation. Regulation of FRC is still and undetermined concept. The controlled increase of FRC, hyperinflation, participates in a number of lung diseases.     

Regional ventilation during spontaneous breathing and mechanical ventilation in dogs

We evaluated the effects of the different patterns of chest wall deformation that occur with different body positions and modes of breathing on regional lung deformation and ventilation. Using the parenchymal marker technique, we determined regional lung behavior during mechanical ventilation and spontaneous breathing in five anesthetized recumbent dogs. Regional lung behavior was related to the patterns of diaphragm motion estimated from X-ray projection images obtained at functional residual capacity (FRC) and end inspiration. Our results indicate that 1) in the prone and supine positions, FRC was larger during mechanical ventilation than during spontaneous breathing; 2) there were significant differences in the patterns of diaphragm motion and regional ventilation between mechanical ventilation and spontaneous breathing in both body positions; 3) in the supine position only, there was a vertical gradient in lung volume at FRC; 4) in both positions and for both modes of breathing, regional ventilation was nonlinearly related to changes in lobar and overall lung volumes; and 5) different patterns of diaphragm motion caused different sliding motions and differential rotations of upper and lower lobes. Our results are inconsistent with the classic model of regional ventilation, and we conclude that the distribution of ventilation is determined by a complex interaction of lung and chest wall shapes and by the motion of the lobes relative to each other, all of which help to minimize distortion of the lung parenchyma.     

Expiratory muscle contribution to tidal volume in head-up dogs

A change from the supine to the head-up posture in anesthetized dogs elicits increased phasic expiratory activation of the rib cage and abdominal expiratory muscles. However, when this postural change is produced over a 4- to 5-s period, there is an initial apnea during which all the muscles are silent. In the present studies, we have taken advantage of this initial silence to determine functional residual capacity (FRC) and measure the subsequent change in end-expiratory lung volume. Eight animals were studied, and in all of them end-expiratory lung volume in the head-up posture decreased relative to FRC [329 +/- 70 (SE) ml]. Because this decrease also represents the increase in lung volume as a result of expiratory muscle relaxation at the end of the expiratory pause, it can be used to determine the expiratory muscle contribution to tidal volume (VT). The average contribution was 62 +/- 6% VT. After denervation of the rib cage expiratory muscles, the reduction in end-expiratory lung volume still amounted to 273 +/- 84 ml (49 +/- 10% VT). Thus, in head-up dogs, about two-thirds of VT result from the action of the expiratory muscles, and most of it (83%) is due to the action of the abdominal rather than the rib cage expiratory muscles.     

阻塞性肺气肿模型的制作

目的在2周内对国际标准实验动物Beagle犬进行肺气肿模型的制作,建立较为标准的肺气肿模型,从而为治疗慢性阻塞性肺疾病（COPD）的方法提供良好的动物模型。方法Beagle犬8只,雌雄各半,2岁,体重13～18kg,雾化吸人木瓜蛋白酶12000U/kg,1次,周,共2周。实验前后测量试验动物肺功能,做胸部CT及病理学比较。结果实验前后动物肺功能,CT及病理学检查均显示较大的差异。8例实验动物的功能残气量（FRC）、肺总量（TLC）、功能残气量比肺总量（FRC/TLC％）、潮气量（VT）和呼吸频率（BR）,在肺气肿模型制作前后做两两比较,结果显示均有统计学差异P〈0.05,血氧饱和度（SpO2）0.05两者间无统计学差异。CT显示肺体积增大,局部肺野透亮度增加有肺大泡形成。试验后病理学检查显示肺泡壁破坏,肺泡间质断裂,肺泡融合,形成典型的全小叶型肺气肿改变。实验后动物出现肺气肿征表现,如气喘,咳嗽及上呼吸道分泌物增等。结论在标准实验动物身上可以较为准确、快速地复制出近似于人类阻塞性肺气肿病理改变的动物模型。     

Effect of increased static lung recoil on bronchial dimesions of excised lungs.

We measured bronchial diameters and lengths during static deflation and inflation in eight excised dog lobes before and after static lung recoil (Pst(L)) had been significantly increased by cooling the lobe for 48 h at 4 degrees C and ventilating it for 3 h. In control lobes, bronchial diameters were the same at any volume even though Pst(L) was different during inflation and deflation. These results agree with those of Hughes et al. (J. Appl. Physiol. 32: 25-35, 1972). However, when Pst(L) was increased, diameters at a given volume were significantly increased over control values; diameters at a given pressure were nearly the same as the controls. Therefore, under these conditions, bronchial diameter did not conform to lung volume. The ventilation process appeared to alter the circumferential elastic properties of the bronchi because diameters at all pressures were slightly larger after ventilation. Bronchial length-volume relationships were the same in both control and ventilated lobes. Thus, when Pst(L) was markedly increased, diameter corresponded best to lung recoil and length to lung volume.     

Effect of mean airway pressure on gas exchange during high-frequency oscillatory ventilation

We studied the effect of mean airway pressure (Paw) on gas exchange during high-frequency oscillatory ventilation in 14 adult rabbits before and after pulmonary saline lavage. Sinusoidal volume changes were delivered through a tracheostomy at 16 Hz, a tidal volume of 1 or 2 ml/kg, and inspired O2 fraction of 0.5. Arterial PO2 and PCO2 (PaO2, PaCO2), lung volume change, and venous admixture were measured at Paw from 5 to 25 cmH2O after either deflation from total lung capacity or inflation from relaxation volume (Vr). The rabbits were lavaged with saline until PaO2 was less than 70 Torr, and all measurements were repeated. Lung volume change was measured in a pressure plethysmograph. Raising Paw from 5 to 25 cmH2O increased lung volume by 48-50 ml above Vr in both healthy and lavaged rabbits. Before lavage, PaO2 was relatively insensitive to changes in Paw, but after lavage PaO2 increased with Paw from 42.8 +/- 7.8 to 137.3 +/- 18.3 (SE) Torr (P less than 0.001). PaCO2 was insensitive to Paw change before and after lavage. At each Paw after lavage, lung volume was larger, venous admixture smaller, and PaO2 higher after deflation from total lung capacity than after inflation from Vr. This study shows that the effect of increased Paw on PaO2 is mediated through an increase in lung volume. In saline-lavaged lungs, equal distending pressures do not necessarily imply equal lung volumes and thus do not imply equal PaO2.     

Closing capacity in awake and anesthetized-paralyzed man

Functional residual capacity (FRC), closing capacity (CC), and (FRC--CC) were determined in 61 supine patients using the 133Xe bolus test. In 28 of the 61 patients measurements were made both while the patients were awake and during anesthesia-paralysis. Both FRC and CC decreased significantly after induction of anesthesia-paralysis. The magnitude of the reduction in CC, but not of FRC, was dependent on the relationship between FRC and CC in the awake state. Patients whose FRC was larger than their CC while awake (group I) showed less decrease in CC than FRC, i.e., (FRC--CC) decreased. By contrast, those patients whose CC was larger than their FRC while awake (group II) showed a greater decrease in CC than in FRC, i.e., (FRC--CC) became less negative. The reduction in CC after induction of anesthesia-paralysis may result from an increased elastic recoil of the lung. The larger reduction in CC in group II patients may have been due to a larger increase in elastic recoil, possibly due to the development of atelactasis.     

Respiratory mechanics and breathing pattern during and following maximal exercise

We looked for evidence of changes in lung elastic recoil and of inspiratory muscle fatigue at maximal exercise in seven normal subjects. Esophageal pressure, flow, and volume were measured during spontaneous breathing at increasing levels of cycle exercise to maximum. Total lung capacity (TLC) was determined at rest and immediately before exercise termination using a N2-washout technique. Maximal inspiratory pressure and inspiratory capacity were measured at 1-min intervals. The time course of instantaneous dynamic pressure of respiratory muscles (Pmus) was calculated for the spontaneous breaths immediately preceding exercise termination. TLC volume and lung elastic recoil at TLC were the same at the end of exercise as at rest. Maximum static inspiratory pressures at exercise termination were not reduced. However, mean Pmus of spontaneous breaths at end exercise exceeded 15% of maximum inspiratory pressure in five of the subjects. We conclude that lung elastic recoil is unchanged even at maximal exercise and that, while inspiratory muscles operate within a potentially fatiguing range, the high levels of ventilation observed during maximal exercise are not maintained for a sufficient time to result in mechanical fatigue.     

Lung volume and interdependence in the pig.

The effect of lung volume on the mechanical interdependence between an obstructed sublobar region of lung and its surrounding tissues was investigated in intact and isolated pig lungs. Interdependence is arbitrarily defined as the effectiveness with which the linkage between the region and surrounding tissue mediates a tendency for inflation to become even whenever it is uneven. We found that when the volume of the surrounding lung (Vl) was high relative to the volume of the obstructed region (Vr), or when they were relatively equal at higher inflation states, interdependence decreased. When Vr was high relative changes in regional shape observed during even and uneven inflation states, we suggest that regional distortion and its effects on regional elastic recoil are important determinants of pulmonary interdependence.