Effects on body position and cholinergic blockade on mechanics of collateral ventilation

We studied the effects of position and cholinergic blockade on the mechanics of collateral ventilation in anesthetized paralyzed dogs. Resistance to collateral flow (Rcoll) is higher when an obstructed segment is dependent than when it is nondependent. Decreases of Rcoll in response to the local infusion of low oxygen mixtures are greater in dependent regions. We conclude that 1) changes in position affect Rcoll directly through local changes in lung volume related to the gradient of pleural pressure; 2) responses of collateral channels to local concentrations of CO2 and O2 are determined by ventilation perfusion relationships, which vary at different heights in the lung; and 3) resting cholinergic tone in the anesthetized dog varies at different heights in the lung.     

Collateral flow resistance and time constants in dog and horse lungs

We studied collateral flow resistance in exsanguinated, excised lower lobes and accessory lobes of dog and horse lungs, respectively. A double lumen catheter obstructed a peripheral airway isolating a segment of the lobe. Oxygen flowed into the segment via a rotameter which measured flow (Vcoll) while the inner catheter recorded segment pressure (Ps). Gas delivered into the segment flowed out via collateral channels. Collateral flow resistance was calculated as (Ps - PL)/Vcoll, where PL = static transpulmonary pressure. Rcoll at PL = 20, 10, and 5 cm H2O averaged 0.24, 1.25, and 2.65 cmH2O.ml-1.s, respectively, in the dog, and 4.53, 6.00, and 12.62 cmH2O.ml-1.s in the horse. At a given PL, Rcoll measured during inflation. At constant PL, Rcoll increased with time at PL = 5 and 10 cmH2O, but was not time dependent at PL = 20 cmH2O. At constant PL, Rcoll increased at Vcoll increased. We conclude Rcoll is greater in horses than in dogs and is a function of PL, Ps - PL, and lung volume history in both species.     

Collateral ventilation during high-frequency oscillation in dogs

Mechanics of collateral channels during high-frequency oscillatory ventilation (HFOV) were assessed in eight anesthetized dogs, using a modification of Hilpert's technique. Base-line functional residual capacity was measured with a body plethysmograph, with inspiratory efforts induced by phrenic nerve stimulation. The resistance (Rcoll) and time constant (Tcoll) of collateral channels at five lung volumes were measured during HFOV and positive end-expiratory pressure (PEEP). Rcoll and Tcoll were significantly higher during HFOV (P less than 0.001); the differences did not correlate with resting lung volumes. The calculated static compliance of the wedged segment was similar during HFOV and PEEP (P greater than 0.005). Mean pressures measured in small airways during HFOV corresponded to the midline between the inflation and deflation limbs of the static pressure-volume curves, indicating similar pressure-volume characteristics of the respiratory system during HFOV and static conditions. We conclude that HFOV increases resistance to gas flow through collateral channels but that this pathway may still be important in gas exchange.     

Effects of lung inflation on pulmonary arterial blood volume in intact dogs.

The isolated effects of alterations of lung inflation and transmural pulmonary arterial pressure (pressure difference between intravascular and pleural pressure) on pulmonary arterial blood volume (Vpa) were investigated in anesthetized intact dogs. Using transvenous phrenic nerve stimulation, changes in transmural pulmonary arterial pressure (Ptm) at a fixed transpulmonary pressure (Ptp) were produced by the Mueller maneuver, and increases in Ptp at relatively constant Ptm by a quasi-Valsalva maneuver. Also, both Ptm and Ptp were allowed to change during open airway lung inflation. Vpa was determined during these three maneuvers by multiplying pulmonary blood flow by pulmonary arterial mean transit time obtained by an ether plethysmographic method. During open airway lung inflation, mean (plus or minus SD) Ptp increased by 7.2 (plus or minus 3.7) cmH2O and Ptm by 4.3 (plus or minus 3.4) cmH2O for a mean increase in Vpa by 26.2 (plus or minus 10.7) ml. A pulmonary arterial compliance term (Delta Vpa/Delta Ptm) calculated from the Mueller maneuver was 3.9 ml/cmH2O and an interdependence term (Delta Vpa/Delta Ptp) calculated from the quasi-Valsalva maneuver was 2.5 ml/cmH2O for a 19% increase in lung volume, and 1.2 ml/cmH2O for an increase in lung volume from 19% to 35%. These findings indicate that in normal anesthetized dogs near FRC for a given change in Ptp and Ptm the latter results in a greater increase of Vpa.     

Temporal and regional variability of collateral resistance response to histamine

Using the wedged bronchoscope technique, we measured the changes in collateral resistance (Rcoll) in dogs resulting from exposure to aerosols of increasing concentrations of histamine. Histamine dose-response curves were performed in each of two to three separate lobar segments of an individual mongrel dog's lungs. Five dogs were studied. The same segments were reexamined on later occasions (2-11 wk apart) to determine whether the responsiveness to histamine had altered with time. Measurements of base-line Rcoll for a given segment were reproducible (coefficient of variation 0.48). In contrast, we observed that the estimated dose of histamine required to increase Rcoll by 50% (ED150Rcoll) was extremely variable both among lung segments of an individual dog on a single experimental day (geometric mean variability of 40-fold) and for a given segment when reexamined on repeated occasions (geometric mean variability of 47-fold). The ED150Rcoll did not correlate with the base-line Rcoll. The degree of variability we observed suggests that peripheral contractile elements are under the influence of powerful local modulating factors that vary both regionally and temporally.     

Differential responses of tissue viscance and collateral resistance to histamine and leukotriene C4

Alterations in tissue viscance (Vti) and collateral resistance (Rcoll) are both used as indexes of peripheral lung responses. However, it is not known whether the two responses reflect the effects of activation of the same contractile elements. We measured differential responses in Vti and Rcoll to histamine and leukotriene (LT) C4 to determine whether each evoked a similar pattern of response. Using the wedged bronchoscope constant-flow technique, we measured Rcoll in lobar segments of anesthetized, paralyzed, open-chest, mechanically ventilated mongrel dogs. In addition, we measured (with an alveolar capsule) alveolar pressure (PA) within the segment under study. This allowed us to calculate Vti, the component of the PA change in phase with segment flow. Rcoll and Vti measurements were obtained under base-line conditions and after local delivery of aerosols generated from histamine and LTC4. In five out of five lobes studied with both histamine and LTC4, the fractional Rcoll response to histamine was greater than the fractional Rcoll response to LTC4. In contrast, in four out of five lobes examined, the fractional increase in Vti accompanying the histamine response was less than the fractional increase in Vti accompanying LTC4 administration. These data suggest that anatomically distinct contractile elements influence Vti and Rcoll insofar as LTC4 and histamine evoke quantitatively different changes in these two indexes of peripheral lung responses.     

Responses of pulmonary stretch receptors during ramp inflations of the lung

Studies were conducted in anesthetized paralyzed dogs to determine how the dynamic and proportional sensitivity of pulmonary stretch receptors change during lung inflation. The firing of each receptor was examined at multiple levels of static transpulmonary pressure and during multiple identical inflations at each of several rates. The averaged response of the receptor was computed and receptor activity related to transpulmonary pressure. On the basis of a quantitative criterion, employed to distinguish type I from type II receptors, the receptors could not be divided into distinct subpopulations. Thus all receptors were treated as coming from a single population. For all receptors we observed that their proportional sensitivity (increases in firing produced by increases in lung expansion at a constant rate of inflation) declined as the lung was inflated. In contrast, the dynamic sensitivity (increases in firing produced by increased rates of inflation at constant transpulmonary pressure) increased or remained relatively constant with increasing lung expansion. Thus, as inflation volume increases, the pulmonary stretch receptor acts increasingly as a rate receptor. The rate of inflation may have a more important role in control of the inspiratory duration than previously realized.     

Distribution of pulmonary vascular resistance in experimental fibrosis

To elucidate mechanisms of pulmonary hypertension in interstitial fibrosis, we compared the left lower lobes (LLL) of six dogs in which fibrosis was induced by radiation and bleomycin with the normal right lower lobes (RLL) for 1) slope and intercept of the vascular pressure-flow (P-Q) curves, 2) segmental resistances with arterial and venous occlusion under base-line conditions, after serotonin and vasodilators, and 3) light-microscopic morphology and morphometry. We found that 1) the total volume and vascular compliance of the fibrotic LLL were five and four times less, respectively, than controls, 2) the slope and intercept of the P-Q curves in the LLL were 154.0 +/- 65.8 (SE) mmHg.l-1.min-1 and 8.2 +/- 1.5 mmHg, respectively, compared with 18.3 +/- 2.3 and 3.2 +/- 0.9 for the RLL, 3) the resistance of the arterial, middle, and venous segments in the LLL were higher than in the RLL, but middle segment resistance rose disproportionately, and 4) constriction of the arterial segment with serotonin was similar in LLL and RLL, and vasodilators were ineffective. Histologically, fibrosis involved 36% of the lung, and the capillary bed was severely obliterated. Arteries showed an increased percentage of medial and intimal thickening and peripheral muscularization; venous abnormalities were less marked. We conclude that pulmonary fibrosis increases vascular resistance mainly in the middle segment, largely by loss of tissue and obliteration of the microvasculature.     

Alveolar liquid pressures in newborn and adult rabbit lungs

To study the effects of lung maturation and inflation on alveolar liquid pressures, we isolated lungs from adult and newborn rabbit pups (1-11 days old). We used the micropuncture technique to measure alveolar liquid pressure at several transpulmonary pressures on lung deflation. Alveolar liquid pressure was greater than pleural pressure but less than airway pressure at all transpulmonary pressures. Alveolar liquid pressure decreased further below airway pressure with lung inflation. At high transpulmonary pressure, alveolar liquid pressure was less in newborn than in adult lungs. To study the effects of edema, we measured alveolar liquid pressures in newborn lungs with different wet-to-dry weight ratios. Alveolar liquid pressure increased with progressive edema. In addition, we compared alveolar liquid and perivenular interstitial pressures in perfused newborn lungs and found that they were similar. Thus alveolar liquid pressure can be used to estimate perivenular interstitial pressure. We conclude that the transvascular pressure gradient for fluid flux into the interstitium might increase with lung inflation and decrease with progressive edema. Furthermore, this gradient might be greater in newborn than adult lungs at high inflation pressures.     

Effect of alveolar and pleural pressures on interstitial pressures in isolated dog lungs

We report the first direct measurements of perialveolar interstitial pressures in lungs inflated with negative pleural pressure. In eight experiments, we varied surrounding (pleural) pressure in a dog lung lobe to maintain constant inflation with either positive alveolar and ambient atmospheric pleural pressures (positive inflation) or ambient atmospheric alveolar and negative pleural pressures (negative inflation). Throughout, vascular pressure was approximately 4 cmH2O above pleural pressure. By the micropuncture servo-null technique we recorded interstitial pressures at alveolar junctions (Pjct) and in the perimicrovascular adventitia (Padv). At transpulmonary pressure of 7 cmH2O (n = 4), the difference of Pjct and Pady from pleural pressure of 0.9 +/- 0.4 and -1.1 +/- 0.2 cmH2O, respectively, during positive inflation did not significantly change (P less than 0.05) after negative inflation. After increase of transpulmonary pressure from 7 to 15 cmH2O (n = 4), the decrease of Pjct by 3.3 +/- 0.3 cmH2O and Pady by 2.0 +/- 0.4 cmH2O during positive inflation did not change during negative inflation. The Pjct-Pady gradient was not affected by the mode of inflation. Our measurements indicate that, in lung, when all pressures are referred to pleural or alveolar pressure, the mode of inflation does not affect perialveolar interstitial pressures.     

Elastic moduli of lungs during postnatal development in the piglet

Several manifestations of lung disease during infancy suggest that mechanical interdependence can be relatively high in newborn lungs. To test this possibility, we measured elastic moduli and pleural membrane tension in lungs excised from piglets ranging in age from less than 12 h to 85 days. Near maximum inflation, newborn lungs (less than 12 h, n = 6) had no detectable pleural membrane tension, although 3- to 5-day-old lungs (n = 6) had tension greater than 5,000 dyn/cm. In contrast, parenchymal recoil was greater in the newborn lungs [19.3 +/- 3.0 (SD) vs. 14.3 +/- 2.4 cmH2O at 90% of maximum inflation volume, P less than 0.01]. Shear moduli were higher (13.5 +/- 4.6 vs. 9.2 +/- 1.5 cmH2O at 15 cmH2O transpulmonary pressure, P less than 0.05) and Poisson ratios were lower in the newborn lungs as compared with the 3- to 5-day-old lungs. Postnatal lung growth between 3 and 85 days was characterized by 1) a constant shear modulus (0.6 times transpulmonary pressure); 2) decrease in the bulk modulus (from 6.8 to 5.1 times transpulmonary pressure, P less than 0.005); and 3) evidence of gas trapping at progressively higher transpulmonary pressures. Therefore, growth of parenchyma in the piglet lung is associated with reduced stiffness to volume change but with no effect on overall stiffness to shape change. Nevertheless, a relatively great stiffness to shape change occurs transiently in newborn piglet lungs.     

Effect of lung inflation on lung blood volume and pulmonary venous flow

Phasic changes in lung blood volume (LBV) during the respiratory cycle may play an important role in the genesis of the respiratory wave in arterial pressure, or pulsus paradoxus. To better understand the effects of lung inflation on LBV, we studied the effect of changes in transpulmonary pressure (delta Ptp) on pulmonary venous flow (Qv) in eight isolated canine lungs with constant inflow. Inflation when the zone 2 condition was predominant resulted in transient decreases in Qv associated with increases in LBV. In contrast, inflation when the zone 3 condition was predominant resulted in transient increases in Qv associated with decreases in LBV. These findings are consistent with a model of the pulmonary vasculature that consists of alveolar and extra-alveolar vessels. Blood may be expelled from alveolar vessels but is retained in extra-alveolar vessels with each inflation. The net effect on LBV and thus on Qv is dependent on the zone conditions that predominate during inflation, with alveolar or extra-alveolar effects being greater when the zone 3 or zone 2 conditions predominate, respectively. Lung inflation may therefore result in either transiently augmented or diminished Qv. Phasic changes in left ventricular preload may therefore depend on the zone conditions of the lungs during the respiratory cycle. This may be an important modulator of respiratory variations in cardiac output and blood pressure.     

Ventilation and perfusion distribution during altered PEEP in the left lung in the left lateral decubitus posture with unchanged tidal volume in dogs

Previous studies in anesthetized humans positioned in the left lateral decubitus (LLD) posture have shown that unilateral positive end-expiratory pressure (PEEP) to the dependent lung produce a more even ventilation distribution and improves gas exchange. Unilateral PEEP to the dependent lung may offer special advantages during LLD surgery by reducing the alveolar-to-arterial oxygen pressure difference {(A-a)PO2 or venous admixture} in patients with thoracic trauma or unilateral lung injury. We measured the effects of unilateral PEEP on regional distribution of blood flow (Q) and ventilation (V(A)) using fluorescent microspheres in pentobarbital anesthetized and air ventilation dogs in left lateral decubitus posture with synchronous lung inflation. Tidal volume to left and right lung is maintained constant to permit the effect on gas exchange to be examined. The addition of unilateral PEEP to the left lung increased its FRC with no change in left-right blood flow distribution or venous admixture. The overall lung V(A)/Q distribution remained relatively constant with increasing unilateral PEEP. Bilateral PEEP disproportionately increased FRC in the right lung but again produced no significant changes in venous admixture or V(A)/Q distribution. We conclude that the reduced dependent lung blood flow observed without PEEP occurs secondary to a reduction in lung volume. When tidal volume is maintained, unilateral PEEP increases dependent lung volume with little effect of perfusion distribution maintaining gas exchange.     

Adaptation to reflex effects of prolonged lung inflation

Adaptation to the reflex effects of sustained changes in lung volume on inspiratory duration (TI), expiratory duration (TE), and the phrenic neurogram was examined. Test inflations in gallamine-paralyzed dogs anesthetized with pentobarbital sodium were made during a 6-min trial while the animal was not ventilated: 2 min at functional residual capacity (FRC), 2 min at elevated airway pressure, and 2 min back at FRC. The dogs were hyperoxygenated and arterial PCO2 was kept constant by an infusion of tris (hydroxymethyl) aminomethane. The maintained inflations produced minimal changes in TI. On return to FRC, TI was prolonged in proportion to the magnitude of the prior inflation. In contrast, inflation produced marked prolongation of TE, which then adapted back toward preinflation values. On return to FRC, TE shortened initially to values below control. This shortening increased with greater prior lung inflations. The times to reestablish steady-state values upon return to FRC differed for TI (14.8 +/- 4.6 s) and TE (33.8 +/- 12.7 s). The magnitude of the phrenic neurogram at a fixed time from onset of inspiration and its slope were unchanged with inflation. These results indicate that respiratory phase durations are influenced not only by pulmonary afferent input within each respiratory cycle but also by prior vagal afferent activity that engages central processes with long, although different, time constants. Afferent input to the slow central process controlling TI is not gated to only one phase of the respiratory cycle.     

Transdiaphragmatic pressure and rib motion in area of apposition during paralysis

Changes in pleural surface pressure in area of apposition of diaphragm to rib cage (delta Ppl,ap), changes in abdominal pressure (delta Pab), and redial displacement of the 11th rib have been recorded in anesthetized, paralyzed dogs during lung inflation or deflation. Above functional residual capacity (FRC) changes in transdiaphragmatic pressure in area of apposition (delta Pdi,ap) were essentially nil in intact (INT) dogs either in lateral or supine posture, and in partially eviscerated (EVS) dogs in lateral posture, either in the 10th or 11th intercostal space. Below FRC delta Pdi,ap could be positive (INT lateral and EVS), nil (EVS), or negative (INT supine and EVS); it could be different in the 10th and 11th intercostal spaces. Hence, with stretched (like with contracted) diaphragm, delta Ppl,ap measured at one site often differs from delta Pab and is not representative of average pressure acting on area of apposition. With volume increase above FRC, the 11th rib moved slightly in and then out in EVS and linearly out in INT. With volume decrease below FRC it moved out progressively in EVS, and it moved in and eventually reversed in INT. In paralyzed dogs in lateral posture the factor having the greatest influence on displacement of the abdominal rib cage is Pab. Mechanical linkage with pulmonary rib cage becomes relevant at large volume, whereas insertional traction of diaphragm becomes relevant at low volume.     

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.     

HGF Expressing Stem Cells in Usual Interstitial Pneumonia Originate from the Bone Marrow and Are Antifibrotic

Background

Pulmonary fibrosis may result from abnormal alveolar wound repair after injury. Hepatocyte growth factor (HGF) improves alveolar epithelial wound repair in the lung. Stem cells were shown to play a major role in lung injury, repair and fibrosis. We studied the presence, origin and antifibrotic properties of HGF-expressing stem cells in usual interstitial pneumonia.

Methods

Immunohistochemistry was performed in lung tissue sections and primary alveolar epithelial cells obtained from patients with usual interstitial pneumonia (UIP, n = 7). Bone marrow derived stromal cells (BMSC) from adult male rats were transfected with HGF, instilled intratracheally into bleomycin injured rat lungs and analyzed 7 and 14 days later.

Results

In UIP, HGF was expressed in specific cells mainly located in fibrotic areas close to the hyperplastic alveolar epithelium. HGF-positive cells showed strong co-staining for the mesenchymal stem cell markers CD44, CD29, CD105 and CD90, indicating stem cell origin. HGF-positive cells also co-stained for CXCR4 (HGF+/CXCR4+) indicating that they originate from the bone marrow. The stem cell characteristics were confirmed in HGF secreting cells isolated from UIP lung biopsies. In vivo experiments showed that HGF-expressing BMSC attenuated bleomycin induced pulmonary fibrosis in the rat, indicating a beneficial role of bone marrow derived, HGF secreting stem cells in lung fibrosis.

Conclusions

HGF-positive stem cells are present in human fibrotic lung tissue (UIP) and originate from the bone marrow. Since HGF-transfected BMSC reduce bleomycin induced lung fibrosis in the bleomycin lung injury and fibrosis model, we assume that HGF-expressing, bone-marrow derived stem cells in UIP have antifibrotic properties.     

Lung mechanics in hypervolemic pulmonary edema.

Extravascular thermal volume of the lung (ETVL) is a double indicator dilution technique of use in measuring pulmonary edema. ETVL and lung mechanics measurements were followed to find a less invasive monitor of pulmonary edema than the double indicator dilution technique. Pulmonary edema was induced by overloading the dogs' circulation with dextran. Phases of overload were defined on the basis of a previous electron microscopic study (Noble et al., Can. Anesthetists Soc. J. 21:275, 1974) of lung biopsies relating anatomic changes to physiologic measurements of ETVL and central blood volume (CBV). Congestion occurred when CBV was elevated and ETVL was not, interstitial edema when ETVL was elevated but smaller than 60% above control and alveolar edema when ETVL greater than 85% above control. Once the dogs were in alveolar edema, they were mechanically ventilated with 4, 8, 12, and 16 cmH2O end-tidal pressure (CPPV). Mean functional residual capacity (FRC) for all 15 dogs did not change up to the time CPPV was applied. Pulmonary resistance did not rise until alveolar edema was present. Once in pulmonary edema, lung compliance always fell as lung water increased. In individual dogs, the compliance fall was directly proportional to the rising lung water. However, the variations in slope and beginning point among dogs made it difficult to predict the amount of lung water from dynamic compliance values. PaO2 fell markedly in alveolar edema as a result of a widened A-a gradient. CPPV did not decrease lung water but did increase FRC and PaO2.     

Effect of inflation on the interaction between the left and right hemidiaphragms.

At resting end expiration [functional residual capacity (FRC)], the actions of the left and right hemidiaphragms on the lung are synergistic. However, the synergism decreases in magnitude as muscle tension decreases. Therefore, the hypothesis was tested in anesthetized dogs that the degree of synergism between the two hemidiaphragms also decreases with increasing lung volume. In a first experiment, the changes in airway opening pressure (DeltaPao) and abdominal pressure (DeltaPab) obtained during simultaneous stimulation of the left and right phrenic nerves (measured changes in pressure) at different lung volumes were compared with the sum of the pressure changes produced by their separate stimulation (predicted changes in pressure). Although the pressure changes decreased markedly with increasing lung volume, the measured DeltaPao and DeltaPab were substantially greater than the predicted values at all lung volumes. The ratio of the measured to the predicted DeltaPao, in fact, remained constant. In a second experiment, radiographic measurements showed that the fractional shortening of the muscle during bilateral contraction at high lung volumes was similar to that during unilateral contraction. During unilateral contraction at high lung volumes, however, the passive hemidiaphragm moved in the cranial direction, whereas, during unilateral contraction at FRC, it moved in the caudal direction. These observations indicate that 1) for a given muscle tension, the synergism between the two halves of the diaphragm is greater at high lung volumes than at FRC; and 2) this difference is primarily related to the greater distortion of the muscle configuration.     

Length and curvature of the dog diaphragm.

Transdiaphragmatic pressure is a result of both tension in the muscles of the diaphragm and curvature of the muscles. As lung volume increases, the pressure-generating capability of the diaphragm decreases. Whether decrease in curvature contributes to the loss in transdiaphragmatic pressure and, if so, under what conditions it contributes are unknown. Here we report data on muscle length and curvature in the supine dog. Radiopaque markers were attached along muscle bundles in the midcostal region of the diaphragm in six beagle dogs of approximately 8 kg, and marker locations were obtained from biplanar images at functional residual capacity (FRC), during spontaneous inspiratory efforts against a closed airway at lung volumes from FRC to total lung capacity, and during bilateral maximal phrenic nerve stimulation at the same lung volumes. Muscle length and curvature were obtained from these data. During spontaneous inspiratory efforts, muscle shortened by 15-40% of length at FRC, but curvature remained unchanged. During phrenic nerve stimulation, muscle shortened by 30 to nearly 50%, and, for shortening exceeding 52%, curvature appeared to decrease sharply. We conclude that diaphragm curvature is nearly constant during spontaneous breathing maneuvers in normal animals. However, we speculate that it is possible, if lung compliance were increased and the chest wall and the diameter of the diaphragm ring of insertion were enlarged, as in the case of chronic obstructive pulmonary disease, that decrease in diaphragm curvature could contribute to loss of diaphragm function.