scholarly journals A Model of the Recruitment-Derecruitment and Volume of Lung Units in an Excised Lung as it is Inflated-Deflated Between Minimum and Maximum Lung Volume

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
D. G. Frazer ◽  
W. G. Lindsley ◽  
W. McKinney ◽  
J. S. Reynolds ◽  
G. N. Franz ◽  
...  
Keyword(s):  
Lung Volume ◽  
Unit Volume ◽  
Transpulmonary Pressure ◽  
Small Signal ◽  
Average Volume ◽  
Static Compliance ◽  
Lung Inflation ◽  
Tissue Properties ◽  
Open Lung ◽  
Lung Unit

The role of the recruitment-derecruitment of small structures in the lung (lung units) as the lung increases and decreases in volume has been debated. The objective of this study was to develop a model to estimate the change in the number and volume of open lung units as an excised lung is inflated-deflated between minimum and maximum lung volume. The model was formulated based on the observation that the compliance of the slowly changing quasi-static pressure-volume (P-V) curve of an excised rat lung can differ from the compliance of a faster changing small sinusoidal pressure volume perturbations superimposed on the curve. In those regions of the curve where differences in compliance occur, the lung tissue properties exhibit nonlinear characteristics, which cannot be linearized using “incremental” or “small signal” analysis. The model attributes the differences between the perturbation and quasi-static compliance to an additional nonlinear compliance term that results from the sequential opening and closing of lung units. Using this approach, it was possible to calculate the normalized average volume and the normalized number of open units as the lung is slowly inflated-deflated. Results indicate that the normalized average volume and the normalized number of open units are not linearly related to normalized lung volume, and at equal lung volumes the normalized number of open units is greater and the normalized average lung unit volume is smaller during lung deflation when compared to lung inflation. In summary, a model was developed to describe the recruitment-derecruitment process in excised lungs based on the differences between small signal perturbation compliance and quasi-static compliance. Values of normalized lung unit volume and the normalized number of open lung units were shown to be nonlinear functions of both transpulmonary pressure and normalized lung volume.

High lung volume increases stress failure in pulmonary capillaries

1992 ◽  
Vol 73 (1) ◽  
pp. 123-133 ◽  
Author(s):  
Z. Fu ◽  
M. L. Costello ◽  
K. Tsukimoto ◽  
R. Prediletto ◽  
A. R. Elliott ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Lung Volume ◽  
Autologous Blood ◽  
Physiological Mechanism ◽  
Transpulmonary Pressure ◽  
Lung Volumes ◽  
Lung Inflation ◽  
Pulmonary Capillaries ◽  
Scanning Electron

We previously showed that when pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to test whether stress failure occurred more frequently at high than at low lung volumes for the same Ptm. Lungs of anesthetized rabbits were inflated to a transpulmonary pressure of 20 cmH2O, perfused with autologous blood at 32.5 or 2.5 cmH2O Ptm, and fixed by intravascular perfusion. Samples were examined by both transmission and scanning electron microscopy. The results were compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O. There was a large increase in the frequency of stress failure of the capillary walls at the higher lung volume. For example, at 32.5 cmH2O Ptm, the number of endothelial breaks per millimeter cell lining was 7.1 +/- 2.2 at the high lung volume compared with 0.7 +/- 0.4 at the low lung volume. The corresponding values for epithelium were 8.5 +/- 1.6 and 0.9 +/- 0.6. Both differences were significant (P less than 0.05). At 52.5 cmH2O Ptm, the results for endothelium were 20.7 +/- 7.6 (high volume) and 7.1 +/- 2.1 (low volume), and the corresponding results for epithelium were 32.8 +/- 11.9 and 11.4 +/- 3.7. At 32.5 cmH2O Ptm, the thickness of the blood-gas barrier was greater at the higher lung volume, consistent with the development of more interstitial edema. Ballooning of the epithelium caused by accumulation of edema fluid between the epithelial cell and its basement membrane was seen at 32.5 and 52.5 cmH2O Ptm. At high lung volume, the breaks tended to be narrower and fewer were oriented perpendicular to the axis of the pulmonary capillaries than at low lung volumes. Transmission and scanning electron microscopy measurements agreed well. Our findings provide a physiological mechanism for other studies showing increased capillary permeability at high states of lung inflation.

Trapped air in ventilated excised rat lungs

1976 ◽  
Vol 40 (6) ◽  
pp. 915-922 ◽  
Author(s):  
D. G. Frazer ◽  
K. C. Weber
Keyword(s):  
Stress Relaxation ◽  
Flow Rate ◽  
Lung Volume ◽  
Transpulmonary Pressure ◽  
Maximum Pressure ◽  
Lung Inflation ◽  
Minimum Pressure ◽  
Trapped Air ◽  
Rat Lungs ◽  
Reference Pressure

Degassed excised rat lungs were ventilated in a water-filled plethysmograph with the carina as the zero pressure reference. Pressure-volume curves were recorded from a minimum transpulmonary pressure (Pmin) of -5 cmH2O to a maximum pressure (Pmin) of 30 cmH2O. An index of the minimun volume for the lung (Vm) divided by the maximum lung volume for the same cycle (Vmax) was used as an index of the amount of air trapped within the lung. As the flow rate was decreased from 38.2 to 1.9 ml/min, there were significant increases in the amount of air trapped in the lung. As the maximum pressure was decreased to 25 and 20 cmH2O, or the minimum pressure was increased to 6 and 11 cmH2O, the amount of trapped air in the lung significantly decreased. The rate of lung inflation had a much greater influence on the amount of trapped air than either the deflation rate or stress relaxation. The results are consistent with the theory that bubbles are formed during inflation and are the main cause of air trapped in the excised lung.

Electrical impedance tomography can monitor dynamic hyperinflation in dogs

1998 ◽  
Vol 84 (2) ◽  
pp. 726-732 ◽  
Author(s):  
Andy Adler ◽  
Norihiro Shinozuka ◽  
Yves Berthiaume ◽  
Robert Guardo ◽  
Jason H. T. Bates
Keyword(s):  
Electrical Impedance Tomography ◽  
Lung Volume ◽  
Measurement Errors ◽  
Electrical Impedance ◽  
Esophageal Pressure ◽  
Dynamic Hyperinflation ◽  
Average Volume ◽  
Impedance Tomography ◽  
Lung Inflation ◽  
Volume Increase

Adler, Andy, Norihiro Shinozuka, Yves Berthiaume, Robert Guardo, and Jason H. T. Bates. Electrical impedance tomography can monitor dynamic hyperinflation in dogs. J. Appl. Physiol. 84(2): 726–732, 1998.—We assessed in eight dogs the accuracy with which electrical impedance tomography (EIT) can monitor changes in lung volume by comparing the changes in mean lung conductivity obtained with EIT to changes in esophageal pressure (Pes) and to airway opening pressure (Pao) measured after airway occlusion. The average volume measurement errors were determined: 26 ml for EIT; 35 ml for Pao; and 54 ml for Pes. Subsequently, lung inflation due to applied positive end-expiratory pressure was measured by EIT (ΔVEIT) and Pao (ΔVPao) under both inflation and deflation conditions. Whereas ΔVPaowas equal under both conditions, ΔVEITwas 28 ml greater during deflation than inflation, indicating that EIT is sensitive to lung volume history. The average inflation ΔVEITwas 67.7 ± 78 ml greater than ΔVPao, for an average volume increase of 418 ml. Lung inflation due to external expiratory resistance was measured during ventilation by EIT (ΔVEIT,vent) and Pes (ΔVPes,vent) and at occlusion by EIT (ΔVEIT,occl), Pes, and Pao. The average differences between EIT estimates and ΔVEIT,occlwere 5.8 ± 44 ml for ΔVEIT,ventand 49.5 ± 34 ml for ΔVEIT,occl. The average volume increase for all dogs was 442.2 ml. These results show that EIT can provide usefully accurate estimates of changes in lung volume over an extended time period and that the technique has promise as a means of conveniently and noninvasively monitoring lung hyperinflation.

Interstitial fibrosis and collateral ventilation

1986 ◽  
Vol 61 (1) ◽  
pp. 300-303 ◽  
Author(s):  
D. M. Berzon ◽  
H. Menkes ◽  
A. M. Dannenberg ◽  
A. Gertner ◽  
P. Terry ◽  
...  
Keyword(s):  
Lung Volume ◽  
Interstitial Fibrosis ◽  
Local Treatment ◽  
Transpulmonary Pressure ◽  
Small Region ◽  
Similar Proportion ◽  
Collateral Flow ◽  
Lung Inflation ◽  
Fibrotic Process ◽  
Residual Capacity

Interstitial fibrosis may increase resistance to collateral flow (Rcoll) because of decreased lung volume and destruction of collateral channels or it may decrease Rcoll because of emphysematous changes around fibrotic regions. In addition, if interstitial fibrosis involves a small region of lung periphery, interdependence from surrounding unaffected lung should produce relatively large changes in volume of the fibrotic region during lung inflation. We studied the effects of interstitial fibrosis on collateral airflow by measuring Rcoll at functional residual capacity (FRC) in nine mongrel dogs before and 28 days after the local instillation of bleomycin into selected lung segments. In six of these dogs Rcoll was also measured at a higher lung volume (transpulmonary pressure = 12 cmH2O above FRC pressure). Rcoll increased in fibrotic lung segments following local treatment with bleomycin. With lung inflation (high transpulmonary pressure) Rcoll fell a similar proportion in fibrotic and nonfibrotic lung regions. These observations suggest that collateral resistance increases in fibrotic segments because lung volume decreases or because collateral pathways are involved directly in the fibrotic process. Compensatory increases in collateral communications do not occur. In addition, pulmonary interdependence does not cause disproportionate increases in volume and decreases in Rcoll of the fibrotic region during lung inflation.

Effect of lung volume on collateral ventilation in the dog

1980 ◽  
Vol 49 (1) ◽  
pp. 9-15 ◽  
Author(s):  
J. Kaplan ◽  
R. C. Koehler ◽  
P. B. Terry ◽  
H. A. Menkes ◽  
R. J. Traystman
Keyword(s):  
Lung Volume ◽  
Transpulmonary Pressure ◽  
Relative Increase ◽  
Small Airways ◽  
Lung Inflation ◽  
Before And After ◽  
Collateral Pathways ◽  
Flow Through ◽  
Collateral Ventilation

We studied the effect of lung volume on resistance through collateral pathways (Rcoll) and small airways (Rsaw) before and after the injection of methacholine into obstructed segments of intact dogs. Before methacholine, Rcoll decreased 15.0 ± 4.9 (SE)% per cmH2O increase in transpulmonary pressure (Ptp) and Rsaw decreased 5.1 ± 7.0 (SE)% per cmH2O increase in Ptp. Following methacholine, lung inflation resulted in similar decreases in Rcoll and Rsaw. The fall in Rcoll was significantly greater than the fall in Rsaw. When pressure in an obstructed segment (Ps) was increased with constant Ptp (nonhomogeneous inflation), Rcoll fell approximately half as much for each cmH2O increase in pressure compared to when Ptp was increased (homogeneous inflation). We conclude 1) that increases in lung volume have small effects on Rsaw so that there is a relative increase in flow through collateral channels serving obstructed poritons of lung and 2) that Rcoll is a function of the size of the obstructed segment that increases more under homogeneous than nonhomogeneous conditions.

Hering–Breuer inflation reflex in young and adult mammals

1981 ◽  
Vol 59 (9) ◽  
pp. 1017-1021 ◽  
Author(s):  
C. Gaultier ◽  
J. P. Mortola
Keyword(s):  
Mechanical Properties ◽  
Respiratory System ◽  
Lung Volume ◽  
Young Animal ◽  
Transpulmonary Pressure ◽  
Lung Inflation ◽  
Stretch Receptors ◽  
Pulmonary Stretch Receptors ◽  
Chemical Stimuli ◽  
Underlying Mechanisms

The apnea following lung inflation (Hering–Breuer expiratory promoting reflex) is a vagally mediated reflex which is initiated by the activation of pulmonary stretch receptors (PSR) and terminated by the interaction of several factors, which include adaptation of PSR, chemical stimuli, level of anaesthesia, and body temperature. Since PSR activity is determined by the changes in airway tension, the interpretation of the strength of vagal reflexes on the basis of changes in lung volume rather than transpulmonary pressure can be misleading when the mechanical properties of the respiratory system are not constant. In this study we compared the reflex apnea resulting from lung inflation of young and adult mammals, the respiratory system of which have very different mechanical properties. If the response is compared on the basis of similar changes in lung volume, it can be considered weaker or stronger in the young depending upon the normalizing parameter used. However, when considered on the basis of the relative changes in transpulmonary pressure, which better reflects the activation of PSR, the reflex is weaker in young rats and rabbits than in their adult counterparts and similar in dogs. The analysis of the underlying mechanisms suggests a weaker vagal contribution in the young animal, but a satisfactory conclusion requires a better knowledge of the factors which, in the younger animals, result in the termination of the apnea.

Effect of lung volume history on rate of edema formation in isolated canine lobe

1978 ◽  
Vol 45 (6) ◽  
pp. 880-884 ◽  
Author(s):  
H. S. Goldberg
Keyword(s):  
Weight Gain ◽  
Hydrostatic Pressure ◽  
Lung Volume ◽  
Interstitial Fluid ◽  
Venous Pressure ◽  
Transpulmonary Pressure ◽  
Fluid Accumulation ◽  
Edema Formation ◽  
Lung Inflation ◽  
Volume History

The effect of lung volume history and prior accumulation of interstitial fluid on rate of edema formation in isolated canine lobes was investigated. Mean pulmonary artery pressure and mean pulmonary venous pressure were kept constant at 40 and 30 cmH2O, respectively. Transpulmonary pressure (Ptp) was varied among 5, 15, and 25 cmH2O by progressive stepwise inflation and deflation. Rate of fluid accumulation was estimated by changes in slow weight gain after a change in Ptp. Although there is continuous interstitial fluid accumulation over the course of the experiment the results indicate that interstitial hydrostatic pressure around leaky vessels at Ptp of 15 cmH2O is reduced by prior lung inflation to Ptp of 25 cmH2O and increased by prior deflation to Ptp of 5 cmH2O. These results suggest that the distribution of interstitial fluid may vary as a function of lung volume history.

Characteristics of lung mechanoreceptors in spotted gar, Lepisosteus oculatus

1987 ◽  
Vol 252 (6) ◽  
pp. R1066-R1072 ◽  
Author(s):  
N. J. Smatresk ◽  
S. Q. Azizi
Keyword(s):  
Lung Volume ◽  
Transpulmonary Pressure ◽  
Volume Changes ◽  
Nerve Activity ◽  
Lung Inflation ◽  
Spotted Gar ◽  
Threshold Volume ◽  
Flow Through ◽  
Lepisosteus Oculatus

Single unit and whole nerve activity were recorded in situ from pulmonary mechanoreceptors in Lepisosteus oculatus in response to step inflation and ramp or flow through ventilation of the lung with air and varying levels of CO2 in air. Slowly adapting receptors (SAR), rapidly adapting receptors (RAR), and CO2-sensitive SAR were identified. Whole nerve activity was often present when transpulmonary pressure was 0 cmH2O and increased due to recruitment and elevated discharge of already-active fibers as lung volume rose. SAR became tonically active once the lung exceeded their threshold volume and demonstrated a rate-sensitive burst of activity on inflation and a rate-sensitive inhibition of activity after deflation of the lung. RAR responded to lung inflation or deflation with a burst of activity. Six of eleven SAR were inhibited by ventilation of the lung with from 6 to 10% CO2 in air, even when lung pressure and volume were kept constant. These receptor discharge characteristics, which were similar to those found for lungfish and amphibians, may account for the reflex responses of gar to lung volume changes.

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

1987 ◽  
Vol 63 (4) ◽  
pp. 1586-1590 ◽  
Author(s):  
J. A. Cooper ◽  
H. van der Zee ◽  
B. R. Line ◽  
A. B. Malik
Keyword(s):  
Lung Volume ◽  
Clearance Rate ◽  
Base Line ◽  
Lung Inflation ◽  
Alveolar Epithelial ◽  
Pulmonary Clearance ◽  
Residual Capacity ◽  
Dose Response Effect ◽  
Relationship Of ◽  
Line P

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.

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