An Improved Physical Lung Model for Teaching Lung Ventilation

This article describes an easily made physical lung model for teaching about lung ventilation. It has rectified some major shortcomings of the bell-jar balloon model by having a fluid-filled “pleural cavity,” a dome-shaped “diaphragm,” and an inflated “lung” at rest. The model can be used to tackle some misconceptions about ventilation as well as to learn some difficult concepts such as the negative pleural pressure and pneumothorax.

Acute effects of thixotropy conditioning of inspiratory muscles on end-expiratory chest wall and lung volumes in normal humans

Thixotropy conditioning of inspiratory muscles consisting of maximal inspiratory effort performed at an inflated lung volume is followed by an increase in end-expiratory position of the rib cage in normal human subjects. When performed at a deflated lung volume, conditioning is followed by a reduction in end-expiratory position. The present study was performed to determine whether changes in end-expiratory chest wall and lung volumes occur after thixotropy conditioning. We first examined the acute effects of conditioning on chest wall volume during subsequent five-breath cycles using respiratory inductive plethysmography ( n = 8). End-expiratory chest wall volume increased after conditioning at an inflated lung volume ( P < 0.05), which was attained mainly by rib cage movements. Conditioning at a deflated lung volume was followed by reductions in end-expiratory chest wall volume, which was explained by rib cage and abdominal volume changes ( P < 0.05). End-expiratory esophageal pressure decreased and increased after conditioning at inflated and deflated lung volumes, respectively ( n = 3). These changes in end-expiratory volumes and esophageal pressure were greatest for the first breath after conditioning. We also found that an increase in spirometrically determined inspiratory capacity ( n = 13) was maintained for 3 min after conditioning at a deflated lung volume, and a decrease for 1 min after conditioning at an inflated lung volume. Helium-dilution end-expiratory lung volume increased and decreased after conditioning at inflated and deflated lung volumes, respectively (both P < 0.05; n = 11). These results suggest that thixotropy conditioning changes end-expiratory volume of the chest wall and lung in normal human subjects.

31P-NMR spectroscopy of isolated perfused rat lung

We obtained 202.5-MHz 31P-nuclear magnetic resonance (NMR) spectra of isolated perfused rat lungs, degassed and inflated, and of lung extract. The spectra included those of ATP, ADP, phosphocreatine (PCr), inorganic phosphate (Pi), phosphomonoesters, phosphodiesters, and a broad component due to the membrane phospholipids. The line width at one-half peak height for beta-ATP was 1.0 ppm for the degassed lung and 1.2 ppm for the inflated lung. This suggests that the air-water interfaces in inflated lung, which produce proton NMR line broadening, do not act prominently in 31P-NMR spectroscopy. In a degassed lung, when perfusion was stopped for up to 30 min, PCr and ATP peaks decreased progressively with time while Pi and phosphomonoester peaks increased. On return of flow, these changes reversed. The intracellular pH values calculated from the difference in magnetic field between PCr and Pi peaks of inflated and degassed lungs were 7.16 +/- 0.10 (SD; n = 4) and 6.99 +/- 0.10 (n = 4), respectively. The change of intracellular pH caused by 30 min of ischemia was -0.2 pH units. Our findings indicate that air-water interfaces should not broaden lung 31P peaks in vivo.

Effects of unilateral hyperinflation on the interpulmonary distribution of pleural pressure

Motivated by single lung transplantation, we studied the mechanics of the chest wall during single lung inflations in recumbent dogs and baboons and determined how pleural pressure (Ppl) is coupled between the hemithoraces. In one set of experiments, the distribution of Ppl was inferred from known volumes and elastic properties of each lung. In a second set of experiments, costal pleural liquid pressure (Pplcos) was measured with rib capsules. Both methods revealed that the increase in Ppl over the ipsilateral or inflated lung (delta Ppli) is greater than that over the contralateral or noninflated lung (delta Pplc). Mean d(delta Pplc)/d(delta Ppli) and its 95% confidence interval was 0.7 +/- 0.1 in dogs and 0.5 +/- 0.1 in baboons. In a third set of experiments in three dogs and three baboons, we prevented sternal displacement and exposed the abdominal diaphragm to atmospheric pressure during unilateral lung inflation. These interventions had no significant effect on Ppl coupling between the hemithoraces. We conclude that lungs of unequal size and mechanical properties need not be exposed to the same surface pressure, because thoracic midline structures and the lungs themselves resist displacement and deformation.

Perfusion dehydration fixes elastin and preserves lung air-space dimensions

We sought a technique to preserve lung tissue for micrography with air-space dimensions unchanged from the fresh state. In our hands, conventional techniques were problematical. Aware of the possibility that distortion might be caused by inadequate mechanical fixation of elastin, we dehydrated the still-inflated lung by intravascular perfusion with graded ethanols. Canine and rabbit lungs so prepared had straighter alveolar septa, greater air-space dimensions, and an improved correlation with light-scattering measurements. Bovine ligamentum nuchae (mostly elastin) was only partially fixed by glutaraldehyde or osmium tetroxide but was effectively stiffened by dehydration. We conclude that perfusion dehydration aids in the faithful preservation of parenchymal configuration, probably by mechanical fixation of elastin.

Measurement of Water Distribution and Transcapillary Solute Flux in Dog Lung by External Radioactivity Counting

1. A method for measuring the pulmonary water compartments in vivo in anaesthetized dogs is described. 2. The technique depends upon the sequential intravenous injection of markers labelled with γ-ray-emitting isotopes. Each is allowed to become evenly distributed throughout the compartment to which it is confined. A calibrated γ-counter placed at the surface of the inflated lung then records a count rate related to the total quantity of isotope in unit volume of tissue. The size of each water compartment can be calculated from the external count rate and the isotopic concentration of the marker in plasma. 3. The markers used were 125I-labelled serum albumin for plasma, [125I]iodide for extracellular water and [125I]iodoantipyrine for total water. 4. The method was extended to calculate transcapillary flux rates of serum albumin and showed that rapid exchange of serum albumin takes place between the plasma and interstitial space. 5. Results obtained non-invasively by the isotopic method were compared with direct measurements. Agreement was good.

Increased Muscularity of the Pulmonary Circulation in Victims of Sudden Infant Death Syndrome

It has recently become apparent that some victims of sudden infant death synclrome (SIDS) are chronically hypoxemic before death. In this study, the structural alterations in the pulmonary circulation of 15 victims of SIDS were examined using precise quantitative morphometric techniques applied to the injected and inflated lung. Increased muscularity of the pulmonary circulation has been demonstrated, as evidenced by the extension of muscle into arteries not usually muscularized during the first year of life, and by an increased thickness of the medial wall in some patients. This confirms the findings of Naeye and further justifies the shift of investigative efforts from the events immediately surrounding death to a search for chronic abnormalities.