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Biomedical subjects

T A Wilson

Publications and source records attributed to T A Wilson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Viscosity and density dependence during maximal flow in man.

Maximal expiratory flow curves were obtained from ten healthy subjects white breathing air and three other gas mixtures with different densities and viscosities. From these data, the magnitudes of the dependence of maximal flow on gas density and viscosity were obtained. The scaling laws of fluid mechanics, together with a model for the flow-limiting mechanism, were used to obtain a prediction of the relationship between the density dependence and the viscosity dependence of maximal flow. Although the data for individual subjects were too variable to allow a precise comparison with this prediction, the relationship between the mean density dependence and the mean viscosity dependence of all usbjects agreed with the theoretic prediction. This agreement supports the assumption, which is frequently made, that flow resistance rather than tissue visoelasticity is the dominant contributor to peripheral resistance. Information on the relationships between the pressure drop to the flow-limiting segment and flow, gas density and viscosity, and lung volume were also obtained.

Air↗
PubMed1980

Prediction of maximal expiratory flow in excised human lungs.

The predictions of the wave-speed theory of flow limitations were tested against measured values of maximal expiratory flow (Vmax) in nine normal excised human lungs. We obtained static pressure-volume curves and deflation pressure-area (PA) curves of the first three to four airway generations. The pressure drop from the alveolus to the flow-limitation site was assumed to consist of a peripheral frictional loss (estimated from a catheter upstream from the flow-limitation site) and a convective acceleration pressure drop. Predicted Vmax was determined graphically by finding the lowest flow for which the Bernoulli PA curve was tangent to one of the bronchial PA curves. At the point of tangency, local flow speed equals local wave speed. At low lung volumes a point of tangency with the PA curves of the first few generations did not exist, and the flow-limitation site was assumed to be the minimal bronchial area at zero transpulmonary pressure. There was good agreement between measured and predicted Vmax. Measured Vmax was not different from Vmax predicted from normal living man. The wave-speed theory predicted flow over much of the vital capacity, but other mechanisms may limit flow at low lung volumes.

Adolescent↗
PubMed1980

Exercise screening of short children for growth hormone deficiency in a family practice setting.

Exercise stimulation tests for growth hormone were performed in two groups of children: 163 patients aged 4 to 20 years had growth hormone measured before and after exercise, and 28 children had growth hormone checked only after excercise. Of 180 exercise stimulation tests performed in the first group, 124 showed an adequate growth hormone response as did 23 of 29 such tests in the second group. Careful instruction and preparation of patients for exercise screening of growth hormone leads to an accuracy for this test of nearly 80 percent.

Adolescent↗
PubMed1979

Improved measurements of shear modulus and pleural membrane tension of the lung.

The continuum solution for the deformation of an elastic half space covered by a membrane is used to interpret measurements of the indentation of lung lobes under a column of fluid. The shear modulus mu of the underlying parenchyma is found to be approximately 0.7 times transpulmonary pressure, independent of species size. The tension in the pleural membrane T increases rapidly with increasing membrane area. For dog lungs, the value of T is 10(3) to 10(4) dyn/cm. For the larger species tested, pigs and horses, T is larger. The continuum solution shows that a concentrated force applied to the pleural surface is distributed over a distance T/mu as it is transmitted across the pleural membrane. The membrane is important in determining the displacement produced by forces that act within a region that is small compared to this distance, approximately 2 cm for dog lungs. By comparing the tension-area curve of the pleural membrane with the pressure-volume curve of the lobe, it is found that the pleural membrane contributes about 20% of the work done by the lung during deflation.

Animals↗
PubMed1979

Distribution of regional volumes and ventilation in excised canine lobes.

A linear elasticity solution for the gravitational deformation of excised lungs was obtained. The accuracy of our solution was examined by comparing predicted and measured displacements of markers glued to the surface of canine lower lobes. The equations describing the strains in a lobe were used to predict the distribution of regional volumes and the slope of phase III (S3) of a single-breath oxygen (SBO2) test. The analysis predicted a negative S3. However, S3 was found to be positive in the five lobes tested, suggesting that factors other than gravity were responsible for the observed pattern of ventilation. In SBO2 tests repeated with increasing delays at end inflation, S3 progressively decreased, became negative, and was eventually abolished. Our equations predicted the most negative observed S3 well. We conclude that continuum mechanics can be used to describe the gravitational deformation of lungs and the resulting effect on ventilation distribution.

Animals↗
PubMed1979

Parenchymal mechanics at the alveolar level.

Three current questions about alveolar mechanics are discussed: how is the liquid lining of the alveolus maintained, how does surface tension affect alveolar geometry and lung recoil, and how does the parenchyma respond to nonuniform deformations? Modeling the parenchyma as an interconnected network of alveolar walls is emphasized and modifications that are needed to make the models quantitatively successful are suggested.--Wilson, T. A. Parenchymal mechanics at the alveolar level.

Animals↗
PubMed1978

Modeling the effect of axial bronchial tension on expiratory flow.

Previous modeling of the expiratory flow-limiting mechanism is extended by including axial tension in the airway walls as one of the forces that affect airway mechanics. The analysis supports the Dawson-Elliott explanation of the plateaus in isovolume pressure-flow (IVPF) curves and shows that axial tension has the effect of increasing maximum flow and introducing a negative-effort-dependent region. Solutions for boundary conditions representing a cannula in the airways are qualitatively different with flow approaching zero as the pressure drop across the system becomes large.

Airway Resistance↗
PubMed1977

Behavior of artificially produced holes in lung parenchyma.

Spherical and cylindrical holes were cut in the parenchyma of isolated dog lung lobes. The holes were insufflated with tantalum dust and the hole diameters were measured along the deflation limb of the lobe pressure-volume curve from transpulmonary pressures of 20 to 0 cmH2O. Hole volume as a fraction of lobe volume was found to be independent of transpulmonary pressure. The hole volume relative to the amount of tissue removed was used to determine the displacement at the hole boundary. A comparison of this displacement with the displacement predicted by a continuum mechanics analysis provides evidence for the applicability of the methods of continuum mechanics and further evidence that the shear modulus of the parenchyma is relatively small.

Animals↗
PubMed1976

Elastic constants of inflated lobes of dog lungs.

The elastic constants of dog lungs were determined at various degrees of inflation. In one set of experiments, the lobes were subjected to deformations that approximated the conditions of uniaxial loading. These data, together with the bulk modulus data obtained from the local slope of the pressure-volume curve, were used to determine the two elastic moduli that are needed to describe small nonuniform deformations about an initial state of uniform inflation. The bulk modulus was approximately 4 times the inflation pressure, and Young's modulus was approximately 1.5 times the inflation pressure. In a second set of experiments, lobes were subjected to indentation tests using cylindric punches 1-3 cm in diameter. The value for Young's modulus obtained from these data was slightly higher, approximately twice the inflation pressure. These experiments indicate that the lung is much more easily deformable in shear than in dilatation and that the Poisson ratio for the lung is high, approximately 0.43.

Animals↗
PubMed1975

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.

Animals↗