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Biomedical subjects

T A Wilson

Publications and source records attributed to T A Wilson.

At least 109 records · Page 6Linked to original sources
PubMed1983

Isodicentric X chromosome in a girl with gonadal dysgenesis.

Chromosomal analysis on a 15-year-old girl with amenorrhea and lack of secondary sexual development showed a normal X chromosome and an isodicentric X chromosome, 46,X, idic(x) (pter leads to q23::q23 leads to pter). Thus the patient has duplicated and deleted X chromosome material. There was no evidence of 45,X mosaicism. Brd U-labeling revealed the abnormal X to be late-replicating.

Adolescent↗
PubMed1983

Axial distortion of airways in the lung.

Axial loads were applied around the circumference of an airway lumen by pulling on a cup-shaped anchor that embedded itself in the airway wall. Axial displacements were measured as a function of distance from the load, and the data were compared to the results of mathematical analyses of continuum mechanics models. In the modeling it was assumed that the elastic tube representing the airway is bonded to the surrounding elastic continuum representing the parenchyma and that axial forces are transmitted between the tube and the continuum by shear stresses at the interface. The agreement between the measured and computed axial displacements supports the hypothesis that the shear stresses are the dominant coupling mechanism. The following quantitative relations between force and displacement were obtained. The axial displacement produced by the load L was approximately 0.05 L/pi alpha mu, where alpha is the airway radius and mu is the shear modulus of the parenchyma. The displacement decayed to approximately one-half this maximal value at two diameters from the load.

Animals↗
PubMed1983

Nonuniform lung deformations.

This review evaluates the progress that has been made in describing the lung as a deformable solid and in using the methods of solid mechanics to answer questions about nonuniform lung deformations and parenchymal interdependence. The interdependence effect on the large intrapulmonary vessels has been successfully analyzed by these methods, but the modeling and analysis of the effects of gravity and chest wall shape on lung expansion are far from complete.

Biomechanical Phenomena↗
PubMed1983

Possible mechanism of action of metoclopramide-induced aldosterone secretion: in vivo and in vitro studies in the sheep.

To define further the mechanism by which metoclopramide, a dopamine antagonist, stimulates aldosterone secretion, seven lambs were injected iv with metoclopramide during a constant infusion of 5% dextrose in water and again during a constant infusion of trimethapan, a ganglionic blocker. In addition, suspensions of adrenal zona glomerulosa cells from the lambs were incubated in vitro in the presence of various concentrations of metoclopramide and known secretagogues. Plasma aldosterone concentrations increased in response to both metoclopramide and trimethaphan. However, during the trimethaphan infusion, no further increase in plasma aldosterone concentrations occurred after metaclopramide injection. In vitro, aldosterone concentrations in the zona glomerulosa cell suspensions increased in the presence of ACTH, potassium, and angiotensin II, but no increase in aldosterone concentration occurred in the presence of metoclopramide. These results suggest that in the sheep, metoclopramide stimulates aldosterone secretion by an indirect mechanism. This mechanism may involve the autonomic nervous system, since ganglionic blockade appeared to abolish the aldosterone response to metoclopramide.

Adrenal Glands↗
PubMed1983

Dopaminergic inhibition of aldosterone secretion in man is independent of the autonomic nervous system.

To determine whether the plasma aldosterone response to metoclopramide, a dopamine antagonist, is mediated by the autonomic nervous system in man, five healthy male volunteers were injected with metoclopramide during an infusion of either 5% dextrose in water or trimethaphan, a ganglionic blocker. Despite evidence of ganglionic blockade during the trimethaphan infusion, the aldosterone response to metoclopramide remained intact. This suggests that the aldosterone response to metoclopramide is not mediated by the autonomic nervous system in man as it appears to be in the sheep, and suggests species variation in the mechanism of this this mineralocorticoid response.

Adult↗
PubMed1982

A computational model for expiratory flow.

A mathematical model of maximal expiratory flow was developed. Coupled equations describing the pressure losses in the flow and the pressure-area behavior of the airway were integrated along the airway from the periphery to the flow-limiting site. Equations describing pressure losses in the flow were adapted from studied of bronchial casts. The bronchial anatomy utilized was that described by Weibel. Bronchial mechanical properties were obtained from measurements in excised human lungs for the central airways and by extrapolations of these data for the peripheral airways. The maximal flow for air and helium predicted by the model agrees with that of five lungs from which mechanical properties were obtained. The model predictions agree with published values of density and viscosity dependence of maximal flow. At high and midlung volumes, maximal flow is determined primarily by the wave-speed mechanism. At low lung volumes, maximal flow is primarily determined by the coupling of viscous pressure losses and airway mechanical properties.

Biomechanical Phenomena↗
PubMed1982

A model for mechanical structure of the alveolar duct.

The appearance of the microstructure of the lung as revealed in transmission and scanning electron micrographs of perfusion-fixed air- and saline-filled lungs suggests the following model for the structure of the alveolar duct. There are two networks of force-bearing elements. The first is an interdependent part of the peripheral connective tissue system that starts from the pleura and extends into the interlobar and interlobular fissures. At the sublobular level, its geometry is not yet fully clear. This network is extended by changes in lung volume and is insensitive to surface tension. The second network is composed of the line elements that form the rims of the alveolar openings. This network is the terminal part of the axial fiber system that surrounds bronchi, bronchioli, and arteries. The line elements of this network are extended by the outward force of surface tension. The two-dimensional alveolar walls that form the alveoli are negligible mechanical components except as platforms for surface tension at the air-liquid interface. An analysis of the mechanics of this model yields relations among surface area, recoil pressure, lung volume, and surface tension that are consistent with published data for lung volumes below 80% of total lung capacity.

Animals↗
PubMed1982

Surface tension-surface area curves calculated from pressure-volume loops.

An energy analysis and data from the literature on the relation among surface area, recoil pressure, and lung volume are used to calculate the surface tension-surface area curves corresponding to pressure-volume loops. The energy analysis has been described earlier (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 50: 921-926, 1981). It is based on the assumption that the tissue structure of the lung constitutes a conservative mechanical system and hence that pressure-volume hysteresis is primarily a result of surface tension-surface area hysteresis. Unlike previous methods of calculating surface tension from recoil pressure, this method does not rely on the assumption that the tissue component of recoil in the air-filled lung is the same as recoil pressure of the saline-filled lung at the same lung volume. The calculated values of surface tension decrease to less than 2 dyn/cm as surface area decreases along the deflation limb of the pressure-volume curve. Surface tension increases very steeply with surface area on the inflation limbs, reaching a limiting value of just under 30 dyn/cm. The shape of the surface tension-surface area curves, unlike the shape of the curves calculated by previous methods, is similar to the shape obtained on surface tension balances for fluid extracted from lungs.

Animals↗
PubMed1982

A pharmacy student searches for psychological predictors of patient compliance.

Pharmacists are becoming more involved in patient counseling and dosage regimen design in an attempt to improve patient compliance. A study was designed and implemented by an undergraduate pharmacy student in an attempt to gain experience in research methodology and to enhance individual clinical involvement. Forty patients, randomly selected at a community pharmacy and a family practice clinic, were administered a Myers-Briggs Type Indicator exam to assess the patient's degree of systematic preference. Refill dates for each patient's hypertensive medications were examined for six months in order to infer compliance. Results of the psychological exam did not accurately predict patient compliance or noncompliance. The student working with only minimal faculty guidance was able to design, implement, analyze, and describe the study. Colleges of pharmacy are encouraged to implement similar clinical research training projects for undergraduate students.

Adult↗
PubMed1981

Relations among recoil pressure, surface area, and surface tension in the lung.

The difference between energy stored in air- and saline-filled lungs is the sum of surface energy and the energy of tissue distortion caused by surface tension. The surface energy is zeta gamma dS, where gamma is surface tension and S is surface area. There is no corresponding relation between tissue energy and measurable variables. However, two equations can be obtained from the expression for the total energy difference. One is the statement that the total energy of the lung is minimum at equilibrium, and the other is the statement of conservation of mechanical energy as lung volume changes. The expression for tissue energy is eliminated between the two equations to obtain a single relation among the variables of interest: recoil pressure, surface area, and surface tension. Published data on recoil pressure and surface area of saline-filled, air-filled, and detergent-washed rabbit lungs are used in these equations to determine surface tension as a function of lung volume. The values of surface tension deduced from this analysis are lower than the values that would be obtained if the additional tissue forces in the air-filled lung were neglected. The contribution of tissue forces to the added recoil of the air-filled lung increases with increasing lung volume and accounts for approximately half the additional recoil at high lung volume.

Biomechanical Phenomena↗
PubMed1981

Ontogeny of blood pressure and the renin-angiotensin-aldosterone system. Sequential studies in the newborn lamb.

To test the hypothesis that the rise in arterial pressure occurring with maturation is due to an increase in the vascular responsiveness to angiotensin II, sequential cumulative doses of angiotensin II were infused intravenously into chronically catheterized newborn lambs maintained on a constant, weight-adjusted sodium intake from birth to 8 weeks of age. Basal mean arterial pressure correlated with both age and weight, but age was a stronger determinant of mean arterial pressure than was weight. No change in the mean arterial pressure response to angiotensin II occurred with maturation. Basal plasma renin activity and plasma aldosterone concentrations were low and did not change significantly with age. Therefore, in the newborn lamb in the sodium replete state, age is a better determinant of arterial pressure than is weight. However, an age-related change in vasoconstrictor responsiveness to angiotensin II does not occur and, therefore, cannot account for the rise in arterial pressure that is observed with maturation.

Aging↗