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Biomedical subjects

W Mitzner

Publications and source records attributed to W Mitzner.

120 records · Page 7Linked to original sources
PubMed1979

Distribution of interstitial compliance and filtration coefficient in canine lung.

Utilizing a modification of the isogravimetric methodology, we have estimated the perivascular interstitial compliance and filtration coefficient in the canine lung. These values averaged 1.8 g/cm H2O and 34 (g/h)/cm H2O, respectively, per 100 g lung wet weight. By studying lungs at both low and high states of inflation (where the alveolar septae are collapsed) we were also able to determine the spatial distribution of both the interstitial compliance and filtration coefficient. We estimate that of the above total interstitial compliance a maximum of 55% is around alveolar septal vessels, 20% around extra-alveolar arteries and 25% around extra-alveolar veins. Of the above total filtration coefficient, 50% represents filtration from alveolar septal vessels, 23% from extra-alveolar arteries, and 27% from extra-alveolar veins. Our results imply that there are finite interstitial compliances communicating with all permeable vessels. Significant pressures can be built up in these spaces, thereby acutely limiting the further formation of interstitial edema.

Animals↗
PubMed1978

Glucocorticoids and the rhesus fetal lung.

The effects of glucocorticoids on primate fetal lung function have not been clearly delineated. In this prospective study of preterm rhesus fetuses exposed in utero to betamethasone for 72 hours, the most significant alteration was a striking increase in maximum lung volumes. Functionally less significant increases in residual lung volumes were also noted. The lungs of the treated fetuses did not exhibit lower extract surface tensions or increased phospholipid concentrations. These findings suggest that the major effect of betamethasone is on lung connective tissue elements, with minimal effects on alveolar surfactant. Additional evidence of the multisystemic effects of glucocorticoids was obtained in that significant differences in fetal, adrenal, hepatic, and placental weights also were observed.

Amniotic Fluid↗
PubMed1977

Effect of transpulmonary and vascular pressures on rate of pulmonary edema formation.

The effect of transpulmonary pressure (Ptp) on rate of extravascular fluid accumulation in isolated canine left lower lobes perfused at constant vascular pressures was investigated. Changes in rate of extravascular fluid accumulation were estimated by changes in rate of slow weight gain. Mean inflow pressure (Ppa) was constant at 34 cmH2O. Mean outflow pressure (Ppv) was constant at either 27.2 cmH2O or 13.6 cmH2O. When increasing Ptp is associated with a derecruitment of vascular beds as the lung changes from predominantly zone III toward zone II, or zone I, there is a decrease in rate of weight gain. When increasing Ptp is not associated with a derecruitment of vascular beds, it is impossible on the basis of these experiments to predict the change in rate of weight gain.

Animals↗
PubMed1976

Effect of thoracic blood volume changes on steady state cardiac output.

We have investigated the extent to which shifts of blood volume out of or into the thoracic region influence the steady state cardiac output. The systemic circulation of anesthetized dogs was replaced with an artificial circuit which stimulated the pertinent mechanical characteristics of an intact circulation. As in the normal animal, the steady state venous return was proportional to the pressure gradient for venous return (i.e, mean systemic minus right atrial pressure). Cardiac function was altered either by administration of epinephrine or by changes in left ventricular afterload. At a constant mean aortic pressure of 100 mm Hg, epinephrine administration increased the steady state cardiac output by 55%. Half of this increase resulted from the lowered mean right atrial pressure (caused by improved cardiac function); the remainder resulted from an increased mean systemic pressure (caused by the volume shift to the systemic circulation). Increases in afterload transferred sufficient volume to the heart-lung compartment to reduce significantly the mean systemic pressure and, hence, the steady state venous return. Our results indicate that the heart-lung compartment contains a significant volume which is under cardiac control. In addition to being able to alter the right atrial pressure, the heart can modulate the steady state cardiac output by adjusting the mean systemic pressure. To this degree the heart can adjust its own venous return.

Animals↗
PubMed1975

Effect of intrathoracic pressure on pressure-volume characteristics of the lung in man.

Quasi-static pressure-volume (P-V) curves in normal seated human subjects were determined with pressure at the airway opening (Pa0) set below (negative pressure), above (positive pressure), or equal to ambient pressure. Dynamic compliance (Cdyn) during controlled continuous negative pressure breathing (CNPB) was also studied. Quasi-static P-V curves at negative pressure were decreased in slope, reflected a decrease in total lung capacity, and intersected the P-V curve obtained at ambient Pa0. At positive pressure the P-V curves showed an increase in slope and an increase in total lung capacity. During CNPB a fall in Cdyn was found. The fall in Cdyn was rapid and persisted for the duration of CNPB. Cdyn promptly returned to control levels when Pa0 was adjusted to ambient pressure.

Adult↗
PubMed1975

Effects of epinephrine on resisitive and compliant properties of the canine vasculature.

The peripheral circulation of 22 anesthetized dogs was separated into three parallel regions, where the outflow from each region could be measured and both outflow and inflow pressures could be controlled. We were thus able to estimate arterial and venous resistance and venous compliance for each region. The pressure dependency of these parameters was determined before and during continuous infusion of epinephrine (3 mug-kg-1 min-1). Epinephrine increased the arterial resistance in all regions but did so in such manner as to increase the fraction of cardiac output perfusing the splanchnic region. The venous resistances were all elevated by epinephrine and showed a greater pressure dependency than during control. Systemic venous complicance was found to be pressure dependent during both control and epinephrine administration, decreasing by nearly 50% from the lowest to the highest venous pressures (4-12 mmHg) investigated. Splanchnic compliance was found to comprise nearly half the total systemic compliance. Results were interpreted using an extension of the parallel compartment model of the peripheral circulation described by Caldini, Permutt, Waddell, and Riley (2).

Animals↗
PubMedDate not supplied

Serial distribution of airway diameters from input impedance and computed tomography.

Indirect measures of airway diameter such as respiratory system input impedance (Zin) have been widely used to infer or quantify bronchoconstriction, or bronchodilation. One such measure, Zin above 100 Hz has been shown to be primarily influenced by airway geometry and airway walls but not by lung and chest wall tissues. We used a recently developed method based on a complex asymmetrically branched network of tubes with nonrigid walls to analyze Zin from 100 to 2,000 Hz in control and bronchoconstricted (histamine injection) dogs. The resulting estimates of airway diameters indicated that peripheral airways were constricted far more (approximately 30% of their control diameters) than central airways (i.e., 0% in the trachea). Separate measurements of changes in airway diameters were made in an excised dog lung using high resolution computed tomography. The observed changes in airway diameter between lung volumes of total lung capacity (TLC) and functional residual capacity (FRC) were quantitatively consistent with those obtained from Zin data in our control dogs at FRC. We conclude that this systems identification method can be used to estimate the distribution of airway diameters from Zin.

Airway Resistance↗
PubMedDate not supplied

The role of chemical (CO2) drive in the apnea induced by high frequency ventilation in the cat.

The purpose of the present study was to compare the relative roles of PaCO2 and pulmonary mechanoreceptors in the generation of apnea during high frequency ventilation (HFV) and conventional mechanical ventilation (CMV) in the anesthetized cat. Our hypothesis was that PaCO2 primarily determines the appearance of apnea, while mechanoreceptor input plays an important but secondary role. We calculated the tidal volume which would have a 50% chance of inducing apnea (VT50) for each combination of ventilator settings, and used it as a standard for comparison of mechanical dynamic inputs. When either 2% or 5% CO2 was added to the bias flow during HFV, the VT50 was significantly increased over that seen with a room air bias flow. Apnea was observed during either mode of ventilation only when PaCO2 was reduced below normocapnic levels. The mean tidal volume associated with each apnea group was larger than that for the corresponding nonapnea group. There was no difference in the PaCO2 for apnea between HFV and CMV, but the EMG of the diaphragm did differ. With HFV-apnea tonic activity was observed, while CMV-apnea showed abolition of all activity. We conclude that both HFV- and CMV-induced apnea depend primarily on lowering the chemical drive (PaCO2), and secondarily on inhibitory mechanical input (VT). The excitation of rapidly adapting receptors during HFV could explain the tonic EMG activity.

Animals↗
PubMedDate not supplied

A method for measurement of cross sectional area, segment length, and branching angle of airway tree structures in situ.

Accurate quantitative measurements of airway and vascular dimensions are essential for evaluating function in both the normal and in the diseased lung. This report describes a new integrated method for three-dimensional (3D) extraction and analysis of pulmonary tree structures using data from High Resolution Computed Tomography (HRCT). Serially scanned two-dimensional (2D) slices of the lower left lobe of isolated dog lungs were stacked to create a volume of data. Airway and vascular trees were extracted using a 3D seeded region-growing algorithm based on differences in CT number between wall and lumen. In the region-growing step, voxels in the lumen are tagged with a distance descriptor to identify points along the tree structure equidistant from the seed point. To obtain quantitative data, we reduced each tree to its central axis. From the central axis, branch length was measured as the distance between two successive branch points, branch angle was measured as the angle produced by two daughter branches, and cross-sectional area was measured from a plane perpendicular to the central axis point. Data derived from these methods can be used to localize and quantify structural differences both during different physiologic conditions and in pathologic lungs.

Algorithms↗