Indicator-dilution curves can be interpreted and analysed by describing the system between injection- and sampling site with a physical model. Till now mainly compartmental and distributed models have been investigated. One feature of distributed models is the possibility to interpret skewness or asymmetry of the curve in terms of a parameter, proportional with the Peclet number, which is a measure of the relative contribution between convection and diffusion in indicator transport. In patients with and without pulmonary edema, we analyzed a number of curves obtained with an intravascular indicator (131I radioiodinated serum albumin, RISA) and a diffusing indicator (tritiated water, THO) over the pulmonary vascular bed. Edema was measured by indexed extravascular lung water and by critical pressure, defined as the difference between pulmonary capillary wedge pressure and plasma colloid osmotic pressure. The significant decrease of the symmetry of the RISA curves with increasing cardiac output we explained by an increasing labyrinth dispersion and increasing turbulence at higher flows. For normals we found all THO curves to be less skew than albumin curves. This difference diminished and even reversed when the degree of pulmonary edema increased. We suggest a hypothesis for this phenomenon by considering various mechanisms responsible for dispersion and capillary exchange of the indicator during transport from injection to sampling site. In normals the contribution of Taylor diffusion during laminar flow in parts of the circulatory system may be responsible for the greater symmetry of THO curves; with increasing pulmonary edema, transcapillary diffusion of THO causes THO curves to become more skew and even more asymmetric when compared with albumin curves.

Capillaries↗

PubMedDate not supplied

Conductance method for the measurement of cross-sectional areas of the aorta.

A modified conductance method to determine the cross-sectional areas (CSAs) of arteries in piglets was evaluated in vivo. The method utilized a conductance catheter having four electrodes. Between the outer electrodes an alternating current was applied and between the inner electrodes the induced voltage difference was measured and converted into a conductance. CSA was determined from measured conductance minus parallel conductance, which is the conductance of the tissues surrounding the vessel times the length between the measuring electrodes of the conductance catheter divided by the conductivity of blood. The parallel conductance was determined by injecting hypertonic saline to change blood conductivity. The conductivity of blood was calculated from temperature and hematocrit and corrected for maximal deformation and changes in orientation of the erythrocytes under shear stress conditions. The equations to calculate the conductivity of blood were obtained from in vitro experiments. In vivo average aortic CSAs. determined with the conductance method CSA(G) in five piglets, were compared to those determined with the intravascular ultrasound method CSA(IVUS). The regression equation between both values was CSA(G)=-0.09+1.00 x CSA(IVUS), r=0.97, n=53. The mean difference between the values was -0.29%+/-5.57% (2 standard deviations). We conclude that the modified conductance method is a reliable technique to estimate the average cross-sectional areas of the aorta in piglets.

Animals↗

PubMedDate not supplied

Comparison of mouth and oesophageal pressure fluctuations during panting against an occlusion.

In four normal volunteers, differences between oesophageal pressure fluctuations (delta Pes) in the upper and lower parts of the oesophagus and mouth pressure fluctuations (delta Pm), simultaneously measured during panting against an occlusion, were evaluated. Averaged quasi static pressure-volume curves were obtained by measuring pressure in the upper and lower thirds of the oesophagus. The differences between delta Pes and delta Pm during panting, due to elastic recoil changes, were predicted from an exponential relationship fitted to the pressure-volume curves. The calculated errors were compared with those observed experimentally. In the lower part of the oesophagus, delta Pes was similar to delta Pm at lung volumes in the range of 50 to 70% of Vmax. Vmax was deduced from the asymptote of the exponential curve. Mean delta Pes/delta Pm was 0.98 +/- 0.08 (SD). In the upper oesophagus, delta Pes was lower than delta Pm. Mean delta Pes/delta Pm was 0.87 in the range of 50 up to 90% of Vmax with an SD +/- 0.15. At lung volumes above 90% of Vmax for the upper oesophagus and above 70% of Vmax for the lower oesophagus, the ratio of delta Pes to delta Pm exceeded 1 and progressively increased. The measured values were often higher than those predicted from the fitted curves, presumably due to a narrowed glottic aperture. We concluded that in normals both the positioning of the oesophageal balloon in the lower oesophagus and a lung volume near functional residual capacity (FRC) are prerequisites for the use of delta Pm as a control for delta Pes, or vice versa, during panting against an occlusion.

Airway Resistance↗

PubMedDate not supplied

Interpretation of changes in spirographic and flow-volume variables after operative treatment in bilateral vocal cord paralysis.

In 13 patients, who underwent a superolateralization of a vocal cord after bilateral vocal cord paralysis, we studied pre- and postoperatively spirometric dynamic and static lung volumes and variables from maximal expiratory and maximal inspiratory flow-volume (MEFV and MIFV) curves. The effects of surgical treatment on these variables have been established by comparing the statistical significance of the changes post- versus preoperative. A significant increase was found in the vital capacity and a significant decrease in the indices associated with the dynamic variability of the obstruction. The most significant changes were found in peak inspiratory flow and peak expiratory flow, and in the inspiratory defined dynamic estimates, as forced inspiratory volume in 1 second and maximal voluntary ventilation at a frequency of 30 c X min-1. Significant correlations, however, were found to exist only for the changes within the group of flow-volume indices and for those within the group of spirographic variables. This led us to the conclusion that for the diagnosis of this type of upper airway obstruction these measurements are additive, reflecting different aspects of airway mechanics.

Adult↗

PubMedDate not supplied

The components of the carbon monoxide diffusing capacity in man dependent on alveolar volume.

The effect of alveolar volume (VA) on diffusing capacity for carbon monoxide (DL), membrane conductance (Dm) and pulmonary capillary blood volume (Qc) was investigated in 39 normal volunteers to study alveolar membrane expansion and capillary volume recruitment. DL/VA was related to alveolar volume breathing air and 95% oxygen respectively. Both relations appeared to be linear with a negative slope and were used to calculate Dm and Qc as a function of VA. The relation between Dm and VA resulted in: Dm = kVAx, where x characterizes the kind of membrane expansion with increasing alveolar volume, when we assume Dm = kA/delta. In this equation, A is the membrane area and delta the membrane thickness. In 36% of our subjects, x was nearly 0.67, which corresponds to an isotropic expansion of diffusion area with alveolar volume without changes in delta. In 41%, x was between 0.67 and 1. We hypothesized that, in these subjects, either some decrease of delta or some recruitment of alveoli was superimposed on the area increase according to x = 2/3. In recruitment, a proportional increase of diffusion area with alveolar volume is assumed, which means x = 1. Subjects over the age of 50 years (n = 12) showed greater variation in the value of x, which was greater than 1.3 in three and less than 0.6 in a further three. The relation between Qc and VA was best described by a second order polynomial, characterized by a maximum above 50% of VAmax. With lung expansion, either a recruitment of capillaries or a better contact between blood and air could occur up to that maximum. Where Qc was decreasing with further rise of VA, we assumed compression of capillaries by stretching of pulmonary tissue.

Adolescent↗