Determination Of Pulmonary Blood Flow Research Articles

Abstract 15081: The Viscoelastic Yield Stress of Blood is Negatively Associated With Pulmonary Blood Flow in the Fontan Circulation

Introduction: In the Fontan (FN) circulation pulmonary blood flow (Qp) is passive, resulting in severely decreased shear rate and velocity in pulmonary arteries to the point of stasis. Yield stress (YS) is the shear stress required for blood to transition from stasis to a moving fluid. Therefore, YS may be a determinant of Qp in FN. We evaluated YS in patients with FN and Glenn (GLN) circulations and whether increased YS is associated with decreased Qp. Methods: We enrolled 20 patients with biventricular (2V) congenital heart disease (CHD) and 41 patients with single ventricle CHD (19 FN and 22 GLN) who were undergoing a clinically indicated cardiac catheterization. Two patients were excluded due to pulmonary vascular disease. We obtained blood samples at the time of catheterization and measured blood viscosity across shear rates 1 s -1 to 1000 s -1 using a Rheolog viscometer We calculated YS by curve-fitting of the viscosity measurements to a Casson fluid model. Hypothesis: We hypothesize that higher yield stress will be associated with lower pulmonary blood flow in Fontan circulation. Results: The FN group was the oldest and had the largest BSA (FN>2V>GLN; p<0.0001). Hematocrit was highest in GLN (GLN>FN>2V; p<). Blood viscosity was higher across all shear rates in GLN compared to both FN and 2V (p<0.001 for all shear rates) and higher in FN than 2V from 1 s -1 to 150 s -1 (p<0.05 for all shear rates). YS was highest in GLN (GLN>FN>2V; p< ). YS was negatively associated with Qp in both FN (R2 0.33, p=0.02) and GLN (R2 0.2, p=0.038), but not 2V (see Figure). Hematocrit was negatively associated with Qp in 2V (R2 0.34, p=0.028) and trended toward negative association in FN (R2 0.27, p=0.099), but not in GLN. Stepwise regression of Hct and YS vs Qp in FN demonstrated YS as the primary predictor of Qp. Conclusions: Our data demonstrate that the yield stress of blood derived from the Casson fluid model is a significant determinant of pulmonary blood flow in FN circulation.

Influence of Bag Volume on Reproducibility of Inert Gas Rebreathing Pulmonary Blood Flow Measurements in Patients with Pulmonary Diseases

Non-invasive inert gas rebreathing (IGR) has shown promising results in the determination of pulmonary blood flow. The volume of the rebreathing bag (V bag) is proposed by the system. However, elderly patients or those with severe pulmonary disease may be unable to rebreathe this volume entirely. We evaluated the effect of adapting V bag on the reproducibility of IGR. A total of 270 valid measurements were obtained from 45 patients with obstruction (group A), restriction (group B), and in healthy controls (group C). Two measurements for each of three different V bag of 1,200, 1,700, and 2,200ml were conducted in the supine position. We found no statistically significant difference of the repeated measurements neither between the different V bag in groups A to C nor between the three groups for identical V bag. There was a weak yet significantly worse coefficient of variation between a V bag of 2,200ml in group A compared with group C with 2,200 and 1,200ml, respectively. Intraclass correlation coefficient and repeatability coefficient yielded significantly worse values in group A for a V bag of 2,200ml compared with healthy controls and lower bag volumes. No difference could be found intraclass nor interclass in groups B and C. V bag can be altered between 1,200 and 2,200ml in most situations without affecting the reproducibility. Attention has to be paid to extreme volumes in obstructive patients. Nevertheless, V bag should be chosen as large as possible and therefore has to be carefully adapted, particularly in patients with obstruction or restriction.

Effects of inertial load and countermeasures on the distribution of pulmonary blood flow.

We assessed the influence of cranial-to-caudal inertial force (+G(z)) and the countermeasures of anti-G suit and positive pressure breathing during G (PBG), specifically during +G(z), on regional pulmonary blood flow distribution. Unanesthetized swine were exposed randomly to 0 G(z) (resting), +3 G(z), +6 G(z), and +9 G(z), with and without anti-G suit and PBG with the use of the Air Force Research Laboratory centrifuge at Brooks Air Force Base (the gravitational force of the Earth, that is, the dorsal-to-ventral inertial force, was present for all runs). Fluorescent microspheres were injected into the pulmonary vasculature as a marker of regional pulmonary blood flow. Lungs were excised, dried, and diced into approximately 2-cm(3) pieces, and the fluorescence of each piece was measured. As +G(z) was increased from 0 to +3 G(z), blood flow shifted from cranial and hilar regions toward caudal and peripheral regions of the lung. This redistribution shifted back toward cranial and hilar regions as anti-G suit inflation pressure increased at +6 and +9 G(z). Perfusion heterogeneity increased with +G(z) stress and decreased at the higher anti-G suit pressures. The distribution of pulmonary blood flow was not affected by PBG. ANOVA indicated anatomic structure as the major determinant of pulmonary blood flow.

Errors due to data reduction in single-breath method for measurement of pulmonary blood flow.

The validity and precision of the single-breath method for determination of pulmonary blood flow suggested by Kim et al. (J. Appl. Physiol. 21: 1338-1344, 1966) have been estimated by a number of workers with very different results. The present work is an analysis of the errors that arise solely due to the data-reduction procedure used to calculate the pulmonary blood flow from the primary data. The analysis, which consists of a computer simulation of the system, shows that very considerable errors may arise from the data-reduction procedure itself and that these errors are very sensitive to small differences in the experimental design. The basic source of errors in the data-reduction procedure seems to be the use of a fitted polynomial to computer derivatives of a nonpolynomial experimental curve. Finally, the analysis suggests a design in which the errors would be quantitatively insignificant.

A new method for noninvasive bedside determination of pulmonary blood flow.

A method is presented for determining the pulmonary blood flow from measurements of the time-averaged end-tidal pCO2 and the CO2 output.

Topology of pulmonary arterioles, capillaries, and venules in the cat

It is shown in this paper that each alveolus is not a unit of microcirculation: It is not supplied by one arteriole and one venule; each arteriole supplies several alveoli, which are connected to other alveoli before draining into venules. The spatial relationship among the arterioles, venules, and capillaries in the lung is not clear in the literature. To clarify the topology, we developed a special method of particulate polymer casting of the vascular tree, and four criteria to decide whether a noncapillary vessel is arterial or venous. Then on each histological cross section of the lung parenchyma, we marked all arteries with white dots, and all veins with red dots, and covered the area of white dots with one color, and the area of red dots with another. A two-colored map emerged. A two-colored cartographic map can only show islands in an ocean. Our histological maps of the cat lung show that the arterial zones are islands, and the venous zone is the ocean. From these maps quantitative information about the arterial and venous zones in the lung is obtained by stereological methods, and the data for the cat are presented. A morphological definition of the average length of capillary blood vessels connecting arterioles and venules is proposed. The average morphological length of capillary blood vessels in cat lung was found to be 556 ± 286 (SD) μm when the transpulmonary pressure was 10 cm H 2O. The average length of capillaries ( L) is an important determinant of pulmonary blood flow: for given arterial and venous pressures, the flow rate is inversely proportional to L 2, the square of the average length; the transit time (time available for diffusion and oxygenation) varies directly with L 2; the regional difference of blood flow also depends on L.

The applicability of the thermodilution method for determination of pulmonary blood flow and pulmonary vascular resistance in infants and children with ventricular septal defects.

The thermodilution method is accepted for measuring cardiac output in adults without shunts. It has been shown to work in animals the same size as newborn infants and has recently been used in children with congenital heart defects. We have proved its clinical applicability in determining the pulmonary blood flow, in twenty-five infants and children with VSD. The pulmonary vascular resistance can be calculated more accurately than by the Fick principle with an assumed O2 consumption, which has often had to be done in earlier studies.

The applicability of the thermodilution method for determination of pulmonary blood flow and pulmonary vascular resistance in infants and children with ventricular septal defects

The thermodilution method is accepted for measuring cardiac output in adults without shunts. It has been shown to work in animals the same size as newborn infants and has recently been used in children with congenital heart defects. We have proved its clinical applicability in determining the pulmonary blood flow, in twenty-five infants and children with VSD. The pulmonary vascular resistance can be calculated more accurately than by the Fick principle with an assumed 02 consumption, which has often had to be done in earlier studies.

Validation of the Starling resistor concept as a determinant of pulmonary blood flow

Validation of the Starling resistor concept as a determinant of pulmonary blood flow