Biomedical subjects

J K Poulsen

Publications and source records attributed to J K Poulsen.

6 recordsLinked to original sources

PubMed1998

Microvascular damage secondary to thromboembologenic arterial injury--a new experimental model.

BACKGROUND AND AIMS: The isolated rat cremaster model is used extensively for evaluating the microcirculation secondary to arterial injury. Current techniques, however, do not allow for assessment of injury and effect within the same animal. The purpose of this study was to develop a model incorporating the following points: visualization of the upstream arterial injury and the downstream microvascular damage in the same animal, analysis of capillary density by randomization of measuring windows throughout the cremaster muscle, and simplification of the arterial injury. MATERIALS AND METHODS: Thirteen male Wistar rats were randomized into two groups. In group I, the entire isolation of the cremaster muscle was performed, without arterial damage. In group II, arterial damage consisting of a standardized pinch was applied to the feeding vessel. RESULTS AND CONCLUSIONS: It was possible to produce a simplified arterial injury and visualize the resulting downstream microvascular damage in the same animal, in a quantitative and randomized fashion. In group I, no thrombus formation was seen. In group II, all animals produced an embolizing arterial thrombus, which was dynamic within the first hour of observation. Capillary density was reduced from 6.5 to 3.5 capillaries/measuring window within the first hour after arterial thromboembolism.

Animals↗

PubMed1997

New semiautomated Doppler method for quantification of volumetric flow: intraoperative validation with multiplane transesophageal color Doppler imaging.

We have validated a new semiautomated method for quantification of volumetric flow applied to multiplane transesophageal color Doppler mapping. This Doppler technique assumes only the incompressibility of the fluid and includes variations of flow area. By computing velocity vectors across a surface normal to the point of scanning, volumetric flow can be measured independently of the angle of incidence between the ultrasonic beam and the direction of blood flow. Mitral valvular flow rate was measured during surgery by transesophageal color Doppler echocardiography in 27 patients undergoing coronary artery bypass grafting at 45 sets of observations. The results were compared with those obtained by the thermodilution technique. The mean of the differences between the thermodilution technique and color Doppler echocardiography was 0.06 +/- 0.866 L/min for the mitral valvular flows (mean of differences [thermodilution-color Doppler] &/- 2 SDs of differences). Thus mitral valvular volumetric flow measured by this color Doppler method showed a close agreement to the thermodilution technique during surgery.

Blood Flow Velocity↗

PubMed1996

A new Doppler method for quantification of volumetric flow: in vivo validation using color Doppler.

OBJECTIVES: This study was designed to assess the accuracy of a new Doppler method for quantification of volumetric flow in vivo. BACKGROUND: Noninvasive assessment of volumetric flow through heart valves and the great vessels remains a clinical goal. We present a new method for quantification of volumetric flow based on color Doppler mapping that computes velocity vectors over a surface normal to the point of scanning. This Doppler technique assumes only the incompressibility of the fluid. The method is basically independent of the angle of incidence between the ultrasound beam and the direction of blood flow and includes variations of flow area. METHODS: The color Doppler method was tested in seven anesthetized pigs by measuring pulmonary volumetric flows using multiplane Doppler echocardiography. The results were compared with those obtained by the thermodilution technique. In addition, volumetric flows across the mitral valve were determined in 10 normal volunteers by transthoracic Doppler echocardiography and compared with flows obtained with velocity-encoded magnetic resonance imaging (MRI). RESULTS: The mean value of the differences between the thermodilution technique and color Doppler were -0.16 +/- 0.94 liter/min for pulmonary volumetric flows (mean value of differences for [Thermodilution-Color Doppler] +/- 2 SD of differences). The mean value of the differences between MRI and color Doppler were 0.21 +/- 0.83 liter/min for mitral valvular volumetric flows (mean value of differences for [MRI-Color Doppler] +/- 2 SD of differences). CONCLUSIONS: The method showed close agreement with thermodilution and MRI for assessment of volumetric flow in vivo. It is therefore a noninvasive method with potential applications for cardiac output measurement and for quantification of volumetric flow of valvular insufficiency and restrictive lesions.

Adult↗

PubMed1996

Measurement of volumetric flow with no angle correction using multiplanar pulsed Doppler ultrasound.

In this paper we show that by scanning at points on the surface of a sphere that the normal angle correction used in pulsed Doppler flow measurements is no longer necessary. Thus, it is possible to measure three-dimensional (3-D) flow using multiplanar ultrasound even though we only get one-dimensional (1-D) velocity information from pulsed Doppler ultrasound. The technique handles the three basic problems in flow measurements using ultrasound Doppler: The variations of the cross-sectional area, the time dependent changes in the velocity field, and the dependency of the angle of insonation. The technique is tested in a flow phantom using different angles of insonation to validate the angle independence of this new technique. Using six different angles of insonation in the range 0 degree to 69 degrees with flowrates in the range of 0-170 ml/s a linear dependence was found to be: measured (color Doppler) = 0.98 real flow (reference) + 1.36 ml/s, with a 95% confidence interval of +/- 13.9 ml/s.

Blood Flow Velocity↗

PubMed1995

Left ventricular blood flow patterns in normal subjects: a quantitative analysis by three-dimensional magnetic resonance velocity mapping.

OBJECTIVES: Magnetic resonance velocity mapping was used to investigate the hypothesis of a vortex motion within the left ventricle interacting with mitral valve motion and inflow velocity. BACKGROUND: In vitro flow visualization studies have suggested the presence of a large anterior vortex inside the left ventricle during mitral inflow. However, to our knowledge the occurrence of this phenomenon has not been demonstrated in the human left ventricle. METHODS: Magnetic resonance velocity mapping was performed in 26 healthy volunteers using a flow-adjusted gradient sequence for three-dimensional flow velocity acquisition in the long-axis plane of the left ventricle. By computer processing, the flow vectors in the left ventricle were visualized and animated dynamically. RESULTS: The early diastolic mitral inflow was apically directed, and a large counterclockwise anterior vortex was created within the left ventricle shortly after the onset of the mid-diastolic semiclosure of the anterior mitral leaflet. During mid-diastolic diastasis, mitral inflow ceased until the flow accelerated again at atrial systole. The final closure of the mitral valve was preceded by a smaller vortex seen at the tips of the mitral leaflets. At systolic ejection, all flow vectors were directed toward the left ventricular outflow tract. The anterior vortex had a radius of 1.62 +/- 0.24 cm (mean +/- SD), and the average angular velocity (i.e., the rotation of an element about the center of the vortex within the central core) was 30.08 +/- 9.98 radians/s. The maximal kinetic energy of the anterior vortex was 4.3 x 10(-4) +/- 7.1 x 10(-5) J. CONCLUSIONS: The hypothesis of a diastolic vortex formation in the human left ventricle was confirmed, and its close temporal relation to the motion of the anterior mitral leaflet was demonstrated.

Adult↗

PubMed1994

Two-dimensional mitral flow velocity profiles in pig models using epicardial Doppler echocardiography.

OBJECTIVES: This study investigated the velocity distribution across the natural mitral valve. BACKGROUND: Information about the blood velocity distribution across the mitral valve is of interest in basic fluid dynamic studies of the natural mitral valve and is needed for precise cardiac output estimates by Doppler echocardiography. METHODS: The velocity distribution across the mitral valve was measured by epicardial Doppler echocardiography in ten 90-kg anesthetized pigs. By rotating the ultrasound transducer in 30 degrees intervals from the apical position, we constructed two-dimensional velocity profiles across the left ventricular inflow tract from diameters from each rotation arranged around a reference point. The time-averaged mitral velocity profile was calculated to estimate the error in cardiac output calculations that may occur with pulsed Doppler ultrasound when a single sample volume is used to record the mean velocity across the mitral orifice. RESULTS: The time-averaged diastolic cross-sectional mitral velocity profiles at the level of the mitral annulus and leaflet tips were variably skewed because of the development of a large anterior vortex in the left ventricle during the deceleration of early diastolic inflow and atrial systole. The ratio of the time-velocity integral of the center sample volume to the spatially averaged time-velocity integral was 1.13 +/- 0.15 (mean +/- SD) (range 0.80 to 1.32). Using regression analysis, we found a correlation between the degree of nonuniformity of the cross-sectional velocity distribution and the peak velocity of the anterior vortex (r = 0.65, p < 0.01). CONCLUSIONS: The assumption of a flat mean velocity profile across the mitral valve can introduce errors of +13 +/- 15% (mean +/- SD) in cardiac output measured with pulsed Doppler ultrasound when one is interrogating a single center sample volume.

Animals↗