Flow measurement at the pump head of centrifugal pumps: comparison of ultrasonic transit time and ultrasonic Doppler systems

Hemodynamic assessment of the development of portal-systemic collaterals in portal hypertensive rats

BACKGROUND

Portal hypertension induced the formation of portal-systemic collaterals. Revealing the developmental change of portal-systemic collaterals is important for future therapy.

METHODS

We observed the evolution of an accessible shunting vessel, the spleno-renal shunt (SRS), in rats after induction of portal hypertension by partial portal vein ligation (PVL). The hemodynamic and histological assessments of SRS were performed by transit time ultrasound and immunohistochemical studies.

RESULTS

The portal pressure of PVL rats surged to 16.5 ± 1.1 mmHg on day 1 after ligation surgery and was maintained at a significantly higher level (13.0 ± 0.4 mmHg) to day 14 when compared to sham rats (p < 0.05). The size or flow of SRS in PVL rats did not change immediately after portal pressure surge. Instead, they increased rapidly on day 4, peaked on day 7, and stabilized thereafter. The size and flow were greater and the resistance of SRS was lower in PVL rats after day 7 (p < 0.05). The anti-Ki67 immunohistochemical study demonstrated positive staining of endothelium in SRS and negative in portal vein or aorta of PVL rats. In addition, the endothelial cells of SRS were stained positive for CD31 and KLF5.

CONCLUSIONS

We concluded that the pressure-induced opening of pre-existing vessels was not the primary underlying mechanism in the formation of SRS. Endothelial proliferating and vascular remodeling process participated actively during the development of SRS. These observations can be used for studying the pathogenesis and developing more effective anti-portal hypertensive therapy in the future.

Advanced suction detection for an axial flow pump

An automatic detection system for ventricular collapse was developed and tested in a first clinical trial as part of a physiological speed control concept for axial flow pumps. From this clinical experience, and based on the acquired data during this trial, an optimization of the developed system was performed. An already-existing database of 784 individual cases was extended. For harmonization of this database an additional 412 snap files were extracted from continuous data recordings and classified manually using a standardized procedure. The already-developed and clinically tested algorithms were supplemented by one additional indicator derived from a preexisting criterion. One threshold value was replaced by application of a numerically optimized nonlinear characteristic curve dependent on heart rate. Finally, in a multidimensional optimization process of the entire suction detection system, 7 individual indicators were adjusted by using 17 independent threshold values. The optimization criteria were applied using a three-level hierarchical system. Within the final database consisting of 1196 snap shots the overall amount of maldetections could be reduced to 23 cases including 5 false positive events (0.42%) and 18 false negative decisions (1.5%). By application of the clinical experience from the first clinical trial of a physiologic control system it became possible to optimize the sensitivity and specificity of the suction detection system to unprecedented accuracy.

Development of a suction detection system for axial blood pumps

Axial flow blood pumps for cardiac assistance have proven their clinical viability and benefit in recent years. However, the clinical systems to date have no direct mechanism to decrease pump speed when adequate supply is not available. This may lead to ventricular collapse or increase the probability of hemolysis and thrombotic risks. Based on various experiences with left ventricular assist device (LVAD) patients in various states of recovery, at implant, in the intensive care unit, in the standard ward, and during physical exercise, 11 different algorithms were developed for the automatic detection of ventricular suction. These detection algorithms analyze the flow pattern for the presence of distinct suction indicators. For selection and optimization of the algorithms, 1000 records from approximately 100 patients were collected. Each record contains 5 s of pump flow, current, and arterial pressure. Three experts classified these records in terms of suction probability and other abnormalities. The optimization was developed in Matlab, capable of solving a fifth-dimensional optimization problem with 256 different algorithm combinations. The optimization resulted in a set of 6 algorithms, each with specific thresholds. The system detects 100% of the known suction events with 0.28% of false-positive interpretations. If tuned to avoid any false-positive detection, 90.7% of the certain events would be detected. A strategy for the development of a robust suction detection system for axial blood pumps was found. This system will be integrated into an automatic pump speed control system to provide adequate perfusion for the LVAD recipient, without excessive unloading of the ventricle.

Cardiac output measurement by pulse dye densitometry using three wavelengths

OBJECTIVES

Pulse dye densitometry (PDD), based on the principles of pulse oximetry and dye-dilution technique, is a less invasive method of measuring cardiac output (CO). We have developed prototype equipment to measure CO in pediatric patients using this technique. The purpose of our study was to evaluate the accuracy of this new PDD system using three wavelengths for pediatric application by comparing measurement with an ultrasound flowmeter.

DESIGN

Laboratory investigation.

SETTING

Hospital physiology research laboratory.

SUBJECTS

A total of 15 young piglets weighing approximately 10 kg each.

INTERVENTIONS

Measurement of CO by PDD was performed using general anesthesia. Indocyanine green, 0.2 mg/kg, was administered intravenously, and CO was calculated from the dye dilution curve obtained by the PDD system. The ultrasound flowmeter probe was placed on the ascending aorta in the animal, and CO was simultaneously calculated.

MEASUREMENTS AND MAIN RESULTS

The two CO values, simultaneously obtained by the ultrasound flowmeter and PDD, were compared during various hemodynamic states. The bias between the CO measured by the ultrasound flowmeter and the CO measured by the PDD system using the reflection-type probe at the central site was 33.8 mL/min and the precision was 293.4 mL/min, indicating that CO measured by PDD had a good correlation with measurements obtained with the ultrasonic method.

CONCLUSION

We measured CO in young piglets at an acceptable level of bias and precision using a prototype PDD device. CO measurement by this new PDD system using three wavelengths can be useful and beneficial for critically ill infants and children. It is simple to perform, requiring an injection of dye into a peripheral intravenous catheter, and it will provide a less invasive bedside measurement of CO.

Improvement of carotid blood flow after carotid endarterectomy--evaluation using intraoperative ultrasound flow measurement

OBJECTIVES

to examine the relationship between the degree of extracranial internal carotid artery (ICA) stenosis and changes in the ipsilateral ICA blood flow after carotid endarterectomy (CEA).

MATERIALS AND METHODS

in a prospective study we studied 51 patients with unilateral 60-99% ICA stenosis (median degree 84%, asymptomatic stenosis n = 13, symptomatic stenosis n = 38). The degree of ICA diameter stenosis was determined by ex-vivo plastination of the surgically removed atherosclerotic specimen and video-assessed planimetry. Intraoperative transit time ultrasound flow measurements of the carotid arteries were performed before and after CEA. Blood flow changes were assessed by mathematical approximations. Statistics were done by use of the Wilcoxon signed Rank test.

RESULTS

common carotid artery (CCA) and ICA median blood flow increased after CEA from 370 and 130 ml/min to 450 and 282 ml/min, respectively (p <.001). The relative increase of ICA blood flow was 5% and 18% for 60-69% and 70-79% ICA stenosis (n.s.) but 70% and 247% for 80-89% and 90-99% stenosis (p <.001 each). Mathematical evaluation (fourth-polynomal function) determined a significant increase of carotid blood flow after CEA in ICA stenosis of > or =82.3%.

CONCLUSIONS

in the absence of severe contralateral ICA occlusive disease a significant increase of ipsilateral ICA blood flow by CEA can be expected in patients with an ICA stenosis of > or =82.3% (linear degree of stenosis, ECST criteria).

New method of cardiac output measurement using ultrasound velocity dilution in rats

The aim of this study was to validate a new technique for the measurement of cardiac output (CO) based on ultrasound and dilution (COUD) in anesthetized rats. A transit time ultrasound (TTU) probe was placed around the rat carotid artery, and ultrasound velocity dilution curves were generated on intravenous injections of saline. CO by COUD were calculated from the dilution curves for normal and portal hypertensive rats in which CO was known to be increased. COUD was compared with the radiolabeled microsphere method and with direct aortic TTU flowmetry for baseline CO and drug-induced CO variations. CO in direct aortic TTU flowmetry was the ascending aorta blood flow measured directly by TTU probe (normal use of TTU flowmetry). The reproducibility of COUD within the same animal was also determined under baseline conditions. COUD detected the known CO increase in portal hypertensive rats compared with normal rats. CO values by COUD were correlated with those provided by microsphere technique or direct aortic TTU flowmetry (adjusted r = 0.76, P < 10(-4) and r = 0.79, P < 0.05, respectively). Baseline CO values and terlipressin-induced CO variations were detected by COUD and the other techniques. Intra- and interobserver agreements for COUD were excellent (intraclass r = 0.99 and 0.98, respectively). COUD was reproducible at least 10 times in 20 min. COUD is an accurate and reproducible method providing low-cost, repetitive CO measurements without open-chest surgery. It can be used in rats as an alternative to the microsphere method and to direct aortic flowmetry.

Volume flow estimation by colour duplex

OBJECTIVE

To assess the accuracy of volume blood flow using a digitised colour duplex scanner.

DESIGN

Observer-blinded experimental study.

MATERIALS AND METHODS

Method comparison was performed with linear regression analysis of 89 paired observations in 11 anaesthetised pigs. A Siemens Sonoline Elegra ultrasound system was used for transcutaneous volume flow estimation using invasive transit time flowmetry by Cardiomed as a reference.

RESULTS

For the individual measurement we found a standard error of the estimate (SEE) of 22 ml/min. For the regression line, however, the SEE was only 0.2 ml/min.

CONCLUSIONS

Digitised colour-duplex sonography has a volume flow measurement error that is too high for single measurements in the individual patient for the method to be useful in clinical decision making, but sufficient for examinations of groups and comparison of groups.