Modified instrument for measuring blood cell aggregation using the screen filtration pressure (SFP) technique

Based on the original technique of Swank, the modification described largely eliminates variation obtained when passing identical blood samples through the original system.     

An isothermal flowmeter with improved frequency response for measuring tissue blood flow

Summary An isothermal flowmeter with improved frequency response for measuring tissue blood flow was developed using thermistors. Direct heating of the thermistors allows a simple construction of small (0.5 mm outer diameter) capillary probes which do not require any additional heating coil. The changes of a feedback current necessary to keep the thermistor at a constant increment above tissue temperature indicate tissue blood flow; a second thermistor compensates variations of tissue temperature. The dynamic performance of the device shows a low-pass characteristic with a cut-off frequency higher than 5 Hz. For low flow rates the output signal was found to be proportional to the flow; for higher flow rates a linearization was necessary. Since tissue temperature can be recorded continuously, intermittent quantitative in-vivo calibration seems possible by evaluation of heater off curves in the perfused and non-perfused tissue. As the flowmeter is insensitive to tissue temperature, it can be used for long-term recordings.This study was supported by the Deutsche Forschungsgemeinschaft (SFB 90, Kardiovasculäres System)A preliminary report of a part of this investigation has been presented at the 46. Meeting of the Deutsche Physiologische Gesellschaft: Pflügers Arch., Suppl.362, R 53 (1976)     

Local heat clearance probes with alternative heating and their application in the measuring of human muscle blood flow

Summary Local heat clearance probes containing two measuring points each surrounded by a heating system, thus enabling an alternative heating of both points, were tested in model experiments and in the measuring of human muscle flood flow. Measurements with alternative heating of both measuring points at the same probe position allow the determination of the degree of homogeneity of local blood flow. Thus inhomogeneity errors in estimating the local heat clearance (heat transport index, HTI), which arise from the fact that the reference measuring point is always slightly coheated, can be avoided. With this modified technique, the chances of finding suitable probe, positions for the measurement of human muscle blood flow are significantly increased.     

Observations on the validity of using “NEN-TRAC” microspheres for measuring organ blood flow

Summary NEN-TRAC brand of radioactive microspheres, 15 m in diameter, have recently become available and therefore organ blood flow (Q) values obtained using these have been compared with values simultaneously obtained with the well-established TRACER brand of microspheres. For all major tissues of the body of two conscious sheep, there was excellent agreement between Q values obtained using NEN-TRAC Ce-141 and TRACER Sr-85 in one sheep, and between Q values obtained using NEN-TRAC Ce-141 and Sn-113 and TRACER Cr-51, Sr-85 and Nb-95 in a second sheep. It is concluded that NEN-TRAC microspheres satisfy the major validation tests to which TRACER microspheres have been previously subjected, and therefore it is valid to proceed with use of the new product.     

Evaluation of the thermodilution technique for measuring coronary sinus blood flow

Summary In hydraulic non-occlusive models, mixing effects were studied with slug-injection and constant-infusion techniques. Measurements were accomplished by means of catheters specially constructed with thermistors. Constant-rate infusion of 5 ml/min of saline at room temperature showed homogeneity of mixing. Good correlation (r=0.936) was found between metered flow ranging from 50–450 ml/min and reciprocal temperature changes.In anesthetized open chest dogs reciprocal temperature changes during constant-infusion thermodilution was compared with coronary sinus flow metered by graduated cylinder and stop-watch. For this purpose all the coronary sinus blood was directed through a tubing system with a Y-connector into the jugular vein. In the range of 50–450 ml/min the metered coronary sinus blood flow and the reciprocal of the observed changes in temperature showed a linear correlation (r=0.949). The reproducibility of the thermodilution method is fairly good. Therefore it is believed that this technique will allow accurate measurement of coronary sinus blood flow.This work was supported by a grant of the Swiss National Fund for Scientific Research.     

Precautions for measuring blood flow during anemia with the microsphere technique

Preliminary data from a study of the effects of anemia on organ blood flow showed large discrepancies between cardiac output measured with the microsphere technique and simultaneous values calculated by the Fick principle. The most likely explanation was that the reference sample drawn according to our standard procedure underestimated the microsphere concentration in arterial blood, resulting in erroneously high blood flow values. In the present experiments we compared our usual reference sample, from a small catheter advanced from a peripheral artery into the brachiocephalic artery (withdrawal rate 1.3 ml/min), with a simultaneous sample from a larger catheter withdrawn at the much higher rate (7.89 ml/min). At hematocrits above 32%, microsphere concentrations from the two catheters were similar, but below 32% the concentration of microspheres in blood from the larger catheter was 30-50% more than from the smaller. The discrepancy was not altered by changing the injection site from left ventricle to left atrium and thus was probably not the result of poor mixing within the heart. It may have been the result of nonhomogeneous distribution of microspheres within larger vessels, perhaps as a consequence of laminar flow and axial streaming of both red blood cells and microspheres during anemia. Whatever the cause, it was possible to eliminate the difference by withdrawing from the smaller catheter at a more rapid rate (2.46 ml/min).     

The in vivo relationship between blood flow, contractions, pH and metabolites in the rat uterus

 Little is known about the relationship between smooth muscle contractile activity and its blood supply. We have therefore investigated this in the rat uterus, using laser-Doppler flow measurement and intra-uterine pressure recordings. We found an inverse linear relationship between flow and contractile activity. There was no evidence for a critical level of flow, above which function is maintained and below which it declines; even small reductions in blood flow decreased uterine force. Force was rapidly restored upon reperfusion. Reactive hyperaemia was absent from all but 6 of the 41 preparations studied. We used ³¹P nuclear magnetic resonance (NMR) spectroscopy to measure concentrations of adenosine triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and intracellular pH (pH_i) simultaneously with force and flow. Reductions in flow were associated with significant reductions in [ATP], [PCr] and pH_i, and an increase in [Pi]. These changes were related to flow significantly and linearly and their effects on force may be additive. These data show that uterine smooth muscle is closely dependent upon its blood supply for maintaining both normal force production and metabolite levels. Consequently, even small decrements in flow may have deleterious functional effects. Received: 17 July 1997 / Received after revision: 1 November 1997 / Accepted: 26 November 1997