The accuracy of regional myocardial blood flow measurements made with microspheres of different sizes is uncertain. Therefore, we simultaneously injected radioactive microspheres of different sizes into the left atria of dogs and sheep; the microsphere diameters were 25µ, 15µ, 9µ, 1-l0µ, and filtered 1-10µ (most > 7µ). Antipyrine was sometimes simultaneously infused for 15-60 seconds. Myocardial blood flow was altered by hemorrhage, tachycardia, supravalvar aortic constriction, or infusion of methoxamine or adenosine triphosphate; left coronary artery branches were occluded on two occasions. Sometimes the percent of untrapped microspheres was estimated. All sizes of microspheres measured similar total myocardial blood flows when the percent of untrapped microspheres was known. All indicators were distributed identically to the right and left ventricular free walls and septum; ischemic areas had a 1% excess of antipyrine. With any pair of microspheres, the larger had a subendocardial excess except for 25µ microspheres, which were in excess compared with 15µ microspheres in the higher flow layer whether it was subendocardial or subepicardial. The greatest difference for any pair of microspheres was 10.53% of flow in a layer. Antipyrine did not define which size of microspheres measured true regional blood flow, since many previously unemphasized limitations were discovered. Nevertheless, we believe that microspheres 9µ in diameter are probably the best for measuring regional myocardial blood flow.

No abstract

The design of telemetry systems for chronic implantation within the body have progressed from simple single-channel devices to complex multichannel systems over the last 15 yr. Although chronic measurements of temperature, ECG, and pressure have been reported with good results, measurements such as dimension and blood flow have been difficult because of heavy power requirements. The design to be described is a multiplex system that will measure up to eight individual parameters simultaneously, including blood flow. Flow is measured using an electromagnetic transducer, and by special design, the normal high power requirements of the electromagnetic technique have been reduced to a few hundred milliwatts. The system is powered by two NiCad, rechargeable batteries which are periodically recharged through the intact skin by induction at 250 kHz to an implanted pickup coil. The presently constructed units have been configured to measure ECG, two pressures, temperature and ascending aortic flow.

The ^Kr method was used to determine the effect of elevated ureteral pressure on total cortical and outer medullary nutrient renal blood flow of pentobarbital-anesthetized dogs. Increased ureteral pressure during mild saline diuresis resulted in increased total nutrient blood flow from 316 to 402 ml/100 g/min. Autoradiographs demonstrated that the increased blood flow is confined to the renal cortex and that juxtamedullary cortical and outer medullary flow is unchanged. Elevated ureteral pressure decreased total renal blood flow from 473 to 381 ml/g/min during copious mannitol diuresis. This is due at least partly to decreased cortical blood flow; we were unable to measure juxtamedullary cortical plus outer medullary blood flow during mannitol diuresis. Isolated renal arteries relaxed when placed in a physiologic salt solution containing 70 mM mannitol. Renin release is increased during elevation of ureteral pressure. We concluded that the mechanism for increased renal blood flow during ureteral occlusion selectively involves the nutrient circulation of the renal cortex.