Application of digital techniques to selective coronary arteriography: use of myocardial contrast appearance time to measure coronary flow reserve.

F oR the past 1~ years in our clinic, determinations of intravascular pressure have been carried out, in a nun> ber of patients undergoing gradual ligation of the common carotid ar tery for the t reatment of intraerania] ancurysms, particularly those situated on the internal carotid artery. These measurements have been made at the t ime of application of the clamp to determine the per-cent reduction in pressure in the distal carotid system following occlusion of the proximal common caroti(l artery. In general, it has been found that patients with a considerable reduction in pressure, e.g., 60 per cent or greater, require a longer period for closure of the clamp and are more likely' to have a neurologic complication as a result of ligation than patients with less reduction in pressure, t lowever, the relationship of reduction in pressure to lhe rate of neurologic complications has not always been as predicted. For inslanee, we have observed serious neurologic complications as a result, of closure of the claml) in patients with a reduction in pressure less than 40 per cent and, contrariwise, patients in whom the reduction in pressure has been as high as 70 per cenl have tolerated gradual closure without difficulty. I t is felt that all accurate knowledge of blood flow through the carotid ar tery 1o be ligated might provide more information regarding the change in intracranial circulatory dynamics a t tendant upon carotid liga-

Studies on carotid artery flow and pressure. Observations in 18 patients during graded occlusion of proximal carotid artery.

The effects of hypoxia (administration of 10 per cent O 2 in N 2 and constriction of the uterine arteries), of hypercapnia (administration of 8 per cent CO 2 in air), and of asphyxia (obstruction of the umbilical circulation) were studied on the fetus in utero in near-term pregnant ewes under spinal anesthesia. Hypoxia and hypercapnia produced increases in the maternal arterial pressure, maternal heart rate, and uterine blood flow. Fetal arterial pressure and carotid and umbilical blood flows increased, while the fetal heart rate decreased. Fetal femoral flow decreased during hypoxia and increased during hypercapnia. There was a delay of five to six minutes between the initiation of hypoxia or hypercapnia and the appearance of fetal circulatory changes. Transient reduction of uterine blood flow evoked insignificant hemodynamic alterations in the mother and fetus. A reduction of flow greater than 50 per cent of control values produced a fetal bradycardia along with increases in fetal arterial pressure, carotid and umbilical flows. Constriction of the umbilical veins with the umbilical arteries intact produced a prompt bradycardia together with a decrease in fetal arterial pressure and regional blood flows. Constriction of the umbilical arteries alone also produced a bradycardia with an initial rise in arterial pressure and carotid flow. Similar changes were observed after cutting the umbilical cord. Elimination of the low resistance of the placenta played a major role in these changes. Placing the lamb in the head-down position caused a marked increase in carotid blood flow without greatly modifying arterial pressure.

https://www.ahajournals.org/doi/pdf/10.1161/01.RES.11.3.423

Hemodynamic Changes in Fetal Lamb in Utero in Response to Asphyxia, Hypoxia, and Hypercapnia

The paper discusses the structure and composition of blood, its viscous properties and how these affect flow, and also the electrical, optical and thermal properties, which can be used to quantify flow. The development of a flow profile is discussed for steady and pulsatile flow in major vessels. The various types of flowmeter which have been developed to take this profile into account are discussed. These include electromagnetic and ultrasonic flowmeters, indicator-dilution methods (including thermal dilution) and various pressure-sensing devices. In small vessels and in bulk tissue the concept of flow profile has no meaning and the measurement methods include indicator-transport methods using radioactive isotopes various forms of plethysmograph, calorimeters and thermal-conductivity probes. Each type of flow measurement method is discussed, together with its advantages and disadvantages.

https://iopscience.iop.org/article/10.1088/0034-4885/39/1/002/pdf

Physical properties of blood and their influence on blood-flow measurement

The effects of intravenous administration of angiotensin on the arterial pressure and on the renal, carotid, iliac, uterine, and femoral blood flows were investigated in dogs and sheep through the use of implanted electromagnetic flowmeters. The rise in arterial pressure was immediate and, within the range of doses employed, presented little relation ship to the dose. The pressor effect of angiotensin was accompanied by a consistent fall in the renal blood flow and a rise in the femoral, iliac, and uterine flows. Carotid flow was less affected. These studies demonstrate the specificity of flow response to a given change in pressure in the various areas of the body.

A. Westersten

Papers

A gated sine wave blood flowmeter

Gated Sine-Wave Electromagnetic Flowmeter