Blood flowmeters

Noninvasive assessment of microcirculation of living organs and tissues using laser

For studying microcirculation of intact tissues or organs, a new noninvasive, heat-transient method using laser photoexcitation is described. As a heating source an argon ion laser or R6G dye laser was used via a quartz fiber optic guide. Infrared radiation from heated tissue was detected by a thermography apparatus. After switching the laser irradiation on and off, a thermal transient curve of a model tissue, the skin, was biphasic: a component with a fast time constant and the other with a slow time constant. The temperature increases of both phases following laser irradiation were linear to the applied power from the laser onto the tissue. The temperature rises as a function of the wavelength of irradiated light have shown that the absorption of the light by tissue hemoglobin is a main heat-generation source. Furthermore, the temperature rises as a function of tissue blood volume and flow have shown that the component with a slow time constant is more related to the tissue hemoglobin concentration and tissue blood flow and heat conductivity. Thus, the analysis of heat-transient curves following laser irradiation gives information as to regional tissue blood volume, blood flow, and tissue heat conductivity.

Accuracy in coronary graft flow measurement

A blood flow calibration apparatus is described for use with electromagnetic flow probes. It is an automatic gravity-flow system, which provides a constant level and therefore constant flow at any preset rate. On several occasions, the use of this device has helped to determine whether flow probes require simple adjustment, factory repair, or replacement. Using this system, a systematic error in the manufacturer's "precalibration" averaging +22% (range, 9 to 50%) has been discovered, and appropriate corrections have been made. The accuracy of these corrections has been confirmed by a rapid, in vivo method of calibration, which also is described and which can be carried out during the conduct of aortocoronary bypass operation. It is recommended that all groups measuring coronary graft flow become familiar with their electromagnetic flowmeter and probes by means such as those described, in the interest of accurate flow measurement after bypass operation.

Thyroid blood flow rate in man. Electromagnetic flowmetry during operation in euthyroid normal gland, nontoxic goiter, and hyperthyroidism

Human thyroid blood flow rate (TBF) was measured during operations by electromagnetic flowmetry in 75 euthyroid patients with normal thyroid tissue, nodular goiter, or solitary adenoma, and in 22 hyperthyroid patients with diffuse or nodular goiter. Blood flow rate was measured in one to four of the thyroid arteries. No difference in blood flow rate was seen between the left and right lobes. The slight difference found between the inferior and superior arteries was not significant. In each subject, total TBF was calculated as 4 times the mean of the recorded blood flow in the single arteries. The total TBF was 31 (9-109) ml/min (inner 95 percentile range) in euthyroid patients, similar in all 3 groups. This is less than in most earlier reports. The relative TBF was 1.2 (0.4-3.8) ml/min/g thyroid tissue in normal thyroid tissue and 0.6 (0.1-3.7) ml/min/g in nontoxic nodular goiter (p less than 0.01). Patients with hyperthyroidism had a higher total TBF 54 (15-197) ml/Min (p less than 0.001), despite preoperative treatment giving euthyroidism, Similar TBF rates were found in 3 hyperthyroid patients given propranolol preoperatively. Electromagnetic flowmetry is applicable to study thyroid blood flow rate. Human TBF shows considerable interindividual variations, which must be kept in mind when studying directly the rate of thyroid hormone secretion from arteriovenous gradients.

Microvascular bypass surgery. Part 2: physiological studies

Intraoperative electromagnetic blood flow measurements were recorded in 15 patients undergoing extracranial-intracranial arterial bypass surgery. The initial average blood flow of 28.2 cc/min supplies 8.4% of the expected flow from one internal carotid artery. Blood flow probably increases postoperatively, as evidenced by angiographic enlargement of the bypass and its recipient cortical arteries.

Electromagnetic blood flowmetry in small vessel surgery. An experimental study

The aim of this work was to study problems in microvascular flowmetry. Special emphasis was placed on the meticulous preparation of the vessel wall in order to improve zero-line stability and on the problems related to the calibration of small electromagnetic flow probes. Electromagnetic flow probes with an inner diameter of 2, 1.5 and 1 nm were used for studies on zero-line drifting and for calibration procedures in a series of rats and rabbits. Principles and tools derived from microvascular surgery, including the binocular microscope, were employed in the preparation of the vessel wall and in the application of the probes. The results obtained indicate an improvement in flow uptake and in zero-line stability following this procedure. Precalibration of small flow probes using laboratory animals should be considered if calibration is not feasible at the time of the flow measurement. Use of the microsurgical technique for vessel preparation is recommended.

Newer techniques of cerebral blood flow measurement

A variety of methods for measuring cerebral blood flow have been developed in the past 25 years since Kety and Schmidt developed their method based on the Fick principle. None of the currently used methods approaches the clinical ideal, since none of the techniques are accurate, reproducible and noninvasive. Most accurate techniques involve catheterization of internal carotid artery and/or jugular vein with those attendant risks. There has been considerable enhancement of our understanding of the pathophysiology of cerebral circulation, particularly in the areas of brain injury and disordered systemic metabolism, but the clinical usefulness of the test at the present time is limited.

A study of Duroziez's murmur of aortic insufficiency in man utilizing an electromagnetic flowmeter

Femoral arterial blood flow was recorded with an electromagnetic flowmeter at the time of open heart surgery on subjects with and without aortic insufficiency. The records demonstrated that subjects with severe aortic insufficiency and Duroziez's murmur had a large amount of retrograde flow in the femoral artery. Those subjects without significant aortic insufficiency and no Duroziez's murmur had little or no backflow. When only a moderate amount of aortic insufficiency was present, the correlation was less satisfactory. In some subjects who had femoral backflow, a second recording was made from the femoral artery after the aortic valve had been replaced, and in these instances there was no longer any measurable backflow. Postoperatively these patients did not have Duroziez's murmur.

It is concluded that Duroziez's crural murmur in subjects with aortic insufficiency is associated with retrograde diastolic femoral arterial blood flow.