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Clinical evidence suggests that blood flow in the retinal vessels varies in progressing diabetic retinopathy, coronary arteriole disease, hypertension and some other clinical situations. The changes of the flow in the blood vessels may serve as a monitor of the disease and as a follow up device for treatment success. Despite their importance direct blood flow velocity measurements are not easily obtainable. Recent advances in the development of a laser Doppler anemometry for the determination of in-vivo retinal blood velocity enables to obtain, with a noninvasive technique, information relevant to the flow of blood in the human retina. The described anemometry system is designed to be integrated, self-aligned and to operate with backscattered light. The influence of the important design parameters as well as focusing of the control volume on the retinal arteries is analyzed. Due to multiscattering of light from the blood cells present simultaneously in the control volume, the electronic signal obtained is very difficult to process and sophisticated signal processing routines are still being developed. At present measurements are used to obtain results with blood flowing in glass tubes of an inside diameter of 50 to 2000 microns. Preliminary experimental and theoretical simulations are currently being performed to validate the principle of the proposed data processing technique. Initial measurements have already produced relative high quality (and thus processable) signals, indicating good prospects for a practical ophthalmic system operation.

A multichannel pulsed ultrasound Doppler instrument designed to measure velocity and volume flow rate quantitatively has been applied for turbulence detection. A 7-MHz transmitting frequency and a phase locked loop technique for the frequency to velocity conversion have been used to obtain high temporal resolution in the single channel mode. To provide for reliable positioning of the single gate within the arterial lumen the device could first be operated in the multichannel mode measuring the velocity profiles with zero crossing detection methods. Measurements of the velocity in the center of the lumen of the common and internal carotid arteries have been recorded on a beat to beat basis. An ensemble average of 16 consecutive pulses was determined. Thereafter, the root mean square of the differences between ensemble average and individual velocity pulses was computed, and a disturbance index was defined by dividing the disturbance velocity by the mean velocity. First clinical results show that the method presented is a valuable complement to the analysis of flow pulse patterns in the transcutaneous examination of carotid arteries.

The substantial repertoire of laser radiation--its coherence, range of intensity and frequency, controlability of focal area and of beam length--has been comprehensively explored in the contexts of micro- and macro-diagnostics of cells, biochemical kinetics, therapy and surgery.

Using a constant temperature anemometer and an L-shaped 1 mm conical hot-film anemometer probe, blood velocities were registered in a patient after implantation of a Starr-Edwards ball valve in the aortic position. Velocities were registered at 41 predetermined points in the ascending aorta, equally distributed over the cross-sectional area. Data were recorded on tape and later analysed to make three-dimensional plots of the velocity profile at 200 time intervals during one "mean" heart cycle, and a film of the velocity profile in this cycle was made. The film gave the impression of great velocity fluctuations at different places in the cross-sectional area.

This report describes the construction technique for a simple and inexpensive cuff occluder for various size blood vessels. The occluder is made from polyvinyl chloride tubing and consist of two main parts, the balloon and catheter section, and the reinforcing back section. The occluders have functioned reliably in chronic dog preparations for up to 3 mo.

To measure blood flow in the intestinal mucosa we built a laser-Doppler flowmeter that consists of a helium-neon laser, an electronic circuit, and a pair of fiber-optic light guides that conduct laser light to the tissue and carry the backscattered light to a photodetector. Because light scattered by moving red blood cells experiences a shift in its frequency, we measured blood flow by detecting the mean Doppler frequency. In isolated loops of canine small bowel, we raised perfusion pressure and found the increases in laser mucosal blood flow were significantly correlated with total blood flow measured by an electromagnetic probe. During infusions of isoproterenol (a selective vasodilator of the mucosa), laser mucosal blood flow increased before total flow increased. Similarly, adenosine (a selective dilator of the muscularis) increased total flow, whereas local mucosal blood flow fell or was unchanged. In addition, reactive hyperemia was sometimes observed in the mucosa but not in the muscularis. These observations indicate that the laser-Doppler technique measures blood flow in the surface tissue and does not reflect blood flow throughout the other tissues of the bowel wall. Instrumental problems identified in this study were 1) the difficulty of calibrating the laser mucosal blood flowmeter in absolute units, 2) the uncertainty of the volume of tissue in which local mucosal blood flow is measured, and 3) the problem of maintaining contact between the optical probe and the tissue. Nevertheless, the method holds great promise because it can detect small ischemic areas, because it could be used in combination with endoscopy, and because it yields a continuous measurement of blood flow in either the muscularis or mucosa.

In order to study the neonatal microcirculation, the capillary hemodynamics in skin was investigated in 43 full-term infants 2-7 days after birth. The nailfold capillaries of the thumb were visualized by means of television microscopy and the capillary blood cell velocity (CBV) was videophotometrically quantified in 107 microvessels. The skin temperature, mean arterial blood pressure, and heel puncture hematocrit were measured simultaneously to evaluate any relation with the CBV. The mean CBV in all infants was 0.38 +/- 0.21 mm/s, with a range of 0.04 to 1.2 mm/s in individual capillaries. There was no correlation between CBV and skin temperature (27-33 degrees C), mean arterial blood pressure (44-68 mm Hg), or postnatal age. However, a significant correlation was found between the log CBV and the skin prick hematocrit (r = -0.64, p less than 0.001). It is concluded that the mean CBV during the 1st wk of life is not significantly different from the capillary velocity reported in adults. Normal variations in skin temperature and mean arterial blood pressure, as well as age differences 2-7 days after birth, do not significantly influence the neonatal skin capillary blood flow. However, the hematocrit is of major importance for skin capillary perfusion in the newborn infant.

Aortic blood flow was measured in 14 patients by means of an electromagnetic flow probe placed around the ascending aorta during cardiac surgery. High fidelity left ventricular pressure was monitored directly, 8 different indices of left ventricular function were derived from these measurements, and compared. Peak aortic blood flow correlated with the conventional indices of left ventricular function derived from left ventricular pressure, but better correlations were obtained for the maximum rate of change of power with respect to time. The clinical advantage of the derivation of this index is small and for clinical purposes peak aortic blood flow and the maximum rate of change of flow provide indices of myocardial performance which are directly available from the instrument.

The response of the pulmonary circulation to hypoxia is generally assessed in terms of cardiac output and pulmonary vascular resistance. However, due to pulsatility, the opposition to blood flow can be described accurately only by the input impedance to the pulmonary bed. For assessment of impedance, a system was developed consisting of implantable pressure transducers and an improved muitichannel continuous wave Doppler flow meter. A computer system was used to analyze the data, which was based on power output of the right heart, power dissipation in the pulmonary circulation, and impedance spectra. Data have been obtained from dogs exposed to various levels of acute hypoxia.

A transcutaneous ultrasonic Doppler technique for measurement of aortic blood-flow velocities has been developed and compared to more established techniques in order to evaluate its potential usefulness. It is possible by this method to quantitate blood velocity in both the ascending aorta and the aortic arch with ease and reliability. Ultrasonic access to the aorta from the suprasternal notch proved adequate in more than 90 per cent of the normal subjects examined. If further clinical trials prove as encouraging, this technique may be of significant value for patient monitoring and cardiac diagnosis.

Presently available Doppler technology has allowed us to substantially increase our understanding of the regulation of the coronary circulation in humans. New technologic developments in this area promise to further enhance our understanding of the operational characteristics of the coronary circulation in patients in normal and pathologic states.

We have investigated the influence of changes of perfusion pressure and local peripheral resistance on blood flow velocity waveform and profile in normal human peripheral arteries. Blood flow velocity and profile were recorded from the distal end of the left brachial artery in ten normal subjects by means of an ultrasonic device. The records were obtained in basal conditions and after blood pressure in the brachial artery and local peripheral vascular resistance were changed, separately or together, by progressive inflation of two arm cuffs, one encircling the proximal half of the left arm and the other the middle part of the left forearm. Both blood flow velocity waveform and profile were shown to be markedly modified by changes in perfusion pressure and local peripheral vascular resistance. Reduction of perfusion pressure decreased both forward and reverse peak velocities, but had the largest effect upon reverse velocity. The upslope and the downslope of the forward velocity wave were left unchanged. Increase in local peripheral vascular resistance markedly augmented reverse peak velocity, whether perfusion pressure was normal or reduced. Increased resistance only slightly influenced peak forward velocity.

A tool was designed and fabricated to simplify the procedure of placing a flow probe around the aortic root in acute animal experiments. The tool was made from a section of silicone rubber tubing which was flattened and tapered at one end. The flow probe was inserted into the open end of the tool, and the tapered end was drawn under the aorta, thus pulling the probe into position. Grooves were also ground into the probe body to ease the installation of the slot cover. During the 2 years that the tool and modified probes were used, they saved time and eliminated rupture of vessels as complications of aortic root flow probe placement.

Noninvasive dynamic measurements of common femoral artery blood flow (CFBF) and stroke volume (CFSV) during supine exercise (SE) and staged post-occlusive reactive hyperemia (PORH) in normal subjects using an echo-Doppler duplex scanner (DS) would provide baseline hemodynamic data in the study of the peripheral circulation in resting, stressed, and diseased conditions. Heart rate (HR), CFBF, and CFSV were determined at rest (R), after 5 minutes of SE on an ergometer (30 rpm) at 30, 60, 90-watt loads and after a 3-minute recovery. The same variables were also calculated after periods of 2-, 5-, and 10-minute thigh occlusions (greater than 240 mm Hg cuff pressure). Measurements of spatial average blood velocities and lumen diameters were used to calculate CFBF. Ankle pressure (AP) and brachial pressure (BP) were determined, and the ratio of systolic AP to systolic BP, the ankle index (AI), was calculated. As in vitro validation of the DS method was accomplished using a hydraulic model of CFBF (r = 0.98). Mean values for maximal CFBF following SE and PORH were 0.81 and 1.53 l/min, respectively. With SE, increases in CFBF and CFSV and decreases in AI were significantly (p less than .05) only at 60- and 90-watt loads. Increases in CFBF and CFSV and decreases in AP and AI were significantly different (p less than .05) from rest for the three occlusion durations and show a linear trend. This study suggests that the DS method can noninvasively and quantitatively measure CFBF and CFSV at rest following SE and during PORH.

A hard seat was equipped with devices sensing arteriolar pulsatile blood flow volume rate, externally developed pressure, and shear, all taken in lateral proximity to the ischial tuberosities of sitting subjects. Tests of 14 geriatric hospitalized patients and 9 healthy young men indicated the following: (1) No young healthy man demonstrated blood flow occlusion at pressure values less than 120mmHg. Of the geriatric hospitalized subjects, 2 occluded at less than 20mmHg. (2) Average shear values developed by the geriatric hospitalized group were 3 times that of the young healthy group. (3) Average pressure values demonstrated by the geriatric hospitalized subjects were roughly equal to those of the younger subjects (roughly 70mmHg). (4) Tipping the seat backwards through 20 degrees produced major benefits to the hospitalized geriatric group in terms of increased blood flow, lessened pressure, and lower shear. The young, healthy group experienced some increase in blood flow with no significant change in sitting reactions when tested in a tipped attitude.

Hemodynamics at the human carotid bifurcation is important to the understanding of atherosclerotic plaque initiation and progression as well as to the diagnosis of clinically important disease. Laser Doppler anemometry was performed in a large scale model of an average human carotid. Pulsatile waveforms and physiologic flow divisions were incorporated. Disturbance levels and shear stresses were computed from ensemble averages of the velocity waveform measurements. Flow in the common carotid was laminar and symmetric. Flow patterns in the sinus, however, were complex and varied considerably during the cycle. Strong helical patterns and outer wall flow separation waxed and waned during each systole. The changing flow patterns resulted in an oscillatory shear stress at the outer wall ranging from -13 to 9 dyn cm-2 during systole with a time-averaged mean of only -0.5 dyn cm-2. This contrasts markedly with an inner wall shear stress range of 17-50, (mean 26) dyn cm-2. The region of transient separation was confined to the carotid sinus outer wall with no reverse velocities detected in the distal internal carotid. Notable disturbance velocities were also time-dependent, occurring only during the deceleration phase of systole and the beginning of diastole. The present pulsatile flow studies have aided in identifying hemodynamic conditions which correlate with early intimal thickening and predict the physiologic level of flow disturbances in the bulb of undiseased internal carotid arteries.

The difficulty of optimally orienting an intravascular loop probe of an extracorporeal field electromagnetic flow meter is circumvented by uniting 2 mutually perpendicular loop sensors into a single flow-diameter probe. When one of the loops is unfavorably oriented in the magnetic field, the orientations of the other loop is more favorable. The most unfavorable case is a 45 degrees angle between the magnetic field and the planes of the loops, when the signal drops to 70.7% of the optimal value. By taking the square root of the sum of the squares of the 2 loop transducer signals, one obtains an output for flow and diameter measurements which is independent of the probe orientation. This operation can be accomplished electronically.

A description of a new Doppler ultrasound flow measuring instrument is given along with representative measurements of blood flow in the canine renal artery and the human aortic arch, renal artery, and transplanted kidney renal artery. The instrument is briefly described, and a discussion of the limitations of the technique is presented.

Two methods are described for the measurement of uterine blood flow in the pregnant rabbit. The first involves the use of a Parks ultrasonic Doppler probe placed over the exposed uterine artery. The second method uses a drop counter system connected between the uterine and jugular veins. The Doppler flowmeter was used to measure uterine arterial blood flow in twenty rabbits on Day 28 or 29 of pregnancy. No significant difference was observed between blood flow on these 2 days and the absolute blood flow to one horn (plus or minus S. E.) was found to be 16.8 plus or minus 1.4 ml/min, equivalent to 27.1 plus or minus 1.8 ml/100 g tissue/min. Using the drop recorder technique, the flow to one uterine horn in eleven rabbits on Day 27 or 28 of pregnancy was 12.5 plus or minus 1.9 ml/min, equivalent to 23.6 plus or minus 3.2 ml/100 g tissue/min. The pressure-flow relationship in the uterine vascular bed was studied using the Doppler flowmeter and graded mechanical occlusion of the arterial supply. Within the range of pressures studied, the flow was found to be linearly related to the arterio-venous pressure difference. This suggests that the uterine vascular bed was fully dilated under the conditions of study.