Velocity Monitoring Research Articles

A new method for fixation of probes for transcranial Doppler ultrasound.

Although monitoring of blood velocity in the cerebral arteries with transcranial Doppler ultrasound is standard practice, methods for fixation of the ultrasound probe to the skull continue to impose a technical challenge. This report describes a novel method of probe fixation in which an inexpensive polymer block is custom-made for each patient to hold the probe at a fixed angle. In addition to comfort and durability, its major advantage is that the polymer block prevents dislodgment of the probe from the intended angle by forces of gravity or by patient movement. Thirty-one temporal windows were monitored with this technique, with stable signals obtained in all subjects despite aggressive movements. Disadvantages include the inability to insonate more than one vessel and the cost for each block. However, the method is quick, is relatively inexpensive, and provides significant advantages of probe stability.

Mechanisms of coronary flow reserve impairment in human hypertension. An integrated approach by transthoracic and transesophageal echocardiography.

The purpose of this study was to investigate the different mechanisms responsible for an impairment of coronary vasodilator capacity in hypertensive subjects by an integrated echocardiographic approach, including transesophageal Doppler echocardiography, which allows noninvasive monitoring of coronary flow velocity in the left anterior descending artery during pharmacological vasodilation. The study population consisted of 17 healthy control subjects and 33 hypertensive subjects: 10 without hypertrophy, 16 with mild to moderate hypertrophy, and 7 with severe left ventricular hypertrophy. Mean systolic and diastolic flow velocities were monitored basally (together with indexes of myocardial oxygen demand, such as heart rate, myocardial inotropism, and left ventricular wall stress) and during infusion of low-dose (0.56 mg/kg per 4 minutes) and high-dose (0.84 mg/kg per 9 minutes) dipyridamole. Coronary reserve was assessed as the ratio of mean diastolic velocity after high-dose dipyridamole and basal diastolic velocity, and minimum coronary resistance as the ratio of diastolic blood pressure and diastolic velocity after high-dose dipyridamole. Compared with the control group, in all hypertensive groups, coronary reserve was similarly decreased (3.54 +/- 0.84 versus 2.59 +/- 0.42, 2.29 +/- 0.46, and 2.43 +/- 0.71; P < .01) and minimum resistance increased (0.56 +/- 0.15 versus 0.75 +/- 0.31, 0.75 +/- 0.19, and 0.78 +/- 0.21 mm Hg.s-1.cm-1; P = NS). These results confirm that coronary reserve in hypertensive individuals is reduced even before the occurrence of left ventricular hypertrophy. The reduction in coronary reserve depends on both an increase in resting coronary flow and an impairment in maximal vasodilator capacity. An increase in resting flow is dependent on higher heart rate and wall stress in hypertensive subjects without ventricular hypertrophy and on increased myocardial mass in hypertensive subjects with hypertrophy. Hypertensive subjects with ventricular hypertrophy also demonstrated a significantly blunted response to low-dose dipyridamole.

Long-term unrestrained measurement of stride length and walking velocity utilizing a piezoelectric gyroscope.

Long-term monitoring of stride length and walking velocity is considered to provide useful information for making decisions on treatment of patients with gait disabilities. The purpose of this study was to develop a device with the following design criteria: lightweight, easy attachment, little hindrance to the natural gait pattern, sufficient memory to record for one day, and practicality in clinical use. The prototype consists of a piezoelectric gyroscope, which detects angular velocity of the thigh of one leg in the sagittal plane, and a microprocessor-based maximum/minimum detector/data logger of a cyclic analog signal associated with the gait cycle. The accuracy of the device was evaluated in 20 normal subjects, seven above-the-knee (A/K) amputees, and ten hemiplegic patients, and relative accuracy within +/-15% was obtained, except for two special cases.

Integrated infrared sensor system for on line monitoring of thermally sprayed particles

The structure and properties of thermally sprayed coatings depend directly on the state of the particles before impact on the substrate or the already deposited coating layers. Monitoring particle parameters can thus provide a unique tool for optimising coating properties as well as controlling spraying processes during coating deposition. In this paper, a new optical sensing device for on line monitoring of temperature, velocity, diameter, and trajectory of in flight particles during coating production is described. Thermal radiation emitted by in flight particles is collected by a sensing head that can be attached to the gun providing continuous monitoring of the spray process. The collected radiation is transmitted through optical fibres to a detection cabinet located away from the dusty environment around the operating spray gun. Tests were carried out on two identical plasma torches with significant differences in deposition efficiency. Measured particle flowrates were in agreement with efficiency differences.

TRANSCRANIAL DOPPLER ULTRASONOGRAPHY IN THE NEUROCRITICAL CARE UNIT

TCD ultrasonography is a noninvasive means to study the cerebral vasculature. By varying the depth and angle of insonation of a pulsed sound wave, the direction and velocity profile of the cerebral arteries can be ascertained. This can be used to identify areas of focal stenosis and increased resistance and to estimate the adequacy of cerebral flow. TCD ultrasonography commonly is used in SAH to detect cerebral vasospasm. Many centers interpret rising velocities as increasing vessel narrowing and initiate medical strategies based on these values. TCD use in head trauma is less clearly defined. TCD ultrasonography is considered an acceptable confirmatory test for the determination of brain death. TCD ultrasonography is capable of studying dynamic cerebrovascular processes. By being able to determine vessel patency, TCD may become a useful adjuvant to thrombolytic therapy. Continuous monitoring of flow velocities and profiles along with testing to cerebrovascular reserve promises to be a future active area of research.

Coronary vein flow velocity changes during transluminal balloon angioplasty: a study using the Doppler guide wire.

The coronary flow velocity changes in the great cardiac and middle cardiac veins, induced by intracoronary administration of nitroglycerine, adenosine, and during percutaneous transluminal coronary angioplasty, were evaluated in 12 patients with significant coronary stenoses, using the Doppler wire (Flowire). Optimal spectral signals of the time-averaged peak flow velocity were obtained in 10 patients. Nitroglycerine produced no significant flow velocity changes (P = 0.13). Adenosine caused a significant augmentation of flow velocity compared to baseline (P = 0.003). During balloon inflation, venous flow velocity decreased (P = 0.007); however, the venous outflow did not cease. A pronounced venous hyperemic response, following balloon deflation, was also documented. The utility of continuous vein flow velocity monitoring with the Flowire, during high-risk and complicated coronary interventions remains to be elucidated.

The link between barium stars and optically bright post-AGB binaries

Systematic radial velocity monitoring programs revealed that all optically bright, high-latitude post-AGB stars that show a near-IR excess in their energy distribution are binaries (see the contribution of R. Waters et al. in these proceedings). A standard AGB evolution for the shorter period objects seems, however, impossible since the orbits are too small to accommodate an AGB star! Non-standard phenomena connected to the specific binary nature have to be invoked in order to understand these systems.

Coronary vein flow velocity changes during transluminal balloon angioplasty: A study using the doppler guide wire

The coronary flow velocity changes in the great cardiac and middle cardiac veins, induced by intracoronary administration of nitroglycerine, adenosine, and during percutaneous transluminal coronary angioplasty, were evaluated in 12 patients with significant coronary stenoses, using the Doppler wire (Flowire). Optimal spectral signals of the time-averaged peak flow velocity were obtained in 10 patients. Nitroglycerine produced no significant flow velocity changes (P = 0.13). Adenosine caused a significant augmentation of flow velocity compared to baseline (P = 0.003). During balloon inflation, venous flow velocity decreased (P - 0.007); however, the venous outflow did not cease. A pronounced venous hyperemic response, following balloon deflation, was also documented. The utility of continuous vein flow velocity monitoring with the Flowire, during high-risk and complicated coronary interventions remains to be elucidated. Cathet Cardiovasc Diagn 40:85–91, 1997. © 1997 Wiley-Liss, Inc.

超音波ドップラ血流速監視装置を用いた冠血管予備能測定

超音波ドップラ血流速監視装置を用いて冠血管血流速を測定することにより,冠動脈末梢の冠血管予備能を定量化し,冠血管危険因子を有さない群と,冠血管危険因子群である高血圧群,喫煙群,糖尿病群,高脂血症群の冠血管予備能を比較検討した。

Cerebrovascular Assessment of the High-Risk Patient

With increased attention to the causes and effects of neurologic injury related to cardiopulmonary bypass anesthesia and surgery, multiple modality examination and monitoring of cerebral function and perfusion in the perioperative period may prove to be advantageous. Transcranial Doppler examination and monitoring is inexpensive, noninvasive, safe, provides unique information about the functional status of the intracranial circulation, and complements the duplex Doppler study of the extracranial carotid vessels of the neck for preoperative evaluation of the surgical patient. The transcranial Doppler examination permits quantitation of blood flow velocity of the intracranial vessels, evaluation of autoregulatory capacity and vasomotor reserve, determination of symmetry of flow velocity in the circle of Willis, assessment of collateral circulatory capacity, examination of vessels not accessible to the duplex Doppler and serves as a baseline for intraoperative monitoring and the postoperative examination. Noninvasive, unilateral or bilateral, continuous monitoring of brain blood flow velocity intraoperatively or postoperatively with trending, storage, and correlation with other physiologic variables provides evidence of cerebral perfusion, occurrence and rate of cerebral embolism, and continuous monitoring of therapeutic interventions. A review of the incidence of stroke and neuropsychologic deficit after bypass surgery is focused on parameters amenable to diagnosis using transcranial Doppler. Patient-specific risk factors for neurologic injury derived from previous studies are discussed as well as risk factors that are related to anesthetic and surgical management and equipment. A description of Doppler technology and the correlation of transcranial Doppler findings with angiography and radionucleotide scans establishes the accuracy of the Doppler examination. The preoperative examination, provocative tests of vasomotor reserve, the evaluation of cerebral collateral circulation, and examples of Doppler applications are discussed.

Increase of posterior cerebral artery blood flow velocity during threshold repetitive magnetic stimulation of the human visual cortex: hints for neuronal activation without cortical phosphenes

To analyze the effects of low intensity repetitive transcranial magnetic stimulation over the occipital cortex on regional cerebral perfusion, bilateral simultaneous monitoring of posterior cerebral artery blood flow velocity was performed using transcranial Doopler ultrasonography in 14 healthy subjects. During 20 s of unilateral magnetic stimulation with 3 Hz and 6 Hz a significant increase of ipsilateral flow velocity was observed during both stimulus conditions (3 Hz, 10.2 ± 3.7%; 6 Hz, 12.8 ± 4.7%). A significantly smaller flow velocity increase occurred also in the contralateral posterior cerebral artery (3 Hz, 8.6 ± 4.0%; 6 Hz, 10.6 ± 4.1%). Flow velocity increases were similar to values reported in the literature for physiological activation paradigms so that excessive excitation of the visual cortex does not seem to occur during repetitive magnetic stimulation. The largest increase of flow velocity was observed in the ipsilateral posterior cerebral artery of 5 subjects who experienced phosphenes in the contralateral visual half-field during stimulation (14.3 ± 4.1%; mean of 3 and 6 Hz stimulation). In the other 9 subjects significant velocity increases indicated cortex activation in the absence of cortical phosphenes. The occurrence of maximum velocity responses within 2–3 heart beats following the first cortex stimulus points to a fast adjustment of cerebral perfusion in response to transcranial brain stimulation.

Are adult transcranial Doppler systems suitable for application in neonates?

Transcranial Doppler systems have not been available for monitoring of cerebral blood flow velocities in neonates because of potential hazardous effects of energy output from standard instruments developed for adult application. Aim of the study was to test commercially available transcranial Doppler instruments for their applicability in neonates and to develop guidelines for adaptation for safe neonatal use. Energy output of five commercially available transcranial Doppler instruments was measured with a hydrophone system and a radiation force balance. At the highest setting and at the nominal 10% attenuation level, five out of five and two out of five instruments, respectively, had an energy output above the recommended limits. Power reduction was not linear in one instrument. Evaluation of safety devices (alarm, freeze mode, energy reduction facilities, display of energy values) showed that none of the tested instruments had an optimal setting for safe neonatal application. Commercially available transcranial Doppler instruments should be evaluated critically for their energy output prior to their application in neonates. Special software for neonatal application of transcranial Doppler systems should be developed in order to provide extremely low energy output levels and devices for indication of duration of Doppler insonation and energy output.

Liquid phase sintering and microstructure development of Ag-clad Tl-1223 superconductor

The phase evolution and electrical properties of Tl-1223 tapes were explored near the incongruent melt temperature. Liquid phase evolution was monitored as a function of time and temperature by an acoustic velocity monitor. The phase development kinetics for Tl-based superconductors are more than one order of magnitude faster than the kinetics of Bi-based superconductors. Three separate powder mixtures (, and ) were used in powder-in-tube processing. Oxygen partial pressure had a significant effect on melt behaviour and microstructure development.

Safety and feasibility of continuous monitoring of coronary flow velocity in acute myocardial infarction by Doppler guide wire

We investigated the safety and limitations of the Doppler guide wire for continuous monitoring of coronary flow velocity outside the catheterization laboratory in 17 patients with acute myocardial infarction. After direct angioplasty, patients were taken to the coronary care unit with the Doppler guide wire positioned within the artery. Flow velocity was continuously monitored. Heparin was titrated to an active clotting time >200 seconds. Clinical outcome and angiographic analyses were evaluated. Flow velocity monitoring was conducted with an 88.2% success rate and lasted for 16 ± 5 hours. Monitoring failed in 2 of the 4 right coronary artery cases. Small amounts of thrombus were seen to adhere to the Doppler guide wire at the end of monitoring. No complications were related to the procedure. No deterioration of angiographic findings was observed. This preliminary study confirmed the safety of the Doppler guide wire for continuous monitoring of coronary flow in patients with acute myocardial infarction.

Middle Cerebral Artery Velocity Correlates with Nitroglycerin‐induced Headache Onset

Headache often accompanies treatment with nitroglycerin, but the cerebral hemodynamic effects and the exact mechanism of the headache are incompletely understood. Transcranial Doppler monitoring allows evaluation and monitoring of changes in blood flow velocity in the large intracranial arteries. The objective of this study was to assess middle cerebral artery (MCA) blood flow velocities with transcranial Doppler monitoring in subjects receiving continuous low-dose nitroglycerin intravenously or by patch, and correlate these with clinical headache. Twenty-eight normal adult men received nitroglycerin (0.12 micrograms/kg/min intravenously [n = 14] or 0.6 mg/min by transdermal patch [n = 14]), for up to 120 minutes, with monitoring of clinical headache status (standard 4-point scale), blood pressure, heart rate, end-expiratory PCO2 (CO2), and right MCA velocity. All subjects developed headache (mean time to onset, 34 min), reaching moderate or severe levels in 20. There were no differences in age, weight, mean blood pressure, mean heart rate, or resting end-tidal CO2 between those whose headache reached a moderate to severe level and those whose headache remained mild. MCA velocity decreased from baseline values at all levels of clinical headache (onset, -17%; moderate, -18%; severe, -16%; nitroglycerin stopped, -19%) (p, 0.0001 by t test for each stage of headache). MCA velocity remained decreased at the time of headache resolution (-14%; p < 0.001). Blood pressure, heart rate, and CO2 did not change significantly. There were no differences related to route of nitroglycerin dosing. These data show that continuous low doses of nitroglycerin by patch or intravenously produce headache in normal male subjects. MCA velocities were significantly decreased at headache onset and at all levels of headache severity. Changes in MCA velocity persisted beyond the clinical headache. These results suggest a direct MCA vasodilatory effect of nitroglycerin. This method may also be used to evaluate the intracranial hemodynamic effects of other vasoactive drugs, even in clinical settings.

The European Southern Observatory planetary search program: Preliminary results

We report on the progress of a program to search for extra‐solar planets using high precision radial velocity (RV) measurements taken at the European Southern Observatory. Instrumental errors in the radial velocity measure are minimized by placing a temperature stabilized molecular iodine absorption cell in front of the entrance slit to the spectrograph. This imposes an iodine absorption spectrum on top of the stellar spectrum. All stellar radial velocity shifts are measured with respect to the iodine absorption spectrum. The current program consists of a sample of 26 F, G, and K dwarfs and 1 dMe star. Radial velocity measurements taken since November 1992 indicate that a typical long‐term radial velocity precision for this program is about 18 m s−1. One of our program stars, τ Cet, shows constant radial velocity variability with a scatter of 6 m s−1. Representative radial velocity measurements are given for three stars showing no significant radial velocity variations, three stars showing variations indicative of low mass companions, and for the triple system α Cen. The radial velocity measurements of α Cen A and B are consistent with the astrometric orbital solution, although the data points have a slightly steeper slope than the calculated orbit. Continued radial velocity monitoring of this star should eventually result in a better orbital solution.

TRIUMF injection line nonintercepting beam energy monitoring through phase measurement

A nonintercepting beam velocity monitoring system has been installed in the 300 keV injection line of the TRIUMF cyclotron to reproduce the injection energy for different ion source beams and monitor any beam energy fluctuations. The monitor is tuned to resonate at 46 MHz and is 3.25 m downstream from the first 23 MHz buncher. The phase difference between the first buncher and the pickup is related to the average beam velocity, i.e., beam energy. The energy sensitivity of the measurement is 1×10−4. The dynamic range of the monitor with beam current is 60 dB, and the measured instantaneous beam intensity can go down to 100 nA. The theory behind the device and the results of beam tests will be described.

Cerebrovascular assessment of the high-risk patient: The role of transcranial doppler ultrasound

With increased attention to the causes and effects of neurologic injury related to cardiopulmonary bypass anesthesia and surgery, multiple modality examination and monitoring of cerebral function and perfusion in the perioperative period may prove to be advantageous. Transcranial Doppler examination and monitoring is inexpensive, noninvasive, safe, provides unique information about the functional status of the intracranial circulation, and complements the duplex Doppler study of the extracranial carotid vessels of the neck for preoperative evaluation of the surgical patient. The transcranial Doppler examination permits quantitation of blood flow velocity of the intracranial vessels, evaluation of autoregulatory capacity and vasomotor reserve, determination of symmetry of flow velocity in the circle of Willis, assessment of collateral circulatory capacity, examination of vessels not accessible to the duplex Doppler and serves as a baseline for intraoperative monitoring and the postoperative examination. Noninvasive, unilateral or bilateral, continuous monitoring of brain blood flow velocity intraoperatively or postoperatively with trending, storage, and correlation with other physiologic variables provides evidence of cerebral perfusion, occurrence and rate of cerebral embolism, and continuous monitoring of therapeutic interventions. A review of the incidence of stroke and neuropsychologic deficit after bypass surgery is focused on parameters amenable to diagnosis using transcranial Doppler. Patient-specific risk factors for neurologic injury derived from previous studies are discussed as well as risk factors that are related to anesthetic and surgical management and equipment. A description of Doppler technology and the correlation of transcranial Doppler findings with angiography and radionucleotide scans establishes the accuracy of the Doppler examination. The preoperative examination, provocative tests of vasomotor reserve, the evaluation of cerebral collateral circulation, and examples of Doppler applications are discussed.

Evidence for acute renal cortical vasoconstriction after uninephrectomy.

The rate of progression of chronic renal failure (CRF) is similar for many diseases, suggesting a common, perhaps intrinsic, renal signal for its progression. The remnant nephron hypothesis of Bricker suggests that CRF may be the result of persistent compensatory renal growth (CRG). Normally, CRG after unilateral nephrectomy (uniNx) ceases within 1 week. Knowledge of the signals that initiate CRG may therefore shed light on the signals responsible for ongoing CRF. The signals responsible for the initiation of compensatory renal growth after uniNx are unknown. Hemodynamic changes in the remaining renal artery have been observed, but there are as yet no data for the main renal compartment which undergoes hypertrophy, the superficial renal cortex. The noninvasive technique of laser-Doppler flowmetry allows the continuous and independent monitoring of blood velocity and blood volume. The product of the two signals is proportional to tissue blood flow per unit volume of the tissue observed. Under controlled conditions in adult male Sprague-Dawley rats, renal cortical blood velocity increased by 22% within 5 min after uniNx and remained elevated at this level for 60 min. Renal cortical blood volume decreased throughout the experiment. Their product, renal cortical blood flow, increased briefly by 14% 5 min after uniNx but decreased over the time of observation in parallel with renal cortical blood volume. The simultaneous increase in blood velocity and decrease in blood volume in the superficial renal cortex acutely after uniNx suggest that vasoconstriction is an early event in compensatory renal growth.

Incidence and effects of increased cerebral blood flow velocity after severe head injury: a transcranial Doppler ultrasound study II. Effect of vasospasm and hyperemia on outcome

Cerebral blood flow velocities were measured in 50 severely head injured (Glasgow Coma Scale (GCS) 8 or less) patients using transcranial Doppler ultrasonography (TCD). Abnormally high TCD velocities were recorded in 35 patients; in 20 this was deemed to be due to vasospasm and in the other 15 to hyperemia. Patients who developed hyperemia also had the highest intracranial pressure (ICP) and the lowest cerebral perfusion pressure (CPP) of the three groups. Outcome was assessed at six months after injury using the Glasgow outcome scale and the disability rating scale. In the normal velocity group 87% of patients had a good outcome, compared with 47% of those with hyperemia and 40% of those with vasospasm. The highest velocity (HVEL), GCS, age, ICP and CPP were entered into a logistic regression analysis. HVEL, age and CPP were found to be the most significant predictors of outcome ( χ 2 = 29.5; p < 0.0001). These factors predicted outcome with 82% accuracy, 86% sensitivity and 76% specificity. Routine monitoring of TCD velocity may be useful in detecting hyperemia and vasospasm after severe head injury, allowing appropriate treatment to be started as early as possible.