Doppler Ultrasound Transducer Research Articles

Increased safety in periodontal surgery: Doppler ultrasound for detection of relevant palatal blood vessels-A proof-of-concept and cross-sectional study.

To evaluate the suitability of a Doppler ultrasound probe in detecting the greater palatine artery or its greater branches non-invasively. The palatal mucosa of 108 participants (median age 34 years, 51 female) was systematically divided into transversal sectors, each aligning with the positions of the upper molars (M), premolars (P) and canine teeth (C), aiming to facilitate precise and consistent localization of the detected palatal blood vessel across different patients. Blood flow of the palatal blood vessels, presumably, was located by scanning the palatal vault bilaterally using an 8-MHz ultrasound probe linked to a transducer. The distance to the corresponding tooth was measured using a millimetre-scale periodontal probe. Within the regions of M2 to P1, the ultrasound transducer gave a delimitable acoustic pulse signal in 80%-98% of all measurements. The measured median distances between the determined position of the artery and the corresponding teeth ranged from 13 to 15 mm, with smaller distances in the anterior region. In several sectors, the distance was significantly higher for men (C: p = .048; P1: p = .041, M1: p < .01; M2: p = .034). Use of the Doppler ultrasound transducer might be a promising approach to non-invasively detect relevant palatine blood vessels preoperatively. It, therefore, might have the potential to reduce the risk of accidental injury during palatal surgery.

Drug-Drug Interaction Between Amlodipine And Clarithromycin In Hypertension Rabbits

This study is the first to examine the possibility of pharmacokinetic interaction in blood circulation using amlodipine and clarithromycin as representatives in hypertension rabbits and identify changes. The current study design required rabbits (n=6) for Pharmacokinetics. In group A, rabbits without treatment were used as control. In group B, were administration of a single dose of amlodipine (0.21mg/kg.BW) for 24 hours. Group C, were administered with a single dose of amlodipine (0.21mg/kg/BW.) and clarithromycin (22 mg/kg/BW.) each 6 hr. for 24 hour. The blood samples were collected from (B and C) groups at time intervals of zero, 1, 2, 3, 4, 6, 8, 12, 24, 36, 48, 60, 72, 96, 120, 144 hours and the drug concentrations were estimated using a spectrophotometer and estimated blood pressure using blood pressure cuff with Doppler ultrasound transducer. An increase in C max and AUC in group C (3.52 μg/ml and 130 μg/ml*h) respectively, indicates the improved bioavailability of amlodipine in the presence of clarithromycin compared with group B (2.03 μg/ml and 96.10 μg/ml*h) respectively. Furthermore, reduction in (CL) with an elevation of (Vd) in the presence of clarithromycin (54.94 L/kg/hr. and 4994 L/kg) in group C respectively, compared with group B (74.31 L/kg/hr and 3715 L/kg) respectively. We studied the influence of clarithromycin on the pharmacodynamics of amlodipine in hypertension rabbits. Interaction of amlodipine with multiple doses of clarithromycin produced a high reduction in blood pressure at 9 after administration and the blood pressure continues redaction. In conclusion, the combination of amlodipine with clarithromycin led to the enhancement of the bioavailability of amlodipine by inhibiting the CYP3A4 enzyme leading to producing a hypotension effect with peak plasma concentration effect in hypertension rabbits.

Fetal heartrate tracking system based on intensity of Doppler signal

Doppler-detected fetal heart rate (FHR) tracking is the primary testing method for assessing fetal well-being during antepartum care. However, owing to fetal movements or maternal position variations, the transducer on the abdomen can be displaced, changing the fetal heart location (FHL) and resulting in frequent signal losses and uninterpretable results. In this study, we present FHR monitoring system for continuously maintaining FHR measurements without specifying the location of the Doppler ultrasound transducer. An algorithm is developed to track the FHL based on the intensity of the received Doppler signal. The performance is evaluated by conducting underwater experiments using an object with repeated movements. The tracking error is 7.93° on the X-axis and 1.42° on the Y-axis. Even with those tracking errors, the FHR is continuously recorded. This system can be used to obtain heart rate records without manipulating the position of the transducer and losing the signal.

Characterization and comparison of a 2-, 4- and 8-MHz central venous catheter ultrasound probe for venous air emboli detection.

This paper presents a concept for detection of venous air emboli inside the superior vena cava using a central venous catheter with integrated Doppler ultrasound transducer installed on the tip. Several Doppler probes each with a single insonation frequencies of 2 MHz, 4 MHz or 8 MHz are characterized and compared for usefulness in this scenario. During in vitro experiments using an artificial blood circulatory with blood mimicking fluid bubbles with defined volumes were injected and recorded as gaseous embolic events. The in vitro results of measured embolus-blood-ratio values (EBR) in respect to the air bubbles volumes and its echogenicity showed a good correlation with the simulation model of spherical cross section scattering of such air bubbles. It is shown that the probe design still needs some improvements using a 4 MHz insonation frequency to get a useable detection sensitivity in such scenario within vena cava superior. The results suggest that it is possible to estimate the air bubble volume corresponding to the EBR using such a catheter probe.

Doppler Ultrasound Technology for Fetal Heart Rate Monitoring: A Review.

Fetal well-being is commonly assessed by monitoring the fetal heart rate (fHR). In clinical practice, the de facto standard technology for fHR monitoring is based on the Doppler ultrasound (US). Continuous monitoring of the fHR before and during labor is performed using a US transducer fixed on the maternal abdomen. The continuous fHR monitoring, together with simultaneous monitoring of the uterine activity, is referred to as cardiotocography (CTG). In contrast, for intermittent measurements of the fHR, a handheld Doppler US transducer is typically used. In this article, the technology of Doppler US for continuous fHR monitoring and intermittent fHR measurements is described, with emphasis on fHR monitoring for CTG. Special attention is dedicated to the measurement environment, which includes the clinical setting in which fHR monitoring is commonly performed. In addition, to understand the signal content of acquired Doppler US signals, the anatomy and physiology of the fetal heart and the surrounding maternal abdomen are described. The challenges encountered in these measurements have led to different technological strategies, which are presented and critically discussed, with a focus on the US transducer geometry, Doppler signal processing, and fHR extraction methods.

Combined Computational and Experimental Approach to Improve the Assessment of Mitral Regurgitation by Echocardiography

Mitral regurgitation (MR) is one of the most frequent valvular heart diseases. To assess MR severity, color Doppler imaging (CDI) is the clinical standard. However, inadequate reliability, poor reproducibility and heavy user-dependence are known limitations. A novel approach combining computational and experimental methods is currently under development aiming to improve the quantification. A flow chamber for a circulatory flow loop was developed. Three different orifices were used to mimic variations of MR. The flow field was recorded simultaneously by a 2D Doppler ultrasound transducer and Particle Image Velocimetry (PIV). Computational Fluid Dynamics (CFD) simulations were conducted using the same geometry and boundary conditions. The resulting computed velocity field was used to simulate synthetic Doppler signals. Comparison between PIV and CFD shows a high level of agreement. The simulated CDI exhibits the same characteristics as the recorded color Doppler images. The feasibility of the proposed combination of experimental and computational methods for the investigation of MR is shown and the numerical methods are successfully validated against the experiments. Furthermore, it is discussed how the approach can be used in the long run as a platform to improve the assessment of MR quantification.

High-frequency Doppler Ultrasound Transducer for the Peripheral Circulatory System

A Doppler ultrasound transducer was designed and implemented to measure the blood flow velocity in tiny vessels near the skin of hands or feet. The geometric parameters of the transducer for defining the observation volume were derived and implemented with an acoustic window made of polystyrene. The observation volume designed in this study was located 6.5 mm from the transducer, which was comparable to the value predicted geometrically. The two-way insertion loss of the transducer was 11.3 dB on ultrasound frequency of 20 MHz, and the 3-dB bandwidth was approximately 2 MHz. In addition, the Doppler shift in the frequency measured by using a Doppler device composed of the transducer and a Doppler signal processing unit was proportional to the flow velocity generated by a homemade flowing system. Finally, we concluded that the transducer could be applied to measure the blood flow velocity in hands or feet.

Predictability of Cerebral Embolization from Aortic Arch Manipulations During Thoracic Endovascular Repair

There is no sensitive tool to monitor embolic events and predict patients at a risk for strokes during thoracic endovascular aortic repair. We examined the relationship between the number of high intensity transient signals (HITS) by transcranial doppler ultrasound and the extent of atherosclerotic plaques in aortic arch. Thirteen patients were treated as a part of a single center United States Food and Drug Administration-approved investigational device exemption for various thoracic aortic pathologies. Bilateral transcranial doppler ultrasound transducers recorded the number of HITS. CT angiography and intravascular ultrasound were used to measure the thickness of mural thrombi and determine their arch location. All 13 patients had detectable HITS, and one patient sustained a stroke. Eleven patients had quantifiable mural thrombi. The highest HITS were observed in patients with thrombi in zones 2 to 3. All three patients with bovine arch had more HITS in the right middle cerebral artery whereas the patients with normal arch anatomy had more HITS in the left middle cerebral artery. The presence of mural thrombi in zones 2 and 3, irrespective of their thickness, was associated with increased HITS during thoracic endovascular aortic repair. This is the first study to characterize the significance of mural thrombi in aortic arch and their relationship to embolic events during aortic arch manipulations.

Clinical Feasibility Study: Measurement of Maternal Heart Rate by an Infrared Sensor integrated in the Tocography Transducer during Cardiotocography

INTRODUCTION: In obstetrics, monitoring of the fetus using CTG is now part of the accepted standard. Most commonly, the fetal heart rate is detected with a Doppler ultrasound transducer (ultrasonic cardiography). In some cases, however, a maternal signal is recorded instead of the child's heart rate. If the maternal heart rate is within a normal range for the fetus (around 130 bpm), the worst case scenario is that the incorrect measurement is not picked up and the recorded heart rate is not interpreted correctly. An asphyctic newborn or a stillbirth are the worst consequences of this avoidable error. However, if the maternal heart rate is also recorded (e.g. using pulsoxymetry or by recording a maternal ECG), concurrence of the two heart rates can be identified and the monitoring staff will be alerted (coincidence detection). In most cases, however, continuous monitoring of the maternal heart rate is omitted in the interests of the patient's comfort. MATERIALS AND METHODOLOGY: A new method of detecting coincidence was examined in this study. The maternal heart rate was measured with a modified tocography transducer (“abdominal pulse sensor”). The advantage of this approach is the incorporation of the measurement of the maternal heart rate into the tocography transducer that is already used during CTG. This means that coincidence analysis will always function without the need for additional cables or sensors. Philips GmbH has developed an “abdominal pulse sensor” for this, which measures the maternal heart rate using two infrared diodes installed in the base of the transducer. The heart rate is determined by photoplethysmography. This method is ideal for measuring the maternal heart rate, as, firstly, penetration of infrared light is not harmful to the fetus and, secondly, the sensor can be integrated into the existing setup used for CTG measurements. RESULTS: In a clinical feasibility study, the “abdominal pulse sensor” was tested on pregnant women 26 weeks or more into their pregnancy. It was demonstrated that the “abdominal pulse sensor” records the maternal heart rate with an acceptable degree of reliability. To this end, the quantity (proportion of actual “abdominal pulse sensor” readings compared to reference ECG readings) and the quality (proportion of “abdominal pulse sensor” readings with an absolute deviation from the ECG < 5 bpm) were determined as target variables. In the second series of measurements with the enhanced “abdominal pulse sensor”, an average reading quality of 96.7 % was achieved. The quantity was 84.2 %. CONCLUSION: On the basis of the data recorded to date, the new CTG system with built-in measurement of the maternal heart rate using the “abdominal pulse sensor” is reliably able to determine the maternal heart rate with a high degree of quality. If the quantity is sufficient, it offers additional safety when monitoring fetuses in utero with the same degree of comfort for the patient. This additional measurement could increase the safety of the unborn child.

Finding on a chest radiograph: A dangerous complication of subclavian vein cannulation

Cannulation of the subclavian vein has its inherent risks. Post procedure chest radiograph is one of the investigations done to rule out immediate complications. Unless the clinician is aware as to what to look for in the radiograph, some of the dangerous complications can be overlooked. Accidental subclavian artery cannulation is identifi ed immediately by color and jet of the blood. Also the position of the catheter tip has to be confi rmed by obtaining the arterial pressure tracing using a pressure transducer. Non availability of Doppler ultrasound and pressure transducer are limiting factors for immediate confi rmation of proper catheter placement. Also, in patients with severe hypotension and reduced oxygen content of blood, accidental arterial puncture may not show the characteristic bright red pulsatile back fl ow of arterial blood. In these situations radiography can be used as a diagnostic tool to rule out subclavian artery cannulation.

Acoustic properties of butadiene and silicone elastomers at megahertz frequencies

A tissue mimic material with a sound velocity of 1540 m s–1 and an acoustic attenuation of 0·5 dB MHz–1 cm–1 is required for calibrating medical Doppler ultrasound transducers. These properties can be obtained with a solid material comprised of a gel containing a high water content. If solid elastomers are to be used to provide a more stable tissue mimic, modelling suggests that the materials would require low viscoelastic damping, with a low glass transition temperature, Tg. Castable polyurethanes have been made using a polybutadiene soft segment and by adding process oil, the acoustic loss has been reduced to 0·9 dB MHz–1 cm–1 with a sound velocity of 1459 m s–1. Unfilled butadiene rubber (with a high-cis microstructure) had an acoustic loss around 1 dB MHz–1 cm–1, the low loss being associated with its low Tg, with a sound velocity of 1567 m s–1. Silicone elastomers made from unfilled poly dimethyl siloxane had an acoustic loss of 0·71 dB MHz–1 cm–1, but the sound velocity was too low at 1033 m s–1. Filler particles were added to raise the sound velocity, but they seemed to act as scattering centres and the composite had high acoustic attenuation. None of the elastomers were able to reproduce the acoustic attenuation characteristics of the tissue mimic gel.

Apparatus for measuring hemodynamic parameters

The present invention is directed toward an ultrasonography apparatus for measuring and/or monitoring hemodynamic activity, such as blood flow. The present invention comprises a doppler ultrasound unit, one or more transducers, and a portable body.

Coronary Artery Assessment by Epicardial Pulsed Doppler Ultrasound

An intraoperative method was developed for direct investigation of the coronary arteries using an epicardial high-frequency two-dimensional Doppler ultrasound transducer. This fingertip 7.5-MHz transducer was used in 30 patients undergoing coronary artery bypass surgery to measure blood flow in the coronary arteries and bypass grafts. In all the patients, clear images of the coronary arteries and the bypass grafts were obtained in the beating heart, and coronary blood flow could be measured to evaluate the degree of stenosis. There were no significant differences between the measurements obtained with the Doppler transducer and a transit-time ultrasonic flowmeter of blood flow in the left internal thoracic artery graft to the left anterior descending coronary artery, indicating that the Doppler method produces accurate and reproducible measurements. This method can provide useful intraoperative information about the coronary artery system in emergency operations such as acute aortic dissection.

Sources of error in maximum velocity estimation using linear phased-array Doppler systems with steady flow

Using linear-array Doppler ultrasound (US) transducers, the measured maximum velocity may be in error and lead to incorrect clinical diagnosis. This study investigates the existence and cause of maximum velocity estimation errors for steady flow of a blood-mimicking fluid in a tissue-mimicking phantom. A specially designed system was used that enabled fine control of flow rate, transducer positioning and transducer angle relative to the flow phantom. Doppler machine settings (transducer aperture size, focal depth, beam-steering, gain) were varied to investigate a wide range of clinical applications. To estimate the maximum velocity, a new signal-to-noise ratio (SNR) independent method was developed to calculate the maximum frequency from an ensemble averaged Doppler power spectrum. This enabled the impact of each factor on the total Doppler error to be determined. When using the new maximum frequency estimator, it was found that the effect of transducer focal depth, intratransducer, intramachine, intermachine (that was tested) and beam-steering did not significantly contribute to maximum velocity estimation errors. Instead, it was the dependence of the maximum velocity on the Doppler angle that made, by far, the greatest contribution to the estimation error. Because our maximum frequency estimator took into account the effect of intrinsic spectral broadening, the degree of overestimation error was not as great as that previously published. Thus, the effects of Doppler angle and intrinsic spectral broadening are the chief sources of Doppler US error and should be the focus of future efforts to improve the accuracy. (E-mail:cobbold@ecf.utoronto.ca)

Cyclic Flow variations after coronary angioplasty in humans: Clinical and angiographic characteristics and elimination with 7E3 monoclonal antiplatelet antibody

Objectives. We tested the hypothesis that cyclic alterations in coronary artery blood flow that occurred after coronary angioplasty could he attenuated or abolished by a monoclonal antibody to the platelet surface membrane GP IIb/IIIa receptor.Background. Coronary artery cyclic flow variations may occur after coronary angioplasty in experimental animal models and humans. In animal models of coronary thrombosis, cyclic alterations in flow often have preceded thrombotic occlusion or reocclusion. Several agents that inhibit platelet function have been shown to attenuate or eliminate cyclic flow variations in these models.Methods. We monitored coronary artery flow in 27 patients for 30 min after coronary angioplasty, using 0.018-in. (0.046 cm) coronary guide wires with pulsed wave Doppler ultrasound transducers on the distal tips. Clinical data were collected and quantitative analyses performed on coronary arteriograms made before and after the angioplasty procedures. We compared findings in patients with and without cyclic flow variations detected.Results. There were 20 men and 7 women. Mean age was 58 years, and 63% had unstable angina. They received standard doses of nitrates, aspirin, heparin, calcium channel antagonists and other medications clinically indicated. Nevertheless, we detected cyclic flow variations in five patients (19%). Four of these patients had stable flow restored with intravenous injection of 0.25 mg/kg normal body weight of monoclonal antibody c7E3 Fab to the platelet GP Ilb/IIIa receptor. In one patient, stable flow was restored by repeat dilation when an immediate angtogram revealed renarrowing. Patients developing cyclic alterations in flow had longer lesions (18.7 ± 7.5 mm vs. 13.1 ± 5.7 mm, p < 0.05) that had responded less well to angioplasty (stenosis postangioplasty 47 ± 13% vs. 33 ± 15%, p < 0.05).Conclusions. Cyclic alterations in coronary artery blood flow may occur in some patients after coronary angioplasty, despite the use of standard antiplotelet, antithrombotic and antivasospastic medications. We found that they could be eliminated by this monoclonal antibody that blocks the final common event of platelet aggregation.

Cardiac motion can alter proximal isovelocity surface area calculations of regurgitant flow

Objectives. This study addressed the hypothesis that motion of the surface containing a regurgitant orifice relative to the Doppler ultrasound transducer can cause differences between actual flow rate and calculations based on the proximal flow convergenceBackground. In vitro studies quantising regurgitant flow rate by proximal flow convergence have been limited to stationary orifices, Clinically, however, valve leaflets generally move relative to the ultrasound transducer during the cardiac cycle and can move at velocities important relative to the measured color aliasing velocities. The transducer therefore senses the vector sum of actual flow velocity toward the orifice and orifice velocity relative to the transducer. This can cause potential overestimation or underestimation of true flow rate, depending on the direction of surface motion.Methods. The hypothesis was explored computationally and tested by pumping fluid at a constant flow rate through an orifice in a plate moving at 0 to 8 cm/s (velocities comparable to those described clinically for mitral and tricuspid annulus motion toward an apical transducer).Results. Surface motion in the same direction as flow caused over-estimation of the aliasing radius and calculated flow rate. Surface motion opposite to the direction of flow (typical for mitral and tricuspid regurgitation viewed from the apex or esophagus) caused underestimation of actual flow rate. The underestimation was greater for lower aliasing velocities (36 ± 11% for 10 cm/s vs. 23 ± 6% for 20 cm/s). Correcting for surface motion provided excellent agreement with actual values (y = 0.97x + 0.10, r = 0.99, SEE = 0.17 liters/min).Conclusions. Physiologic motion of the surface containing a regurgitant orifice can cause substantial differences between actual flow rate and that calculated by the proximal flow convergence technique. Low aliasing velocities used to optimize that technique can magnify this effect. Such errors can be minimized by using higher aliasing velocities (compatible with the need to measure the aliasing radius) or eliminated by correcting for surface velocity determined by an M-mode ultrasound scan.

Assessment of coronary conductance and resistance vessel reactivity in response to nitroglycerin, ergonovine and adenosine: In vivo studies with simultaneous intravascular two-dimensional and Doppler ultrasound

Objectives. The aim of this study was to determine the differential effects of nitroglycerin, ergonovine and adenosine on the resistantce vessels in vivo by using a Doppler-tipped guide wire in combination with an ultrasound imaging catheter.Background. Catheter-based two-dimensional intravascular ultrasound yields images of the coronary arteries from which cross-sectional areas can be measured. Intravascular Doppler ultrasound techniques allow measurement of coronary blood flow velocity. The simultaneous use of the two techniques can yield anatomic and physiologic information on conductance and resistance vessels but has not been tried in the coronary arteries.Methods. In 15 dogs, we studied coronary Bow and vascular reactivity in response to pharmacologic agents using two approaches: 1) a 30-MHz, 4.3F imaging catheter placed alongside a 0.018-in. (0.046 cm) Doppler wire in the circumflex or left anterior descending coronary artery (n = 5); 2) the ultrasound imaging catheter introduced directly over a 0.014-in. (0.036 cm) Doppler wire (n = 10). Vasodilator and vasoconstrictor responses were studied by using intracoronary nitroglycerin (50,100 and 200 μg), ergonovine (200 μg) and adenosine (6 mg).Results. Nitroglycerin caused a dose-dependent increase in epicardial coronary artery cross-sectional area and, to a lesser extent, in average peak flow velocity, resulting in an increase in volumetric coronary blood flow of 39% and 59% at the doses of 100 and 200 μg, respectively. With these doses of nitroglycerin, the decrease in diastolic to systolic velocity ratio and the increased change in cross-sectional area from end-diastole to end-systole suggested an enhanced epicardial coronary artery compliance. With ergonovine, a 12% reduction in epicardial coronary artery cross-sectional area was seen, without a significant change in average peak velocity, resulting in a 15% decrease in volumetric coronary blood flow. Adenosine caused a 270% increase in average peak velocity but no change in epicardial coronary artery cross-sectional area, resulting in a 270% increase in volumetric bood flow.Conclusions. This study demonstrates that nitroglycerin and ergonovine predominantly influence coronary conductance arteries whereas adenosine mainly dilates coronary resistance vessels. These findings also demonstrate that the combined use of a two-dimensional and a Doppler ultrasound transducer within one catheter assembly can provide information on the differential effects of vasoactive agents on the epicardial and microvascular coronary circulation.

Aortic compliance measured by non-invasive Doppler ultrasound: Description of a method and its reproducibility

1. Aortic compliance (expressed as percentage increase in lumen diameter for a pulse pressure of 10 mmHg) was calculated from the characteristic pulse wave velocity deduced from 'foot to foot' transit times of the blood flow pulse over a measured length of aorta. Two continuous wave Doppler ultrasound transducers were used: one insonating the root of the left subclavian artery, the other the abdominal aorta proximal to its bifurcation. Measurements were made after the subject had been supine for 5 min to achieve stable conditions. 2. Transit times were calculated on-line in real-time from the delay between the start of the systolic upstroke in the flow velocity sonograms recorded by the two transducers. 3. Within-visit variation was minimized by measuring over 45 cardiac cycles repeated three separate times and calculating an overall mean value for aortic compliance. A full measurement took 5-10 min. 4. Reproducibility of this overall mean value of aortic compliance was assessed at 1 month in 30 subjects (aged 60 +/- 7 years, mean +/- SD) and at 3 months in 23 different subjects (59 +/- 8 years). Aortic compliance values ranged from 0.1 to 2.0%/10 mmHg. 5. The mean paired difference between aortic compliance values was -0.02 between 0 and 1 months, and 0.03 between 0 and 3 months, with respective 95% confidence limits of -0.06 to 0.03 and -0.03 to 0.09 embracing zero, thus not differing significantly from baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in fetal hemodynamics with terbutaline treatment and premature labor

The aim of this study was to examine the fetal hemodynamic effects of terbutaline treatment and premature labor. Image-directed pulsed and continuous wave Doppler ultrasound studies, using 3.3-MHz and 5-MHz transducers (GE PASII and ATL echocardiographic machines), were used to assess fetal cardiac blood velocities in three groups of pregnancies matched for menstrual age (MA). Group 1: 13 normal pregnancies, mean MA 31 weeks. Group 2: 7 women in premature labor prior to tocolytic therapy, mean MA 32 weeks. Group 3: 8 women treated with terbutaline, average dose 18.8 mg daily, for previous premature labor, mean MA 31 weeks. Heart rate averaged 150 bpm, 135 bpm, and 127 bpm in the terbutaline, premature labor, and normal groups, respectively, and each were significantly different from each other. Products of time velocity interval and heart rate at the aortic valves were 1603 cm +/- 140 cm, 1413 cm +/- 190 cm and 1238 cm +/- 200 cm, and at the mitral valves 1102 cm +/- 170 cm, 812 cm +/- 110 cm, and 878 cm +/- 150 cm in the terbutaline, premature labor, and the normal groups, respectively. Aortic and mitral blood velocity products of time velocity integrals and heart rates were significantly higher (p = 0.01) in the terbutaline group relative to the normal group. In addition, the terbutaline group was significantly higher than the labor group at the mitral valve (p = 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Incidence of Venous Air Embolism during Cesarean Section Is Unchanged by the Use of a 5 to 10?? Head-Up Tilt

One hundred healthy parturients were divided at random into two demographically similar groups and were positioned for cesarean section either horizontally or flexed 5 to 10 degrees head up, with a 15 degrees lateral tilt. A Doppler ultrasound transducer was positioned over the fourth intercostal space parasternally. Initially, two patients received spinal, three general, and 95 epidural anesthesia. Two patients subsequently needed general for failed epidural anesthesia. Changes in Doppler heart tones (greater than 15 sec duration) indicative of venous air embolism (VAE) were identified 15 times in 11 patients--seven in supine and four in head-up patients (no statistically significant difference). Six awake patients (three horizontal, three head-up) developed chest tightness or pain during surgery, but only one episode correlated with VAE. No patient developed breathlessness. Moderate hypotension (greater than 10% decrease in systolic arterial pressure [SAP]) occurred in seven of 11 (63.6%) patients with, and in 26 (29.2%) of 89 patients without, VAE (P less than 0.001). More severe hypotension (SAP less than 90 mm Hg) due to bleeding occurred once. We conclude that a modest (5-10 degrees) head-up position does not influence the occurrence of VAE in patients having cesarean section. An 11% incidence of clinically insignificant VAE, although low, is still worrisome, as even small air bubbles in the circulation are potentially harmful, especially if the foramen ovale is patent. VAE during cesarean section should be anticipated and the anesthetic management planned accordingly.