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Biomedical subjects

L Segadal

Publications and source records attributed to L Segadal.

At least 37 records · Page 2Linked to original sources
PubMed1988

Simultaneous measurement of velocity, diameter, flow and pressure in the ascending aorta of cats. Evaluation of an extractable Doppler ultrasound probe for continuous monitoring of aortic blood flow.

To evaluate an extractable Doppler ultrasound probe designed for monitoring postoperative aortic flow in infants, simultaneous measurements of velocity, diameter, electromagnetic flow estimates, and pressure in the ascending aorta were recorded in cats. Doppler flow calculators were designed to provide flow estimates based on preset constant or measured instantaneous aortic diameter. Doppler sample volume was extended to about 1.2 X 1.6 X 4.0 mm. By pharmacological interventions, a wide range of flow rates and pressures were obtained, some of which were outside physiological values. The prototype probe described here was well suited for implantation in aortas with outer diameter 8-12 mm. Correlation coefficients between Doppler and electromagnetic estimated flow for 140 samples were 0.908 and 0.959 for constant and instantaneous diameter, respectively. Mean difference between the two methods was calculated, as well as the 95% confidence limits (2SD) of the differences. Limits of agreement, in stable haemodynamic situations without drugs, were -20.0 and 22.4% of mean average flow for constant diameter Doppler flow estimates, and -14.5 and 15.1% of electromagnetic flow values for instantaneous diameter estimates. These limits increased when all samples were taken into account, but the limits for instantaneous diameter estimates were reduced from -33.1 and 32.4 to -23.9 and 19.3% after removal of data obtained during isoprenaline infusion, which introduced extreme high flow/low pressure situations. This Doppler method seems well suited for postoperative monitoring of aortic flow in infants. Errors observed in larger aortas with an asymmetric flow profile do not seem to be present in smaller vessels within normal values of flow and pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Blood velocity distribution in the human ascending aorta.

Mapping of blood velocities across the lumen of the ascending aorta was performed in eight patients during open-heart surgery. A Doppler ultrasound probe was constructed to measure velocities in 2 mm steps from the maximum convexity to the maximum concavity of aorta, 6 to 7 cm above the aortic valve. In five patients with angina and normal aortic valves, velocity profiles were very similar and showed the following main features: a skewed peak systolic velocity profile with the highest velocity along the left posterior wall, a bidirectional velocity profile in late systole and early diastole with retrograde velocities along the left posterior wall, and a sustained antegrade flow along the convexity well into diastole. The resultant mean velocity profile had the highest velocity at the convex side and a central minimum velocity. In patients with Medtronic-Hall tilting disc prostheses, where the larger opening was oriented backwards and to the right, mean flow velocity profile was skewed in the opposite direction of normal. Moreover, instant systolic velocity profiles were much more irregular and dependent on the exact orientation of the prosthesis. In one patient with aortic valvular disease, very irregular and different velocity profiles were found. Based on a symmetry assumption, overall mean velocity for the total cross section was computed, and the magnitude of error in estimation of total flow from measurement of velocities at different depths was calculated. To measure total flow in the aorta, i.e., cardiac output, by single-gated Doppler technique, the most representative sampling site was about one-third of the diameter from the convex wall.

Adult↗
PubMed1985

Continuous measurement of aortic blood velocity, after cardiac surgery, by means of an extractable Doppler ultrasound probe.

A new method has been developed for the continuous measurement of aortic blood velocity in patients following cardiac surgery. Using an extractable Doppler ultrasound probe placed on the ascending aorta, the changes in aortic velocity were recorded up to 24 h postoperatively, in 14 patients undergoing coronary bypass surgery. Volume flow rate is calculated from the mean velocity, the diameter of the aorta and the angle between the ultrasound beam and the direction of the blood flow, by means of an analogue flow calculator. Estimation of aortic flow showed a correlation of r = 0.79 with cardiac output measured by a thermodilution technique. The main advantage of the system is that it allows continuous monitoring of cardiac output, as well as short and long-term trend analyses, during the early postoperative period.

Aorta↗
PubMed1985

Budd-Chiari syndrome with obstruction of the inferior caval vein: successful treatment by cavosplenoatrial shunt.

A 27-year-old man had a 10-month history of recurrent ascites, massive edema, and extreme fatigue. The diagnosis of Budd-Chiari syndrome with severe stenosis of the retrohepatic part of the inferior caval vein had been established. Medical treatment had failed to prevent further deterioration. A single 14 mm Gore-Tex graft (W.L. Gore & Associates, Inc. Elkton, Md.) was used to establish a cavosplenoatrial shunt. The postoperative recovery was uneventful. All signs of ascites and edema disappeared within 8 weeks after surgery. In connection with repair of a ventral hernia 8 months later, a liver biopsy specimen revealed partial normalization of liver histology and an angiography demonstrated a patent shunt. Two and a half years after the initial operation he developed a bleeding peptic ulcer demanding emergency surgery. The shunt was again found patent. Three years after the first operation the patient is free of symptoms and working full time.

Adult↗
PubMed1983

Bipolar atrial application of a new temporary pacing lead after cardiac operations.

A new temporary pacing lead. Medtronic Model 6400, with a defined electrode surface area of 7.5 mm2, has been clinically and electrophysiologically evaluated during bipolar atrial application in 20 patients after cardiac operations. A silicon disc was used for fixation of the electrodes to the right atrium in 10 patients, and an atrial plication technique was used in the other 10. Myocardial stimulation threshold and resistance were measured throughout the postoperative period. Atrial electrograms were recorded on magnetic tape for computer analysis of amplitudes, slew rates, and signal source impedance. No significant differences (p greater than 0.1) were found in myocardial stimulation threshold between the two fixation modes. During constant-current pacing, median threshold rose from 0.65 mA to 2.3 mA. Stimulation resistance, measured during constant-voltage pacing, fell from 567 to 365 omega, with a subsequent rise to 425 omega before electrode removal. Again no difference was found between silicon disc and plication fixation of the electrodes. P-wave amplitudes were significantly higher with plication than with silicon disc fixation (2.26 versus 0.86 mV, p less than 0.01), as were slew rates (0.34 versus 0.18 V/s, p less than 0.05). Signal source impedance had a magnitude of 6 k omega. The electrodes were used successfully in 12 (60%) of the patients for diagnosis and/or treatment of arrhythmias. We find the new lead well suited for atrial application.

Aged↗
PubMed1982

Determination of adenine nucleotides and inosine in human myocard by ion-pair reversed-phase high-performance liquid chromatography.

An isocratic high-performance liquid chromatographic system for the quantitation of AMP, ADP and ATP is presented. The separations were achieved at room temperature by reversed-phase chromatography (Supelcosil LC-18). The standard solvent was 220 mM potassium phosphate, pH 6.9, 1% (v/v) methanol and 0.3 mM tetrabutylammonium hydrogen sulphate. A selective retention of the adenine nucleotides as a group relative to the mono-, di- and triphosphates of guanosine, uridine and cytidine was observed under these experimental conditions. The adopted procedure was applied to the separation of adenine nucleotides in biological extracts, i.e., human myocard. The adenine nucleotides in an extract of myocard were quantitated in less than 20 min. Only 5-10 mg (wet weight) of myocard were needed in order to determine the energy charge of a myocardial sample. Also inosine was easily quantitated in this liquid chromatographic system.

Adenine Nucleotides↗
PubMed1982

Estimation of flow in aortocoronary grafts with a pulsed ultrasound Doppler meter.

A newly developed pulsed ultrasound Doppler meter was used for measurement of blood flow in aortocoronary vein grafts during operation. The results were compared with measurements obtained with conventional electromagnetic flowmetry. In 27 grafts, excellent agreement was found between electromagnetic flow probes thoroughly calibrated for varying hematocrit on fresh veins in vitro, and a clip-on type of Doppler probe (r = 0.86). In vitro calibration showed a close correspondence (r = 0.98) with the Doppler technique with no dependency on hematocrit and no need for zero calibration. The use of a conventional electromagnetic flowmeter showed strong dependency on recent calibration, both for saline and for varying hematocrit. Zero-calibration was necessary for every single graft measurement. The application of ultrasound Doppler meters of high quality together with clip-on probes of proper design proved to be superior to electromagnetic flowmetry for intraoperative blood flow measurements.

Blood Flow Velocity↗
PubMed1982

Clinical and electrophysiological properties of a new temporary pacemaker lead after open-heart surgery.

A new temporary pacemaker lead, Medtronic 6400, with a solid defined electrode surface area of 7.5 mm2, has been implanted in 50 patients after open-heart surgery. One electrode was inserted intramyocardially on the right ventricle, while another was placed extracardially and served as a reference lead. Forty-six of the patients were followed postoperatively with measurements of myocardial stimulation threshold and resistance. In 25 of the patients, electrograms were recorded on magnetic tape for further computer analysis of amplitudes, slew rates, and signal source impedance. During constant current pacing, myocardial stimulation threshold increased from a median of 0.4 mA one hour postoperatively to a maximum value of 2.3 mA. In two patients (4.3%) intermittent pacing failure was seen. Stimulation resistance fell from a median of 875 omega to a minimum of 487 omega, with a subsequent increase of 598 omega before electrode removal. Both mean electrogram amplitude (7.35 mV) and slew rate (0.82 V/s) had their minimum values on the sixth postoperative day. Intermittent sensing failure was observed in 2/25 patients (8%). Signal source impedance was of a magnitude not likely to contribute to sensing failure. No complications were seen from the use of this lead. The new electrode is an important improvement in temporary pacemaker lead design.

Adult↗
PubMed1982

Salvage of the severely ischaemic limb by intra-arterial prostacyclin (PGI2) infusion. A case report.

A 75-year-old male patient with impending gangrene of the left lower limb due to advanced arteriosclerosis was treated with intra-arterial infusion of prostacyclin (PGI2). Pain at rest disappeared completely soon after treatment was started. Blood flow to the extremity measured by a Doppler velocity meter increased significantly during PGI2 infusion. Although some reduction in flow was found after termination of the infusion, the flow values up to 6 weeks after treatment were still markedly higher than pretreatment levels.

Aged↗
PubMed1982

New temporary pacing lead for use after cardiac operations.

A newly designed temporary pacemaker lead (Medtronic Model 6400), which has a solid defined electrode surface area of 7.5 mm2, was compared with a multifilamental stainless steel electrode in common use (Davis & Geck, DG). Thirty-nine patients had both types of electrodes inserted intramyocardially in the right ventricle. A DG electrode fastened to the pericardium served as a reference lead. In addition to the standard Medtronic 7.5 mm2 electrode (n = 11), specially made Medtronic electrodes with areas of 5 mm2 (n = 10), 10 mm2 (n = 10), or 7.5 mm2 with platinum-iridium tips (n = 8) were studied. Measurements of myocardial stimulation threshold and resistance were made in both electrodes throughout the postoperative period. The patients' electrograms were recorded on magnetic tape for computer analysis of amplitudes and slew rates. The Medtronic 7.5 mm2 electrodes showed overall better results than 5 and 10 mm2 leads. Maximum stimulation threshold on the Medtronic 7.5 mm2 electrodes was medium 3.4 mA versus 10 mA on DG electrodes (p less than 0.001). The tissue resistance on Medtronic 7.5 mm2 was almost double than on the Davis & Geck electrodes (median 311 ohms versus 164 ohms on the day of minimum resistance, p less than 0.001). There were no significant differences in electrogram amplitudes between the two electrode types studied (5.52 versus 4.68 mV, p greater than 0.1), but the slew rates were significantly higher on the Medtronic (0.56 versus 0.37 V/sec; p less than 0.01). The new lead is an important innovation in temporary pacemaker lead design compared to the commonly used multifilamental leads.

Adult↗
PubMed1981

Pulmonary circulation and loss of microspheres from the lung following acute pulmonary venous occlusion.

The pulmonary vein from right upper lobe was ligated in 15 rats while 15 others served as controls. Prior to occlusion, 15 mum microspheres were injected into the superior caval vein. Another population of 15 mum microspheres was similarly given 1 min, 10 min or 30 min after ligation. All rats were killed 5 min after the second microsphere injection. The weight of the ligated lobe was 63% higher than that of the controls. This was probably due to acute vascular congestion since no significant oedema developed. Increased weight caused a reduction in the number of preocclusion microspheres per gram of tissue in the ligated lobe. In addition a gradual loss of preocclusion microspheres took place following pulmonary venous ligation. After 35 min of ligation, 30% of the preocclusion spheres had disappeared from the ligated lobe. Postocclusion flow through the pulmonary artery into right upper lobe was estimated by microspheres from the second injection, and averaged 5% of normal flow. Following acute venous occlusion, a rapid dilatation of the bronchopulmonary communicating system probably takes place. By reversal of the flow in this system, blood and microspheres can be drained into the bronchial venous circulation. In spite of methodological problems caused by acute congestion and loss of microspheres after pulmonary venous occlusion, we consider the microsphere method to be useful for further studies of collateral lung circulation.

Animals↗
PubMed1979

Sick sinus syndrome treated with permanent pacemaker in 109 patients. A follow-up study.

During the last decade implantation of permanent pacemakers has become the treatment of choice for patients suffering from the sick sinus syndrome (SSS). We have followed up 112 SSS patients treated with permanent pacemakers in Haukeland Hospital in the period 1966--76. The pacemakers were later removed from three of the patients. In the remaining 109 patients the SSS was characterized by tachy-bradyarrhythmias (TBA) in 44 and bradyarrhythmias (BA) in 65. Before implantation, 68 patients had syncopes and 27 severe dizziness. After implantation, symptomatic improvement was apparent in 104 patients; only three still had syncopes. During the follow-up period (mean 34.4 months), 29 patients died (yearly mortality 9.3%). There was no significant difference in total mortality between patients with TBA and with BA. Concomitant disturbances in atrioventricular (AV) conduction occurred in 35.8% of the patients. Among 79 of 80 patients still alive, five had developed total AV block, 19 had stable atrial fibrillation, 12 of these were possibly pacemaker-independent (ventricular rate greater than 60/min). Systemic embolization was observed in 16 patients, more frequently in the TBA (12/44) than in the BA group (4/65) (p less than 0.001). It is concluded that permanent pacemakers have an excellent symptomatic effect in patients with SSS. The prognosis is mainly determined by the presence or absence of coronary heart disease and/or heart failure.

Adolescent↗
PubMed1979

Evaluation of the microsphere-method for determination of cardiac output.

Cardiac output was determined by means of radioactive microspheres, 15 +/- 5 microns in diameter. Blood flow in the ascending aorta was measured by an electromagnetic flowmeter. In eight cats thirty-eight simultaneous measurements were made of cardiac output and aortic flow. The observations correlated well (r = 0.89), with a mean difference of 5.2%, probably corresponding to coronary blood flow. Continuous flow recordings showed no alterations in aortic flow during the injections of microspheres; arterial blood pressure and heart rate remained unchanged even after six injections, each consisting of about 2 x 10(5) spheres per kg body weight. Tests for shunting of microspheres were performed and revealed shunt fractions in the systemic circulation of about 8%, with no significant shunting through the lungs. The microsphere method for determining cardiac output is thought to be an accurate method, suitable for small and medium sized animals.

Animals↗