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PubMed2001

Improvement of phase-contrast flow measurements: opposite directional flow-encoding technique to eliminate the influence of the Maxwell term phase errors.

A new method termed the opposite directional flow-encoding (ODFE) technique is proposed to increase the accuracy and the reproducibility of phase-contrast flow measurements by correcting the non-linear background of velocity images induced by concomitant magnetic fields (Maxwell terms). In this technique, the volume flow rate is calculated from the difference of two region of interest (ROI) values derived from two velocity images obtained by reversing the flow-encoding direction. To evaluate the technique, various phantom experiments were carried out and volume blood flow rates of internal carotid arteries (ICAs) were measured in four volunteers. The technique could measure the volume flow rates of the phantom with higher accuracy (mean absolute percentage error = 1.04%) and reproducibility (coefficient of variation = 1.18%) than conventional methods. Flow measurements with the technique was not significantly affected by ROI size variation, measuring position, and flow obliquity not exceeding 30 degrees. The volume flow rates in the ICAs of a volunteer were measured with high reproducibility (coefficient of variation = 2.89% on the right, 1.48% on the left), and the flow measurement was not significantly affected by ROI size variation. The ODFE technique can minimize the effect of the non-linear background due to Maxwell terms. The technique allows use of ROIs of approximate size including the flow signal and provides accurate and objective phase-contrast flow measurements.

Adult↗
PubMed1999

Regional endocardial mapping of spontaneous and induced atrial fibrillation in patients with heart disease and refractory atrial fibrillation.

We performed simultaneous catheter mapping of right and left atrial regions at onset and during sustenance of spontaneous atrial fibrillation (AF) in patients with ischemic and/or hypertensive heart disease. Seventeen patients with structural heart disease had spontaneous and electrically induced AF episodes mapped from their onset simultaneously in multiple right and left atrial regions. Atrial premature complexes (APCs) that initiated spontaneous AF had coupling intervals ranging from 260 to 400 ms (mean 332 +/- 61), most commonly arising from the lateral right atrium (31%), right atrioventricular junction (13%), atrial septum (6%), superior left atrium (25%), or inferior left atrium (25%). APC morphology on surface electrocardiograms did not correlate with origin in specific atrial regions. The earliest regions of atrial activation for the first AF cycle were the lateral right atrium (n = 5), superior left atrium (n = 4), distal or mid coronary sinus (n = 4), atrial septum (n = 2), and right atrioventricular junction at the His bundle location (n = 2). Spontaneous AF at onset usually showed discrete but irregular electrograms at virtually all right and left atrial sites mapped, with a reproducible region of AF initiation in all 8 patients with multiple events. The region of earliest atrial activation at spontaneous AF onset was in close proximity to the APC origin in 15 of 16 patients (94%), and 39 of 40 episodes (97%) mapped. Stable patterns of right and left atrial activation were observed at AF onset in 14 patients. Induced AF elicited with right atrial stimulation demonstrated different sites of earliest regional atrial activation at onset compared with spontaneous AF events in 4 of 8 patients. However, discrete intracardiac electrograms were also present in induced AF in all of the mapped atrial regions. Furthermore, the site of extrastimulus delivery in induced AF was also found to be in close proximity to the earliest region of atrial activation for the first AF beat. We conclude that spontaneous AF is initiated by APCs arising in different right or left atrial regions in patients with structural heart disease and the initial region of atrial activation in AF is in proximity to the region of APC origin. Organized and repetitive electrical activation is frequently observed in both right and left atria at AF onset. Although electrically induced AF may have different activation patterns than spontaneous AF at onset in many patients, both types of AF demonstrate organization and earliest atrial activation in proximity to the initiating APC.

Aged↗
PubMed1987

Noninvasive measurement of blood flow and extraction fraction.

We describe the theory of a technique for the noninvasive measurement of organ blood flow which is based on the principle of fractionation of cardiac output and is applicable with any recirculating gamma emitting tracer. The technique effectively determines the count rate that would be recorded over the organ if the tracer behaved like radiolabelled microspheres and was completely trapped in the organ's vascular bed on first pass. After correction for organ depth, the estimated first pass activity plateau, expressed as a fraction of the injected dose, is equal to the organ's fraction of the cardiac output (CO). By extending the theory, organ extraction fraction of extractable tracers or mean transit time of nonextractable tracers can be measured. Renal blood flow (RBF) to the normal left kidney in 18 subjects without evidence of renal disease was estimated by the technique to be 10.4% CO (S.D. 1.2), for the right kidney 9.0% CO(S.D. 1.1), and for both, 19.4% CO (S.D. 1.5). In a separate series of eight patients, RBF values were highly reproducible when obtained on successive days (standard deviation of change: 0.67% CO for the left kidney, 0.63% CO for the right and 0.78% CO for both). The extraction fraction of DTPA (filtration fraction) was 8.5% (1.7) in the left kidney and 9.7% (2.1) in the right kidney. This parameter was less reproducible than RBF, with standard deviations of the changes equal to 1.17% for the left kidney and 1.31% for the right. Stable, well-functioning, renal allografts in children had a mean blood flow of 20.6% CO (S.D. 3.7). Transplant blood flow in eight patients with rejection was less than 5.2% CO. In patients without splenomegaly, splenic blood flow, splenic extraction fraction of sulphur colloid and splenic red cell mean transit time were 4.3% CO (S.D. 0.9), 41% (S.D. 13.8), and 36.9 s (S.D. 4.6), respectively.

Blood Circulation↗
PubMed1995

Validation of right ventricular volume measurements by magnetic resonance imaging in small hearts using a fetal lamb model.

RATIONALE AND OBJECTIVES: Cine-magnetic resonance (MR) imaging is established as an accurate method of determining cardiac ventricular volumes in adults but has not been validated for the smaller ventricular volumes found in infants. The purpose of the authors study was to evaluate the accuracy and reproducibility of MR imaging to measure small ventricle volumes. METHODS: The volume of silicone-rubber casts of the right ventricle of 11 fetal lamb hearts was measured by MR imaging using different imaging planes and slice section thicknesses and by water displacement. RESULTS: The ventricle volumes of the 11 hearts ranged from 0.45 to 3.00 mL. Accurate and reproducible values for the right ventricle volumes were obtained by MR imaging. Thin sections (3 mm) in the axial plane produced the best results. CONCLUSIONS: Based on studies in the nonmoving heart, MR imaging can accurately measure the small ventricular volumes expected in infants.

Animals↗
PubMedDate not supplied

A noninvasive electromagnetic flowmeter.

The reliability and reproducibility of peripheral blood flow data obtained by a noninvasive electromagnetic flowmeter were tested using seven male and three female volunteers aged 15-46 years. Each subject was studied under multiple testing conditions in which time, subject's metabolic state, and electrode placement were varied. Each condition was repeated within 1 to 8 weeks to obtain test-retest data. Intraclass reliability coefficients of 0.864-0.998 were obtained on all pulsatile components both within a given measurement sessions and from one day to the next. The size and shape of the waveforms obtained from the data did not significantly differ from one another, thus indicating excellent reproducibility. No significant differences were found between data obtained from the right leg and that obtained from the left. The noninvasive electromagnetic flowmeter was found capable of providing reliable and reproducible data. For data analysis, the second of two consecutive curves seems to be the best choice for clinical assessment.

Adolescent↗
PubMed1975

Influences of exercise and endurance training on the oxygen dissociation curve of blood under in vivo and in vitro conditions.

In experiments with graded exercise of 15 men (6 untrained, 3 semitrained, 6 endurance-trained) the trained subjects showed a massive shift to the right of the in vivo O2 dissociation curve (ODC) of femoral venous blood. At a saturation of 20 to 25% (18 mkp/sec) Po2 was about 9 mm Hg higher for the trained than for the untrained group. The following factors play a role: 1. The 2,3-diphosphoglycerate [2,3-DPG] concentration was increased by 15 to 20% in the trained group which explains about 2 mm Hg of the diffenence in Po2-2. Exercise acidosis in the femoral venous blood depends to a large extent on CO2 in the trained, but on lactic acid in the untrained group. At low saturations the CO2-Bohr effect increases sharply thus having a greater importance in the trained subjects. This factor can explain about 2 mm Hg of the difference. However, influence of chloride and 2,3-DPG on the Bohr effect must be taken into consideration. 3. Since the large ODC-shift to the right of the trained group was not reproducible under in vitro conditions, it is suggested that a rapidly decaying unknown substance accounts for the remaining difference in Po2.

Acid-Base Equilibrium↗
PubMed1980

Permanent radiofrequency ventricular pacing for management of drug-resistant ventricular tachycardia.

Three patients with frequent episodes of symptomatic, sustained ventricular tachycardia that often required physician intervention were treated with a permanent patient-activated radiofrequency ventricular pacemaker for self-termination of ventricular tachycarida. Before pacemaker implantation, electrophysiologic testing revealed the tachycardia to be resistant to all approved and several investigational antiarrhythmic drugs. In all three patients, ventricular tachycardia was reliably and reproducibly terminated with brief bursts of rapid right ventricular apical pacing over several hundred trials. No patient had rapid ventricular pacing-induced acceleration of ventricular tachycardia or pacing-induced ventricular fibrillation. Since the implantation of a radiofrequency ventricular pacemaker an average of 13.7 months ago, all episodes of ventricular tachycardia (average 43/patient) have been terminated successfully by radiofrequency pacing, and no patient has required hospitalization for an arrhythmia-related problem.

Aged↗
PubMed1994

A comparison of human masseter muscle thickness measured by ultrasonography and magnetic resonance imaging.

Non-invasive imaging techniques such as computerized tomography, magnetic resonance imaging (MRI), and ultrasonography enable measurements of the cross-section and thickness of human jaw muscles in vivo, providing an indication of the maximal force a muscle can exert. In 15 adult Caucasian men the thickness of the masseter muscle was registered bilaterally on three different levels by ultrasonography. Scans were made on the contracted and relaxed muscle. A comparison was then made with measurements from serial MRI scans, using univariate analysis of variance for repeated measurements and Pearson's correlation coefficients. Variances of the repeated measurements were calculated for the different scanning levels and the different muscle conditions and tested for homogeneity. For both the ultrasound and MRI measurements there was no difference in thickness between the left and right muscle. The registration level with highest reproducibility was halfway between the origin and insertion. Measurements from the contracted muscle were more reproducible than those from the relaxed muscle. The relaxed muscle thickness measured by ultrasonography was smaller than that measured by MRI. The correlation between ultrasound and MRI was significant for the upper and middle level of scanning (p < 0.001). The highest correlation was found between MRI (relaxed) and ultrasound (contracted) at the middle level (R = 0.83, p < 10(-6)). The conclusion is that ultrasonography is an accurate and reproducible method for measuring the thickness of the masseter in vivo. It allows for large-scale longitudinal study of changes in jaw-muscle thickness during growth in relation to change in biomechanical properties of masticatory muscles.

Adult↗
PubMed1993

Tolerance to self-administration of cocaine in rats: time course and dose-response determination using a multi-dose method.

To assess tolerance to cocaine in a self-administration paradigm, rats were trained to self-administer cocaine (0.25 mg/injection) on a fixed-ratio 2 (FR2) schedule of reinforcement. The development of tolerance was studied during chronic administration of cocaine (20 mg/kg per 8 h for 10 days), given either contingently (self-administered by the rats) or non-contingently (infused by the experimenter). Both contingent and non-contingent administration of cocaine produced comparable tolerance, as indicated by a faster rate of cocaine self-administration (the average inter-reinforcer time, ISRT, decreased significantly). Tolerance developed by day 2 of the chronic regimen and reached a floor value (60% of baseline) from day 4 through day 10. Termination of chronic cocaine then resulted in recovery from tolerance, with ISRTs returning to baseline within 6 days of termination. A second set of experiments determined whether tolerance could be studied using a multi-dose method to obtain dose-response data in a single session. A system of multiple pumps allowed testing of three doses of cocaine during a single experimental session. Cocaine dose-response curves obtained from the multi-dose method: (i) did not differ from that obtained from a single-dose method; (ii) were reproducible; and (iii) were shifted to the right by Schering 23390. Rats were then subjected to a 7-day chronic regimen of infused cocaine (20 mg/kg per 8 h) or infused saline. At the end of this chronic cocaine period, they were tested with the multi-dose method. Chronic cocaine, as compared to chronic saline, shifted the cocaine dose-response curve to the right, indicating that the multi-dose method can be successfully applied to demonstrate tolerance to the effects of cocaine in a self-administration paradigm.

Animals↗
PubMed2003

Comparative characteristics of respiratory pattern responses to microinjection of kainic acid into different parts of the nucleus ambiguus.

Experiments on anesthetized rats were performed using local chemical exclusion of neurons with kainic acid to study the relative roles of the rostral, intermediate, and caudal parts of the nucleus ambiguus in the mechanisms controlling respiration. The characteristics of the respiratory rhythm and pattern responses to chemical exclusion of different parts of this nucleus were observed. In particular, sequential exclusion of the left and right rostral parts of the nucleus ambiguus reproducibly induced significant decreases in the respiration rate and respiratory volume in the first minutes; in 83% of experiments, there was also irreversible respiratory arrest. Exclusion of symmetrical intermediate parts of the nucleus ambiguus was followed by bradypnea and decreases in pulmonary ventilation, the greatest respiratory effects being noted only after injection of kainic acid into the second symmetrical area, irreversible respiratory arrest being seen in 50% of cases. Exclusion of symmetrical caudal areas of the nucleus ambiguus resulted only in small decreases in respiratory frequency without significant changes in respiratory volume and gave rise to the smallest incidence of respiratory arrest, i.e., 33%.

Animals↗
PubMed1983

The evaluation of right ventricular performance using krypton-81m.

The availability of krypton-81m suitable for intravenous injection provides an easy means for assessing right ventricular function. The superimposition of the other heart chambers does not constitute a problem. The activity in the left heart is negligible and the study can be performed in the right anterior oblique position to obtain optimal separation between the right atrium and the right ventricle. Lung activity is quite high and should be corrected before computing the right ventricular ejection fraction. This correction can be accomplished by performing Tc-99m MAA perfusion scintigraphy. The measurement of the right ventricular ejection fraction appears to be reproducible with very small inter-and intraobserver variability. Good quality phase and amplitude images can be obtained with such high count rates.

Cardiac Output↗
PubMed1998

Temporal patterns of evoked cerebral blood flow during reading.

This study describes the dynamics of flow activation by reading and investigates the potential use of repeated flow velocity measurements for the lateralization of speech. Using simultaneous transcranial Doppler recordings from both middle cerebral arteries and averaging techniques in 25 healthy volunteers, we describe the changes in blood flow velocity caused by repetitive reading tasks of variable duration in comparison with a resting state. Reading aloud evoked a characteristic temporal flow pattern in both hemispheres, consisting of three relative maxima in flow velocity during and after activation. Flow velocities lower than baseline were common during longer lasting activation. The amplitudes of two of the observed peaks decreased depending on the duration of the task. Reading silently produced a markedly different temporal pattern of activation than reading aloud. There were individually reproducible significant side to side differences. Right-handed persons (n = 15) almost without exception showed a significantly higher increase in flow velocity on the left hemisphere (e.g., reading silently 8.7% versus 5.3%; P < 0.0001). Three out of ten left-handed individuals, however, exhibited no significant side to side difference or exhibited lateralization to the right during one or more of the tasks. These findings suggest that reading induces task-specific temporal patterns of regional neuronal activity, which show habituation with longer duration of activation. Additionally, the observed side to side differences could be useful to predict language dominance.

Adult↗
PubMed1978

Coronary artery spasm in a patient with unstable angina pectoris.

A 32-year-old male with the clinical syndrome of unstable angina is presented. During cardiac catheterization and coronary cineangiography, the coronary arteries were found to be free of atherosclerosis, but segmental spasm of the right coronary artery was observed. Spasm was reproduced, but to a milder degree, upon the administration of ergonovine maleate intravenously. The patient was discharged on a regimen of oral nylidrin HCL, with symptomatic improvement.

Adult↗
PubMed1989

Quantification of regional cerebral blood flow with IMP-SPECT. Reproducibility and clinical relevance of flow values.

Single-photon emission computed tomography with N-isopropyl[123I]-p-iodoamphetamine (IMP-SPECT) was performed in 14 normal volunteers (seven men and seven women aged 25.1 +/- 5.3 years) and 29 patients with cerebrovascular disease (18 men and 11 women aged 54.1 +/- 13.7 years). The fluid microsphere model was used to estimate cerebral blood flow (CBF). Normal subjects were scanned twice, 1 week apart, to determine the reproducibility of the CBF estimates. Hemispheric blood flow (hCBF) was calculated as the mean of regional cerebral blood flow (rCBF) values in 16 gray matter regions per hemisphere. In normal subjects mean hCBF was 68 ml/100 g/min. The highest rCBF was found in the occipital cortex, followed by the frontal, temporal, and parietal cortexes. CBF values were reproducible (p less than 0.001 except the right thalamic region, where p less than 0.01). Intraindividual variation ranged between 0.3% and 15%. Women exhibited significantly higher (16%, p less than 0.02) CBF than men. Patients were subdivided into groups with reversible (n = 19) and persistent (n = 10) symptoms. Significant hCBF differences between the affected and the contralateral hemispheres were recorded only in the group with reversible symptoms (p less than 0.005), whereas the group with persistent symptoms showed a significant bilateral decrease of hCBF compared with normal subjects and patients with reversible symptoms. Focal CBF was significantly lower in patients with completed stroke than in patients with transient symptoms (p less than 0.001). Our results indicate that IMP-SPECT can be used for the routine estimation of CBF in normal and pathologic states.

Aged↗
PubMed1999

Chronic acalculous cholecystitis: reproduction of pain with cholecystokinin and relief of symptoms with cholecystectomy.

Over 500,000 patients undergo cholecystectomy annually in the United States for symptoms of upper abdominal discomfort and pain ascribed to gallbladder disease. However, approximately 5%, or 25,000 of these cases do not have gallstones on ultrasound examination but typically present with chronic symptoms of biliary colic. These patients often present as challenging diagnostic dilemmas and are often treated as if their symptoms are secondary to peptic ulcer disease or other gastrointestinal-related disorders. In 1992, we began to use the cholecystokinin (CCK) challenge test on patients with normal ultrasound examinations of the gallbladder but who had chronic symptoms resembling biliary colic. The CCK test was considered positive if the identical symptoms of discomfort or pain, usually in the right upper quadrant of the abdomen, were reproduced. This study describes the first 24 patients who had a positive CCK challenge test and chose to undergo cholecystectomy for relief of their symptoms. No patient was lost to follow-up evaluation at 1 to 24 months after operation.

Abdominal Pain↗
PubMed2002

[Endotracheal tube and trachebronchial obstruction due to a large blood clot. Case report].

A case of endotracheal tube and tracheobronchial acute obstruction caused by a large blood clot reproducing in part the trachea and the right bronchial tree is reported. The event has been anticipated by recurring hemoptyses whose source remained unknown despite any examination. Having established by simple manoeuvres that the obstruction was located at the endotracheal tube level, the tube was removed together with the blood clot without more invasive techniques like rigid or flexible bronchoscopy, embolectomy catheter of fibrinolytic agents. On the other side, those techniques should be used in case of obstruction located under the endotracheal tube. Albeit obstruction of endotracheal tubes due to blood clots is a frequent complication in critical care setting, this case is reported for the peculiar dimension and morphology of the clot, underlying that a precise diagnosis of the obstruction level allows the use of the most suitable technique for its removal.

Aged↗