Biomedical subjects

K Bjørnstad

Publications and source records attributed to K Bjørnstad.

15 recordsLinked to original sources

PubMed2000

Semiautomatic contour detection in ultrasound M-mode images.

We have developed a method for semiautomatic contour detection in M-mode images. The method combines tissue Doppler and grey-scale data. It was used to detect: 1. the left endocardium of the septum, the endocardium and epicardium of the posterior wall in 16 left ventricular short-axis M-modes, and 2. the mitral ring in 38 anatomical M-modes extracted pair-wise in 19 apical four-chamber cine-loops (healthy subjects). We validated the results by comparing the computer-generated contours with contours manually outlined by four echocardiographers. For all boundaries, the average distance between the computer-generated contours and the manual outlines was smaller than the average distance between the manual outlines. We also calculated left ventricular wall thickness and diameter at end-diastole and end-systole and lateral and septal mitral ring excursions, and found, on average, clinically negligible differences between the computer-generated indices and the same indices based on manual outlines (0.8-1.8 mm). The results were also within published normal values. In conclusion, this initial study showed that it was feasible in a robust and efficient manner to detect continuous wall boundaries in M-mode images so that tracings of left ventricular wall thickness, diameter and long axis could be derived.

Blood Flow Velocity↗

PubMed2000

Strain rate imaging by ultrasonography in the diagnosis of coronary artery disease.

Regional strain rate in the left ventricle can be assessed in real time and color mapped. The method is termed strain rate imaging (SRI), and findings correspond well with 2-dimensional echocardiography. This study addresses SRI as a method for localizing coronary lesions, compared with standard echocardiography. Twenty patients with acute myocardial infarction who underwent coronary angiography for clinical reasons were examined with SRI and standard echocardiography. Wall motion was graded by SRI color and separately by wall thickening. Strain rate imaging and 2-dimensional echocardiography results agreed well. An infarct-related artery was identified from angiograms combined with electrocardiograms. Both methods identified an infarct-related artery in 19 possible cases and had equal sensitivity and specificity for wall segments affected by lesion. Combining the information from both methods did not change accuracy. The study validates SRI as a method for assessing regional wall function in coronary artery disease. The advantages of SRI are discussed and measurements of strain rates are given.

Adult↗

PubMed1997

How does computer-assisted digital wall motion analysis influence observer agreement and diagnostic accuracy during stress echocardiography?

This study assessed interobserver and intraobserver variation and diagnostic accuracy during 25 dipyridamole stress echocardiography tests interpreted with different analysis systems: a) computer display of high frame rate digital cineloops (47 frames/s); b) computer display of lower frame rate digital cineloops (24 frames/s); and c) videotape recordings. The majority of the patients (84%) had documented coronary artery disease with baseline wall motion abnormalities due to previous myocardial infarctions and/or coronary bypass surgery, thus comprising a population with difficult interpretation of stress echocardiography. Diagnostic accuracy was assessed using coronary angiography as reference method. Interobserver and intraobserver agreement was highest when analysis was performed from computer-displayed cineloops, 96 and 92%, respectively, compared to 84 and 80% respectively, using videotape recordings. Sensitivity for identification of coronary artery stenosis was similar using digital cineloops with high frame rate or videotape recordings (67% to 80% for both systems), and tended to be lower using cineloops with lower frame rate for analysis (53%). Inter- and intraobserver differences for wall motion score index were not significantly influenced by the analysis system. We conclude that computer assisted analysis with high frame rate of the displayed cineloops provides optimal observer agreement and diagnostic accuracy in the same range as videotape analysis in patients undergoing stress echocardiography.

Adult↗

PubMed1996

Clinical and echocardiographic follow-up after aortic valve reconstruction with bovine or autologous pericardium.

Eighty-six patients, mean age 29 +/- 15 years, underwent aortic valve reconstruction with bovine or autologous pericardial tissue. Mean clinical follow-up was 35 months. Echocardiographic data were assessed in 65 patients with follow-up > or = 6 months. There were two in-hospital and three late deaths. Warfarin was not given, and no thromboembolic events occurred. Five (6%) patients needed reoperation because of severe aortic regurgitation. Peak aortic valve gradients remained low (26 +/- 14 mm Hg for the bovine group and 16 +/- 16 mm Hg for the autologous group). One patient is awaiting surgery for aortic stenosis after 76 months. Leaflet thickening at latest follow-up was marked in six (9%) patients. Left ventricular dimensions normalized postoperatively and showed only insignificant increase during follow-up. This technique is a promising alternative to valve prosthesis in selected patients; however, longer follow-up is necessary to assess long-term results.

Adolescent↗

PubMed1996

The importance of transesophageal echocardiography during surgery of the thoracic aorta.

OBJECTIVES: To assess left ventricular dimensions and cardiac output during thoracic and thoracoabdominal aortic aneurysm repair. MATERIAL AND METHODS: Nine patients undergoing thoracic and thoracoabdominal aneurysm repair using direct cross-clamping without shunt or by-pass were studied prospectively. Prior to, during cross-clamping (XC) and after declamping left ventricular cross-sectional areas were monitored with transesophageal echocardiography. A pulmonary artery catheter was used for measurements of cardiac output with the thermodilution technique. RESULTS: Cardiac output increased 43% from baseline during XC (p < 0.01) and was still 55% above baseline at declamping (p < 0.05). Left ventricular end-systolic inner area was reduced 32% during XC (p < 0.01). Pulmonary artery pressures and central venous pressure increased during declamping (p < 0.05). Heart rate increased 38% from 66 beats/ min to 92 beats/min (p < 0.01) and was still 30% elevated at declamping (p < 0.01). CONCLUSION: During thoracic aortic XC, cardiac output is increased and left ventricular end-systolic dimension is reduced. TEE is a valuable supplement to pressure measurements for the evaluation of cardiac function during surgery of the thoracic aorta.

Aged↗

PubMed1996

Evaluation of reference systems for quantitative wall motion analysis from three-dimensional endocardial surface reconstruction: an echocardiographic study in subjects with and without myocardial infarction.

Six relevant computer-implemented reference systems for three-dimensional quantitative assessment of left ventricular wall motion abnormalities were compared with visual wall motion analysis of two-dimensional images. Endocardial borders were traced in three apical echocardiographic views at end-diastole and end-systole in 10 patients with myocardial infarction and 5 healthy subjects, and three-dimensional reconstruction of endocardial surfaces was performed. End-diastolic and end-systolic surfaces were aligned in a common axis system depending on the reference system, and systolic wall motion was assessed at 1,024 points on the endocardial surface. The localization of abnormal wall motion was displayed in bull's-eye maps, and the area was determined as a percentage of total endocardial area. For each reference system, the segmental concordance between three-dimensional computerized and visual assessment was determined. The best agreement between computerized and visual analysis was obtained with a reference system based on wall motion towards the major ventricular axis, whereas the poorest result was obtained using the center of left ventricular cavity as reference. Correlation between the estimated area of wall motion abnormality and visually determined wall motion score index was best using the aligned center of mitral valve plane as reference (r = .92).

Adult↗

PubMed1995

Digital high frame rate stress echocardiography for detection of coronary artery stenosis by high dose dipyridamole stress testing.

Diagnostic accuracy of high dose dipyridamole stress echocardiography (0.84 mg i.v./kg) for detecting coronary artery stenosis was assessed in 94 patients undergoing coronary angiography, and adverse effects were registered in the total study population of 120 patients. Echocardiographic analysis was performed with digital systolic cineloops with high frame-rate (47 frames/sec) for optimal left ventricular wall motion display. Results showed sensitivity of 73% for detection of arterial luminal stenosis > or = 75% or retrograde collateral flow to an occluded coronary artery. Sensitivity for detection of 1-vessel stenosis was 43% (6 of 14 patients), and for 2- and 3-vessel disease 79% (19 of 24) and 88% (16 of 18), respectively. Specificity was 92% (35 of 38), diagnostic accuracy 81%. The stenosed coronary artery was correctly localized in 85% of positive tests. Dipyridamole-induced increase in wall motion score index differed significantly between patients with 1-, 2-, and 3-vessel disease (0.02 +/- 0.17, 0.15 +/- 0.17, and 0.27 +/- 0.24, respectively), and early positive tests (dipyridamole dose of 0.56 mg/kg) were almost exclusively seen in patients with multivessel disease. Six patients (5%) developed symptomatic bradycardia and hypotension during the test. In conclusion, dipyridamole stress echocardiography is useful for detection and localization of coronary artery stenosis, particularly in patients with multivessel disease.

Collateral Circulation↗

PubMed1995

Cardiovascular response in patients with and without myocardial ischaemia during dobutamine echocardiography stress test for coronary artery disease.

Dobutamine is widely used in cardiac stress testing for coronary artery disease and myocardial viability. To assess the systemic cardiovascular response during dobutamine echocardiography stress testing, we investigated nine patients without myocardial ischaemia (group 1, aged 48 to 72 years) and nine patients with myocardial ischaemia during the test (group 2, aged 53 to 73 years), by use of Doppler/echocardiography and subclavian artery pulse trace calibrated with brachial artery pressures. Peripheral resistance, total arterial compliance, and aortic characteristic impedance were estimated using a 3-element windkessel model of the systemic circulation. During infusion of dobutamine up to 40 micrograms kg-1 min-1, arterial pressure was maintained near baseline levels, whereas heart rate and cardiac index increased, more so in group 1 (mean: 89 and 79%) than in group 2 (58 and 52%; P < 0.05 vs. group 1). Peripheral resistance was decreased by > or = 32% at peak stress, whereas characteristic impedance was maintained at or above baseline in both groups, and total arterial compliance was not significantly altered. The cardiovascular response in group 2 was not influenced by the wall motion abnormalities. Thus, in these patients the inotropic, chronotropic, and vasodilatory effects of dobutamine balanced the ischaemic impairment of left ventricular function during the stress test.

Aged↗

PubMed1995

Comparison of digital dipyridamole stress echocardiography and upright bicycle stress echocardiography for identification of coronary artery stenosis.

This study compared the diagnostic accuracy of dipyridamole (0.84 mg i.v./10 min) and bicycle stress echocardiography in 37 patients with inconclusive standard bicycle electrocardiography (ECG) tests; all underwent coronary angiography. Sensitivity for detection of coronary stenosis with dipyridamole echocardiography was 68% (21 of 31 patients), and for 1-, 2- and 3-vessel disease 56, 69 and 83%, respectively. Overall bicycle echocardiography sensitivity was 84%, and 78, 88 and 83% for patients with 1-, 2- and 3-vessel disease, respectively. Dipyridamole echocardiography was negative in all 6 patients with negative coronary angiography (specificity 100%), bicycle echocardiography was positive in 2 (specificity 67%). We conclude that dipyridamole echocardiography tends to be less sensitive in patients with mild disease, but is more specific than bicycle echocardiography.

Adult↗

PubMed1994

Noninvasive study of left ventricular function and systemic haemodynamics during dipyridamole echocardiography stress test.

Left ventricular function and systemic haemodynamics were noninvasively assessed during cardiac stress testing with dipyridamole (0.84 mg kg-1 i.v.) in 10 subjects (44-61 years) with normal coronary arteries (group 1), and in 14 patients (46-77 years) with coronary artery disease either without (group 2, n = 6) or with (group 3, n = 8) echocardiographic evidence for myocardial ischaemia during test. Left ventricular wall motion and dimensions, and aortic root pressure and flow were obtained by Doppler echocardiography combined with an externally traced subclavian artery pulse calibrated with brachial artery pressures. Peripheral arterial resistance, total arterial compliance, and aortic characteristic impedance were estimated from aortic root pressure and flow, by use of a three-element windkessel model of the systemic circulation. Left ventricular ejection fraction improved from baseline to peak stress in group 1 (mean +/- SD: 62 +/- 6% vs. 65 +/- 6%, P = 0.05), whereas it was not significantly changed in group 2 (58 +/- 10% vs. 56 +/- 6%) and decreased in group 3 (53 +/- 10% vs. 43 +/- 10%, P < 0.05). Otherwise, the haemodynamic response was similar in the three groups: heart rate and cardiac index increased by at least 30% and 37%, respectively, whereas stroke index and arterial pressures were maintained at or slightly above baseline. Peripheral resistance decreased by at least 22%, and total arterial compliance and aortic characteristic impedance were not significantly altered during test. The worsening of wall motion abnormality at peak stress in group 3 was not significantly related to the change in systemic haemodynamics. Thus, dipyridamole acted predominantly on the arterioles without significantly influencing the large systemic arteries. Myocardial ischaemia during test impaired regional and global left ventricular function, but did not influence the systemic haemodynamic response.

Adult↗

PubMed1994

Angiographic findings of silent ischaemia following aortocoronary bypass surgery.

Silent ischaemia, defined as ST-depression > or = 1 mm without chest pain, was found on exercise testing in 22 (10.7%) of 206 patients who underwent aortocoronary bypass surgery in the period from March 1983 to November 1985. Exercise testing was performed 4.9 (range 3.6-6.7) years after operation on an electrically braked bicycle. Sixteen of the 22 patients were free from chest pain, while the remaining six had slight to moderate angina pectoris on exercise. Coronary angiography was performed in 21 patients with silent ischaemia; one of the 22 patients died before this investigation. Some 13 patients had one or more occluded grafts, one a new stenosis in a native vessel and five incomplete myocardial revascularization. For the remaining two patients, no aetiology for the ischaemia was found, and revascularization appeared to be complete. Before surgery, 13 patients had three-vessel disease, six two-vessel disease and three one-vessel disease. At follow-up, two patients had three-vessel disease, ten two-vessel disease and seven one-vessel disease. The value of identifying patients with silent ischaemia after aortocoronary bypass surgery with regard to life expectancy and quality is controversial. Subsets of patients, namely, those with main-stem stenosis and three-vessel disease, may benefit from secondary operation. Identification of these patients may therefore be of clinical importance.

Adult↗

PubMed1989

Ruminal degradation and outflow of amino acids in cows.

Two rumen- and duodenum-cannulated cows were used to study the disappearance rate, degradation in, and outflow from the rumen of four amino acids administered individually into the rumen at the following dose levels (mmol): lysine 273-547-820, tyrosine 276-496-828, isoleucine 381-762-1143 methionine 335. Calculations were based on the use of PEG (polyethylene glycol, 4000) as liquid marker for determination of the volume and dilution rate of rumen fluid. At the same dry matter intake a comparison was made between the influence of a high-forage and a low-forage diet. At the lowest dose level, the initial rates of disappearance (mmol/l per h) were 0.52 for lysine, 0.48 for tyrosine, 0.55 for isoleucine and 0.58 for methionine. The rates increased with increasing dose levels. The fractions of administered amino acids flowing out of the rumen and the fractions degraded in the rumen were studied over an 11 h period. At the lowest dose level, outflow (mmol/11 h) amounted to 42 and 54 for lysine, 36 and 29 for tyrosine, 93 and 48 for isoleucine, 104 and 75 for methionine on the high and low forage diet, respectively. The corresponding figures for degradation were 232 and 209, 239 and 247, 287 and 333, 226 and 259 mmol/11 h. The fractions of an administered amino acid flowing intact out of the rumen increased, and the fractions degraded in the rumen decreased, with increasing doses.

Amino Acids↗

PubMed1985

Inhibitory effects of some long-chain unsaturated fatty acids on mitochondrial beta-oxidation. Effects of streptozotocin-induced diabetes on mitochondrial beta-oxidation of polyunsaturated fatty acids.

Evidence showing that some unsaturated fatty acids, and in particular docosahexaenoic acid, can be powerful inhibitors of mitochondrial beta-oxidation is presented. This inhibitory property is, however, also observed with the cis- and trans-isomers of the C18:1(16) acid. Hence it is probably the position of the double bond(s), and not the degree of unsaturation, which confers the inhibitory property. It is suggested that the inhibitory effect is caused by accumulation of 2,4-di- or 2,4,7-tri-enoyl-CoA esters in the mitochondrial matrix. This has previously been shown to occur with these fatty acids, in particular when the supply of NADPH was limiting 2,4-dienoyl-CoA reductase (EC 1.3.1.-) activity [Hiltunen, Osmundsen & Bremer (1983) Biochim. Biophys. Acta 752, 223-232]. Liver mitochondria from streptozotocin-diabetic rats showed an increased ability to beta-oxidize 2,4-dienoyl-CoA-requiring acylcarnitines. Docosahexaenoylcarnitine was also found to be less inhibitory at lower concentrations with incubation under coupled conditions. With uncoupling conditions there was little difference between mitochondria from normal and diabetic rats in these respects. This correlates with a 5-fold stimulation of 2,4-dienoyl-CoA reductase activity found in mitochondria from streptozotocin-diabetic rats.

Animals↗

PubMedDate not supplied

Interobserver and intraobserver variation for analysis of left ventricular wall motion at baseline and during low- and high-dose dobutamine stress echocardiography in patients with high prevalence of wall motion abnormalities at rest.

Interobserver and intraobserver variation for analysis of left ventricular regional wall motion during dobutamine stress echocardiography was assessed. Computer-displayed cineloops from 33 patients, 25 with baseline wall motion abnormalities, were analyzed by two observers blinded for patient data. Assessment included (1) baseline wall motion abnormalities, (2) evidence of myocardial viability at 10 micrograms/kg/min dobutamine, and (3) evidence of myocardial ischemia at 30 to 40 micrograms/kg/min. Wall motion score index was calculated at each stage. Interobserver and intraobserver agreement for baseline wall motion abnormalities was 100%. Interobserver agreement for viability and ischemia was 84% and 82%, respectively; intraobserver agreement was 92% and 85%, respectively. Mean interobserver differences in wall motion score index ranged from 0.06 +/- 0.14 at baseline to 0.09 +/- 0.20 at high doses (p < 0.05 at all levels); mean intraobserver differences ranged from 0.001 +/- 0.14 to 0.01 +/- 0.15 (difference not significant at all levels).

Adult↗

PubMedDate not supplied

Systemic arterial compliance early and late after a first acute myocardial infarction.

Systemic arterial properties and left ventricular function were assessed by Doppler echocardiography and a calibrated subclavian artery pulse tracing early (5 weeks) and late (27 months) after a first acute myocardial infarction in 19 patients aged 44-77 years and in healthy subjects matched for age, gender, and arterial blood pressure. Total arterial compliance (3-element windkessel model) was reduced by 26% (p < 0.001) from early to late assessment, and left-ventricular end-diastolic and end-systolic volumes were increased by 11 and 18%, respectively (p < 0.05). Peripheral resistance and characteristic impedance were not significantly changed. The healthy matched subjects had arterial compliance similar to patients at early assessment, but tended to be higher at late. Thus, 2.3 years after a first acute myocardial infarction with moderate left ventricular dilatation, arterial distensibility was significantly decreased whereas peripheral resistance was not changed.

Adult↗