Biomedical subjects

K Terp

Publications and source records attributed to K Terp.

8 recordsLinked to original sources

PubMed1999

Functional remodelling and left ventricular dysfunction after repeated ischaemic episodes. A chronic experimental porcine model.

This experimental study was set up to investigate left ventricular function and remodelling after repeated ischaemic episodes using magnetic resonance imaging (MRI). A significant reduction in mortality due to coronary heart disease (CHD) has been explained by both a decline in the incidence of acute myocardial infarction (AMI) and an improved post-AMI survival rate, suggesting a change in the natural history of CHD. Experimental intracoronary microembolization can induce different ischaemic patterns and the functional impact of repeated ischaemic episodes different from occlusion of central epicardial arteries can be studied. In this study repeated intracoronary microembolizations were performed in 20 domestic pigs. After 129 d, MRI was performed for assessment of left ventricular volume, mass and wall stress. Six pigs underwent serial MRI at baseline, immediately after embolization and at the end of the observation period. Microembolizations induced acute myocardial infarct expansion and increased left ventricular wall stress preceding chronic remodelling. End systolic and end diastolic volumes increased from 15.1 +/- 2.7 cm3 to 41.3 +/- 11.5 cm 3 (p < 0.002), and from 52.0 +/- 6.7 cm3 to 81.1 +/- 9.2 cm3 (p < 0.0007), respectively. End systolic wall stress increased from and 17.5 +/- 2.7 to 29.7 +/- 6.2 N/m2 (p < 0.001). Left ventricular filling pressures and cardiac index were unchanged. Histological examination revealed a diffuse pattern of perivascular fibrosis covering 12 +/- 3% of the left ventricular wall. This study demonstrates that repeated ischaemic episodes different from confined regional myocardial infarctions induce acute infarct expansion and chronic left ventricular remodelling in pigs. Serial assessment of absolute left ventricular volumes and mass is important during acute/chronic remodelling.

Animals↗

PubMed1998

The hemodynamic impact of diffuse myocardial ischemic lesions: an animal experimental model based on intracoronary microembolization.

In ischemic heart disease, left ventricular function is affected by a diffuse and segmental loss of myocardium. The decline in the incidence of myocardial infarction and improved early revascularization in acute transmural ischemia predict a change in the natural history of ischemic heart disease. It is now believed that, minor ischemic episodes, which are known to induce multifocal myocardial degeneration, will predominate in the near future. The objective of the present study was to develop a clinically relevant experimental model for investigation of the pathophysiological significance of diffuse ischemic myocardial lesions. Cardiac performance was gradually depressed by selective intracoronary microembolization in 13 pigs. Left ventricular function was quantitated by ejection fraction (EF), pulmonary pressure, cardiac output, and derivatives of left ventricular pressure. Left ventricular volume was estimated by epicardial echocardiography, using a new, unbiased stereological volume estimator. A chronic substudy was performed in order to characterize the histological changes and to evaluate the feasibility of establishing a chronic preparation of the model. Embolization induced acute left ventricular dysfunction; left ventricular pressure change decreased from 966+/-274 to 637+/-146 mmHg/s, and early diastolic relaxation from 1403+/-515 to 824+/-344 mmHg/s, respectively. Ejection fraction decreased by 45%+/-5% and cardiac output by 29%+/-11%. End-diastolic volume increased significantly, from 66.1+/-13.2 to 77.0+/-19.4 cm3, and end-systolic volume increased from 35.9+/-13.9 to 52.3+/-7.6 cm3. No change in heart rate or left ventricular filling pressure was observed. Diffuse ischemic myocardial injury was identified after a mean follow-up of 40 days. Intracoronary microembolization induces acute left ventricular dysfunction due to microinfarcts. Increased left ventricular end-diastolic volume is the initial compensatory response to the acute impairment of cardiac performance in nontransmural myocardial ischemia. This model is suitable for the evaluation of the hemodynamic changes secondary to acute and chronic diffuse loss of functional myocardium.

Animals↗

PubMed1998

Pharmacological characterization of coronary small arteries from pigs with chronic ischaemic myocardial remodelling.

1. The effect of chronic ischaemic myocardial remodelling on small coronary artery reactivity in vitro was studied in a newly developed pig model. 2. Pigs were subjected to selective intracoronary embolizations with microspheres in the left anterior descending artery and circumflex artery causing scattered myocardial fibrosis. After an observation period of 130 days, heart dimensions and ejection fraction were determined with magnetic resonance imaging. Small arteries were isolated from the left ventricle and mounted as ring preparations in a myograph. Control arteries were taken from matched non-embolized pigs. 3. Compared with control pigs, end-systolic and diastolic volumes increased and left ventricular mass nearly doubled in embolized pigs. This indicates substantial myocardial hypertrophy, as the fraction area of fibrosis was only 12%. 4. Coronary small arteries preconstricted with 30 mmol/l KCI showed a normal contractile response to acetylcholine and 5-hydroxytryptamine. Sensitivity of the relaxation to bradykinin was nearly 3-fold increased and also slightly enhanced to isoprenaline in arteries from embolized pigs compared with controls, whereas relaxation to 5-hydroxytryptamine in the presence of ketanserin was similar. After inhibition of nitric oxide synthase with NG-nitro-L-arginine the sensitivity to acetylcholine increased to a similar extent in arteries from embolized pigs and controls. NG-Nitro-L-arginine abolished the relaxing effects of bradykinin and of 5-hydroxytryptamine in the presence of ketanserin. 5. We conclude that both the contractile function of the smooth muscle cells and the endothelial production or action of nitric oxide is preserved or slightly enhanced in coronary small arteries from pigs with chronic myocardial remodelling.

Acetylcholine↗

PubMed1997

New semiautomated Doppler method for quantification of volumetric flow: intraoperative validation with multiplane transesophageal color Doppler imaging.

We have validated a new semiautomated method for quantification of volumetric flow applied to multiplane transesophageal color Doppler mapping. This Doppler technique assumes only the incompressibility of the fluid and includes variations of flow area. By computing velocity vectors across a surface normal to the point of scanning, volumetric flow can be measured independently of the angle of incidence between the ultrasonic beam and the direction of blood flow. Mitral valvular flow rate was measured during surgery by transesophageal color Doppler echocardiography in 27 patients undergoing coronary artery bypass grafting at 45 sets of observations. The results were compared with those obtained by the thermodilution technique. The mean of the differences between the thermodilution technique and color Doppler echocardiography was 0.06 +/- 0.866 L/min for the mitral valvular flows (mean of differences [thermodilution-color Doppler] &/- 2 SDs of differences). Thus mitral valvular volumetric flow measured by this color Doppler method showed a close agreement to the thermodilution technique during surgery.

Blood Flow Velocity↗

PubMed1996

A new Doppler method for quantification of volumetric flow: in vivo validation using color Doppler.

OBJECTIVES: This study was designed to assess the accuracy of a new Doppler method for quantification of volumetric flow in vivo. BACKGROUND: Noninvasive assessment of volumetric flow through heart valves and the great vessels remains a clinical goal. We present a new method for quantification of volumetric flow based on color Doppler mapping that computes velocity vectors over a surface normal to the point of scanning. This Doppler technique assumes only the incompressibility of the fluid. The method is basically independent of the angle of incidence between the ultrasound beam and the direction of blood flow and includes variations of flow area. METHODS: The color Doppler method was tested in seven anesthetized pigs by measuring pulmonary volumetric flows using multiplane Doppler echocardiography. The results were compared with those obtained by the thermodilution technique. In addition, volumetric flows across the mitral valve were determined in 10 normal volunteers by transthoracic Doppler echocardiography and compared with flows obtained with velocity-encoded magnetic resonance imaging (MRI). RESULTS: The mean value of the differences between the thermodilution technique and color Doppler were -0.16 +/- 0.94 liter/min for pulmonary volumetric flows (mean value of differences for [Thermodilution-Color Doppler] +/- 2 SD of differences). The mean value of the differences between MRI and color Doppler were 0.21 +/- 0.83 liter/min for mitral valvular volumetric flows (mean value of differences for [MRI-Color Doppler] +/- 2 SD of differences). CONCLUSIONS: The method showed close agreement with thermodilution and MRI for assessment of volumetric flow in vivo. It is therefore a noninvasive method with potential applications for cardiac output measurement and for quantification of volumetric flow of valvular insufficiency and restrictive lesions.

Adult↗

PubMed1996

Validation of a new transit time ultrasound flowmeter in man.

OBJECTIVES: To validate the new CardioMed CM 4000 transit time ultrasound apparatus for intraoperative measurement of volume blood flow in vivo in man. DESIGN: Open, prospective series. MATERIALS: Thirteen patients undergoing in situ saphenous vein grafting for chronic critical leg ischaemia and 12 patients subjected to myocardial revascularisation with the internal thoracic artery as coronary bypass. METHODS: During operations, volume blood flows were measured simultaneously by exsanguination from the cut distal end of the in situ saphenous vein graft or the internal thoracic artery and by the transit time flowmeter equipment. In addition, the feasibility to detect arteriovenous fistula during in situ saphenous vein grafting was examined. RESULTS: Within the examined blood flow range, the volume blood flow determined by the transit time method corresponded to the directly measured blood flow. For in situ saphenous vein grafts: y = -2.4 + 0.95.x (r = 0.99; 35 measurements in 13 patients), and for internal thoracic artery grafts: y = -9.6 + 1.1.x (r = 0.99; 21 measurements in 12 patients), where y is blood flow determined by transit time, and x is directly measured blood flow by exsanguination (r = correlation coefficient) as calculated by the least squares regression method. Fistula detection was easy and swift. CONCLUSIONS: The transit time apparatus was simple to use during intraoperative settings and gave fast, precise measurements of volume blood flow.

Adult↗

PubMed1996

Hemodynamic evaluation of a new bileaflet valve prosthesis: an acute animal experimental study.

BACKGROUND AND AIMS OF THE STUDY: A newly developed heart valve (Medtronic Parallel) was tested in an acute animal experimental model. METHODS: Five prototype valves were implanted in the aortic position in seven 90 kg pigs to enable acute evaluation of the hemodynamic performance in terms of turbulent stresses and transvalvular pressure drop. Turbulent stresses in the ascending aorta were measured using a 10 MHz perivascular Doppler echocardiographic transducer designed to measure the radical velocity component at 17 different points covering the aortic cross-sectional area. RESULTS: The drop in transvalvular peak pressure measured with fluid-filled catheters showed a non-linear relationship with cardiac output and was always < 12 mmHg. The Reynolds normal stresses were < 60 N/m2 in systole within 50 ms time windows, which is insufficient to cause mechanical damage of the formed elements of the blood. CONCLUSIONS: From a hemodynamic point of view the performance of the Medtronic Parallel aortic valve is fully acceptable and within the range of other similar, currently available mechanical valves.

Animals↗

PubMed1993

Assessing the severity of aortic valve stenosis by spectral analysis of cardiac murmurs (spectral vibrocardiography). Part II: Clinical aspects.

Assessing the severity of aortic stenosis remains an important clinical problem. The turbulent pressure fluctuations generated by the jet downstream of the stenotic valve produce vibrations in the aortic wall. These vibrations are transmitted through the chest to the skin surface, where they can be recorded as systolic ejection murmurs. The purpose of the present study was to estimate the transvalvular aortic pressure difference by spectral analysis of heart murmurs (spectral vibrocardiography). Forty-four patients with clinical signs of aortic stenosis underwent cardiac catheterization to measure the transvalvular pressure difference. In a double blind prospective study, precordial vibrations were measured prior to catheterization using a dedicated heart sound analyzer (Vibrocard 2000) to calculate the spectral ratio of murmur energy between 100-500 Hz and 20-500 Hz. Three different weighting filters were used to compensate for individual differences in the transthoracic attenuation of murmurs. The square root of the murmur energy ratio correlated linearly with the mean transvalvular pressure difference (r = 0.80, SEE = 13 mmHg) and with the peak transvalvular pressure difference (r = 0.81, SEE = 16 mmHg). The use of individual compensation filters improved the correlation. This study shows that it is possible to estimate the transvalvular pressure difference in patients with aortic valve stenosis by spectral analysis of heart murmurs. It is a fast, simple and cost effective technique, which requires less skill than conventional methods.

Adult↗