Biomedical subjects

H Nygaard

Publications and source records attributed to H Nygaard.

At least 55 records · Page 3Linked to original sources

PubMed1993

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

Assessing the severity of aortic stenosis remains an important clinical problem. The turbulent pressure fluctuations generated by the confined jet down-stream 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 measured as systolic ejection murmurs. The purpose of the present study was to find the relationship between the severity of aortic valve stenosis and the frequency content of the precordial systolic murmurs, and to evaluate the transthoracic attenuation of murmurs and its variation from patient to patient. Twenty-four patients with clinical signs of aortic stenosis underwent cardiac catheterization to measure the peak transvalvular pressure difference. The mean energy density spectrum of the measured systolic precordial murmurs was calculated and the murmur energy ratio between 100-500 Hz and 20-500 Hz was correlated to the transvalvular pressure difference. The inter-individual variability of the transthoracic attenuation was evaluated by calculating the transthoracic transfer function from simultaneous measurements of precordial vibrations at the second right intercostal space and intravascular recordings of high frequency pressure fluctuations in the ascending aorta. The transvalvular pressure difference and the square root of the murmur energy ratio correlated well (r = 0.81, SEE = 27 mmHg). In the frequency range from 10-500 Hz the transthoracic transfer function could be modelled by a low-pass filter function with a low frequency attenuation of 36 +/- 7.7 dB (mean +/- SD), a corner frequency of 26 +/- 12 Hz and an attenuation slope of -29 +/- 7.9 dB/decade. Spectral analysis of systolic murmurs might be an attractive non-invasive addition to the array of techniques already in use for assessing the severity of aortic stenosis. It is a simple and cost effective technique, and requires less skill and time for data analysis than conventional methods.

Adult↗

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↗

PubMed1992

Two-dimensional color-mapping of turbulent shear stress distribution downstream of two aortic bioprosthetic valves in vitro.

Since artificial heart valve related complications such as thrombus formation, hemolysis and calcification are considered related to flow disturbances caused by the inserted valve, a thorough hemodynamic characterization of heart valve prostheses is essential. In a pulsatile flow model, fluid velocities were measured one diameter downstream of a Hancock Porcine (HAPO) and a Ionescu-Shiley Pericardial Standard (ISPS) aortic valve. Hot-film anemometry (HFA) was used for velocity measurements at 41 points in the cross-sectional area of the ascending aorta. Three-dimensional visualization of the velocity profiles, at 100 different instants during one mean pump cycle, was performed. Turbulence analysis was performed as a function of time by calculating the axial turbulence energy within 50 ms overlapping time windows during the systole. The turbulent shear stresses were estimated by using the correlation equation between Reynolds normal stress and turbulent (Reynolds) shear stress. The turbulent shear stress distribution was visualized by two-dimensional color-mapping at different instants during one mean pump cycle. Based on the velocity profiles and the turbulent shear stress distribution, a relative blood damage index (RBDI) was calculated. It has the feature of combining the magnitude and exposure time of the estimated shear stresses in one index, covering the entire cross-sectional area. The HAPO valve showed a skewed jet-type velocity profile with the highest velocities towards the left posterior aortic wall. The ISPS valve revealed a more parabolic-shaped velocity profile during systole. The turbulent shear stresses were highest in areas of high or rapidly changing velocity gradients. For the HAPO valve the maximum estimated turbulent shear stress was 194 N m-2 and for the ISPS valve 154 Nm-2. The RBDI was the same for the two valves. The turbulent shear stresses had magnitudes and exposure times that might cause endothelial damage and sublethal or lethal damage to blood corpuscules. The RBDI makes comparison between different heart valves easier and may prove important when making correlation with clinical observations.

Aortic Valve↗

PubMed1992

Quantitation of the turbulent stress distribution downstream of normal, diseased and artificial aortic valves in humans.

Damage to blood corpuscles seems to be related to the magnitude and exposure time of the turbulent shear stresses (TSS). According to in vitro studies the critical TSS level for lethal erythrocyte and thrombocyte damage is 150-400 N/m2, for exposure times within physiological ranges. To study the distribution of TSS in the human ascending aorta, a hot-film anemometer needle probe was used to register blood velocities at 41 evenly distributed measuring points in the cross-sectional area 5-6 cm downstream of the aortic annulus. Measurements were made in the ascending aorta after normal aortic valves (prior to coronary bypass surgery), after stenotic aortic valves, and after implantation of either St. Jude Medical or Starr Edwards Silastic Ball valves. Three-dimensional visualization of velocity profiles were performed and Reynolds normal stresses (RNS) were calculated within 50-ms overlapping time windows in systole. By coordinating the mean RNS for each time window and for all 41 measuring points, 2-dimensional color-coded mapping of the RNS distribution was made. Based on the velocity profiles and the RNS distribution a relative blood damage index (RBDI) was calculated to incorporate the magnitude and exposure time for RNS in the entire cross-sectional area into one parameter. Turbulent shear stresses were estimated by using a previously determined correlation equation between RNS and TSS. After normal aortic valves, RNS was below 4 N/m2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Three-dimensional visualization of velocity profiles in the porcine abdominal aortic trifurcation.

To study the local distribution of blood velocities in the abdominal aorta and trifurcation, hot-film anemometry was used for point blood velocity measurements in the entire cross-sectional area in the abdominal aorta and abdominal aortic trifurcation in pigs weighing 90 kg. The geometry was visualized by use of a casting procedure. General hemodynamic and geometric parameters in the abdominal aorta were comparable to values found in humans. The porcine trifurcation differed somewhat from the human bifurcation. The velocity measurements in the abdominal aorta showed consistently skewed velocity profiles with the highest velocities at the anterior vessel wall. No signs of developed turbulence were found. Velocity measurements in the external iliac vessels showed high velocities at the flow divider, and low velocities with signs of retrograde flow during part of diastole at the lateral vessel wall.

Animals↗

PubMed1991

Velocity field studies at surgically imposed arterial stenoses on the abdominal aorta in pigs.

In order to describe velocity profiles and the size of deterministic and non-deterministic velocity disturbances at arterial stenoses, symmetrical and asymmetrical stenoses with intended area reductions of 50% ('moderate') and 85% ('severe') were applied on the abdominal aorta in six pigs. Blood velocities were registered by hot-film anemometry in 21 measuring points distributed across the vessel cross-sectional area in one pre-stenotic and three post-stenotic positions. Signal analysis included ensemble averaging, the high-pass filtering technique, and three-dimensional visualization. None of the stenoses affected the pre-stenotic velocity field. Downstream moderate stenoses flow separation and vortex formation were present. Moderate asymmetric stenoses induced turbulence in the post-stenotic velocity field. Immediately downstream of severe stenoses a prominent post-stenotic jet was present. Farther downstream, a multitude of coherent vortices and turbulence dominated the flow field. The transverse distribution of turbulence intensity paralleled with the peak systolic velocity profile, whereas transverse profiles of the relative turbulence intensity (turbulence intensity/mean velocity) revealed peak values in flow field locations with high velocity gradients. Velocity parameters for symmetric and asymmetric severe stenoses were highly comparable. However, the exact degree of stenosis was significantly higher for symmetrical (85%) than for asymmetrical (76%) stenoses. Therefore, recalling that stenosis severity strongly influences the development of velocity disturbances, this indicates that asymmetry of a stenosis is a predictor for blood velocity disturbances.

Animals↗

PubMed1990

Estimation of turbulent shear stresses in pulsatile flow immediately downstream of two artificial aortic valves in vitro.

Measuring turbulent shear stresses is of major importance in artificial heart valve evaluation. Bi- and unidirectional fluid velocity measurements enable calculation of Reynolds shear stress [formula: see text] and Reynolds normal stress [formula: see text]. tau is important due to the relation to hemolysis and thrombus formation, but sigma is the only obtainable parameter in vivo. Therefore, determination of a correlation factor between tau and sigma is pertinent. In a pulsatile flow model, laser Doppler (LDA) and hot-film (HFA) anemometry were used for simultaneous bi- and unidirectional fluid velocity measurements downstream of a Hall Kaster and a Hancock Porcine aortic valve. Velocities were registered in two flow field locations and at four cardiac outputs. The velocity signals were subjected to analog signal processing prior to digital turbulence analysis, as a basis for calculation of tau and sigma. A correlation factor of 0.5 with a correlation coefficient of 0.97 was found between the maximum Reynolds shear stress and Reynolds normal stress, implying [formula: see text]. In vitro estimation of turbulent shear stresses downstream of artificial aortic valves, based on the axial velocity component alone, seems possible.

Aortic Valve↗

PubMed1989

Turbulent stresses downstream of porcine and pericardial aortic valves implanted in pigs.

Because late valve-related complications such as hemolysis and thromboembolic events are considered related to flow disturbances caused by the inserted valve, velocity fields downstream of aortic valve prostheses were studied in pigs. Acute hemodynamic evaluation of size 25-mm porcine and pericardial aortic valve prostheses 1 diameter downstream of the valve ring was performed using dynamic three-dimensional visualization of velocity profiles and spatial distribution of turbulence. Point blood velocity signals obtained with a 1-mm hot-film anemometer needle probe were used to compute Reynolds normal stresses (RNS) by calculation of the turbulent velocity energy of the axial velocity component in the systole. The porcine valves caused a skewed velocity and turbulence profile revealing mean spatial systolic RNS at 70 nm-2 +/- 35 nm-2 (+/- SD). The spatial maximum RNS was 275 +/- 139 nm-2. Corresponding values for the pericardial valves were 20 +/- 11 nm-2 and 72 +/- 46 nm-2. The pericardial valves revealed plug-shaped velocity profiles and turbulent profiles with slightly higher RNS values at the stent posts. From a hemodynamic point of view, these acute studies indicate superiority of the pericardial valves compared to the porcine valves. The turbulent stresses found in this study are of a magnitude that may cause blood corpuscular and endothelial damage.

Animals↗

PubMed1988

In vitro stress measurements in the vicinity of six mechanical aortic valves using hot-film anemometry in steady flow.

Based on hot-film anemometry, point velocity measurements in the total cross sectional area 1 and 2 diameters downstream of: Björk-Shiley Standard, Convex-Concave and Monostrut, Hall-Kaster (Medtronic-Hall), St. Jude Medical and Starr-Edwards Silastic Ball aortic valves were made. The spatial distribution of Reynolds Normal Stresses (RNS) was visualized three-dimensionally in order to point out where and to what extent the highest RNSs were found. The measurements were made in steady flowing glycerol mixture at flow rates 10, 20 and 30 l. min-1 corresponding to mean velocities of 27, 54 and 81 cm s-1. The highest maximum RNS values were around 250 Nm-2 and were found downstream of the Björk-Shiley Monostrut and Starr-Edwards Ball valves. The lowest maximum RNSs were found downstream of the St. Jude Medical and Hall-Kaster (Medtronic-Hall) valves (125-140 Nm-2). The Starr-Edwards valve had the highest mean RNS (117 Nm-2) followed by the Björk-Shiley Monostrut (87 Nm-2). These simplified measurements of artificial heart valve performances concerning RNS, enhance the interpretation of results in more complicated flow models not to say in vivo.

Aortic Valve↗

PubMed1988

Turbulent stress measurements downstream of six mechanical aortic valves in a pulsatile flow model.

In a pulsatile flow model aortic Björk-Shiley Standard, Convex-Concave and Monostrut valves were investigated together with the Hall-Kaster (Medtronic-Hall), St Jude Medical and Starr-Edwards Silastic Ball valve using hot-film anemometry. Three-dimensional visualization of average systolic Reynolds normal stresses (RNS) reflected the design of the valves. Mean average RNS were used for comparison of the fluid dynamic performance along with Velocity Energy Ratio (VER100) and Turbulence Energy Ratio (TER) as a relative turbulence intensity for pulsatile flow. Mean average RNS ranged from 13.2 to 37.6 Nm-2 for all the valves with the highest levels for the Björk-Shiley Standard and Starr-Edwards Ball valve and lowest values for the St Jude Medical valve and with the Hall-Kaster (Medtronic-Hall), Björk-Shiley Convex-Concave and Monostrut valves in between.

Aortic Valve↗

PubMed1988

A model for acute haemodynamic studies in the ascending aorta in pigs.

Since data on velocity fields in the ascending aorta downstream of normal aortic valves in pigs have not yet been obtained velocity profiles were visualised using a hot film anemometer needle probe before and after total cardiopulmonary bypass and cold cardioplegic arrest. Furthermore, measurements were made during increased heart rate and cardiac output. A dynamic three dimensional visualisation of velocity fields showed a skewed clockwise rotating velocity profile, developing from peak systole and continuing throughout the systolic deceleration phase. This pattern was consistent regardless of the haemodynamic state. Heart rate was increased to 180 beats.min-1 and cardiac output by a maximum of 91%. It is concluded that the pig model is valuable for haemodynamic studies in the ascending aorta before and after cold cardioplegic arrest and that the velocity profiles found in this study are important basic data for velocity field studies downstream of artificial heart valves implanted in the aortic position.

Animals↗

PubMed1988

Velocity fields and turbulent stresses downstream of biological and mechanical aortic valve prostheses implanted in pigs.

Since detailed knowledge about velocity fields downstream of heart valve prostheses obtained from in vitro studies has not been followed up by similar detailed studies in vivo a pig model for acute velocity field studies downstream of aortic valve prostheses was established. Two mechanical and two bioprosthetic valves were studied and a dynamic three dimensional visualisation of velocity fields one diameter downstream performed under different haemodynamic conditions in a total of 22 pigs. The Ionescu-Shiley pericardial valve had velocity fields very similar to the normal native porcine aortic valve. The Edwards-Carpentier porcine valve caused a jet type flow, and the valve design of the St Jude Medical and Björk-Shiley Monostrut valves was reflected in the velocity profile. Normalised (mean(SEM] systolic Reynolds normal stresses in the total cross sectional area were: native porcine 15(1.5) Nm-2; St Jude Medical 24(3.4) Nm-2; Björk-Shiley Monostrut 25(1.6) Nm-2; Edwards-Carpentier Supra-annular 51(6.6) Nm-2; Ionescu-Shiley Pericardial 19(2.0) Nm-2. Reynolds normal stresses were higher in areas of rapidly changing or constantly high velocity gradients.

Animals↗

PubMed1988

Zuclopenthixol and melperon in the treatment of elderly patients: a double-blind, controlled, multi-centre study.

A double-blind study was carried out in 53 elderly patients in 6 geriatric nursing homes to assess the effectiveness of the neuroleptics, zuclopenthixol and melperon (flubuperone), in the relief of restlessness, aggressiveness and other such symptoms. The initial daily dose was 4 mg zuclopenthixol or 75 mg melperon, increased if necessary over the treatment period of 4 weeks. Assessments were made on entry and after 1, 2 and 4 weeks of treatment of the overall severity of illness and of individual symptoms. The results showed that there was significant improvement in the condition of patients in both treatment groups and a significant reduction in mean total as well as in the main single symptom scores. These changes were already apparent after 1 week of treatment. Although there was a tendency for faster improvement in the zuclopenthixol group, there were no significant differences between the groups in any of the parameters assessed. Side-effects were few and generally mild and transient.

Aged↗

PubMed1988

Analysis of velocity in the ascending aorta in humans. A comparative study among normal aortic valves, St. Jude Medical and Starr-Edwards Silastic Ball valves.

To analyze velocity spectral energy distribution in humans, blood velocities were recorded by means of hot-film anemometry at 41 predetermined measurement points in the cross-sectional area of the ascending aorta approximately 6 cm downstream of the aortic valves. Measurements were made in 8 patients with normal aortic valves, in 4 after insertion of a St. Jude Medical (SJM) aortic valve and in 3 after insertion of a Starr-Edwards Silastic Ball (SSB) aortic valve. Data analysis based on Fast Fourier Transform demonstrated that turbulence energy was lower in patients with normal aortic valves than in patients after insertion of an artificial valve in the aortic position and probably more pronounced after SSB valves than after SJM valves. The spatial distribution of the turbulence energy above 100 Hz was more irregular than corresponding laminar velocities previously presented. The VER100 (Velocity Energy Ratio at 100 Hz, i.e. the velocity energy above 100 Hz divided by the total velocity energy) proved useful for evaluating differences in flow disturbances downstream of different aortic valves. The mean VER100 in the three categories of patients were respectively 0.3, 1.4, and 2.1%.

Adult↗

PubMed1987