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Biomedical subjects

H Piene

Publications and source records attributed to H Piene.

At least 37 records · Page 2Linked to original sources
PubMed1991

[Consequences of diagnostics with magnetic tomography].

Physicians referring patients to examinations by magnetic resonance tomography (MT) were asked to answer almost identical questionnaires before and after the examination. The questions referred to diagnosis and planned patient management. Impact of MT was measured by examining the changes in patient diagnoses and planned management after the MT scans. In 33% of the group (400 patients) the main diagnosis (four digit ICD-9 code) changed after MT. Diagnostic security was better for 43%, and further diagnostic follow-up changed for 56%, surgery for 20% and radiation therapy for 11%. MT was assumed to have had real consequences for 33% of the patients in terms of significant changes in the doctors planned management or in his concept of the disease. In a follow-up study 1.5-2 years after MT, 64% of the referring doctors were of the opinion that the MT scan had had consequences for the patient and they placed the emphasis on less active patient follow-up after MT.

Follow-Up Studies↗
PubMed1991

Haemodynamic effects of arterial compliance, total peripheral resistance, and glyceryl trinitrate on regurgitant volume in aortic regurgitation.

STUDY OBJECTIVE: Afterload reduction is known to reduce regurgitant flow in patients with aortic regurgitation. Both arterial compliance and total peripheral resistance are determinants of afterload. The aim of this study was to evaluate the influence of arterial compliance and total peripheral resistance on the regurgitant volume. DESIGN: The values of arterial compliance and total peripheral resistance were assessed during aortic regurgitation at different regurgitant orifice areas in eight pigs before and after a bolus of glyceryl trinitrate. In a computer model the importance of arterial compliance and total peripheral resistance on the regurgitant volume was assessed by keeping each of them constant while the other variable was changed. MEASUREMENTS AND MAIN RESULTS: In both the experimental and computer models a very strong correlation was found between decreased total peripheral resistance and decreased regurgitant volume. Arterial compliance was of hardly any importance. A bolus of glyceryl trinitrate reduced regurgitant volumes and regurgitant fractions significantly. CONCLUSIONS: Total peripheral resistance is an important factor in influencing the regurgitant volumes at a given regurgitant orifice area in aortic regurgitation, while arterial compliance is of less importance. Glyceryl trinitrate effectively reduces the regurgitant volumes by its effect on peripheral resistance.

Animals↗
PubMed1991

Segmental aortic wall stiffness from intravascular ultrasound at normal and subnormal aortic pressure in pigs.

Segmental aortic wall stiffness was calculated from intravascular ultrasound images and intravascular pressures in six pigs at normal and subnormal aortic pressures (21 sequences of pressures and areas before and after boli of intravenous nitroglycerin). The wall stiffness was expressed as the pressure-strain elastic modulus (Ep). The Ep was calculated from the formula: Ep = delta PR delta R-1 (P, pressure; R, radius) in two different ways. First from maximal and minimal values of pressure and area. Second as the slope of linear regression line of delta PR as a function of delta R from 29 simultaneous recorded pressures and images. The average Ep value for all sequences in the different segments was 0.58 +/- 0.55 10(5) Pa (Method 1) and 0.50 +/- 0.40 10(5) Pa (Method 2). Ep increased with the distance from the heart at normal aortic pressures. At subnormal aortic pressures after intravenous nitroglycerin this relationship was not so evident. At subnormal aortic pressures the calculated Ep values were significantly reduced in the lower half of the abdominal aorta. The phase lag, i.e. hysteresis, between pressure and diameter was demonstrated. Our study shows the applicability of intravascular ultrasound as a tool to evaluate arterial wall stiffness.

Animals↗
PubMed1991

Position of interventricular septum during heart cycle in anesthetized dogs.

The impact of the transseptal pressure gradient (TSP) during the entire heart cycle has not been assessed. This study explores in anesthetized open-chest dogs the interventricular septum's relative position to the anteroposterior transverse diameter (Dap) of the left ventricle (LV). By varying preload and afterload for both LV and right ventricle (RV) and inotropy in LV, a wide range of TSP was generated. By ultrasonomicrometry the distance between the Dap and the midpoint of septum was recorded. 1) Loops of the septal-LV free-wall diameter vs. Dap showed that the LV transverse cross section independent of loading conditions tended to reach a circular form during systole. 2) Paradoxical movement of the intraventricular septum occurred when TSP was less than zero but was not dependent on an increase of TSP. 3) TSP's influence on septum's position was reduced to one-tenth when changing from end diastole to end systole. 4) During systole independent of level of LV performance, LV pressure had approximately 50% less influence on septal position than RV pressure. 5) During depressed LV performance a similar pattern was evident during diastole. 6) The pericardium had no influence on septum's position. This study demonstrates that the position of the intraventricular septum is significantly influenced by the time-varying elastance of LV and the septum itself, and that RV pressure changes have a greater impact on septal position than LV pressure changes.

Anesthesia, Intravenous↗
PubMed1991

[Radiology in Scandinavia].

In 1987 the Nordic Institutes of Hospital Research joint co-operation on medical technology assessment (NEMT) performed a study of the national differences in the utilization of diagnostic techniques in the radiological laboratories. Major differences between the countries were found in both total and specific examination rates. In total numbers of conventional investigations, Finland performed about 60 per cent more investigations than the average of Sweden, Denmark and Norway, which all were of the same level of approximately 470 examinations per 1,000 inhabitants. The difference was attributed mainly to X-ray investigations executed at the primary health care level in Finland. Other remarkable differences were in particular observed in techniques of increasing or decreasing importance.

Angiography↗
PubMed1990

Estimation of arterial compliance in aortic regurgitation: three methods evaluated in pigs.

Three methods for measuring arterial compliance when aortic regurgitation is present are examined. The first two methods are based on a Windkessel model composed of two elements, compliance C and resistance R. Arterial compliance was estimated from diastolic pressure waveforms and diastolic regurgitant flow for one method, and from systolic aortic pressure waveforms and systolic flow for the other method. The third method was based on a three-element Windkessel model, composed of characteristic resistance r, compliance C and resistance R. In this method arterial compliance was calculated by adjusting the model to the modulus and phase of the first harmonic term of the aortic input impedance. The three methods were compared and validated in six anaesthetised pigs over a broad range of aortic pressures. The three methods were found to give quantitatively similar estimates of arterial compliance at mean aortic pressures above 60 mm Hg. Below 60 mm Hg, estimates of arterial compliance varied widely, probably because of poor validity of the Windkessel models in the low pressure range.

Animals↗
PubMed1990

Quantification of aortic regurgitation by Doppler echocardiography: a new method evaluated in pigs.

We have developed a method to quantify aortic regurgitant orifice and volume, based on measurements of the velocity of the regurgitant jet, aortic systolic flow, the systolic and diastolic arterial pressures, a Windkessel arterial model, and a parameter estimation technique. In six pigs we produced aortic regurgitant flows between 2.1 and 17.8 ml per beat, i.e. regurgitant fractions from 0.06 to 0.58. Pulmonary and aortic flows were measured with electromagnetic flow probes, aortic pressure was measured invasively, and the regurgitant jet velocity was obtained with continuous-wave Doppler. The parameter estimation procedure was based on the Kalman filter principle, resulting primarily in an estimate of the regurgitant orifice area. The area was multiplied by the velocity integral of the regurgitant jet to estimate regurgitant volume. A strong correlation was found between the regurgitant volumes obtained by parameter estimation and the electromagnetic flow measurement. These results from our study in pigs suggest that it may be possible to quantify regurgitant orifice and volume in patients completely noninvasively from Doppler and blood pressure measurements.

Animals↗
PubMed1990

Estimation of regurgitant volume and orifice in aortic regurgitation combining CW Doppler and parameter estimation in a Windkessel-like model.

A method for noninvasive estimation of regurgitant orifice and volume in aortic regurgitation is proposed and tested in anesthetized open chested pigs. The method can be used with noninvasive measurement of regurgitant jet velocity with continuous wave ultrasound Doppler measurements together with cuff measurements of systolic and diastolic systemic pressure in the arm. These measurements are then used for parameter estimation in a Windkessel-like model which include the regurgitant orifice as a parameter. The aortic volume compliance and the peripheral resistance are also included as parameters measurements in the open chest pigs are used. Electromagnetic flow measurements in the ascending aorta and pulmonary artery are used for control, and a correlation between regurgitant volume obtained from parameter estimation and electromagnetic flow measurements of 0.95 over a range from 2.1 to 17.8 mL is obtained.

Animals↗
PubMed1988

Optimal and actual end systolic pressure-volume relations in dogs and rabbits. Including new method of Emax determination.

Under the assumption that a ventricle and its arterial load are normally matched according to work optimization, a relation between left ventricular (LV) mechanical performance as described by the slope (Emax) of the end systolic pressure-volume relationship (ESPVR), mean systolic pressure during ejection (mSLVP), and stroke volume (SV), is proposed: optimum Emax = E' = mSLVP/SV. Slope (Emax) was obtained, in 6 dogs and 9 rabbits, by establishing relations among ejected volume and LV diameter squared (D2) in control beats, and among pressure and D2 at end systole (ES) in series of beats of varying load, accomplished either by acute aortic constriction (AOC) or inferior caval occlusion (IVCO). Slope in dogs was also obtained by direct measurements of ventricular volume by a conductance catheter and the results were compared with the above method. A dimensionless index, alpha = Emax/E', (optimal value = 1.0) was calculated to indicate how well the ventricle and arterial system were matched. In dogs, E' = 10.9 +/- 2.1 mmHg ml-1, Emax = 8.1 +/- 2.6 (AOC) and 7.1 +/- 2.5 (IVCO), hence alpha = 0.79 +/- 0.23 (AOC) and 0.68 +/- 0.15 (IVCO). In rabbits, E' = 54.1 +/- 20.0 mmHg ml-1, Emax = 64.8 +/- 15.9 (mmHg ml-1), hence alpha = 1.23 +/- 0.33. Alpha = 1.0 fell outside the 95% confidence interval only in experiments of dogs subjected to IVCO.

Animals↗
PubMed1988

Optimal matching between canine left ventricle and afterload.

A parabolic relationship exists between ventricular external work and arterial load at given preload and contractility. Previous data indicate that the working point falls close to the parabola optimum. By combining the left ventricular (LV) end-systolic pressure-volume relationship (ESPVR) and an equation describing external stroke work, optimum values of stroke volume (SV), the slope (Emax) of the ESPVR, and arterial resistance (Rp) corresponding with the optimum (i.e., mSV, mEmax, mRp) were obtained. Experiments in anesthetized dogs were performed to test whether mSV, mEmax, and mRp also correspond to observed SV, Emax, and Rp at three different levels of volume load (right atrial pressure, RAP) before and after acute depression of LV contractility. Comparisons of observed and optimal values of SV, Emax, and Rp were made before and after LV depression. Before embolization, the ratios were SV/mSV 1.10-1.20 (RAP 5-15 mmHg); Emax/mEmax 1.21-1.41; and Rp/mRp 0.84-0.69. After LV depression, SV/mSV was 0.80-0.83, Emax/mEmax was 0.78-0.71, and Rp/mRp was 1.56-1.46. The ratios were all significantly changed (P less than 0.01) by the induced LV depression. The present analysis may offer a new tool to detect nonoptimal relations between cardiac and arterial functions.

Animals↗
PubMed1986

Left ventricular end-systolic pressure volume relations in healthy young men.

The purpose of the present study was to establish the relationship of left ventricular end-systolic volume vs. mean systemic pressure in variously afterloaded beats in a group of healthy, young, men (n = 6, age 24 +/- 0.9 years). The relationship was expressed by the slope (Emax) of the line connecting pressure-volume co-ordinates and its extrapolated intercept (Vd) of the volume axis. The slope was calculated by linear regression of mean systemic arterial pressure (mean SAP, measured by catheter in the radial artery) vs. end-systolic left ventricular volume (ESV, estimated from cross-sectional, 4-chamber echocardiographic images). Recordings were obtained at resting, reduced (nitroglycerin infusion), and elevated (metaoxedrin infusion) blood pressure. Individual Emax values ranged from 1.05 to 2.01 mmHg ml-1; Vd was consistently found to be negative, ranging from -4.7 to -54.8 ml. All individual relations were statistically significant (P less than 0.05 to P less than 0.001). Group values were Emax = 1.27 +/- 0.25 (SE) mmHg ml-1, Vd = -43.3 +/- 7.5 (SE) ml, and Emax indexed for body surface area, Emax ind = 2.54 +/- 0.49 (SE) mmHg ml-1 m-2. We further examined the validity of proposed optimal relations among Emax, heart rate (HR) and systemic resistance (Rs): Emax/HR = Rs, and among ejection fraction (EF), EDV and Vd: EF = 0.5 (1 - EDV/Vd). For the group Emax/HR = 0.023 +/- 0.003 and Rs = 0.016 +/- 0.004 (mmHg ml-1 min-1), i.e., a deviation from equivalence of 30% (P less than 0.001). EF (= 0.72 +/- 0.02) deviated by 18% (P less than 0.001) from its proposed optimum (0.5 (1 - Vd/EDV) = 0.61 +/- 0.06).

Adult↗
PubMed1986

The effect of contractility and preload on matching between the canine left ventricle and afterload.

We define matching between ventricle and afterload to imply that the ventricle is adapted to its afterload to yield maximum external work output. For the ventricle, this optimal adaption will depend on end-diastolic dimension, heart rate, and contractility. Because contractility is impaired during ventricular failure, we propose that the adaption between ventricle and load is not as good during failure as during normal conditions. According to our definition, this implies that during failure external work output is less than maximum. Ventricle-load matching is then not present, i.e., a mismatch exists between ventricle and load. This hypothesis was tested in a canine preparation in which arterial load of the left ventricle was varied from one beat to the next. Left ventricular depression was induced by injections of 50 micron microspheres into the left coronary bed. We observed left ventricular stroke volume and external work during afterload variations at three different preload levels before and after microembolization. Before embolization the control observations of work and stroke volume were positioned at the apex of parabolas relating work to stroke volume. After embolization, however, control observations fell down along the left limb of the parabolas. These observations were independent of preload. Thus this study, carried out in a preparation with the heart in situ, supports the idea that the normal left ventricle is matched to its load and demonstrates ventricle-load mismatch when the left ventricle is failing.

Animals↗
PubMed1985

External work and arterial load in canine left ventricular ischaemic failure: evidence of ventricle-load mismatch.

It has been proposed that a normal ventricle and its arterial load constitute a matched system, and that such matching is not present during ventricular failure, i.e., failure represents a state of mismatch between ventricle and arterial load. To investigate this assumption we studied the relationship between external work and load in an equatorial segment of left ventricle (LV) in an intact canine preparation under the hypothesis that the LV works at the peak of the work versus load relationship during control conditions, but is shifted from this peak during LV failure. LV systolic wall force (F) and circumferential segment work (W) were calculated in eight pentobarbital anaesthetized, open-chest dogs from LV pressure (P) and anterior-posterior diameter (D) before and after induction of LV ischaemic failure (50 micron microspheres were injected into the left coronary vascular bed). Variations of arterial load were created by acute partial occlusions of the aorta, raising aortic pressure by 45 mm Hg before and 15 mm Hg during failure. Before failure W was unaffected by the variations of arterial load, but W decreased significantly during failure. From the relation between end-systolic F and D, theoretically optimal F (Fopt) corresponding to maximum W was estimated. Before failure the observed F did not differ significantly from Fopt, but the observed F was significantly greater than Fopt during failure. These findings support the notion that ventricular failure represents a state of mismatch between the ventricle and its systolic load.

Animals↗
PubMed1984

Impedance matching between ventricle and load.

Impedance matching in the cardiovascular system is discussed in light of two models of ventricle and load: a Thevenin equivalent consisting of a hydromotive pressure source and an internal, source resistance and compliance in parallel; and a time-varying compliance filled from a constant pressure source and ejecting into a load of three components, a central resistor, a compliance, and a peripheral resistance. According to the Thevenin analog, the energy source and the load are matched when the load resistance is T/t times the internal source resistance (T is total cycle length, t is systolic time interval). Both from this model and from the variable compliance model it appears that optimum matching between source and load depends on the compliance of the Windkessel, as low compliance shifts the matching load resistance to a low value. Animal experiments (isolated cat hearts) indicated that both left and right ventricles at normal loads work close to their maxima of output hydraulic power, and, according to experiments in the right ventricle, maximum power output is related to load resistance and compliance as predicted by the above models. From an experimentally determined relationship among instantaneous ventricular pressure and volume (right ventricle of isolated cat hearts), an optimum load impedance was calculated on the basis of the assumption that the ratio between stroke work and static, potential energy developed in the ventricular cavity is maximum. The optimum load impedance found by this procedure closely resembles the normal input impedance of the cat lung vessel bed.

Biomedical Engineering↗