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T van der Werf

Publications and source records attributed to T van der Werf.

At least 55 records · Page 3Linked to original sources
PubMed1987

Reference values for pulsed Doppler signals from the blood flow on both sides of the aortic valve.

Pulsed Doppler signals were recorded in 215 healthy subjects, 120 males and 95 females, between 1 and 65 years of age. The measurements were performed in the left ventricular outflow tract (LVOT) and in the ascending aorta (AAO). Amplitude spectra from the Doppler signals were stored in digital form together with adjustment data for the instrument, the simultaneously registered ECG and respiration signal. The maximum velocity (Vmax), the maximum acceleration (Amax) and the width of the velocity distribution around Vmax (width) were derived from these spectra and used for the characterization of the signals. These parameters were computed without observer interaction using a computer program. Effects of age, sex, body surface area, heart rate and respiration were studied. Reference ranges were calculated. The following conclusions can be drawn: Vmax and Amax in the AAO decrease clearly with increasing age from approximately 100 to 60 cm s-1 and from 2000 to 1000 cm s-2 (medians), respectively. The variation of the width in the AAO is greater for people over 45 years. Vmax, Amax and width in the LVOT increase slightly with advancing age from approximately 60 to 80 cm s-1, 800 to 1000 cm s-2 and 12 to 15 cm s-1 (medians), respectively. These parameters of flow were either unrelated or only weakly related to other physiological variables in this study group.

Adolescent↗
PubMed1986

The influence of anatomic evolution of coronary artery disease on left ventricular contraction: an angiographic follow-up study of 300 nonoperated patients.

The impact of the evolution of obstructive coronary artery disease (CAD) on left ventricular (LV) function was studied in 300 nonoperated patients who had had two angiographic studies. The interval between studies ranged from 6 months to 10 years (mean 29.6 months). Quantitative analysis of LV contractions in right anterior oblique projections was performed with the use of a computer program for calculation of ejection fraction (EF) and regional wall motion (RWM) according to the method of Leighton. No progression of CAD was found in 131 patients. Progression of CAD was found in 169 patients. In the patients without progression and in 75 patients who had progression to less than total obstruction, no changes in EF and RWM were found. In the 67 patients in whom progression from less than 90% narrowing to occlusion had occurred a significant decrease in EF and RWM was found. In the 27 patients with progression from subtotal narrowing to occlusion, however, no change in LV function was found. A myocardial protective value of angiographically visible preexistent collaterals could not be demonstrated. We conclude that absence of progression of CAD implies that LV function does not deteriorate and that slow progression to occlusion, via a stage of subtotal narrowing, generally does not influence LV function.

Cardiac Catheterization↗
PubMed1985

Is there an indication for coronary angiography in patients under 60 years of age with no or minimal angina pectoris after a first myocardial infarction?

Coronary angiography and exercise stress tests were performed in 91 consecutive patients under 60 years of age having either no or only mild angina pectoris with or without medication after a first myocardial infarction. Nine (10%) patients had angiographic high risk coronary artery disease defined as three vessel disease, left main stenosis, or proximal stenosis of the left anterior descending artery. Eighteen patients had a positive electrocardiographic exercise stress test including eight of the nine patients with angiographic high risk coronary artery disease. It may be concluded therefore that coronary angiography to detect high risk coronary artery disease in this group can be restricted to patients with a positive exercise stress test. This policy would obviate the need for about 80% of coronary angiograms performed in this age group.

Adult↗
PubMed1985

Some circulatory aspects of the oxygen transport in patients with emphysema.

67 patients were studied by pulmonary function and heart catheterization at rest, during exercise and after 20 min 100% oxygen breathing. 14 patients were diagnosed as having COLD without chronic respiratory insufficiency (CRI). 45 patients were considered to be suffering from pulmonary emphysema (COLD + CRI). In this group, 23 patients had normal hemoglobin concentrations (CHb), 14 patients demonstrated decreased values and 8 had secondary polycythemia. All groups of patients had a normal cardiac output (CO), oxygen consumption (VO2) and pulmonary wedge pressure (Pw) at rest and after oxygen breathing. In the group with COLD and CRI high values for pulmonary vascular resistance (Rp) were found, most pronounced in those with polycythemia. All groups of patients except the polycythemia group demonstrated a significant decrease of Rp during oxygen breathing, but only a slight decrease of pulmonary arterial pressure (Ppa). It can be concluded that a normal quantity of oxygen transport to peripheral tissues in patients with arterial hypoxemia can be achieved by maintaining normal values for arterial mixed venous oxygen content without a shift of the oxygen dissociation curve.

Adult↗
PubMed1984

A computer-aided method to evaluate the function of implanted Björk-Shiley prosthetic heart valves.

Evaluation of the function of implanted prosthetic valves is important in early diagnosis of valve dysfunction. Björk-Shiley valves contain two radiopaque rings, which are projected as ellipses in cineradiography. From these ellipses the actual valve opening angle can be calculated. A computer-aided method was developed that enables measurement of ellipse characteristics reliably, independent of projection angle and valve opening. It is demonstrated that calculated and real opening angles differ less than 2 degrees with this method. Using the same technique the tilting angle of the valve ring during the cardiac cycle is computed for evaluation of progression of valve dehiscense in case of a paravalvular leak. Application of the method to patient data is illustrated by three cases. The method is suitable for use by technicians. It can be implemented on a small microprocessor system. The method proved to be a powerful tool in the evaluation of patients with implanted Björk-Shiley valves.

Aortic Valve↗
PubMed1984

The concept of apparent cardiac arrest as a prerequisite for coronary digital subtraction angiography.

This study was undertaken to evaluate the possible use of digital subtraction applied after selective coronary arteriography. An identical position of the objects with and without contrast medium is an absolute requirement for the application of subtraction techniques. Because coronary arteries are in continuous motion, the subtraction technique cannot be applied without certain precautions. In our study, only images from corresponding moments in the cardiac cycle before and after contrast injection were matched for subtraction, that is, the concept of apparent cardiac arrest. To prevent variations in cardiac contractions due to varying RR intervals, heart rate was controlled by regular right atrial stimulation. Moreover, the stimulation rate and cine frequency were in synchrony, which was effected by triggering both on the frequency of the electric main alternating current (50 cycles/s). In this way, each cardiac cycle contains exactly the same number of frames at corresponding moments. A combination of the application of the concept of apparent cardiac arrest with the subtraction technique in 12 patients resulted in good quality images. Furthermore, better visualization of capillary filling with contrast material was obtained than with conventional coronary arteriography.

Capillaries↗
PubMed1984

Prognostic value of Q waves, R/S ratio, loss of R wave voltage, ST-T segment abnormalities, electrical axis, low voltage and notching: correlation of electrocardiogram and left ventriculogram.

Data on the correlation of left ventricular segmental wall motion and electrocardiographic findings are, except for Q waves and ST segment elevation, still controversial. Therefore, in addition to Q waves and ST segment elevation, eight features of the electrocardiogram were studied in 265 patients, 61 with normal coronary arteries and 204 with coronary artery disease. Patients with a QRS duration of 0.12 second or greater were excluded. Left ventricular wall motion was assessed in the 30 degrees right anterior oblique and the 60 degrees left anterior oblique projections and analyzed by the Stanford method and a modification of that method, respectively. Asynergy of a particular segment correlated well with the presence of Q waves in the corresponding electrocardiographic lead or leads, but was also found in other segments. There was a significant (p less than 0.001) correlation between the number of leads with Q waves and the degree of extension of asynergy. The R/S ratio in lead V1 and Q waves in lead V6 appeared to be the most informative about the posterior wall. Loss of R wave voltage had a lower predictive value for segmental asynergy than did Q waves in the same lead. Among patients with electrocardiographic findings of an infarct, asynergy was found in 83 to 94%. Patients having Q waves in combination with ST segment elevation manifested more severe asynergy than did patients whose Q waves were not associated with ST elevation. New data are presented for lateral and posterior infarction. Patients having left-axis deviation, low voltage and QRS notching had severe asynergy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Assessment of the opening angle of implanted Björk-Shiley prosthetic valves.

A method has been developed in which cineradiography is used for the assessment of the opening angle of implanted Bjork-Shiley prosthetic valves. The method is based on the fact that the ring and the disc, which are known to be circular, appear to be elliptical on x-ray films. The spatial position of the valve can be retrieved from the characteristics of these ellipses when vectoranalysis is applied. The method's accuracy does not depend on the position of the patient with respect to the direction of the x-ray beam. The accuracy of the method was demonstrated with the use of a phantom valve. The difference between the measured and the real opening angle was -0.7 +/- 1.8 degrees (mean +/- SD). Results were reproducible in patients to within -0.1 +/- 1.8 degrees. In 18 patients with normally functioning valves it could be demonstrated with frame-by-frame analysis (interval between frames 20 msec) that the valves opened very rapidly up to about 60 degrees. Closing patterns varied. In one of our patients with valvular thrombosis insufficient valvular opening could be demonstrated by our method before the patient's complaints drew attention to the valvular dysfunction.

Cineradiography↗
PubMed1982

Clinical relevance of postextrasystolic potentiation.

The significance and clinical relevance of postextrasystolic potentiation resides in the fact that any change in duration of the cardiac cycle results in a change in the contractile behavior of the heart. Since neither a normal nor a diseased heart ever beats strictly regularly, postextrasystolic potentiation is continuously operative, and all hemodynamic or circulatory data obtained in the intact organism are affected by it. This means that postextrasystolic potentiation should be taken into account when cardiovascular clinical data are analyzed and subsequently used for diagnosis or treatment. Postextrasystolic potentiation used as an intervention for the evaluation of residual viable myocardium in scar tissue areas in patients with coronary heart disease may contribute to out insights in the prognosis of and therapeutic judgments in those patients. Postextrasystolic potentiation is a fundamental physiologic property of all myocardium under all circumstances and as such does not allow for integrating or averaging data obtained during more than one cardiac cycle, if cardiac rhythm has not been strictly regular. This fact is insufficiently appreciated in nuclear cardiology and two-dimensional echocardiography.

Animals↗
PubMed1981

Determination of coronary artery diameter and contrast medium concentration from angiograms - possibilities and limitations.

The quantification of coronary arterial stenosis is a great clinical importance. The coronarograms obtained with the usual X-ray systems are severely distorted. The principal effects, underlying this distortion are the focal spot dimensions, blurring due to object movements and noise due to individual X-ray photons. Some general assessment, as well as a simplified procedure are given. Under the assumptions of a cylindrical artery and a Gaussian curve for its density graph, a relation can be derived to calculate the artery diameter. Application to test objects show that this is a practicable method.

Angiography↗
PubMed1975

Quantitative estimation of valvular incompetence.

The regurgitant flow (Qreg) through incompetent valves can be assessed by subtracting effective cardiac output (Qeff) from total left ventricular output (Qtot). Qeff was determined with the thermodilution method. A new correction factor for true injected quantity of indicator was developed and a procedure for rapid estimation of (see article) deltaT(t)dt was tested. Qtot was determined with the aid of quantitative left ventriculography. In 10 patients without incompetent valves no significant difference between Qeff and Qtot could be demonstrated. Qreg in 11 patients with mitral incompetence ranged from 0.5 till 4.7 1-min-1 m-2 and in 12 patients with aortic incompetence from 0.9 till 11.2 1-min-1 m-2. The relation of left ventricular enddiastolic volume (Ved in ml-m-2) and Qreg (in 1-min-m-2) is expressed by the regression equation: Ved = 21.7 Qreg + 59.2 (correlation coefficient 0.91), demonstrating a good relationship of regurgitant flow and volume load fo the left ventricle. Follow-up of these patients is important to detect guidelines for operation indications base on quantitative measurements of Ved and Qreg.

Adolescent↗