Regurgitant flow through heart valves: a hydraulic model applicable to ultrasound Doppler measurements.
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Heart Valve Diseases↗
Biomedical subjects
D Loyd
Publications and source records attributed to D Loyd.
Are there sex differences in the long-term outcome of schizophrenia? Comparisons with mania, depression, and surgical controls.
Female schizophrenics have been reported to have a better prognosis than male schizophrenics. However, earlier reports rarely used either operational criteria for schizophrenia or appropriate comparison groups. Using data collected as part of a long-term follow-up and family study, the authors examined outcome by sex of 186 schizophrenics, 212 depressives, 86 manics, and 145 surgical controls. When the authors controlled for differences in the age and sex distributions of the diagnostic groups, sex did not make a significant contribution to the explanation of outcome differences between diagnoses or within diagnoses. Examination of outcomes within diagnoses revealed only a nonsignificant trend for female manics to have a better long-term outcome than male manics.
Adult↗
Quantification of heart valve regurgitation: a critical analysis from a theoretical and experimental point of view.
A theoretical analysis is presented regarding factors of importance for the determination of distance of intrusion of the regurgitant jet in heart valve regurgitation. The analysis is based on hydrodynamic theory. In the idealized model situation, for a circular hole, the intrusion of the regurgitant jet is linearly related to the product of the fluid mean velocity in the orifice and the diameter of the orifice. This was also shown to be true in an experimental fluid model. Thus, volume regurgitation cannot be quantified by the measurement of distance of intrusion of the regurgitant jet alone. On the other hand, an estimate of volume regurgitation can, in the idealized situation, be obtained if mean fluid velocity in the orifice, distance of intrusion of the jet and regurgitation time are known.
Aortic Valve Insufficiency↗
Cancer in children of parents exposed to hydrocarbon-related industries and occupations.
Recent animal and human studies suggest that prenatal exposure to carcinogens may increase the risk of childhood malignancy. The Texas Childhood Cancer Study (1976-1977) was designed to test the hypothesis that parental exposure to hydrocarbon-related occupations or industries increases this risk. The study subjects, parents of children with and without cancer, were questioned about their job histories. Parents of 296 children with cancer were not exposed to hydrocarbon-related occupations or industries more often than the uncles and aunts of these children, the parents of neighborhood children, or the parents of 283 children without cancer. During the year before birth, odds ratios for fathers of children seen at a hematology clinic with cancer relative to the uncles of these children (0.93), the fathers of neighborhood children (1.33), and the fathers of children seen at the clinic without cancer (0.50) were not statistically significantly different from 1.00 (p greater than 0.05). This lack of association persisted for the year after birth, the year before diagnosis, and the interval from the year before birth to the year of diagnosis; for different diagnoses; for different ages at diagnosis; and for the industries and occupations of female as well as male parents.
Adolescent↗
Estimation of volume flow rate by surface integration of velocity vectors from color Doppler images.
A new Doppler echocardiographically based method has been developed to quantify volume flow rate by surface integration of velocity vectors (SIVV). Electrocardiographic-gated color Doppler images acquired in two orthogonal planes were used to estimate volume flow rate through a bowl-shaped surface at a given time and distance from the probe. To provide in vitro validation, the method was tested in a hydraulic model representing a pulsatile flow system with a restrictive orifice. Accurate estimates of stroke volume (+/- 10%) were obtained in a window between 1.2 and 1.6 cm proximal to the orifice, just before the region of prestenotic acceleration. By use of the Bernoulli's equation, the estimated flows were used to generate pressure gradient waveforms across the orifice, which agreed well with the measured flows. To demonstrate in vivo applicability, the SIVV method was applied retrospectively to the determination of stroke volume and subaortic flow from the apical three-chamber and five-chamber views in two patients. Stroke volume estimates along the left ventricular outflow tract showed a characteristic similar to that in the in vitro study and agreed well with those obtained by the Fick oxygen method. The region where accurate measurements can be obtained is affected by instrumental factors including Nyquist velocity limit, wall motion filter cutoff, and color flow sector angle. The SIVV principle should be useful for quantitative assessment of the severity of valvular abnormalities and noninvasive measurement of pulsatile volume flows in general.
Animals↗
The shape of the proximal isovelocity surface area varies with regurgitant orifice size and distance from orifice: computer simulation and model experiments with color M-mode technique.
The hemispheric proximal isovelocity surface area method for quantification of mitral regurgitant flow (i.e., Qc = 2 pi r2v), where 2 pi r2 is the surface area and v is the velocity at radius r, was investigated as distance from the orifice was increased. Computer simulations and steady flow model experiments were performed for orifices of 4, 6, and 8 mm. Flow rates derived from the centerline velocity and hemispheric assumption were compared with true flow rates. Proximal isovelocity surface area shape varied as distance from each orifice was increased and could only be approximated from the hemispheric equation when a certain distance was exceeded: > 7, > 10, and > 12 mm for the 4, 6, and 8 mm orifices, respectively. Prediction of relative error showed that the best radial zone at which to make measurements was 5 to 9, 6 to 14 and 7 to 17 mm for the 4, 6, and 8 mm orifices, respectively. Although effects of a nonhemispheric shape could be compensated for by use of a correction factor, a radius of 8 to 9 mm can be recommended without the use of a correction factor over all orifices studied if a deviation in calculated as compared with true flow of 15% is considered acceptable. These measurements therefore have implications for the technique in clinical practice.
Blood Flow Velocity↗
Two-dimensional color Doppler flow velocity profiles can be time corrected with an external ECG-delay device.
Although two-dimensional ultrasound color flow imaging is often considered to be a real-time technique, the acquisition time for two-dimensional color images may be up to 200 msec. Time correction is therefore necessary to obtain correct flow velocity profiles. We have developed a time-correction method in which a specially designed unit detects the QRS complex from the patient and creates a trig pulse that is delayed incrementally in relation to the QRS complex. This trig pulse controls the acquisition of the ultrasound images. A number of consecutively delayed images, with known incremental delay between the sweeps, can thus be stored in the memory of the echocardiograph and transferred digitally to a computer. The time-corrected flow velocity profile is obtained by interpolation of data from the time-delayed profiles. The system was evaluated in a Doppler string phantom test. With this technique it is possible to study time-corrected flow velocity profiles without the need to alter existing ultrasound Doppler equipment.
Blood Flow Velocity↗
Subaortic flow profiles in aortic valve disease: a two-dimensional color Doppler study.
With time-corrected color Doppler echocardiography, the aortic subvalvular spatial flow velocity profile was registered in two perpendicular planes in 10 patients with aortic valve disease and in 5 healthy control subjects. Patients with predominant aortic valve stenosis had a fairly flat profile, and the subvalvular diameter, obtained from left parasternal two-dimensional tissue imaging, provided a good estimate of the mean of the two transverse flow axes. This explains the accuracy in determination of stroke volume and aortic valve area that is reported in studies on patients with aortic valve stenosis when the continuity equation is used. However, the use of apical pulsed Doppler ultrasound registrations from the left ventricular outflow tract and parasternal two-dimensional echocardiography for flow area calculation may introduce large errors in calculated stroke volume in certain patients with aortic regurgitation and in normal subjects, because of a non-flat spatial velocity profile or an inaccurate estimate of flow area.
Aged↗
Problems in timing of respiration with the nasal thermistor technique.
When one analyzes transvalvular and venous flow velocity patterns, it is important to relate them to respiration. For this reason a nasal thermistor technique is often used, although it is known that this signal is delayed in relation to intrathoracic pressure changes. The magnitude and variation in delay have not been investigated previously and were, therefore, studied in a model experiment in 10 normal subjects, in 10 patients with obstructive, and in 10 patients with restrictive pulmonary disease. Esophageal pressure variations measured with an air-filled balloon served as a gold standard for intrathoracic pressure changes. During basal conditions there was, for both patient groups and normal subjects, a considerable delay of the thermistor signal. The average delay for all subjects was 370 msec with a wide variation (from 120 to 720 msec). At higher breathing frequencies the delay shortened to 310 msec (P < 0.01) but there was still a wide variation (ranging from 200 to 470 msec). Theoretic calculations show that the delay caused by the respiratory system accounts for only a minor portion of the total delay. Model experiments confirmed that the response characteristics of the thermistor probes limit the accuracy in timing of respiration. The total delay with the investigated thermistor technique is too long and variable to fulfil clinical demands.
Adult↗
Pressure half-time does not always predict mitral valve area correctly.
A theory is presented elucidating factors that influence the pressure half-time. By combining the Bernoulli and continuity equations and making certain assumptions about the shape of the atrioventricular pressure difference decay, it can be shown that valve area, volume transported across that area, and initial pressure difference influence the pressure half-time according to a formula in which the pressure half-time is related to V/(Ao square root of delta po), where V is the transported volume across the orifice with the area Ao, and delta po is the initial pressure difference across that area. In a subsequent hydraulic model experiment pressure half-time was determined for three different hole areas, with various initial volumes and initial pressure gradients. We did not obtain a unique relation between the pressure half-time and area. Instead the results supported our theory, and we found a close linear relationship between area and V/(T0.5 square root of delta po) (correlation coefficient [r] = 0.998), as predicted in the theory (T0.5 = pressure half-time). Clinical examples in which the pressure half-time may be misleading in the assessment of severity of mitral stenosis are presented.
Blood Pressure↗
Determination of regurgitant flow and volume by integrating actual proximal velocities over hemispheres (IPROV) in two orthogonal planes.
The proximal acceleration technique is a promising technique for quantification of regurgitant valve flow. Although the shape of the regurgitant proximal isovelocity field has been shown to vary with orifice size, geometry, and driving pressure, normally the centerline velocity alone is used for estimation of flow. In this model study of pulsatile flow, two-dimensional and spectral Doppler data were transferred digitally to a computer in which proximal velocity fields were corrected for time and angle errors. With the purpose of improving accuracy, flow was estimated by integrating proximal velocities over nonisovelocity spheric control surfaces in the best zone of measurement (0.15 to 0.45 m/sec at an angle up to +/- 45 degrees from the center line) in two perpendicular planes. Three regurgitant volumes in the range of 5 to 21 ml were studied for circular (diameters of 4, 6, and 8 mm), crescent, and diagonal orifices. The quotient between effective orifice area, estimated by dividing peak flow with peak velocity in the vena contracta, and true orifice area (Aeff = Q(tm)/Vo(tm)) was 0.66 (range 0.60 to 0.79), 0.50 (0.48 to 0.52), and 0.67 (0.66 to 0.68) for the circular, crescent, and diagonal orifices, respectively. Regurgitant volume estimated by multiplying effective orifice area by the velocity-time integral in the vena contracta (V = Aeff.velocity-time integral) ranged from 92% to 115% of the true volume for the circular, 89% to 92% for the crescent, and 105% to 112% for the diagonal orifices, respectively. It is possible to calculate regurgitant volume correctly with data acquisition from multiple hemispheres and planes and postprocessing of data. This amendment of the proximal acceleration technique has great advantage over the center-line method, especially when the orifice is asymmetric.
Blood Flow Velocity↗
Understanding continuous-wave Doppler signal intensity as a measure of regurgitant severity.
Continuous-wave Doppler signal intensity is commonly expected to reflect the severity of mitral regurgitation. Physical principles predict that alignment of the imaging beam, flow velocity, and turbulence can also be important or even dominant determinants of continuous-wave Doppler signal intensity. The reliability of tracking regurgitant severity with continuous-wave Doppler signal intensity was assessed in vitro with varying volume, velocity, turbulence, and beam alignment. The conditions wherein continuous-wave Doppler signal intensity increased with regurgitant volume were specific but poorly predictable combinations of orifice size, flow volume, and perfect beam alignment. Under other conditions flow velocity and turbulence effects dominated, and continuous-wave Doppler signal intensity did not reflect changing regurgitant volume. Continuous-wave Doppler signal intensity-based impressions of regurgitant severity may be unreliable and even misleading under some circumstances.
Echocardiography, Doppler↗
A hybrid equation for simulation of perfused tissue during thermal treatment.
Bio-heat equations (BHEs) are necessary for predicting tissue temperature during thermal treatment. For some applications, however, existing BHEs describe the convective heat transfer by the blood perfusion in an unsatisfactory way. The two most frequently used equations, the BHE of Pennes and the k(eff) equation, use for instance either a heat sink or an increased thermal conductivity in order to account for the blood perfusion. Both these methods introduce modelling inaccuracies when applied to an ordinary tissue continuum with a variety of vessel sizes. In this study, a hybrid equation that includes both an increased thermal conductivity and a heat sink is proposed. The equation relies on the different thermal characteristics associated with small, intermediate and large sized vessels together with the possibilities of modelling these vessels using an effective thermal conductivity in combination with a heat sink. The relative importance of these two terms is accounted for by a coefficient beta. For beta = 0 and beta = 1, the hybrid equation coincides with the BHE of Pennes and the k(eff) equation, respectively. The hybrid equation is used here in order to simulate temperature fields for two tissue models. The temperature field is greatly affected by beta, and the effect is dependent on, e.g. the boundary conditions and the power supply. Since the BHE of Pennes and the k(eff) equation are included in the hybrid equation, this equation can also be useful for evaluation of the included equations. Both these heat transfer modes are included in the proposed equation, which enables implementation in standard thermal simulation programmes.
Animals↗