Biomedical subjects

J D Thomas

Publications and source records attributed to J D Thomas.

At least 19 recordsLinked to original sources

PubMed1992

Relation between Doppler color flow variables and invasively determined jet variables in patients with aortic regurgitation.

OBJECTIVES: The purpose of this study was to test the hypothesis that invasively derived jet variables including regurgitant orifice area and momentum determine the characteristics of Doppler color flow jets in patients with aortic regurgitation. BACKGROUND: In vitro studies have demonstrated that the velocity distribution of a regurgitant jet is best characterized by the momentum of the jet, which incorporates orifice area and velocity of flow through the orifice. METHODS: Peak jet momentum, peak flow rate and regurgitant orifice area were determined with intraaortic Doppler catheter and cardiac catheterization techniques in 22 patients with chronic aortic regurgitation. These invasively derived variables were compared with apical and parasternal long-axis Doppler color echocardiographic variables obtained in the catheterization laboratory. RESULTS: Jet momentum increased significantly with the angiographic grade of regurgitation. The apical color jet area of aortic regurgitation increased linearly with jet momentum and regurgitant orifice area in vivo, but the correlations were only moderately good (r = 0.63 and 0.65, respectively). Color jet length also increased linearly with jet momentum and with regurgitant orifice area. There was only a trend for Doppler color jet width to increase with all invasively derived jet variables. CONCLUSIONS: Whereas jet area by Doppler color flow imaging is directly related to both orifice area and jet momentum in vivo, Doppler color variables measured in planes normal to the orifice do not correlate well enough with either jet momentum or regurgitant orifice area to predict jet flow variables in patients with aortic regurgitation. It is likely that the important influence of adjacent boundaries will limit the use of the velocity distribution of aortic regurgitant jets for determining the severity of disease.

Aortic Valve Insufficiency↗

PubMed1992

Effects of intra-ischemic blood pressure on outcome from 2-vessel occlusion forebrain ischemia in the rat.

Halothane anesthetized Sprague-Dawley rats underwent 10 min of bilateral carotid artery occlusion with mean arterial pressure (MAP) held at 30, 50 or 60 mmHg. Sham rats did not undergo ischemia. A 7-day recovery interval was allowed. Intra-ischemic electroencephalographic (EEG) changes, behavioral function (Days 5-7), and histologic injury (Day 7) were evaluated. Under similar conditions, cerebral blood flow was determined after 10 min ischemia by the [3H]nicotine indicator fractionation technique. EEG isoelectricity was observed in 11 of 11, 5 of 10, and 2 of 11 rats in the 30 mmHg, 50 mmHg, and 60 mmHg groups respectively. Neither passive avoidance cross-over latencies nor general motor scores were affected by intra-ischemic MAP and no differences from sham performance were observed. The per cent of CA1 neurons counted as dead (left and right hemispheres combined) was significantly affected by intra-ischemic MAP (72, 46 and 28% in the 30 mmHg, 50 mmHg, and 60 mmHg groups, respectively; P less than 0.001). A greater than 50% CA1 neuronal mortality rate was present only in those rats exhibiting EEG isoelectricity. However, the number of rats demonstrating greater than a 25% interhemispheric difference in CA1 neuronal loss was greatest in the 50 mmHg group (P less than 0.02). Hippocampal blood flow decreased in association with severity of hypotension (8 +/- 1, 35 +/- 8, and 48 +/- 2 ml/100 g/min (mean +/- S.E.M.) for 30, 50, and 60 mmHg, respectively; P less than 0.01). Again, however, the greatest variability in blood flow was observed at MAP = 50 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Numerical modeling of ventricular filling.

The fluid dynamical and physiological assumptions underlying general mathematical modeling of ventricular filling are outlined. We then describe the use of a lumped parameter model and computer simulation to study how the early transmitral velocity profile is affected by isolated changes in ventricular compliance and relaxation, atrial pressure and compliance, and valvular morphology. We show that the transmitral velocity is fundamentally affected by two physical determinants: the transmitral pressure difference and the net compliance of the atrium and the ventricle. These physical determinants in turn are specified by the various physiologic parameters of interest. This approach has shown that peak velocity is most strongly affected by initial left atrial pressure, lowered somewhat by prolonged relaxation, low atrial and ventricular compliance, and systolic dysfunction. Peak acceleration is directly affected by atrial pressure and inversely affected by the time constant of isovolumic relaxation, with little influence of compliance, whereas the deceleration rate is almost purely given by mitral valve area divided by instantaneous atrioventricular compliance at the end of the rapid filling wave.

Animals↗

PubMed1992

Quantification of mitral regurgitation with the proximal flow convergence method: a clinical study.

Accurate quantitation of valvular incompetence remains an important goal in clinical cardiology. It has been shown previously that when color flow Doppler mapping is used, simple measurements of apparent jet size do not correlate closely with regurgitant flow rate and regurgitant fraction. Recently the proximal flow convergence method has been proposed to quantify valvular regurgitation by analysis of the converging flow field proximal to a regurgitant lesion. Flow rate Q can be calculated as Q = 2 pi r2v(a), where v(a) is the aliasing velocity at a distance r from the orifice. In 54 patients (43 with sinus rhythm and 11 with atrial fibrillation) who had at least mild mitral regurgitation according to semiquantitative assessment, regurgitant stroke volume, regurgitant flow rate, and regurgitant fraction were calculated with the proximal flow convergence method and compared with values that were obtained by the Doppler two-dimensional echocardiographic method. Regurgitant stroke volumes (Vr) as calculated by the proximal flow convergence method correlated very closely with values that were obtained by the Doppler two-dimensional method, with r = 0.93 (y = 0.95x + 0.55) and delta Vr = -0.3 +/- 4.0 cm3. Regurgitant flow rates (Q) as calculated by both methods showed a similar correlation: r = 0.93 (y = 0.95x + 54) and delta Q = -34 +/- 284 cm3/min. The correlation for regurgitant fraction (RF) as calculated by both techniques showed r = 0.89 (y = 0.98x + 0.006) and delta RF = -0.005 +/- 0.06. All correlations were slightly better for the group of patients with sinus rhythm than for the study group of patients with atrial fibrillation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Isovolumic relaxation time varies predictably with its time constant and aortic and left atrial pressures: implications for the noninvasive evaluation of ventricular relaxation.

The isovolumic relaxation time (IVRT) is an important noninvasive index of left ventricular diastolic function. Despite its widespread use, however, the IVRT has not been related analytically to invasive parameters of ventricular function. Establishing such a relationship would make the IVRT more useful by itself and perhaps allow it to be combined more precisely with other noninvasive parameters of ventricular filling. The purpose of this study was to validate such a quantitative relationship. Assuming isovolumic relaxation to be a monoexponential decay of ventricular pressure (pv) to a zero-pressure asymptote, it was postulated that the time interval from aortic valve closure (when pv = p(o)) until mitral valve opening (when pv = left atrial pressure, pA) would be given analytically by IVRT = tau[log(p(o))-log(pA)], where tau is the time constant of isovolumic relaxation and log is to the base e. To test this hypothesis we analyzed data from six canine experiments in which ventricular preload and afterload were controlled nonpharmacologically. In addition, tau was adjusted with the use of beta-adrenergic blockade and calcium infusion, as well as with hypothermia. In each experiment data were collected before and after the surgical formation of mitral stenosis, performed to permit the study of a wide range of left atrial pressures. High-fidelity left atrial, left ventricular, and aortic root pressures were digitized, the IVRT was measured from the aortic dicrotic notch until the left atrioventricular pressure crossover point, and tau was calculated by nonlinear least-squares regression.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

New perspectives in the assessment of cardiac chamber dimensions during development and adulthood.

The use of body surface area to assess the normalcy of cardiac dimensions has several limitations. To determine whether cardiac dimensions can be assessed by other indexes of body size and growth, this study evaluated the relations between cardiac dimensions assessed by two-dimensional echocardiography and age, height, weight and body surface area. The study group included 268 normal persons aged 6 days to 76 years of age. The dimensions examined included the aortic anulus, left atrium and left ventricular end-diastolic diameter, each measured in the parasternal long-axis plane, and left ventricular length measured from the apical two-chamber view. The analysis confirmed that the heart and great vessels grow in unison and at a predictable rate after birth, reaching 50% of their adult dimensions at birth, 75% by 5 years and 90% by 12 years. Although each cardiac dimension related linearly with height (aortic anulus, r = 0.96; left atrium, r = 0.91; left ventricular diameter, r = 0.94; left ventricular length, r = 0.93), the relations among age, weight and body surface area were best expressed by quadratic equations. Multiple regression confirmed that after adjustment for height, other indexes including age, gender, weight and body surface area had no independent effect on the prediction of each dimension. Therefore, because height is a nonderived variable that relates linearly with cardiac dimensions independent of age, it offers a simple yet accurate means of assessing the normalcy of cardiac dimensions in children and adults.

Adolescent↗

PubMed1992

Calculation of atrioventricular compliance from the mitral flow profile: analytic and in vitro study.

The quantitative assessment of ventricular diastolic function is an important goal of Doppler echocardiography. Hydrodynamic analysis predicts that the net compliance (Cn) of the left atrium and ventricle can be quantitatively predicted from the deceleration rate (dv/dt) of the mitral velocity profile by the simple expression: Cn = - A/rho dv/dt, where A is effective mitral valve area and rho is blood density. This formula was validated using an in vitro model of transmitral filling where mitral valve area ranged from 0.5 to 2.5 cm2 and net compliance from 0.012 to 0.023 cm3/(dynes/cm2) (15 to 30 cm3/mm Hg). In 34 experiments in which compliance was held constant throughout the filling period, net atrioventricular compliance was accurately calculated from the E wave downslope and mitral valve area (r = 0.95, p less than 0.0001). In a second group of experiments, chamber compliance was allowed to vary as a function of chamber pressure. When net compliance decreased during diastole (as when the ventricle moved to a steeper portion of its pressure-volume curve), the transorifice velocity profile was concave downward, whereas when net compliance increased, the velocity profile was concave upward. Application of the preceding formula to these curved profiles allowed instantaneous compliance to be calculated throughout the filling period (r = 0.93, p less than 0.001). Numeric application of a mathematic model of mitral filling demonstrated the accuracy of this approach in both restrictive and nonrestrictive orifices.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial Function↗

PubMed1992

Intestinal water and solute absorption studies: comparison of in situ perfusion with chronic isolated loops in rats.

The effects of lumenal glucose on jejunal water transport and the influence of glucose-induced water absorption on solute uptake from single-pass perfusions are compared in anesthetized rats in situ and isolated chronic loops in unanesthetized rats in vivo. While the magnitudes of solute membrane permeabilities are consistently higher in the chronic loop system, the effects on water transport and its promotion of jejunal solute uptake are comparable between the two experimental systems. The effect of glucose-induced water absorption on the enhanced/baseline jejunal uptake ratio of the hydrophilic drug, acetaminophen, is greater than that for the lipophilic drug, phenytoin, in both experimental systems. The fact that chronic loop effective solute permeabilities were equivalent to solute membrane permeabilities in situ is consistent with greater lumenal fluid mixing in vivo. In addition, in situ body temperature affects the uptake of phenytoin but not acetaminophen, water, or glucose. This suggests that active and paracellular solute transport is not compromised in situ, while membrane partitioning and diffusion of lipophilic species are more sensitive to experimental conditions.

Acetaminophen↗

PubMed1992

A study of the sugar chemoreception niches of two bulinid snail hosts of schistosomiasis.

Components of the sugar chemoreception niches of two host snails of urinary schistosomiasis, namely Bulinus globosus (Morelet) and Bulinus rohlfsi (Clessin), were measured by using a buccal mass olfactometer. Among the polysaccharides tested, amylose was found to be the strongest phagostimulant for adults and juveniles of both snail species. Other phagostimulants identified were maltose and xylose for B. rohlfsi and maltotriose for B. globosus. The a(1-4)-glucosidic linkage and the presence of glucose residues were found to be key factors in the stimulus recognition system of the snails. The possible use of these findings in the design of controlled-release formulations for the selective removal of schistosome host snails is considered. The ecological implications of these studies are also examined.

Amylopectin↗

PubMed1992

Noninvasive measurement of the time constant of left ventricular relaxation using the continuous-wave Doppler velocity profile of mitral regurgitation.

BACKGROUND: The time constant of isovolumic relaxation (tau) is an important parameter of ventricular diastolic function, but the need for invasive measurement with high-fidelity catheters has limited its use in general clinical cardiology. The Doppler mitral regurgitant velocity spectrum can be used to estimate left ventricular (LV) pressure throughout systole and may provide a new noninvasive method for estimating tau. METHODS AND RESULTS: Mitral regurgitation was produced in nine dogs, and ventricular relaxation was adjusted pharmacologically and with hypothermia. High-fidelity ventricular pressures were recorded, and tau was calculated from these hemodynamic data (tau H) assuming a zero-pressure asymptote. Continuous-wave mitral regurgitant velocity profiles were obtained, and the ventriculo-atrial (VA) pressure gradient was calculated by the simplified Bernoulli equation; tau was calculated from the Doppler data from the time of maximal negative dP/dt until LV-LA pressure crossover. Three methods were used to correct the Doppler VA gradient to better approximate the LV pressure before calculating tau: 1) adding actual LA V wave pressure (to yield tau LA); 2) adding 10 mm Hg (tau 10); and 3) no adjustment at all (actual VA gradient used to calculate tau 0). The agreement between tau H and the three Doppler estimates of tau was assessed by linear regression and by the mean and standard deviation of the error between the measurements (delta tau). the measurements (delta tau). tau H ranged from 29 to 135 msec. Without correction for LA pressure, the Doppler estimate of tau seriously underestimated tau H: tau 0 = 0.30 tau H + 9.4, r = 0.79, delta tau = -35 +/- 18 msec. This error was almost completely eliminated by adding actual LA pressure to the VA pressure gradient: tau LA = 0.92 tau H + 7.6, r = 0.95, delta tau = 2 +/- 7 msec. Addition of a fixed LA pressure estimate of 10 mm Hg to the VA gradient yielded an estimate that was almost as good: tau 10 = 0.89 tau H + 4.9, r = 0.88, delta tau = -2 +/- 12 msec. In general, tau was overestimated when actual LA pressure was below this assumed value, and vice versa. Numerical analysis demonstrated that assuming LA pressure to be 10 mm Hg should yield estimates of tau accurate to +/- 15% between true LA pressures of 5 and 20 mm Hg. CONCLUSIONS: This study demonstrates that the Doppler mitral regurgitant velocity profile can be used to provide a direct and noninvasive measurement of tau. Because mitral regurgitation is very common in cardiac patients, this method may allow more routine assessment of tau in clinical and research settings, leading to a better understanding of the role of impaired ventricular relaxation in diastolic dysfunction and the effect of therapeutic interventions.

Animals↗

PubMed1992

Impact of finite orifice size on proximal flow convergence. Implications for Doppler quantification of valvular regurgitation.

Analysis of velocity acceleration proximal to a regurgitant valve has been proposed as a method to quantify the regurgitant flow rate (Qo). Previous work has assumed inviscid flow through an infinitesimal orifice, predicting hemispheric isovelocity shells, with calculated flow rate given by Qc = 2 pi rN2vN, where vN is user-selected velocity of interest and rN is the distance from that velocity to the orifice. To validate this approach more rigorously and investigate the impact of finite orifice size on the assumption of hemispheric symmetry, numerical and in vitro modeling was used. Finite-difference modeling demonstrated hemispheric shape for contours more than two orifice diameters from the orifice. More proximal than this (where the measured velocity vN exceeded 3% of the orifice velocity vo), flow was progressively underestimated, with a proportional error delta Q/Qo nearly identical to the ratio of contour velocity to orifice velocity, vN/vo. For the in vitro investigations, flow rates from 4.3 to 150 cm3/sec through 0.3 and 1.0 cm2 circular orifices were imaged with color Doppler with aliasing velocities from 19 to 36 cm/sec. Overall, the calculated flow (assuming hemispheric symmetry) correlated well with the true flow, Qc = 0.88Qo-7.82 (r = 0.945, SD = 12.2 cm3/sec, p less than 0.0001, n = 48), but progressively underestimated flow when the vN approached the orifice velocity vo. Applying a correction factor predicted by the numerical modeling, delta Q was improved from -13.81 +/- 13.01 cm3/sec (mean +/- SD) to +1.54 +/- 5.67 cm3/sec.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Circulation↗

PubMed1991

Doppler echocardiographic estimation of mitral valve area during changing hemodynamic conditions.

Patients with mitral stenosis often present during periods of hemodynamic stress such as pregnancy or infections. The Doppler pressure half-time method of mitral valve area (MVA) determination is dependent on the net atrioventricular compliance as well as the peak transmitral gradient. The continuity equation method of MVA determination is based on conservation of mass and may be less sensitive to changes in the hemodynamic state. To test this hypothesis, 17 patients admitted for catheterization with symptomatic mitral stenosis and no more than mild regurgitation underwent Doppler echocardiography at rest and during supine bicycle exercise targeted to an increase in heart rate by 20 to 30 beats/minute. Net atrioventricular compliance was also estimated noninvasively. Cardiac output and transmitral gradient increased significantly during exercise (p less than 0.001), while net atrioventricular compliance decreased (p less than 0.001). MVA by the pressure half-time method increased significantly during exercise from 1.0 +/- 0.2 to 1.4 +/- 0.4 cm2 (p less than 0.001). There was no significant difference in MVA estimation using the continuity equation comparing rest to exercise, with the mean area remaining constant at 0.8 +/- 0.3 cm2 (p = 0.83). Thus, during conditions of changing hemodynamics, the continuity equation method for estimating MVA may be preferable to the pressure half-time method.

Adult↗

PubMed1991

Patterns of normal transvalvular regurgitation in mechanical valve prostheses.

The magnitude and spatial distribution of normal leakage through mechanical prosthetic valves were studied in an in vitro model of mitral regurgitation. The effective regurgitant orifice was calculated from regurgitant rate at different transvalvular pressure differences and flow velocities. This effective orifice area was 0.6 to 2 mm2 for three tilting disc prostheses (Medtronic-Hall sizes 21, 25 and 29) and 0.2 to 1.1 mm2 for three bileaflet valves (St. Jude Medical sizes 21, 25 and 33). In the single disc valves, Doppler color flow examination disclosed a prominent central regurgitant jet around the central hole for the strut, accompanied by minor leakage along the rim of the disc (central to peripheral jet area ratio 3.3 +/- 1.2). The bileaflet prostheses showed a peculiar complex pattern: in planes parallel to the two disc axes, convergent peripherally arising jets were visualized, whereas in orthogonal planes several diverging jets were seen. Mounting the disc and bileaflet valves on a water-filled tube allowed reproduction and interpretation of this pattern: for the bileaflet valve, the jets originated predominantly from valve ring protrusions that contained the axis hinge points and created a converging V pattern in planes parallel to the leaflets and a diverging V pattern in orthogonal planes. Similar patterns were observed during transesophageal echocardiography in 20 patients with a normally functioning St. Jude prosthesis. In 10 patients with a Medtronic-Hall valve, a dominant central jet was observed with one or more smaller peripheral jets. The median central to peripheral jet area ratio was 5 to 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗

PubMed1991

Echocardiographic assessment of patients with infectious endocarditis: prediction of risk for complications.

To enhance the echocardiographic identification of high risk lesions in patients with infectious endocarditis, the medical records and two-dimensional echocardiograms of 204 patients with this condition were analyzed. The occurrence of specific clinical complications was recorded and vegetations were assessed with respect to predetermined morphologic characteristics. The overall complication rates were roughly equivalent for patients with mitral (53%), aortic (62%), tricuspid (77%) and prosthetic valve (61%) vegetations, as well as for those with nonspecific valvular changes but no discrete vegetations (57%), although the distribution of specific complications varied considerably among these groups. There were significantly fewer complications in patients without discernible valvular abnormalities (27%). In native left-sided valve endocarditis, vegetation size, extent, mobility and consistency were all found to be significant univariate predictors of complications. In multivariate analysis, vegetation size, extent and mobility emerged as optimal predictors and an echocardiographic score based on these factors predicted the occurrence of complications with 70% sensitivity and 92% specificity in mitral valve endocarditis and with 76% sensitivity and 62% specificity in aortic valve endocarditis.

Adult↗

PubMed1991

Impact of orifice geometry on the shape of jets: an in vitro Doppler color flow study.

To investigate the influence of orifice geometry on the three-dimensional shape of jets, an in vitro Doppler color flow study was performed. Jets were formed by discharging blood through round orifices and through orifices with major/minor axis ratios of 2:1, 3:1 and 5:1. These were repeated with orifice areas of 0.1, 0.3 and 0.5 cm2. For turbulent and laminar jets formed by these orifices, Doppler color flow images were obtained from two orthogonal scanning planes aligned with the major and minor orifice axes. Jet width was measured at 1 cm intervals from 0 to 5 cm from the orifice and used to calculate jet eccentricity (ratio of major to minor axis widths) and the rate of divergence of the jet walls. Jets were observed to diverge more rapidly along walls aligned with the orifice minor axis rather than along the major axis. This differential spreading led to the development of circular symmetry at a short distance from the orifice. Jet divergence (theta) occurred more rapidly for turbulent jets and for jets formed by larger orifices: theta (zero) = 0.80 + 6.3.A + 7.0.T + 0.47.E-OR (r = 95, p less than 0.0001, n = 48), where A is orifice area (cm2); T is 0 for laminar jets, 1 for turbulent jets and E-OR combines orifice eccentricity and scanning orientation, ranging from -5 for 5:1 orifices imaged along the major axis, 0 for circular orifices to 5 for 5:1 orifices imaged along the minor axis. Within the jet, eccentricity decayed approximately exponentially with distance from the orifice, more rapidly for turbulent jets, more slowly for the larger and more eccentric orifices.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗

PubMed1991

Immediate regional endocardial surface expansion following coronary occlusion in the canine left ventricle: disproportionate effects of anterior versus inferior ischemia.

The exact time of onset of functional expansion after acute myocardial infarction/ischemia remains unclear in spite of its potential link to chronic pathologic infarct expansion and its potential implications for therapy. To examine this early change in ventricular morphology, 14 open-chest dogs were studied with two-dimensional echocardiography before and after occlusion (10 minutes) of the left anterior descending coronary artery (LAD, n = 7) or circumflex artery (CIRC, n = 7). The endocardial surface area (ESA) and the area of abnormal wall motion (AWM) were reconstructed from the echocardiographic data using a previously reported technique for quantitatively mapping the ESA and extent of AWM. For the total group (N = 14), the mean ESA before occlusion was 48.9 +/- 9.8 cm2, increasing to 65.7 +/- 18.9 cm2 at 10 minutes occlusion (p less than 0.001). For the LAD subgroup, the mean ESA before occlusion was 50.7 +/- 9.3 cm2, increasing to 79.1 +/- 14.1 cm2 at 10 minutes following occlusion (p less than 0.001). For the CIRC subgroup, the mean ESA before occlusion was 47.1 +/- 10.8 cm2, increasing to 52.3 +/- 12.6 cm2 at 10 minutes after occlusion (p less than 0.001). The ESA increase for the LAD subgroup was significantly larger than that of the CIRC subgroup (LAD range 14.5 to 49.9 cm2 versus CIRC range 1.5 to 9 cm2, p less than 0.0001). Coronary occlusion resulted in similarly sized regions of AWM for both subgroups (LAD, 31.3 +/- 12.2 cm2 versus CIRC, 25.9 +/- 10.3 cm2, p = n.s.). For the LAD group, the largest increase in endocardial circumference occurred within the zone of AWM at the apex (39.9 +/- 12%). The endocardial surface area therefore expands immediately after coronary occlusion and the magnitude of this process is primarily related to the site (anteroapical) rather than to the extent of AWM.

Animals↗

PubMed1991

The effects of regurgitant orifice size, chamber compliance, and systemic vascular resistance on aortic regurgitant velocity slope and pressure half-time.

The determinants of the aortic regurgitant velocity profile have been investigated using computer and in vitro simulations in which regurgitant orifice area, ventricular and aortic compliance, and systemic vascular resistance could be independently varied. In the study, regurgitant fraction was altered, either by changing the size of the regurgitant orifice or by holding the regurgitant orifice constant and changing chamber compliance or systemic vascular resistance. Upon increasing regurgitant fraction by increasing the size of the regurgitant orifice, the slope got steeper and the pressure half-time shortened, the response anticipated in current clinical practice. However, when the regurgitant orifice was kept constant and regurgitation fraction was increased by increasing the systemic vascular resistance or by increasing the compliance of the left ventricle, slope became less steep and pressure half-time lengthened. Multivariate analysis was used to quantify the relationship of regurgitant fraction to slope and pressure half-time. When orifice area was allowed to vary, slope was related directly (multiple r = 0.78, p less than 0.001) and half-time was related inversely (multiple r = 0.66, p less than 0.001) to regurgitant fraction. With the orifice area fixed, however, directionally opposite responses were seen; slope varied inversely (multiple r = 0.87, p less than 0.001), whereas half-time varied directly (multiple r = 0.88, p less than 0.001) with regurgitant fraction. This study suggests that the utility of the slope and pressure half-time of the regurgitant velocity tracing in clinical practice relates to their ability to discriminate regurgitant orifices of differing sizes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve Insufficiency↗

PubMed1991

Effective aortic regurgitant orifice area: description of a method based on the conservation of mass.

The natural history of aortic regurgitation is incompletely understood in part because of the lack of a simple method to estimate the defect size. A method of determining the effective regurgitant orifice area that combines Doppler catheter and Doppler echocardiographic techniques and is based on the principle of conservation of mass (the continuity equation) is described. To validate the application of the Doppler catheter system for measuring regurgitant supravalvular diastolic flow, an in vitro model of retrograde aortic flow was used. These studies indicated that measurements of supravalvular retrograde velocity with the Doppler catheter accurately reflect retrograde diastolic velocity when the aorta is less than 4.8 cm in diameter. Twenty-three patients undergoing cardiac catheterization were studied; 20 of these patients had aortic regurgitation. Retrograde supravalvular diastolic velocity was determined from a Doppler catheter positioned above the aortic valve. The effective regurgitant orifice area was calculated with use of the Doppler catheter-derived regurgitant volume and mean transvalvular diastolic velocity as determined by either catheterization or continuous wave Doppler echocardiography. The catheterization-derived regurgitant orifice area increased with the angiographic grade of as follows: 1+ (0.04 to 0.10 cm2), 2+ (0.15 to 0.49 cm2), 3+ (0.29 to 1.11 cm2) and 4+ (1.24 to 1.33 cm2). By combining Doppler catheter, echocardiographic and cardiac catheterization techniques, the effective aortic regurgitant orifice area may be estimated; this hydrodynamic area correlates with grading by supravalvular aortography. Calculation of this area provides a quantitative alternative to aortography for estimating the severity of aortic regurgitation but should be used with caution in patients with a markedly dilated aorta.

Aortic Valve Insufficiency↗