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Biomedical subjects

H D Allen

Publications and source records attributed to H D Allen.

At least 73 records · Page 4Linked to original sources
PubMed1987

Does transducer selection affect aortic arch velocities?

The hypothesis tested was that transducers of different types and shapes would produce different peak and mean ascending aortic (AAo) velocities. Additionally, we sought to determine if mean and peak velocity recorded from the descending aorta (DAo) were similar to velocities in the AAo. Twenty-eight consecutive individuals who had normal hearts were studied. AAo velocities were measured with four transducers including a nonimaging device that transmitted Doppler at right angles to the transducer handle, a 30-degree angled continuous wave transducer, an imaging transducer that transmitted Doppler in line with the transducer handle, and a second imaging transducer that sectored at 25 degrees to the transducer handle. DAo was studied with a standard in-line imaging transducer. Results showed that mean and peak AAo velocities recorded by transducers that transmitted off the axis of the transducer handle were similar, but the transducer that imaged along the transducer handle axis produced significantly lower peak and mean velocities. The problem that caused lower velocity for the on-axis transducer was inability to image the area immediately posterior to the sternum to permit alignment in the azimuthal dimension. The continuous wave transducer provided a wide spectral dispersion. Mean DAo velocity was similar to mean AAo velocity, but variability was large.

Adolescent↗
PubMed1987

Doppler echocardiographic observations of pulmonary and transvalvular velocity changes after birth and during the early neonatal period.

To evaluate the qualitative and quantitative changes in Doppler velocities in the normal fetus and newborn, 61 echo Doppler studies were performed in 18 neonates, nine of whom were also studied as fetuses. Four studies were inadequate in fetuses (one pulmonary artery, two mitral, and one tricuspid) and some post natal studies were inadequate due to inability to separate atrioventricular valve E and A velocity component waveforms (one tricuspid, three mitral). Heart rates for fetuses and newborns more than 24 hours of age and less than 24 hours of age were similar. Pulmonary artery diastolic velocities consistent with patent ductus arteriosus were present in 11 of 12 examinations at less than 6 hours of age, in 5 of 13 examined at 6 to 24 hours of age, and in 2 of 27 examined after 24 hours of age. Pulmonary artery times to peak velocity were similar in fetuses, m = 46, SD = 3 msec, and in neonates less than 6 hours of age, m = 51, SD = 13 msec, but lengthened significantly, p less than 0.05, at 6 to 24 hours (m = 69, SD = 14 msec). These changes are probably due to the dramatic changes in pulmonary vascular pressure that occur after birth. Data from 6 to 24 hours and greater than 24 hours (m = 78, SD = 13 msec) were similar. Significant differences existed for transmitral valve E/A ratios, which increased from m = 0.85 in utero to m = 1.17 (p less than 0.05) after birth, with no significant change thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Circulation↗
PubMed1987

Measurement of cardiac output and exercise factor by pulsed Doppler echocardiography during supine bicycle ergometry in normal young adolescent boys.

The purposes of this study were to determine the ability of pulsed Doppler echocardiography to consistently and accurately measure cardiac output during exercise, and to measure the exercise factor by Doppler methodology when oxygen consumption was simultaneously measured. Thirty-four healthy young adolescent male volunteers (mean age 13 years) were recruited. Submaximal exercise was performed by supine bicycle ergometry. Cardiac output was calculated as mean velocity X cross-sectional area. Successful rest and exercise determinations of cardiac output were obtained in 81% (n = 52) of the studies. Mean cardiac output increased from 4.6 to 8.9 liters/min (p less than 0.001) during exercise and mean oxygen consumption increased from 212 to 899 ml/min (p less than 0.001). Doppler-estimated rest and exercise cardiac outputs correlated well with simultaneously measured oxygen consumption (r = 0.89, SEE = 1.2 liters/min; y = 0.006 X 3.2 liters/min). Mean exercise factor was 6.4 (1.2 SD). Twenty-six pairs of rest and exercise cardiac output determinations by Doppler technique and indirect Fick method were simultaneously compared in a subset population (r = 0.86, SEE = 1.4 liters/min; slope = 0.93, y intercept = 1.4 liters/min). Results of this study demonstrate that cardiac output and exercise factor can be estimated by pulsed Doppler echocardiography during exercise.

Adolescent↗
PubMed1986

Relation of Still's murmur, small aortic diameter and high aortic velocity.

The origin of Still's innocent murmur, first described in 1909, is obscure. Seventy normal children and young adults, 29 with Still's murmur and 41 with no murmur, were studied. Pulsed Doppler and 2-dimensional echocardiography were used to evaluate possible causes, including tricuspid regurgitation, left ventricular bands, ascending and descending aortic and pulmonary velocities, ascending aortic diameter, and magnitude of spectral widths. Mean ascending aortic diameter relative to body surface area was significantly smaller for the group with Still's murmur (p less than 0.001). Since cardiac output was similar for the 2 groups, the average peak ascending velocity (133 cm/s) and average peak descending aortic velocity (118 cm/s) were significantly higher in the innocent murmur group as compared to similar respective means in the control group without the murmur (107 and 104 cm/s, respectively) (p less than 0.001 and p less than 0.01, respectively). No significant differences were found when the 2 groups were compared with respect to mean peak pulmonary artery velocity adjusted for body size, spectral widths in the ascending and descending aorta and in the pulmonary artery, and the presence of tricuspid regurgitation or ventricular bands. These observations suggest that the origin of Still's murmur is related to a small ascending aortic diameter with concomitant high aortic blood flow velocity.

Adolescent↗
PubMed1986

Balloon dilation angioplasty for coarctation of the aorta.

Eleven patients with coarctation of the aorta (C of A) underwent balloon dilation angioplasty at the University of Arizona from November 1983 to January 1985. Eight had previously undergone surgery and 3 had native C of A. Two operations were considered unsuccessful: 1 in a patient who underwent tube graft--descending aortic anastomosis narrowing and 1 in a patient with a native wedge type of C of A. Overall mean gradient fell from 47 to 13 mm Hg immediately after the procedure. Mean gradient at repeat catheterization in 7 patients (mean 8 months after angioplasty) was 6 mm Hg. Five patients showed a transient increase in the gradient measured on the day after angioplasty, with 3 showing a fairly marked increase. Values returned to levels equal to or less than gradients measured immediately after the procedure. Angiographic findings at follow-up catheterization in 7 patients showed no evidence of aneurysm formation in either the operative group or in the 2 patients with native C of A who had a membrane type of deformity. Mean C of A to ascending aortic diameter ratios increased from 0.44 to 0.80. At repeat angiography, the mean ratio was 0.76 in the 7 patients studied. Further longitudinal studies in these patients are necessary before reaching conclusions about the advantage of this procedure over surgery, but these early longitudinal results are encouraging for the populations studied: postoperative patients and patients with native membrane types of C of A.

Adolescent↗
PubMed1986

Can the technique for Doppler estimate of pulmonary stenosis gradient be simplified?

Although Doppler echocardiography has been demonstrated to accurately predict the pressure drop across the pulmonary valve in patients with pulmonary valve stenosis, prior reports have stressed the need to correct for beam-flow intercept angles, to use simultaneous imaging, and to utilize the subcostal approach. The purpose of this study was to determine the accuracy of estimating the pressure drop in pulmonary stenosis patients by means of nonimaging Doppler applied without angle correction from precordial examination. Pressure drop estimated by Doppler was compared to that measured by strain gauge manometry at catheterization. Data for 39 patients (21 simultaneous measurements; 18 nonsimultaneous) were evaluated. Results for the entire group showed a good correlation (r = 0.94; SEE = 7.9 mm Hg). The correlation for simultaneous measurement improved somewhat (r = 0.95; SEE = 5.9), but the difference was not significant. Comparison of the slope and intercept of data of this study to those of prior studies, which advocated more complex methodology, indicated that results were essentially similar and that use of the additional steps did not confer a significantly improved result. We conclude that the simplified methodology utilized in this study provides accurate Doppler estimates of pressure gradient in patients with pulmonary stenosis.

Adolescent↗
PubMed1986

Maturational changes in myocardial pump performance in newborn lambs.

We examined the left ventricular stroke volume response to fluid loading in 24 acutely instrumented newborn lambs and the right ventricular response in 12 lambs. Newborn lambs (group 1, ages 2 to 4 days) demonstrated a limited response to acute volume loading for both left and right ventricles. With maturation, the left ventricle exhibited a progressively greater ability to respond to acute volume loading, with greater peak stroke volumes achieved at higher end-diastolic pressures. The response of the right ventricle remained limited at all ages examined, with peak stroke volume achieved at lower end-diastolic pressures. We conclude that postnatal maturation of the left ventricle results in a progressively greater stroke volume response in older lambs, while the response of the right ventricle remains limited.

Aging↗
PubMed1986

Hemodynamic responses of the acutely stressed neonatal right ventricle: a maturational study in lambs.

Right ventricular Starling responses to acute volume infusion in newborn lambs were compared to those in older groups of lambs. When peak stroke volume/kg was reached during infusion, right ventricular end-diastolic pressures for the newborn group were significantly lower (p less than 0.001) than those obtained for older groups, in spite of significantly higher resting and peak stroke volumes in the two younger groups. Newborn lambs developed tricuspid regurgitation and right-to-left foraminal shunting, demonstrated by echocardiography, at a mean end-diastolic pressure of 7.5 mm Hg. No right-to-left shunting was noted in older lambs. This study demonstrated a blunted Starling response in the newborn lamb's right ventricle. The response to volume loading improved with maturation, but was still less than that reported for the left ventricle. Clinical implications regarding right ventricular immaturity and inadequate response to altered hemodynamic situations are raised.

Aging↗
PubMed1986

Accuracy and pitfalls of Doppler evaluation of the pressure gradient in aortic coarctation.

Although the pressure gradient in aortic coarctation can usually be obtained by comparison of upper and lower limb blood pressures measured by sphygmomanometry, some patients may have upper or lower limb arterial compromise as a result of prior procedures or anomalous origin of the subclavian arteries, either of which may preclude accurate gradient measurement. To determine whether Doppler echocardiography could predict the pressure gradient, the Doppler method was used to predict transcoarctation gradients in 35 studies and the data were compared with the gradients measured at catheterization. Jet velocities were not adequately obtained by Doppler recording in three neonates with coarctation and patent ductus arteriosus, leaving 32 studies for analysis. The mean age of the study patients was 6 +/- 5.8 years. The mean Doppler-estimated gradient, calculated using only jet velocities distal to the obstruction (V2) in the modified Bernoulli equation, was 44 +/- 17 mm Hg, and the mean catheterization gradient was 36 +/- 21 mm Hg (p = NS; r = 0.91, SEE = 7.0 mm Hg; slope = 0.75, y = 17.3 mm Hg). The mean Doppler-estimated gradient using both the pre- and postcoarctation velocities (V1 and V2) in the modified Bernoulli equation (n = 26) was 36 +/- 20 mm Hg, and the mean catheterization gradient was 36 +/- 21 mm Hg (p = NS; r = 0.98, SEE = 4.2 mm Hg; slope = 0.91, y = 2.8 mm Hg). Doppler echocardiography closely estimated the pressure gradient in aortic coarctation, and estimation of the gradient improved when the velocities proximal as well as distal to the obstruction were included in the modified Bernoulli equation.

Adolescent↗
PubMed1986

Doppler echocardiographic estimation of systolic pulmonary artery pressure in patients with aortic-pulmonary shunts.

The objective of this study was to determine if the pressure drop across various types of aortic-pulmonary shunts could be accurately estimated by Doppler echocardiography, and if systolic pulmonary pressure could be estimated by referencing the pressure drop across the aortic-pulmonary shunt to systolic systemic arterial pressure measured by cuff sphygmomanometry. This was done in 22 patients and Doppler results were compared with pulmonary artery pressure measured directly by strain gauge manometry. Adequate Doppler waveforms were obtained in 21 of 22 patients; 3 had a Waterston shunt, 10 had a Blalock-Taussig shunt, 1 had a left pulmonary artery-aortic anastomosis, 6 had a patent ductus arteriosus and 1 had an aortic-pulmonary window. Systolic pulmonary artery pressure estimated by Doppler echocardiography ranged from 12 to 90 mm Hg (mean 41.3 +/- 21.4 [SD] ), and measured by strain gauge manometry ranged from 20 to 90 mm Hg (mean 44.7 +/- 20.7) (p = NS, r = 0.94, SEE = 7.4 mm Hg; slope = 0.90, y intercept = 7.4 mm Hg). Systolic pulmonary artery to aortic pressure ratios predicted by Doppler recording ranged from 0.1 to 1.0 (mean 0.4 +/- 0.2 [SD] ); when calculated from direct measurement it ranged from 0.2 to 1.0 (mean 0.4 +/- 0.2) (p = NS, r = 0.92; SEE = 0.08, slope = 0.80, y intercept = 0.09). This study demonstrates that Doppler echocardiography provides an estimation of pressure drop across aortic-pulmonary shunts, and that the data can be used to estimate systolic pulmonary artery pressure by subtracting the estimated pressure drop from the systolic systemic arterial pressure.

Adolescent↗
PubMed1985

Echocardiographic ventricular shape analysis in congenital heart disease with right ventricular volume or pressure overload.

In this 2-dimensional (2-D) echocardiographic study, a computerized Fourier analysis technique refined from one that allows quantification of changes in septal shapes in normal fetuses, newborns and infants allowed analysis of left ventricular (LV) shapes in 14 patients with right ventricular (RV) volume overload (atrial septal defects), 5 with volume and pressure overload (total anomalous pulmonary venous connection), and 10 with pressure overload (complete transposition of the great arteries [TGA] with intact ventricular septum). Diastolic shape factors in the 3 groups were significantly different from those of normal subjects (p less than 0.01). Highest diastolic values were found in patients with TGA (mean 4.59 +/- 1.28). Systolic shape factors were similar in patients with atrial septal defect and normal subjects. Significant differences existed between normal subjects and patients with total anomalous pulmonary venous connection, with the greatest differences in systolic shape factor being 5.61 for TGA vs 1.87 (p less than 0.005) for normal subjects. Shape factor correlated well with hemodynamic data for RV/LV systolic pressure ratios (r = 0.93, p less than 0.001) for normalized interventricular pressure differences (r = -0.95, p less than 0.001). The lower the normalized systolic pressure difference or the higher the RV/LV ratio, the more the septum encroached into the LV cavity. Significant but weaker correlations were noted for values during diastole. Quantitative application of Fourier shape factor analysis to LV shapes allows numerical expression of visually interpreted distortions over a wide range of geometric alterations.

Cardiac Volume↗
PubMed1985

Quantitative assessment by Doppler echocardiography of pulmonary or aortic regurgitation.

This study quantitates semilunar valve regurgitation by Doppler measurement of flows. The patients selected had single semilunar valve regurgitation; the other semilunar valve was normal. For the regurgitant valve, forward and reverse flows were measured in the great vessel distal to the abnormal valve, and reverse flow was subtracted from total forward flow to yield net flow. Net flow was compared with forward flow distal to the normal semilunar valve. If all values were computed accurately, net flow should equal forward flow distal to the normal semilunar valve. Twenty patients were studied and 18 had satisfactory recordings. Mean flow in the normal great vessel (3,511 ml/min) was not significantly different from mean net flow in the vessel with the abnormal valve (3,590 ml/min). The correlation coefficient for the paired flow measurements was +0.91 (685 ml [standard error of the estimate]). The slope of the relation was 0.88 and the intercept was 502 ml. Percent regurgitation varied from 29 to 73% and the percentage generally corresponded to clinical estimates. It is concluded that this method, which includes an internal control for each patient, is useful and reasonably accurate for clinical use in patients with pulmonary regurgitation, and appears clinically useful in some patients with aortic regurgitation.

Adolescent↗
PubMed1985

Transatrial septal velocity measurement by Doppler echocardiography in atrial septal defect: correlation with Qp:Qs ratio.

Right atrial velocities measured perpendicular to the atrial septum by Doppler echocardiography in patients with atrial septal defects (ASD) have a discernible morphology that may bear a relation to shunt magnitude. The integral of the right atrial Doppler waveform was compared with shunt magnitude measured at cardiac catheterization or nuclear shunt scan in 17 ASD patients. For control subjects, the mean right atrial velocity was 15 +/- 4 cm/s (+/- standard deviation) and that for ASD patients was 41 +/- 11 cm/s (p less than 0.001). Doppler pulmonary-to-systemic flow ratio (Qp:Qs) correlated with catheterization Qp:Qs ratio (n = 9, r = 0.85, SEE = 0.27) and with nuclear Qp:Qs ratios (n = 8, r = 0.60, SEE = 0.51). Mean transatrial septal velocity in ASD patients correlated with catheterization Qp:Qs ratio (n = 9, r = 0.8, SEE = 6.0) and with simultaneous Doppler Qp:Qs ratio (n = 16, r = 0.89, SEE = 4.9, y = 16.2 +/- 8.3). Although Qp:Qs ratio can be approximated by measuring pulmonary and systemic flow by Doppler echocardiography in many ASD patients, this newly described method allows estimation of Qp:Qs ratio. It is useful when these more conventional measurements cannot be performed because of turbulence or when inadequate imaging prevents Doppler pulmonary to systemic flow measurement.

Adolescent↗