Acceleration Slope Research Articles

Skeletal muscle contraction in healthy volunteers: assessment with Doppler tissue imaging.

To evaluate Doppler tissue imaging (DTI) in the measurement and characterization of skeletal muscle movement and contraction. Five healthy male subjects were examined with a commercially available ultrasound imaging unit modified for DTI. Velocities of the rectus femoris and gastrocnemius-soleus muscle motion were measured during the patellar and ankle reflexes, respectively. Velocity profiles were analyzed after digitization of the DTI images. Time to peak velocity, velocity range, and relaxation time were examined in each case over three contractions. For reflex contractions, reproducibility was examined by determining the latency period, area under the velocity curve, and duration of contraction for each of five consecutive reflexes. Isotonic muscle contraction could be distinguished from passive movement by a higher tissue velocity range, by a more rapid initial acceleration slope, and by the velocity differential across the muscle. The intensity and duration of the contraction and plateau and relaxation phases of isotonic contraction could be measured in all muscle groups. DTI provides detailed information about the dynamics of skeletal muscle contraction.

Echocardiographic description of the CarboMedics bileaflet prosthetic heart valve

Objectives. The aim of this study was to describe the echocar-diographic appearance of the normal CarboMedics prosthesis in the aortic and mitral positions.Background. Echocardiography is the standard method of assessing prosthetic valves. However, new valve designs may still be marketed without an accompanying echocardiographic description. The CarboMedics prosthesis is in widespread use, but few noninvasive hemodynamic data have been published.Methods. Echocardiography was performed in 147 patients with a total of 96 normally functioning CarboMedics prostheses in the aortic position and 75 in the mitral position; in 24 patients, valves were implanted in both positions. The following variables were measured: peak and mean transvalvular velocities, peak and mean instantaneous gradient estimated from the modified Bernoulli equation, aortic acceleration slope, pressure half-time, transvalvular flow and effective orifice area using the continuity equation. Patterns of regurgitation were observed by trans-thoracic study in an valves and by transesophageal study in selected mitral valve prostheses.Results. For the aortic valve prostheses, estimated mean gradient ranged between 6 and 19 mm Hg. Effective area differed markedly among the anulus diameters (p < 0.001), with a mean value of 1 cm2for the 19-mm valve and 2.6 cm2for the 29-mm valve. For the mitral valve prostheses, mean gradient ranged from 3 to 7 mm Hg. There were a total of four washing leaks, one on either side of each pivotal point, and these lasted throughout systole or diastole. One jet was commonly more prominent than the other three.Conclusions. The CarboMedics prosthesis offered relatively little resistance to forward flow except at small anulus diameters. The washing jets were prominent and would be easy to misdiagnose as a sign of paraprosthetic regurgitation.

Intra- and interobserver reproducibility of Doppler-assessed indexes of left ventricular diastolic function in a population-based study (the Framingham Heart Study)

The reproducibility of a variety of Doppler indexes of diastolic function in an epidemiotogic setting and in atrial fibrillation have not been reported. This study examined the reproducibility of left ventricular inflow in subjects in sinus rhythm (n = 80) and atrial fibrillation (n = 12), randomly selected from the original cohort of the Framingham Heart Study. The following Doppler indexes were assessed for all subjects: peak and integral of early (E) diastolic inflow velocity, acceleration slope and time, deceleration slope and time, and pressure half-time. For subjects in sinus rhythm, the following parameters also were measured: the peak and integral of late (A) diastolic inflow velocity, ratios of peak velocities and integrals E/A, and atrial filling fraction. Intraobserver and interobserver variability were evaluated by statistical methods including Student's f test of the systematic differences (bias), percent bias, correlation coefficients, measurement precision, and percent precision. In subjects in sinus rhythm, although the interobserver bias was statistically significant for most of the parameters, it was <10% for all but 1 parameter (acceleration time). For the peak and integral measures, the intra- and interobserver correlations were ≥ 0.89, with intra- and interobserver percent precision measures within 2.2 to 13.0% of the corresponding mean values. The acceleration, deceleration and pressure half-time measures had somewhat lower correlations (interobserver correlations ranging from 0.59 to 0.96), with percent precision measures further from the corresponding means (interobserver percent precision ranging from 10.1 to 19.5%). The analyses of subjects with atrial fibrillation showed similar trends, despite the biologic (cycle-to-cycle) variability intrinsic to this arrhythmia. In conclusion, in an epidemiologic setting, the majority of Doppler indexes of diastolic function demonstrate excellent measurement reproducibility, especially the peak and time velocity integral measurements. Measurement variability may limit the reproducibility of early diastolic acceleration and deceleration parameters.

The characteristics of hepatic venous flow velocity pattern in patients with pulmonary hypertension by pulsed Doppler echocardiography.

To determine the characteristic change in the Doppler hepatic venous flow velocity pattern in patients with pulmonary hypertension (PH), 21 patients with PH in sinus rhythm were examined with pulsed Doppler echocardiography. The control group included 13 subjects with chest pain syndrome and normal pulmonary arterial pressure. The hepatic vein Doppler signal was biphasic with one peak during ventricular systole (S wave) and the other in diastole (D wave). A reversed signal was recorded after contraction (A wave). The peak velocity of the A wave (Va), S wave (Vs), and D wave (Vd), the time velocity integral of these waves (VIa, VIs, and VId), the acceleration time (t-AC), and the slope of acceleration (s-AC) in the S wave were measured. Compared with controls the PH group had a higher value of Va (26.88 +/- 10.30 vs 13.41 +/- 3.69 cm/sec; p less than 0.01), VIa (2.55 +/- 1.18 vs 1.20 +/- 0.34 cm; p less than 0.01), VIa/(VIs+VId) (0.34 +/- 0.22 vs 0.14 +/- 0.06; p less than 0.01), and s-AC (372 +/- 156 vs 203 +/- 103 cm/sec2; p less than 0.01). They also had a shorter t-AC (101 +/- 32 vs 136 +/- 27 msec; p less than 0.01). There was a weak correlation between the reversed atrial flow and the right heart pressures (r = 0.43 to 0.66). Thus, the hepatic venous flow velocity pattern by Doppler echocardiography is clinically useful in evaluating pulmonary hypertension.

Atrioventricular Electrotonic Interaction in Complete Atrioventricular Block: An Experimental Model Using Radiofrequency Energy in the Rabbit Heart

Provided the conditions for electrotonic transmission exist, an automatic focus surrounded by a block zone may be externally modulated. The atrioventricular (AV) electrotonic interaction was studied in 16 perfused rabbit hearts with supra-Hisian complete AV block induced using low radiofrequency energy doses (2.5 watts; 10 seconds). In nine experiments the sinus node was preserved (group I), whereas in seven it was removed maintaining an AV nodal rhythm (group II). The V-V (ventricular cycle length) and V-A (coupling of the intervening atrial beat) in both groups, and also the A-A (atrial cycle length) and A-V (coupling of the intervening ventricular beat) intervals in group II, were measured beat by beat after current delivery. The phase response curves V-V versus V-A, and A-A versus A-V showed AV interaction in five experiments from group I, and in four from group II, as follows: (1) accelerating phase response curve, characterized by a pacemaker acceleration (V-V or A-A abbreviation) at a critical V-A or A-V coupling interval; maximum acceleration could be progressively (phase response curve without rapid cross-over) or briskly (phase response curve with rapid crossover) reached; from this point onwards acceleration decreased with a further increase in V-A or A-V coupling interval (acceleration slope). (2) Biphasic phase response curve, characterized by initial delaying and late accelerating phases. Maximum acceleration and the acceleration slope were both smaller in accelerating phase response curves without rapid cross-over. On reverting complete block in two experiments, a progressive increase in maximum acceleration and acceleration slope was observed. (1) AV interaction in complete AV block can be manifested as accelerating or biphasic phase response curves; (2) transition from electrotonic interaction to conduction seems to be a continuum.

The Effect of Hematocrit Alterations on Cerebral Vascular CO2 Reactivity in Newborn Baboons

To evaluate whether baseline hematocrit affects cerebral vascular reactivity to CO2, we studied the cerebral blood flow velocity in the internal carotid artery of newborn baboons, using a pulsed Doppler technique with direct imaging. Velocity responses to varying arterial CO2 tension (PaCO2) levels were first tested under baseline hematocrit (mean +/- SD, 35.9 +/- 4.7%), after hemodilution (hematocrit 20.3 +/- 2.7%), and after hemoconcentration (hematocrit 52.7 +/- 5.2%). The data were analyzed using multiple regression models, in which blood flow velocity values were the dependent variables, and PaCO2, hematocrit, and their interaction terms (product) were the independent variables. Models for the maximum systolic velocity, time-averaged mean velocity, and the end-diastolic velocity revealed a highly significant PaCO2 effect; with each mm Hg PaCO2 increase, the velocities increased between 2.9 and 3.6% (21.8-27% per 1 kPa). PaCO2 and hematocrit interaction terms were also highly significant and inversely related to velocity (negative slopes) in the maximum systolic velocity and time-averaged mean velocity models, suggesting that when the hematocrit is high, the PaCO2-induced increase in flow velocity would be attenuated, and when the hematocrit is low, such a response would be accentuated. The hematocrit effect on PaCO2 reactivity was maximal on maximum systolic velocity and least on end-diastolic velocity. Systolic velocity acceleration slope was significantly reduced when the hematocrit was high, and increased when the hematocrit was low. Based on these findings, we conclude that hematocrit is an important variable affecting the rate of kinetic energy change in the large vessels, thereby influencing cerebral vascular PaCO2 reactivity as assessed in Doppler studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Reference values and reproducibility of Doppler echocardiography in the assessment of the tricuspid valve and right ventricular diastolic function in normal subjects

The Doppler echocardiographic indexes of the tricuspid and mitral valves were assessed in 74 normal subjects (35 women and 39 men, mean age 45 years). A reproducibility study was also performed to examine the various sources of technical and biological variability. There were significantly higher peak early and late flow velocities across the mitral valve than across the tricuspid valve (0.67 ± 0.13 and 0.47 ± 0.12 vs 0.51 ± 0.08 and 0.35 ± 0.09 m·s −1, respectively; all p < 0.0001). There was no significant difference between the early:late (E:A) velocity ratios of the 2 valves (1.65 ± 0.73 vs 1.75 ± 0.67, p < 0.01). There was a steeper mitral early deceleration slope (−3.59 ± 1.07 vs −2.95 ± 0.91 m·s −2) but no significant difference in pressure half-times across the 2 valves (47 ± 7 vs 51 ± 12 ms, p < 0.1). No influence of gender or body surface area could be demonstrated. There was a weak but significant relation between mitral peak early, peak atrial velocity and E:A ratio and age (r = −0.39, p < 0.001, r = 0.23, p < 0.01, and r = −0.245, p < 0.01, respectively). There was no significant correlation between any of the tricuspid flow parameters and age. Respiration caused pronounced variability in the tricuspid Doppler indexes and all tricuspid flows were sampled and analyzed only during inspiration. The intra- and interobserver variabilities were small for all of the Doppler indexes measured, but the day-to-day variability was quite significant especially for the pressure halftime, deceleration and acceleration slope values. The present study documents in detail the normal Doppler flow characteristics of the tricuspid valve and compares them with the normal mitral flow parameters in the same subject.

Doppler blood flow velocity waveforms in alpha-thalassemia hydrops fetalis.

Doppler shift blood flow velocity-time waveforms in the umbilical arteries (UA), aorta (A), and inferior vena cava (IVC) in eight fetuses with alpha-thalassemia (alpha-thal) hydrops fetalis were described. The UA waveforms in these fetuses with anemia in utero depicted a hyperdynamic circulatory state with a relative increase in acceleration slope, more linear decline from maximum systole to end diastole, and reduced spectral broadening. The aortic waveforms similarly displayed distorted systolic peaks, flow turbulence, and greatly elevated diastolic frequencies. Reversal of end diastolic flow in the IVC also indicated cardiac decompensation in these fetuses. Progressive changes in these waveforms were apparent in two fetuses that had serial evaluation. In another four fetuses in which alpha-thal major was diagnosed in the second trimester by DNA analysis and had Doppler evaluation before termination of pregnancy, consistent changes in the UA, A, and IVC waveforms were not observed. This study confirms the potential usefulness of Doppler spectral waveforms in depicting altered hemodynamic changes in the fetus and in the evaluation of hydrops fetalis. Doppler ultrasound examination can be included as part of the routine workup of hydrops fetalis.

Doppler sonographic flow measurement in the anterior cerebral artery and celiac trunk in infants with coarctation syndrome in comparison with healthy infants

15 infants (gestational age 47 +/- 11 weeks; weight 3180 +/- 1082 g) with angiocardiographically proven coarctation of the aorta and 53 healthy infants (gestational age 39 +/- 8 weeks; weight 2830 +/- 1418 g) were investigated by echocardiography and pulsed doppler sonography. In all children pulsed doppler recordings were obtained in the anterior cerebral artery (prestenotic reference vessel) and the truncus coeliacus (poststenotic reference vessel). Nine variables were measured from each doppler signal: The maximal systolic velocity, the endsystolic and enddiastolic velocity, the pulsatility-index, the acceleration slope (peak rate of acceleration), the deceleration slope (peak rate of deceleration), the antegrade flow time and the acceleration and deceleration time. The healthy infants showed a pulsatile flow profile in the anterior cerebral artery and the truncus coeliacus. In normal subjects the maximal systolic velocity and the acceleration slope in the truncus coeliacus were always higher than in the anterior cerebral artery. There was no difference in the endsystolic and enddiastolic velocity, the pulsatility-index, the flow times and the deceleration slope. In children with coarctation of the aorta a decreased and nonpulsatile flow in the truncus coeliacus could be shown. The following variables were significantly lower than in the healthy control group: The maximal systolic velocity, the pulsatility-index, the acceleration and deceleration slope and the antegrade flow time and acceleration time. In the anterior cerebral arteries of children with coarctation the maximal systolic and enddiastolic velocity were significantly higher than in the healthy control group. Pulsed doppler recordings were obtained in 9 patients after surgical correction: The maximal systolic and endsystolic velocity, the pulsatility-index, the acceleration and deceleration slope in the truncus coeliacus increased significantly although these values were lower than in the healthy control group. The flow parameters in the anterior cerebral arteries postoperatively showed no significant difference from the preoperative values. Pulsed dopplersonography of the flow in the anterior cerebral artery and the truncus coeliacus is a good method for diagnosis of coarctation of the aorta and postoperative controls.

The assessment of the feto-placental circulation with continuous wave doppler ultrasound

Continuous wave Doppler ultrasound was used together with B-mode real time ultrasound to study feto-placental blood flow in utero. The results of 887 examinations on 221 patients are presented. The fetal heart rate acceleration slope and pulsatility index (P.I.) of the audiofrequency ultrasound display were analysed. There was a significant reduction in fetal heart rate ( P < 0.001) and P.I. ( P < 0.001) with advancing gestational age in normal pregnancy. In contrast, in retarded intrauterine growth a significant increase in P.I. values was observed in 77% of patients.

Simulation of strong ground motions

abstractThe estimation of potential strong ground motions at short epicentral distances (Δ = 10 to 25 km) resulting from large earthquakes, M ≧ 6.5, generally requires extrapolation of a limited data set. The goal of this project has been to quantify the extrapolation through a simulation technique that relies heavily upon the more extensive data set from smaller magnitude earthquakes. The simulation utilizes the smaller events as Green's functions for the elements of a larger fault. Comparison of the simulated peak acceleration and duration with the data from the Parkfield earthquake is very good. Simulation of three earthquakes, M = 5.5, 6.5, and 7.0 indicate that the slope of the peak acceleration versus distance curve (Δ = 5 to 25 km) flattens, for strike-slip earthquakes, as the magnitude increases.