Showing papers on "Cardiac cycle published in 1994"

Reference ranges for fetal venous and atrioventricular blood flow parameters

Abstract: This cross-sectional study establishes reference ranges with gestation for Doppler parameters of fetal venous and atrioventricular blood flow. Color flow Doppler was used to examine 143 normal singleton pregnancies at 20-40 weeks' gestation. Flow velocity waveforms were recorded from the ductus venosus, right hepatic vein and inferior vena cava. The waveforms are triphasic, reflecting ventricular systole, early diastole and atrial contraction. Peak velocities for these parameters were measured with pulsed Doppler and a new index, the peak velocity index for veins (PVIV), was calculated. Similarly, time-averaged maximum velocities for the whole cardiac cycle were measured and the pulsatility index for veins (PIV) was calculated. Flow velocity waveforms were also recorded at the level of the atrioventricular valves and the ratios of peak velocities at early diastolic filling (E) and atrial contraction (A) were calculated. Regression analysis was used to define the association of each measured and calculated Doppler parameter with gestational age. Blood flow velocities in the fetal veins and velocities and E/A ratios across the atrioventricular valves increased significantly with gestation, whereas PVIV and PIV decreased. Blood flow velocities were highest in the ductus venosus and lowest in the right hepatic vein, and PVIV and PIV were highest in the hepatic vein and lowest in the ductus venosus. In the ductus venosus, there was always forward flow throughout the heart cycle, whereas in the inferior vena cava and hepatic vein during atrial contraction, flow was away from or towards the heart or there was no flow. Pulsatility of flow velocity waveforms in the venous system is the consequence of changes in pressure difference between the venous system and the heart during the heart cycle. The finding that PVIV and PIV decrease with gestation is consistent with decreasing cardiac afterload and maturation of diastolic ventricular function.

The discharge behaviour of single vasoconstrictor motoneurones in human muscle nerves.

Abstract: 1. The discharge behaviour of fourteen single sympathetic vasoconstrictor efferents was studied using a tungsten microelectrode inserted percutaneously into a motor fascicle of the radial or peroneal nerve in eight awake supine subjects. Units were classified as vasoconstrictor because their firing properties correlated appropriately to changes in cardiac interval and arterial pressure. 2. On average, individual vasoconstrictor units discharged in only 21% of heart beats, with an overall mean frequency of 0.47 Hz. Usually only one spike was generated per cardiac cycle. Calculated from cardiac cycles in which a unit fired from two to seven spikes, the mean within-burst firing rate was 18.8 +/- 2.5 Hz (mean +/- S.E.M.); but instantaneous frequencies above 50 Hz were occasionally observed. 3. Measured from a defined R-wave of the ECG, the spike onset latency varied over 358 +/- 33 ms, suggesting considerable variation of synaptic delays in the baroreflex arc. This latency had a relatively uniform temporal relationship with the burst onset or peak latency, compatible with a fixed recruitment order of individual sympathetic neurones. 4. In view of the low average firing rate of individual units we suggest that the variable instantaneous firing rates may optimize the contractile responses of vascular smooth muscle.

Noninvasive pulsed infrared spectrophotometer.

Abstract: A method and apparatus for monitoring glucose, ethyl alcohol and other blood constituents in a noninvasive manner. The measurements are made by monitoring infrared absorption of the desired blood constituent in the long infrared wavelength range. The long wavelength infrared energy generated by source (400) is passed through a finger (406). To prevent the high energy source from burning or causing patient discomfort, shutter (404) and bandpass filters (410) cause only short bursts of energy to be sent through the finger with a very low duty cycle and low optical bandwidth. The bursts are further synchronized by shutter (404) with systole and diastole of the cardiac cycle so that only two pulses are sent per heart beat, one during diastole and one during systole. The detection signals measured at detectors (412) during application of these bursts of energy are used to calculate the concentration of blood constituents in accordance with a polynomial equation.

Quantification of ischaemia induced vulnerability by precordial T wave alternans analysis in dog and human.

Abstract: Objective: The aim was to examine the regional specificity of T wave alternans and the value of precordial ECG monitoring for non-invasive tracking of cardiac vulnerability during acute coronary artery occlusion and reperfusion in animals and humans. Methods: The left ventricular ECG was monitored during two acute occlusions of the left anterior descending coronary artery and subsequent reperfusion in each of 61 chloralose anaesthetised dogs, and over 150000 beats were analysed. In subgroups of these animals, lead II and precordial lead V5 were monitored or epicardial electrograms were recorded. In seven patients, lead II and precordial leads V5 were monitored during angioplasty. T wave alternans magnitude was quantified by complex demodulation. The same recording equipment and analytical methods were used in the clinical and experimental studies. Results: A close temporal correspondence and linear correlation was found between T wave alternans magnitude – but not ST segment depression or ventricular premature beat incidence – and the incidence of spontaneous ventricular tachycardia and fibrillation during acute coronary artery occlusion and reperfusion. Epicardial electrograms showed alternans to be regionally specific, occurring in the ischaemic but not in the normal zones, and to predict spontaneous ventricular fibrillation and ventricular tachycardia (sensitivity = 79%, specificity = 86%). A significant linear relationship (r = 0.86, p<0.01) between alternans magnitude detected in V5 and the left ventricular intracavitary lead indicates that the precordial leads could be used to assess cardiac vulnerability from the body surface. Lead V5 showed greater resolution than lead II. In humans, the precordial leads overlying the ischaemic zone were superior to lead II or Frank leads for alternans detection during both the occlusion and the reperfusion phases. In both animals and humans, alternation invariably occurred during the first half of the T wave, coinciding with the vulnerable period of the cardiac cycle and suggesting an important electrophysiological link to cardiac vulnerability. Conclusions: Alternans is regionally specific and is linearly projected to the precordium. Quantification of its magnitude in the precordial ECG may provide a non-invasive means for tracking cardiac vulnerability during acute myocardial ischaemia and reperfusion in both animals and humans. Cardiovascular Research 1994; 28 :1440-1449

Vessel diameter changes during the cardiac cycle

Abstract: Retinal vessel diameter, which is an important parameter in blood flow measurement, is affected by pulsation during the cardiac cycle and by vasomotion. This project studied these changes by analysing three monochromatic fundus photographs taken in eight arbitrary parts of the cardiac cycle of 10 healthy subjects. It was found that the venous diameter decreased in early systole, increasing thereafter to a maximum level in early diastole and then declined towards end diastole. The maximum change of 4.82% (between early systole and early diastole) (p = 0.03) represents a 9.83% change in volumetric blood flow. The arterial diameter peaked in mid-late systole, increasing by 3.46% (p = 0.01); this represents a blood flow increase of 7.04%. Vasomotion led to changes of 3.71% and 2.61% in arteries and veins respectively. It is concluded that for accurate measurement of retinal blood flow, fundus photographs should be taken synchronised with the electrocardiogram.

Direct Negative Inotropic and Lusitropic Effects of Sevoflurane

Abstract: BACKGROUND Volatile anesthetics depress left ventricular mechanical performance during multiple phases of the cardiac cycle. The effects of sevoflurane on systolic and diastolic function have yet to be fully evaluated. This investigation characterized the systemic and coronary hemodynamic, inotropic, and lusitropic actions of sevoflurane in chronically instrumented dogs in the presence and absence of autonomic nervous system (ANS) reflexes. METHODS Because ANS activity may influence the actions of volatile anesthetics in vivo, experiments were conducted in both ANS-intact and ANS-blocked animals. Eighteen experiments were performed in nine dogs chronically instrumented for measurement of aortic and left ventricular pressure, rate of change of left ventricular pressure, subendocardial segment length, diastolic coronary blood flow velocity, and cardiac output. The preload recruitable stroke work slope was used to assess myocardial contractility. Diastolic function was evaluated by a time constant of isovolumic relaxation, maximum segment lengthening velocity during rapid ventricular filling, and a regional chamber stiffness constant. Dogs were assigned to receive sevoflurane with or without pharmacologic blockade of the ANS in a random fashion. On separate experimental days, systemic and coronary hemodynamics and left ventricular pressure--segment length diagrams and waveforms were recorded in the conscious state and during sevoflurane anesthesia (1.0, 1.25, 1.5, and 1.75 MAC). RESULTS In dogs with intact ANS reflexes, sevoflurane caused significant (P < 0.05) increases in heart rate and dose-related decreases in mean arterial pressure, left ventricular systolic pressure, cardiac output, and diastolic coronary vascular resistance. Sevoflurane also decreased myocardial contractility (preload recruitable stroke work slope 96 +/- 4 in the conscious state to 42 +/- 3 mmHg at 1.75 MAC). Sevoflurane prolonged isovolumic relaxation (time constant of isovolumic relaxation 35 +/- 1 in the conscious state to 51 +/- 3 ms at 1.75 MAC) and decreased rapid ventricular filling (maximum segment lengthening velocity 40.2 +/- 6.0 in the conscious state to 21.8 +/- 3.8 mm.s-1 at 1.75 MAC) without affecting regional chamber stiffness. Sevoflurane caused similar alterations in functional indices of left ventricular systolic and diastolic performance in autonomically blocked dogs. CONCLUSIONS Sevoflurane caused direct negative inotropic and lusitropic effects in chronically instrumented dogs with and without ANS blockade.

The application of breath hold phase velocity mapping techniques to the measurement of coronary artery blood flow velocity: phantom data and initial in vivo results.

Abstract: A segmented kappa-space breath hold phase velocity mapping technique has been developed for the study of coronary artery blood flow velocity. In vitro validation has been performed using a number of pulsatile flow phantoms and the accuracy of the technique for determining the velocity increase at the site of a stenosis demonstrated in several phantom models. Examples of both in-plane and through-plane velocity maps of the left anterior descending and right coronary arteries of normal subjects in early diastole are presented. In one subject, through-plane velocity maps were obtained in the right and left anterior descending arteries throughout the cardiac cycle in order to generate flow velocity time curves. The problems associated with coronary artery velocity mapping are discussed.

LDA Measurements of Mean Velocity and Reynolds Stress Fields Within an Artificial Heart Ventricle

Abstract: Laser Doppler Anemometry measurements of mean (ensemble average) velocities and turbulent (Reynolds) stresses at 140 locations within the left ventricle of the Penn State 70 cc electric artificial heart/ventricular assist device are reported at 8 times during the cardiac cycle. Mean velocity patterns indicate that the surfaces of the blood sac and valve tracts are exposed to significant levels of wall shear stress (good wall washing) during some portion of the flow cycle, and there is no location where the flow is stagnant over the entire flow cycle. This implies that thrombus deposition within the artificial heart should be suppressed. Turbulent stresses in the main pumping chamber and the outflow tracts of the tilting disk valves do not exceed 2000 dynes/cm2. The highest turbulent stresses (20,000 dynes/cm2) and smallest turbulent microscales (6 microns) are found in the regurgitant jets on the minor orifice side of the aortic valve during diastole and the mitral valve during systole. Taken together, the data suggest that improvements in artificial heart fluid mechanics will come through valve design and pump operating conditions, not pumping chamber design.

Oscillatory motion of the normal cervical spinal cord.

Abstract: PURPOSE: To determine the normal pattern of cervical spinal cord motion with measurement of cervical spinal cord velocity by means of phase-contrast magnetic resonance (MR) imaging. MATERIALS AND METHODS: Spinal cord velocity was measured in 11 healthy subjects with a modified gradient-echo pulse sequence on a conventional 1.5-T MR imaging system that generated phase images sensitive to slow motion. Prospective electrocardiogram gating was used to assess velocity as a function of the cardiac cycle. The accuracy of velocity measurements was estimated with images of a phantom moving at constant velocity. RESULTS: The cervical spinal cord moves with an oscillatory pattern in the craniocaudal direction. The maximum velocity (7.0 mm/sec +/- 1.4 [standard deviation]) in the caudal direction occurred approximately 109 msec +/- 20 after electrical cardiac systole. The maximum velocities in subsequent oscillations decreased toward zero before the next cardiac systole. CONCLUSION: The cervical spinal cord oscillate...

Dynamic three-dimensional echocardiography with a computed tomography imaging probe: initial clinical experience with transthoracic application in infants and children with congenital heart defects.

Abstract: OBJECTIVE--To assess the clinical applicability of a prototype computed tomographic echocardiographic imaging probe in paediatric patients with congenital heart disease. DESIGN--A phased array echocardiographic transducer (64 elements, 5 MHz) mounted on a sliding carriage was used transthoracically in various positions on the chest. The transducer moves from the outflow tract to the apex of the heart in 0.5 to 1.3 mm increments and records a tomographic slice of the heart at each increment level. Parallel images are recorded at a frame rate of 25-30 images/s. At each level a complete cardiac cycle is recorded. The images are digitised and stored in the image processing computer, which reconstructs the anatomical structures of the heart in a three-dimensional format by means of different grey scales. PATIENTS--45 paediatric patients (age range 3 days to 17 years) with various congenital heart defects who had been admitted to hospital for diagnostic or therapeutic cardiac catheterisation or surgery. RESULTS--Good quality echocardiographic pictures were obtained in all but two of the 45 patients. Three-dimensional reconstructions of the heart were possible from transthoracic echocardiograms. The recorded cardiac chambers and valves were displayed in three-dimensions in real time (four-dimensionally). The heart was also displayed in real time in any desired plane and in up to five planes simultaneously without having to change the position of the transducer on the chest. Different parts of the heart were displayed in a view similar to that seen by a surgeon during an operation. Image acquisition took 3-5 minutes and three-dimensional reconstruction of various cardiac structures 20-90 minutes. CONCLUSIONS--The computed tomographic imaging probe facilitates acquisition of echocardiographic data as multiple planes can be obtained from one transducer position. Display of three-dimensional structures of the heart may enhance the understanding of cardiac anatomy.

Preliminary Analysis of the Effects of Blood Vessel Movement on Blood Flow Patterns in the Coronary Arteries

Abstract: Blood flow patterns are believed to be involved in the formation and progression of arterial diseases. It is possible that the normal physiologic movement of blood vessels during the cardiac cycle affects blood flow patterns significantly. For example, the contraction of the heart in systole and subsequent relaxation in diastole create movements of the coronary arteries, as evidenced in real-time angiography. The effects of this movement on coronary artery flow patterns have never been previously analyzed. This work was undertaken to provide a preliminary estimate of the importance of the effects of such physiologic movements on blood flow patterns in the coronary arteries. A Womersley-type solution was used to determine the effect of axial movement on the wall shear rate in a simplified model of the coronary arteries. The pulsatile pressure gradient was derived from previously published coronary artery flow waveforms. The axial movement function was obtained from a three-dimensional reconstruction of a biplanar coronary angiogram. Significant changes in wall shear rate were noted when the movement was taken into account. The maximum and minimum wall shear rates were 10 percent smaller and 107 percent larger in magnitude respectively, and the Oscillatory Shear Index (OSI) was doubled. Most of the changes in wall shear rate were observed in systole, when the pressure gradient is minimal and the movement is strongest. The results indicate that blood vessel movement during the cardiac cycle has a significant effect on hemodynamic phenomena which have been associated with the development of atherosclerosis.

Mitral annular function assessed by 3D imaging for mitral valve surgery.

Abstract: We developed a surgical technique for mitral valve reconstruction without a prosthetic ring. This procedure may have two advantages. One is avoidance of the potential thrombogenicity of the prosthetic ring, and the other is that this procedure may maintain the normal function of mitral annulus. To clarify the latter advantage, we defined a method for 3D assessment of the heart, especially for the dynamic changes of the mitral annulus. 3D images of the heart, including both mitral and tricuspid annuli in eight phases during the cardiac cycle, were reconstructed from magnetic resonance images of seven normal subjects, and used for this study. To depict the changes in the annular shape, we determined the following parameters of the annular function: (a) annular excursion, (b) direction of motion (direction cosine) and (c) orientation of the annulus (direction cosine) for the annular motion, (d) annular area and (e) displacement of the anterior portion from the approximated plane of the annulus. The data for the systolic annular motion indicate that the mitral annulus moves towards the apex with slight caudal deviation, with the excursion of 12.1 mm. The change in annular orientation indicates that the mitral annulus shows translational motion during systole. The mitral area was reduced by 25.6% (n = 5) from mid-diastole to mid-or late systole. Displacement at the anterior portion of the annulus did not change markedly during systole. The results demonstrate the physiologic function of the mitral annulus in normal subjects. This method will be applied to the clinical study of mitral valve reconstruction surgery. Based on the differences in annular length in intact and excised states, we describe the intact state of the posterior leaflet as "natural redundancy." Restoration of this natural redundancy has been a hallmark of successful mitral repair for over 20 years.

Method and apparatus for assessing cardiovascular performance

Abstract: A method of assessing the cardiovascular performance of a subject, by: applying periodically, in synchronism with every n th heart cardiac cycle wherein "n" is at least two, external pressure pulsations on a peripheral organ of the subject sufficient to alter ventricular loading; acquiring data representative of the ventricular pressure, and data representative of the ventricular volume, of the subject's heart over a plurality of heart cardiac cycles; and utilizing such data for assessing the cardiovascular performance of the subject. Ventricular loading may be altered by impeding ventricular ejection (changing afterload), and/or by altering venous return to the heart (changing preload).

Pulsatile Velocity Measurements in a Model of the Human Abdominal Aorta Under Simulated Exercise and Postprandial Conditions

Abstract: This study examines the hemodynamics of the abdominal aorta during physiological changes in flow rates and pulse rate that occur under exercise and postprandial conditions. Hemodynamic measurements were performed using an in vitro model which took into account seven major branches, the curvature, and the pulsatile nature of blood flow of the abdominal aorta. Magnetic Resonance Imaging velocimetry employing phase-velocity encoding was used to measure the pulsatile axial velocity profiles for the entire cross-section at three axial locations. Under simulated exercise conditions, the forward velocities were approximately double those seen during rest, and the flow reversal seen for resting conditions was greatly reduced. Near the posterior wall of the infrarenal aorta, the velocities were negative for only 21 percent of the cardiac cycle as compared with 82 percent for resting conditions. Postprandial conditions produced a 25 percent reduction in peak velocity and a 33 percent reduction in mean velocity near the left anterior wall of the aorta just distal to the superior mesenteric artery (in comparison with resting conditions). The changes that can occur in abdominal aorta hemodynamics under different physiologic conditions may affect the rate of progression of atherosclerosis at this site.

Quantitative blood flow measurement using steady-state transport-induced adiabatic fast passage

Abstract: A subtractive time of flight technique for MR angiography and quantitative blood flow measurement. Proton spins of water in the arterial supply to a tissue or organ are inverted in a steady-state fashion by applying constant amplitude off-resonance radio frequency pulses in the presence of a constant linear magnetic field gradient to effect adiabatic fast passage transport-induced inversion of spins which move in the direction of the gradient. An angiogram is formed by subtracting an image acquired with the arterial inversion pulse from a control image acquired with no arterial inversion. By inverting the spins in a steady-state manner, no cardiac gating is necessary for imaging organs. However, cardiac gating is desirable when imaging the heart so that spins of blood passing through the coronary arteries can be inverted during systole, when most of the blood is in the left ventricle, and imaged at end diastole, when most of the blood is in the coronary arteries. A coronary angiogram is then formed by subtracting images acquired with and without the inversion pulse. Also, by applying several inverting and imaging pulses during a cardiac cycle in accordance with the technique of the invention, a characteristic banding pattern may be formed in the fluid whereby each band corresponds to a population of spins that experienced inversion due to a single RF pulse. Since the width of the inversion band is proportional to the duration of the RF pulse and the velocity of the spin, measurement of the thickness of the inverted and uninverted bands allows for calculation of flow velocity. By gating such a pulse sequence to the cardiac cycle, time resolved in vivo velocity measurements may be made.

Abnormal subendocardial function in restrictive left ventricular disease.

Abstract: OBJECTIVE--To study possible disturbances in left ventricular long axis function in patients with a restrictive filling pattern. DESIGN--Prospective examination of the left ventricular transverse and longitudinal axes, transmitral flow, and the apexcardiogram. SETTING--A tertiary referral centre for cardiac diseases. SUBJECTS--21 normal subjects, age (SD) 51(11); 30 patients of similar age with a restrictive left ventricular filling pattern, defined as short early diastolic deceleration time less than the lower 95% confidence limit of the normal value (120 ms). 20 patients had a normal and 10 had an increased left ventricular end diastolic cavity size. RESULTS--Mitral Doppler echocardiography: E wave velocity was high only in patients with a normal cavity size. A wave velocity was greatly reduced in the two groups (P < 0.001) so that the E/A ratio was abnormally high. The relative A wave amplitude on the apexcardiogram was greatly increased in the two groups: 46(15)% (mean (SD)) and 54(4)% v 15(5)%. Minor axis: Fractional shortening was reduced from 30(10)% to 17(7)% in patients with normal cavity size and to 13(4.2)% in those with a dilated cavity (P < 0.001), as was the posterior wall thickening fraction from 100(30)% to 42(20)% and 50(25)% respectively (P < 0.001). Total systolic epicardial motion was normal and isovolumic relaxation time was short in the two groups. Long axis: Left ventricular abnormalities included reduced total amplitude of motion and its component during atrial systole (P < 0.001 for the two groups at both sites). Peak long axis shortening and lengthening were decreased at both left ventricular sites (P < 0.001). The time intervals from q wave of the electrocardiogram and A2 (aortic valve closure) to the onset of shortening and lengthening respectively were increased (both P < 0.001). Right ventricular long axis function was similarly affected but to a lesser extent. CONCLUSION--Left ventricular long axis function is consistently abnormal in patients with restrictive disease whether or not cavity size is increased. Not only are the extent and peak velocity of shortening reduced, but during diastole the peak early diastolic lengthening rate and amplitude during atrial systole are impaired. Early diastolic long axis motion is asynchronous with respect to transmitral flow and left ventricular minor axis. These effects will impair the overall left ventricular systolic and diastolic function independently of any decrease in passive cavity compliance. Unlike fibrosis, these long axis abnormalities are potentially amenable to treatment.

Effect of left ventricular contractile performance on passive left atrial filling—Clinical study using radionuclide angiography

Abstract: Many invasive and noninvasive methods have been used to study the cardiac atria; however, few allow quantitative measurement of atrial function. To determine the interaction between left ventricular (LV) contraction and left atrial (LA) filling, gated radionuclide angiography was conducted in 30 normal subjects (24 men and 6 women, mean age 58 +/- 10 years, range 26-68). LV and LA time-activity curves and their first-derivative curves were obtained simultaneously by using the method of Bough et al. The LV ejection fraction (64 +/- 18%) and LV peak ejection rate (LVPER; 3.42 +/- 0.27 EDV/s) were computed from these curves. As indices of LA filling, LA fractional emptying (38 +/- 12%) and LA peak filling rate (LAPFR; 2.86 +/- 0.17 LAVmax/s)--the latter being defined as the peak rate of LA filling during the LA filling phase--were also computed from these curves. In all subjects, the timing of the LVPER coincided with the occurrence of LAPFR, and there was a significant positive correlation between the LVPER and LAPFR (r = 0.81, p < 0.001), indicating that the LAPFR was strongly affected by the degree of LVPER. Thus, these results indicate that LV contractile performance plays an important role in determining LA passive filling during ventricular systole.

Selective cardiac activity analysis atrial fibrillation detection system and method and atrial defibrillator utilizing same

Abstract: An atrial defibrillator applies cardioverting electrical energy to the atria of a human heart in need of cardioversion. The defibrillator includes an electrode pair and a sense amplifier associated with the atria of the heart for sensing electrical activity of the heart during a plurality of cardiac cycles to provide a cardiac signal. A detector is responsive to the cardiac signal for detecting cardiac events. During each cardiac cycle of the plurality of cardiac cycles, a time for counting is established wherein each time for counting has a total duration less than the duration of its corresponding cardiac cycle. A counter counts the cardiac events detected by the detector during the time for counting of the plurality of cardiac cycles to provide a cardiac event count. A comparator compares the cardiac event count to a predetermined cardiac event count. If the cardiac event count is greater than the predetermined cardiac event count, the atria are deemed to be in fibrillation and a cardiovertor applies cardioverting electrical energy to the atria to cardiovert the detected atrial fibrillation.

MRA studies of arterial stenosis: Improvements by diastolic acquisition

Abstract: Cardiac-phase-specific data acquisition is used to reduce signal loss in MR Angiography resulting from disturbed flow. RF pulses are delivered continuously throughout the cardiac cycle, but incrementation of phase-encoding gradients and data storage are enabled only during the chosen part of the cycle. Studies in a stenotic pulsatile flow phantom demonstrate that poststenotic signal loss is primarily determined by the mean flow velocity, and is not appreciably affected by acceleration or deceleration of the mean flow rate. The signal loss is least in diastole. In vivo studies in patients with carotid artery disease show that data acquisition in diastole reduces the apparent degree and extent of carotid bifurcation stenosis and provides a crisper definition of the vascular lumen. The additional time required for cardiac-phase-specific acquisition can be reduced by gating only the lower-order phase-encoding lines while retaining acceptable image quality.

Absent septal q wave: a marker of the effects of abnormal activation pattern on left ventricular diastolic function.

Abstract: OBJECTIVE--To investigate the possible mechanical associations of the presence or absence of the septal q wave. STUDY DESIGN--Retrospective and prospective study of 63 patients with various left ventricular diseases and 10 controls by electrocardiography, echocardiography, and pulsed Doppler recordings. SETTING--Tertiary cardiac referral centre. PATIENTS--73 subjects were studied. 26 had absent septal q waves and a QRS duration 115 ms, but an absent septal q wave predicted its presence with a specificity of 90% and sensitivity of 86%. In patients with a post-ejection shortening, the onset of left ventricular systolic long axis shortening was delayed and the extent of its lengthening during the pre-ejection period increased, indicating delayed and incoordinate onset of tension development. During diastole, post-ejection shortening was associated with a prolonged isovolumic relaxation period and the time from A2 to the onset of transmitral flow. Peak mitral E wave flow velocity was reduced due to a fall in acceleration time although acceleration rate itself was unchanged. CONCLUSION--Loss of the normal septal q wave is associated with considerable mechanical consequences throughout the cardiac cycle, from the pre-ejection period to atrial systole, and apparently causes asynchronous subendocardial function.

Transition to Turbulence in Pulsatile Flow Through Heart Valves—A Modified Stability Approach

Abstract: The presence of turbulence in the cardiovascular system is generally an indication of some type of abnormality. Most cardiologists agree that turbulence near a valve indicates either valvular stenosis or regurgitation, depending on the phase of its occurrence during the cardiac cycle. As no satisfying analytical solutions of the stability of turbulent pulsatile flow exist, accurate, unbiased flow stability criteria are needed for the identification of turbulence initiation. The traditional approach uses a stability diagram based upon the stability of a plane Stokes layer where alpha (the Womersley parameter) is defined by the fundamental heart rate. We suggest a modified approach that involves the decomposition of alpha into its frequency components, where alpha is derived from the preferred modes induced on the flow by interaction between flow pulsation and the valve. Transition to turbulence in pulsatile flow through heart values was investigated in a pulse duplicator system using three polymer aortic valve models representing a normal aortic valve, a 65 percent stenosed valve and a 90 percent severely stenosed valve, and two mitral valve models representing a normal mitral valve and a 65 percent stenosed valve. Valve characteristics were closely simulated as to mimic the conditions that alter flow stability and initiate turbulent flow conditions. Valvular velocity waveforms were measured by laser Doppler anemometry (LDA). Spectral analysis was performed on velocity signals at selected spatial and temporal points to produce the power density spectra, in which the preferred frequency modes were identified. The spectra obtained during the rapid closure stage of the valves were found to be governed by the stenosis geometry. A shift toward higher dominant frequencies was correlated with the severity of the stenosis. According to the modified approach, stability of the flow is represented by a cluster of points, each corresponding to a specific dominant mode apparent in the flow. In order to compare our results with those obtained by the traditional approach, the cluster of points was averaged to collapse into a single point that represents the flow stability. The comparison demonstrates the bias of the traditional stability diagram that leads to unreliable stability criteria. Our approach derives the stability information from measured flow phenomena known to initiate flow instabilities. It differentiates between stabilizing and destabilizing modes and depicts an unbiased and explicit stability diagram of the flow, thus offering a more reliable stability criteria.

Influence of heart rate and left atrial pressure on pulmonary venous flow pattern in dogs

Abstract: In six open-chest anesthetized dogs we investigated the effect of heart rate (HR) on the relationship between left atrial pressure (LAP) and pulmonary venous flow (QPV). QPV was measured by ultrasonic transit time during volume loading and right atrial pacing. Consistent with previous studies, we found a negative correlation between LAP and mean flow rate during atrial systole divided by mean flow rate in the R-R interval. However, this relationship was shifted upward by tachycardia. The QPV maximum amplitude divided by mean flow rate in the R-R interval increased with loading but decreased with tachycardia. mean flow rate during ventricular systole divided by mean flow rate during the R-R interval increased with both loading and tachycardia. Regression coefficients for HR and LAP as predictors of these indexes were all significantly different from zero (P = 0.0001). We conclude that HR significantly influences the relationship between the QPV pattern and LAP. This could be a limitation of the pulmonary venous flow pattern as an indicator of left ventricular diastolic function.