Showing papers on "Cardiac cycle published in 1988"

Human heart: tagging with MR imaging--a method for noninvasive assessment of myocardial motion.

Abstract: Specified regions of the myocardium can be labeled in magnetic resonance (MR) imaging to serve as markers during contraction. The technique is based on locally perturbing the magnetization of the myocardium with selective radio-frequency (RF) saturation of multiple, thin tag planes during diastole followed by conventional, orthogonal-plane imaging during systole. The technique was implemented on a 0.38-T imager and tested on phantoms and volunteers. In humans, tags could be seen 60-450 msec after RF saturation, thus permitting sampling of the entire contractile phase of the cardiac cycle. Tagged regions appear as hypointense stripes, and their patterns of displacement reflect intervening cardiac motion. In addition to simple translation and rotation, complex motions such as cardiac twist can be demonstrated. The effects of RF pulse angle, relaxation times, and heart rate on depiction of the tagged region are discussed.

Mitral anulus motion. Relation to pulmonary venous and transmitral flows in normal subjects and in patients with dilated cardiomyopathy

Abstract: The dynamics between mitral anulus motion, and, thus, motion of the base of the heart, and filling of the left atrium and ventricle were studied by Doppler echocardiography in 12 normal subjects and 28 patients with dilated cardiomyopathy. The normal motion of the mitral anulus is associated with two phases of inflow from the pulmonary veins. The first phase (J) of pulmonary venous inflow occurs during ventricular systole, concomitant with the descent of the mitral anulus toward the ventricular apex, the extent of which is 12.8 +/- 1.4 mm. The end of the descent of the anulus occurs at the cessation of aortic ejection. About 100 msec later, a rapid recoil of the mitral anulus toward the atrium coincides with the onset of transmitral filling. This rapid recoil contributes to the displacement of blood from the atria into the ventricles in early diastole. The second phase (K) of pulmonary venous flow begins in early diastole, with its peak occurring about 50 msec after the peak of transmitral flow. During atrial contraction, the mitral anulus moves slightly (2.4 +/- 0.7 mm) toward the atrium and then returns toward its initial position within 120 msec. This motion coincides with the A wave of transmitral flow. In patients with dilated cardiomyopathy, pulmonary venous flow and mitral anulus motion are markedly altered in comparison with normal subjects. In all patients, motion of the mitral anulus is either reduced or absent.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac and pulmonary physiological analysis via intracardiac measurements with a single sensor

Abstract: Physiological activity of a patient is detected and analyzed by means of a single sensor situated in the vascular system of the patient. Pulmonary activity is derived from analysis of changes in cardiac activity, such as sensed from blood flow, pressure or volume changes, measured in a preferred embodiment as impedance change within the right heart. Pulmonary activity is separated from cardiac activity implicit in such changes by filtering lower and higher frequency components. The separated signals are processed to derive control signals for stimulating the heartbeat in a pacemaker system, preferably by a single sensor-stimulator electrode implanted within the right heart. Thus, a single functional parameter, namely intra-cardiac impedance, varying both with the intrathoracic pressure fluctuations following respiration and with cardiac contraction is representative of the pulmonary activity and of the cardiac activity. Resulting derived sub-signals then provide information regarding cardiac and pulmonary activity and are used to monitor the patient's condition and control variably the rate of a cardiac pacemaker.

Transient atrial dysfunction after conversion of chronic atrial fibrillation to sinus rhythm.

Abstract: Although conversion of atrial fibrillation (AF) to sinus rhythm can usually be accomplished by electrical or drug therapy, effective atrial systole may not be restored. To investigate the return of atrial transport function and its relation to the duration of the arrhythmia, Doppler echocardiography was performed after conversion in 18 patients with acute AF ( 1 week duration) and 15 control patients. Flow velocities during rapid filling (E wave) and atrial systole (A wave) were measured in both left and right ventricles. Patients in the acute AF group had left ventricular A waves (49 ± 4 cm/s) and AE ratios (0.97 ± 0.1) similar to those of the control patients (55 ± 7 cm/s, 0.87 ± 0.08, respectively). In contrast, patients in the chronic AF group had much smaller A waves (19 ± 5 cm/s) and AE ratios (0.30 ± 0.08) than those in the other 2 groups (p < 0.001). Five patients with chronic AF (36%) had complete left atrial paralysis (AE = 0) despite normal sinus P waves. Measurements in the right ventricle showed similar differences among the groups. Patients with chronic AF who maintained sinus rhythm showed an increase in AE ratio to control levels, from 0.45 ± 0.1 to 0.93 ± 0.1 (p = 0.003) at 48 days (average) after conversion. Thus, atrial transport function is normal after brief periods of AF, but reduced or absent when conversion is achieved after the arrhythmia has been sustained >1 week. The mechanism is not known. Atrial contribution to filling gradually increases after conversion.

Time-resolved magnetic resonance angiography.

Abstract: A time-resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology. © 1988 Academic Press, Inc.

Comparison of pulsed Doppler echocardiography and radionuclide angiography in the assessment of left ventricular filling.

Abstract: To determine the relation between Doppler echocardiographic and radionuclide angiographic indexes of left ventricular (LV) filling, 42 patients were studied using both techniques. From Doppler mitral flow velocity profiles, the percent of LV filling due to atrial systole (percent atrial contribution) and at one-third of diastole (one-third filling fraction), the peak filling rate and the peak filling rate normalized for LV enddiastolic volume and the time from mitral valve opening to peak early velocity and from aortic valve closure to peak early velocity were determined. Good correlations were found between percent atrial contribution (r = 0.83) and one-third filling fraction (r = 0.67) using the 2 techniques. However, Doppler normalized peak filling rate correlated only weakly with radionuclide peak filling rate (r = 0.33, p Thus, Doppler echocardiography and radionuclide angiography agree on relative diastolic filling indexes but not on peak filling rates or useful diastolic time intervals. Relative filling indexes, such as percent atrial contribution and one-third filling fractions, therefore, may be the most reliable noninvasive indicators of diastolic function.

Methods of cardiac gating applied potential tomography.

Abstract: Electrical impedance of the heart, pulmonary perfusion and the great blood vessels can only be achieved by synchronising the data collection with cardiac activity. Due to low signal-to-noise ratio, temporal averaging is needed to improve the image quality. In this study several methods of ECG gating are attempted to synchronise the applied potential tomography (APT) serial data collection with the cardiac cycle. They alloy the authors to collect sequential images time-locked with the R-wave of the patient, and hence image the pulsatile movement of blood. Different methods are examined for their sampling speeds, noise levels and ability to image before systole. A method of image data rearrangement in order to provide an apparent increase in speed is also discussed.

Assessment of aortic pressure‐volume relationships with an impedance catheter

Abstract: Volume measurements obtained with an impedance catheter (impedance volume measurements) have been used previously in determining pressure-volume relationships in the right and left ventricles and in the right atrium. The purpose of the present study was to determine the utility of impedance volume techniques in the assessment of aortic pressure-volume relationships in animals and humans. Experiments to develop this methodology were first performed in ten anesthetized dogs, with simultaneous measurements of aortic pressure (micromanometer), diameter (ultrasonic crystals), and impedance volume. Transient (20 sec) inferior vena cava (IVC) occlusion and nitroprusside infusion resulted in a reproducible series of aortic pressure-volume and pressure-diameter points. In each case changes in impedance volume closely paralleled changes in diameter. From the wide range of pressure-volume points, it was possible to construct pressure-volume plots for a single cardiac cycle, as well as longer loops over a 20–40 mm Hg pressure range. End-systolic and end-diastolic pressure-volume points could subsequently be identified, which outlined a more precise pressure-volume relationship that was linear in six cases and curvilinear in four cases, depending on the level of aortic pressure. We extended these techniques to human subjects undergoing diagnostic cardiac catheterization. Studies using the impedance catheter in the aorta were performed in 11 patients. Aortic pressure-volume curves were elicited during Valsalva maneuver to obtain data over a range wider than that of a single cardiac cycle. Measurements of relative volume were calibrated with simultaneous M-mode echocardiography in three patients We conclude that pressure-volume relationships in the aorta can be assessed with impedance volume techniques, making possible in vivo measurements of arterial compliance. Potential nonlinearities in aortic P-V relationships requrie that the assessment of aortic compliance encompass as much as possible of the physiologic range of pressure and volume.

Atrial systole: its role in normal and diseased hearts.

Abstract: The importance of atrial systole in cardiac physiology was first recognized by William Harvey in 1628: “ ... and if at this time with its auricle alone beating you cut off the apex of the heart with a pair of scissors, you will see the blood flow out of the wound with each beat of the auricle. You will thus realise that the blood gets into the ventricles not through any pull exerted by the distended heart but through the driving force exerted by the beat of the auricles” [ 11. It appears from this quotation, however, that Harvey believed ventricular filling was wholly active and caused by atrial systole. His observations were unsurpassed until the late 19th century when further evidence for the presystolic role of atrial contraction was derived from the intraventricular pressure curve of the horse. Chaveau & Marey in 1863 showed a “small but well defined wave before the sharp systolic rise” [2]. In the early 20th century more exact measurements of cardiac physiology were made and the diastolic filling of the ventricles was studied experimentally. Yandall Henderson [3] in 1906, using an isolated heart preparation and plethysmography to measure volume changes in the ventricle, showed that diastolic ventricular filling was mainly passive and found only a small increase in volume coincident with atrial systole. He concluded that “the contraction of the auricles increases the ventricular volume to the extent of a few drops at most”. Henderson’s results were later criticised by Gesell [2], who felt that the plethysmography equipment used by Henderson was insensitive to rapid changes in volume and that changes in the outer contours of the heart may not represent what was happening inside. This was borne out by the work of Hermann Straub [4], who in 19 10, using isolated mammalian hearts and sensitive plethysmography repeated Henderson’s early experiments. He showed a marked increase in ventricular volume after atrial contraction. Subsequently, Gesell performed a series of experiments [2,5,6] in isolated heart preparations in order to define the role of atrial systole

Fine structure, mechanism of heart function and haemodynamics in the prosobranch gastropod molluscLittorina littorea (L.)

Abstract: The heart, main blood vessels, and associated structures ofLittorina littorea were examined by scanning and transmission electron microscopy. The auricle is subdivided into two compartments, one receiving blood from the gill and opening to the nephridial gland vein, the other connecting with the latter anteriorly and the ventricle posteriorly. Video recordings were made of the beating heart in vivo and revealed that the auricle expelled blood not only to the ventricle, but also the nephridial gland vein at systole and provided further evidence of tidal flow of blood in the vein. There is clear indication that the constant volume mechanism of auricular re-filling is not strictly true inLittorina. Blood pressure in the heart and major vessels was measured using a servo-nulling micropressure system. The rate of formation of urine (derived by filtration of blood through the auricular wall) was measured using [51Cr] EDTA as a blood marker. Basal blood pressure was slightly above ambient (0.7 cm H2O). Peak systolic pressure in the ventricle (3.8 cm H2O) was synchronised with a subambient trough in pericardial pressure (−1.0 cm H2O); these pressure pulses were out of phase with that of the auricle (2.3 cm H2O) at systole. The observations are consistent in broad terms with a constant volume mechanism, but this does not take into account urine formation or filling of the nephridial gland vein. A filtration pressure of 1.5 cm H2O has been demonstrated across the auricular wall throughout the cardiac cycle. Colloidal back pressure appears to be negligible. The mean rate of urine formation is 0.26 μl g−1 min−1.

Pulmonary blood velocity profile variability in open-chest dogs: Influence of acutely altered hemodynamic states on profiles, and influence of profiles on the accuracy of techniques for cardiac output determination

Abstract: Clinical investigations focused on finding characteristics of noninvasively obtained measurements of pulmonary blood velocity that can be used to quantitate pulmonary blood flow and/or pulmonary pressure have often yielded results whose imprecision has been attributed to flow pattern variability. To determine flow pattern variability in an in vivo animal model in varying hemodynamic states, main pulmonary artery blood velocity waveforms were recorded in 17 dogs at 2-mm intervals along an anterior to posterior wall-oriented axis using a 20-MHz pulsed Doppler needle probe. Control data were obtained before the animals were subjected to altered flow (atrial level shunts) and pressure (10% O2 inhalation) states. Instantaneous velocity profiles were computed throughout the cardiac cycle. Estimates of pulmonary blood flow were obtained assuming an elliptical model of the pulmonary artery which allowed computation of velocity at all points in the cross section, based on the measured values along the axis. Model-based estimates were compared to measured values and estimates obtained in the traditional fashion, i.e., the product of centerline velocity and cross-sectional area. Results clearly showed marked interanimal variability, even in control states. Reverse flow in the posterior half of the vessel, which tended to become more pronounced with increased pulmonary artery pressure, was observed during late systole and early diastole. Elevated pulmonary blood flow tended to increase the maximum velocities along the anterior wall relative to midline velocities. Neither estimate of cardiac output yielded consistently accurate results (r=0.77 for model-based method,r=0.80 for area times central velocity method). Findings of this study, which highlight the dependency of waveform characteristics on sampling site, the large degree of intersubject variability, and the need for large or multiple sample volumes for pulmonary blood flow determination, help clarify inconsistencies observed by clinicians and suggest that future work with animal models will facilitate a greater understanding of the determinants of human pulmonary velocity waveforms.

Relationship between beat to beat interval and left ventricular function in patients with atrial fibrillation

Abstract: In atrial fibrillation, the relation between the rhythm and volume of the pulse has long been of interest. However, changes in preload in this condition have not been fully addressed since beat to beat measurement of filling volume have been difficult until recently. In the present study, we evaluated left ventricular outflow and inflow velocity using pulsed Doppler echocardiography and correlated these results with the R-R interval in the individual patient. The study population consisted of 12 patients with atrial fibrillation, aged 36 to 69 years (mean 54 years). The etiology of atrial fibrillation was idiopathic in 10 and 2 patients had dilated cardiomyopathy. Stroke and filling volume were calculated as a pruduct of the flow velocity integral of left ventricular outflow and inflow velocity, and the cross-sectional area of aortic and mitral annulus, respectively. In 10 patients with idiopathic atrial fibrillation, significant positive correlations were observed between the preceding R-R interval and both the stroke volume and the filling volume of the preceding beat when the R-R interval was shorter than 600 msec. Stroke volume and filling volume of the preceding beat were almost constant, independent of the preceding R-R interval when the preceding R-R interval was longer than 600 msec, the interval necessary for the completion of the preceding rapid filling. In the same preceding R-R interval, a larger stroke volume was observed in a shorter pre-preceding R-R interval. In 2 patients with dilated cardiomyopathy no relationship could be observed between the preceding R-R interval and the filling volume of the preceding beat or the stroke volume. In patients with a normally functioning left ventricle (idiopathic atrial fibrillation), reduced cycle length and filling volume in the preceding cardiac cycle appear to be the underlying cause of the regulation of stroke volume, dependent on Starling's law. However, in patients with dilated cardiomyopathy no significant correlation was observed between the preceding R-R interval and both the filling volume of the preceding beat and the stroke volume. In these patients the left ventricle may have limited contractile reserve and altered diastolic re-coil forces possibly due to degenerative changes of myocardium. Pulsed Doppler echocardiography provides a non-invasive method of evaluating the instantaneous changes in left ventricular flow dynamics caused by atrial fibrillation and understanding its fundamental mechanism.

Doppler Atrial Shunt Flow Patterns in Patients with Secundum Atrial Septal Defect: Determinants, Limitations, and Pitfalls

Abstract: Fifteen patients with uncomplicated secundum atrial septal defect underwent studies with real-time color-coded two dimensional flow imaging, pulsed Doppler echocardiographic examination, and simultaneous pressure recordings from the left and right atrium to determine the flow-pressure dynamics of the atrial shunt flow. In all 15 patients both the color flow mapping and pulsed Doppler studies revealed that the shunt flow was mainly from left to right, occurring both during ventricular systole and diastole. It started in early systole, reached a peak in late systole to early diastole, and lasted throughout diastole with an accentuation in late diastole during atrial contraction. The amplitude of the flow velocity, the direction, and the magnitude of the shunt flow, however, changed from phase to phase during the cardiac cycle. It correlated well with the phasic variation of the interatrial pressure difference, which usually revealed a peak pressure gradient that occurred in early systole between the x descent and v wave and during the period of v wave and a wave of the left atrial pressure tracing. Right to left shunt was not detected in any of the 15 patients by color flow mapping studies. A minor reversal of the shunt flow, however, was frequently detected at the beginning of ventricular systole and sometimes also in the middle of diastole by pulsed Doppler echocardiography. The reversal of shunt flow correlated with the minor reversal of pressure gradient that occurred during the z point, x descent, and y descent of the left atrial pressure tracing. In conclusion, left to right shunt flow occurs both during ventricular systole and diastole in uncomplicated secundum atrial septal defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast limited flip angle MR subtraction angiography.

Abstract: A fast MR angiography method is introduced that is capable of generating difference images of blood vessels in scan times of 10-20 s. This is an order of magnitude faster than many previous methods. The fundamental concept of this approach is to use cardiac gating and acquire several phase encodings at least twice during each cardiac cycle using limited flip angles (LFAs) and repetition times in the 20 to 50 ms range. The encodings acquired during diastole are subtracted from those acquired during systole to generate the difference image. The contrast in the difference image is due both to the influx of unsaturated spins and to the loss of phase coherence of systolic blood moving at high velocity along a magnetic gradient. The systolic peak of the cardiac cycle is determined during reconstruction by shifting the systolic and diastolic "windows" until the difference signal is maximized. Ghost artifacts due to pulsatile flow are eliminated by a phase reordering technique similar in concept to those developed for suppression of breathing artifacts. Arteries in thick slices are successfully imaged and initial in vivo results are presented.

Cardiac function by magnetic resonance imaging

Abstract: Gated magnetic resonance imaging of the heart displays cardiac structures with excellent resolution. This ability should be useful for assessment of cardiac physiology where acquisition of systolic and diastolic images is required. In this study, left ventricular ejection fraction was determined in 50 patients from oblique long axis views of the left ventricle using the area length formula. Angulated views were obtained by electronic gradient angulation. For comparison, all patients had monoplane angiocardiography in the RAO position. Forty-five patients were also studied by radionuclide ventriculography. Ejection fractions determined by MRI and angiocardiography were closely correlated (r=0.90). Correlation between MRI and radionuclide ventriculography was also acceptable (r=0.79). In addition to global left ventricular function, MR images provide information about regional wall motion. In order to acquire a three-dimensional set of images at various phases of the cardiac cycle, shorter imaging times are mandatory. A new imaging technique with potential for functional studies uses low flip angles, short repetition times and gradient refocused echoes. Up to 40 images can be obtained within one cardiac cycle. When displayed in a looped fashion, visual assessment of cardiac motion, intracardiac blood flow, and systolic wall thickening is possible. Potential advantages of functional studies by MRI are the concomitant acquisition of anatomical information and the three dimensional frame of reference.

Impaired vagal heart rate control in aortic valve stenosis.

Abstract: Impaired reflex control of heart rate seems to be associated with increased risk of sudden cardiac death. To assess the effect of aortic valve stenosis on parasympathetic heart rate control we measured the heart rate responses to deep breathing and to standing up, non-invasive measures of cardiac parasympathetic activity, in 24 patients with valvular aortic stenosis and in 24 healthy asymptomatic subjects of the same age group. All but one of the patients were symptomatic and the mean aortic valve pressure gradients ranged from 32 to 114 mmHg. The heart rate response to deep breathing was significantly (P >0.05) lower in valve patients than in the healthy subjects. The heart rate changes evoked by standing up, however, did not differ significantly between the groups. The heart rate response to deep breathing was inversely weakly related to the left ventricular end-diastolic pressure ( r = −0.41, P > 0.05), but not significantly to the aortic valve pressure gradient, valve area, left ventricular ejection fraction or presence of coronary artery disease. Our results suggest that the impairment of reflex heart rate control is common in patients with significant aortic valve stenosis.

Deformation of the dog aortic valve ring during the cardiac cycle

Abstract: Changes in strain in the line of aortic valve leaflet attachment (aortic ring) were measured during the cardiac cycle by means of an inductive technique. To that purpose coils were sutured to each commissure and base point of the aortic ring, when the animals were on a cardiopulmonary bypass. After bypass and stabilization of the hemodynamic variables changes in the aortic strain were measured at aortic pressures ranging from 4 to 20 kPa. Aortic pressure at the level of the commissure points and left ventricular pressure were measured to assess transvalvular pressure. Commissure strain appeared to depend on aortic and transvalvular pressure throughout the cardiac cycle. At an aortic pressure of 10 kPa (75 mm Hg), the derivative of commissure strain to aortic pressure was found to be 1.9×10−5±1.2×10−5 Pa−1 (mean ±SD). During the ventricular ejection phase commissure strain was 0.04±0.03 higher than during ventricular filling. Maximum variations in basal strain during the cardiac cycle ranged from 0.03 to 0.15. During the ejection phase the basal segments adjoining the myocardium shortened whereas the segment close to the non-contracting anterior mitral valve leaflet lengthened. Strain between a base and a commissure point of the aortic ring were synchronous with the cardiac cycle, but no specific pattern could be found.

A new method to determine left ventricular pressure-volume loops in the clinical setting.

Abstract: Left ventricular pressure-volume (P-V) loops provide a complete definition of cardiac performance but have been difficult to obtain in the clinical setting. Accordingly, we have developed a new technique for acquiring P-V loops during and after cardiac surgical procedures using portable first-pass radionuclide angiocardiography coupled with intraventricular micromanometer catheters. Using this technique 35 serial left ventricular P-V loops were acquired in 12 patients during and after coronary artery bypass grafting. Dynamic radionuclide left ventricular volume and micromanometer pressure were acquired simultaneously to generate the P-V loops. Moreover, simultaneous measurement of both volume and pressure allowed comparison of the timing of end diastole (ED) and end systole (ES) defined by each of the two cardiac parameters. For 208 EDs and 243 ESs analyzed volume-defined ED occurred 8 +/- 27 msec (s.d.) later in the cardiac cycle than pressure-defined ED while volume-defined ES occurred 29 +/- 27 msec (s.d.) earlier than pressure-defined ES. It is concluded that measurement of cardiac P-V loops with this new technique is clinically feasible and that a close agreement has been demonstrated between the timing of cardiac events defined either by volume or pressure criteria.

A non-linear elastic model of contraction of ischaemic segments

Abstract: Previous studies have characterised the motion of the myocardium using a linear time varying elastance model, ie, they have sought to characterise the relationship between left ventricular volume and internal pressure as linear, but with time varying slopes over the cardiac cycle. However, the motion of myocardium during regional ischaemia has not been characterised by such models. Studies of totally ischaemic tissue and of myocardium in diastole have characterised the relationship between tension or stress and segment length as exponential. It is the purpose of this study to present a new model in which myocardial contraction is expressed as an exponential, but time varying elastic relationship. In this model tension, T, is related to segment length according to the formula T=eα(t)L+β, where α(t) rises with systole and falls in diastole. This model was applied to the motion of hypokinetic segments noted in a series of conscious dogs studied for other purposes. Hypokinetic segments display early systolic bulging, decreased systolic shortening, and early diastolic recoil. These particular types of segment motion are naturally predicted by this model. Furthermore, the motion of myocardial segments as they become increasingly ischaemic may be predicted, including a gradual shift to the right and narrowing of the tension-length loop. α was noted to be independent of loading change, and thus may be viewed as an index of contractility. This model thus predicts the pattern of motion of hypokinetic segments and provides new insight into myocardial contractility.

Right ventricular tardokinesis in cardiac contusion: a new observation on phase images.

Abstract: The usefulness of gated blood pool (GBP) scintigraphy in evaluating cardiac contusion among trauma patients was examined. In ten of 62 patients who sustained blunt chest trauma, phase images of GBP studies demonstrated delayed onset of right ventricular (RV) contractions (RV tardokinesis). Clinical charts of these ten patients were reviewed to determine the significance of this finding. Only one had no supportive evidence of cardiac injury. Four patients were determined to have clinically significant cardiac contusion on the basis of the occurrence of arrhythmias of cardiac failure during their hospital course. These patients had ventricular histogram widths greater than 30 degrees of the entire cardiac cycle at half maximum height and had a bifid peak in their ventricular contraction histograms. Of the 52 patients who did not have RV tardokinesis, only one had a clinically significant cardiac contusion, resulting in a false-negative rate of 2% for the test. This new observation of RV tardokinesis may be ...