Showing papers on "Cardiac cycle published in 1990"

First-pass cardiac perfusion: evaluation with ultrafast MR imaging.

Abstract: The authors studied cardiac perfusion by administering gadolinium diethylenetriaminepentaacetic acid (DTPA) in conjunction with an ultrafast imaging technique that produces strongly T1-weighted images. The method consisted of a 180 degrees inversion pulse, followed by a gradient-echo acquisition with a very short repetition time (less than 4 msec). Each image was acquired throughout a small fraction of the cardiac cycle. The method was applied in an isolated perfused rat heart model (acquisition time = 116 msec) and in human subjects without known cardiac disease (acquisition time = 125 msec). Fast, high-resolution images (128 X 128 matrix) were created by combining sequentially acquired small matrixes. After bolus administration of Gd-DTPA in the perfused rat heart model, contrast was pronounced between the nonperfused myocardium and perfused normal myocardium. First-pass wash-in and washout phases of the contrast material were observed in the perfused rat heart model and in human subjects. Results demonstrated the clinical feasibility of first-pass perfusion studies of the heart. The studies can be performed on a conventional whole-body imaging system with standard hardware.

Pacing systems and methods for control of the ventricular activation sequence

Abstract: Apparatus and methods for improving the ventricular activation sequence of the heart by pacing at an advantageous selected ventricular location to achieve shortening of the QRS complex or pacing at multiple advantageous selected ventricular locations, either simulataneously or with a programmed delay or delays between firings, to achieve shortening of the QRS complex in combination with producing a desirable and efficient ventricular motion. During a cardiac cycle initiated by intrinsic cardiac activity, stimulating impulses may be directed to advantageous selected locations of the ventricles by employing intrinsic cardiac signals to trigger the stimulating impulses, either simultaneously or with a programmed delay or delays between the sensed event or events and firing event or events, to provide improved mechanical and electrical ventricular function.

Doppler studies of vena cava flows in human fetuses. Insights into normal and abnormal cardiac physiology.

Abstract: We examined vena cava Doppler flow velocity tracings from 69 fetuses between 22 and 40 weeks' gestation. Twenty-three fetuses had arrhythmias. Fifteen fetuses had absent end-diastolic Doppler velocities in the umbilical artery, a condition associated with intrauterine growth retardation, and 15 normal fetuses with normal umbilical artery Doppler velocity ratios were matched by gestational age. In studies in 16 additional fetuses, inferior vena cava Doppler velocity waveforms were compared with superior vena cava Doppler velocity waveforms. Peak velocities and time-velocity integrals of forward or reverse flow during systole, early diastole, and atrial contraction were measured. In addition, the time-velocity integral during flow coincident with atrial contraction (a wave) was expressed as a percent of the time-velocity integral of total forward flow during both systole and early diastole. Systolic-to-diastolic ratios of inferior vena cava forward time-velocity integrals were not significantly different from systolic-to-diastolic ratios of superior vena cava forward time-velocity integrals (p = 0.86), but the percent of blood moving in a reverse direction during atrial contraction in the inferior vena cava was greater than the percent of blood moving in a reverse direction in the superior vena cava (p less than 0.05). Relative forward flow in early diastole in the group of normal fetuses increased with advancing gestational age (r = 0.60, p less than 0.05). During premature atrial contractions flow in the inferior vena cava was reversed, and the percent of reverse flow during atrial systole increased significantly from 4.5 +/- 0.3% to 28.3 +/- 3.7% (mean +/- SEM, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomic characteristics and valvular function of the transplanted heart: transthoracic versus transesophageal echocardiographic findings.

Abstract: In orthotopic heart transplantation atrial size and geometry are altered, whereas ventricles and atrioventricular valves remain structurally unchanged. To analyze the anatomy and function of the transplanted heart, 20 heart transplant recipients, with a mean age of 46.0 +/- 11.8 years, were examined with transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE). Both methods showed atrial enlargement and abnormal configurations of the atria. Although valve leaflet structure appeared normal, TEE showed mitral regurgitation in 13 patients (TTE, 11), mitral prolapse in three patients (TTE, two), tricuspid regurgitation in 17 patients (TTE, 17), and tricuspid prolapse in two patients (TTE, one). Only by TEE, "pseudoaneurysms" of the donor part of the interatrial septum were found in six patients and of the receiver part in one patient, possibly as consequence of unequal thickness, asynchronous contraction, and cyclic torsion of both atrial components during the cardiac cycle. Spontaneous atrial echo contrast--again visualized only by TEE--was seen in five patients and a left atrial thrombus in three patients. Spontaneous echo contrast and thrombus formation were associated. One patient with a thrombus had had peripheral arterial embolism. We conclude that, compared with TTE, TEE offers superior imaging of cardiac anatomy, intraatrial abnormalities, and function of the atrioventricular valves. Mitral and tricuspid incompetence are frequent after orthotopic heart transplantation and may be related to abnormal atrial size and function, leading to impaired functional integrity of the valvular apparatus. The high incidence of atrial spontaneous echo contrast and thrombi suggests that antiplatelet or anticoagulant therapy may be advisable in heart transplant recipients with these findings.

Does volume catheter parallel conductance vary during a cardiac cycle

Abstract: Absolute left ventricular volume measurement by the conductance (volume) catheter requires subtraction of the conductance contribution from structures extrinsic to the cavity blood pool. Previously, this parallel conductance volume (Vp) has been assumed constant throughout the cardiac cycle, and the technique described for its estimation in situ yields a single value. We present a new method for parallel conductance determination that yields multiple estimates during systole, enabling an assessment of Vp variability [Vp(t)]. For isolated blood-perfused ejecting canine left ventricles with empty (vented) right ventricles, Vp(t) displayed virtually no variation throughout systole. For in situ hearts, despite the presence of other cardiac chambers, Vp(t) also displayed little variation, with no statistically significant deviation from its mean value throughout systole. Volume signal simulations found the new technique to be less sensitive to signal noise and thus more robust than the one previously published. The isolated and in situ heart data indicate that for the left ventricle, the parallel conductance is relatively constant throughout normal ejection.

Portal blood flow in congestive heart failure: pulsed duplex sonographic findings.

Abstract: Twenty-one patients with congestive heart failure were examined with duplex sonographic scanning of the portal vein. The Doppler sonographic findings were compared with those of healthy subjects, patients with chronic liver disease, and patients with Budd-Chiari syndrome. Increasing pulsatility of the Doppler signals was demonstrated in 11 patients with severe congestive heart failure. Two patients with severe congestive heart failure showed decreasing pulsatility of portal Doppler signals in response to therapeutic procedures. Portal flow patterns suggestive of severe congestive heart failure include a monophasic forward flow with peak velocity in ventricular diastole and gradual diminution of velocity throughout ventricular systole (n = 5), a reversed flow velocity in ventricular systole (n = 3), and vena cava-like biphasic forward velocity peaks during each cardiac cycle (n = 2). The time-velocity waveform shape of portal flow is, to a large degree, influenced by the mechanical events in the right side of the heart in severe congestive heart failure.

Phasic regional myocardial inflow and outflow: comparison of theory and experiments

Abstract: We developed a theory for regional blood flow in the beating heart and validated it with measurements of coronary arterial inflow and venous outflow in the open-chest anesthetized dog. The model used measured aortic, left ventricular, and coronary sinus pressures as input data under control conditions and during long diastoles induced by vagal stimulation. A nonlinear two-compartment lumped model for each transmural layer was obtained by spatial averaging a continuum description of the myocardial microcirculation based on morphometric measurements and appropriate fluid and vascular mechanics principles. The chief results and conclusions of the study are 1) an intramyocardial time constant on the order of 1 s is required to explain the phase opposition between inflow and outflow; 2) capillary and venous perfusion are in phase with arterial pressure, and arterial flow is out of phase with arterial pressure except in superficial intramural layers; 3) subendocardial retrograde systolic flow increases with increased contractility and time constants and decreased arterial pressure; and 4) endocardial capillary and venule volume change by 5.5 and 10%, respectively, during the control cardiac cycle.

Pulmonary vascular cine MR imaging: a noninvasive approach to dynamic imaging of the pulmonary circulation.

Abstract: Cine gradient-recalled magnetic resonance (MR) imaging, which has flow sensitivity and high temporal resolution, may potentially yield both morphologic and dynamic flow-related information in the pulmonary vasculature. The authors used this modality to evaluate pulmonary vessels in 12 healthy subjects and in 14 patients with a variety of cardiopulmonary disorders. Normal pulmonary arteries and veins were characterized by distinctive signal intensity and diameter variations as well as motion of the vessels during the cardiac cycle. Patients with pulmonary arterial hypertension demonstrated loss of the normal pulsatile systolic increase and diastolic decline in velocity-related signal intensity and in diameter of the proximal pulmonary arteries. Disorders of pulmonary venous signal and diameter profiles during the cardiac cycle, which show a characteristic biphasic pattern in healthy subjects, were identified in five patients with mitral valvular disease. These initial results indicate that cine MR imaging ...

Pulmonary venous flow determined by Doppler echocardiography in mitral stenosis.

Abstract: Recent studies have shown that pulmonary venous flow is normally biphasic. Both phases depend on changes in left atrial pressure that occur during the cardiac cycle. 1–3 The first phase corresponds to ventricular systole and is dependent on ventricular contraction and on a timed relaxation of the left atrium. The second phase occurs during diastole and follows the reduction in atrial pressure during the rapid transmitral flow and ventricular filling. In mitral stenosis (MS), flow rate across the mitral valve is reduced, as is the rate of left atrial pressure decay and left ventricular pressure rise. 4 These changes in left atrial hemodynamics may affect left atrial filling from the pulmonary veins. Moreover, many patients with MS have atrial fibrillation. This arrythmia results in a reduced systolic (J) phase of pulmonary venous flow. 1,5 The present study examines the pattern of pulmonary venous flow velocity in patients with MS.

Regional left ventricular wall motion abnormalities in idiopathic dilated cardiomyopathy

Abstract: An evaluation and a comparison of left ventricular regional wall motion were performed in 32 patients with idiopathic dilated cardiomyopathy, none of whom had coronary artery diameter stenosis exceeding 20% in any major artery, and 17 control subjects, using frame by frame video intensity analysis of digitized ventriculograms. This technique evaluates the whole cardiac cycle in short overlapping intervals and yields information for systolic and diastolic events, without assumptions regarding the position and orientation of the ventricle. Diastolic regional wall motion abnormalities were found in 31 of 32 patients and systolic abnormalities were present in 16 patients. Asynchronous regions most commonly detected during diastole were anteroapical and apical; they were found in 19 of 32 patients. Regional contraction abnormality was observed in the apical and the anteroapical regions in 6 of 16 patients. Dilatation-induced changes in left ventricular shape exaggerate the phenomenon of higher wall stress at the apex of the normal ventricle. Basal wall motion is thus relatively preserved in dilated cardiomyopathy.

Invasive evaluation of left ventricular diastolic performance.

Abstract: Diastole can be divided into four phases: 1. isovolumic relaxation; 2. early filling; 3. diastasis; and 4. atrial systole. The amount of left ventricular (LV) filling that occurs during each of these phases depends on: 1. myocardial relaxation; 2. the passive characteristics of the LV; 3. the characteristics of the left atrium, pulmonary veins and mitral valve; and 4. the heart rate. When diastolic function is normal, the net effect of these factors results in LV filling sufficient to produce an adequate cardiac output, while mean pulmonary venous pressure is maintained below 12 mm Hg. Diastolic dysfunction is normally manifest as pulmonary congestion. In the absence of systolic dysfunction, abnormal diastolic performance is usually due to abnormal relaxation and/or changes in the passive LV characteristics, external compression or disease of the mitral valve and left atrium. Invasive studies can quantify the rate of myocardial relaxation from the time course of the fall of LV pressure during isovolumic relaxation and the passive LV properties from the LV diastolic pressure-volume relation. In addition, frame-by-frame analysis of contrast ventriculography and conductance determination of LV volume can quantify the pattern of LV diastolic filling. Normally, at rest, most LV filling occurs early in diastole. Conditions that produce diastolic dysfunction, such as LV hypertrophy and ischemia, are associated with reduced early diastolic filling and an augmented importance of atrial systole. It is important to recognize that such patterns can occur in patients without clinically apparent diastolic dysfunction and in normals if left atrial pressure is sufficiently elevated. Furthermore, a normal pattern can occur in patients with severe diastolic dysfunction. Reduced early diastolic filling in the absence of pulmonary congestion indicates the loss of diastolic reserve, since the left atrium is being used as a booster-pump. This pattern of diastolic filling in a patient with symptoms of pulmonary congestion suggests diastolic dysfunction, even if systolic LV performance is normal.

The Jugular Venous Pressure and Pulse Contour

Abstract: Information that can be derived from an assessment of the jugular venous pulse includes determination of the mean venous pressure, venous pulse contour, and presence and type of cardiac dysrhythmias . The jugular venous pressure is usually assessed by observing the right side of the patient's neck. The normal mean jugular venous pressure, determined as the vertical distance above the midpoint of the right atrium, is 6 to 8 cm H 2O . Deviations from this normal range reflect either hypovolemia (i .e ., mean venous pressure less than 5 cm H 2O) or impaired cardiac filling (i .e ., mean venous pressure greater than 9 cm H 2O). The normal jugular venous pulse contains three positive waves . By convention these are labeled "a," "c," and "v" (Figure 19 .1) . These positive deflections occur, respectively, before the carotid upstroke and just after the P wave of the ECG (a wave) ; simultaneous with the upstroke of the carotid pulse (c wave) ; and during ventricular systole until the tricuspid valve opens (v wave) . The a wave is generated by atrial contraction, which actively fills the right ventricle in end-diastole . The c wave is caused either by transmission of the carotid arterial impulse through the external and internal jugular veins or by the bulging of the tricuspid valve into the right atrium in early systole . The v wave reflects the passive increase in pressure and volume of the right atrium as it fills in late systole and early diastole . Normally the crests of the a and v waves are approximately equal in amplitude. The descents or troughs (Figure 19 .1) of the jugular venous pulse occur between the "a" and "c" wave ("x" descent), between the "c" and "v" wave ("x` descent), and between the "v" and "a" wave ("y" descent). The x and x' descents reflect movement of the lower portion of the right atrium toward the right ventricle during the final phases of ventricular systole . The y descent represents the abrupt termination of the downstroke of the v wave during early diastole after the tricuspid valve opens and the right ventricle begins to fill passively. Normally the y descent is neither as brisk nor as deep as the x descent. Abnormalities in the jugular venous pulse may be reflected in either the mean pressure, amplitude, or configuration of the positive waves or negative troughs, or in the sequence or absence of the positive waves . In this chapter emphasis is placed on measurement of the jugular venous pressure, use of the venous pulse to determine cardiac rhythm, and the more common cardiac problems of pulmonary hypertension, tricuspid regurgitation, and constrictive pericarditis .

Cardiac function of the leopard shark, Triakis semifasciata

Abstract: The pressure difference between the cardinal sinus and the pericardium, and the transmural ventricular diastolic pressure at rest and during swimming in the leopard shark, Triakis semifasciata, was measured to characterize the mechanism of cardiac filling in chronically-instrumented fish and to evaluate cardiac responses to swimming. Echo-Doppler and radiographic imaging were also used to fully describe the cardiac cycle. Swimming induces an increase in preload as manifested by a large increment of cardinal sinus pressure (0.26/0.20 [systolic/diastolic] to 0.49/0.32 kPa) which always exceeds pericardial pressure. Increases in both mean ventricular diastolic transmural pressure (0.30–0.77 kPa) and cardinal sinus pressure during swimming suggest increased cardiac filling by vis a tergo as the mechanism for augmenting cardiac output. In contrast to mammals, the fluid-filled pericardial space of elasmobranchs is considerably larger and the pericardium itself does not move in concert with the heart throughout the cardiac cycle. Also, modest increases in heart rate drastically curtail the duration of diastole, which becomes much less than that of systole, a phenomenon not found in mammals. In the absence of tachycardia (<40 bpm), ventricular filling is characterized by a period of early rapid filling, and a late period of filling owing to atrial systole, separated by a period of diastasis. Ventricular filling in elasmobranchs is thus biphasic and is not solely dependent on atrial systole. Atrial diastole is characterized by three filling periods associated with atrial relaxation, ventricular ejection, and sinus venosus contraction. The estimated ventricular ejection fraction of Triakis (80%) exceeds that of the mammalian left ventricle.

System and method for recognizing pacemaker-mediated tachycardia

Abstract: A pacemaker mediated tachycardia (PMT) is detected by circuitry within an implantable pacemaker. The PMT is detected by first detecting a tachycardia condition that includes a prescribed number of consecutive cardiac cycles having a rate faster than a prescribed rate. Each cardiac cycle of the tachycardia condition includes a natural atrial event, i.e., a P-wave, and a paced ventricular event, i.e., a V-pulse generated by a pacemaker. After the prescribed number of such cardiac cycles, e.g., two to ten, a P-V delay in a single cardiac cycle is modified by a first prescribed amount, e.g., 50 milliseconds. The time interval of a V-P interval associated with at least one cardiac cycle preceding the modified P-V delay is then compared to a V-P interval immediately following the modified P-V delay. Only if the difference between the V-P intervals thus measured is less than a second prescribed amount, e.g., 25 milliseconds, is a PMT indicated. If a PMT is indicated, a PMT termination regimen, e.g., extending PVARP, is automatically invoked by the pacemaker for a prescribed number of cardiac cycles, such as one or two cardiac cycles.

Relation of filling pattern to diastolic function in severe left ventricular disease.

Abstract: M mode and Doppler echocardiograms, apex cardiograms, and phonocardiograms were recorded in 50 patients with severe ventricular disease of varying aetiology to examine how left ventricular filling is disturbed by cavity dilatation. The size of the left ventricular cavity was increased in all with a mean (SD) transverse diameter of 7.2 (0.8) cm at end diastole and 6.3 (0.8) cm at end systole. All were in sinus rhythm and 35 had functional mitral regurgitation. In nine patients, in whom filling period was less than 170 ms, transmitral flow showed only a single peak, representing summation. In the remainder there was a strikingly bimodal distribution of filling pattern. In 12 the ventricle filled dominantly with atrial systole (A fillers). Isovolumic relaxation was long (75 (35) ms) and wall motion incoordinate; mitral regurgitation was present in only one. In most (29) the left ventricle filled predominantly during early diastole (E fillers). Mitral regurgitation, which was present in 26, was much more common than in the A fillers, while the isovolumic relaxation time (10 (24) ms) was much shorter and the normal phase relations between flow velocity and wall motion were lost. In 24 E fillers no atrial flow was detected. In four there was no evidence of any mechanical activity, suggesting "atrial failure". In 20, either the apex cardiogram or the mitral echogram showed an A wave, implying that atrial contraction had occurred but had failed to cause transmitral flow, showing that ventricular filling was fundamentally disturbed in late diastole. A series of discrete abnormalities of filling, beyond those shown by Doppler alone, could thus be detected in this apparently homogeneous patient group by a combination of non-invasive methods. The presence and nature of these abnormalities may shed light on underlying physiological disturbances.

Cardiac assistance by atrial or ventricular cardiomyoplasty.

Abstract: Dynamic cardiomyoplasty was conceived to enhance cardiac performance by assisting myocardial contraction. Technically, this procedure consists of placing a pedicled latissimus dorsi muscle flap around the heart and subsequent muscle electrostimulation in synchrony with ventricular systole. Three types of dynamic cardiomyoplasty can be considered. (1) Atrial or ventricular reinforcement is accomplished by wrapping the latissimus dorsi muscle flap around the heart to support hypokinetic or akinetic areas secondary to congenital or acquired diseases. The atrial reinforcement may be performed to improve atrial output after Fontan-type procedures. (2) Ventricular substitution is performed to replace a portion of the ventricular wall. Autologous pericardium is used to create a neoendocardium and facilitate hemostatic closure of the ventricle. The pedicled latissimus dorsi is then secured to replace the resected myocardium. (3) The two previous techniques of ventricular substitution and reinforcement are combined. This reconstructive procedure, which normalizes the ventricular geometrical shape, is particularly useful after extended cardiac resections, such as is done in treatment of large ventricular aneurysms, cardiac tumors, or echinococcal cyst formations. At present, improvement in ventricular function has been obtained in 12 patients at our institution. Preoperative severe cardiac dysfunction was present in all of these patients (New York Heart Association functional class III or IV). Postoperative echocardiography, multigated acquisition scan, and hemodynamic studies demonstrate an improvement in ventricular function and no impairment of ventricular compliance by the muscle flap. After a mean follow-up period of 18 months, all patients are in functional class I or II. We believe that dynamic cardiomyoplasty prolongs and improves the quality of life of patients suffering from severe chronic and irreversible myocardial dysfunction by improving ventricular contraction and limiting cardiac dilatation.

Intraoperative assessment of pulmonary vein flow.

Abstract: This study was undertaken to assess the suitability for intraoperative pulmonary vein flow measurements in 15 patients undergoing coronary artery bypass grafting. Using two-dimensional color Doppler transesophageal echocardiography, all four pulmonary veins--right upper and lower and left upper and lower pulmonary veins were easily visualized. Pulmonary vein flow was pulsatile. J wave occurred in the ventricular systole with relaxation of the left atrium and K wave in the ventricular diastole with relaxation of the left ventricle. There were differences in suitability for flow measurements among four pulmonary veins: (1) consistent visualization; (2) stable visualization throughout measurement; (3) minimal angle between ultrasonic beam and pulmonary vein course; and (4) minimal shift of sampling volume during measurement. The left pulmonary veins were suitable for flow velocity measurement by transesophageal echocardiography. The left lower pulmonary vein was stable for visualization once it was visualized although the angle was occasionally large. The left upper pulmonary vein was consistently visualized although the angle was occasionally large. On the other hand, the right pulmonary veins were unsuitable for flow measurement. Since sampling volume shifted in the direction of the long axis by the average of 5 to 6 mm during cardiac cycle, it should be positioned inside of the pulmonary vein at about 5 mm from the orifice of the left atrium.

A closed-loop control scheme for intraaortic balloon pumping

Abstract: The beneficial hemodynamic efforts of intraaortic balloon pumping (IABP) are critically dependent on balloon timing relative to the diastolic phase of the cardiac cycle. A microprocessor-based controller has been developed to implement real-time automation of IABP using P-R intervals to regulate balloon deflation and systolic time intervals to trigger balloon inflation in a semiautomatic fashion. Experiments were performed on anesthetized open-chest dogs. Simultaneous measurements of aortic pressure and flow, coronary flow, and left ventricular pressure were recorded. Muscle segment lengths in normal and ischemic border zones were also measured from implanted pairs of endocardial ultrasonic dimension gages. P-waves were obtained from atrial cardiograms, and heart sounds were detected using a special filtering circuit. Both signals were input together with ECG to automate IABP timing. Systolic time intervals were calculated in real time. IABP efficacy was assessed from changes in aortic flow, coronary flow, tension time index, end diastolic pressure, and the endocardial viability ratio. >

Pulsed Doppler evaluation of left ventricular filling in subjects with pathologic and physiologic third heart sound.

Abstract: Haemodynamic studies suggest that the rapid deceleration of left ventricular inflow at the end of early diastole may play an important role in the genesis of the third heart sound (S3). To confirm this hypothesis non-invasively, pulsed Doppler of transmitral flow was used. Mitral flow velocity wave was recorded in 20 post-infarction patients with audible S3 (Group 1), in 20 young healthy individuals with physiologic S3 (Group II), in 20 postinfarction patients without S3 (Group III) and in 20 normal adults (Group IV). Peak flow velocity in early diastole (Ev), peak flow velocity during atrial systole (Av), the Ev/Av ratio, the deceleration of early diastolic flow (EF slope), the ratio of the time velocity integral of early diastole to the total time velocity integral (TVle/TVlt) and the isovolumic relaxation time (IVRT) were measured from Doppler recordings. The time relation between S3, the mitral valve motion on M-mode tracing, and the mitral flow velocity wave were analysed comparing the intervals from the second sound to Ev (A2-Ev), to the E point of mitral valve motion (A2-Em)and to the S3 (A2-S3). In groups land II Ev/A v ratio was higher (respectively 4.4 ± 2.2 and 2.8±1.1) than in group III (0.8 ±0.4) and IV (1.3 ± 0.3). Similar results were found for the TVle/TVlt ratio. In both groups with S3, EF slope was significantly steeper (respectively 9 ± 1.8 and 7.5 ±1.1 ms) than in normal adults (4–4 ±11 ms) and patients without S3 (3.6 ±1.1 ms). The IVRT in S3 groups was shorter than in group III and IV. In all subjects, S3 was synchronous with Ev point and persisted during the EF slope. In fact A2-Ev and A2-S3 were almost equal (I33±15vs 134 ±15). In conclusion our data support the concept that, whatever the underlying haemodynamic conditions, the genesis of S3 is related to an enhanced early filling phase followed by a rapid haltingvf inflow.

Influence of the pericardium on ventricular loading during respiration.

Abstract: The influence of the pericardium on ventricular loading during respiration was studied in 17 acutely instrumented anesthetized dogs. Changes in intrapericardial surface pressures (Ppe) on the ventricles were measured by use of air-filled flat latex balloons during acute changes in ventricular loading with the chest open or during negative intrathoracic pressure (NITP) produced by phrenic nerve stimulation with the chest closed. Ppe always demonstrated a phasic change within a cardiac cycle, with its maximum near end diastole and minimum near end systole, and a waveform similar to ventricular dimensions measured by sonomicrometer crystals. With the chest open we found that 1) inferior vena caval constriction decreased Ppe on both ventricles at end diastole (P less than 0.01), 2) aortic constriction increased Ppe on both ventricles at end systole and end diastole (P less than 0.05), and 3) pulmonary artery constriction increased Ppe on the right ventricle (RV) (P less than 0.01) while decreasing Ppe on the left ventricle (LV) at end diastole (P less than 0.05). Thus regional Ppe over a ventricle is influenced by changes in ventricular loading conditions. During NITP with lung volume either constant or increased, Ppe over the anterolateral LV decreased less than two independent extrapericardial measures of intrathoracic pressure, and this resulted in an increased transpericardial pressure at end systole (P less than 0.05) and end diastole (P less than 0.01). During NITP with increased transpericardial pressure, Ppe over the anterior LV, lateral LV, and RV inflow showed small regional differences, but all decreased less than esophageal pressure (P less than 0.01). These results sugges that the increase in transpericardial pressure during late diastole to early systole, produced by increases in ventricular volume during NITP, could effectively attenuate the increases in ventricular preload and afterload caused by respiration, analogous to a negative feedback loop.

Variability of Doppler Echocardiographic Indexes of Left Ventricular Filling in Transplant Recipients and in Normal Subjects

Abstract: This study examines the reproducibility and variability of pulsed wave Doppler versus continuous wave Doppler ultrasound indexes of left ventricular filling in cardiac allograft recipients and in normal subjects. The following indexes were studied: isovolumic relaxation time, pressure half-time, peak early mitral flow velocity, and peak mitral flow velocity after atrial systole. Intraobserver and interobserver variability were assessed by regression analysis. Individual components of variance (subject, reader, beat, day, and tracing) were estimated in a subset of five patients and five normal subjects, and estimated total variance defined for each group. Temporal (day-to-day) variability for 95% confidence was estimated for these patients and for normal subjects. Temporal variability in the group from which the subsets were drawn was measured from absolute and percent change in values on two occasions. Estimated and observed 95% confidence limits were compared. Intersubject variability was the largest component of variance in both transplant recipients and in normal subjects. For all indexes in transplant recipients (in the absence of rejection) and normal subjects, observed absolute mean differences (± 2 standard deviations) between values from recordings taken on two different days were larger than the 95% confidence limits estimated from the components of variance analysis. The observed 95% limits for transplant recipients versus normal subjects were as follows: isovolumic relaxation time, 20 msec versus 6 msec; pressure half-time, 16 msec versus 9 msec; peak early mitral flow velocity, 32 cm per second versus 17 cm per second; and peak mitral flow velocity after atrial systole, 28 cm per second versus 10 cm per second. Thus the reproducibility of Doppler indexes of left ventricular filling in normal subjects cannot be applied to heart transplant recipients. For serial monitoring of left ventricular filling in transplant recipients, changes in the values of each subject, rather than absolute values, must be used.

Vagal action on atrioventricular conduction and its inhibition by sympathetic stimulation and neuropeptide Y in anaesthetised dogs

Abstract: The observed change in atrioventricular conduction time (PR interval) in response to vagal stimulation is the result of two opposing effects; PR interval increases in response to the direct action of the vagus on atrioventricular nodal cells (direct effect), and the accompanying slowing of heart rate acts to decrease PR interval (indirect effect). The relationships between these opposing effects were studied in anaesthetised dogs. This study has shown that the increase in PR interval in response to vagal stimulation is well correlated with vagal stimulation frequency and can be regarded as linear. This is so for unpaced and paced hearts. We have also shown there is an increase in the sensitivity of the relationship between increase in PR interval and vagal stimulation frequency during pacing. This increase in sensitivity is attributable to the elimination of the indirect effect of the slowing of heart rate. During atrial pacing, the relationship between pulse interval and PR interval resembles a hyperbola. At low-pulse intervals (i.e. fast heart rates) the PR interval increases. This is in agreement with previous qualitative findings and is related to the functional refractory period of the atrioventricular cells. The action of sympathetic stimulation and injection of neuropeptide Y has not been studied previously. The vagally induced increase in atrioventricular conduction time is attenuated for many minutes following stimulation of the cardiac sympathetic nerve at 16 Hz for 2 min or by intravenous injection of neuropeptide Y (25-50 micrograms/kg). Stimulation of the right cardiac sympathetic nerve evokes a significantly stronger inhibition of the vagally induced prolongation of pulse interval than stimulation of the left sympathetic nerve. On the other hand, stimulation of the left or right sympathetic nerves cause similar inhibition of vagal action on atrioventricular conduction time.