Showing papers on "Cardiac cycle published in 1991"

An Introduction to Cardiovascular Physiology

Abstract: Overview of the Cardiovascular System The Cardiac Cycle The Cardiac Myocyte: Excitation and Contraction Initiation and Nervous Control of Heartbeat Electrocardiography and Arrhythmias Control of Stroke Volume and Cardiac Output Assessment of Cardiac Output and Peripheral Pulse Haemodynamics: Flow, Pressure and Resistance The Endothelial Cell The Microcirculation and Solute Exchange Circulation of Fluid Between Plasma, Interstitium and Lymph Vascular Smooth Muscle: Excitation, Contraction and Relaxation Control Of Blood Vessels: I Intrinsic Control Control Of Blood Vessels: II Extrinsic Control by Nerves and Hormones Specialization in Individual Circulations Cardiovascular Receptors, Reflexes and Central Control Coordinated Cardiovascular Responses Cardiovascular Responses in Pathological Situations

Phase contrast cine magnetic resonance imaging.

Abstract: Phase contrast cine magnetic resonance imaging (MRI) combines the flow-dependent contrast of phase contrast MRI with the ability of cardiac cine imaging to produce images throughout the cardiac cycle. Two pulse sequence types are used for sensitivity to flow in one direction, whereas four are needed for sensitivity in all directions. Several alternatives for synchronization of the data to the cardiac cycle exist. Retrospectively interpolated methods can image the entire cardiac cycle efficiently. Rapid interleaving of the various sequence types ensures immunity to motion misregistration. The technique produces images in which contrast is related to flow velocity as well as magnitude images such as those of conventional cine MRI. The data can be interpreted qualitatively to demonstrate the presence, magnitude, and direction of flow, and quantitatively to provide estimates of flow velocity, volume flow rate, and displaced volumes. Phase contrast cine MRI is helpful in the diagnosis of aortic dissections, in the study of flow distributions in large vessels such as pulmonary arteries, as well as in smaller vessels such as carotid and basilar arteries, and in the evaluation of complex anatomical variants. Future developments are expected to reduce imaging time and expand the quantitative applications.

Normal flow patterns of intracranial and spinal cerebrospinal fluid defined with phase-contrast cine MR imaging.

Abstract: A phase-contrast cine magnetic resonance (MR) imaging technique was used to study normal dynamics of cerebrospinal fluid (CSF) in 10 healthy volunteers and four patients with normal MR images. This pulse sequence yielded 16 quantitative flow-encoded images per cardiac cycle (peripheral gating). Flow encoding depicted craniocaudal flow as high signal intensity and caudo-cranial flow as low signal intensity. Sagittal and axial images of the head, cervical spine, and lumbar spine were obtained, and strategic sites were analyzed for quantitative CSF flow. The onset of CSF systole in the subarachnoid space was synchronous with the onset of systole in the carotid artery. CSF systole and diastole at the foramen of Monro and aqueduct were essentially simultaneous. The systolic and diastolic components were different in the subarachnoid space, where systole occupied approximately 40% and diastole 60% of the cardiac cycle, compared with the ventricular system, where they were equal. This difference results in systole in the intracranial and spinal subarachnoid spaces preceding that in the ventricular system; the same is true for diastole. The fourth ventricle and cisterna magna serve as mixing chambers. The high-velocity flow in the cervical spine and essentially no flow in the distal lumbar sac indicate that a portion of the capacitance necessary in this essentially closed system resides in the distal spinal canal.

Usefulness of systolic excursion of the mitral anulus as an index of left ventricular systolic function.

Abstract: Studies in both humans and nonhuman animals show that the mitral anulus changes its size, shape and position during the cardiac cycle. 1–3 Left ventricular (LV) contraction results in shortening along both the short and long axis of the left ventricle. With each systole, the mitral anulus moves toward the apex in a cephalocaudal direction. 1–3 It has also been observed that the displacement of the mitral anulus during the systole is reduced with dilated cardiomyopathy. 4 We examined the relation between the amount of systolic excursion of the mitral anulus and LV systolic function as measured by radionuclide ventriculography and a variety of echocardiographic techniques.

Spatial distribution of connexin43, the major cardiac gap junction protein, in the developing and adult rat heart.

Abstract: The developmental appearance and spatial distribution pattern of gap junctions were studied in prenatal and adult rat hearts. Gap junctions were visualized immunohistochemically with an antibody raised against a unique cytoplasmic epitope of connexin43, and the spatial distribution pattern was determined by three-dimensional reconstruction. The results demonstrate that from embryonic day 13 onward, connexin43 becomes detectable immunohistochemically in the myocardium of atria and ventricles. No expression is initially detectable in the myocardium of the sinus venosus, the sinoatrial node, the posterior wall of the atrium and pulmonary veins, the interatrial septum, the atrioventricular canal, including atrioventricular node and bundle, the interventricular septum, and the outflow tract. The developmental increase in the density of gap junctions in atria and ventricles of prenatal hearts correlates well with the reported developmental increase in conduction velocity. Whereas connexin43 becomes expressed in the derivatives of the sinus venosus (except for the sinoatrial node) and in the subepicardial layer of the ventricular free wall shortly before birth, it remains undetectable in the atrioventricular node and bundle and the proximal part of the ventricular conduction tissue, even in the adult heart. The apparent absence of an abundant expression of connexin43 at a location with a supposedly high conduction velocity (i.e., the atrioventricular bundle and bundle branches) is unexpected. These observations were confirmed in studies of the adult mouse heart, which showed, in addition, that connexin32 is not expressed in any part of the heart.

Quantification of and correction for left ventricular systolic long-axis shortening by magnetic resonance tissue tagging and slice isolation.

Abstract: BACKGROUNDMeasurement of regional left ventricular (LV) function is predicted on the ability to compare equivalent LV segments at different time points during the cardiac cycle. Standard techniques of short-axis acquisition in two-dimensional echocardiography, cine computed tomography, and standard magnetic resonance imaging (MRI) acquire images from a fixed plane and fail to compensate for through-plane motion. The shortening of the left ventricle along its long axis during systole results in planar images of two different levels of the ventricle, leading to error in any derived functional measurements. LV systolic long-axis motion was measured in 19 normal volunteers using MRI.METHODS AND RESULTSWith a selective radio frequency (RF) tissue-tagging technique, three short-axis planes were labeled at end diastole and standard spin-echo images were acquired at end systole in the two- and four-chamber orientations. Persistence of the tags through systole allowed visualization of the intersecting short-axis t...

Pulmonary blood flow after total cavopulmonary shunt.

Abstract: The pattern of pulmonary blood flow was studied in three patients after a total cavopulmonary shunt procedure. Doppler studies showed a phasic pattern of flow which varied with the respiratory cycle. Pulmonary blood flow was increased with normal inspiration, and was much augmented by the Mueller manoeuvre. This suggests that flow was occurring when a negative intrathoracic pressure was generated. During a brief Valsalva manoeuvre blood flowed away from the lungs. With a sustained Valsalva manoeuvre there was no spontaneous forward flow; instead there was low velocity pulsatile pulmonary blood flow that coincided with ventricular systole. Left ventricular cavity dimensions decreased, reflecting a considerably reduced pulmonary blood flow. Pulmonary blood flow after the total cavopulmonary shunt operation is critically dependent on changes in intrathoracic pressure. This has important implications in terms of the immediate postoperative management of these patients.

Radionuclide angiographic evaluation of left ventricular diastolic function.

Abstract: Left ventricular diastolic function is altered in the majority of patients with cardiac diseases, especially those characterized by myocardial ischemia or hypertrophy. In many circumstances, such abnormalities related to impaired relaxation or reduced distensibility may precede evidence of left ventricular systolic dysfunction. Radionuclide angiography may be adapted to study the rapid filling phase of diastole, the duration of the isovolumic relaxation phase, the relative contributions of rapid filling and atrial systole to left ventricular stroke volume, and the relation between regional nonuniformity of left ventricular function and global filling properties. Technical aspects of data acquisition that must be considered for such studies include the effects of cardiac cycle length fluctuations, temporal resolution, temporal smoothing, and normalization parameters. As noninvasive radionuclide methods (and any other analyses using purely noninvasive techniques) do not permit assessment of the left atrial-left ventricular pressure gradient or the simultaneous evaluation of changes in left ventricular pressure and volume during relaxation and filling, complete clinical interpretation of "abnormal" left ventricular filling indexes, or changes in these indexes after interventions, is not possible. Despite the inherent limitations of noninvasive assessment of left ventricular diastolic function, radionuclide evaluation of left ventricular filling may provide clinically useful insights, especially in patients with congestive heart failure symptoms and normal left ventricular systolic function.

Reconstruction of sequential cardiac in-plane displacement patterns on the chest wall by laser speckle interferometry

Abstract: Time-average speckle interferometry has been applied to obtain displacement patterns on the chest wall produced by cardiac action, in the absence of breathing, during various phases of the cardiac cycle. This has been achieved by an electronic shutter, controlled by the electrocardiogram of the subject. The recorded holographic plates processed under identical conditions are scanned by the pointwise method to obtain the absolute displacements at various locations corresponding to the activities of the various cardiac chambers and valves. These data are transformed to a 40*30 matrix by an interpolation method and, from this, three-dimensional displacement plots are reconstructed by an IBM PC/AT computer. These patterns show the displacements over the entire cardiac area corresponding to the activities of various regions during the cardiac cycle. The apex and aortic valve areas show the maximum displacements during the systolic phase. During the diastolic phase the activities over the low-pressure atrial regions are also observed. The results obtained outline the functional details of the normal heart and the activities over various areas are in agreement with those obtained by other noncontact techniques. >

An echocardiographic assessment of atrial mechanical behaviour.

Abstract: Relations between movement of the atrioventricular ring and changes in left atrial and ventricular dimensions were studied by echocardiography and compared with apexcardiography and Doppler mitral flow velocity traces in 20 healthy controls and in patients with left ventricular hypertrophy (n = 28) or dilatation (n = 16). During left ventricular systole the atrioventricular ring, a structure common to ventricle and atrium, moved towards the ventricular apex, thus increasing left atrial volume. This action matched pulmonary venous return because it was in phase with the transverse left atrial dimension measured from aortic root to posterior left atrial wall. During early diastole, the mitral ring moved rapidly towards the atrium as transmitral flow accelerated. This requires a force directed from ventricle to atrium, likely to be the result of elastic recoil arising from compression of the ventricular myocardium or stretching of the atrial myocardium during ventricular systole. Two additional mechanisms of ventricular filling with atrial systole were recognised: (a) an increase in ventricular volume as the atrioventricular ring moved upwards and (b) transverse left ventricular expansion by pressure driven transmitral flow. The former is undetectable by Doppler from the apex; it accounted for 10% of ventricular filling in the healthy controls, but for significantly less in those with ventricular dilatation. In left ventricular hypertrophy, left ventricular filling was maintained by both mechanisms compensating for the reduced increase in volume early in diastole. Interactions between the atrium and ventricle are functionally important during ventricular systole, early diastole, and in atrial systole. They are not included in the traditional separation of atrial function into reservoir, conduit, and pump functions.

The Physiology of the Alligator Heart: the Cardiac Cycle

Abstract: Pressure recordings from the heart and major arteries of the alligator show that a conventional relationship exists between the left ventricle and the right aorta. Pressure gradients from ventricle to aorta during systole are very small. Right aortic blood flow rises rapidly to a single peak and then falls more gradually until aortic valve closure. The right ventricle is connected both to the pulmonary arteries and to the left aorta. Right ventricular pressures show that systole is a two-stage process. Initially, blood leaves to the low-resistance lung circuit, though appreciable pressure gradients exist across the pulmonary outflow tract. Active contraction of the pulmonary outflow tract stops pulmonary ejection and a second-stage pressure rise is seen in the right ventricle. When systemic blood pressures are high, this second-stage pressure does not reach the levels recorded in the left aorta, and the left aortic valves remain closed so that lung and body circuits are functionally separate. An alternation of flow is found in the left aorta under these conditions, with reversed flow during systole and forward flow during diastole. Flow rates are extremely low, compared with those in the right aorta or pulmonary arteries, and the foramen of Panizza has very little significance in the cardiac cycle. If the systemic blood pressures are low, the second stage of systole in the right ventricle gives rise to pressures that are higher than those in the left aorta, the left aortic valves open and blood is ejected to the systemic circulation, giving a right-to-left shunt. This can occur with no changes in pulmonary pressures or flows. Left aortic flow is not dependent on increased constriction of the pulmonary outflow tract, which continues to function as an on-off active valve. Constriction within the lung vasculature may, on some occasions, be significant in establishing left aortic flow, but it is clear from the present work that low systemic blood pressure is a factor of crucial importance.

Atrial contribution to ventricular filling in mitral stenosis.

Abstract: BACKGROUNDThe importance of the contribution of atrial systole to ventricular filling in mitral stenosis is controversial. The cause of reduced cardiac output following the onset of atrial fibrillation may be due to an increased heart rate, a loss of booster pump function, or both.METHODS AND RESULTSWe studied the atrial contribution to filling under a variety of conditions by combining noninvasive studies of patients with computer modeling. Thirty patients in sinus rhythm with mild-to-severe stenosis were studied with two-dimensional and Doppler echocardiography for measurement of mitral flow velocity and mitral valve area (MVA). The mean +/- SD atrial contribution to left ventricular filling volume was 18 +/- 10% and varied inversely with mitral resistance. Patients with mild mitral stenosis (MVA, 1.8 +/- 0.7 cm2) and severe mitral stenosis (MVA, 0.9 +/- 0.2 cm2) had atrial contributions of 29 +/- 4% and 9 +/- 5%, respectively. The pathophysiological mechanisms responsible for these trends were further ...

Transesophageal Echo-Doppler Echocardiographic Assessment of Pulmonary Venous Flow Patterns

Abstract: Fifty-eight of 61 consecutive patients undergoing transesophageal echo-Doppler echocardiography provided excellent signals to permit assessment of pulmonary venous blood flow patterns. Normal antegrade pulmonary venous flow during ventricular systole was biphasic and was characterized by a short, low velocity (28 ± 17 cm/sec), early systolic jet (P1), and longer, higher velocity (41 ± 23 cm/sec), late systolic jet (P2). Antegrade pulmonary venous flow during ventricular diastole (P3) was of moderate velocity (34 ± 17 cm/sec) and was monophasic; during atrial contraction there was transient, low velocity (−17 ± 11 cm/sec) and reversal of flow (P4). The early systolic antegrade venous flow (P1) was absent or reversed in rhythm disorders, which interrupted normal synchronized atrioventricular activation. These rhythm disorders also were associated with diminished peak flow velocities during late systole (P2). Abnormalities in systolic left ventricular function and mitral regurgitation also had this effect. Diastolic flow velocities (P3) remained constant, except in patients with mitral regurgitation. In these patients diastolic peak flows were significantly increased above normal. In cases of atrial fibrillation or ventricular pacing the late diastolic reversal of flow resulting from atrial contraction (P4) Was absent. Conclusions: Transesophageal echo-Doppler echocardiography gives high quality signals of pulmonary venous inflow to help assess function of the left ventricle and left atrium. Multiple factors affect the patterns. This study suggests caution in the interpretation of abnormal patterns, particularly of reduced systolic pulmonary vein flow in the presence of left ventricular dysfunction, atrial fibrillation, ventricular pacing, and mitral regurgitation.

Systolic and diastolic time intervals in the critically ill patient.

Abstract: OBJECTIVE The waveform of the first derivative of thoracic electrical bioimpedance was used to calculate systolic time intervals of the cardiac cycle, preejection period/left ventricular ejection time ratio, and diastolic time intervals, isovolumic relaxation period/filling time ratio. DESIGN Prospective clinical study. Waveforms were examined from 913 normal and abnormal tracings from a thoracic electrical bioimpedance monitor. This monitor was coupled to a two-channel strip-chart recorder that identified preejection period/LV ejection time and isovolumic relaxation period/filling time in 86% of the tracings. SETTING Two university-affiliated hospitals and one community hospital. PATIENTS We assessed 100 subjects (ranging in age from 17 to 93 yrs) under various conditions. MEASUREMENTS AND MAIN RESULTS Data from 15 normal subjects were used as a reference series to define normative values. Preejection period/left ventricular ejection time ratio was 0.35 +/- 0.1 (SD) and was consistent with data from systolic time intervals derived from simultaneous study of the ECG recording, carotid artery tracing, and phonocardiography. The diastolic time ratio (isovolumic relaxation period/filling time) was 0.4 +/- 0.2, in agreement with normal values derived by echocardiography and angiography. In a subgroup of 17 critically ill patients, a correlative study of simultaneously measured thoracic electrical bioimpedance, nuclear stethoscope, and radionuclide ventriculography was conducted. Systolic functions were compared by the ejection fraction derived by preejection period/left ventricular ejection time ratio displayed on the thoracic electrical bioimpedance monitor and by the radionuclide technique, and were found to be 57 +/- 13.8% and 58 +/- 8.6%, respectively (r2 = .49; y = 4.06x + 0.94; p less than .02; n = 17). Increased diastolic time ratios with normal or near-normal systolic time intervals were documented in nine (53%) of 17 critically ill patients with low systolic index. CONCLUSION Both systolic and diastolic time intervals can be investigated noninvasively at the bedside by the thoracic electrical bioimpedance technique to provide a better understanding of left heart function.

Propagation of depolarization and repolarization processes in the myocardium-an anisotropic model

Abstract: A three-dimensional finite-elements model of the left and right ventricles has been developed to study the process of myocardial electrical activation. The anisotropic properties are demonstrated during simulation of an abnormal cardiac cycle, when propagating is initiated at an ectopic ventricular site. Ischemia is simulated by low conduction velocities in the ischemic zone and wide dispersion of values in nearby locations; automaticity is described by restimulating cells in the injured area; the dangerous effects of a premature beat leading to reentry are simulated by reduction of propagation velocity in cells that are reactivated while they repolarized. The different activation patterns are calculated throughout the myocardium and on its surface. The generated surface activation maps are not sensitive to minute changes in location of the foci of activation within the normal conduction system. The maps show sensitivity to pathological velocities, ischemic areas, and the existence of ectopic foci. Thus, the model, with its distributed properties, may be useful for electrocardiographic studies due to its low sensitivity to normal cell-to-cell variability, but high sensitivity to the existence of abnormally propagating myocardial activity. >

Reconstruction of out-of-plane cardiac displacement patterns as observed on the chest wall during various phases of ECG by capacitance transducer

Abstract: The out-of-plane displacements due to cardiac action were measured on the chest wall by an electronic distance measurement technique which is based on the variation of the capacitance between the probe and moving surface. The displacements were measured at 36 locations over the entire cardiac region along with ECG (electrocardiogram) measurements and were directly fed to an IBM PC/AT computer after analog-to-digital conversion. From these data, the displacement patterns for the whole region during the complete cardiac cycle could be reconstructed in a perspective view. The sequential analysis of the displacements shows the details of the cardiac events. and the results obtained are in agreement with other techniques. The averaged displacements over various regions of the heart for normal subjects are also presented. The data acquisition system and measurement results are presented and discussed. >

Echo-Doppler evaluation of the effects of heart rate increments on left atrial pump function in normal human subjects.

Abstract: It is commonly believed that the atrial contribution to left ventricular filling increases during heart rate increments. However, the relative contribution of the pump function (atrial systole) and of the passive role (diastasis and reservoir) of the atrium to end-diastolic left ventricular filling is not well known. In order to investigate this problem, we performed a two-dimensional echo-Doppler study during right atrial pacing. Transmitral flow velocity curves were obtained by means of pulsed Doppler. Pacing was performed (1) at the lowest heart rate at which it was possible to obtain a stable capture of the atria, (2) at the heart rate at which the early and late Doppler filling waves almost completely overlapped. In both stages pacing was interrupted for a few seconds to obtain some post-pacing beats. Doppler tracings recorded at rest, during pacing and in the immediate post-pacing beats were analysed to obtain well-known parameters of atrial contribution: atrial peak flow velocity, early to atrial peak flow velocity ratio, and time-velocity integral of the atrial wave. Furthermore, in order to distinguish end-diastolic passive flow from the active contribution of atrial systole to filling, we superimposed the envelope of the last Doppler curve obtained during atrial pacing over the envelope of the first post-pacing curve. In this way the area of the atrial wave of the paced beat was divided by the mid-diastolic part of the post-pacing one into two areas, the integrals of which correspond to the active and passive atrial contribution respectively. At higher heart rates we observed that: (I) atrial peak flow velocity remains unchanged; (2) the ratio of early to atrial peak flow velocity decreases significantly; (3) atrial contribution to filling, evaluated as the overall atrial wave integral, increases significantly; (4) the active atrial contribution does not increase, which means that the increase in atrial wave integral is totally due to the increment in the end-diastolic passive flow. We conclude that: (1) the active contribution of the atrial systole to left ventricular filling does not increase during tachycardia; (2) the parameters commonly used to evaluate atrial contribution to filling (early to atrial peak flow velocity ratio and atrial integral) can cause an over estimation as they cannot distinguish between active and passive end-diastolic flow; (3) the relative importance of these two components mainly depends on heart rate and must be considered carefully in various clinical and experimental conditions.

Behavioral modulation patterns fit an animal model of vagus-cardiac pacemaker interactions

Abstract: The present study used a computer model of the dynamic interaction between the vagus nerve and the sinoatrial pacemaker membrane potential in the heart of the rabbit to reconstruct heart rate changes under vagal excitation conditions. We asked whether a hypothetical pattern of vagal acetylcholine (ACh) release, which was based on human heart rate results in a reaction time task, could be fit to this model. The reconstructed heart rate results showed changes that were highly consistent with experimental human heart rate changes. The model reliably reproduced effects of parameters such as intrinsic heart rate level, ACh stimulus intensity, and ACh stimulus duration. In addition, the effects of anticipatory vagal ACh release, stimulus-induced ACh, and subsequent blocking of ACh, which usually interact in human cardiac cycle time functions, could be untangled in the reconstructed heart rate results. We concluded that the mathematical model may be useful for formulating hypotheses and constructing experimental task designs for studies of human heart rate.

Circulatory mechanics in the toad Bufo marinus. II, Haemodynamics of the arterial windkessel

Abstract: This study examines the importance of vascular elasticity to arterial haemodynamics in a poikilothermic vertebrate. Pulsatile blood pressure, flow and vessel diameter were recorded at several locations within the arterial tree of the toad, Bufo marinus . We then determined the dynamic elastic modulus, the pulse wave velocity and the hydraulic impedance characteristics of the aorta. The relatively low heart rate and short arterial tree, and a pulse velocity of about 2.5ms −1 , combine to give a transit time for the pressure pulse through aorta that is only 3% of the cardiac cycle. Consequently, wave propagation effects seen in mammals, such as peripheral amplification, distortion and secondary pressure peaks due to reflections, are not apparent. Instead, the aorta acts as a simple Windkessel and inflation by the heart occurs almost simultaneously throughout. Pressure waveforms are nearly identical at proximal and distal locations, and flow pulsatility is reduced progressively through the elastic aorta.

Cardiac cycle length modulates cardiovascular regulation that is dependent on previous beat contraction history.

Abstract: Previous studies of the beat-to-beat regulation of left ventricular performance in the intact cardiovascular system have shown that the performance of the left ventricle on any one beat is influenced by the mechanical events of the previous beat, so-called previous beat contraction history. The general hypothesis investigated in this study is that previous beat contraction history occurs because of the perturbation of one or more biochemical processes with time courses that are long relative to one cardiac cycle. If this is true, then previous beat contraction history should depend on the interval between beats and, therefore, should extend beyond the previous beat to two, or even three, previous beats as heart rate is increased. Hemodynamic responses to random preload and afterload changes were measured in 11 anesthetized open-chest dogs on right heart bypass at three paced heart rates. Multiple linear regression was used to analyze these hemodynamic sequences and identify variables from the previous one, two, or three beats that were important in the mechanical history dependence of left ventricular function. The results of this analysis showed that under baseline conditions, all 11 hearts showed one beat of history dependence, with only two of 11 hearts showing a dependence on the previous two or three beats. At the highest heart rate, all 11 hearts still showed one beat of history dependence, but 10 of 11 hearts showed two beats of history dependence, and four of 11 showed three beats of history dependence (p less than 0.05). A general framework for the mechanism underlying these findings, which relates previous beat contraction history to the interval-dependent mechanical restitution phenomenon, is proposed and discussed.

Interpretation of cardiac pathophysiology from pressure waveform analysis: The left-sided v wave

Abstract: The left-sided V wave is dependent on both left atrial and ventricular pressure/volume filling relationship. The cardiac rhythm and timing of atrial systole also influences the V wave. The morphology of the V wave can reflect the severity of mitral regurgitation with stenosis, but valve areas in this setting may be better assessed by a pressure half-time method. Finally, as queried in our first patient example, V wave alternans is a reflection of left ventricular pressure alternans in a failing heart. Other signs of poor left ventricular function in Figure 1 also included an elevated minimal diastolic pressure and markedly elevated left ventricular end diastolic pressure. Hemodynamic findings of poor left ventricular function will be addressed in detail in a later "Rounds."

Pulmonary venous flow in cardiac tamponade: influence of left ventricular dysfunction and the relation to pulsus paradoxus.

Abstract: The pattern of left atrial filling was studied in nine closed-chest dogs during cardiac tamponade before and after production of microembolic left ventricular dysfunction produced by intracoronary injection of 54 +/- 4 microns (SD) microspheres. With cardiac tamponade, a significant increase in the ratio of systolic/diastolic pulmonary venous flow velocity integral both before (1.65 +/- 0.24 versus 2.77 +/- 0.43 [SE], p less than 0.05) and after production of left ventricular dysfunction (0.57 +/- 0.12 versus 1.77 +/- 0.44, p less than 0.05) was seen. Compared with baseline, cardiac tamponade caused a significant inspiratory decrease in systolic pulmonary venous velocity both before (7.3 +/- 2.0 versus 1.2 +/- 1.4 cm/sec) and after left ventricular dysfunction (3.4 +/- 0.4 versus 1.0 +/- 0.9 cm/sec, both p less than 0.05). The magnitude of respiratory variation (expiration-inspiration) of the pulmonary venous flow velocity integral with tamponade was significantly greater before than after left ventricular dysfunction (1.6 +/- 0.2 cm versus 0.8 +/- 0.2 cm, p less than 0.05). A significant correlation was found between the inspiratory fall in aortic systolic pressure and the flow velocity integral of pulmonary venous flow before left ventricular dysfunction (r = 0.58, p less than 0.05). After coronary embolization, neither pulsus paradoxus nor significant respiratory variation (expiration-inspiration) of the pulmonary venous flow integral was observed with cardiac tamponade. In this model of cardiac tamponade and left ventricular dysfunction, left atrial filling occurs predominantly during ventricular systole. These changes may be helpful in recognizing hemodynamically significant pericardial effusion and have implications for the pathophysiology of cardiac tamponade.

Cardiac function in hypothermia.

Abstract: Hypothermia retards cardiac contraction and prolongs the subphases of the cardiac cycle in varying degrees. Six anaesthetized beagle dogs were catheterized and cooled between ice bags until the aortic blood temperature was 25 degrees C and then rewarmed to normothermia. The speed of relaxation decreased to a half from its value in normothermia as indicated by the time constant of exponential isovolumic ventricular pressure fall and by the change in the negative dp/dt. It is suggested that retardation of relaxation is connected with temperature dependent changes in calcium kinetics. Decrease of cardiac output was mediated mainly by decreased stroke volume indicating sympathetic tone in spite of cold narcosis.

Relation between cyclic variation in echo amplitude and segmental contraction in normal and abnormal hearts.

Abstract: OBJECTIVE--To study the relation between cardiac systolic activity and cardiac cycle dependent variation in the ultrasound signal arising from within the myocardium. DESIGN--Regional echo amplitude was used as a measure of the myocardial ultrasound signal. Relative echo amplitude values were assigned by standardising echo gain using the posterior parietal pericardium as an in-vivo calibration. M mode measurements of the left ventricle were used to assess cardiac systolic activity. Subjects were studied prospectively. Analysis of echo amplitude was performed by investigators who were blinded to the results of the M mode analysis. The influence of impaired left ventricular performance and abnormal wall motion were assessed. PATIENTS--11 cardiomyopathy patients with impaired ventricular function, eight patients with severe pulmonary hypertension and reversed septal motion, and 19 healthy controls. SETTING--All subject studies were performed at Harefield Hospital. Echo amplitude analysis was performed at the Royal Brompton Hospital. MAIN OUTCOME MEASURES--Cyclic variation in echo amplitude was determined as the change in echo amplitude from end diastole to end systole. Additionally, an index of cyclic variation defined as the ratio of the cyclic change in echo amplitude to end diastolic echo amplitude was measured. Both cyclic variation and the cyclic variation index were analysed to see whether they correlated with left ventricular dimensions, fractional shortening, and systolic wall thickening. RESULTS--Stepwise regression analysis showed systolic wall thickening to be the most significant independent variable that correlated with the cyclic variation index for both the septum and posterior wall (r = 0.68, p = 0.0001, septum; r = 0.69, p = 0.0001, posterior wall). The slopes and intercepts for both regression equations were similar (y = 0.005x + 0.006, septum; y = 0.006x + 0, posterior wall). Subgroup analysis showed that the healthy controls, patients with cardiomyopathy, and patients with pulmonary hypertension had similar slopes and intercepts for their individual regression equations. CONCLUSIONS--These data support the hypothesis of a quantitative relation between the extent of cyclic variation of echo amplitude and the degree of segmental myocardial shortening, as measured by systolic wall thickening, which is not significantly influenced by location within the myocardium, left ventricular performance, or wall motion. They provide further evidence of the usefulness of quantitative analysis of myocardial echo amplitude in the study of regional myocardial function in both normal and injured myocardium.

Acute, reversible tricuspid insufficiency: creation in canine model

Abstract: Relatively few methods have been described for the creation of valvular insufficiency in an animal model. Those presented involve limitations such as permanent destruction of the valves or lack of control over the degree of regurgitation produced. We describe a method of acute reversible tricuspid insufficiency that can be easily created and controlled in anesthetized dogs. The model employs a wire spiral that is advanced through the atrioventricular canal from the right atrium. The spiral causes regurgitation by preventing complete apposition of the valve leaflets while permitting retrograde flow to occur through the spiral lumen. The degree of regurgitation can be controlled by the use of spirals of different sizes. Creation of tricuspid insufficiency is demonstrated by the onset of right atrial pressure V waves, a "ballooning" of the right atrium during ventricular systole, palpation of an atrial thrill, or by color Doppler echocardiography. In 14 dogs, right atrial pressure increased from a control value of 9 +/- 3 (mean +/- SD) mmHg to 10 +/- 3 and 12 +/- 3 mmHg, respectively, with spirals of 1.5 and 2.2 cm in diameter (both P less than 0.05). With the 2.2-cm spiral, aortic blood pressure decreased from a control value of 104 +/- 20 to 83 +/- 17 mmHg (P less than 0.05), and cardiac output decreased from 73 +/- 26 to 59 +/- 19 ml.min-1.kg-1 (P less than 0.05). This model is reversible, allows repeated trials of various grades of regurgitation, does not require ventriculotomy, and is relatively nonarrhythmogenic.