Cardiac cycle

About: Cardiac cycle is a research topic. Over the lifetime, 3290 publications have been published within this topic receiving 96159 citations.

The Heart of the Salamander (Salamandra salamandra, L.), with Special Reference to the Conducting (Connecting) System and Its Bearing on the Phylogeny of the Conducting Systems of Mammalian and Avian Hearts

Abstract: Nine salamander hearts have been studied histologically by means of serial sections, cut in each of three planes (transverse, frontal and sagittal), and stained with haemalum and eosin, van Gieson's acid fuchsin and iron-haematoxylin, and by the protargol method of Bodian. This study has demonstrated muscular continuity between the several cardiac chambers, and the entire absence of any specialized muscle or 'nodal tissue' at the junctional sites or in any other part of the heart. The heart muscle forms a continuum. The cardiac muscle fibres are characterized by their large size (i.e. breadth); they have the same general histological characters in all parts of the heart. Measurements are given for the fibres from various parts of the hearts of the salamander and frog. The muscular connexions between the various cardiac chambers have been studied in detail. In each of the chambers the musculature is arranged in a basket-work fashion, but at each of the junctional sites the muscle suddenly changes to a regular circular arrangement. The sinus, at its junction with the right atrium, contains muscle only in its ventral wall, and it is this wall only of the sinus which thus establishes muscular continuity with the ring of muscle (S-A ring) around the sinu-atrial opening. The musculature of both atria is continuous with that of the ventricle in two ways. From the ring of muscle (A-V ring) surrounding the common opening of the atria into the ventricle, the atrio-ventricular funnel dips down into the ventricle, and the caudal border of this funnel is continuous (a) with an invaginated part of the base of the ventricle, and (b) more extensively with ventricular papillary muscles, which, in their turn, are continued into the inner ventricular trabeculae about the middle level of the ventricle. The A-V funnel is homogeneous in structure; no one part of its circumference differs from another. The ventricular muscle is directly continued into that of the bulbus cordis, in which latter chamber the muscle is entirely circular. The course which the wave of contraction takes during its transmission from the sinus throughout the heart has been deduced from the study of the details of the continuity of the musculature of the various cardiac chambers. To a large extent this deduction has been confirmed by superimposing tracings of the outline of the pulsating heart, made from the slow-motion cinephotographic records. This latter study has revealed many of the details of the phases of the cardiac cycle. The delay in the transmission of the wave of contraction from one cardiac chamber to the next is accounted for by the relatively long path which the impulse has to traverse at the junctional sites, where the muscle is arranged in a circular fashion, without postulating the existence of specialized 'block fibres' at these sites. The branching of the muscle fibres has the effect of converting the morphological circular arrangement of the fibres at these junctions into a physiological spiral. The glycogen content of the various parts of the frog's heart, as revealed by staining with carmine, is found to increase in the order sinus, atria, ventricle and bulbus cordis. This is correlated with a similar increasing order of density of musculature and work done, the glycogen being a reserve potency for the energy of muscular contraction. The fact that the intrinsic rhythmic rates of the several chambers decrease in the same order as the glycogen content increases may or may not be coincidental. Cutting and ligature experiments, with cinephotographic and kymographic records, reveal the intrinsic rhythmic rates of the various cardiac chambers of the salamander heart. No satisfactory reason has yet been adduced to account for the different intrinsic rhythmic rates of the several parts of the heart when these are isolated from each other. The dorsal mesocardium has been traced in its entirety. The sinu-ventricular fold is a part of the continuous dorsal mesocardium and does not constitute a direct muscular sinu-ventricular connexion. The distribution of the intracardiac nerve cells has been noted and the probable pathway of migration of these nerve cells in the embryo has been suggested. The significance of the results of this investigation in relation to the phylogeny of the specialized conducting system of the hearts of homoiothermal vertebrates (mammals and birds) is discussed. The view is expressed that the cardiac conducting systems of homoiothermal vertebrates constitute a neomorphic development, correlated with functional requirements, and are not remnants of more extensive tissues of similar structure in the lower vertebrate heart. Variations in this newly evolved formation probably account for the different descriptions of such elements in various mammalian and avian hearts.

Modeling pressure-flow relations in cardiac muscle in diastole and systole.

Abstract: Pressure-flow relations were calculated for a symmetrical, maximally dilated, crystalloid-perfused coronary vascular network embedded in cardiac muscle in (static) diastole and (static) systole at two muscle lengths: slack length and 90% of maximal muscle length (Lmax). The calculations are based on the "time-varying elastance concept." That is, the calculations include the mechanical properties of the vascular wall and the (varying) mechanical properties of the myocardial tissue (in cross-fiber direction). We found that, at any given perfusion pressure, coronary flow is smaller in systole than in diastole. Relative reduction in vascular cross-sectional area, which forms the basis of flow impediment, was largest for the smallest arterioles. At a constant perfusion pressure of 62.5 mmHg, the transition from (static) diastole to (static) systole at constant muscle length ("isometric contraction") was calculated to reduce flow by 74% (from 18.9 to 5.0 ml x min(-1) x g(-1)) and by 64% (from 12.6 to 4.6 ml x min(-1) x g(-1)) for the muscle fixed at slack length and 90% of Lmax, respectively. At this perfusion pressure, contraction with 14% shortening (from 90% of Lmax in diastole to slack length in systole) was calculated to reduce flow by 61% (from 12.6 to 5.0 ml x min(-1) x g(-1)). Increasing muscle length from slack length to 90% of Lmax decreases coronary flow by 34% in diastole and by 8% in systole. We conclude that modeling cardiac contraction on the basis of the time-varying elastic properties of the myocardial tissue can explain coronary flow impediment and that contractions, with or without shortening, have a larger effect on coronary flow than changes in muscle length.

Assessment of synchrony relationships between the native left ventricle and the HeartMate left ventricular assist device.

Abstract: Background: It has been suggested that the cardiac cycle becomes synchronized with the LVAD. Synchronization between the left ventricle and the LVAD may be important for ventricular unloading and coronary flow. In this study, we assessed the synchrony between the cardiac and LVAD cycles. Methods: We studied 24 patients with HeartMate LVAD support. Native heart rate from an electrocardiogram and LVAD rate were measured at rest and peak exercise. Three patients underwent simultaneous invasive pressure measurement from the left ventricle and the aorta, and 3 patients underwent simultaneous recording of electrocardiogram and LVAD electrical signal. Results: Resting heart rate was significantly higher than LVAD rate (96 ± 17 vs 66 ± 15 beats [b]/min, p r = 0.25). Peak heart rate was significantly higher than LVAD rate (142 ± 16 vs 102 ± 14 b/min, p r = 0.31). Electrical signal recording confirmed the absence of cardiac–LVAD synchrony. Pressure measurements revealed a cyclical intraventricular pressure variation, determined by the relationship between the cardiac and LVAD cycles. Intraventricular pressure was lowest when left ventricular systole occurred during pump filling and highest when left ventricular systole occurred during pump ejection. Conclusions: The cardiac and LVAD cycles are not in synchrony at rest or at peak exercise. However, a cyclical variation in left ventricular pressure exists, dependent upon the phasic relationship of the cardiac–LVAD cycles, which significantly effects ventricular loading. Better understanding of this relationship may be important in developing assist devices for optimal left ventricular unloading and improvement of myocardial recovery.

Spatiotemporal image correlation using high-definition flow: a new method for assessing ovarian vascularization.

Abstract: Objective. The purpose of this study was to describe a new method for assessing ovarian vascularization using spatiotemporal image correlation (STIC)-high-definition flow (HDF). Methods. Thirty healthy premenopausal fertile women were assessed in the follicular part of the menstrual cycle by transvaginal sonography. A 4-dimensional STIC-HDF volume was obtained from the nondominant ovary to assess 3-dimensional (3D) vascular indices (vascularization index [VI] and flow index [FI]) during one cardiac cycle in each women. Using 1-cm3 spherical sampling, we calculated the VI and FI from the most vascularized part of the ovarian stroma at two different moments of the cardiac cycle (systole and diastole). System settings were kept constant for all of the patients (pulse repetition frequency, 0.9 kHz; gain, 0.8; and depth, 40 mm). We calculated the VI and FI ratios between systole and diastole. Results. The mean VI during systole (11.485%; SD, 6.7%) was significantly higher than during diastole (8.653%; SD, 5.6%; P< .0001). The mean FI values during systole (47.799 [unitless]; SD, 5.8) and diastole (47.791; SD, 6.0) were nearly identical (P = .993). The VI ratio was 1.35 (95% confidence interval, 1.28-1.42), which means that the mean VI was 35% higher during systole compared to diastole, whereas the FI during systole and diastole remained constant (FI ratio, 1.00; 95% confidence interval, 0.96-1.04). There was a high correlation between VI values during systole and diastole (r 2 = 0.94), whereas this correlation was weaker for the FI (r 2 = 0.45). Condusions. The STIC-HDF method allows assessment of 3D vascular indices throughout the cardiac cycle. Vascularization index calculation is affected by the moment of the cardiac cycle during which the measurement is taken. However, it seems that FI calculation is not affected by the cardiac cycle in the normal nondominant ovary.

Left Atrial Strain Determinants During the Cardiac Phases

Abstract: The present study investigated the determinants of left atrial (LA) strain in all phases of the cardiac cycle.LA strain by speckle-tracking echocardiography allows the assessment of LA function in each phase of the cardiac cycle. However, its determinants and its relation with left ventricular (LV) function have not yet been fully described.The authors performed a retrospective analysis in 127 patients with different cardiovascular pathologies. Using 2-dimensional speckle tracking in 4- and 2-chamber apical views we derived both LA and LV strain curves. Strain-strain loops were reconstructed using LV strain and the corresponding, synchronized LA strain data. Linear regressions were calculated for the entire strain-strain loop as well as for the 3 phases of the cardiac cycle (systole, and early and late diastole). The association between LA strain parameters and LV systolic and diastolic parameters was studied. The prediction of cardiovascular events was evaluated for both measured and predicted LA strain and other parameters.LA and LV strain curves presented excellent correlations with an R2 > 0.90 for the cardiac cycle, and R2 > 0.97 for its phases. Moreover, the ratios of LV/LA maximal volumes and the slopes of the LA-LV strain-strain loops of the individual patients correlated well (R2 = 0.75). In each phase of the cardiac cycle, LA strain parameters correlated well with the corresponding LV strain and the LV-LA volume ratio (R2 > 0.78). No significant difference in predictive ability of cardiovascular events or atrial fibrillation between the measured and predicted LA strain was observed (P > 0.05 for both).In the absence of abnormal LA/LV volume exchange, LA strain is, to a large extent, determined by LV strain and further modulated by the ratio of LV and LA volumes. Nonetheless, measuring LA strain is of high clinical interest because it integrates several parameters into a single, robust, and reproducible measurement.