Cardiac cycle

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

Characterization of the extravascular component of coronary resistance by instantaneous pressure-flow relationships in the dog.

Abstract: SUMMARY To investigate the mechanical effects of the myocardium on the blood perfusion of the canine left ventricle, phasic total left ventricular (LV) coronary blood flow, perfusion pressure, LV pressure, aortic flow rate, and LV segment length were recorded continuously in an open-chested dog heart preparation. These variables were analyzed on a digital computer and time synchronized so that coronary pressure-flow curves could be drawn for various instants in the cardiac cycle. During diastole, the pressure-flow relationship is linear, changing to a nonlinear curve with the onset of systole. To estimate phasic patterns of coronary resistance and intramyocardial pressure (IMP), a model based on the vascular waterfall mechanism was developed and fitted to the experimental data. The results of this operation show inferred coronary resistance patterns that increase during ejection and remain constant during diastole and isovolumic contraction. Assuming LV pressure to represent endocardial IMP, the estimated epicardial IMP signal averages 42.1 ± 13.3% of peak LV pressure at this instant of peak pressure. Furthermore, increases in end-diastolic volume reduced the changes in inferred coronary resistance taking place during ejection, but the epicardial IMP signal remained practically unchanged. Circ Res 45: 378-390, 1979

Mimicking the cardiac cycle in intact cardiomyocytes using diastolic and systolic force clamps; measuring power output

Abstract: Aims A single isolated cardiomyocyte is the smallest functional unit of the heart. Yet, all single isolated cardiomyocyte experiments have been limited by the lack of proper methods that could reproduce a physiological cardiac cycle. We aimed to investigate the contractile properties of a single cardiomyocyte that correctly mimic the cardiac cycle. Methods and results By adjusting the parameters of the feedback loop, using a suitably engineered feedback system and recording the developed force and the length of a single rat cardiomyocyte during contraction and relaxation, we were able to construct force-length relations analogous to the pressure-volume relations at the whole heart level. From the cardiac loop graphs, we obtained, for the first time, the power generated by one single cardiomyocyte. Conclusion Here, we introduce a new approach that by combining mechanics, electronics and a new type optical force transducer, can measure the force-length relationship of a single isolated cardiomyocyte undergoing a mechanical loop that mimics the pressure-volume cycle of a beating heart.

Atriogenic Mitral Valve Reflux: Diastolic Mitral Incompetence Following Isolated Atrial Systoles

Abstract: Cardiac and aortic pressures were recorded after stellate ganglionectomy and vagotomy. Acute heart block was produced by injecting the atrioventricular node, and atrial and ventricular systoles were controlled electronically to occur independently or in any desired relationship. Angiocardiograms recorded on video tape after injections of 4 ml 69% Renovist into the left ventricle were analyzed with a videodensitometer able to detect small refluxes of contrast medium into the left atrium and correlate them with phases of the cardiac cycle. When ventricular driving was temporarily suspended but atrial driving continued, pressure records indicated mitral valve closure after each atrial systole, but reflux of contrast medium into the atrium occurred after each systole not followed by a normally sequenced ventricular systole. Driving with a 2: 1 atrioventricular stimulation resulted in reflux, with the alternate atrial contraction dissociated from ventricular systole. Thus, the mitral valve was not effectively closed by atrial systoles that were not followed by normally sequenced ventricular systoles.

Cyclic and radial variation of the echogenicity of blood in human carotid arteries observed by harmonic imaging.

Abstract: To better understand the characteristics of erythrocyte aggregation in flowing blood, echogenicity variation in blood was observed both in vitro and in vivo. However, few noninvasive observations of blood echogenicity variation during the cardiac cycle in human arteries have been reported. In the present study, to reduce the dynamic range between the blood vessel lumen and the surrounding tissue, coded harmonic images were acquired from human carotid arteries using a GE LOGIQ 700 Expert system (GE, Milwaukee, WI, USA) with an M12L probe, which enabled the noninvasive detection of the cyclic and radial variation of echogenicity in arterial vessels. It was found that blood echogenicity increased during systole, reaching a maximum at peak systole and then decreased to a weak level during diastole. The echogenicity profiles of blood along the vessel diameter were found to be approximately parabolic in the cardiac cycle, except for the hypoechoic zone near the center of the vessel at peak systole. The present results for human carotid arteries corroborate previous in vitro observations that showed a cyclic and radial variation of blood echogenicity, which was thought to be caused by the enhancement of erythrocyte aggregation due to the combined effects of flow acceleration and shear rate during systole.