Cardiac cycle

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

Noninvasive pulsed infrared spectrophotometer.

Abstract: A method and apparatus for monitoring glucose, ethyl alcohol and other blood constituents in a noninvasive manner. The measurements are made by monitoring infrared absorption of the desired blood constituent in the long infrared wavelength range. The long wavelength infrared energy generated by source (400) is passed through a finger (406). To prevent the high energy source from burning or causing patient discomfort, shutter (404) and bandpass filters (410) cause only short bursts of energy to be sent through the finger with a very low duty cycle and low optical bandwidth. The bursts are further synchronized by shutter (404) with systole and diastole of the cardiac cycle so that only two pulses are sent per heart beat, one during diastole and one during systole. The detection signals measured at detectors (412) during application of these bursts of energy are used to calculate the concentration of blood constituents in accordance with a polynomial equation.

Initial phase of ventricular systole: asynchronous contraction.

Abstract: The initial phase of ventricular systole has been termed the phase of isometric contraction because all the cardiac valves are closed while the pressure is rapidly elevated. Cyclic changes in the dimensions of the left ventricle, recorded by gauges applied directly to the ventricular walls have consistently exhibited an abrupt expansion of the internal diameter, external circumference and external length of the chamber at the onset of systole. Apparently the longitudinal axis of the chamber is abruptly shortened by early contraction of papillary muscles and trabeculae carnae. The lateral walls bulge outward so that the chamber assumes a more spherical configuration as the internal pressure rises. It is doubtful that any of the myocardial fibers actually contract without a change in length, and the term "isometric contraction" is not appropriate for this phase. The initial stage of ventricular systole is actually a period of asynchronous contraction or sphericalization.

A four-dimensional study of the aortic root dynamics.

Abstract: Objective Although aortic root expansion has been well studied, its deformation and physiologic relevance remain controversial. Three-dimensional (3-D) sonomicrometry (200Hz) has made time-related 4-D study possible. Methods Fifteen sonomicrometric crystals were implanted into the aortic root of eight sheep at each base (three), commissures (three), sinuses of Valsalva (three), sinotubular junction (three), and ascending aorta (three). In this acute, open-chest model, the aortic root geometric deformations were time related to left ventricular and aortic pressures. Results During the cardiac cycle, aortic root volume increased by mean+/-1 standard error of the mean (SEM) 33.7+/-2.7%, with 36.7+/-3.3% occurring prior to ejection. Expansion started during isovolumic contraction at the base and commissures followed (after a delay) by the sinotubular junction. At the same time, ascending aorta area decreased (-2.6+/-0.4%). During the first third of ejection, the aortic root reached maximal expansion followed by a slow, then late rapid decrease in volume until mid-diastole. During end-diastole, the aortic root volume re-expanded by 11.3+/-2.4%, but with different dynamics at each area level. Although the base and commissural areas re-expanded, the sinotubular junction and ascending aorta areas kept decreasing. At end-diastole, the aortic root had a truncated cone shape (base area>commissures area by 51.6+/-2.0%). During systole, the root became more cylindrical (base area>commissures area by 39.2+/-2.5%) because most of the significant changes occurred at commissural level (63.7+/-3.6%). Conclusion Aortic root expansion follows a precise chronology during systole and becomes more cylindrical - probably to maximize ejection. These findings might stimulate a more physiologic approach to aortic valve and aortic root surgical procedures.

Measurement of right and left ventricular systolic time intervals by echocardiography.

Abstract: One of the noninvasive methods of evaluating left ventricular performance is the measurement of left ventricular systolic time intervals (LVSTI). However, noninvasive measurement of right ventricular systole by this technique has been unreliable because of the inability to accurately time the onset of right ventricular ejection. Excellent correlation of LVSTI measured from the carotid pulse and those determined from the echocardiogram was demonstrated in 15 patients. STI of the right ventricle (RVSTI) were measured in a similar fashion from the pulmonary valve echo in 11 normal children. Right ventricular ejection time (RVET) was longer than left ventricular injection time (LVET). Right ventricular pre-ejection period and RPEP was shorter than left ventricular pre-ejection period (LPEP). In 15 children with transposition of the great arteries (TGA) the situation was reversed. RVET was shortened and RPEP was prolonged as the right ventricle contracted against systemic resistance; whereas, the LVET lengthened and LPEP shortened with ejection into a low pressure pulmonary circuit. Our studies in a total of 41 patients indicate the accurate, noninvasive measurement of right, as well as left, ventricular STI can be obtained with the use of echocardiography.