Cardiac cycle

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

Comparison of acoustic quantification and Doppler echocardiography in assessment of left ventricular diastolic variables.

Abstract: OBJECTIVE--To assess the haemodynamic correlations of the waveforms of left ventricular area change obtained by automated boundary detection with newly developed acoustic quantification technology. DESIGN--The timing of events in the cardiac cycle was identified on the wave-form automated boundary detection and was correlated with the corresponding timing derived from pulsed wave Doppler flow velocity traces of the mitral valve and left ventricular outflow tract. The amounts of area change during the rapid filling phase and during atrial contraction were correlated with the time-velocity integrals of early and late diastolic ventricular filling obtained from Doppler tracings of the mitral inflow. SETTING--A university medical school echocardiography laboratory. SUBJECTS--16 healthy volunteers and 19 patients referred for echocardiographic studies. RESULTS--A significant correlation was found between the methods for measurement of the time from the R wave to mitral valve opening (r = 0.72, p < 0.01), isovolumic relaxation time (r = 0.62, p < 0.01), and ejection time (r = 0.54, p < 0.01). The change of total area that occurred during rapid filling and atrial filling phases measured from the acoustic waveform correlated with the time-velocity integrals of the early and late diastolic mitral valve inflow velocity derived from Doppler echocardiography (r = 0.60 and r = 0.80, respectively). CONCLUSION--The waveform of left ventricular area obtained by the automated boundary detection technique identifies the phases of the cardiac cycle and correlates with Doppler values of left ventricular diastolic function. Therefore, this new method of automated boundary detection has potential uses in the assessment of left ventricular diastolic function.

Cardiac wall motion-based automatic capture verification system and method

Abstract: An improved implantable cardiac stimulating device that performs cardiac wall motion-based automatic capture verification system is provided. Pacing pulses of varying energy content are administered to a patient's heart, and the response of the patient's heart is sensed by a cardiac wall motion sensor. The cardiac wall motion sensor provides a signal which is analyzed to determine the patient's capture threshold, defined as the minimum amount of electrical stimulation required to evoke a cardiac contraction. The device then sets the amount of electrical stimulation at a level safely above the measured capture threshold. Capture verification may be performed at predetermined time intervals, on demand, or upon the occurrence of a significant cardiac event. Capture verification can also be performed on every pacing pulse delivered by the implantable cardiac stimulating device.

PRES: the controlled noninvasive stimulation of the carotid baroreceptors in humans.

Abstract: To study physiological and psychological effects of baroreceptor activity, the cervical neck cuff technique has been frequently used to stimulate the carotid baroreceptors mechanically. Using this technique, no satisfying control conditions to date have been available. Because the carotid stretch receptors are sensitive not only to the pressure level, but also to the rate of change, it is possible to manipulate the receptor firing through changes in carotid pulse amplitude. The device described here relies on the application of short changes in cuff pressure tied to different phases within the cardiac cycle (phase related external suction (PRES)). A brief external suction during systole has potent stimulatory effects on baroreceptors whereas the application of the very same pressure pulse during diastole inhibits the firing burst associated with the pulse wave. To allow an ongoing period of stimulation, a sequence of alternating negative/positive pressure pulses is applied. In the stimulation condition, the R-wave of the electrocardiogram triggers a negative pulse which is followed by a positive one during diastole. In the control condition this relationship is reversed. Two experiments are reported confirming different baroreceptor effects of the two conditions. PRES allows for blind or double-blind experiments to investigate effects of baroreceptor activity on physiology and behavior.

Quantitative blood flow measurement using steady-state transport-induced adiabatic fast passage

Abstract: A subtractive time of flight technique for MR angiography and quantitative blood flow measurement. Proton spins of water in the arterial supply to a tissue or organ are inverted in a steady-state fashion by applying constant amplitude off-resonance radio frequency pulses in the presence of a constant linear magnetic field gradient to effect adiabatic fast passage transport-induced inversion of spins which move in the direction of the gradient. An angiogram is formed by subtracting an image acquired with the arterial inversion pulse from a control image acquired with no arterial inversion. By inverting the spins in a steady-state manner, no cardiac gating is necessary for imaging organs. However, cardiac gating is desirable when imaging the heart so that spins of blood passing through the coronary arteries can be inverted during systole, when most of the blood is in the left ventricle, and imaged at end diastole, when most of the blood is in the coronary arteries. A coronary angiogram is then formed by subtracting images acquired with and without the inversion pulse. Also, by applying several inverting and imaging pulses during a cardiac cycle in accordance with the technique of the invention, a characteristic banding pattern may be formed in the fluid whereby each band corresponds to a population of spins that experienced inversion due to a single RF pulse. Since the width of the inversion band is proportional to the duration of the RF pulse and the velocity of the spin, measurement of the thickness of the inverted and uninverted bands allows for calculation of flow velocity. By gating such a pulse sequence to the cardiac cycle, time resolved in vivo velocity measurements may be made.