Cardiac cycle

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

Pulmonary vein flow pattern in man during thoracotomy.

Abstract: Pulmonary vein flow (PVF) pattern was traced with an electromagnetic flowmeter in 10 patients with normal hearts undergoing operations for pulmonary diseases. Instantaneous pulmonary artery flow, ECG, pulmonary artery pressure and left atrial pressure were recorded simultaneously. The pulsatile flow patterns obtained corresponded well to those previously found in dogs, and were remarkably similar to caval flow pattern. A constant and inverse relationship between the contour of the right atrial pressure and the PVF pattern was found. In 3 patients, PVF was reversed by atrial systole; otherwise the flow was forward throughout the cardiac cycle. The influence of positive pressure ventilation was small, consisting of a slight initial inspiratory increase followed by a decrease during the latter half of inspiration.

Instantaneous mitral valve leaflet velocity and its relation to left ventricular wall movement in normal subjects.

Abstract: Echocardiograms showing mitral valve leaflets, interventricular septum, and posterior wall of the left ventricle simultaneously were recorded at a paper speed of 100 mm/s in 20 normal subjects. These records were manually digitized and a computer was used to derive mitral valve velocity, left ventricular dimension, and its rate of change continuously throughout a single cardiac cycle. The pattern of instantaneous mitral valve velocity with respect to time was similar in all subjects studied, showing a peak opening rate of 400 +/- 60 mm/s (mean +/- 1 SD), and continuously changing velocity throughout the period of mid-diastolic closure. The peak diastolic closure rate was 250 +/- 60 mm/s and thus appreciably higher than average velocities obtained by manually measuring the slope. A close time relation existed between mitral valve and left ventricular wall movement in early diastole. Forward movement of the anterior leaflet began 1 +/- 6 ms after the onset of outward wall movement, and peak velocity was reached 2 +/- 7 ms after the maximum rate of change of dimension. Later, a discontinuity in wall movement at the end of rapid filling preceded a corresponding discontinuity in the mitral valve velocity tracing by 5 +/- 10 ms. The technique, therefore, allows continuous measurement of mitral valve velocity, and demonstrates its close relation to left ventricular wall movement during diastole.

A comparison of the indirect estimate of mean arterial pressure calculated by the conventional equation and calculated to compensate for a change in heart rate.

Abstract: The standard equation used to calculate mean arterial pressure (MAP) assumes that diastole persists for 2/3 and systole for 1/3 of each cardiac cycle. This ratio is altered when heart rate increases, and therefore we investigated the efficacy of predicting MAP during exercise using non-invasive indirect methods. Eight subjects exercised on a cycle ergometer for 3 minute intervals to elicit heart rates between 100-110, 120-130, 140-150, 160-170, and 180-190 beats/min. In the last minute of each 3 min interval an ECG recording was taken and systolic (SP) and diastolic (DP) blood pressure was measured by manual auscultation. MAP was calculated for each heart rate interval by: MAP=DP+1/3(SP-DP) (method A), and MAP= DP + Fs(SP- DP) (method B), where Fs is the fraction of the cardiac cycle comprising systole, measured from the ECG. Fs increased from 0.35+/-0.049 at rest to 0.47+/-0.039 at a heart rate of 180-190 beats/min. MAP measured by method B was consistently greater than MAP calculated by method A at all heart rates greater than resting heart rate (p<0.01). The error incurred when using the standard MAP equation (method A) to derive MAP during exercise (measured as the percentage difference between method A and B) increased linearly with heart rate (r=0.98). The standard MAP equation should not be applied during exercise, as it does not account for the change in the systolic: diastolic period ratio as heart rate increases.

Mitral Annular Dynamics in Mitral Annular Calcification: A Three-Dimensional Imaging Study.

Abstract: Background The mitral annulus displays complex conformational changes during the cardiac cycle that can now be quantified by three-dimensional echocardiography. Mitral annular calcification (MAC) is increasingly encountered, but its structural and dynamic consequences are largely unexplored. The objective of this study was to describe alterations in mitral annular dimensions and dynamics in patients with MAC. Methods Transthoracic three-dimensional echocardiography was performed in 43 subjects with MAC and 36 age- and sex-matched normal control subjects. Mitral annular dimensions were quantified, using dedicated software, at six time points (three diastolic, three systolic) during the cardiac cycle. Results In diastole, the calcified annulus was larger and flatter than normal, with increased anteroposterior diameter (29.4 ± 0.6 vs 27.8 ± 0.6 mm, P = .046), reduced height (2.8 ± 0.2 vs 3.6 ± 0.2 mm, P = .006), and decreased saddle shape (8.9 ± 0.6% vs 11.4 ± 0.6%, P = .005). In systole, patients with MAC had greater annular area at all time points ( P P P = .04) in control subjects but not in those with MAC ( P = NS). Valvular alterations were also noted; although mitral valve tent length decreased during systole in both groups, decreases were less in patients with MAC ( P P = .006 vs control subjects, but nonsignificant for patients with mild MAC). Conclusions Quantitative three-dimensional echocardiography provides new insights into the dynamic consequences of MAC. This imaging technique demonstrates that the mitral annulus is not made smaller by calcification. However, there is loss of annular contraction, particularly along the anteroposterior diameter, and loss of early systolic folding along the intercommissural diameter. Associated valvular alterations include smaller than usual declines in tenting during systole. These quantitative three-dimensional echocardiographic data provide new insights into the dynamic physiology of the calcified mitral annulus.

Modeling of the Transfer Function of the Heart-Thorax Acoustic System in Dogs

Abstract: A computer model capable of reflecting the dynamic bevior of the heart-thorax acoustic system is used to study the transmission of the first and second heart sounds originating within the left ventricle through the heart muscle and the thoracic tissues of dogs. The input signal of the model is the phonocardiogram recorded within the left ventricle, while the output signal is the phonocardiogram recorded on the chest wall over the apex of the heart. Changes in the transmission path characteritics are modeled by varying the frequency response of an equivalent acoustic system throughout the cardiac cycle. Experimental measurements in dogs were used to determine the general characteristics of left ventricular and apical first and second heart sound spectra, and from these, the transfer and coherence functions of the heart-thorax acoustic system. Results show that the transfer function of the heart-thorax acoustic system changes during the cardiac cycle. For the seven animals studied, it would appear that the contribution of left ventricular first and second sounds to the apical phonocardiogram is significant for frequencies below 70 Hz and negligible for frequencies above 250 Hz. In addition, it is shown that 80 percent of the power of sounds recorded on the chest wall arises from linear transmission of sounds recorded within the left ventricle through the heart-thorax acoustic system. The other 20 percent is due to thoracic noise, noncoherent cardiac contributions, and nonlinearity of the acoustic system.