Cardiac cycle | EPFL Graph Search

The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. After emptying, the heart relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A normally performing heart must be fully expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 second to complete the cycle. There are two atrial and two ventricle chambers of the heart; they are paired as the left heart and the right heart—that is, the left atrium with the left ventricle, the right atrium with the right ventricle—and they work in concert

Coronary waves during valsalva maneuver measured during catheterization

Maria Cristina Rolandi

The mechanical interactions between heart contraction and perfusion of the heart are difficult to study in humans because of the restrictions in inducing changes in hemodynamic and cardiac mechanics parameters during catheterization. We hypothesize that the Valsalva maneuver can induce such alterations in the cardiac-coronary mechanical interaction and that these variations can be studied with the Wave Intensity Analysis. In order to interpret eventual changes in the wave intensity, a deep understanding of the effect of the Valsalva maneuver on the coronary circulation is needed. A particular attention has to be payed on the effect of the control of the microvascular resistance that is known to compensate for eventual alterations in the surrounding hemodynamic conditions when vessel tone is intact. In the catheterization laboratory, coronary pressure and flow velocity signals were recorded simultaneously by a new guidewire developed by Volcano Corporation. Aortic pressure, left ventricular pressure and ECG were acquired by the catheterization laboratory setup and recorded together with coronary hemodynamic signals. Left ventricular performance parameters were derived per beat from the noninvasive recording of the finger pressure using the Nexfin monitor developed by BMEYE B.V. In order to match the output data of coronary hemodynamic and left ventricular performance parameters, a dedicated program has been written in Delphi. An analysis of the per-beat data was performed in order to study the relative dependence of the parameters during the Valsalva maneuver. Pilot results of the Wave Intensity Analysis were obtained with an existing custom-made program also written in Delphi. Our study shows that the Valsalva maneuver caused a profound stress in the whole cardiovascular system. The well-known changes of the aortic pressure were transmitted also to the left ventricle and the coronary microcirculation. The data show that this stress caused a small but significant decrease in the flow velocity. As expected, the microvascular resistance varied with the same pattern as the coronary pressure trying to keep the flow constant. With respect to the decrease in stroke volume, cardiac output and contractility, the left ventricular performance was strongly compromised: pulse pressure generation and cardiac contraction were almost annulled. The decrease in systolic left ventricular pressure of almost 40% and the 2 fold increase in the end-diastolic left ventricular pressure confirm the decrease in the pumping action. Consequentially, the oxygen consumption of the heart decreased to 40% of the baseline level but only after an initial increase at the onset of the strain by 10%. The results also show that the timing of variation of the parameters was not the same. Especially the left ventricular end-diastolic pressure changed more rapidly than the perfusion pressure. Pilot results on Wave Intensity Analysis (WIA) show that the Valsalva maneuver gave rise to changes in the Wave Intensity pattern suggesting that the speed of the reflected waves has indeed been altered. Our results agree with previous studies that reveal a slight decrease in the flow velocity due to the Valsalva maneuver. Nevertheless, our results contradict the belief that ascribes the decrease in flow velocity to the decrease in oxygen consumption. We assume that the flow decrease is due to mechanical factors, especially the rise of left ventricular end-diastolic pressure. The results shown on WIA are pilot results and some work is still needed in this direction to obtain more information on the coronary-cardiac interaction. However, these results give confidence about the use of the Valsalva maneuver as an intervention affecting external parameters and thus they are useful in the study of coronary-cardiac interaction in humans.

2009

Physiological noise in human cerebellar fMRI

Denis Butticaz, João Pedro Forjaco Jorge, Rolf Gruetter, Wietske Van der Zwaag

Objectives To compare physiological noise contributions in cerebellar and cerebral regions of interest in high-resolution functional magnetic resonance imaging (fMRI) data acquired at 7T, to estimate the need for physiological noise removal in cerebellar fMRI. Materials and methods Signal fluctuations in high resolution (1 mm isotropic) 7T fMRI data were attributed to one of the following categories: task-induced BOLD changes, slow drift, signal changes correlated with the cardiac and respiratory cycles, signal changes related to the cardiac rate and respiratory volume per unit of time or other. R2adj values for all categories were compared across regions of interest. Results In this high-resolution data, signal fluctuations related to the phase of the cardiac cycle and cardiac rate were shown to be significant, but comparable between cerebellar and cerebral regions of interest. However, respiratory related signal fluctuations were increased in the cerebellar regions, with explained variances that were up to 80 % higher than for the primary motor cortex region. Conclusion Even at a millimetre spatial resolution, significant correlations with both cardiac and respiratory RETROICOR components were found in all healthy volunteer data. Therefore, physiological noise correction is highly likely to improve the temporal signal-to-noise ratio (SNR) for cerebellar fMRI at 7T, even at high spatial resolution.

Springer Verlag2015

An extracellular matrix protein microarray to study endothelial to mesenchymal transformation in mitral valve endothelial cells

Blaise Calpe

In the developing heart, a subset of endothelial cells (ECs) undergo a process of endothelial to mesenchymal transformation (EMT) that leads to the remodeling of the cardiac cushions and the formation of the cardiac valves. Understanding how microenvironmental cues regulate EMT has important implication for the treatment of congenital heart valve diseases and for heart valve tissue engineering. Here a set of extracellular matrix (ECM) proteins and growth factors (GF) were tested to determine the extent of regulation of EMT in adult ovine mitral valve endothelial cells (MVECs). Traditional cell culture dishes present limitations on large scale screening of cells-microenvironments interactions. To address this problem, a high throughput cellular microarray platform was developed. Using a contact printer, 84 different combinations of ECM proteins and GF were microarrayed on a modified glass slide. The slides were seeded with MVECs and immunostained against EMT maker alpha smooth muscle actin ([alpha]-SMA). Fluorescence images of each spot of the microarray were taken with a microscope equipped with an automated stage. These images were analyzed with a custom image processing routine developed with CellProfiler to assess the percentage of cells expressing [alpha]-SMA on each ECM combination.

2011

Coronary waves during valsalva maneuver measured during catheterization

Maria Cristina Rolandi

2009