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Pressure–Volume Loop of the Left Ventricle
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The area within the pressure–volume loop represents the stroke work (mechanical energy) done by the heart during a single contraction. This represents the external work of the ventricle. During isovolumetric contraction, pressure develops within the ventricle. Although there is no ejection and therefore no external work, energy is expanded to generate potential energy, and this is converted to heat during diastole. The triangle formed by the End-systolic pressure line, end-diastolic pressure line and the line representing iso-volumic relaxation represents internal work and this correlates the heat generated by the heart during a single contraction (Figure 26.9). The total mechanical work plus the heat generated by the heart during contraction is represented by the pressure–volume area (PVA) (Figure 26.9). The PVA correlates well with the amount of oxygen consumed by the myocardium during a single contraction. When PVA is extrapolated to zero pressure, myocardial oxygen consumption is still present. This basal oxygen consumption in the absence of pressure development is required to keep the cells alive, and activation energy is required for the biochemical processes associated with excitation–contraction coupling.
The intra-aortic balloon pump: Principles and use
Published in John Edward Boland, David W. M. Muller, Interventional Cardiology and Cardiac Catheterisation, 2019
At the beginning of isovolumetric contraction, the mitral valve closes, the left ventricle is full of blood, and the left ventricular pressure increases without a change in left ventricular volume because the aortic valve is closed. When left ventricular pressure exceeds that within the aortic root, the aortic valve opens. This marks the end of isovolumetric contraction, at which point the phase of rapid ejection begins, and blood rushes out of the left ventricle into the aorta. As the left ventricle continues to contract, the ventricular and aortic pressures attain their maximum values, the peak systolic pressures. The period of reduced ejection follows on immediately from the rapid ejection period, and the left ventricular volume continues to fall. Ventricular pressure also falls during this period, until ventricular pressure falls below that of the aorta, causing the aortic valve to close. This marks the end of ventricular systole.28,29
The heart
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
After systole, the ventricles abruptly relax and the ventricular pressure decreases rapidly. Pressure in the aorta, which has peaked at 120 mmHg during systole, remains above 100 mmHg and the blood in the distended artery is immediately forced back toward the ventricle down a pressure gradient. The backward movement of blood snaps the aortic valve shut. The closure of this valve results in the second heart sound (“dub”). During this portion of ventricular diastole, there is a period of several milliseconds in which ventricular pressure is dissipating and falling back toward zero. Because atrial pressure is close to zero, the AV valve remains closed. Therefore, during this phase of isovolumetric relaxation, both valves leading into and out of the chamber are closed. As with isovolumetric contraction, there is no change in the blood volume of the ventricle during this phase of isovolumetric relaxation. When the ventricular pressure falls to a point at which it is once again exceeded by atrial pressure, the AV valve opens, ventricular filling occurs, and the cardiac cycle begins again.
Subclinical cardiovascular dysfunction in children and adolescents with asthma
Published in Journal of Asthma, 2022
Zeynep Karakaya, Özlem Cavkaytar, Öykü Tosun, Mustafa Arga
M-mod trace was obtained from the point where the tricuspid annulus was joined to the lateral free wall in the apical four-chamber view for the tricuspid annular plane systolic excursion (TAPSE) measurement. The mitral and tricuspid pulsed Doppler signals were recorded in the apical four-chamber view, with the Doppler sample volume placed at the tip of the mitral valve. Pulse wave sampling volume was placed on the corner of the left ventricle, which is next to the mitral lateral leaflet in apical four-chamber view, in order to obtain left ventricle TDI. Epiq 7 c Matrix Philips Echocardiography Systems (Eindhoven, The Netherlands) S 5-1 probe was used for echocardiography. Echocardiography settings were as follows: gain and filter minimal, compress and reject maximum, velocity range −30 and +30 cm/min, and sampling volume width 5 mm. The end expiration apnea period was used so that measurements were not affected by respiration. The Doppler trace obtained by this method was used to record the isovolumetric contraction time (ICT), isovolumetric relaxation time (IRT), and ejection time (ET) which were used to calculate the myocardial performance index (MPI) (MPI = ICT + IRT/ET). M-mode echocardiography was used to assess the function of LV, both during systole as well as during diastole.
Morning blood pressure surge is associated with the severity of stable coronary artery disease in hypertensive patients
Published in Clinical and Experimental Hypertension, 2021
Hazar Harbalıoğlu, Onur Kaypaklı
Standard 2-dimensional and Doppler echocardiography were performed using a commercially available echocardiographic machine (Vivid 7 R GE Medical System, Horten, Norway). LV ejection fraction (EF) was determined by the biplane Simpson’s method (6). Left ventricular mass (LVM) was calculated using the Devereux formula (7): LVM = 1.04[(LVDd+IVSth+PWth)3 – (LVDd)3] –13.6. The pulsed-wave Doppler recordings of the mitral inflow velocities were obtained from apical four-chamber views by placing the sample volume between the tips of the mitral leaflets. Conventional Doppler indices were measured, including: the peak early (E) and late (A) transmitral filling velocities and the ratio of early to late peak velocities (E/A). The isovolumetric relaxation time (IVRT) was measured from the closure of the aortic valve to the opening of the mitral valve. The isovolumetric contraction time (ICT) was obtained from the closure of the mitral valve to the opening of the aortic valve. The ejection time (ET) was measured from the opening to the closure of the aortic valve on the LV outflow velocity profile. Myocardial performance index (MPI) was determined by using the equation: MPI = (ICT + IVRT)/ET (8). Tissue Doppler measurements were calculated from an average of five consecutive cardiac cycles.
Echocardiographic follow-up to right ventricular modifications in secondary pulmonary hypertension to diabetes in rats
Published in Clinical and Experimental Hypertension, 2021
Gustavo López y López, Ana Yessica Tepox Galicia, Fausto Atonal Flores, Jorge Flores Hernández, Francisco Pérez Vizcaino, Abel E. Villa Mancera, García González Miguél, Alejandro Reynoso Palomar
The mitral valve flow can be seen in Figure 11, obtained using a pulsed Doppler on the diabetic group (Figure 11b) and the control group (Figure 11a) during week 12. In both images, we can distinguish the isovolumetric contraction time (IVCT), isovolumetric relaxation time (IVRT), and ejection time (ET). We can observe that for the diabetic group, the IVCT is null, the IVRT is increased, and the ET is decreased and has lost its shape. These changes were not shown by the control group. The changes in myocardial performance time for the diabetic group, evaluated using the Tei index, showed an increase from week 8 that became significant at week 12 (0.644 ± 0.058) of the study, compared with the control group (0.451 ± 0.027). This increase in the group of diabetics is very high, as it was 42.72% and is parallel to the risk of heart failure, because it reflects low myocardial performance. These modifications coincide with the qualitative evaluation of the Tei index (Figure 11).