Contour of Pressure and Flow Waves in Arteries
Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos in McDonald's Blood Flow in Arteries, 2022
Use of arterial tonometry (Avolio et al., 1988; Kelly et al., 1988a, 1988b; Saba et al., 1993; Vaitkevicius et al., 1993; London et al., 1995; Chen et al., 1996, 1997) has provided fresh information on pressure wave transmission to the upper limbs in humans and indeed fresh insight into the effects of aging and of vasoactive drugs on the arterial pressure wave (O'Rourke, 1988; Kelly et al., 1989a, 1989b; O'Rourke et al., 1989a, 1989b, 1992a, 1992b, 1993a; O'Rourke and Kelly, 1993; Adji et al., 2016). This is discussed later (see Chapter 27) and has important implications for interpretation of sphygmomanometric pressures with different therapies in humans (O'Rourke, 1990a; O'Rourke et al., 1993a; Chen et al., 1996, 1997; Williams et al., 2006; Miyashita et al., 2010; Ong et al., 2011; Levi-Marpillat et al., 2014). A full chapter (Chapter 25) is devoted to the concept of central aortic pressure that arises from this.
Physical and functional growth and development
Nick Draper, Helen Marshall in Exercise Physiology, 2014
At birth, the occlusion of the umbilical cord and the initiation of breathing result in many circulatory and respiratory changes and the resultant closure of the three circulatory shunts. As the fetus passes along the birth canal the thorax is compressed, expelling the majority of amniotic fluid from the lungs. The expansion of the lungs, as the newborn takes its first breaths, reduces pulmonary vascular resistance and elevates systemic blood pressure, resulting in an increased blood flow through the pulmonary (lung) vessels. Secondly, with the occlusion of the umbilical cord, blood pressure in the left atrium rises above that in the right atrium, responsible for the closure of the foramen ovale. An increase in systemic, and hence aortic, pressure allows blood to flow along the pulmonary artery, with the eventual full closure of the ductus arteriosus. Failure of the foramen ovale and/or the ductus arteriosus to close properly at birth may lead to paediatric heart complications. The ductus venosus is generally closed at birth, with full elimination by around two weeks of age.
Dynamics of the Aortic Valve
Mano Thubrikar in The Aortic Valve, 2018
The most dominant feature of a functioning aortic valve is the extremely rapid motion of its leaflets during opening and closing of the valve. In conventional angiography the valve appears either open or closed, and the leaflet motion between these two phases occurs too rapidly to be seen. To study the opening and closing process the leaflet motion has to be studied at a high speed. Thubrikar et al. studied the canine aortic valve in vivo using the marker-fluoroscopy technique in which cineradiographic recordings were made at a rate of 500 frames/s. The reported observations are original and not yet published. Figure 37 shows the arrangement of markers in the aortic valve used in their study. The markers were placed in both in the radial and circumferential directions to study the motion of the leaflet in these two directions. The markers were also placed in the commissures for orientation of the valve. The markers were visualized under X-ray in an appropriate orientation and from the marker positions the leaflet motion was determined. The aortic pressure ranged from 70/30 to 188/152 mmHg and the heart rate from 33 to 150 beats/min in their study.
Two episodes of remote ischemia preconditioning improve motor and sensory function of hind limbs after spinal cord ischemic injury
Published in The Journal of Spinal Cord Medicine, 2020
Salah Omar Bashir, Mohamed Darwesh Morsy, Dalia Fathy El Agamy
The procedure of anesthesia and induction of SC-IRI in rats of this study was done as previously described in our labs.36 Rats were anesthetized with intraperitoneal (i.p.) injection of 60 mg/kg ketamine and 5 mg/kg xylazine and were given an intravenous (i.v.) dose of 150 IU/kg heparin. Rats were placed in a supine position of a heating pad to maintain body temperature at 37°C and their femoral and carotid arteries were cannulated with catheters to measure distal arterial pressure (DAP) and proximal arterial pressure (PAP), respectively. A midline laparotomy was conducted and a microvascular surgical clamp was placed over the abdominal aorta below the left renal vein and just above aortic bifurcation for continuous complete occlusion of the aorta for 45 min. This has been confirmed by the immediate sustained decreased in distal aortic pressure. During the occlusion procedure, the proximal aortic pressure was maintained approximately at 40 mmHg by blood withdrawal in a collecting circuit filled with heparinized saline (4 U/ml) which was always maintained at 37°C. At the end of the ischemic period, reperfusion was done by releasing the aortic clamp and the heparinized blood was reperfused back to the rats over a period of 1 min.
Technical aspects and limitations of fractional flow reserve measurement
Published in Acta Cardiologica, 2019
Stepan Jerabek, Tomas Kovarnik
Not removing the insertion needle, or leaving the Y connector open, can also cause an inappropriate pressure measurement. These situations artificially reduce Pa by 5–10 mmHg [16]. The aortic pressure can also be underestimated if the guiding catheter is wedged in the coronary ostium. A higher than real aortic pressure, on the other hand, can be obtained using a side-hole catheter. This is a consequence of the pressure gradient that occurs under certain conditions between the lateral openings and the end of the catheter [17]. The presence of a contrast medium in the catheter leads to significant damping. Therefore, in each phase of calibration or measurement the catheter should be flushed thoroughly with saline. It is also important to ensure that the level of the pressure transducer in relation to the patient does not change during the test.
Central arterial pressure and patient-specific model parameter estimation based on radial pressure measurements
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Dániel Gyürki, Tamás Horváth, Sára Till, Attila Egri, Csilla Celeng, György Paál, Béla Merkely, Pál Maurovich-Horvat, Gábor Halász
In this method, the pressure is known at the periphery (e.g. the radial or the carotid artery). The first step is to perform an original (forward in time) simulation on the subgraph distal to the point whose pressure is known, to acquire the velocity of that point as well. The second step is to calculate one segment backwards, towards the heart. In this step the characteristic lines run from the distal end of the vessel, opposite to the pulse wave propagation, in contrast to the original method of characteristics, where the lines march forward in time. The velocity, pressure and the deformation values are calculated at the intersection points of these lines. When the backward marching characteristic lines reach the starting node of the segment, another forward simulation is performed on the new subgraph, to acquire the velocities of the other segments of that junction. Then a new backward marching is started from that point, repeating these steps. The march from the periphery is continued until the characteristic lines reach the heart. Therefore, the aortic pressure curve is calculated from the peripheral pressure measurement. The authors tested their method on a model arterial network and achieved high accuracy. Our research is based on this method, and is referred to later as backward calculation.
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