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Integrated Cardiovascular Responses
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
In congestive cardiac failure (Figure 32.7), a square-wave response is observed. The blood pressure is elevated throughout phase II, there is no overshoot in phase IV and there is little change in heart rate. The increased blood volume and raised peripheral venous pressure maintain venous return to the heart and the in cardiac output. The raised intrathoracic pressure is transmitted on to the aorta, resulting in a raised blood pressure.
Interventional Therapies for Essential Hypertension
Published in Giuseppe Mancia, Guido Grassi, Konstantinos P. Tsioufis, Anna F. Dominiczak, Enrico Agabiti Rosei, Manual of Hypertension of the European Society of Hypertension, 2019
Konstantinos P. Tsioufis, Kyriakos Dimitriadis, Alex Kasiakogias, Vassilios Papademetriou
The creation of an AV fistula results in blood flow parallel to the systemic circulation, leading to a reduction in systemic vascular resistance and cardiac afterload (15). It is well known that peripheral AV fistulae in haemodialysis patients are accompanied by decreases in BP and peripheral resistance (16,17). However, BP reduction due to the shunt in turn leads to sympathetic activation. The increase in venous return and sympathetic activation result in an increase in cardiac output. The percentage of the cardiac output that the shunt holds needs therefore to reach a threshold over which any increase in systemic resistance and cardiac output fail to maintain the baseline BP, eventually leading to its reduction. On the other hand, the increased cardiac preload leads to higher right atrial and pulmonary capillary wedge pressure that may attenuate the baroreceptor reflex (along with sympathetic activation) as well as trigger the release of natriuretic peptides. Furthermore, a central AV anastomosis reduces effective arterial blood volume to a new baseline without depleting other volume capacitance spaces, and thus without neurohormonal activation. This is of particular interest for the ageing aorta, where the stress-strain curve shifts to the left; after the anastomosis, for any increase in intravascular volume, a milder increase in BP is expected, restoring arterial compliance (18).
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
The larger veins in the legs lie close to the skeletal muscle beds and can be compressed with skeletal muscle contraction. This compression pushes the venous blood forward toward the heart (and the valves prevent the backflow when the muscles relax). This is referred to as the skeletal muscle pump, and it is a factor in encouraging venous return. Other factors that aid in venous return include the respiratory suction (the negative pressure created on inspiration) and the diastolic suction (created during isovolumic relaxation); these help create a pressure gradient between the veins and the right atrium.
In search of mechanisms to explain the unquestionable benefit derived from sodium-glucose cotransporter-2 (SGLT-2) inhibitors use in heart failure patients
Published in Postgraduate Medicine, 2023
Angel Lopez-Candales, Khalid Sawalha, Betty M. Drees, Nicholas B. Norgard
To better explain stressed and unstressed blood volume better, let us review some physiology. Veins contain about 70% of TBV in comparison to arteries where it contains approximately 30%[31]. Guyton el at. described a model of venous return in 1955 along with the factors that influence its physiology, he highlighted three variables that independently affect the venous return: (a) the vascular resistance, (b) the mean systemic pressure, and (c) the right atrial pressure[32]. Among all these three variables, the mean systemic pressure is the least in getting the attention it deserves; this may be due to the complex and intricate system that makes the attempts to define its importance difficult. It is basically the pressure measured in the vascular system if the blood flow were to cease[33]. It is determined by the TBV present in the venous system and the compliance of that vascular bed to dilate of constrict. Physiologically speaking, it is the required volume of fluid to fill the vascular bed where it exerts a force on the vessel walls, and this is what is known as UBV. Now, any volume that will exert a rising pressure (above that normal one) on the vascular bed is known as SBV[33]. Therefore, it is related to venous constriction and dilation and that veno-constriction shifts blood volume from the unstressed to the stressed pool, resulting in increased pulmonary venous pressure, pulmonary edema, and thus HF.
Effects of trunk muscle activation on trunk stability, arm power, blood pressure and performance in wheelchair rugby players with a spinal cord injury
Published in The Journal of Spinal Cord Medicine, 2022
Ingrid Kouwijzer, Mathijs van der Meer, Thomas W.J. Janssen
Next to limited stability and strength, loss of sympathetic innervation under the lesion level is another important factor that impairs performance in WR athletes with high SCI. There is less vasoconstriction in the nonworking muscles of the legs and trunk, resulting in venous pooling and a lower venous return to the heart.15–17 Therefore, blood pressure (BP) is generally low and less capable of rising in response to exercise. Moreover, there is a direct effect on heart rate in high SCI lesions.16–19 Due to loss of sympathetic innervation, heart rate is only moderately capable of rising in response to exercise by decreasing parasympathetic input. As loss of sympathetic innervation is not part of the classification criteria, athletes with a high SCI have a disadvantage compared to athletes with other disabilities with the same motor impairment19–22; they will have a lower maximum heart rate, lower aerobic power and peak power output.19,23
The influence of Body Roundness Index on sensorial block level of spinal anaesthesia for elective caesarean section: an observational study
Published in Journal of Obstetrics and Gynaecology, 2020
Betul Kozanhan, Omer Bardak, Mahmut Sami Tutar, Sibel Ozler, Munise Yildiz, Ibrahim Solak
A higher sensory block level may contribute to circulatory instability and lead hypotension after spinal anaesthesia in parturients. Circulatory regulation influenced by a blockade of the sympathetic nervous system producing decreases in both venous return and systemic vascular resistance. Increased abdominal content with the pregnant uterus and visceral adipose tissue are the further risk factors for an event of hypotension following neuraxial anaesthesia, as a result of widespread displacement of the intra-abdominal content, and vascular compression that exacerbates the aortocaval compression. It is known that higher BMI is associated with higher intra-abdominal pressure (Abdel-Razeq et al. 2010; Fuchs et al. 2013). In the present study, hypotension occurred in 55.2% of the patients and bradycardia occurred in 24.2% of the patients. We found a significant correlation between BRI and the maximum sensory block level; however, the episodes of hypotension were unrelated to BRI. This result may be due to the potential metabolic and cardiovascular changes linked with increased BRI (Chang et al. 2015; Zhang et al. 2016).