Baroreceptor Reflex Components and Their Alteration in Hypertension
Irving H. Zucker, Joseph P. Gilmore in Reflex Control of the Circulation, 2020
The baroreflex maintains blood pressure around a set point under normal physiological conditions. An increase in blood pressure is, therefore, expected to stimulate baroreceptors and result in reflex adjustments to revert it to control levels. In hypertensive individuals, the baroreflex mechanism maintains its capacity to buffer acute changes in blood pressure but this is done at a much higher set point. This has been described as “resetting of baroreceptors” (Kezdi, 1953). This phenomenon has also been demonstrated in renal hypertensive dogs (McCubbin, 1958) and rabbits (Aars, 1968; Angell-James, 1973, 1974a,b). In these studies, the electrical activity of the carotid sinus and aortic nerves was recorded. The threshold pressure to activate carotid sinus and aortic baroreceptors was higher in hypertensive animals when compared to that in normotensive controls. Despite high blood pressure, carotid occlusion response could still be elicited, indicating that the baroreflex was still functional.
Age-Related Changes in the Autonomic Nervous System
David Robertson, Italo Biaggioni in Disorders of the Autonomic Nervous System, 2019
The baroreflex is a complex neural feedback loop that rapidly restores the blood pressure to its normal set-point during transient physiologic perturbations. This neural feedback mechanism involves: tonic signals from baroreceptors located in the carotid arteries, aortic arch, right atrium and lung to inhibitory vasomotor centers of the brainstem; central nervous system integration of these signals; efferent sympathetic and parasympathetic nerve activity; and effector organ response. Most of the current information about baroreflex function and aging is derived from measurements of cardiovascular responses to stimulation of baroreceptors. A progressive age-related impairment in baroreflex function has been well demonstrated by a reduction in the cardioinhibitory response to hypertensive stimuli such as phenylephrine infusion and phase IV of the Valsalva maneuver, and by a blunted cardioacceleratory response to hypotensive stressors such as upright posture, lower body negative pressure or nitroprusside infusion.
Falls Risk and Prevention in the Diabetic Patient
Medha N. Munshi, Lewis A. Lipsitz in Geriatric Diabetes, 2007
The ability to stand and walk upright is dependent on maintaining an adequate BP to perfuse the brain and other vital organs. Ordinarily, the baroreflex maintains a normal BP by increasing heart rate and vascular resistance in response to transient reductions in stretch of arterial baro-receptors in the carotid arteries and aorta, and by decreasing these parameters in response to an increase in stretch of baroreceptors. Normal human aging is associated with a reduction in baroreflex sensitivity. This is evident in the blunted cardioacceleratory response to stimuli such as upright posture, nitroprusside infusion, and lower-body negative pressure which all lower arterial pressure, as well as a reduced bradycardic response to drugs such as phenylephrine that elevate pressure. Furthermore, baroreflex impairment is manifest by an increase in BP variability during common daily activities (20), often with potentially dangerous BP reductions during hypotensive stresses such as upright posture or meal digestion. With the superimposition of conditions such as diabetic autonomic neuropathy, or medications with hypotensive effects, orthostatic and postprandial hypotension may result, causing falls and syncope in elderly people.
Baroreflex control model for cardiovascular system subjected to postural changes under normal and orthostatic conditions
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
V. L. Resmi, R. G. Sriya, N. Selvaganesan
The integrated block diagram of cardiovascular system and baroreflex control is shown in Figure 1. The red and blue arrows in Figure 1 indicate the flow of oxygenated blood and deoxygenated blood, respectively. The upper block represents cardiopulmonary system which includes the blood flow between heart and lungs. The middle block represents cardiovascular system which consists of heart and systemic vasculature. The heart block is characterized by contractility (c), heart rate (H) and stroke volume (Vstr). The vasculature is characterized by arterial and venous pressures (Pa, Pv), compliances (Cv, Ca) and peripheral resistance (R). The lower block represents baroreflex control which consists of baroreceptors, medulla oblongata and sympathetic and parasympathetic control. The baroreceptor takes MAP as the input and produces firing rates (n) which are given as information to the medulla oblongata. This produces chemical tones (Ts, Tp) which controls the heart and vascular characteristics.
Acute restraint stress increases blood pressure and oxidative stress in the cardiorenal system of rats: a role for AT1 receptors
Published in Stress, 2020
Gabriel T. do Vale, Drieli Leoni, Arthur H. Sousa, Natália A. Gonzaga, Daniela L. Uliana, Davi C. La Gata, Leonardo B. Resstel, Cláudia M. Padovan, Carlos R. Tirapelli
Clinical and experimental studies have shown that psychological stress has a direct impact in the cardiovascular system (Grippo & Johnson, 2009; Rozanski, Blumenthal, & Kaplan, 1999). The impact of stress in the cardiovascular system is affected by the chronicity of the stressor stimulus (Crestani, 2016). In this sense, chronic stress increases baseline values of mean arterial pressure (MAP) and heart rate (HR) (Duarte, Cruz, Leão, Planeta, & Crestani, 2015; Nalivaiko, 2011). Alterations of autonomic activity are also associated with chronic stress. In this regard, it has been described that chronic stress increased the sympathetic tone to the heart (Duarte et al., 2015) and that this response contributes to the increased susceptibility to cardiac arrhythmias (Grippo et al., 2004). Impaired baroreflex function was also described after chronic stress (Almeida, Duarte, Oliveira, & Crestani, 2015; Duarte et al., 2015). Thus, exposure to long-term stressful events is associated with enduring autonomic imbalance and cardiovascular dysfunctions (Crestani, 2016). On the other hand, acute stress induces physiological changes in the autonomic nervous system. These responses, which are mainly characterized by changes in the cardiovascular system, are short-term adaptive mechanisms to aversive threats that maintain homeostasis and ensure survival. Cardiovascular changes in response to acute stress include increase in blood pressure, HR, and cardiac output (Busnardo, Tavares, & Correa, 2014; Crestani, Tavares, Alves, Resstel, & Correa, 2010; Dos Reis, Fortaleza, Tavares, & Corrêa, 2014).
The association between orthostatic hypotension and cognition and stroke: a meta-analysis of prospective cohort studies
Published in Blood Pressure, 2020
Min Min, Tingting Shi, Chenyu Sun, Mingming Liang, Yun Zhang, Shun Tian, Yehuan Sun
In this meta-analysis, we provided evidence of strong links between OH and both worse cognition and stroke. Our findings were consistent with the results of previous systematic reviews [5,33,34]. Compared with the recently published study [34], in which OH was found to be associated with a decreased cognitive performance score, our approach was different from theirs. The authors of the previous study extracted the mean and standard deviation of the decreased cognition score, and we extracted the risk ratio. As expected, hypertensive participants with OH had higher risks for developing dementia, in line with the results reported in one recent study [35]. Studies have indicated that both hypertension [36] and OH [37] are associated with impaired baroreflex. Coexistent OH and hypertension represent a more severe baroreflex dysfunction and exaggerated blood pressure variability. In addition, among elderly people, there was a significant relationship between OH and dementia. For stroke, a statistically significant link was observed among participants younger than 65 years.
Related Knowledge Centers
- Aortic Arch
- Autonomic Nervous System
- Baroreceptor
- Blood Pressure
- Carotid Sinus
- Heart Rate
- Medulla Oblongata
- Orthostatic Hypotension
- Homeostasis
- Neuron