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Diseases of the Aorta
Published in Mary N. Sheppard, Practical Cardiovascular Pathology, 2022
The normal aorta has a thin intima lined by endothelium with a few underlying elastic and collagen fibres, a prominent media containing parallel elastic lamellae separated by smooth-muscle cells, collagen fibres and a mucoid ground substance rich in proteoglycans and an adventitia consisting of fat, thick and thin-walled blood vessels with an outer layer of collagen with surface mesothelial cells (Fig. 8.1). There are often prominent lymphocytic aggregates around blood vessels in the adventitia which are not linked to medial inflammation which increase with age (Fig. 8.2). Aortic chemoreceptor tissue is distributed along the aorta, pulmonary arterial trunk, and subclavian arteries. These are commonly called ‘aortic’ bodies. Aortic bodies are sensory chemoreceptors and baroreceptors scattered throughout the aortic arch and its branches. Similar to the carotid body, aortic body chemoreceptors sense changes in Pao2, Paco2 and pH in the arterial blood. Signals from aortic body chemoreceptors travel via the vagus nerve to the medulla where respiratory centres are stimulated, increasing ventilatory drive. These can be seen scattered in the adventitia of the aorta with neuroendocrine cells positive for neuroendocrine markers and sustentacular cells positive for S-100, surrounded by ganglion cells and large nerve bundles (Figs. 8.3, 8.4). Be aware of their existence in resection specimens.
Neurohumoral Control of the Pulmonary Circulation
Published in Irving H. Zucker, Joseph P. Gilmore, Reflex Control of the Circulation, 2020
There is now a relatively extensive body of evidence that supports the concept that arterial chemoreceptor activation can reflexly modulate the pulmonary circulation. Aviado et al. (1957) observed that whole-body anoxia results in pulmonary vasoconstriction that is abolished following carotid sinus and aortic nerve section. They concluded that the pulmonary vasoconstriction is the result of reflex activation of carotid and aortic chemoreceptors. However, their experimental preparation did not allow them to control a number of active and passive mechanisms that could have mediated the response. Daly and Daly (1959) developed an experimental preparation that not only allowed them to selectively perfuse the carotid bodies with hypoxic blood, but also to control for several passive mechanisms (e.g., perfusion of the bronchial circulation) that could modulate the response. They observed that selective stimulation of the carotid-body chemoreceptors with hypoxic blood results in pulmonary vasoconstriction. This effect is masked by concomitant changes in the bronchial circulation. Stern et al. (1964) demonstrated that stimulation of the aortic body with nicotine results in an increase in calculated PVR. This response is abolished by both pharmacological and surgical denervation. In a subsequent study, these same investigators (Stern and Braun, 1966) noted that at least a portion of the increase in PVR in response to aortic chemoreceptor stimulation is due to an increase in pulmonary venous resistance.
Acute hypoxia and hyperventilation
Published in Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol, Handbook of Aviation and Space Medicine, 2019
Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol
Hypoxic ventilatory response (HVR) is a reflex which increases ventilatory drive in an attempt to maintain oxygen levels when PAO2 <55–60 mmHg (7.3–8.0 kPa): Fall in PAO2 detected in peripheral chemoreceptors (mainly carotid but also aortic body).HVR reduces PACO2 through hyperventilation, enabling fractional concentration of O2 within alveolus to increase.Subsequent fall in PAO2 is less than expected for given reduction in PB (see Figure 9.2).
Obstructive sleep apnea: personalizing CPAP alternative therapies to individual physiology
Published in Expert Review of Respiratory Medicine, 2022
Brandon Nokes, Jessica Cooper, Michelle Cao
It is worth mentioning here that there are two chemoreceptive sensors with converging data on the respiratory pattern generator; the pre-Botzinger complex (preBotC) [54]. The carotid body is the principle O2 sensor in humans (the aortic body appears to be less relevant) [55]. This organ is unique in that it has the most blood flow per gram of tissue in the human body, allowing for rapid detection of subtle polymodal chemical cues by highly specialized glomus cells [56]. This arrangement facilitates changes in neural output in response to subtle changes in O2 partial pressure, pH, glucose, etc. Of note, there appear to be two distinct populations of glomus cells: 1) chemosensory – dopamine beta hydroxylase positive, express nicotinic receptors, elaborate norepinephrine in response to hypoxia, and are inhibited by dopamine, and 2) sympatho-excitatory – tyrosine hydroxylase positive, express purinergic receptors (P2X3), elaborate adenosine triphosphate (ATP) in response to hypoxia, and can be stimulated with angiotensin II [56,57]. These two glomus cell populations drive the ventilatory and sympathetic responses to hypoxia, respectively. These subtleties are worth considering, because medications such as anti-dopaminergic agents and anti-purinergic agents (such as Ticagrelor) can exert effects on ventilatory control stability through their actions on the carotid body [58,59].
Profile of the Ovation ALTO abdominal stent graft for the treatment of abdominal aortic aneurysms: overview of its safety and efficacy
Published in Expert Review of Medical Devices, 2021
Mark Gregory, Matt Metcalfe, Kate Steiner
The Ovation ALTO endograft system consists of an aortic body and two iliac limbs and includes several modifications from its predecessor, the Ovation iX. The aortic body comprises a supra-renal Nitinol stent component responsible for fixation to the aortic wall, and an infra-renal component made of low-permeability graft material responsible for sealing the aneurysm neck. Sealing is achieved through injection of low viscosity radiopaque polymer into the sealing rings, supplied by a network of inflatable channels within the low permeability graft material. An autoinjector is used to inject the polymer at a consistent pressure. The components of the main body of the ALTO graft are illustrated in Figure 3.
The Altura endograft system for endovascular aneurysm repair: presentation of its unique design with clinical implications
Published in Expert Review of Medical Devices, 2022
Efstratios Georgakarakos, Konstantinos Dimitriadis, Gioultzan Memet Efenti, Georgios I Karaolanis, Christos Argyriou, George S. Georgiadis
The aortic body of Altura comes in three diameters, 24, 27, and 30 mm, all carrying a constant 24.4 mm length plus a short transition zone of 11 mm before ending to the distal (limb) segment; the latter has a constant length of 60 mm and a diameter of 13 mm (Figure 3). The 24 mm main body applies to infrarenal diameters of 18–22 mm, while the 27 mm and 30 mm main-bodies apply to infrarenal diameters of 21–25 mm and 24–28 mm, respectively. The suprarenal stent is 20 mm long.