Integrating the theories of Darwin and Bernoulli: Maladaptive baroreceptor network dysfunction may explain the pathogenesis of aortic aneurysms

Baroreceptors in the Aortic Arch and Their Potential Role in Aortic Dissection and Aneurysms

The arterial baroreflex is a key autonomic regulator of blood pressure whose dysfunction has been related to several cardiovascular diseases. Changes in blood pressure are sensed by specific mechanosensory proteins, called baroreceptors, particularly located in the outer layer of the carotid sinus and the inner curvature of the aortic arch. The signal is propagated along the afferent nerves to the central nervous system and serves as negative feedback of the heart rate. Despite extensive research, the precise molecular nature of baroreceptors remains elusive. Current knowledge assumes that baroreceptors are ion channels at the nerve endings within the outer layer of the arteries. However, the evidence is based mainly on animal experiments, and the specific types of mechanosensitive receptors responsible for the signal transduction are still unknown. Only a few studies have investigated mechanosensory transmission in the aortic arch. In addition, although aortic dissection, and particularly type A involving the aortic arch, is one of the most life-threatening cardiovascular disorders, there is no knowledge about the impact of aortic dissection on baroreceptor function. In this review, we aim not to highlight the regulation of the heart rate but what mechanical stimuli and what possible ion channels transfer the corresponding signal within the aortic arch, summarizing and updating the current knowledge about baroreceptors, specifically in the aortic arch, and the impact of aortic pathologies on their function.

The link between carotid artery disease and ischemic stroke may be partially attributable to autonomic dysfunction and failure of cerebrovascular autoregulation triggered by Darwinian maladaptation of the carotid baroreceptors and chemoreceptors

Carotid artery stenosis is generally thought to induce stroke by either compromising cerebral perfusion or inciting embolic phenomena. Carotid baroreceptors and chemoreceptors are vital adaptations for cerebrovascular autoregulation that can behave mal-adaptively in the setting of modern diseases such as atherosclerosis. We hypothesize that acute cerebrovascular events may be partially attributable to autonomic dysfunction and cerebrovascular autoregulatory failure secondary to carotid sensor maladaptations. Specifically, we propose that atherosclerotic disease at the carotid bifurcation can interfere with baroreceptor and chemoreceptor function by buffering against accurate detection of physical and chemical parameters. Misperceptions of hypoxia and hypotension can trigger sympathetic bias and autonomic dysfunction which perturb cerebrovascular autoregulation and vasomotor tone, thereby compromising cerebral perfusion. The preferential association of strokes with morning arousal, stress, acute physical activity, winter months, illness, and older age may relate to this phenomenon. Sympathetic bias promotes inflammation and coagulation, a link likely forged during prehistoric evolution when trauma represented a more significant factor in natural selection. In the setting of carotid sensor dysfunction, the resulting inflammation and coagulation can promote acute cardiovascular events. The ensuing cerebral ischemia can induce further derangement of cerebrovascular autoregulation and upregulate adrenergia, inflammation, and coagulation in a feed-forward manner. Inflammation and coagulation can also exacerbate carotid sensor dysfunction by iteratively worsening atherosclerosis. Angioplasty, stenting, and endarterectomy may inadvertently cause acute and chronic carotid sensor dysfunction through manipulation, material interposition, and balloon-induced baroreceptor injury. Acute strokes during these procedures may result from carotid sensor dysfunction rather than embolization. Carotid body and sinus electro-modulation and non-balloon atherectomy represent new methods to prevent or treat cerebrovascular events. Pharmacologic modulation of autonomic balance, such as adrenergic blockade, long presumed contraindicated due to risk of cerebral hypoperfusion, may counter-intuitively offer benefit during acute strokes. Novel diagnostic paradigms may include functional analysis of carotid sensors as well as measurement of the anatomic thickness of calcified and non-calcified plaque near the carotid body. Carotid sensor dysfunction may be a source of systemic sympathetic bias and autonomic dysfunction observed during aging and, by association, many of the ailments associated with senescence. Modulation of carotid sensors may yield pervasive health benefits beyond those found by treating cerebrovascular disease.