A positive feedback sympathetic pressor reflex during stretch of the thoracic aorta in conscious dogs.

Abstract

The role of pressor sympathetic reflexes in circulatory control was investigated in conscious dogs. Animals were previously instrumented with a 6- to 8-cm rigid core cannula covered by an inflatable rubber cylinder in the thoracic aorta, a pressure catheter implanted in the aorta above the cannula, and a second catheter inserted into the aorta below the cannula through a femoral artery. Two piezoelectric crystals were positioned at opposing adventitial sites to measure aortic distension with ultrasound techniques. After recovery from surgery, the diameter of the aortic segment surrounding the cannula was increased by 9.6 +/- 0.4% from 16 +/- 1 mm by inflating the rubber cylinder, without obstructing blood flow. Mean aortic pressure rose 31 +/- 3% from 100 +/- 3 mm Hg and heart rate 20 +/- 3% from 91 +/- 3 beats/min (P less than 0.01). The pressor response was abolished by alpha-adrenergic blockade (phentolamine 1 mg/kg, iv). The heart rate response was reduced either by beta-blockade (propranolol 1 mg/kg, iv) or muscarinic blockade (atropine 0.2 mg/kg, iv) and abolished by their combination. During aortic stretch, the sensitivity of the baroreflex was reduced 57 +/- 7% from 18 +/- 2 msec/mm Hg (P less than 0.01). The pressor response was increased by 49 +/- 8% after bilateral carotid sinus nerve section and vagotomy. These excitatory reflex responses were obtained in absence of any pain reaction. Thus, in the conscious dog, aortic distension within physiological ranges induces a potent pressor sympathetic reflex with positive feedback characteristics. Such a pressor reflex not only occurs in the presence of functioning baroreflexes, but is also capable of reducing their sensitivity.

Cardiovascular control in women with fibromyalgia syndrome: do causal methods provide nonredundant information compared with more traditional approaches?

“…However, on the basis of the present results, a deficient afferent baroreceptor feedback restraining the sympathetic activity may take place in these patients. On the other hand, it must be taken into account that the relationship between baroreceptor activity and sympathetic activity is bidirectional: an increase of sympathetic activity might be an effect of a baroreflex unloading, as well as a direct effect of a central sympathetic drive restraining, as a consequence, baroreflex activity (16), thus supporting that the reduced baroreceptor function observed in the fibromyalgia patients might result from a central primary sympathetic hyperactivity previously hypothesized (7). Even though it was not possible to clarify whether the reduced BRS leads to the sympathetic hyperactivity in FMS, this study has an important clinical implication regarding the risk of hypertension in this population.…”

Early Progression of the Autonomic Dysfunction Observed in Pediatric Type 1 Diabetes Mellitus

“…Considering that exogenous insulin increases efferent sympathetic activity 18 and provokes a shift of the balance between LF and HF components of RR variability toward LF, 19 we might hypothesize a mechanistic role for therapeutic insulin in the observed alterations in autonomic indices, in addition to the possible direct effects of endothelial dysfunction, 20,21 oxidative stress, 22,23 Rho/Rho-kinase pathway, 24 arginase mechanisms, 20 and adhesion molecules in initiating sympatho-sympathetic positive feedback reflexes 25 from the arterial sites and thereby reducing baroreflex gain. As a corollary, the lack of relationship between glycosylated hemoglobin and other parameters suggests that this index might be a less sensitive indicator of diabetic complications affecting cardiovascular regulatory mechanisms, in particular, changes in heart rate variability and blood pressure variability.…”

Relative contribution of aortic and carotid baroreflexes to heart rate control in man during steady state and dynamic increases in arterial pressure.

“…These could include the cardiopulmonary baroreflexes and the possible role of sympathetic excitatory afferents from the aortic arch as described by Pagani et al (36).…”