The ANA has been compared to a computer circuit (sensor, afferent pathway, CNS integration, efferent pathway).
- Baroreceptors located in the carotid sinus and aortic arch react to alterations in stretch caused by changes in blood pressure (Fig. 15-4: Blood pressure and heart rate response to a Valsalva maneuver (A, normal; B, abnormal in a patient with cervical quadriplegia)). Volatile anesthetics interfere with baroreceptor function; thus, anesthetic-induced decreases in blood pressure may not evoke changes in heart rate. Compliance of stretch receptors and their sensitivity may be altered by carotid sinus atherosclerosis. (Carotid artery disease may be a source of hypertension rather than a result.)
- Venous baroreceptors located in the right atrium and great veins produce an increased heart rate when the right atrium is stretched by increased filling pressure (Bainbridge reflex). Slowing of the heart rate during spinal anesthesia may reflect activation of venous baroreceptors as a result of decreased venous return.