Cardiac Physiology

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Cardiac Reflexes
Baroreceptor Reflex (Carotid Sinus Reflex)
Responsible for the maintenance of blood pressure
Important role during acute blood loss and shock
Volatile anesthetics (particularly halothane) inhibit the heart rate component.
Concomitant use of calcium channel blockers, ACE inhibitors, or PDE inhibitors will lessen the cardiovascular response.
Patients with chronic hypertension often exhibit perioperative circulatory instability as a result of a decrease in their baroreceptor reflex response

Chemoreceptor Reflex
Mediated by
 Chemosensitive cells in the carotid bodies and the aortic body.
 Sinus nerve of Hering and vagus nerve
 Chemosensitive area of the medulla
At PaO2 <50 mm Hg or in acidosis
 respiratory centers stimulated and increasing ventilatory drive.
Activation of the parasympathetic system
 reduction in heart rate and myocardial contractility

Bainbridge reflex
Elicited by
stretch receptors located in the right atrial wall and the cavoatrial junction
vagal afferent signals
Cardiovascular center in the medulla
↑ right-sided filling pressure inhibits parasympathetic activity →↓ heart rate.
Direct effect on the SA node by stretching the atrium.
Depends on the underlying heart rate before stimulation.

Bezold-Jarisch reflex
Elicited by
 chemoreceptors and mechanoreceptors within the LV wall
 Vagal afferents
 ↑ parasympathetic tone
Noxious ventricular stimuli induces the triad of hypotension, bradycardia, and coronary artery dilatation.
Implicated in cardiovascular conditions
 Myocardial ischemia or infarction
 Thrombolysis
 Revascularization
 Syncope
Less pronounced in patients with
 Cardiac hypertrophy
 Atrial fibrillation

Valsalva Maneuver
Valsalva maneuver → ↓CO and BP.
Sensed by baroreceptors → sympathetic stimulation
↑heart rate and myocardial contractility.

When the glottis opens, venous return ↑ →↑BP.
Sensed by baroreceptors → stimulate parasympathetic efferent pathways to the heart.

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