cardiac reflexes & anaesthetic implications

CARDIAC REFLEXES

Cardiac Reflexes

Chairperson –Dr.S.B.Gangadhar

Moderator – Dr. Abhishek. M.S

Presenter – Dr. Daber

CARDIAC REFLEXES

• Fast acting reflex loops between the heart and CNS that contribute to regulation of cardiac function and the maintenance of physiologic haemostasis

• Specific cardiac receptors elicit the physiologic responses by various pathways.

Introduction

CARDIAC REFLEXES

• Cardiac receptors are linked to CNS by myelinated or unmyelinated afferent fibersthat travel along the vagus nerve.

• Cardiac receptors are in the atria, ventricles, pericardium, and coronary arteries.

• Extracardiac receptors are located in the great vessels and carotid artery.

Introduction

CARDIAC REFLEXES

Introduction

• Sympathetic and parasympathetic nerve input is processed in the CNS.

• After central processing, efferent fibers to the heart or the systemic circulation will provoke a particular reaction.

• The response of cardiovascular system to efferent stimulation varies with age and duration of the underlying condition.

CARDIAC REFLEXES

Afferent nerve

Sympathetic & Para sympathetic Input

processed in the CNS

Efferent nerve

Heart /Systemic circulation

Particular Reaction

CARDIAC REFLEXES

Reflexes

1. Baroreceptor Reflex

2. Chemoreceptor Reflex

3. Brain Bridge Reflex

4. Bezold-Jarisch Reflex

5. Valsalva Maneuver

6. Cushing Reflex

7. Occulocardiac Reflex

CARDIAC REFLEXES

Baroreceptor reflex

(Carotid Sinus Reflex)

CARDIAC REFLEXES

• The best known of nervous mechanisms for arterial pressure control (baroreceptor reflex)

• Baroreceptors are stretch receptors found in the carotid body, aortic body and the wall of all large arteries of the neck and thorax.

• Respond progressively at 50-170 mm Hg.

• Respond more to a rapidly changing pressure than stationary pressure.

CARDIAC REFLEXES

• Changes in arterial blood pressure are monitored by circumfrential and logitudinalstretch receptors located in the carotid sinus and aortic arch.

• The nucleus solitarius, located in the cardiovascular center of the medulla, recievesthe impulse from these stretch receptors through afferent glossopharyngeal and vagusnerves.

CARDIAC REFLEXES

• The cardiovascular center in medulla consists of two functionally different areas;

– LATERALLY & ROSTRALLY- This area is responsiplefor increasing blood pressure

– CENTRALLY & CAUDALLY- This area is responsible for lowering arterial blood pressure.

• Typically, the stretch recptors are activated if systemic blood pressure is greater than 170 mmof Hg

CARDIAC REFLEXES

• The response from depressor system includes decreased sympathetic activity, leading to decrease in cardiac contractility, heart rate and vascular tone.

• In addition, activation of the parasymapathetic system further decreases the heart rate, myocardial contractility.

• Reverse effects are elicited with the onset of hypotension

CARDIAC REFLEXES

BLOOD PRESSURE GREATER THAN 170 mmof Hg

ACTIVATES THE STRETCH RECEPTORS IN CARTOTID SINUS AND AROTIC ARCH

AFFERENT NERVES – GLOSSOPHARYNGEAL & VAGUS CARRIES THE IMPULSE TO CARDIOVASCULAR CENTER IN MEDULLA

CENTER IN MEDULLA – LATERALLY & ROSTRALLY – INCREASES B.PCENTRALLY & CAUDALLY - LOWERS B.P

DECREASED IN SYMPATHETIC ACTIVITY & ACTIVATION OF PARASYMPATHTIC SYSTEM

CARDIAC REFLEXES

Anaesthetic Implication

• It plays important role during acute blood loss and shock.

• However, the reflex arch looses its functional capacity when arterial blood pressure is less than 50mmmofHg

• Hormonal status and therefore sex difference may alter the baroreceptor reflex.

CARDIAC REFLEXES

• Volatile anaesthetics particularly Halothane inhibit the heart rate component of this reflex.

• Calcium channel blockers, ACE inhibitors, phosphodiestrase inhibitors will lessen the cardiovascular response of raising the blood pressure through the baroreceptor reflex.

• Patients with chronic hypertension often exhibit per operative circulatory instability as a result of a decrease in their baroreceptor reflex response.

CARDIAC REFLEXES

Reflexes






6. Cushing Reflex


CARDIAC REFLEXES

CHEMORECPTOR REFLEX

CARDIAC REFLEXES

• Chemosensitive cells are located in the carotid bodies and the aortic body.

• These cell responds to changes in pH status and blood O2 tension.

CARDIAC REFLEXES

• At an arterial partial O2 pressure of less than 50mmof Hg or in condition of acidosis, the chemoreceptors send their impulses along the sinus nerve of Henring and vagus nerve to chemosensitive area of medulla.

• This area responds by stimulating the respiratory centers and there by increasing the ventilatory drive.

CARDIAC REFLEXES

• In addition, activation of the parasympathetic system, leads to a reduction in heart rate,andmyocardial contractility

• In the case, of persistant hypoxia, the CNS will be directly stimulated, with a resultant increase in sympathetic activity.

CARDIAC REFLEXES

PaO2 OF LESS THAN 50mmHg OR ACIDOSIS

CHEMORECEPTOR CELLS

CAROTID BODY

AORTIC BODY

GLOSSOPHARYNGEAL AND VAGUS NERVE

CHEMOSENSITIVE AREA IN MEDULLA

INCREASING VENTILATORY DRIVE, ACTIVATION OF PARASYMPATHETIC SYSTEM

CARDIAC REFLEXES

Anaesthetic implications

1. All anaesthetic drugs (except ketamine, ether and nitrous oxide) cause a dose- dependent reduction in ventilatory minute volume.

• This can be due to either a reduction in the respiratory rate (e.g. opioids), a reduction in the tidal volume (e.g. volatile anaesthetics) or both (e.g. propofol).

CARDIAC REFLEXES

• As alveolar ventilation decreases the PaCO2 increases.

• Hypercapnia causes vasodilation, tachycardia, arrhythmias, hypertension and in an awake patient, headache, confusion, tremor, sedation and eventually coma (CO2 narcosis).

• All of these effects can be seen in the postoperative period

CARDIAC REFLEXES

2. Under normal conditions the PaCO2 of arterial blood is the predominant factor controlling ventilation.

• Any increase in PaCO2 is detected by peripheral (carotid bodies) and central (medullary) chemoreceptors. As a result there is a linear increase in ventilation of approximately 2 l/min for each 1 mmHg rise in PaCO2.

CARDIAC REFLEXES

• This ventilatory response to carbon dioxide is reduced by virtually all anaesthetic drugs (the main exception being ether) until excessively high concentrations are produced.

• As a result, anaesthetised patients become hypercapnic.

CARDIAC REFLEXES

3. In addition, anaesthetics have two further undesirable effects on ventilation;

• Firstly after a period of mechanical ventilation the threshold at which the PaCO2 stimulates the return of spontaneous ventilation is increased, thus delaying the return of spontaneous ventilation

• Secondly, the ventilatory response to acidosis is blunted, reducing a patient’s ability to compensate.

CARDIAC REFLEXES

Reflexes






6. Cushing Reflex


CARDIAC REFLEXES

Brain Bridge Reflex

CARDIAC REFLEXES

• It is elicited by stretch receptors located in the right atrial wall and the cavo atrial junction.

CARDIAC REFLEXES

• An increase in the right sided filling pressure sends vagal afferent signals to the cardiovascular center in the medulla

• These afferent signals inhibit the parasympathetic system activity, thereby increasing the heart rate.

CARDIAC REFLEXES

• Acceleration of heart rate also results from a direct effect on the SA node by the stretching the atrium.

• The changes in heart rate are dependent on the underlying heart rate before stimulation.

CARDIAC REFLEXES

INCREASE IN RIGHT SIDED FILLING PRESSURE

STRETCH RECEPTORS

(R) ATRIAL WALL

CAVOATRIAL JUNCTION

CARDIOVASCULAR CENTER IN MEDULLA

INHIBIT PARASYMPATHETIC ACTIVITYTHEREBY, INCREASING HEART RATE

CARDIAC REFLEXES

ANAESTHETIC IMPLICATIONS

• The Bainbridge reflex and the baroreceptor act antagonistically to control heart rate.

• The baroreceptor reflex acts to decrease heart rate when blood pressure rises.

• When blood volume is increased, the Bainbridge reflex is dominant; when blood volume is decreased, the baroreceptor reflex is dominant.

CARDIAC REFLEXES

Reflexes






6. Cushing Reflex


CARDIAC REFLEXES

BEZOLD- JARISCH REFLEX

CARDIAC REFLEXES

• It responds to ventricular stimuli sensed by the chemoreceptors and mechanoreceptors within the left ventricular wall by inducing the triad of

– Hypotension

– Bradycardia

– Coronary artery dilatation

• The activated receptors communicate along unmyelinated vagal afferent type C fibers.

CARDIAC REFLEXES

• It produce increase in parasympathetic tone.

• Because it invokes bradycardia, the Bezold jarischreflex is thought of as a cardioprotective Reflex

• The reflex has been implicated in physiologic response to a range of cardiovascular conditions such as Myocardial ischemia, thrombolysis,orrevascularisation and syncope.

CARDIAC REFLEXES

• Bezold Jarisch reflex may be less pronounced in patients with cardiac hypertrophy or atrialfibrillation.

CARDIAC REFLEXES

Reflexes






6. Cushing Reflex


CARDIAC REFLEXES

Valsalva Maneuver

CARDIAC REFLEXES

• Forced Expiration against a closed glottis produces-

– Increased Intrathoracic pressure

– Increased central venous pressure

– Decreased Venous return

• Cardiac output and blood pressure will be decreased after the valsalva maneuver

CARDIAC REFLEXES

• This decrease will be sensed by baroreceptorsand will reflexively result in an increase in heart rate and myocardial contractility through sympathetic stimulation.

• When the glottis open, venous return increases and causes the heart to respond by vigorous contraction and an increase in blood pressure.

CARDIAC REFLEXES

• This increase in arterial blood pressure will in turn, be sensed by baroreceptors, thereby stimulating the parasympathetic efferent pathway to the heart.

CARDIAC REFLEXES

FORCED EXP AGAINST A CLOSED GLOTTIS

INCREASED INTRATHORACIC PRESSUREINCREASED CVP AND DECREASED VENOUS RETURN

DECREASED CARDIAC OUTPUT & BP

STIMULATE BARORECPTORS

↑HR,↑MYOCARDIAL CONTRACTILITY BY SYMPATHETIC (+)

CARDIAC REFLEXES

WHEN GLOTTIS OPENS

VENOUS RETURN ↑

CAUSES HEART TO RESPOND BY VIGOROUS CONTRACTION & ↑BP

STIMULATE BARORECPTORS

STIMULATION OF PARA SYMPATHETIC SYSTEM

CARDIAC REFLEXES

Reflexes






6. Cushing Reflex


CARDIAC REFLEXES

CUSHING REFLEX

CARDIAC REFLEXES

• The cushing reflex is a result of cerebral ischemia caused by intracranial pressure

• Cerebral ischemia at the medullary vasomotor center induces initial activation of the sympathetic nervous system

• This activation will leads to increase in heart rate, arterial blood pressure, and myocardial contractility in an effort to improve cerebral perfusion

CARDIAC REFLEXES

CEREBRAL ISCHEMIA AT MEDULLARY VASOMOTOR CENTER

STIMULATE SYMPATHETIC

SYSTEM

INCREASE HR,ARTERIAL BP, MYOCARDIAL CONTRACTILITY

IMPROVE CEREBRAL PERFUSION

CARDIAC REFLEXES


Chemoreceptor reflex is useful in regulation

of blood pressure when it falls to a level

between 40 and 70 mmHg.

But if the blood pressure below 40 mmHg,

the last ray of hope for survival is the central

nervous system (CNS) ischemia response.

So it sometimes called the “last ditch stand”

pressure control mechanism.

CARDIAC REFLEXES

OCULOCARDIAC REFLEX

CARDIAC REFLEXES

• This pressure is provoked by pressure applied to the globe of the eye or traction on the surrounding structures.

• Stretch receptors are located in the extraocular muscles.

• Once activated, stretch receptors will send afferent signals through short and long ciliarynerves.

CARDIAC REFLEXES

• This ciliary nerves will merge with ophthalmic division of trigeminal nerve at the ciliaryganglion.

• The trigeminal nerves will carry the impulse to gasserian ganglion,thereby resulting in increased parasympathetic tone and subsequent BRADYCARDIA.

CARDIAC REFLEXES


• The incidence during ophthalmic surgery ranges from 30% to 90%

• Administration of Glycopyrrolate or atropine reduces the incidence of Bradycardia during surgery.

CARDIAC REFLEXES

PRESSURE APPLIED ON GLOBE OR SURROUNDING STRUCTURES

STRETRCH RECEPTORS IN EXTRAOCULAR MUSCLES

SEND IMPULSE THROUGH SHORT AND LONG CILIARY NERVES

CILIARY NERVES MERGE WITH OPHTHALMIC DIVISION OF TRIGEMINAL NERVE AT CILIARY GANGLION

GASSERIAN GANGLION

INCREASED PARASYMPATHETIC TONE

BRADYCARDIA

CARDIAC REFLEXES

CONCLUSION

CARDIAC REFLEXES

CARDIAC REFLEXES

Thank you..!!

cardiac reflexes & anaesthetic implications

Health & Medicine