1. Cardiac reflexes and implications in anaesthetic practice
Dr. Anuradha Patel
University College of Medical Sciences & GTB Hospital, Delhi

2. Cardiac Reflex Fast acting reflex loops between the heart and CNS
Regulates cardiac function
Maintains physiologic homeostasis
Cardiac receptors are linked to CNS by myelinated / unmyelinated afferents of vagus nerve
Cardiac receptors are present in
Atria
Ventricles
Pericardium
Coronary arteries

3. Myelinated / unmyelinated afferent of vagus nerve
Cardiac receptor 
Myelinated / unmyelinated afferent of vagus nerve
Central processing of sympathetic and parasympathetic nerve input in the CNS
Efferent fibres
Heart or systemic circulation
Particular reaction

4. Afferent fibres of cardiac receptors (in vagus nerve)
Myelinated fibres (25%)
Unmyelinated fibres (75%)
Present in walls of atria and atriocaval junction
Present in walls of all cardiac chambers

5. Cardiac innervation
Sympathetic nerve – noradrenergic fiber; Parasympathetic nerve- cholinergic fiber
Noradrenergic sympathetic nerve
to the heart increase the cardiac rate (chronotropic effect)
the force of cardiac contraction (inotropic effect).
Cholinergic vagal cardiac fibers decrease the heart rate.

7. Cardiovascular Reflexes
Baroreceptor reflex (carotid sinus reflex) (pressure receptor reflex)
Chemoreceptor reflex
Bainbridge atrial reflex (volume reflex) (atrial stretch reflex)
Bezold-Jarisch reflex (cardiopulmonary reflex)
Oculocardiac reflex (trigeminovagal reflex)
Cushing’s reflex
Valsalva maneuver

8. Baroreceptor Reflex (carotid sinus reflex) (pressor receptor reflex)
Reflex initiated by stretch receptors, called baroreceptors or pressor receptors
Baroreceptors are present in
Carotid sinus
Aortic arch
Walls of right atrium at the entrance of SVC and IVC
Walls of left atria at the entrance of pulmonary vein
These receptors in low pressure part of the circulation are called as cardiopulmonary receptors
They are stimulated by distension of the structure in which they are located
 pressure in these structures are associated with  discharge rate

9. Baroreceptor areas in the carotid sinus and aortic arch

10. Carotid sinus
At the bifurcation of the common carotid arteries
the root of internal carotid artery shows a little bulge
has stretch receptors in the adventitia
are sensitive to arterial pressure fluctuations
Afferent nerves from these stretch receptors travel in the carotid sinus nerve which is a branch of the glossopharyngeal nerve (IXth cranial nerve)

11. Baroreceptor system for controlling BP

12. Aortic Arch
baroreceptors are also present in the adventitia of the arch of aorta
have functional characteristics similar to the carotid sinus receptors.
their afferent nerve fibers travel in the aortic nerve,
branch of the vagus nerve. (Xth cranial nerve)

13. Pathways involved in the medullary control of BP

14. Basic pathways involved in the medullary control of heart rate by the vagus nerves

15. Buffer nerves activity
The carotid sinus nerves and vagal fibers from the aortic arch are commonly called the buffer nerves
At normal blood pressure levels, the fibers of the buffer nerve discharge at a low rate.
When the pressure in the sinus and aortic arch rises, the discharge rate increases;
when the pressure falls, the rate declines.

16. Discharges (vertical lines) in a single afferent nerve fiber from the carotid sinus at various levels of mean MAP, plotted against changes in aortic pressure with time

17. Fall in systemic blood pressure produced by raising the pressure in the isolated carotid sinus of a normal monkey to various values

18. Activation of the baroreceptors at different levels of arterial pressure. I, change in carotid sinus nerve impulses per second; P, change in arterial blood pressure in mm Hg.

19. Baroreceptors respond extremely rapidly to changes in BP (within fraction of seconds)
Response much more to rapidly changing BP than to stationary pressure
Maintains BP through a negative feedback loop

20. Role in acute blood loss and shock

22. Importance of the baroreceptor reflex
To keep the arterial pressure relatively constant
Short term regulation of blood pressure in the range of 70 mmHg to 150 mmHg, maintain the mean blood pressure at about 100 mmHg
Pressure buffer system – reduce the blood fluctuation during the daily events, such as changing of the posture, respiration and excitement

23. Baroreceptor Resetting
Baroreceptor will adapt to the long term change of blood pressure.
That is, if the blood pressure is elevated for a longer time, as in chronic HTN, the set point will transfer to the elevated mean blood pressure
So there is decrease baroreceptor response in pts with chronic HTN
This makes the baroreceptor system unimportant for long-term regulation of arterial pressure

24. CCBs, ACE-inhibitors, PDE inhibitors -  cardiovascular response of increasing BP through this reflex
Baroreceptors are compromised by diabetic neuropathy
Volatile anaesthetics (particularly halothane) inhibit HR component of the reflex
These reflexes are well preserved with moderate doses of fentanyl but high doses depresses this reflex

25. Chemoreceptor Reflexes
Mediated by
Peripheral chemoreceptors
Carotid bodies
Aortic bodies
Central chemoreceptors
Medulla (associated with cardiovascular control “centers”)
Sinus nerve of Hering (branch of 9th cranial nerve) and vagus nerve

26. Peripheral Chemoreceptors
Present in carotid & aortic bodies
2 mm in size
Supplied with abundant blood flow through a small nutrient artery (senses changes in BP)
Rich sensory innveration
Rate of response is fast

27. Chemoreceptor areas in carotid and aortic bodies
CAROTID BODY
AORTIC BODY

28. Respiratory control by peripheral chemoreceptors in the carotid and aortic bodies

29. Highest blood flow – 2000 ml/100 g/min
Carotid bodies
2 in number
2 mg weight
Highest blood flow – 2000 ml/100 g/min
Present at bifurcation of each common carotid artery
Innervated by sinus nerve (branch of 9th nerve)
Aortic bodies
1-3 in numbers
Adjacent to aorta
Near the aortic arch
Near root of subclavian artery
Innervated by 10th nerve

30. Central chemoreceptoprs – medulla (slow response)
Cardiac control centres in medulla oblongeta
Cardioaccelerator stimulatory centre (VMC)
Cardioaccelerator inhibitory centre (CIC)
Sympathetic stimulation
Parasympathetic stimulation

31. Cardiovascular centers of the brainstem
Medulla oblongata is essential to Cardiovascular centers

32. Central & peripheral chemoreceptors respond to changes in chemical composition of blood or surrounding fluid
Central chemoreceptors respond only to acidosis
Peripheral chemoreceptors are sensitive to changes in arterial O2 and CO2 tension and to pH
Increasingly important when mean arterial pressure falls below 60 mmHg (i.e. when arterial baroreceptor firing rate is at minimum)

33. PaO2 < 50 mmHg / acidosis /  PaCO2
Stimulate chemoreceptor in carotid & aortic bodies
Sinus nerve of Hering & vagus nerve
Medullary vasomotor centres
Stimulate respiratory centres
Directly stimulates sympathetic system
Indirectly catecholamine secretion from the adrenal medulla
 pulm ventilation
 BP
 BP

34. Bainbridge Atrial Reflex (atrial stretch reflex, volume reflex)
 vagal tone
 right sided filling pressure
Stretching of atria
Stimulates stretch receptors present in right atrial wall & cavoatrial junction
Vagal myelinated afferent fibres
Directly stimulates SA node
Cardiovascular center of medulla
 HR
Efferents of vagus nerve
Inhibit parasympathetic activity
 HR

35. Bainbridge Atrial Reflex
Spinal or epidural anaesthesia 
Venous pooling in periphery
Decreased stimulation of cardiac stretch receptor
Decreased activity of cardiac sympathetic nerve
Vagal predominance
Decease heart rate

36. Reflex depends upon the preexisting heart rate
With slow heart rate, it causes progressive tachycardia
With pre-existing tachycardia, there is no effect
It helps prevent collection of blood in veins, atria and pulmonary circulation
It inhibits ADH release and promote secretion of ANP
Denervation of vagi to heart eliminate this reflex
The Bainbridge and baroreceptor reflex acts antagonistically to control heart rate
When blood volume is increased, the Bainbridge reflex is dominant, when it is decreased, baroreceptor reflex is dominant

37. Bezold-Jarisch reflex (cardiopulmonary reflex)
Reflex triggered by
Intracoronary injection of veratrum alkaloids, serotonin, nicotine, capsaicin, phenyldiguamide
Coronary ischemia (MI)
Bradykinin, PGI2, Arachidonic acid
Ventricular distension
Coronary angioplasty
Thrombolysis
Revascularization
Syncope

38. Bezold-Jarisch reflex (cardiopulmonary reflex)
Triggering factors
Stimulates cardiopulmonary chemoreceptors and mechanoreceptors of LV wall
Unmyelinated vagal afferent type C fibres
Inhibit medullary vasomotor centre
 parasympathetic tone
Triad of – bradycardia, hypotension, peripheral vasodilatation

39. Bezold-Jarisch reflex
Responsible for hypotension during regional anaesthesia

40. MI / Coronary reperfusion
Molecules generated during ischemia and reperfusion such as free radicals and PG 
Stimulate cardiac inhibitory receptors (present in inferior & posterior walls of heart)
Hypotension
Bradycardia and renal vasodilatation
Sudden cardiac death
Decreases myocardial oxygen demand and augments renal perfusion (protective reflex)

41. Cardio-protective reflex, regulates BP in conjunction with baroreceptor reflex
Less pronounced in patients with cardiac hypertrophy & AF
Veratrum alkaloid can be used as an antihypertensive agent
Reflex dangerous in acute MI, coronary angiography, aortic stenosis and vaso-vagal syncope

42. Prevention
Prophylactic  blockers
Treatment
 blockers & vagolytics (e.g. disopyramide)
Atropine for bradycardia

43. Oculocardiac Reflex (Trigemino-vagal Reflex, Aschner Phenomenon, Aschner Reflex, Aschner Dagini Reflex)
Reflex triggered by
Pressure on globe
Traction on the extraocular muscle (esp. medial rectus muscle) as in strabismus surgery
Ocular trauma
Severe pain
Orbital compression due to hematoma or edema
Procedures under topical anaesthesia
Orbital injections
Hypercapnia or hypoxemia
Fentanyl, sufentanil and remifentanil

44. Stimulates stretch receptors of extraocular muscle
Pressure on the globe of the eye or traction on the extraocular muscles
Stimulates stretch receptors of extraocular muscle
Afferents of short and long ciliary nerves
Ciliary ganglion
Ophthalmic division of trigeminal nerve
Gasserian ganglion
Sensory nucleus of trigeminal in the floor of 4th ventricle
Efferents of vagus nerves (vagal cardiac depressor nerve)
Parasympathetic stimulation
Bradycardia / hypotension / asystole / AV block / ventricular ectopy

45. Oculocardiac reflex

46. Treatment
Immediate
Cessation of manipulation
IV atropine: – 0.4 mg/kg or 7 µg/kg increments
Lignocaine infiltration – near extrinsic muscles in case of recurrence
IV epinephrine 6-12 mg for hypotension
Prevention
Indicated in patients with h/o conduction block, vaso-vagal responses or -blocker therapy
Premedication with anti-cholinergics (atropine or glycopyrrolate) (block efferent pathway)
Retrobulbar block with 1-3 ml of 1-2% lidocaine

47. Reponses ceases with repeated stimulation
Reflex is more sensitive in neonates and children, especially during squint surgery
Incidence during ophthalmic surgery: 30-90%

48. Cushing Reflex Reflex activated by Cerebral edema
Hematoma – subdural, epidural, contusion, ICH
Foreign body
Depressed skull fracture
Hydrocephalus
Hypoventilation
Venous sinus thrombosis
IC-SOL: Tumor, hematoma, abscess
Brainstem compression
Acute traumatic brain injury
Craniotomy
Neuroendoscopy

49. Compression of cerebral arteries
 CSF pressure /  ICT
Compression of cerebral arteries
Cerebral ischemia at the medullary VMC ( CO2 in blood,  lactic acid in VMC)
Stimulates vasoconstrictor and cardioaccelerator neurons in VMC
Sympathetic stimulation
 HR,  BP,  myocardial contractility  improve cerebral perfusion
Stimulaes baroreceptors
Reflex bradycardia

50. Triad of HTN, bradycardia and apnea
Seen in 33% of patients with  ICT
Inhalational agents are generally associated with  ICT
Both thiopental and propofol  ICT
Occurrence of bradycardia & HTN is used as warning sign of  ICT during neuroendoscopy

51. Treatment
Treated by measures to reduce ICP rather than pharmacological treatment of HTN
Elevate head to 30-45°
Control HTN
Avoid hypoxia (pO2 <60 mmHg)
Ventilate to normocarbia (pCO mmHg)
Sedation
Drain 3-5 ml CSF if ventriculostomy present
Hyperosmolar agents – mannitol, urea, glycerol
3% NaCl infusion
Barbiturates – thiopentone
Systemic diuretics – furosemide, ethacrynic acid
steroids – dexamethasone

52. Valsalva Maneuver
Forced expiration against a closed glottis (after full inspiration)
 Intrathoracic pressure ( BP initially)
Compression of veins ( CVP)
 VR,  CO
 BP
Inhibit baroreceptors
Sympathetic stimulation
 HR
 myocardial contractility

53. Opening of glottis (return of intrathoracic pressure to normal)
 VR
 myocardial contractility
 BP
Stimulates baroreceptors
Stimulates parasympathetic efferent pathways to the heart
 BP,  HR

54. Phase I
Transient rise in BP due to increased intra-thoracic and intra-abdominal pressure
Phase II
Fall of BP followed by recovery
Increased HR due to sympathetic activation
Phase III
Fall in BP due to release of intrathoracic pressure
Phase IV
Increase in BP due to “overshoot” of cardiac output into a vasoconstricted peripheral circulation
Fall in HR with transient bradycardia, in the normal state, until after the BP overshoot

56. Valsalva ratio
Stimulus
Expiration of 40 mmHg for 15 sec
Afferent
Baroreceptors, glossopharyngeal, vagus nerves
Central
Nucleus tactus solitarus
Efferent
Vagus and sympathetic nervous system
Response
HR & BP changes
VR=Max HR/min HR
A normal VR indicates an intact baroreceptor mediated increase and decrease in HR
A decreased VR reflects baroreceptror and cardiovagal dysfunction
Normal value is a ratio of >1.21

57. In sympathectomized patients, HR changes occur since baroreceptors and vagi are intact
In autonomic insufficiency HR changes does not occur

58. Head up tilt table test
Stimulus
Decreased central blood volume
Afferent
Baroreceptors, vagus, glossopharyngeal nerves
Central
NTS, RVLM, hypothalamus
Efferent
Sympathetic vasomotor
Response
HR and BP changes
This test is the BP and HR response to an orthostatic challenge as a measure of sympathetic function
It is used to assess orthostatic intolerance caused by sympathetic nervous system dysfunction and to detect any predisposition to vasovagal syncope

59. Respiratory sinus arrhythmia
Index of cardiac vagal function
HR variability in synchrony with respiration
RR interval on an ECG is shortened during inspiration and prolong during expiration

60. Thank You