1. Cardiac reflexes, How
to prevent it.
Dr Imran Sheikh.

3. Afferent nerve
↓
Symp and para symp N input
processed in the CNS
↓
Efferent nerve
↓
Heart /Systemic circulation
↓
Particular Reaction

4. Cardiac reflexes
 Fast acting reflex loops between the
heart and CNS.
Contribute to regulation of cardiac
function and maintenance of
homeostasis.
Cardiac receptors –linked to CNS by
myelinated or un myelinated afferent
fibres that travel along the vagus N.

6. Cardiac receptors--- found in atria,
venticles, pericardium and coronary
arteries.
Extra cardiac receptors--- Great vessels
and Carotid.A.
Response varies with age and the
duration of underlying condition that
elicited the reflex in the first instance.

7. Baro receptor reflex
(Carotid sinus reflex)
• Responsible for maintenance of BP
• Capable of regulating arterial BP around a
preset value through a negative feed back
loop
• Also capable of establishing a prevailing
set point of BP when the preset value has
been reset because of c/c HTN.

8. Changes in BP---monitored by
circumferential and longitudinal stretch
receptors located in carotid sinus and
aortic arch

9. 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

10. Carotid sinus (Contd…)
 Afferent nerves from these
stretch receptors travel in
the carotid sinus nerve
 which is a branch of the
glossopharyngeal nerve.
(IXth cranial nerve)

11. 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,
which is a branch of the vagus nerve.
(Xth cranial nerve)

12. Cardiovascular centre in medulla
• Nucleus solitarius
• CV centre has
Area for inc BP Area for dec BP
Located laterally and Located centrally and
rostrally. Caudally.

14. Concept and mechanism of
baroreceptor reflex
Any drop in systemic arterial pressure decreases the
discharge in the buffer nerves,
and there is a compensatory rise in blood pressure
and cardiac output.
Any rise in blood pressure produce dilation of the
arterioles and decreases cardiac output until the
blood pressure returns to its previous normal level.

15. Arterial
Pressure
Baroreceptor
Carotid Sinus
Aortic Arch
Sinus Nerve
Nucleus solitarius

16. Reverse effects ----- onset of hypotension.
The reflex arch loses its capacity at BP < 50 mm Hg
Hormonal diff and hence sex diff have been
implicated in altered baroreceptor responses.

17. Volatile anesth (esp Halothane) inhibit the HR
component of the reflex.
Concomitant use of CCBs and ACEIs OR PDEIs will
lessen the CV response of raising BP through
baroreceptor reflex
→ Direct effect on peripheral vasculature
→Interference in CNS signalling pathway(imp)

18. Baroreceptor Resetting
 Baroreceptor will adapt to the long term change of
blood pressure.
 That is, if the blood pressure is elevated for a long
period of time, several days or years, the set point will
transfer to the elevated mean blood pressure.
 Obviously, the adaptation of the baroreceptor
prevents the baroreceptor reflex from acting as a
long term control system.
 That makes the baroreceptor system unimportant for
long-term regulation of arterial pressure

19. Chemoreceptor reflex

21.  Response: Stimulation of
chemoreceptors leads to a reflex
increase in vasomotor tone,
 which causes generalized
vasoconstriction and hence a
rise in blood pressure.
 Importance: Chemoreceptor
mechanism is important in
regulation of blood pressure when
it fall below the range in which
baroreceptors act (70 mmHg).

22. Stimulates resp centre and causes
increase in ventilatory drive.
Also stimulates para symp system

23. Bain bridge Reflex
Elicited by stretch receptors located in the Rt atrial
wall and cavoatrial junction.
↑Rt sided filling pressure Vagal afferent
Cardiovascular centre in medulla
inhibition of parasymp system
↑HR

24. o ↑ HR ---also from direct effect on SA node by
stretching the atrium.
o The changes in HR dependent on underlying HR
before stimulation.

25. • 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.

26. Bezold-Jarish Reflex
• Responds to noxius ventricular stimuli
• Sensed by chemoreceptors and
mechanoreceptors with in LV wall,
by inducing triad of
→Hypotension
→Bradycardia
→Coronary artery dilatation

27. Afferent-----Unmyelinated vagal afferent
type C fibres
Reflexively increase parasymp: tone.
As it involves bradycardia, this reflex is
thought of as a cardio protective reflex

28. Implicated in the physiologic response to
a range of cardio vascular conditions…
→Myocardial ischemia/infarction
→thrombolysis
→revascularisation
→Syncope

29. Cushing Reflex(CNS ischemic response)
Result of cerebral ischemia due to ↑ICP.
 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.

30.  As the name indicates, it is evoked by ischemia
(poor blood flow) of the central nervous system.
 CNS ischemia reduces blood flow to the vasomotor
centre (VMC).
 Reduction in blood flow to the VMC leads to
reduced Po2 and elevated Pco2 in the medulla
region.
 Both these factors stimulate the VMC directly,
leading to vasoconstriction and consequently rise in
blood pressure.

31. One of the most powerful of all the activators of the
sympathetic vasoconstrictor system.
Not one of the usual mechanisms of regulating normal
pressure.
It is an emergency arterial pressure control system that
acts rapidly & powerfully to prevent further decrease in
arterial pressure whenever blood flow to the brain
decreases dangerously close to the lethal level.

32. Blood flow
to
vasomotor
centre
decreased
significantl
y
Effect is
due to
failure of
slowly
flowing
blood to
carry C02
away from
vasomoto
r centre.
Neurons
in
vasomotor
center
respond
to
ischemia
directly
Systemic
arterial
pressure
rises as
high as
the heart
can pump.
Degree of
vasoconstr
iction can
be intense
enough to
totally
occlude
some
peripheral
vessels
Eg : The
kidneys
may
totally
cease
urine
productio
n because
of
arteriolar
constrictio
n

33. Oculocardiac reflex
Pressure applied to the globe of the
eye or traction on the surrounding
structures.
Incidence ---- 30%---90%

34. Stretch receptors--- present in
Extraocular Ms
Afferent through short & long ciliary Ns.
The ciliary Ns will merge with ophthalmic
division of the Trigeminal N at the ciliary
ganglion.
Gasserian ganglion.
↑Para symp tone & Bradycardia

36. Valsalva maneuver
Forced exp against a closed glottis→↑intra thoracic
pressure,↑CVP,
↓Venous return.
↓CO & BP
This decrease will stimulate baroreceptors
↑HR,↑Myocardial contractility by sympathetic (+)

37. When glottis opens
Venous return ↑
Causes heart to respond by vigorous contraction
& ↑BP.
Sensed by Baroreceptors
Stimulation of para sympathetic system.

38. Recto cardiac reflex
Dilatation of the anal canal and
instrumentation of the anal rectum also
may evoke cardiovascular responses.
Bradycardia.
Hypotension.
Afferents ----- chiefly over the pelvic N.
Efferents ----- Vagus.

39. Pelvic reflexes
Mobilisation of uterus
Traction on the uterus (more usual)
Hypotension.
Circulatory depression-----when large tumours are
lifted from pelvis
(Reflex or Mechanical).

40. Celiac plexus Reflex
Manifested by marked falls in BP and
absence of systolic sounds while taking
BP.
Pulse may be slow/imperceptible
Bradycardia.
↓BP ----- narrowing of pulse pressure
More likely when stomach is pulled.
Traction on gallbladder, hilum of liver,
or retraction of the duodenum.

41. Diaphragmatic traction reflex
(Brewer-Luckhardt reflex)
• Manipulation or traction on the
diaphragm often results in drop in
BP, esp the systolic, accompanied by
bradycardia.
• Downward traction on the liver or
traction on the gallbladder, produces
similar acute effects.
• Should be distinguished from
mechanical hypotension.

42. Nasocardiac reflex
Stimulation of the nasal cavity by a nasal
speculum, a nasal retractor, or an ET
tube, when anaesthesia is in adequate or
in the absence of topical anaesthesia
Bradycardia (predominant
manifestation).
Hypotension.

43. Afferent- Maxillary div of trigeminal.N &
ethmoidal N.
Efferent- Vagus N.
Response- Bradycardia, drop in BP.

44. Intrathoracic Reflexes
• Stimuli to Vagal N endings with in the thorax
Esophageal reflex
Pericardial reflex
Pleural reflex
Hilar reflex
( Prophylaxis and Rx- Atropinisation and infiltration
of the hilar area with 1% procaine before
manipulation)

45. Tracheal reflex
Afferent and efferent Vagus.
VAGO VAGAL REFLEX.
Stimulation – Layngospasm, and/or
bronchospasm will occur in light anaesth:
Ineffective breathing movt called
Bucking.
Bradycardia and arrhythmias and
hypotension may result

46. Causes:
 Tracheal intubation
Inflation of the endotracheal cuff
Presence of mucus or other foreign
material
Stimulation from a tracheal suction
catheter through the endotracheal
tube

47. Peritoneal and mesenteric reflex
• Pulling or stretching the peritoneum or pulling the
mesenteries
Bradycardia and Hypotension
Often accompanied by spasm of the larynx and even
apnoea.
Traction on the ovaries--- similar response.

48. Periosteal reflex
Afferent- Somatic N fibres
 Efferent- Vagus N
Apnea occurs often followed by tachypnea with
varying degrees of laryngospasm
Hypotension freq folowed by tachycardia

49. Prevention and Rx
Atropine- most widely used and
effective agent in prevention and Rx of
parasympathomimetic reflex
responses.
Topical anaesthesia- can eliminate the
reflex at the afferent component.*
Intravascular Lignocaine is more eff
than topical and obtunds the
cardiovascular responses to upper resp
and thoracic induced reflexes.
CV resp during abdominal Sx.

50. Prevention and Rx (Cond…)
Continous infusion of lignocaine
(2mg/min) after an initial loading dose of
100 mg IV is recommended.

51. During Sx…..
Cessation of the applied stimulus
IV Atropine (5 – 10 μg/kg)
Vasopressors- If persistent hypotensive
response.(ephedrine in fractional doses
of 5mg)
Increase the depth of anaesthesia.