CARDIOVASCULAR CARDIOVASCULAR REFLEXESREFLEXES

Heart Heart Blood vesselsBlood vessels

Circulatory adjustment - centrally Circulatory adjustment - centrally regulated – works with local regulated – works with local

mechanism – minimize fluctuation of mechanism – minimize fluctuation of MABP – maintain perfusion .MABP – maintain perfusion .

HistoryHistory

Pioneers -- * C. Heymans Pioneers -- * C. Heymans J . BouckaertJ . Bouckaert Eric Neil 1930Eric Neil 1930They studied on the carotid sinus reflexes.They studied on the carotid sinus reflexes.Prior to ’30s : @ Marey’s law in 1859, Prior to ’30s : @ Marey’s law in 1859, @ Bezold – Jarish reflex ,@ Bezold – Jarish reflex , @Bainbride reflex 1914@Bainbride reflex 1914

Prof. A.S.Paintal in 1953 – atrial stretch receptorsProf. A.S.Paintal in 1953 – atrial stretch receptors

3 Components3 Components Afferent nervesAfferent nerves CNSCNS Efferent nervesEfferent nerves – controlling the cardiac – controlling the cardiac

& pulmonary function – maintaining & pulmonary function – maintaining homeostasis .homeostasis .

CV reflexes involves ( heart & blood vessels )CV reflexes involves ( heart & blood vessels )

Autonomic Control Autonomic Control - sympathetic - sympathetic - para sympathetic- para sympathetic Medullary Control Medullary Control - vasomotor center- vasomotor center - cardiac vagal center- cardiac vagal center

Autonomic Supply of C.V.S.Autonomic Supply of C.V.S.

Autonomic control of heartAutonomic control of heart

Heart : Sympathetic - outflow from T1-T5 , supply Heart : Sympathetic - outflow from T1-T5 , supply nodal tissue and muscle .nodal tissue and muscle . + ve chronotropic+ ve chronotropic , , inotropicinotropic, , dromotropic and bathmotropicdromotropic and bathmotropic actions.actions. Parasympathetic - Parasympathetic - via vagus nerve , supply via vagus nerve , supply SA node , AV node and SA node , AV node and atria , atria , no vagalno vagal motor supply tomotor supply to ventricleventricle.. - ve effects on heart . - ve effects on heart . vagal tone.vagal tone.

Autonomic control of blood vesselsAutonomic control of blood vessels

Blood vessel : Blood vessel : Sympathetic -- Sympathetic -- vasoconstrictor tonicvasoconstrictor tonic

infleunce , ( all blood vessels -infleunce , ( all blood vessels -arterioles,small arteries , metaarterioles are arterioles,small arteries , metaarterioles are densely innervated densely innervated except capillariesexcept capillaries and and venulesvenules ) increase BP .venoconstriction ) increase BP .venoconstriction increases venous return.increases venous return.

Parasympathetic -- insignificant role .Parasympathetic -- insignificant role .

Sympathetic innervation of blood Sympathetic innervation of blood vesselvessel

Autonomic ControlAutonomic Control

Vasodilatation :Vasodilatation :- Inhibition of sympathetic constrictor fibres,Inhibition of sympathetic constrictor fibres,- Stimulation of sym. cholinergic fibres ,Stimulation of sym. cholinergic fibres ,- Axon reflex .Axon reflex .

Medullary ControlMedullary Control- Formed by neurons of reticular substance of Formed by neurons of reticular substance of

medulla and lower third of pons in the floor of medulla and lower third of pons in the floor of the 4the 4thth ventricle . ventricle .

Two separate centres :Two separate centres : *Vasomotor center – pressor &*Vasomotor center – pressor & depressor areadepressor area * Cardiac vagal centers – NTS* Cardiac vagal centers – NTS - Dorsal MN- Dorsal MN - Nuc. ambiguus- Nuc. ambiguus

Vasomotor centreVasomotor centre

-- -- increaseincrease vasomotor dischargevasomotor discharge causes causes arteriolar constriction , rise of BP & arteriolar constriction , rise of BP & thereby increases venous return .thereby increases venous return .

-- decrease vasomotor discharge causes -- decrease vasomotor discharge causes vasodilatation , fall of BP & decrease in vasodilatation , fall of BP & decrease in venous return .venous return .

Input to V.M.CInput to V.M.C..

↓BaroLung via vagusLimbic cortex

Ant. hypo

↑ChemoAscending pain

Ascending proprioceptiveLimbic cortex(post.hypo.

↑CO2O2

V.M.C.

Cardiac nucleiCardiac nuclei

Cardiac vagal centreCardiac vagal centre

Stimulation : Stimulation : Bradycardia , decrease cardiac output , Bradycardia , decrease cardiac output ,

decrease BP. decrease BP. Mechanism ~ directly on heart by vagusMechanism ~ directly on heart by vagus ~ NTS – stimulates inhibitory ~ NTS – stimulates inhibitory interneuron – inhibits VMC-interneuron – inhibits VMC- causing decrease sympcausing decrease symp & increase vagal activity . & increase vagal activity .

Control of VMC by Higher Nervous Control of VMC by Higher Nervous CenterCenter

Supramedullary neural networks , mainly Supramedullary neural networks , mainly from cortex & limbic system also from cortex & limbic system also contributes signals to the medullary contributes signals to the medullary centers and accordingly integrates various centers and accordingly integrates various cardio-vascular reflexes .cardio-vascular reflexes .

Higher center controlHigher center control

Reflexes controlling CV functionsReflexes controlling CV functions1.1. Baroreceptor reflexBaroreceptor reflex2.2. Cardiopulmonary baro-chemo reflexCardiopulmonary baro-chemo reflex3.3. Chemoreceptor reflexChemoreceptor reflex4.4. Cushings reflexCushings reflex5.5. Somasympathetic reflexSomasympathetic reflex6.6. Bainbridge reflexBainbridge reflexAll these are short term regulatory All these are short term regulatory

mechanism and –ve feedback reflexes .mechanism and –ve feedback reflexes .

Baroreceptor reflexBaroreceptor reflex

Baroreceptors are extensively branched, Baroreceptors are extensively branched, knobby, coiled, spray type myelinated nerve knobby, coiled, spray type myelinated nerve endings found in the adventitia layer of the endings found in the adventitia layer of the arterial wall and stimulated by stretch .arterial wall and stimulated by stretch .

Classification :Classification :Functionally grouped as high pressure and low Functionally grouped as high pressure and low

pressure baroreceptors.pressure baroreceptors.Anatomically grouped as arterial and cardiac Anatomically grouped as arterial and cardiac

baroreceptors .baroreceptors .

Functional groupFunctional groupHigh pressure baroreceptor located at –High pressure baroreceptor located at – carotid sinus / aortic arch / wall of left carotid sinus / aortic arch / wall of left ven/ root of rt. subclavian artery/ junction of ven/ root of rt. subclavian artery/ junction of thyroid art. with common carotid artery.thyroid art. with common carotid artery.

Low pres baroreceptors ( cardiopulmonary rec)Low pres baroreceptors ( cardiopulmonary rec) atrial receptors scattered in the wall of atrial receptors scattered in the wall of rt and lt atrium / entrance of veins in both rt and lt atrium / entrance of veins in both atriums / wall of pulmonary trunk and its rt andatriums / wall of pulmonary trunk and its rt andlt division.lt division.

Baroreceptor reflexBaroreceptor reflex

Results of baroreceptor activityResults of baroreceptor activity

Baroreceptor discharge---Baroreceptor discharge---vasodilatationvasodilatation,, venodilatationvenodilatation,,dec.B.Pdec.B.P dec.H.R.&C.Odec.H.R.&C.O.. Depress respirationDepress respiration

Baroreceptor responseBaroreceptor response

Buffer nerve actionBuffer nerve action Responds to changing MAP& pulse Pr.Responds to changing MAP& pulse Pr. Beroreceptor resettingBeroreceptor resetting Respond to pressureRespond to pressure Response to sudden change of postureResponse to sudden change of posture Role on long-term B.P.controlRole on long-term B.P.control

Activation of the baroreceptor at Activation of the baroreceptor at different level of arterial pressuredifferent level of arterial pressure

Typical carotid sinus reflex showing Typical carotid sinus reflex showing arterial pressure change by carotid arterial pressure change by carotid

clampingclamping

Cardiac baroreceptorCardiac baroreceptor

Scattered endocardially,innervated by Xth Scattered endocardially,innervated by Xth Atrial stretch receptors—2 typesAtrial stretch receptors—2 types Type A receptorType A receptor Type B receptorType B receptor Stimulated by volume change,cause Stimulated by volume change,cause vaso-vaso- dilatation,dec.B.P.&inc.H.Rdilatation,dec.B.P.&inc.H.R.. Volume reflexVolume reflex Bainbridge reflex Bainbridge reflex

Ventricular receptorVentricular receptor

Scattered throughout lt.vent.&interventicul-Scattered throughout lt.vent.&interventicul- -lar septum.-lar septum. Discharge irregularly when maximally sti.Discharge irregularly when maximally sti. Impulse travel via vagus.Impulse travel via vagus.Cause hypotension & bradycardia.Cause hypotension & bradycardia.Help to maintain vagal tone at rest.Help to maintain vagal tone at rest.

Bezold –Jarisch reflexBezold –Jarisch reflex Coronary chemoreflex-activation of chemosensitive Coronary chemoreflex-activation of chemosensitive

vagal C fibervagal C fiber in cardio-pul. in cardio-pul. region- cause profound region- cause profound bradycardia,hypobradycardia,hypo-- --tension,apnea& rapid shallow breathingtension,apnea& rapid shallow breathing..*Elicited by capsaicin,serotonin,veratridine&*Elicited by capsaicin,serotonin,veratridine&phenylbiguanide injected to lt.coronary Ar.phenylbiguanide injected to lt.coronary Ar.Pulmonary chemoreflex-similar action.Pulmonary chemoreflex-similar action.*Also found in acute myocardial ischemia&during*Also found in acute myocardial ischemia&duringCoronary angiograpyCoronary angiograpy

Chemoreceptor reflexChemoreceptor reflex

Found in carotid &aortic bodies.Found in carotid &aortic bodies. Highly vascular;sensitive to hypercarbia,Highly vascular;sensitive to hypercarbia, hypoxia & acidosis.hypoxia & acidosis. Signal travel from carotid via IXth& aorticSignal travel from carotid via IXth& aortic via Xth nerve.via Xth nerve. Stimulation result activation of pressor Stimulation result activation of pressor

area of VMC,inspiratory center & area of VMC,inspiratory center & N.ambiguusN.ambiguus

Chemoreceptor reflexChemoreceptor reflex

Chemo -reflexChemo -reflex

N.T.S.

V.M.C. N. Ambiguus Inspiratorycenter

CNS ischaemic responseCNS ischaemic response

BP falls BP falls below 60 mmHgbelow 60 mmHg - flow to VMC - flow to VMC reduced significantly to cause CNS reduced significantly to cause CNS ischaemia - resulting in accumulation of ischaemia - resulting in accumulation of CO2 & Lactic acid locally – which in turn CO2 & Lactic acid locally – which in turn excite the pressor area of VMC - effecting excite the pressor area of VMC - effecting increase in BP.increase in BP.

Powerful of all sympathetic activators .Powerful of all sympathetic activators .LAST DITCH Stand .LAST DITCH Stand .

Cushing ReflexCushing Reflex Harvey Cushing – 1902Harvey Cushing – 1902It results from increase pressure of CSF It results from increase pressure of CSF

around the brain in the cranial vault – around the brain in the cranial vault – resulting in compromising the vascular resulting in compromising the vascular supply to the VMC – initiating CNS supply to the VMC – initiating CNS ischaemic like response to restore blood ischaemic like response to restore blood supply to the vital centers of the brain .supply to the vital centers of the brain .

The resultant increase in BP activates the The resultant increase in BP activates the baroreceptor reflex –baroreceptor reflex – bradycardia bradycardia ..

Somatosympathetic ReflexSomatosympathetic Reflex

Reflex arising from nociceptive stimuli-Reflex arising from nociceptive stimuli- Pressor effect-somatic pain afferentPressor effect-somatic pain afferent Depressor effect-visceral pain afferent Depressor effect-visceral pain afferent

Reflexes mediated by skeletal muscle & Reflexes mediated by skeletal muscle & nerve- nerve-

Abdominal compression reflexAbdominal compression reflex

Applied aspectsApplied aspects

Carotid sinus massageCarotid sinus massage Stokes-Adams syndromeStokes-Adams syndrome Neurogenic hypertentionNeurogenic hypertention Vasovagal syncopeVasovagal syncope Valsalva’s maneuverValsalva’s maneuver Muller’s maneuverMuller’s maneuver