18. ACTION POTENTIAL
• Fast-response action potentials
– His-Purkinje system
– Atrial or ventricular cardiomyocytes
• Slow-response action potentials
– SA and AV nodes.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28. Cardiac work
• Stroke work output of the heart
– Amount of energy that the heart converts to
work during each heartbeat while pumping
blood into the arteries.
• Minute work output
– Total amount of energy converted to work in
1 minute
– stroke work output × heart rate.
29. Types of Cardiac Work
• Volume-pressure work or External work
– Used to move the blood from the low-
pressure veins to the high-pressure arteries.
• Kinetic energy of blood flow or Internal
work
– used to accelerate the blood to its velocity
of ejection through the aortic and pulmonary
valves.
31. EFFICIENCY OF CARDIAC
CONTRACTION
• The ratio of work output to total chemical
energy expenditure.
• Maximum efficiency of the normal heart
is between 20 and 25 %
• In heart failure, it can be 5 – 10%
32.
33.
34.
35.
36.
37. CARDIAC OUTPUT
●Co is a quantity of blood pumped into
the aorta each minute by the heart
Normal value is 5-6 lit/min
CO =HR*SV
39. 1)VENOUS RETURN
• CO IS DIRECTLY PROPOTIONAL TO
VENOUS RETURNS.
FACTORS AFFECTING VENOUS RETURN
●Respiratory pump
●Muscle pump
●Gravity
●Venous presser
40. 2)Force of contraction
●PERLOAD
It is stretching of cardiac muscles fiber at
the end of diastole just before contraction.
it is depend upon venous return &
ventricles filling.
it is directly propotional to co.
●AFTERLOAD
It is the force against which the ventricle
must contract &eject the blood.
it is invesely propotional to CO
42. Heart Rate
• Most variable determinant
• Controlled by multiple systems
– cardiac conduction system
– central nervous system
– autonomic nervous system
– pharmacologic controls
43. Effect of increasing HR on cardiac
function
• Shortening of systole
• Shortening of diastole
– Decreased myocardial perfusion time
– Decreased ventricular filling
– Rate dependent change in SV
• Rate dependent change in cardiac output
• Rate dependent positive inotropic effect
44. Blood pressure
• Arterial blood pressure is defined as the
lateral pressure exerted by the contained
column of blood in the wall of arteries.
• REGULATION OF BP
1)NERVOUS MECHANISM
by baroreceptor
chemoreceptor
2)RENAL MECHANISM
by renin angiotensin mechanism
45. 3)Hormonal mechanism
● HORMONS WILL INCREASING BP
ADRENALINE
NORADRENALINE
THYROXINE
ALDOSTERONE
ANGIOTENSIN
SEROTONIN
●HORMONS WILL DECREASING BP
BRADYKININ
HISTAMIN
ACETYLCHOLINE
PROSTAGLANDIN
49. Baroreceptor 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.
51. 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.
52.
53. 4)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.
54. 5)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
55. 6)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.
56. 7) Cushing Reflex
Cerebral ischemia at the medullary vasomotor
center
↓
Activation of the sympathetic nervous system
↓
↑ HR, BP, and myocardial contractility
↓
Improve cerebral perfusion
• As a result of the high vascular tone, reflex
bradycardia mediated by baroreceptors will
ensue.
57. 8) Oculocardiac Reflex
Stretch receptors
↓
Short and long ciliary nerves
↓
Ophthalmic division of the trigeminal nerve
↓
Gasserian ganglion
↓
Increased parasympathetic tone
↓
Bradycardia.
• Incidence during ophthalmic surgery-
30% to 90%.
58. references
• Essentials of medical physiology : K.
Sembuligam 5 edi
• Textbook of medical physiology : Guyton &
hall
• Textbook of physiology : A.K.Jain
• Review of medical physiology : William F.
Ganong 22 edi
• Internet
