Blood pressure

1. An Introduction to Cardiology
Nikhil Vaishnav, Clinical Coordinator
Department of Paramedical & Health Science

2. Blood Pressure
CHAPTER-10

3. Introduction
Image source : Google
Blood pressure is the force exerted by the blood against the wall of the
blood vessel.
It is expressed in terms of systolic pressure(maximum during one heartbeat)
over diastolic pressure (minimum in between two heartbeats).
It is measured in millimeters of mercury (mmHg).
Systolic blood pressure is defined as maximum pressure exerted in the
arteries during systole of the heart .
Diastolic blood pressure is defined as minimum pressure exerted in the
arteries during the diastole of the heart.
Blood pressure is a vital signs .

4. Blood pressure

5. sphygmomanometer
A sphygmomanometer, also
known as a blood pressure
monitor, or blood pressure gauge,
is a device used to measure blood
pressure.
Mean arterial pressure: an
average blood pressure in arteries
during a single cardiac cycle.
Normal value is 70-100 mmHg.
MAP = SBP + 2 (DBP)
3

6. Image source : Google

8. Categories of blood pressure
Blood pressure category

9. AHA 2017 Blood pressure

10. Factors determining blood pressure
Blood pressure determining
factors
Blood pressure
depends on the
cardiac output and
systemic vascular
resistance (SVR).

11. Cardiac output(CO)
Cardiac output (CO) is the volume of blood being pumped by the heart per
minute.
CO = Heart rate × Stroke volume.
Normal Cardiac output is 5-6 litre per minute.
Stroke volume(SV) is volume of blood pumped from the ventricle per beat.
Normal stroke volume is approx.70 ml blood per minute .

13. Factors affecting stroke
volume

14. Systemic vascular resistance(SVR)
SVR refers to the resistance to blood flow offered by all of the systemic
vasculature, excluding the pulmonary vasculature.
Also referred as total peripheral resistance (TPR) & peripheral vascular
resistance (PVR).
SVR is simply the resistance the heart must overcome in order to pump
blood into the rest of the body.
SVR is determined by changes in blood vessel diameters, changes in
blood viscosity

15. SVR calculation

16. Vasodilation(Blood vessel diameter increases) leads to decreased
SVR.
Vasoconstriction( blood vessel diameter decreased ) leads to
increased SVR.
SVR is used in calculations of blood pressure, blood flow, and
cardiac function

17. Blood vessel diameter and
SVR

18. SVR is decreased directly by
1. Anemia
2. Fever
3. Hyperthyroidism
4. Sepsis
5. Anaphylaxis
6. Anesthetics
SVR is increased by conditions such as
1. Hypothermia
2. Hypovolemia
3. Pheochromocytoma
4. Stress response
5. Syndromes of low cardiac output

19. SHORT TERM BLOOD PRESSURE REGULATORY MECHANISM
Short term mechanism activates within few seconds
It includes sympathetic nervous system (SNS) & Vascular
endothelium.

20. SNS regulation of blood pressure
SNS BP regulation

21. BARORECEPTOR REFLEXES
Baroreceptors are also called as pressoreceptors.
These are specialized nerve cells or sensors located in carotid sinus &
arch of aorta.
They sense the blood pressure and relay the information to vasomotor
centres in medulla of the brainstem.
When BP is low, firing of Baroreceptors inhibited , decreased impulses
sent to the medulla of brainstem.
Then parasympathetic activity is decreased and increased sympathetic
activity leads to increased heart rate , increased cardiac output thus blood
pressure is increased .

22. Baroreceptor Reflexes

23. Baroreceptor reflexes

24. Baroreceptor reflex

27. SNS RECEPTORS

28. CHEMORECEPTOR REFLEXES
Chemoreceptors are chemosensitive cells that respond to change in the
pCo2 and pH levels.
Chemoreceptors are located in the carotid bodies and aortic arch .
These are sensitive to change in arterial carbon dioxide, oxygen and pH
levels .
There are 2 types of chemoreceptor cells.
A. Peripheral chemoreceptor
B. Central chemoreceptor.

29. Peripheral Chemoreceptors are
situated in the aorta and carotid
arteries.
These receptors monitor
changes in blood oxygen and pH
level.
On the basis of the changes in
blood oxygen and pH level, these
receptors mediate immediate
response in breathing , blood
pressure and heart rate
Central Chemoreceptors
trigger responses in
breathing, heart rate and
blood pressure .
This receptors are triggered
by chronic change in the pH
of interstitial fluid of the
brain.
Located in the medulla of
the brain.

30. Chemoreceptor reflex

31. Chemoreceptor reflex

32. Chemoreceptor regulation
of blood pressure

33. CNS ISCHEMIC RESPONSE
It is one of the most powerful activators of the sympathetic vasoconstrictor
system.
It is an emergency arterial pressure control system .
CNS ischemic response is also known as Cushing reflex.
It is stimulated due to cerebral ischemia(MAP below 20 mm of hg ).
There is reduced blood supply to the vasomotor center of the brain. It leads
to accumulation of Co2 and lactic acid.
It leads to strong excitation of the vasomotor center . Vasomotor center
activation causes vasoconstriction and inotropic action.
Eventually arterial blood pressure is increased .

34. CNS ischemic response

35. VASCULAR ENDOTHELIUM
The Vascular endothelium is a single cell layer that lines the blood vessels.
Endothelium causes adhesion and aggregation of neutrophils and stimulate
smooth muscle growth.
Endothelium contains both vasodilator & vasoconstrictor substances .
Endothelium derived relaxing factor(EDRF) or Nitric oxide and prostacyclin
are both vasodilators.
Endothelin(ET) , produced by endothelium is a powerful vasoconstrictor.
There are 3 subclasses of Endothelin: ET-1, ET-2, ET-3. ET-1 causes adhesion
and aggregation of neutrophils and stimulates smooth muscle growth.

36. LONG TERM BLOOD PRESSURE REGULATORY MECHANISM
Long term mechanisms include renal and endocrine system that regulate
arteriolar resistance and blood volume.
It activates within days to week.

37. RENAL SYSTEM REGULATION
Kidneys regulates the blood pressure via
1. ECF volume
2. Renin-angiotensin-aldosterone system(RAAS)
3. Prostaglandins
4. The natriuretic peptides

38. ECF VOLUME
When blood pressure falls, kidney controls sodium excretion. There is
water and sodium retention by kidney.
So ECF volume is increased .
Venous return is increased, lead to increased cardiac output.
Eventually blood pressure is increased.

40. RENIN ANGIOTENSIN SYSTEM(RAS)
Blood pressure and fluid balance in the body is regulated by renin-angiotensin
system(RAS).
When blood volume or sodium levels in the body are low , kidney cells release
the enzyme, renin.
Renin converts Angiotensinogen, which is produced in the liver, to the hormone
angiotensin I.
An enzyme ACE or angiotensin-converting enzyme found in the lungs converts
angiotensin I into angiotensin II.

41. Angiotensin II causes blood vessels to constrict and blood pressure to increase
Angiotensin II stimulates the release of the hormone aldosterone in the
adrenal glands.
Aldosterone causes the renal tubules to retain sodium and water and excrete
potassium.
Angiotensin II and aldosterone increases blood volume, blood pressure and
sodium levels in the blood .

42. RENIN ANGIOTENISN
SYSTEM

43. RENIN ANGIOTENISN
SYSTEM

44. RENIN ANGIOTENISN
SYSTEM

45. PROSTAGLANDINS
Prostaglandins (PGE2 & PGI2) secreted by the renal medulla
Prostaglandins have a vasodilator effect on the systemic circulation.
So Prostaglandin causes decreased SVR and lower BP.

46. NATRIURETIC PEPTIDES
Atrial natriuretic peptide(ANP) & b-type natriuretic peptide(BNP) are
secreted by heart cell.
These antagonize the effects of ADH & aldosterone.
It results in natriuresis(excretion of sodium in urine ) & Diuresis.
There is reduced blood volume and reduced BP

47. ENDOCRINE SYSTEM REGULATION
Endocrine system regulates the blood pressure via:
A. Epinephrine
B. Aldosterone
C. Antidiuretic hormone

48. EPINEPHRINE
When there is decreased blood pressure, sympathetic nervous
system is activated via baroreceptor or chemoreceptor.
SNS stimulation leads to epinephrine release.
Epinephrine Increases heart rate & myocardial contractility .
Increased heart rate increases cardiac output.
Thus blood pressure is maintained in the body .

49. ALDOSTERONE
Aldosterone hormone is released by adrenal cortex in response to
Angiotensin II.
Aldosterone stimulate the kidney to retain sodium and water . Thus Blood
volume increased .
Cardiac output is increased .
Blood pressure is increased.

52. ANTIDIURETIC HORMONE(ADH)
When blood pressure is low , ADH is released from the posterior Pituitary
gland.
There is Reabsorption of water in distal & collecting tubules in kidneys.
ECF volume increased .
Blood volume & CO increased Thus blood pressure increased .

53. ADH BP regulation

54. ADH BP regulation

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