Blood pressure and its control Flashcards Preview

PH1124 > Blood pressure and its control > Flashcards

Flashcards in Blood pressure and its control Deck (22):
1

Blood pressure measurement

MAP = (P systolic - P diastolic)/3 + P diastolic

MAP is a time weighted average of blood pressure

2

What causes Korotkoff sounds?

Laminar flow if efficient
Turbulence occurs when blood velocity too high for diameter of vessel e.g. atherosclerotic plaque
Turbulent flow is inefficient
Generates noise

3

Reasons for variability of blood pressure

Age
Time of day
Gender
White coat syndrome
Fitness
Body weight

4

Physical factors affecting MAP

Flow from the heart
Resistance to flow
Pressure in the veins
Therefore MAP= CO x TPR

5

Influence of cardiac output on MAP

Increased flow rate through a vessel of fixed diameter increases pressure

6

Influence of resistance on MAP

Resistance to flow = viscosity x length / r^4
Radius of a blood vessel is the main determinant of flow/ resistance to flow

7

Short term control of blood pressure

Reflex control regulated by the autonomic nervous system
Heart rate (chronotropy)
Force of contraction (inotropy)
Contraction/ relaxation of blood vessels

8

Longer term control of blood pressure

Endocrine control of fluid balance
Increased/decreased diuresis
Increased/decreased thirst

9

Arterial baroreceptors

Pressure sensitive receptors that respond to stretch
Stretch increases the frequency of firing
Static sensitivity: respond to change in pressure
Dynamic sensitivity: respond to change in pressure

10

Baroreceptor sensitivity- central resetting

Exercise- work sensors in skeletal muscle cause resetting of baroreflex to a higher pressure, allows pressure to rise without impairing mechanisms of increase cardiac output

11

Baroreceptor sensitivity- peripheral resetting

Threshold for baroreceptors resets to higher pressure after a few days, ensures best sensitivity to changes in BP, downside is unreliable information about BP

12

Baroreceptor sensitivity- structural changes

If arterial walls become less compliant intraluminal pressure causes less stretch therefore baroreceptors are not as stretchy anymore
Causes: old age, hypertension

13

Other types of sensor involved in control

Myelinated veno-atrial mechanoreceptors- sense central blood volume, cause reflex tachycardia and diuresis, redistribution of blood from veins
Non-myelinated mechanoreceptrs- activity weak unless heart distended, reflex is bradycardia and peripheral vasodilation
Coronary artery baroreceptors- function like arterial baroreceptors
Chemosensors- respond to ischaemic metabolites, produce sympathetic activation and rise in BP

14

Responses to hypotension

Acute hypotension leads to decreased baroreceptor traffic, CNS control in the medulla/hypothalamus decrease PNS and increase SNS
Vasoconstriction, venoconstriction, increased force of contraction and increased heart rate

15

Long term control of BP- regulation of plasma volume

Renin angiotensin system
Atrial natriuretic peptide
Vasopressin (increases blood volume)
Thirst

16

Vasopressin

Release controlled by osmoreceptors and baroreceptors
Stimulated by increase in osmolarity and fall in BP
Reduces water excretion from the kidneys
SUpports blood pressure during hypovolaemia

17

Atrial natriuretic peptide (ANP)

Secreted from atria in response to stretch
Increases renal salt and water excretion
Causes a shift from plasma to interstitial compartment

18

Thirst

Osmosis out of cells into the circulation stimulated thirst
Increased water intake increases blood volume

19

Specific clinical example- shock

Definition- pathologic failure of tissue perfusion
Causes: hypovolemic shock, septic shock, cardiogenic shock, anaphylactic shock
Symptoms: pale, cold and sweaty skin, pulse rapid and weak, pulse pressure reduced, breathing rapid and shallow, urine output reduced, mental confusion/loss of consciousness

20

Hypovolemic shock

0-20%: no change in MAP, no need for clinical intervention
20-30%: possible fall in MAP, treatment required
30-40%: 50-70mmHg fall in MAP, severe possible non-recoverable

21

Physiological compensation for shock (short term)

Sympathetic nervous activation
Peripheral vasoconstriction, venoconstriction, bradycardia
Increase in vascular resistance, increase in circulating volume, increase in cardiac output
All leads to increased blood pressure

22

Physiological compensation for shock (long term)

Increase in blood volume by increasing angiotensin/aldosterone, increasing ADH, decreasing ANP, increasing thirst, increasing erythropoetin