Physiology of hypertension

Question 1

Define hypotension

Answer 1

less than 90/60 mmHg

Question 2

Define normotension

Answer 2

between 90/60 and 129/85 mmHg

Question 3

Define high normotension

Answer 3

between 130/85 and 139/89 mmHg

Question 4

Define stage 1 hypertension

Answer 4

between 140/90 and 159/99 mmHg

Question 5

Define stage 2 hypertension

Answer 5

between 160/100 and 179/119 mmHg

Question 6

Define stage 3 hypertension

Answer 6

greater than 180/120 mmHg

Question 7

Define Pulse Pressure (PP)

Answer 7

the difference between systolic and diastolic blood pressure

Question 8

Define Mean Arterial Blood Pressure (MABP)

Answer 8

the average arterial pressure exerted over the course of a cardiac cycle

Question 9

What formula estimates MABP?

Answer 9

MABP = DP + 1/3(SP-DP)

or

MABP = DP + 1/3(PP)

[MABP is closer to diastolic pressure as diastole lasts twice as long as systole]

Question 10

Describe elastic recoil in the aorta and why this is important

Answer 10

the aorta contains elastic tissue
this allows it to expand during ventricular contraction once the aortic valve opens and blood pressure increases and store energy
once the valve shuts this stored energy be released maintaining the pressure in the aorta and therefore maintaining the flow of blood through the peripheral circulation while the ventricle refills prior to the next contraction and valve reopening
this allows for less turbulent flow and a more constant pressure throughout the circulatory system at all times

Question 11

What formula relates MABP to CO and TPR?

Answer 11

MABP = CO x TPR
[TPR = total peripheral distance, sometimes known as systemic vascular resistance]

CO = HR x SV
therefore:
MABP = HR x SV x TPR

Question 12

What 4 factors affect MABP?

Answer 12

blood volume

cardiac output

resistance of the system to blood flow - arteriole vasoconstriction increases resistance thus increases MABP

relative distribution of blood between arterial and venous blood vessels - venous vasodilation can increase the amount of blood available on the venous side of the circulatory system and thus decrease MABP

Question 13

Where are baroreceptors located?

Answer 13

stretch receptors (baroreceptors) exist in the wall of the arch of the aorta and in the carotid sinus

aorta = terminal end of vagus nerve
carotid sinus = terminal end of glossopharyngeal nerve

Question 14

Describe the baroreceptor reflex

Answer 14

nerve endings (baroreceptors) are used to monitor BP by firing more often when they are stretched as pressure increases

the receptors send info to the CNS (medullary cardiovascular control centre) about MABP

if MABP decreases, the receptors decrease their input and this results in activation of the sympathetic nervous system and inactivation of the parasympathetic nervous system

if MABP increases, the receptors increase their input and this results in activation of the parasympathetic nervous system and inactivation of the sympathetic nervous system

overall effect = regulate MABP by increasing or decreasing HR, SV (and to a lesser extent TPR by constricting or relaxing blood vessels)

Question 15

Describe the low atrial baroreceptor reflex

Answer 15

baroreceptors also found in atrial walls - monitors venous return
the more they are squashed as atrial wall stretches the more they fire and they are used to monitor atrial blood volume and feedback on heart rate
an increase in stretch (ie an increase in venous return) leads to an increase in heart rate (not force of contraction) - Bainbridge effect

Question 16

What stimulates the release of ANP and BNP?

Answer 16

ANP = atrial natriuretic peptide
BNP = brain natriuretic peptide

ANP released due to atrial stretch from increased blood volume
BNP released from ventricular stretch - marker of heart failure

Question 17

Where do natriuretic peptides act and what effect do they have?

Answer 17

act on natriuretic peptide receptors (NPRs) and activation of these receptors leads to a net increase in salt and water excretion (and decrease central sympathetic output) to reduce blood volume and thus pressure

Question 18

Describe the Renin-Angiotensin-Aldosterone system

Answer 18

RAAS is a system for controlling effective circulating blood volume and this is a determinant of MABP

angiotensin 2 is a vasoconstrictor directly and this will increase TPR and MABP directly

hormonal system so not as fast as the neuronal systems of controlling MABP but very important in potential causes of hypertension and pharmacology for it’s management

Question 19

What can cause vasovagal syncope?

Answer 19

exact cause not known
stress can cause cortical override of the autonomic control

Question 20

What does vasovagal syncope result in and how does this occur?

Answer 20

bradycardia, hypotension and apnoea

via overstimulation of the parasympathetic nervous system and decrease sympathetic output causing a sudden fall in MABP and perfusion pressure to the brain

Question 21

What causes the fight or flight response?

Answer 21

increased input to the sympathetic nervous system causing a generalised increase in muscle tone and sensory attention
causes release of noradrenaline and acetylcholine to redistribute blood flow to appropriate tissues
also increases cardiac output (increasing HR and contractile force) and so increases MABP

Question 22

What is primary (essential) hypertension?

Answer 22

no identifiable underlying pathology

Question 23

What is secondary hypertension?

Answer 23

identifiable underlying pathological cause