Control Of Bood Pressure & Hypertension Flashcards
What is the function of the arterial baroreceptor reflex? Where are the sensing sites?
Detect the mean arterial pressure
Sensing sites in aortic arch and carotid sinus
What kind of sensing site receptors are in the aortic arch and carotid sinus?
Stretch receptors
Walls of aortic arch and carotid sinus are able to stretch - the more they are stretch the higher the firing rate
Which nerves travel to the brain from the aortic arch and carotid sinus baroreceptors? Where do they lead?
Nerves:
Aortic via vagus nerve
Carotid via glossopharyngeal nerve
Lead to: medullary cardiovascular centres (able to correct the MAP by mechanisms previously covered)
What other inputs go to medullary cardiovascular centres?
ALL ARE FEEDBACK RESPONSE
Most important is the arterial baroreceptors
Other inputs:
cardiopulmonary baroreceptors (blood volume)
central chemoreceptors (arterial PCO2 and PO2 - respiratory drive and oxygen distribution)
chemoreceptors in muscle (metabolite concentrations)
joint receptors (joint movement)
What is the Valsalva manoeuvre?
Forced expiration against a closed glottis (trying to breathe out without letting the air out e.g. while doing a poo it increases pressure in thorax and abdomen aiding defication)
How does the Valsalva manouvre impact the cardiovascular system?
Increased thoracic pressure —> reduces filling pressure from the veins —> reduces venous return, reduces EDV, reduced SV, reduces CO, reduces MAP
Essentially blood builds up in the veins
What happens after performing valsalva manouvre?
During Valsalva manoeuvre blood builds up in the veins
After manoeuvre this floods back into heart
Venous return is restored so massive increase in SV (as preload on heart improved)
Due to massive SV baroreflex reduces heart rate and blood pressure
How does the kidney regulate plasma volume?
By making the collecting duct very permeable to water will result in lots of water reabsorption, little urine, therefore conserve plasma volume
Making collecting duct very impermeable to water will result in little reabsorption, lots of urine (diuresis), and a reduction of plasma volume
Which 3 hormone systems control plasma volume?
Renin-angiotensin-aldosterone system Antidiuretic factor (ADH, vasopressin) Atrial natriuretic peptide & brain natriuretic peptide
Where is renin produced?
Juxtaglomerular (granule cells) of the kidney
What triggers renin production (3)?
Trigger = low MAP indicated by:
Activation of sympathetic nerves to the juxtaglomerular apparatus
Decreased distension of different arterioles (renal baroreflex)
Decreased delivery of Na+/Cl- through tubule
What is the effect of Renin?
Renin converts inactive angiotensinogen —> angiotensin 1 —> angiotensin 2 by angiotensin converting enzyme (ACE)
What are the effects of angiotensin 2?
Increasing MAP by:
- increase release of ADH from pituitary (increases water permeability of collecting duct = increasing plasma volume) + increases thirst
- vasoconstriction (increases total peripheral resistance)
Where is Antidiuretic factor (ADH, vasopressin) produced and released?
Synthesised in hypothalamus
Released from posterior pituitary
What triggers production of ADH?
Low plasma volume and/or MAP, indicated by:
Decreased blood volume
Increase in osmolarity of interstitial fluid
Circulating angiotensin 2
What does ADH do (2)?
Increases MAP by:
Increasing permeability of collecting duct to H2O (increase plasma volume) Causes vasoconstriction (increasing MAP)
Where is atrial natriuretic peptide & brain natriuretic peptide produced?
Produced and released from myocardial cells in the atria and ventricles
What triggers Atrial natriuretic peptide & brain natriuretic peptide?
Increased distension of the atria and ventricles
What does Atrial natriuretic peptide & brain natriuretic peptide do?
Decreases MAP by:
Increasing exertion of Na+
Inhibit release of renin
Act on medullary CV centres to reduce MAP
What is hypertension?
High blood pressure
What are the NICE/BHS values for hypertension
140/90mmHg
What is the blood pressure values for stage 1 hypertension? (Clinical & ABPM)
Clinic blood pressure = 140/90mmHg or higher
ABPM daytime average = 135/85 or higher
What is the blood pressure values for stage 2 hypertension?
Clinic blood pressure = 160/100mmHg or higher
ABPM daytime average = 150/95mmHg or higher
What is the risk factors of hypertension (13)?
Smoking Diabetes Mellitus Renal disease Male sex Hyperlipidaemia Previous MI/stroke Left ventricular hypertrophy Age (decreased arterial compliance) Salt intake Alcohol intake High BMI Stress Low birthweight African population (salt retainers)
What is primary and secondary hypertension? What percentage of cases are primary vs secondary?
Primary hypertension = no cause found (80-90%)
Secondary hypertension = cause found (10-20%)
How is blood pressure controlled (2)?
Sympathetic nervous system:
- vasoconstriction (peripheral resistance)
- reflex tachycardia (increased cardiac output)
- increase SV (increased cardiac output)
Renin-angiotensin-aldosterone system:
- maintenance of sodium balance
- control of blood volume
- control of blood pressure
Why do we treat hypertension?
Number 1 medical cause of death worldwide
Reduce cerebrovascular disease by 40-50%
Reduce MI by 16-30%
Why do we treat hypertension during pregnancy?
Hypertension during pregnancy is the 2nd most common cause of maternal and fetal death - complicates up to 10% of pregnancies
What types of hypertension occur during pregnancy (3)?
Chronic hypertension- present before patient became pregnant (30% will develop preeclampsia)
Gestational pregnancy - hypertension which occurs during pregnancy (increased protein in urine - kidney damage)
Preeclampsia- hypertensive emergency (BP>140/90mmHg and poteinuria > 300mg/24hr)
How is hypertension treated during pregnancy?
Many medications are teratogenic or fetotoxic
Pre-pregnancy planning is essential for treatment of chronic hypertension
- NOT ACE or ARB
If gestational: Nifedipine modified-release, methyl dopa, labetalol, atenolol
Preeclampsia: same as gestational PLUS intravenous: labetalol OR hydralazine OR esmolol
What are the categories for a hypertensive emergency?
BP >180/120mmHg
Evidence of acute target organ failure
What is the protocol for a hypertensive emergency?
Hospital admission for BP reduction
Aim to lower systolic BP by 10-20% in 1st hour then to 160/100mmHg over next 6hrs (in everyone except acute ischaemic stroke and aortic dissection) —> aggressive & rapid lowering of BP associated with increased morbidity and mortality
Start oral medication as soon as target BP achieved & ween of IV medications over 12-24hrs
What is the ONLY indication for rapidly lowering BP in hypertensive emergency?
Ischaemic stroke - BP>185/110mmHg who are eligible for/or received thrombolysis within previous 24hrs OR BP>220/120mmHg in those not eligible for thrombolysis
Aortic dissection - systolic BP should be lowered rapidly to target of 100-120mmHg systolic
What is hypertensive urgency?
Severely elevated BP with no evidence of acute organ damage
What is the protocol for hypertensive urgency?
Patient doesn’t need admitted and can be started on dual oral therapy and assessed after 24hrs
What is orthostatic hypotension? What are symptoms?
Low blood pressure when you stand up from sitting or lying down
Blood pressure decrease of 20mmHg systolic and/or 10mmHg diastolic drop within 3mins of standing
Symptoms: dizzy and light headed - may cause fainting (syncope)
What are the risks of orthostatic hypotension?
Syncope along with danger of falling and risk of fractures (detrimental QOL)
Increased cardiovascular risk
Heart failure and atrial fibrillation
Increased prevalence of stroke and coronary artery disease
What are the causes of orthostatic hypotension (5)?
Ageing Diabetes Antihypertensive drugs Auto-immune systemic diseases Neurological syndromes
Treatments of orthostatic hypotension
Movements which mobilise volume from lower parts of the body or stimulate pressure receptors leading to vasoconstriction
Tilt bed so patient has head up
Cold glass of weather before bed
Lack of evidence supporting preventative drugs
