Hypertension and antihypertensive drugs Flashcards
What is BP?
- Driving force to perfuse organs with blood
- Not uniform throughout body
- Commonly measure and report systolic and diastolic
- Cyclical
- Physiological variable
How do we calculate mean arterial blood pressure?
- Cardiac output x total peripheral resistance
- DBP + ((SBP-DBP)/3)
How is blood pressure regulated by the sympathetic nervous system?
- Decrease in blood pressure
- Increased sympathetic activity
- Activation of B1 adrenoceptors on heart causes increased cardiac output
- Activation of A1 adrenoceptors on smooth muscle causes increased venous return and increased peripheral resistance
- Activation of B1 adrenoceptors on kidney leads to increased renin
How is blood pressure regulated by the kidneys?
- Decreased renal blood flow increases renin production
- Leads to increase in angiotensin II
- Decreased glomerular filtration increases sodium and water retention
- Results in increased aldosterone and increased blood volume
- Increased aldosterone leads to increased angiotensin II
- Angiotensin II causes increased peripheral resistance
How is peripheral resistance changed?
- Smooth muscle tone changes TPR
- Vasoconstriction causes increased peripheral resistance
- Requires increased BP to drive blood through systemic circulation
Outline the pathophysiology of hypertension
- Cause still not completely understood
- Leads to vascular changes including remodelling, thickening, hypertrophy
- Increased vasoactive substances including ET-1, AngII
- Vascular remodelling also occurs as a result of local salt sensitivity
What do hyperinsulinaemia and hyperglycaemia lead to?
- Endothelial dysfunction
- Increased reactive oxygen species
- Nitric oxide signalling reduced
What is the ultimate result of hypertension?
- Permanent medial hypertrophy of vasculature
- Increased TPR
- Decreased compliance of vessels
- End organ damage (renal, peripheral vascular disease, aneurysm, vascular dementia)
- Hypertensive heart disease causes left ventricular hypertrophy and dilated cardiac failure
- Increased morbidity and mortality
How is hypertension defined?
- BP of 140/90 is defined as hypertension
- A reduction in BP (both systolic and diastolic) reduces cardiovascular risk
What are some different causes of hypertension?
- Essential/primary/idiopathic hypertension - 90% of cases
- Secondary hypertension - to other pathology
- Pre hypertension
- Isolated systolic/diastolic hypertension
- White coat/clinic
How can we increase awareness of hypertension?
- Screen those at risk
- Increase public awareness of risk factors
- Appropriate lifestyle changes to limit risk
- Reliable measurements based on clinical guidelines
- Regular monitoring and refinement of medication once initiated
- Hypertension is a silent killer
How is a clinical diagnosis of hypertension made?
- Sitting, relaxed and arm is supported
- Both arms
- If >15 mmHg difference, repeat measurement and use arm with higher reading
- Take measurements over a period of visits
- Can also do ambulatory BP and home BP measurements
- Determine whether emergency treatment is required
- Cardiovascular disease risk and end organ damage need to be assessed
What are some target blood pressures for different categories of patients?
- <140/90 in <80 years old, including type II diabetes
- <150/90 > 80 years old
- <135/85 type 1 diabetes
Outline stage 1 hypertension
- Clinic BP ranging from 140/90 mmHg to 159/99 mmHg
- ABPM/HBPM average reading >135/85 mmHg
Outline stage 2 hypertension
- Clinic BP ranging from 160/100 mmHg to 180/120 mmHg
- ABPM/HBPM average reading >150/95 mmHg
Outline stage 3 hypertension
- Clinic systolic BP of 180 mmHg or higher
- Or clinic diastolic BP of 120 mmHg or higher
How can we prevent prehypertension from developing into hypertension?
- Promotion of regular exercise
- Modified healthy/balanced diet
- Reduction in stress and increased relaxation
- Limited/reduced alcohol intake
- Discourage excessive caffeine consumption
- Smoking cessation
- Reduction in dietary sodium
What is prehypertension defined as?
- > 120/80 but <140/90 mmHg
What are the primary hypertension therapeutic agents?
- Angiotensin converting enzyme inhibitors
- Angiotensin receptor blockers
- Calcium channel blockers
- Diuretics (thiazide and thiazide like)
Where is ACE found?
- Found on luminal surface of capillary endothelial cells
- Predominantly in lungs
What is the function of ACE?
- Catalyses conversion of angiotensin I to potent, active vasoconstrictor
- Angiotensin II
How does angiotensin II exert its effects?
- Angiotensin II affords action through AT1 (and AT2 receptors)
- AT1 receptor typical of classic angiotensin-II actions e.g. vasoconstriction
- Stimulates aldosterone (acts at distal renal tubule)
- Cardiac and vascular muscle cell growth
- Vasopressin (ADH) release from posterior pituitary
How do angiotensin II and aldosterone increase BP?
- Vasoconstriction
- Increasing circulating blood volume
How do ACE inhibitors work?
- Inhibits circulating and tissue ACE
- Causes reduction in angiotensin II activity
- Vasodilation
- Reduced aldosterone release
- Reduced ADH release
- Reduced cell growth and proliferation
- Contribute to antihypertensive effects
Do ACE inhibitors prevent all production of angiotensin II?
- No
- Angiotensin II also produced from angiotensin I independently of ACE via chymases
Give some examples of ACE inhibitors?
- Lisinopril
- Ramipril
What are some adverse side effects of ACE inhibitors?
- Hypotension
- Dry cough
- Hyperkalaemia (lower aldosterone leads to increased [K+])
- Cause or worsen renal failure (especially renal artery stenosis)
- Angioedema
Why do ACE inhibitors cause a dry cough?
- Bradykinin is also a substrate for ACE
- Use of ACE inhibitors prevents breakdown of bradykinin
What are the contraindications of ACEi?
- Renal artery stenosis
- AKD
- Pregnancy
- Idiopathic angioedema
What are the drug interactions of ACEi?
- Increases activity of K+ drugs due to reduced aldosterone
- NSAIDs disrupt renal function through action on efferent arteriole and ion imbalance
- Other antihypertensive agents
Give some examples of angiotensin II and receptor antagonists
- Candesartan
- Losartan