Lecture 5 2/11/25 Flashcards
What are the two main determinants of blood pressure?
-peripheral resistance
-cardiac output
Which factors help to regulate blood pressure?
-baroreceptor reflex
-renin-angiotensin system
-aldosterone
What are the characteristics of the baroreceptor reflex?
-rapid responder
-deals with minute-to-minute changes in BP
-responds to pressure or stretch
Where are the most important baroreceptors located?
-aortic arch
-carotid sinus
What are the characteristics of the renin-angiotensin-aldosterone system (RAAS)?
-long-term regulation
-can have systemic and local effects
When is RAAS activated as a compensatory measure?
in response to a reduction in blood pressure
What can lead to chronic activation of RAAS?
-endothelial dysfunction
-tissue fibrosis
-cellular remodeling
-proteinuria
What are the steps of RAAS?
-hypovolemia triggers the kidneys to produce renin
-renin converts angiotensinogen produced by the liver into angiotensin 1
-angiotensin 1 is converted into angiotensin 2 via ACE-converting enzyme
-angiotensin 2 triggers the adrenal glands to produce aldosterone
-angiotensin 2 also acts as a potent vasoconstrictor at the arteries
-the effects of angiotensin 2 at these sites improves blood volume and pressure
How does angiotensin 2 increase GFR?
angiotensin 2 leads to constriction of the efferent arteriole, which increases glomerular capillary pressure and increases GFR
What is the function of ACE-inhibitors?
to inhibit ACE-converting enzyme and prevent angiotensin 1 converting to angiotensin 2
What is the function of angiotensin receptor blockers?
to inhibit the action of angiotensin 2 on the adrenal glands and the arteries
What are the characteristics of aldosterone?
-mineralocorticoid produced in the zona glomerulosa of the adrenal gland
-stimulated for release by angiotensin 2 and hyperkalemia
What are the effects of aldosterone on the kidneys?
-act on the principal cells
-potassium excretion
-sodium retention
What are the characteristics of hypoadrenocorticism?
-deficiency in glucocorticoid and mineralocorticoid/aldosterone
-leads to increased K+
-leads to decreased Na+
How does hyperaldosteronism impact electrolytes?
-increased Na+
-decreased K+
What considerations must be kept in mind when measuring BP?
-breed
-temperament
-method
-operator skill
-interpatient variability
-conscious vs. anesthetized
-standardized protocol
What is the best setting for a blood pressure reading?
-acclimated to a quiet room
-with the owner
-no sedation
-comfortable restraint
What are the characteristics of BP cuff size?
-want the cuff width to be 30-40% of the circumference of the cuff site
-too narrow/loose overestimates BP
-too wide/tight underestimates BP
Which sites are commonly used when placing a BP cuff?
-limb
-tail base
Where should the cuff be in relation to the heart?
level with the heart base
What are the steps to follow when taking a BP measurement?
-ensure a calm, motionless patient
-discard first reading
-take 5 to 7 measurements and average the readings
What should be included in the record regarding BP measurement?
-cuff size and site
-animal position
-values obtained
-rationale for excluding any values
-final/average result
-interpretation
-person who completed measurements
What is the gold standard for BP measurement?
arterial catheterization, direct method
What are the indirect/non-invasive methods of BP measurement?
-doppler ultrasonic flow detector
-oscillometry
Which BP measurement is most accurate when using a doppler in dogs and cats?
dogs: measures systolic arterial BP
cats: predicts mean arterial BP
What are the pros of the doppler?
-inexpensive
-works for variety of patient sizes
-audible signal
What are the cons of the doppler?
-affected by patient motion
-peripheral vasoconstriction can make it difficult to hear
Which reading is most accurate with oscillometric measurement?
mean arterial BP
What are the pros of oscillometric measurement?
-simple
-easy to use
What are the cons of oscillometric measurement?
-affected by patient motion
-less accurate
What are the different types of hypertension?
“white coat”/situational hypertension
-secondary hypertension
-idiopathic or primary hypertension
What are the characteristics of white coat hypertension?
-consequence of anxiety/stress
-due to catecholamine response
-animal is normotensive in other situations
-no treatment required
What are the characteristics of secondary hypertension?
-persistent, pathologic increase in BP concurrent with disease, drugs, or toxins
-most common cause of pathological hypertension in dogs and cats
-serial BP monitoring should occur
What can cause secondary hypertension to persist despite treatment of the underlying disease?
vascular remodeling
What are some examples of endocrine diseases that can cause secondary hypertension?
-diabetes mellitus
-hyperthyroidism
-hyperadrenocorticism
-hyperaldosteronism
-pheochromocytoma
What are the characteristics of idiopathic/primary hypertension?
-persistent, pathologic hypertension in the absence of an underlying identifiable cause
-must perform extensive rule-out of other causes
-difficult to prove in dogs and cats
-contributing factors include genetics, lifestyle, and environment
Which organs are the target of damage associated with hypertension?
-eyes
-brain
-heart
-kidneys
When should BP measurements be taken?
-patient presents with clinical abnormalities consistent with hypertensive target organ damage
-disease is present that is associated with secondary hypertension
-patient is over 9 years of age; annual wellness screening
What are the systolic blood pressure ranges?
- <140: normotensive, minimal organ damage risk
- 140-159: pre-hypertensive, low organ damage risk
- 160-179: hypertensive, moderate organ damage risk
- 180+: severely hypertensive, high organ damage risk
How often should patients have blood pressure rechecked, based on their initial reading?
- 180+: recheck in 1 to 2 weeks
- 140-179: recheck in 4 to 8 weeks
- 140-159: monitor/recheck in 6 months
What are the goals of hypertension treatment?
-minimize risk of ongoing target organ damage
-gradually reduce BP over the course of multiple weeks
-bring systolic BP to less than 160 mmHg
Which RAAS inhibitor medication options are available for managing high BP?
-ACE-inhibitors like enalapril and benazepril
-ARBs like telmisartan
-aldosterone antagonists like spironolactone (not common)
What are the characteristics of RAAS inhibitors?
-frontline treatment for mild to moderate hypertension in dogs
-weak antihypertensive; reduce by 10-15 mmHg
What are the side effects of RAAS inhibitors?
-GI side effects
-decreased Na
-increased K
-worsening of azotemia
When are RAAS inhibitors contraindicated?
-monotherapy for severe hypertension in dogs
-frontline treatment in cats
-dehydrated patients
-azotemic patients (use caution)
Why is it important to avoid RAAS inhibitors in dehydrated patients?
the drug will cause dilation of the efferent arteriole, which will cause a drop in GFR
What are the characteristics of calcium channel blockers such as amlodipine?
-cause arterial vasodilation and reduce vascular resistance
-frontline therapy in cats
-used in combination with RAAS inhibitors in dogs with severe hypertension
-should NOT be used as monotherapy in dogs
What are the side effects of calcium channel blockers?
-hypotension
-gingival hyperplasia
-peripheral edema
What is the treatment for hypertensive emergencies?
parenteral CRI treatment and 24 hour care; goal is to gradually decrease BP over several hours
