Feline systemic hypertension Flashcards
What are the parameters implicated in blood pressure
Blood pressure is determined by total peripheral resistance and cardiac output
- cardiac output is the product of stroke volume and heart rate
Explain how blood pressure is controlled
Blood pressure is under the control of the central nervous system
- which receives feedback from sensory receptors located within the peripheral vasculature (e.g., baroreceptors)
Baroreceptors are locating within the walls of the carotid sinus and aortic arch
- they respond to stretch within these vessels
- they facilitate short term blood pressure control, allowing for rapid adjustments
Blood pressure is also influenced by systemically circulating hormones (e.g., renin-angiotensin-aldosterone system) and locally derived vasoconstrictor and vasodilatory metabolites
Explain how systemic hypertension can lead to progressive kidney disease
Within kidneys, autoregulation maintains blood flow and glomerular filtration rate over a range of systemic pressures
- hypertension may override this autoregulatory mechanism, leading to glomerular hypertension and the development of glomerulosclerosis
Glomerular hypertension can cause damage to the permselective nature of the glomerular filtration barrier and increased transfer of protein from the glomerular capillaries to the filtrate entering the proximal tubule
- increased absorption of protein by the proximal tubular cells may stimulate the production of inflammatory mediators and cytokines, exacerbating interstitial nephritis and contributing to progressive kidney disease
What are the effects of angiotensin II
Vasoconstriction, resulting in increased total peripheral resistance
Increased cardiac output
Vascular remodeling and increased vascular stiffening
Increased aldosterone
Stimulation of central nervous system activity
What kind of feline patients required blood pressure testing
Cats with evidence of target organ damage
- ocular signs (e.g., retinal hemorrhage, retinal detachment, subretinal edema or hyphema)
- intracranial neurologic signs (e.g., obtundation, focal facial seizures, photophobia)
- auscultable cardiac abnormalities (e.g., gallop rhythms, systolic heart murmurs)
Cats with known or suspected chronic renal disease, hyperthyroidism, adrenal abnormalities, including cats treated for hyperthyroidism within the past 6 months
Middle-aged to older cats as a routine screening measure
How is the cuff size chosen to do a BP measure
Irrespective of whether Doppler or oscillometric methods are used, the limb or tail circumference should be measured and a cuff with a width approximately 40% of the circumference should be chosen for measurement
What are the key facts for amlodipine
Amlodipine besylate is
- a dihydropyridine calcium-channel blocking agent
- is a safe and effective therapy for HTA in cats
- decreases SBP by an average of 30-50 mm Hg
- it also decreases the degree of proteinuria (a clinical parameter that has been linked with survival)
Dose:
- starting dose: 0.125 mg/kg/24h
- up to 0.25 mg/kg/24h
Explain the classification of hypertension based on risk of target organ damage
Normotensive
- < 140 mmHg
- minimal
Prehypertensive
- 140-159 mmHg
- low
Hypertensive
- 160-179 mmHg
- moderate
Severely hypertensive
- > 180 mmHg
- high
Explain the mechanism of action of RAAS
Decreased arterial pressure, decreased renal tubular sodium:chloride ratio, and activation of the sympathetic nervous system leads to renin secretion, transforming angiotensinogen into angiotensin I and then, via the ACE, transformation of angiotensin I to angiotension II
Angiotensin II stimulates the adrenal cortex to secrete aldosterone
What are the effect of aldosterone
Myocardial remodeling
Glomerular sclerosis
Tubular atrophy
Arteriosclerosis
Interstitial fibrosis
How is blood volume regulated
Blood volume is regulated by the kidneys, mainly through pressure natriuresis and the RAAS
Pressure natriuresis couples water and sodium excretion in response to changes in blood volume and cardiac output
RAAS directly affects the systemic vascular resistance (mainly arteriolar size) via the potent vasoconstrictor angiotensin II, and affects blood volume through renal reabsorption of sodium and water via aldosterone
What are the main causes for secondary hypertension
CKD
HYPERTHYROIDISM
Primary hyperaldosteronism
Hyperadrenocorticism
Phaeochromocytoma
Secondary hypertension is the most common form of hypertension seen in cats
