Expansion
Raised cardiac output early, raised systemic vascular resistance later
Expansion
Since MAP = cardiac output x systemic vascular resistance, hypertension must involve one or both.
Early: cardiac output is often mildly raised, with normal resistance.
Established: output returns to normal but resistance is raised, through arteriolar vasoconstriction and structural remodelling with a thickened wall and narrowed lumen.
Contributing mechanisms:
- Sympathetic overactivity
- Renin-angiotensin-aldosterone activation
- Sodium retention and a resetting of the renal pressure natriuresis relationship, so a higher pressure is needed to excrete the same sodium load
- Endothelial dysfunction with reduced nitric oxide
- Arterial stiffening, especially in older patients, giving isolated systolic hypertension
The baroreceptors reset to defend the higher pressure, which is why they do not correct it.
Drug classes map onto the mechanisms: ACE inhibitors and angiotensin receptor blockers, calcium channel blockers for resistance, thiazides for sodium and volume, and beta blockers for output and renin.