Hypertension

Epidemiology of HTN

Prevalence depends on criteria used; in U.S. 25.3% have diastolic BP > 90 mmHg, 14.5% > 95 mmHg

worldwide prevalence is 15%, U.S.A prevalence is 25%

BP varies throughout the day (high in the a.m., rising to mid-afternoon peak, falls to nadir when asleep at night)

90% of HTN is primary (Essential)

10% of HTN is secondary

60% of secondary is due to Renal Parechymal disease, 30% due to Renovascular disease, and 10% due to endocrine causes.

Risk Factors for HTN

AA > whites, old > young, obese > lean, Ý Na⁺ intake > ß Na⁺intake, (+) Family H_x > (-) Family H_x

Salt and HTN

Multiple studies have shown that dietary salt intake is important in the pathogenesis of essential HTN.

"Salt Sensitive Essential Hypertension" 50-60% of patients respond to ß NaCl intake (AA’s even more so)

Consequences of Hypertension

Ý risk of Coronary Artery Disease, CHF, Atherothrombotic Brain Infarction (the Ý risk µ Ý BP, therefore higher BP = higher risk)

Ý risk of MORTALITY from both stroke and coronary artery disease with Ý diastolic BP

HTN affects arterioles in the kidney causing Medial fibromuscular proliferation and Hyaline arteriolar sclerosis

30-40% of HTN patients have Left Ventricular Hypertrophy (LVH) demonstrable on echocardiography

HTN is additive with cigarettes and cholesterol as risk factors for stroke and myocardial infarction.

Hemodynamics of HTN

normal BP = normal CO x normal TPR, Ý BP = normal CO x Ý TPR, TPR sustains the Ý BP in the HTN patient

Factors that regulate BP

Affect TPR:

Affect CO:

Kidney – transplantation evidence suggests that the kidney plays a central role in the development and maintenance of HTN

animals engineered with HTN can be "cured" if their kidneys are switched with a normal animal (the normal animal gets HTN)
HTN humans who have had their kidneys removed and then got a transplant no longer had HTN

Guyton's Autoregulation Theory of Essential Hypertension: (or Why is CO normal in HTN?)

The Ý in renal vascular resistance occurs in the efferent arterioles because Renal Plasma Flow is ß but GFR remains normal. The Ý in efferent constriction Þ Ý Filtration Fraction Þ Na and H₂O retention Þ EC volume expansion.

Renal Salt Retention Þ Extracellular Volume Expansion Þ Increased CO Þ Increased Peripheral Blood Flow Þ Ý TPR That Returns Peripheral Blood Flow to Normal (i.e. Autoregulation) Þ ß CO Þ Ý BP = normal CO x Ý TPR