Kidney parenchymal hypertension

1. What is the epidemiology of hypertension?

Hypertension remains a common disease among Americans. Data from the National Health and Nutrition Examination Survey reveal that 29% of Americans are hypertensive; this prevalence rate has remained stable for the past 15 years. African Americans bear the highest burden, as over 41% are hypertensive. Other racial groups (i.e. Whites, Asians, and Hispanics) demonstrate hypertension prevalence of 25% to 28%. During this time period, blood pressure (BP) control has improved, largely through the increased use of angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARB), and thiazide-type diuretics in single-pill or multiple-pill combinations. In 2001 to 2002, only 45% of treated hypertensive patients achieved control, defined as BPs <140/90 mm Hg (or <130/80 mm Hg for diabetic patients or chronic kidney disease [CKD] patients [patients with estimated glomerular filtration rates (GFR) <60 mL/min per 1.73 m ² or urinary albumin concentrations >200 mg/g creatinine]). By 2009 to 2010, 60% of treated hypertensive patients had achieved control. However, BP control remains difficult for African Americans, Hispanics, patients with diabetes, and CKD patients. Compared to Caucasians, African Americans and Hispanics are 1.4- and 1.3-fold less likely to achieve control. Again, the greater use of thiazide-type diuretics improves BP control for African Americans. Nearly 70% of treated hypertensive patients without significant comorbidities achieved control by 2009 to 2010, though only approximately 45% of patients with either diabetes mellitus or CKD achieved control.

Obesity complicates hypertension treatment. A cross-sectional study of German hypertensive patients showed that obese patients (i.e., patients with body mass indices ≥30 kg/m ² ) are 1.4- to 2-fold less likely to achieve BP control, compared to normal weight hypertensive patients. While

• 12% of Americans are currently diabetic

  • by 2050, diabetic prevalence may increase to more than 25%

• 36.5% of Americans are currently obese

  • by 2030, 41% may be obese, and 11% may be severely obese

• 15% of Americans suffer from CKD

  • by 2030, the prevalence of CKD in adults over the age of 30 may be close to 50%

Recent epidemiologic studies confirm the association of albuminuria and poor BP control in patients with CKD. In a study of 232 US veterans with CKD, proteinuria, not estimated GFR, was found to be an independent predictor of systolic BP. Among the independent predictors of hypertension (age, race, and number of antihypertensive medications), proteinuria most strongly correlated with hypertension. Compared to estimated GFR, albuminuria (or proteinuria) is a stronger determinant of hypertension; albuminuria is also a stronger determinant of poor BP control.

2. What is the cardiovascular disease risk?

The World Health Organization estimates that hypertension is directly responsible for 13% of all deaths worldwide, and its effect is largely independent of a country’s underlying wealth. The Center for Disease Control and Prevention determined that hypertension-related deaths for Americans 45 years of age and older (i.e., hypertension was listed as a cause of death on death certificates) increased 62% between 2000 and 2013, though, as a primary cause of death, hypertension remained stable during this time period (17.5% of all deaths). The Prospective Studies Collaboration, a meta-analysis of 1 million patients, showed that cardiovascular mortality risk began with BPs as low as 115/75 mm Hg, and, for patients 40 to 69 years old, each 20/10 mm Hg increase in BP increased cardiovascular mortality 2-fold.

Whether a J-curve—the point at which low BPs treated within the physiologic range increase cardiovascular risk—exists, is controversial. This is of interest, as the coronary arteries receive significant perfusion during diastole; low diastolic BPs may predispose patients to adverse outcomes. The Prospective Studies Collaboration did not note a J-curve, though older studies have, especially in hypertensive patients with underlying cardiovascular disease who achieve diastolic BPs <85 to 90 mmHg.

CKD imparts increased cardiovascular risk as well. A large meta-analysis of nearly 267,000 patients with diabetes mellitus, hypertension, or cardiovascular disease showed that both low estimated GFRs and albuminuria independently increased all-cause and cardiovascular mortality. Compared to patients with an estimated GFR of 95, cardiovascular mortality risk increased 73% in patients with an estimated GFR of 45, and increased 208% in patients with an estimated GFR of 15. Patients with albumin-to-creatinine ratios of 10, 30, and 300 mg/g experienced a 13%, 55%, and 159% increase in cardiovascular mortality risk, compared to patients with an albumin-to-creatinine ratio of 5 mg/g.