Secondary Studies

Hypertension can sometimes be related to problems with the thyroid. High blood pressure can result from hypothyroidism, when the thyroid gland doesn’t produce enough thyroid hormone, or hyperthyroidism, when it produces too much thyroid hormone. The thyroid-stimulating hormone, or TSH, test can be done to determine if a thyroid problem might be causing hypertension.

A TSH test measures the amount of thyroid-stimulating hormone in your blood. Normal values of TSH range from 0.4 to 4.0 milli-international units per liter (mIU/L). Hypothyroidism causes a higher-than-normal TSH level, while hyperthyroidism causes a lower-than-normal TSH level.

There is a growing body of evidence suggesting that sleep apnea can cause high blood pressure. Sleep apnea is a disorder that causes your breathing to stop or become very shallow while you’re sleeping. Pauses in breathing can last from a few seconds to minutes, and can occur 30 times or more in an hour. People with sleep apnea often snore loudly. Sleep apnea is diagnosed based on medical and family history, a physical exam, and sleep study results.

A sleep study conducted by a sleep specialist, called nocturnal polysomnography, monitors heart, lung, and brain activity, as well as breathing patterns, arm and leg movements, and blood oxygen levels while you sleep. Your provider may ask you to do home sleep tests with a portable monitoring device, which will measure your heart rate, blood oxygen level, airflow, and breathing patterns.

The most common treatment for sleep apnea is a machine called CPAP, which stands for Continuous Positive Airway Pressure. CPAP delivers air pressure through a mask placed over your nose while you sleep. The air pressure keeps upper airway passages open so that you can breathe normally.

A very rare cause of high blood pressure is a tumor of the adrenal gland called a pheochromocytoma. Patients with this tumor experience high blood pressure that comes and goes, and symptoms that include dizziness, sweating, and heart palpatations. These patients may also experience a sudden loss of weight. All of these symptoms are due to the abnormal release of the hormone epinephrine from the adrenal gland. Removal of the tumor usually relieves all of the symptoms, including the hypertension.

The way to detect the tumor is to look for the excess hormone or its byproducts. Because secretion of the hormone may not be constant, the best way to look for it is using a 24-hour urine collection. If at any time during those 24 hours there has been an excess secretion of epinephrine, it is excreted through the kidneys in the form called metanephrine. Testing for this substance in the urine results in an elevated level if a pheochromocytoma is present.

Overproduction of cortisol by the adrenal glands can result in hypertension, along with many other signs and symptoms, including changes in the distribution of fat and hair, and changes in your skin. Collectively, these changes are called Cushing syndrome, and can be caused by anything that makes the adrenal glands produce more cortisol.

To diagnose Cushing syndrome, the first step is to measure cortisol levels. There are a variety of approaches to this diagnosis, but two of the most frequently used tests are the measurement of cortisol levels in urine, and the dexamethasone suppression test. Since excess cortisol is excreted in the urine, elevated levels over a 24-hour period give an indication that Cushing syndrome may be the cause of the hypertension.

A more specific test is the dexamethasone suppression test. In a normal situation, dexamethasone suppresses cortisol production by the adrenal glands. To do the test, the patient is given a dose of dexamethasone at bedtime. In the morning, blood is drawn to determine the plasma cortisol level. In the absence of Cushing syndrome, the plasma cortisol is suppressed below a certain level. If Cushing syndrome is present, no suppression is seen. This test can be administered in a variety of ways that help determine why the adrenal glands are producing too much cortisol.

Because the kidney continuously filters your blood, it is strategically placed to detect changes in blood pressure. If the kidney senses a decrease in blood pressure and/or blood volume, it responds by secreting powerful substances to increase the pressure.

Renin is one of these substances and by acting on other proteins in the body, it results in constriction of the blood vessels, which increases the pressure inside them. If the blood vessels leading to the kidneys are blocked or narrowed, less blood reaches the kidney. The kidney then “thinks” that there is less blood and less pressure than is needed for the body to survive. As a result, renin is secreted and blood pressure rises, even though there is no loss of blood volume.

There are several tests available to diagnose renovascular hypertension. They can be grouped into two main types:

• Anatomic imaging, and
• Physiologic measurement

Anatomic imaging tests are most commonly used. They include Doppler ultrasound, magnetic resonance imaging studies, or MRI, and angiography, which includes the injection of dye directly into the renal arteries so that they show up clearly on X-ray.

Ultrasound uses sound waves to image your kidneys and measure the speed of blood flowing through the renal arteries. An abnormal blood flow rate is usually seen if a significant obstruction exists.

MRI studies allow your provider to visualize blood flowing through the renal arteries in a different way. This test produces the best images of these vessels; however, not all people are good candidates for an MRI. If you have any metallic device implanted, like a pacemaker or an artificial joint, or if you’re severely claustrophobic, this test may not be possible.

Finally, an angiogram can be performed to look directly at the vessels. During this procedure, a thin hollow tube called a catheter is passed into the femoral, or groin, artery, and a special dye, called contrast media, is injected through the catheter into the renal vessels. X-ray pictures are taken to measure the degree of vessel narrowing.

The advantage of an angiogram is that, if necessary, the narrowed area of the vessel can be expanded with a tiny balloon that fits through the catheter. This can provide at least a temporary fix for the problem. The downside is that there are certain risks associated with any invasive procedure. These include:

• Bleeding
• Infection
• Damage to the blood vessels, and
• Adverse reaction to the contrast media

You may want to discuss these possibilities with your provider if you’re a candidate for an angiogram.

The most common physiologic study is the captopril test. In this test, the baseline level of renin in the blood is determined by drawing blood. Then an oral dose of captopril is given and, after a period of time, the plasma renin level is measured again.

Because captopril blocks the activity of one of the proteins that renin works on, the blood pressure should fall. This decrease in blood pressure is detected by both kidneys, but especially by the one that has a blocked blood supply. This kidney responds by secreting a large amount of renin. So an exaggerated renin response after the dose of captopril is suggestive of a renal cause for hypertension. Alternatively, nuclear imaging can be performed during this study and the blood flow to the kidneys measured directly.

Talk with your provider for more information and recommendations about these tests.

If a patient has additional risk factors other than hypertension, then it’s more likely that they may have a heart attack or stroke. That’s why evaluating all the risk factors is important.

Keep in mind, some of the risk factors are genetic, such as being male or post-menopausal, some are behavioral like smoking or using tobacco, lack of exercise, and obesity, and some are biochemical. For example, a person who has diabetes along with hypertension is more likely to have a negative outcome than someone with hypertension alone. In this case, their fasting blood glucose level is checked.

Lipid levels are also risk factors that need to be addressed. A simple blood test can check cholesterol, low-density lipoprotein, or LDL, and high-density lipoprotein, or HDL, allowing a cardiac risk index to be calculated. The cardiac risk index is one way to predict if you might have an increased risk of having a heart attack. The specific level of total cholesterol and LDL that are acceptable depend upon all of your risk factors. In general, the more risk factors, the lower your cholesterol and LDL need to be.

It’s helpful to understand the terms used by your healthcare provider. Total cholesterol is all of the cholesterol in the bloodstream, both “good” and “bad.” LDL is also known as “bad” cholesterol, as this is the cholesterol absorbed from your diet through the intestines. HDL is referred to as “good” cholesterol because it is cholesterol that is moved from your body’s fat stores to the liver where it is used to build healthy tissue. LDL can be lowered by removing cholesterol from your diet. HDL can be increased by removing cholesterol from your diet and by exercising.

One way of gauging your risk for heart disease is to examine the ratio between “good” cholesterol and “bad” cholesterol. This ratio is usually seen as LDL/HDL . An ideal ratio is 3.5. Keep in mind that if your ratio falls under 4.5, you don’t usually need to be concerned. If your ratio is over 4.5, it’s best to consult with your provider.