- Resource Centers
What Is a Biological Rhythm?
Our bodies'"rhythms,"also known as our biological clocks, take their cue from the environment and the rhythms of the solar system that change night to day and lead one season into another. A biological rhythm that is 24 hours long is referred to as a "circadian rhythm."
You can think of your circadian rhythm as an internal clock, which is based on your sleep-activity cycle. Our internal clocks are influenced by our genetic makeup and affect how our bodies work throughout the day and night.
Over a 24-hour period, certain bodily functions occur at certain times in the day. For example, some hormones are released by the brain early in the morning, whereas others are released while you are sleeping.
Researchers have found that certain diseases follow the body's circadian rhythm. For example, osteoarthritis worsens during the day and is most bothersome in the evening. And diseases such as high blood pressure and angina, or chest pain, also follow a certain circadian rhythm.
If I Have High Blood Pressure, Does My Blood Pressure Vary Through the Day?
In 70% to 90% of patients with high blood pressure, blood pressure drops during the nighttime and goes higher during the early morning period. As you can see in the graph, your blood pressure and heart rate are highest during the hours of 6:00 in the morning to 12:00 noon. This is because certain hormones that give you boosts of energy, called adrenaline and noradrenaline, are also highest during this time.
Is This Increase in Early Morning Blood Pressure Bad?
Researchers have found that many types of life-threatening events, such as stroke and heart attack, happen more often during this early morning period. This may be due to rises in blood pressure and heart rate, and also to increases in certain hormones, such as angiotensin, renin, aldosterone, and adrenaline. These hormones tighten your blood vessels and make your heart work harder to pump blood to the body. If you have a buildup of "gunk"called plaques in your blood vessels that slows down blood, these stresses can lead to a stroke or heart attack.
A healthy lifestyle can often help people with high blood pressure. Also, scientists have developed certain high blood pressure and angina medications, which, when taken at bedtime, release higher amounts of drug in the early morning hours and lower amounts at night. These medications are known as "chronotherapeutic."
What Do You Mean by "Chronotherapeutic"?
Coordinating biological rhythms with medical treatment is called chronotherapy. It considers a person's biological rhythms in determining the timing? and sometimes the amount?of medication to improve how a drug works in your body and/or reduce unpleasant side effects.
What Are These Chronotherapeutic Medications?
The FDA has approved 3 chronotherapeutic agents. Cardizem LA (diltiazem HCl) and Covera HS (verapamil HCl) are approved to treat high blood pressure and angina. Verelan PM (verapamil HCl) is approved only for high blood pressure. You can consult your physician or pharmacist to see if any of these medications are right for you.
Dr. Page is an assistant professor of clinical pharmacy at UCHSC, School of Pharmacy and a clinical specialist with the Division of Cardiology/Heart Transplantation at the University of Colorado Hospital.