So, what is blood pressure, anyway?

by Baxter

If you read yoga magazines or read online articles about yoga and your health, you often come across a warning to avoid this or modify that yoga asana if you suffer from high blood pressure or hypertension another term used for high blood pressure). But it turns out that there are a lot of differing opinions about how and what to change about a typical yoga practice if you have hypertension (HTN), and not a great deal of agreement on the best approach to take. However, before we get into that, I thought it would be helpful to discuss what blood pressure is, and how it is determined, as well as why HTN needs to be addressed either via lifestyle changes or medical intervention.

So, what is blood pressure? Well, it is a measurement we take—usually in your upper arm via a blood pressure cuff—that measures the pressure in the arteries of your arm. When you are sitting or standing with your arms at your sides, the place where blood pressure reading is taken is in line with your heart and its main artery, the thoracic aorta. Now we are measuring the pressure downstream in an artery in the arm, but it seems to correlate well with the pressures inside the heart and aorta. The top number of a blood pressure reading, called the systolic blood pressure, is the amount of pressure the blood in your arteries is exerting on the elastic, stretchy walls of the artery when the heart is at its maximum point of contraction. On average, it runs around 120mmHg’s of mercury in a normal healthy person. The bottom number, called the diastolic blood pressure, is the pressure at the time the heart is most relaxed between beats and is filling with more blood coming in from the body and lungs. A healthy average for that number is 80.  So, if your blood pressure, on average over the course of the day, is at 120/80 or below, it is said to be in the normal range.

Arctic Moon by Michele Macartney-Filgate

Via observations and studies, if your blood pressure averages 140/90 or above over the course of the day, you are said to have high blood pressure or hypertension. If you fall between 120/80 and 140/90, you are now said to have a condition called “pre-hypertension,” a no man’s land where it seems you are at a greater risk of developing HTN over time. More on HTN and why it’s important later.

Let’s go back to the concept of blood pressure for a few more moments. Your blood pressure is not a constant figure, but changes as your physical, mental and emotional activities change. It often goes up during exercise, stressful situations, and emotionally charged interactions, as well as varying with your body position of reclining, sitting or standing. It must vary dynamically to accommodate our changing situations throughout the day. Maintaining the proper blood pressure for our changing needs is a complex system that involves many of the body’s systems, including hormones, brain activity, and specialized receptors for pressure in the some of the biggest arteries in the body, called baroreceptors. As these various components of the blood pressure regulation interact, they result in dynamic fluid changes within the blood vessels and heart, via changing the blood flow in the vessels, the heart rate and the intensity of the contraction of the heart itself. Other organs also get involved, such as the kidneys, which are asked to help lower blood pressure at times by filtering out more water from the blood to decrease the overall amount of fluid in the system. Other parts of our nervous system can also influence the blood pressure readings. Your autonomic nervous system, composed of the two opposing and balancing parts, the sympathetic (Flight, Fight or Freeze response) and the parasympathetic (Rest and Digest response), can either increase or decrease your blood pressure, depending on how activated they are.

A few more thoughts on the general topic of blood pressure. Although we have defined the situation where blood pressure is elevated above the normal level and is considered potentially dangerous if left untreated, the opposite situation can also exist. That is, your blood pressure can be lower than normal, and this situation is called hypotension. Highly trained runners, especially long distance runners, can have blood pressures that average 100/60 or even lower and feel no worse for the wear. However, in other situations, hypotension can create symptoms that indicate it is not a normal adaptation to good aerobic fitness, such as lightheadedness, dizziness on standing and fainting. So next time, we will look at the conditions of hypertension and hypotension in more detail, and begin to discuss how yoga could fit into plan for better health for these students. Special thanks today to both Shari Ser and PubMed for their insights on blood pressure, as well as all my teachers back at UC College of Medicine in Ohio!