The way that I learned to explain how blood pressure works is through the following analogy:
If your heart is your fist that is gently holding a bag of fluid (let’s say purple gatorade) with a straw leading out of it, the systolic rate (top number when measuring blood pressure) is the amount of resistance that the straw applies to the fluid when it attempts to leave the bag.
In real life, this would be your aorta (the artery that allows oxygenated blood to flow from your heart to the rest of your body).
So if the straw’s circumference is bigger, there is less pressure—if the straw’s circumference is smaller, the pressure is greater. The greater the pressure, the higher the systolic blood pressure number.
The diastolic rate (the bottom number) is the amount of pressure that is exerted onto the straw (or arteries) when the heart is at rest in between your heart beats.
So when your body tells your heart to pump faster and to expand the circumference of your blood vessels, your systolic blood pressure will go down. Because your arteries and blood vessels have expanded to allow more blood through, they exert less pressure during diastole (when your heart is at rest), which then causes a drop in diastolic blood pressure
It is through this manner that infrared saunas will lower your blood pressure—expanding the means by which blood is transported through your body allowing for better and faster circulation. Because your body is also put into the parasympathetic state, you are more relaxed and your feelings of stress will be reduced.
This all results in less stress upon your body, mind and heart–all resulting in greater health.