Blood pressure depends on a couple of factors: primarily fluid/blood volume, blood vessel resistance and cardiac output (the amount your heart has to pump out to replenish your body). I won't bore you with the details.
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1) Gravity is less of a factor:
- Your heart no longer has to pump blood against gravity in order to recirculate blood from your extremities so its output can be reduced. Blood returns to the heart much easier when you’re horizontal rather than vertical. Think about trying to pour gravy up a tube versus letting it run horizontally in a tube. The pumping action is less necessary.
2) Less resistance because of vasodilation
- Heat causes your blood vessels to dilate. The wider the radius of your blood vessels the less resistance your heart has to pump against. This means less pressure in the circulatory system. Think of when you put your thumb over the end of the garden hose to increase pressure versus letting it seep out naturally.
3) Less fluid volume due to dehydration
- Losing water: You may be in a big bucket of water but you’re still sweating the water you do have in your body into that bucket. With less fluid in your system your heart can take a break. Think of trying to crawl under an air mattress full of water versus one that has half as much water in it.
- Losing sodium: sodium retains water so the more sodium you sweat out the less water you will retain, compounding the effect mentioned above.
4) Mental relaxation
- Your blood pressure drops when you are relaxed because your body is taken out of fight or flight mode, it no longer needs to put out as much blood as possible to your muscles to prepare you for action.
5) Physical relaxation
- Your muscles will loosen and warm up from the hot water, further reducing the need for your heart to have to warm them up and replenish them with nutrients. Another effect this has is decreasing resistance, if your muscles are not as tight the arteries and veins won’t have to work so hard to get blood past them.
6) Temperature regulation
- One of your heart’s major jobs is to keep you warm, since the hot water is already doing this your heart doesn’t have to work as hard.
The effects of hot tubs dropping your blood pressure too much can be: dizziness, fainting, weakness, light-headedness, reduced ability to concentrate, blurred vision, fatigue all mainly from a lack of blood flow to the brain. The longer you’re in the hot tub the more powerful effects these facts will have on you.
- Once the air that’s cooler than the water you were just in hits your skin your blood vessels and pores will constrict. This constriction will increase the pressure in the cardiovascular system. Think about putting your thumb over the garden hose nozzle.
2) Orthostatic hypotension
- Since you’ve depleted a significant amount of fluid and it hasn’t been pumping forcefully back to your heart your blood pressure will temporarily drop. This can cause symptoms of low blood pressure immediately after standing up from the hot tub. If you have low blood pressure to start with, once you stand up it’s going to be difficult for your body to return to its regular blood pressure due to having to antagonize all of the factors hot tubs pose on you, particularly gravity.
3) Rebound hypertension
- Your body is programmed to maintain homeostasis so your blood pressure will rise again once you’re on your feet. If you have high blood pressure in general this extreme fluctuation may exacerbate your high blood pressure and cause hypertensive symptoms which you may only experience when stressed or at random times when your blood pressure peaks.
The effects of your blood pressure increasing after getting out of the hot tub are pulsating pounding especially in the back of your head, fatigue, confusion, shortness of breath, anxiety, nose bleed, pounding chest, chest pain or irregular heartbeat
Tips: Don’t stay in the hot tub for longer than 15 minutes at a time. Consult with your Doctor whether you should be using hot tubs if you have a heart condition or previous history of blood pressure issues. Always have someone around when you use a hot tub. To take the guessing game out of whether your blood pressure is being affected by being in the hot tub invest in your own blood pressure monitor.
As a Naturopathic Doctor, I treat people with low blood pressure and high blood pressure on a steady basis. Some individuals with high blood pressure need to be medicated while we work on bringing blood pressure down naturally. Most Doctors will tell you that low blood pressure is not anything to worry about. It may not be dangerous per se but can definitely be the root of your fatigue, light-headedness or general weakness. The most important thing is to find the underlying cause of why your blood pressure is too low or too high. The kidneys and adrenal glands both affect blood pressure as well so it's important to make sure they are in good health if hot tub-related symptoms occur.
Thanks for reading! If you have any questions, concerns or anything to add feel free to comment or email me.
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Bachelor of Kinesiology
Advantage Chiropractic and Massage