We know what pressure is, it’s the feeling of being leaned on, or pushed on, by some external force. And of course, we know that blood travels in biological pipes called vessels.
What is Blood Pressure?
The NHS website describes blood pressure as a measure of the force that your heart uses to pump blood around your body. This is exactly the same in animals.
But what does that MEAN?
It can be helpful to think of blood-vessels in terms of central heating pipes, with a pump (in this case, the heart) to push blood around it.
Regarding High Blood Pressure:
The more water being pushed through a pipe at once, the higher the pressure. Sometimes the pressure goes too high, with more water in the pipe than the pipe can cope with. This might damage the pipes, putting pressure on them from the inside. If there is a weakness in the pipe or seal somewhere, it might spring a leak
Why might the pressure be too high in a vein?
Perhaps water is not leaving the body as it should be doing through the kidneys.
Alternatively, the pipes in an area might be too narrow (for example, in a damaged liver or heart), increasing resistance to blood flow and a build-up of pressure behind.
The adrenal gland, which plays a part in regulating blood pressure, may be damaged, or high sugar in the bloodstream may change the water balance (in diabetes). There are other rare mechanisms that may be involved.
So what happens if the pressure is too high?
- If blood pressure goes high once or twice, the body has mechanisms (e.g. in the kidneys) to redress the balance. But if the blood pressure is consistently a little too high, or goes extremely high just once, then more permanent damage can occur.
- The blood vessels will be overloaded, encouraging blood to leak through the blood vessel walls into places where blood wouldn’t normally go. Even if it doesn’t leak, the extra blood pushing on the blood vessel walls from inside, can impact on the tissues surrounding the vessel.
- When this happens in the eye, animals may go blind. In the brain, there may be ‘wobbly’ episodes, depression, head-tilts, circling, staggering or even fitting.
- Water will be forced out at the kidneys, causing an excess of urination and over time, damaging the kidney, even leading to kidney failure
- The pump (the heart) may have to work harder, leading to cardiac damage
- And to fluid build-up in the lungs
- Unexplained nose-bleeds may occur
How about LOW blood pressure?
On the other hand, if the pressure drops too low, it is difficult for the fluid / blood in the system to get to wherever it’s going. We’ve all been in those old houses where you turn a tap on and wait for the water to arrive. When it does, it might come in fits and starts. You wouldn’t want this to happen to the blood flow in an animal’s body.
What happens if the pressure is too low?
- Blood (carrying oxygen and fuel) will get to the brain and other body tissues less reliably.
- Even when it gets there, oxygen and nutrients might pass less reliably into the body’s cells.
- This includes the brain cells, leading to confusion and in-coordination.
- And the muscle cells, leading a drop in activity, fatigue and collapse.
- The gums may appear pale because less blood is getting to them
- Furthermore, there will be an increase in thirst in order to correct the problem.
- There may be faster, shallow breathing
What causes this?
Blood pressure goes low when there is not enough blood to fill the blood vessels. Reasons for this include (but are not limited to):
- A major leak in the system somewhere, i.e. a large bleed
- Kidneys not working properly – water that shouldn’t, escaping
- Not enough water in the system (severe dehydration)
- The heart pumping inadequately
- The blood vessels dilating e.g. in anaphylactic shock
There is an ideal blood pressure for an animal’s body and it is a good idea not stray too far outside it, for too long.
Some animals, for example those with chronic underlying illnesses, are at a greater risk of this happening than others.Sometimes, blood pressure may go too high or low suddenly e.g. in the event of a bleed. The body has mechanisms to ‘put itself right,’ but if it doesn’t, the consequences can be severe.