Could your cat have high blood pressure?
Published 27/10/2015 | 00:00
Tabitha the cat stared at me with wide open eyes and her hair stood on end. She looked frightened, which was the last thing I wanted her to be. You may wonder what was spooking Tabitha. It wasn't a Halloween ghost or fireworks (as you might expect this week). Instead it was something much simpler: She was nervous because the vet was about to take her blood pressure.
Increased blood pressure is a normal reaction to stress, and there's nothing wrong with that. When an animal gets excited or frightened, it's normal for the heart to start beating faster and harder, and the blood vessels to dilate, increasing the blood flow to the muscles. The body is getting ready for "fight or flight", which is often the best method of self-preservation in frightening circumstances. This is known as "physiological increased blood pressure".
The issue that I am talking about this week is different: so-called "pathological high blood pressure". This happens when the blood pressure increases to an abnormally high level during normal daily activities. Most people will have had their own blood pressure taken by their doctor, so they are aware of its importance in monitoring general health. In fact, in the veterinary world, the concept of routinely measuring blood pressure is new. Twenty years ago, it was almost never done. Now, it is becoming standard procedure, especially for older cats.
One of the main reasons why blood pressure was not measured in animals in the past is that the simple cuff and stethoscope method used by doctors on humans does not work on pets.
The principle of measuring blood pressure is that the inflatable cuff around the arm cuts off the blood flowing through the arteries. Normally, the doctor can hear the blood flowing through the arteries with the stethoscope. As the cuff inflates, an increasing amount of pressure is applied to the arteries. At the point where the pressure applied by the cuff is the same as the blood pressure, the doctor can suddenly no longer hear the blood flowing in the arteries. This then allows the blood pressure to be measured.
The cuff aspect of this set up does work well in pets: it is simply placed on a pet's lower front leg. But the stethoscope part does not work: it is impossible to hear the flow of blood in a pet's arteries with a stethoscope. The technological advance which has allowed pet blood pressure to be measured is simple: an ultra-sensitive sound-sensing machine called a "Doppler" is able to pick up the sound of blood flow. So vets attach a cuff around the pet's leg, inflate it, then use the Doppler machine attached to an amplifier to detect the point at which blood stops flowing through the arteries. Since this technology was introduced, it has become a routine procedure to take pets' blood pressure.
Even though it is now easier to do, vets still don't take blood pressure measurements as often as human doctors for a simple reason: animals do not suffer from strokes or heart disease linked to high blood pressure in the same way as humans. However it's increasingly recognised that there are other serious consequences that can follow high blood pressure, especially in cats, and that's why measuring blood pressure has become an important part of caring for older animals.
In pets, high blood pressure is often associated with other underlying illnesses. Over 90% of dogs and over 60% of cats with kidney disease also have high blood pressure. And nearly 90% of cats with hyperthyroidism (an overactive thyroid gland) have high blood pressure. Sometimes treatment of the underlying disease can be enough to bring the blood pressure back to normal, but often daily medication is needed, using tablets to reduce the blood pressure.
If high blood pressure is not treated, there is a risk of damage to the eyes, kidneys, brain, liver and heart. The eyes are most sensitive, and the most common scenario that vets see in practice is when an elderly cat suddenly goes completely blind. An examination shows that there has been haemorrhage at the back of the eyes, causing damage to the retina, and when the blood pressure is taken, it's sky high. It's too late to do anything in such cases, so the aim of vets is to pre-empt this outcome, identifying cats with high blood pressure before their eyes are damaged. If medication can bring the blood pressure back to normal levels, affected cats can be prevented from developing blindness.
And that's why Tabitha was in front of me, staring at me with wide eyes. She's thirteen, and she is being treated for an over-active thyroid gland, but does she also need blood pressure medication? A stressed cat will always have high blood pressure, so before measuring it, I took my time, talking to her quietly. She eventually calmed down, and she seemed pleasantly relaxed as I inflated the cuff and measured her blood pressure. Predictably, it was 30% higher than normal.
Tabitha is now on blood pressure tablets every evening: there's a high chance that they will save her eyesight by keeping her blood pressure low. If you have an elderly cat, ask your vet about blood pressure measurement: Remember: early detection can prevent blindness.