Hypertension (high blood pressure) is being increasingly recognised as a problem in pets, particularly older cats, and is usually associated with underlying disease.
When the heart contracts a pulse of blood is forced through the arteries and this generates the systolic blood pressure. In between heart contractions the pressure falls - this is the diastolic pressure. Systolic pressure does not remain the same at all times. Arteries are constantly being narrowed or dilated to direct blood to whichever organs are most active at the time.
Blood pressure also tends to increase a little with age. As animals age the blood vessels become less elastic and do not dilate as easily. This has the effect of increasing blood pressure.
What causes hypertension?
In animals hypertension is usually secondary to other problems. In cats the most common link is with kidney failure but some cats with an overactive thyroid gland (hyperthyroidism) may also develop hypertension.
Why does hypertension cause problems?
The increased pressure in the blood vessels damages the vessel walls, causing bleeding and blood clot formation. This can cause severe problems if the blood vessels of the eye, kidney, heart or brain are affected. There is also extra strain put on the heart muscle as it has to pump against greater resistance.
The symptoms are usually associated with the underlying cause (in kidney failure these can include weight loss, increased thirst, poor appetite and vomiting) but signs associated directly with blood vessel damage are also seen. These can include sudden onset blindness, strokes and other neurological problems.
How do we diagnose hypertension?
We can measure blood pressure with the equipment shown in the picture above. A cuff is placed around the forelimb (or tail) and the cuff is inflated. As the cuff is gradually deflated the machine can detect systolic and diastolic pressure, mean arterial pressure and the pulse rate. This is very well tolerated by both cats and dogs.
As blood pressure can increase with the stress of coming into the surgery we sometimes have to keep the cat in for a few hours to get used to the environment. Numerous measurements are taken over this time in order to get an accurate assessment.
How do we treat hypertension?
If we can identify an underlying cause then this should be treated. If the blood pressure is only mildly elevated this may be enough to bring the pressure down into the normal range. However in many cases it is necessary to use drugs to directly lower the blood pressure. As animals have different responses to these drugs we need to monitor the blood pressure to ensure we are treating it effectively.
Will my cat get better?
In cases where just treating the underlying disease is not effective in reducing blood pressure additional drugs are required and these are usually continued for the rest of the animal's life. The sudden onset blindness caused by hypertension in some cats is permanent but continued treatment for hypertension is worthwhile to prevent further damage to the brain, heart and kidneys.
Other uses of blood pressure measurement
Apart from diagnosing hypertension there are other situations where it is useful for us to be able to easily measure your pet's blood pressure. It can be useful as part of critical care for very sick or injured animals, and can be very useful in combination with fluid therapy (intravenous drips) to help us monitor the effectiveness of the treatment.