Veterinarians commonly diagnose hypertension with a Doppler system that detects blood flow acoustically. This method uses an inflatable cuff with a gauge that measures pressure within it, a stethoscope and a unit that uses Doppler signals to detect blood flow. The veterinarian or technician places the cuff around a limb, inflates it until blood blood flow in the limb is blocked and then gradually deflates the cuff until blood flow is detected once again.
The pressure at which blood flow is detected upon gradual deflation of the cuff is called the systolic blood pressure. This is the pressure in the artery when the heart is actively contracting. The diastolic pressure, which is difficult to measure using this technique, is the pressure in the arteries when the heart is relaxing. Blood pressure is measured in millimeters of mercury (mmHg), corresponding to the height in millimeters that a pressure is capable of raising a column of mercury in a vertically oriented tube.
The average systolic blood pressure in humans is 120 mmHg. Cats’ normal systolic blood pressure is also around 120 mmHg, with that of older cats often being somewhat higher. A systolic blood pressure of greater than 170 mmHg prompts concern for hypertension in cats.
Just as in people, cats can experience “white coat syndrome,” an episode of anxiety when faced with veterinarians that causes their blood pressure to spike, says cardiologist Bruce Kornreich, DVM, Ph.D., ACVIM, at Cornell. Allowing cats 30 minutes to acclimate to the clinic before taking readings and averaging the results of three or more readings will often produce more accurate results.