Feline systemic hypertension: the how and why of blood pressure

Feline systemic hypertension is a clinically significant disease in cats. It can be idiopathic in origin, occur secondary to a concurrent disease or to toxin ingestion, or seen as a reaction to situational stress. Chronic hypertension can lead to severe tissue injury which will often manifest at so called ‘target organs’, and can cause renal, cardiovascular, ocular, or neurological changes. An important part of diagnosis and evaluating anti-hypertensive therapy is obtaining accurate, reliable and repeatable blood pressure measurements. However, measuring blood pressure to this standard is not as easy as it sounds. Readings will vary with patient temperament, patient position, operator experience, and measurement method, which makes it difficult to know what the expected blood pressure ranges should be for the individual patient. Trained veterinary nurses, working to and maintaining a standard protocol can maximise the reliability of results.

Blood pressure is the force exerted on the vessel wall which is measured in millimetres of mercury (mmHg). Blood pressure is affected by two factors; cardiac output, or the amount of blood ejected from the left ventricle in systole, and by the diameter and elasticity of the arterial walls, known as systemic vascular resistance. This can be simplified by the equation: Blood pressure = cardiac output x systemic vascular resistance