The arterial blood pressure in mammals is regulated through several complex biological mechanisms. These factors influencing arterial blood pressure (systolic arterial pressure SAP, diastolic arterial pressure DAP) are of renal, endocrine, neurogenic and cardiovascular nature. In the dog and cat a change of sympathetic tone caused by foreign people and/or environment is mainly responsible for a possible fast increase of blood pressure under clinical conditions. This phenomenon occurs also in people and is sometimes called the "white coat" effect. However it is also known that certain persons and possibly the attitude of the clinical examination team may produce excitement or anxiety and thereby influence blood pressure. The main cause of a "true" hypertension in small animals is chronic renal disease. This over the last ten years is especially well documented in the feline species, it may occur together with retinopathy, retinal bleeding and retinal detachment as an ophthalmologic indicator of hypertension. Sudden blindness is a well-known result of these ocular changes. Hyperthyroidism and hypertrophic cardiomyopathy may also be diagnosed in hypertensive animals. Primarily in dogs hyperadrenocorticism and occasionally pheochromocytomas may lead to hypertension in combination with other clinical signs of these diseases. Hypotension may be observed in small animal patients in shock and hypovolemia, with Morbus Addison, in chronic heart failure, hypothyroidism and possibly of toxic and/or infectious origin. Clinical case material will be used to demonstrate the clinical picture and possible treatment of some of the above-mentioned conditions. In a number of serial investigations dogs and cats under different conditions and in different states of relaxation were carried out. In the dog study 100 dogs were measured with an oscillometric (Memoprint) and a Doppler machine resulting in slightly higher systolic values for the Doppler measurements. When a group of 46 dogs weighing less than 15 kg were put in an extra "low weight" group the Doppler group again showed slightly higher values and the Oscillometry Group changed also only insignificantly. In a group of 14 dogs repeated measurements were performed over about 15 minutes trying to calm the dogs down as much as possible. In about 80 % of the animals the SAP/DAP pressure dropped. In 7 % of the dogs only the SAP increased and in 7 % of the dogs only DAP increased. A moderate combined SAP/DAP increase appeared in the rest.

In repeated multiple measurements of SAP in 136 cats using the Doppler technique over an average time period of 20 minutes the blood pressure increased in 12,8 % (15 to 60 mmHg) of the animals, showing a growing intolerance regarding the whole procedure. In about 17 % of the cats examined the blood pressure diminished only a little (5-15 mmHg), which was not considered a significant drop of SAP. However in more than two thirds (70,5 %) of our feline patients the blood pressure decreased between 20 and 90 mmHg during the adaptation time and between repeated measurements. Out of this group the highest number of cats (n=80 / 59 %) exhibited only a moderate decrease of 20 to 40 mmHg. In a separate study out of 54 cats with cardiomyopathies 26 cats were hypertensive and diagnosed to have hypertrophic cardiomyopathy. All cats of this group were treated with an ACE-inhibitor (Ramipril 0,125 mg/kg/day). Over an average time period of about 3 months the SAP dropped. In 14 cats with "severe hypertension" (250-300 mmHg) SAP dropped from 285,7 ± 17,6 to 241,4 ± 45,9. In cats with "hypertension" (180-250 mmHg) the averaged measured SAP decreased from 212 ±17, 2 to 173 ±44,1 mmHg. Only four of these 54 cats were diagnosed to have hyperthyroidism and solely one cat of these hyperthyroid cats was hypertensive.

Treatment in general:All blood pressure changes occurring with underlying diseases such as hyper- and hypothyroidism, hypo- and hyperadrenocorticism etc. were treated according to the basic condition. Most animals received ACE-inhibitors such as Ramipril, Enalapril and Benazepril and some patients also received other cardio active drugs. Hypertensive cats received ACE inhibitors (Ramipril 0,125 mg/kg/day or Enalapril 0,5 mg/kg/day) and all cats with SAP above 200 mmHg Amlodipine (0,625-1,25 mg/cat/day).