[Classification of oscillatory states of blood pressure after bleeding in cats (author's transl)].

Blood pressure and heart rate responses were recorded on bleeding of blood volume of 1 ml/kg body weight (test input) from the abdominal aorta of cat. Forward path gain, backward path gain and minification were determined from blood pressure responses to test input. Oscillations in blood pressure were elicited spontaneously or artificially after bleeding of blood volume of 5 ml/kg body weight (conditioning input). The oscillatory states are classified into latent state, underdamped oscillatory state and harmonic oscillatory state. Open loop gain decreased in the latent state but increased in the other states. Therefore, oscillation was hard to elicit in the latent state. Minification, however, enlarged in the latent state, making the system irritable to disturbances and reducing its control accuracy. In the latent state, an insensible disturbance increased backward path gain and open loop gain to induce the oscillations. There was an increase of heart rate at an elicitation of oscillation in any state and a decrease of heart rate made it damped. Therefore, the heart rate regulatory system plays a main role in the feedback path of the blood pressure regulatory system and an increase of heart rate by an insensible disturbance or test input increases backward path gain.