Servo-controlled hind-limb electrical stimulation for short-term arterial pressure control

Background: Autonomic neural intervention is a promising tool for modulating the circulatory system thereby treating some cardiovascular diseases. Methods and Results: In 8 pentobarbital-anesthetized cats, it was examined whether the arterial pressure (AP) could be controlled by acupuncture-like hind-limb electrical stimulation (HES). With a 0.5-ms pulse width, HES monotonically reduced AP as the stimulus current increased from 1 to 5 mA, suggesting that the stimulus current could be a primary control variable. In contrast, the depressor effect of HES showed a nadir approximately 10 Hz in the frequency range between 1 and 100 Hz. Dynamic characteristics of the AP response to HES approximated a second-order low-pass filter with dead time (gain: -10.2±1.6 mmHg/mA, natural frequency: 0.040±0.004 Hz, damping ratio 1.80±0.24, dead time: 1.38±0.13 s, mean ± SE). Based on these dynamic characteristics, a servo-controlled HES system was developed. When a target AP value was set at 20 mmHg below the baseline AP, the time required for the AP response to reach 90% of the target level was 38±10 s. The steady-state error between the measured and target AP values was 1.3±0.1 mmHg. Conclusions: Autonomic neural intervention by acupuncture-like HES might provide an additional modality to quantitatively control the circulatory system.