FIG. 3.

Probe and brain temperatures in patient 1. The upper chart shows the temperature control of the probe. As the PID feedback control system attempts to maintain the probe temperature at 5°C, the temperature fluctuates between 2°C and 8°C. The lower chart indicates the brain temperature; however, the thermocouple measuring the temperature was placed on the probe surface, not on the brain. While the thermocouple was removed from the brain in the intervals between coolings, the temperatures were lower than during the cooling periods. The brain temperature reached 8°C in an average of 50 sec after the attachment of the probe. Among the four cooling trials, the first and third were successful; in the second trial, the probe had insufficient contact with the brain, and in the fourth trial, the delay in the temperature drop was due to the control system.