[Difference of arterial pressure regulatory mechanism between awake and anesthetized human subjects]

This experiment was conducted to clarify difference of arterial pressure regulatory mechanism between awake and anesthetized human subjects. In 18 subjects who were scheduled for surgical operations, passive tilting test was performed both in awake and anesthetized conditions. Arterial pressure and heart rate were measured during four types of tilting test, i.e., 1. supine-10 degrees head down tilt 2. 10 degrees head down tilt-supine 3. supine-10 degrees head up tilt 4. 10 degrees head up tilt-supine. Relative changes in arterial pressure and heart rate in response to these four tilting tests were compared. After postural changes, all anesthetized subjects showed significant arterial pressure changes followed by restoration of arterial pressure towards control level with opposite changes of heart rate. This initial arterial pressure changes were mainly induced by shift of blood due to gravity and subsequent arterial pressure and heart rate changes were mainly by baro-receptor reflex. On the other hand, awake subjects showed transient increase of heart rate immediately after tilting followed by arterial pressure rise 2 to 3 seconds later in all four tilting tests. However, arterial pressure did not change so remarkably as in anesthetized condition and remained almost constant during tilting test. In awake subjects, their arterial pressure was regulated rapidly and reflex control of arterial pressure was masked. This rapid regulation of arterial pressure may be induced directly by higher central nervous system.