Acute carotid baroreflex resetting in conscious dogs.

1. Acute baroreflex resetting in the control of arterial pressure was studied in six chronically instrumented, conscious dogs. Following aortic baroreceptor denervation, the carotid sinuses were surgically prepared for reversible vascular isolation. 2. During the experiments both carotid sinuses were temporarily isolated from the systemic circulation and conditioned with a pulsatile pressure. The carotid sinus conditioning pressure (CPCSP) was at a level of 100, 140 or 60 mmHg for 20 min each. Carotid sinus pressure (CSP) versus mean arterial pressure (MAP) baroreflex curves were constructed after each conditioning period. 3. The baroreflex curves were shifted downward and to the left at low CPCSP and upward and to the right at high CPCSP. 4. We used four parameters to quantify baroreflex resetting. These were: (1) the set point pressure (PSP), (2) the threshold pressure (PTh), (3) BP50 or mid-point pressure and (4) the CSP at maximum gain (PGmax). At high CPCSP, these four parameters were increased by 18.5 +/- 4.0, 23.4 +/- 4.3, 21.7 +/- 5.0 and 22.0 +/- 5.1 mmHg, respectively (P less than 0.05). 5. Resetting was not complete in these studies. The extent of resetting was approximately 50% for upward and 35% for downward baroreflex conditioning. 6. Analysis of the present experimental data indicates that when the cardiovascular system is exposed to a short-term hyper- or hypotension, the baroreflex is capable of correcting the baseline arterial pressure while preserving its ability to buffer transient disturbances as a result of partial resetting.