Sensitivity of arterial baroreflex changes during daily activity.

1. Continuous ambulatory arterial pressure monitoring was performed by telemetry in 34 hypertensive and four normotensive subjects and arterial baroreflex sensitivity was evaluated by computer analysis of pulse wave. Three consecutive pulses were selected, on two criteria, from the 24 h recording: (i) progressive and linear increase or decrease in systolic arterial pressure and heart period, (ii) change of systolic arterial pressure in three pulses exceeds a threshold value. The systolic arterial pressure and heart period of three pulses were averaged and the slopes of systolic arterial pressure and heart period were calculated as baroreflex sensitivity. 2. When the threshold value was set to 5 mmHg, baroreflex sensitivity measured by the present method correlated with baroreflex sensitivity as measured by the phenylephrine method (r = 0.667, P less than 0.001). 3. The baroreflex sensitivity from the pressor-bradycardia and the depressor-tachycardia reflex decreased as threshold value was increased from 3 to 4 mmHg to over 20 mmHg. With the pressor-bradycardia reflex, the initial systolic arterial pressure of three pulses did not change, but the initial heart period shortened progressively as the threshold increased. With the depressor-tachycardia reflex, the initial systolic arterial pressure increased and the initial heart period shortened progressively. This suggests that the sensitivity of arterial baroreflex changes dynamically according to input of reflex are during daily activity.