Abstract
Human carotid arterial baroreceptors have been stimulated by applying subatmospheric pressures to a box enclosing the neck, and the cardiovascular responses to this stimulation have been observed. For each cardiac cycle, the heart rate, arterial pressure and stroke volume were measured in order that the transient cardiovascular behavior might be observed. The pressure in the box was gradually decreased and was then maintained at a constant level. Results obtained are as follows: (1) The heart rate decreases proportionately to the pressure in the box as the pressure is gradually decreased. After the pressure attains the constant level, the heart rate recovers slightly. These imply that the control mechanism of the heart rate including baroreceptors has differential characteristics. (2) Cardiac output and arterial pressure decrease soon after the pressure decreases. After the pressure reaches the constant level, cardiac output returns to the control value, whereas the arterial pressure hardly changes. This would suggest that the total peripheral vascular resistance decreases when the pressure decreases. Further, the experiments have been simulated by using a mathematical model of the whole vascular control mechanism which the authors had proposed. The simulated results were compared with the experimental ones. The comparison supports the implication described above about the characteristics of the baroreceptors.
