Emile L. Boulpaep
When faced with a patient who appears seriously ill, clinicians focus their immediate attention on the patient's vital signs: temperature, respiratory rate, pulse, and blood pressure. These parameters are aptly named vital because they reflect the most fundamental aspects of health and even survival; a significant abnormality in any of these components indicates that emergent care is required.
In this chapter, we focus on blood pressure, a critical hemodynamic factor and one that is easily measured. An adequate blood pressure is necessary for proper organ perfusion. Too low, and we say that the patient is in shock. Too high, and we say that the patient is hypertensive; an acute and profound elevation of the blood pressure can be just as dangerous as a sudden plummeting of blood pressure. Here, we examine both the short- and long-term mechanisms that the body uses to regulate arterial blood pressure.
Because the arterial blood pressure depends to a large degree on the cardiac output, we also examine the regulation of this critical parameter. Finally, because cardiac output also depends on the venous return of blood to the heart, we discuss the matching between input (i.e., venous return) and cardiac output.