Systemic Arterial Pressure Regulation
- Fine-tuned regulation of the systemic arterial pressure is an important physiological priority. Hypotension can result in light-headedness or syncope whereas chronic hypertension can cause severe vascular disease over time. Regulation of the systemic arterial pressure appears to occur on two different time-scales which are coordinated by different physiological systems. Minute-to-minute, short-term control appears to be coordinated by the autonomic nervous system whereas the kidneys appear to be responsible for day-to-day, long-term blood pressure control.
- On the most fundamental level systemic arterial pressure is dependent on the cardiac output and systemic vascular resistance. Recall from hemodynamic integration that for any vascular system the blood pressure gradient = (Blood Flow Volume) x Resistance. The application of this equation to the entire systemic circulation allows for a basic understanding of systemic arterial pressure regulation.
- Whole-body Application
- The "Blood Pressure Gradient" of the entire systemic circulation is simply the systemic arterial pressure minus the right atrial pressure. Since the pressure in the right atrium is small or nearly zero we can largely ignore this variable. Consequently, the "Blood Pressure Gradient" can simply be replaced by the "Systemic Arterial Pressure". The "Blood Flow Volume" of the entire systemic circulation is simply the cardiac output of the heart. The "Resistance" of the entire systemic circulation is simply the systemic vascular resistance.
- Systemic Arterial Pressure Equation
- Replacing the above variables with their whole-body equivalents gives the following equation
- (Systemic Arterial Pressure) = (Cardiac Output) x (Systemic Vascular Resistance)
- Consequently, changes in the arterial pressure can be achieved by changing the systemic vascular resistance or by changing the cardiac output. The following sections describe how systemic vascular resistance and cardiac output are modulated at short and long timescales.