Hemodynamic Integration

  • The hemodynamic values of blood pressure gradient, resistance, and blood flow volume through a given segment of vasculature are ultimately all interconnected by a central hemodynamic equation
  • This equation states that: Blood Flow Volume (ml/min) = Blood Pressure Gradient/Resistance
  • It can be rearranged as follows: Blood Pressure Gradient = (Blood Flow Volume) x Resistance
  • This general equation can be used to understand the flow of blood through discrete segments of the vasculature, across entire organs, or across entire sections of the circulatory system. In each case, when two points within the vasculature are defined, the volume of blood flow per unit time between these points will be related as described above to the relative blood pressure gradient between these two points and the resistance of the intervening vasculature.
  • Renal Blood Flow
    • The volume of blood flowing through the entire kidney per unit time, known as the renal blood flow will be related to the blood pressure gradient across the entire organ and the resistance of the entire organ
    • Therefore: Renal Blood Flow = (Renal Artery Pressure - Renal Vein Pressure)/(Renal Resistance)
  • Cardiac Output
    • The cardiac output is essentially the entire volume of blood flowing through the systemic circulation and is thus related to the pressure gradient across the systemic circulation and the resistance of the systemic circulation
    • Therefore: Cardiac Output = (Mean Systemic Arterial Pressure - Mean Right Atrial Pressure)/Systemic Vascular Resistance
    • However, because the Right Atrial Pressure is usually very close to atmospheric pressure, this term is usually dropped from the equation
    • Consequently: Cardiac Output = Systemic Arterial Pressure/Systemic Vascular Resistance
    • Rearranging: Systemic Arterial Pressure = Cardiac Output x Systemic Vascular Resistance