Surplus hemodynamic energy (SHE) in blood flow is the extra energy generated by a pulsatile device when adequate pulsatility is achieved. It is a measure of the amount of energy in the blood flow that is available to overcome resistance and deliver oxygen and nutrients to the tissues.
SHE is calculated by subtracting the mean arterial pressure (MAP) from the energy equivalent pressure (EEP). The EEP is a measure of the total energy in the blood flow, taking into account both the pressure and the flow rate. The following formulas can be applied to specifically calculate MAP, EEP and SHE.
Energy Equivalent Pressure (EEP)
= mmHg........................................(1)
Where P is pressure in mmHg
Q is flowrate in mL/min3
Mean Arterial Pressure (MAP)
= mmHg…........….........................................(2)
Surplus Haemodynamic Energy (SHE) = 1332(EEP-MAP) erg/cm3 ..................................(3)
Where 1332 is the empirical constant converting pressure (mmHg) to energy (erg/cm3)
Relative SHE (rSHE) = (EEP-MAP)/MAP .......................................................................(4)
Where rSHE is dimensionless
Total Haemodynamic Energy (THE) = 1332 EEP erg/cm3 …............................................(5)
An illustration:
SHE is important for several reasons. First, it helps to overcome the resistance of the blood vessels and deliver blood to the tissues. Second, it helps to maintain organ function, particularly in organs such as the brain and kidneys. Third, it helps to prevent thrombosis (blood clots).
SHE is reduced in a number of conditions, including heart failure, peripheral artery disease, and aortic stenosis. This can lead to a number of problems, such as tissue ischemia and organ damage. SHE can be increased by using pulsatile devices, such as left ventricular assist devices (LVADs) and pulsatile heart-lung machines.
Understanding the role of SHE, Triphasic Medical has developed and built a unique, patented pump to allow control of SHE in flow loops and future applications in cardiopulmonary bypass surgery, peripheral vascular disease and ventricular assist devices.
