Study on the Fluid Dynamics of the Human Circulatory System

The question of why patients with mechanical pumps that aids failing hearts have increased blood pressure and a higher risk of brain stroke is one that has perplexed many doctors. The implication of this fact is that the use of implantable mechanical pumps or Ventricular Assist Devices (VAD) remain low despite the extremely high need for them.

We set out to study the fluid dynamics of the human circulatory system to try and find some insights to address these questions.

VADs are continuous flow devices that help the heart push out blood from its lower chambers. They allow a continuous stream of blood to flow through the heart due to which there is no pulse. Manufacturers opt for this design as compared with pulsatile pumps because they are easier to design and can be miniaturised.

Although prior to implantation, patients have low blood pressure, within a few months of getting these pumps, they become hypertensive increasing their risk for brain strokes. The mechanism of hypertension was always assumed to have an endocrine basis, but this study changed that notion. We found that the physics of non-pulsation flow, mainly increased impedance, contributed greatly to high blood pressure. We also found that people with this kind of hypertension can be treated without medicines. An artificially generated pulse in these devices by software manipulation will bring blood pressure back to normal.

The study also showed that the posterior communicating arteries – the blood vessel at the base of the brain – played a vital role in strokes in this situation. If these arteries are clear without blocks, the risk of strokes is reduced even in normal people. This implies that if blockage is tested for in regular checks, there is a high probability that we can prevent or delay strokes.