We might think that science has long mastered this essential and universal physics that lies behind every heartbeat. Still, the pumping seems logical, but no one had until now been able to explain how the heart fills with blood. Researchers have finally found the answer, drawn from hydraulic forces.
The mechanisms that cause blood to flow into the ventricles of the heart during filling, or diastolic, were only partially understood. While titins (proteins in heart muscle cells known to function as springs) release elastic energy when filling up, a recent study by researchers from Karolinska Institutet and KTH Royal Institute of Technology , in Sweden, suggests that hydraulic forces (the same ones involved in the brakes of electric cars or other forklifts) are also at work. These results were detailed in the journal Scientific Reports.
Hydraulic force is a pressure exerted by a liquid on a given area. It is exploited in all kinds of mechanical processes. Regarding our heart the size of a human fist, the idea is the same. This is divided into four chambers: two upper (the atria) and two lower (the two ventricles). Deoxygenated blood leaves the right ventricle of the heart and travels to the lungs which return oxygenated blood via the left atrium. This oxygenated blood is then pumped out of the left ventricle to supply oxygen to the rest of the body before re-entering the right atrium of the heart. So far, so good. But although scientists are very familiar with this process, what was unclear so far was how and why it happens.
Using magnetic resonance (CMR), they did cardiovascular imaging to measure the size of the two chambers during diastole (the phase when the ventricles fill with blood) in healthy participants. The researchers found that the upper atrium (or atrium) was smaller than the ventricle throughout diastole. Therefore, when the valve between the two chambers opens, blood will rush into the ventricle to equalize the pressure. The geometry of the heart thus determines the magnitude of the force, this being fed by the size of the heart chambers relative to each other during the pumping process.
The scientists note that this new approach could lead to new treatments for heart failure. These treatments would involve reducing the size of the atrium to equalize pressure during diastole, heart failure most often being the consequence of an enlarged atrium. The hydraulic force is indeed uneven, reduced and the heart is unable to fill with blood properly.