HEALTH
THE HEART AND DIVING AN ALTERNATIVE WAY TO MONITOR A DIVER’S HEART FUNCTIONING UNDERWATER FEATURE GIUSEPPE DI TURSI
Underwater phases of the measurement protocol. Divers were required to stay still to avoid undesired artefacts through the collected signals. Photo by Antonio Angelo Calasso (Altamarea Snc).
Statistics show that about one-third of all diving accidents are due to an acute cardiac event, that is why monitoring heart activity more closely in relation to diving activities, is of crucial importance. Cardiac health is mainly affected by aging. As the years advance, all the structures of the heart become stiffer. Left ventricle muscles get thicker, its volume declines, and the heart may increase slightly in size. Consequently, the heart may both fill and empty more slowly, thus injecting less blood into circulation. The rise of heart rate and cardiac output in response to physical activity is not as effective and maximum heart rate is diminished. Cardiovascular health may be negatively influenced by undesired reactions following the body’s adaptation to immersion too. Physiologically speaking, immersion in water near the temperature of the human body results in blood shift to the chest cavity together with narrowing of peripheral vessels. The additional blood volume is responsible for enlarging all four heart chambers, increasing the filling pressure on the right side of the heart, thus resulting in more than a 30-percent rise in cardiac output. Vasoconstriction, so there is more flow resistance, is accountable for a slight growth in overall blood pressure.To 116 DIVERS FOR THE ENVIRONMENT | JUNE 2022
maintain homeostasis, heart rate and cardiac output decline, but it must exert itself more to ensure adequate flow throughout the body. However, these mechanisms may trigger adverse responses, such as arrhythmias, that may be life-threatening for individuals with previously undiagnosed diseases. Therefore, the need to track physiological parameters in diving has arisen. Extensive research has been performed on what happens before and after the dive. However, the latest studies have shown that some variables experience significant changes when observed during the dive, even though they seem to remain stable pre and post-diving, such variations can be identified by monitoring the heart. That is why the adoption of telemonitoring solutions is a hot topic in the scuba diving field, offering the possibility to gain additional insights of the heart functioning during a dive. Within this context, at Politecnico di Milano in Italy, an explorative study aiming at assessing the feasibility of characterising the cardiac activity on subjects during scuba dives – more specifically its mechanical counterpart – was set up by the research group of Professor Caiani, in the circumstances of a research
project (Kinosomno) funded by the Italian Space Agency. These experiments were possible by performing the acquisitions using the EcgMove 4 device (movisens, GmbH) worn under a drysuit; such a device includes a single channel ECG, and a 3-axis accelerometer and gyroscope, which are able to measure simultaneously the cardiac electrical activity and the chest’s vibrations provoked by the cardiac mechanical activity. As the muscle mass of the atria is small compared with that of the ventricles, the vibrations registered mainly reflect the ventricular activity, in particular relevant to the opening and closing of the aortic and mitral valves. The resulting signal is known as the seismocardiogram (SCG), which may powerfully complement methods of detecting heart electrical activity (such as electrocardiography). On the other hand, the complexity of the signal makes it more challenging to analyse it. However, the SCG contains the frequency components of both ECG and respiration, making it highly potential for the simultaneous monitoring of heart and respiratory rates with relatively less complicated measuring procedures. Additionally, due to the technology advancement of the microelectromechanical system (MEMS), the signal can be acquired at a much lower cost than before.
