Our health is intimately tied to the functioning of our cardiovascular and respiratory systems. So it behooves us to fully understand the system that literally transports our life’s blood, carrying oxygen to all of our vital organs and tissues. The complex electrical and mechanical interactions of the cardiopulmonary system make it well suited to solutions that can be derived through engineering principles and approaches.
Traditional Biomedical Engineering Applications
The classic—and most obvious—examples of biomedical engineering in this area are the artificial heart, stents and pacemakers.
The demand for heart transplants far exceeds the number of donor hearts available; so quite a bit of research has gone into developing and advancing artificial hearts. Those currently on the market—although more advanced than the original Jarvik heart, first implanted in 1982—are still relatively basic and not entirely understood in terms of how they interact with the circulatory system.
Stents that are used to expand constricted coronary arteries have been around for more than 20 years. Research continues into biomaterials that are longer lasting than the original metal stents. These absorbable and drug-eluting stents can help resist rejection by the body.
Pacemakers work in conjunction with the electrical system of the heart. These implantable computers sense the electrical activity of the heart to help control arrhythmias. They can take over when a patient experiences too slow a heart rate (bradycardia) or help control an abnormal heart rhythm (e.g. atrial fibrillation). They can even respond to a person’s level of activity and adjust the heart rate accordingly. Such control has traditionally been accomplished using multiple electrical leads going to each of the heart’s four chambers. New research has resulted in pacemakers with smaller leads. Down the road, pacemakers will no longer need leads at all.
For control and management of patients with a heart rate that is too fast (tachycardia), Implantable Cardioverter Defibrillators (ICDs) are employed. Modern ICDs manage ventricular tachycardias (VTs) and ventricular fibrillation (VF) using a tiered therapy. For fast heart rates below a set limit (typically 180 bpm), overdrive pacing can be employed to bring the rate down to a normal range. For VTs over this set limit and for VF episodes, the ICDs can deliver defibrillation shocks via leads implanted in the patient’s heart.
Medtronic’s EnRhythm® pacemaker delivers electric pulses to both the right atrium and right ventricle, reducing unnecessary pacing to the right ventricle when the heart is in normal rhythm. This Managed Ventricular Pacing (MVP®) can help to reduce the risk of heart failure and atrial fibrillation associated with unnecessary pacing in the right ventricle.
When abnormal rhythms cannot otherwise be controlled, cardiac ablation techniques can be used to destroy defective electrical pathways. Using an ablation catheter, the tissue at the opening of the pulmonary vein is purposefully damaged, either using a laser, by freezing it (cryoablation) or by applying heat (radiofrequency or RF ablation).
Oftentimes, as we age, we experience problems with our aortic valve which must either be repaired or replaced. This has traditionally required open heart surgery. New technologies from companies including Edwards Lifesciences, Abbott and Medtronic would allow treatment using minimally invasive catheters. These catheters are currently in clinical trials.
The work of biomedical engineers is evident throughout the practice of cardiology, from blood pressure monitors to defibrillators to the heart-lung machine used during open heart surgery.
Mathematical Modeling
Much of the recent progress made in the development of diagnostic and therapeutic devices in the cardiovascular area is the result of modeling the cardiopulmonary system.
There are currently several groups involved in detailed modeling of the lungs that describe airflow in and out of the lungs, blood-gas exchange, and so forth. As part of the Physiome Project, multi-scale computer models of various bodily systems are being developed down to the level of a single cell. The project has generated a comprehensive model of the heart—including 3D fluids—that is seen as one of the most successful examples of simulating an entire organ. The resulting model can be used for a variety of applications, including the testing of proposed drug interventions to see how they would affect the functioning of the heart.
Understanding how the heart functions at the mathematical level will enable us to better understand the cardiopulmonary systems of individual patients. Currently, physicians base therapeutic decisions on sporadic readings that are analyzed based on general knowledge from clinical trials and other population-based statistics. But that does not necessarily serve an individual patient. By structuring mathematical equations that provide coefficients that vary for each patient—whether young or old, sick or healthy, male or female—we can provide real-time feedback to achieve better therapeutic outcomes.
One area in which mathematical analysis is coming into play is the evaluation of Holter tape. Using standard equipment, mathematical algorithms will be able to look for patterns within the approximately 115,000 heartbeats captured during a 24-hour EKG monitoring. By analyzing the time between beats, clinicians will be able to detect patterns indicative of congestive heart failure impossible to glean through manual inspection.
Cardiopulmonary systems engineering is one area in which collaboration with the medical community is essential. EMBS physician members can help direct the efforts of biomedical engineers to enhance the quality of patient data and improve the quality of patient care. Join Us