In work published in the April issue of Experimental Biology and Medicine, simple and interesting heart rate dynamics in premature human infants is reported – reversible transitions to large-amplitude periodic oscillations – and the appearance and disappearance of these periodic oscillations is described by a simple mathematical model, called a Hopf bifurcation.
The work was carried out by Abigail Flower, as part of her PhD thesis in biophysics, working together with Randall Moorman and Douglas Lake at the University of Virginia, and John Delos, at the College of William and Mary.
Dr. Moorman explained the background of this research. "Two periodic cycles of heart rate have been known for over a century. One is respiratory sinus arrhythmia, the coupling of heart rate to breathing (our heart rate increases when we inhale and decreases when we exhale). Another cycle of heart rate is correlated with a cycle of blood pressure called Mayer waves. Abby's work is quite different".
Dr. Flower examines a different and previously uncharacterized heart rate cycle involving large decelerations of heart rates of infants in neonatal intensive care units (NICU's). A deceleration is a decrease in heart rate followed by a return to the base rate. She devised a heart rate deceleration detector using a pattern-matching algorithm inspired by wavelet theory, and applied it to a large clinical database. She found that large decelerations are common, and similar in shape among infants; they are usually isolated, but they sometimes appear in clusters. In rare cases a deceleration appears every fifteen seconds for epochs as long as two days. These long periodic sequences of decelerations occur spontaneously – they were not induced by controlled means – so they must be a normal or pathological mode of regular dynamics in the human cardiac pacemaking system near the time of birth.
This phenomenon is interesting from both clinical and dynamical perspectives. Periodic decelerations are dynamically interesting because they show that the control system of the heart rate can go into a previously uncharacterized oscillatory mode. Presently there is no physiological explanation for this phenomenon. Dr. Flower developed a mathematical theory, based upon Hopf bifurcation theory, which describes the abrupt beginnings and endings of clusters of periodic decelerations. A Hopf bifurcation is the most general theory describing how a system can change from stable to oscillatory. Such bifurcations occur for example in laser systems, oscillatory chemical reactions, predator-prey dynamics, and in the Hodgkin-Huxley model of the firing of nerve cells.
Dr. Moorman said "These observations and computations therefore provide a new point of contact with mathematical models of the heart rate control system. The group is presently investigating models of the control loops connecting heart rate with respiration and blood pressure to see whether the available models show such behavior."
Heart rate decelerations, whether periodic or not, are clinically interesting because clusters of decelerations in neonates are statistically correlated with impending sepsis, a severe bacterial infection of the bloodstream. Clusters of decelerations may begin to appear as many as 24 hours before any clinical signs of illness, so deceleration detection can provide early warning of bacterial infection in this vulnerable population.
"One of the pleasures of this kind of work is its interdisciplinary nature" said Dr. Delos. "As an undergraduate, Abby did a senior project with me in physics, studying the hydrogen atom. Then a few years ago she emailed me and asked if I would like to participate in this project, working with her and Randall, a cardiologist, and Doug, a statistician. Since then I've been like a kid in a candy store, absorbing all the knowledge I could, and working intensely – maybe I should say playing intensely – trying to make sense of the data. People have been using electronic methods to monitor the heart for over a century. Now Abby has developed new, continuous, noninvasive, purely electronic methods to monitor infants for infectious disease. It is a delightful result."
Related methods of clinical monitoring, using noninvasive electronic observations and advanced mathematical tools to monitor for infectious disease, are now in use in more than 1000 NICU beds, and a large randomized clinical trial is underway to test the effect on infants' outcomes.
Dr. Steven R. Goodman, Editor-in-Chief of Experimental Biology and Medicine, said "In this outstanding interdisciplinary study Dr. Flowers has reported interesting heart rate dynamics in premature human infants. This research team from the University of Virginia and the College of William and Mary has elegantly described reversible transitions to large-amplitude periodic oscillations by a mathematical model based upon Hopf bifurcation theory."
Experimental Biology and Medicine is the journal of the Society of Experimental Biology and Medicine. To learn about the benefits of society membership visit www.sebm.org. If you are interested in publishing in the journal please visit www.ebmonline.org.
Nanoparticles as a Solution against Antibiotic Resistance?
15.12.2017 | Friedrich-Schiller-Universität Jena
Plasmonic biosensors enable development of new easy-to-use health tests
14.12.2017 | Aalto University
DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.
Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...
MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.
Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...
Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...
Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.
To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...
The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.
Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...
11.12.2017 | Event News
08.12.2017 | Event News
07.12.2017 | Event News
15.12.2017 | Power and Electrical Engineering
15.12.2017 | Materials Sciences
15.12.2017 | Life Sciences