Heart Sounds

First, find your pulse on the side of your neck. Now breathe normally for several seconds. When you feel a regular pulse, exhale once, then inhale slowly and deeply. Did you feel your heartbeat speed up slightly? What you've just felt is called respiratory sinus arrhythmia. Don't worry —There's nothing wrong with you. Respiratory sinus arrhythmia is an example of normal, healthy heart-rate variability.

cartoon man’s insides and organs

Ankit Chander, an engineering science major at Penn State, has studied heart rate variability since last summer. "What is interesting," he says, "is that this field, on numerous occasions, has been shown to be a significant indicator of health. The first time this was recognized was in 1965, when two obstetricians realized that fetal mortality was highly correlated with how metronome-like the fetus's heart rate was. The more metronome-like it was, the less likely the fetus was to make it. So when you"—he takes a deep breath and taps on his chest —"feel that increase, that shows the health of your autonomic nervous system."

The autonomic nervous system keeps functions like body temperature, heart rate, and blood pressure within normal ranges. It is separated into two active parts: the sympathetic and the parasympathetic. When the sympathetic part is dominant, the heart rate and blood pressure increase and digestion slows down. Conversely, when the parasympathetic part is dominant, heart rate and blood pressure decrease and digestion increases.

Take respiratory sinus arrhythmia, for instance. When you inhaled deeply, receptors in your heart recognized that the blood flow to the heart had increased, and they sent that message to your brain. "In the cardiovascular system, supplying oxygenated blood to the body is a primary concern," Chander says. "If the heart sees lots of blood ready to enter it, it is highly advantageous to get that blood going into the heart, into the lungs, and back to the body that needs the oxygen." To do this, the autonomic nervous system temporarily weakened your parasympathetic responses. That's why your heart rate increased —your sympathetic responses strengthened for a few seconds.

Last summer, working with James Pawelczyk, associate professor in the College of Health and Human Development, Chander used a technique called signal analysis to create models for the relationship between heart rate and blood pressure. "Signal analysis is, essentially, time-to-frequency conversions," he explains. "Let's say I was graphing your heart rate, so say I have your EKG." He grabs my notebook and meticulously draws a few squiggles: one small, one big, one medium, flat line, then small, big, medium again. He points to one of the big peaks. "So this is your heart's big contraction. So, lubb," he says, then moves his finger to a point to the right of that peak, "dup. Those are the heart sounds that you hear. So what I'll do from that is I'll graph this distance versus time." He indicates the distance between the first big peak and the second, which is the heart rate measured in milliseconds. "So when these peaks are really far apart, you get a slow heart rate. And then from that I can graph the frequency." Once he has made his calculations, he can use mathematical transfer functions to predict blood pressure from heart rate, and vice versa.

Chander plans to use his summer research as the basis for his honors thesis. He is thinking of using signal analysis to study left ventricular assist devices—devices placed in the heart after congestive heart failure which cut down on the energy the heart exerts to pump, allowing it to heal more quickly. After these devices are in place, patients' heart rates tend to vary more. Chander remarks, "The autonomic nervous system affects the entire body—it affects the digestive system, it affects respiration—so the fact that we're just trying to heal the heart with these devices and we're seeing restoration to a normal state everywhere in the body . . . that's a very positive thing."

Ankit Chander is an engineering science major in the College of Engineering and the Schreyer Honors College. His thesis advisers are James Pawelczyk, Ph.D., asso-ciate professor of physiology and kinesiology in the College of Health and Human Development, 119 Noll Lab, University Park, PA 16802; 814-865-3453; jap18@psu.edu; and Roger Gaumond, D.Sc., associate professor of bioengineering in the College of Engineering, 233 Hallowell Bldg.; 865-1407; r5g@psu.edu. Chander's work was funded by the Heather L. Rayle Summer Scholarship. Writer Marleah Peabody graduated in May 2000 with a B.A. and honors in English.

kinesiology

Last Updated January 10, 2014