By Marleah Peabody
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 slow-ly 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.
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 cor-related 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 in-crease, that shows the
health of your autonomic nervous system."
The autonomic nervous sys-tem 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. Conver-sely, when the parasympathetic part is
dominant, heart rate and blood pressure decrease and digestion increases.
Take respiratory sinus arrhyth-mia, 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, supply-ing 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 auto-nomic nervous system tempo-rarily 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 pro-fessor 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 con-traction. 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 dis-tance 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 fre-quency." 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 sys-tem 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.
