"I was standing in my
kitchen and turned to put something on the table. Next thing I knew, I was
on the floor."
"I turned to grab Fifi's leash and tipped right
over."
David Solomon hears turning and falling stories all the
time. As a clinical neurologist who specializes in ills that usually
involve the inner ear's vestibular system, Solomon has seen many patients
who complain of falling. A number of them suffer from dizziness or
vertigo. But he's noticed that some people fall who have neither. Nor are
they particularly frail. They tend to fall while turning.
"How do you maintain a stable gaze and body during a turn? Reflexes," says Solomon.
Little is known about what triggers falls, says
Solomon, newly arrived at Hopkins from the University of Pennsylvania. And
because it's difficult to know where to begin a search, exploring the tie
between turning and taking a tumble makes sense. Solomon spends his
non-clinic time in his Kennedy Krieger laboratory, exploring parameters of
movement and position when people turn. The idea is to define normal
turning and compare it with that of patients with disorders like
Parkinson's disease (PD) that make them prone to fall.
Basically,
the ability to keep upright depends on a flow of signals from the visual
system, the inner ear and from muscles, tendons and joints that relay
feedback on body position. The brain and inner ear make sense of those
signals. And the latter responds with reflexes that maintain
posture.
"We know inner ear reflexes control eye movement and know
pretty much how they do it," says Solomon. "But now we're interested in
how they also control the muscles important in turning: those in your
ankle, leg and hip. How you maintain both a stable gaze and a stable body
during a turn depends on those reflexes."
Take slipping, for
example. Most people turn with a foot pivot-the slip of one foot relative
to the ground. And to do that effectively and not fall, says Solomon, the
inner ear must monitor the slip. Is it too far? Not enough? Can you move
your feet quickly enough to stop the slip so you don't end up in a leg
tangle like Goofy on skis?
All this is fodder for Solomon's basic
studies which involve measuring people's body inertia, angular momentum
and other staples of college physics. But with that baseline laid, he's
now characterizing disease. Early work suggests how patients differ from
the norm and might be helped.
With PD or with some types of
vestibular loss, for example, patients tend to turn en bloc: The head's
fixed to the body and joints are stiff. Turns are slow, often via multiple
steps instead of a pivot. "So we 're trying to offer a rational approach,
driven by data, to make patients more stable-to identify specific joints
or muscles you could have physical therapists loosen up."
Solomon's
studies may apply, he says, to deep brain stimulation (DBS), the
electrode-based treatment for some PD patients that's brought dramatic
improvement in hand movement and lessening tremor. "You might boost
posture and walking if you knew how to vary stimulation to affect
appropriate muscles. Perhaps our work will show a new spot for the
electrode, or a perfect way to tune it, to do even more for patients."
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