Behind the Black Box: Medical Instruments

Why Do We Care?

• Medical equipment can be used to understand the human body better.– Diagnosis– Monitoring– Treatment

• Also 6 Billon Dollar Industry.

Part of A Bigger System

• Throughout human history, engineering has driven the advance of civilization.

• Even now, the world has multiple issues on which engineers could be working.

• As a result, the National Academy of Engineering (NAE) has defined some challenges facing us in this century.

14 Grand Challenges• Make solar energy economical• Provide energy from fusion• Develop carbon sequestration methods• Manage the nitrogen cycle• Provide access to clean water• Restore and improve urban infrastructure• Advance health informatics• Engineer better medicines• Reverse-engineer the brain• Prevent nuclear terror• Secure cyberspace• Enhance virtual reality• Advance personalized learning• Engineer the tools of scientific discovery

Some Background Anatomy Review

“Lub-Dub”

• The “lub” sound comes first in the heartbeat and is the longer of the two heart sounds.

• The “lub” sound is produced by the closing of the AV valves at the beginning of ventricular systole.

• The shorter, sharper “dub” sound is similarly caused by the closing of the semilunar valves at the end of ventricular systole.

The Cardiac Cycle

• Systole: The atria contract and push blood into the ventricles. The ventricles contract to push blood into the aorta and pulmonary trunk.

• Diastole: All 4 chambers of the heart are in diastole as blood pours into the heart from the veins. The ventricles fill to about 75% capacity during this phase and will be completely filled only after the atria enter systole.

Circulation

Pulse Plethysmograph

• This pulsatile change in blood pressure results in a value change in the somewhat elastic blood vessels in the body.

• A pulse plethysmograph measures volume changes using light transmittance.

Some Math Review

Blood Oximetry

• Oxygenated blood absorbs light at 660nm (red light), whereas deoxygenated blood absorbs light preferentially at 940nm (infra-red).

• Pulse oximeters consist of two light emitting diodes, at 600nm and 940nm, and two light collecting sensors, which measure the amount of red and infra-red light emerging from tissues traversed by the light rays.

Now Something Fun

• Divide into 4 groups at the lab tables. • You should have a device called a pulse oximeter on

your table. • Take your heart rate without the pulse oximeter first.• Have someone else record your waveform.• Next ….