Page 93 - Handbook of Biomechatronics

88 Jeff Christenson

The QRS complex indicates ventricle depolarization and contraction. The
T wave shows ventricular repolarization. The U wave indicates recovery of
the Purkinje conduction fibers (Purves et al., 2008b).
Heart rate is often correlated with physical exertion, so you also request
Jacob to have two EKG recordings performed, one with his old system while
walking at various rates on a treadmill, and one with his new at the same
speeds and durations. You hope to see that while using the new system,
Jacob has a slower heart rate.

6.3 O 2 Light Sensors
A less refined method of heart rate sensing is through use of an optical sensor.
By shining a near infrared (IR) light into a finger or earlobe and measuring
the intensity of the light on the opposite side, the pulse rate of the person can
be calculated, as well as how oxygenated is the blood. As more blood is in the
reflection zone, the less light will be shine through, facilitating pulse rate cal-
culation. Also, the more oxygen which the hemoglobin has absorbed, the
less the light intensity, allowing for oxygenation calculation (Silverthorn
et al., 2007).
While doing the EKG recordings, you decide to also use an O 2 light sen-
sor to corroborate the data. You place an O 2 light sensor on Jacob’s thumb
and record his heart rate while he uses the two prosthetic devices.

6.4 Oxygen Consumption Sensor
Respiration is constantly output as a signal to the environment when breath-
ing. It is useful to analyze the rate and oxygen content of inhalation and
exhalation. Such metrics are often related to energy consumption (Chan
et al., 2013).
Oxygen sensors are a fuel cell with a gas permeable membrane at one
end. The cell contains an electrolyte, anode, and cathode. As oxygen passes
through the membrane, a chemical reaction occurs between the elements,
creating a voltage which can be monitored and recorded by a computer
(Nieman et al., 2003). The person whose breath is being monitored must
wear a mask which controls the flow of inhaled and exhaled air.
With Jacob on the treadmill, you fit him with an oxygen mask to mea-
sure the oxygen content of his inhalations and exhalations. You hope to see
that he consumes less oxygen with the new system, indicating that the new
device is easier for him to use.