Biomedical Engineering Reference
In-Depth Information
FIGURE 10.25
Temporal artery thermometry.
is normally lower than core body temperature, there is a cooling effect at the skin surface
due to the radiative heat loss to the surrounding air. To account for errors due to the natural
heat loss, the hand-held scanning thermometer measures ambient temperature at the same
time it measures the absolute temperature of the skin surface over the temporal artery and
computes arterial temperature using a heat balance equation.
Ingestible Temperature Pill
Heat exhaustion (also known as hyperthermia or heatstroke) occurs when the body can-
not adequately dissipate an internal rise in core body temperature. It can be caused by an
excessive exposure to heat or dehydration—particularly in football players during sporting
activities, astronauts during space flights, or soldiers, and can ultimately lead to life-threat-
ening brain damage or even death. To minimize the potential of heatstroke, an ingestible
thermometer pill was developed in the mid-1980s in collaboration with NASA (Figure 10.26)
to monitor core body temperature in real-time with an accuracy of 0.1
C. Once ingested into
the body, the
3
4
-inch-long battery-operated pill transmits wirelessly core body temperature
as it travels harmlessly through the gastrointestinal tract. A small quartz crystal oscillator
inside the pill vibrates at a frequency that is proportional to core body temperature. The pill
converts this change in crystal frequency to a magnetic field with a radius of about 1 meter
that can be picked up wirelessly by an external data recorder. The silicone-coated pill
remains in the body for about 24-36 hours before it is excreted.
10.4 BLOOD GAS SENSORS
CO
2
and pH) are frequently performed on
critically ill patients in both the operating room and the intensive care unit. They are used
by the physician to adjust mechanical ventilation or to administer pharmacological agents.
These measurements provide information about the respiratory and metabolic imbalances
in the body and reflect the adequacy of blood oxygenation and CO
2
elimination.
Measurements of arterial blood gases (
p
O
2
,
p
