L5 - Bioinstrumentation and Body Temperature

Bioinstrumentation

Clinical Data

• Temperature
• Oxygen saturation
• Blood pressure
• Biopotential

Laboratory Data

• pH
• Glucose
• Light absorbance
• Fluorescence

Sensors

Sensor	Material	Measure
Thermal sensors	Thermocopple	Body temperature
Mechanical sensors	Piezoelectric materials	Force/Pressure
Electrical sensors	Electrodes	Electric Potential
Chemical sensors	Ion-selective electrodes, Amperometric sensor	Presence/Concentration of specific chemical
Optical sensors	Photodiode arrays, photomultiplier tubes	UV, visible , or IR light

Fever

1. Macrophages at a site of infection or inflammation
2. Release pyrogens into the blood
3. Acts on cells in hypothalamus
4. Release messengers that raise body temperature

Glass Thermometers

• Mercury/Alcohol is confined to a reservoir connected to a narrow glass tube, it is then expanded when warmed.
• Pre-calibration is done by marking freezing point as 0 and boiling point as 100. (assuming water expands at a linear rate)

Glass thermometers is slow, and mercury is highly toxic to the nervous system.

Celsius and Fahrenheit

$$T_{degC}=\frac{5}{9}(T_{degF}-32)$$

Electronic Thermometers

• Uses thermocouples/thermistors

It will usually underestimate the core body temperature

Thermocouple

$$R_T=R_0{e}^{\beta (\frac{1}{T}-\frac{1}{T_0})}$$

$R_T$	Measured resistance
$R_0$	Resistance at $T_0$
$T$	Temperature ($\mathrm{K}$)
$T_0$	Reference temperature ($298\mathrm{K}$)
$\beta$	Material characteristic coefficient

To obtain a decaying curve, $\beta$ is positive because $\frac{1}{T}-\frac{1}{T_0}$ is negative.

Infrared (IR) Thermometers

1. Body emits IR radiation
2. Thermopile detector/pyroelectric crystal converts IR radiation to heat
3. Heat is turned into electrical signal ($\propto$ IR energy)

It will underestimate the core body temperature

Catheterization

• Catheter (long and thin tube made of a biocompatible, flexible polymers)
• Can be loaded with sensors for temperature, blood pressure, etc.

Although being the most accurate, it is invasive, expensive and risky.