Effects of temperature on peripheral blood oxygen saturation determined

by pulse oximetry
Introduction
Oxygen saturation is an essential element in the management and understanding of patient
care. Oxygen is tightly regulated within the body because hypoxemia can lead to many acute
adverse effects on individual organ systems. These include the brain, heart, and kidneys.
Oxygen saturation measures how much hemoglobin is bound to oxygen compared to how
much hemoglobin remains unbound. At the molecular level, hemoglobin consists of 4
globular protein subunits. Each subunit is associated with a heme group. Each hemoglobin
molecule subsequently has 4 heme-binding sites readily available to bind oxygen. Therefore,
hemoglobin can carry up to 4 oxygen molecules during oxygen transport in the blood. Due to
the critical nature of tissue oxygen consumption in the body, it is essential to monitor current
oxygen saturation. A pulse oximeter can measure oxygen saturation (see Image. Pulse
Oximeter). It is a noninvasive device placed over a person's finger. It measures light
wavelengths to determine the ratio of the current levels of oxygenated hemoglobin to
deoxygenated hemoglobin.

Principle
The pulse oximeter consists of a probe containing LEDs and a photodetector. The LEDs emit
light at fixed, selected wavelengths (Red light, 600 to 750 nm and infrared light, 850 to 1000
nm. The photodetector measures the quantity of light transmitted through a selected vascular
bed, such as a fingertip or earlobe. Pulse oximetry uses the Beer-Lambert law of light
absorption. This law describes how light is absorbed when it passes through a clear solvent,
such as plasma, that contains a solute that absorbs light at a specific wavelength, such as
hemoglobin. The absorption spectra of oxygenated and reduced hemoglobin differ. For this
reason, arterial blood appears red, while venous blood appears blue. However, because living
tissue absorbs light, it is difficult to determine the ratio of saturation of hemoglobin in the
body. The oximeter probe overcomes this difficulty by emitting light pulses, 1 red and 1
infrared. A detector is placed opposite the lights on the other side of the tissue. The diodes
switch on and off in rapid sequence, and the detector measures the differences. The
measurements feed into an algorithm in a microprocessor where the oxyhemoglobin
saturation is calculated and eventually displayed to the user (see Image. Monitor Shows
Mixed Venous Oxygen Saturation Value).

Materials
1. Pulse oximeter with compatible sensors
2. Thermometer (for monitoring skin and ambient temperature)
3. Environmental chamber or heating and cooling devices (e.g., ice packs, warm water
baths)
4. Subjects or volunteers (with ethical approval)
5. Alcohol wipes (for cleaning sensors)
6. Stopwatch or timer
7. Data collection sheet or software for recording measurements
Procedure
1. Participant Preparation
Recruit healthy, consenting volunteers.
Ensure participants rest for at least 10 minutes at room temperature (~22°C) to
stabilize baseline measurements.
Exclude individuals with conditions that may affect peripheral perfusion (e.g.,
Raynaud’s phenomenon).
2. Baseline SpO₂ Measurement
Attach the pulse oximeter sensor to a finger.
Record baseline SpO₂ and heart rate at room temperature.
3. Controlled Temperature Manipulation
Cold Condition:
Apply an ice pack or place the participant’s hand in a water bath at 10°C for 2
minutes.
Measure and record SpO₂, heart rate, and skin temperature.
Warm Condition:
Use a heating pad or place the hand in a water bath at 40°C for 2 minutes.
Measure and record SpO₂, heart rate, and skin temperature.
Repeat: Perform at least three cycles for each condition for consistency.
4. Ambient Temperature Manipulation
Use an environmental chamber to expose the entire body to temperatures ranging
from 15°C to 35°C.
Record SpO₂, heart rate, and skin temperature at each 5°C increment.
5. Data Analysis
Compare SpO₂ readings across temperature conditions using statistical methods (e.g.,
paired t-tests or ANOVA).
Advantages and disadvantages of pulse oximetry
The advantage of such a system is that it is noninvasive and allows for the conscious
monitoring of mouse heart rate while simultaneously monitoring the blood oxygen saturation.
the measured hemoglobin oxygen saturation may not always reflect accurately the respiratory
sufficiency, as the measured oxygen saturation reflects only the percent hemoglobin
saturation and not necessarily the amount of delivered oxygen. In cases of severe anemia, the
actual amount of oxygen delivered is low despite a high percent saturation. Additionally,
carboxyhemoglobin and methemoglobin all lead to falsely elevated oxygen saturation.