Vessel calibre and haemoglobin effects on pulse oximetry
M P McEwen1, G P Bull, K J Reynolds
1School of Computer Science, Engineering & Mathematics, Flinders University, Adelaide, Australia. Mark.McEwen@flinders.edu.au
Physiological Measurement
|July 29, 2009
Summary
Pulse oximetry accuracy can be improved by understanding how blood vessel size and hemoglobin affect readings. This study reveals these factors influence light transmission, impacting pulse oximeter measurements.
Area of Science:
- Biomedical Engineering
- Physiological Measurement
Background:
- Pulse oximetry is a vital clinical tool but suffers from empirical calibration needs and biases.
- Peripheral vasoconstriction and varying hemoglobin concentrations can affect pulse oximetry readings.
Purpose of the Study:
- To enhance understanding of the photoplethysmography signal used in pulse oximetry.
- To investigate the impact of blood vessel caliber and hemoglobin concentration on pulse oximetry measurements.
Main Methods:
- Measured light transmission across a wide spectrum through fingers of 57 individuals with known hemoglobin concentrations.
- Recorded digital temperature and performed simulations of light transmission through finger models.
- Analyzed ratios of pulsatile light attenuation, a key metric in pulse oximetry.
Main Results:
- Pulsatile light attenuation ratios were found to depend on peripheral temperature and blood hemoglobin concentration.
- Both in vivo and simulation results indicated pulsatile light attenuation is proportional to blood absorption coefficients only at low values.
- Discrete blood vessels act as barriers to light transmission, influencing pulse oximeter outputs.
Conclusions:
- Pulse oximeter outputs are influenced by hemoglobin concentration and the caliber of pulsing blood vessels.
- Vasoconstriction and vasodilation significantly affect blood vessel caliber, thereby impacting pulse oximetry.
- The influence of discrete blood vessels may explain discrepancies between the Beer-Lambert model and empirical pulse oximetry calibration.
Related Concept Videos
01:24Pulse Oximetry
Pulse oximetry, or SpO2, is a non-invasive method for continuously monitoring arterial oxygen saturation (SaO2). This procedure involves attaching a probe or sensor to the patient's fingertip, forehead, earlobe, or nose bridge. The sensor works by detecting changes in oxygen saturation levels through light signals generated by the oximeter and reflected by the pulsing blood under the probe.
Purpose
Average SpO2 values are greater than 95%. If the readings fall below 90%, it indicates that...
Purpose
Average SpO2 values are greater than 95%. If the readings fall below 90%, it indicates that...
01:19Guidelines For Measuring Vital Signs
Following these guidelines can help nurses accurately measure vital signs, assess changes in patient conditions, and provide timely treatment when necessary. Adhering closely to the guidelines ensures the accuracy and reliability of the results.
Before taking a patient's vital signs, a nurse would consider and assess the patient's comfort level and ensure appropriate equipment is available.
Before taking a patient's vital signs, a nurse would consider and assess the patient's comfort level and ensure appropriate equipment is available.
01:19Special considerations while measuring oxygen saturation
Assessing respiratory rate concurrently with pulse measurement is fundamental to patient care, providing valuable insights into the patient's respiratory function. The normal breathing rate for an adult usually falls within a normal range of 12 to 20 breaths per minute. Abnormal respiratory rates can signal underlying health conditions or the need for immediate intervention.
Ensuring accuracy in vital sign recordings while prioritizing patient comfort and minimizing anxiety is important.
Ensuring accuracy in vital sign recordings while prioritizing patient comfort and minimizing anxiety is important.
01:17Assessment of Diffusion and Perfusion
Understanding and evaluating diffusion and perfusion is critical in assessing a patient's respiratory and circulatory health. These processes play key roles in maintaining the body's internal environment, ensuring that tissues receive adequate oxygen while waste products are efficiently removed.
The Role of Diffusion in Respiration
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle...
The Role of Diffusion in Respiration
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle...
01:27Oxygen Transport in the Blood
Hemoglobin (Hb) is a crucial molecule in the human body, consisting of four polypeptide chains, each bound to an iron-containing heme group. This unique structure enables hemoglobin to bind to oxygen, with each molecule capable of combining with four molecules of oxygen, leading to rapid and reversible oxygen loading. When fully loaded with oxygen, it is called oxyhemoglobin, while hemoglobin that has released oxygen is called reduced hemoglobin or deoxyhemoglobin. As hemoglobin binds oxygen,...
01:30Equipments Used To Measure Blood Pressure
Direct Method
This invasive approach involves cannulating a peripheral artery. During each cardiac contraction, pressure generates mechanical motion within the catheter, transmitted through rigid, fluid-filled tubing to a transducer. This transducer converts mechanical motion into electrical signals displayed as waveforms on a monitor. An automatic flushing system prevents blood backflow. Due to the potential risk of unexpected arterial blood loss, this method is primarily used in intensive...
This invasive approach involves cannulating a peripheral artery. During each cardiac contraction, pressure generates mechanical motion within the catheter, transmitted through rigid, fluid-filled tubing to a transducer. This transducer converts mechanical motion into electrical signals displayed as waveforms on a monitor. An automatic flushing system prevents blood backflow. Due to the potential risk of unexpected arterial blood loss, this method is primarily used in intensive...