Oximetry

Oxygen saturation is a relative measure of the quantity of dissolved or carried oxygen in a given medium. In medicine, oxygen saturation (S_O2) is measured as percentage of hemoglobin binding sites occupied by oxygen in the bloodstream. At low partial pressures of oxygen, most hemoglobin is deoxygenated.

The oxygen saturation level may be measured from different areas of the body and include:

• Arterial oxygen saturation (Sa_O2) to measure of the amount of oxygen bound to hemoglobin in the arterial system; commonly referred to Saturation of Peripheral Oxygen (Sp_O2) a when measured using oximetry
  
• Venous oxygen saturation (Sv_O2) to measure how much oxygen the body consumes
• Tissue oxygen saturation (St_O2) can be measured by near infrared spectroscopy to estimate tissue oxygenation in various conditions.

Arterial oxygen saturation can be measured using non-invasive oximetry techniques and avoids technical and ethical concerns associated with arterial sampling for blood oxygen (O₂) level determination.

Pulse oximetry or oximetry is a non-invasive method, which relies on the light absorption characteristics of saturated hemoglobin and thus allows monitoring of the oxygenation of a subject's haemoglobin. This involves placing a sensor on a thin part of the subject’s anatomy such as a fingertip or earlobe. A light containing both red and infrared wavelengths is passed from one side to the other. These light waveforms are transmitted by a semiconductor light emitting diode and detected by a photodetector.

Oximetry determines Sa_O2 by analyzing two wavelengths of light (660 nm and 910 nm) that are differentially absorbed by specific hemoglobin structures in the blood. Oxygenated hemoglobin (HbO₂) absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin (Hb) absorbs more red light and allows more infrared light to pass through. The relative absorption of these wavelengths reflects the ratio of oxygenated to total hemoglobin and this ratio is expressed as a percentage. As oximetry does not detect the presence of carboxyhemoglobin and methemoglobin, Sa_O2 must strictly be referred to as SpO2. For a healthy human adult, a Sp_O2 of 97% to 99% is considered normal.

LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

GLP and 21 CFR Part 11
For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

PowerLab Data Acquisition Systems
The PowerLab is a high-performance data acquisition unit suitable for a wide range of research applications. Typical applications include human and animal physiology, pharmacology, neurophysiology, biology, zoology, biochemistry, and biomedical engineering. Units are capable of recording at speeds of up to 400 000 samples per second continuously to disk (aggregate), and are compatible with instruments, signal conditioners and transducers supplied by ADInstruments, as well as many other brands. In addition to standard single-ended BNC inputs, 4 differential Pod ports are also available for direct connection of Pod signal conditioners and appropriate transducers. These systems include:

• ML866 PowerLab 4/30 - 4 Channels
  
• ML870 PowerLab 8/30 – 8 Channels
• ML880 PowerLab 16/30 – 16 Channels

PowerLab can also record pulse oximetry signals from meters that have an analog voltage recorder output such as those provided by:

• Nonin Medical Inc.
• Nellcor
• Datex-Ohmeda

Signal Conditoner
The Oximeter Pod connects to PowerLab models with Pod Ports or to the ML305 Pod Expander for use with PowerLabs without Pod Ports.

The Oximeter Pod takes approximately 10 seconds to determine an accurate output from the time it is plugged in and the transducer is attached to the subject. It only provides a reading of Sp_O2, with no associated pulse rate signal. The Oximeter Pod will provide an output signal between 70 to 100% Sp_O2 (values below 70% will not be registered). It provides one reading per second with a resolution of 1%.

Blood oxygen saturation (Sp_O2) in human subjects can be monitored with the:
ML320/F Oximeter Pod (Finger clip) that is supplied with a Finger Sp_O2 Sensor
ML320/E Oximeter Pod (Ear clip) that is supplied with an Ear Clip Sp_O2 Sensor

Blood oxygen saturation (Sp_O2) in animals can be monitored with the:
ML325/AC Animal Oximeter Pod (Animal Clip) that is supplied with an Animal Clip Sp_O2 Sensor
ML325/AW Animal Oximeter Pod (Tail Wrap) that is supplied with a Tail Wrap Sp_O2 Sensor

Sensors
MLT321 SpO2 Finger Clip
MLT322 SpO2 Ear Clip
MLT323 SpO2 Animal Clip
MLT324 SpO2 Tail Wrap

Human G protein Beta-3 subunit variant does not alter hypercarbic or hypoxic ventilatory response

H J Exner; H Groeben; D Rosskopf; W Siffert and J Peters, Clinical Physiology, 612-620, 2001

In human inspiratory and expiratory CO2 and O2 tensions were measured continuously near the subject's mouth by a mass spectrometer (RAMS M100; Marquette Hellige Medical, Hamburg, Germany)……… Instantaneous respiratory gas flow was measured by a low resistance transit-time ultrasonic flow meter (TUBA; Neltec AG, Kilchberg, Switzerland), and all gas volumes were corrected to BTPS conditions. Flow measurements were calibrated by passing several times a known volume of air through the flow head in either direction using a special large syringe………Arterial oxygen saturation was measured by pulse oximetry (Nellcor BP-1000, Nellcor, Hayward, USA). Arterial blood pressure and pulse rate were measured every minute by oscillometry (DinaMap, Critikon Inc., Tampa, USA). Instantaneous respiratory CO2 and O2 tensions, respiratory gas flow, and arterial oxygen saturation were stored on-line (MacLab, Chart Software spirometry chart extension, WissTech, Spechbach, Germany) on a laptop computer (sample frequency: 20 Hz per channel). Data were reduced off-line using the stored digital data to derive tidal volume, minute ventilation, and endexpiratory PCO2 and PO2, respectively.

Sleep-Disordered Breathing and School Performance in Children.

David Gozal, Pediatrics, 616-620, 1998

Children were screened for obstructive sleep apnea syndrome at home using a detailed parental questionnaire and a single night recording of pulse oximetry and transcutaneous partial pressure of carbon dioxide. ... overnight recording of pulse oximetry (SpO2) and pulse signal (Nellcor N 200; Nellcor Inc, Hayeard, CA) and trancutaneous carbon dioxide tension (TcCO2); Sensor-Medics Transcend Cutaneous Gas System; SensorMedics, Yorba Linda, CA) at home... Analog signals were digitally acquired onto a Macintosh PowerBook computer system at 60 Hz (sic) sampling frequency using MacLab. Subsequent off-line analysis was performed by a custom-designed program using Igor software (WaveMetrics, Lake Oswego, OR).