Absorbance of two light wavelengths through human fingertip during small changes in hand position, using a light transmission probe

Abstract

Absorbance of two light wavelengths through human fingertip during small changes in hand position, using a light transmission probe (Nellcor DS100A Adult SpO2 sensor) These are data from a paper submitted to Physiological Measurement. This journal has a policy that data be shared in a data repository. The study “Effect of venous pressure on light absorbance by the finger” was ethically approved by the School of Engineering Ethics Officer in the University of Edinburgh. At the time the study was done, this process involved a standard form that was submitted to, and approved by, the department’s research administrator. The Principal Investigators were Dr Gordon Drummond (School of Medicine and Veterinary Medicine) and Dr Jamie Marland (School of Engineering). Written informed consent was obtained from all subjects. Conditions. The subjects were non smokers and had not recently taken food or caffeine. They were allowed time to acclimatise to a warm environment. The study room was quiet and dimly lit. The mean room air temperature was 23.7(SD 0.9) °C, and never cooler than 22°C: relative humidity was between 34 and 45%. The subject sat in a comfortable upholstered armchair with full back and head support. The left arm and hand, with hand pronated and the fingers outstretched, were supported in a padded trough with the elbow flexed at about 30° from the extended position. The entire arm was aligned in a horizontal plane at the level of the shoulder, using arm supports suspended using a pulley system so that the arm could be promptly moved, with no subject effort, to either raise or lower the hand by exactly 5 cm above and below the original position, with an axis of rotation close to the shoulder. Measurements A standard sphygmomanometer cuff, (14 cm x 48 cm) containing a flexible elastic bladder (10×28 cm) was loosely wrapped around the subject’s left wrist and lower forearm and firmly secured. When deflated, this cuff did not constrict the wrist. A pulse oximeter transmission probe (Nellcor DS100A Adult SpO2 sensor, Covidien, Mansfield, MA02048 USA), with two light emitting diodes (LEDs, 660 nm and 905 nm wavelengths) and a photodiode detector, was applied to the middle finger. We made sure the end of the fingertip did not touch the inside of the probe. During recording, the hand was covered first in a black felt glove and then an opaque black plastic bag. The probe was connected to a commercial pulse oximeter analogue front-end board (AFE4490SPO2EVM, Texas Instruments, Dallas, Tx USA). Data were sampled at 370 Hz using the manufacturer’s GUI software (Texas Instruments), recorded to a battery powered laptop computer, and subsequently processed using Python3 software. Before each study, the light intensity from the LEDs in the probes was measured without the finger present. The probe was fixed open using black vertical cardboard props at each edge of the finger location, so that it was held open in the position it would take when the finger was inserted, and all extraneous light was excluded. The power settings for the LEDs were adjusted to prevent saturation of the photodiode sensor pathway, and then not changed for the duration of the study. These values were used as measures of the incident radiant flux (ϕi). Absorbance was later calculated as log10 (ϕi / ϕt), where ϕt was the recorded signal. After recording started there was an initial 2 minute run-in period. The arm was then moved to the first study position, either 5 cm above or below the horizontal. To minimise any order effect, this position was randomised for each subject, either up or down, using allocation by sealed envelope. The starting position is indicated in the subject data. After five minutes in the first position, the arm was moved to the alternative position for another five minutes, and then placed horizontally for a recovery period of two minutes. In the second phase of the study, the arm was moved into the up position for 5 minutes of observation. The wrist cuff was then inflated, in less than five seconds, to a pressure of 10 cm water (water manometer) and this pressure was sustained for a further 5 minute period of observation. The times of these events are stated in the data. Each CSV file is for a single subject. The data have been processed to represent Absorbance, as stated above in this description The columns are labelled. Time is in seconds from the recording start. The file basic data contains Subject numbers, physical data, times of recording periods, and hand position for the first and second time periods. Skin pigment noted if not white