Jimmie Hagblad

Technical issues related to the long-term monitoring of blood flow at different depths using LDF and PPG

The aim of this study was to evaluate an integrated probe using LDF and multiple PPG, for the long-term aspects of skin temperature and blood flow variations at different tissue depths, and especially to investigate whether the presence of the probe affects the temperature. Measurements of temperature and blood flow were performed over 60 min on the lower back of ten subjects, lying on a mattress. The surface temperature of the skin was also measured before and after the 60 min period, and repeated with three probe configurations with the probe switched on, turned off and in the absence of a probe. A general increase in the blood flow was found to occur during the 60 min interval at all depths reached by this probe, but with variations over time. No difference was found in temperatures recorded for the different probe configurations. According to our measurements, the presence of the probe does not affect the skin surface temperature at 60 min. Our investigation shows that skin temperature can be expected to increase and approach the body core temperature by just lying in supine position on the mattress. The increase in temperature and blood flow that is known to occur, possibly attributable to pressure-induced vasodilatation, must be taken into consideration when performing these kinds of measurements.

Assessment of the Optical Interference in a PPG-LDF System Used for Estimation of Tissue Blood Flow

The aim of this study is to assess the optical cross interference in a system including laser Doppler flowmetry (LDF) and photoplethysmography (PPG) with regard to the illuminating power of PPG-LEDs and distance between the light detector/s and light source/s.

Long term monitoring of blood flow at multiple depths - observations of changes.

Detecting reduced circulation, which is a major factor in the development of pressure ulcers, can be done using optical methods. PPG and LDF can be combined and used to evaluate blood flow at different depths. In this study the use of a probe combining PPG and LDF to monitor multiple tissue depths is evaluated. The effects on blood flow and temperature without additional provocation was examined. Measurements were performed during 60 min and the use of an active probe was compared with the use of a semi-active probe turned off a major part of the time. Changes in temperature and blood flow using these probe configurations (active and semi-active probe) are compared; four different 5 min segments during a 60 min measurement. A general increase in both temperature and blood flow is found but this increase could not be concluded to occur due to the light sources of the probe.