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     Juerg Senior Member Username: Juerg Post Number: 2550 Registered: 04-2006 |
We just got some new info from our Friends in the Nederlands, whio worked on some of the ideas with NIRS and horses. So the next step up is the use of the trends and the FaCT ideas of using TSI % and tHb to find the optimal level or LBP without blood taken. At the end see a print out from a step test TSI % and tHb and it showed up exactly where the LBP was.Following some info from Artinis ( Netherland ) Here a summary. The principles of near-infrared spectroscopy (NIRS) is based on the fact that near-infrared (NIR) light can travel relatively easily through the tissue. This in contrast to visible light, which will be reflected or absorbed in the most superficial layers of the skin. The transparency of the tissue is due to the fact that the NIR light is mainly absorbed by only two chromophores, hemoglobin (Hb) and myoglobin (Mb), being the oxygen transporters of the blood and within the muscle cell. Roughly, they exist in two forms; with oxygen and without oxygen. The absorption of the NIR light by Hb and Mb is oxygen dependent, indicating that Hb/Mb with oxygen absorb another part of the NIR light, than Hb/Mb without oxygen. The ability to discriminate between oxy- and deoxy- forms of Hb/Mb is of great importance as it enables the measurement of tissue oxygenation. By choosing the right wavelengths for application of the modified Lambert-Beer law, local information about changes in absorption can be obtained and converted to changes in oxygenation. The methodology of NIRS is widespread in hospitals and research institutes. However, there are only very few reports of the use of NIRS in horses or other bigger animals. In this application note we will give some short examples on how it can be applied to horses. Example 1 The measurement was performed on the left prefrontal brain of the horse, with the horse laying on its right side. The physiological variables where: heart rate: 40 bpm, blood pressure 262/262 mmHg), arterial saturation 95%, inspired carbon dioxide fraction 3.6 %, ventilation rate 8/minute. The NIRS data was sampled at 10Hz and unfiltered, with optode distance of 3 cm. The skin underneath the optode holder was shaved. A differential pathlength factor of 4 was used. All graphs are displaying absolute concentration changes (microM) of the following chromophores over time in seconds. HbDiff gives an indication of the level of oxygenation in the brain. Red line – O2Hb Blue line – HHb Green line – tHb (= O2Hb+HHb) Brown line – HbDiff (= O2Hb-HHb) With spectral analysis tool built in the OxySoft analysis program (see top graph, FFT transform) the breathing rhythm can be clearly visualized in the signals, at a frequency of about 8/minute (see highest peak). Also the heart beat inside the brain becomes visible, found to be about 40 beats/min (second highest peak, not being a multiple of the first). This coincides with the heart rate measured with ECG. Note that the heartbeat is only visible in the O2Hb and tHb signals, which is to be expected as with this saturation on the arterial side of the blood supply. Furthermore we observe a small deoxygenation during the display of 4 minutes. The blood volume remains relatively constant. Please note that the measured arterial saturation does not give any indication on the actual de-oxygenation of the local muscle. NIRS measurements in equine science NIRS measurements in equine science / June 2010 2/2 Example 2 This measurement was performed with two channels. One channel was attached to the left tibia, the other channel to the right tibia muscle, with the horse laying on its side (position A), then on its back (position B).The physiological variables where the same as in example 1. Just like in Example 1 we can even more clearly observe rhythm of around 8/minute and the heart beat of 39 bpm. As expected we find the exact same pulsatile signals on both channels. Position A (see picture on the right) When the horse was laying on its right side, channel Tx1 was on the left leg (upwards) and channel Tx2 was on right leg (downwards). An interesting observation here is that the side on which the horse is laying starts to deoxygenate. This is demonstrated by the ever decreasing HbDiff signal in the following graph. In the same time the blood volume increases which is probably due to blood pooling because of gravity effects. This is demonstrated by the increasing tHb signal in the graph. The other leg did not show a deoxygenation. Position B (see picture on the left) Immediately after the horse was tilted to its back (all legs pointing upwards) the probes were replaced on the same position. On the side which had been downwards the blood (tHb) is now flowing out of the leg and even tends to show an increase in oxygenation. NIRS measurements in equine science / June 2010 3/2 Position B (see picture) Immediately after the horse was tilted to its back (all legs pointing upwards) the probes were replaced on the same position. On the side which had been downwards the blood (tHb) is now flowing out of the leg and even tends to show an increase in oxygenation. Conclusions It has been shown that it is possible to study hemodynamics and oxygenation changes in equine brain and muscle with the Oxymon MkIII system. Heartbeat and breathing rhythms could be clearly measured and verified by other established monitoring equipment. Since the horse was under anesthesia no specific muscle or brain activity was recorded nor expected. Signal levels (transmitted light) were high enough and stable. Blood flow changes where observed in muscle due to stretching and moving of the legs. The most interesting observation in muscle was that the side the horse was laying on was being deoxygenated. These results show that some relative simple measurements already show interesting and maybe clinically relevant observations. Most probably even more interesting and important findings can be done in the awake horse where brain function and muscle physiology can be studied in rest but also during running on the treadmill. Combining the OXYMON MkIII measurements with for example pressure measurements underneath a saddle can reveal where the pressure becomes to high to maintain an adequate oxygenation. Please contact the Artinis team if you want to discuss any other ideas or if you have questions for us regarding the technique.   |