**5. Experimental detection of oxygen waveforms**

116 Infrared Spectroscopy – Life and Biomedical Sciences

wavelengths, 730 and 810 nm. The sensor, ( "SomaSensor"), is applied to the forehead with an integrated medical-grade adhesive. Two sensors can be placed in the forehead near Fp1 and Fp2. The spatially resolved spectroscopy (SRS) method is applied by using in the sensor two source-detector distances: a "near" (shallow), 3 cm from the source and a "far" (deep), 4 cm from the source. Both sample almost equally the shallow layers in the tissue volumes directly under the light sources and detectors in the sensor, but the distant "far" penetrates deeper into the brain. Using the SRS method, subtraction of the near signal from the far should leave a signal originating predominantly in the brain cortex. The measurement takes place in real time, providing an immediate indication of a change in the critical balance of

According to the producers: "Using the model at a 4 cm source-detector spacing and no signal subtraction, the overlying tissue and skull contribute, on average, about 45 percent of the signal while 55% is cerebral in origin. Subtracting the data from the 3 cm spacing (as the Oximeter does) reduces this extracerebral contribution to less than 15 percent. While the potential exists to develop an instrument that will reduce the extracerebral contribution to zero, subject-dependent variations in anatomy and physiology will likely cause variations of ±10%. While the extracerebral contribution is not zero, the noninvasive Somanetics INVOS Cerebral Oximeter provides a "predominately cerebral" measurement where over 85 percent of the signal, on average, is exclusively from the

The INVOS Cerebral Oximeter is an important tool in surgery rooms, saving lives and expenses. The producers explain: " Declining cerebral oximeter values occur frequently in cardiac surgery and reflect the changing haemodynamic profile of the balance between brain oxygen delivery and consumption. Since low rSO2 values correlate with adverse neurological and other outcomes, continuous assessment is a valuable patient management tool. Declining or low cerebral oximeter values are corrected with simple interventions".

The hemoencephalograph (HEG) is a single-distance CW spectrophotometer, which uses NIR light with two wavelengths, 660 and 850 nm. The light source consist of closely spaced emitting diodes (LED optodes). The source and an optode light receiver are mounted on a

The HEG measures the ratio of the intensity of the 660 nm light to the intensity of the 850

The HEG is not intended to measure rSO2. Nevertheless it is an important tool in the

Hershel Toomim, the inventor of HEG has noticed that he can influence the outcome by looking at the results. Since then many people were able to increase the HEG readings via

The HEG became an important tool for training local brain oxygenation. The HEG is a very sensitive device. The distance between the source and receiver is the same as the distance of the shallow detector of the Somanetics INVOS Cerebral Oximeter. Therefore the INVOS Oximeter covers larger brain tissue and is more stable and less influenced by biofeedback.

headband. The distance between the source and receiver is 3 cm.

oxygen delivery and oxygen consumption.

brain" (www.somanetics.com).

**4.2 The HEG** 

nm light.

biofeedback research.

such a biofeedback.

We started this research in Israel in the Pulmonary Unit of the Soroka University Hospital in Beer-Sheva. The study protocol was approved by the Helsinki (Ethics) Committee of the Soroka University Hospital. The investigation conforms with the principles outlined in the Declaration of Helsinki. The nature of the study was explained, and all subjects gave written consent to participate.

At the beginning our research was based on capnometer measurements of end tidal CO2 (EtCO2). The capnometer measures the CO2 concentration of the expired air. During the inspiration or breath holding the capnometer indications are zero. The capnometer enable us to follow the breathing periodicity.

We continued the research in the USA using the INVOS Cerebral Oximeter model 5100B of Somanetics Corporation and a capnometer of Better Physiology, Ltd. Both devices are noninvasive. The INVOS Cerebral Oximeter is based on most recent technological developments of near infrared spectroscopy (NIRS). With this device data are collected of regional oxygen saturation (rSO2) near the forehead with two optical sensors (for more details see www.somanetics.com). In addition to rSO2 one can determine the Blood Volume Index (BVI), which is an indicator of blood changes in the brain. This is a relative quantity, which could not be normalized with our oximeter.

The fastest recording rate of the 5100B oximeter is every 12 seconds from both left and right sensors. This time is much longer then the average period of about 4 seconds of normal respiration. In order to detect oxygenation periodicity we had to study respiration periods of about 36 seconds or larger (i.e. 3 data points or more for each breathing period). This is still a rather small amount of data points per respiration period. We have compensated for this small number by using a cubic spline interpolation of the data points, adding new interpolation points through this method. The cubic spline interpolation is a very effective method of smooth interpolation.

We found six people well acquainted with yoga pranayama, who could easily perform breathing exercises with periods around 36 seconds. All of them performed the following routine which lasted for 15 minutes.

They were asked to breathe in the following way: to inhale for 4 units of time (UOT), to hold the breath for 16 UOT and to exhale for 8 UOT, this we denote as the 4:16:8 (pranayama) routine.

The unit of time (UOT) is about 1 second. The yoga practitioners develop an internal feeling of UOT which they employ in their practices. They learn to feel their pulse or they learn to count in a constant pace. Often they practice with eyes closed. In order not to distract or

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 119

Fig. 2b. As Fig.2a.

Fig. 2c. As Fig.2a.

induce additional stress we preferred not to supply an external uniform UOT. The primary concern for this research was to have a constant periodicity and in this case the practitioners have succeeded to maintain it. The data were analyzed with spectral analysis which took into account non-stationary developments, which were subtracted from rSO2 and BVI data. Sharp picks corresponding to the breathing periodicity were found in the spectral analysis of EtCO2 (the amount of CO2 during expiration).

The motivation for this exercise was to see the relation of rSO2 (oxygenation) to the increasing amount of PaCO2. Actually instead of PaCO2 the end tidal CO2 (EtCO2) was measured (the maximal CO2 at exhalation), a quantity which approximate well the PaCO2**.** The periodicity of rSO2 was studied during the 4:16:8 respiration period (of approximately 32 UOT).

The rSO2 was measured with the aid of two sensors placed on the forehead, detecting oxygenation from the left hemisphere (frontal part in about 3 cm depth) and the right hemisphere (frontal part in about 3 cm depth)**.** At the same time data for evaluation of BVI were collected. In Fig. 2 the results of simultaneous measurements of EtCO2, rSO2 and differences in BVI are presented for the 6 subjects.

In order to check more precisely the periodic behavior, spectral analysis was performed on the EtCO2 data and the interpolated rSO2 and BVI data. The rSO2 and BVI data have a nonstationary component. The spectral analysis was performed on the raw EtCO2 data and on rSO2 and BVI interpolated data from which the non-stationary components were subtracted. The results are shown in Fig. 2a., Fig. 2b, Fig. 2c, Fig. 2d, Fig. 2e, Fig. 2f and Table 1. There is a clear overlapping between the periodicity of EtCO2 and the periodicities of rSO2 and BVI.

Fig. 2a. On the left hand side are given from the bottom to top: the readings of the capnometer in mm Hg, rSO2 from the right sensor (subtracted with 8%), rSO2 from the left sensor, the difference of BVI from the right sensor, and the difference of BVI from the left sensor (increased by 10). On the right hand side the corresponding spectral analyses of the waveforms are given.

Fig. 2b. As Fig.2a.

induce additional stress we preferred not to supply an external uniform UOT. The primary concern for this research was to have a constant periodicity and in this case the practitioners have succeeded to maintain it. The data were analyzed with spectral analysis which took into account non-stationary developments, which were subtracted from rSO2 and BVI data. Sharp picks corresponding to the breathing periodicity were found in the spectral analysis

The motivation for this exercise was to see the relation of rSO2 (oxygenation) to the increasing amount of PaCO2. Actually instead of PaCO2 the end tidal CO2 (EtCO2) was measured (the maximal CO2 at exhalation), a quantity which approximate well the PaCO2**.** The periodicity of

The rSO2 was measured with the aid of two sensors placed on the forehead, detecting oxygenation from the left hemisphere (frontal part in about 3 cm depth) and the right hemisphere (frontal part in about 3 cm depth)**.** At the same time data for evaluation of BVI were collected. In Fig. 2 the results of simultaneous measurements of EtCO2, rSO2 and

In order to check more precisely the periodic behavior, spectral analysis was performed on the EtCO2 data and the interpolated rSO2 and BVI data. The rSO2 and BVI data have a nonstationary component. The spectral analysis was performed on the raw EtCO2 data and on rSO2 and BVI interpolated data from which the non-stationary components were subtracted. The results are shown in Fig. 2a., Fig. 2b, Fig. 2c, Fig. 2d, Fig. 2e, Fig. 2f and Table 1. There is a clear overlapping between the periodicity of EtCO2 and the periodicities of rSO2 and BVI.

rSO2 was studied during the 4:16:8 respiration period (of approximately 32 UOT).

Fig. 2a. On the left hand side are given from the bottom to top: the readings of the

capnometer in mm Hg, rSO2 from the right sensor (subtracted with 8%), rSO2 from the left sensor, the difference of BVI from the right sensor, and the difference of BVI from the left sensor (increased by 10). On the right hand side the corresponding spectral analyses of the

of EtCO2 (the amount of CO2 during expiration).

differences in BVI are presented for the 6 subjects.

waveforms are given.

Fig. 2c. As Fig.2a.

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 121

 **PaCO2 rSO2 right rSO2 left BVI right BVI left AG** 1.47 (1.42-1.51) 1.49 (1.45-1.53) 1.48 (1.45-1.54) 1.49 (1.42-1.53) 1.42 (1.38-1.47) **NK** 2.15 (2.12-2.18) 2.14 (2.12-2.17) 2.14 (2.12-2.17) ------------------ 2.14 (2.11-2.17) **ML** 2.03 (1.98-2.07) 2.05 (2.01-2.15) 2.03 (1.95-2.08) 2.03 (1.99-2.07) 2.03 (2.00-2.06) **JM** 1.30 (1.26-1.34) 1.30 (1.26-1.33) 1.30 (1.17-1.40) 1.33 (1.29-1.37) 1.35 (1.31-1.38) **DZ** 1.62 (1.59-1.65) 1.62 (1.59-1.67) 1.62 (1.60-1.65) 1.63 (1.61-1.67) 1.61 (1.57-1.65) **DG** 1.70 (1.65-1.73) 1.79 (1.65-1.82) 1.70 (1.62-1.82) 1.66 (1.62-1.89) 1.71 (1.61-1.74)

Table 1. The position of the dominant frequencies (in units of 1/minute) of Fig. 2 in the

Can simple exercises be devised to increase cerebral blood flow (CBF) and/or cerebral oxygenation? We investigated exactly that question by using three different techniques, namely: a simple breathing procedure, solving an arithmetic problem and biofeedback.

Elsewhere (Gersten , 2011) we have analyzed the influence of arterial partial pressure of CO2 (PaCO2) on CBF and found that it may dramatically change the CBF. The changes involve the blood flow of the whole brain. It is a global effect. These results were used in another investigation (Gersten et al., 2011) in which yoga practitioners were increasing their PaCO2

spectral analysis, in parenthesis the extension of the half width is given.

through periodic yoga (pranayama) breathing techniques.

Fig. 2f. As Fig.2a.

**6. Simple exercises** 

Fig. 2d. As Fig.2a.

Fig. 2e. As Fig.2a.

Fig. 2f. As Fig.2a.

Fig. 2d. As Fig.2a.

Fig. 2e. As Fig.2a.


Table 1. The position of the dominant frequencies (in units of 1/minute) of Fig. 2 in the spectral analysis, in parenthesis the extension of the half width is given.
