**1. Introduction**

110 Infrared Spectroscopy – Life and Biomedical Sciences

vibratory stimulus was fixed. Namely, bottom-up processing of sensory information from afferent fibers is influenced by its top-down processing. On the other hand, it remains unclear what directly reduced the activity of the right premotor area. To answer this question, it is necessary to examine if an object presented outside the angle of illusion changes the degree of illusory movements. In addition, it will be necessary to study the status of activities of visual cortical areas as well as of prefrontal areas rather than study

[1] Roll JP, et al: Kinaesthetic role of muscle afferents in man, studied by tendon vibration

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[3] Naito E et al: Illusory arm movements activate cortical motor areas: a positron emission

[4] Naito E et al: Kinesthetic illusion of wrist movement activates motor-related areas.

[5] Naito E, et al: Internally simulated movement sensations during motor imagery activate cortical motor areas and the cerebellum. J Neurosci 22: 3683-3691, 2002 [6] Naito E, et al: Somatic sensation of hand-object interactive movement is associated with activity in the left inferior parietal cortex. J Neurosci 26: 3783-3790, 2006 [7] Naito E, et al: Human superior parietal lobule is involved in somatic perception of bimanual interaction with an external object. J Neurophysiol 99: 695-703,2008 [8] Naito E, et al: Dominance of the right hemisphere and role of area 2 in human

[9] Schroeter L, et al:Age dependency of the hemodynamic response as measured by

[10] Ehrsson HH, et al: That's my hand! Activity in premotor cortex reflects feeling of

[11] Lankner JR: Some proprioceptive influences on the perceptual representation of body

functional near-infrared spectroscopy.Neuroimage19: 555-564,2003

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premotor areas.

**5. References** 

Breathing may have dramatic effects on the human cerebral blood flow (CBF) and cognition. This was already known long time ago to Chinese (Li Xiuling, 2003), Hindus (Kuvalayananda, 1983) and Tibetans (Mullin, 1996). The main parameter influencing the CBF is the arterial partial pressure of carbon dioxide (PaCO2). About 70% increase in PaCO2 may double the blood flow (Sokoloff, 1989, Guyton, 1991). The increase of blood flow to the brain results in an increase of nutrients and oxygen, which may influence to great extent brain's physiology.

On the other hand lowering the PaCO2 through hyperventilation found an application in neurosurgery (Feihl and Perret, 1994).

An evaluation of the CBF dependence on PaCO2 was given by Gersten (Gersten, 2011). The human normal value of PaCO2 is about 40 mmHg. Fig. 1 depicts our estimation of the changes of CBF as a result of changing PaCO2 from normal. The estimate is based on the data of Refs. (Reivich 1964, Ketty and Schmidt 1948, Raichle et all 1970). An increase of only 12.5% from normal in PaCO2 leads to the state of hypercapnia (PaCO2 above 45 mm Hg).

With aging both CBF and PaCO2 tends to fall down, therefore breathing exercises (or procedures) with the aim to increase PaCO2 and CBF might be important in preventing and alleviating neurodegenerative diseases. They may be also important in improving intellectual abilities. The amount of PaCO2 in our arteries is proportional to the CO2 which was metabolized by the organism and inversely proportional to the lung ventilation (i.e. to the amount of air exchanged between the lungs and the environment in one minute).

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 113

deoxy-hemoglobin (Hb) and cytochrome oxidase (CtOx). In the last 20 years there was an

The devices that were used in our experiments were : Somanetics's INVOS Brain Oximeter (IBO) and Toomim's HEG spectrophotometer. The performances of both devices were compared including their merits and drawbacks. The IBO is based on extensive efforts of an R&D group to develop a reliable device, which measures well the rSO2. It is now used efficiently in operating rooms, saving human lives and expenses. Its use for research however has two drawbacks: the sampling rate is too small and the readings are limited to only two significant digits. The HEG device does not have these drawbacks, but is not developed sufficiently at this time to measure rSO2. We have measured the HEG readings and compared them with the rSO2 readings of the IBO. Our findings show that the HEG can

Results of an experiment are presented whose aim is to explore the relationship between respiration and cerebral oxygenation. Measurements of end tidal CO2 (EtCO2) were taken simultaneously with cerebral oxygen saturation (rSO2) using the INVOS Cerebral Oximeter of Somanetics. Due to the device limitations we could explore only subjects who could perform with a breathing rate of around 2/min or less. Six subjects were used who were experienced in yoga breathing techniques. They performed an identical periodic breathing exercise including periodicity of about 2/min. The results of all six subjects clearly show a periodic change of cerebral oxygenation with the same period as the breathing exercises.

We tested the hypothesis that simple breathing exercises may significantly increase cerebral blood flow (CBF) and/or cerebral oxygenation. Eighteen subjects ranging in age from nineteen to thirty nine participated in a four-stage study during which measurements of end tidal CO\_2 (EtCO2 - by capnometer) and local brain oxygenation (by near-infrared spectroscopy (NIRS) sensor) were taken. The four stages were 1) baseline, 2) breathing exercises, 3) solving an arithmetic problem, and 4) biofeedback. During the breathing exercises there was a significant increase in EtCO2 indicating a significant increase in global CBF. The increase in global CBF was estimated on the basis of a theoretical model. During the arithmetic and biofeedback tasks there was a significant increase in the local (Fp1) oxygenation, but it varied between the different participants. The results may lead to new clinical applications of CBF and brain oxygenation monitoring and behavioral control.

The study of the human brain made a big step forward with the introduction of noninvasive techniques, among them the near-infrared spectroscopy (NIRS). This technique allows to measure the oxygenation of the brain tissue (Alfano et al., 1997, 1998; Chance 1998, 1998a; Delpy and Cope, 1997; Hoshi, 2003; Obrig, 2003; Rolfe, 2000; Strangman et al., 2002). The light, with wavelengths 650-1000 nm, penetrates superficial layers of the human body, among them the skin, the scull and the brain. It is either scattered within the tissue or

The visible light has wavelengths 400-700 nm, some individuals can see up to 760 nm. Formally, the red light extends within the wavelengths of 630-760 nm, and the near infrared

enormous growth in the instrumentation and applications of NIRS.

Similar periodic changes in blood volume index were observed as well.

absorbed by absorbers present in the tissue (chromophores).

be used to measure relative changes of rSO2.

**2. Fundamentals of NIRS** 

Fig. 1. Estimated changes of human CBF from normal (100%) against *PaCO*<sup>2</sup> . Normal *PaCO*<sup>2</sup> =40 mm Hg is assumed, it corresponds to ordinate value of 100%. From (Gersten, 2011).

An instantaneous way to change PaCO2 can be accomplished by influencing the ventilation. Respiratory periodicities were observed in fMRI, but they were treated as artifacts (Windischberger et al., 2002) or as a noise (Raj et al., 2001). The main research effort was directed towards the elimination of the effect of the respiratory periodicities. Our aim is to study the effect of respiration on brain's oxygenation and performance.

Near infrared spectroscopy (NIRS) is an efficient way to probe brain's oxygenation (Rolfe, 2000; Thavasothy et al., 2002; Elwell et al., 1996). Brain oxygenation increases with an increase of PaCO2 (Imray et al.,2000, Thavasothy et al., 2002). In this chapter we examine the dependence of brain's oxygenation on PaCO2.

The technique of near infrared spectroscopy (NIRS) allows to measure the oxygenation of the brain tissue. The particular problems involved in detecting regional brain oxygenation (rSO2) are discussed. The dominant chromophore (light absorber) in tissue is water. Only in the NIR light region of 650-1000 nm, the overall absorption is sufficiently low, and the NIR light can be detected across a thick layer of tissues, among them the skin, the scull and the brain. In this region, there are many absorbing light chromophores, but only three are important as far as the oxygenation is concerned. They are the hemoglobin (HbO2), the

Fig. 1. Estimated changes of human CBF from normal (100%) against *PaCO*<sup>2</sup> . Normal *PaCO*<sup>2</sup> =40 mm Hg is assumed, it corresponds to ordinate value of 100%. From (Gersten,

study the effect of respiration on brain's oxygenation and performance.

dependence of brain's oxygenation on PaCO2.

An instantaneous way to change PaCO2 can be accomplished by influencing the ventilation. Respiratory periodicities were observed in fMRI, but they were treated as artifacts (Windischberger et al., 2002) or as a noise (Raj et al., 2001). The main research effort was directed towards the elimination of the effect of the respiratory periodicities. Our aim is to

Near infrared spectroscopy (NIRS) is an efficient way to probe brain's oxygenation (Rolfe, 2000; Thavasothy et al., 2002; Elwell et al., 1996). Brain oxygenation increases with an increase of PaCO2 (Imray et al.,2000, Thavasothy et al., 2002). In this chapter we examine the

The technique of near infrared spectroscopy (NIRS) allows to measure the oxygenation of the brain tissue. The particular problems involved in detecting regional brain oxygenation (rSO2) are discussed. The dominant chromophore (light absorber) in tissue is water. Only in the NIR light region of 650-1000 nm, the overall absorption is sufficiently low, and the NIR light can be detected across a thick layer of tissues, among them the skin, the scull and the brain. In this region, there are many absorbing light chromophores, but only three are important as far as the oxygenation is concerned. They are the hemoglobin (HbO2), the

2011).

deoxy-hemoglobin (Hb) and cytochrome oxidase (CtOx). In the last 20 years there was an enormous growth in the instrumentation and applications of NIRS.

The devices that were used in our experiments were : Somanetics's INVOS Brain Oximeter (IBO) and Toomim's HEG spectrophotometer. The performances of both devices were compared including their merits and drawbacks. The IBO is based on extensive efforts of an R&D group to develop a reliable device, which measures well the rSO2. It is now used efficiently in operating rooms, saving human lives and expenses. Its use for research however has two drawbacks: the sampling rate is too small and the readings are limited to only two significant digits. The HEG device does not have these drawbacks, but is not developed sufficiently at this time to measure rSO2. We have measured the HEG readings and compared them with the rSO2 readings of the IBO. Our findings show that the HEG can be used to measure relative changes of rSO2.

Results of an experiment are presented whose aim is to explore the relationship between respiration and cerebral oxygenation. Measurements of end tidal CO2 (EtCO2) were taken simultaneously with cerebral oxygen saturation (rSO2) using the INVOS Cerebral Oximeter of Somanetics. Due to the device limitations we could explore only subjects who could perform with a breathing rate of around 2/min or less. Six subjects were used who were experienced in yoga breathing techniques. They performed an identical periodic breathing exercise including periodicity of about 2/min. The results of all six subjects clearly show a periodic change of cerebral oxygenation with the same period as the breathing exercises. Similar periodic changes in blood volume index were observed as well.

We tested the hypothesis that simple breathing exercises may significantly increase cerebral blood flow (CBF) and/or cerebral oxygenation. Eighteen subjects ranging in age from nineteen to thirty nine participated in a four-stage study during which measurements of end tidal CO\_2 (EtCO2 - by capnometer) and local brain oxygenation (by near-infrared spectroscopy (NIRS) sensor) were taken. The four stages were 1) baseline, 2) breathing exercises, 3) solving an arithmetic problem, and 4) biofeedback. During the breathing exercises there was a significant increase in EtCO2 indicating a significant increase in global CBF. The increase in global CBF was estimated on the basis of a theoretical model. During the arithmetic and biofeedback tasks there was a significant increase in the local (Fp1) oxygenation, but it varied between the different participants. The results may lead to new clinical applications of CBF and brain oxygenation monitoring and behavioral control.
