**6. Simple exercises**

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 through periodic yoga (pranayama) breathing techniques.

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 123

participated in the experiment in which HEG and CO2 data were recorded for 5 intervals of baseline, simple breathing exercises, simple arithmetic tasks and biofeedback. The results show that almost all participants could increase their brain oxygenation or CBF, but in each case it was strongly dependent on one of the three methods used. We can conclude that it is possible to substantially increase local oxygenation or global CBF using one of the three methods described above, but the preferred method is highly individual. The protocol of this research was approved by the IRB of Hunter College of the City

It is well known that breathing patterns affect the CO2 levels in the arteries (Fried and Grimaldi, 1993), which in turn can affect cerebral (brain's) blood circulation and oxygenation. Mental work and biofeedback may affect both local as well as global oxygen

The influence of breathing exercises, problem solving and biofeedback on brain oxygen and CO2 arterial levels were considered in an experiment outlined below. The experiment dealt

1. The physiological effects of mild breathing exercises on increasing CO2 and oxygen

2. The physiological effects of problem solving (a particular case of mental performance)

An experiment dealing with the second and third topic gives qualitative information about how much the oxygen levels will rise during problem solving and biofeedback, while an experiment dealing with the first topic will give the same information, but this time, from breathing exercises. It is important to note that in the first topic global CBF is concerned,

The participants were connected to the two devices needed for the experiment: the capnometer that measured end tidal CO2 and the Cerebral Oximeter. The connection used was made via a sensor placed on the forehead at Fp1. The CO2 levels were estimated using a capnometer produced by Better Physiology LTD, which measures end tidal CO2 (EtCO2) of the exhaled air (EtCO2 is highly correlated with the PaCO2 levels of the arteries). All participants received their own new nasal insert which were sterilized before each use and connected to the capnometer. The data were detected via USB output cable connected to the

The oxygen levels were estimated using two devices: the HEG which was calibrated to the INVOS Cerebral Oximeter produced by Somanetics Corp. (see www.somanetics.com) and based on advanced near infrared spectroscopy (NIRS) technology. A sensor was attached to the forehead measuring the oxygenation in a depth of about one inch inside the brain. The devices that were used were non-invasive and FDA approved, fully automated and did not

The data of the capnometer and oximeters were combined together and analyzed using Matlab subprograms. The participants were asked to do paced breathing exercises as

3. The physiological effects of biofeedback on the CO2 and oxygen levels in the brain.

while in the second and third topic the local brain oxygenation at the Fp1 area.

University of New York.

levels in the brain.

with 3 topics

**6.1 Methods and materials** 

levels in the brain.

on the CO2 and oxygen levels in the brain.

computer and stored for subsequent review.

require special precautions. The data were stored on a computer.

We will demonstrate that significant increase of PaCO2 (and of total CBF) can be achieved with untrained people using very simple breathing procedures. The reason for that is the dependence of PaCO2 on ventilation (West, 1992)

$$\text{PaCO}\_2 = \text{K} \frac{\dot{V}\_{\text{CO2}}}{\dot{V}\_A}, \text{ K} = 863 \, mm \, \text{Hg} \tag{1}$$

where *CO*<sup>2</sup> *<sup>V</sup>* is the CO2 production (dependent on the metabolism) and *VA* is the alveolar ventilation. This means that the PaCO2 is inversely proportional to ventilation. Therefore it is possible to control the PaCO2 by either breathing slowly (and not increasing the tidal volume substantially) or by holding the breath. Untrained people increase their tidal volume while breathing more slowly, but the overall effect is usually a slight increase in PaCO2. People trained in breathing exercises may increase their PaCO2 considerably by learning to control their tidal volume. For very small ventilation a correction is needed to the PaCO2 formula (Riggs, 1970),

$$\text{PaCO}\_2 = K \frac{\dot{V}\_{\text{CO}\_2}}{\dot{V}\_A - \dot{V}\_D}, \quad \dot{V}\_D = 2.07 \text{ l/min} \quad \text{ } \tag{2}$$

where *VD* is the contribution of the dead space.

It is well known that concentrating on a mental problem changes brain's oxygenation locally (Chance et al, 1993). This finding was also applied further to solving a simple arithmetic problem on local brain oxygenation near the Fp1 area.

Hershel Toomim (Toomim et al., 2004) developed the device called hemoencephalograph (HEG), whose readings is related to regional cerebral oxygenation (Gersten et. al, 2007c). The device has many advantageous features which allowed us to use it in our experiment. Toomim has observed that he can influence the results by looking at the HEG display, which is essentially a biofeedback technique used by us as well. As a result of Toomim findings many biofeedback experiments were conducted with the HEG, confirming the effect. The readings of the HEG are very sensitive to changes in the range of normal oxygenation of the brain. This is not the case with INVOS brain oximeters used in operation rooms whose main aim is to detect abnormally low oxygenation states. For that reason we preferred to use the HEG to detect biofeedback effects even though it is much simpler and less sophisticated compared with INVOS cerebral oximeters (Gersten et al., 2009).

The readings of the HEG are normalized to 100 (SD=20), the average on 154 adult attendants at professional meetings (Toomim et al, 2004). We have compared (Gersten et al., 2009) the readings of HEG with the regional saturation of oxygen (rSO2) readings of the INVOS cerebral oximeter of Somanetics. This allowed us to make estimates of the ratios of rSO2 using the HEG. We found,

$$\mathbf{x}\_1/\mathbf{x}\_2 = \ln(\mathbf{y}1/32.08)/\ln(\mathbf{y}2/32.08), \mathbf{x} \equiv \mathbf{r}\mathbf{S}\mathbf{O}\_2, \mathbf{y} \equiv \text{HEG reading},\tag{3}$$

where ln is the natural logarithm, but the ratio of logarithms does not depend on logarithm's basis.

Measurements were taken using HEG and a capnometer (a device measuring end tidal CO2) simultaneously. End tidal CO2 is closely related to PaCO2. Eighteen subjects participated in the experiment in which HEG and CO2 data were recorded for 5 intervals of baseline, simple breathing exercises, simple arithmetic tasks and biofeedback. The results show that almost all participants could increase their brain oxygenation or CBF, but in each case it was strongly dependent on one of the three methods used. We can conclude that it is possible to substantially increase local oxygenation or global CBF using one of the three methods described above, but the preferred method is highly individual. The protocol of this research was approved by the IRB of Hunter College of the City University of New York.

#### **6.1 Methods and materials**

122 Infrared Spectroscopy – Life and Biomedical Sciences

We will demonstrate that significant increase of PaCO2 (and of total CBF) can be achieved with untrained people using very simple breathing procedures. The reason for that is the

<sup>2</sup> , 863 *CO*

<sup>2</sup> , 2.07 /min *CO D*

(1)

, (2)

is the alveolar

*A*

*PaCO K K mmHg <sup>V</sup>*

ventilation. This means that the PaCO2 is inversely proportional to ventilation. Therefore it is possible to control the PaCO2 by either breathing slowly (and not increasing the tidal volume substantially) or by holding the breath. Untrained people increase their tidal volume while breathing more slowly, but the overall effect is usually a slight increase in PaCO2. People trained in breathing exercises may increase their PaCO2 considerably by learning to control their tidal volume. For very small ventilation a correction is needed to the PaCO2

*V*

*A D*

less sophisticated compared with INVOS cerebral oximeters (Gersten et al., 2009).

The readings of the HEG are normalized to 100 (SD=20), the average on 154 adult attendants at professional meetings (Toomim et al, 2004). We have compared (Gersten et al., 2009) the readings of HEG with the regional saturation of oxygen (rSO2) readings of the INVOS cerebral oximeter of Somanetics. This allowed us to make estimates of the ratios of rSO2

 x1/x2 = ln(y1/32.08)/ln(y2/32.08), x ≡ rSO2, y ≡ HEG readings, (3) where ln is the natural logarithm, but the ratio of logarithms does not depend on

Measurements were taken using HEG and a capnometer (a device measuring end tidal CO2) simultaneously. End tidal CO2 is closely related to PaCO2. Eighteen subjects

It is well known that concentrating on a mental problem changes brain's oxygenation locally (Chance et al, 1993). This finding was also applied further to solving a simple arithmetic

Hershel Toomim (Toomim et al., 2004) developed the device called hemoencephalograph (HEG), whose readings is related to regional cerebral oxygenation (Gersten et. al, 2007c). The device has many advantageous features which allowed us to use it in our experiment. Toomim has observed that he can influence the results by looking at the HEG display, which is essentially a biofeedback technique used by us as well. As a result of Toomim findings many biofeedback experiments were conducted with the HEG, confirming the effect. The readings of the HEG are very sensitive to changes in the range of normal oxygenation of the brain. This is not the case with INVOS brain oximeters used in operation rooms whose main aim is to detect abnormally low oxygenation states. For that reason we preferred to use the HEG to detect biofeedback effects even though it is much simpler and

*V PaCO K V l V V*

2

2

is the contribution of the dead space.

problem on local brain oxygenation near the Fp1 area.

where *CO*<sup>2</sup> *<sup>V</sup>* is the CO2 production (dependent on the metabolism) and *VA*

dependence of PaCO2 on ventilation (West, 1992)

formula (Riggs, 1970),

using the HEG. We found,

logarithm's basis.

where *VD*

It is well known that breathing patterns affect the CO2 levels in the arteries (Fried and Grimaldi, 1993), which in turn can affect cerebral (brain's) blood circulation and oxygenation. Mental work and biofeedback may affect both local as well as global oxygen levels in the brain.

The influence of breathing exercises, problem solving and biofeedback on brain oxygen and CO2 arterial levels were considered in an experiment outlined below. The experiment dealt with 3 topics


An experiment dealing with the second and third topic gives qualitative information about how much the oxygen levels will rise during problem solving and biofeedback, while an experiment dealing with the first topic will give the same information, but this time, from breathing exercises. It is important to note that in the first topic global CBF is concerned, while in the second and third topic the local brain oxygenation at the Fp1 area.

The participants were connected to the two devices needed for the experiment: the capnometer that measured end tidal CO2 and the Cerebral Oximeter. The connection used was made via a sensor placed on the forehead at Fp1. The CO2 levels were estimated using a capnometer produced by Better Physiology LTD, which measures end tidal CO2 (EtCO2) of the exhaled air (EtCO2 is highly correlated with the PaCO2 levels of the arteries). All participants received their own new nasal insert which were sterilized before each use and connected to the capnometer. The data were detected via USB output cable connected to the computer and stored for subsequent review.

The oxygen levels were estimated using two devices: the HEG which was calibrated to the INVOS Cerebral Oximeter produced by Somanetics Corp. (see www.somanetics.com) and based on advanced near infrared spectroscopy (NIRS) technology. A sensor was attached to the forehead measuring the oxygenation in a depth of about one inch inside the brain. The devices that were used were non-invasive and FDA approved, fully automated and did not require special precautions. The data were stored on a computer.

The data of the capnometer and oximeters were combined together and analyzed using Matlab subprograms. The participants were asked to do paced breathing exercises as

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 125

Fig. 3. The HEG readings and the capnometer displays (EtCO2) of participant No. 3are shown for the 4 cases: baseline (subplot HC31), breathing exercise (subplot HC32), arithmetic problem (subplot HC33) and biofeedback (subplot HC34). The upper curves are the HEG readings, the lower curves the CO2 values (at exhale). The numbers with numbers in

Subplot HC34 of Fig. 3 is very interesting. In this case the subject was looking at the display of the HEG line trying mentally to raise it up. The performance (without previous training) is very impressive. Starting from baseline values the HEG readings were climbing up for about 2.5 minutes to values about 30% higher (a local increase of oxygenation at the Fp1 area). This case teaches us that in the evaluation of the results we must not only consider average values but also the maximal values which are an indicative of the possible potential. The respiration pattern indicates a slow but a very deep breathing (hyperventilation). The arterial CO2 decreased for more than 20% which should lead to a significant decrease of

While analyzing the data we must take into account that the participants were performing their tasks for the first time. Most of the tasks were performed relatively well. Most participants were able to increase their mean HEG readings in at least one task. When averaging all participant's data there were no significant changes were found, indicating

More informative, are the ratios of the maxima to the mean of the baseline. The maxima indicate the potential of the exercises. These maximal values should be easily reached with

global CBF. The biofeedback was very successful in spite of the hyperventilation.

that no one method was preferable.

parenthesis are the mean values and standard deviations respectively.

instructed by the experimenters. Before the 3 experiments baseline data were taken for 5 minutes using the INVOS oximeter, and another 5 minutes using the HEG and capnometer. The participants were prevented from seeing the screens of the devices in order to avoid biofeedback.

In the first experiment (lasting 5 minutes) participants were asked to walk slowly, breathe in for 3 steps, hold their breath during the next 3 steps, exhale during the next 3 steps, and hold their breath for the next 3 steps after exhaling. We made sure that the participants understood these instructions. The participants also did not see the screens of the devices in order to avoid biofeedback.

In the second experiment (lasting 5 minutes) participants were given an arithmetical problem to solve while being attached to the HEG and capnometer. The theoretical basis for this experiment is that more oxygen is needed while solving problems. A simple arithmetical problem of subtracting the number 7 continuously, starting from 1200 (1193,1186,...) was used. The participants were again prevented to see the screens of the devices in order to avoid biofeedback.

In the third experiment (lasting 5 minutes) participants were asked to look at the HEG display trying to raise the curve by mental feedback. This time they were allowed to look at the display.

## **6.2 Participants**

The participants were 18 participants from the introductory course to psychology (PSY 100) in Hunter College of the City University of New York. All participants had to sign an informed consent. At least two experimenters were present during each experiment. The confidentiality of the participants was protected.

#### **6.3 Results**

All experimental results of all participants can be found in (Gersten et al., 2011a).

To better illustrate the results a few examples of HEG and CO2 data will be included. In Fig. 3, subplot HC31, the baseline data of participant No. 3 are displayed. The HEG baseline was not constant during the 5 minutes of data taking.

In the subplot HC32 the result of the breathing exercise are displayed. Even though this was a first trial, the CO2 pattern seems to be quite periodic. The CO2 pattern has a periodicity of about 15 secs per period, while normal breathing has a periodicity of about 4 secs per period. The prolongation of the respiratory period should lead to an accumulation of arterial CO2 and an increase of global CBF, provided there is no greater increase in the tidal volume. In this case there was only small increase in arterial CO2 but a significant increase in oxygenation (HEG). The increase of arterial CO2 depends on the control over the tidal volume. Individuals trained in this breathing exercise, can easily increase their arterial CO2 by about 20-30%.

Solving the arithmetic problem (see Fig. 3, subplot HC33) led to an increase of the HEG readings (oxygenation), but we notice that the respiration was speeded up probably due to increased tension. After all, to subtract 7 and calculate and evaluate the result in the mind is not a very pleasant enterprise.

instructed by the experimenters. Before the 3 experiments baseline data were taken for 5 minutes using the INVOS oximeter, and another 5 minutes using the HEG and capnometer. The participants were prevented from seeing the screens of the devices in order to avoid

In the first experiment (lasting 5 minutes) participants were asked to walk slowly, breathe in for 3 steps, hold their breath during the next 3 steps, exhale during the next 3 steps, and hold their breath for the next 3 steps after exhaling. We made sure that the participants understood these instructions. The participants also did not see the screens of the devices in

In the second experiment (lasting 5 minutes) participants were given an arithmetical problem to solve while being attached to the HEG and capnometer. The theoretical basis for this experiment is that more oxygen is needed while solving problems. A simple arithmetical problem of subtracting the number 7 continuously, starting from 1200 (1193,1186,...) was used. The participants were again prevented to see the screens of the

In the third experiment (lasting 5 minutes) participants were asked to look at the HEG display trying to raise the curve by mental feedback. This time they were allowed to look at

The participants were 18 participants from the introductory course to psychology (PSY 100) in Hunter College of the City University of New York. All participants had to sign an informed consent. At least two experimenters were present during each experiment. The

To better illustrate the results a few examples of HEG and CO2 data will be included. In Fig. 3, subplot HC31, the baseline data of participant No. 3 are displayed. The HEG baseline

In the subplot HC32 the result of the breathing exercise are displayed. Even though this was a first trial, the CO2 pattern seems to be quite periodic. The CO2 pattern has a periodicity of about 15 secs per period, while normal breathing has a periodicity of about 4 secs per period. The prolongation of the respiratory period should lead to an accumulation of arterial CO2 and an increase of global CBF, provided there is no greater increase in the tidal volume. In this case there was only small increase in arterial CO2 but a significant increase in oxygenation (HEG). The increase of arterial CO2 depends on the control over the tidal volume. Individuals trained

Solving the arithmetic problem (see Fig. 3, subplot HC33) led to an increase of the HEG readings (oxygenation), but we notice that the respiration was speeded up probably due to increased tension. After all, to subtract 7 and calculate and evaluate the result in the mind is

All experimental results of all participants can be found in (Gersten et al., 2011a).

in this breathing exercise, can easily increase their arterial CO2 by about 20-30%.

biofeedback.

the display.

**6.3 Results** 

**6.2 Participants** 

order to avoid biofeedback.

devices in order to avoid biofeedback.

confidentiality of the participants was protected.

was not constant during the 5 minutes of data taking.

not a very pleasant enterprise.

Fig. 3. The HEG readings and the capnometer displays (EtCO2) of participant No. 3are shown for the 4 cases: baseline (subplot HC31), breathing exercise (subplot HC32), arithmetic problem (subplot HC33) and biofeedback (subplot HC34). The upper curves are the HEG readings, the lower curves the CO2 values (at exhale). The numbers with numbers in parenthesis are the mean values and standard deviations respectively.

Subplot HC34 of Fig. 3 is very interesting. In this case the subject was looking at the display of the HEG line trying mentally to raise it up. The performance (without previous training) is very impressive. Starting from baseline values the HEG readings were climbing up for about 2.5 minutes to values about 30% higher (a local increase of oxygenation at the Fp1 area). This case teaches us that in the evaluation of the results we must not only consider average values but also the maximal values which are an indicative of the possible potential. The respiration pattern indicates a slow but a very deep breathing (hyperventilation). The arterial CO2 decreased for more than 20% which should lead to a significant decrease of global CBF. The biofeedback was very successful in spite of the hyperventilation.

While analyzing the data we must take into account that the participants were performing their tasks for the first time. Most of the tasks were performed relatively well. Most participants were able to increase their mean HEG readings in at least one task. When averaging all participant's data there were no significant changes were found, indicating that no one method was preferable.

More informative, are the ratios of the maxima to the mean of the baseline. The maxima indicate the potential of the exercises. These maximal values should be easily reached with

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 127

Fig. 5. The HEG readings and the capnometer displays (EtCO2) are shown for the 4 cases: baseline (subplot HC21), breathing exercise (subplot HC22), arithmetic problem (subplot HC23) and biofeedback (subplot HC24). The upper curves are the HEG readings, the lower

In Fig. 5 participant No. 2 had difficulty performing the breathing exercise (the CO2 pattern in subplot HC22). Although the 3 step pattern was kept correctly, the participant was inhaling during some of the breath holding periods. When done correctly the 3 step breathing cycle should last for about 15 seconds. As the participant was breathing in between, the average breath length was only 7.2 seconds. Interestingly the HEG waveform of subplot HC22 has a period of about 15 seconds irrespective of the breathing in between

The performance of the breathing exercises, when well performed, the period should be longer than 10 seconds. Twelve of 18 participants have performed the breathing exercise

Interestingly the HEG waveform has the same periodicity as the CO2 pattern. This coincidence is well presented in Fig. 6, where the correlation between the power spectra of

curves the CO2 values (at exhale).

the 3 step pattern.

well.

practice. There was a maximal increase of 30% during breathing exercises, 32% during solving the arithmetic problem and 28% during the biofeedback.

Results with rSO2 ratios determined according to Eq. (3) are quite similar to the HEG ratios, indicating that the HEG ratios are quite reliable in estimating the rSO2 changes.

Of the 18 participants 14 were able to increase the HEG readings by at least 10% during one of the exercises (5 during the breathing exercise, 9 while solving the arithmetic problem, 8 during the biofeedback). Of the 18 participants 7 were able to increase the HEG readings by at least 18% during one of the exercises (3 during the breathing exercise, 6 while solving the arithmetic problem, 5 during the biofeedback).

The breathing exercise was the most difficult for the participants. It took them an average of 6 minutes to fully understand the instructions. The exercise required some discipline and experience. Most of the participants performed it relatively well.

Fig. 4 shows that participant No. 9 has performed the breathing exercises relatively well (subplot HC92). His CO2 pattern was periodic and amplitude stable. The pattern was not completely smooth. This is understandable, since it was his first attempt to perform the exercise. In the same subplot, the corresponding HEG curve is very interesting. The HEG waveform has the same period as the CO2 pattern.

Fig. 4. The HEG readings and the capnometer displays (EtCO2) are shown for the 4 cases: baseline (subplot HC91), breathing exercise (subplot HC92), arithmetic problem (subplot HC93) and biofeedback (subplot HC94). The upper curves are the HEG readings, the lower curves the CO2 values (at exhale).

practice. There was a maximal increase of 30% during breathing exercises, 32% during

Results with rSO2 ratios determined according to Eq. (3) are quite similar to the HEG ratios,

Of the 18 participants 14 were able to increase the HEG readings by at least 10% during one of the exercises (5 during the breathing exercise, 9 while solving the arithmetic problem, 8 during the biofeedback). Of the 18 participants 7 were able to increase the HEG readings by at least 18% during one of the exercises (3 during the breathing exercise, 6 while solving the

The breathing exercise was the most difficult for the participants. It took them an average of 6 minutes to fully understand the instructions. The exercise required some discipline and

Fig. 4 shows that participant No. 9 has performed the breathing exercises relatively well (subplot HC92). His CO2 pattern was periodic and amplitude stable. The pattern was not completely smooth. This is understandable, since it was his first attempt to perform the exercise. In the same subplot, the corresponding HEG curve is very interesting. The HEG

Fig. 4. The HEG readings and the capnometer displays (EtCO2) are shown for the 4 cases: baseline (subplot HC91), breathing exercise (subplot HC92), arithmetic problem (subplot HC93) and biofeedback (subplot HC94). The upper curves are the HEG readings, the lower

indicating that the HEG ratios are quite reliable in estimating the rSO2 changes.

solving the arithmetic problem and 28% during the biofeedback.

experience. Most of the participants performed it relatively well.

arithmetic problem, 5 during the biofeedback).

waveform has the same period as the CO2 pattern.

curves the CO2 values (at exhale).

Fig. 5. The HEG readings and the capnometer displays (EtCO2) are shown for the 4 cases: baseline (subplot HC21), breathing exercise (subplot HC22), arithmetic problem (subplot HC23) and biofeedback (subplot HC24). The upper curves are the HEG readings, the lower curves the CO2 values (at exhale).

In Fig. 5 participant No. 2 had difficulty performing the breathing exercise (the CO2 pattern in subplot HC22). Although the 3 step pattern was kept correctly, the participant was inhaling during some of the breath holding periods. When done correctly the 3 step breathing cycle should last for about 15 seconds. As the participant was breathing in between, the average breath length was only 7.2 seconds. Interestingly the HEG waveform of subplot HC22 has a period of about 15 seconds irrespective of the breathing in between the 3 step pattern.

The performance of the breathing exercises, when well performed, the period should be longer than 10 seconds. Twelve of 18 participants have performed the breathing exercise well.

Interestingly the HEG waveform has the same periodicity as the CO2 pattern. This coincidence is well presented in Fig. 6, where the correlation between the power spectra of

Probing Brain Oxygenation Waveforms with Near Infrared Spectroscopy (NIRS) 129

The most important finding of our experiments is the periodic correlation between respiration, oxygenation and blood volume changes. The results clearly show a periodic change of cerebral oxygenation with the same period as the breathing exercises, indicating that with each breath the brain oxygenation was periodically changing. Similar periodic changes in blood volume indicate that the brain pulsates with a frequency of respiration.

Present results were achieved by using very slow breathing patterns with the INVOS Cerebral Oximeter (ICO). If the present ICO devices will be modified to allow sampling of rSO2 at frequencies higher than the frequency of normal respiration and higher than the heart rate, it will be possible to observe new types of brain waveforms. These waveforms may have new information about brain oxygenation, cognitive function, brain pulsation and brain motion. Under these circumstances it will be possible to understand much better the correlations between respiration and brain physiology. The sampling of rSO2 should go up to, or preferably above 4 Hz. The accuracy of the reading device also should be changed from 2 significant digits to 3 digits. We believe that these changes will enable new explorations and new insights on the influence of respiration on brain's physiology. The HEG, which does not measure directly the rSO2 can serve this purpose by using Eq. (3), which determines the ratios of rSO2. The difference between the ICO and the HEG is that the ICO penetrates dipper into the brain, while the HEG penetrates only the surface near the probe. The ICO results are more stable and are related to larger volumes in the

Neurodegenerative diseases are characterized by low CBF, in our research we have found effective ways to increase CBF. We will continue our research in order to explore the possibilities of increased CBF and its influences on intellectual abilities and on fighting degenerative diseases. Devices displaying the oxygenation periodic waveforms should be

Our method to obtain the above results is through the use of human subjects. This is a new avenue in approaching the study of CBF, brain oxygenation, improving the cognitive

Our three methods used in simple execises can be used on the general population, are noninvasive, without the use of pharmaceuticals and have no side effects. They differ from each other in that the breathing affects mostly the global blood flow, arithmetic problem solving

Both our theoretical and experimental work differs from other studies due the specific instrumentation and our experimental procedure. Most of the results came close to our

We concluded that breathing can be used effectively to control CBF by the ventilatory control of end tidal CO2. This research may have implications for complementary diagnosis and treatment of conditions involving regional cerebral metabolism such as cerebral vascular ischemia, seizures disorders, stroke, Alzheimer's disease, and more. Following that thought could lead us to improved cognitive function through a higher supply of oxygen to

We foresee future more detailed investigations to be made in the area of the effect of CO2 on specific regions of the brain. This would be of great interest because a higher CO2 supply

developed for new diagnostic and research purposes.

function and especially in view of the growing elderly population.

and biofeedback affects the regional blood flow (in our case the Fp1 region).

brain.

expectation.

specific regions of the brain.

the EtCO2 periodic pattern and the corresponding HEG periodic pattern is depicted by their multiplication. The power spectra are normalized to unity. Maximal correlation is achieved when the multiplication is equal to one.

Fig. 6. The correlation between the power spectra of the EtCO2 periodic pattern and the corresponding HEG periodic pattern is depicted by their multiplication. The power spectra are normalized to unity. Maximal correlation is achieved when the multiplication is equal to one.
