# Right-Left Asymmetry of Prefrontal Cerebral Oxygenation: Does it Depend on Systemic Physiological Activity, Absolute Tissue Oxygenation or Hemoglobin Concentration?

Scholkmann, Felix; Zohdi, Hamoon; Wolf, Ursula (2020). Right-Left Asymmetry of Prefrontal Cerebral Oxygenation: Does it Depend on Systemic Physiological Activity, Absolute Tissue Oxygenation or Hemoglobin Concentration? Advances in Experimental Medicine and Biology, 1232:105-112.

## Abstract

BACKGROUND

We have repeatedly observed a right-left asymmetry (RLA) of prefrontal cerebral oxygenation of subjects during the resting state.

AIM

To clarify if the RLA is a reliably observable phenomenon at the group level and whether it is associated with systemic physiology, absolute tissue oxygen saturation (StO$_{2}$) or total hemoglobin concentration ([tHb]).

MATERIAL AND METHODS

StO$_{2}$ and [tHb] values at the right and left prefrontal cortex (PFC) were calculated for two 5- min resting phases based on data from 76 single measurements (24 healthy adults, aged 22.0 ± 6.4 years). StO$_{2}$ and [tHb] were measured with an ISS OxiplexTS frequency domain near-infrared spectroscopy device. In addition, end-tidal CO$_{2}$ (P$_{ET}$CO$_{2}$), heart rate (HR), respiration rate (RR) and the pulse-respiration quotient (PRQ = HR/RR) were measured and analyzed for the two phases.

RESULTS

On the group level it was found that i) StO$_{2}$ was higher at the right compared to the left PFC (for both phases), ii) RLA of StO$_{2}$ (∆StO$_{2}$ = StO$_{2}$ (right)-StO$_{2}$ (left) was independent of P$_{ET}$CO$_{2}$, HR and PRQ, and iii) ∆StO$_{2}$ was associated with absolute StO$_{2}$ and [tHb] values (positively and negatively, respectively).

DISCUSSION AND CONCLUSION

This study shows that i) RLA of StO$_{2}$ at the PFC is a real phenomenon, and that ii) ∆StO$_{2}$ at the group level does not depend on P$_{ET}$CO$_{2}$, HR, RR or PRQ, but on absolute StO$_{2}$ and [tHb]. We conclude that the RLA is a real effect, independent of systemic physiology, and most likely reflects genuine properties of the brain, i.e. different activity states of the two hemispheres.

## Abstract

BACKGROUND

We have repeatedly observed a right-left asymmetry (RLA) of prefrontal cerebral oxygenation of subjects during the resting state.

AIM

To clarify if the RLA is a reliably observable phenomenon at the group level and whether it is associated with systemic physiology, absolute tissue oxygen saturation (StO$_{2}$) or total hemoglobin concentration ([tHb]).

MATERIAL AND METHODS

StO$_{2}$ and [tHb] values at the right and left prefrontal cortex (PFC) were calculated for two 5- min resting phases based on data from 76 single measurements (24 healthy adults, aged 22.0 ± 6.4 years). StO$_{2}$ and [tHb] were measured with an ISS OxiplexTS frequency domain near-infrared spectroscopy device. In addition, end-tidal CO$_{2}$ (P$_{ET}$CO$_{2}$), heart rate (HR), respiration rate (RR) and the pulse-respiration quotient (PRQ = HR/RR) were measured and analyzed for the two phases.

RESULTS

On the group level it was found that i) StO$_{2}$ was higher at the right compared to the left PFC (for both phases), ii) RLA of StO$_{2}$ (∆StO$_{2}$ = StO$_{2}$ (right)-StO$_{2}$ (left) was independent of P$_{ET}$CO$_{2}$, HR and PRQ, and iii) ∆StO$_{2}$ was associated with absolute StO$_{2}$ and [tHb] values (positively and negatively, respectively).

DISCUSSION AND CONCLUSION

This study shows that i) RLA of StO$_{2}$ at the PFC is a real phenomenon, and that ii) ∆StO$_{2}$ at the group level does not depend on P$_{ET}$CO$_{2}$, HR, RR or PRQ, but on absolute StO$_{2}$ and [tHb]. We conclude that the RLA is a real effect, independent of systemic physiology, and most likely reflects genuine properties of the brain, i.e. different activity states of the two hemispheres.

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