Torsten Passie, Uwe Hartmann, Udo Schneider and Hinderk M. Emrich from Department of Clinical Psychiatry and Psychotherapy, Medical School Hannover, Hannover, Germany published the following study in 2003:
On the function of groaning and hyperventilation during sexual intercourse: intensification of sexual experience by altering brain metabolism through hypocapnia. DOI: http://dx.doi.org/10.1016/S0306-9877(03)00010-0
Sexual arousal is accompanied by some typical physiological reaction patterns. Another typical feature of sexual intercourse is involuntary sound production implying in its more intense forms acceleration of breathing (hyperventilation). Up to now no study examined spCO2 during intense sexual intercourse, but there is evidence that some degree of hyperventilation with its physiological consequences may often be induced during sexual intercourse. This article discusses implications of hyperventilation during sexual intercourse for alterations of consciousness and subjective experience in the light of recent studies of brain metabolic changes during states of hyperventilation. Groaning and hyperventilation are interpreted in this context as a psychophysiological mechanism to deepen states of sexual trance.
Let’s look at the science first:
Hyperventilation often occurs through fast deep breathing and it results in a state, where more carbon dioxide gets removed from the blood stream than the body produces, resulting in a drop of carbon dioxide concentration, which is known as hypocapnia. Hypocapnia then leads to a 30-50% decrease in the blood flow to the cortex of the brain, resulting in less than normal supply of oxygen to the brain. This in turn affects the balance between cortical and limbic system control, letting the limbic system become more dominant. Basically this change leads to less thinking and more feeling, resulting in more intense emotions and euphoric mood states.