In addition, the resultant rise in pH of the blood (‘respiratory alkalosis’) acts on brainstem sensors. This reduces the normal breathing rate. Once the hyperventilation ceases, oxygen to the brain will be further reduced.
The Valsalva Manoeuver A process where a person forcibly tries to breath out while closing the airway (throat and nose). This is the common procedure used to clear one’s ears and restore hearing after ears are effected by pressure changes eg in an aeroplane or elevator.
By employing the Valsalva Manoeuver, just as the carotid pressure is applied, the increased pressure in the chest cavity will further restrict venous blood return to the heart. This will accentuate the effect of jugular vein obstruction, reduce cardiac output and further lower cerebral oxygen supply. The Manoeuver can be maintained until consciousness is lost.
Risks and Difficulties
There are several important factors that can affect the usefulness of this method. The technique is critical. The pressure points must be correctly identified, and the pressure applied correctly.
Practice (with a trusted friend) is recommended to ensure loss of consciousness can be reliably and consistently achieved. The simultaneous use of hyperventilation and the Valsalva Manoeuvre can be rehearsed (and perfected). The friend can release the pressure as soon as fainting occurs.
To ensure that there is absolutely no chance of failure some urge the simultaneous use of a plastic bag over the head and secured lightly around the neck before pressure to the baroreceptors is applied.