Excessive duration and / or intensity of activities that mimic valsalva manoeuvres, " i . e . " that increase intrathoracic pressure, can cause barotrauma, and hence pregnancy ( and constipation and other causes of excessive straining ) can be a precipitating cause of Hamman's syndrome.
22.
This is not to be confused with stage 4 of the Valsalva maneuver, in which the release of high intrathoracic pressure previously generated by forced expiration against a closed glottis, now restores venous return and cardiac output into a vasoconstricted circulation, stimulating the vagus nerve and leading to a slowing of the heart, or bradycardia.
