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The Valsalva maneuver may be used to arrest episodes of supraventricular tachycardia. [12] [13] Blood pressure (BP) rises at onset of straining-because the increased intrathoracic pressure (ITP) is added to the pressure in the aorta. It then falls because the ITP compresses the veins, decreasing the venous return and cardiac output.
Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury and at rest, is normally 7–15 mmHg for a supine adult. This equals to 9–20 cmH 2 O, which is a common scale used in lumbar punctures. [1]
The sudden impact on the thorax causes an increase in intrathoracic pressure. [4] In order for traumatic asphyxia to occur, a Valsalva maneuver is required when the traumatic force is applied. [6] Exhalation against the closed glottis along with the traumatic event causes air that cannot escape from the thoracic cavity.
There is increased intrathoracic pressure and decreased cardiac output following the Valsalva maneuver. This eventually leads to a significant decrease in circulation to the brain and ultimately, loss of consciousness. There is no postictal phase (as is seen with seizures), no incontinence, and the child is fine in between spells.
The cause of Hamman's syndrome is most commonly unknown (idiopathic). 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.
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The maneuver as originally described by Antonio Valsalva in 1704 was performed against a closed glottis, which only elicits the increase in intrathoracic and intra-abdominal pressure. Both are described as the Valsalva maneuver, but only the variant which pressurises the nasopharynx is useful in scuba diving.