Effect of Intrathoracic Pressure Regulation on Decreased Cerebral Perfusion (4hour)

Inclusion Criteria: * ≥18 years of age * intubated and mechanically ventilated on a volume controlled mode * head injury or other intracranial pathology and compromised cerebral perfusion * arterial line in place or alternative with continuous pressure monitoring * SpO2 ≥90% * mean arterial pressure \>55 * admission to ICU or about to undergo neurosurgery with planned placement of an invasive intracranial pressure monitor * inclusion presents no significant delays to planned emergent neurosurgery * prior written informed consent Exclusion Criteria: * cardiac or pulmonary injury * confirmed pneumothorax or hemothorax * serious neck injury resulting in neck swelling with jugular venous compression * evidence of ongoing uncontrolled bleeding * respiratory disease such as COPD, interstitial lung disease, or other parenchymal or pulmonary vascular disease * marked hypertension at time of device use defined as systolic blood pressure \>180 mmHg * congestive heart failure * women with positive serum or urine pregnancy test or breast feeding