Administratively closed by IRB after continuing review was never submitted and no patients enrolled.

The purposes of our study are to: 1) determine the incidence of paradoxical response to chest wall loading in mechanically ventilated patients; 2) identify sub-populations in which it is most likely to occur (e.g., severe ARDS); and 3) standard the bedside procedure for demonstrating this physiology.

Mechanical ventilation can be a life-saving intervention for patients with respiratory failure, but the acutely injured lung is vulnerable to further damage if positive pressure ventilation is not employed judiciously. "Lung protective ventilation" encompasses a group of practices intended to minimize ventilator-induced lung injury (VILI) and includes the delivery of low tidal volumes (to minimize dynamic lung strain) and the prevention of injuriously high airway pressures (to minimize lung stress). The prone position, which compresses (or "loads") the chest wall, more evenly distributes volume and pressure, mitigates the damaging effects of stress/strain, and improves clinical outcomes in patients with severe respiratory failure from adult respiratory distress syndrome (ARDS).

Chest wall loading would not be expected to produce these beneficial effects in the supine position-quite the opposite; it usually results in net volume loss and higher airway pressures in response to an unchanging tidal volume. A paradoxical response to chest wall loading, leading to decreased airway pressures, however, was recently reported in a group of patients with advanced lung disease secondary to COVID-19. In this cohort, a paradoxical decrease in airway pressures was elicited during a brief period of manual compression of the abdomen.

This maneuver, which is non-invasive, free of cost, and gives real-time information, may have important diagnostic (and potentially therapeutic) implications for ventilator management in patients with respiratory failure.

Inclusion Criteria: Non-surgical patients admitted to the ICU at Regions Hospital (St. Paul, MN) or Methodist Hospital (St. Louis Park, MN), receiving mechanical ventilation for any reason, and breathe passively during mechanical ventilation

Exclusion Criteria:

1. Age < 18 years old
2. Pregnancy at the time of their inclusionary hospitalization
3. Recent (< 30 days) abdominal or chest wall surgery (including spine)
4. Recent (< 30 days) abdominal or chest wall trauma (including spine)
5. Traumatic brain injury, intracranial bleed, or recent neurologic surgery
6. Family member or representative not available to provide informed consent
7. Not passive while receiving mechanical ventilation support
8. Hemodynamic instability

This study did not enroll any participants so there is no IPD to be shared.