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Respiratory Failure & Mechanical Ventilation

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Cycling asynchrony on the ventilator assessed by expiratory muscle EMG (Transversus abdominis):

The above graph shows the relationship between the flow over time waveform and the activities of the expiratory muscles measure by EMG. The relationship of neural expiratory time to ventilator expiratory time was assessed by measuring the phase angle, expressed in degrees. If neural activity began simultaneously with the ventilator, the phase angle (0) was zero. Neural activity beginning after the offset (termination) of inflation by the ventilator resulted in a positive phase angle (60 degrees for subject 1). Neural activity beginning before the offset of inflation by the ventilator resulted in a negative phase angle (45 degrees for subject 2)

The second graph shows waveforms airway pressure (Paw), flow, and transversus abdominis electromyogram in a critically ill patient with chronic obstructive pulmonary disease receiving pressure control of 15 cm H2O. Expiratory muscle activity (vertical dotted line) began when mechanical inflation was only partly completed. Note there is also a small airway pressure spike near the end of mechanical inflation, which coincides with the patient’s neural expiratory activity. This is an example of delayed cycling (patient started to exhale prior to the ventilator cycling).

Ghassan Kheirallah


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