A mechanical ventilator that is connected to a 50 psig gas source, and uses an electrically powered solenoid valve to control the respiratory frequency and I:E ratio can be described as _________________________
A. pneumatically powered
B. electrically powered
C. flow cycled
D. open-loop controlled
ANS: C?A. Correct response: Pneumatically powered ventilators operate via a 50 psig gas source and generally incorporate a high-pressure reducing regulator to reduce the high source pressure to a lower working pressure. The solenoid is electrically powered to perform certain ventilator functions, but electricity is not the power that is used to perform the work of ventilating the patient.
B. Incorrect response: Electrically powered ventilators employ alternating current of 110 to 115 volts. This electrical power is reduced and converted to direct current for the purpose of depositing air into the lungs of patients.
C. Incorrect response: A flow-controlled ventilator maintains a constant flow throughout the inspiratory phase despite changes in lung compliance and airway resistance.
D. Incorrect response: Open-loop ventilation refers to systems that are unintelligent and require the clinician to make ventilator adjustments when certain conditions change. Closed-loop systems are described as intelligent because they can sense a change in input, and respond accordingly to render a different output.
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