Which of the following terms are phase variables? I. inspiration II. flow III. cycle IV. trigger

A. I, II only
B. III, IV only
C. I, III only
D. II, IV only

?ANS: B?I. Incorrect response: Inspiration and exhalation are phases of the respiratory cycle, not phase variables.
II. Incorrect response: Flow is not a phase variable.
III. Correct response: Cycle and trigger are referred to as phase variables in the context described below. Every breath has four phases: (1) the change from exhalation to inspiration (trigger), (2) the variable that reaches a plateau before the end of inspiration, but is not responsible for terminating inspiration (limit), (3) the change from inspiration to exhalation (cycle), and (4) baseline (i.e., PEEP).
IV. Correct response: The term trigger applies to the phase variable that causes inspiration to begin. Inspiration can be either pressure, volume, flow, or time triggered.