Apatient with spontaneous respirations is breathing:

Spontaneous breathing trial. A goal for most patients on mechanical ventilation is to be weaned from the ventilator. The weainig process is highly dependent on the patient's pathology,but the final common pathway to ventilator independence always includes at least one trail of spontaneous breathing.

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Your answer is  d.)relationship between pressure and air volume and led to the understanding of how respiration works