The volume of isoflow is a test designed to detect pathologic changes occurring in the small airways and may be more sensitive than conventional PFTs. Helium has the unique property of lowering gas density. Therefore, after the patient breathes a helium–oxygen gas mixture, the effects of convective acceleration and turbulence are negated. Any abnormality observed in the F-V loop, then, results from an increase in resistance to laminar (nonturbulent) flow, which indicates small airway abnormalities or lung disease.
Have the patient assume a seated position. Place nose clips on the nose and instruct the patient to breathe normally through a mouthpiece/filter (bacterial/viral) combination into the spirometer.
Have the patient perform a baseline F-V loop, which is recorded by a spirometer on an X-Y recorder.
Have the patient next breathe a mixture of 80% He and 20% O2 for several breaths and then perform another F-V loop maneuver; this is the heliox F-V loop.
Superimpose the F-V loop tracings and measure the volume of isoflow at the point at which the two loops intersect.
Pretest Patient Care
Explain the purpose and procedure of the test.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Explain the possible need for follow-up testing and treatment.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.