Peak Inspiratory Flow (PIF) is one of a multitude of spirometric measurements. PIF is generally measured on large spirometric machines and has not therefore been the subject of extensive serial home monitoring.
The In-Check product makes this prospect a reality and opens the door to a greater understanding of PIF.
Measurements of sub-maximal inspiratory flows are valuable when training patients in the correct use of medical inhaler devices. Recent studies have indicated target inspiratory flows for many of the inhaled medication devices commonly used to deliver medication in respiratory diseases.
Feedback to the patient from In-Check measurement enables the patient to adjust their inhalation technique to best suit their own inhaler.
In some patients who complain of nasal obstruction, nasal airway patency is quite normal, and the symptom is due to consciousness of some other abnormality of the nasal cavity, such as a prominent turbinate. In other cases, surprisingly low readings are obtained in some patients, who are unaware of nasal obstruction, because they have got used to it. Quiet breathing through the nose can in such cases be achieved in spite of a peak nasal inspiratory flow reading as low as 50.
Such patients are often unaware that they breathe through the mouth for much of the time.
Reversibility of nasal obstruction can be assessed by measuring the PNIF after application of a nasal decongestant such as ephedrine by spray or drops. If the PNIF is not raised to a reading of over 100 by such treatment, then the obstruction may be associated with mucosa oedema, extensive polyps or anatomical abnormality. A trial of topical or systemic steroids may also bring the PNIF into the normal range (100 to 300 l/min).
Allergen or pharmacological mediator (e.g. histamine) application to the nasal mucosa in doses halving PNIF is usually associated with only minor and transient discomfort. Details of a simplified allergen provocation test have been published (ref. 1)
This may be useful in drug or immunotherapy trials in rhinitis, or for assessing the importance of environmental factors at home or work in individual patients with rhinitis. Cyclic changes in nasal airway patency can also be investigated, as can late responses to allergen provocation.