Nasal peak expiratory flow and nasal congestion in women: how many subjects are enough?

Abstract

Background: Nasal peak expiratory flow is an inexpensive, simple, widely used method to measure changes in nasal congestion. Objective: This study was performed in order to define the normal variation in nasal peak expiratory flow and to evaluate and quantify the relationship between subjective scores of nasal obstruction and nasal peak expiratory flow in women. Materials & methods: We followed 41 healthy, nonmedicating, normally menstruating women for 3 to 6 months. They registered nasal peak expiratory flow and subjective nasal congestion (scored 0–4) every morning and evening. Results: We found that if the aim of a study is to detect a difference in nasal peak expiratory flow corresponding to 1 subjective score step out of 4, different values have to be used for the power calculations, depending on what congestion scores are expected in the study population. If a low score level is expected, more subjects are required. Conclusion: Our data make adequate power calculations possible for studies in female populations with different degrees of nasal congestion.