Clinical correlants of changes in nasal flow/resistance (Rn) measurements.

It has been suggested that changes in nasal airways flow/resistance imply clinical betterment and increased nasal patency, and that patients with congestion sense relief when treatment improves their Rn values by 20% or more, speculations supported by inferences from lower airways dynamics. This hypothesis was tested in a double-blind study of the nasal decongestant potency of phenylpropanolamine/aromatic oil, phenilpropanolamine, aromatic oil and placebo syrups given to 80 patients with common colds who were followed for 6 hours. Rn was determined by electronic posterior rhinometry; patients estimated their degree of nasal congestion with a 6-ranked subjective scale. Statistical techniques included paired and unpaired t-tests, chi-square analysis, analysis of covariance to determine comparisons of within-group differences, differences between drug and placebo groups, and determination of the number in each group improving 20% or more from control Rn. Correlation coefficients relating Rn values to subjective responses were determined by pairing these for each patient and applying standard regression analysis. Despite a strong placebo effect, mean Rn changes ranked the efficacy of the 4 test mixtures, with the 20% improvement criterion allowing the sharpest separation of active mixtures from inactive. In regression analysis the correlation coefficient of 0.56 and the regression slope of 0.66 were both significant (p = 0.01 or better); the latter figure implied that a 1 unit difference on the subjective scale corresponded to a 0.66 unit difference on the Rn scale. With an average objective reading of 3.77 a 1 unit change n the subjective rating perceptible to the subject as a difference in the state of his nasal congestion was equivalent to a mean Rn change of 17.5%. This supports our prior assumption, indicating that a 17.5% to 20% improvement in Rn is experienced as clinical relief. Further, subjective rating scales appear to be statistically sound as a means of assessment of the status of the nasal airways.