- Top of page
- Materials and methods
Background: The measurement of peak nasal inspiratory flow (PNIF) provides a simple, cheap, fast and readily available tool for determining the extent of nasal airway patency. However, there are questions regarding its repeatability when used to assess the degree of nasal obstruction in large populations. Therefore, this study aimed to evaluate the repeatability of PNIF measurements and to assess their association with the signs and symptoms of rhinitis.
Methods: The PNIF, rhinitis symptoms, judged by Meltzer questionnaire and rhinitis signs, as determined by anterior rhinoscopy, were assessed in 283 adults representative of the general population. One training and two test PNIF measurements were recorded during the same session.
Results: The PNIF was highly reproducible (ICC = 0.92; 95% limits of agreement: ±36 l/min). The PNIF was strongly correlated with rhinitis signs, measured by anterior rhinoscopy (rs = −0.38, P < 0.0001) but was not correlated with rhinitis symptoms, measured by questionnaire (rs = −0.11, P = 0.057). Differences in PNIF for subjects categorized as asymptomatic, mild or moderate/severe on the basis of rhinitis signs, were highly significant (P < 0.0001), but less significant on the basis of rhinitis symptoms (P = 0.04). A PNIF cut-off of 115 l/min had moderately high specificity (72%) and sensitivity (65%) and a high negative predictive value (90%) for moderate/severe signs of rhinitis.
Conclusion: In a large general population-based sample of young adults, PNIF was highly reproducible and closely related to the signs of rhinitis, as determined by clinical examination. The PNIF provides information that is qualitatively different to that provided by symptom scores and may be useful to measure the extent of nasal obstruction.
Nasal obstruction is a common manifestation of rhinitis. It is characterized by insufficient airflow through the nose and is often associated with inflammation of the nasal mucosa. Nasal obstruction is difficult to quantify directly by clinical examination so objective assessments such as rhinomanometry and acoustic rhinometry are commonly used. However, these methods require complex and expensive equipment and are limited to use by highly trained operators. Subjective assessments of patient symptoms, using questionnaires, are also essential for diagnostic and research purposes. However, subjective and objective measurements of nasal obstruction do not always correlate. Therefore, a simple, objective measurement of nasal airflow would be a very useful tool for assessing nasal patency. For these purposes, peak nasal inspiratory flow (PNIF) offers a simple, cheap and noninvasive method. In addition, PNIF may provide an objective index for evaluating the effects of new pharmacological therapies as well as the effect of nasal allergen challenge.
The PNIF measurements have been used in several studies to assess nasal patency (1) where they have been shown to be at least as sensitive as acoustic rhinometry (2, 3) and active anterior rhinomanometry (4, 5), the latter of which is currently considered the gold standard for measuring nasal resistance. Furthermore, several independent investigations have demonstrated strong, positive correlations between the subjective sensation of nasal obstruction, determined using patient questionnaires and PNIF (6, 7). However, not all studies have reported such strong correlations and some have actually shown little concordance between these different measurements (8).
The PNIF has previously been used to evaluate the efficacy of intranasal medications (9–11) and to assess the effects of nasal challenge with mannitol, histamine or allergen on nasal obstruction (3, 12–14). In addition, PNIF has been used pre- and postoperatively to measure the success of nasal surgery (15, 16). However, the results from some studies have raised questions about the repeatability and sensitivity of PNIF measurements (17–19) and have suggested that they are of limited use as indices of nasal patency (20).
Most previous studies have been conducted in study populations limited to healthy subjects, without rhinitis, and/or have been conducted in a small number of subjects (21). Therefore, further studies to evaluate the repeatability of PNIF measurements and the relationships between PNIF and nasal signs and symptoms using large group of subjects, which include both rhinitic and nonrhinitic subjects, are needed to evaluate the utility of PNIF measurements for clinical and epidemiological purposes. Therefore, this study aimed to investigate the repeatability of PNIF measurements in a large group of subjects and to assess the sensitivity and specificity of PNIF for nasal signs and symptoms in a general population sample of young adults. Use of a study sample that is representative of the general population allows estimation of the positive and negative predictive value of findings, in that setting.
- Top of page
- Materials and methods
This study examined the repeatability of PNIF measurements in a large population of young adults and assessed their utility for identifying the presence and severity of rhinitis signs and symptoms. The results showed that once the significant training effect was taken into consideration, PNIF measurements were reproducible. Furthermore, they were significantly related to the severity of physical signs of rhinitis, determined by physical examination. Although we were able to identify a normal subject group and derive prediction equations for PNIF, albeit in a very restricted age range, we found no additional advantage in using percentage predicted values to estimate the risk of signs or symptoms of rhinitis. However, an absolute PNIF of 115 l/min had moderately high specificity and sensitivity and high negative predictive value for moderate/severe signs of rhinitis.
The repeatability of the PNIF measurements in this study is similar to that reported elsewhere. In this study, the ICC was 0.92 and 95% limits of agreement were ±36 l/min. The ICC is comparable with that obtained by Cho et al. (28) who reported a coefficient of 0.89 using a similar inhalation technique and the same brand of portable meter to measure PNIF rates in 12 healthy subjects over a period of 5 consecutive days.
The availability of normal values for PNIF might reasonably be assumed to be a prerequisite for the use of PNIF in clinical practice, however at present, no such data set has been published. In our sample of young adults, in the very narrow age range of 28–30 years, we found that in a normal group defined by the absence of allergic sensitization or self-reported hay fever, PNIF was independently related to spirometric lung volumes, but not additionally related to height, weight or gender. These findings are consistent with previous studies in adults that found that PNIF was independent of height and age (19) and was strongly correlated with a number of pulmonary parameters including FEV1, peak expiratory flow rates and FVC (5). It seems likely that respiratory muscle strength would play a role in determining inspiratory flow and that this might be indirectly related to body size or lung size. However, we found that using a prediction equation derived from our normal subject group to calculate predicted values for PNIF for our population did not improve the sensitivity or specificity of PNIF for signs or symptoms of rhinitis. This suggests that the predictor variables identified in this study are only weakly associated with PNIF and do not account for a high proportion of the variance. A larger population study that includes a broader range of age groups would be needed to define a more robust set of normal values.
In population studies and in many clinical settings, the diagnosis of rhinitis can be difficult because of the lack of objective diagnostic criteria that can be applied easily in these settings. In the absence of evidence from physical examination by an appropriately qualified doctor, the diagnosis and the classification of severity usually depends on a report of typical rhinitis symptoms. This study has shown that there is a highly significant, but imperfect association between the severity of current symptoms of rhinitis and physical signs of reduced nasal patency, and that PNIF measurements are more closely associated with nasal obstruction than with symptoms of rhinitis. This suggests that the information provided by PNIF is qualitatively different from that provided by information about symptoms. Since both types of information might contribute to the diagnosis, PNIF measurements are likely to have considerable utility in these settings. Information about current symptoms can be readily obtained from the patient, but objective evidence obtained from a physical examination conducted by a specialist ENT doctor may not be. The present study shows that a PNIF above 115 l/min has good specificity and a high negative predictive value for moderate/severe signs of rhinitis, suggesting that PNIF measurements could be useful to exclude nasal obstruction as a cause of current rhinitic symptoms in the setting of population screening. However, in the clinical setting, where the prior probability of rhinitis would probably be higher, the negative predictive value, and hence its utility for ‘ruling out’ rhinitis, would be lower. In contrast, the positive predictive value of the PNIF in this study was low, indicating that there were a high proportion of subjects with low PNIF values that did not have evidence of moderate or severe nasal obstruction. The positive predictive value would be higher in population with a higher prevalence of rhinitis and nasal obstruction, as would expected in the clinical setting.
A measurement of PNIF is likely to reflect nasal obstruction at the time of measurement. Longitudinal studies would be needed to determine if a low PNIF can predict prognosis or response to treatment or if re-occurring episodes of rhinitis cause irreversible reduction in PNIF and/or permanent obstruction in the upper airways, a situation analogous to remodelling in the lower airways (29).
The results from this study show that PNIF measurements reflect the severity of nasal signs of rhinitis in a general population sample of young adults. The strong association between PNIF and rhinitis signs, determined by physical examination, suggests that PNIF measurements may provide useful, objective information about nasal obstruction that is additional to that provided by subjective symptom scoring. In addition, like peak expiratory flow rate it may aid in the assessment of subjects who have impaired symptom perception.