Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB076

Poster Communications

Evaluation of the methods used to measure sniff nasal inspiratory pressure in healthy human subjects

R. Wilding1, E. Richards1, M. Thynne2, M. M. Subhan1

1. School of Biomedical Sciences, University of Plymouth, Plymouth, United Kingdom. 2. Chest Clinic, University Hospitals Plymouth NHS Trust, Plymouth, Devon, United Kingdom.

Maximal inspiratory pressure (MIP) is currently used to assess respiratory muscle strength (RMS), however it requires significant effort. Falsely low values are common, especially in patients with neuromuscular disorders [1]. In contrast, sniff nasal inspiratory pressure (SNIP) is a natural manoeuvre, so subjects find it easier. Therefore SNIP has been recommended to scrutinise inspiratory muscle weakness after a low MIP [2]. However, limited guidelines and varied approaches regarding the optimal method of measuring SNIP exist [3, 4]. The aim of this study was to investigate the effects of inter-measurement time, left/right nostril and contralateral occlusion on SNIP measurements in healthy subjects. We performed a pilot study comparing inter-measurement time differences in SNIP measured in 10 healthy subjects, depending on whether repeats were performed 30, 60 or 90 s apart. Furthermore, our study tested four methods of measuring SNIP in a randomised order in 52 healthy subjects, aiming to compare results obtained from right nostril left occluded, right nostril left non-occluded, left nostril right occluded and left nostril right non-occluded. We also attempted to determine the optimal number of repeats that would eliminate any learning effect, but not pose risk of fatigue. The study was given ethical approval by the Research Ethics committee, University of Plymouth. All participating subjects gave informed and signed consent. SNIP was measured from functional residual capacity via a probe (MicroRPM, Micromedical) in one nostril, and subjects were instructed to perform a short, sharp sniff. A repeated-measures ANOVA tested differences between the mean maximal SNIP for each method and position. Unpaired t-testing compared differences between occluded and non-occluded and also between left and right nostrils. p<0.05 was considered significant for t-tests, while a p<0.0125 was considered significant for ANOVA. There were no significant inter-measurement time differences in SNIP depending on the interval between repeats (p=0.98). Occluded SNIP was significantly higher than non-occluded (73.4 vs. 56.1 cmH2O, p<0.00001), while left or right SNIP did not significantly differ (63.6 vs. 66.0 cmH2O, p=0.60). There was no learning effect continuing after 20 repeats (p = 0.64), and SNIP did not decline during 80 repeats. Overall, occluded SNIP is a more reliable RMS indicator than non-occluded SNIP, as there is reduced risk of underestimation. Allowing subjects to choose which nostril to insert the probe is appropriate, as this did not significantly affect SNIP, but may increase ease of performance. Ultimately, if our findings are replicated in similar trials performed on patients with respiratory muscle weakness, they could be used to develop guidelines on how to perform a reliable SNIP, increasing the use of this test in clinical settings.

Where applicable, experiments conform with Society ethical requirements