We conducted a clinical study at the Auckland University of Technology BioDesign Lab between April and July 2019. Ten healthy volunteers (age range, 20 to 63 years; mean ± standard deviation, 43.1± 18.5 years; males 8, females 2) were recruited for this study. Exclusion criteria were a history of allergic rhinitis, sinusitis, or previous nasal surgery. All volunteers underwent a nasal endoscopic examination by an otolaryngologist. Volunteers with a significant septal deviation, turbinate abnormalities or inflammation were excluded. The volunteer was also excluded if the gas sampling tube was unable to pass comfortably along the floor of the volunteer’s nasal cavity to the nasopharynx.
Prior to and after gas testing, the nostril patency status was determined by using two spirometers adapted to measure individual nostril airflow. Each volunteer was asked to strongly exhale via the nose, while holding a spirometer against each nostril (Fig. 1). Peak exhaled airflow measurement for each side of the nose was then compared, with the side demonstrating the greatest airflow being designated ‘patent’ and the side showing a lower value labelled as ‘congested’.
NO concentrations were measured by a rapid response chemiluminescence NO analyser (Logan Research Limited LR2149 series NO gas analyser, UK), calibrated prior to every participant test using a calibration gas mixture (200 ppb, BOC). A small diameter (0.79 mm internal diameter x 1.59 mm external diameter) polytetrafluoroethylene (PTFE - Teflon) gas sampling tube (Cole-Palmer, C-P06407-41), was connected at one end to the NO analyser via a hydrophobic disc filter element (PTFE 1 micron filter). The other loose end of the Teflon gas sampling tube had two additional small side holes to prevent the tube from sucking against the walls of the nasal airway. All gas sampling was undertaken with a sampling flow rate of 0.25 litres/min for a period of 40 seconds using a data sampling rate of 40 milliseconds.
After identifying the patent side of the nose using the nasal spirometer test, the NO concentration at the nasal vestibule was measured. This entailed the gas sampling tube being held at the left nostril (without occluding the right nostril) and the volunteer was asked to breathe `normally', while the tidal nasal airflow was sampled over a 40 second period. This procedure was then repeated with the gas sampling tube held at the right nostril.
The gas sampling tube was then passed into the volunteer’s patent nostril, along the floor of their nose until it was stationed in the nasopharynx. This was confirmed by the participant experiencing the sensation of the tube abutting against the nasopharynx wall and visual confirmation of the graduated tube length. Once the participant was comfortable, nasopharynx NO concentration measurement was undertaken. This entailed first measuring during BNB, before undertaking UNB repeated for both sides of the nose, with the order decided by coin toss.
On conclusion of testing, the measuring tube was removed from the nose and the state of the nasal cycle again determined using the spirometers.
Acquired data was transferred in .txt format from the gas analyser to a PC for analysis using an external USB hard drive. Data analysis was split into the different breathing conditions in the measurement and undertaken using MatLab script (MathWorks, USA). After identifying all gas concentration inhalation peaks in the datasets, their mean was then calculated for each of the three different breathing conditions. Descriptive statistics were then applied to the relative data grouped by breathing condition using IBM SPSS version 24. In SPSS, a Shapiro-Wilk parametric test was used to test if the data is normally distributed [12].