Abstract
Objective
The aim of this study is to validate the applicability of the PolyVinyliDene Fluoride (PVDF) nasal sensor to assess the nasal airflow, in healthy subjects and patients with nasal obstruction and to correlate the results with the score of Visual Analogue Scale (VAS).
Methods
PVDF nasal sensor and VAS measurements were carried out in 50 subjects (25-healthy subjects and 25 patients). The VAS score of nasal obstruction and peak-to-peak amplitude ( V p-p ) of nasal cycle measured by PVDF nasal sensors were analyzed for right nostril (RN) and left nostril (LN) in both the groups. Spearman’s rho correlation was calculated. The relationship between PVDF nasal sensor measurements and severity of nasal obstruction (VAS score) were assessed by ANOVA.
Results
In healthy group, the measurement of nasal airflow by PVDF nasal sensor for RN and LN were found to be 51.14 ± 5.87% and 48.85 ± 5.87%, respectively. In patient group, PVDF nasal sensor indicated lesser nasal airflow in the blocked nostrils (RN: 23.33 ± 10.54% and LN: 32.24 ± 11.54%). Moderate correlation was observed in healthy group ( r = − 0.710, p < 0.001 for RN and r = − 0.651, p < 0.001 for LN), and moderate to strong correlation in patient group ( r = − 0.751, p < 0.01 for RN and r = − 0.885, p < 0.0001 for LN).
Conclusion
PVDF nasal sensor method is a newly developed technique for measuring the nasal airflow. Moderate to strong correlation was observed between PVDF nasal sensor data and VAS scores for nasal obstruction. In our present study, PVDF nasal sensor technique successfully differentiated between healthy subjects and patients with nasal obstruction. Additionally, it can also assess severity of nasal obstruction in comparison with VAS. Thus, we propose that the PVDF nasal sensor technique could be used as a new diagnostic method to evaluate nasal obstruction in routine clinical practice.
1
Introduction
The human respiration depends on the dynamics of the nasal airflow. The slight anatomical changes in the nasal cavity can affect the dynamics of the human respiration. Ideally, the right and left side of the nose in each breathing cycle should have identical airflow, resistance, and volume changes . Nasal airflow entirely depends on how open/obstructed is the nasal cavity (i.e., nasal patency). Nasal airflow is inversely proportional to the nasal obstruction, i.e., the more the nasal airflow, the lesser is the nasal obstruction and vice versa. Therefore, by evaluating the nasal airflow, it is possible to assess the nasal obstruction. Nasal obstruction may be caused due to nasal anatomic abnormalities and/or mucosal disease. It is also a common symptom in patients attending the oto-rhino-laryngological (Ear, Nose and Throat; ENT) clinics affecting individuals of all age groups. Major anomalies such as septum deviations, inspiration alar collapse, nasal polyps and mucosa can be directly visualized by examining the structures of the nose by a clinician.
In general, nasal obstruction can be assessed objectively and subjectively by different methods/instruments . The most commonly used instruments for the objective assessment of nasal obstruction are rhinomanometry, acoustic rhinometry, and Peak Nasal Inspiratory Flowmeter(PNIF). Rhinomanometry measures the nasal obstruction by evaluating the nasal airflow and trans-nasal pressure during respiration . It uses pneumotachometer and pressure transducer to quantify the nasal resistance to the nasal airflow. It is a good research tool that is very sensitive for small measurements. Hence active rhinomanometry has been recommended by the Standardization Committee of the European Rhinologic Society . A major disadvantage of the rhinomanometry is that it is expensive and is not easily portable, thus making its usage limited for routine clinical purpose. An acoustic rhinometry evaluates the cross-sectional area of nasal cavity in terms of area-distance graph by measuring echoes of sound impulses sent in the respiration tract, mainly through the nose . The disadvantages of this method are, it is not only expensive, but also requires skilled operator and cannot be easily portable. PNIF evaluates the nasal airflow (in liters/minute) passing through the tube, when a subject maximally inhales air . Though PNIF is inexpensive and portable as compared to its counterparts like rhinomanometry and acoustic rhinometry, it does not give unilateral measurement. PNIF measures the complete nasal airflow and requires a maximum co-operation from patients. Therefore, there is a need of instruments that are practical, cost-effective, portable, reliable, and requires minimal co-operation from patients to evaluate nasal obstruction objectively.
Other than the above mentioned objective methods, the nasal obstruction can also be measured subjectively by using Visual Analogue Scale (VAS) . Basically VAS is a subjective perception or experience of patients about their nasal obstruction and it is well validated and reliable parameter .
In this paper, we report about a newly developed PolyVinyliDeneFluoride (PVDF) nasal sensor technique for objective measurement of nasal airflow. PVDF is a non-reactive, flexible, light weight and a bio-compatible polymer available in various thicknesses and size and has a strong piezoelectric property . Piezoelectricity is the ability of the material to produce voltage whenever it is mechanically stressed/strained. PVDF is used in many biomedical applications because of its piezoelectric and pyroelectric properties .
In our previous study, we have successfully evaluated our newly designed and developed PVDF nasal sensor with one of the objective technique (PNIF) to assess deviated nasal septum . The aim of our present work is to investigate the use of PVDF nasal sensor as a diagnostic tool to assess the nasal obstruction in comparison with the subjective technique namely, VAS.
2
Methods and materials
2.1
Subjects
The present study was conducted at M. S. Ramaiah Medical College and Hospital, Bangalore, India after obtaining necessary approval from the institutional review board. Written consent was obtained from all subjects before their participation in the study. We recruited 50 subjects and divided them into two groups. The first group was a healthy group consisting of 25 (18 male and 7 female) subjects with the age of 29 ± 8 years. The second group was a patient group consisting of 25 (20 male and 5 female) subjects with complaints of nasal obstruction with the age of 31 ± 9 years. Healthy subjects were volunteers recruited from hospital staff members and medical interns without any complaints of nasal obstruction, whereas, the patient group was recruited from the Out-Patient Department (OPD) of Ear, Nose and Throat, who consulted with a complaint of nasal obstruction. The main criterion for patients to enrol in this study was the presence of nasal obstruction without any additional nasal pathology. Prior to performing the study using PVDF nasal sensor, all crusting and nasal mucosa were removed from nasal cavity (without the use of any nasal decongestant).
2.2
PVDF nasal sensor
PVDF (supplied by Precision acoustic, UK) is a piezoelectric film that produces voltage whenever it is subjected to mechanical stress/strain. The mechanical stress/stain in this work is caused due to nasal air flow. The PVDF film with length 10 mm, width 5 mm and thickness 28 μm is firmly adhered to a plastic base in such a way that it forms a cantilever configuration leaving the other end free for deflection. The double enamelled copper wires (diameter 0.07 mm) were attached on top and bottom surfaces of the PVDF film using aluminium conducting tape. This arrangement (PVDF film in cantilever configuration with the leads attached on both the surfaces) forms the nasal sensor . Two such PVDF nasal sensors were taken and attached to the flexible strings on either side of the headphone as shown in Fig. 1 . PVDF nasal sensors were positioned below the right and left nostrils without disturbing the normal breathing of subjects. The pulsating air flow due to the inspired and expired air impinges on these two identical PVDF nasal sensors leading to bending strain. This bending mechanical strain results in the voltage signal from the sensor, corresponding to breathing cycle of the respective nostrils.
2.3
Device set-up
The complete experimental set-up used for the measurement of nasal airflow consists of headphone mounted with PVDF nasal sensor, signal conditioning box, Data Acquisition card (DAQ) and a computer. The signal conditioning circuitry consists of pre-amplifier, low-pass filter and an amplifier. The output of the PVDF nasal sensor was less (30 to 40 m V p-p ). Therefore, a charge sensitive pre-amplifier was used to amplify the output of the PVDF nasal sensor. The frequency of the normal human respiration is known to be in the range of 0.2–0.5 Hz. Hence a second order low-pass filter with a cut-off frequency of 3Hz was designed to filter out the unwanted signals. The filtered PVDF nasal sensor signal was fed to the amplifier (with gain 10) for good amplification. Finally, the amplified output voltage signal (breathing signal) was fed to the data acquisition card (NI-6008 card), which was interfaced with the computer for recoding and storing the signal for further analysis.
2.4
Visual Analogue Scale (VAS)
Detailed physical examination was performed by an oto-rhino-laryngologist, using a bright light source and a nasal speculum (an instrument that gently spreads open the nostril) for each subject’s right nostril (RN) and left nostril (LN). After physical examination, VAS with score 0–10 was used to evaluate the nasal obstruction experienced by the subject. Each subject answered the standardized questionnaire. Information regarding the presence or absence of the nasal obstruction as well as the side of nostril (LN or RN) where nasal obstruction is present was obtained from the subjects. Further their perception of nasal obstruction during normal breathing was marked on a score of 0–10 VAS for each nostril separately. The VAS score used in the present study is as follows,
- (i)
0 corresponds to ‘no obstruction’,
- (ii)
1–3 corresponds to ‘mild obstruction’,
- (iii)
4–7 corresponds to ‘moderate obstruction’ and
- (iv)
8–10 corresponds to ‘severe obstruction’.
2.5
Recording breathing signal using PVDF nasal sensor
A complete device setup for recording the breathing signal was kept on a table in a well-ventilated room with normal room temperature and humidity. Each subject was asked to sit on a chair in a relaxed position. Subsequently, the subject was asked to wear the headphone mounted with PVDF nasal sensors. The headphone was flexible enough to fit the same conveniently for different head sizes. A constant distance of 5 mm was maintained between each PVDF nasal sensor and nostril for all the subjects. After suitably positioning the PVDF nasal sensor, the subject was instructed to perform normal breathing. While recoding the breathing signal/data, an initial signal/data for 30 seconds was truncated to avoid the possible artefacts due to wearing of head phones. The breathing signal was recorded for 2 minutes duration and stored as an ‘.lvm’ file in a computer. The average time duration taken to perform each PVDF nasal sensor measurement was about 5–6 minutes.
2.6
Analysis of breathing signal
The breathing signal recorded using the PVDF nasal sensor consists of each breathing cycle’s peak-to-peak amplitude ( V p-p ), which directly corresponds to the magnitude of air-flow from the nostril. A computer algorithm was developed using MATLAB [version 7.5.0.342 (R2007b)] software for the calculation of average peak-to-peak amplitude for the entire breathing cycle of each nostril separately.
The calculations of the percentage of nasal airflow are performed as follows,
Total nasal airflow = Right nostril airflow measured in V p ‐ p + Left nostril airflow measured in V p ‐ p
Right nasal airflow percentage = Right nostril airflow measured in V p ‐ p Total nasal airflow × 100
Left nasal airflow percentage = Left nostril airflow measured in V p ‐ p Total nasal airflow × 100
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