Response characteristics for thermal and pressure devices commonly used for monitoring nasal and oral airflow during sleep studies

Abstract

We examined thermocouple and pressure cannulae responses to oral and nasal airflow using a polyester model of a human face, with patent nasal and oral orifices instrumented with a dual thermocouple (F-ONT2A, Grass) or a dual cannula (0588, Braebon) pressure transducer (± 10 cm H2O, Celesco) system. Tidal airflow was generated using a dual compartment facemask with pneumotachographs (Fleisch 2) connected to the model orifices. During nasal breathing: thermocouple amplitude = 0.38 Ln [pneumotachograph amplitude] + 1.31 and pressure cannula amplitude = 0.93 [pneumotachograph amplitude](2.15); during oral breathing: thermocouple amplitude = 0.44 Ln [pneumotachograph amplitude] + 1.07 and pressure cannula amplitude = 0.33 [pneumotachograph amplitude](1.72); (all range ∼ 0.1-∼ 4.0 L s(-1); r(2) > 0.7). For pneumotachograph amplitudes <1 L s(-1) (linear model) change in thermocouple amplitude/unit change in pneumotachograph amplitude was similar for nasal and oral airflow, whereas nasal pressure cannula amplitude/unit change in pneumotachograph amplitude was almost four times that for oral. Increasing oral orifice area from 0.33 cm(2) to 2.15 cm(2) increased oral thermocouple amplitude/unit change in pneumotachograph amplitude by ∼ 58% but decreased pressure cannula amplitude/unit change in pneumotachograph amplitude by 49%. For pneumotachograph amplitudes up to 1 L s(-1), alterations in inspiratory/expiratory ratios or total respiratory time did not affect the sensitivity of either nasal or oral pressure cannulae or the nasal thermocouple, but the oral thermocouple sensitivity was influenced by respiratory cycle time. Different nasal and oral responses influence the ability of these systems to quantitatively assess nasal and oral airflow and oro-nasal airflow partitioning.

Sensitivity and specificity of hypopnoea detection using nasal pressure in the presence of a nasal expiratory resistive device (Provent®)

“…Peak inspiratory and expiratory airflow reported during sleep in human subjects are reported to be as high as 0.4-0.5 L s −1 , with the resultant amplitude of the airflow signal being up to 1 L s −1 (Clark et al 1998). The relationship between the amplitude of the flow and pressure signal is linear for the nasal pressure cannula, as we have demonstrated previously (Gehring et al 2014). Thus, the ability to detect hypopneas will be similar across a large range of flow amplitudes.…”

“…An anatomically correct face model was constructed of photopolymer (FullCure720, Objet Geometries Ltd, Israel) using a 3D printing process to reproduce a laser generated 3D image obtained from an impression model of a male human face. The printing process incorporated two identical nasal passages and an oral airway (see figure 1) (Gehring et al 2014). Nasal passage internal dimensions (including the nasal valve zone) were based on acoustic rhinometry measurements (cross-sectional area versus distance) obtained from a single human subject (Gehring et al 2014).…”

“…The printing process incorporated two identical nasal passages and an oral airway (see figure 1) (Gehring et al 2014). Nasal passage internal dimensions (including the nasal valve zone) were based on acoustic rhinometry measurements (cross-sectional area versus distance) obtained from a single human subject (Gehring et al 2014). The nasal passages were connected at the rear of the model to a pneumotachograph (Fleisch, Gould, Netherlands) to allow quantification of nasal passage airflow (V ̇) as generated by a constant airflow pump or via a human subject using a mouthpiece.…”

“…Meas. 35 (2014) 2447 (Kirkness et al 2011, Gehring et al 2014. Using this model, we have recently compared the response characteristics of thermal and pressure devices for measuring nasal and oral airflow (Gehring et al 2014).…”

“…35 (2014) 2447 (Kirkness et al 2011, Gehring et al 2014. Using this model, we have recently compared the response characteristics of thermal and pressure devices for measuring nasal and oral airflow (Gehring et al 2014). In the present study, we use our bench model to compare the accuracy of both methods for detection of hypopneic events relative to 'gold-standard' pneumotachograph measurements of nasal airflow.…”