Pitot-tube flowmeter for quantification of airflow during sleep

Evaluating Airflow Sensor Methods: Precision in Indirect Calorimetry

This study assesses the impact of three volumetric gas flow measurement methods-turbine (fT); pneumotachograph (fP), and Venturi (fV)-on predictive accuracy and precision of expired gas analysis indirect calorimetry (EGAIC) across varying exercise intensities. Six males (Age: 38 ± 8 year; Height: 178.8 ± 4.2 cm;V ̇ O 2 peak $$ \dot{V}{\mathrm{O}}_2\mathrm{peak} $$ : 42 ± 2.8 mL O2 kg-1 min-1) and 14 females (Age = 44.6 ± 9.6 year; Height = 164.6 ± 6.9 cm;V ̇ O 2 peak $$ \dot{V}{\mathrm{O}}_2\mathrm{peak} $$ = 45 ± 8.6 mL O2 kg-1 min-1) were recruited. Participants completed physical exertion on a stationary cycle ergometer for simultaneous pulmonary minute ventilation (V ̇ $$ \dot{V} $$ ) measurements and EGAIC computations. Exercise protocols and subsequent conditions involved a 5-min cycling warm-up at 25 W min-1, incremental exercise to exhaustion (V ̇ O 2 $$ \dot{V}{\mathrm{O}}_2 $$ ramp test), then a steady-state exercise bout induced by a constant Watt load equivalent to 80% ventilatory threshold (80% VT). A linear mixed model revealed that exercise intensity significantly affectedV ̇ O 2 $$ \dot{V}{\mathrm{O}}_2 $$ measurements (p < 0.0001), whereas airflow sensor method (p = 0.97) and its interaction with exercise intensity (p = 0.91) did not. Group analysis of precision yielded aV ̇ O 2 $$ \dot{V}{\mathrm{O}}_2 $$ CV % = 21%; SEM = 5 mL O2 kg-1 min-1. Intra- and interindividual analysis of precision via Bland-Altman revealed a 95% confidence interval (CI) precision benchmark of 3-5 mL kg-1 min-1. Agreement among methods decreased at power outputs elicitingV ̇ $$ \dot{V} $$ up to 150 L min-1, indicating a decrease in precision and highlighting potential challenges in interpreting biological variability, training response heterogeneity, and test-retest comparisons. These findings suggest careful consideration of airflow sensor method variance across metabolic cart configurations.

Quantifying ventilation by X-ray velocimetry in healthy adults

RATIONALE

X-ray velocimetry (XV) has been utilized in preclinical models to assess lung motion and regional ventilation, though no studies have compared XV-derived physiologic parameters to measures derived through conventional means.

OBJECTIVES

To assess agreement between XV-analysis of fluoroscopic lung images and pitot tube flowmeter measures of ventilation.

METHODS

XV- and pitot tube-derived ventilatory parameters were compared during tidal breathing and with bilevel-assisted breathing. Levels of agreement were assessed using the Bland-Altman analysis. Mixed models were used to characterize the association between XV- and pitot tube-derived values and optimize XV-derived values for higher ventilatory volumes.

MEASUREMENTS AND MAIN RESULTS

Twenty-four healthy volunteers were assessed during tidal breathing and 11 were reassessed with increased minute ventilation with bilevel-assisted breathing. No clinically significant differences were observed between the two methods for respiratory rate (average Δ: 0.58; 95% limits of agreement: -1.55, 2.71) or duty cycle (average Δ: 0.02; 95% limits of agreement: 0.01, 0.03). Tidal volumes and flow rates measured using XV were lower than those measured using the pitot tube flowmeter, particularly at the higher volume ranges with bilevel-assisted breathing. Under these conditions, a mixed-model based adjustment was applied to the XV-derived values of tidal volume and flow rate to obtain closer agreement with the pitot tube-derived values.

CONCLUSION

Radiographically obtained measures of ventilation with XV demonstrate a high degree of correlation with parameters of ventilation. If the accuracy of XV were also confirmed for assessing the regional distribution of ventilation, it would provide information that goes beyond the scope of conventional pulmonary function tests or static radiographic assessments.

Obesity, tidal volume, and pulmonary deposition of fine particulate matter in children with asthma

BACKGROUND

Obese children with asthma are more vulnerable to air pollution, especially fine particulate matter (PM_2.5), but reasons are poorly understood. We hypothesised that differences in breathing patterns (tidal volume, respiratory rate and minute ventilation) due to elevated body mass index (BMI) may contribute to this finding.

OBJECTIVE

To investigate the association of BMI with breathing patterns and deposition of inhaled PM_2.5.

METHODS

Baseline data from a prospective study of children with asthma were analysed (n=174). Tidal breathing was measured by a pitot-tube flowmeter, from which tidal volume, respiratory rate and minute ventilation were obtained. The association of BMI z-score with breathing patterns was estimated in a multivariable model adjusted for age, height, race, sex and asthma severity. A particle dosimetry model simulated PM_2.5 lung deposition based on BMI-associated changes in breathing patterns.

RESULTS

Higher BMI was associated with higher tidal volume (adjusted mean difference (aMD) between obese and normal-range BMI of 25 mL, 95% CI 5-45 mL) and minute ventilation (aMD 453 mL·min^-1, 95% CI 123-784 mL·min^-1). Higher tidal volumes caused higher fractional deposition of PM_2.5 in the lung, driven by greater alveolar deposition. This translated into obese participants having greater per-breath retention of inhaled PM_2.5 (aMD in alveolar deposition fraction of 3.4%, 95% CI 1.3-5.5%), leading to worse PM_2.5 deposition rates.

CONCLUSIONS

Obese children with asthma breathe at higher tidal volumes that may increase the efficiency of PM_2.5 deposition in the lung. This finding may partially explain why obese children with asthma exhibit greater sensitivity to air pollution.

Comparison of airway pressures and expired gas washout for nasal high flow versus CPAP in child airway replicas

Background

For children and adults, the standard treatment for obstructive sleep apnea is the delivery of continuous positive airway pressure (CPAP). Though effective, CPAP masks can be uncomfortable to patients, contributing to adherence concerns. Recently, nasal high flow (NHF) therapy has been investigated as an alternative, especially in CPAP-intolerant children. The present study aimed to compare and contrast the positive airway pressures and expired gas washout generated by NHF versus CPAP in child nasal airway replicas.

Methods

NHF therapy was investigated at a flow rate of 20 L/min and compared to CPAP at 5 cmH₂O and 10 cmH₂O for 10 nasal airway replicas, built from computed tomography scans of children aged 4–8 years. NHF was delivered with three different high flow nasal cannula models provided by the same manufacturer, and CPAP was delivered with a sealed nasal mask. Tidal breathing through each replica was imposed using a lung simulator, and airway pressure at the trachea was recorded over time. For expired gas washout measurements, carbon dioxide was injected at the lung simulator, and end-tidal carbon dioxide (EtCO₂) was measured at the trachea. Changes in EtCO₂ compared to baseline values (no intervention) were assessed.

Results

NHF therapy generated an average positive end-expiratory pressure (PEEP) of 5.17 ± 2.09 cmH₂O (mean ± SD, n = 10), similar to PEEP of 4.95 ± 0.03 cmH₂O generated by nominally 5 cmH₂O CPAP. Variation in tracheal pressure was higher between airway replicas for NHF compared to CPAP. EtCO₂ decreased from baseline during administration of NHF, whereas it increased during CPAP. No statistical difference in tracheal pressure nor EtCO₂ was found between the three high flow nasal cannulas.

Conclusion

In child airway replicas, NHF at 20 L/min generated average PEEP similar to CPAP at 5 cm H₂O. Variation in tracheal pressure was higher between airway replicas for NHF than for CPAP. The delivery of NHF yielded expired gas washout, whereas CPAP impeded expired gas washout due to the increased dead space of the sealed mask.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01880-z.

Feasibility of three-dimensional facial imaging and printing for producing customised nasal masks for continuous positive airway pressure

Rationale

Delivery of continuous positive airway pressure (CPAP) is the standard treatment for obstructive sleep apnoea in children and adults. Treatment adherence is a major challenge, as many patients find the CPAP mask uncomfortable. The study aim was to demonstrate the feasibility of delivered CPAP through customised nasal masks by assessing mask leak and comfort of customised masks compared to commercially available CPAP masks.

Methods

Six healthy adult volunteers participated in a crossover study including commercial masks in three different sizes (petite, small/medium and large) from the same supplier and a customised mask fabricated for each subject using three-dimensional facial scanning and modern additive manufacturing processes. Mask leak and comfort were assessed with varying CPAP levels and mask tightness. Leak was measured in real time using an inline low-resistance Pitot tube flow sensor, and each mask was ranked for comfort by the subjects.

Results

Mask leak rates varied directly with CPAP level and inversely with mask tightness. When ranked for comfort, three subjects favoured the customised mask, while three favoured a commercial mask. The petite mask yielded the highest mask leaks and was ranked least comfortable by all subjects. Relative mask leaks and comfort rankings for the other commercial and customised masks varied between individuals. Mask leak was comparable when comparing the customised masks with the highest ranked commercial masks.

Conclusion

Customised masks successfully delivered target CPAP settings in all six subjects, demonstrating the feasibility of this approach.

This research details a methodology for fabrication of customised noninvasive ventilation masks based on 3D facial scans to use as an alternative to commercially available masks for the delivery of continuous positive airway pressurehttps://bit.ly/35WspAg

An assessment of a simple clinical technique to estimate pharyngeal collapsibility in people with obstructive sleep apnea

Study Objectives

Quantification of upper airway collapsibility in obstructive sleep apnea (OSA) could help inform targeted therapy decisions. However, current techniques are clinically impractical. The primary aim of this study was to assess if a simple, novel technique could be implemented as part of a continuous positive airway pressure (CPAP) titration study to assess pharyngeal collapsibility.

Methods

A total of 35 participants (15 female) with OSA (mean ± SD apnea–hypopnea index = 35 ± 19 events/h) were studied. Participants first completed a simple clinical intervention during a routine CPAP titration, where CPAP was transiently turned off from the therapeutic pressure for ≤5 breaths/efforts on ≥5 occasions during stable non-rapid eye movement (non-REM) sleep for quantitative assessment of airflow responses (%peak inspiratory flow [PIF] from preceding 5 breaths). Participants then underwent an overnight physiology study to determine the pharyngeal critical closing pressure (Pcrit) and repeat transient drops to zero CPAP to assess airflow response reproducibility.

Results

Mean PIF of breaths 3–5 during zero CPAP on the simple clinical intervention versus the physiology night were similar (34 ± 29% vs. 28 ± 30% on therapeutic CPAP, p = 0.2; range 0%–90% vs. 0%–95%). Pcrit was −1.0 ± 2.5 cmH2O (range −6 to 5 cmH2O). Mean PIF during zero CPAP on the simple clinical intervention and the physiology night correlated with Pcrit (r = −0.7 and −0.9, respectively, p &lt; 0.0001). Receiver operating characteristic curve analysis indicated significant diagnostic utility for the simple intervention to predict Pcrit &lt; −2 and &lt; 0 cmH2O (AUC = 0.81 and 0.92), respectively.

Conclusions

A simple CPAP intervention can successfully discriminate between patients with and without mild to moderately collapsible pharyngeal airways. This scalable approach may help select individuals most likely to respond to non-CPAP therapies.

Reductions in dead space ventilation with nasal high flow depend on physiological dead space volume: metabolic hood measurements during sleep in patients with COPD and controls

Nasal high flow (NHF) reduces minute ventilation and ventilatory loads during sleep but the mechanisms are not clear. We hypothesised NHF reduces ventilation in proportion to physiological but not anatomical dead space.11 subjects (five controls and six chronic obstructive pulmonary disease (COPD) patients) underwent polysomnography with transcutaneous carbon dioxide (CO₂) monitoring under a metabolic hood. During stable non-rapid eye movement stage 2 sleep, subjects received NHF (20 L·min^-1) intermittently for periods of 5-10 min. We measured CO₂ production and calculated dead space ventilation.Controls and COPD patients responded similarly to NHF. NHF reduced minute ventilation (from 5.6±0.4 to 4.8±0.4 L·min^-1; p<0.05) and tidal volume (from 0.34±0.03 to 0.3±0.03 L; p<0.05) without a change in energy expenditure, transcutaneous CO₂ or alveolar ventilation. There was a significant decrease in dead space ventilation (from 2.5±0.4 to 1.6±0.4 L·min^-1; p<0.05), but not in respiratory rate. The reduction in dead space ventilation correlated with baseline physiological dead space fraction (r²=0.36; p<0.05), but not with respiratory rate or anatomical dead space volume.During sleep, NHF decreases minute ventilation due to an overall reduction in dead space ventilation in proportion to the extent of baseline physiological dead space fraction.

The Efficacy of Low-Level Continuous Positive Airway Pressure for the Treatment of Snoring

STUDY OBJECTIVES

To assess effects of low-level continuous positive airway pressure (CPAP) on snoring in habitual snorers without obstructive sleep apnea (OSA).

METHODS

A multicenter prospective in-laboratory reversal crossover intervention trial was conducted between September 2013 and August 2014. Habitual snorers were included if they snored (inspiratory sound pressure level ≥ 40 dBA) for ≥ 30% all sleep breaths on a baseline sleep study (Night 1), and if significant OSA and daytime somnolence were absent. Included participants then underwent a CPAP titration study at 2, 4, or 6 cm H₂O (Night 2) to examine snoring responses to step-increases in nasal pressure, a treatment night at optimal pressure (Night 3), followed by baseline night (Night 4). At each pressure, snoring intensity was measured on each breath. Snoring frequency was quantified as a percentage of sleep breaths at thresholds of 40, 45, 50, and 55 dBA. Sleep architecture and OSA severity were characterized using standard measurements.

RESULTS

On baseline sleep studies, participants demonstrated snoring at ≥ 40 dBA on 53 ± 3% and ≥ 45 dBA on 35 ± 4% of breaths. Snoring frequency decreased progressively as nasal pressure increased from 0 to 4 cm H₂O at each threshold, and plateaued thereafter. CPAP decreased snoring frequency by 67% and 85% at 40 and 45 dBA, respectively. Intervention did not alter sleep architecture and sleep apnea decreased minimally.

CONCLUSIONS

Low-level CPAP below the range required to treat OSA diminished nocturnal snoring, and produced uniform reduction in nightly noise production below the World Health Organization's limit of 45 dBA.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT01949584.

Nasal high-flow therapy reduces work of breathing compared with oxygen during sleep in COPD and smoking controls: a prospective observational study

Patients with chronic obstructive pulmonary disease (COPD) endure excessive resistive and elastic loads leading to chronic respiratory failure. Oxygen supplementation corrects hypoxemia but is not expected to reduce mechanical loads. Nasal high-flow (NHF) therapy supports breathing by reducing dead space, but it is unclear how it affects mechanical loads of patients with COPD. The objective of this study was to compare the effects of low-flow oxygen and NHF therapy on ventilation and work of breathing (WOB) in patients with COPD and controls during sleep. Patients with COPD (n = 12) and controls (n = 6) were recruited and submitted to polysomnography to measure sleep parameters and ventilation in response to administration of oxygen and NHF. A subset of six patients also had an esophageal catheter inserted for the purpose of measuring WOB. Patients with COPD had similar minute ventilation (V̇e) but lower tidal volumes than matched controls. With oxygen, [Formula: see text]was increased and V̇e was reduced in both controls and patients with COPD, but there was an increase in transcutaneous CO₂ levels. NHF produced a greater reduction in V̇e and was associated with a reduction in CO₂ levels. Although NHF halved WOB, oxygen produced only a minor reduction in this parameter. We conclude that oxygen produced little change in WOB, which was associated with CO₂ elevations. On the other hand, NHF produced a large reduction in V̇e and WOB with a concomitant decrease in CO₂ levels. Our data indicate that NHF improves alveolar ventilation during sleep compared with oxygen and room air in patients with COPD and therefore can decrease their cost of breathing.

NEW & NOTEWORTHY

Nasal high-flow (NHF) therapy can support ventilation in patients with chronic obstructive pulmonary disease during sleep by decreasing the work of breathing and improving CO₂ levels. On the other hand, oxygen supplementation corrects hypoxemia, but it produces only a minimal reduction in work of breathing and is associated with increased CO₂ levels. Therefore, NHF can be a useful method to assist ventilation in patients with increased respiratory mechanical loads.

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

Nasal expiratory resistive valves (Provent(®)) have been proposed as novel therapy for obstructive sleep apnea. We compared pressure measurements from a standard nasal pressure catheter used to assess nasal airflow during sleep with those from nasal expiratory resistive device with attached proprietary nasal pressure cannula. Nasal pressure cannula or Provent(®) + proprietary nasal pressure cannula were attached to a bench model of human anterior nares and nasal passages, and pressure measured (P). Respiratory airflows generated by a subject breathing were applied to rear of model and airflow (V) measured via pneumotachograph. Airflow amplitude (ΔV) was plotted against pressure amplitude (ΔP). Hypopnoea detection (<50% ΔV) sensitivity and specificity was tested by expressing ΔP in terms of two reference breaths: reference breath 1, ΔV 0.55 L s(-1) = 100%; and reference breath 2, ΔV 0.45 L s(-1) = 100%. ΔP/ΔV relationships were linear for ΔV ≤ 0.55 L s(-1); ΔP = 0.37ΔV + 0.16 (nasal pressure cannula), ΔP = 2.7ΔV + 0.12 (Provent(®) + proprietary nasal pressure cannula); both R(2) > 0.65, p < 0.0001; p < 0.0001 for between slope difference). For nasal pressure cannula, specificity of hypopnoea detection differed between reference breaths one and two (80.2% and 40.0%, respectively), and Provent(®) + proprietary nasal pressure cannula (30.3% and 74.2%, respectively). Quantification of airflow obstruction in the presence of Provent(®) + proprietary nasal pressure cannula is greatly influenced by the reference breath chosen to determine a reduction in nasal airflow. Reported variability in therapeutic response to nasal expiratory resistive devices may relate to differences in measurement technique specificity used to quantify the severity of sleep disordered breathing.

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

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.

Developing quantitative physiological phenotypes of sleep apnea for epidemiological studies

Existing physiological databases have not been sufficiently detailed to provide relevant and important information for characterizing the pathophysiology of obstructive sleep apnea. Critical collapsing pressure (P(CRIT)) is a standard method for determining upper airway patency during sleep, however is labor intensive and prohibits large-scale studies. Based on previously published data indicating R(US) does not significantly vary between groups, our aim was to develop an approach to estimate the P(CRIT) from airflow at atmospheric pressure (V(atm)). In a dataset of 126 subjects, where P(CRIT) and R(US) were measured using standard techniques. We then determined the minimum sample size required to estimate the R(US) mean and variance by utilizing a bootstrap procedure (30 times for n=3 to 126). We first estimated the minimum number of subjects needed for obtaining a group for a two-tailed (z=1.96) standard error for R(US) in the population. Then in 75 individuals, quantitative estimates of airflow were obtained at atmospheric pressure. Using the estimated R(US) and atmospheric, we determined an estimated P(CRIT) (ЄP(CRIT)). Bland-Altman plots were generated to determine the agreement between the measured P(CRIT) and ЄP(CRIT). For the entire population the mean ± SEM R(US) was 23 ± 1 cmH(2)O/L/s (± 95% CI: 21, 25). ~40 subjects represent the minimum sample required to estimate the population variance within ± 2 SEM. In the subsample with atmospheric flow measurements, a linear regression model (ЄP(CRIT) [cmH(2)O] = V(@PN) [L/s]x-23[cmH(2)O/L/s]), ЄP(CRIT) ranged from 0 to -9.6 cmH(2)O. In the Bland-Altman analysis there was no mean difference between the measured P(CRIT) and ЄP(CRIT) (-0.01 cmH(2)O; p=0.8) with upper and lower limits of agreement at ± 2.3 cmH(2)O. The variance of upstream resistance approaches a constant value in groups with approximately 40 subjects. Utilizing a fixed up-stream resistance to estimate P(CRIT) from the airflow at atmospheric pressure agrees with the measured values. These data suggest that measurements of quantitative airflow during standard polysomnography can be used to determine upper airway properties in large cohorts.

Pulmonary mechanics during mechanical ventilation

The use of mechanical ventilation has become widespread in the management of hypoxic respiratory failure. Investigations of pulmonary mechanics in this clinical scenario have demonstrated that there are significant differences in compliance, resistance and gas flow when compared with normal subjects. This paper will review the mechanisms by which pulmonary mechanics are assessed in mechanically ventilated patients and will review how the data can be used for investigative research purposes as well as to inform rational ventilator management.