Inspiratory Flow Research Articles

Modeling ventilation of patients with interstitial lung disease at rest and exercise: a bench study.

The ventilatory physiopathology of patients with interstitial lung disease (ILD) remains poorly understood. We aimed to personalize a mechanical simulator to model healthy and ILD profiles ventilation, and to evaluate the effect of spontaneous breathing on respiratory mechanics at rest and during exercise. In a 2-compartment lung simulator (ASL 5000®), we modeled 1 healthy and 3 ILD profiles, at rest and during exercise, based on physiological data from literature and patients. Measurements were: tidal volume, end-expiratory lung volume, driving pressure, transpulmonary driving pressure, dynamic alveolar strain, mechanical power, and time lag of inspiratory flow between compartments 1 and 2. Healthy and ILD models were validated: maximum differences between real and simulated tidal volume were 5% (96ml) and 6% (54ml) at rest and during exercise respectively, considered clinically negligible. When we simulated lung inhomogeneity (compliance in compartment 1 > compartment 2), tidal volume, end-expiratory lung volume, driving pressure and mechanical power increased in compartment 1 and decreased in compartment 2. Driving transpulmonary pressure and dynamic alveolar strain increased in compartment 2 and decreased in compartment 1. Time lag of inspiratory flow between compartments 1 and 2 was positively correlated with a difference of compliance between compartments (r = 0.98, CI95% (0.9106; 0.9962), p < 0.0001). In this bench study, we personalized a mechanical simulator thatmodels the lung inhomogeneity and spontaneous breathing of healthy subjects and ILD patients at rest and during exercise. Our results suggest that lung inhomogeneity could increase lung vulnerability to volo-atelec-trauma mechanisms in ILD. Further physiological studies are needed to evaluate the impact of this vulnerability on acute or chronic ILD worsening.

Study of Physiological Adaptations in Vertical Kilometer Runners: Focus on Cardiorespiratory and Local Muscle Demands

Background: Research into key performance factors in trail running, particularly in vertical kilometer (VK) races, is crucial for effective training and periodization. However, recent studies on metabolic and cardiorespiratory responses during VK races, especially using field tests, are limited. Objectives: Therefore, the aim of this study is to evaluate the metabolic and cardiorespiratory responses during a VK field test, identifying differences based on sex and performance level, as well as key performance factors and their deterioration due to fatigue. Fifteen trained trail runners (ten males and five females, 19 to 38 years old) perform a VK race. Methods: The global physiological response is evaluated using the portable gas analyzer Cosmed K5 and the local response using near-infrared spectroscopy technology. Results: In gender comparisons, the ANCOVA test shows significant differences (p &lt; 0.05) in the ventilation, tidal volume, expiratory time-to-inspiratory time ratio, inspiratory flow rate, end-tidal CO2 partial pressure, heart rate, oxygen pulse, and total hemoglobin. Additionally, the performance comparison reveals significant differences in the variables’ velocity, oxygen consumption, carbon dioxide production, ventilation, dead space-to-tidal volume ratio, total time of the breathing cycle, expiratory time-to-inspiratory time ratio, inspiratory duty cycle, expiratory fractions of CO2, quadriceps saturation index, and VE/VCO2 ratio. Finally, the correlation analysis shows oxygen consumption (r = −0.80 mean; r = −0.72 peak), carbon dioxide production (r = −0.91 mean; r = −0.75 peak), expiratory time-to-inspiratory time ratio (r = 0.68 peak), ventilation (r = −0.58 mean), and quadriceps saturation index (r = 0.54 mean; r = −0.76 coefficient of variation) as the key performance factors in the VK race. Conclusions: Overall, the physiological analysis indicates the importance of local muscular adaptations and respiratory system capacity in this type of short-duration race.

The Effect of the Nasal Structure on the Olfactory Cleft Airflow: A Systematic Review.

Conductive olfactory losses mainly involve obstruction of the olfactory cleft (OC) and diminished OC airflow. This study investigated the association between abnormal nasal structure and OC airflow. A systematic search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis to identify studies on the effect of the nasal structure on the OC airflow and olfaction. A total of 11 studies were included. Nasal vestibule morphological variabilities directly impact the transport of molecules in odorant-laden air to the OC. A greater airflow vortex and a narrower vestibule region intensified the airflow vortex toward the olfactory region. Middle turbinectomy significantly increased the average flux to the OC. The location of the major airflow and airflow velocity maxima shifted towards the OC in patients with septal deviation. The airflow has been redirected into the upper part of the nasal airway in patients with inferior turbinate hypertrophy. For patients with unilateral cleft lip, unilateral nasal airflow on the cleft side has a lower rate and flow. The mean velocity in the posterior OC correlated well with olfaction compared to that in the anterior OC. The nasal polyps (NP) within the middle meatus increased the olfactory airflow but did not enhance the olfaction. NP in the olfactory region or anterior to the olfactory region significantly decreased the olfactory airflow and olfaction. Furthermore, obstruction of the OC did not change the nasal patency. When the OC shape presented with a stenotic slit or lumen structure among patients with conductive olfactory dysfunction without NP, the inspiratory velocity and flow rate within OC were significantly lower than in the healthy control group. Various nasal structural factors affect patterns of OC airflow and olfaction. Identifying the related airflow-limiting structures may promote the comprehensive evaluation of conductive olfactory losses in patients with olfactory dysfunction.

A novel method for positive airway pressure delivery: pulsating airflow.

The primary objective is to determine if pulsating airflow can achieve therapeutic pharyngeal pressure levels without requiring a tight-sealing mask. A pilot study included 12 nasal-breathing adults who are currently using positive airway pressure (PAP) for therapy. Patients were awake, and pharyngeal pressures were measured using a miniature pressure probe inserted through their nares. Pulsating airflow was applied via a nasal cannula with a customized valve. The inspiratory flow rate was increased until the pharyngeal pressure matched or exceeded the participant's prescribed PAP level. The expiratory flow rate was maintained at a constant low level of continuous airflow. The study demonstrated that pulsating airflow could generate pharyngeal pressures equivalent to or higher than those achieved with PAP therapy in all participants. The peak inspiratory pressures with pulsating airflow followed an oscillatory pattern matching the pulsation frequency. The mean peak pressure increased linearly with the pulsating flow rate. Compared to a high-flow nasal cannula, pulsating airflow produced significantly higher inspiratory pharyngeal pressures, reaching nearly 20 cmH2O. Pulsating airflow could be a viable method for delivering PAP therapy to patients with respiratory or sleep disorders without needing a tight-sealing mask. Further research is required to establish whether this method can improve patient compliance with PAP therapy, assess long-term safety and efficacy, and explore the impact of varying pulsation parameters on treatment outcomes.

Why NIV setting definitions may be tricky: trigger sensitivity

Noninvasive ventilation (NIV) is widely use in children. The spontaneous/timed (S/T) mode is the most common used mode for home NIV. Different devices are available, and the manufacturers are free to name the modes and define the settings, with no regulation. In particular, the definitions of the trigger sensitivities still differ between manufacturers and/or devices. The inspiratory trigger (TgI) sensitivity may be set according to a numerical or word-rating scale, while the expiratory trigger (TgE) sensitivity may be set as a percentage of the peak inspiratory flow, or using a numerical or word rating scale which correspond to specific predefined percentages of inspiratory flow. Moreover, the TgE sensitivity may be set according to the peak inspiratory flow or to the diminution of peak inspiratory flow, which may be very confusing. Patient-ventilator asynchrony (PVA) may be due to an inadequate comprehension of the settings by the user, which is challenging. We report here the cases of four children and adolescents with an incorrect setting of the TgI and/or TgE, leading to PVA. This pleads for a harmonization of the definitions of the settings, and in particular of the trigger sensitivities. In the meanwhile, NIV professionals should be aware of the different definitions to avoid setting errors leading to PVA.

Analyzing Phenotypes Post-Exposure in Allergic Rhinitis (APPEAR) in the Environmental Exposure Unit (EEU).

Previous studies have defined clinical phenotypes of allergic rhinitis (AR) after allergen exposure using the time course of the total nasal symptom score (TNSS). We aimed to validate previously proposed AR phenotypes across different allergens (birch, grass, ragweed, house dust mite) following exposure in the Environmental Exposure Unit (EEU). The Analyzing Phenotypes Post-Exposure in Allergic Rhinitis (APPEAR) database comprises 153 participants from EEU studies conducted between 2010-2021 by Kingston Allergy Research. TNSS, nasal congestion symptom scores, and percent change in peak nasal inspiratory flow from baseline (%ΔPB) were recorded for each participant. Participants were phenotyped using previously described criteria RESULTS: 65 participants (42.5%) were classified as Early-phase Responders (EPR), 58 (37.9%) as Protracted Early-phase Responders (pEPR), 13 (8.5%) as Dual Responders (DR), and 17 (11.1%) as Low Responders (LoR). Significant negative correlations exist between TNSS and %ΔPB (r = -0.99, p<0.0001), and nasal congestion symptom score and %ΔPB (r = -0.99, p<0.0001). At the beginning of the late-phase AR response (6 to 7 hours), pEPRs had significantly higher TNSS compared to EPRs, DRs, and LoRs (p<0.0001). By the end of the study (up to 12 hours), DRs and pEPRs had significantly higher TNSS compared to EPRs and LoRs (p<0.0001). Visible and statistical validity between the phenotypes were also confirmed by assessing participants' mean TNSS and mean %ΔPB over time when grouping by phenotype. This study confirms distinct phenotypes exist in the late-phase AR response amongst different allergens and in a greater sample size than described previously, which could provide clinical benefit.

Flow Profiles Identify Sources of Poor Metered Dose Inhaler Technique: An observational study in long-term pMDI users

BackgroundInhaled medications are commonly used as therapy for obstructive lung disease (OLD) yet poor technique from pressurized metered dose inhalers (pMDI) can severely limit drug delivery and therapeutic efficacy. A novel flow sensor has been developed to characterize inhalation flow profiles from pMDIs. Research QuestionAmong OLD subjects, flow profiles during pMDI inhalation maneuvers would expose poor patterns of pMDI use, which can be used to remediate pMDI technique. Study Design and MethodsA novel flow sensor was coupled to a placebo pMDI inhaler to characterize inhalation technique in 70 OLD participants from a pulmonary clinic. pMDI inhalation flow profiles generated actuation timing, mean inspiratory airflow (MIF) and inspired volume before and after visualizing these features. McNemar’s was used to characterize the impact of training on pMDI inhalation metrics. The post-actuation inspired volume was normalized to inspiratory capacity (IC). ResultsAmong participants with 17.4 (SD = 17.9) years of pMDI use, flow profiles uncovered mistimed actuations in 47.1% and poor inspiratory flow rates in 30.0% of subjects. After visualizing flow profiles, participants improved actuation timing (c2(1) =12.042, p < .001), mean inhaled volume (87.9 to 105.6% of IC, p<0.001) and the combined inhalation metrics (c2(1) =8.45, p = 0.003). InterpretationFlow profiles helped uncover and remediate specific defects in pMDI technique in the majority of chronic OLD users. Flow profiles from inhaled medications can be used to enhance drug delivery to the lung.

Accuracy of Real-Time Data Provided by Mechanical Insufflation-Exsufflation Devices.

Mechanical insufflation-exsufflation (MI-E) is crucial to assist patients with impaired cough, especially those with neuromuscular diseases. Despite recent advancements that enable real-time display of peak expiratory flow (PEF) and inspiratory volume, accurately monitoring these parameters with MI-E devices during treatment can still present challenges. A bench study that used a mechanical lung connected to 3 MI-E devices (EOVE-70; E-70 and Comfort Cough II) was conducted to evaluate PEF and inspiratory volume monitoring accuracy. Two clinical conditions were tested, low and normal compliance, with 6 different MI-E settings tested: +20/-20, +30/-30, +40/-40, +40/-50, +40/-60, and +40/-70 cm H2O. PEF (L/min) and inspiratory volume (mL) displayed on the screen were recorded cycle by cycle, while a pneumotachograph connected to the mechanical lung was used to measure the actual PEF and inspiratory volume for data comparison. Flow bias was assessed by calculating the difference (PEF - peak inspiratory flow) and ratio (PEF to peak inspiratory flow) between flows. All devices systematically underestimated PEF, with device A showing the smallest estimation error (-7.4 [-10.1; -6] %). Devices B and C exhibited larger errors (-26.5 [-29.2; -25.6] and (-29.9 [-30.7; -28.7] %, respectively). All the devices underestimated inspiratory volume, with device B showing the smallest estimation error (-15.1 [-21.2; -12.3] %). Device A exhibited a significantly larger error (-26.9 [-30.3; -24.8] %). The error from device C (-17.7 [-34.5; -13.8] %) was not statistically different from device B. Device type, high pressure settings (> +40/-40 cm H2O), and a lung model compliance of 60 mL/cm H2O were the main contributors to error in estimating PEF and inspiratory volume. Finally, we observed differences of PEF-to-peak inspiratory flow ratio and PEF minus peak inspiratory flow differences achieved. Our study highlighted consistent underestimation of PEF and inspiratory volume across MI-E devices. Improving device monitoring is essential for guiding MI-E therapy and ensuring patient safety.

Allergic rhinitis: a brief overview of the etiopathogenesis and rehabilitation of patients

The article presents a brief overview of modern literature sources concerning the prevalence, etiopathogenetic approaches in the diagnosis and treatment of allergic rhinitis. The relevance of the problem under consideration is due to the high prevalence of this pathology, the variety of etiopathogenetic mechanisms and the variability of classifications. One of the most popular classifications is seasonal. When studying pathogenetic mechanisms, the following patterns were revealed: the nasal mucosa is the main air conditioner of the respiratory tract and the first line of defense against infectious agents transmitted by airborne droplets. These roles require maintaining and restoring epithelial integrity and the ability to initiate immune responses. When conditions or factors are present that compromise the integrity of the mucosa, the epithelium releases alarmins and other molecular patterns associated with damage that trigger repair mechanisms but can also cause protective inflammation. In allergic rhinitis, the same mechanisms can activate the development of the disease. Many authors consider various diagnostic methods for allergic rhinitis. Such as a detailed and competent collection of complaints and anamnesis, including family history, physical examination, endoscopic examination of the nasal cavity, rhinomanometry, skin prick tests, radiological studies, including computed tomography of the paranasal sinuses, intradermal tests, study of total and specific immunoglobulins E in blood serum, basophil activation test, nasal provocation test, nasal cytology and biopsy histology, acoustic rhinometry, nasal inspiratory peak flow testing, and nitric oxide measurements are used. Attention is also paid to laboratory and instrumental methods for the differential diagnosis of rhinitis of pseudoallergic origin; the following methods are used: ultrasound diagnostics of the hepatobiliary system, biochemical blood test, and immunological studies. Treatment of patients with allergic rhinitis requires an integrated and interdisciplinary approach and, of course, requires differential and personalized methods taking into account etiopathogenetic mechanisms.

Inhaler device selection for people with asthma or chronic obstructive pulmonary disease.

There are many types of inhaler device, each with its own characteristics, benefits and limitations. Inhaler device selection should be individualised. Assessment of the patient's inspiratory flow, dexterity, coordination and preferences can help guide selection of a device that the patient can and will use effectively. For patients who require multiple inhaled drugs, prescribing combination inhalers and avoiding the use of more than one type of inhaler device can reduce errors in inhaler technique and improve adherence. Inhaler technique and adherence should be regularly reviewed. Environmental impact of inhalers can be reduced by optimising symptom control to minimise the need for short-acting beta2 agonists, and choosing inhalers with a low carbon footprint.

Monitoring and modulating respiratory drive in mechanically ventilated patients.

Respiratory drive is frequently deranged in the ICU, being associated with adverse clinical outcomes. Monitoring and modulating respiratory drive to prevent potentially injurious consequences merits attention. This review gives a general overview of the available monitoring tools and interventions to modulate drive. Airway occlusion pressure (P0.1) is an excellent measure of drive and is displayed on ventilators. Respiratory drive can also be estimated based on the electrical activity of respiratory muscles and measures of respiratory effort; however, high respiratory drive might be present in the context of low effort with neuromuscular weakness. Modulating a deranged drive requires a multifaceted intervention, prioritizing treatment of the underlying cause and adjusting ventilator settings for comfort. Additional tools include changes in PEEP, peak inspiratory flow, fraction of inspired oxygen, and sweep gas flow (in patients receiving extracorporeal life-support). Sedatives and opioids have differential effects on drive according to drug category. Monitoring response to any intervention is warranted and modulating drive should not preclude readiness to wean assessment or delay ventilation liberation. Monitoring and modulating respiratory drive are feasible based on physiological principles presented in this review. However, evidence arising from clinical trials will help determine precise thresholds and optimal interventions.

Inhaler personalisation based on peak inspiratory flow (PIF) among dry powder inhaler users: a pilot randomised control trial (RCT) in COPD.

Dry powder inhalers (DPIs) are commonly used among patients with Chronic Obstructive Pulmonary Disease (COPD). These inhalers are breath-actuated, and require patients to generate sufficient peak inspiratory flow (PIF) to disaggregate the drug powder into respirable fine particles and deliver it to the lower airway tracts. Inhaler personalisation based on PIF among DPI users has not been studied in Malaysia, thus we conducted the present pilot study to determine the feasibility of conducting such research among COPD patients. This was an open-label pilot randomised control trial, conducted from June 2021-January 2022 at the respiratory clinic of Hospital Canselor Tuanku Muhriz, Universiti Kebangsaan Malaysia. Measurement of PIF was performed with In-Check DIAL G16 among adult COPD patients treated with DPI and had suboptimal PIF. Eligible subjects were randomised using block randomisation into two groups, either the interventional group or the control group. Twenty-two COPD patients fulfilled the study criteria and were randomised to intervention (n = 11) and control (n = 11) groups. For the interventional group, there were statistically significant improvements between baseline and at 12 weeks for both FEV1 and CAT scores. The mean (% predicted) FEV1 were 54.6 ± 20.4% and 56.6 ± 19.8% (p = 0.026), pre-and post-intervention. The mean CAT score at baseline was 24.4 ± 5.8 and reduced to 19.6 ± 4.4 at 12 weeks (p = 0.012). For the control group, the mean (% predicted) FEV1 at baseline was 58.0 ± 21.9% and 56.5 ± 20.7% at 12 weeks, with no statistical significance difference (p = 0.143). However, there was a statistically significant difference in CAT scores at baseline and 12 weeks, with a mean of 26.5 ± 6.1 and 23.3 ± 5.6, respectively (p = 0.010). The findings from the present pilot RCT highlighted that inhaler personalisation based on PIF among COPD patients was feasible and practical.

A self-regulated expiratory flow device for mechanical ventilation: a bench study

IntroductionUnregulated expiratory flow may contribute to ventilator-induced lung injury. The amount of energy dissipated into the lungs with tidal mechanical ventilation may be used to quantify potentially injurious ventilation. Previously reported devices for variable expiratory flow regulation (FLEX) require, either computer-controlled feedback, or an initial expiratory flow trigger. In this bench study we present a novel passive expiratory flow regulation device.MethodsThe device was tested using a commercially available mechanical ventilator with a range of settings (tidal volume 420 ml and 630 ml, max. inspiratory flow rate 30 L/min and 50 L/min, respiratory rate 10 min−1, positive end-expiratory pressure 5 cmH2O), and a test lung with six different combinations of compliance and resistance settings. The effectiveness of the device was evaluated for reduction in peak expiratory flow, expiratory time, mean airway pressure, and the reduction of tidal dissipated energy (measured as the area within the airway pressure–volume loop).ResultsMaximal and minimal reduction in peak expiratory flow was from 97.18 ± 0.41 L/min to 25.82 ± 0.07 L/min (p < 0.001), and from 44.11 ± 0.42 L/min to 26.30 ± 0.06 L/min, respectively. Maximal prolongation in expiratory time was recorded from 1.53 ± 0.06 s to 3.64 ± 0.21 s (p < 0.001). As a result of the extended expiration, the maximal decrease in I:E ratio was from 1:1.15 ± 0.03 to 1:2.45 ± 0.01 (p < 0.001). The greatest increase in mean airway pressure was from 10.04 ± 0.03 cmH2O to 17.33 ± 0.03 cmH2O. Dissipated energy was significantly reduced with the device under all test conditions (p < 0.001). The greatest reduction in dissipated energy was from 1.74 ± 0.00 J to 0.84 ± 0.00 J per breath. The least reduction in dissipated energy was from 0.30 ± 0.00 J to 0.16 ± 0.00 J per breath. The greatest and least percentage reduction in dissipated energy was 68% and 33%, respectively.ConclusionsThe device bench tested in this study demonstrated a significant reduction in peak expiratory flow rate and dissipated energy, compared to ventilation with unregulated expiratory flow. Application of the device warrants further experimental and clinical evaluation.

Application of computational fluid dynamics to investigate pathophysiological mechanisms in exercise-induced laryngeal obstruction.

The underlying pathophysiological mechanisms of exercise-induced laryngeal obstruction (EILO) remain to be fully established. It is hypothesized that high inspiratory flow rates can exert a force on laryngeal airway walls that contribute to its inward collapse causing obstruction. Computational fluid dynamics (CFD) presents an opportunity to explore the distribution of forces in a patient-specific upper airway geometry. The current study combined exercise physiological data and CFD simulation to explore differences in airflow and force distribution between a patient with EILO and a healthy matched control. Participants underwent incremental exercise testing with continuous recording of respiratory airflow and laryngoscopic video, followed by an MRI scan. The respiratory and MRI data were used to generate a subject-specific CFD model of upper respiratory airflow. In patient with EILO, the posterior supraglottis experiences an inwardly directed net force, whose magnitude increases nonlinearly with larger flow rates, with slight changes in the direction toward the center of the airway. The control demonstrated an outwardly directed force at all regions of the wall, with a magnitude that increases linearly with larger flow rates. A comparison is made between the CFD results and endoscopic visualization of supraglottic collapse, and a very good agreement is found. The current study presents the first hybrid physiological and computational approach to investigate the pathophysiological mechanisms of EILO, with preliminary findings showing great potential, but should be used in larger sample sizes to confirm findings.NEW & NOTEWORTHY The current study is the first to use a hybrid combined computational fluid dynamics (CFD) and exercise physiology approach to investigate pathophysiology in exercise-induced laryngeal obstruction (EILO). The hybrid methodology is a promising approach to explore the pathophysiological mechanisms underlying the condition. Notable differences occur in the distribution of airflow and wall forces between the EILO and control participants, which align with symptoms and visual observations.

Peak Inspiratory Flow and Inhaler Prescription Strategies in a Specialized COPD Clinical Program: A Real-World Observational Study

BackgroundCOPD inhaler regimens should be appropriate for the patient’s peak inspiratory flow (PIF) and should ideally consist of single or similar device(s). Research QuestionsIn a subspecialized COPD clinic: 1What is the prevalence of patients with suboptimal PIF and with inappropriate device(s) for measured PIF? 2Are there patient-related risk factors associated with suboptimal PIF? 3What is the prevalence of patients with non-single inhaler therapy (SIT)/non-similar devices? 4Does point-of-care PIF affect clinical decision-making? Study Design and MethodsIn this single-center real-world observational study, PIF was measured systematically at every outpatient visit in a subspecialized COPD clinic and point-of-care results were provided to the clinician. Co-primary outcomes were the prevalence of outpatients with suboptimal PIF and with inappropriate devices for measured PIF. Secondary outcomes were patient-related risk factors associated with suboptimal PIF, the prevalence of non-SIT/non-similar devices, the prevalence of regimens consisting of either inappropriate device(s) for measured PIF and/or non-SIT/non-similar devices, and the effect of point-of-care PIF on clinical decision-making. ResultsSuboptimal PIF was identified in 45 of 161 participants (28%) and inappropriate device(s) for measured PIF were identified in 18 (11.2%) participants. Significant associations were observed between suboptimal PIF and age (1.09 [1.04,1.15]), female sex (10.30 [4.45,27.10]), height (0.92 [0.88,0.96]), BMI (0.90 [0.84,0.96]) and FEV1 (0.09 [0.03,0.26]). Following adjustment for age and sex, the association between suboptimal PIF and BMI, but not height, remained significant. Non-SIT and/or non-similar devices were identified in 50 (31.1%) participants. Regimens consisting of either inappropriate device(s) for measured PIF and/or non-SIT/non-similar devices were observed in fifty-nine (36.6%) participants. Inhaler prescription changes were observed in this latter group (3.39 [1.76,6.64]), as well as in patients with suboptimal PIF already on SIT/similar regimens (2.93 [1.07,7.92]). InterpretationSuboptimal PIF and inappropriate devices for measured PIF are highly prevalent in outpatients from a subspecialized COPD clinic. Female sex, reduced FEV1 and low BMI are important, readily identifiable risk factors for suboptimal PIF and point-of-care PIF can inform clinical decision-making.

Analyzing the inspiratory airflow unsteadiness in the respiratory tract using dynamic mode decomposition method

To enhance the understanding of airflow characteristics in the human respiratory tract, the inspiratory airflow field was simulated under both tidal and quasi-steady inspiratory flow rates at the mouth inlet using the large eddy simulation method. Special attention was paid on analyzing the inspiratory airflow unsteadiness using the dynamics mode decomposition (DMD) method based on the vorticity field and comparing it with the proper orthogonal decomposition (POD) method. The following novel findings were obtained. (1) Power spectral density indicates that the inspiratory airflow is highly turbulent in the pharynx–larynx region. The vorticity field in the upper airway is more affected by inspiratory patterns compared to turbulence fluctuations. (2) The DMD results indicate that the shear flow in the pharynx–larynx region is mainly caused by flow under low-frequency modes, while the disturbances of the jet flow are caused by flow under multiple frequency modes. Steady-state inspiratory pattern demonstrates the decay characteristics different from the tidal inspiratory pattern. (3) Compared to the POD method, which may contain multiple frequency components, the DMD decomposition yields modes with a single frequency, enabling a more accurate capture of the frequency and decay characteristics of the respiratory flow under each mode. In conclusion, this study demonstrates that the DMD method is more suitable for studying the respiratory airflow unsteadiness and further confirms the necessity of adopting clinically measured inspiratory data to investigate airflow unsteadiness.

Oscillatory airflow through the hypopharyngeal and supraglottic airway

Exercise-induced laryngeal obstruction (EILO) is a known cause of exertional dyspnoea, characterised by paradoxical inward collapse of laryngeal tissues. The pathophysiological mechanisms of EILO remain to be fully established, but insufficient mechanical resistance of laryngeal tissues to air-induced loads is hypothesised. It is understood that airflow and anatomic configurations of the airway play a key role in the wall pressure distribution of the larynx. While breathing is a cyclic process with directional changes of airflow, the literature is confined to steady, unidirectional airflow. It is necessary to assess the role of oscillatory airflow on the loads on the laryngeal airway. This study investigates the effect of oscillatory airflow on the laryngeal flow fields and air-induced loads. A computational fluid dynamics model of the upper respiratory tract (URT) is developed using the Reynolds-averaged Navier-Stokes equations. Five oscillatory airflow cases through a single geometry are considered, utilising sinusoidal breathing cycles with different breathing frequencies (24, 32 and 40 breaths per minute) and peak inspiratory flow rates (96, 168 and 240 L/min). Results include the airflow velocity distribution in the URT, and the air-induced pressure and forces. It is demonstrated that inspiratory velocity distribution varies with breathing frequency and intensity. The force acting on the URT walls are in-phase with the airflow rate and therefore exhibit quasi-steady behaviour. These findings are also reflected in the force vectors acting on the aryepiglottic folds and indicate that air-induced closure of the supraglottis in EILO is influenced by the breathing intensity rather than the breathing frequency.

Evaluation of a new hyperbaric oxygen ventilator during pressure-controlled ventilation.

The stability of a new hyperbaric ventilator (Shangrila590, Beijing Aeonmed Company, Beijing, China) at different clinically relevant pressures in a hyperbaric chamber during pressure-controlled ventilation (PCV) was investigated. The ventilator was connected to a test lung in the multiplace hyperbaric chamber. The inspiratory pressure (PI) of the ventilator was set to 1.0, 1.5, 2.0, 2.5 and 3.0 kPa (approximately 10, 15, 20, 25 and 30 cmH₂O). The compliance and resistance of the test lung were set to 200 mL·kPa⁻¹ and 2 kPa·L⁻¹·s⁻¹, respectively. Experiments were conducted at 101, 203 and 284 kPa ambient pressure (1.0, 2.0 and 2.8 atmospheres absolute respectively). At each of the 5 PI values, the tidal volume (VT), peak inspiratory pressure (Ppeak) and peak inspiratory flow (Fpeak) displayed by the ventilator and the test lung were recorded for 20 cycles. Test lung data were considered the actual ventilation values. The ventilation data were compared among the three groups to evaluate the stability of the ventilator. At every PI, the Ppeak detected by the ventilator decreased slightly with increasing ambient pressure. The Fpeak values measured by the test lung decreased substantially as the ambient pressure increased. Nevertheless, the reduction in VT at 284 kPa and PI 30 cmH₂O (compared to performance at 101 kPa) was comparatively small (approximately 60 ml). In PCV mode this ventilator provided relatively stable VT across clinically relevant PI values to ambient pressures as high as 284 kPa. However, because Fpeak decreases at higher ambient pressure, some user adjustment might be necessary for precise VT maintenance during clinical use at higher PIs and ambient pressures.

Effects of breathing exercises on young swimmers’ respiratory system parameters and performance

Breathing exercises are widely used to enhance respiratory function and athletic performance. This study aimed to assess the efficacy of a modified exercise regimen on respiratory parameters and its effect on the performance of young swimmers in competition. Thirty-one swimmers aged 16–17 from various clubs in Latvia were selected, comprising an experimental group (n = 15, height: 174.36 ± 7.85 cm, weight: 65.80 ± 9.35 kg, body mass index: 21.60 ± 1.54) and a control group (n = 16, height: 180.78 ± 7.05 cm, weight: 69.90 ± 6.49 kg, body mass index: 21.40 ± 1.56). With an average of eight years of experience, participants trained for approximately 43–45 weeks annually (pool and gym sessions), with an average training duration of 20 ± 2 hours per week. Measurements were conducted on days one and 30, involving spirometry and swimming performance assessment based on the best results in the freestyle 100-meter distance. The experiment consisted of a modified breathing exercise performed thrice weekly for four weeks. Significant improvements were observed in the experimental group compared to the control group in forced vital capacity (p = 0.02), peak inspiratory flow (p = 0.001), and performance (p = 0.001), with p-values &lt; 0.05. However, no significant changes were noted in peak expiratory flow (p = 0.46 &gt; 0.05). The findings indicate that modified breathing exercises effectively enhance respiratory parameters and performance in competitive swimmers.

Post-insufflation diaphragm contractions in patients receiving various modes of mechanical ventilation

BackgroundDuring mechanical ventilation, post-insufflation diaphragm contractions (PIDCs) are non-physiologic and could be injurious. PIDCs could be frequent during reverse-triggering, where diaphragm contractions follow the ventilator rhythm. Whether PIDCs happens with different modes of assisted ventilation is unknown. In mechanically ventilated patients with hypoxemic respiratory failure, we aimed to examine whether PIDCs are associated with ventilator settings, patients’ characteristics or both.MethodsOne-hour recordings of diaphragm electromyography (EAdi), airway pressure and flow were collected once per day for up to five days from intubation until full recovery of diaphragm activity or death. Each breath was classified as mandatory (without-reverse-triggering), reverse-triggering, or patient triggered. Reverse triggering was further subclassified according to EAdi timing relative to ventilator cycle or reverse triggering leading to breath-stacking. EAdi timing (onset, offset), peak and neural inspiratory time (Tineuro) were measured breath-by-breath and compared to the ventilator expiratory time. A multivariable logistic regression model was used to investigate factors independently associated with PIDCs, including EAdi timing, amplitude, Tineuro, ventilator settings and APACHE II.ResultsForty-seven patients (median[25%-75%IQR] age: 63[52–77] years, BMI: 24.9[22.9–33.7] kg/m2, 49% male, APACHE II: 21[19–28]) contributed 2 ± 1 recordings each, totaling 183,962 breaths. PIDCs occurred in 74% of reverse-triggering, 27% of pressure support breaths, 21% of assist-control breaths, 5% of Neurally Adjusted Ventilatory Assist (NAVA) breaths. PIDCs were associated with higher EAdi peak (odds ratio [OR][95%CI] 1.01[1.01;1.01], longer Tineuro (OR 37.59[34.50;40.98]), shorter ventilator inspiratory time (OR 0.27[0.24;0.30]), high peak inspiratory flow (OR 0.22[0.20;0.26]), and small tidal volumes (OR 0.31[0.25;0.37]) (all P ≤ 0.008). NAVA was associated with absence of PIDCs (OR 0.03[0.02;0.03]; P < 0.001). Reverse triggering was characterized by lower EAdi peak than breaths triggered under pressure support and associated with small tidal volume and shorter set inspiratory time than breaths triggered under assist-control (all P < 0.05). Reverse triggering leading to breath stacking was characterized by higher peak EAdi and longer Tineuro and associated with small tidal volumes compared to all other reverse-triggering phenotypes (all P < 0.05).ConclusionsIn critically ill mechanically ventilated patients, PIDCs and reverse triggering phenotypes were associated with potentially modifiable factors, including ventilator settings. Proportional modes like NAVA represent a solution abolishing PIDCs.