A portable fan-based device for evaluating lung function in horses by the forced oscillation technique.

Objective. The assessment of lung mechanics in horses is nowadays based on invasive methods that may require sedation. The forced oscillation technique (FOT) allows the non-invasive assessment of respiratory mechanics during spontaneous breathing, but current devices are complex, cumbersome, expensive, and difficult to be applied in horses.Approach. We developed a portable FOT device based on a novel approach in which the pressure waveforms are generated by a servo-controlled ducted fan. This new approach allows the design of devices that are more sturdy, compact, and portable compared to already existing approaches. The prototype includes 1) a small microcontroller-based electronic board for controlling the fan and measuring flow and pressure and 2) an optimized data processing algorithm.Main results. This device provides a maximum error of 0.06 cmH2O·s/L and 0.15 cmH2O·s/L in measuring respiratory resistance and reactance duringin-vitrovalidation. A pilot study was also performed on three healthy horses and three horses with severe equine asthma (SEA) and it demonstrated good tolerability and feasibility of the new device. Total respiratory system resistance (Rrs) and reactance (Xrs) significantly differed (p< 0.05) between groups. At 5 Hz,Rrswas 0.66 ± 0.02 cmH2O·s/L and 0.94 ± 0.07 cmH2O·s/L in healthy and in SEA, respectively.Xrs0.38 ± 0.02 cmH2O·s/L and -0.27 ± 0.05 cmH2O·s/L.Significance. This novel approach for applying FOT allowed the development of a small, affordable, and portable device for the non-invasive evaluation of respiratory mechanics in spontaneously breathing horses, providing a useful new tool for improving veterinary respiratory medicine. Moreover, our results provide supporting evidence of the value of this novel approach for developing portable FOT devices also for applications in humans.

Artificial intelligence for quality control of oscillometry measures.

BACKGROUND: The forced oscillation technique (FOT) allows non-invasive lung function testing during quiet breathing even without expert guidance. However, it still relies on an operator for excluding breaths with artefacts such as swallowing, glottis closure and coughing. This manual selection is operator-dependent and time-consuming. We evaluated supervised machine learning methods to exclude breaths with artefacts from data analysis automatically. METHODS: We collected 932 FOT measurements (Resmon Pro Full, Restech) from 155 patients (6-87 years) following the European Respiratory Society (ERS) technical standards. Patients were randomly assigned to either a training (70%) or test set. For each breath, we computed 71 features (including anthropometric, pressure stimulus, breathing pattern, and oscillometry data). Univariate filter, multivariate filter and wrapper methods for feature selection combined with several classification models were considered. RESULTS: Trained operators identified 4333 breaths with- and 10244 without artefacts. Features selection performed by a wrapper method combined with an AdaBoost tree model provided the best performance metrics on the test set: Balanced Accuracy = 85%; Sensitivity = 79%; Specificity = 91%; AUC-ROC = 0.93. Differences in FOT parameters computed after manual or automatic breath selection was less than ∼0.25 cmH2O*s/L for 95% of cases. CONCLUSION: Supervised machine-learning techniques allow reliable artefact detection in FOT diagnostic tests. Automating this process is fundamental for enabling FOT for home monitoring, telemedicine, and point-of-care diagnostic applications and opens new scenarios for respiratory and community medicine.

Effect of stimulating waveform and of data processing on respiratory impedance measurement.

OBJECTIVE: Several commercial and custom-made forced oscillation technique (FOT) devices are used to assess respiratory system impedance. The impulse oscillometry system (IOS) is a widespread device, which yields similar but not identical results to those provided by other FOT systems. Differences may be related to the forcing waveform, the device hardware, or the data processing algorithms. We evaluated the agreement between resistance (R rs) and reactance (X rs) measurements while alternating between different forcing waveforms and data processing algorithms. APPROACH: We performed pre- and post-bronchodilator measurements in 20 patients with respiratory complaints. We generated pulse waveforms using an IOS, and sinusoidal oscillations by replacing the IOS loudspeaker with customized loudspeaker providing a 5 Hz sinusoidal pressure signal. Pressure and flow were measured using the IOS sensors and breathing circuit. We developed a data processing algorithm compatible to both forcing signals. We also applied commercial IOS software during pulse waveform and a least mean square (lms) algorithm during sinusoidal waveform. MAIN RESULTS: The median (5th, 95th percentile) differences between R rs and X rs were (1) -0.35 (-2.49, 1.23) and 0.16 (-1.63, 3.07 cmH2O*s l-1, when the same algorithm was used during pulse vs sinusoidal stimulus; (2) 0.34 (-2.33, 5.98) and 0.57 (-2.64, 6.09) cmH2O*s l-1, when our algorithm and the IOS software were used during pulse waveform; and (3) 0.33 (-1.20, 6.05) and 0.25 (-4.94, 4.28) cmH2O*s l-1 when the IOS software was used during pulse and the lms algorithm during sinusoidal waveforms. SIGNIFICANCE: Both forcing signal and data processing contribute to differences in impedance values measured by different FOT devices.

Telemonitoring in Chronic Obstructive Pulmonary Disease (CHROMED). A Randomized Clinical Trial.

RATIONALE: Early detection of chronic obstructive pulmonary disease (COPD) exacerbations using telemonitoring of physiological variables might reduce the frequency of hospitalization. OBJECTIVES: To evaluate the efficacy of home monitoring of lung mechanics by the forced oscillation technique and cardiac parameters in older patients with COPD and comorbidities. METHODS: This multicenter, randomized clinical trial recruited 312 patients with Global Initiative for Chronic Obstructive Lung Disease grades II to IV COPD (median age, 71 yr [interquartile range, 66-76 yr]; 49.6% grade II, 50.4% grades III-IV), with a history of exacerbation in the previous year and at least one nonpulmonary comorbidity. Patients were randomized to usual care (n = 158) or telemonitoring (n = 154) and followed for 9 months. All telemonitoring patients self-assessed lung mechanics daily, and in a subgroup with congestive heart failure (n = 37) cardiac parameters were also monitored. An algorithm identified deterioration, triggering a telephone contact to determine appropriate interventions. MEASUREMENTS AND MAIN RESULTS: Primary outcomes were time to first hospitalization (TTFH) and change in the EuroQoL EQ-5D utility index score. Secondary outcomes included: rate of antibiotic/corticosteroid prescription; hospitalization; the COPD Assessment Tool, Patient Health Questionnaire-9, and Minnesota Living with Heart Failure questionnaire scores; quality-adjusted life years; and healthcare costs. Telemonitoring did not affect TTFH, EQ-5D utility index score, antibiotic prescriptions, hospitalization rate, or questionnaire scores. In an exploratory analysis, telemedicine was associated with fewer repeat hospitalizations (-54%; P = 0.017). CONCLUSIONS: In older patients with COPD and comorbidities, remote monitoring of lung function by forced oscillation technique and cardiac parameters did not change TTFH and EQ-5D. Clinical trial registered with www.clinicaltrials.gov (NCT 01960907).

Optimizing positive end-expiratory pressure by oscillatory mechanics minimizes tidal recruitment and distension: an experimental study in a lavage model of lung injury.

INTRODUCTION: It is well established that during mechanical ventilation of patients with acute respiratory distress syndrome cyclic recruitment/derecruitment and overdistension are potentially injurious for lung tissues. We evaluated whether the forced oscillation technique (FOT) could be used to guide the ventilator settings in order to minimize cyclic lung recruitment/derecruitment and cyclic mechanical stress in an experimental model of acute lung injury. METHODS: We studied six pigs in which lung injury was induced by bronchoalveolar lavage. The animals were ventilated with a tidal volume of 6 ml/kg. Forced oscillations at 5 Hz were superimposed on the ventilation waveform. Pressure and flow were measured at the tip and at the inlet of the endotracheal tube respectively. Respiratory system reactance (Xrs) was computed from the pressure and flow signals and expressed in terms of oscillatory elastance (EX5). Positive end-expiratory pressure (PEEP) was increased from 0 to 24 cm H2O in steps of 4 cm H2O and subsequently decreased from 24 to 0 in steps of 2 cm H2O. At each PEEP step CT scans and EX5 were assessed at end-expiration and end-inspiration. RESULTS: During deflation the relationship between both end-expiratory and end-inspiratory EX5 and PEEP was a U-shaped curve with minimum values at PEEP = 13.4 ± 1.0 cm H2O (mean ± SD) and 13.0 ± 1.0 cm H2O respectively. EX5 was always higher at end-inspiration than at end-expiration, the difference between the average curves being minimal at 12 cm H2O. At this PEEP level, CT did not show any substantial sign of intra-tidal recruitment/derecruitment or expiratory lung collapse. CONCLUSIONS: Using FOT it was possible to measure EX5 both at end-expiration and at end-inspiration. The optimal PEEP strategy based on end-expiratory EX5 minimized intra-tidal recruitment/derecruitment as assessed by CT, and the concurrent attenuation of intra-tidal variations of EX5 suggests that it may also minimize tidal mechanical stress.

Airway distensibility with lung inflation after allogeneic haematopoietic stem-cell transplantation.

The ability to reverse induced-bronchoconstriction by deep-inhalation increases after allogeneic haematopoietic stem-cell transplantation (HSCT), despite a decreased total lung capacity (TLC). We hypothesized that this effect may be due to an increased airway distensibility with lung inflation, likely related to an increment in lung stiffness. We studied 28 subjects, 2 weeks before and 2 months after HSCT. Within-breath respiratory system conductance (G(rs)) at 5, 11 and 19 Hz was measured by forced oscillation technique (FOT) at functional residual capacity (FRC) and TLC. Changes in conductance at 5Hz (G(rs5)) were related to changes in lung volume (ΔG(rs5)/ΔV(L)) to estimate airway distensibility. G(rs) at FRC showed a slight but significant increase at all forcing frequencies by approximately 12-16%. TLC decreased after HSCT whereas the ΔG(rs5)/ΔV(L) ratio became higher after than before HSCT and was positively correlated (R2=0.87) with lung tissue density determined by quantitative CT scanning. We conclude that airway caliber and distensibility with lung inflation are increased after HSCT. This effect seems to be related to an increase in lung stiffness and must be taken into account when interpreting lung function changes after HSCT.

Positive end-expiratory pressure optimization with forced oscillation technique reduces ventilator induced lung injury: a controlled experimental study in pigs with saline lavage lung injury.

INTRODUCTION: Protocols using high levels of positive end-expiratory pressure (PEEP) in combination with low tidal volumes have been shown to reduce mortality in patients with severe acute respiratory distress syndrome (ARDS). However, the optimal method for setting PEEP is yet to be defined. It has been shown that respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT) at 5 Hz, may be used to identify the minimal PEEP level required to maintain lung recruitment. The aim of the present study was to evaluate if using Xrs for setting PEEP would improve lung mechanics and reduce lung injury compared to an oxygenation-based approach. METHODS: 17 pigs, in which acute lung injury (ALI) was induced by saline lavage, were studied. Animals were randomized into two groups: in the first PEEP was titrated according to Xrs (FOT group), in the control group PEEP was set according to the ARDSNet protocol (ARDSNet group). The duration of the trial was 12 hours. In both groups recruitment maneuvers (RM) were performed every 2 hours, increasing PEEP to 20 cmH2O. In the FOT group PEEP was titrated by monitoring Xrs while PEEP was reduced from 20 cmH2O in steps of 2 cmH2O. PEEP was considered optimal at the step before which Xrs started to decrease. Ventilatory parameters, lung mechanics, blood gases and hemodynamic parameters were recorded hourly. Lung injury was evaluated by histopathological analysis. RESULTS: The PEEP levels set in the FOT group were significantly higher compared to those set in the ARDSNet group during the whole trial. These higher values of PEEP resulted in improved lung mechanics, reduced driving pressure, improved oxygenation, with a trend for higher PaCO2 and lower systemic and pulmonary pressure. After 12 hours of ventilation, histopathological analysis showed a significantly lower score of lung injury in the FOT group compared to the ARDSNet group. CONCLUSIONS: In a lavage model of lung injury a PEEP optimization strategy based on maximizing Xrs attenuated the signs of ventilator induced lung injury. The respiratory system reactance measured by FOT could thus be an important component in a strategy for delivering protective ventilation to patients with ARDS/acute lung injury.

Optimisation of positive end-expiratory pressure by forced oscillation technique in a lavage model of acute lung injury.

PURPOSE: We evaluated whether oscillatory compliance (C(X5)) measured by forced oscillation technique (FOT) at 5 Hz may be useful for positive end-expiratory pressure (PEEP) optimisation. METHODS: We studied seven pigs in which lung injury was induced by broncho-alveolar lavage. The animals were ventilated in volume control mode with a tidal volume of 6 ml/kg. Forced oscillations were superimposed on the ventilation waveform for the assessment of respiratory mechanics. PEEP was increased from 0 to 24 cmH(2)O in steps of 4 cmH(2)O and subsequently decreased from 24 to 0 in steps of 2 cmH(2)O. At each 8-min step, a CT scan was acquired during an end-expiratory hold, and blood gas analysis was performed. C(X5) was monitored continuously, and data relative to the expiratory hold were selected and averaged for comparison with CT and oxygenation. RESULTS: Open lung PEEP (PEEP(ol)) was defined as the level of PEEP corresponding to the maximum value of C(X5) on the decremental limb of the PEEP trial. PEEP(ol) was on average 13.4 (± 1.0) cmH(2)O. For higher levels of PEEP, there were no significant changes in the amount of non-aerated tissue (V(tissNA)%). In contrast, when PEEP was reduced below PEEP(ol), V(tissNA)% dramatically increased. PEEP(ol) was able to prevent a 5% drop in V(tissNA)% with 100% sensitivity and 92% specificity. At PEEP(ol) V(tissNA)% was significantly lower than at the corresponding PEEP level on the incremental limb. CONCLUSIONS: The assessment of C(X5) allowed the definition of PEEP(ol) to be in agreement with CT data. Thus, FOT measurements of C(X5) may provide a non-invasive bedside tool for PEEP titration.

Lung recruitment assessed by total respiratory system input reactance.

PURPOSE: ALI and ARDS are associated with lung volume derecruitment, usually counteracted by PEEP and recruitment maneuvers (RM), which should be accurately tailored to the patient's needs. The aim of this study was to investigate the possibility of monitoring the amount of derecruited lung by the forced oscillation technique (FOT). METHODS: We studied six piglets (26 +/- 2.5 kg) ventilated by a mechanical ventilator connected to a FOT device that produced sinusoidal pressure forcing at 5 Hz. The percentage of non-aerated lung tissue (V (tiss)NA%) was measured by whole-body CT scans at end-expiration with zero end-expiratory pressure. Respiratory system oscillatory input reactance (X (rs)) was measured simultaneously to CT and used to derive oscillatory compliance (C (X5)), which we used as an index of recruited lung. Measurements were performed at baseline and after several interventions in the following sequence: mono-lateral reabsorption atelectasis, RM, bi-lateral derecruitment induced by broncho-alveolar lavage and a second RM. RESULTS: By pooling data from all experimental conditions and all pigs, C (X5) was linearly correlated to V (tiss)NA% (r (2) = 0.89) regardless of the procedure used to de-recruit the lung (reabsorption atelectasis or pulmonary lavage). Separate correlation analysis on single pigs showed similar regression equations, with an even higher coefficient of determination (r (2) = 0.91 +/- 0.07). CONCLUSION: These results suggest that FOT and the measurement of C (X5) could be a useful tool for the non-invasive measurement of lung volume recruitment/derecruitment.

Airway hyperresponsiveness with chest strapping: A matter of heterogeneity or reduced lung volume?

Chest wall strapping has been recently shown to be associated with an increase in airway responsiveness to methacholine. To investigate whether this is the result of the decreased lung volume or an increased heterogeneity due to chest wall distortion, ten healthy volunteers underwent a methacholine challenge at control conditions and after selective strapping of the rib cage, the abdomen or the whole chest wall resulting in similar decrements of functional residual capacity and total lung capacity but causing different distribution of the bronchoconstrictor. Methacholine during strapping reduced forced expiratory flow, dynamic compliance, and reactance at 5Hz and increased pulmonary resistance and respiratory resistance at 5Hz that were significantly greater than at control and associated with a blunted bronchodilator effect of the deep breath. However, no significant differences were observed between selective and total chest wall strapping, suggesting that the major mechanism for increasing airway responsiveness with chest wall strapping is the breathing at low lung volume rather than regional heterogeneities.