Development of clinical tools to estimate the breathing effort during high-flow oxygen therapy: A multicenter cohort study.

INTRODUCTION AND OBJECTIVES: Quantifying breathing effort in non-intubated patients is important but difficult. We aimed to develop two models to estimate it in patients treated with high-flow oxygen therapy. PATIENTS AND METHODS: We analyzed the data of 260 patients from previous studies who received high-flow oxygen therapy. Their breathing effort was measured as the maximal deflection of esophageal pressure (ΔPes). We developed a multivariable linear regression model to estimate ΔPes (in cmH2O) and a multivariable logistic regression model to predict the risk of ΔPes being >10 cmH2O. Candidate predictors included age, sex, diagnosis of the coronavirus disease 2019 (COVID-19), respiratory rate, heart rate, mean arterial pressure, the results of arterial blood gas analysis, including base excess concentration (BEa) and the ratio of arterial tension to the inspiratory fraction of oxygen (PaO2:FiO2), and the product term between COVID-19 and PaO2:FiO2. RESULTS: We found that ΔPes can be estimated from the presence or absence of COVID-19, BEa, respiratory rate, PaO2:FiO2, and the product term between COVID-19 and PaO2:FiO2. The adjusted R2 was 0.39. The risk of ΔPes being >10 cmH2O can be predicted from BEa, respiratory rate, and PaO2:FiO2. The area under the receiver operating characteristic curve was 0.79 (0.73-0.85). We called these two models BREF, where BREF stands for BReathing EFfort and the three common predictors: BEa (B), respiratory rate (RE), and PaO2:FiO2 (F). CONCLUSIONS: We developed two models to estimate the breathing effort of patients on high-flow oxygen therapy. Our initial findings are promising and suggest that these models merit further evaluation.

A novel method to quantify breathing effort from respiratory mechanics and esophageal pressure.

Breathing effort is important to quantify to understand mechanisms underlying central and obstructive sleep apnea, respiratory-related arousals, and the timing and effectiveness of invasive or noninvasive mechanically assisted ventilation. Current quantitative methods to evaluate breathing effort rely on inspiratory esophageal or epiglottic pressure swings or changes in diaphragm electromyographic (EMG) activity, where units are problematic to interpret and compare between individuals and to measured ventilation. This paper derives a novel method to quantify breathing effort in units directly comparable with measured ventilation by applying respiratory mechanics first principles to convert continuous transpulmonary pressure measurements into "attempted" airflow expected to have arisen without upper airway obstruction. The method was evaluated using data from 11 subjects undergoing overnight polysomnography, including six patients with obesity with severe obstructive sleep apnea (OSA), including one who also had frequent central events, and five healthy-weight controls. Classic respiratory mechanics showed excellent fits of airflow and volume to transpulmonary pressures during wake periods of stable unobstructed breathing (means ± SD, r2 = 0.94 ± 0.03), with significantly higher respiratory system resistance in patients compared with healthy controls (11.2 ± 3.3 vs. 7.1 ± 1.9 cmH2O·L-1·s, P = 0.032). Subsequent estimates of attempted airflow from transpulmonary pressure changes clearly highlighted periods of acute and prolonged upper airway obstruction, including within the first few breaths following sleep onset in patients with OSA. This novel technique provides unique quantitative insights into the complex and dynamically changing interrelationships between breathing effort and achieved airflow during periods of obstructed breathing in sleep.NEW & NOTEWORTHY Ineffective breathing efforts with snoring and obstructive sleep apnea (OSA) are challenging to quantify. Measurements of esophageal or epiglottic pressure swings and diaphragm electromyography are useful, but units are problematic to interpret and compare between individuals and to measured ventilation. This paper derives a novel method that uses esophageal pressure and respiratory mechanics first principles to quantify breathing effort as "attempted" flow and volume in units directly comparable with measured airflow, volume, and ventilation.

Assessing breathing effort by barometric whole-body plethysmography and its relationship with prognosis in client-owned cats with respiratory distress.

BACKGROUND: Cats in respiratory distress have limited tolerance for manipulation, hindering clinical monitoring. Minute volume (MV) can be utilized to rate dyspnea in humans, but its relationship with respiratory distress in cats remains poorly investigated. HYPOTHESIS: Cats with respiratory distress will show higher MV per kg body weight (MV/BW) than normal cats, and the MV/BW increase will correlate with survival. ANIMALS: Fifty-two cats with respiratory distress from lung parenchymal disease, pleural space disease, lower airway obstruction (LAO), or upper airway obstruction were recruited since 2014. METHODS: This is a prospective observational study. Study cats were placed in a transparent chamber, allowing clinicians to easily observe their breathing status and record ventilation using barometric whole-body plethysmography (BWBP). Ventilatory variables of the 52 cats were compared with those of 14 historic control cats. Follow-up data, including disease category, clinical outcomes, and survival, were prospectively collected. RESULTS: Cats in respiratory distress demonstrated significantly higher MV/BW (397 mL/kg; range, 158-1240) than normal cats (269 mL/kg; range, 168-389; P < .001). Among the etiologies, cats with LAO, parenchymal, and pleural space disease exhibited higher-than-normal MV/BW trends. A cutoff value of 373 mL/kg (1.4-fold increase) indicated abnormally increased breathing efforts (sensitivity, 67%; specificity, 93%). MV/BW was independently associated with increased cardiorespiratory mortality in cats with respiratory distress (adjusted hazard ratio 1.17, 95% confidence interval [CI] 1.02-1.35; P = .03). CONCLUSIONS AND CLINICAL IMPORTANCE: Breathing efforts in cats can be noninvasively quantified using BWBP. Measurement of MV/BW could serve as a prognostic index for monitoring cats experiencing respiratory distress.

Individual response in patient's effort and driving pressure to variations in assistance during pressure support ventilation.

BACKGROUND: During Pressure Support Ventilation (PSV) an inspiratory hold allows to measure plateau pressure (Pplat), driving pressure (∆P), respiratory system compliance (Crs) and pressure-muscle-index (PMI), an index of inspiratory effort. This study aims [1] to assess systematically how patient's effort (estimated with PMI), ∆P and tidal volume (Vt) change in response to variations in PSV and [2] to confirm the robustness of Crs measurement during PSV. METHODS: 18 patients recovering from acute respiratory failure and ventilated by PSV were cross-randomized to four steps of assistance above (+ 3 and + 6 cmH2O) and below (-3 and -6 cmH2O) clinically set PS. Inspiratory and expiratory holds were performed to measure Pplat, PMI, ∆P, Vt, Crs, P0.1 and occluded inspiratory airway pressure (Pocc). Electromyography of respiratory muscles was monitored noninvasively from body surface (sEMG). RESULTS: As PSV was decreased, Pplat (from 20.5 ± 3.3 cmH2O to 16.7 ± 2.9, P < 0.001) and ∆P (from 12.5 ± 2.3 to 8.6 ± 2.3 cmH2O, P < 0.001) decreased much less than peak airway pressure did (from 21.7 ± 3.8 to 9.7 ± 3.8 cmH2O, P < 0.001), given the progressive increase of patient's effort (PMI from -1.2 ± 2.3 to 6.4 ± 3.2 cmH2O) in line with sEMG of the diaphragm (r = 0.614; P < 0.001). As ∆P increased linearly with Vt, Crs did not change through steps (P = 0.119). CONCLUSION: Patients react to a decrease in PSV by increasing inspiratory effort-as estimated by PMI-keeping Vt and ∆P on a desired value, therefore, limiting the clinician's ability to modulate them. PMI appears a valuable index to assess the point of ventilatory overassistance when patients lose control over Vt like in a pressure-control mode. The measurement of Crs in PSV is constant-likely suggesting reliability-independently from the level of assistance and patient's effort.

Effects of wearing different facial masks on respiratory symptoms, oxygen saturation, and functional capacity during six-minute walk test in healthy subjects.

Background: During the current COVID-19 pandemic and increased air pollution levels, wearing a facial mask has been recommended. This study aimed to compare the impact of wearing different masks when performing a submaximal functional activity (six-minute walk test; 6MWT) on respiratory symptoms, oxygen saturation, and functional capacity. Methods: Twenty-nine subjects (10 men, 19 women; age 22 ± 1 yr.; FEV1/FVC 0.90 ± 0.01) performed four rounds of 6MWT wearing different masks (surgical (Medima SK, Thailand), handmade cloth, and N95 (3M AuraTM 1870+, USA)) and while not wearing a mask. Respiratory symptoms (dyspnea and breathing effort), oxygen saturation, and other physiological parameters were assessed before and after each walking trial. Results: Six-minute walking distances were comparable between walking trials (P = 0.59). At the end of minute 6, a significant difference between groups was found on dyspnea (P = 0.02) and breathing effort (P < 0.001). Post hoc tests showed that wearing a cloth mask significantly increased dyspnea (P = 0.004) compared to wearing a surgical mask. Wearing a cloth mask also significantly increased breathing effort compared to wearing a surgical mask (P < 0.001) and not wearing a mask (P < 0.001). Likewise, while wearing an N95 mask, breathing effort significantly increased compared to wearing a surgical mask (P = 0.007) and not wearing a mask (P = 0.002). Conclusions: Wearing different masks while performing submaximal functional activity results in no differences in functional performance, oxygen saturation, heart rate, or blood pressure. However, wearing cloth masks and N95 masks results in higher respiratory symptoms.

[Patient self-inflicted lung injury (P-SILI) : From pathophysiology to clinical evaluation with differentiated management]. / "Patient self-inflicted lung injury" (P-SILI) : Von der Pathophysiologie zur klinischen Evaluation mit differenziertem Management.

The establishment of assisted spontaneous breathing is a phase of ventilation therapy that is generally considered to be beneficial and not dangerous. However, recent findings regarding potential damage from vigorous spontaneous breathing effort should be noticed in patients with acute injured lungs. This syndrome is called patient self-inflicted lung injury. Physicians, nurses and respiratory therapists should be aware of this issue. Parameters that can be determined using esophageal pressure measurement or simple maneuvers on the respirator are helpful when deciding to implement and to monitor assisted spontaneous breathing, even in the acute phases of lung damage. In addition to monitoring, there are therapeutic options for dealing with high respiratory drive or increased breathing effort.

The starting rate for high-flow nasal cannula oxygen therapy in infants with bronchiolitis: Is clinical judgment enough?

OBJECTIVES: To determine whether in infants with bronchiolitis admitted to a pediatric intensive care unit (PICU) the starting rate for high-flow nasal cannula (HFNC) therapy set by the attending physicians upon clinical judgment meets patients' peak inspiratory flow (PIF) demands and how it influences respiratory mechanics and breathing effort. METHODOLOGY: We simultaneously obtained respiratory flow and esophageal pressure data from 31 young infants with moderate-to-severe bronchiolitis before and after setting the HFNC rate at 1 L/kg/min (HFNC-1), 2 L/kg/min (HFNC-2) or upon clinical judgment and compared data for PIF, respiratory mechanics, and breathing effort. RESULTS: Before HFNC oxygen therapy started, 16 (65%) infants had a PIF less than 1 L/kg/min (normal-PIF) and 15 (45%) had a PIF more than or equal to 1 L/kg/min (high-PIF). Normal-PIF-infants had higher airway resistance (p < .001) and breathing effort indexes (e.g., pressure rate product per min [PTP/min], p = .028) than high-PIF-infants. Starting the HFNC rate upon clinical judgment (1.20-2.05 L/kg/min) met all infants' PIFs. In normal-PIF-infants, the clinically judged flow rate increased PIF (p = .081) and tidal volume (p = .029), reduced airway resistance (p = .011), and intrinsic positive end-expiratory pressure (p = .041), whereas, in both high-PIF and normal-PIF infants, it decreased respiratory rate (p < .001) and indexes of breathing effort such as PTP/min (in normal-PIF infants, p = .004; in high-PIF infants, p = .001). The 2 L/kg/min but not 1 L/kg/min rate induced similar effects. CONCLUSIONS: The wide PIF distribution in our PICU population of infants with bronchiolitis suggests two disease phenotypes whose therapeutic options might differ. An initial flow rate of nearly 2 L/kg/min meets patients' flow demands and improves respiratory mechanics and breathing effort.

The Effect of Initial Oxygen Exposure on Diaphragm Activity in Preterm Infants at Birth.

Background: The initial FiO2 that should be used for the stabilization of preterm infants in the delivery room (DR) is still a matter of debate as both hypoxia and hyperoxia should be prevented. A recent randomized controlled trial showed that preterm infants [gestational age (GA) < 30 weeks] stabilized with an initial high FiO2 (1.0) had a significantly higher breathing effort than infants stabilized with a low FiO2 (0.3). As the diaphragm is the main respiratory muscle in these infants, we aimed to describe the effects of the initial FiO2 on diaphragm activity. Methods: In a subgroup of infants from the original bi-center randomized controlled trial diaphragm activity was measured with transcutaneous electromyography of the diaphragm (dEMG), using three skin electrodes that were placed directly after birth. Diaphragm activity was compared in the first 5 min after birth. From the dEMG respiratory waveform several outcome measures were determined for comparison of the groups: average peak- and tonic inspiratory activity (dEMGpeak and dEMGton, respectively), inspiratory amplitude (dEMGamp), area under the curve (dEMGAUC) and the respiratory rate (RR). Results: Thirty-one infants were included in this subgroup, of which 29 could be analyzed [n = 15 (median GA 28.4 weeks) and n = 14 (median GA 27.9 weeks) for the 100 and 30% oxygen group, respectively]. Tonic diaphragm activity was significantly higher in the high FiO2-group (4.3 ± 2.1 µV vs. 2.9 ± 1.1 µV; p = 0.047). The other dEMG-parameters (dEMGpeak, dEMGamp, dEMGAUC) showed consistently higher values in the high FiO2 group, but did not reach statistical significance. Average RR showed similar values in both groups (34 ± 9 vs. 32 ± 10 breaths/min for the high and low oxygen group, respectively). Conclusion: Preterm infants stabilized with an initial high FiO2 showed significantly more tonic diaphragm activity and an overall trend toward a higher level of diaphragm activity than those stabilized with an initial low FiO2. These results confirm that a high initial FiO2 after birth stimulates breathing effort, which can be objectified with dEMG.

A brief airway occlusion is sufficient to measure the patient's inspiratory effort/electrical activity of the diaphragm index (PEI).

Pressure generated by patient's inspiratory muscles (Pmus) during assisted mechanical ventilation is of significant relevance. However, Pmus is not commonly measured since an esophageal balloon catheter is required. We have previously shown that Pmus can be estimated by measuring the electrical activity of the diaphragm (EAdi) through the Pmus/EAdi index (PEI). We investigated whether PEI could be reliably measured by a brief end-expiratory occlusion maneuver to propose an automated PEI measurement performed by the ventilator. Pmus, EAdi, airway pressure (Paw), and flow waveforms of 12 critically ill patients undergoing assisted mechanical ventilation were recorded. Repeated end-expiratory occlusion maneuvers were performed. PEI was measured at 100 ms (PEI0.1) and 200 ms (PEI0.2) from the start of the occlusion and compared to the PEI measured at the maximum Paw deflection (PEIoccl, reference). PEI0.1 and PEI0.2 tightly correlated with PEIoccl, (p < 0.001, R2 = 0.843 and 0.847). At a patient-level analysis, the highest percentage error was -64% and 50% for PEI0.1 and PEI0.2, respectively, suggesting that PEI0.2 might be a more reliable measurement. After correcting the error bias, the PEI0.2 percentage error was lower than ± 30% in all but one subjects (range - 39 to + 29%). It is possible to calculate PEI over a brief airway occlusion of 200 ms at inspiratory onset without the need for a full patient's inspiratory effort. Automated and repeated brief airway occlusions performed by the ventilator can provide a real time measurement of PEI; combining the automatically measured PEI with the EAdi trace could be used to continuously display the Pmus waveform at the bedside without the need of an esophageal balloon catheter.

High vs. Low Initial Oxygen to Improve the Breathing Effort of Preterm Infants at Birth: Study Protocol for a Randomized Controlled Trial.

Background: Although most preterm infants breathe at birth, their respiratory drive is weak and supplemental oxygen is often needed to overcome hypoxia. This could in turn lead to hyperoxia. To reduce the risk of hyperoxia, currently an initial low oxygen concentration (21-30%) is recommended during stabilization at birth, accepting the risk of a hypoxic period. However, hypoxia inhibits respiratory drive in preterm infants. Starting with a higher level of oxygen could lead to a shorter duration of hypoxia by stimulating breathing effort of preterm infants, and combined with subsequent titration based on oxygen saturation, prolonged hyperoxia might be prevented. Study design: This multi-center randomized controlled trial will include 50 infants with a gestational age between 24 and 30 weeks. Eligible infants will be randomized to stabilization with an initial FiO2 of either 1.0 or 0.3 at birth. Hereafter, FiO2 will be titrated based on the oxygen saturation target range. In both groups, all other interventions during stabilization and thereafter will be similar. The primary outcome is respiratory effort in the first 5 min after birth expressed as average minute volume/kg. Secondary outcomes include inspired tidal volumes/kg, rate of rise to maximum tidal volume/kg, percentage of recruitment breaths with tidal volumes above 8 mL/kg, duration of hypoxia and hyperoxia and plasma levels of markers of oxidative stress (8-iso-prostaglandin F2α). Discussion: Current resuscitation guidelines recommend oxygen titration if infants fail to achieve the 25th percentile of the SpO2 reference ranges. It has become clear that, using this approach, most preterm infants are at risk for hypoxia in the first 5 min after birth, which could suppress the breathing effort. In addition, for compromised preterm infants who need respiratory support at birth, higher SpO2 reference ranges in the first minutes after birth might be needed to prevent prolonged hypoxia. Enhancing breathing effort by achieving an adequate level of oxygenation could potentially lead to a lower incidence of intubation and mechanical ventilation in the delivery room, contributing to a lower risk on lung injury in high-risk preterm infants. Measuring 8-iso-prostaglandin F2α could lead to a reflection of the true amount of oxygen exposure in both study groups.

Assessing breathing effort in mechanical ventilation: physiology and clinical implications.

Recent studies have shown both beneficial and detrimental effects of patient breathing effort in mechanical ventilation. Quantification of breathing effort may allow the clinician to titrate ventilator support to physiological levels of respiratory muscle activity. In this review we will describe the physiological background and methodological issues of the most frequently used methods to quantify breathing effort, including esophageal pressure measurement, the work of breathing, the pressure-time-product, electromyography and ultrasound. We will also discuss the level of breathing effort that may be considered optimal during mechanical ventilation at different stages of critical illness.

Prolonged partial obstruction during sleep is a NREM phenomenon.

OBJECTIVE: Prolonged partial obstruction (PPO) is a common finding in sleep studies. Although not verified, it seems to emerge in deep sleep. We study the effect of PPO on sleep architecture or sleep electroencephalography (EEG) frequency. METHODS: Fifteen OSA patients, 15 PPO + OSA patients and 15 healthy subjects underwent a polysomnography. PPO was detected from Emfit mattress signal. Visual sleep parameters and median NREM sleep frequency of the EEG channels were evaluated. RESULTS: The amount of deep sleep (N3) did not differ between the PPO + OSA and control groups (medians 11.8% and 13.8%). PPO + OSA-patients' N3 consisted mostly of PPO. PPO + OSA patients had lighter sleep than healthy controls in three brain areas (Fp2-A1, C4-A1, O1-A2, p-values < 0.05). CONCLUSION: PPO evolved in NREM sleep and especially in N3 indicating that upper airway obstruction does not always ameliorate in deep sleep but changes the type. Even if PPO + OSA-patients had N3, their NREM sleep was lighter in three EEG locations. This might reflect impaired recovery function of sleep.

The Breathing Effort of Very Preterm Infants at Birth.

OBJECTIVE: To compare the respiratory effort of very preterm infants receiving positive pressure ventilation (PPV) with infants breathing on continuous positive airway pressure (CPAP), directly after birth. STUDY DESIGN: Recorded resuscitations of very preterm infants receiving PPV or CPAP after birth were analyzed retrospectively. The respiratory effort (minute volume and recruitment breaths [>8 mL/kg], heart rate, oxygen saturation, and oxygen requirement were analyzed for the first 2 minutes and in the fifth minute after birth. RESULTS: Respiratory effort was analyzed in 118 infants, 87 infants receiving PPV and 31 infants receiving CPAP (median gestational age, 28 weeks [IQR, 26-29] vs 29 weeks [IQR, 29-30; P < .001); birth weight, 1059 g [IQR, 795-1300] vs 1205 g [IQR, 956-1418; P = .06]). The minute volume of spontaneous breaths of infants receiving PPV was lower at 2 minutes (37 mL/kg/minute [IQR, 15-69] vs 188 mL/kg/minute [IQR, 128-297; P < .001]) and at 5 minutes (112 mL/kg/minute [IQR, 46-229] vs 205 mL/kg/minute [IQR, 174-327; P < .001]). Recruitment breaths occurred less in the PPV group at 2 minutes (0 breaths/minute [IQR, 0-1] vs 4 breaths/minute [IQR, 1-8; P < .001]) and 5 minutes (0 breaths/minute [IQR, 0-3] vs 2 breaths/minute [IQR, 0-11; P = .01). The heart rate was lower in the PPV group (94 beats/minute [IQR, 68-128] vs 124 beats/minute [IQR, 100-144; P = .02]) as was oxygen saturation (50% [IQR, 35%-66%] vs 67% [IQR, 34%-80%; P = .04]), but not different at 5 minutes (heart rate, 149 beats/minute [IQR, 131-162] vs 150 beats/minute [IQR, 132-160; P = NS]; oxygen saturation , 91% [IQR, 80%-95%] vs 92% [IQR, 89%-97%; P = NS]). The oxygen requirement was higher (at 2 minutes, 30% [IQR, 21%-53%] vs 21% [IQR, 21%-29%; P = .05]; at 5 minutes, 39% [IQR, 22%-91%] vs 22% [IQR, 21%-31%; P = .003]). CONCLUSION: Very preterm infants breathe at birth when receiving PPV, but the respiratory effort was significantly lower when compared with infants receiving CPAP only. The reduced breathing effort observed likely justified applying PPV in most infants.

The Key Roles of Negative Pressure Breathing and Exercise in the Development of Interstitial Pulmonary Edema in Professional Male SCUBA Divers.

BACKGROUND: Immersion pulmonary edema is potentially a catastrophic condition; however, the pathophysiological mechanisms are ill-defined. This study assessed the individual and combined effects of exertion and negative pressure breathing on the cardiovascular system during the development of pulmonary edema in SCUBA divers. METHODS: Sixteen male professional SCUBA divers performed four SCUBA dives in a freshwater pool at 1 m depth while breathing air at either a positive or negative pressure both at rest or with exercise. Echocardiography and lung ultrasound were used to assess the cardiovascular changes and lung comet score (a measure of interstitial pulmonary edema). RESULTS: The ultrasound lung comet score was 0 following both the dives at rest regardless of breathing pressure. Following exercise, the mean comet score rose to 4.2 with positive pressure breathing and increased to 15.1 with negative pressure breathing. The development of interstitial pulmonary edema was significantly related to inferior vena cava diameter, right atrial area, tricuspid annular plane systolic excursion, right ventricular fractional area change, and pulmonary artery pressure. Exercise combined with negative pressure breathing induced the greatest changes in these cardiovascular indices and lung comet score. CONCLUSIONS: A diver using negative pressure breathing while exercising is at greatest risk of developing interstitial pulmonary edema. The development of immersion pulmonary edema is closely related to hemodynamic changes in the right but not the left ventricle. Our findings have important implications for divers and understanding the mechanisms of pulmonary edema in other clinical settings.

The Effect of Inspiratory Resistance on Exercise Performance and Perception in Moderate Normobaric Hypoxia.

Seo, Yongsuk, Jeremiah Vaughan, Tyler D. Quinn, Brittany Followay, Raymond Roberge, Ellen L. Glickman, and Jung-Hyun Kim. The effect of inspiratory resistance on exercise performance and perception in moderate normobaric hypoxia. High Alt Med Biol. 18:417-424, 2017. PURPOSE: Respirators are simple and efficient in protecting workers against toxic airborne substances; however, their use may limit the physical performance of workers. The purpose of this study was to determine the effect of inspiratory resistance on physical performance and breathing perception in normobaric hypoxia. METHOD: Nine healthy men wore a tight-fitting respiratory mask outfitted with one of four different inspiratory resistors (R) (0, 1.5, 4.5, 7.5 cm H2O/L/Sec) while exercising at normobaric hypoxia (17% O2) at submaximal exercise workloads of 50, 100, and 150 W on a cycle ergometer for 10 minutes each, followed by a maximal oxygen uptake (VO2max) test to exhaustion. RESULTS: Maximal power output at R7.5 was significantly lower than R0 (p = 0.016) and R1.5 (p = 0.035). Respiration rate was significantly reduced at R4.5 (p = 0.011) and R7.5 (p ≤ 0.001) compared with R0. Minute ventilation was significantly decreased in R7.5 compared with R0 (p = 0.003), R1.5 (p = 0.010), and R4.5 (p = 0.016), whereas VO2 was not significantly changed. Breathing comfort (BC) and breathing effort (BE) were significantly impaired in R7.5 (BC: p = 0.025, BE: p = 0.001) and R4.5 (BC: p = 0.007, BE: p = 0.001) compared with R0, but rating of perceived exertion (RPE) remained unchanged. CONCLUSIONS: Added inspiratory resistance limited maximal power output and increased perceptions of BC and BE in normobaric hypoxia. However, low-to-moderate inspiratory resistance did not have a deleterious effect on VO2 or RPE at submaximal or maximal exercise. Perceptual and physiological characteristics of respirators of varying inspiratory resistances should be considered by manufacturers and end users during design and respirator selection processes.

Ultrasound to assess diaphragmatic function in the critically ill-a critical perspective.

Ultrasound of the diaphragm in critically ill patients has become a diagnostic technique of emerging interest among clinicians and scientists. The advantages include that it is widely available, non-invasive and examination can be performed after relatively short training and at low costs. It is used to estimate muscle mass by measurement of muscle thickness and diagnose weakness by the assessment of diaphragm movement during unassisted breathing. Thickening of the muscle during inspiration has been used to quantify force generation. The enthusiasm that surrounds this topic is shared by many clinicians and we agree that ultrasound is a valuable tool to screen for diaphragm dysfunction in intensive care unit (ICU) patients. However, in our opinion much more studies are required to validate ultrasound as a tool to quantify breathing effort. More sophisticated ultrasound techniques, such as speckle tracking imaging are promising techniques to evaluate respiratory muscle function in patients, including the critically ill.

Mandible behaviour interpretation during wakefulness, sleep and sleep-disordered breathing.

The mandible movement (MM) signal provides information on mandible activity. It can be read visually to assess sleep-wake state and respiratory events. This study aimed to assess (1) the training of independent scorers to recognize the signal specificities; (2) intrascorer reproducibility and (3) interscorer variability. MM was collected in the mid-sagittal plane of the face of 40 patients. The typical MM was extracted and classified into seven distinct pattern classes: active wakefulness (AW), quiet wakefulness or quiet sleep (QW/S), sleep snoring (SS), sleep obstructive events (OAH), sleep mixed apnea (MA), respiratory related arousal (RERA) and sleep central events (CAH). Four scorers were trained; their diagnostic capacities were assessed on two reading sessions. The intra- and interscorer agreements were assessed using Cohen's κ. Intrascorer reproducibility for the two sessions ranged from 0.68 [95% confidence interval (CI): 0.59-0.77] to 0.88 (95% CI: 0.82-0.94), while the between-scorer agreement amounted to 0.68 (95% CI: 0.65-0.71) and 0.74 (95% CI: 0.72-0.77), respectively. The overall accuracy of the scorers was 75.2% (range: 72.4-80.7%). CAH MMs were the most difficult to discern (overall accuracy 65.6%). For the two sessions, the recognition rate of abnormal respiratory events (OAH, CAH, MA and RERA) was excellent: the interscorer mean agreement was 90.7% (Cohen's κ: 0.83; 95% CI: 0.79-0.88). The discrimination of OAH, CAH, MA characteristics was good, with an interscorer agreement of 80.8% (Cohen's κ: 0.65; 95% CI: 0.62-0.68). Visual analysis of isolated MMs can successfully diagnose sleep-wake state, normal and abnormal respiration and recognize the presence of respiratory effort.