Reverse Triggering during Controlled Ventilation: From Physiology to Clinical Management.

Reverse triggering dyssynchrony is a frequent phenomenon recently recognized in sedated critically ill patients under controlled ventilation. It occurs in at least 30-55% of these patients and often occurs in the transition from fully passive to assisted mechanical ventilation. During reverse triggering, patient inspiratory efforts start after the passive insufflation by mechanical breaths. The most often referred mechanism is the entrainment of the patient's intrinsic respiratory rhythm from the brainstem respiratory centers to periodic mechanical insufflations from the ventilator. However, reverse triggering might also occur because of local reflexes without involving the respiratory rhythm generator in the brainstem. Reverse triggering is observed during the acute phase of the disease, when patients may be susceptible to potential deleterious consequences of injurious or asynchronous efforts. Diagnosing reverse triggering might be challenging and can easily be missed. Inspection of ventilator waveforms or more sophisticated methods, such as the electrical activity of the diaphragm or esophageal pressure, can be used for diagnosis. The occurrence of reverse triggering might have clinical consequences. On the basis of physiological data, reverse triggering might be beneficial or injurious for the diaphragm and the lung, depending on the magnitude of the inspiratory effort. Reverse triggering can cause breath-stacking and loss of protective lung ventilation when triggering a second cycle. Little is known about how to manage patients with reverse triggering; however, available evidence can guide management on the basis of physiological principles.

Impact of cognitive capacity on physical performance in chronic obstructive pulmonary disease patients: A scoping review.

Background: Chronic obstructive pulmonary disease (COPD) is often accompanied by impaired cognitive and physical function. However, the role of cognitive function on motor control and purposeful movement is not well studied. The aim of the review was to determine the impact of cognition on physical performance in COPD. Methods: Scoping review methods were performed including searches of the databases: MEDLINE, EMBASE, Cochrane Systematic Reviews, Cochrane (CENTRAL), APA PsycINFO, and CINAHL. Two reviewers independently assessed articles for inclusion, data abstraction, and quality assessment. Results: Of 11,252 identified articles, 44 met the inclusion criteria. The review included 5743 individuals with COPD (68% male) with the forced expiratory volume in one second range of 24-69% predicted. Cognitive scores correlated with strength, balance, and hand dexterity, while 6-min walk distance (n = 9) was usually similar among COPD patients with and without cognitive impairment. In 2 reports, regression analyses showed that delayed recall and the trail making test were associated with balance and handgrip strength, respectively. Dual task studies (n = 5) reported impaired balance or gait in COPD patients compared to healthy adults. Cognitive or physical Interventions (n = 20) showed variable improvements in cognition and exercise capacity. Conclusions: Cognition in COPD appears to be more related to balance, hand, and dual task function, than exercise capacity.

Handgrip Strength as a Reflection of General Muscle Strength in Chronic Obstructive Pulmonary Disease.

Muscle dysfunction is one of the main features in individuals with chronic obstructive pulmonary disease (COPD). Handgrip strength (HS) has been used as a representation of general muscle strength in various populations, and a few studies found correlation between HS and other measures of upper and lower limbs' muscle strength in the general population, although this was not yet studied in depth in COPD. The aims of this study were to verify if HS is cross-sectionally well correlated with upper and lower limbs' muscle strength in individuals with COPD, and to identify a new cutoff for handgrip weakness in this population. HS was assessed by a dynamometer, whereas other muscle strength assessments comprised maximal voluntary contraction (MVC) of the quadriceps femoris and 1-repetition maximum (1RM) of biceps and triceps brachii, pectoralis major, latissimus dorsi and quadriceps femoris. Additional assessments included pulmonary function and volumes, body composition and exercise capacity. Fifty individuals with COPD were studied (65 ± 7 years; FEV1 51 ± 14%pred). HS showed moderate-to-strong correlations with all 1-RM assessments (0.62

Muscle and cerebral oxygenation during cycling in chronic obstructive pulmonary disease: A scoping review.

To synthesize evidence for prefrontal cortex (PFC), quadriceps, and respiratory muscle oxygenation using near-infrared spectroscopy (NIRS) during cycling in individuals with chronic obstructive pulmonary disease (COPD). A scoping review was performed searching databases (inception-August 2020): Ovid MEDLINE, EMBASE, Cochrane Systematic Reviews, Cochrane Central Register of Controlled Clinical Trials, CINAHL, SPORTDiscus and Pedro. The search focused on COPD, cycling, and NIRS outcomes. 29 studies (541 COPD participants) were included. Compared to healthy individuals (8 studies), COPD patients at lower cycling workloads had more rapid increases in vastus lateralis (VL) deoxygenated hemoglobin (HHb); lower increases in VL total hemoglobin (tHb) and blood flow; and lower muscle tissue saturation (StO2). Heliox and bronchodilators were associated with smaller and slower increases in VL HHb. Heliox increased VL and intercostal blood flow compared to room air and supplemental oxygen in COPD patients (1 study). PFC oxygenated hemoglobin (O2Hb) increased in COPD individuals during cycling in 5 of 8 studies. Individuals with COPD and heart failure demonstrated worse VL and PFC NIRS outcomes compared to patients with only COPD-higher or more rapid increase in VL HHb and no change or decrease in PFC O2Hb. Individuals with COPD present with a mismatch between muscle oxygen delivery and utilization, characterized by more rapid increase in VL HHb, lower muscle O2Hb and lower muscle StO2. PFC O2Hb increases or tends to increase in individuals with COPD during exercise, but this relationship warrants further investigation. NIRS can be used to identify key deoxygenation thresholds during exercise to inform PFC and muscle oxygenation.

Energy expenditure per minute in different activities and body positions and its association with the classification as physically active or inactive in daily life in individuals with COPD.

Objective: To describe and compare energy expenditure (EE)/minute walking and in different body postures in individuals with COPD; and to investigate if EE/minute walking is a predictor of their classification as physically active or inactive. Methods: Physical activity (PA) in daily life was objectively assessed using two PA monitors for 7 days and data were analyzed on a minute-by-minute basis. Predominant minutes were separated into walking, standing, sitting, and reclined, and EE/minute (a reflection of PA intensity) was then calculated in each of these four activities and postures. Participants were classified as active and inactive according to the criteria proposed by the American College of Sports Medicine (ACSM). Results: 43 individuals were evaluated (65±8 years; FEV1 50±14% predicted). A binary logistic regression model yielded that, regardless of the time spent walking/day, EE/minute walking was a significant predictor of the classification as physically active (OR=18.2 [2 - 165]; p=0.01), together with BMI (OR=0.68 [0.5 - 0.9]; p=0.008) (model: Chi-square = 22.431, p< 0.05; R2 [Nagelkerke] = 0.556). In the active group, significantly higher EE/minute was observed for walking and standing in comparison both to sitting and reclined. However, in the inactive group, there were significant differences in EE/minute only when comparing walking versus reclined and standing versus reclined. Conclusion: In individuals, with COPD, EE/minute walking is a significant predictor of being classified as physically active, independently of the time spent walking/day. Each additional kilocalorie/minute spent walking increases in 18 times the chances to be classified as physically active in daily life.

Are the Effects of High-Intensity Exercise Training Different in Patients with COPD Versus COPD+Asthma Overlap?

PURPOSE: This study aimed to investigate whether patients with chronic obstructive pulmonary disease (COPD) presenting asthma overlap (ACO) benefit similarly in comparison to patients with only COPD after a 12-week high-intensity exercise training (ET) program. METHODS: Subjects with a diagnosis of COPD alone or ACO were evaluated and compared before and after a high-intensity ET program composed of walking and cycling plus strengthening exercises of the upper and lower limbs (3 days/week, 3 months, 36 sessions). Assessments included spirometry, bioelectrical impedance, 6-min walk test (6MWT), London Chest Activity of Daily Living Scale (LCADL), Hospital anxiety and depression Scale, modified Medical Research Council Scale (mMRC), Saint George Respiratory Questionnaire (SGRQ), and respiratory and peripheral muscle strength [manovacuometry and 1-repetition maximum test (quadriceps femoris, biceps and triceps brachialis), respectively]. ACO was defined according to Sin et al. (Eur Respir J 48(3):664-673, 2016). RESULTS: The sample was composed of 74 subjects (57% male, age 67 ± 8 years, BMI 26 (21-32) kg/m2, FEV1 47 ± 17%predicted), and 12 (16%) of them were classified as presenting ACO. Both groups improved pulmonary function, 6MWT, peripheral and inspiratory muscle strength, LCADL, and SGRQ after ET (p < 0.005 for all). There were no significant interactions between ACO and COPD on ET effects (p > 0.05 for all). Likewise, there was no difference in the proportion of patients achieving the minimum clinical important difference for 6MWT and mMRC. CONCLUSION: High-intensity exercise training generates similar benefits in patients with COPD regardless of whether presenting asthma overlap or not.

The Gini Coefficient: A New Approach to Assess Physical Activity Inequality in COPD.

Increasing physical activity (PA) is a complex and challenging task in patients with chronic obstructive pulmonary disease (COPD). However, some questions are raised regarding the evaluation of PA in these patients: Have all aspects of PA evaluation in patients with COPD already been explored in the scientific literature and clinical practice? What is the clinical importance of assessing PA inequality? PA inequality is defined as the Gini coefficient (Ginicoef) of the PA distribution of a population and is already shown to have implications for public health in the general population. It is a simple tool that might allow a better understanding of PA disparities among different COPD populations, although to our knowledge there is no previous investigation of PA inequality in patients with COPD using the Ginicoef. In this perspective study we have provided examples of the Ginicoef use in different scenarios. Future studies might try to apply it in order to identify subpopulations with higher PA inequality, and perhaps are therefore more prone to benefit most from interventions specifically tailored to promote PA. In summary, we propose the quantification of PA inequality with the Ginicoef as a tool that might allow us to see PA even more comprehensively than we already do, expanding our perspective on PA in patients with COPD.

Functional Status of Patients with COPD Assessed by London Chest Activity of Daily Living Scale: Gender Association and Validity of a Cutoff Point.

PURPOSE: Whether the difference in the impact of chronic obstructive pulmonary disease (COPD) on the functional status of men and women stems from clinical distinctions or to the measuring instrument used is unclear. Like most instruments for assessing functional limitation in COPD, the interpretation of the results of the London Chest Activity of Daily Living (LCADL) scale is limited because a lack of a valid cutoff point to this scale. For that, this study sought to compare the functional status between men and women with COPD; and propose a cutoff point for LCADL capable of discriminating the prognosis of these individuals. METHODS: A sample of 138 subjects with moderate-severe COPD was evaluated by the LCADL. The percentage of the individual maximum score was used to obtain a cutoff point capable of discriminating patients with the worse prognosis according to the BODE Index. The cutoff point was also tested in an independent sample (n = 70). RESULTS: Regarding the total score, domestic and leisure domains of the LCADL, men had better scores than women (P ≤ 0.01). The cutoff point found was 37% (area under the curve = 0.70, 95% confidence interval = 0.60-0.80, sensitivity = 0.55 and specificity = 0.74). Individuals who scored ≥ 37% had a worse prognosis and level of physical activities of daily living than those who scored below (P ≤ 0.02). CONCLUSION: When evaluated by the LCADL, men and women with COPD present difference in the functional status. The established cutoff point (37%) adequately discriminates individuals regarding the prognosis, contributing to improve the interpretation capacity of the LCADL.

Cluster analysis identifying patients with COPD at high risk of 2-year all-cause mortality.

The objective of the article is to identify clusters of patients with COPD according to factors known to be associated with mortality and to verify whether clusters' assignment is associated with 2-year mortality. Patients ( n = 141) were evaluated by bioelectrical impedance, maximal inspiratory pressure (MIP), one-repetition maximum test of the quadriceps femoris (1RMQF) and BODE index (body mass index; airflow obstruction (spirometry); dyspnea (modified Medical Research Council scale); and exercise capacity (6-minute walk test (6MWT) distance). Vital status was retrospectively checked 2 years after the assessments, and time to death was quantified for those deceased in this period. K-means analysis identified two clusters. Patients in cluster one (CL I, n = 69) presented an impaired clinical status in comparison to cluster two (CL II, n = 72). Receiver operating characteristics curves identified the cutoffs discriminating patients composing CL I: forced expiratory volume in the first second <44%pred; 6MWT <479 m; 1RMQF <19 kg; and maximum inspiratory pressures <73 cmH2O (area under the curve range 0.750-0.857). During the follow-up, 19 (13%) patients deceased, 15 in CL I (22%) and 4 in CL II (0.06%) ( p = 0.005). CL I was associated with a higher risk of 2-year mortality (hazard ratio (95% confidence interval): 4.3 (1.40-12.9), p = 0.01). A cluster of patients with COPD highly associated with 2-year mortality was statistically identified, and cutoffs to identify these subjects were provided.

Sedentary Behaviour and Physical Inactivity in Patients with Chronic Obstructive Pulmonary Disease: Two Sides of the Same Coin?

Despite the growing interest in sedentarism, there is no available information on the profile of patients with COPD according to sedentary behaviour (SB) and with a detailed analysis of minute-by-minute bouts. Hence, the aims of this study were to quantify the time spent in SB, light activities and moderate-to-vigorous physical activities (MVPA) and to verify the relationship of MVPA and SB in individuals with COPD, as well as to identify the profile of those physically (in)active and (non)-sedentary. A cross-sectional study in which physical activity in daily life was objectively assessed through the use of SenseWear Pro 2 Armband (BodyMedia) during 2 consecutive weekdays, 12 h/day. Analysis was performed minute-by-minute for each day of each patient. MVPA comprised time spent >3 metabolic equivalents (MET), whereas light activities corresponded to time spent between 1.5 and 3 MET and SB to time spent <1.5 MET. A total of 137 subjects with COPD (66 ± 8years; FEV1 46 [31-57] %pred; BMI 26 [22-30] kg/m2) were analysed. Time spent in MVPA and SB presented strong negative correlation (r = -0.72, P < 0.001). Minute-by-minute analysis showed that patients with COPD spend most of their time in SB. SB accounted for 40% of all bouts >1 minute, whereas only 14% these bouts concern MVPA. Patients combining two positive characteristics (physically active and non-sedentary) have better clinical profile than others. In conclusion, SB is negatively correlated with MVPA in patients with COPD. Furthermore, patients classified as physically active (i.e., those who reach MVPA recommendations) in combination with a non-sedentary lifestyle present markedly better clinical conditions.

Airway opening pressure maneuver to detect airway closure in mechanically ventilated pediatric patients.

Background: Airway closure, which refers to the complete collapse of the airway, has been described under mechanical ventilation during anesthesia and more recently in adult patients with acute respiratory distress syndrome (ARDS). A ventilator maneuver can be used to identify airway closure and measure the pressure required for the airway to reopen, known as the airway opening pressure (AOP). Without that maneuver, AOP is unknown to clinicians. Objective: This study aims to demonstrate the technical adaptation of the adult maneuver for children and illustrate its application in two cases of pediatric ARDS (p-ARDS). Methods: A bench study was performed to adapt the maneuver for 3-50 kg patients. Four maneuvers were performed for each simulated patient, with 1, 2, 3, and 4 s of insufflation time to deliver a tidal volume (Vt) of 6 ml/kg by a continuous flow. Results: Airway closure was simulated, and AOP was visible at 15 cmH2O with a clear inflection point, except for the 3 kg simulated patient. Regarding insufflation time, a 4 s maneuver exhibited a better performance in 30 and 50 kg simulated patients since shorter insufflation times had excessive flowrates (>10 L/min). Below 20 kg, the difference in resistive pressure between a 3 s and a 4 sec maneuver was negligible; therefore, prolonging the maneuver beyond 3 s was not useful. Airway closure was identified in two p-ARDS patients, with the pediatric maneuver being employed in the 28 kg patient. Conclusions: We propose a pediatric AOP maneuver delivering 6 ml/kg of Vt at a continuous low-flow inflation for 3 s for patients weighing up to 20 kg and for 4 s for patients weighing beyond 20 kg.

Continuous measurements of respiratory muscle blood flow & oxygen consumption using non-invasive FD-NIRS & DCS.

Prior studies of muscle blood flow and muscle specific oxygen consumption have required invasive injection of dye and Magnetic Resonance Imaging, respectively. Such measures have limited utility for continuous monitoring of the respiratory muscles. Frequency domain near-infrared spectroscopy and diffuse correlation spectroscopy (FD-NIRS & DCS) can provide continuous surrogate measures of blood flow index (BFi) and metabolic rate of oxygen consumption (MRO2). This study aimed to validate sternocleidomastoid FD-NIRS & DCS outcomes against electromyography (EMG) and mouth pressure (Pm) during incremental inspiratory threshold loading (ITL). Six females and six male healthy adults (mean±SD; 30±7 years, maximum inspiratory pressure 118±61 cmH2O) performed incremental ITL starting at low loads (8±2 cmH2O) followed by 50g increments every two minutes until task failure. FD-NIRS & DCS continuously measured sternocleidomastoid oxygenated and deoxygenated hemoglobin+myoglobin (oxy/deoxy[Hb+Mb]), tissue saturation of oxygen (StO2), BFi, and MRO2. Ventilatory parameters including inspiratory Pm were also evaluated. Pm increased during incremental ITL (P<0.05), reaching -47[-74 - -34] cmH2O (median[25%-75%IQR] at task failure. Ventilatory parameters were constant throughout ITL (all P>0.05). Sternocleidomastoid BFi and MRO2 increased from the start of the ITL (both P<0.05). Deoxy[Hb+Mb] increased close to task failure, concomitantly with a constant increase in MRO2, and decreased StO2. Sternocleidomastoid deoxy[Hb+Mb], BFi, StO2 and MRO2 obtained during ITL via FD-NIRS & DCS correlated with sternocleidomastoid EMG (all P<0.05). In healthy adults, FD-NIRS & DCS can provide continuous surrogate measures of respiratory BFi and MRO-2. Increasing sternocleidomastoid oxygen consumption near task failure was associated with increased oxygen extraction and reduced tissue saturation.

An Individual Barrier Enclosure Actively Removing Aerosols for Airborne Isolation: A Vacuum Tent.

BACKGROUND: Aerosol barrier enclosure systems have been designed to prevent airborne contamination, but their safety has been questioned. A vacuum tent was designed with active continuous suctioning to minimize risks of aerosol dispersion. We tested its efficacy, risk of rebreathing, and usability on a bench, in healthy volunteers, and in an ergonomic clinical assessment study. METHODS: First, a manikin with airway connected to a breathing simulator was placed inside the vacuum tent to generate active breathing, cough, and CO2 production; high-flow nasal cannula (HFNC) was applied in the manikin's nares. Negative pressure was applied in the vacuum tent's apex port using wall suction. Fluorescent microparticles were aerosolized in the vacuum tent for qualitative assessment. To quantify particles inside and around vacuum tent (aerosol retention), an airtight aerosol chamber with aerosolized latex microparticles was used. The vacuum tent was tested on healthy volunteers breathing with and without HFNC. Last, its usability was assessed in 5 subjects by 5 different anesthesiologists for delivery of full anesthesia, including intubation and extubation. RESULTS: The vacuum tent was adjusted until no leak was visualized using fluorescent particles. The efficacy in retaining microparticles was confirmed quantitatively. CO2 accumulation inside the vacuum tent showed an inverse correlation with the suction flow in all conditions (normal breathing and HFNC 30 or 60 L/min) in bench and healthy volunteers. Particle removal efficacy and safe breathing conditions (CO2, temperature) were reached when suctioning was at least 60 L/min or 20 L/min > HFNC flow. Five subjects were successfully intubated and anesthetized without ergonomic difficulties and with minimal interference with workflow and an excellent overall assessment by the anesthesiologists. CONCLUSIONS: The vacuum tent effectively minimized aerosol dispersion. Its continuous suction system set at a high suction flow was crucial to avoid the spread of aerosol particles and CO2 rebreathing.

Effects of inspiratory muscle training on exertional breathlessness in patients with unilateral diaphragm dysfunction: a randomised trial.

Background: Unilateral diaphragm dysfunction (UDD) is an underdiagnosed cause of dyspnoea. Inspiratory muscle training (IMT) is the only conservative treatment for UDD, but the mechanisms of improvement are unknown. We characterised the effects of IMT on dyspnoea, exercise tolerance and respiratory muscle function in people with UDD. Methods: 15 people with UDD (73% male, 61±8 years) were randomised to 6 months of IMT (50% maximal inspiratory mouth pressure (PI,max), n=10) or sham training (10% PI,max, n=5) (30 breaths twice per day). UDD was confirmed by phrenic nerve stimulation and persisted throughout the training period. Symptoms were assessed by the transitional dyspnoea index (TDI) and exercise tolerance by constant-load cycle tests performed pre- and post-training. Oesophageal (Pes) and gastric (Pga) pressures were measured with a dual-balloon catheter. Electromyography (EMG) and oxygenation (near-infrared spectroscopy) of respiratory muscles were assessed continuously during exercise. Results: The IMT group (from 45±6 to 62±23% PI,max) and sham group (no progression) completed 92 and 86% of prescribed sessions, respectively. PI,max, TDI scores and cycle endurance time improved significantly more after IMT versus sham (mean between-group differences: 28 (95% CI 13-28) cmH2O, 3.0 (95% CI 0.9-5.1) points and 6.0 (95% CI 0.4-11.5) min, respectively). During exercise at iso-time, Pes, Pga and EMG of the scalene muscles were reduced and the oxygen saturation indices of the scalene and abdominal muscles were higher post- versus pre-training only in the IMT group (all p<0.05). Conclusion: The effects of IMT on dyspnoea and exercise tolerance in UDD were not mediated by an improvement in isolated diaphragm function, but may reflect improvements in strength, coordination and/or oxygenation of the extra-diaphragmatic respiratory muscles.

Prefrontal cortex activation during incremental inspiratory loading in healthy participants.

We aimed to investigate whether changes in prefrontal cortex (PFC) oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) associates with inspiratory muscle effort during inspiratory threshold loading (ITL) in healthy participants. Participants performed an incremental ITL. Breathing pattern, partial pressure of end-tidal CO2 (PETCO2), mouth pressure and O2Hb and HHb over the right dorsolateral PFC, sternocleidomastoid (SCM), and diaphragm/intercostals (Dia/IC) were monitored. Fourteen healthy participants (8 men; 29 ± 5 years) completed testing. Dyspnea was higher post- than pre-ITL (5 ± 1 vs. 0 ± 1, respectively; P<0.05). PFC O2Hb increased (P < 0.001) and HHb decreased (P = 0.001) at low loads but remained stable with increasing ITL intensities. PFC total hemoglobin increased at task failure compared to rest. SCM HHb increased throughout increasing intensities. SCM and Dia/IC total hemoglobin increased in the at task failure compared to rest. PETCO2 did not change (P = 0.528). PFC is activated early during the ITL but does not show central fatigue at task failure despite greater dyspnea and an imbalance of SCM oxygen demand and delivery.

Onset and Offset Detection of Respiratory EMG Data Based on Energy Operator Signal.

Onset and offset detection of electromyography (EMG) data is an important step in respiratory muscle coordination assessment. Impaired respiratory coordination can indicate breathing disorders and lung diseases. In this paper, we present an algorithm for onset and offset timing detection of real-world EMG signals from respiratory muscles, which are contaminated with electrocardiogram (ECG) artifacts. The algorithm is based on the Energy Operator signal, has a low computational cost, and includes a filtering procedure to remove ECG artifacts from EMG. Analysis of EMG signals from 2 respiratory muscles of 5 participants' data shows high agreement between the algorithm and manual method with a mean difference between two methods of 0.0407 seconds.

Semi-automated Detection of the Timing of Respiratory Muscle Activity: Validation and First Application.

Background: Respiratory muscle electromyography (EMG) can identify whether a muscle is activated, its activation amplitude, and timing. Most studies have focused on the activation amplitude, while differences in timing and duration of activity have been less investigated. Detection of the timing of respiratory muscle activity is typically based on the visual inspection of the EMG signal. This method is time-consuming and prone to subjective interpretation. Aims: Our main objective was to develop and validate a method to assess the respective timing of different respiratory muscle activity in an objective and semi-automated manner. Method: Seven healthy adults performed an inspiratory threshold loading (ITL) test at 50% of their maximum inspiratory pressure until task failure. Surface EMG recordings of the costal diaphragm/intercostals, scalene, parasternal intercostals, and sternocleidomastoid were obtained during ITL. We developed a semi-automated algorithm to detect the onset (EMG, onset) and offset (EMG, offset) of each muscle's EMG activity breath-by-breath with millisecond accuracy and compared its performance with manual evaluations from two independent assessors. For each muscle, the Intraclass Coefficient correlation (ICC) of the EMG, onset detection was determined between the two assessors and between the algorithm and each assessor. Additionally, we explored muscle differences in the EMG, onset, and EMG, offset timing, and duration of activity throughout the ITL. Results: More than 2000 EMG, onset s were analyzed for algorithm validation. ICCs ranged from 0.75-0.90 between assessor 1 and 2, 0.68-0.96 between assessor 1 and the algorithm, and 0.75-0.91 between assessor 2 and the algorithm (p < 0.01 for all). The lowest ICC was shown for the diaphragm/intercostal and the highest for the parasternal intercostal (0.68 and 0.96, respectively). During ITL, diaphragm/intercostal EMG, onset occurred later during the inspiratory cycle and its activity duration was shorter than the scalene, parasternal intercostal, and sternocleidomastoid (p < 0.01). EMG, offset occurred synchronously across all muscles (p ≥ 0.98). EMG, onset, and EMG, offset timing, and activity duration was consistent throughout the ITL for all muscles (p > 0.63). Conclusion: We developed an algorithm to detect EMG, onset of several respiratory muscles with millisecond accuracy that is time-efficient and validated against manual measures. Compared to the inherent bias of manual measures, the algorithm enhances objectivity and provides a strong standard for determining the respiratory muscle EMG, onset.

High-intensity exercise impairs extradiaphragmatic respiratory muscle perfusion in patients with COPD.

The study investigated whether high-intensity exercise impairs inspiratory and expiratory muscle perfusion in patients with chronic obstructive pulmonary disease (COPD). We compared respiratory local muscle perfusion between constant-load cycling[sustained at 80% peak work rate (WRpeak)] and voluntary normocapnic hyperpnea reproducing similar work of breathing (WoB) in 18 patients [forced expiratory volume in the first second (FEV1): 58 ± 24% predicted]. Local muscle blood flow index (BFI), using indocyanine green dye, and fractional oxygen saturation (%StiO2) were simultaneously assessed by near-infrared spectroscopy (NIRS) over the intercostal, scalene, rectus abdominis, and vastus lateralis muscles. Cardiac output (impedance cardiography), WoB (esophageal/gastric balloon catheter), and diaphragmatic and extradiaphragmatic respiratory muscle electromyographic activity (EMG) were also assessed throughout cycling and hyperpnea. Minute ventilation, breathing pattern, WoB, and respiratory muscle EMG were comparable between cycling and hyperpnea. During cycling, cardiac output and vastus lateralis BFI were significantly greater compared with hyperpnea [by +4.2 (2.6-5.9) L/min and +4.9 (2.2-7.8) nmol/s, respectively] (P < 0.01). Muscle BFI and %StiO2 were, respectively, lower during cycling compared with hyperpnea in scalene [by -3.8 (-6.4 to -1.2) nmol/s and -6.6 (-8.2 to -5.1)%], intercostal [by -1.4 (-2.4 to -0.4) nmol/s and -6.0 (-8.6 to -3.3)%], and abdominal muscles [by -1.9 (-2.9 to -0.8) nmol/s and -6.3 (-9.1 to -3.4)%] (P < 0.001). The difference in respiratory (scalene and intercostal) muscle BFI between cycling and hyperpnea was associated with greater dyspnea (Borg CR10) scores (r = -0.54 and r = -0.49, respectively, P < 0.05). These results suggest that in patients with COPD, 1) locomotor muscle work during high-intensity exercise impairs extradiaphragmatic respiratory muscle perfusion and 2) insufficient adjustment in extradiaphragmatic respiratory muscle perfusion during high-intensity exercise may partly explain the increased sensations of dyspnea.NEW & NOTEWORTHY We simultaneously assessed the blood flow index (BFI) in three respiratory muscles during hyperpnea and high-intensity constant-load cycling sustained at comparable levels of work of breathing and respiratory neural drive in patients with COPD. We demonstrated that high-intensity exercise impairs respiratory muscle perfusion, as intercostal, scalene, and abdominal BFI increased during hyperpnea but not during cycling. Insufficient adjustment in respiratory muscle perfusion during exercise was associated with greater dyspnea sensations in patients with COPD.