Inspiratory Maneuvers Research Articles

Diaphragm Recruitment Increases during a Bout of Targeted Inspiratory Muscle Training

The extent to which the diaphragm is targeted during a bout of inspiratory muscle training (IMT) is unknown. The purpose of this study was to characterize the relative activation patterns of the diaphragm and extradiaphragmatic inspiratory muscles during a bout of IMT and to determine whether diaphragmatic recruitment can be increased by giving subjects specific diaphragmatic breathing instructions (IMTdi). Ten healthy men were instrumented with surface EMG electrodes on the sternocleidomastoid (EMGscm), scalenes (EMGsca), parasternal intercostals (EMGpic), and seventh intercostal space (EMG7ic). A multipair esophageal electrode catheter measured crural diaphragmatic EMG (EMGdi) and transdiaphragmatic pressure (Pdi). Trial 1 of IMT involved 25 dynamic inspiratory maneuvers at 40% of maximal inspiratory mouth pressure using a variable flow resistive loading device where subjects were free to choose their own inspiratory muscle recruitment strategy. Trial 2 involved the same procedures, but subjects were given specific instructions to actively recruit their diaphragm. Cervical magnetic stimulation of the phrenic nerves verified the absence of diaphragmatic fatigue before commencing the second trial. Compared with IMT, IMTdi resulted in a significant increase in EMGdi (56 ± 12 vs 73 ± 10%max, P = 0.002) and Pdi swings (39 ± 14 vs 64 ± 17 cm H2O, P < 0.0001) and a decrease in EMGsca (52 ± 21 vs 36 ± 22%max, P = 0.04). There was no difference in EMG7ic (26 ± 19 vs 33 ± 21%max, P = 0.36), EMGpic (31 ± 24 vs 25 ± 15%max, P = 0.22), and EMGscm (58 ± 21 vs 45 ± 24%max, P = 0.08) when comparing IMT versus IMTdi, respectively. Simple diaphragmatic breathing instructions can significantly increase the recruitment of the diaphragm during IMT compared with a bout of IMT where individuals are free to choose their own inspiratory muscle recruitment strategy.

Effects of superimposed tissue weight on regional compliance of injured lungs

Computed tomography (CT), together with image analysis technologies, enable the construction of regional volume (VREG) and local transpulmonary pressure (PTP,REG) maps of the lung. Purpose of this study is to assess the distribution of VREG vs PTP,REG along the gravitational axis in healthy (HL) and experimental acute lung injury conditions (eALI) at various positive end-expiratory pressures (PEEPs) and inflation volumes.Mechanically ventilated pigs underwent inspiratory hold maneuvers at increasing volumes simultaneously with lung CT scans. eALI was induced via the iv administration of oleic acid. We computed voxel-level VREG vs PTP,REG curves into eleven isogravitational planes by applying polynomial regressions.Via F-test, we determined that VREG vs PTP,REG curves derived from different anatomical planes (p-values<1.4E-3), exposed to different PEEPs (p-values<1.5E-5) or subtending different lung status (p-values<3E-3) were statistically different (except for two cases of adjacent planes).Lung parenchyma exhibits different elastic behaviors based on its position and the density of superimposed tissue which can increase during lung injury.

Acute effects of different inspiratory efforts on ventilatory pattern and chest wall compartmental distribution in elderly women

It is not completely described how aging affect ventilatory kinematics and what are the mechanisms adopted by the elderly population to overcome these structural modifications. Given this, the aim was to evaluate the acute effects of different inspiratory efforts on ventilatory pattern and chest wall compartmental distribution in elderly women. Variables assessed included: tidal volume (Vt), total chest wall volume (Vcw), pulmonary rib cage (Vrcp%), abdominal rib cage (Vrca%) and abdominal compartment (Vab%) relative contributions to tidal volume. These variables were assessed during quiet breathing, maximal inspiratory pressure maneuver (MIP), and moderate inspiratory resistance (MIR; i.e., 40% of MIP). 22 young women (age: 23.9±2.5 years) and 22 elderly women (age: 68.2±5.0 years) participated to this study. It was possible to show that during quiet breathing, Vab% was predominant in elderly (p<0.001), in young, however, Vab% was similar to Vrcp% (p=0.095). During MIR, Vrcp% was predominant in young (p<0.001) and comparable to Vab% in elderly (p=0.249). When MIP was imposed, both groups presented a predominance of Vrcp%. In conclusion, there are differences in abdominal kinematics between young and elderly women during different inspiratory efforts. In elderly, during moderate inspiratory resistance, the pattern is beneficial, deep, and slow. Although, during maximal inspiratory resistance, the ventilatory pattern seems to predict imminent muscle fatigue.

Lower esophageal sphincter pressure measurement under standardized inspiratory maneuveurs.

Background: Through rhythmic variations, the diaphragm influence lower esophageal sphincter (LES) pressure acting as an external sphincter. LES pressure recording is characterized by increased pressure in inspiration due to contraction of the diaphragmatic crura that involves the sphincter. Aim: To describe a method of measuring LES pressure during standardized inspiratory maneuvers with increasing loads. Methods: The study population comprised of eight healthy female volunteers (average age of 31.5 years). An esophageal high-resolution manometry and impedance system was used for measuring the LES pressure during 3-second inspiratory efforts under 12, 24 and 48 cm H2O loads (Threshold maneuvers). Results: There was a significant difference between the average maximum LES pressure and the average maximum basal LES pressure during the first (76.19±17.92 difference, p=0.0008), second (86.92±19.01 difference, p=0.0004), and third seconds of the maneuver (90.86±17.93 difference, p=0.0002), with 12, 24 and 48 cmH2O loads. Conclusion: This maneuver is a standardization of the inspiratory LES pressure and may better differentiate patients with reflux disease from healthy individuals, and may also be useful for monitoring the treatment of these patients through inspiratory muscle training.

Sex, Lungs, And Forced Expiratory Flows

Women display lower maximal, forced expiratory flows (FEFs) across the vital capacity range compared with height- and age-matched men. This sex-difference on FEFs is believed to increase the prevalence of ventilatory constraint in women compared with men at a given ventilation during exercise. It remains unclear whether this sex-difference in FEFs is evident when absolute lung size is taken into account. Purpose: To investigate the influences of sex, TLC and residual volume on FEFs at rest, and during exercise in healthy adults. METHODS: Forty-seven untrained adults (24 women; 29 ± 6 yrs) with normal pulmonary function (>90% pred.) participated in this study. Subjects completed 9 min of constant-load cycling at 75% of the peak work rate achieved during an incremental cycling test. TLC and RV were obtained at rest and at the end of exercise using He-dilution, and inspiratory and forced vital capacity manoeuvres. FEFs were obtained at 25, 50 and 75% of vital capacity (FEF25%, FEF50% and FEF75%, respectively). Multivariate analyses of covariance (MANCOVA) were used to examine the effect of sex on FEFs after controlling for RV and TLC. RESULTS: Height, TLC and RV were larger for men than women (P < 0.05), as expected. The TLC to height ratio was greater in men than women (45 ± 9 ml·cm-1 v 35 ± 5 ml·cm-1, P < 0.05). FEFs increased during exercise for both sexes (P < 0.05), suggesting bronchodilation. The MANCOVA revealed a main-effect of sex on FEFs at rest and during exercise, where FEFs were systematically higher for men than women (P < 0.05). Importantly, however, the main-effect of sex on FEFs disappeared when TLC and RV were entered into the model as covariates. CONCLUSIONS: The differences in FEFs of our subjects could not be explained on the basis of sex alone. Instead, our analyses suggests that FEFs appear similar between young men and women if one controls for static lung volumes - a result that was also observed in the presence of exercise-induced bronchodilation. Thus, the higher prevalence of ventilatory constraint during exercise in women compared with height-matched men is likely the result of women having a smaller TLC relative to their height, as opposed to a sexual dimorphism in airway size/caliber for a given lung size (dysanapsis). Supported by NIH Grant HL71478

Measuring lung function using sound waves: role of the forced oscillation technique and impulse oscillometry system.

Measuring lung function is an important component in the decision making process for patients with obstructive airways disease (OAD). Not only does it help in arriving at a specific diagnosis, but it also helps in evaluating severity so that appropriate pharmacotherapy can be instituted, it helps determine prognosis and it helps evaluate response to therapy. Spirometry is currently the most commonly performed lung function test in clinical practice and is considered to be the gold standard diagnostic test for asthma and COPD. However, spirometry is not an easy test to perform because the forceful expiratory and inspiratory manoeuvres require good patient co-operation. Children aged <5 years, elderly people and those with physical and cognitive limitations cannot perform spirometry easily.

Increased inspiratory esophagogastric junction pressure in systemic sclerosis: an add-on to antireflux barrier.

To investigate crural diaphragm (CD) function in systemic sclerosis (SSc) using high-resolution manometry and standardized inspiratory maneuvers. Eight SSc volunteers (average age, 40.1 years; one male) and 13 controls (average age, 32.2 years; six males) participated in the study. A high-resolution manometry/impedance system measured the esophagus and esophagogastric junction (EGJ) pressure profile during swallows and two respiratory maneuvers: sinus arrhythmia maneuver (SAM; the average of six EGJ peak pressures during 5-s deep inhalations) and threshold maneuver (TM; the EGJ peak pressures during forced inhalation under 12 and 24 cmH2O loads). Inspiratory diaphragm lowering (IDL) was taken as the displacement of the EGJ high-pressure zone during the SAM. SSc patients had lower mean lower esophageal sphincter pressure than controls during normal breathing (19.7±2.8 mmHg vs 32.2±2.7 mmHg, P=0.007). Sinus arrhythmia maneuver pressure was higher in SSc patients than in controls (142.6±9.4 mmHg vs 104.6±13.8 mmHg, P=0.019). Sinus arrhythmia maneuver pressure normalized to IDL was also higher in SSc patients than in controls (83.8±13.4 mmHg vs 37.5±6.9 mmHg, P=0.005). Threshold maneuver pressures normalized to IDL were also greater in SSc patients than in controls (TM 12 cmH2O: 85.1±16.4 mmHg vs 43.9±6.3 mmHg, P=0.039; TM 24 cmH2O: 85.2±16.4 mmHg vs 46.2±6.6 mmHg, P=0.065). Inspiratory diaphragm lowering in SSc patients was less than in controls (2.1±0.3 cm vs 3±0.2 cm, P=0.011). SSc patients had increased inspiratory EGJ pressure. This is an add-on to EGJ pressure and indicates that the antireflux barrier can be trained.

A Potential Echocardiographic Classification for Constrictive Pericarditis Based on Analysis of Abnormal Septal Motion.

BackgroundConstrictive pericarditis is an uncommon condition that could be easily confused with congestive heart failure. In symptomatic patients, septal "wobble" on echocardiography may be an important sign of constrictive physiology. This study was planned to investigate the effects of constriction on septal motion as identified by echocardiography.MethodsIn this retrospective observational study, nine consecutive patients with constriction underwent careful echocardiographic analysis of the interventricular septum (IVS) with slow motion 2-dimensional echocardiography and inspiratory manoeuvres. Six patients who had undergone cardiac magnetic resonance imaging underwent similar analysis. Findings were correlated with haemodynamic data in five patients who had undergone cardiac catheterisation studies.ResultsIn mild cases of constriction a single wobble of the IVS was seen during normal respiration. In more moderate cases a double motion of the septum (termed "double wobble") was seen where the septum bowed initially into the left ventricle (LV) cavity in diastole then relaxed to the middle only to deviate again into the LV cavity late in diastole after atrial contraction. In severe cases, the septum bowed into the LV cavity for the full duration of diastole (pan-diastolic motion). We describe how inspiration also helped to characterize the severity of constriction especially in mild to moderate cases.ConclusionEchocardiography appears a simple tool to help diagnose constriction and grade its severity. Larger studies are needed to confirm whether the type of wobble motions helps to grade the severity of constrictive pericarditis.

S55 Neural Respiratory Drive Using Parasternal Electromyography In Clinically Stable Cystic Fibrosis Patients: A Physiological Marker Of Lung Disease Severity And Exercise Capacity

Introduction Measurement of neural respiratory drive, using parasternal intercostal muscle electromyography (EMGpara), has previously been shown to relate to pulmonary function impairment and exercise-induced breathlessness in advanced cystic fibrosis (CF). This measure reflects the load on the respiratory system and the capacity of the respiratory muscles and therefore may provide a composite measure of overall lung disease severity. In order to utilise EMGpara clinically in CF, its relationship to standard physiological outcome measures requires further investigation across a broad range of disease severities. Aim: To investigate the relationships between EMGpara and standard measures of pulmonary function and exercise performance in patients with CF. Methods Thirty patients with clinically stable CF were recruited. EMGpara was recorded during five minutes of tidal breathing using electrodes positioned in the second intercostal space directly lateral to the sternum. Peak EMGpara per breath was averaged over the final minute of the recording and expressed as a percentage of EMGpara recorded during a maximal inspiratory manoeuvre (EMGpara%max). Spirometry, lung volumes by body plethysmography and an incremental shuttle walking test (ISWT) with breath by breath metabolic data were also performed. Results Patient characteristics, EMGpara%max, measures of pulmonary function and exercise performance are shown in Table 1. EMGpara%max was significantly associated with residual volume/total lung capacity ratio (RV/TLC, r = 0.724, p 1 % pred. r = -0.648, p pleth /TLC, r = 0.625, p 2peak, r = -0.665, p = 0.001). Weaker relationships were observed between ISWT distance and pulmonary function (FEV 1 r = 0.518 p = 0.006, RV/TLC r = -0.451 p = 0.024, FRC pleth /TLC r = -0.299 p 0.147) and VO 2peak (FEV 1 r = 0.521 p = 0.008, RV/TLC r = -0.505 p = 0.014, FRC pleth /TLC r = -0.389 p = 0.066). Conclusion EMGpara correlates strongly with conventional pulmonary function measures in CF and has a closer relationship with exercise capacity than standard pulmonary function parameters. EMGpara%max therefore represents a promising marker of CF lung disease severity.

Regional distribution of lung compliance by image analysis of computed tomograms

Computed tomography (CT) can yield quantitative information about volume distribution in the lung. By combining information provided by CT and respiratory mechanics, this study aims at quantifying regional lung compliance (CL) and its distribution and homogeneity in mechanically ventilated pigs. The animals underwent inspiratory hold maneuvers at 12 lung volumes with simultaneous CT exposure at two end-expiratory pressure levels and before and after acute lung injury (ALI) by oleic acid administration. CL and the sum of positive voxel compliances from CT were linearly correlated; negative compliance areas were found. A remarkably heterogeneous distribution of voxel compliance was found in the injured lungs. As the lung inflation increased, the homogeneity increased in healthy lungs but decreased in injured lungs. Image analysis brought novel findings regarding spatial homogeneity of compliance, which increases in ALI but not in healthy lungs by applying PEEP after a recruitment maneuver.

Effect of inhaler design variables on paediatric use of dry powder inhalers.

Age appropriateness is a major concern of pulmonary delivery devices, in particular of dry powder inhalers (DPIs), since their performance strongly depends on the inspiratory flow manoeuvre of the patient. Previous research on the use of DPIs by children focused mostly on specific DPIs or single inspiratory parameters. In this study, we investigated the requirements for a paediatric DPI more broadly using an instrumented test inhaler. Our primary aim was to assess the impact of airflow resistance on children’s inspiratory flow profiles. Additionally, we investigated children’s preferences for airflow resistance and mouthpiece design and how these relate to what may be most suitable for them. We tested 98 children (aged 4.7–12.6 years), of whom 91 were able to perform one or more correct inhalations through the test inhaler. We recorded flow profiles at five airflow resistances ranging from 0.025 to 0.055 kPa0.5.min.L−1 and computed various inspiratory flow parameters from these recordings. A sinuscope was used to observe any obstructions in the oral cavity during inhalation. 256 flow profiles were included for analysis. We found that both airflow resistance and the children’s characteristics affect the inspiratory parameters. Our data suggest that a medium-high resistance is both suitable for and well appreciated by children aged 5–12 years. High incidences (up to 90%) of obstructions were found, which may restrict the use of DPIs by children. However, an oblong mouthpiece that was preferred the most appeared to positively affect the passageway through the oral cavity. To accommodate children from the age of 5 years onwards, a DPI should deliver a sufficiently high fine particle dose within an inhaled volume of 0.5 L and at a peak inspiratory flow rate of 25–40 L.min−1. We recommend taking these requirements into account for future paediatric inhaler development.

The clinical relevance of dry powder inhaler performance for drug delivery

Although understanding of the scientific basis of aerosol therapy with dry powder inhalers (DPIs) has increased, some misconceptions still persist. These include the beliefs that high resistance inhalers are unsuitable for some patients, that extra fine (<1.0 μm) particles improve peripheral lung deposition and that inhalers with flow rate-independent fine particle fractions (FPFs) produce a more consistent delivered dose to the lungs. This article aims to clarify the complex inter-relationships between inhaler design and resistance, inspiratory flow rate (IFR), FPF, lung deposition and clinical outcomes, as a better understanding may result in a better choice of DPI for individual patients. The various factors that determine the delivery of drug particles into the lungs are reviewed. These include aerodynamic particle size distribution, the inspiratory manoeuvre, airway geometry and the three basic principles that determine the site and extent of deposition: inertial impaction, sedimentation and diffusion. DPIs are classed as either dependent or independent of inspiratory flow rate and vary in their internal resistance to inspiration. The effects of these characteristics on drug deposition in the airways are described using data from studies directly comparing currently available inhaler devices. Clinical experience shows that most patients can use a high resistance DPI effectively, even during exacerbations. Particles in the aerodynamic size range from 1.5-5 μm are shown to be optimal, as particles <1.0 μm are very likely to be exhaled again while those >5 μm may impact on the oropharynx. For DPIs with a constant FPF at all flow rates, less of the delivered dose reaches the central and peripheral lung when the flow rate increases, risking under-dosing of the required medication. In contrast, flow rate-dependent inhalers increase their FPF output at higher flow rates, which compensates for the greater impaction on the upper airways as flow rate increases. The technical characteristics of different inhalers and the delivery and deposition of the fine particle dose to the lungs may be important additional considerations to help the physician to select the most appropriate device for the individual patient to optimise their treatment.

Effects of Ventilation and Catheter Position on Catheter Movement on the Tricuspid Annulus during Ablation in Children

There are little data on the effect of catheter position and mechanical ventilation on ablation catheter stability during electrophysiology study in children. We sought to determine the magnitude of catheter movement with mechanical ventilation, the effect of ventilation maneuvers on catheter movement, and to compare the degree of movement observed between the right lateral (RL) and right posteroseptal (RPS) regions. From June 2012 to June 2013, patients ≤ 21 years of age undergoing ablation for supraventricular tachycardia with CARTO® 3 (Biosense Webster, Diamond Bar, CA, USA) were included. During mapping the ablation catheter was placed in the RPS and RL regions and the magnitude of catheter movement (mm) was measured using CARTO® 3. Measurements were made during routine ventilation and with a maximal inspiration maneuver between end-expiration (ENDEX) and peak-inspiration (PEAKINS). Twenty-one patients were included: 12 males (57%), age 13 ± 3 years, weight 55 ± 14 kg. Indications for ablation were: 10 Wolff-Parkinson-White, seven atrioventricular node re-entry tachycardia, four concealed accessory pathway. Mechanical ventilation was used in all cases. The magnitude of catheter movement was 3.6 ± 1.7 mm with routine ventilation and 6.2 ± 4.1 mm between ENDEX and PEAKINS (P ≤ 0.01). Catheter movement was greater in the RL compared to the RPS region with routine ventilation (RL 4.3 ± 1.6 vs RPS 3.0 ± 1.5; P < 0.01) and between ENDEX and PEAKINS (RL 8.3 ± 4.7 vs RPS 4.0 ± 1.7; P < 0.01). Ventilation and catheter position both have significant impact on the degree of catheter movement during ablation. Movement was greatest in the RL position. This may partially explain the lower success rates of ablation in the RL region.

Inspiratory High Frequency Airway Oscillation Attenuates Resistive Loaded Dyspnea and Modulates Respiratory Function in Young Healthy Individuals

Direct chest-wall percussion can reduce breathlessness in Chronic Obstructive Pulmonary Disease and respiratory function may be improved, in health and disease, by respiratory muscle training (RMT). We tested whether high-frequency airway oscillation (HFAO), a novel form of airflow oscillation generation can modulate induced dyspnoea and respiratory strength and/or patterns following 5 weeks of HFAO training (n = 20) compared to a SHAM-RMT (conventional flow-resistive RMT) device (n = 15) in healthy volunteers (13 males; aged 20–36 yrs). HFAO causes oscillations with peak-to-peak amplitude of 1 cm H2O, whereas the SHAM-RMT device was identical but created no pressure oscillation. Respiratory function, dyspnoea and ventilation during 3 minutes of spontaneous resting ventilation, 1 minute of maximal voluntary hyperventilation and 1 minute breathing against a moderate inspiratory resistance, were compared PRE and POST 5-weeks of training (2×30 breaths at 70% peak flow, 5 days a week). Training significantly reduced NRS dyspnoea scores during resistive loaded ventilation, both in the HFAO (p = 0.003) and SHAM-RMT (p = 0.005) groups. Maximum inspiratory static pressure (cm H2O) was significantly increased by HFAO training (vs. PRE; p<0.001). Maximum inspiratory dynamic pressure was increased by training in both the HFAO (vs. PRE; p<0.001) and SHAM-RMT (vs. PRE; p = 0.021) groups. Peak inspiratory flow rate (L.s−1) achieved during the maximum inspiratory dynamic pressure manoeuvre increased significantly POST (vs. PRE; p = 0.001) in the HFAO group only. HFAO reduced inspiratory resistive loading–induced dyspnoea and augments static and dynamic maximal respiratory manoeuvre performance in excess of flow-resistive IMT (SHAM-RMT) in healthy individuals without the respiratory discomfort associated with RMT.

The pre-ejection period during the Muller manoeuvre: mismatch or misreading?

In this issue of the Journal of Clinical Monitoring andComputing, Dr. Vistisen and colleagues emphasise theinadequacy of the variation in the pre-ejection period (PEP)following deep breathing to predict the hemodynamicresponse to controlled haemorrhage [1]. The present clin-ical report may lead to the implication that this marker ofhypovolemia should be disregarded in cases of spontaneousventilation.The PEP includes excitation–contraction coupling andisovolumic contraction. Accordingly, the normovolemic leftventricle has a short PEP, whereas a hypovolemic ventriclehasalongPEP.Inthisregard,mechanistically,searching thepreload prediction from the pre-ejection period measure-ment makes sense. Indeed, there have been numerous pub-lished studies, both in human patients and in various animalmodels supporting the use of the pre-ejection period tocharacterise the preload [2]. These findings are based ondirect observations and are independent of the type of res-piration, as studies have been performed under conditions ofspontaneous [3] and mechanical ventilation [4, 5].With this in mind, it is rather surprising that little workhas been done to measure the reliability of these systolictime intervals during deep inspiration and/or the Mullermanoeuvre [6]. The article by Vistisen et al. addresses thisissue by presuming that through its impact on the respira-tory change in PEP (DPEP), a deep breathing manoeuvrecould be a preload varying method useful for predicting themagnitude of change in the cardiac output (CO) followingblood donation in healthy volunteers. Interestingly, it mightseem strange that the authors found that it was impossibleto demonstrate such a predictive value. So far, thehypothesised underlying physiology was confirmed, aswhatever the deep breathing frequency (0.1 vs. 0.167 Hz),the manoeuvre induces characteristic fluctuations in thePEP pattern. However, the authors demonstrated thatbecause the PEP is a parameter that is strongly dependenton heart rate variability (HRV), the DPEP also depends onthe respiratory induced HRV (RMSSD).On a first reading, there are several open questionsarising from the study of Dr. Vistisen et al.; perhaps themost important is the reason why the cyclic change in thePEP (DPEP) was not able to predict the stroke volumeresponses to controlled haemorrhage. Indeed, it might seemstrange that at the same time, the authors demonstrate thatwhatever the deep breathing frequency (0.1 vs. 0.167 Hz),this manoeuvre induces significant characteristic fluctua-tions in the PEP values. Although, we may speculate that anoisy pulse plethysmographic signal may make an accurateassessment of the DPEP difficult [7]; in this regard themethodology used by the authors is perfect.In principle, the absence of the clinical relevance ofcyclic changes in the PEP while the same parameter issensitive to a deep inspiratory manoeuvre may result fromthe influence of the expiratory phase on the PEP mea-surements [8]. Indeed, a forced inspiratory manoeuvre maybe followed by a forced expiratory effort that increases theleft-ventricular afterload through an increase in theabdominal pressure. Taking everything into consideration,

Respiratory motor output during an inspiratory capacity maneuver is preserved despite submaximal exercise

It is unknown whether respiratory motor output is constrained during exhaustive exercise in healthy adults. We hypothesised that neural inhibition did occur; to test this hypothesis we measured diaphragm EMG from a maximal inspiratory capacity maneuver (EMGdi-IC) at rest and during exercise. EMGdi-IC was measured before and after the amplitude of the diaphragm EMG entered a plateau phase in eleven healthy adults undertaking exercise at 60% and 80% of maximal workload achieved from incremental exercise. The mean EMGdi-IC at rest was 65±16% of the maximum that could be obtained from a battery of inspiratory tasks. Before and after the plateau phase of diaphragm EMG, EMGdi-IC was 68±13% and 72±12% (p>0.05) during 60% of the maximum workload, and was 70±13% and 78±13% (p>0.05) during 80% of the maximum workload achieved on an incremental test. A further sub-study in which 5 participants exercised at 90% of the maximum workload also showed that EMGdi-IC was not diminished during exercise. Our data show that exercise condition does not reduce the magnitude of EMGdi-IC. This argues against neural inhibition as feature of submaximal exercise in healthy adults.

Difusión de monóxido de carbono

El uso del monóxido de carbono para comprobar la teoría de la difusión simple produjo una de las más útiles y simples pruebas de función pulmonar que hoy día se usa en la mayoría de los laboratorios de función pulmonar en el mundo. El cálculo de la capacidad de difusión de monóxido de carbono es el producto de dos medidas simultáneas, la tasa constante de captación del gas y el volumen alveolar, razón por la cual éste es un determinante de la medida junto con otras variables fisiológicas como el valor de la hemoglobina, la altura sobre el nivel del mar, el volumen sanguíneo capilar y variables técnicas como calidad de la maniobra inspiratoria, tiempo de la apnea inspiratoria e intervalo entre pruebas. Hay un gran número de valores normales predichos y ecuaciones de referencia y no hay un consenso para su utilización.En cuanto a la interpretación, la noción que la difusión se corrige para un volumen alveolar determinado es incorrecta y este aspecto se explicara en detalle en el desarrollo de la presente revisión.

Expiratory muscle fatigue does not regulate operating lung volumes during high-intensity exercise in healthy humans

To determine whether expiratory muscle fatigue (EMF) is involved in regulating operating lung volumes during exercise, nine recreationally active subjects cycled at 90% of peak work rate to the limit of tolerance with prior induction of EMF (EMF-ex) and for a time equal to that achieved in EMF-ex without prior induction of EMF (ISO-ex). EMF was assessed by measuring changes in magnetically evoked gastric twitch pressure. Changes in end-expiratory and end-inspiratory lung volume (EELV and EILV) and the degree of expiratory flow limitation (EFL) were quantified using maximal expiratory flow-volume curves and inspiratory capacity maneuvers. Resistive breathing reduced gastric twitch pressure (-24 ± 14%, P = 0.004). During EMF-ex, EELV decreased from rest to the 3rd min of exercise [39 ± 8 vs. 27 ± 7% of forced vital capacity (FVC), P = 0.001] before increasing toward baseline (34 ± 8% of FVC end exercise, P = 0.073 vs. rest). EILV increased from rest to the 3rd min of exercise (54 ± 8 vs. 84 ± 9% of FVC, P = 0.006) and remained elevated to end exercise (88 ± 9% of FVC). Neither EELV (P = 0.18) nor EILV (P = 0.26) was different at any time point during EMF-ex vs. ISO-ex. Four subjects became expiratory flow limited during the final minute of EMF-ex and ISO-ex; the degree of EFL was not different between trials (37 ± 18 vs. 35 ± 16% of tidal volume, P = 0.38). At end exercise in both trials, EELV was greater in subjects without vs. subjects with EFL. These findings suggest that 1) contractile fatigue of the expiratory muscles in healthy humans does not regulate operating lung volumes during high-intensity sustained cycle exercise; and 2) factors other than "frank" EFL cause the terminal increase in EELV.

Physiologic effects and regional ventilation of high-frequency positive-pressure ventilation using a conventional ventilator in a severe ARDS animal model associated with an inspiratory pause or recruitment maneuvers

Protective mechanical ventilation (MV) in ARDS is based on reduced stretch of pulmonary tissue, sometimes resulting in severe hypoventilation that can be avoided when using high respiratory rate. High-frequency positive-pressure ventilation (HFPPV) has not been fully explored, especially when associated with other strategies aiming to avoid hypercapnia.

Cardiac Output Response to Norepinephrine in Postoperative Cardiac Surgery Patients

We studied the variable effects of norepinephrine infusion on cardiac output in postoperative cardiac surgical patients in whom norepinephrine increased mean arterial pressure. We hypothesized that the directional change in cardiac output would be determined by baseline cardiac function, as quantified by stroke volume variation, and the subsequent changes in mean systemic filling pressure and vasomotor tone. Intervention study. ICU of a university hospital. Sixteen mechanically ventilated postoperative cardiac surgery patients. Inspiratory holds were performed at baseline-1, during increased norepinephrine infusion, and baseline-2 conditions. We measured mean arterial pressure, heart rate, central venous pressure, cardiac output, stroke volume variation and, with use of inspiratory hold maneuvers, mean systemic filling pressure, then calculated resistance for venous return and systemic vascular resistance. Increasing norepinephrine by 0.04 ± 0.02 μg·kg·min increased mean arterial pressure 20 mm Hg in all patients. Cardiac output decreased in ten and increased in six patients. In all patients mean systemic filling pressure, systemic vascular resistance and resistance for venous return increased and stroke volume variation decreased. Resistance for venous return and systemic vascular resistance increased more (p = 0.019 and p = 0.002) in the patients with a cardiac output decrease. Heart rate decreased in the patients with a cardiac output decrease (p = 0.002) and was unchanged in the patients with a cardiac output increase. Baseline stroke volume variation was higher in those in whom cardiac output increased (14.4 ± 4.2% vs. 9.1 ± 2.4%, p = 0.012). Stroke volume variation >8.7% predicted the increase in cardiac output to norepinephrine (area under the receiver operating characteristic curve 0.900). The change in cardiac output induced by norepinephrine is determined by the balance of volume recruitment (increase in mean systemic filling pressure), change in resistance for venous return, and baseline heart function. Furthermore, the response of cardiac output on norepinephrine can be predicted by baseline stroke volume variation.