Clinical aspects of respiratory muscle dysfunction in the critically ill

[Evaluation of the Functional Reserve and Exercise Tolerance in Patients with CHF in Clinical Trials (Consent Document of the Editorial board of the Journal of Cardiology, the Board of the Society of Specialists in Heart Failure (SSHF) and Working Group "Non-drug treatment methods" of SSHF)]

Assessing the functional capacity and exercise tolerance is an important and widely used research tool in patients with heart failure. It is used not only in cardiac rehabilitation and physical therapy, but also for inclusion criteria and outcome measures in studies of drug interventions. This document outlines the scope, guidelines for the implementation and interpretation, and limitations of the methods for assessing the functional capacity and exercise tolerance in clinical trials in patients with heart failure.

Methods and Applications in Respiratory Physiology: Respiratory Mechanics, Drive and Muscle Function in Neuromuscular and Chest Wall Disorders

Individuals with neuromuscular and chest wall disorders experience respiratory muscle weakness, reduced lung volume and increases in respiratory elastance and resistance which lead to increase in work of breathing, impaired gas exchange and respiratory pump failure. Recently developed methods to assess respiratory muscle weakness, mechanics and movement supplement traditionally employed spirometry and methods to evaluate gas exchange. These include recording postural change in vital capacity, respiratory pressures (mouth and sniff), electromyography and ultrasound evaluation of diaphragmatic thickness and excursions. In this review, we highlight key aspects of the pathophysiology of these conditions as they impact the patient and describe measures to evaluate respiratory dysfunction. We discuss potential areas of physiologic investigation in the evaluation of respiratory aspects of these disorders.

Cambios fisiológicos relacionados con entrenamiento muscular respiratorio en pacientes con ventilación mecánica

Introducción. El entrenamiento muscular respiratorio es una técnica fisioterapéutica usada para incrementar la fuerza de la musculatura respiratoria, sin embargo pocos estudios han abordado los cambios fisiológicos relacionados con esta intervención en pacientes con ventilación mecánica.Objetivo. Determinar los cambios fisiológicos relacionados con el entrenamiento muscular respiratorio en pacientes con ventilación mecánica.Materiales y métodos. Se realizó un análisis de datos secundarios en el marco del estudio “Eficacia del entrenamiento muscular respiratorio en el destete de la ventilación mecánica en pacientes con ventilación mecánica por 48 horas o más: Un ensayo clínico controlado”. La población estuvo conformada por los 62 pacientes del grupo experimental del estudio principal, quienes recibieron entrenamiento muscular respiratorio. Los valores de frecuencia cardiaca, frecuencia respiratoria, presión arterial, saturación de oxígeno y volumen corriente fueron registrados. La diferencia entre el promedio de cada una de las variables fue analizada mediante la prueba de t pareada, mientras que para el análisis de los cambios fisiológicos entre sesiones de entrenamiento se empleó la prueba de Kruskal-Wallis.Resultados. Se observaron diferencias significativas entre las variables fisiológicas antes y después del entrenamiento muscular respiratorio (p<0.05), a excepción del volumen corriente y la presión arterial media (p>0.05). Por el contrario, no se observaron diferencias significativas en ninguna de las variables fisiológicas entre sesiones de entrenamiento (p>0.05)Conclusiones. El entrenamiento muscular respiratorio es una intervención terapéutica viable y tolerable en esta población.

Inspiratory flow-resistive breathing, respiratory muscle-induced systemic oxidative stress, and diaphragm fatigue in healthy humans

We questioned whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow-resistive breathing, whether the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. Eight young and healthy participants attended the laboratory for four visits on separate days. During the first visit, height, body mass, lung function, and maximal inspiratory mouth and transdiaphragmatic pressure (P_dimax) were assessed. During visits 2-4, participants undertook inspiratory flow-resistive breathing with either no resistance (control) or resistive loads equivalent to 50 and 70% of their P_dimax (P_dimax50% and P_dimax70%) for 30 min. Participants undertook one resistive load per visit, and the order in which they undertook the loads was randomized. Inspiratory muscle pressures were higher (P < 0.05) during the 5th and Final min of P_dimax50% and P_dimax70% compared with control. Plasma F₂-isoprostanes increased (P < 0.05) following inspiratory flow-resistive breathing at P_dimax70%. There were no increases in plasma protein carbonyls or total antioxidant capacity. Furthermore, although we evidenced small reductions in transdiapragmaic twitch pressures (P_diTW) after inspiratory flow-resistive breathing at P_dimax50% and P_dimax70%, this was not related to the increase in plasma F₂-isoprostanes. Our novel data suggest that it is only when sufficiently strenuous that inspiratory flow-resistive breathing in humans elicits systemic oxidative stress evidenced by elevated plasma F₂-isoprostanes, and based on our data, this is not related to a reduction in P_diTW.NEW & NOTEWORTHY We examined whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow-resistive breathing, whether the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. It is only when sufficiently strenuous that inspiratory flow-resistive breathing elevates plasma F₂-isoprostanes, and our novel data show that this is not related to a reduction in transdiaphragmatic twitch pressure.

The effects of fatigue and oxidation on contractile function of intact muscle fibers and myofibrils isolated from the mouse diaphragm

The goal of this study was to investigate the effects of repetitive stimulation and the oxidant H₂O₂ on fatigue of diaphragm intact fibers and in myofibrils measured with different Ca²⁺ concentrations. Intact fibers were isolated from mice diaphragm, and twitch and tetanic contractions (500 ms duration) were performed at different frequencies of stimulation ranging from 15 Hz to 150 Hz to establish a force-frequency relation before and after a fatigue and recovery protocol, without or after a treatment with H₂O₂. Fatigue was induced with isometric contractions (500 ms, 40 Hz) evoked every 0.8 seconds, with a total of 625 tetani. After the fatigue, the force recovery was followed by invoking tetanic contractions (500 ms, 40 Hz) every 1 min, with a total duration of 30 min. Individual myofibrils were also isolated from the mouse diaphragm and were tested for isometric contractions before and after treatment with H₂O₂ and NAC. In a second series of experiments, myofibrils were activated at different pCa (pCa = -log₁₀ [Ca²⁺]), before and after H₂O₂ treatment. After 15 minutes of H₂O₂ treatment, the myofibrillar force was decreased to 54 ± 12% of its control, maximal value, and a result that was reversed by NAC treatment. The force was also decreased after myofibrils were treated with H₂O₂ and activated in pCa ranging between 4.5 and 5.7. These results suggest that fatigue in diaphragm intact fibers and at the myofibrils level is caused partially by oxidation of the contractile proteins that may be responsible for changing the force in various levels of Ca²⁺ activation.

Respiratory Muscle Assessment in Acute Guillain-Barré Syndrome

PURPOSE

Guillain-Barré Syndrome (GBS) is a life-threatening disease due to respiratory muscle involvement. This study aimed at objectively assessing the course of respiratory muscle function in GBS subjects within the first week of admission to an intensive care unit.

METHODS

Medical Research Council Sum Score (MRC-SS), vigorimetry, spirometry, and respiratory muscle function tests (inspiratory/expiratory muscle strength: PImax/PEmax, sniff nasal pressure: SnPna) were assessed twice daily. GBS Disability Score (GBS-DS) was assessed once daily. On days one (d1) and seven (d7), blood gases and twitch mouth pressure during magnetic phrenic nerve stimulation (Pmo,tw) were additionally evaluated.

RESULTS

Nine subjects were included. MRC-SS, vigorimetry, PImax, and SnPna increased between d1 and d7. GBS-DS, spirometry and Pmo,tw remained unaltered. Only SnPna correlated closely with the MRC-SS on both d1 (r = 0.77, p = 0.02) and d7 (r = 0.74, p = 0.02).

CONCLUSION

SnPna was the only parameter that correlated with MRC-SS, while the current gold standard of spirometry measurement did not.

Muscle dysfunction in chronic obstructive pulmonary disease: update on causes and biological findings

Respiratory and/or limb muscle dysfunction, which are frequently observed in chronic obstructive pulmonary disease (COPD) patients, contribute to their disease prognosis irrespective of the lung function. Muscle dysfunction is caused by the interaction of local and systemic factors. The key deleterious etiologic factors are pulmonary hyperinflation for the respiratory muscles and deconditioning secondary to reduced physical activity for limb muscles. Nonetheless, cigarette smoke, systemic inflammation, nutritional abnormalities, exercise, exacerbations, anabolic insufficiency, drugs and comorbidities also seem to play a relevant role. All these factors modify the phenotype of the muscles, through the induction of several biological phenomena in patients with COPD. While respiratory muscles improve their aerobic phenotype (percentage of oxidative fibers, capillarization, mitochondrial density, enzyme activity in the aerobic pathways, etc.), limb muscles exhibit the opposite phenotype. In addition, both muscle groups show oxidative stress, signs of damage and epigenetic changes. However, fiber atrophy, increased number of inflammatory cells, altered regenerative capacity; signs of apoptosis and autophagy, and an imbalance between protein synthesis and breakdown are rather characteristic features of the limb muscles, mostly in patients with reduced body weight. Despite that significant progress has been achieved in the last decades, full elucidation of the specific roles of the target biological mechanisms involved in COPD muscle dysfunction is still required. Such an achievement will be crucial to adequately tackle with this relevant clinical problem of COPD patients in the near-future.

Diagnostic methods to assess inspiratory and expiratory muscle strength

Impairment of (inspiratory and expiratory) respiratory muscles is a common clinical finding, not only in patients with neuromuscular disease but also in patients with primary disease of the lung parenchyma or airways. Although such impairment is common, its recognition is usually delayed because its signs and symptoms are nonspecific and late. This delayed recognition, or even the lack thereof, occurs because the diagnostic tests used in the assessment of respiratory muscle strength are not widely known and available. There are various methods of assessing respiratory muscle strength during the inspiratory and expiratory phases. These methods are divided into two categories: volitional tests (which require patient understanding and cooperation); and non-volitional tests. Volitional tests, such as those that measure maximal inspiratory and expiratory pressures, are the most commonly used because they are readily available. Non-volitional tests depend on magnetic stimulation of the phrenic nerve accompanied by the measurement of inspiratory mouth pressure, inspiratory esophageal pressure, or inspiratory transdiaphragmatic pressure. Another method that has come to be widely used is ultrasound imaging of the diaphragm. We believe that pulmonologists involved in the care of patients with respiratory diseases should be familiar with the tests used in order to assess respiratory muscle function.Therefore, the aim of the present article is to describe the advantages, disadvantages, procedures, and clinical applicability of the main tests used in the assessment of respiratory muscle strength.

MiR-181a: a potential biomarker of acute muscle wasting following elective high-risk cardiothoracic surgery

Introduction

Acute muscle wasting in the critically ill is common and associated with significant morbidity and mortality. Although some aetiological factors are recognised and muscle wasting can be detected early with ultrasound, it not possible currently to predict in advance of muscle loss those who will develop muscle wasting. The ability to stratify the risk of muscle wasting associated with critical illness prior to it becoming clinically apparent would provide the opportunity to predict prognosis more accurately and to intervene at an early stage. MicroRNAs are small non-coding RNAs that modulate post-transcriptional regulation of translation, some are tissue specific and can be detected and quantified in plasma. We hypothesised that certain plasma microRNAs could be biomarkers of ICU acquired muscle weakness.

Methods

Plasma levels of selected microRNAs were measured in pre- and post-operative samples from a previously reported prospective observational study of 42 patients undergoing elective high-risk cardiothoracic surgery, 55% of whom developed muscle wasting.

Results

The rise in miR-181a was significantly higher on the second post-operative day in those who developed muscle wasting at 1 week compared to those who did not (p = 0.03). A rise in miR-181a of greater than 1.7 times baseline had 91% specificity and 56% sensitivity for subsequent muscle wasting. Other microRNAs did not show significant differences between the groups.

Conclusion

Plasma miR-181a deserves further investigation as a potential biomarker of muscle wasting. Additionally, since mir-181a is involved in both regulation of inflammation and muscle regeneration and differentiation; our observation therefore also suggests directions for future research.

Transcranial direct-current stimulation reduced the excitability of diaphragmatic corticospinal pathways whatever the polarity used

We investigated effects of transcranial direct-current stimulation (tDCS) on the diaphragmatic corticospinal pathways in healthy human. Anodal, cathodal, and sham tDCS were randomly applied upon the left diaphragmatic motor cortex in twelve healthy right-handed men. Corticospinal pathways excitability was assessed by means of transcranial magnetic stimulation (TMS) elicited motor-evoked-potential (MEP). For each tDCS condition, MEPs were recorded before (Pre) tDCS then after 10 min (Post1, at tDCS discontinuation in the anodal and cathodal sessions) and 20 min (Post2). As result, both anodal and cathodal tDCS significantly decreased MEP amplitude of the right hemidiaphragm at both Post1 and Post2, versus Pre. MEP amplitude was unchanged versus Pre during the sham condition. The effects of cathodal and anodal tDCS applied to the diaphragm motor cortex differ from those observed during tDCS of the limb motor cortex. These differences may be related to specific characteristics of the diaphragmatic corticospinal pathways as well as to the diaphragm's functional peculiarities compared with the limb muscles.

Respiratory diseases and muscle dysfunction

Many respiratory diseases lead to impaired function of skeletal muscles, influencing quality of life and patient survival. Dysfunction of both respiratory and limb muscles in chronic obstructive pulmonary disease has been studied in depth, and seems to be caused by the complex interaction of general (inflammation, impaired gas exchange, malnutrition, comorbidity, drugs) and local factors (changes in respiratory mechanics and muscle activity, and molecular events). Some of these factors are also present in cystic fibrosis and asthma. In obstructive sleep apnea syndrome, repeated exposure to hypoxia and the absence of reparative rest are believed to be the main causes of muscle dysfunction. Deconditioning appears to be crucial for the functional impairment observed in scoliosis. Finally, cachexia seems to be the main mechanism of muscle dysfunction in advanced lung cancer. A multidimensional therapeutic approach is recommended, including pulmonary rehabilitation, an adequate level of physical activity, ventilatory support and nutritional interventions.

Sniff nasal inspiratory pressure and sleep disordered breathing in childhood neuromuscular disorders

The ease of sniff nasal inspiratory pressure testing may extend application of respiratory muscle assessment to younger and cognitively-impaired children. We sought to quantify sniff nasal inspiratory pressure in childhood neuromuscular disorders, and to correlate this measure with conventional pulmonary function tests and overnight polysomnography. Thirty children (mean 9.7 ± 3.8 years, range 4.3-16.5 years) with diagnosed neuromuscular disorders (Duchenne muscular dystrophy, spinal muscular atrophy, Becker muscular dystrophy, congenital myopathy, facioscapulohumeral muscular dystrophy, myotonic dystrophy, multi-minicore disease) underwent assessment. Thirty-seven percent displayed cognitive impairment. Those with neuromuscular disorders were then compared with 32 volunteer age- and gender-matched controls (mean 10.9 ± 2.9 years, range 6.6-17.2 years) with normal respiratory function. Twenty-three children with neuromuscular disorders also underwent overnight polysomnography. Children with neuromuscular disorders demonstrated significantly impaired sniff nasal inspiratory pressure, maximal inspiratory pressure, FEV(1) and FVC (p<0.05). A positive correlation was identified between daytime sniff nasal inspiratory pressure and maximal inspiratory pressure (r=0.58), FEV(1) (r=0.55) and FVC (r=0.46), though not with polysomnography variables (respiratory disturbance index, nadir SpO(2), peak CO(2)). Moderate prevalence of nocturnal hypoxia was observed, and 32% of children demonstrated sleep disordered breathing. Sniff nasal inspiratory pressure assessment was well tolerated, representing a promising surrogate measure for assessment of respiratory function in childhood neuromuscular disorders.

Mechanisms of skeletal muscle weakness

Skeletal muscle weakness is an important feature of numerous -pathological conditions and it may also be a component in normal ageing. Decreased muscular strength can be due to decreased muscle mass and/or intrinsic defects in the muscle cells. In this chapter we will discuss decreased force production due to mechanisms intrinsic to skeletal muscle cells. We will mainly use data from mouse disease models to exemplify defects at various sites in the cellular activation-contraction pathway. We will show that depending on the underlying problem, muscle weakness can be due decreased Ca²(+) release from the sarcoplasmic reticulum, reduced myofibrillar Ca²(+) sensitivity and/or decreased ability of the cross-bridges to generate force.

Excitation-contraction coupling and minor triadic proteins in low-frequency fatigue

Low-frequency fatigue (LFF) is characterized by a proportionally greater loss of force at low compared with high activation frequencies and a prolonged recovery. Recent work suggests a calcium-induced uncoupling of excitation-contraction coupling underlies LFF. Here, newly characterized triadic proteins are described, and possible mechanisms by which they may contribute to LFF are suggested.

Surgical Intensive Care Unit Mobility is Increased after Institution of a Computerized Mobility Order Set and Intensive Care Unit Mobility Protocol: A Prospective Cohort Analysis

In some populations, intensive care unit (ICU) mobility has been shown to be safe and beneficial. We gathered data on 50 nonintubated surgical patients in a 10-bed surgical ICU (SICU) who met physiologic inclusion criteria beginning in May 2008 (A group). In January 2009, we began mandatory entry of computerized mobility orders as part of a standardized ICU order set. We also created a mobility protocol for nurses in this ICU. We then collected data on 50 patients in this postintervention cohort (B group). Both groups had similar baseline characteristics. A group patients had some form of mobility orders entered in 29 patients (58%) versus 47 patients (82%) in the B group, P < 0.05. In the A group, 11 patients (22%) were mobilized; in the B group, 40 patients (80%) were mobilized, P < 0.05. In our SICU patient population, mandatory entry of computerized mobility orders as part of a standard SICU order set and establishment of an ICU mobility nursing protocol was associated with an increase in number of mobility orders entered as well as an increase in SICU patient activity. Further studies should focus on measurement of the effect of mobility interventions on patient outcomes.

Tension-time index as a predictor of extubation outcome in ventilated children

RATIONALE

Indices that assess the load on the respiratory muscles, such as the tension-time index (TTI), may predict extubation outcome.

OBJECTIVES

To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children.

METHODS

Eighty children (median [range] age 2.1 yr [0.15-16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied.

MEASUREMENTS AND MAIN RESULTS

TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n = 80) and TTdi greater than 0.15 (n = 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well.

CONCLUSIONS

Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.

Measurement of maximal inspiratory pressure in ventilated children

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX(OCC)) to that when a unidirectional valve (PIMAX(UNI)), which allowed expiration, but not inspiration was used. Twenty-two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX(UNI) was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX(UNI) (45.5 (15.2) cmH(2)O) was significantly greater than mean (SD) PIMAX(OCC) (30.9 (9.0) cmH(2)O) (P < 0.0001). The mean (SD) expired volume during PIMAX(UNI), was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15 sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 sec or eight breaths (99% CI of mean).

Diaphragm electromyography using an oesophageal catheter: current concepts

The usefulness of diaphragm electromyography recorded from an oesophageal electrode depends on a reliable signal which is free of artefact. The diaphragm EMG (electromyogram) recorded from chest wall surface electrodes may be unreliable because of signal contamination from muscle activity other than the diaphragm. Initially, the oesophageal electrode catheter for human studies had only one electrode pair, which could be difficult to position accurately and was influenced by a change in lung volume. Recently, a multipair oesophageal electrode has been developed which allows a high-quality EMG to be recorded. In the present review, the progress of oesophageal electrode design is outlined. The effects of signal contamination, electrode movement and particularly the effect of change in lung volume on the diaphragm EMG are discussed. The diaphragm EMG, recorded from a multipair oesophageal electrode, is useful to assess neural respiratory drive and diaphragm function in different groups of patients with respiratory disease, including patients with neuromuscular disease and sleep-disordered breathing, and those in the intensive care unit. When combined with cervical and cranial magnetic stimulation, an oesophageal electrode can be used to partition the central respiratory response time and phrenic nerve conduction time.

Pulmonary function, muscle strength and mortality in old age

Numerous reports have linked extremity muscle strength with mortality but the mechanism underlying this association is not known. We used data from 960 older persons without dementia participating in the Rush Memory and Aging Project to test two sequential hypotheses: first, that extremity muscle strength is a surrogate for respiratory muscle strength, and second, that the association of respiratory muscle strength with mortality is mediated by pulmonary function. In a series of proportional hazards models, we first demonstrated that the association of extremity muscle strength with mortality was no longer significant after including a term for respiratory muscle strength, controlling for age, sex, education, and body mass index. Next, the association of respiratory muscle strength with mortality was attenuated by more than 50% and no longer significant after including a term for pulmonary function. The findings were unchanged after controlling for cognitive function, parkinsonian signs, physical frailty, balance, physical activity, possible COPD, use of pulmonary medications, vascular risk factors including smoking, chronic vascular diseases, musculoskeletal joint pain, and history of falls. Overall, these findings suggest that pulmonary function may partially account for the association of muscle strength and mortality.

Weaning Strategies in Problem Patients

Weaning usually accounts for approximately 40–50% of the total duration of mechanical ventilation. Approximately two-thirds of patients can tolerate withdrawal of ventilation without the need for more gradual weaning, but there are a significant number of patients for whom weaning is difficult. Weaning failure is defined as the failure of a spontaneous breathing trial, or the need for re-intubation within 48 hours of extubation. This article reviews the causes of failure to wean, and outlines a practical approach to dealing with the difficult-to-wean patient. The key to successful weaning combines an approach which optimises ventilation at night, adopts a stepwise approach to reducing ventilatory dependence during the day, and uses non-invasive ventilation as a ‘bridge’ out of the ICU. Having a weaning protocol and ensuring it is initiated in a timely manner is likely to be as important as what is in the protocol.

Non-invasive ventilation applied for recovery from exercise-induced diaphragmatic fatigue

Background:

Exercise-induced diaphragmatic fatigue (DF) is conventionally considered to reflect impaired diaphragm function resulting from load imposed on the diaphragm during exercise and is known to be reduced by the application of non-invasive ventilation (NIV) during heavy-intensity exercise testing (HEET). On that physiological condition NIV applied for diaphragm unloading during recovery from exercise should be capable of accelerating recovery from DF and therewith prolonging exercise time to exhaustion and limiting the development of DF during a subsequent HEET compared to recovery during spontaneous breathing.

Methods:

Seven highly-trained subjects (V’O_2max 62.7±7.8 ml/kg/min) performed four HEET at 85% V’O_2max with 60 min of recovery during I spontaneous breathing and II NIV between two HEET.

Results:

Twitch transdiaphragmatic pressure (TwPdi) during supramaximal magnetic phrenic nerve stimulation decreased (p<0.04) following first HEET and subsequently completely recovered (p>0.2) during I and II. Following second HEET TwPdi comparably decreased (I 0.24±0.21 vs II 0.32±0.29 kPa; p=0.17). Exercise time to exhaustion during second HEET was equal during I and II (I 514±49 vs II 511±92 s; p=0.88).

Conclusions:

In conclusion, NIV applied for diaphragm unloading during recovery following HEET does neither affect recovery from DF nor subsequent exercise performance thereby providing further evidence that DF might reflect post-exercise diaphragm shielding rather than impaired diaphragm function.

Physiotherapy for adult patients with critical illness: recommendations of the European Respiratory Society and European Society of Intensive Care Medicine Task Force on Physiotherapy for Critically Ill Patients

The Task Force reviewed and discussed the available literature on the effectiveness of physiotherapy for acute and chronic critically ill adult patients. Evidence from randomized controlled trials or meta-analyses was limited and most of the recommendations were level C (evidence from uncontrolled or nonrandomized trials, or from observational studies) and D (expert opinion). However, the following evidence-based targets for physiotherapy were identified: deconditioning, impaired airway clearance, atelectasis, intubation avoidance, and weaning failure. Discrepancies and lack of data on the efficacy of physiotherapy in clinical trials support the need to identify guidelines for physiotherapy assessments, in particular to identify patient characteristics that enable treatments to be prescribed and modified on an individual basis. There is a need to standardize pathways for clinical decision-making and education, to define the professional profile of physiotherapists, and increase the awareness of the benefits of prevention and treatment of immobility and deconditioning for critically ill adult patients.

Diabetic polyneuropathy is associated with respiratory muscle impairment in type 2 diabetes

AIMS/HYPOTHESIS

Diabetes has a major negative effect on intensive care unit outcome. This has been partly attributed to impaired respiratory neuromuscular function. However, data on respiratory neuromuscular involvement in diabetes are lacking. This study therefore aimed to assess respiratory neuromuscular function related to diabetic polyneuropathy in patients with type 2 diabetes.

METHODS

Respiratory neuromuscular function was assessed by the use of volitional tests and twitch mouth (TwPmo) and twitch transdiaphragmatic (TwPdi) pressures during non-volitional bilateral anterior magnetic phrenic nerve stimulation in 21 male type 2 diabetic patients without pulmonary disease and in 23 healthy, well-matched controls (forced expiratory volume in 1 s 103 +/- 11 vs 103 +/- 12% predicted; p = 0.9).

RESULTS

Both volitionally assessed maximal inspiratory and expiratory mouth pressures, and sniff nasal and transdiaphragmatic pressures were comparable between diabetic patients and controls (p > 0.1 for all). TwPmo was reduced in diabetic patients compared with controls (1.3 +/- 0.5 vs 1.0 +/- 0.4 kPa; p = 0.04), while TwPdi was comparable (1.7 +/- 0.5 vs 1.6 +/- 0.7 kPa; p = 0.6). Following subgroup analysis, patients with no or mild polyneuropathy (n = 10) as assessed by neurological disability scoring had normal respiratory neuromuscular function, whereas patients with moderate or severe polyneuropathy (n = 11) presented with markedly impaired respiratory neuromuscular function as indicated by TwPmo (1.3 +/- 0.4 vs 0.8 +/- 0.3 kPa; p = 0.01) and TwPdi (1.9 +/- 0.6 vs 1.1 +/- 0.4 kPa; p < 0.01).

CONCLUSIONS/INTERPRETATION

With regard to volitional tests, diabetes does not affect respiratory neuromuscular function. In contrast, the application of non-volitional phrenic nerve stimulation provides strong evidence that diabetic polyneuropathy, as simply assessed by neurological disability scoring, is associated with substantially impaired respiratory neuromuscular function in type 2 diabetic patients.

Reactive oxygen species and fatigue-induced prolonged low-frequency force depression in skeletal muscle fibres of rats, mice and SOD2 overexpressing mice

Skeletal muscle often shows a delayed force recovery after fatiguing stimulation, especially at low stimulation frequencies. In this study we focus on the role of reactive oxygen species (ROS) in this fatigue-induced prolonged low-frequency force depression. Intact, single muscle fibres were dissected from flexor digitorum brevis (FDB) muscles of rats and wild-type and superoxide dismutase 2 (SOD2) overexpressing mice. Force and myoplasmic free [Ca(2+)] ([Ca(2+)](i)) were measured. Fibres were stimulated at different frequencies before and 30 min after fatigue induced by repeated tetani. The results show a marked force decrease at low stimulation frequencies 30 min after fatiguing stimulation in all fibres. This decrease was associated with reduced tetanic [Ca(2+)](i) in wild-type mouse fibres, whereas rat fibres and mouse SOD2 overexpressing fibres instead displayed a decreased myofibrillar Ca(2+) sensitivity. The SOD activity was approximately 50% lower in wild-type mouse than in rat FDB muscles. Myoplasmic ROS increased during repeated tetanic stimulation in rat fibres but not in wild-type mouse fibres. The decreased Ca(2+) sensitivity in rat fibres could be partially reversed by application of the reducing agent dithiothreitol, whereas the decrease in tetanic [Ca(2+)](i) in wild-type mouse fibres was not affected by dithiothreitol or the antioxidant N-acetylcysteine. In conclusion, we describe two different causes of fatigue-induced prolonged low-frequency force depression, which correlate to differences in SOD activity and ROS metabolism. These findings may have clinical implications since ROS-mediated impairments in myofibrillar function can be counteracted by reductants and antioxidants, whereas changes in SR Ca(2+) handling appear more resistant to interventions.

Inspiratory muscle strength in chronic obstructive pulmonary disease depending on disease severity

Staging criteria for COPD (chronic obstructive pulmonary disease) include symptoms and lung function parameters, but the role of reduced inspiratory muscle strength related to disease severity remains unclear. Therefore the present study tested whether inspiratory muscle strength is reduced in COPD and is related to disease severity according to GOLD (Global Initiative for Chronic Obstructive Lung Disease) criteria and assessed its clinical impact. PImax (maximal inspiratory mouth occlusion pressure), SnPna (sniff nasal pressure) and TwPmo (twitch mouth pressure) following bilateral anterior magnetic phrenic nerve stimulation were assessed in 33 COPD patients (8 GOLD0, 6 GOLDI, 6 GOLDII, 7 GOLDIII and 6 GOLDIV) and in 28 matched controls. Furthermore, all participants performed a standardized 6 min walking test. In comparison with controls, PImax (11.6±2.5 compared with 7.3±3.0 kPa; P<0.001), SnPna (9.7±2.5 compared with 6.9±3.3 kPa; P<0.001) and TwPmo (1.6±0.6 compared with 0.8±0.4 kPa; P<0.001) were markedly lower in COPD patients. TwPmo decreased with increasing COPD stage. TwPmo was correlated with walking distance (r=0.75; P<0.001), dyspnoea (r=−0.61; P<0.001) and blood gas values following exercise (r>0.57; P<0.001). Inspiratory muscle strength, as reliably assessed by TwPmo, decreased with increasing severity of COPD and should be considered as an important factor in rating disease severity and to reflect burden in COPD.

New physiological insights into exercise-induced diaphragmatic fatigue

Data on the dynamic process and time-point of manifestation of exercise-induced diaphragmatic fatigue (DF) are lacking. Therefore, this study was aimed assessing dynamic changes of diaphragmatic strength during exercise and determining the time-point of DF manifestation. Fourteen trained subjects (maximal oxygen uptake (VO2(max)) 59.3+/-5.5 ml/min/kg) performed standardized exercise protocols (maximal workload: 85% VO2(max)) followed by recovery (6 min). Ergospirometric data and twitch transdiaphragmatic pressure (TwPdi) were consecutively assessed. DF was induced (TwPdi-rest: 2.34+/-0.26 versus TwPdi-end-recovery 2.01+/-0.21 kPa, p<0.01). TwPdi progressively increased during exercise (TwPdi-rest: 2.34+/-0.26 versus TwPdi-maximal-workload: 3.28+/-0.38 kPa, p<0.001). DF was detectable immediately after exercise-termination (TwPdi-maximal-workload: 3.28+/-0.38 versus TwPdi-early-recovery 2.55+/-0.34 kPa, p<0.001). TwPdi during exercise was highly correlated to workload, VO2(max) and dyspnea (r=0.96/r=0.92/r=0.97; all p<0.0001). In conclusion, diaphragmatic strength progressively increases with increasing workload, and DF manifests after - rather than during - exercise. In addition, TwPdi is highly correlated to key-measures of ergospirometry, approving the physiological thesis that muscle strength is progressively enhanced and escapes fatiguing failure during high-intensity exercise performance.

Moving our critically ill patients: mobility barriers and benefits

Diagnosis and resuscitation for critically ill patients have improved in the last 25 years, and survival has also increased. With improvements in mortality, the field of critical care has seen increased opportunities to improve posthospital quality of life for survivors of critical illness. This article focuses particularly on how mobilization may improve quality of life for patients.

Impact of impaired inspiratory muscle strength on dyspnea and walking capacity in sarcoidosis

BACKGROUND

Dyspnea and fatigue are frequent but poorly understood symptoms in sarcoidosis patients. This study was aimed at assessing the clinical impact of inspiratory muscle impairment on dyspnea and exercise tolerance. This is the first study using nonvolitional tests that are independent of the patient's cooperation and motivation in addition to volitional tests of inspiratory muscle strength in patients with sarcoidosis.

METHODS

Peak maximal inspiratory mouth pressure (Pimaxpeak), maximal inspiratory pressure sustained for 1.0 s (Pimax1.0), twitch mouth pressure (TwPmo), lung function test results, blood gas measurements, 6-min walking distance (6MWD), and Borg dyspnea scale (BDS) scores were assessed in 24 male sarcoidosis patients and 24 healthy male control subjects matched for age and body mass index.

RESULTS

Mean (+/- SD) Pimaxpeak (95.2 +/- 25.3% vs 124.6 +/- 23.4% predicted, respectively; p < 0.001) and Pimax1.0 (85.6 +/- 31.4% vs 125.8 +/- 26.8% predicted, respectively; p < 0.001) were lower in sarcoidosis patients compared to control subjects. TwPmo tended to be lower in sarcoidosis patients, and there were three patients who had TwPmo values of < 1.0 kPa, which is a strong indicator of inspiratory muscle weakness. The mean 6MWD was 582 +/- 97 m in sarcoidosis patients and 638 +/- 65 in control subjects (p = 0.025). The mean BDS score was higher in sarcoidosis patients (3.3 +/- 1.7 vs 0.2 +/- 0.5, respectively; p < 0.001). Compared to maximal inspiratory pressure, lung function parameters, and blood gas levels, TwPmo was the strongest predictor for 6MWD (r = 0.663; p = 0.003) and BDS score (r = 0.575; p = 0.012) in sarcoidosis patients following multiple linear regression analysis.

CONCLUSIONS

Impairment of inspiratory muscle strength occurs in sarcoidosis patients, and has been suggested to be an important factor causing dyspnea and reduced walking capacity, but this is only reliably detectable when using nonvolitional tests of inspiratory muscle strength.

Controlled twitch mouth pressure reliably predicts twitch esophageal pressure

The present study hypothesized that twitch mouth pressure (TwPmo) can reliably predict intrathoracic pressure swings reflected by twitch esophageal pressure (TwPes) using a controlled and automated trigger technique. TwPmo, TwPes, and transdiaphragmatic pressure (TwPdi) following bilateral anterior magnetic phrenic nerve stimulation were measured in 21 healthy subjects using an inspiratory pressure trigger (0.5kPa, experiment 1), an expiratory pressure trigger (0.5kPa, experiment 2), an inspiratory flow trigger (40ml/s, experiment 3), and no trigger at relaxed functional residual capacity (experiment 4). TwPmo and TwPes were correlated as follows: r=0.99, p<0.0001 (experiment 1); r=0.67, p=0.001 (experiment 2); r=0.96, p<0.0001 (experiment 3); no correlation (experiment 4). Bland and Altman analysis revealed most narrow limits of agreement for TwPmo and TwPes in experiment 1: bias (range) 0.15kPa (-0.03 to 0.32). TwPmo is an excellent predictor for TwPes when using a fully automated and controlled inspiratory pressure trigger. Thus, measurement of TwPmo could become a standard means assessing inspiratory muscle strength.

Electrophysiologic evaluation of phrenic nerve and diaphragm function after coronary bypass surgery: Prospective study of diabetes and other risk factors

OBJECTIVE

Phrenic neuropathy after coronary artery bypass grafting has been related to various risk factors with conflicting results. The aim of this study was to assess the incidence, characteristics, and clinical consequences of phrenic neuropathy and the influence of diabetes and other risk factors.

METHODS

We conducted an observational, prospective study of parallel groups including 94 consecutive patients subjected to coronary artery bypass grafting, half of them with diabetes and associated polyneuropathy. Electrophysiologic study of phrenic nerve conduction as the reference method, chest radiography, diaphragm ultrasound, and functional respiratory tests were performed 24 to 48 hours before and 7 days after surgery. In those patients showing phrenic neuropathy, explorations were repeated, including needle diaphragmatic electromyography, at 1, 3, 6, 9, 12, 18, and 24 months or until recovery.

RESULTS

Fifteen of the 94 patients (16%) had phrenic neuropathy, 9 in the left side, 3 on the right, and 3 bilateral. Nine (60%) of the affected patients had diabetes, but diabetes did not represent a greater risk of neuropathy (relative risk 1.5, 95% confidence interval 0.6-3.9). Multivariate analysis showed no association of phrenic nerve injury with age, sex, ejection fraction, diabetes, use of internal thoracic artery, or number of grafts as risk factors. Phrenic neuropathy did not result in greater morbidity, and most patients recovered in less than 1 year.

CONCLUSIONS

None of the risk factors studied, including diabetes, influenced the appearance of phrenic neuropathy, thus indicating a role for nerve damage during surgery. Low morbidity and relatively rapid recovery were observed.

Muscle force and fatigue in patients with sepsis and multiorgan failure

INTRODUCTION

Neuromuscular abnormalities are found frequently in sepsis and multiorgan failure (MOF). Surprisingly, however, there are no data on maximum skeletal muscle force and fatigue in these patients.

OBJECTIVES

To test the research hypotheses that adductor pollicis (AP) force would be lower in patients with sepsis, whereas fatigue would not differ between patients and immobilized but not infected volunteers.

DESIGN AND SETTING

Prospective study; university intensive care unit and laboratory.

PATIENTS

Patients with sepsis and MOF (sequential organ failure assessment (SOFA) score >10) and healthy volunteers.

INTERVENTIONS

Fatigue was evoked during 20[Symbol: see text]min of intermittent tetanic ulnar nerve stimulation achieving 50% of maximum AP muscle force.

MEASUREMENTS AND RESULTS

We measured evoked AP muscle force and fatigue, and compound muscle action potential (CMAP), and performed standard electrophysiological tests in 13 patients, and in 7 volunteers before and after immobilization. Maximum force (20+/-16 vs 65+/-19N; p<0.01) and CMAP (3.6+/-2.5 vs 10+/-2.5 mV; p<0.05) were markedly decreased in patients; however, fatigue and ulnar nerve conduction velocity did not differ from volunteers, and a decrement of CMAP was not observed with nerve stimulation frequencies up to 40 Hz. All patients with critical illness polyneuropathy, and an additional 50% of those without, had significant muscle weakness.

CONCLUSION

Peripheral muscle force is markedly decreased in sepsis, without evidence for an increased fatigability. Muscle weakness was most likely due to a sepsis-induced myopathy and/or axonal neuropathy, and was not the result of an immobilization atrophy.

N-ACETYLCYSTEINE PROTECTS THE RATS AGAINST PHRENIC NERVE DYSFUNCTION IN SEPSIS

This study investigates the association of oxidative stress with the function of the phrenic nerve and inquires whether N-acetylcysteine (NAC) may counteract the possible detrimental effects. Thirty rats were divided into three groups: sham, cecal ligation and puncture (CLP), and CLP plus NAC treatment. Sepsis was produced by the CLP procedure. NAC was administered at 70 mg/day for 7 days. Electrophysiology was evaluated by the needle electromyography of the diaphragm and phrenic nerve conduction study. Oxidative stress was evaluated by malondialdehyde (MDA), nitrite/nitrate (NN), and reduced-glutathione (ReGSH) levels and myeloperoxidase (MPO) and catalase (CAT) activities in the phrenic nerve. In the CLP group, ReGSH and CAT were decreased (P = 0.0001, P = 0.07, respectively); and MDA, MPO, and NN were increased (P = 0.02, P = 0.0001, P = 0.043, respectively), compared with the sham group. NAC administration increased the ReGSH (P = 0.036) and decreased the MDA, MPO, and NN (P = 0.008, P = 0.01, P = 0.032, respectively), compared with the CLP group. In the CLP group, electrophysiology revealed reductions in the number of motor unit action potentials (P = 0.0001) and prolongations in the latency of the compound nerve action potential (P = 0.0001), indicating phrenic nerve neuropathy. NAC administration significantly ameliorated these electrophysiological alterations (P = 0.011, P = 0.0001, respectively), compared with the CLP group. The present results showed that intraabdominal sepsis is closely associated with phrenic nerve neuropathy. In addition, NAC administration protects the rats against the detrimental events of sepsis.

Inspiratory muscular activation during threshold® therapy in elderly healthy and patients with COPD

Inspiratory muscles training in COPD is controversial not only in relation to the load level required to produce muscular conditioning effects but also in relation to the group of patients benefiting from the training. Consequently, inspiratory muscular response assessment during Threshold therapy may help optimizing training strategy. The objective of this study was to evaluate the participation of the diaphragm and the sternocleidomastoid (SMM) muscle to overcome with a 30% Threshold load using surface electromyography (sEMG) and to analyze the correlation between SMM activation, maximum strength level of inspiratory muscles (MIP) and obstruction degree in COPD patients (FEV1). We studied seven healthy elderly subjects, mean age of 68+/-4 years and seven COPD patients, FEV1 45+/-17% of the predicted value, with mean age 66+/-8 years. sEMG analysis of SMM muscles and diaphragm were obtained through RMS (root-mean-square) during three stages: pre-loading, loading and post-loading.

RESULTS

In the COPD group, the RMS of the SMM increased 28% during load (p<0.05) while the RMS of the diaphragm remained constant. In the elderly there was a trend of a 11% increase in diaphragm activity and of 7% in SMM activity but, without reaching significance levels. SMM activity demonstrated good correlation with the obstruction level (r=-0.537).

CONCLUSION

To overcome the load required by Threshold therapy, COPD patients demonstrated an increase of accessory muscles activity, represented by SMM. For the same relative load this increase seems to be proportional to the degree of pulmonary obstruction.

Rehabilitation of medical and acute care patients

Cancer and serious systemic illness result in several physiologic changes that involve multiple body systems. While the primary conditions are addressed with traditional modalities of medicine, the side effects, secondary changes, and complications can be ameliorated or even prevented with rehabilitation and supportive care. This article reviews problems facing the oncologic and critically ill animal, discusses basic techniques in the management of these animals, and highlights the essential role of rehabilitation in obtaining maximal functional capacity in the critically ill patient.

Influence of different trigger techniques on twitch mouth pressure during bilateral anterior magnetic phrenic nerve stimulation

BACKGROUND

The trigger has a key role when assessing the twitch mouth pressure (Tw Pmo), since a "gentle" inspiratory or expiratory effort is needed for triggering to ensure an open glottis during twitch, but which also guarantees only very mild changes of transdiaphragmatic pressure following changes in lung volume.

STUDY OBJECTIVES

To test if different trigger mechanisms cause different Tw Pmo values, if the predefined trigger criteria were accomplished, and if the breathing maneuver during triggering can influence the Tw Pmo.

DESIGN

Experimental study.

SETTING

Respiratory muscle and lung function laboratory of a university hospital.

PARTICIPANTS

Twenty healthy men (mean age, 25.6 +/- 1.2 years [+/- SD]; mean FEV(1), 105.9 +/- 11.5% of predicted).

MEASUREMENTS

Tw Pmo produced by bilateral anterior magnetic phrenic nerve stimulation was measured using an inspiratory flow trigger (40 mL/s), an inspiratory pressure trigger, and an expiratory pressure trigger (3.75 mm Hg). All trigger criteria were controlled.

RESULTS

Unusable pressure-time curves occurred in 40% during expiratory triggering, but not during inspiratory triggering. For inspiratory pressure (flow) triggering, 10% (30%) of the predefined trigger criteria were exceeded by 50%, indicating that a "gentle" inspiratory effort was not warranted. The Tw Pmo was higher during inspiratory compared to expiratory triggering (analysis of variance, p < 0.05). The Tw Pmo during inspiratory pressure and flow triggering were comparable and significantly correlated (r = 0.70, p < 0.0001). The time between start of inspiration and trigger release, and the pressure-time product during that period ranged widely, but this could not predict the Tw Pmo (multiple linear regression).

CONCLUSIONS

The trigger technique influences the Tw Pmo with higher values during inspiratory compared to expiratory triggering. Expiratory triggering more often produced unusable pressure-time curves. Inspiratory flow and pressure triggering is comparably useful in healthy subjects, but this might be different in patients. The trigger criteria need to be controlled to warrant a gentle breathing effort.

Intrafractional tumor motion: lung and liver

Three-dimensional (3D) dose distribution has been improved by 3D conformation and intensity modulation in external radiotherapy. Interfractional uncertainty has been reduced by image-guided setup techniques. Reduction of ambiguity because of intrafractional target motion is the next step forward. Respiratory organ motion is known to be the largest intrafractional organ motion. Radiotherapy techniques controlling, gating, or tracking respiratory motion are under investigation to use smaller safety margins and higher doses for moving tumors. However, data on intrafractional tumor motion are sparse. We developed a fluoroscopic real-time tracking system and implantation techniques of fiducial markers for moving organs and have been accumulating knowledge about internal tumor motion. We also found the importance of 4-dimensional treatment planning to account for tumor motion in precision radiotherapy. This article reviews the current basic knowledge on respiratory physiology and summarizes the accumulating knowledge on internal motion of lung and liver tumors.

The neurologic assessment and treatment of the “difficult to extubate” patient

Neurologic issues are involved in the patient who is difficult to wean. Assessing the patient and performing a complete neurologic examination are important when developing a successful weaning strategy. The neurologist contributes to this process by providing expertise in the various neurologic conditions and skill in performing a thorough neurologic examination.