Diaphragm muscle fiber injury after inspiratory resistive breathing

Dynamic equilibrium of skeletal muscle macrophage ontogeny in the diaphragm during homeostasis, injury, and recovery

The diaphragm is a unique skeletal muscle due to its continuous activation pattern during the act of breathing. The ontogeny of macrophages, pivotal cells for skeletal muscle maintenance and regeneration, is primarily based on two distinct origins: postnatal bone marrow-derived monocytes and prenatal embryonic progenitors. Here we employed chimeric mice to study the dynamics of these two macrophage populations under different conditions. Traditional chimeric mice generated through whole body irradiation showed virtually complete elimination of the original tissue-resident macrophage pool. We then developed a novel method which employs lead shielding to protect the diaphragm tissue niche from irradiation. This allowed us to determine that up to almost half of tissue-resident macrophages in the diaphragm can be maintained independently from bone marrow-derived monocytes under steady-state conditions. These findings were confirmed by long-term (5 months) parabiosis experiments. Acute diaphragm injury shifted the macrophage balance toward an overwhelming predominance of bone marrow (monocyte)-derived macrophages. However, there was a remarkable reversion to the pre-injury ontological landscape after diaphragm muscle recovery. This diaphragm shielding method permits analysis of the dynamics of macrophage origin and corresponding function under different physiological and pathological conditions. It may be especially useful for studying diseases which are characterized by acute or chronic injury of the diaphragm and accompanying inflammation.

The oesophageal balloon for respiratory monitoring in ventilated patients: updated clinical review and practical aspects

There is a well-recognised importance for personalising mechanical ventilation settings to protect the lungs and the diaphragm for each individual patient. Measurement of oesophageal pressure (P oes) as an estimate of pleural pressure allows assessment of partitioned respiratory mechanics and quantification of lung stress, which helps our understanding of the patient's respiratory physiology and could guide individualisation of ventilator settings. Oesophageal manometry also allows breathing effort quantification, which could contribute to improving settings during assisted ventilation and mechanical ventilation weaning. In parallel with technological improvements, P oes monitoring is now available for daily clinical practice. This review provides a fundamental understanding of the relevant physiological concepts that can be assessed using P oes measurements, both during spontaneous breathing and mechanical ventilation. We also present a practical approach for implementing oesophageal manometry at the bedside. While more clinical data are awaited to confirm the benefits of P oes-guided mechanical ventilation and to determine optimal targets under different conditions, we discuss potential practical approaches, including positive end-expiratory pressure setting in controlled ventilation and assessment of inspiratory effort during assisted modes.

Hypercapnia in Advanced Chronic Obstructive Pulmonary Disease: A Secondary Analysis of the National Emphysema Treatment Trial

RATIONALE

Hypercapnia develops in one third of patients with advanced chronic obstructive pulmonary disease (COPD) and is associated with increased morbidity and mortality. Multiple factors in COPD are thought to contribute to the development of hypercapnia including increased carbon dioxide (CO2) production, increased dead space ventilation, and the complex interactions of deranged respiratory system mechanics, inspiratory muscle overload and the ventilatory control center in the brainstem. However, these factors have not previously been systematically analyzed in a large, well-characterized population of severe COPD patients.

METHODS

This is a secondary analysis of the clinical, physiologic and imaging data from the National Emphysema Treatment Trial (NETT). All patients with complete baseline data for the key predictor variables were included. An inclusive list of 32 potential predictor variables were selected a priori based on consensus of the investigators and literature review. Stepwise variable selection yielded 10 statistically significant associations in multivariate regression.

RESULTS

A total of 1419 patients with severe COPD were included in the analysis; mean age 66.4 years (standard deviation 6.3), 38% females, and 422 (29.7%) had baseline hypercapnia. Key variables associated with hypercapnia were low resting partial pressure of oxygen in blood, low minute ventilation (Ve), high volume of exhaled carbon dioxide, low forced expiratory volume in 1 second, high residual volume, lower % emphysema on chest computed tomography, use of oxygen, low ventilatory reserve (high Ve/maximal voluntary ventilation), and not being at high altitude. Low diffusing capacity for carbon monoxide showed a positive association with hypercapnia in univariate analysis but a negative correlation in multivariate analysis. Measures of dyspnea and quality of life did not associate with degree of hypercapnia in multivariable analysis.

CONCLUSION

Hypercapnia in a well-characterized cohort with severe COPD and emphysema is chiefly related to poor lung mechanics, high CO2 production, and a reduced ventilatory capability. Hypercapnia is less impacted by gas exchange abnormalities or the presence of emphysema.

Respiratory muscle senescence in ageing and chronic lung diseases

Ageing is a progressive condition that usually leads to the loss of physiological properties. This process is also present in respiratory muscles, which are affected by both senescent changes occurring in the whole organism and those that are more specific for muscles. The mechanisms of the latter changes include oxidative stress, decrease in neurotrophic factors and DNA abnormalities. Ageing normally coexists with comorbidities, including respiratory diseases, which further deteriorate the structure and function of respiratory muscles. In this context, changes intrinsic to ageing become enhanced by more specific factors such as the impairment in lung mechanics and gas exchange, exacerbations and hypoxia. Hypoxia in particular has a direct effect on muscles, mainly through the expression of inducible factors (hypoxic-inducible factor), and can result in oxidative stress and changes in DNA, decrease in mitochondrial biogenesis and defects in the tissue repair mechanisms. Intense exercise can also cause damage in respiratory muscles of elderly respiratory patients, but this can be followed by tissue repair and remodelling. However, ageing interferes with muscle repair by tampering with the function of satellite cells, mainly due to oxidative stress, DNA damage and epigenetic mechanisms. In addition to the normal process of ageing, stress-induced premature senescence can also occur, involving changes in the expression of multiple genes but without modifications in telomere length.

ERS statement on respiratory muscle testing at rest and during exercise

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

Assessing breathing effort in mechanical ventilation: physiology and clinical implications

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

Respiratory Training Late After Fontan Intervention: Impact on Cardiorespiratory Performance

Fontan palliation allows patients with "single ventricle" circulation to reach adulthood with an acceptable quality of life, although exercise tolerance is significantly reduced. To assess whether controlled respiratory training (CRT) increases cardiorespiratory performance. 16 Adolescent Fontan patients (age 17. 5 ± 3.8 years) were enrolled. Patients were divided into CRT group (n = 10) and control group (C group, n = 6). Maximal cardiopulmonary test (CPT) was repeated at the end of CRT in the CRT group and after an average time of 3 months in the C group. In the CRT group a CPT endurance was also performed before and after CRT. In the CRT group there was a significant improvement in cardiovascular and respiratory response to exercise after CRT. Actually, after accounting for baseline values, the CRT group had decreased breathing respiratory reserve (- 15, 95% CI -22.3 to - 8.0, p = 0.001) and increased RR peak (+ 4.8, 95% CI 0.7-8.9, p = 0.03), VE peak (+ 13.7, 95% CI 5.6-21.7, p = 0.004), VO2 of predicted (+ 8.5, 95% CI 0.1-17.0, p = 0.05), VO2 peak (+ 4.3, 95% CI 0.3 to 8.2, p = 0.04), and VO2 workslope (+ 1.7, 95% CI 0.3-3.1, p = 0.02) as compared to the control group. Moreover, exercise endurance time increased from 8.45 to 17.7 min (p = 0.01). CRT improves cardiorespiratory performance in post-Fontan patients leading to a better aerobic capacity.

Preoperative physiotherapy in subjects with idiopathic pulmonary fibrosis qualified for lung transplantation: implications on hospital length of stay and clinical outcomes

BACKGROUND

Lung transplantation (LTx) candidates with chronic disease are more prone to exercise limitations. Preoperative physiotherapy (PP) can improve exercise tolerance, which in some patients, is severely impaired, often leaving them housebound. The aim of this study was to answer this question: In patients with idiopathic pulmonary fibrosis (IPF) qualifying for LTx, is PP effective in improving postoperative outcomes and reducing length of stay (LOS) after transplantation?

METHODS

Six major databases were searched up to December 2015. We did not apply limits to publication date, date, gender, or language. Citations were accepted if they discussed preoperative physiotherapeutic treatment in patients with IPF waiting for LTx.

RESULTS

After the full texts were read, three papers met the inclusion criteria and were included. All of these papers had an observational design. In total, 55 subjects with IPF and awaiting LTx were observed.

CONCLUSIONS

The effectiveness of PP in improving postoperative outcomes and reducing LOS following LTx remains unclear, although it appears to benefit IPF patients who qualify for LTx by improving their health status, physical activity levels, and respiratory-related symptoms.

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.

Ventilatory failure, ventilator support, and ventilator weaning

The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system.

Ventilation and respiratory mechanics

During dynamic exercise, the healthy pulmonary system faces several major challenges, including decreases in mixed venous oxygen content and increases in mixed venous carbon dioxide. As such, the ventilatory demand is increased, while the rising cardiac output means that blood will have considerably less time in the pulmonary capillaries to accomplish gas exchange. Blood gas homeostasis must be accomplished by precise regulation of alveolar ventilation via medullary neural networks and sensory reflex mechanisms. It is equally important that cardiovascular and pulmonary system responses to exercise be precisely matched to the increase in metabolic requirements, and that the substantial gas transport needs of both respiratory and locomotor muscles be considered. Our article addresses each of these topics with emphasis on the healthy, young adult exercising in normoxia. We review recent evidence concerning how exercise hyperpnea influences sympathetic vasoconstrictor outflow and the effect this might have on the ability to perform muscular work. We also review sex-based differences in lung mechanics.

Sedation and paralysis

Sedation is used almost universally in the care of critically ill patients, especially in those who require mechanical ventilatory support or other life-saving invasive procedures. This review will focus on the sedation strategies for critically ill patients and the pharmacology of commonly used sedative agents. The role of neuromuscular blocking agents in the ICU will be examined and the pharmacology of commonly used agents is reviewed. Finally a strategy for rational use of these sedative and neuromuscular blocking agents in critically ill patients will be proposed.

Chronic intrinsic transient tracheal occlusion elicits diaphragmatic muscle fiber remodeling in conscious rodents

BACKGROUND

Although the prevalence of inspiratory muscle strength training has increased in clinical medicine, its effect on diaphragm fiber remodeling is not well-understood and no relevant animal respiratory muscle strength training-rehabilitation experimental models exist. We tested the postulate that intrinsic transient tracheal occlusion (ITTO) conditioning in conscious animals would provide a novel experimental model of respiratory muscle strength training, and used significant increases in diaphragmatic fiber cross-sectional area (CSA) as the primary outcome measure. We hypothesized that ITTO would increase costal diaphragm fiber CSA and further hypothesized a greater duration and magnitude of occlusions would amplify remodeling.

METHODOLOGY/PRINCIPAL FINDINGS

Sprague-Dawley rats underwent surgical placement of a tracheal cuff and were randomly assigned to receive daily either 10-minute sessions of ITTO, extended-duration, 20-minute ITTO (ITTO-20), partial obstruction with 50% of cuff inflation pressure (ITTO-PAR) or observation (SHAM) over two weeks. After the interventions, fiber morphology, myosin heavy chain composition and CSA were examined in the crural and ventral, medial, and dorsal costal regions. In the medial costal diaphragm, with ITTO, type IIx/b fibers were 26% larger in the medial costal diaphragm (p<0.01) and 24% larger in the crural diaphragm (p<0.05). No significant changes in fiber composition or morphology were detected. ITTO-20 sessions also yielded significant increases in medial costal fiber cross-sectional area, but the effects were not greater than those elicited by 10-minute sessions. On the other hand, ITTO-PAR resulted in partial airway obstruction and did not generate fiber hypertrophy.

CONCLUSIONS/SIGNIFICANCE

The results suggest that the magnitude of the load was more influential in altering fiber cross-sectional area than extended-duration conditioning sessions. The results also indicated that ITTO was associated with type II fiber hypertrophy in the medial costal region of the diaphragm and may be an advantageous experimental model of clinical respiratory muscle strength training.

Electrical activity of the diaphragm during extubation readiness testing in critically ill children

OBJECTIVES

To investigate the electrical activity of the diaphragm during extubation readiness testing.

DESIGN

Prospective observational trial.

SETTING

A 29-bed medical-surgical pediatric intensive care unit.

PATIENTS

Mechanically ventilated children between 1 month and 18 yrs of age.

INTERVENTIONS

Twenty patients underwent a standardized extubation readiness test using a minimal pressure support ventilation strategy. A size-appropriate multiple-array esophageal electrode (electrical diaphragmatic activity catheter), which doubled as a feeding tube, was inserted. The electrical diaphragmatic activity, ventilatory parameters, and spirometry measurements were recorded with the Servo-i ventilator (Maquet, Solna, Sweden). Measurements were obtained before the extubation readiness test and 1 hr into the extubation readiness test.

MEASUREMENTS AND MAIN RESULTS

During extubation readiness testing, the ratio of tidal volume to delta electrical diaphragmatic activity was significantly lower in those patients who passed the extubation readiness test compared to those who failed the extubation readiness test (extubation readiness test, pass: 24.8 ± 20.9 mL/μV vs. extubation readiness test, fail: 67.2 ± 27 mL/μV, respectively; p = .02). Delta electrical diaphragmatic activity correlated significantly with neuromuscular drive assessed by airway opening pressure at 0.1 secs (before extubation readiness test: r = .591, p < .001; during extubation readiness test: r = .682, p < .001). Eight out of 20 patients had ventilator dys-synchrony identified with electrical diaphragmatic activity during extubation readiness testing.

CONCLUSIONS

Patients who generate higher diaphragmatic activity in relation to tidal volume may have better preserved diaphragmatic function and a better chance of passing the extubation readiness test as opposed to patients who generate lower diaphragmatic activity in relation to tidal volume, indicating diaphragmatic weakness. Electrical activity of the diaphragm also may be a useful adjunct to assess neuromuscular drive in ventilated children.

Role of the respiratory muscles in acute respiratory failure of COPD: lessons from weaning failure

It is problematic to withhold therapy in a patient with chronic obstructive pulmonary disease (COPD) who presents with acute respiratory failure so that detailed physiological measurements can be obtained. Accordingly, most information on respiratory muscle activity in patients experiencing acute respiratory failure has been acquired by studying patients who fail a trial of weaning after a period of mechanical ventilation. Such patients experience marked increases in inspiratory muscle load consequent to increases in resistance, elastance, and intrinsic positive end-expiratory pressure. Inspiratory muscle strength is reduced secondary to hyperinflation and possibly direct muscle damage and the release of inflammatory mediators. Most patients recruit both their sternomastoid and expiratory muscles, even though airflow limitation prevents the expiratory muscles from lowering lung volume. Even when acute hypercapnia is present, patients do not exhibit respiratory center depression; indeed, voluntary activation of the diaphragm, in absolute terms, is greater in hypercapnic patients than in normocapnic patients. Instead, the major mechanism of acute hypercapnia is the development of rapid shallow breathing. Despite the marked increase in mechanical load and decreased force-generating capacity of the inspiratory muscles, patients do not develop long-lasting muscle fatigue, at least over the period of a failed weaning trial. Although the disease originates within the lung parenchyma, much of the distress faced by patients with COPD, especially during acute respiratory failure, is caused by the burdens imposed on the respiratory muscles.

Impaired isotonic contractility and structural abnormalities in the diaphragm of congestive heart failure rats

BACKGROUND

Metabolic alterations and decreased isometric force generation have been demonstrated in different animal models for congestive heart failure (CHF). However, as few morphological examinations have been performed on the CHF diaphragm, it is unknown if structural abnormalities comprise a substrate for diaphragm dysfunction in CHF. Therefore, we investigated CHF diaphragm isometric and isotonic contractility together with the presence of structural abnormalities.

METHODS

Isometric twitch (P(t)) and maximal (P(o)) force, shortening velocity and power generation were determined in diaphragm bundles from rats with CHF, induced by myocardial infarction, and sham-operated rats. Immunofluorescence staining of myosin and sarcolemmal components fibronectin, laminin and dystrophin was performed on diaphragm cryosections. Electron microscopy was used to study the ultrastructure of diaphragm fibres.

RESULTS

P(t) and P(o) were respectively approximately 30% and approximately 20% lower in CHF diaphragm bundles than sham. Maximal shortening velocity was reduced by approximately 20% and maximal power generation by approximately 35%. Structural abnormalities were frequently observed in CHF diaphragm fibres and were mainly marked by focal degradation of sarcomeric constituents and expansion of intermyofibrillar spaces with swollen and degenerated mitochondria. Immunofluorescence microscopy showed reduced staining intensities of myosin in CHF diaphragm fibres compared to sham. No differences were found regarding the distribution of fibronectin, laminin and dystrophin, indicating an intact sarcolemma in both groups.

CONCLUSION

This study demonstrates impaired isometric and isotonic contractility together with structural abnormalities in the CHF diaphragm. The sarcolemma of CHF diaphragm fibres appeared to be intact, excluding a role for sarcolemmal injuries in the development of CHF diaphragm dysfunction.

Diaphragm adaptations in patients with COPD

Inspiratory muscle weakness in patients with COPD is of major clinical relevance. For instance, maximum inspiratory pressure generation is an independent determinant of survival in severe COPD. Traditionally, inspiratory muscle weakness has been ascribed to hyperinflation-induced diaphragm shortening. However, more recently, invasive evaluation of diaphragm contractile function, structure, and biochemistry demonstrated that cellular and molecular alterations occur, of which several can be considered pathologic of nature. Whereas the fiber type shift towards oxidative type I fibers in COPD diaphragm is regarded beneficial, rendering the overloaded diaphragm more resistant to fatigue, the reduction of diaphragm fiber force generation in vitro likely contributes to diaphragm weakness. The reduced diaphragm force generation at single fiber level is associated with loss of myosin content in these fibers. Moreover, the diaphragm in COPD is exposed to oxidative stress and sarcomeric injury. This review postulates that the oxidative stress and sarcomeric injury activate proteolytic machinery, leading to contractile protein wasting and, consequently, loss of force generating capacity of diaphragm fibers in patients with COPD. Interestingly, several of these presumed pathologic alterations are already present early in the course of the disease (GOLD I/II), although these patients appear not limited in their daily life activities. Treatment of diaphragm dysfunction in COPD is complex since its etiology is unclear, but recent findings indicate the ubiquitin-proteasome pathway as a prime target to attenuate diaphragm wasting in COPD.

Chronic upper airway resistive loading induces growth retardation via the GH/IGF-I axis in prepubescent rats

The effect of upper airway loading on longitudinal bone growth and various components of the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis has not been fully elucidated. In the present study, the effect of chronic resistive airway loading (CAL) in a prepubescent rat model on linear bone growth and weight gain was investigated. We hypothesize that CAL induced in prepubescent rats will lead to impaired longitudinal growth due to impairment in circulating and liver GH/IGF-I parameters. The tracheae of 22-day-old rats were obstructed by tracheal banding to increase inspiratory esophageal pressure. The GH/IGF-I markers were analyzed using ELISA, RT-PCR, and Western immunoblot analysis 14 days after surgery. Animals exhibited impaired longitudinal growth as demonstrated by reduction of tibia and tail length gains by 40% ( P < 0.0001) and body weight gain by 24% ( P < 0.0001). No differences were seen in total body energy balance, i.e., oxygen consumption, daily food intake, or arterial blood gases. Circulating GH, IGF-I, and IGF binding protein-3 (IGFBP-3) levels were reduced by 40% ( P = 0.037), 30% ( P < 0.006), and 27% ( P = 0.02), respectively, in the CAL group. Liver IGF-I mRNA level decreased by 20% ( P < 0.0002), whereas GH receptor mRNA and protein expression were unchanged. We conclude that impaired longitudinal growth in prepubescent CAL rats is related to a decrease in GH, IGF-I, and IGFBP-3 levels.

Respiratory loading intensity and diaphragm oxidative stress:N-acetyl-cysteine effects

We hypothesized that resistive breathing of moderate to high intensity might increase diaphragm oxidative stress, which could be partially attenuated by antioxidants. Our objective was to assess the levels of oxidative stress in the dog diaphragm after respiratory muscle training of a wide range of intensities and whether N-acetyl-cysteine (NAC) might act as an antioxidant. Twelve Beagle dogs were anesthetized with 1% propophol, tracheostomized, and subjected to continuous inspiratory resistive breathing (IRB) (2 h/day for 2 wk). They were further divided into two groups ( n = 6): NAC group (oral NAC administration/24 h for 14 days) and control group (placebo). Diaphragm biopsies were obtained before (baseline biopsy) and after (contralateral hemidiaphragm) IRB and NAC vs. placebo treatment. Oxidative stress was evaluated in all diaphragm biopsies through determination of 3-nitrotyrosine immunoreactivity, protein carbonylation, hydroxynoneal protein adducts, Mn-SOD, and catalase, using immunoblotting and immunohistochemistry. Both protein tyrosine nitration and protein carbonylation were directly related to the amount of the respiratory loads, and NAC treatment abrogated this proportional rise in these two indexes of oxidative stress in response to increasing inspiratory loads. A post hoc analysis revealed that only the diaphragms of dogs subjected to high-intensity loads showed a significant increase in both protein tyrosine nitration and carbonylation, which were also significantly reduced by NAC treatment. These results suggest that high-intensity respiratory loading-induced oxidative stress may be neutralized by NAC treatment during IRB in the canine diaphragm.

Respiratory muscle plasticity

Plasticity of respiratory muscles must be considered in the context of their unique physiological demands. The continuous rhythmic activation of respiratory muscles makes them among the most active in the body. Respiratory muscles, especially the diaphragm, are non-weight-bearing, and thus, in contrast to limb muscles, are not exposed to gravitational effects. Perturbations in normal activation and load known to induce plasticity in limb muscles may not cause similar adaptations in respiratory muscles. In this review, we explore the structural and functional properties of the diaphragm muscle and their response to alterations in load and activity. Overall, relatively modest changes in diaphragm structural and functional properties occur in response to perturbations in load or activity. However, disruptions in the normal influence of phrenic innervation by frank denervation, tetrodotoxin nerve block and spinal hemisection, induce profound changes in the diaphragm, indicating the substantial trophic influence of phrenic motoneurons on diaphragm muscle.

Chronic resistive airway loading reduces weight due to low serum IGF-1 in rats

One of the consequences of chronic resistive airway loading in rats is malfunction in body weight gain post-surgery. The lower body weight of the obstructed animals was not related to lower caloric intake or to the oxygen consumption/food intake ratio. In the current study, we determined whether the retardation in body weight gain was related to impairment of serum insulin-like growth factor-1 (IGF-1) level or due to activation of inflammatory factors 21 weeks post-surgery. During the observation period, the airway-loaded animals (n=8) gained 44% less body weight (P<0.001) compared with controls (n=8) with no apparent effect on skeletal growth, i.e., body, tail and tibia length. Chronic airway-loaded animals had 32.5% lower serum IGF-1 levels (P<0.001) compared to the controls. Interleukin-6 and tumor necrosis factor-alpha levels were below 30 pg/ml in both groups. These data suggest that the weight loss in the chronic airway-loading rats is associated with a decreased IGF-1 level and not to activation of the inflammatory response.

Differential Cytokine Gene Expression in the Diaphragm in Response to Strenuous Resistive Breathing

Strenuous resistive breathing induces plasma cytokines that do not originate from circulating monocytes. We hypothesized that cytokine production is induced inside the diaphragm in response to resistive loading. Anesthetized, tracheostomized, spontaneously breathing Sprague-Dawley rats were subjected to 1, 3, or 6 hours of inspiratory resistive loading, corresponding to 45-50% of the maximum inspiratory pressure. Unloaded sham-operated rats breathing spontaneously served as control animals. The diaphragm and the gastrocnemius muscles were excised at the end of the loading period, and messenger ribonucleic acid expression of tumor necrosis factor-alpha, tumor necrosis factor-beta, interleukin (IL)-1alpha, IL-1beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IFN-gamma, and two housekeeping genes was analyzed using multiprobe RNase protection assay. IL-6, IL-1beta, and, to lesser extents, tumor necrosis factor-alpha, IL-10, IFN-gamma, and IL-4 were significantly increased in a time-dependent fashion in the diaphragms but not the gastrocnemius of loaded animals or in the diaphragm of control animals. Elevation of protein levels of IL-6 and IL-1beta in the diaphragm of loaded animals was confirmed with immunoblotting. Immunostaining revealed IL-6 protein localization inside diaphragmatic muscle fibers. We conclude that increased ventilatory muscle activity during resistive loading induces differential elevation of proinflammatory and antiinflammatory cytokine gene expression in the ventilatory muscles.

Short-term influences of lung volume reduction surgery on the diaphragm in emphysematous hamsters

With emphysema, diaphragm length adaptation results in shortened fibers. We hypothesize that passive diaphragm stretch occurring acutely after lung volume reduction surgery (LVRS) results in fiber injury. Bilateral LVRS was performed in emphysematous hamsters. Studies were performed 1 (D1) and 4 (D4) days after LVRS, and compared with sham-treated groups. Sarcolemmal rupture was evident in 10.9% of fibers in LVRS-D1 and reduced to 1.6% in LVRS-D4. Ultrastructural analysis revealed focal abnormalities in both LVRS-D1 and LVRS-D4 animals in over one-third of fibers. Myofibrillar disruption was not observed in sham-treated animals. Diaphragm insulin-like growth factor-I (IGF-I) was increased in LVRS-D4 compared with other emphysematous groups. Increased IGF-I immunoreactivity was localized to types IIA and I fibers. The abundance of the splice variant of IGF-I mRNA sensitive to muscle stretch (IGF-IEb) increased 3.2-fold in LVRS D-4 diaphragms, compared with emphysema-sham animals. The main form of IGF-I mRNA was unchanged. Marked force deficit was observed in the LVRS-D1 diaphragm, compared with emphysema-sham and emphysema (no surgery) animals. These data highlight a markedly compromised ventilatory pump acutely after LVRS. Acute fiber stretch predisposes to muscle fiber injury and may also be a necessary mechanotransductive stimulus for fiber remodeling as the diaphragm adapts to reduced lung volume.

Regenerative capacity of the dystrophic (mdx) diaphragm after induced injury

Duchenne muscular dystrophy is characterized by myofiber necrosis, muscle replacement by connective tissue, and crippling weakness. Although the mdx mouse also lacks dystrophin, most muscles show little myofiber loss or functional impairment. An exception is the mdx diaphragm, which is phenotypically similar to the human disease. Here we tested the hypothesis that the mdx diaphragm has a defective regenerative response to necrotic injury, which could account for its severe phenotype. Massive necrosis was induced in mdx and wild-type (C57BL10) mouse diaphragms in vivo by topical application of notexin, which destroys mature myofibers while leaving myogenic precursor satellite cells intact. At 4 h after acute exposure to notexin, >90% of diaphragm myofibers in both wild-type and mdx mice demonstrated pathological sarcolemmal leakiness, and there was a complete loss of isometric force-generating capacity. Both groups of mice showed strong expression of embryonic myosin within the diaphragm at 5 days, which was largely extinguished by 20 days after injury. At 60 days postinjury, wild-type diaphragms exhibited a persistent loss ( approximately 25%) of isometric force-generating capacity, associated with a trend toward increased connective tissue infiltration. In contrast, mdx diaphragms achieved complete functional recovery of force generation to noninjured values, and there was no increase in muscle connective tissue over baseline. These data argue against any loss of intrinsic regenerative capacity within the mdx diaphragm, despite characteristic features of major dystrophic pathology being present. Our findings support the concept that significant latent regenerative capacity resides within dystrophic muscles, which could potentially be exploited for therapeutic purposes.

Respiratory muscle injury, fatigue and serum skeletal troponin I in rat

To evaluate injury to respiratory muscles of rats breathing against an inspiratory resistive load, we measured the release into blood of a myofilament protein, skeletal troponin I (sTnI), and related this release to the time course of changes in arterial blood gases, respiratory drive (phrenic activity), and pressure generation. After approximately 1.5 h of loading, hypercapnic ventilatory failure occurred, coincident with a decrease in the ratio of transdiaphragmatic pressure to integrated phrenic activity (P(di)/ integral Phr) during sighs. This was followed at approximately 1.9 h by a decrease in the P(di)/ integral Phr ratio during normal loaded breaths (diaphragmatic fatigue). Loading was terminated at pump failure (a decline of P(di) to half of steady-state loaded values), approximately 2.4 h after load onset. During 30 s occlusions post loading, rats generated pressure profiles similar to those during occlusions before loading, with comparable blood gases, but at a higher neural drive. In a second series of rats, we tested for sTnI release using Western blot-direct serum analysis of blood samples taken before and during loading to pump failure. We detected only the fast isoform of sTnI, release beginning midway through loading. Differential detection with various monoclonal antibodies indicated the presence of modified forms of fast sTnI. The release of fast sTnI is consistent with load-induced injury of fast glycolytic fibres of inspiratory muscles, probably the diaphragm. Characterization of released fast sTnI may provide insights into the molecular basis of respiratory muscle dysfunction; fast sTnI may also prove useful as a marker of impending respiratory muscle fatigue.

Disorders of the respiratory muscles

The act of breathing depends on coordinated activity of the respiratory muscles to generate subatmospheric pressure. This action is compromised by disease states affecting anatomical sites ranging from the cerebral cortex to the alveolar sac. Weakness of the respiratory muscles can dominate the clinical manifestations in the later stages of several primary neurologic and neuromuscular disorders in a manner unique to each disease state. Structural abnormalities of the thoracic cage, such as scoliosis or flail chest, interfere with the action of the respiratory muscles-again in a manner unique to each disease state. The hyperinflation that accompanies diseases of the airways interferes with the ability of the respiratory muscles to generate subatmospheric pressure and it increases the load on the respiratory muscles. Impaired respiratory muscle function is the most severe consequence of several newly described syndromes affecting critically ill patients. Research on the respiratory muscles embraces techniques of molecular biology, integrative physiology, and controlled clinical trials. A detailed understanding of disease states affecting the respiratory muscles is necessary for every physician who practices pulmonary medicine or critical care medicine.

Strenuous resistive breathing induces plasma cytokines: role of antioxidants and monocytes

Inspiratory resistive breathing increases plasma cytokines, yet the stimulus (or stimuli) and source(s) remain unknown. We tested the role of reactive oxygen species as stimuli and of monocytes as sources of resistive breathing-induced cytokines. Six healthy subjects performed two resistive breathing sessions at 75% of maximum inspiratory pressure before and after a combination of antioxidants (vitamin E 200 mg, vitamin A 50,000 IU, and vitamin C 1,000 mg per day for 60 days, allopurinol 600 mg/day for 15 days, and N-acetylcysteine 2 g/day for 3 days before the second session). Blood was drawn before, at the end, and at 30 and 120 minutes after resistive breathing. Before antioxidants, plasma cytokine levels (determined by enzyme-linked immunosorbent assay) increased secondary to resistive breathing (tumor necrosis factor-alpha and interleukin [IL]-6 by twofold and IL-1beta by threefold). After antioxidants, plasma IL-1beta became undetectable. The tumor necrosis factor-alpha response to resistive breathing was abolished, and the IL-6 response was significantly blunted. Intracellular cytokine detection (by flow cytometry) showed no change in either the percentage of monocytes producing the cytokines or their mean fluorescence intensity both before and after antioxidants. We conclude that oxidative stress is a major stimulus for the resistive breathing-induced cytokine production and that monocytes play no role in this process.

[Interleukin 10 and tumor necrosis factor alpha gene expression in respiratory and peripheral muscles. Relation to sarcolemmal damage]

BACKGROUND

Tumor necrosis factor alpha (TNF-alpha) has been implicated in loss of muscle mass in chronic obstructive pulmonary disease and other consumptive processes. TNF-alpha production would be related to inflammation arising from pulmonary disease itself or, alternatively, from smoking, and would be carried to the muscle through the blood stream. However, it has also been suggested that TNF-alpha may be expressed directly in muscle tissue. Regardless the site of production of TNF-alpha, its relation to subsequent muscle damage is unclear.

OBJECTIVE

We studied the expression of TNF-alpha and an interleukin inhibitor of its production (IL-10) in the main respiratory muscles and a peripheral muscle in the dog.

METHOD

Nine young, male Beagle dogs were included. From all animals we obtained a biopsy of the diaphragm (Dph) and external intercostal (ExtI) muscles and a leg muscle (internal vastus of the quadriceps, IntV). TNF-alpha and IL-10 gene expressions were measured through the analysis of messenger RNA levels, using reverse transcription and polymerase chain reaction. We also assessed sarcolemmal damage using intracellular fibronectin detection (immunohistochemistry).

RESULTS

The expression of both cytokines showed wide interindividual variability. On the one hand, TNF-alpha (was very low in Dph and ExtI (0.02 0.03 and 0.05 0.06 a.u., respectively), but relatively high in the IntV (0.14 0.08 a.u.). IL-10 expression, on the other hand was low in the Dph (0.06 0.05 a.u.) and slightly higher in the ExtI (2.7 1.9 a.u., p < 0.01) and IntV (1.6 1.7 a.u.). Sarcolemmal damage was minimal in all three muscles and was related to TNF-alpha expression in the peripheral muscle (r = 0.682, p < 0.05).

CONCLUSIONS

1) TNF-alpha and IL-10 appear to be constitutively expressed within the skeletal muscle in dogs. 2) Basal TNF-alpha expression is lower in respiratory muscles than in peripheral muscles. 3) The expression in the latter is related to membrane damage.

Procion orange tracer dye technique vs. identification of intrafibrillar fibronectin in the assessment of sarcolemmal damage

BACKGROUND

The use of Procion orange dye (POD) is one of the most widely accepted techniques to assess sarcolemmal damage. This phenomenon has been related to functional adaptation in skeletal muscles. The POD method includes intravenous injection of this colorant in vivo, enabling its identification inside those fibres with membrane leaks (fluorescence). However, the safety of the use of POD has not been proven.

AIM

This study was designed to compare POD with a safer alternative, involving the identification of intracellular fibronectin using specific antibodies.

METHOD

Eight Swiss mice were submitted to electrical stimulation of the lower limbs at different frequencies (10-80 Hz). Subsequently, the POD solution was infused, and samples from the vastus medialis muscle were obtained 24 h later. Samples were processed and serial sections were analysed using immunohistochemistry (monoclonal antibodies against fibronectin) and epifluorescence microscopy.

RESULTS

Ninety-eight per cent of the fibres were equally classified by both techniques, which in addition showed good correlation (percentages of damaged fibres, r = 0.998, P < 0.001) and concordance (R1 = 0.82) in quantitative terms.

CONCLUSIONS

Although the two techniques compared here are based on different principles, both are comparable in assessing sarcolemmal damage. This would facilitate comparisons between human and experimental studies. In addition, the fibronectin technique appears to be a suitable alternative for long-term studies including repeated biopsies.

Mechanical ventilation protects against diaphragm injury in sepsis: interaction of oxidative and mechanical stresses

Overproduction of nitric oxide (NO) with attendant oxidative and nitrosative stress has been implicated in sepsis-induced diaphragm dysfunction. Here we determined the impact of controlled mechanical ventilation (MV) on rat diaphragm sarcolemmal injury, inducible NO synthase (iNOS) expression, and oxidative stress during endotoxemia. At 4 h after injection of endotoxin, impaired sarcolemmal integrity and decreased force production by the diaphragm were observed in spontaneously breathing rats. The use of MV during endotoxemia largely eliminated sarcolemmal damage and significantly improved diaphragm force production. These benefits were not associated with alterations in either iNOS expression or protein carbonyls (marker of oxidation), which remained abnormally elevated in septic diaphragms despite MV. Therefore, we hypothesized that the protection afforded by MV was due to its ability to decrease the level of mechanical stress placed on the sarcolemma, because the latter could be hyperfragile in the setting of increased oxidative stress. Using an in vitro system to independently modulate oxidative and mechanical stresses, we confirmed that these two factors act together in a synergistic fashion to favor sarcolemmal injury. Accordingly, our data suggest that MV protects the diaphragm during sepsis by abrogating an injurious interaction between oxidative and biomechanical stresses imposed on the sarcolemma.

Injury of the human diaphragm associated with exertion and chronic obstructive pulmonary disease

Injury of the diaphragm may have clinical relevance having been reported in cases of sudden infant death syndrome or fatal asthma. However, examination of diaphragm injury after acute inspiratory loading has not been reported. The purpose of this study was to determine whether an acute inspiratory overload induces injury of the human diaphragm and to determine if diaphragm from chronic obstructive pulmonary disease (COPD) is more susceptible to injury. Eighteen patients with COPD and 11 control patients with normal pulmonary function (62 +/- 10 yr) undergoing thoracotomy or laparotomy were studied. A threshold inspiratory loading test was performed prior to surgery in a subset of seven patients with COPD and five control patients. Samples of the costal diaphragm were obtained during surgery and processed for electron microscopy analysis. Signs of sarcomere disruption were found in all diaphragm samples. The range of values of sarcomere disruption was wide (density: 2-45 abnormal areas/100 microm(2); area fractions: 1.3-17.3%), significantly higher in diaphragm from patients with COPD (p < 0.05) and with the greatest injury after inspiratory loading. We conclude that sarcomere disruption is common in the human diaphragm, is more evident in patients with COPD, and is higher after inspiratory loading, especially in the diaphragm of those with COPD.

The voluntary drive to breathe is not decreased in hypercapnic patients with severe COPD

How do the respiratory centres of patients with chronic obstructive pulmonary disease (COPD) and hypercapnia respond to acute increases in inspiratory load? A depressed respiratory motor output has long been postulated, but studies on this issue have yielded inconsistent results, partly due to limitations of investigative techniques. Many of these limitations can be overcome by the twitch interpolation technique, which is capable of accurately quantifying the degree of diaphragmatic activation, termed the voluntary drive to breathe. The hypothesis that patients with COPD and hypercapnia compensate for an acute increase in mechanical load on the inspiratory muscles with a lower voluntary drive to breathe than is the case with normocapnic patients was tested. Measurements were obtained in 15 patients with COPD, six of whom displayed hypercapnia and nine normocapnia. The maximum degree of diaphragmatic activation, expressed as a voluntary activation index (mean +/- SEM), was higher in hypercapnic than in normocapnic patients (98.7 +/- 0.7 versus 94.5 +/- 0.9% (p = 0.006)), as was the mean value (94.5 +/- 0.7 versus 88.5 +/- 1.9% (p = 0.01)). Within-patient values of the index were also less variable in the hypercapnic patients (coefficients of variation, 3.4 +/- 0.3 versus 6.1 +/- 0.9%, p = 0.01). Multiple regression analysis revealed the ratio of dynamic elastance to maximum transdiaphragmatic pressure, an index of inspiratory muscle loading, and pH as the only variables that correlated with maximum voluntary activation index (r2 = 0.69, p = 0.02 for each variable). Contrary to the hypothesis, it was concluded that voluntary activation of the diaphragm was greater and less variable in hypercapnic patients than normocapnic patients with severe chronic obstructive pulmonary disease during an acute increase in inspiratory mechanical load. Whether greater diaphragmatic recruitment during episodes of a severe exacerbation of chronic obstructive pulmonary disease provides a survival advantage for hypercapnic patients with chronic obstructive pulmonary disease remains to be determined.

Morphological and functional recovery from diaphragm injury: an in vivo rat diaphragm injury model

Our objective was to develop an in vivo model to study the timing and mechanisms underlying diaphragm injury and repair. Diaphragm injury was induced in anesthetized rats by the application of a 100 mM caffeine solution for a 10-min period to the right abdominal diaphragm surface. Diaphragms were removed 1, 4, 6, 12, 24, 48, 72, and 96 h and 10 days after the injury, with contractile function being assessed in strips in vitro by force-frequency curves. The extent of caffeine-induced membrane injury was indicated by the percentage of fibers with a fluorescent cytoplasm revealed by inward leakage of the procion orange dye. One hour after caffeine exposure, 32.9 ± 3.1 (SE) % of fibers showed membrane injury that resulted in 70% loss of muscle force. Within 72–96 h, the percentage of fluorescent cells decreased to control values. Muscle force, however, was still reduced by 30%. Complete muscle strength recovery was observed 10 days after the injury. Whereas diaphragmatic fiber repair occurred within 4 days after injury induction, force recovery took up to 10 days. We suggest that the caffeine-damaged rat diaphragm is a useful model to study the timing and mechanisms of muscle injury and repair.

Improved coil design for functional magnetic stimulation of expiratory muscles

Our studies have demonstrated effective stimulation of the expiratory muscles in patients with spinal cord injury (SCI) using functional magnetic stimulation (FMS). The observed contraction of the expiratory muscles and functional improvement of the pulmonary functions make functional magnetic stimulation an appropriate tool for expiratory muscle training. To fully capitalize on the benefits of FMS for expiratory muscle training, this study aimed to optimize the magnetic coils (MCs). The primary goal of this study was to investigate how two parameters of the MC size and winding structure, would affect expiratory muscle training. By varying these parameters, our approach was to conceptualize and evaluate the induced electric field and nerve activation function distributions of six coils, round 9.2, 13.7, and 20 cm, and spiral 9.2-, 13.7-, and 20-cm coils in the computer modeling phase. Round 9.2 cm, spiral 13.7 cm, and spiral 20-cm coils were also evaluated in experimental studies for induced electrical field and in clinical studies of expiratory muscles. Both the computer models and experimental measurements indicated that the spiral 20-cm coil can not only stimulate more expiratory spinal nerves but can also stimulate them more evenly. In addition, coils with larger diameters had better penetration than those with smaller diameters. The clinical results showed that the spiral 20-cm coil produced higher expiratory pressure, flow, and volume in five able-bodied subjects, and it was the coil of choice among the subjects when asked their preferences. In our attempt to optimize MC design for FMS of expiratory muscle training, we followed the designing guidelines set out in our previous study and arrived at a more effective tool.

Diaphragm injury in individuals with airflow obstruction

The purpose of this study was to describe the nature of diaphragm injury, to quantify the injury and number of macrophages at the light microscopic level, and to determine their association with airflow obstruction in humans. Partial-thickness diaphragm biopsies were obtained from 21 subjects going for thoracotomy surgery (FEV(1): 74 +/- 34% predicted; range: 16 to 122% predicted). Cross sections cut from frozen diaphragm were processed with H&E or processed for immunohistochemistry using the monoclonal antibody Ber-MAC3 (DAKO Corp., Carpinteria, CA) to label macrophages. Area fractions (A(A)) or the proportions of the cross- sectional area were determined by point counting all viable fields of H&E-stained diaphragm cross sections. A(A) were 66.2 +/- 9.0% for normal muscle, 17.6 +/- 7.2% for abnormal muscle, and 16.3 +/- 4.2% for connective tissue. Percent predicted FEV(1) was inversely related to the A(A) of abnormal muscle (r = -0.53, p < 0.01) and directly related to the A(A) of normal muscle (r = 0.37, p < 0.05). The number of macrophages was not related to % predicted FEV(1) (mean +/- SD: 0.41 +/- 0.18/fiber; 52 +/- 19/mm(2)). We conclude that increasing severity of airflow obstruction is associated with an increased A(A) of abnormal diaphragm and a decreased A(A) of normal diaphragm.

[Metabolic activity of the external intercostal muscle of patients with COPD]

INTRODUCTION

The external intercostal muscle is a relevant contributor to ventilatory work in situations of overloading. Like other respiratory muscles, the external intercostal muscle seems to undergo a process of structural remodeling to adapt to a situation of functional disadvantage. However, findings from published studies of morphology have differed to a certain degree. On the one hand, the proportion of fibers involved in anaerobic metabolism increases; on the other hand, the number of capillaries also increases, an occurrence that would facilitate aerobic metabolism.

OBJECTIVE

This study was designed to analyze the activity of several key enzymes involved in the principal metabolic pathways in the external intercostal muscles of patients with COPD.

METHODOLOGY

We studied 6 patients with COPD (65 +/- 8 years, BMI 23 +/- 3 kg/m2, FEV1 51 +/- 9% ref, RV 184 +/- 38% ref, PaO2 81 +/- 10 mmHg) and 6 control subjects matched for age and anthropometric variables but with normal lung function. External intercostal muscle samples were taken from each patient (fifth intercostal space, non-dominant side). The samples were treated by conventional spectrophotometry to determine enzyme activity as follows: citrate synthase (CS, Krebs cycle), phosphofructokinase (PFK, by common glycolysis), lactate dehydrogenase (LDH, anaerobic glycolysis) and creatine phosphokinase (CPK, use of energy reserves).

RESULTS

Patients with COPD showed greater PFK enzyme activity (93 +/- 25 versus 44 +/- 9 micromol/min/g of fresh weight; p = 0.001) and LDH (308 +/- 42 versus 231 +/- 29 micromol/min/g; p < 0.01) than did control subjects. However, CS and CPK activity was similar in both groups (82 +/- 31 versus 90 +/- 20 micromol/min/g and 4017 +/- 1734 versus 3048 +/- 464 micromol/min/g, respectively), although the latter displayed noteworthy dispersion of values among COPD patients, with levels in some patients being three-fold greater than in controls. RV was directly related to glycolytic enzyme activity (with PFK, r = 0.716, p < 0.01; with LDH r = 0.697, p < 0.05) and PFK and LDH also correlated with each other (r = 0.737, p < 0.01).

CONCLUSIONS

Based on the enzyme activity studied, oxidative activity seems to be conserved in the external intercostal muscle of patients with COPD. Activity in the glycolytic pathway seems to increase and the increase is proportional to the severity of COPD. These findings are probably the expression of a combination of adaptive structural factors.

Lipopolysaccharide-induced diaphragmatic contractile dysfunction and sarcolemmal injury in mice lacking the neuronal nitric oxide synthase

In this study we evaluated the role of the neuronal nitric oxide synthase (nNOS) in lipopolysaccharide (LPS)-induced diaphragmatic contractile dysfunction and sarcolemmal injury. Wild-type (WT) mice or mice deficient in the nNOS gene (nNOS(-/-)) were injected with either saline (control) or Escherichia coli LPS (LPS groups) and sacrificed 12 h later. The diaphragm was then examined for NOS expression, NOS activity, and in-vitro contractility. We also assessed sarcolemmal injury in isolated muscle strips under resting condition and after 3 min of artificial stimulations. In WT mice, LPS injection reduced maximum force to about 75% of that of control animals and raised total NOS activity significantly due to the induction of the iNOS isoform. Although muscle fiber injury was minimal under resting condition, the percentage of injured fibers in control and LPS-injected mice approached 27% and 40% of total fibers, respectively, in response to artificial stimulation. By comparison, LPS injection in nNOS(-/-) mice elicited a worsening of muscle contractility (maximum force < 60% of control animals) but elicited degrees of sarcolemmal injury similar to those observed in the WT animals. In addition, muscle NOS activity and iNOS protein level in nNOS(-/-) mice injected with LPS reached about 10% and 60% of that of WT animals, respectively (p < 0.05 compared with WT animals). Protein level of endothelial NOS isoform in the diaphragm was not altered by LPS injection in either WT or nNOS(-/-) animals. We conclude that nNOS plays a protective role in attenuating the negative influence of sepsis on diaphragmatic contractility but is not involved in the pathogenesis of sepsis-induced sarcolemmal injury.