The diaphragm: contractile properties and fatigue

The Application of Diaphragm Ultrasound in Chronic Obstructive Pulmonary Disease: A Narrative Review

Chronic Obstructive Pulmonary Disease (COPD) is a prevalent condition that poses a significant burden on individuals and society due to its high morbidity and mortality rates. The diaphragm is the main respiratory muscle, its function has a direct impact on the quality of life and prognosis of COPD patients. This article aims to review the structural measurement and functional evaluation methods through the use of diaphragmatic ultrasound and relevant research on its application in clinical practice for COPD patients. Thus, it serves to provide valuable insights for clinical monitoring of diaphragm function in COPD patients, facilitating early clinical intervention and aiding in the recovery of diaphragm function.

Tissue Doppler imaging of the diaphragm and outcome of weaning from mechanical ventilation

Purpose

This study aimed to employ tissue Doppler imaging to monitor diaphragmatic peak velocity and acceleration during contraction and relaxation in mechanically ventilated patients, with the objective of assessing the potential utility of this technique in predicting weaning outcomes.

Methods

A total of 89 adult subjects were recruited in this study. After 30 min of spontaneous breathing trial, the diaphragm motion parameters, including peak contraction velocity, peak relaxation velocity, contraction acceleration and relaxation acceleration, were measured in real time using tissue Doppler imaging. According to the results of weaning, the patients were divided into successful weaning group and failed weaning group. The differences of diaphragmatic tissue Doppler imaging monitoring indicators between the two groups were analysed, and the receiver operating characteristic curve was drawn to analyse the value of each ultrasound parameter in predicting weaning.

Results

In the successful weaning group, there were 61 subjects, while in the failed weaning group, there were 28 subjects. The peak contraction velocity, peak relaxation velocity, contraction acceleration and relaxation acceleration of the diaphragm were significantly higher in the failed weaning group compared to the successful weaning group (P < 0.05). The area under the curve of diaphragmatic peak contraction velocity, peak relaxation velocity, diaphragmatic contraction acceleration and diaphragmatic relaxation acceleration were 0.81 (0.72-0.91), 0.85 (0.77-0.93), 0.74 (0.63-0.86) and 0.86 (0.78-0.94), respectively.

Conclusions

The diaphragm ultrasonic tissue Doppler imaging variables can serve as predictive indicators for weaning mechanical ventilation in patients, thus providing an effective tool to assist critical care physicians in determining the optimal timing for weaning mechanical ventilation.

Distinct transcriptomic profile of satellite cells contributes to preservation of neuromuscular junctions in extraocular muscles of ALS mice

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disorder characterized by progressive weakness of almost all skeletal muscles, whereas extraocular muscles (EOMs) are comparatively spared. While hindlimb and diaphragm muscles of end-stage SOD1G93A (G93A) mice (a familial ALS mouse model) exhibit severe denervation and depletion of Pax7 + satellite cells (SCs), we found that the pool of SCs and the integrity of neuromuscular junctions (NMJs) are maintained in EOMs. In cell sorting profiles, SCs derived from hindlimb and diaphragm muscles of G93A mice exhibit denervation-related activation, whereas SCs from EOMs of G93A mice display spontaneous (non-denervation-related) activation, similar to SCs from wild-type mice. Specifically, cultured EOM SCs contain more abundant transcripts of axon guidance molecules, including Cxcl12 , along with more sustainable renewability than the diaphragm and hindlimb counterparts under differentiation pressure. In neuromuscular co-culture assays, AAV-delivery of Cxcl12 to G93A-hindlimb SC-derived myotubes enhances motor neuron axon extension and innervation, recapitulating the innervation capacity of EOM SC-derived myotubes. G93A mice fed with sodium butyrate (NaBu) supplementation exhibited less NMJ loss in hindlimb and diaphragm muscles. Additionally, SCs derived from G93A hindlimb and diaphragm muscles displayed elevated expression of Cxcl12 and improved renewability following NaBu treatment in vitro . Thus, the NaBu-induced transcriptomic changes resembling the patterns of EOM SCs may contribute to the beneficial effects observed in G93A mice. More broadly, the distinct transcriptomic profile of EOM SCs may offer novel therapeutic targets to slow progressive neuromuscular functional decay in ALS and provide possible "response biomarkers" in pre-clinical and clinical studies.

Diaphragm movement sensor for phrenic nerve monitoring during cryoballoon procedures: the first clinical evaluation

Background and aims

Right phrenic nerve palsy is the most frequent complication of cryoballoon procedures. The SMARTFREEZE™ console (Boston Scientific, St. Paul, MN, USA) has integrated a new tool for diaphragm monitoring-the Diaphragm Movement Sensor; however, it has not been evaluated in clinical practice. We aimed to assess the diagnostic performance of the Diaphragm Movement Sensor based on compound motor action potential data recorded simultaneously.

Methods

Thirty consecutive patients (mean age 63.2 ± 10.2 years) were included. We simultaneously recorded the compound motor action potential and the Diaphragm Movement Sensor during cryoapplications in the right pulmonary veins. The right phrenic nerve was paced at 60 per minute, 12 V and 2.9 ms. Compound motor action potential monitoring with a 30% decrease cutoff for the diagnosis of phrenic nerve threatening was considered the gold standard. The Diaphragm Movement Sensor decrease threshold was also set at 30%.

Results

Considering compound motor action potential monitoring, phrenic nerve threatening occurred 11 times (in seven patients) among 84 cryoapplications (13.1%) at the right pulmonary veins. The sensitivity and specificity of the Diaphragm Movement Sensor were, respectively, 33% (95% CI: 7%-70%) and 49% (95% CI: 38%-61%; P < 0.001). The predictive positive and negative values for the Diaphragm Movement Sensor were, respectively, 7% (95% CI: 2%-20%) and 86% (95% CI: 72%-95%). The Diaphragm Movement Sensor gave an erroneous diagnosis in 44/84 cryoapplications (52.4%).

Conclusions

The diagnostic performance of the Diaphragm Movement Sensor is low, and the relevance of its use in clinical practice may be debated.

Paced breathing and respiratory movement responses evoked by bidirectional constant current stimulation in anesthetized rabbits

Objective: Diaphragm pacing (DP) is a long-term and effective respiratory assist therapy for patients with central alveolar hypoventilation and high cervical spinal cord injury. The existing DP system has some limitations, especially high price, inconvenience preoperative evaluation methods and diaphragm fatigue easily. Our objective was to develop a DP system and evaluated reliability through hardware testing and animal experiments. Methods: A DP system with bidirectional constant current was designed, manufactured and tested. Effects of a wide range of stimulus amplitudes (range: .5-2.5 mA) and frequencies (range: 10-250 Hz) on airflow and corresponding inspired volume were investigated during DP. Differences in airflow characteristics under various stimulation parameters were evaluated using power function. ECG interference in diaphragm electromyography (EMGdi) was filtered out using stationary wavelet transform to obtain pure EMGdi (EMGdi_p). 80-min period with a tendency for diaphragm fatigue by root mean square (RMS) and centroid frequency (f _c ) of EMGdi_p was studied. Results: The increase of stimulus frequency and amplitude in animals resulted in different degrees of increase in envoked volume. Significant difference in Airflow Index (b) between anesthesia and DP provided a simple, non-invasive and feasible solution for phrenic nerve conduction function test. Increased stimulation duration with the developed DP system caused less diaphragm fatigue. Conclusion: A modular, inexpensive and reliable DP was successfully developed. Its effectiveness was confirmed in animal experiments. Significance: This study is useful for design of future implantable diaphragmatic pacemakers for improving diaphragm fatigue and convenient assessment of respiratory activity in experiments.

Stimulation of both inspiratory and expiratory muscles versus diaphragm-only paradigm for rehabilitation in severe chronic obstructive pulmonary disease patients: a randomized controlled pilot study

BACKGROUND

Chronic obstructive pulmonary disease (COPD), a progressive lung disease, might improve with neuromuscular electrical stimulation. No trials on inspiratory plus expiratory neuromuscular electrical stimulation have been conducted yet.

AIM

The aim of this study was to evaluate the safety and effectiveness of inspiratory plus expiratory neuromuscular electrical stimulation in subjects with severe COPD.

DESIGN

This was a multicenter, prospective, randomized controlled trial.

SETTING

The subjects were outpatients enrolled from Beijing Chao-Yang Hospital affiliated with Capital Medical University, Tianjin Chest Hospital, and the First Hospital of Hebei Medical University.

POPULATION

Subjects had stable COPD with severe respiratory impairment.

METHODS

Using a computer statistical software, 120 stable subjects were randomly allocated (1:1) to receive inspiratory plus expiratory neuromuscular electrical stimulation (study group) and diaphragm pacing (control group). Demographic and clinical data were collected before, and after 2, and 4 weeks of the trial. The intention-to-treat analysis was conducted. The primary outcome was to analyze the changes in functional exercise capacity, estimated as six-minute walk distance (6MWD), following electrical stimulation for 4 weeks. The secondary outcomes were changes in modified Medical Research Council score, forced expiratory volume in 1 second (FEV<inf>1</inf>), FEV<inf>1</inf>% predicted, and FEV<inf>1</inf> ratio forced vital capacity (FEV<inf>1</inf>/FVC) following electrical stimulation for 4 weeks.

RESULTS

The change in 6MWD was greater in the study group (65.53±39.45 m) than in the control group (26.66±32.65 m). The mean between-group difference at the fourth week was 29.07 m (95% confidence interval, 16.098-42.035; P<0.001). There were no significant between-group differences in the secondary outcomes after 4 weeks of electrical stimulation. For GOLD-4 COPD subjects, FEV<inf>1</inf> and FEV<inf>1</inf>/FVC improved in the study group (P<0.05). No electrical stimulation-related serious adverse events were observed in either group.

CONCLUSIONS

6MWD were increased significantly, without adverse events, after four weeks of treatment of inspiratory plus expiratory neuromuscular electrical stimulation in stable patients with severe COPD, suggesting that this protocol benefits COPD rehabilitation.

CLINICAL REHABILITATION IMPACT

The results of this study suggest that the simultaneous use of inspiratory plus expiratory neuromuscular electrical stimulation as an adjunct therapy may improve the functional exercise capacity of severe stable COPD subjects.

Diaphragm Ultrasound in Cardiac Surgery: State of the Art

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

New method for evaluating maximal respiratory pressures: Concurrent validity, test-retest, and inter-rater reliability

BACKGROUND

Maximal respiratory pressures (MRP) obtained at functional residual capacity (FRC) may reflect the real respiratory muscle pressure.

OBJECTIVES

To evaluate concurrent validity, test-retest, and inter-rater reliability of MRP performed with a new instrument in healthy individuals, and to compare values obtained at different volumes in healthy individuals and individuals with COPD.

METHODS

MRP of 100 healthy individuals were obtained using the TrueForce and the MicroRPM® at residual volume (RV) and total lung capacity (TLC) to evaluate concurrent validity. MRP were obtained at FRC using the TrueForce to evaluate reliability. Comparisons of inspiratory pressure values (FRC compared to RV) and expiratory pressure values (FRC compared to TLC) were performed with 100 healthy individuals and 15 individuals with COPD.

RESULTS

The intraclass correlation coefficient (ICC) was 0.77 and 0.86 for concurrent validity for inspiratory and expiratory pressures, respectively. Test-retest reliability showed an ICC of 0.87 for inspiratory pressure, and 0.78 for expiratory pressure; inter-rater reliability showed an ICC of 0.91 for inspiratory pressure, and 0.84 for expiratory pressure. Measurements performed at RV and TLC were higher when compared to FRC [mean difference (95%CI)= -8.30 (-11.82, -4.78) cmH2O; -37.29 (-42.63, -31.96) cmH2O] in healthy individuals, and -11.09 (-15.83, -6.35) cmH2O; -57.14 (-71.05, -43.05) cmH2O in COPD, for inspiratory and expiratory pressures, respectively.

CONCLUSION

MRP performed with the TrueForce presented good concurrent validity, good test-retest reliability, excellent inter-rater reliability for inspiratory pressure and good inter-rater reliability for expiratory pressure. MRP were lower when obtained at FRC for healthy individuals and with COPD.

Thoracic mobility and its relation to pulmonary function and rib-cage deformity in patients with early onset idiopathic scoliosis: a long-term follow-up

STUDY DESIGN

A group of adult patients with idiopathic scoliosis, diagnosed before the age of ten, at a mean of 26.5 years after treatment with either brace or surgery during childhood and adolescence attended a clinical follow-up.

OBJECTIVES

To evaluate the relation between thoracic mobility, rib-cage deformity, and pulmonary function. Long-term studies of pulmonary function in relation to thoracic mobility after treatment in this patient group have not been published.

METHODS

A total of 106 patients, 57 braced and 49 operated patients, attended the follow-up. We examined thoracic mobility (range of motion of the thoracic spine, thorax expansion, and breathing movements) and rib-cage deformity (curve size and trunk deformity) as well as pulmonary function, especially total lung capacity (TLC). Respiratory muscle strength was evaluated in a subgroup.

RESULTS

Thoracic range of motion was significantly less among the surgically treated patients compared with both the brace-treated and comparison group. Thorax expansion and breathing movements during maximal breathing were significantly reduced in the scoliotic patients compared with the reference values, with no significant differences between the treatment groups. The brace-treated group had better pulmonary function than the operated group, as measured by the TLC, forced vital capacity (FVC), and forced expiratory volume in one second (FEV1) (percentage of predicted values). The respiratory muscle strength was significantly lower only in the surgically treated patients when compared with reference values. The results of a multivariate analysis revealed that the strongest factors explaining TLC percentage of predicted were gender, brace model, and smoking habits.

CONCLUSIONS

Thoracic mobility was significantly reduced at mean 26.5 years after completed treatment in both brace-treated and surgically treated patients with early onset scoliosis, compared with the reference values, which did not influence TLC as strongly as gender, brace model, and smoking habits.

LEVELS OF EVIDENCE

Level III.

The Effect of Inspiratory Muscle Training on Duchenne Muscular Dystrophy: A Meta-analysis

PURPOSE

This study reports the respiratory muscle training effect on strength and endurance in individuals with Duchenne muscular dystrophy.

METHODS

Articles published from 1984 to 2017 were reviewed. Six articles met the inclusion criteria that included within-subject control or between-subject control group, participants with a diagnosis of only Duchenne muscular dystrophy, participation in respiratory muscle training intervention, and outcome measures of endurance and strength. Effect sizes were calculated for each study and overall, weighted mean effect sizes for strength and endurance outcome measures.

RESULTS

There was a large effect for improving respiratory endurance and a moderate effect for muscle strength. However, these effects were not significant.

CONCLUSION

Findings justify further exploration of the potential benefits of respiratory muscle training for individuals with Duchenne muscular dystrophy.

Disorders of the Diaphragm

Pathologic processes that involve the central nervous system, phrenic nerve, neuromuscular junction, and skeletal muscle can impair diaphragm function. When these processes are of sufficient severity to cause diaphragm dysfunction, respiratory failure may be a consequence. This article reviews basic diaphragm anatomy and physiology and then discusses diagnostic and therapeutic approaches to disorders that result in unilateral or bilateral diaphragm dysfunction. This discussion provides a context in which disorders of the diaphragm and their implications on respiratory function can be better appreciated.

Assessment of Pulmonary Function After Osteopathic Manipulative Treatment vs Standard Pulmonary Rehabilitation in a Healthy Population

CONTEXT

Standard pulmonary rehabilitation (SPR) does not use osteopathic manipulative treatment (OMT), but OMT has potential to improve lung function and patient perception of breathing.

OBJECTIVE

To analyze the immediate effects of OMT and SPR techniques on pulmonary function using spirometry and subjective ratings in young, healthy persons.

METHODS

Participants were healthy students recruited from the Lake Erie College of Osteopathic Medicine-Bradenton and were randomly assigned to either the OMT or SPR group. During the first 4 weeks, each participant in the OMT group received 1 OMT technique (rib raising, doming of the diaphragm, thoracic lymphatic pump, and thoracic high velocity, low amplitude), and each participant in the SPR group received 1 SPR treatment (tapotement, pursed lip breathing, saline nebulizer, and rest) per week. Treatments were then ranked based on positive change in pulmonary function as measured by forced expiratory volume in the first second of expiration (FEV1) and forced vital capacity (FVC). During the fifth week, the OMT group received the 2 highest-ranked OMT techniques, and the SPR group received the 2 highest-ranked SPR treatments. During the sixth week, the OMT group received the highest-ranked OMT and SPR treatment, while the SPR group received the same treatment combination but in the reverse order. Pulmonary function, as measured through FEV1, FVC, and FEV1/FVC, were collected before and after each treatment or treatment combination. Participants subjectively rated change in breathing after each treatment.

RESULTS

A total of 53 students participated in the study, with 28 in the OMT group and 25 in the SPR group. In the OMT group, rib raising yielded the highest positive mean (SD) change of 0.001 (0.136) L in FEV1 and 0.052 (0.183) L in FVC, followed by lymphatic pump, with a change of 0.080 (0.169) L in FEV1 and -0.031 (0.229) L in FVC. In the SPR group, pursed lip breathing yielded the highest positive mean (SD) change of 0.101 (0.278) L in FEV1 and 0.031 (0.179) L in FVC, followed by tapotement, with a change of 0.045 (0.229) L in FEV1 and 0.061 (0.239) L in FVC. Saline treatment significantly decreased lung function. All other treatments did not result in any significant changes in lung function. Overall, SPR subjective ratings were significantly lower than ratings for both OMT and combination (OMT+SPR) treatments.

CONCLUSIONS

Saline significantly reduced lung function and had low subjective posttreatment ratings in young healthy adults. Additionally, OMT and combination OMT and SPR significantly improved subjective breathing more than SPR alone. Future applications of this study include evaluating OMT and SPR effects on lung function in patients with various pulmonary conditions.

Multiparametric Analysis of Sniff Nasal Inspiratory Pressure Test in Middle Stage Amyotrophic Lateral Sclerosis

The relaxation rates and contractile properties of inspiratory muscles are altered with inspiratory muscle weakness and fatigue. This fact plays an important role in neuromuscular disorders patients and had never been extensively studied in amyotrophic lateral sclerosis (ALS). In this cross-sectional study, these parameters were investigated non-invasively through nasal inspiratory sniff pressure test (SNIP) in 39 middle stage spinal onset ALS subjects and compared with 39 healthy controls. ALS patients were also divided into three subgroups according to a decline in their percentage of predicted forced vital capacity (FVC_%pred) as well as a decline in the ALS functional rating scale score and its respiratory subscore (R-subscore) in order to determine the best parameter linked to early respiratory muscle weakness. When compared with healthy subjects, middle stage ALS subjects exhibited a significantly lower (p < 0.0001) maximum relaxation rate and maximum rate of pressure development (MRPD), as well as a significantly higher (p < 0.0001) tau (τ), contraction time, and half-relaxation time. The results from receiver operating characteristic curves showed that MRPD (AUC 0.735, p < 0.001) and FVC_%pred (AUC 0.749, p = 0.009) were the best discriminator parameters between ALS patients with ≤30 and >30 points in the ALS functional rating scale. In addition, 1/2RT (AUC 0.720, p = 0.01), FVC_%pred (AUC 0.700, p = 0.03), τ (AUC 0.824, p < 0.0001), and MRPD (AUC 0.721, p = 0.01) were the parameters more sensitive in detecting a fall of three points in the R-subscore. On the other hand, MRPD (AUC 0.781, p < 0.001), τ (AUC 0.794, p = 0.0001), and percentage of predicted of SNIP (AUC 0.769, p = 0.002) were the parameters able to detect a fall in 30% of the FVC_%pred in middle stage ALS patients. The contractile properties and relaxation rates of the diaphragm are altered in middle stage spinal onset ALS when compared with healthy subjects. These parameters are able to discriminate between those middle stage ALS subjects with early decline in inspiratory muscle function and those who not.

Diaphragm: A vital respiratory muscle in mammals

The diaphragm is a respiratory muscle that is primarily responsible for the respiratory function in normal individuals. In mammals, the diaphragm muscle has been studied from the early days of zoology, comparative and experimental anatomy, physiology, medicine, physics, and philosophy. However, even with these early advances in knowledge pertaining to the diaphragm, comprehensive morphological data on the diaphragm are still incomplete. In this review, we summarize the beginnings of the morphological description of the diaphragm, and we describe the current status of the known morphological and embryological features. In addition, we correlate how the impairment of the diaphragm muscle in Duchenne muscular dystrophy (DMD) can lead to patient deaths. DMD is the most common X-linked muscle degenerative disease and is caused by a lack of dystrophin protein. Dystrophin is an important muscle protein that links the cellular cytoskeleton with the extracellular matrix. In the absence of dystrophin, the muscle becomes susceptible to damage during muscle contraction. This review allows researchers to obtain an overview of the diaphragm, transcending the morphological data from animals described in conventional literature.

Interpreting diaphragmatic movement with bedside imaging, review article

The diaphragm is the most important muscle of respiration. At equilibrium, the load imposed on the diaphragmatic muscles from transdiaphragmatic pressure balances the force generated by diaphragmatic muscles. However, procedural and nonprocedural thoracic and abdominal conditions may disrupt this equilibrium and impair diaphragmatic function. Diaphragmatic dysfunction is associated with respiratory insufficiency and poor outcome. Therefore, rapid diagnosis and early intervention may be useful. Ultrasound imaging provides quick and accurate bedside assessment of the diaphragm. Various imaging techniques have been suggested, using 2-dimensional and M-mode technology. Diaphragm viewing depends on the degree of robe movement, determined by the angle of incidence of the ultrasound beam and by the direction of probe movement. In this review, we will discuss the function of the diaphragm focusing on clinically important anatomical and physiological properties of the diaphragm. We will review the literature regarding various sonographic techniques for diaphragm assessment. We will also explore the evidence for the role of the tidal displacement of subdiaphragmatic organs as a surrogate for diaphragm movement.

Computed tomography confirms a reduction in diaphragm thickness in mechanically ventilated patients

PURPOSE

Patients who require mechanical ventilation (MV) may experience diaphragm atrophy, which may delay the discontinuation of MV. Here, we used computed tomographic (CT) scans to confirm this phenomenon.

METHOD AND MATERIALS

Patients who underwent two chest CT scans while on MV were retrospectively evaluated. Diaphragm thickness was measured using a three-dimensional CT image processing program.

RESULTS

Thirteen patients, including 8 men, who underwent 26 CT scans were assessed. The mean age was 67.8 ± 7.5 years. The interval between CT scans was 18.4 ± 14.9 days. The first CT scans revealed that the mean thicknesses of the left and right sides of the diaphragm were 3.8 ± 0.6 and 3.9 ± 0.8 mm, respectively (total: 7.7 ± 1.4 mm). These values were significantly reduced to 3.4 ± 0.6 and 3.5 ± 0.9 mm, respectively, (total: 6.9 ± 1.5 mm) after the second scan (P < .01). No significant change in body weight (57.3 ± 12.6 vs. 56.7 ± 11.6 kg) or body mass index (21.8 ± 5.1 vs. 21.6 ± 4.8 kg/m(2)) was observed.

CONCLUSION

Computed tomography confirmed that diaphragm thickness was reduced in critically ill patients who underwent MV.

Ultrasonographic assessment of the diaphragm in chronic obstructive pulmonary disease patients: relationships with pulmonary function and the influence of body composition - a pilot study

BACKGROUND

Skeletal muscle weakness with loss of fat-free mass (FFM) is one of the main systemic effects of chronic obstructive pulmonary disease (COPD). The diaphragm is also involved, leading to disadvantageous conditions and poor contractile capacities.

OBJECTIVES

We measured the thickness of the diaphragm (TD) by ultrasonography to evaluate the relationships between echographic measurements, parameters of respiratory function and body composition data.

METHODS

Thirty-two patients (23 males) underwent (1) pulmonary function tests, (2) echographic assessment of TD in the zone of apposition at various lung volumes, i.e. TD at residual volume (TDRV), TD at functional residual capacity (TDFRC) and TD at total lung capacity (TDTLC), and (3) bioelectrical body impedance analysis. The BMI and the BODE (BMI-Obstruction-Dyspnea-Exercise) index values were reported.

RESULTS

TDRV, TDFRC and TDTLC measured 3.3, 3.6 and 6 mm, respectively, with good intraobserver reproducibility (0.97, 0.97 and 0.96, respectively). All the TDs were found to be related to FFM, with the relationship being greater for TDFRC (r(2) = 0.39 and p = 0.0002). With regard to lung volumes, inspiratory capacity (IC) was found to be closely related to TDTLC (r(2) = 0.42 and p = 0.0001). The difference between TDTLC and TDRV, as a thickening value (TDTLCRV), was closely related to FVC (r(2) = 0.34 and p = 0.0004) and to air-trapping indices (RV/TLC, FRC/TLC and IC/TLC): the degree of lung hyperinflation was greater and the TDTLCRV was less. Finally, we found a progressive reduction of both thicknesses and thickenings as the severity of IC/TLC increased, with a significant p value for the trend in both analyses (p = 0.02).

CONCLUSIONS

Ultrasonographic assessment of the diaphragm could be a useful tool for studying disease progression in COPD patients, in terms of lung hyperinflation and the loss of FFM. © 2014 S. Karger AG, Basel.

Influence of diaphragmatic mobility on hypercapnia in patients with chronic obstructive pulmonary disease

A reduction in diaphragm mobility has been identified in patients with chronic obstructive pulmonary disease (COPD) and has been associated with a decline in pulmonary function parameters. However, little information exists regarding the potential role of diaphragm mobility on hypercapnia in COPD. A new method of assessing the mobility of the diaphragm, using ultrasound, has recently been validated. The purpose of the present study was to investigate the relationship between diaphragm mobility and pulmonary function parameters, as well as that between arterial blood gas values and diaphragm mobility, in COPD patients. Thirty seven COPD patients were recruited for pulmonary function test, arterial blood gas analysis and diaphragm mobility using ultrasound to measure the craniocaudal displacement of the left branch of the portal vein. There were significant negative correlations between diaphragmatic mobility and P(a)CO(2) (r = -0.373, P = 0.030). Diaphragmatic mobility correlated with airway obstruction (FEV(1), r = 0.415, P = 0.011) and with ventilatory capacity (FVC, r = 0.302, P = 0.029; MVV, r = 0.481, P = 0.003). Diaphragmatic mobility also correlated significantly with pulmonary hyperinflation. No relationship was observed between diaphragm mobility and P(a)O(2) (r = -0.028, P = 0.873). These findings support a possibility that the reduction in diaphragm mobility relates to hypercapnia in COPD patients.

[Inspiratory muscles strength training in recreational athletes]

INTRODUCTION

Respiratory muscles strength and endurance influence athletic performance. Besides conventional spirometry, sniff test, inspiratory and expiratory maximal pressures can directly assess respiratory muscle strength. Respiratory muscles can be train through a device offering inspiratory and expiratory resistance.

METHODS

Nineteen subjects aged 18 to 30 years and practicing leisure sport trained inspiratory muscles on Powerbreathe(®) for eight weeks. Resistance was set at 85% of maximal inspiratory pressure determined during a preliminary session. Evaluation was made trough voluntary and non-invasive methods on Macro 5000(®) (PI max, PE max and sniff test).

RESULTS

An increase of 21.77% of the maximum inspiratory pressure, 17% of the maximum expiratory pressure and 18% of the sniff test are recorded after eight weeks of training.

CONCLUSIONS

A specific training of inspiratory muscles (Powerbreathe(®) Sports performance) increases the power of these muscles (voluntary and non-invasive tests).

Relevant surgical anatomy of the chest wall

The chest wall, like other regional anatomy, is a remarkable fusion of form and function. Principal functions are the protection of internal viscera and an expandable cylinder facilitating variable gas flow into the lungs. Knowledge of the anatomy of the whole cylinder (ribs, sternum, vertebra, diaphragm, intercostal spaces, and extrathoracic muscles) is therefore not only important in the local environment of a specific chest wall resection but also in its relation to overall function. An understanding of chest wall kinematics might help define the loss of function after resection and the effects of various chest wall substitutes. Therefore, this article is not an exhaustive anatomic description but a focused summary and discussion.

Phrenic nerve stimulation

Weakness of the limbs and respiratory muscles has increasingly been found to be a frequent event that complicates the medical history of patients in Intensive Care. The problem normally affects more serious cases and presents as muscular weakness leading to flaccid paralysis and difficulty in weaning patients off mechanical ventilation. This latter sign leads the intensivist to suspect possible involvement of the neuromuscular respiratory system. Unfortunately, in-depth clinical assessment of the neuromuscular respiratory system is difficult with critically ill patients, and electrophysiological studies have been used instead to overcome this problem. Of these latter, electric and electromagnetic stimulation of the phrenic nerve have been successful (along with needle electromyography of the diaphragm) in identifying the causes of neuromuscular respiratory insufficiency, especially in Intensive Care. In this brief chapter, we will be discussing the technique of electric stimulation of the phrenic nerve and neuromuscular respiratory insufficiency within the field of critical illness polyneuropathy.

Effect of salbutamol on respiratory muscle function and ventilation in awake canines

The effect of the beta-agonist bronchodilator salbutamol on respiratory muscles and ventilation is uncertain. The presence of beta2 receptors on skeletal muscles and increased diaphragm contractility in vitro with salbutamol predict a significant effect that has not been confirmed, in vivo in non-fatigued diaphragm or in clinical studies using standard bronchodilator dosages. Therefore, we infused salbutamol at a higher dosage (23.3 microg/min) used clinically for treatment of respiratory emergencies, while measuring directly the length, shortening and EMG activation of costal and crural diaphragm, parasternal intercostal and transversus abdominis muscles, in 10 awake canines. At this salbutamol dosage, ventilation and tidal volume increased significantly during both resting and CO2-stimulated breathing. Salbutamol elicited significant increases in respiratory muscle shortening with much smaller increases in EMG activity, so the proportionally greater muscle shortening per unit EMG showed increased muscle contractility. The effects of salbutamol were not extinguished by inspiratory flow resistance or fluid challenge but were reversed specifically by the beta-blocker, propranolol. This study demonstrates that, in sufficient intravenous dosage, the beta-agonist salbutamol elicits increased ventilation and a beta2 receptor-mediated increase in contractility of respiratory muscles.

Maximal respiratory static pressures in patients with different stages of COPD severity

BACKGROUND

In this study, we analyzed maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) values in a stable COPD population compared with normal subjects. We evaluated the possible correlation between functional maximal respiratory static pressures and functional and anthropometric parameters at different stages of COPD. Furthermore, we considered the possible correlation between airway obstruction and MIP and MEP values.

SUBJECT AND METHODS

110 patients with stable COPD and 21 age-matched healthy subjects were enrolled in this study. Patients were subdivided according to GOLD guidelines: 31 mild, 39 moderate and 28 severe.

RESULTS

Both MIP and MEP were lower in patients with severe airway impairment than in normal subjects. Moreover, we found a correlation between respiratory muscle function and some functional and anthropometric parameters: FEV1 (forced expiratory volume in one second), FVC (forced vital capacity), PEF (peak expiratory flow), TLC (total lung capacity) and height. MIP and MEP values were lower in patients with severe impairment than in patients with a slight reduction of FEV1.

CONCLUSION

The measurement of MIP and MEP indicates the state of respiratory muscles, thus providing clinicians with a further and helpful tool in monitoring the evolution of COPD.

Effects of Partial Isothermic Immersion on the Spirometry Parameters of Tetraplegic Patients

STUDY OBJECTIVES

Our objective was to compare under controlled conditions the effect of immersion on spirometry parameters of patients with tetraplegia vs those of normal individuals.

DESIGN AND PATIENTS

Twenty-three otherwise well tetraplegic subjects were compared to a control group of 11 similar healthy subjects before and during 5 to 15 min of isothermal immersion in water to shoulder level.

RESULTS

Measured at baseline, tetraplegic subjects exhibited significant pulmonary restriction, characterized by a mean FVC of 54.9 +/- 14.6% of the predicted value (range, 23.2 to 80.4%), whereas all controls subjects had > 80% of predicted values. Immersion increased the FVC of tetraplegic patients an average of 18.4 +/- 18.7% above basal measurements, while that of the control group worsened (DeltaFVC, - 8.8 +/- 4.4%). Among the tetraplegic patients, the lower the preimmersion vital capacity, the greater the percentage of improvement following immersion (r = 0.79; 95% confidence interval, - 0.91 to - 0.56; p < 0.0001). No relationship was found between the time elapsed since cervical cord injury or its level and the degree of improvement.

CONCLUSIONS

Water activities play an important role in the rehabilitation of patients with spinal cord injury. Immersion in isothermal water at shoulder level, under strictly controlled experimental conditions, reduces the vital capacity of normal individuals, while it improves in a group of patients with tetraplegia. The observed phenomenon seems to be mediated by an improvement in breathing mechanics, impaired by cervical cord injury.

Effect of Spinal Cord Injury on the Respiratory System

There are >200,000 persons living with a spinal cord injury in the United States, with approximately 10,000 new cases of traumatic injury per year. Advances in the care of these patients have significantly reduced acute and long-term mortality rates, although life expectancy remains decreased. This article will review the alterations in respiratory mechanics resulting from a spinal cord injury and will examine the contribution of respiratory complications to morbidity and mortality associated with various types of spinal cord injury.

Respiratory muscle testing

Respiratory muscles are a vital component of the respiratory system. Compromise in the function of respiratory muscles is assessed with a careful history, determination of the breathing frequency, and observation of the pattern of thoracoabdominal movements in the upright and supine positions. The most important diagnostic tools include measurement of lung volumes, FVC, oximetry, Pi(max) and Pe(max), and SNIP. Measurement of Pes and Pga pressures, Tw Pmo, phrenic nerve stimulation, magnetic stimulation, and EMG add new dimensions to the study of these muscles. These tools are helpful in understanding patients with acute and chronic disease that affects the respiratory muscles.

Effect of free radical scavengers on diaphragmatic contractility in septic peritonitis

We investigated the effects of polyethylene glycol-adsorbed superoxide dismutase (PEG-SOD), polyethylene glycol-adsorbed catalase (PEG-CAT), and DMSO on diaphragmatic contractility and malondialdehyde (MDA) concentrations in septic peritonitis in vitro. One hundred eighty-six rats were divided into two groups. One group (CLP group) was treated with cecal ligation and perforation (CLP), and the other (sham group) was treated with laparotomy. PEG-SOD, PEG-CAT, and DMSO were administered intraperitoneally 30 min before and 12 h after CLP. The left hemidiaphragm was removed at 10 h or 16 h after the operation. We assessed the diaphragmatic contractility by twitch characteristics and force-frequency curves in vitro. We measured MDA concentrations, as an index of oxygen-derived free radical-mediated lipid peroxidation, and the activities of two main antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GPx), as an index of antioxidant defenses, after CLP. Diaphragmatic force generation capacity was significantly reduced after CLP. Diaphragmatic MDA levels were significantly elevated after CLP. PEG-SOD, PEG-CAT, and DMSO significantly improved diaphragmatic contractility and prevented the elevation in diaphragmatic MDA concentrations after CLP. Diaphragmatic SOD activities were significantly increased after CLP. These results suggest that several types of oxygen-derived free radicals play a role in the reduction in diaphragmatic contractility after CLP.

Glucocorticoid-induced alterations in the rate of diaphragmatic fatigue

These experiments tested the hypothesis that in vitro diaphragmatic fatigue resistance is enhanced in animals treated with glucocorticoids. Female Sprague-Dawley rats (4 months old) were randomly assigned to a control (N =12) or glucocorticoid treatment group (N =12). Treatment animals were injected daily for 8 days with prednisolone (5 mg kg(-1)); control animals were injected with the same volume of the vehicle. Twenty-four hours after the last injection, the following in vitro diaphragmatic contractile properties were examined in costal diaphragm strips: maximal twitch (P(t)) half time to peak tension (1/2 TPT), half relaxation time (1/2 RT), force-frequency relationship, and the rate of fatigue development. Diaphragmatic fatigue was assessed by monitoring the decrease in force production (measured as percent of initial force) over a 60-min contractile period. The in vitro fatigue protocol incorporated a supramaximal stimulus delivered at 30 Hz every 2 s with a train duration of 250 ms (duty cycle 12.5%). Citrate synthase (CS), superoxide dismutase (SOD), and water content of the costal diaphragm were also determined. Glucocorticoid administration induced an 18.9% (P<0.05) decrease in animal body weight when compared to the control. Similar weight losses also occurred in the diaphragm with a decrease (P<0.05) in mass of 16.5% compared to the control. Furthermore, prednisolone treatment resulted in a significant reduction in the cross-sectional area (CSA) of type IIb fibres with no change in the CSA area of type I and IIa fibres. 1/2 TPT and 1/2 RT were significantly prolonged (P<0.05) in the glucocorticoid treated rats whereas the force-frequency curve was unaltered (P>0.05). Fatigue resistance was greater in the glucocorticoid group (P<0.05); the relative force production differed between groups at the end of 1 min of contractions and remained different throughout the 60-min fatigue protocol. Citrate synthase, SOD, and water content were not different between groups. These experiments support the hypothesis that costal diaphragm strips of glucocorticoid-treated rats possess a greater resistance to fatigue. We postulate that this fatigue resistance is due to glucocorticoid-induced changes muscle fibre type composition.

Discharge of group IV phrenic afferent fibers increases during diaphragmatic fatigue

The discharge of single unit group III (n=7) and group IV (n=8) phrenic afferent fibers was recorded during rhythmic diaphragmatic contractions before and after the onset of fatigue. Compared to pre-fatigue impulse activity, group IV, but not group III, phrenic afferent fibers discharged more (p<0.05) during rhythmic diaphragmatic contractions when the diaphragm was fatigued. This increase in group IV fiber discharge during diaphragmatic fatigue provides electrophysiological evidence consistent with the notion that group IV phrenic afferent fibers comprise the afferent arm of a fatigue-induced inhibitory reflex originating in the diaphragm.

Effects of isoproterenol on diaphragmatic contractility in septic peritonitis

We investigated the effects, and the mechanism of the effects, of isoproterenol on diaphragmatic contractility and fatigue in septic peritonitis in vitro. Ninety-six rats were divided into two groups of 48. One group (CLP group) was treated with cecal ligation and perforation (CLP) and the other (sham group) was treated with laparotomy. The left hemidiaphragm was removed at 16 h after the operation. We assessed the diaphragmatic contractility by twitch characteristics and force-frequency curves in vitro. Diaphragm fatigue was induced by rhythmically stimulating strips to contract at 60/ min (20 Hz, 0.33-s trains, 1 train/s) over a 4-min period. Force-frequency curves were determined before and after fatigue. Isoproterenol (10(-9), 10(-8), and 10(-7) M), a beta-adrenoceptor agonist, was cumulatively administered to the organ bath. Isoproterenol significantly increased diaphragmatic contractility. There were no significant changes in diaphragmatic contractility in the sham group. Isoproterenol (10(-7) M) significantly accelerated diaphragmatic recovery of fatigue and increased cAMP levels both in the sham group and the CLP group. Propranolol (10(-7) M), a general beta-adrenoceptor blocker, completely abolished the positive inotropic effect of isoproterenol (10(-7) M) and increased cAMP levels in the CLP group. Dibutyryl cAMP (10(-3) M), a derivative of cyclic AMP, mimicked the effects of isoproterenol in the CLP group. These results suggest that isoproterenol increases diaphragmatic contractility and accelerates diaphragmatic recovery of fatigue in septic peritonitis by activating the adenylate cyclase system.

Neural drive to the diaphragm after lung volume reduction surgery

STUDY OBJECTIVES

The aim of this study was to investigate prospectively the changes in neural drive to the diaphragm in the first year after lung volume reduction surgery (LVRS) in patients with COPD.

PATIENTS AND METHODS

In 14 patients with severe emphysema (mean +/- SD; age, 53.7 +/- 8.3 years; FEV(1), 0.64 +/- 0. 18 L; residual volume [RV], 5.33 +/- 1.25 L; PaO(2), 62.3 +/- 9.0 mm Hg; PaCO(2), 39.0 +/- 6.0 mm Hg), we assessed lung function, arterial blood gases, maximal exercise capacity (Wmax), and oxygen uptake (f1.gif" BORDER="0">O(2)max); intrinsic positive end-expiratory pressure (PEEPi); diaphragmatic strength (transdiaphragmatic pressure, Pdisniff) and endurance capacity (tlim); central diaphragmatic drive assessed by root mean square analysis of the esophageal electromyogram (rmsdia); and isotime dyspnea during loaded breathing tests (BS).

RESULTS

Despite a significant increase (expressed as a percentage of baseline) in FEV(1) (40.6%) and a decrease in RV (30.0%) and PEEPi (75.7%) 1 month after LVRS, the improvements in Wmax (31.2%) and f1.gif" BORDER="0">O(2)max (13.7%); Pdisniff (25.4%) and tlim (64.9%); rmsdia (34.6%); and BS (21.7%) did not reach statistical significance (p < 0.05) until 6 months after LVRS. Arterial blood gases did not change significantly. Significant correlations were found between decrease in rmsdia and changes in PEEPi (r = 0.69), Wmax (r = -0.56), Pdisniff (r = -0.65), tlim (r = -0.59), and BS (r = 0.71) 6 months after LVRS.

CONCLUSIONS

Our results show that LVRS is able to increase the efficacy of the respiratory pump and by this way reduce ventilatory drive and respiratory effort sensation.

The effects of dantrolene on the contraction, relaxation, and energetics of the diaphragm muscle

Dantrolene is used in patients with muscle spasticity and is the only known effective treatment for malignant hyperthermia. However, its effects on muscle relaxation and energetics are unknown and may have important consequences in diaphragmatic function. We studied the effects of dantrolene (10(-8) to 10(-4) M) on diaphragm muscle strips (n = 12) in the hamster in vitro (Krebs-Henseleit solution, 29 degrees C, 95% oxygen/5% carbon dioxide) in response to tetanic stimulation (50 Hz). We studied contraction and relaxation under isotonic and isometric conditions, as well as energetics. Data are mean +/- SD. Dantrolene induced a negative inotropic effect in the hamster diaphragm (active force at 10(-4) M: 34% +/- 7% of baseline; P < 0.05) but did not significantly modify the curvature of the force-velocity relationship. Dantrolene did not significantly modify isotonic relaxation. Dantrolene, up to 10(-5) M, did not significantly impair isometric relaxation. In conclusion, dantrolene induced a marked negative inotropic effect on diaphragm muscle without affecting myothermal efficiency and relaxation.

IMPLICATIONS

Dantrolene induced a significant and concentration-dependent negative inotropic effect on diaphragm muscle but did not modify isotonic relaxation, which suggests no alteration of the calcium reuptake by the sarcoplasmic reticulum; up to 10(-5) M dantrolene did not alter isometric relaxation, i.e., myofilament calcium sensitivity. Dantrolene did not modify the energetics of diaphragm muscle.

The unidirectional valve is the best method to determine maximal inspiratory pressure during weaning

OBJECTIVES

Although maximal inspiratory pressure (MIP) is used as an index of inspiratory muscular strength, there is no consensus on how to measure it. We compared, during weaning from mechanical ventilation, two methods of measurement to determine which shows the greater values (MIPbest) and is more reproducible. One method measured MIP when negative pressure was maintained for at least 1 s after a forceful expiration, and the other method measured MIP with a unidirectional expiratory valve (MIPuni).

DESIGN

The study had a crossover design, and patients randomly performed three measurements of each method (t1). The procedure was repeated by the same observer after 20 min (t2). The maximal value in each method was considered.

SETTING

ICU, Hospital A.C. Camargo, São Paulo, Brazil.

PATIENTS

Fifty-four consecutive patients undergoing short-term mechanical ventilation who became eligible for the study when their physicians decided to restore spontaneous breathing.

RESULTS

MIPbest values were arrived at using MIPuni 75% of the time either in tl or t2. MIPuni yielded a higher average of MIPbest values in t1 and t2 (p < 0.0001). The effort-to-effort coefficient of variation of one method compared with the other during t1 and t2 was similar (p > 0.2 for t1; p > 0.8 for t2). Also, when comparing tl and t2, the coefficients of variation were similar for each method (p > 0.62).

CONCLUSIONS

Because MIPuni displayed the maximal values, it is the best method for estimating MIP in patients undergoing short-term mechanical ventilation. The reproducibility of consecutive measurements was similar between the methods, even after a short period of time.

Diaphragmatic function is markedly altered in cerulein-induced pancreatitis

OBJECTIVE

To assess diaphragmatic function in vitro during experimental cerulein-induced acute pancreatitis.

DESIGN

Prospective, randomized, controlled animal trial.

SETTING

Research laboratory at a large university medical center.

SUBJECTS

Twenty male Sprague-Dawley rats, weighing 180 to 200 g.

INTERVENTIONS

Sodium chloride 0.9% or cerulein (5 microg/kg/hr) was infused for 6 hrs.

MEASUREMENTS AND MAIN RESULTS

Isometric force generated during electrical stimulation of costal diaphragmatic strips was measured 6 hrs after the end of infusion. Diaphragmatic strength was assessed at different frequencies (10, 20, 30, 50, and 100 Hz). Endurance index was the time until the force generated during the 30 Hz repetitive stimulation decreased to 50% of the initial value (T50%). Histologic examination of the diaphragm was performed. A decrease averaging 40% in diaphragmatic strength generation was observed for all frequencies of stimulation in the pancreatitis group. Compared with the control group, this decrease was associated with a reduction in T50% (30.9 +/- 12.5 [SD] and 46.4 +/- 10.8 secs in pancreatitis and control, respectively; p< .05). No histologic alteration of the diaphragm was observed.

CONCLUSIONS

Acute pancreatitis induced marked diaphragmatic dysfunction. Although the precise mechanisms responsible for this alteration are not precisely determined, diaphragmatic dysfunction may play a role in pancreatitis-associated respiratory failure.

[Fiber morphometry of the external intercostal muscle. Comparison of dominant and nondominant sides in patients with severe COPD]

The general morphometric characteristics of the external intercostal muscle (EIM) of patients with chronic respiratory disease have been well described. Because this muscle is highly accessible, it can provide an ideal model for longitudinal studies using consecutive biopsies of both sides. Whether or not the EIM fiber phenotype is homogeneous on dominant (D) and non dominant (ND) sides is unknown, however. To evaluate possible structural differences in right and left EIM in patients with COPD, eight patients (63 +/- 7 years of age) were enrolled. Lung function, respiratory muscle power, general muscle power and nutritional state were evaluated. Biopsies of the fifth EIM were taken from both sides. Specimens were processed in parallel manner to determine conventional morphometry (hematoxylin-eosin staining), including minimum diameter (Dm) and fiber area (Ar) in cross sections. Fibers were typed by ATPase (at pH 4.2, 4.6 and 9.4) and NADH-TR staining. Nutrition was normal in all patients. All patients had severe COPD (FEV1 27 +/- 7% of reference, limits 13 to 38% of reference) with air entrapment (RV 163 +/- 36% of reference, limits 181 to 276% of reference). None of the patients showed respiratory insufficiency at rest (PaO2 72 +/- 7 mmHg). Peripheral musculoskeletal power measured by manual dynamometer showed no significant right-left differences: D 29 +/- 2 and ND 28 +/- 3 dynes. Morphometric study of 16 muscle specimens showed no significant differences between fiber size on D and ND sides. DmD was 47 +/- 10 microns and ArD, was 2,595 +/- 1,249 microns2. DmD was 49 +/- 9 microns and ArD was 2,636 +/- 953 microns2. Likewise, no significant differences were found between D and ND fiber types: type ID 51 +/- 4% and type IID 49 +/- 5% versus type IND 52 +/- 4% and type IIND 48 +/- 4%. EIM on N and ND sides is homogeneous at the fifth intercostal space. This finding, along with the scarcely invasive nature of the technique for collecting specimens leads us to suggest that longitudinal studies might be performed on the structural effects of various pharmacological or physical treatments followed by COPD patients

[Cellular homogeneity in diverse portions of the diaphragm]

The diaphragm is the main inspiratory muscle. It is composed of two parts, the costal and crural, with both anatomical and functional differences. The general morphometric characteristics of the diaphragm have been described in various species but homogeneity throughout the muscle has not been adequately studied. The aim of this study was to evaluate the fiber phenotype of various parts of the diaphragm. The entire diaphragm muscles of five New Zealand rabbits were removed and each was divided into quarters. The specimens were processed for morphometry (hematoxyllineosin stains, NADH-TR and ATPase at pH levels of 4.2, 4.6 and 9.4). For each portion we measured percent and size of fibers, expressing the latter as minimum diameter (Dm), measured area (Ar) and calculated area (Ac). Left and right diaphragm hemispheres (20 portions examined) were similar for fiber percentages and sizes. For left and right halves, respectively 50 +/- 2 and 51 +/- 4% of fibers were type I; type I Dm measurements were 38 +/- 5 and 41 +/- 4 microns; type I Ar values were 1798 +/- 481 and 2030 +/- 390 micron 2; type I Ac values were 1181 +/- 360 and 1321 +/- 382 micron 2; type II Dm values were 46 +/- 4 and 46 +/- 5 microns; type II Ar values were 2466 +/- 388 micron 2 and 2539 +/- 456 micron 2; type II Ac data were 1642 +/- 255 and 1655 +/- 382 micron 2. We likewise found no differences between costal and crural portions of the muscle (n = 20). For costal and crural portions, respectively, 50 +/- 3 and 50 +/- 2% of fibers were type I; type I Dm sizes were 39 +/- 5 and 40 +/- 4 microns; type I Ar measurements were 1859 +/- 521 and 1964 +/- 365 micron 2; type I Ac figures were 1231 +/- 317 and 1266 +/- 288 micron 2; type II Dm were 47 +/- 4 and 44 +/- 3 microns; type II Ar were 2563 +/- 481 and 2430 +/- 331 micron 2; type II Ac were 1729 +/- 373 and 1557 +/- 212 micron 2. Type II fibers, however, were somewhat larger than type I fibers in all portions (p = 0.001). New Zealand rabbit diaphragm muscle has similar percentages of slow and rapid contraction fibers. The size is not different from that observed in other species of mammals of similar size. Fiber type proportions are similar throughout the muscle, with more type II fibers present in all areas. The morphometric characters, therefore, suggest an homogeneous throughout the diaphragm, suggesting homogeneous response of the muscle to usual loads, and also suggesting the possibility of proposing longitudinal morphometric studies using this species as a model.

Diaphragm shortening and intrathoracic pressure during hypercapnia in rats

The purpose of this study was to determine the relationship between intrathoracic pressure (delta ITP) and diaphragm shortening (DS) during the development of diaphragm fatigue. Fatigue of the diaphragm was produced by having rats breath 15% CO2 in O2. Diaphragm shortening increased significantly to 178% of control during the first 5 min of hypercapnia and then decreased to 86% of control at approximately 80 min. Twenty minutes after terminating hypercapnia, DS increased to 115% of the prehypercapnic value. delta ITP increased to 199% of control following 5 min of hypercapnia and continued to increase, reaching 267% of control at the end of the hypercapnic period. Twenty minutes later, delta ITP was 147% of control. These results illustrate that during increased respiratory work, DS can decrease while intrathoracic pressure remains increased. These findings suggest that intrathoracic pressure may not always reflect the contractile status of the diaphragm. These findings are consistent with other studies indicating that as the diaphragm fatigues, accessory respiratory muscle activity increases to maintain delta ITP.

Maximal inspiratory pressure and inspiratory muscle endurance time in asthmatic children: reproducibility and relationship with pulmonary function tests

Respiratory muscle strength, assessed by maximal inspiratory mouth pressure (PImax), and endurance, assessed as the length of time a subject could breathe against inspiratory resistance with a target mouth pressure > or = 70% of PI,max (Tlim), were measured in 20 symptomless asthmatic children, in order to assess the reproducibility of such measurements and their relationship to traditional pulmonary function tests or tests of bronchial hyperresponsiveness. After recording lung volumes and bronchial response to methacholine, PI,max and Tlim were measured twice in the same morning, with a 30-minute interval between each experimental trial. Mean (+/-SD) values of PI,max were 72.2 +/- 20.6 cmH2O in the first and 75.8 +/- 22.9 cmH2O in the second trial. Tlim was 154 +/- 65 and 164 +/- 66 seconds in the first and in the second trial respectively. A lack of agreement between different measurements was seen for both PI,max and Tlim. The coefficient of repeatability was 24.8 for PI,max and 92.3 for Tlim. A significant correlation between age and PI,max as well as between body mass index and PI,max were shown; no similar correlation was found for Tlim. No correlation was found between PI,max and Tlim in either of the two successive runs or between either PI,max or Tlim and lung volumes or bronchial response to methacholine. Our study shows that at this time the reproducibility of PI,max or Tlim in children with asthma in remission seems to be poor, although PI,max has a better reproducibility than Tlim. A standardized procedure to measure PI,max, should be obtainable in the near future. This would improve its clinical usefulness since PI,max is the only noninvasive test to assess respiratory muscle strength that can identify subjects at risk to develop respiratory muscle fatigue during an acute asthmatic attack.

Conducting and voltage-dependent behaviors of the native and purified SR Ca2+-release channels from the canine diaphragm

The ryanodine-sensitive Ca2+-release channel of the canine diaphragm sarcoplasmic reticulum (SR) was characterized using biochemical assays and the planar lipid bilayer technique. Diaphragm SR membranes have a [3H]ryanodine-binding capacity (Bmax) of 1.2 pmol/mg protein and a binding affinity (K(D)) of 6.3 nM. The conductance of the native channel was 330 pS in 50 mM/250 mM trans/cis CsCH3SO3 and was reduced to 71 pS by 10 mM Ca2+ trans. The Ca2+-release channel was purified as a 400 kDa protein on SDS-PAGE and displayed a conductance of 715 pS in 200 mM KCl. The native and purified Ca2+ channels were activated by micromolar Ca2+ and ATP and inhibited by Mg2+, ryanodine and ruthenium red. Although diaphragm muscle contraction was shown to depend on extracellular Ca2+ like cardiac muscles, we provide evidence that the diaphragm SR Ca2+-release channel may be classified as a skeletal ryanodine receptor isoform. First, the IC50 for [3H]ryanodine binding was in the same range as estimated for skeletal SR, with 20 nM. Second, the channel was maximally activated by 10-30 microM cytoplasmic Ca2+ and inhibited at higher concentrations. Third, ryanodine binding to the diaphragm SR was less sensitive to Ca2+ than cardiac SR, with EC50, values of 50 and 1 microM, respectively. Finally, Ca2+-release activity and [3H]ryanodine binding capacity of the diaphragm and skeletal SR were similarly more sensitive to Mg2+ than cardiac SR. Together, these results suggest a predominantly skeletal-type of excitation-contraction coupling in the diaphragm.

Pulmonary rehabilitation for patients with advanced lung disease

Pulmonary rehabilitation has gradually become a cornerstone of treatment for patients with advanced lung disease. Although most of the data that has resulted in the acceptance of this therapeutic modality has been obtained from studies of patients with chronic obstructive pulmonary disease, the basic principles and tools are applicable to patients with many other limiting chronic diseases of the respiratory system. Because new therapeutic strategies, such as lung volume reduction surgery and lung transplantation, require well-conditioned patients, pulmonary rehabilitation is becoming a crucial component of the overall treatment strategy of many patients who heretofore were deemed untreatable. This article reviews the basic definitions, objectives, components, and outcomes of pulmonary rehabilitation in order to provide the reader with a practical and inclusive overview of the topic.

Almitrine and doxapram decrease fatigue and increase subsequent recovery in isolated rat diaphragm

The effects of almitrine bimesylate and doxapram HCl on isometric force produced by in vitro rat diaphragm were studied during direct muscle activation at 37 degrees C. Doxapram and almitrine ameliorate respiratory failure clinically by indirectly increasing phrenic nerve activity. This study was carried out to investigate possible direct actions of these agents on the diaphragm before and after fatigue of the fibers. Two age groups of animals were chosen [6-14 wk (group 1) and 50-55 wk (group 2)] because it is known that increasing age decreases a muscle fiber's resistance to fatigue. Muscle strips were isolated from both group 1 and group 2 and directly stimulated (2-ms pulse duration, 5-15 V) to produce twitch tensions of 1.3 and 2.1 N/cm2, respectively. At low concentrations, doxapram (</=20 microg/ml) and almitrine (</=12 microg/ml) had no effect on twitch contraction or 100-Hz tetanic tension. However, 40 microg/ml doxapram and 30 microg/ml almitrine increased twitch tension by 9.0 +/- 1.4 and 11.6 +/- 1.9%, respectively, in animals of group 2 (n = 5). A fatigue protocol consisting of low-frequency stimulation (30-Hz trains, 250-ms duration every 2 s for 5 min) caused a reduction of twitch tension in animals of group 1 (48 +/- 4% of control) and group 2 (28 +/- 4% of control). At 90 min postfatigue, the twitch tension recovered to 72 +/- 3 and 42 +/- 2% of control values in group 1 and group 2, respectively. In the presence of doxapram (20 microg/ml), there was a significant increase in the recovery of twitch tension at 90 min in group 1 and group 2 (84.5 +/- 3.2 and 80.1 +/- 2.8%, respectively) compared with controls at 90 min postfatigue. In the presence of almitrine (12 microg/ml), there was a full recovery from fatigue in group 1 animals (100% of control) and a recovery to 95.6 +/- 2.1% of control in group 2 animals at 90 min. These results demonstrate a significant improvement in the rapidity and magnitude of recovery from fatigue in the rat diaphragm muscle in the presence of both doxapram and, especially, almitrine. These effects may be due to changes in intracellular calcium, ADP/ATP ratios, or oxygen free radical scavenging.