Diaphragm length during tidal breathing in patients with chronic obstructive pulmonary disease

Mucopolysaccharidosis (MPS IIIA) mice have increased lung compliance and airway resistance, decreased diaphragm strength, and no change in alveolar structure

Mucopolysaccharidosis type IIIA (MPS IIIA) is characterized by neurological and skeletal pathologies caused by reduced activity of the lysosomal hydrolase, sulfamidase, and the subsequent primary accumulation of undegraded heparan sulfate (HS). Respiratory pathology is considered secondary in MPS IIIA and the mechanisms are not well understood. Changes in the amount, metabolism, and function of pulmonary surfactant, the substance that regulates alveolar interfacial surface tension and modulates lung compliance and elastance, have been reported in MPS IIIA mice. Here we investigated changes in lung function in 20-wk-old control and MPS IIIA mice with a closed and open thoracic cage, diaphragm contractile properties, and potential parenchymal remodeling. MPS IIIA mice had increased compliance and airway resistance and reduced tissue damping and elastance compared with control mice. The chest wall impacted lung function as observed by an increase in airway resistance and a decrease in peripheral energy dissipation in the open compared with the closed thoracic cage state in MPS IIIA mice. Diaphragm contractile forces showed a decrease in peak twitch force, maximum specific force, and the force-frequency relationship but no change in muscle fiber cross-sectional area in MPS IIIA mice compared with control mice. Design-based stereology did not reveal any parenchymal remodeling or destruction of alveolar septa in the MPS IIIA mouse lung. In conclusion, the increased storage of HS which leads to biochemical and biophysical changes in pulmonary surfactant also affects lung and diaphragm function, but has no impact on lung or diaphragm structure at this stage of the disease.NEW & NOTEWORTHY Heparan sulfate storage in the lungs of mucopolysaccharidosis type IIIA (MPS IIIA) mice leads to changes in lung function consistent with those of an obstructive lung disease and includes an increase in lung compliance and airway resistance and a decrease in tissue elastance. In addition, diaphragm muscle contractile strength is reduced, potentially further contributing to lung function impairment. However, no changes in parenchymal lung structure were observed in mice at 20 wk of age.

An augmented hybrid multibaseline and referenceless MR thermometry motion compensation algorithm for MRgHIFU hyperthermia

PURPOSE

A hybrid principal component analysis and projection onto dipole fields (PCA-PDF) MR thermometry motion compensation algorithm was optimized with atlas image augmentation and validated.

METHODS

Experiments were conducted on a 3T Philips MRI and Profound V1 Sonalleve high intensity focused ultrasound (high intensity focused ultrasound system. An MR-compatible robot was configured to induce motion on custom gelatin phantoms. Trials with periodic and sporadic motion were introduced on phantoms while hyperthermia was administered. The PCA-PDF algorithm was augmented with a predictive atlas to better compensate for larger sporadic motion.

RESULTS

During periodic motion, the temperature SD in the thermometry was improved from1 . 1 ± 0 . 1 $$ 1.1\pm 0.1 $$ to0 . 5 ± 0 . 1 ∘ $$ 0.5\pm 0.{1}^{\circ } $$ C with both the original and augmented PCA-PDF application. For large sporadic motion, the augmented atlas improved the motion compensation from the original PCA-PDF correction from8 . 8 ± 0 . 5 $$ 8.8\pm 0.5 $$ to0 . 7 ± 0 . 1 ∘ $$ 0.7\pm 0.{1}^{\circ } $$ C.

CONCLUSION

The PCA-PDF algorithm improved temperature accuracy to <1°C during periodic motion, but was not able to adequately address sporadic motion. By augmenting the PCA-PDF algorithm, temperature SD during large sporadic motion was also reduced to <1°C, greatly improving the original PCA-PDF algorithm.

Quantifying Normal Diaphragmatic Motion and Shape and their Developmental Changes via Dynamic MRI

Background

The diaphragm is a critical structure in respiratory function, yet in-vivo quantitative description of its motion available in the literature is limited.

Research Question

How to quantitatively describe regional hemi-diaphragmatic motion and curvature via free-breathing dynamic magnetic resonance imaging (dMRI)?

Study Design and Methods

In this prospective cohort study we gathered dMRI images of 177 normal children and segmented hemi-diaphragm domes in end-inspiration and end-expiration phases of the constructed 4D image. We selected 25 points uniformly located on each 3D hemi-diaphragm surface. Based on the motion and local shape of hemi-diaphragm at these points, we computed the velocities and sagittal and coronal curvatures in 13 regions on each hemi-diaphragm surface and analyzed the change in these properties with age and gender.

Results

Our cohort consisted of 94 Females, 6-20 years (12.09 + 3.73), and 83 Males, 6-20 years (11.88 + 3.57). We observed velocity range: ∼2mm/s to ∼13mm/s; Curvature range -Sagittal: ∼3m -1 to ∼27m -1 ; Coronal: ∼6m -1 to ∼20m -1 . There was no significant difference in velocity between genders, although the pattern of change in velocity with age was different for the two groups. Strong correlations in velocity were observed between homologous regions of right and left hemi-diaphragms. There was no significant difference in curvatures between genders or change in curvatures with age.

Interpretation

Regional motion/curvature of the 3D diaphragmatic surface can be estimated using free-breathing dynamic MRI. Our analysis sheds light on here-to-fore unknown matters such as how the pediatric 3D hemi-diaphragm motion/shape varies regionally, between right and left hemi-diaphragms, between genders, and with age.

Selective dysfunction of the crural diaphragm in patients with chronic restrictive and obstructive lung disease

BACKGROUND

Gastroesophageal reflux (GER) is known to be associated with chronic lung diseases. The driving force of GER is the transdiaphragmatic pressure (Pdi) generated mainly by costal and crural diaphragm contraction. The latter also enhances the esophagogastric junction (EGJ) pressure to guard against GER.

METHODS

The relationship between Pdi and EGJ pressure was determined using high resolution esophageal manometry in patients with interstitial lung disease (ILD, n = 26), obstructive lung disease (OLD, n- = 24), and healthy subjects (n = 20).

KEY RESULTS

The patient groups did not differ with respect to age, gender, BMI, and pulmonary rehabilitation history. Patients with ILD had significantly higher Pdi but lower EGJ pressures as compared to controls and OLD patients (p < 0.001). In control subjects, the increase in EGJ pressure at all-time points during inspiration was greater than Pdi. In contrast, the EGJ pressure during inspiration was less than Pdi in 14 patients with ILD and 7 patients with OLD. The drop in EGJ pressure was usually seen after the peak Pdi in ILD group (p < 0.0001) and before the peak Pdi in OLD group, (p = 0.08). Nine patients in the ILD group had sliding hiatus hernia, compared to none in control subjects (p = 0.003) and two patients in the OLD, (p = 0.04).

CONCLUSIONS AND INFERENCES

A higher Pdi and low EGJ pressure, and dissociation between Pdi and EGJ pressure temporal relationship suggests selective dysfunction of the crural diaphragm in patients with chronic lung diseases and may explain the higher prevalence of GERD in ILD as seen in previous studies.

Computed tomography reveals hypertrophic remodelling of the diaphragm in cystic fibrosis but not in COPD

Background

Computed tomography (CT) is increasingly used for assessing skeletal muscle characteristics. In cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), reduced limb muscle mass predicts poor clinical outcomes. However, the degree to which quantity or quality of respiratory and nonrespiratory muscles is affected by these diseases remains controversial.

Methods

Thoracic CT images of 29 CF, 21 COPD and 20 normal spirometry control subjects were analysed to measure indices of muscle quantity (volume or cross-sectional area) and quality (radiodensity) in respiratory (diaphragm, abdominal) and nonrespiratory (pectoralis, lumbar paraspinal) muscles. Multivariable linear regression assessed relationships of CT measurements with body mass index (BMI), forced expiratory volume in 1 s (FEV1) % pred, inflammation and infection biomarkers, nutritional status and CF genotype.

Results

Diaphragm volume in CF was significantly higher than in COPD (by 154%) or controls (by 140%). Abdominal muscle area in CF was also greater than in COPD (by 130%). Nonrespiratory muscles in COPD had more low radiodensity muscle (marker of lipid content) compared to CF and controls. In CF but not COPD, higher BMI and FEV1 % pred were independently associated with higher diaphragm and/or abdominal muscle quantity indices. Serum creatinine also predicted respiratory and nonrespiratory muscle quantity in CF, whereas other biomarkers including genotype correlated poorly with muscle CT parameters.

Conclusions

Our data suggest that the CF diaphragm undergoes hypertrophic remodelling, whereas in COPD the nonrespiratory muscles show altered muscle quality consistent with greater lipid content. Thoracic CT can thus identify distinctive respiratory and nonrespiratory muscle remodelling signatures associated with different chronic lung diseases.

Clinical Changes of Respiratory Parameters in Institutionalized Older Adults after a Physiotherapy Program Combining Respiratory and Musculoskeletal Exercises

Nowadays pulmonary diseases are an increasingly important cause of morbidity and mortality. Diaphragmatic breathing is a controlled-breathing technique that aims to optimize thoracoabdominal movements. The aim of this study was to apply a respiratory and musculoskeletal physiotherapy program in institutionalized older adults and to assess the effects on their pulmonary function tests and oxygen saturation. A randomized double-blind clinical trial was conducted with thirty institutionalized older adults, randomly assigned to a control group (CG), who conducted musculoskeletal exercises; or an experimental group (EG) who, in addition, carried out diaphragmatic breathing, administered for eight weeks, three times/week. Outcomes were pulmonary function variables (forced vital capacity, FVC; forced expired volume at 1 s, FEV1; the FEV1/FVC ratio) and oxygen saturation (SpO2) before and after treatment. Normality of the distributions was tested with Saphiro-Wilk and the pre-post improvement was assessed with a two-sample Mann-Whitney test. Significance level was corrected for multiple comparisons using Benjamini-Hochberg correction (p < 0.04). There was a clinically significant improvement of FVC and FEV1 for the EG. Moreover, the EG showed a statistically significant increase of SpO2 (p = 0.028) after treatment when compared to CG. A physiotherapy program combining breathing and musculoskeletal exercises, improved respiratory parameters in institutionalized older adults.

Diaphragm Morphology Assessed by Computed Tomography in Chronic Obstructive Pulmonary Disease

Rationale: Chronic obstructive pulmonary disease (COPD) is associated with abnormal skeletal muscle morphology and function. Objectives: To test the hypothesis that in vivo diaphragm muscle morphology assessed by computed tomography (CT) imaging would be associated with COPD severity, exacerbations, health status, and exercise capacity. Methods: The COPD Morphometry Study is a cross-sectional study that enrolled a clinical sample of smokers with COPD. Spirometry was performed and COPD severity was defined according to guidelines. Three-dimensional left hemidiaphragm morphology was segmented from contiguous axial CT images acquired at maximal inspiration, yielding quantitative measures of diaphragm CT density in Hounsfield units, dome height, and muscle volume. Exacerbations prompting pharmacotherapy or hospitalization in the preceding 12 months and St. George's Respiratory Questionnaire for COPD were assessed. Incremental symptom-limited cycle ergometry quantified peak oxygen uptake ([Formula: see text]o_2Peak). Associations were adjusted for age, sex, body height, body mass index, and smoking status. Results: Among 65 smokers with COPD (75% male; [mean ± standard deviation (SD)] 56 ± 26 pack-years; forced expiratory volume in 1 second [FEV₁] percentage predicted 55 ± 23%), mean diaphragm CT density was 3.1 ± 10 Hounsfield units, dome height was 5.2 ± 1.3 cm, and muscle volume was 57 ± 24 cm³. A 1-SD decrement in the diaphragm CT density was associated with 8.3% lower FEV₁, 3.27-fold higher odds of exacerbation history, 9.7-point higher score on the St. George's Respiratory Questionnaire for COPD, and 2.5 ml/kg/min lower [Formula: see text]o_2Peak. A 1-SD decrement in dome height was associated with 11% lower FEV₁ and 1.3 ml/kg/min lower [Formula: see text]o_2Peak. There were no associations with diaphragm volume observed. Conclusions: CT-assessed diaphragm morphology was associated with COPD severity, exacerbations, impaired health status, and exercise intolerance. The mechanisms and functional impact of lower diaphragm CT density merit investigation.

Effects of core-postural stabilisation on fluoroscopy diaphragmatic measurement and dyspnea in chronic obstructive pulmonary disease: A randomized single-blinded clinical trial

BACKGROUND:

While respiratory and core-postural stabilisation has recently gained a widespread acceptance to improve pulmonary function and dyspena, the therapeutic effects of and rationale underlying the use of respiratory and core-postural stabilisation in the management of patients with chronic obstructive pulmonary disease have not been investigated.

OBJECTIVE:

This study aimed to compare the effects of abdominal breathing and respiratory and core-postural stabilisation on diaphragmatic movement and pulmonary function.

METHODS:

Fourteen patients with moderate chronic obstructive pulmonary disease were randomly assigned to either the respiratory and core-postural stabilisation or abdominal breathing group. All patients underwent fluoroscopy-guided chest X-ray imaging and pulmonary function tests before and after the interventions; the modified Medical Research Council questionnaire was also administered before and after the interventions. Six sessions of either intervention were consistently provided. The obtained data were assessed using independent t-tests and Wilcoxon signed-rank test with a significance threshold of P< 0.05.

RESULTS:

Respiratory and core-postural stabilisation was more effective in increasing diaphragmatic movements than abdominal breathing (P< 0.05). Pulmonary function tests revealed more significant differences in the forced vital capacity (FVC(%)predicted) only after respiratory and core-postural stabilisation (P= 0.004). The Medical Research Council questionnaire score was significantly different within the Respiratory and core-postural stabilisation group (P= 0.014).

CONCLUSIONS:

Our novel results suggest that the effects of respiratory and core-postural stabilisation breathing on diaphragmatic movement and pulmonary function were superior to those of abdominal breathing in patients with chronic obstructive pulmonary disease.

Reduction of COPD Hyperinflation by Endobronchial Valves Improves Intercostal Muscle Morphology on Ultrasound

Background and Objectives

Parasternal intercostal ultrasound morphology reflects spirometric COPD severity. Whether this relates to the systemic nature of COPD or occurs in response to hyperinflation is unknown. We aimed to assess changes in ultrasound parasternal intercostal muscle quantity and quality (echogenicity) in response to relief of hyperinflation. We hypothesised that reduction in hyperinflation following endobronchial valve (EBV) insertion would increase ultrasound parasternal thickness and decrease echogenicity.

Methods

In this prospective cohort study, eight patients with severe COPD underwent evaluation of health-related quality of life, lung function, and sonographic thickness of 2^nd parasternal intercostal muscles and diaphragm thickness, both before and after EBV insertion. Relationships between physiological and radiographic lung volumes, quality of life and ultrasound parameters were determined.

Results

Baseline FEV₁ was 1.02L (SD 0.37) and residual volume (RV) was 202% predicted (SD 41%). Median SGRQ was 63.26 (range 20–70.6). Change in RV (−0.51 ± 0.9L) following EBV-insertion showed a strong negative correlation with change in parasternal thickness (r = −0.883) ipsilateral to EBV insertion, as did change in target lobe volume (−0.89 ± 0.6L) (r = −0.771). Parasternal muscle echogenicity, diaphragm thickness and diaphragm excursion did not significantly change.

Conclusions

Dynamic changes in intercostal muscle thickness on ultrasound measurement occur in response to relief of hyperinflation. We demonstrate linear relationships between intercostal thickness and change in hyperinflation following endobronchial valve insertion. This demonstrates the deleterious effect of hyperinflation on intrinsic inspiratory muscles and provides an additional mechanism for symptomatic response to EBVs.

Diagnostic and clinical values of non-cardiac ultrasound in COPD: A systematic review

BACKGROUND

Clinical and research utility of non-cardiac ultrasound (US) in chronic obstructive pulmonary disease (COPD) has been widely investigated. However, there is no systematic review assessing the clinical values of non-cardiac US techniques in COPD.

METHODS

We systematically searched electronic databases from inception to 24 June 2020. Two independent reviewers in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines extracted data. A narrative synthesis of the results was conducted considering non-cardiac US techniques that looked for diaphragm, muscles and bones in patients with COPD.

RESULTS

In total, 2573 abstracts were screened, and 94 full-text papers were reviewed. A total of 54 studies met the inclusion criteria. Thirty-five studies assessed the diaphragm, while 19 studies evaluated different muscles, including limb muscles and pulmonary lesions in COPD using US. Of the 54 included studies, 30% (16/54) evaluated the changes in either limb muscles or diaphragmatic features before and after physical interventions; 67% (36/54) assessed the correlations between sonographic features and COPD severity. Indeed, 14/15 and 9/13 studies reported a significant reduction in diaphragm excursion and thickness in COPD compared with healthy subjects, respectively; this was correlated significantly with the severity and prognosis of COPD. Three studies reported links between diaphragm length and COPD, where lower diaphragm length correlated with poorer prognosis and outcomes. Quadriceps (rectus femoris), ankle dorsiflexor (tibialis anterior) and vastus lateralis were the most common muscles in COPD assessed by US. More than 70% (12/17) of the studies reported a significant reduction in the cross-sectional area (CSA) of the rectus femoris, rectus femoris and vastus lateralis thickness in COPD compared with healthy subjects. Quadriceps CSA and thickness correlated positively with COPD prognosis, in which patients with reduced quadriceps CSA and thickness have higher risk of exacerbation, readmission and death.

CONCLUSION

US measurements of diaphragm excursion and thickness, as well as lower limb muscles strength, size and thickness, may provide a safe, portable and effective alternative to radiation-based techniques in diagnosis and prognosis as well as tracking improvement postintervention in patients with COPD.

Ultrasonographic assessment of skeletal muscle mass and diaphragm function in patients with chronic obstructive pulmonary disease: A case-control study

BACKGROUND

Although muscle dysfunction is a major contributor to morbidity in chronic obstructive pulmonary disease (COPD), assessment of skeletal muscle, and diaphragm function is not routinely performed in COPD patients.

OBJECTIVES

(1) The aim is to assess muscle dysfunction in COPD by measuring the zone of apposition of diaphragm, diaphragm excursion, thickness of diaphragm, and rectus femoris cross-sectional area (RFCSA) with ultrasonography.(2) To correlate the above assessments with spirometric parameters; notably forced expiratory volume in 1 s (FEV₁).

METHODS

Twenty-four consecutive stable COPD patients and 18 controls were included after obtaining written informed consent. Demographic and clinical data, spirometric values, 6-min walk distance, and sonographic parameters mentioned above were compiled for the analysis.

RESULTS

All included participants were male with a mean age of 62.5 ± 8.4 years. The mean FEV₁in cases was 1.12 ± 0.4 L versus 2.41 ± 0.5 L in controls. The diaphragm thickness (1.8 ± 0.5 mm vs. 2.2 ± 0.6 mm;P = 0.005) and RFCSA was significantly lower in COPD patients (4.8 ± 1.3 cm^[2] vs. 6.12 ± 1.2 cm^[2];P = 0.02). However, diaphragm excursion (5.35 ± 2.8 cm vs. 7 ± 2.6 cm) although lower in COPD patients, was not significantly different between the groups. Correlation between FEV₁and ultrasound diaphragm measurements and RFCSA by Spearman's Rho correlation was poor (ρ= 0.2).

CONCLUSION

Ultrasonographic assessment of the diaphragm and rectus femoris can be used as markers to assess skeletal muscle dysfunction in COPD as diaphragmatic function and RFCSA were lower in COPD patients.

Diaphragm-protective mechanical ventilation

PURPOSE OF REVIEW

Diaphragm dysfunction is common in mechanically ventilated patients and predisposes them to prolonged ventilator dependence and poor clinical outcomes. Mechanical ventilation is a major cause of diaphragm dysfunction in these patients, raising the possibility that diaphragm dysfunction might be prevented if mechanical ventilation can be optimized to avoid diaphragm injury - a concept referred to as diaphragm-protective ventilation. This review surveys the evidence supporting the concept of diaphragm-protective ventilation and introduces potential routes and challenges to pursuing this strategy.

RECENT FINDINGS

Mechanical ventilation can cause diaphragm injury (myotrauma) by a variety of mechanisms. An understanding of these various mechanisms raises the possibility of a new approach to ventilatory management, a diaphragm-protective ventilation strategy. Deranged inspiratory effort is the main mediator of diaphragmatic myotrauma; titrating ventilation to maintain an optimal level of inspiratory effort may help to limit diaphragm dysfunction and accelerate liberation of mechanical ventilation.

SUMMARY

Mechanical ventilation can cause diaphragm injury and weakness. A novel diaphragm-protective ventilation strategy, avoiding the harmful effects of both excessive and insufficient inspiratory effort, has the potential to substantially improve outcomes for patients.

Physical signs in patients with chronic obstructive pulmonary disease

We reviewed the various physical signs of chronic obstructive pulmonary disease, their pathogenesis, and clinical importance. We searched PubMed, EMBASE, and the CINAHL from inception to March 2018. We used the following search terms: chronic obstructive pulmonary disease, physical examination, purse-lip breathing, breath sound intensity, forced expiratory time, abdominal paradox, Hoover's sign, barrel-shaped chest, accessory muscle use, etc. All types of studies were chosen. Globally, history taking and clinical examination of the patients is on the wane. One reason can be a significant development in the field of medical technology, resulting in overreliance on sophisticated diagnostic machines, investigative procedures, and medical tests as first-line modalities of patient's management. In resource-constrained countries, detailed history taking and physical examination should be emphasized as one of the important modalities in patient's diagnosis and management. Declining bedside skills and clinical aptitude among the physician is indeed a concern nowadays. Physical diagnosis of chronic obstructive pulmonary disease (COPD) is the quickest and reliable modalities that can lead to early diagnosis and management of COPD patients. Bedside elicitation of physical signs should always be the starting point for any diagnosis and therapeutic approach.

Study of the diaphragm in chronic obstructive pulmonary disease using ultrasonography

Aims and Objectives

The study aims to compare the changes in the diaphragm in chronic obstructive pulmonary disease (COPD) patients in Indian population with the help of ultrasound-guided examination. (1) Changes in thickness of the diaphragm during respiration( to rule out diaphragm muscle atrophy). (2) The movement of the diaphragm(correlates with strength and endurance of diaphragm fibres) . (3) Zone of apposition(gives mechanical advantage to diaphragm). (4) Correlation with COPD severity by global initiative for chronic obstructive lung disease (GOLD) staging.

Subjects and Methods

Forty-eight COPD patients attending OPD of DY Patil Hospital were recruited in the study and twenty age-matched controls were taken. Detailed history, pulmonary function test examination, and diaphragm study under ultrasonography was done.

Results

The movement of diaphragm was reduced in mild to moderate COPD (A and B) but increased in COPD with Grade C. Movement of diaphragm was significantly more in cases with COPD Grade B (2.329 cm) and C (2.269 cm) as compared to controls (1.891 cm). Mean diaphragmatic thickness during inspiration and expiration, change in thickness, and zone of apposition were significantly higher in patients with COPD score Grade C as compared to Grade A or B. Zone of apposition was significantly decreased in Grade A (3.257 cm) and B (3.429 cm) compared to control (4.268 cm), while it was significantly increased in cases with Grade C (5.138 cm).

Conclusion

The diaphragm is the main muscle of respiration, and study of diaphragm is very important in COPD. The diaphragm thickness, movement, and zone of apposition were significantly reduced in mild to moderate COPD but increased in severe COPD. This cannot be explained by physiotherapy or collagen accumulation. Hence, diaphragm muscle biopsy and electromyogram study in COPD patients will be required to get a better understanding of this muscle in COPD.

Utility of ultrasound assessment of diaphragmatic function before and after pulmonary rehabilitation in COPD patients

Background

Pulmonary rehabilitation (PR) may improve respiratory symptoms and skeletal muscle strength in patients with COPD. We aimed to evaluate changes in ultrasound (US) measurements of diaphragmatic mobility and thickness after PR in COPD patients and to test its correlation with PR outcomes.

Methods

Twenty-five COPD patients were enrolled and underwent a diaphragm US assessment before and after a 12-week PR program.

Results

We found a correlation between the intraindividual percentage of change in the diaphragmatic length of zone of apposition at functional residual capacity (ΔLzapp%) and the change in 6-minute walking distance (6MWD) after PR (rho=0.49, P=0.02). ΔLzapp% was significantly higher in patients with improved 6MWD and COPD Assessment Test (CAT) score (mean rank=12.03±2.57 vs 6.88±4.37; P=0.02). A ΔLzapp% of ≥10% was able to discriminate among patients with improved 6MWD, with a sensitivity of 83% and a specificity of 74%. The area under the receiver operating characteristic curve for ΔLzapp% was 0.83. A cutoff value of ≥9% of ΔLzapp% had a positive predictive value in discriminating a reduction in ≥2 points of CAT score after PR, with a sensitivity and a specificity of 80% and 62%, respectively.

Conclusion

Diaphragm US assessment represents a useful prognostic marker of PR outcomes in COPD patients.

Inspiratory muscle activation increases with COPD severity as confirmed by non-invasive mechanomyographic analysis

There is a lack of instruments for assessing respiratory muscle activation during the breathing cycle in clinical conditions. The aim of the present study was to evaluate the usefulness of the respiratory muscle mechanomyogram (MMG) for non-invasively assessing the mechanical activation of the inspiratory muscles of the lower chest wall in both patients with chronic obstructive pulmonary disease (COPD) and healthy subjects, and to investigate the relationship between inspiratory muscle activation and pulmonary function parameters. Both inspiratory mouth pressure and respiratory muscle MMG were simultaneously recorded under two different respiratory conditions, quiet breathing and incremental ventilatory effort, in 13 COPD patients and 7 healthy subjects. The mechanical activation of the inspiratory muscles was characterised by the non-linear multistate Lempel–Ziv index (MLZ) calculated over the inspiratory time of the MMG signal. Subsequently, the efficiency of the inspiratory muscle mechanical activation was expressed as the ratio between the peak inspiratory mouth pressure to the amplitude of the mechanical activation. This activation estimated using the MLZ index correlated strongly with peak inspiratory mouth pressure throughout the respiratory protocol in both COPD patients (r = 0.80, p<0.001) and healthy (r = 0.82, p<0.001). Moreover, the greater the COPD severity in patients, the greater the level of muscle activation (r = -0.68, p = 0.001, between muscle activation at incremental ventilator effort and FEV₁). Furthermore, the efficiency of the mechanical activation of inspiratory muscle was lower in COPD patients than healthy subjects (7.61±2.06 vs 20.42±10.81, respectively, p = 0.0002), and decreased with increasing COPD severity (r = 0.78, p<0.001, between efficiency of the mechanical activation at incremental ventilatory effort and FEV₁). These results suggest that the respiratory muscle mechanomyogram is a good reflection of inspiratory effort and can be used to estimate the efficiency of the mechanical activation of the inspiratory muscles. Both, inspiratory muscle activation and inspiratory muscle mechanical activation efficiency are strongly correlated with the pulmonary function. Therefore, the use of the respiratory muscle mechanomyogram can improve the assessment of inspiratory muscle activation in clinical conditions, contributing to a better understanding of breathing in COPD patients.

Breathing techniques in patients with chronic obstructive pulmonary disease (COPD)

Background:Breathing techniques are included in the rehabilitation program of patients with chronic obstructive pulmonary disease (COPD). The efficacy of breathing techniques aiming at improving symptoms of dyspnea and eliciting physiological effects is discussed in this paper. In patients with COPD, breathing techniques aim to relieve symptoms and ameliorate adverse physiological effects by: 1) increasing strength and endurance of the respiratory muscles; 2) optimizing the pattern of thoracoabdominal motion; and 3) reducing dynamic hyperinflation of the rib cage and improving gas exchange. Evidence exists to support the effectiveness of pursed lips breathing, forward leaning position, active expiration and inspiratory muscle training, but not for diaphragmatic breathing. Careful patient selection, proper and repeated instruction and control of the techniques, and assessment of the effects are necessary. Despite the evidence that breathing techniques are effective, several problems need to be resolved. The limited evidence for the transfer of the effects of breathing techniques during resting conditions to exercise conditions raises several questions. Do breathing techniques have to be practiced during activities of daily living?

Action of the diaphragm on the rib cage

When the diaphragm contracts, pleural pressure falls, exerting a caudal and inward force on the entire rib cage. However, the diaphragm also exerts forces in the cranial and outward direction on the lower ribs. One of these forces, the "insertional force," is applied by the muscle at its attachments to the lower ribs. The second, the "appositional force," is due to the transmission of abdominal pressure to the lower rib cage in the zone of apposition. In the control condition at functional residual capacity, the effects of these two forces on the lower ribs are nearly equal and outweigh the effect of pleural pressure, whereas for the upper ribs, the effect of pleural pressure is greater. The balance between these effects, however, may be altered. When the abdomen is given a mechanical support, the insertional and appositional forces are increased, so that the muscle produces a larger expansion of the lower rib cage and, with it, a smaller retraction of the upper rib cage. In contrast, at higher lung volumes the zone of apposition is decreased, and pleural pressure is the dominant force on the lower ribs as well. Consequently, although the force exerted by the diaphragm on these ribs remains inspiratory, rib displacement is reversed into a caudal-inward displacement. This mechanism likely explains the inspiratory retraction of the lateral walls of the lower rib cage observed in many subjects with chronic obstructive pulmonary disease (Hoover's sign). These observations support the use of a three-compartment, rather than a two-compartment, model to describe chest wall mechanics.

Radiologic manifestations of bronchoscopic lung volume reduction in severe chronic obstructive pulmonary disease

OBJECTIVE. Bronchoscopic lung volume reduction promises to become an effective treatment option in severe chronic obstructive pulmonary disease. Several techniques are currently being investigated, including implantation of devices into the lung and instillation of hot water vapor or polymer. This article reviews the spectrum of radiologic manifestations on chest radiography and CT that occur after the intervention. CONCLUSION. Familiarity with the intended effects and adverse events will aid the radiologist in supporting bronchoscopic lung volume reduction.

Analysis of diaphragmatic movement before and after pulmonary rehabilitation using fluoroscopy imaging in patients with COPD

Background

The diaphragm is the principal inspiratory muscle. The purpose of this study was to assess improvements in diaphragmatic movement before and after pulmonary rehabilitation in patients with chronic obstructive pulmonary disease (COPD), using a fluoroscopy-guided chest X-ray.

Patients and methods

Among 117 patients with COPD receiving pulmonary rehabilitation who underwent the initial fluoroscopy-guided chest X-ray and pulmonary function test, 37 of those patients who underwent both initial and follow-up fluoroscopy and pulmonary function tests were enrolled in this study. After hospital education, participants received pulmonary rehabilitation through regular home-based training for at least 3 months by the same physiatrist. We assessed the changes in diaphragm area with fluoroscopy-guided posteroanterior chest X-rays between pre- and postpulmonary rehabilitation. To minimize radiation hazards for subjects, the exposure time for fluoroscopy to take chest X-rays was limited to less than 5 seconds.

Results

There were significant improvements (2,022.8±1,548.3 mm² to 3,010.7±1,495.6 mm² and 2,382.4±1,475.9 mm² to 3,315.9±1,883.5 mm²; right side P=0.001 and left side P=0.019, respectively) in diaphragmatic motion area during full inspiration and expiration in both lungs after pulmonary rehabilitation. Pulmonary function tests showed no statistically significant difference between pre- and postpulmonary rehabilitation.

Conclusion

The study suggests that the strategy to assess diaphragm movement using fluoroscopy is a relatively effective tool for the evaluation of pulmonary rehabilitation in COPD patients in terms of cost and time savings compared with computed tomography or magnetic resonance imaging.

Action of the isolated canine diaphragm on the lower ribs at high lung volumes

The normal diaphragm has an inspiratory action on the lower ribs, but subjects with chronic obstructive pulmonary disease commonly have an inward displacement of the lateral portions of the lower rib cage during inspiration. This paradoxical displacement, conventionally called 'Hoover's sign', has traditionally been attributed to the direct action of radially oriented diaphragmatic muscle fibres. In the present study, the inspiratory intercostal muscles in all interspaces in anaesthetized dogs were severed so that the diaphragm was the only muscle active during inspiration. The displacements of the lower ribs along the craniocaudal and laterolateral axes and the changes in pleural pressure (∆Ppl) and transdiaphragmatic pressure were measured during occluded breaths and mechanical ventilation at different lung volumes between functional residual capacity (FRC) and total lung capacity. From these data, the separate effects on rib displacement of ∆Ppl and of the force exerted by the diaphragm on the ribs were determined. Isolated spontaneous diaphragm contraction at FRC displaced the lower ribs cranially and outward, but this motion was progressively reversed into a caudal and inward motion as lung volume increased. However, although the force exerted by the diaphragm on the ribs decreased with increasing volume, it continued to displace the ribs cranially and outward. These observations suggest that Hoover's sign is usually caused by the decrease in the zone of apposition and, thus, by the dominant effect of ∆Ppl on the lower ribs, rather than an inward pull from the diaphragm.

Lung hyperinflation in chronic obstructive pulmonary disease: mechanisms, clinical implications and treatment

Lung hyperinflation is highly prevalent in patients with chronic obstructive pulmonary disease and occurs across the continuum of the disease. A growing body of evidence suggests that lung hyperinflation contributes to dyspnea and activity limitation in chronic obstructive pulmonary disease and is an important independent risk factor for mortality. In this review, we will summarize the recent literature on pathogenesis and clinical implications of lung hyperinflation. We will outline the contribution of lung hyperinflation to exercise limitation and discuss its impact on symptoms and physical activity. Finally, we will examine the physiological rationale and efficacy of selected pharmacological and non-pharmacological 'lung deflating' interventions aimed at improving symptoms and physical functioning.

The effects of a physiotherapy programme on patients with a pleural effusion: a randomized controlled trial

Objective:

To investigate the effects of a physiotherapy protocol on patients with pleural effusion.

Design:

Randomized controlled trial.

Setting:

University hospital.

Participants:

A total of 104 consecutive inpatients with a medical diagnosis of pleural effusion.

Intervention:

Patients were randomly allocated to a control group receiving standard treatment (medical treatment and drainage) or an intervention group treated with physiotherapy added to standard treatment. The physiotherapy programme included deep breathing exercises, mobilizations and incentive spirometry.

Main outcome measures:

Spirometric predicted values and chest radiographs were measured before treatment and at discharge and the length of hospital stay was recorded. Assessors were blinded to the intervention.

Results:

A comparative analysis showed a significant improvement of spirometric parameters in the intervention group; pre-to-post hospitalization predicted values showed significant changes in vital capacity (73.1 ± 12.6% to 72.13 ± 13.7 %, P<0.001 ), forced expiratory volume in first second (72.13 ± 13.7% to 78.98 ± 16.9%, P<0.001) and forced expiratory flow at 25-75 % (64.8 ± 35.1% to 76.78 ± 35.3%, P=0.198) compared to the control group that showed no significant changes across treatment. The radiographic findings showed better scores on the affected side of the thorax at discharge in the physiotherapy group. Length of hospital stay was also significantly ( P=0.014) shorter in the intervention group (26.7 ± 8.8 days) compared to the control group (38.6 ± 10.7 days).

Conclusions:

A physiotherapy programme added to standard treatment improves the spirometric parameters and the radiological findings and reduces the hospital stay in patients with a pleural effusion.

The relationships between tracheal index and lung volume parameters in mild-to-moderate COPD

BACKGROUND

Although elongated morphological changes in the trachea are known to be related to lung function in chronic obstructive pulmonary disease (COPD), whether the tracheal morphological changes are associated with airflow limitations or overinflation of the lung in the early stages of COPD has not yet been determined. Thus, our aim was to investigate the association of tracheal index (TI) with lung function parameters, including lung volume parameters, in COPD patients with mild-to-moderate airflow limitations.

MATERIALS AND METHODS

A retrospective study was conducted in 193 COPD patients with GOLD grades 1-2 (post-bronchodilator forced expiratory volume in 1s [FEV1] ≥ 50% predicted with FEV1/forced vital capacity ratio ≤ 70%; age range, 40-81) and 193 age- and gender-matched subjects with normal lung function as a control group (age range, 40-82). Two independent observers measured TI at three anatomical levels on chest radiographs and CT scans.

RESULTS

Compared with the control group, TI was reduced significantly and "saber-sheath trachea" was observed more frequently in COPD patients. Patients with GOLD grade 2 disease had a lower TI than those with GOLD grade 1. TI had apparent inverse correlations with total lung capacity, functional residual capacity, and residual volume, regardless of the anatomical level of the trachea. Even after adjustments for covariates, this association persisted.

CONCLUSIONS

TI is reduced even in mild-to-moderate COPD patients, and TI measured on chest CT shows significant inverse relationships with all lung volume parameters assessed, suggesting that tracheal morphology may change during the early stages of COPD.

No room to breathe: the importance of lung hyperinflation in COPD

Patients with chronic obstructive pulmonary disease (COPD) are progressively limited in their ability to undertake normal everyday activities by a combination of exertional dyspnoea and peripheral muscle weakness. COPD is characterised by expiratory flow limitation, resulting in air trapping and lung hyperinflation. Hyperinflation increases acutely under conditions such as exercise or exacerbations, with an accompanying sharp increase in the intensity of dyspnoea to distressing and intolerable levels. Air trapping, causing increased lung hyperinflation, can be present even in milder COPD during everyday activities. The resulting activity-related dyspnoea leads to a vicious spiral of activity avoidance, physical deconditioning, and reduced quality of life, and has implications for the early development of comorbidities such as cardiovascular disease. Various strategies exist to reduce hyperinflation, notably long-acting bronchodilator treatment (via reduction in flow limitation and improved lung emptying) and an exercise programme (via decreased respiratory rate, reducing ventilatory demand), or their combination. Optimal bronchodilation can reduce exertional dyspnoea and increase a patient's ability to exercise, and improves the chance of successful outcome of a pulmonary rehabilitation programme. There should be a lower threshold for initiating treatments appropriate to the stage of the disease, such as long-acting bronchodilators and an exercise programme for patients with mild-to-moderate disease who experience persistent dyspnoea.

The effect of posture on asynchronous chest wall movement in COPD

Chronic obstructive pulmonary disease (COPD) patients often show asynchronous movement of the lower rib cage during spontaneous quiet breathing and exercise. We speculated that varying body position from seated to supine would influence rib cage asynchrony by changing the configuration of the respiratory muscles. Twenty-three severe COPD patients (forced expiratory volume in 1 s = 32.5 ± 7.0% predicted) and 12 healthy age-matched controls were studied. Measurements of the phase shift between upper and lower rib cage and between upper rib cage and abdomen were performed with opto-electronic plethysmography during quiet breathing in the seated and supine position. Changes in diaphragm zone of apposition were measured by ultrasounds. Control subjects showed no compartmental asynchronous movement, whether seated or supine. In 13 COPD patients, rib cage asynchrony was noticed in the seated posture. This asynchrony disappeared in the supine posture. In COPD, upper rib cage and abdomen were synchronous when seated, but a strong asynchrony was found in supine. The relationships between changes in diaphragm zone of apposition and volume variations of chest wall compartments supported these findings. Rib cage paradox was noticed in approximately one-half of the COPD patients while seated, but was not related to impaired diaphragm motion. In the supine posture, the rib cage paradox disappeared, suggesting that, in this posture, diaphragm mechanics improves. In conclusion, changing body position induces important differences in the chest wall behavior in COPD patients.

Neuromuscular ultrasound for evaluation of the diaphragm

Neuromuscular clinicians are often asked to evaluate the diaphragm for diagnostic and prognostic purposes. Traditionally, this evaluation is accomplished through history, physical exam, fluoroscopic sniff test, nerve conduction studies, and electromyography (EMG). Nerve conduction studies and EMG in this setting are challenging, uncomfortable, and can cause serious complications, such as pneumothorax. Neuromuscular ultrasound has emerged as a non-invasive technique that can be used in the structural and functional assessment of the diaphragm. In this study we review different techniques for assessing the diaphragm using neuromuscular ultrasound and the application of these techniques to enhance diagnosis and prognosis by neuromuscular clinicians.

Diaphragm efficiency estimated as power output relative to activation in chronic obstructive pulmonary disease

Muscle efficiency increases with fiber length and decreases with load. Diaphragm efficiency (Eff(di)) in healthy humans, measured as power output (Wdi) relative to the root mean square of diaphragm electromyogram (RMS(di)), increases with hyperpnea due to phasic activity of abdominal muscles acting to increase diaphragm length at end expiration (L(di ee)) and decrease inspiratory load. In chronic obstructive pulmonary disease (COPD), hyperpnea may decrease Eff(di) if L(di ee) decreases and load increases due to airflow obstruction and dynamic hyperinflation. To examine this hypothesis, we measured Eff(di) in six COPD subjects (mean forced expiratory volume in 1 s: 54% predicted) when breathing air and at intervals during progressive hypercapnic hyperpnea. Wdi was measured as the product of mean inspiratory transdiaphragmatic pressure (ΔPdi(mean)), diaphragm tidal volume measured fluoroscopically, and 1/inspiratory duration. Results were compared with those of six healthy subjects reported previously. In COPD, L(di ee) was normal when breathing air. ΔPdi(mean) and Wdi increased normally, and RMS(di) increased disproportionately (P = 0.01) with hyperpnea, and, unlike health, inspiratory capacity (IC), L(di ee), and Eff(di) did not increase. IC and L(di ee) were constant with hyperpnea because mean expiratory flow increased as expiratory duration decreased (r(2) = 0.65), and because expiratory flow was terminated actively by the balance between expiratory and inspiratory muscle forces near end expiration, and these forces increased proportionately with hyperpnea (r(2) = 0.49). At maximum ventilation, diaphragm radius of curvature at end inspiration increased in COPD (P = 0.04) but not controls; diaphragm radius of curvature at end inspiration and ln(Eff(di)) were negatively correlated (P = 0.01). Thus in COPD with modest airflow obstruction, Eff(di) did not increase normally with hyperpnea due to a constant L(di ee) and inspiratory flattening of the diaphragm.

[Respiratory pump failure. Clinical symptoms, diagnostics and therapy]

The total anatomical and functional apparatus which allows normal ventilation of the lungs is known as the respiratory pump. An insufficiency of this system, which can be caused by a multitude of reasons, primarily affects the inspiratory musculature and especially the diaphragm. One of the essential clinical characteristics is rapid shallow breathing. Exhaustion of the repiratory musculature due to acute respiratory insufficiency is normally clinically registered but can also be functionally determined in particular by the maximum static inspiratory closed mouth pressure. A further option is invasive measurement of the transdiaphragmal pressure, which however is not suitable as a routine procedure. Mechanical ventilation is used as treatment of respiratory pump insufficiency independent of the cause. This is initially a non-invasive procedure but if unsuccessful intubation and invasive ventilation are indicated. The technical developments in the field of extracorporeal gas exchange systems are very promising. However, in view of the insufficient data, ventilation procedures using masks and tubes still remain the first choice methods.

Mechanism of the lung-deflating action of the canine diaphragm at extreme lung inflation

When lung volume in animals is passively increased beyond total lung capacity (TLC; transrespiratory pressure = +30 cmH2O), stimulation of the phrenic nerves causes a rise, rather than a fall, in pleural pressure. It has been suggested that this was the result of inward displacement of the lower ribs, but the mechanism is uncertain. In the present study, radiopaque markers were attached to muscle bundles in the midcostal region of the diaphragm and to the tenth rib pair in five dogs, and computed tomography was used to measure the displacement, length, and configuration of the muscle and the displacement of the lower ribs during relaxation at seven different lung volumes up to +60 cmH2O transrespiratory pressure and during phrenic nerve stimulation at the same lung volumes. The data showed that 1) during phrenic nerve stimulation at 60 cmH2O, airway opening pressure increased by 1.5 ± 0.7 cmH2O; 2) the dome of the diaphragm and the lower ribs were essentially stationary during such stimulation, but the muscle fibers still shortened significantly; 3) with passive inflation beyond TLC, an area with a cranial concavity appeared at the periphery of the costal portion of the diaphragm, forming a groove along the ventral third of the rib cage; and 4) this area decreased markedly in size or disappeared during phrenic stimulation. It is concluded that the lung-deflating action of the isolated diaphragm beyond TLC is primarily related to the invaginations in the muscle caused by the acute margins of the lower lung lobes. These findings also suggest that the inspiratory inward displacement of the lower ribs commonly observed in patients with emphysema (Hoover's sign) requires not only a marked hyperinflation but also a large fall in pleural pressure.

Influence of the distribution of emphysema on diaphragmatic motion in patients with chronic obstructive pulmonary disease

PURPOSE

We investigated whether the distribution of emphysema on computed tomography (CT) images can affect chest wall motion in patients with chronic obstructive lung disease (COPD).

MATERIALS AND METHODS

The subjects were 35 male patients with COPD (age, 69.7 ± 6.2 years). The RA-950 (the ratio of lung volume under -950 HU to total lung volume on CT) was measured separately for the upper and lower halves of the lung. We analyzed the flatness of the diaphragm (Kdome) and its motion (ΔLappo) using dynamic magnetic resonance imaging. Paradoxical motion (Mpr) represented the ratio of the paradoxical diaphragmatic movement (downward or upward) when the lung area decreased or increased, respectively, to he total diaphragm movement (expressed as a percent). These parameters were analyzed in correlation with pulmonary function tests and St. George Respiratory Questionnaire (SGRQ) scores.

RESULTS

The RA-950 of the lower lung zone correlated significantly with the Kdome (P = 0.033), ΔLappo (P = 0.006), Mpr (%) (P = 0.001), forced expiratory volume at 1 s (% predicted; P < 0.001), and activity score of the SGRQ (p = 0.017). The RA-950 of the upper lung zone did not correlate with these parameters.

CONCLUSION

In COPD patients, the distribution of emphysema on CT correlates with airflow obstruction and abnormal diaphragmatic motion.

Respiratory muscle function and activation in chronic obstructive pulmonary disease

Inspiratory muscles are uniquely adapted for endurance, but their function is compromised in chronic obstructive pulmonary disease (COPD) due to increased loads, reduced mechanical advantage, and increased ventilatory requirements. The hyperinflation of COPD reduces the flow and pressure-generating capacity of the diaphragm. This is compensated by a threefold increase in neural drive, adaptations of the chest wall and diaphragm shape to accommodate the increased volume, and adaptations of muscle fibers to preserve strength and increase endurance. Paradoxical indrawing of the lower costal margin during inspiration in severe COPD (Hoover's sign) correlates with high inspiratory drive and severe airflow obstruction rather than contraction of radially oriented diaphragm fibers. The inspiratory muscles remain highly resistant to fatigue in patients with COPD, and the ultimate development of ventilatory failure is associated with insufficient central drive. Sleep is associated with reduced respiratory drive and impairments of lung and chest wall function, which are exaggerated in COPD patients. Profound hypoxemia and hypercapnia can occur in rapid eye movement sleep and contribute to the development of cor pulmonale. Inspiratory muscles adapt to chronic loading with an increased proportion of slow, fatigue-resistant fiber types, increased oxidative capacity, and reduced fiber cross-sectional area, but the capacity of the diaphragm to increase ventilation in exercise is compromised in COPD. In COPD, neural drive to the diaphragm increases to near maximal levels in exercise, but it does not develop peripheral muscle fatigue. The improvement in exercise capacity and dyspnea following lung volume reduction surgery is associated with a substantial reduction in neural drive to the inspiratory muscles.

Respiratory muscle fiber remodeling in chronic hyperinflation: dysfunction or adaptation?

The diaphragm and other respiratory muscles undergo extensive remodeling in both animal models of emphysema and in human chronic obstructive pulmonary disease, but the nature of the remodeling is different in many respects. One common feature is a shift toward improved endurance characteristics and increased oxidative capacity. Furthermore, both animals and humans respond to chronic hyperinflation by diaphragm shortening. Although in rodent models this clearly arises by deletion of sarcomeres in series, the mechanism has not been proven conclusively in human chronic obstructive pulmonary disease. Unique characteristics of the adaptation in human diaphragms include shifts to more predominant slow, type I fibers, expressing slower myosin heavy chain isoforms, and type I and type II fiber atrophy. Although some laboratories report reductions in specific force, this may be accounted for by decreases in myosin heavy chain content as the muscles become more oxidative and more efficient. More recent findings have reported reductions in Ca(2+) sensitivity and reduced myofibrillar elastic recoil. In contrast, in rodent models of disease, there is no consistent evidence for loss of specific force, no consistent shift in fiber populations, and atrophy is predominantly seen only in fast, type IIX fibers. This review challenges the hypothesis that the adaptations in human diaphragm represent a form of dysfunction, secondary to systemic disease, and suggest that most findings can as well be attributed to adaptive processes of a complex muscle responding to unique alterations in its working environment.

Optoelectronic Plethysmography has Improved our Knowledge of Respiratory Physiology and Pathophysiology

It is well known that the methods actually used to track thoraco-abdominal volume displacement have several limitations. This review evaluates the clinical usefulness of measuring chest wall kinematics by optoelectronic plethysmography [OEP]. OEP provides direct measurements (both absolute and its variations) of the volume of the chest wall and its compartments, according to the model of Ward and Macklem, without requiring calibration or subject cooperation. The system is non invasive and does not require a mouthpiece or nose-clip which may modify the pattern of breathing, making the subject aware of his breathing. Also, the precise assessment of compartmental changes in chest wall volumes, combined with pressure measurements, provides a detailed description of the action and control of the different respiratory muscle groups and assessment of chest wall dynamics in a number of physiological and clinical experimental conditions.

Drive to the human respiratory muscles

The motor control of the respiratory muscles differs in some ways from that of the limb muscles. Effectively, the respiratory muscles are controlled by at least two descending pathways: from the medulla during normal quiet breathing and from the motor cortex during behavioural or voluntary breathing. Neurophysiological studies of single motor unit activity in human subjects during normal and voluntary breathing indicate that the neural drive is not uniform to all muscles. The distribution of neural drive depends on a principle of neuromechanical matching. Those motoneurones that innervate intercostal muscles with greater mechanical advantage are active earlier in the breath and to a greater extent. Inspiratory drive is also distributed differently across different inspiratory muscles, possibly also according to their mechanical effectiveness in developing airway negative pressure. Genioglossus, a muscle of the upper airway, receives various types of neural drive (inspiratory, expiratory and tonic) distributed differentially across the hypoglossal motoneurone pool. The integration of the different inputs results in the overall activity in the muscle to keep the upper airway patent throughout respiration. Integration of respiratory and non-respiratory postural drive can be demonstrated in respiratory muscles, and respiratory drive can even be observed in limb muscles under certain circumstances. Recordings of motor unit activity from the human diaphragm during voluntary respiratory tasks have shown that depending on the task there can be large changes in recruitment threshold and recruitment order of motor units. This suggests that descending drive across the phrenic motoneurone pool is not necessarily consistent. Understanding the integration and distribution of drive to respiratory muscles in automatic breathing and voluntary tasks may have implications for limb motor control.

Diaphragm length and neural drive after lung volume reduction surgery

RATIONALE

Patients with chronic obstructive pulmonary disease have shorter inspiratory muscles and higher motor unit firing rates during quiet breathing than do age-matched healthy subjects. Lung volume reduction surgery (LVRS) in patients with chronic obstructive pulmonary disease improves lung function, exercise capacity, and quality of life.

OBJECTIVES

We studied the effect of LVRS on length and motor unit firing rates of diaphragm and scalene muscles.

METHODS

Diaphragm length was estimated by ultrasound and magnetometers, and firing rates were recorded with needle electrodes in patients (five females and seven males) with severe chronic obstructive pulmonary disease, before and after surgery.

MEASUREMENTS AND MAIN RESULTS

Pre-LVRS total lung capacity was 135 +/- 10% predicted (mean +/- SD), and FEV1 was 30 +/- 12% predicted. After surgery, median firing frequency of diaphragmatic motor units fell from 17.3 +/- 4.2 to 14.5 +/- 3.4 Hz (p < 0.001), and scalene motor unit firing rates were reduced from 15.3 +/- 6.9 to 13.4 +/- 3.8 Hz (p < 0.001). Tidal volume and diaphragm length change during quiet breathing did not change, but at end expiration, the zone of apposition length of diaphragm against the rib cage (L(Zapp)) increased (30 +/- 28%, p = 0.004). Improvements in quality-of-life measures and exercise performance after surgery were related to increased forced vital capacity and L(Zapp).

CONCLUSIONS

Increased diaphragm length resulted in lower motor unit firing rates and reduced breathing effort, and this is likely to contribute to improved quality of life and exercise performance after LVRS.

Efficiency of the normal human diaphragm with hyperinflation

We evaluated an index of diaphragm efficiency (Eff(di)), diaphragm power output (Wdi) relative to electrical activation, in five healthy adults during tidal breathing at usual end-expiratory lung volume (EELV) and diaphragm length (L(di ee)) and at shorter L(di ee) during hyperinflation with expiratory positive airway pressure (EPAP). Measurements were repeated with an inspiratory threshold (7.5 cmH(2)O) plus resistive (6.5 cmH(2)O.l(-1).s) load. Wdi was the product of mean inspiratory transdiaphragmatic pressure (DeltaPdi(mean)), diaphragm volume displacement measured fluoroscopically, and 1/inspiratory duration (Ti(-1)). Diaphragm activation, measured with esophageal electrodes, was quantified by computing root-mean-square values (RMS(di)). With EPAP, 1) EELV increased [mean r(2) = 0.91 (SD 0.01)]; 2) in four subjects, L(di ee) decreased [mean r(2) = 0.85 (SD 0.07)] and mean Eff(di) decreased 34% per 10% decrease in L(di ee) (P < 0.001); and 3) in one subject, gastric pressure at EELV increased two- to threefold, L(di ee) was unchanged or increased, and Eff(di) increased at two of four levels of EPAP (P < or = 0.006, ANOVA). Inspiratory loading increased Wdi (P = 0.003) and RMS(di) (P = 0.004) with no change in Eff(di) (P = 0.63) or its relationship with L(di ee). Eff(di) was more accurate in defining changes in L(di ee) [(true positives + true negatives)/total = 0.78 (SD 0.13)] than DeltaPdi(mean).RMS(di)(-1), RMS(di), or DeltaPdi(mean).Ti (all <0.7, P < or = 0.05, without load). Thus Eff(di) was principally a function of L(di ee) independent of inspiratory loading, behavior consistent with muscle force-length-velocity properties. We conclude that Eff(di), measured during tidal breathing and in the absence of expiratory muscle activity at EELV, is a valid and accurate measure of diaphragm contractile function.

Effects of chronic hypobaric hypoxia on contractile properties of rat sternohyoid and diaphragm muscles

1. Chronic hypoxia occurs in a variety of circumstances, including respiratory disease and exposure to altitude, and is known to affect respiratory muscle structure. However, little is known about its effects on respiratory muscle contractile properties. 2. Rats were exposed to normoxia (n = 16) or hypobaric hypoxia (n = 16; barometric pressure 450 mmHg) for 6 weeks. Contractile properties were measured in isolated sternohyoid and diaphragm muscles in warmed, oxygenated Krebs' solution. Isometric twitch and tetanic tension, contraction time, half-relaxation time and tension-frequency relationship were determined using field stimulation with platinum electrodes. Fatigue was induced by stimulation at 40 Hz with 300 msec trains of 0.5 Hz for 5 min. 3. Chronic hypoxia had no effect on bodyweight, but did increase haematocrit. Chronic hypoxia increased specific force development in both muscles and increased sternohyoid fatigue. Chronic hypoxia had no effect on contractile kinetics in either muscle, but shifted the tension-frequency relationship to the left in the diaphragm. 4. Therefore, chronic hypoxia alters rat respiratory muscle force and fatigue, either due to the direct effects of hypoxia or to increased muscle activation.