Estimation of diaphragm length in patients with severe chronic obstructive pulmonary disease

Correlation Between Diaphragmatic Excursion and Exercise Tolerance Improvement Following Pulmonary Rehabilitation in Patients with Chronic Obstructive Pulmonary Disease-Obstructive Sleep Apnea Overlap Syndrome

Purpose

We assess the predictive value of diaphragm excursion (DE) in enhancing exercise tolerance following pulmonary rehabilitation (PR) among patients with COPD-OSA overlap syndrome.

Material and Methods

This prospective cohort study enrolled 63 patients diagnosed with COPD-OSA overlap syndrome who actively participated in a PR program from January 2021 to May 2023. Among these, 58 patients successfully completed the 20-week PR program, with exercise tolerance assessed through the measurement of six-minute walk distance (6MWD), and DE evaluated by ultrasonography. The responder to PR in terms of exercise ability was defined as a patient who showed an increase of >30m in 6MWD. The cutoff value for predicting PR response based on DE was determined using receiver operating characteristic (ROC) curves.

Results

Following the PR program, significant improvements were observed in mMRC, 6MWD, DE during deep breathing, and diaphragm thickness fraction (DTF). Of the participants, 33 patients (57%) were classified as responders, while 25 patients (43%) were considered non-responders. Baseline values of FEV1% predicted, 6MWD, DE during deep breathing, DTF, and PaO2 exhibited a significant elevation in responders as compared to non-responders. The changes of 6MWD were positively associated with the baseline values of DTF and DE during deep breathing, FEV1% predicted and PaO2, while negatively correlated with baseline value of mMRC. The predictive performance in terms of the area under the ROC curve for determining responder's DTF was found to be 0.769, accompanied by a sensitivity of 85% and specificity of 68%, using a cutoff value at 17.26%. Moreover, it was observed that DE during deep breathing could predict the area under the ROC curve for responders to be 0.753, with a sensitivity of 91% and specificity of 56% at a cutoff value of 3.61cm.

Conclusion

Diaphragm excursion serves as a valuable predictor for determining the enhancement of exercise tolerance following PR in patients with COPD-OSA overlap syndrome.

Trial Registration

ChiCTR1800020257, www.chictr.org.cn/index.aspx.

Respiratory muscle training program supplemented by a cell-phone application in COPD patients with severe airflow limitation

PURPOSE

The purpose of this study was to implement a respiratory muscle training program through a mobile phone application for COPD patients with severe airflow limitation.

METHODS

We conducted an experimental study to determine the efficacy of a six-month mobile phone application. At least three times a week for six months the patients would participate in an online training session. We evaluated the lung volumes, maximal inspiratory and expiratory pressure (MIP/MEP) and diaphragm amplitude. The tests were performed at the beginning and at the end of the study.

RESULTS

Thirty-four patients with severe COPD, aged between 44 and 67 years (Mean ± SD, 59.29 ± 6.063), accepted to follow a rehabilitation program based on the use of the Pneumocontrol application. We observed on increased of MEP from the pre-rehabilitation state (83.41 cmH2O) to the post-rehabilitation state (95.03 cmH2O), z = 5.087, p < 0.001. Also, the median MIP significantly increased from the pre-rehabilitation state to the post-rehabilitation state, z = 5.052, p < 0.001. Diaphragmatic distance also increased from 2.81 cm to 3.44 cm, z = 5.069, p < 0.001.

CONCLUSION

Respiratory muscle training supplemented through a cell phone-based application can improve respiratory muscle strength and diaphragm mobility.

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.

Computed tomographic thoracic morphologic indices in normal subjects and patients with chronic obstructive pulmonary disease: Comparison with spiral CT densitometry and pulmonary function tests

OBJECTIVES

To determine what computed tomographic (CT) dimensions can predict obstructive lung disease on routine chest CT scans by comparing morphological and densitometric CT findings with pulmonary function test (PFT) in normal subjects and patients with chronic obstructive pulmonary disease (COPD).

MATERIALS AND METHODS

Consecutive patients (n = 646; 260 females and 386 males; mean age 54.9 years, ranged 20-90 years) who received chest CT scans with densitometry during a 3-month period were retrospectively analyzed in single center. PFT was undertaken in 235 patients (152 males, 83 females) at same times of CT scanning. The patients were grouped by age (<30 years, 31-45 years, 46-60 years, and >61 years). CT parameters including tracheal, azygoesophageal, thoracic vertical, anterior-posterior (AP), transverse diameters, transverse cardiac diameter, diameters of main, right, and left pulmonary arteries, and CT densitometric values including lung volume and density (-900 to -1000 Hounsfield Units, HU), low attenuation value cluster (default threshold: -950 HU) were compared with PFT values. Spearman correlation coefficients was used to evaluate the relationship between the CT indices and PFT.

RESULTS

Ninety of 235 patients with PFT were smokers (76 males, 14 females). Obstructive PFT was detected in 65 patients (27.7%: 46 males, 19 females). Male smokers with obstructive PFT displayed significantly larger thoracic anterior-posterior (mean: normal, 172.3 cm versus COPD, 185.9 cm, p = 0.0001) and smaller transverse diameters (mean: normal, 247.0 cm vs. COPD, 235.8 cm, p = 0.01), and increased right pulmonary artery diameter (mean: normal, 20.3 cm v s. COPD, 22.1 cm, p < 0.001), and increased left pulmonary artery diameter (mean: normal, 19.7 cm vs. COPD, 20.6 cm, p < 0.025). The lung parenchyma density (-1000 to -900 HU) and greater concentration of largest cluster on densitometry were significantly different between normal and obstructive PFT pattern in male smoker. Residual volume and total lung capacity are positively correlated with lung volume and lung density (-1000 to -800) of densitometry.

CONCLUSIONS

CT findings of the overexpansion of the lungs, such as increases in the vertical diameter of the lung and decreases in the transverse diameter of the heart, can be significant as indirect findings of early chronic obstructive diseases. However, despite the significant CT findings in male smokers, particularly those in their 40s, most lung function parameters were not decidedly abnormal.

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.

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.

Postoperative Respiratory Muscle Dysfunction

Postoperative pulmonary complications are responsible for significant increases in hospital cost as well as patient morbidity and mortality; respiratory muscle dysfunction represents a contributing factor. Upper airway dilator muscles functionally resist the upper airway collapsing forces created by the respiratory pump muscles. Standard perioperative medications (anesthetics, sedatives, opioids, and neuromuscular blocking agents), interventions (patient positioning, mechanical ventilation, and surgical trauma), and diseases (lung hyperinflation, obesity, and obstructive sleep apnea) have differential effects on the respiratory muscle subgroups. These effects on the upper airway dilators and respiratory pump muscles impair their coordination and function and can result in respiratory failure. Perioperative management strategies can help decrease the incidence of postoperative respiratory muscle dysfunction. Such strategies include minimally invasive procedures rather than open surgery, early and optimal mobilizing of respiratory muscles while on mechanical ventilation, judicious use of respiratory depressant anesthetics and neuromuscular blocking agents, and noninvasive ventilation when possible.

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.

Effect of acute inflation on the mechanics of the inspiratory muscles

When the lung is inflated acutely, the capacity of the diaphragm to generate pressure, in particular pleural pressure (Ppl), is impaired because the muscle during contraction is shorter and generates less force. At very high lung volumes, the pressure-generating capacity of the diaphragm may be further reduced by an increase in the muscle radius of curvature. Lung inflation similarly impairs the pressure-generating capacity of the inspiratory intercostal muscles, both the parasternal intercostals and the external intercostals. In contrast to the diaphragm, however, this adverse effect is largely related to the orientation and motion of the ribs, rather than the ability of the muscles to generate force. During combined activation of the two sets of muscles, the change in Ppl is larger than during isolated diaphragm activation, and this added load on the diaphragm reduces the shortening of the muscle and increases muscle force. In addition, activation of the diaphragm suppresses the cranial displacement of the passive diaphragm that occurs during isolated intercostal contraction and increases the respiratory effect of the intercostals. As a result, the change in Ppl generated during combined diaphragm-intercostal activation is greater than the sum of the pressures generated during separate muscle activation. Although this synergistic interaction becomes particularly prominent at high lung volumes, lung inflation, either bilateral or unilateral, places a substantial stress on the inspiratory muscle pump.

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.

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.

Disorders of the respiratory muscles

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

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

Diaphragm function is compromised in severe chronic obstructive pulmonary disease (COPD) by hyperinflation, but its ability to shorten and contribute to tidal volume is uncertain. We estimated coronal diaphragm length by measuring zone of apposition length with ultrasound and rib cage diameters with magnetometers, in 10 male patients with severe COPD and 10 age- and sex-matched control subjects. Diaphragm length was 20% shorter in patients at residual volume (413 and 536 mm in patients and control subjects, respectively) and FRC (381 and 456 mm, respectively), but was not different at total lung capacity (312 and 336 mm, respectively). Zone of apposition length was reduced 50% at residual volume and FRC in patients, but was larger at a given absolute lung volume than in control subjects. There were no differences in tidal volume (0.8 L), tidal changes in zone of apposition length (20 mm) and diaphragm length (38 and 42 mm), and tidal volume displaced by the diaphragm (0.6 L), even though mean FRC in patients was similar to predicted total lung capacity. Although the diaphragm is shorter at FRC in patients with COPD, its motion and change in length during tidal breathing is similar to that in control subjects.