Dynamic changes in the zone of apposition and diaphragm length during maximal respiratory efforts

Diaphragm Ultrasound in Different Clinical Scenarios: A Review with a Focus on Older Patients

Diaphragm muscle dysfunction is increasingly recognized as a fundamental marker of several age-related diseases and conditions including chronic obstructive pulmonary disease, heart failure and critical illness with respiratory failure. In older individuals with physical frailty and sarcopenia, the loss of muscle mass and function may also involve the diaphragm, contributing to respiratory dysfunction. Ultrasound has recently emerged as a feasible and reliable strategy to visualize diaphragm structure and function. In particular, it can help to predict the timing of extubation in patients undergoing mechanical ventilation in intensive care units (ICUs). Ultrasonographic evaluation of diaphragmatic function is relatively cheap, safe and quick and can provide useful information for real-time monitoring of respiratory function. In this review, we aim to present the current state of scientific evidence on the usefulness of ultrasound in the assessment of diaphragm dysfunction in different clinical settings, with a particular focus on older patients. We highlight the importance of the qualitative information gathered by ultrasound to assess the integrity, excursion, thickness and thickening of the diaphragm. The implementation of bedside diaphragm ultrasound could be useful for improving the quality and appropriateness of care, especially in older subjects with sarcopenia who experience acute respiratory failure, not only in the ICU setting.

Diaphragm Ultrasound in Critically Ill Patients on Mechanical Ventilation—Evolving Concepts

Mechanical ventilation (MV) is a life-saving respiratory support therapy, but MV can lead to diaphragm muscle injury (myotrauma) and induce diaphragmatic dysfunction (DD). DD is relevant because it is highly prevalent and associated with significant adverse outcomes, including prolonged ventilation, weaning failures, and mortality. The main mechanisms involved in the occurrence of myotrauma are associated with inadequate MV support in adapting to the patient’s respiratory effort (over- and under-assistance) and as a result of patient-ventilator asynchrony (PVA). The recognition of these mechanisms associated with myotrauma forced the development of myotrauma prevention strategies (MV with diaphragm protection), mainly based on titration of appropriate levels of inspiratory effort (to avoid over- and under-assistance) and to avoid PVA. Protecting the diaphragm during MV therefore requires the use of tools to monitor diaphragmatic effort and detect PVA. Diaphragm ultrasound is a non-invasive technique that can be used to monitor diaphragm function, to assess PVA, and potentially help to define diaphragmatic effort with protective ventilation. This review aims to provide clinicians with an overview of the relevance of DD and the main mechanisms underlying myotrauma, as well as the most current strategies aimed at minimizing the occurrence of myotrauma with special emphasis on the role of ultrasound in monitoring diaphragm function.

Ultrasonographic Assessment of Diaphragmatic Function and Its Clinical Application in the Management of Patients with Acute Respiratory Failure

Acute respiratory failure (ARF) is a common life-threatening medical condition, with multiple underlying etiologies. In these cases, many factors related to systemic inflammation, prolonged use of steroids, and lung mechanical abnormalities (such as hyperinflation or increased elastic recoil due to pulmonary oedema or fibrosis) may act as synergic mechanisms leading to diaphragm dysfunction. The assessment of diaphragm function with ultrasound has been increasingly investigated in the emergency department and during hospital stay as a valuable tool for providing additional anatomical and functional information in many acute respiratory diseases. The diaphragmatic ultrasound is a noninvasive and repeatable bedside tool, has no contraindications, and allows the physician to rapidly assess the presence of diaphragmatic dysfunction; this evaluation may help in estimating the need for mechanical ventilation (and the risk of weaning failure), as well as the risk of longer hospital stay and higher mortality rate. This study presents an overview of the recent evidence regarding the evaluation of diaphragmatic function with bedside ultrasound and its clinical applications, including a discussion of real-life clinical cases.

Respiratory muscle testing in amyotrophic lateral sclerosis: a practical approach

In amyotrophic lateral sclerosis (ALS), respiratory muscle weakness leads to respiratory failure and death. Non-invasive positive pressure ventilation (NIPPV) appears to reduce lung function decline, thus improving survival and quality-of-life of patients affected by the disease. Unfortunately, clinical features and timing to start NIPPV are not well defined. Starting from recent findings, we examine established and novel tests of respiratory muscle function that could help clinicians decide whether and when to start NIPPV in ALS. Non-invasive tests estimate the function of inspiratory, expiratory, and bulbar muscles, whereas clinical examination allows to assess the overall neurologic and respiratory symptoms and general conditions. Most of the studies recommend that together with a thorough clinical evaluation of the patient according to current guidelines, vital capacity, maximal static and sniff nasal inspiratory pressures, maximal static expiratory pressures and peak cough expiratory flow, and nocturnal pulse oximetry be measured. A sound understanding of physiology can guide the physician also through the current armamentarium for additional supportive treatments for ALS, such as symptomatic drugs and new treatments to manage sialorrhea and thickened saliva, cough assistance, air stacking, and physiotherapy. In conclusion, careful clinical and functional evaluation of respiratory function and patient's preference are key determinants to decide "when" and "to whom" respiratory treatments can be provided.

Ultrasound Sensors for Diaphragm Motion Tracking: An Application in Non-Invasive Respiratory Monitoring

This paper introduces a novel respiratory detection system based on diaphragm wall motion tracking using an embedded ultrasound sensory system. We assess the utility and accuracy of this method in evaluating the function of the diaphragm and its contribution to respiratory workload. The developed system is able to monitor the diaphragm wall activity when the sensor is placed in the zone of apposition (ZOA). This system allows for direct measurements with only one ultrasound PZT5 piezo transducer. The system generates pulsed ultrasound waves at 2.2 MHz and amplifies reflected echoes. An added benefit of this system is that due to its design, the respiratory signal is less subject to motion artefacts. Promising results were obtained from six subjects performing six tests per subject with an average respiration detection sensitivity and specificity of 84% and 93%, respectively. Measurements were compared to a gold standard commercial spirometer. In this study, we also compared our measurements to other conventional methods such as inertial and photoplethysmography (PPG) sensors.

Airflow limitation is accompanied by diaphragm dysfunction

Chronic airflow limitation, caused by chronic obstructive pulmonary disease (COPD) or by asthma, is believed to change the shape and the position of the diaphragm due to an increase in lung volume. We have made a comparison of magnetic resonance imaging (MRI) of diaphragm in supine position with pulmonary functions, respiratory muscle function and exercise tolerance. We have studied the differences between patients with COPD, patients with asthma, and healthy subjects. Most interestingly we found the lung hyperinflation leads to the changes in diaphragmatic excursions during the breathing cycle, seen in the differences between the maximal expiratory diaphragm position (DPex) in patients with COPD and control group (p=0.0016). The magnitude of the diaphragmatic dysfunction was significantly related to the airflow limitation expressed by the ratio of forced expiratory volume in 1 s to slow vital capacity (FEV(1)/SVC), (%, p=0.0007); to the lung hyperinflation expressed as the ratio of the residual volume to total lung capacity (RV/TLC), (%, p=0.0018) and the extent of tidal volume constrain expressed as maximal tidal volume (V(Tmax)), ([l], p=0.0002); and the ratio of tidal volume to slow vital capacity (V(T)/SVC), (p=0.0038) during submaximal exercise. These results suggest that diaphragmatic movement fails to contribute sufficiently to the change in lung volume in emphysema. Tests of respiratory muscle function were related to the position of the diaphragm in deep expiration, e.g. neuromuscular coupling (P(0.1)/V(T)) (p=0.0232). The results have shown that the lung volumes determine the position of the diaphragm and function of the respiratory muscles. Chronic airflow limitation seems to change the position of the diaphragm, which thereafter influences inspiratory muscle function and exercise tolerance. There is an apparent relationship between the position of the diaphragm and the pulmonary functions and exercise tolerance.

Ultrasound Evaluation of Mechanical Properties of Individual Muscles-Tendons during Active Contraction

A new method to accurately measure the mechanical properties of individual muscles and tendons under active contraction is presented. An individual muscle is activated selectively to different intensities through electrical stimulation with adjustable amplitude, frequency, and pulse width. During the course of active contraction of the stimulated muscle, muscle fiber pennation angle, muscle fascicle length, tendon length are measured by ultrasonography in vivo and non-invasively. The force produced by the stimulated muscle is derived from the measured joint torque and the moment arm recorded by a 3-D motion tracking system. The relationship between the force produced by the selected individual muscle and the muscle and tendon architectural parameters are studied quantitatively for the flexor carpi ulnaris and flexor carpi radialis.

Força muscular respiratória: comparação entre nuligestas e primigestas

A gestação influencia o sistema respiratório originando mudanças anatômicas e fisiológicas que podem repercutir nos índices da força muscular respiratória. O objetivo do presente trabalho foi comparar a pressão respiratória máxima entre nuligestas e primigestas no terceiro trimestre gestacional e associá-la ao predito por Neder et al.,1999. Foi realizado estudo do tipo corte transversal com 80 mulheres (40 nuligestas e 40 primigestas no terceiro trimestre gestacional) entre 20 e 29 anos, eutróficas e sem histórico de doença cardiorrespiratória. A média dos valores obtidos para pressão inspiratória máxima (Pimáx) foi: -93,95 cmH2O nas nuligestas e -87,78 cmH2O nas primigestas, mostrando haver diferença estatística (p=0,0182). Para pressão expiratória máxima (Pemáx) foram alcançados 98,28 cmH2O e 96,73 cmH2O, respectivamente, não sendo estatisticamente significante (p=0,710). Não obstante,as modificações anatômicas e fisiológicas ocorridas durante a gestação verificou-se que apenas a Pimáx estava diminuída quando comparada ao grupo das nuligestas, enquanto que a Pemáx não apresentou alteração significativa. No mais, não foi observada concordância entre valores encontrados e preditos por Neder et al., 1999.

Effects of pneumoperitoneum on the amplitude of diaphragmatic excursion in pigs

OBJECTIVE

To study the effects that pneumoperitoneum achieved through carbon dioxide insufflation has on diaphragmatic excursion in pigs.

METHODS

A total of 14 male Landrace pigs, 30 to 45 days of age and weighing five to seven kilograms each, were used. The sample was randomly and equally divided into two groups: one (n = 7) in which pneumoperitoneum was maintained at 10 mmHg for 60 minutes; and another (n = 7) in which pneumoperitoneum was maintained at 15 mmHg (also for 60 minutes). After anesthetic induction, the animals were intubated. Flow volume was monitored, and the amplitude of diaphragmatic excursion was analyzed using noninvasive ultrasound imaging of the right hemidiaphragm.

RESULTS

In both groups, restricted diaphragmatic excursion was observed only during the procedure. There was no statistical difference between the two pressure levels studied.

CONCLUSION

The amplitude of diaphragmatic excursion was restricted during abdominal insufflation, independent of the pressure level (within the 10-15 mmHg range), during the study period.

Repercussões respiratórias do pneumoperitônio induzido em suínos

Objetivo: Estudar, na faixa tida como segura, as repercussões respiratórias de diferentes pressões de pneumoperitônio, com dióxido de carbono, induzido em suínos. Métodos: Foram utilizados 14 suínos machos, da raça Landrace, pesando entre cinco e sete quilos, com 30 a 45 dias de idade. A amostra foi subdividida igualitariamente em Grupo A (pneumoperitônio com 10mmHg durante 60 minutos) e Grupo B (pneumoperitônio com 15mmHg durante 60 minutos). Após a indução anestésica, os animais foram intubados, sendo monitorado o volume corrente (VC) e a saturação periférica de oxigênio (SpO2). Resultados: Não houve diferença estatística nos valores do VC e SpO2 antes, durante e após a indução do pneumoperitônio. Conclusão: O pneumoperitônio, nos níveis pressóricos de 10 a 15mmHg, não causou alteração significativa nos padrões respiratórios de suínos, durante o período de tempo estudado.

Measurement of muscle contraction with ultrasound imaging

To investigate the ability of ultrasonography to estimate muscle activity, we measured architectural parameters (pennation angles, fascicle lengths, and muscle thickness) of several human muscles (tibialis anterior, biceps brachii, brachialis, transversus abdominis, obliquus internus abdominis, and obliquus externus abdominis) during isometric contractions of from 0 to 100% maximal voluntary contraction (MVC). Concurrently, electromyographic (EMG) activity was measured with surface (tibialis anterior only) or fine-wire electrodes. Most architectural parameters changed markedly with contractions up to 30% MVC but changed little at higher levels of contraction. Thus, ultrasound imaging can be used to detect low levels of muscle activity but cannot discriminate between moderate and strong contractions. Ultrasound measures could reliably detect changes in EMG of as little as 4% MVC (biceps muscle thickness), 5% MVC (brachialis muscle thickness), or 9% MVC (tibialis anterior pennation angle). They were generally less sensitive to changes in abdominal muscle activity, but it was possible to reliably detect contractions of 12% MVC in transversus abdominis (muscle length) and 22% MVC in obliquus internus (muscle thickness). Obliquus externus abdominis thickness did not change consistently with muscle contraction, so ultrasound measures of thickness cannot be used to detect activity of this muscle. Ultrasound imaging can thus provide a noninvasive method of detecting isometric muscle contractions of certain individual muscles.

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.

Volume displaced by diaphragm motion in emphysema

To examine the effect of hyperinflation on the volume displaced by diaphragm motion (DeltaVdi), we compared nine subjects with emphysema and severe hyperinflation [residual volume (RV)/total lung capacity (TLC) 0.65 +/- 0.08; mean +/- SD] with 10 healthy controls. Posteroanterior and lateral chest X rays at RV, functional residual capacity, one-half inspiratory capacity, and TLC were used to measure the length of diaphragm apposed to ribcage (Lap), cross-sectional area of the pulmonary ribcage, DeltaVdi, and volume beneath the lung-apposed dome of the diaphragm. Emphysema subjects, relative to controls, had increased Lap at comparable lung volumes (4.3 vs. 1.0 cm near predicted TLC, 95% confidence interval 3.4-5.2 vs. 0-2.1), pulmonary rib cage cross-sectional area (emphysema/controls 1.22 +/- 0.03, P < 0.001 at functional residual capacity), and DeltaVdi/DeltaLap (0.25 vs. 0.14 liters/cm, P < 0.05). During a vital capacity inspiration, relative to controls, DeltaVdi was normal in five (1.94 +/- 0.51 liters) and decreased in four (0.51 +/- 0.40 liters) emphysema subjects, and volume beneath the dome did not increase in emphysema (0 +/- 0.36 vs. 0.82 +/- 0.80 liters, P < 0.05). We conclude that DeltaVdi can be normal in emphysema because 1) hyperinflation is shared between ribcage and diaphragm, preserving Lap, and 2) the diaphragm remains flat during inspiration.

Effects of increased ventilatory drive on motor unit firing rates in human inspiratory muscles

This study was designed to determine whether increased neural drive increases firing rates of inspiratory motoneurons uniformly in humans. The discharge of single motor units in the diaphragm, parasternal intercostal and scalene muscles was recorded with monopolar electrodes. Ventilation was increased threefold with an external dead space. The discharge of 516 motor units was sampled in four subjects. All but 4 units increased their discharge rate during inspiration with only 46 discharging tonically during expiration. With increased dead space, discharge frequencies of diaphragmatic motor units increased from 11.0 +/- 2.7 to 17.7 +/- 3.3 Hz (mean +/- SD; p < 0.001). However, firing rates increased for parasternal intercostals from 10.0 +/- 1.6 to only 11.9 +/- 1.9 Hz (p < 0.001), and for scalenes from 8.7 +/- 1.8 to only 9.5 +/- 1.2 Hz (p < 0.05). Proportionate increases in rib cage and abdominal expansion accompanied the increased ventilation with added dead space. These results suggest that previously reported predominant increase in firing rates of diaphragmatic motor units in patients with chronic airflow limitation reflects the normal response of respiratory motor output to increased neural drive. The motoneuron pools of the parasternal intercostals and scalenes may show more prominent recruitment than frequency modulation.

Is there a role for transversus abdominis in lumbo-pelvic stability?

There has been considerable interest in the literature regarding the function of transversus abdominis, the deepest of the abdominal muscles, and the clinical approach to training this muscle. With the development of techniques for the investigation of this muscle involving the insertion of fine-wire electromyographic electrodes under the guidance of ultrasound imaging it has been possible to test the hypotheses related to its normal function and function in people with low back pain. The purpose of this review is to provide an appraisal of the current evidence for the role of transversus abdominis in spinal stability, to develop a model of how the contribution of this muscle differs from the other abdominal muscles and to interpret these findings in terms of the consequences of changes in this function.

Abdominal motor unit activity during respiratory and nonrespiratory tasks

Abdominal muscles serve multiple roles, but the functional organization of their motoneurons remains unclear. To gain insight, we recorded single motor unit potentials from the internal oblique (IO) and transversus abdominis (TA) muscles of three standing subjects during quiet breathing, a leg lift, and an expiratory threshold load. Inspiratory airflow, recorded from a pneumotachometer, provided tidal volumes and respiratory cycle timing. Fine wires, implanted under ultrasonic imaging, detected single motor unit potentials that were visually distinguished by their spike morphology. From the number of spikes, firing profiles, times of occurrence in the respiratory cycle, and their onset, instantaneous, mean, and peak firing frequencies we deduced that 1) breathing patterns varied across tasks, 2) different motor units were recruited for each task with essentially no overlap, 3) their firing displayed prominent expiratory activity during each task, and 4) the recruitment levels and discharge patterns of IO and TA were different. We conclude that the IO and TA motor pools receive a strong central respiratory drive, yet each pool receives its own distinct, task-dependent synaptic input.

Contraction of the human diaphragm during rapid postural adjustments

1. The response of the diaphragm to the postural perturbation produced by rapid flexion of the shoulder to a visual stimulus was evaluated in standing subjects. Gastric, oesophageal and transdiaphragmatic pressures were measured together with intramuscular and oesophageal recordings of electromyographic activity (EMG) in the diaphragm. To assess the mechanics of contraction of the diaphragm, dynamic changes in the length of the diaphragm were measured with ultrasonography. 2. With rapid flexion of the shoulder in response to a visual stimulus, EMG activity in the costal and crural diaphragm occurred about 20 ms prior to the onset of deltoid EMG. This anticipatory contraction occurred irrespective of the phase of respiration in which arm movement began. The onset of diaphragm EMG coincided with that of transversus abdominis. 3. Gastric and transdiaphragmatic pressures increased in association with the rapid arm flexion by 13.8 +/- 1.9 (mean +/- S.E.M.) and 13.5 +/- 1.8 cmH2O, respectively. The increases occurred 49 +/- 4 ms after the onset of diaphragm EMG, but preceded the onset of movement of the limb by 63 +/- 7 ms. 4. Ultrasonographic measurements revealed that the costal diaphragm shortened and then lengthened progressively during the increase in transdiaphragmatic pressure. 5. This study provides definitive evidence that the human diaphragm is involved in the control of postural stability during sudden voluntary movement of the limbs.

Rib cage mechanics during quiet breathing and exercise in humans

During exercise, large pleural, abdominal, and transdiaphragmatic pressure swings might produce substantial rib cage (RC) distortions. We used a three-compartment chest wall model (J. Appl. Physiol. 72: 1338-1347, 1992) to measure distortions of lung- and diaphragm-apposed RC compartments (RCp and RCa) along with pleural and abdominal pressures in five normal men. RCp and RCa volumes were calculated from three-dimensional locations of 86 markers on the chest wall, and the undistorted (relaxation) RC configuration was measured. Compliances of RCp and RCa measured during phrenic stimulation against a closed airway were 20 and 0%, respectively, of their values during relaxation. There was marked RC distortion. Thus nonuniform distribution of pressures distorts the RC and markedly stiffens it. However, during steady-state ergometer exercise at 0, 30, 50, and 70% of maximum workload, RC distortions were small because of a coordinated action of respiratory muscles, so that net pressures acting on RCp and RCa were nearly the same throughout the respiratory cycle. This maximizes RC compliance and minimizes the work of RC displacement. During quiet breathing, plots of RCa volume vs. abdominal pressure were to the right of the relaxation curve, indicating an expiratory action on RCa. We attribute this to passive stretching of abdominal muscles, which more than counterbalances the insertional component of transdiaphragmatic pressure.

Effect of chronic hyperinflation on diaphragm length and surface area

We have used three-dimensional reconstructions obtained with spiral computed tomography to measure total diaphragm length (Ldl) and surface area (Adl), the length (Ldo) and surface area (Ado) of the dome, and the length (Lap) and surface area (Aap) of the zone of apposition in 10 hyperinflated patients with severe chronic obstructive pulmonary disease, or COPD (FEV1 = 27% predicted: FRC = 225% predicted) and 10 normal subjects matched for age, sex, and height. Measures of Ldl, Adl, Lap, and Aap decreased linearly between FRC and TLC in the two groups, but Ldo and Ado did not change. On average, patients' Adl and Aap at FRC were reduced to 73% and 54% of normal values, whereas Ado was unaffected. When compared at similar absolute lung volumes, mean diaphragm dimensions were similar in patients with COPD and normal subjects, but individual values were very variable in both groups. This variability was partly accounted for by differences in body weight: i.e., the greater the weight, the longer the diaphragm. We conclude that (1) patients with COPD have marked reductions in Adl and Aap at FRC but have diaphragm dimensions similar to those of normal subjects when compared at similar absolute lung volumes, and (2) normal subjects and patients with COPD show substantial intersubject variability in diaphragm dimensions that is partly explained by differences in body weight.

Changes in pennation with joint angle and muscle torque: in vivo measurements in human brachialis muscle

1. Estimates of pennation in human muscles are usually obtained from cadavers. In this study, pennation of human brachialis was measured in vivo using sonography. Effects of static and dynamic changes in elbow angle and torque were investigated. 2. Pennation was measured in eight subjects using an 80 mm, 5 MHz, linear-array ultrasound transducer to generate sagittal images of the brachialis during maximal and submaximal isometric contractions at various elbow angles. It was shown that estimates of pennation were reproducible, representative of measurements made throughout the belly of the muscle and not distorted by compression of the muscle with the transducer or rotation of the muscle out of the plane of the transducer. 3. Mean resting pennation was 9.0 +/- 2.0 deg (S.D., range 6.5-12.9 deg). When the muscle was relaxed there was no effect of elbow angle on pennation. However, during a maximal isometric contraction (MVC), with the elbow flexed to 90 deg, pennation increased non-linearly with elbow torque to between 22 and 30 deg (mean 24.7 +/- 2.4 deg). The effect of increasing torque was small when the elbow was fully extended. The relationship between elbow angle, elbow torque and brachialis pennation suggests that the relaxed brachialis muscle is slack over much of its physiological range of lengths. 4. There was no hysteresis in the relationship between torque and pennation during slow isometric contractions (0.2 MVC s-1), and the relationship between elbow angle and pennation was similar during slow shortening and lengthening contractions. 5. Two consequences follow from these findings. Firstly, intramuscular mechanics are complex and simple planar models of muscles underestimate the increases in pennation which occur during muscle contraction. Second, spindle afferents from relaxed muscles may not encode joint angle over the full range of movement.

Respiratory muscle fatigue

Ventilatory failure may accompany a variety of pulmonary and neuromuscular diseases. There has been much controversy about whether this failure is due to respiratory muscle fatigue at peripheral sites or a failure of drive at sites within the central nervous system. The chapter reviews this topic.