Integrated approach for in vivo evaluation of respiratory muscles mechanics

Biomechanical characteristics of rib fracture fixation systems

BACKGROUND

The primary aim of this study was to determine and compare the biomechanical properties of a fractured or intact rib after implant fixation on an embalmed thorax.

METHODS

Five systems were fixated on the bilateral fractured or intact (randomly allocated) 6th to 10th rib of five post-mortem embalmed human specimens. Each rib underwent a four-point bending test to determine the bending structural stiffness (Newton per m²), load to failure (Newton), failure mode, and the relative difference in bending structural stiffness and load to failure as compared to a non-fixated intact rib.

FINDINGS

As compared to a non-fixated intact rib, the relative difference in stiffness of a fixated intact rib ranged from -0.14 (standard deviation [SD], 0.10) to 0.53 (SD 0.35) and for a fixated fractured rib from -0.88 (SD 0.08) to 0.17 (SD 0.50). The most common failure mode was a new fracture at the most anterior drill hole for the plate and screw systems and a new fracture within the anterior portion of the implant for the clamping systems.

INTERPRETATION

The current fixation systems differ in their design, mode of action, and biomechanical properties. Differences in biomechanical properties such as stiffness and load to failure especially apply to fractured ribs. Insight in the differences between the systems might guide more specific implant selection and increase the surgeon's awareness for localizing hardware complaints or failure.

Thorax Dynamic Modeling and Biomechanical Analysis of Chest Breathing in Supine Lying Position

During respiration, the expansion and contraction of the chest and abdomen are coupled with each other, presenting a complex torso movement pattern. A finite element (FE) model of chest breathing based on the HUMOS2 human body model was developed. One-dimensional muscle units with active contraction functions were incorporated into the model based on Hill's active muscle model so as to generate muscle contraction forces that can change over time. The model was validated by comparing it to the surface displacement of the chest and abdomen during respiration. Then, the mechanism of the coupled motion of the chest and abdomen was analyzed. The analyses revealed that since the abdominal wall muscles are connected to the lower edge of the rib cage through tendons, the movement of the rib cage may cause the abdominal wall muscles to be stretched in both horizontal and vertical in a supine position. The anteroposterior and the right-left diameters of the chest will increase at inspiration, while the right-left diameter of the abdomen will decrease even though the anteroposterior diameter of the abdomen increases. The external intercostal muscles at different regions had different effects on the motion of the ribs during respiration. In particular, the external intercostal muscles at the lateral region had a larger effect on pump handle movement than bucket handle movement, and the external intercostal muscles at the dorsal region had a greater influence on bucket handle movement than pump handle movement.

Comparison of physical properties of voluntary coughing, huffing and swallowing in healthy subjects

Coughing, huffing and swallowing protect the airway from aspiration. This study was conducted to compare the physical properties of voluntary coughing, huffing and swallowing in healthy subjects. Ten healthy men were asked to huff, cough and swallow repeatedly. Electromyograms (EMGs) were recorded from the left side of the external oblique (EO), sternocleidomastoid, suprahyoid (SH) and thyrohyoid muscles. Airflow was recorded using a face mask with two-way non-rebreathing valves. The expiratory velocity of huffing and coughing and the SH EMG of all actions presented high intraclass correlation coefficients (> 0.8). The inspiratory and expiratory velocities did not differ significantly between coughing and huffing. The expiratory acceleration of coughing was significantly higher than that of huffing, whereas the expiratory volume of coughing was significantly smaller than that of huffing. The EO EMG of coughing and huffing were significantly larger than that of swallowing. The EO EMG activity during the expiratory phase was significantly higher than that of the other phases of both coughing and huffing. The SH EMG of coughing and huffing were significantly smaller than that of swallowing. Correlation analysis revealed that the expiratory velocity of coughing was strongly positively correlated with that of huffing. The expiratory volume of huffing was significantly positively correlated with hand grip strength. These results suggest that EO and SH muscle activities during huffing or coughing differ those during swallowing, and huffing and coughing may work similarly in expiratory function.

Biomechanical investigation of different surgical strategies for the treatment of rib fractures using a three-dimensional human respiratory model

Rib fracture is a common injury and can result in pain during respiration. Conservative treatment of rib fracture is applied via mechanical ventilation. However, ventilator-associated complications frequently occur. Surgical fixation is another approach to treat rib fractures. Unfortunately, this surgical treatment is still not completely defined. Past studies have evaluated the biomechanics of the rib cage during respiration using a finite element method, but only intact conditions were modelled. Thus, the purpose of this study was to develop a realistic numerical model of the human rib cage and to analyse the biomechanical performance of intact, injured and treated rib cages. Three-dimensional finite element models of the human rib cage were developed. Respiratory movement of the human rib cage was simulated to evaluate the strengths and limitations of different scenarios. The results show that a realistic human respiratory movement can be simulated and the predicted results were closely related to previous study (correlation coefficient>0.92). Fixation of two fractured ribs significantly decreased the fixation index (191%) compared to the injured model. This fixation may provide adequate fixation stability as well as reveal lower bone stress and implant stress compared with the fixation of three or more fractured ribs.

Surface electromyography in inspiratory muscles in adults and elderly individuals: A systematic review

INTRODUCTION

Electromyography (EMG) helps to evaluate disorders and pulmonary behavior, as impairments in respiratory muscle function are associated with the development of diseases. There is a wide range of methods and protocols used to record and analyze EMG obtained from respiratory muscles, demonstrating a lack of standardization.

OBJECTIVE

To identify the most common procedures used to record surface EMG (sEMG) of inspiratory muscles in adults and elderly individuals through a systematic review (primary), and to evaluate the quality of the report presented by the studies (secondary).

METHOD

Studies published from January 1995 until June 2018 were searched for in the Web of Science, PubMed, LILACS, EBSCO and Embase databases. Only studies evaluating sEMG of inspiratory muscles were included.

RESULTS

The electronic search retrieved a total of 6697 titles and 92 of them were included. A great variability on the methods applied to both recording and processing/analyzing data was found. Therefore, the synthesis of practical/clinical evidence to support immediate recommendations was impaired. In general, the descriptions presented by the studies are poor.

CONCLUSION

The most common procedures used for sEMG were identified. Methodological studies with objective comparisons were fundamental for improving standardization, given the impossibility of recommendations from this review.

The impact of breathing pattern and rate on inspiratory muscles activity

Different rehabilitation programs are used to relieve dyspnea for hyper-inflated lung patients. In this study, a new approach, based on integrated changes in respiratory rate and pattern, for inspiratory muscles rehabilitation and training was examined utilizing noninvasive measurements of the two inspiratory muscles (rib cage inspiratory and neck inspiratory muscles) activity during controlled breathing in healthy subjects. Muscles activity was measured using electromyography, while subjects, breathed at different combinations of respiratory rate (6, 10, 16 breath per minutes) and inspiratory duty cycles (TI/Ttot). The results clearly show that both muscles were most active at the lowest evaluated respiratory rate, and that alteration of the duty cycle at the lowest rate significantly (p< 0.05) changes their electrical activity. Breathing at low respiratory rate RR is recommended for hyper-inflated lung patients in order to improve their gas exchange, therefore, it is recommended for these patients to find their most effective combination of RR and TI/Ttot and to use control breathing to practice their breath at optimum combination.

Fixation of a human rib by an intramedullary telescoping splint anchored by bone cement

A novel concept for rib fixation is presented that involves the use of a bioresorbable polymer intramedullary telescoping splint. Bone cement is used to anchor each end of the splint inside the medullary canal on each side of the fracture site. In this manner, rib fixation is achieved without fixation device protrusion from the rib, making the splint completely intramedullary. Finite element analysis is used to demonstrate that such a splint/cement composite can preserve rib fixation subjected to cough-intensity force loadings. Computational fluid dynamics and porcine rib experiments were used to study the anchor formation process required to complete the fixation.

Structural integrity of intramedullary rib fixation using a single bioresorbable screw

BACKGROUND

Operative management of flail chest injury is receiving increasing interest. However, we have noticed in our own practice the difficulty in achieving reliable results with posterior rib fracture fixation. In this article, we analyze and model the physiologic forces acting on posterior rib fractures and assess the suitability of an intramedullary screw fixation technique in this site.

METHODS

Computerized finite element analysis (FEA) was used to model a typical sixth rib and analyze the physiologic forces that act on the rib in vivo. A fracture in the posterior aspect of the rib was incorporated into the model, and an intramedullary screw fixation concept was assessed, using both a bioabsorbable polymer screw and a stainless steel screw.The records of 120 consecutive patients with flail chest were reviewed, and 26 patients were identified as having multiple posterior rib fractures with displacement. These patients formed a clinical correlation group by which to assess the FEA model.

RESULTS

FEA modeling of the posterior rib fracture showed likely posterior displacement in response to physiologic forces. Review of the 26 patients with flail chest and displaced posterior fractures confirmed the direction of displacement. Modeling of an intramedullary screw fixation showed significant stresses in the bone/screw contact areas (stainless steel solution) and the prosthesis itself (bioabsorbable polymer solution)

CONCLUSION

This FEA model demonstrates that physiologic forces cause posterior displacement at posterior rib fracture sites. Fixation solutions to counteract these forces need to overcome significant stresses at both the bone/prosthesis contact regions and within the prosthetic material itself.

LEVEL OF EVIDENCE

Epidemiologic/therapeutic study, level V.

Atividade mioelétrica dos músculos respiratórios em crianças asmáticas durante manobra inspiratória máxima

OBJETIVOS: avaliar a atividade dos músculos escalenos e esternocleidomastóideo (ETMD) no período basal e durante manobra de pressão inspiratória máxima (PImax) em crianças asmáticas. MÉTODOS: foram estudadas 15 crianças, divididas em grupo asma (n=8) e grupo controle (n=7). Foi realizada a análise da função pulmonar e da PImax através da espirometria e da manovacuometria, respectivamente. A atividade mioelétrica dos músculos escaleno e ETMD foram realizadas pela eletromiografia de superfície durante período basal e manobra de PImax. RESULTADOS: a eletromiografia de superfície (EMGs) basal do músculo escaleno é maior no grupo asma quando comparado ao grupo controle. Diferentemente, a EMGs basal do músculo ETMD não apresentou diferença significativa nos grupos estudados. O percentual da EMGs dos músculos escaleno e ETMD durante manobra de PImax foi maior no grupo asma quando comparado ao grupo controle. CONCLUSÕES: EMGs do escaleno durante o período basal está aumentada em crianças asmáticas. A atividade eletromiográfica do músculo ETMD no período basal é similar em ambos os grupos estudados. A EMGs dos músculos ETMD e escaleno na geração de pressão intratorácica, durante a manobra de PImax, está aumentada em crianças asmáticas.

A joint computational respiratory neural network-biomechanical model for breathing and airway defensive behaviors

Data-driven computational neural network models have been used to study mechanisms for generating the motor patterns for breathing and breathing related behaviors such as coughing. These models have commonly been evaluated in open loop conditions or with feedback of lung volume simply represented as a filtered version of phrenic motor output. Limitations of these approaches preclude assessment of the influence of mechanical properties of the musculoskeletal system and motivated development of a biomechanical model of the respiratory muscles, airway, and lungs using published measures from human subjects. Here we describe the model and some aspects of its behavior when linked to a computational brainstem respiratory network model for breathing and airway defensive behavior composed of discrete "integrate and fire" populations. The network incorporated multiple circuit paths and operations for tuning inspiratory drive suggested by prior work. Results from neuromechanical system simulations included generation of a eupneic-like breathing pattern and the observation that increased respiratory drive and operating volume result in higher peak flow rates during cough, even when the expiratory drive is unchanged, or when the expiratory abdominal pressure is unchanged. Sequential elimination of the model's sources of inspiratory drive during cough also suggested a role for disinhibitory regulation via tonic expiratory neurons, a result that was subsequently supported by an analysis of in vivo data. Comparisons with antecedent models, discrepancies with experimental results, and some model limitations are noted.

Coordination of respiratory muscles assessed by means of nonlinear forecasting of demodulated myographic signals

Pulmonary diseases such as obstructive sleep apnea syndrome (OSAS) affect function of respiratory muscles. Individuals with OSAS suffer intermittent collapse of the upper airways during sleep due to unbalanced forces generated by the contraction of the diaphragm and upper airway dilator muscles. Respiratory rhythm and pattern generation can be described via nonlinear or coupled oscillators; therefore, the resulting activation of different respiratory muscles may be related to complex nonlinear interactions. The aims of this work were: to evaluate locally linear models for fitting and prediction of demodulated myographic signals from respiratory muscles; and to analyze quantitatively the influence of a pulmonary disease on this nonlinear forecasting related to low and moderate levels of respiratory effort. Electromyographic and mechanomyographic signals from three respiratory muscles (genioglossus, sternomastoid and diaphragm) were recorded in OSAS patients and controls while awake during an increased respiratory effort. Variables related to auto and cross prediction between muscles were calculated from the r(2) coefficient and the estimation of residuals, as functions of prediction horizon. In general, prediction improved linearly with higher levels of effort. A better prediction between muscle activities was obtained in OSAS patients when using genioglossus as the predictor signal. The prediction was significant for more than two respiratory cycles in OSAS patients compared to only a half cycle in controls. It could be concluded that nonlinear forecasting applied to genioglossus coupling with other muscles provides a promising assessment to monitor pulmonary diseases.

An internet-based system for home monitoring of respiratory muscle disorders

Home telemonitoring is of great interest in respiratory medicine where large numbers of people have long term conditions. We developed a telemedicine instrument for home monitoring of patients with disturbed respiratory muscles. The instrument measures the maximum inspiratory pressure (Pimax), the inspiratory time constant (τ(i)) and connects to the Internet through TCP/IP protocol. The instrument was evaluated by means of a comparative analysis in 18 normal individuals and 15 COPD patients. In close agreement with the pathophysiology, a reduction in Pimax (p < 0.0001) and an increase in τ(i) (p < 0.001) was observed in COPD patients. We concluded that the developed system could be a useful tool for the evaluation of inspiratory muscle and for the implementation of telemedicine services, contributing to reduce the costs of the assistance offered to patients with respiratory diseases.

Inspiratory muscles experience fatigue faster than the calf muscles during treadmill marching

The possibility that respiratory muscles may fatigue during extreme physical activity and thereby become a limiting factor leading to exhaustion is debated in the literature. The aim of this study was to determine whether treadmill marching exercise induces respiratory muscle fatigue, and to compare the extent and rate of respiratory muscle fatigue to those of the calf musculature. To identify muscle fatigue, surface electromyographic (EMG) signals of the inspiratory (sternomastoid, external intercostals), expiratory (rectus abdominis and external oblique) and calf (gastrocnemius lateralis) muscles were measured during a treadmill march of 2 km at a constant velocity of 8 km/h. The extent of fatigue was assessed by determining the increase in root-mean-square (RMS) of EMG over time, and the rate of fatigue was assessed from the slope of the EMG RMS versus time curve. Results indicated that (i) the inspiratory and calf muscles are the ones experiencing the most dominant fatigue during treadmill marching, (ii) the rate of fatigue of each muscle group was monotonic between the initial and terminal phases of exercise, and (iii) the inspiratory muscles fatigue significantly faster than the calf at the terminal phase of exercise, and are likely to fatigue faster during the initial exercise as well. Accordingly, this study supports the hypothesis that fatigue of the inspiratory muscles may be a limiting factor during exercise.

Mechanics of Respiratory Muscles in Single-Lung Transplant Recipients

BACKGROUND

Emphysema and pulmonary fibrosis force the patients to breathe at an abnormal lung volume, which alters the lengths of the respiratory muscles and thereby their work capability is reduced. After single-lung transplantation, muscle function is restored on the side of the transplant but it may be asymmetric to that on the side of the native diseased lung.

OBJECTIVE

Investigating the hypothesis that single-lung transplantation induces mechanical asymmetry of the respiratory muscles on the two sides.

METHODS

Simultaneously noninvasive measurements of inspiratory and expiratory mouth pressure, airflow rate and electromyography signals from the sternomastoid, external intercostal, rectus abdominis and external oblique muscles were acquired during different breathing maneuvers. The study group included 10 single-lung transplant recipients (5 with pulmonary fibrosis and 5 with emphysema) and 10 healthy controls.

RESULTS

Analysis of the finding shows a significant lower global strength of the respiratory muscles of single-lung transplant recipients compared to that of healthy subjects. No significant difference in the EMG signals of respiratory muscles was found either between the different groups or between the sides of the transplant and the native lung in the patient groups. Both single-lung transplant recipients and healthy subjects demonstrated high EMG activity of the inspiratory muscles during inspiration at different breathing efforts.

CONCLUSION

Patients after single-lung transplantation have lower respiratory muscle strength than healthy subjects, but apparently normal electrical activity. The lower global respiratory muscle strength emphasizes the importance of their rehabilitation before and after single-lung transplantation.

Changes in peak expiratory flow and respiratory strength during the menstrual cycle

This study evaluated the spirometry and respiratory static pressures in 17 young women, twice a week for three successive ovulatory menstrual cycles to determine if such variables changed across the menstrual, follicular, periovulatory, early-to-mid luteal and late luteal phases. The factors phases of menstrual cycle and individual cycles had no significant effect on the spirometry variables except for peak expiratory flow (PEF) and respiratory static pressures. Significant weak positive correlations were found between the progesterone:estradiol ratio and PEF and between estrogen and tidal volume (r = 0.37), inspiratory time (r = 0.22), expiratory time (r = 0.19), maximal inspiratory pressure (r = 0.25) and maximal expiratory pressure (r = 0.20) and for progesterone and maximal inspiratory pressure (r = 0.32) during the early-to-mid luteal phase. Although most parameters of the spirometry results did not change during the menstrual cycle, the correlations observed between sexual hormones and respiratory control variables suggest a positive influence of sexual female hormones controlling the thoracic pump muscles in the luteal phase.

Anatomical model of the human trunk for analysis of respiratory muscles mechanics

A realistic two-dimensional (2D) model of the human trunk was developed for quantitative analysis of the relative contribution to breathing mechanics of seven groups of respiratory muscles. Along with noninvasive measurements of electromyography (EMG) signals from respiratory muscles near the skin surface, it provides predictions for the forces generated by inner respiratory muscles as well as the instantaneous work of each muscle. The results revealed that inspiratory muscles reach their maximal force towards the end of inspiration, while expiratory muscles reach their maximal force at mid-expiration. Inspiratory muscles contributed to the work of breathing even at low efforts, while that of the expiratory muscles was observed only at relatively high efforts. The study clearly showed that the diaphragm muscle generates forces, which are of the same order as those generated by other inspiratory muscles, but performed 60-80% of the inspiratory work. The contribution of the external intercostal muscle to inspiration was not negligible, especially at high breathing efforts.

Breathing power of respiratory muscles in single-lung transplanted emphysematic patients

Single-lung transplantation may induce asynchronous performance between the respiratory muscles of the chest. The objective of this study was to investigate the influence of a single transplanted lung on respiratory muscle mechanics. The force and power of the sternomastoid, external intercostal and external oblique muscles were evaluated throughout a range of respiratory maneuvers in emphysematic patients with a single transplanted lung and compared with that of healthy subjects. A significant differences was observed between the force, work and power of the muscles on the two sides of the chest in emphysematic patients (P<0.05). The control group demonstrated higher averaged maximal force, work and power. The total work done during either inspiration or expiration by the external intercostal and external oblique muscles on the side of the transplanted lung were higher compared with that of the native lung side and compared with the control group. The asynchrony between the lungs after single-lung transplant leads to asynchronous muscle force and work and lesser muscle strength compared to healthy subjects.

Different breathing patterns in healthy and asthmatic children: responses to an arithmetic task

Asthma patients have been reported to be sensitive to breathlessness, independent of the degree of airway obstruction. Paying attention and task performance may induce changes in breathing pattern and these in turn may mediate such a feeling. The present experiment investigates whether strained breathing induced by an arithmetic task was different in children with asthma compared to healthy children.

METHODS

Seven healthy and eight asthmatic but symptom-free school children were equipped with electrodes for surface electromyographic (EMG) measurements of diaphragm, abdominal and intercostal (IC) muscles and with a strain gauge to monitor the pattern of breathing at rest and during an arithmetic task. The relative duration of exhalation and the relative speed of exhalation are used as measures of straining. The phase angle of maximal respiratory muscle activities relative to the maximal chest extension (MCE) are additional discriminating parameters.

RESULTS

Asthmatic children breathed more slowly and already at rest the phase of their respiratory muscle activity appears to be different. While in healthy children the maximal activity of the (left)abdominal muscles occurred 5+/-29% later than the MCE, in children with asthma the maximal activity occurred 26+/-30% of the cycle earlier than MCE. In children with asthma the activity of the IC muscles starts weaning already at 10+/-30% before MCE, in contrast to the healthy children in which intercostal muscle weaning starts only at 1+/-24% after MCE. During arithmetic, the significant difference between the groups in this respect disappeared.

CONCLUSION

Children with asthma show, even at rest, signs of respiratory muscle straining, probably in order to keep close control over the airflow in a similar way as healthy children during mental tasks. Such a 'careful' breathing pattern may work to prevent airway irritation also when they are free of symptoms.