Exercise training decreases intercostal and transversus abdominis muscle blood flows in heart failure rats during submaximal exercise.

Diaphragm muscle blood flow (BF) and vascular conductance (VC) are elevated with chronic heart failure (HF) during exercise. Exercise training (ExT) elicits beneficial respiratory muscle and pulmonary system adaptations in HF. We hypothesized that diaphragm BF and VC would be lower in HF rats following ExT than their sedentary counterparts (Sed). Respiratory muscle BFs and mean arterial pressure were measured via radiolabeled microspheres and carotid artery catheter, respectively, during submaximal treadmill exercise (20 m/min, 5 % grade). During exercise, no differences were present between HF + ExT and HF + Sed in diaphragm BFs (201 ± 36 vs. 227 ± 44 mL/min/100 g) or VCs (both, p > 0.05). HF + ExT compared to HF + Sed had lower intercostal BF (27 ± 3 vs. 41 ± 5 mL/min/100 g) and VC (0.21 ± 0.02 vs. 0.31 ± 0.04 mL/min/mmHg/100 g) during exercise (both, p < 0.05). Further, HF + ExT compared to HF + Sed had lower transversus abdominis BF (20 ± 1 vs. 35 ± 6 mL/min/100 g) and VC (0.14 ± 0.02 vs. 0.27 ± 0.05 mL/min/mmHg/100 g) during exercise (both, p < 0.05). These data suggest that exercise training lowers the intercostal and transversus abdominis BF responses in HF rats during submaximal treadmill exercise.

Intercostal and vastus lateralis microcirculatory response to a sympathoexcitatory manoeuvre in patients with chronic obstructive pulmonary disease.

Patients with COPD present with systemic vascular malfunctioning and their microcirculation is possibly more fragile to overcome an increase in the sympathetic vasoconstrictor outflow during sympathoexcitatory situations. To test the skeletal muscle microvascular responsiveness to sympathoexcitation, we asked patients with COPD and age- and sex-matched controls to immerse a hand in iced water [Cold Pressor Test (CPT)]. Near-infrared spectroscopy detection of the indocyanine green dye in the intercostal and vastus lateralis microcirculation provided a blood flow index (BFI). BFI divided by mean blood pressure (MBP) provided an index of microvascular conductance (BFI/MBP). The CPT decreased BFI and BFI/MBP in the intercostal (P = 0.01 and < 0.01, respectively) and vastus lateralis (P = 0.08 and 0.03, respectively) only in the COPD group, and the per cent BFI and BFI/MBP decrease was similar between muscles (P = 0.78 and 0.85, respectively). Thus, our findings support that sympathoexcitation similarly impairs intercostal and vastus lateralis microvascular regulation in patients with COPD.

Biomechanical Evaluation of Intercostal Muscles in Healthy Children and Adolescent Idiopathic Scoliosis: A Preliminary Study.

Spine deformity during adolescent idiopathic scoliosis can induce a rib-cage deformity. This bone deformity can have direct consequences on the chest-wall muscles, including intercostal muscles, leading to respiratory impairments in individuals with severe cases. The aim of this study was to determine whether shear-wave elastography can be used to measure intercostal-muscle shear-wave speed (SWS) in healthy children and those with adolescent idiopathic scoliosis (AIS). Nineteen healthy participants and 16 with AIS took part. SWS measurements were taken by three operators, twice each. Average SWS was 2.3 ± 0.4 m/s, and inter-operator reproducibility was 0.2 m/s. SWS was significantly higher during apnea than in normal breathing (p < 0.01) in both groups. No significant difference was observed between groups in apnea or in normal breathing. Characterization of the intercostal muscles by ultrasound elastography is therefore feasible and reliable for children and adolescents with and without scoliosis.

Limitations of surface EMG estimate of parasternal intercostal to infer neural respiratory drive.

BACKGROUND: Recently, surface EMG of parasternal intercostal muscle has been incorporated in the "ERS Statement of Respiratory Muscle Testing" as a clinical technique to monitor the neural respiratory drive (NRD). However, the anatomy of the parasternal muscle risks confounding EMG "crosstalk" activity from neighboring muscles. OBJECTIVES: To determine if surface "parasternal" EMG: 1) reliably estimates parasternal intercostal EMG activity, 2) is a valid surrogate expressing neural respiratory drive (NRD). METHODS: Fine wire electrodes were implanted into parasternal intercostal muscle in 20 severe COPD patients along with a pair of surface EMG electrodes at the same intercostal level. We recorded both direct fine wire parasternal EMG (EMGPARA) and surface estimated "parasternal" EMG (SurfEMGpara) simultaneously during resting breathing, volitional inspiratory maneuvers, apnoea with extraneous movement of upper extremity, and hypercapnic ventilation. RESULTS: Surface estimated "parasternal" EMG showed spurious "pseudobreathing" activity without any airflow while real parasternal EMG was silent, during apnoea with body extremity movement. Surface estimated "parasternal" EMG did not faithfully represent real measured parasternal EMG. Surface estimated "parasternal" EMG was significantly less active than directly measured parasternal EMG during all conditions including baseline, inspiratory capacity and hypercapnic ventilation. Bland-Altman analysis showed consistent bias between direct parasternal EMG recording and surface estimated EMG during stimulated breathing. CONCLUSION: Surface "parasternal" EMG does not consistently or reliably express EMG activity of parasternal intercostal as recorded directly by implanted fine wires. A chest wall surface estimate of parasternal intercostal EMG may not faithfully express NRD and is of limited utility as a biomarker in clinical applications.

Balance and musculoskeletal flexibility in children with obesity: a cross-sectional study.

BACKGROUND: Studies on the influence of obesity on different physical parameters such as postural balance and musculoskeletal flexibility are limited and have reported varying results. OBJECTIVES: Measure effect of childhood obesity on balance and musculoskeletal flexibility in Saudi children. DESIGN: Cross-sectional. SETTING: Physiotherapy laboratory. SUBJECTS AND METHODS: The study included a representative sample of Saudi elementary school children selected from a convenience sample of 150 children. Balance was examined using the Biodex balance system. Calf muscle flexibility was measured by the weight-bearing ankle lunge test while the chest flexibility was measured by the chest expansion test. MAIN OUTCOME MEASURES: Postural stability indices and flexibility parameters. SAMPLE SIZE: 90 elementary school children aged 6 to 11 years, 47 of normal weight and 43 obese children. RESULTS: All stability indices at different stability levels were significantly impaired in children with obesity ( P≤.05). In terms of musculo-skeletal flexibility, the weight-bearing lunge test distance was shorter in children with obesity ( P=.01). In the chest expansion test, there was no significant difference between the two groups ( P=.32). CONCLUSIONS: Postural balance at different stability levels was impaired in children with obesity and in all planes. The calf muscles were less flexible in obese children. LIMITATIONS: Unblinded, convenience sample so findings are not generalizable. CONFLICT OF INTEREST: None.

Impact of moderate-severe persistent allergic rhinitis on thoraco-abdominal kinematics and respiratory muscle function.

Objective: To assess thoraco-abdominal kinematics, respiratory muscle strength and electromyographic activity of the diaphragm (EAdi) in moderate-severe allergic rhinitis (AR) patients. Methods: A cross-sectional study involving 40 individuals (20 in the AR group) and 20 in the control group [CG]) was conducted. Ventilatory pattern and chest wall volume distribution (optoelectronic plethysmography), respiratory muscle strength (manovacuometry and sniff nasal inspiratory pressure [SNIP]), and EAdi were assessed in both groups. Results: The AR patients had impaired thoraco-abdominal kinematics (reduced total chest wall volume) (p = 0.004), lower values of total respiratory cycle time (p = 0.014) and expiratory time (p = 0.006). They also presented an increase of percentage contribution of the abdominal rib cage (p = 0.475) and respiratory rate (p = 0.019). A positive correlation among pulmonary rib cage tidal volume and MIP (r = 0.544; p < 0.001), SNIP (r = 0.615; p < 0.001), and MEP (r = 0.604; p < 0.001) was observed. After adjusting for age, BMI and gender through multivariate analysis, the individuals with AR presented lower values ​​of MIP (ß = -24.341; p < 0.001), MEP (ß = -0.277; p < 0.001), SNIP (ß = -34.687; p < 0.001) and RMS (ß = -0.041; p = 0.017). Conclusions: The individuals with moderate-severe persistent AR had worse respiratory muscle strength, diaphragm activation and chest wall volume distribution with a higher abdominal contribution to tidal volume than the control group. These findings reinforce the notion that the upper and lower airways work in an integrated and synergistic manner.

Impaired sarcoplasmic reticulum Ca2+ release is the major cause of fatigue-induced force loss in intact single fibres from human intercostal muscle.

KEY POINTS: Changes in intramuscular Ca2+ handling contribute to development of fatigue and disease-related loss of muscle mass and function. To date, no data on human intact living muscle fibres have been described. We manually dissected intact single fibres from human intercostal muscle and simultaneously measured force and myoplasmic free [Ca2+ ] at physiological temperature. Based on their fatigue resistance, two distinct groups of fibres were distinguished: fatigue sensitive and fatigue resistant. Force depression in fatigue and during recovery was due to impaired sarcoplasmic reticulum Ca2+ release in both groups of fibres. Acidification did not affect force production in unfatigued fibres and did not affect fatigue development in fatigue-resistant fibres. The current study provides novel insight into the mechanisms of fatigue in human intercostal muscle. ABSTRACT: Changes in intracellular Ca2+ handling of individual skeletal muscle fibres cause a force depression following physical activity and are also implicated in disease-related loss of function. The relation of intracellular Ca2+ handling with muscle force production and fatigue tolerance is best studied in intact living single fibres that allow continuous measurements of force and myoplasmic free [Ca2+ ] during repeated contractions. To this end, manual dissections of human intercostal muscle biopsies were performed to isolate intact single fibres. Based on the ability to maintain tetanic force at >40% of the initial value during 500 fatiguing contractions, fibres were classified as either fatigue sensitive or fatigue resistant. Following fatigue all fibres demonstrated a marked reduction in sarcoplasmic reticulum Ca2+ release, while myofibrillar Ca2+ sensitivity was either unaltered or increased. In unfatigued fibres, acidosis caused a reduction in myofibrillar Ca2+ sensitivity that was offset by increased tetanic myoplasmic free [Ca2+ ] so that force remained unaffected. Acidification did not affect the fatigue tolerance of fatigue-resistant fibres, whereas uncertainties remain whether or not fatigue-sensitive fibres were affected. Following fatigue, a prolonged force depression at preferentially low-frequency stimulation was evident in fatigue-sensitive fibres and this was caused exclusively by an impaired sarcoplasmic reticulum Ca2+ release. We conclude that impaired sarcoplasmic reticulum Ca2+ release is the predominant mechanism of force depression both in the development of, and recovery from, fatigue in human intercostal muscle.

High-frequency spinal cord stimulation in a subacute animal model of spinal cord injury.

High-frequency spinal cord stimulation (HF-SCS) applied at the T2 spinal level results in physiologic activation of the inspiratory muscles in C2 spinal-sectioned dogs. Although the bulbo-spinal fibers were cut, they likely survived the duration of acute experiments, and inspiratory muscle activation may have involved stimulation of these fibers. In two anesthetized, C2 paralyzed, intubated, and mechanically ventilated dogs, HF-SCS (300 Hz) was applied at the T2 level. The effectiveness of HF-SCS in generating inspired volume (V) and negative airway pressures (P) was evaluated over a period of 5 days during which time the bulbo-spinal fibers would have degenerated. Because the effectiveness of HF-SCS may be adversely affected by deterioration of these fibers and/or the condition of the animal, low-frequency (50 Hz) SCS (LF-SCS) was also performed and served as a control. All vital signs, oxygen saturation, and end-tidal Pco2 remained stable over the 5-day period. V and P also remained stable over the study period. For example, mean V and P were 771 ± 25 ml and 64 ± 1 cmH2O with HF-SCS (3 mA) during the initial and 674 ± 59 ml and 63 ± 5 cmH2O on the final day. Comparable values during LF-SCS (8 mA) were 467 ± 12 ml and 48 ± 1 cmH2O during the initial and 397 ± 20 ml and 42 ± 2 cmH2O on the final day. Because V and P in response to HF-SCS remained stable over a 5-day period following which the bulbo-spinal fibers would have degenerated, the mechanism of HF-SCS does not depend upon the viability of these tracts. HF-SCS therefore may be a useful method to restore ventilation in chronic ventilator dependent tetraplegics. NEW & NOTEWORTHY This study indicates that the respiratory responses to high-frequency spinal cord stimulation applied at the T2 level results in activation of the inspiratory motoneuron pools via interneuronal circuits and/or the inspiratory motoneurons directly and does not depend upon activation of long descending inspiratory bulbo-spinal fibers. This method therefore, may provide an alternative method to restore ventilation in ventilator dependent spinal cord injured patients.

Effects of an 8-week selective corrective exercises program on electromyography activity of scapular and neck muscles in persons with upper crossed syndrome: Randomized controlled trial.

OBJECTIVES: Postural disorders disturb muscle activity and lead to joint dysfunction. This study aimed to evaluate the effects of an 8-week selective corrective exercises program on electromyography activity of scapular and neck muscles in persons with upper crossed syndrome (UCS). DESIGN: Randomized controlled trial. SETTING: Exercise evaluation was conducted in a laboratory setting. PARTICIPANT: Study recruited 30 healthy males with UCS from university students, who were then randomly divided into the control group (age = 20.14 ±â€¯1.71 years; height = 176.86 ±â€¯4.7 cm; BMI = 21.20 ±â€¯1.96 kg/m2) and the exercise group (age = 21.44 ±â€¯2.06 years; height = 174.2 ±â€¯4.0 cm; BMI = 20.62 ±â€¯3.9 kg/m2). MAIN OUTCOME MEASURES: Electromyography activity of upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), serratus anterior (SA), and sternocleidomastoid (SCM) was recorded before and after 8-week exercise program. RESULTS: T-test results revealed that baseline activity of SA (P < 0.05), had increased while UT (P < 0.05) and SCM (P < 0.05) activity as well as UT/SA (P < 0.05) and UT/LT (P < 0.05) ratios had decreased. In connection with these finding the effect sizes were large. CONCLUSION: Eight week corrective exercises balance muscles activity and can be used to manage developing upper quadrant musculoskeletal disorders in person with UCS.

Effect of radical prostatectomy on involuntary pelvic floor muscle contraction.

AIMS: Radical prostatectomy may cause stress urinary incontinence (SUI). We compared continent and incontinent men after radical prostatectomy, in regard to the change of the temporal pattern of pelvic floor activation during cough. METHODS: Twenty-two patients were included in this prospective, multicentric study. All patients gave their informed consent. Simultaneous recordings of electromyographic activity of external anal sphincter (EAS EMG) and external intercostal muscle (EIC EMG) during cough were performed with a pair of pregelled surface electrodes. Cough effort caused an involuntary pelvic contraction. Intercostal muscles recording was chosen because they are one of the muscular components of cough initiation with diaphragm muscle. Twenty-four-hour pad-weighing test was used to quantify urinary incontinence. The primary endpoint was the latency between the onset of EIC EMG and EAS EMG (RT3), during a cough effort. We also measured the contraction time, the maximum EAS EMG activity, and the area under the curve. RESULTS: All the patients were analyzed: 12 continent and 10 with SUI. The median age was 66 years old. Both groups were similar except in term of follow-up. Median latency was increased by -1.7 ms (-47.9; +34.2) to 55.8 ms (+47.5; +80) in patients with SUI (P = 0.0033; Table 2). The duration of the contraction, the maximum EAS EMG activity and the area under the curve were not different. CONCLUSIONS: The latency between the onset of EIC EMG and EAS EMG is increased in patients with SUI after radical prostatectomy. It may be one of the reasons for SUI in these patients.

Pelvic floor muscle activation in stress urinary incontinent women: Impact of a distraction task.

AIMS: Our purpose was to explore the involvement of cognition in voluntary and involuntary pelvic floor muscle (PFM) contraction in stress urinary incontinent women. METHODS: PFM contraction monitored by surface electromyography (EMG) was measured without a mental distraction task (DT), and with a DT called "paced auditory serial additional test" (PASAT). Forty stress incontinent women performed voluntary contractions of the external anal sphincter (EAS), and reflex EAS contractions induced by means of coughing were studied using the external intercostal muscle (EIC) EMG pattern. RESULTS: A DT altered PFM pre-activation when coughing: the reaction time between EIC muscle contraction and EAS contraction (called RT3) was respectively -54.94 ms (IQR -87.12; 3.12) without the PASAT and -3.99 ms (IQR: -47.92; 18.69) with a DT (P = 0.02, Wilcoxon's test). Concerning voluntary contraction, women activated their PFM sooner without than with a DT. CONCLUSION: The PASAT altered voluntary and reflex contractions of the PFM in stress urinary incontinent women. Our study suggests that cognition plays a role in urinary pathophysiology. Future studies should investigate rehabilitation programs that consider the role of cognition in stress urinary incontinent women.

Inspiratory pressure-generating capacity is preserved during ventilatory and non-ventilatory behaviours in young dystrophic mdx mice despite profound diaphragm muscle weakness.

KEY POINTS: Respiratory muscle weakness is a major feature of Duchenne muscular dystrophy (DMD), yet little is known about the neural control of the respiratory muscles in DMD and animal models of dystrophic disease. Substantial diaphragm muscle weakness is apparent in young (8-week-old) mdx mice, although ventilatory capacity in response to maximum chemostimulation in conscious mice is preserved. Peak volume- and flow-related measures during chemoactivation are equivalent in anaesthetized, vagotomized wild-type and mdx mice. Diaphragm and T3 external intercostal electromyogram activities are lower during protracted sustained airway occlusion in mdx compared to wild-type mice. Yet, peak inspiratory pressure generation is remarkably well preserved. Despite profound diaphragm weakness and lower muscle activation during maximum non-ventilatory efforts, inspiratory pressure-generating capacity is preserved in young adult mdx mice, revealing compensation in support of respiratory system performance that is adequate, at least early in dystrophic disease. ABSTRACT: Diaphragm dysfunction is recognized in the mdx mouse model of muscular dystrophy; however, there is a paucity of information concerning the neural control of dystrophic respiratory muscles. In young adult (8 weeks of age) male wild-type and mdx mice, we assessed ventilatory capacity, neural activation of the diaphragm and external intercostal (EIC) muscles and inspiratory pressure-generating capacity during ventilatory and non-ventilatory behaviours. We hypothesized that respiratory muscle weakness is associated with impaired peak inspiratory pressure-generating capacity in mdx mice. Ventilatory responsiveness to hypercapnic hypoxia was determined in conscious mice by whole-body plethysmography. Diaphragm isometric and isotonic contractile properties were determined ex vivo. In anaesthetized mice, thoracic oesophageal pressure, and diaphragm and EIC electromyogram (EMG) activities were recorded during baseline conditions and sustained tracheal occlusion for 30-40s. Despite substantial diaphragm weakness, mdx mice retain the capacity to enhance ventilation during hypercapnic hypoxia. Peak volume- and flow-related measures were also maintained in anaesthetized, vagotomized mdx mice. Peak inspiratory pressure was remarkably well preserved during chemoactivated breathing, augmented breaths and maximal sustained efforts during airway obstruction in mdx mice. Diaphragm and EIC EMG activities were lower during airway obstruction in mdx compared to wild-type mice. We conclude that ventilatory capacity is preserved in young mdx mice. Despite profound respiratory muscle weakness and lower diaphragm and EIC EMG activities during high demand in mdx mice, peak inspiratory pressure is preserved, revealing adequate compensation in support of respiratory system performance, at least early in dystrophic disease. We suggest that a progressive loss of compensation during advancing disease, combined with diaphragm dysfunction, underpins the development of respiratory system morbidity in dystrophic diseases.

Measurement of Diaphragmatic Electrical Activity by Surface Electromyography in Intubated Subjects and Its Relationship With Inspiratory Effort.

BACKGROUND: Quantification of patient effort during spontaneous breathing is important to tailor ventilatory assistance. Because a correlation between inspiratory muscle pressure (Pmus) and electrical activity of the diaphragm (EAdi) has been described, we aimed to assess the reliability of surface electromyography (EMG) of the respiratory muscles for monitoring diaphragm electrical activity and subject effort during assisted ventilation. METHODS: At a general ICU of a single university-affiliated hospital, we enrolled subjects who were intubated and on pressure support ventilation (PSV) and were on mechanical ventilation for > 48 h. The subjects were studied at 3 levels of pressure support. Airway flow and pressure; esophageal pressure; EAdi; and surface EMG of the diaphragm (surface EAdi), intercostal, and sternocleidomastoid muscles were recorded. Respiratory cycles were sampled for off-line analysis. The Pmus/EAdi index (PEI) was calculated by relying on EAdi and surface EAdi (surface PEI) from an airway pressure drop during end-expiratory occlusions performed every minute. RESULTS: surface EAdi well correlated with EAdi and Pmus, in particular, after averaging breaths into deciles (R = 0.92 and R = 0.84). When surface PEI was used with surface EAdi, it provided a reliable estimation of Pmus (R = 0.94 in comparison with measured Pmus). CONCLUSIONS: During assisted mechanical ventilation, EAdi can be reliably monitored by both EAdi and surface EMG. The measurement of Pmus based on the calibration of EAdi was also feasible by the use of surface EMG.

Parasternal intercostal muscle ultrasound in chronic obstructive pulmonary disease correlates with spirometric severity.

In chronic obstructive pulmonary disease (COPD), loss of computed tomography (CT)-measured intercostal mass correlates with spirometric severity. Intercostal muscle ultrasound offers a repeatable and radiation-free alternative, however requires validation. We aimed to determine the reliability of parasternal intercostal muscle ultrasound, and the concurrent validity of parasternal ultrasound with clinicometric parameters. Twenty stable COPD patients underwent ultrasound measurement of thickness and echogenicity of 2nd and 3rd parasternal intercostal muscles, dominant pectoralis major and quadriceps, and diaphragm thickness; spirometry; and chest CT. Intra-rater intraclass correlation (ICC) for ultrasound intercostal thickness was 0.87-0.97 depending on site, with echogenicity ICC 0.63-0.91. Inter-rater ICC was fair to excellent. Ultrasound intercostal thickness moderately correlated with FEV1% predicted (r = 0.33) and quadriceps thickness (r = 0.31). Echogenicity correlated negatively with FEV1% predicted (r = -0.32). CT-measured lateral intercostal mass correlate negatively with parasternal ultrasound intercostal thickness. These data confirm ultrasound of parasternal intercostal musculature is reproducible. Lower intercostal muscle quantity and quality reflects greater COPD spirometric severity. This novel tool may have biomarker potential for both the systemic effects of COPD on muscle as well as local disruption of respiratory mechanics. The negative correlation between CT and ultrasound measurements may reflect complex site-dependent interactions between respiratory muscles and the chest wall.

Clinical importance of cross-sectional area of intercostal muscles in patients with chronic obstructive pulmonary disease.

INTRODUCTION: Limb muscle wasting is one of main systemic manifestation of chronic obstructive pulmonary disease (COPD). However, the change of respiratory muscle is unclear. OBJECTIVES: This study assessed the cross-sectional area (CSA) of the intercostal muscles (ICMs) in patients with COPD, using chest computed tomography (CT) and determined its association with the clinical characteristics of COPD. METHODS: They retrospectively reviewed 60 patients with stable COPD and compared them with 30 controls. CSA (mm2 ) of the ICM on chest CT was measured at the midline level of the lateral arch of the bilateral first rib with a 3-mm slice thickness by using CT histogram software. The association with the clinical characteristics of COPD and with the control groups was assessed. RESULTS: CSA of the ICM and the CSA/body mass index (BMI) were lower in the COPD group than in the control group. Patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 4 had a significantly lower CSA of the ICM than patients with stage 1, 2, and 3. CSA of the ICM was positively associated with FEV1 , %FEV1 predicted, FEV1 /FVC ratio, and BMI and negatively associated with age. However, there were no associations with PaO2 , PaCO2 , smoking status, 6-minute walk test, frequency of acute exacerbation of COPD, and serum C-reactive protein level. CONCLUSION: Intercostal muscle atrophy occurs in COPD patients and is associated with severity of airway obstruction, BMI, and increasing age.

Compensatory plasticity in diaphragm and intercostal muscle utilization in a rat model of ALS.

In SOD1G93A transgenic rat model of ALS, breathing capacity is preserved until late in disease progression despite profound respiratory motor neuron (MN) cell death. To explore mechanisms preserving breathing capacity, we assessed inspiratory EMG activity in diaphragm and external intercostal T2 (EIC2) and T5 (EIC5) muscles in anesthetized SOD1G93A rats at disease end-stage (20% decrease in body mass). We hypothesized that despite significant phrenic motor neuron loss and decreased phrenic nerve activity, diaphragm electrical activity and trans-diaphragmatic pressure (Pdi) are maintained to sustain ventilation. We alternatively hypothesized that EIC activity is enhanced, compensating for impaired diaphragm function. Diaphragm, EIC2 and EIC5 muscle EMGs and Pdi were measured in urethane-anesthetized, spontaneously breathing female SOD1G93A rats versus wild-type littermates during normoxia (arterial PO2 ~90mmHg, PCO2 ~45mmHg), maximal chemoreceptor stimulation (MCS: 10.5% O2/7% CO2), spontaneous augmented breaths and sustained tracheal occlusion. Phrenic MNs were counted in C3-5; T2 and T5 ventrolateral MNs were counted. In end-stage SOD1G93A rats, 29% of phrenic MNs survived (vs. wild-type), yet integrated diaphragm EMG amplitude was normal. Nevertheless, maximal Pdi decreased ~30% vs. wild type (p<0.01) and increased esophageal to gastric pressure ratio (p<0.05), consistent with persistent diaphragm weakness. Despite major T2 and T5 MN death, integrated EIC2 (100% greater than wild type) and EIC5 (300%) EMG amplitudes were increased in mutant rats during normoxia (p<0.01), possibly compensating for decreased Pdi. Thus, despite significant phrenic MN loss, diaphragm EMG activity is maintained; in contrast, Pdi was not, suggesting diaphragm dysfunction. Presumably, increased EIC EMG activity compensated for persistent diaphragm weakness. These adjustments contribute to remarkable preservation of breathing ability despite major respiratory motor neuron death and diaphragm dysfunction.

Effects of unilateral airway occlusion on rib motion and inspiratory intercostal activity in dogs.

Unilateral bronchial occlusion, a complication of many lung diseases, causes dyspnea but the mechanism of this symptom is uncertain. In this study, electromyographic (EMG) activity in the parasternal and external intercostal muscles in the third intercostal space and inspiratory motion of the third rib on both sides of the thorax were assessed during occlusion of a main bronchus for a single breath in anesthetized dogs. Occlusion produced a 65% increase in external intercostal EMG activity in both hemithoraces without altering parasternal EMG activity. Concomitantly, the inspiratory cranial rib motion showed a 50% decrease on both sides of the thorax. These changes were unaffected by bilateral vagotomy. However, when an external, caudally oriented force was applied to the third rib on the right or left side so that its inspiratory cranial displacement was abolished, activity in the adjacent external intercostals showed a twofold increase, but rib motion and external activity in the contralateral hemithorax remained unchanged. It is concluded that during occlusion of a main bronchus, the increase in external intercostal activity is induced by the decrease in inspiratory cranial rib displacement in both hemithoraces, and that this decrease is determined by the increase in pleural pressure swings on both sides of the mediastinum. This mechanism, combined with the decrease in PaO2, induces similar alterations when unilateral bronchial occlusion is maintained for a series of consecutive breaths.

Is parasternal intercostal EMG an accurate surrogate of respiratory neural drive and biomarker of dyspnea during cycle exercise testing?

Recent evidence suggests that surface electromyography of the parasternal intercostals (EMGpara) can be a non-invasive alternative to diaphragmatic EMG (EMGdi) for estimating neural respiratory drive (NRD) during cardiopulmonary exercise testing (CPET). The purpose of this study was to determine if non-respiratory muscles influence EMGpara by having subjects place their hands on (Hon) and off (Hoff) the handlebars during cycling-based CPET. Ten healthy adults performed an incremental cycling test until volitional exhaustion. Participants were instrumented with an esophageal electrode catheter to measure EMGdi, and surface electrodes on the 2nd intercostal space to measure EMGpara. Subjects alternated between 30s of Hon and 30s Hoff during each exercise stage. There were no differences in EMGdi across all exercise intensities. However, EMGpara was significantly greater during the Hon vs. Hoff condition at all exercise intensities (p<0.05). These results suggest that EMGpara may not be an appropriate surrogate of NRD during cycle exercise testing due to co-activation of adjacent skeletal muscles.

Influence of a distraction task on the involuntary reflex contraction of the pelvic floor muscles following cough.

AIMS: To explore the involvement of a distraction task in involuntary reflex pelvic floor muscle contraction following cough. METHODS: Informed consent was obtained from 33 healthy volunteers. Involuntary contraction of the external anal sphincter (EAS) was induced by means of coughing. Cough efforts were elicited by electronic order. The electromyographic (EMG) activity of the EAS was recorded during involuntary contraction elicited by coughing. The trials were carried out twice: combined (or not) with a mental distraction task; the paced auditory serial additional test (PASAT). Reaction time (RT) defined as latency between the stimulus and maximum EAS EMG activity (RT1), latency between the stimulus and external intercostal (EIC) muscle EMG activity (RT2), latency between EIC EMG activity and EAS EMG activity (RT3), duration of the contraction, and the area under the EAS EMG activity curve (perineal contraction) were measured. RESULTS: The distraction task altered anticipation of the PFM contraction: RT3 was -80.00 ms (IQR -107; -56) without the PASAT versus -56.67 ms (IQR: -94; -2) with the distraction task (ratio 0.71, P = 0.0045, Wilcoxon test). RT2 was altered during the distraction task: 583.33 ms (IQR: 344-775) without PASAT versus 652.71 ms (503-790) during PASAT (ratio 1.12, P = 0.031, Wilcoxon test). Finally, when the two conditions (respectively with and without the mental distraction task) were compared, there was a significant difference between the area under the EAS EMG activity curve (0.0115 mv sec vs. 0.0103 mv sec, ratio 0.90, P = 0.023). CONCLUSIONS: The mental distraction task altered involuntary reflex contraction of the pelvic floor muscles. Neurourol. Urodynam. 36:160-165, 2017. © 2015 Wiley Periodicals, Inc.

Physiological markers of exercise capacity and lung disease severity in cystic fibrosis.

BACKGROUND AND OBJECTIVE: Peak aerobic capacity (VO2 peak) is an important outcome measure in cystic fibrosis (CF), but measurement is not widely available and can be influenced by patient motivation, pain and fatigue. Alternative markers of disease severity would be helpful. Neural respiratory drive, measured using parasternal intercostal muscle electromyography (EMGpara), reflects the load to capacity balance of the respiratory system and provides a composite measure of pulmonary function impairment in CF. The aim of the study was to investigate the relationship between exercise capacity, EMGpara and established measures of pulmonary function in clinically stable adult CF patients. METHODS: Twenty CF patients (12 males, median (range) age: 22.3 (17.0-43.1) years) performed the 10-m incremental shuttle walk test (ISWT) maximally with contemporaneous measures of aerobic metabolism. EMGpara was recorded from second intercostal space at rest and normalized using peak electromyogram activity obtained during maximum respiratory manoeuvres and expressed as EMGpara%max (EMGpara expressed as a percentage of maximum). RESULTS: VO2 peak was strongly correlated with ISWT distance (r = 0.864, P < 0.0001). Lung gas transfer (TL CO) % predicted was best correlated with VO2 peak (r = 0.842, P < 0.0001) and ISWT distance (r = 0.788, P < 0.0001). EMGpara%max also correlated with VO2 peak (-0.757, P < 0.0001), while the relationships between exercise outcome measures and forced expiratory volume in 1 s (FEV1 ) % predicted and forced vital capacity (FVC) % predicted were less strong. A TL CO% predicted of <70.5% was the strongest predictor of VO2 peak <32 mL/min/kg (area under the curve (AUC): 0.96, 100% sensitivity, 83.3% specificity). ISWT distance and EMGpara%max also performed well, with other pulmonary function variables demonstrating poorer predictive ability. CONCLUSION: TL CO% predicted and EMGpara%max relate strongly to exercise performance markers in CF and may provide alternative predictors of lung disease progression.