RESUMO
Inspiratory tongue dilatory movement is believed to be mediated via changes in neural drive to genioglossus. However, this has not been studied during quiet breathing in humans. Therefore, this study investigated this relationship and its potential role in obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue dilatory movement, quantified with tagged magnetic resonance imaging, and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in nine controls [apnoea-hypopnea index (AHI) ≤5 events/h] and 37 people with untreated OSA (AHI >5 events/h). Measurements were obtained for 156 neuromuscular compartments (85%). Analysis was adjusted for nadir epiglottic pressure during inspiration. Only for 106 compartments (68%) was a larger anterior (dilatory) movement associated with a higher phasic EMG [mixed linear regression, beta = 0.089, 95% CI [0.000, 0.178], t(99) = 1.995, P = 0.049, hereafter EMGâ/mvtâ]. For the remaining 50 (32%) compartments, a larger dilatory movement was associated with a lower phasic EMG [mixed linear regression, beta = -0.123, 95% CI [-0.224, -0.022], t(43) = -2.458, P = 0.018, hereafter EMGâ/mvtâ]. OSA participants had a higher odds of having at least one decoupled EMGâ/mvtâ compartment (binary logistic regression, odds ratio [95% CI]: 7.53 [1.19, 47.47] (P = 0.032). Dilatory tongue movement was minimal (>1 mm) in nearly all participants with only EMGâ/mvtâ compartments (86%, 18/21). These results demonstrate that upper airway dilatory mechanics cannot be predicted from genioglossus EMG, particularly in people with OSA. Tongue movement associated with minimal genioglossus activity suggests co-activation of other airway dilator muscles. KEY POINTS: Inspiratory tongue movement is thought to be mediated through changes in genioglossus activity. However, it is unknown if this relationship is altered by obstructive sleep apnoea (OSA). During awake supine quiet nasal breathing, inspiratory tongue movement, quantified with tagged magnetic resonance imaging (MRI), and inspiratory phasic genioglossus EMG normalised to maximum EMG were measured in four tongue compartments of people with and without OSA. Larger tongue anterior (dilatory) movement was associated with higher phasic genioglossus EMG for 68% of compartments. OSA participants had an â¼7-times higher odds of having at least one compartment for which a larger anterior tongue movement was not associated with a higher phasic EMG than controls. Therefore, higher genioglossus phasic EMG does not consistently translate into tongue dilatory movement, particularly in people with OSA. Large dilatory tongue movements can occur despite minimal genioglossus inspiratory activity, suggesting co-activation of other pharyngeal muscles.
Assuntos
Apneia Obstrutiva do Sono , Vigília , Humanos , Vigília/fisiologia , Músculos Faríngeos , Movimento/fisiologia , Língua , EletromiografiaRESUMO
Substantia nigra (SN) hyperechogenicity, viewed with transcranial ultrasound, is a risk marker for Parkinson's disease. We hypothesized that SN hyperechogenicity in healthy adults aged 50-70 years is associated with reduced short-interval intracortical inhibition in primary motor cortex, and that the reduced intracortical inhibition is associated with neurochemical markers of activity in the pre-supplementary motor area (pre-SMA). Short-interval intracortical inhibition and intracortical facilitation in primary motor cortex was assessed with paired-pulse transcranial magnetic stimulation in 23 healthy adults with normal (n = 14; 61 ± 7 yrs) or abnormally enlarged (hyperechogenic; n = 9; 60 ± 6 yrs) area of SN echogenicity. Thirteen of these participants (7 SN- and 6 SN+) also underwent brain magnetic resonance spectroscopy to investigate pre-SMA neurochemistry. There was no relationship between area of SN echogenicity and short-interval intracortical inhibition in the ipsilateral primary motor cortex. There was a significant positive relationship, however, between area of echogenicity in the right SN and the magnitude of intracortical facilitation in the right (ipsilateral) primary motor cortex (p = .005; multivariate regression), evidenced by the amplitude of the conditioned motor evoked potential (MEP) at the 10-12 ms interstimulus interval. This relationship was not present on the left side. Pre-SMA glutamate did not predict primary motor cortex inhibition or facilitation. The results suggest that SN hyperechogenicity in healthy older adults may be associated with changes in excitability of motor cortical circuitry. The results advance understanding of brain changes in healthy older adults at risk of Parkinson's disease.
Assuntos
Excitabilidade Cortical , Córtex Motor , Doença de Parkinson , Humanos , Idoso , Córtex Motor/diagnóstico por imagem , Doença de Parkinson/diagnóstico por imagemRESUMO
STUDY DESIGN: Secondary analysis of a randomised controlled trial. OBJECTIVES: Our primary study showed that increasing inspiratory muscle strength with training in people with chronic (>1 year) tetraplegia corresponded with reduced sensations of breathlessness when inspiration was loaded. This study investigated whether respiratory muscle training also affected the respiratory sensations for load detection and magnitude perception. SETTING: Independent research institute in Sydney, Australia. METHODS: Thirty-two adults with chronic tetraplegia participated in a 6-week, supervised training protocol. The active group trained the inspiratory muscles through progressive threshold loading. The sham group performed the same protocol with a fixed threshold load (3.6 cmH2O). Primary measures were load detection threshold and perceived magnitudes of six suprathreshold loads reported using the modified Borg scale. RESULTS: Maximal inspiratory pressure (PImax) increased by 32% (95% CI, 18-45) in the active group with no change in the sham group (p = 0.51). The training intervention did not affect detection thresholds in the active (p = 0.24) or sham (p = 0.77) group, with similar overall decreases in Borg rating of 0.83 (95% CI, 0.49-1.17) in active and 0.72 (95% CI, 0.32-1.12) in sham group. Increased inspiratory muscle strength reduced slope magnitude between Borg rating and peak inspiratory pressure (p = 0.003), but not when pressure was divided by PImax to reflect contraction intensity (p = 0.92). CONCLUSIONS: Training reduces the sensitivity of load sensations for a given change in pressure but not for a given change in contraction intensity.
Assuntos
Traumatismos da Medula Espinal , Adulto , Humanos , Traumatismos da Medula Espinal/complicações , Exercícios Respiratórios , Academias e Institutos , Quadriplegia , SensaçãoRESUMO
NEW FINDINGS: What is the central question of this study? Does a single session of repeated bouts of acute intermittent hypoxic breathing enhance the motoneuronal output of the limb muscles of healthy able-bodied participants? What is the main finding and its importance? Compared to breathing room air, there were some increases in motoneuronal output following acute intermittent hypoxia, but the increases were variable across participants and in time after the intervention and depended on which neurophysiological measure was checked. ABSTRACT: Acute intermittent hypoxia (AIH) induces persistent increases in output from rat phrenic motoneurones. Studies in people with spinal cord injury (SCI) suggest that AIH improves limb performance, perhaps via postsynaptic changes at cortico-motoneuronal synapses. We assessed whether limb motoneurone output in response to reflex and descending synaptic activation is facilitated after one session of AIH in healthy able-bodied volunteers. Fourteen participants completed two experimental days, with either AIH or a sham intervention (randomised crossover design). We measured H-reflex recruitment curves and homosynaptic post-activation depression (HPAD) of the H-reflex in soleus, and motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS) and their recruitment curves in first dorsal interosseous. All measurements were performed at rest and occurred at baseline, 0, 20, 40 and 60 min post-intervention. The intervention was 30 min of either normoxia (sham, F i O 2 ${F_{{\rm{i}}{{\rm{O}}_{\rm{2}}}}}$ ≈ 0.21) or AIH (alternate 1-min hypoxia [ F i O 2 ${F_{{\rm{i}}{{\rm{O}}_{\rm{2}}}}}$ ≈ 0.09], 1-min normoxia). After AIH, the H-reflex recruitment curve shifted leftward. Lower stimulation intensities were needed to evoke 5%, 50% and 99% of the maximal H-reflex at 40 and 60 min after AIH (P < 0.04). The maximal H-reflex, recruitment slope and HPAD were unchanged after AIH. MEPs evoked by constant intensity TMS were larger 40 min after AIH (P = 0.027). There was no change in MEP recruitment or the maximal MEP. In conclusion, some measures of the evoked responses from limb motoneurones increased after a single AIH session, but only at discrete time points. It is unclear to what extent these changes alter functional performance.
Assuntos
Neurônios Motores , Traumatismos da Medula Espinal , Animais , Potencial Evocado Motor , Humanos , Hipóxia , Neurônios Motores/fisiologia , Ratos , Estimulação Magnética TranscranianaRESUMO
STUDY DESIGN: An international multi-centred, double-blinded, randomised sham-controlled trial (eWALK). OBJECTIVE: To determine the effect of 12 weeks of transcutaneous spinal stimulation (TSS) combined with locomotor training on walking ability in people with spinal cord injury (SCI). SETTING: Dedicated SCI research centres in Australia, Spain, USA and Scotland. METHODS: Fifty community-dwelling individuals with chronic SCI will be recruited. Participants will be eligible if they have bilateral motor levels between T1 and T11, a reproducible lower limb muscle contraction in at least one muscle group, and a Walking Index for SCI II (WISCI II) between 1 and 6. Eligible participants will be randomised to one of two groups, either the active stimulation group or the sham stimulation group. Participants allocated to the stimulation group will receive TSS combined with locomotor training for three 30-min sessions a week for 12 weeks. The locomotor sessions will include walking on a treadmill and overground. Participants allocated to the sham stimulation group will receive the same locomotor training combined with sham stimulation. The primary outcome will be walking ability with stimulation using the WISCI II. Secondary outcomes will record sensation, strength, spasticity, bowel function and quality of life. TRIAL REGISTRATION: ANZCTR.org.au identifier ACTRN12620001241921.
Assuntos
Traumatismos da Medula Espinal , Estimulação da Medula Espinal , Humanos , Modalidades de Fisioterapia , Qualidade de Vida , Ensaios Clínicos Controlados Aleatórios como Assunto , Traumatismos da Medula Espinal/complicações , Caminhada/fisiologiaRESUMO
KEY POINTS: Impaired pharyngeal anatomy and increased airway collapsibility is a major cause of obstructive sleep apnoea (OSA) and a mediator of its severity. Upper airway reflexes to changes in airway pressure provide important protection against airway closure. This study shows increased pharyngeal collapsibility and attenuated genioglossus reflex responses during expiration in people with OSA. ABSTRACT: Upper airway collapse contributes to obstructive sleep apnoea (OSA) pathogenesis. Pharyngeal dilator muscle activity varies throughout the respiratory cycle and may contribute to dynamic changes in pharyngeal collapsibility. However, whether upper airway collapsibility and reflex responses to changes in airway pressure vary throughout the respiratory cycle in OSA is unclear. Thus, this study quantified differences in upper airway collapsibility and genioglossus electromyographic (EMG) activity and reflex responses during different phases of the respiratory cycle. Twelve middle-aged people with OSA (2 female) were fitted with standard polysomnography equipment: a nasal mask, pneumotachograph, two fine-wire intramuscular electrodes into the genioglossus, and a pressure catheter positioned at the epiglottis and a second at the choanae (the collapsible portion of the upper airway). At least 20 brief (â¼250 ms) pressure pulses (â¼-11 cmH2 O at the mask) were delivered every 2-10 breaths during four conditions: (1) early inspiration, (2) mid-inspiration, (3) early expiration, and (4) mid-expiration. Mean baseline genioglossus EMG activity 100 ms prior to pulse delivery and genioglossus reflex responses were quantified for each condition. The upper airway collapsibility index (UACI), quantified as 100 × (nadir choanal - epiglottic pressure)/nadir choanal pressure during negative pressure pulses, varied throughout the respiratory cycle (early inspiration = 43 ± 25%, mid-inspiration = 29 ± 19%, early expiration = 83 ± 19% and mid-expiration = 95 ± 11% (mean ± SD) P < 0.01). Genioglossus EMG activity was lower during expiration (e.g. mid-expiration vs. mid-inspiration = 76 ± 23 vs. 127 ± 41% of early-inspiration, P < 0.001). Similarly, genioglossus reflex excitation was delayed (39 ± 11 vs. 23 ± 7 ms, P < 0.001) and reflex excitation amplitude attenuated during mid-expiration versus early inspiration (209 ± 36 vs. 286 ± 80%, P = 0.009). These findings may provide insight into the physiological mechanisms of pharyngeal collapse in OSA.
Assuntos
Apneia Obstrutiva do Sono , Idoso , Eletromiografia , Feminino , Humanos , Pessoa de Meia-Idade , Músculos Faríngeos , Faringe , Polissonografia , Reflexo , SonoRESUMO
KEY POINTS: Respiration plays a key role in the circulation of cerebrospinal fluid (CSF) around the central nervous system. During inspiration increased venous return from the cranium is believed to draw CSF rostrally. However, this mechanism does not explain why CSF has also been observed to move caudally during inspiration. We show that during inspiration decreased intrathoracic pressure draws venous blood from the cranium and lumbar spine towards the thorax. We also show that the abdominal pressure was associated with rostral CSF displacement. However, a caudal shift of cervical CSF was seen with low abdominal pressure and comparably negative intrathoracic pressures. These results suggest that the effects of epidural blood flow within the spinal canal need to be considered, as well as the cranial blood volume balance, to understand respiratory-related CSF flow. These results may prove useful for the treatment of CSF obstructive pathology and understanding the behaviour of intrathecal drug injections. ABSTRACT: It is accepted that during inspiration, cerebrospinal fluid (CSF) flows rostrally to compensate for decreased cranial blood volume, caused by venous drainage due to negative intrathoracic pressure. However, this mechanism does not explain observations of caudal CSF displacement during inspiration. Determining the drivers of respiratory CSF flow is crucial for understanding the pathophysiology of CSF flow disorders. To quantify the influence of respiration on CSF flow, real-time phase-contrast magnetic resonance imaging (MRI) was used to record CSF and blood flow, while healthy subjects (5:5 M:F, 25-50 years) performed either a brief expiratory or inspiratory effort between breaths. Transverse images were taken perpendicular to the spinal canal in the middle of the C3 and L2 vertebrae. The same manoeuvres were then performed after a nasogastric pressure catheter was used to measure the intrathoracic and abdominal pressures. During expiratory-type manoeuvres that elevated abdominal and intrathoracic pressures, epidural blood flow into the spinal canal increased and CSF was displaced rostrally. With inspiratory manoeuvres, the negative intrathoracic pressure drew venous blood from C3 and L2 towards the thoracic spinal canal, and cervical CSF was displaced both rostrally and caudally, despite the increased venous drainage. Regression analysis showed that rostral displacement of CSF at both C3 (adjusted R2 = 0.53; P < 0.001) and L2 (adjusted R2 = 0.38; P < 0.001) were associated with the abdominal pressure. However, with low abdominal pressure and comparably negative intrathoracic pressure, cervical CSF flowed caudally. These findings suggest that changes in both the cranial and spinal pressures need to be considered to understand respiratory CSF flow.
Assuntos
Imageamento por Ressonância Magnética , Respiração , Volume Sanguíneo , Líquido Cefalorraquidiano , Humanos , Região Lombossacral , Coluna VertebralRESUMO
KEY POINTS: Respiratory muscle strength is compromised in people with tetraplegia, which may be compensated for by an increase in neural drive to the diaphragm. We found that the discharge frequencies of diaphragm motor units are higher in people with chronic tetraplegia compared with able-bodied people during quiet breathing. Furthermore, we found that the area of single motor unit potentials was increased in people with tetraplegia. These results suggest an increased motoneurone output to the diaphragm and remodelling of diaphragm motor units to maintain ventilation in tetraplegia. ABSTRACT: People with tetraplegia have reduced inspiratory muscle strength, â¼40% of able-bodied individuals. Paralysed or partially paralysed respiratory muscles as a result of tetraplegia compromise lung function, increase the incidence of respiratory infections and can cause dyspnoea. We hypothesised that reduced inspiratory muscle strength in tetraplegia may increase neural drive to the inspiratory muscles to maintain ventilation. We recorded the discharge properties of single motor units from the diaphragm in participants with chronic tetraplegia (8 males, 42-78 years, C3-C6 injury, AIS A-C) and able-bodied control participants (6 males matched for age and body mass index). In each group, 117 and 166 single motor units, respectively, were discriminated from recordings in the costal diaphragm using a monopolar electrode. A linear mixed-effects model analysis showed higher peak discharge frequencies of motor units during quiet breathing in tetraplegia (17.8 ± 4.9 Hz; mean ± SD) compared with controls (12.4 ± 2.2 Hz) (P < 0.001). There were no differences in tidal volume, inspiratory time or mean air flow between groups. Motor unit potentials in tetraplegia, compared with controls, were larger in amplitude (1.1 ± 0.7 mV and 0.5 ± 0.3 mV, respectively, P = 0.007) and area (1.83 ± 1.49 µV ms and 0.69 ± 0.52 µV ms, respectively, P = 0.003). The findings indicate that diaphragm motor unit remodelling is likely to have occurred in people with chronic tetraplegia and that there is an increase in diaphragm motor unit discharge rates during quiet breathing. These neural changes ensure that ventilation is maintained in people with chronic tetraplegia.
Assuntos
Diafragma , Alta do Paciente , Eletromiografia , Humanos , Masculino , Quadriplegia , Respiração , Músculos RespiratóriosRESUMO
KEY POINTS: Coordination of the neuromuscular compartments of the tongue is critical to maintain airway patency. Currently, little is known about the extent to which regional tongue dilatory motion is coordinated in heathy people and if this coordination is altered in people with obstructive sleep apnoea (OSA). We show that regional tongue muscle coordination in people with and without OSA during wakefulness is associated with effective airway dilatation during inspiration, using dynamic tagged magnetic resonance imaging. The maximal movement of four compartments of the tongue were correlated and occurred concurrently towards the end of inspiration. If tongue movement was observed, people with more severe OSA had larger movement and moved more compartments (up to four) to maintain airway patency, while people without OSA moved only one compartment. These results suggest that airway patency is preserved during wakefulness in people with OSA via active dilatory movement of the genioglossus. ABSTRACT: Maintaining airway patency when supine requires neural drive to the genioglossus horizontal and oblique neuromuscular compartments (superior fan-like and inferior horizontal genioglossus, regions that are innervated by different branches of the hypoglossal nerve) to be coordinated during breathing, but it is unknown if this coordination is altered in obstructive sleep apnoea (OSA). This study aimed to assess coordination of airway dilatory motion across four mid-sagittal tongue compartments during inspiration (i.e. anterior and posterior of the horizontal and oblique compartments), and compare it in controls and OSA patients. Fifty-four participants (12 women, aged 20-73 years) underwent dynamic 'tagged' magnetic resonance imaging during wakefulness. Ten participants had no OSA [apnoea hypopnoea index (AHI) < 5 events h-1 ], 14 had mild OSA (5 < AHI ≤ 15 events h-1 ), 12 had moderate OSA (15 < AHI ≤ 30 events h-1 ) and 18 had severe OSA (AHI > 30 events h-1 ). A higher AHI was associated with a greater anterior movement of the anterior and posterior horizontal compartments (Spearman, r = -0.32, P = 0.02 for both), but not in the oblique compartments. If movement was observed, higher OSA severity was associated with an anterior movement of a greater number of compartments. Controls only moved the posterior horizontal compartment while the anterior horizontal compartment also moved in OSA participants. Oblique compartments moved only in people with severe OSA. The maximal anterior inspiratory movement of the four compartments was highly correlated (Spearman, P < 0.001) and occurred concurrently. The posterior horizontal compartment had the greatest anterior motion. These results suggest that airway patency is preserved during wakefulness in people with OSA via active dilatory movement of the genioglossus.
Assuntos
Apneia Obstrutiva do Sono , Vigília , Adulto , Idoso , Feminino , Humanos , Nervo Hipoglosso , Pessoa de Meia-Idade , Respiração , Língua , Adulto JovemRESUMO
BACKGROUND: Respiratory complications remain a leading cause of morbidity and mortality in people with acute and chronic tetraplegia. Respiratory muscle weakness following spinal cord injury-induced tetraplegia impairs lung function and the ability to cough. In particular, inspiratory muscle strength has been identified as the best predictor of the likelihood of developing pneumonia in individuals with tetraplegia. We hypothesised that 6 weeks of progressive respiratory muscle training (RMT) increases respiratory muscle strength with improvements in lung function, quality of life and respiratory health. METHODS: Sixty-two adults with tetraplegia participated in a double-blind randomised controlled trial. Active or sham RMT was performed twice daily for 6 weeks. Inspiratory muscle strength, measured as maximal inspiratory pressure (PImax) was the primary outcome. Secondary outcomes included lung function, quality of life and respiratory health. Between-group comparisons were obtained with linear models adjusting for baseline values of the outcomes. RESULTS: After 6 weeks, there was a greater improvement in PImax in the active group than in the sham group (mean difference 11.5 cmH2O (95% CI 5.6 to 17.4), p<0.001) and respiratory symptoms were reduced (St George Respiratory Questionnaire mean difference 10.3 points (0.01-20.65), p=0.046). Significant improvements were observed in quality of life (EuroQol-Five Dimensional Visual Analogue Scale 14.9 points (1.9-27.9), p=0.023) and perceived breathlessness (Borg score 0.64 (0.11-1.17), p=0.021). There were no significant improvements in other measures of respiratory function (p=0.126-0.979). CONCLUSIONS: Progressive RMT increases inspiratory muscle strength in people with tetraplegia, by a magnitude which is likely to be clinically significant. Measurement of baseline PImax and provision of RMT to at-risk individuals may reduce respiratory complications after tetraplegia. TRIAL REGISTRATION NUMBER: Australian New Zealand Clinical Trials Registry (ACTRN 12612000929808).
Assuntos
Exercícios Respiratórios , Quadriplegia/fisiopatologia , Quadriplegia/reabilitação , Músculos Respiratórios/fisiopatologia , Adulto , Idoso , Método Duplo-Cego , Dispneia/etiologia , Feminino , Humanos , Inalação , Pulmão/fisiopatologia , Masculino , Pressões Respiratórias Máximas , Pessoa de Meia-Idade , Força Muscular , Quadriplegia/complicações , Qualidade de Vida , Avaliação de SintomasRESUMO
BACKGROUND: Expiratory muscle weakness leads to difficult ventilator weaning. Maintaining their activity with functional electrical stimulation (FES) may improve outcome. We studied feasibility of breath-synchronized expiratory population muscle FES in a mixed ICU population ("Holland study") and pooled data with our previous work ("Australian study") to estimate potential clinical effects in a larger group. METHODS: Holland: Patients with a contractile response to FES received active or sham expiratory muscle FES (30 min, twice daily, 5 days/week until weaned). Main endpoints were feasibility (e.g., patient recruitment, treatment compliance, stimulation intensity) and safety. Pooled: Data on respiratory muscle thickness and ventilation duration from the Holland and Australian studies were combined (N = 40) in order to estimate potential effect size. Plasma cytokines (day 0, 3) were analyzed to study the effects of FES on systemic inflammation. RESULTS: Holland: A total of 272 sessions were performed (active/sham: 169/103) in 20 patients (N = active/sham: 10/10) with a total treatment compliance rate of 91.1%. No FES-related serious adverse events were reported. Pooled: On day 3, there was a between-group difference (N = active/sham: 7/12) in total abdominal expiratory muscle thickness favoring the active group [treatment difference (95% confidence interval); 2.25 (0.34, 4.16) mm, P = 0.02] but not on day 5. Plasma cytokine levels indicated that early FES did not induce systemic inflammation. Using a survival analysis approach for the total study population, median ventilation duration and ICU length of stay were 10 versus 52 (P = 0.07), and 12 versus 54 (P = 0.03) days for the active versus sham group. Median ventilation duration of patients that were successfully extubated was 8.5 [5.6-12.2] versus 10.5 [5.3-25.6] days (P = 0.60) for the active (N = 16) versus sham (N = 10) group, and median ICU length of stay was 10.5 [8.0-14.5] versus 14.0 [9.0-19.5] days (P = 0.36) for those active (N = 16) versus sham (N = 8) patients that were extubated and discharged alive from the ICU. During ICU stay, 3/20 patients died in the active group versus 8/20 in the sham group (P = 0.16). CONCLUSION: Expiratory muscle FES is feasible in selected ICU patients and might be a promising technique within a respiratory muscle-protective ventilation strategy. The next step is to study the effects on weaning and ventilator liberation outcome. TRIAL REGISTRATION: ClinicalTrials.gov, ID NCT03453944. Registered 05 March 2018-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03453944 .
Assuntos
Estimulação Elétrica/métodos , Músculos Respiratórios/inervação , Idoso , Idoso de 80 Anos ou mais , Estudos de Coortes , Estimulação Elétrica/instrumentação , Estudos de Viabilidade , Feminino , Mortalidade Hospitalar/tendências , Humanos , Masculino , Medicare/estatística & dados numéricos , Medicare/tendências , Modelos de Riscos Proporcionais , Respiração Artificial/instrumentação , Respiração Artificial/métodos , Músculos Respiratórios/fisiopatologia , Estudos Retrospectivos , Estados UnidosAssuntos
Hipóxia , Neurônios Motores , Hipóxia/fisiopatologia , Neurônios Motores/fisiologia , Humanos , AnimaisRESUMO
What determines which motor units are active in a motor task? In the respiratory muscles, motor units are recruited according to their mechanical advantages. We describe a principle of motor unit recruitment by neuromechanical matching due to mechanisms in the spinal cord that sculpt descending drive to motoneurons. This principle may be applicable to movements in nonrespiratory muscles.
Assuntos
Neurônios Motores/fisiologia , Movimento/fisiologia , Recrutamento Neurofisiológico , Músculos Respiratórios/fisiologia , Medula Espinal/fisiologia , Humanos , Músculo Esquelético/fisiologiaRESUMO
BACKGROUND: For every day a person is dependent on mechanical ventilation, respiratory and cardiac complications increase, quality of life decreases and costs increase by > $USD 1500. Interventions that improve respiratory muscle function during mechanical ventilation can reduce ventilation duration. The aim of this pilot study was to assess the feasibility of employing an abdominal functional electrical stimulation (abdominal FES) training program with critically ill mechanically ventilated patients. We also investigated the effect of abdominal FES on respiratory muscle atrophy, mechanical ventilation duration and intensive care unit (ICU) length of stay. METHODS: Twenty critically ill mechanically ventilated participants were recruited over a 6-month period from one metropolitan teaching hospital. They were randomly assigned to receive active or sham (control) abdominal FES for 30 min, twice per day, 5 days per week, until ICU discharge. Feasibility was assessed through participant compliance to stimulation sessions. Abdominal and diaphragm muscle thickness were measured using ultrasound 3 times in the first week, and weekly thereafter by a blinded assessor. Respiratory function was recorded when the participant could first breathe independently and at ICU discharge, with ventilation duration and ICU length of stay also recorded at ICU discharge by a blinded assessor. RESULTS: Fourteen of 20 participants survived to ICU discharge (8, intervention; 6, control). One control was transferred before extubation, while one withdrew consent and one was withdrawn for staff safety after extubation. Median compliance to stimulation sessions was 92.1% (IQR 5.77%) in the intervention group, and 97.2% (IQR 7.40%) in the control group (p = 0.384). While this pilot study is not adequately powered to make an accurate statistical conclusion, there appeared to be no between-group thickness changes of the rectus abdominis (p = 0.099 at day 3), diaphragm (p = 0.652 at day 3) or combined lateral abdominal muscles (p = 0.074 at day 3). However, ICU length of stay (p = 0.011) and ventilation duration (p = 0.039) appeared to be shorter in the intervention compared to the control group. CONCLUSIONS: Our compliance rates demonstrate the feasibility of using abdominal FES with critically ill mechanically ventilated patients. While abdominal FES did not lead to differences in abdominal muscle or diaphragm thickness, it may be an effective method to reduce ventilation duration and ICU length of stay in this patient group. A fully powered study into this effect is warranted. TRIAL REGISTRATION: The Australian New Zealand Clinical Trials Registry, ACTRN12617001180303. Registered 9 August 2017.
Assuntos
Estimulação Elétrica/métodos , Desmame do Respirador/instrumentação , APACHE , Adulto , Idoso , Estado Terminal/epidemiologia , Estado Terminal/terapia , Método Duplo-Cego , Estimulação Elétrica/instrumentação , Feminino , Humanos , Unidades de Terapia Intensiva/organização & administração , Unidades de Terapia Intensiva/estatística & dados numéricos , Tempo de Internação/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Projetos Piloto , Reto do Abdome/irrigação sanguínea , Reto do Abdome/fisiopatologia , Desmame do Respirador/métodos , Desmame do Respirador/normasRESUMO
STUDY DESIGN: Randomised, controlled, crossover study. OBJECTIVES: Paired corticospinal-motoneuronal stimulation (PCMS) involves repeatedly pairing stimuli to corticospinal neurones and motoneurones to induce changes in corticospinal transmission. Here, we examined whether PCMS could enhance maximal voluntary elbow flexion in people with cervical spinal cord injury. SETTING: Neuroscience Research Australia, Sydney, Australia. METHODS: PCMS comprised 100 pairs of transcranial magnetic and electrical peripheral nerve stimulation (0.1 Hz), timed so corticospinal potentials arrived at corticospinal-motoneuronal synapses 1.5 ms before antidromic motoneuronal potentials. On two separate days, sets of five maximal elbow flexions were performed by 11 individuals with weak elbow flexors post C4 or C5 spinal cord injury before and after PCMS or control (100 peripheral nerve stimuli) conditioning. During contractions, supramaximal biceps brachii stimulation elicited superimposed twitches, which were expressed as a proportion of resting twitches to give maximal voluntary activation. Maximal torque and electromyographic activity were also assessed. RESULTS: Baseline median (range) maximal torque was 11 Nm (6-41 Nm) and voluntary activation was 92% (62-99%). Linear mixed modelling revealed no significant differences between PCMS and control protocols after conditioning (maximal torque: p = 0.87, superimposed twitch: p = 0.87, resting twitch: p = 0.44, voluntary activation: p = 0.36, biceps EMG: p = 0.25, brachioradialis EMG: 0.67). CONCLUSIONS: Possible explanations for the lack of effect include a potential ceiling effect for voluntary activation, or that PCMS may be less effective for elbow flexors than distal muscles. Despite results, previous studies suggest that PCMS is worthy of further investigation.
Assuntos
Articulação do Cotovelo/fisiologia , Potencial Evocado Motor/fisiologia , Córtex Motor/fisiologia , Tratos Piramidais/fisiologia , Traumatismos da Medula Espinal/terapia , Estimulação Magnética Transcraniana/métodos , Adulto , Estudos Cross-Over , Articulação do Cotovelo/inervação , Estimulação Elétrica/métodos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Neurônios Motores/fisiologia , Músculo Esquelético/fisiologia , Traumatismos da Medula Espinal/diagnóstico , Traumatismos da Medula Espinal/fisiopatologia , Adulto JovemRESUMO
KEY POINTS: A cortical contribution to breathing, as indicated by a Bereitschaftspotential (BP) in averaged electroencephalographic signals, occurs in healthy individuals when external inspiratory loads are applied. Chronic obstructive pulmonary disease (COPD) is a condition where changes in the lung, chest wall and respiratory muscles produce an internal inspiratory load. These changes also occur in normal ageing, although to a lesser extent. In the present study, we determined whether BPs are present during quiet breathing and breathing with an external inspiratory load in COPD compared to age-matched and young healthy controls. We demonstrated that increased age, rather than COPD, is associated with a cortical contribution to quiet breathing. A cortical contribution to inspiratory loading is associated with more severe dyspnoea (i.e. the sensation of breathlessness). We propose that cortical mechanisms may be engaged to defend ventilation in ageing with dyspnoea as a consequence. ABSTRACT: A cortical contribution to breathing is determined by the presence of a Bereitschaftspotential, a low amplitude negativity in the averaged electroencephalographic (EEG) signal, which begins â¼1 s before inspiration. It occurs in healthy individuals when external inspiratory loads to breathing are applied. In chronic obstructive pulmonary disease (COPD), changes in the lung, chest wall and respiratory muscles produce an internal inspiratory load. We hypothesized that there would be a cortical contribution to quiet breathing in COPD and that a cortical contribution to breathing with an inspiratory load would be linked to dyspnoea, a major symptom of COPD. EEG activity was analysed in 14 participants with COPD (aged 57-84 years), 16 healthy age-matched (57-87 years) and 15 young (18-26 years) controls during quiet breathing and inspiratory loading. The presence of Bereitschaftspotentials, from ensemble averages of EEG epochs at Cz and FCz, were assessed by blinded assessors. Dyspnoea was rated using the Borg scale. The incidence of a cortical contribution to quiet breathing was significantly greater in participants with COPD (6/14) compared to the young (0/15) (P = 0.004) but not the age-matched controls (6/16) (P = 0.765). A cortical contribution to inspiratory loading was associated with higher Borg ratings (P = 0.007), with no effect of group (P = 0.242). The data show that increased age, rather than COPD, is associated with a cortical contribution to quiet breathing. A cortical contribution to inspiratory loading is associated with more severe dyspnoea. We propose that cortical mechanisms may be engaged to defend ventilation with dyspnoea as a consequence.
Assuntos
Potenciais Evocados , Doença Pulmonar Obstrutiva Crônica/fisiopatologia , Respiração , Músculos Respiratórios/fisiologia , Idoso , Idoso de 80 Anos ou mais , Envelhecimento , Dispneia , Eletromiografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Músculos Respiratórios/inervação , Adulto JovemRESUMO
KEY POINTS: Protective reflexes in the throat area (upper airway) are crucial for breathing. Impairment of these reflexes can cause breathing problems during sleep such as obstructive sleep apnoea (OSA). OSA is very common in people with spinal cord injury for unknown reasons. This study shows major changes in protective reflexes that serve to keep the upper airway open in response to suction pressures in people with tetraplegia and OSA. These results help us understand why OSA is so common in people with tetraplegia and provide new insight into how protective upper airway reflexes work more broadly. ABSTRACT: More than 60% of people with tetraplegia have obstructive sleep apnoea (OSA). However, the specific causes are unknown. Genioglossus, the largest upper-airway dilator muscle, is important in maintaining upper-airway patency. Impaired genioglossus muscle function following spinal cord injury may contribute to OSA. This study aimed to determine if genioglossus reflex responses to negative upper-airway pressure are altered in people with OSA and tetraplegia compared to non-neurologically impaired able-bodied individuals with OSA. Genioglossus reflex responses measured via intramuscular electrodes to â¼60 brief (250 ms) pulses of negative upper-airway pressure (â¼-15 cmH2 O at the mask) were compared between 13 participants (2 females) with tetraplegia plus OSA and 9 able-bodied controls (2 females) matched for age and OSA severity. The initial short-latency excitatory reflex response was absent in 6/13 people with tetraplegia and 1/9 controls. Genioglossus reflex inhibition in the absence of excitation was observed in three people with tetraplegia and none of the controls. When the excitatory response was present, it was significantly delayed in the tetraplegia group compared to able-bodied controls: excitation onset latency (mean ± SD) was 32 ± 16 vs. 18 ± 9 ms, P = 0.045; peak excitation latency was 48 ± 17 vs. 33 ± 8 ms, P = 0.038. However, when present, amplitude of the excitation response was not different between groups, 195 ± 26 vs. 219 ± 98% at baseline, P = 0.55. There are major differences in genioglossus reflex morphology and timing in response to rapid changes in airway pressure in people with tetraplegia and OSA. Altered genioglossus function may contribute to the increased risk of OSA in people with tetraplegia. The precise mechanisms mediating these differences are unknown.
Assuntos
Músculos Faríngeos/fisiologia , Quadriplegia/fisiopatologia , Reflexo , Apneia Obstrutiva do Sono/fisiopatologia , Respiradores de Pressão Negativa , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Plasticity can be induced at human corticospinal-motoneuronal synapses by delivery of repeated, paired stimuli to corticospinal axons and motoneurons in a technique called paired corticospinal-motoneuronal stimulation (PCMS). To date, the mechanisms of the induced plasticity are unknown. To determine whether PCMS-induced plasticity is dependent on N-methyl-d-aspartate receptors (NMDARs), the effect of the noncompetitive NMDAR antagonist dextromethorphan on PCMS-induced facilitation was assessed in a 2-day, double-blind, placebo-controlled experiment. PCMS consisted of 100 pairs of stimuli, delivered at an interstimulus interval that produces facilitation at corticospinal-motoneuronal synapses that excite biceps brachii motoneurons. Transcranial magnetic stimulation elicited corticospinal volleys, which were timed to arrive at corticospinal-motoneuronal synapses just before antidromic potentials elicited in motoneurons with electrical brachial plexus stimulation. To measure changes in the corticospinal pathway at a spinal level, biceps responses to cervicomedullary stimulation (cervicomedullary motor evoked potentials, CMEPs) were measured before and for 30 min after PCMS. Individuals who displayed a ≥10% increase in CMEP size after PCMS on screening were eligible to take part in the 2-day experiment. After PCMS, there was a significant difference in CMEP area between placebo and dextromethorphan days ( P = 0.014). On the placebo day PCMS increased average CMEP areas to 127 ± 46% of baseline, whereas on the dextromethorphan day CMEP area was decreased to 86 ± 33% of baseline (mean ± SD; placebo: n = 11, dextromethorphan: n = 10). Therefore, dextromethorphan suppressed the facilitation of CMEPs after PCMS. This indicates that plasticity induced at synapses in the human spinal cord by PCMS may be dependent on NMDARs. NEW & NOTEWORTHY Paired corticospinal-motoneuronal stimulation can strengthen the synaptic connections between corticospinal axons and motoneurons at a spinal level in humans. The mechanism of the induced plasticity is unknown. In our 2-day, double-blind, placebo-controlled study we show that the N-methyl-d-aspartate receptor (NMDAR) antagonist dextromethorphan suppressed plasticity induced by paired corticospinal-motoneuronal stimulation, suggesting that an NMDAR-dependent mechanism is involved.
Assuntos
Neurônios Motores/metabolismo , Plasticidade Neuronal , Tratos Piramidais/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Adolescente , Adulto , Potencial Evocado Motor , Feminino , Humanos , Masculino , Neurônios Motores/fisiologia , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Tratos Piramidais/fisiologia , Sinapses/metabolismo , Sinapses/fisiologiaRESUMO
KEY POINTS: During breathing, there is differential activity in the human parasternal intercostal muscles and the activity is tightly coupled to the known mechanical advantages for inspiration of the same regions of muscles. It is not known whether differential activity is preserved for the non-respiratory task of ipsilateral trunk rotation. In the present study, we compared single motor units during resting breathing and axial rotation of the trunk during apnoea. We not only confirmed non-uniform recruitment of motor units across parasternal intercostal muscles in breathing, but also demonstrated that the same motor units show an altered pattern of recruitment in the non-respiratory task of trunk rotation. The output of parasternal intercostal motoneurones is modulated differently across spinal levels depending on the task and these results help us understand the mechanisms that may govern task-dependent differences in motoneurone output. ABSTRACT: During inspiration, there is differential activity in the human parasternal intercostal muscles across interspaces. We investigated whether the earlier recruitment of motor units in the rostral interspaces compared to more caudal spaces during inspiration is preserved for the non-respiratory task of ipsilateral trunk rotation. Single motor unit activity (SMU) was recorded from the first, second and fourth parasternal interspaces on the right side in five participants in two tasks: resting breathing and 'isometric' axial rotation of the trunk during apnoea. Recruitment of the same SMUs was compared between tasks (n = 123). During resting breathing, differential activity was indicated by earlier recruitment of SMUs in the first and second interspaces compared to the fourth space in inspiration (P < 0.01). By contrast, during trunk rotation, the same motor units showed an altered pattern of recruitment because SMUs in the first interspace were recruited later and at a higher rotation torque than those in the second and fourth interspaces (P < 0.05). Tested for a subset of SMUs, the reliability of the breathing and rotation tasks, as well as the SMU recruitment measures, was good-excellent [intraclass correlation (2,1): 0.69-0.91]. Thus, the output of parasternal intercostal motoneurones is modulated differently across spinal levels depending on the task. Given that the differential inspiratory output of parasternal intercostal muscles is linked to their relative mechanical effectiveness for inspiration and also that this output is altered in trunk rotation, we speculate that a mechanism matching neural drive to muscle mechanics underlies the task-dependent differences in output of axial motoneurone pools.
Assuntos
Músculos Intercostais/fisiologia , Contração Muscular , Trabalho Respiratório , Adulto , Humanos , Músculos Intercostais/inervação , Nervos Intercostais/fisiologia , Masculino , Pessoa de Meia-Idade , Recrutamento NeurofisiológicoRESUMO
KEY POINTS: In the adult turtle spinal cord, action potential generation in motoneurones is inhibited by spillover of serotonin to extrasynaptic serotonin 1A (5-HT1A ) receptors at the axon initial segment. We explored whether ingestion of the 5-HT1A receptor partial agonist, buspirone, decreases motoneurone excitability in humans. Following ingestion of buspirone, two tests of motoneurone excitability showed decreases. F-wave areas and persistence in an intrinsic muscle of the hand were reduced, as was the area of cervicomedullary motor evoked potentials in biceps brachii. Our findings suggest that activation of 5-HT1A receptors depresses human motoneurone excitability. Such a depression could contribute to decreased motoneurone output during fatiguing exercise if there is high serotonergic drive to the motoneurones. ABSTRACT: Intense serotonergic drive in the turtle spinal cord results in serotonin spillover to the axon initial segment of the motoneurones where it activates serotonin 1A (5-HT1A ) receptors and inhibits generation of action potentials. We examined whether activation of 5-HT1A receptors decreases motoneurone excitability in humans by determining the effects of a 5-HT1A receptor partial agonist, buspirone, on F waves and cervicomedullary motor evoked potentials (CMEPs). In a placebo-controlled double-blind study, 10 participants were tested on two occasions where either placebo or 20 mg of buspirone was administered orally. The ulnar nerve was stimulated supramaximally to evoke F waves in abductor digiti minimi (ADM). CMEPs and the maximal M wave were elicited in biceps brachii by cervicomedullary stimulation and brachial plexus stimulation, respectively. Following buspirone intake, F-wave area and persistence, as well as CMEP area, were significantly decreased. The mean post-pill difference in normalized F-wave areas and persistence between buspirone and placebo days was -27% (-42, -12; 95% confidence interval) and -9% (-16, -2), respectively. The mean post-pill difference in normalized CMEP area between buspirone and placebo days showed greater variation and was -31% (-60, -2). In conclusion, buspirone reduces motoneurone excitability in humans probably via activation of 5-HT1A receptors at the axon initial segment. This has implications for motor output during high drive to the motoneurones when serotonin may spill over to these inhibitory receptors and consequently inhibit motoneurone output. Such a mechanism could potentially contribute to fatigue with exercise.