Subject(s)
Hypoxia , Motor Neurons , Hypoxia/physiopathology , Motor Neurons/physiology , Humans , AnimalsABSTRACT
Acute intermittent hypoxia (AIH) can induce sustained facilitation of motor output in people with spinal cord injury (SCI). Most studies of corticospinal tract excitability in humans have used 9% fraction inspired oxygen ([Formula: see text]) AIH (AIH-9%), with inconsistent outcomes. We investigated the effect of single sessions of 9% [Formula: see text] and 12% [Formula: see text] AIH (AIH-12%) on corticospinal excitability of a hand and leg muscle in able-bodied adults. Ten naïve participants completed three sessions on separate days comprising 15 epochs of 1 min of AIH-9%, AIH-12%, or sham (SHAM-21%) followed by 1 min of room air (21% [Formula: see text]) in a randomized crossover design. Motor-evoked potentials (MEPs; n = 30, â¼1 mV) elicited at rest by transcranial magnetic stimulation and maximal M-waves (Mmax) evoked by peripheral nerve stimulation were measured from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles at baseline and at â¼0, 20, 40, and 60 min post intervention. AIH-9% induced the greatest reduction in peripheral oxygen saturation (to 85% vs. 93% and 100% in AIH-12% and SHAM-21%, respectively; P < 0.001) and the greatest increase in ventilation [by 22% vs. 12% and -3% in AIH-9%, AIH-12%, and SHAM-21%, respectively (P < 0.001)]. There was no difference in MEP amplitudes (%Mmax) after any of the three conditions (AIH-9%, AIH-12%, SHAM-21%) for both the FDI (P = 0.399) and TA (P = 0.582). Despite greater cardiorespiratory changes during AIH-9%, there was no evidence of corticospinal facilitation (tested with MEPs) in this study. Further studies could explore variability in response to AIH between individuals and other methods to measure motor facilitation in people with and without spinal cord injuries.NEW & NOTEWORTHY This is the first study that tests whether acute intermittent hypoxia (AIH) induces motor output facilitation in humans after two different doses of AIH (9% and 12% [Formula: see text]) and the reproducibility of participant responses after a repeat AIH intervention at 9% AIH. There was no motor output facilitation in response to either dose of AIH. The results question the effectiveness of a single 30-min session of AIH in inducing motor output facilitation, tested in this way.
Subject(s)
Evoked Potentials, Motor , Hypoxia , Lower Extremity , Muscle, Skeletal , Transcranial Magnetic Stimulation , Humans , Male , Evoked Potentials, Motor/physiology , Hypoxia/physiopathology , Adult , Female , Muscle, Skeletal/physiopathology , Transcranial Magnetic Stimulation/methods , Lower Extremity/physiopathology , Young Adult , Pyramidal Tracts/physiopathology , Cross-Over Studies , Upper Extremity/physiopathology , Spinal Cord Injuries/physiopathologyABSTRACT
Intramuscular recordings of single motor unit activity from parasternal intercostal muscles show a rostrocaudal gradient in timing and amplitude of inspiratory activity. This study determined the feasibility of surface electromyographic activity (EMG) to measure graded parasternal intercostal activity in young females and males during quiet breathing and breathing with inspiratory resistive loads. Surface EMGs were recorded from the 1st-to-5th parasternal intercostal muscles during 10 min of breathing. EMGs were processed to remove 50 Hz and electrocardiogram artifacts and integrated. Amplitude and onset time of inspiratory activity were measured from waveform averages triggered at the onset of inspiratory flow. Onset times were measured independently by two assessors, blinded to interspace and EMG scale, with excellent agreement (ICC3,k = 0.86). The onset of inspiratory activity in the 1st-to-3rd interspaces was at or within â¼400 ms of the start of inspiratory airflow, but activity in the caudal (4th and 5th) spaces was delayed by up to â¼1,000 ms (P < 0.001). There was no main effect of sex on onset time (P = 0.07), but an interaction with interspace (P < 0.001) revealed that inspiratory activity in the caudal interspaces was delayed by 15% of inspiratory time in female participants compared with 30% of inspiratory time in male participants. Inspiratory loads did not affect EMG onset time (P = 0.31). Thus, surface EMG is feasible to assess the onset time of inspiratory activity as a marker of inspiratory neural drive and pattern of activation across spaces, in both females and males.NEW & NOTEWORTHY We demonstrated that surface EMG is a valid method to measure graded inspiratory EMG in the parasternal intercostal muscles in healthy young male and female participants during quiet breathing and loaded breathing. Across the 1st-to-5th interspaces, there was more homogenous activation in women and more graded activity in men across parasternal intercostal muscles during breathing. By recording surface EMG from both male and female participants, we have revealed sex differences in inspiratory activity across intercostal muscles.
Subject(s)
Intercostal Muscles , Respiration , Humans , Male , Female , Electromyography/methods , Intercostal Muscles/physiologyABSTRACT
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.
Subject(s)
Sleep Apnea, Obstructive , Wakefulness , Humans , Wakefulness/physiology , Pharyngeal Muscles , Movement/physiology , Tongue , ElectromyographyABSTRACT
STUDY DESIGN/SETTING: Secondary analysis. OBJECTIVES: To compare the change in maximal inspiratory pressure (PImax) over the first 4 weeks of two different inspiratory muscle training (IMT) protocols and explore if either method is more effective for people with spinal cord injury. METHODS: Data originated from two published studies. Participants completed flow-resistive IMT (F-IMT) at 80% daily PImax, 7 days/week (supervised weekly), or threshold IMT (T-IMT) at 30-80% weekly PImax, twice-daily, 5 days/week (supervised every session). Seven participants from each trial were matched by training adherence, level of spinal cord injury, impairment grade (A-C), and height. Differences between F-IMT and T-IMT groups in training intensity, breaths taken, inspiratory work, and the change in the PImax from baseline at the end of week four were analysed. RESULTS: Over 4 weeks, there was no difference in the change in PImax between groups (Absolute change in PImax (cmH2O): p = 0.456, Percent change in PImax relative to baseline: p = 0.128). F-IMT participants trained at a higher intensity (median: 77 vs 22 cmH2O, p = 0.001 and 80% baseline vs 61% baseline, p = 0.038) but took fewer breaths (840 vs 1404 breaths, p = 0.017) than T-IMT participants. Inspiratory work was similar between groups (64,789 vs 65,910 (% PImax × number of breaths), p = 0.535). CONCLUSIONS: Our findings support both methods of IMT as the change in PImax and inspiratory work were similar between groups. However, daily high-intensity F-IMT with intermittent supervision, required fewer breaths and less participant and therapist time. Future studies should examine optimal dosage and supervision required to achieve increased PImax.
Subject(s)
Respiratory Muscles , Spinal Cord Injuries , Humans , Physical Therapy Modalities , Respiratory Muscles/physiology , Respiratory Therapy/methodsABSTRACT
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.
Subject(s)
Spinal Cord Injuries , Adult , Humans , Spinal Cord Injuries/complications , Breathing Exercises , Academies and Institutes , Quadriplegia , SensationABSTRACT
Transcutaneous spinal cord stimulation (TSS) is purported to improve motor function in people after spinal cord injury (SCI). However, several methodology aspects are yet to be explored. We investigated whether stimulation configuration affected the intensity needed to elicit spinally evoked motor responses (sEMR) in four lower limb muscles bilaterally. Also, since stimulation intensity for therapeutic TSS (i.e., trains of stimulation, typically delivered at 15-50 Hz) is sometimes based on the single-pulse threshold intensity, we compared these two stimulation types. In non-SCI participants (n = 9) and participants with a SCI (n = 9), three different electrode configurations (cathode-anode); L1-midline (below the umbilicus), T11-midline and L1-ASIS (anterior superior iliac spine; non-SCI only) were compared for the sEMR threshold intensity using single pulses or trains of stimulation which were recorded in the vastus medialis, medial hamstring, tibialis anterior, medial gastrocnemius muscles. In non-SCI participants, the L1-midline configuration showed lower sEMR thresholds compared to T11-midline (p = 0.002) and L1-ASIS (p < 0.001). There was no difference between T11-midline and L1-midline for participants with SCI (p = 0.245). Spinally evoked motor response thresholds were ~13% lower during trains of stimulation compared to single pulses in non-SCI participants (p < 0.001), but not in participants with SCI (p = 0.101). With trains of stimulation, threshold intensities were slightly lower and the incidence of sEMR was considerably lower. Overall, stimulation threshold intensities were generally lower with the L1-midline electrode configuration and is therefore preferred. While single-pulse threshold intensities may overestimate threshold intensities for therapeutic TSS, tolerance to trains of stimulation will be the limiting factor in most cases.
Subject(s)
Spinal Cord Injuries , Spinal Cord Stimulation , Humans , Spinal Cord Injuries/therapy , Muscle, Skeletal/physiology , Quadriceps Muscle , Spinal Cord Stimulation/methods , ElectrodesABSTRACT
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.
Subject(s)
Cortical Excitability , Motor Cortex , Parkinson Disease , Humans , Aged , Motor Cortex/diagnostic imaging , Parkinson Disease/diagnostic imagingABSTRACT
Background: People with a spinal cord injury (SCI) have a high rate of bowel-related morbidity, even compared with people with other neurological disorders. These complications lower quality of life and place a financial burden on the health system. A noninvasive intervention that improves the bowel function of people with an SCI should reduce morbidity, improve quality of life, and lead to cost savings for health care providers. Objectives: To investigate the effectiveness of noninvasive abdominal functional electrical stimulation (FES) for improving bowel function in people with a chronic SCI. Methods: A prospective, double-blinded, 1:1 randomized, placebo-controlled intervention trial will be conducted with 80 adults with chronic SCI (>12 months since injury) above T8 single neurological level. The intervention will be a 45-minute abdominal FES (or placebo) session, 3 days per week, for 6 weeks. Main Study Parameters/Endpoints: Primary endpoint is whole gut transit time before and after 6 weeks of abdominal FES. Secondary endpoints measured before and after 6 weeks of abdominal FES are (1) colonic transit time; (2) quality of life (EQ-5D-5L); (3) participant-reported bowel function (International SCI Bowel Function Basic Data Set Questionnaire and visual analogue scale); (4) respiratory function (forced vital capacity, forced expiratory volume in 1 second, peak expiratory flow, maximal inspiratory pressure, and maximal expiratory pressure); (5) bladder symptoms (Neurogenic Bladder Symptom Score); (6) daily bowel management diary; and (7) unplanned hospital visits. Conclusion: Safety data will be collected, and a cost utility analysis using quality of life scores will be performed. Trial registration: Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12621000386831.
Subject(s)
Spinal Cord Injuries , Adult , Humans , Quality of Life , Prospective Studies , Australia , Electric Stimulation , Randomized Controlled Trials as TopicABSTRACT
Altered neural processing and increased respiratory sensations have been reported in chronic obstructive pulmonary disease (COPD) as larger respiratory-related evoked potentials (RREPs), but the effect of healthy-aging has not been considered adequately. We tested RREPs evoked by brief airway occlusions in 10 participants with moderate-to-severe COPD, 11 age-matched controls (AMC) and 14 young controls (YC), with similar airway occlusion pressure stimuli across groups. Mean age was 76 years for COPD and AMC groups, and 30 years for the YC group. Occlusion intensity and unpleasantness was rated using the modified Borg scale, and anxiety rated using the Hospital Anxiety and Depression Scale. There was no difference in RREP peak amplitudes across groups, except for the N1 peak, which was significantly greater in the YC group than the COPD and AMC groups (p = 0.011). The latencies of P1, P2 and P3 occurred later in COPD versus YC (p < 0.05). P3 latency occurred later in AMC than YC (p = 0.024). COPD and AMC groups had similar Borg ratings for occlusion intensity (3.0 (0.5, 3.5) [Median (IQR)] and 3.0 (3.0, 3.0), respectively; p = 0.476) and occlusion unpleasantness (1.3 (0.1, 3.4) and 1.0 (0.75, 2.0), respectively; p = 0.702). The COPD group had a higher anxiety score than AMC group (p = 0.013). A higher N1 amplitude suggests the YC group had higher cognitive processing of respiratory inputs than the COPD and AMC groups. Both COPD and AMC groups showed delayed neural responses to the airway occlusion, which may indicate impaired processing of respiratory sensory inputs in COPD and healthy aging.
Subject(s)
Airway Obstruction , Healthy Aging , Pulmonary Disease, Chronic Obstructive , Humans , Aged , Respiratory System , Respiratory Rate , Evoked PotentialsABSTRACT
In human applied physiology studies, the amplitude of recorded muscle electromyographic activity (EMG) is often normalized to maximal EMG recorded during a maximal voluntary contraction. When maximal contractions cannot be reliably obtained (e.g. in people with muscle paralysis, anterior cruciate ligament injury, or arthritis), EMG is sometimes normalized to the maximal compound muscle action potiential evoked by stimulation, the Mmax. However, it is not known how these two methods of normalization affect the conclusions and comparability of studies. To address this limitation, we investigated the relationship between voluntary muscle activation and EMG normalized either to maximal EMG or to Mmax. Twenty-five able-bodied adults performed voluntary isometric ankle plantarflexion contractions to a range of percentages of maximal voluntary torque. Ankle torque, plantarflexor muscle EMG, and voluntary muscle activation measured by twitch interpolation were recorded. EMG recorded at each contraction intensity was normalized to maximal EMG or to Mmax for each plantarflexor muscle, and the relationship between the two normalization approaches quantified. A slope >1 indicated EMG amplitude normalized to maximal EMG (vertical axis) was greater than EMG normalized to Mmax (horizontal axis). Mean estimates of the slopes were large and had moderate precision: soleus 8.7 (95% CI 6.9 to 11.0), medial gastrocnemius 13.4 (10.5 to 17.0), lateral gastrocnemius 11.4 (9.4 to 14.0). This indicates EMG normalized to Mmax is approximately eleven times smaller than EMG normalized to maximal EMG. Normalization to maximal EMG gave closer approximations to the level of voluntary muscle activation assessed by twitch interpolation.
Subject(s)
Isometric Contraction , Muscle Contraction , Adult , Humans , Electromyography/methods , Muscle Contraction/physiology , Isometric Contraction/physiology , Torque , Muscle, Skeletal/physiologyABSTRACT
In healthy individuals, loading inspiratory muscles by brief inspiratory occlusion produces a short-latency inhibitory reflex (IR) in the electromyographic (EMG) activity of scalene and diaphragm muscles. This IR may play a protective role to prevent aspiration and airway collapse during sleep. In people with motor and sensory complete cervical spinal cord injury (cSCI), who were able to breathe independently, this IR was predominantly absent. Here, we investigated the reflex response to brief airway occlusion in 16 participants with sensory incomplete cSCI [American spinal injury association impairment scale (AIS) score B or C]. Surface EMG was recorded from scalene muscles and the lateral chest wall (overlying diaphragm). The airway occlusion evoked a small change in mouth pressure resembling a physiological occlusion. The short-latency IR was present in 10 (63%) sensory incomplete cSCI participants; significantly higher than the IR incidence observed in complete cSCI participants in our previous study (14%; P = 0.003). When present, mean IR latency across all muscles was 58 ms (range 29-79 ms), and mean rectified EMG amplitude decreased to 37% preocclusion levels. Participants without an IR had untreated severe obstructive sleep apnea (OSA), in contrast to those with an IR, who had either had no, mild, or treated OSA (P = 0.002). Insufficient power did not allow statistical comparison between IR presence or absence and participant clinical characteristics. In conclusion, spared sensory connections or intersegmental connections may be necessary to generate the IR. Future studies to establish whether IR presence is related to respiratory morbidity in the tetraplegic population are required.NEW & NOTEWORTHY Individuals with incomplete cSCI were tested for the presence of a short latency reflex inhibition of inspiratory muscles, by brief airway occlusion. The reflex was 4.5 times more prevalent in this group compared with those with complete cSCI and is similar to the incidence in able-bodied people. Participants without this reflex all had untreated severe OSA, in contrast to those with an IR, who either had no, mild, or treated OSA. This work reveals novel differences in the reflex control of inspiratory muscles across the cSCI population.
Subject(s)
Cervical Cord , Humans , Reflex , MusclesABSTRACT
This study investigated sensations of breathing following tetraplegia. Fifteen people with chronic tetraplegia and fifteen healthy able-bodied controls matched for age, sex, height, and weight participated. Sensations of breathing were quantified by determining the threshold for detecting an added resistance during inspiration. In a separate task, the perceived magnitudes of six suprathreshold resistive loads were determined with a modified Borg scale. The detection threshold of 0.34 cmH2O/L/s [standard deviation (SD) 0.14] in the tetraplegia group was higher than the 0.23 cmH2O/L/s (SD 0.10) threshold for able-bodied controls (P = 0.004). Both participant groups perceived larger loads to be more effortful, with the Borg effort rating increasing linearly with the peak inspiratory pressure generated at each load. The relationship between Borg effort rating and peak inspiratory pressure was steeper in participants with tetraplegia than in able-bodied controls (P = 0.001), but there was no difference when pressure was divided by maximal inspiratory pressure (P = 0.95). Despite a higher detection threshold, the findings suggest that the perceived magnitude of a suprathreshold inspiratory load is not impaired in chronic tetraplegia and that load magnitude perception is related to the maximal, and not absolute, inspiratory muscle force.NEW & NOTEWORTHY Sensations of breathing are thought to be impaired following chronic tetraplegia. The detection threshold for an added resistive load during inspiration was higher in people with tetraplegia than in healthy able-bodied participants. However, for inspiratory loads above the detection threshold, the perceived magnitude of a resistive load as a function of the peak inspiratory pressure was greater in tetraplegia. Load magnitude perception was comparable between participant groups when peak pressure was divided by maximal inspiratory pressure.
Subject(s)
Respiration , Sensation , Humans , Respiratory Function Tests , Quadriplegia , Perception/physiology , Airway ResistanceABSTRACT
Tongue and upper airway dilator muscle movement patterns during quiet breathing vary in people with obstructive sleep apnea (OSA). Many patients have inadequate or counterproductive responses to inspiratory negative airway pressure that likely contributes to their OSA. This may be due, at least in part, to inadequate or nonhomogeneous reflex drive to different regions of the largest upper airway dilator, genioglossus. To investigate potential regional heterogeneity of genioglossus reflex responses in OSA, brief suction pulses were applied via a nasal breathing mask and an electromyogram (EMG) was recorded in four regions (anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal) using intramuscular fine wire electrodes in 15 people with OSA. Genioglossus short-latency reflex excitation amplitude had regional heterogeneity (horizontal vs. oblique regions) when expressed in absolute units but homogeneity when normalized as a percentage of the immediate (100 ms) prestimulus EMG. Regional variability in reflex morphology (excitation and inhibition) was present in one-third of the participants. The minimum cross-sectional area (CSA) of the pharyngeal airway was quantified using MRI and may be related to the amplitude of the short-latency reflex response to negative pressure as we found that people with a smaller CSA tended to have a greater reflex amplitude (e.g., horizontal region r2 = 0.41, P = 0.01). These findings highlight the complexity of genioglossus reflex control, the potential for regional heterogeneity, and the functional importance of upper airway anatomy in mediating genioglossus reflex responses to rapid changes in negative pressure in OSA.NEW & NOTEWORTHY Our findings indicate that 30% of participants had regional heterogeneity in reflex morphology (excitation/inhibition) to brief pulses of negative upper-airway pressure across anterior oblique, anterior horizontal, posterior oblique, and posterior horizontal regions of the genioglossus muscle. Reflex excitation amplitude was proportional to prestimulus drive, with increased activation in oblique compared with horizontal regions of the posterior tongue. People with narrower upper-airway anatomy tended to have increased genioglossus reflex amplitude to negative pressure pulses during wakefulness.
Subject(s)
Sleep Apnea, Obstructive , Electromyography , Humans , Reflex/physiology , Tongue/physiology , Wakefulness/physiologyABSTRACT
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.
Subject(s)
Motor Neurons , Spinal Cord Injuries , Animals , Evoked Potentials, Motor , Humans , Hypoxia , Motor Neurons/physiology , Rats , Transcranial Magnetic StimulationABSTRACT
STUDY OBJECTIVES: To characterize how mandibular advancement enlarges the upper airway via posterior tongue advancement in people with obstructive sleep apnea (OSA) and whether this is associated with mandibular advancement splint (MAS) treatment outcome. METHODS: One-hundred and one untreated people with OSA underwent a 3T magnetic resonance (MRI) scan. Dynamic mid-sagittal posterior tongue and mandible movements during passive jaw advancement were measured with tagged MRI. Upper airway cross-sectional areas were measured with the mandible in a neutral position and advanced to 70% of maximum advancement. Treatment outcome was determined after a minimum of 9 weeks of therapy. RESULTS: Seventy-one participants completed the study: 33 were responders (AHI<5 or AHI≤10 events/hr with >50% AHI reduction), 11 were partial responders (>50% AHI reduction but AHI>10 events/hr), and 27 nonresponders (AHI reduction<50% and AHI≥10 events/hr). Responders had the greatest naso- and oropharyngeal tongue anterior movement (0.40 ± 0.08 and 0.47 ± 0.13 mm, respectively) and oropharyngeal cross-sectional area enlargement (6.41 ± 2.12%) per millimeter of mandibular advancement. A multivariate model that included tongue movement and percentage of airway enlargement per millimeter of mandibular advancement along with baseline AHI correctly classified 69.2% (5-fold cross-validated 62.5%, n = 39) of participants in response categories when the jaw was advanced in the range that would usually be regarded as sufficient for clinical efficacy (> 4 mm). In comparison, a model using only baseline AHI correctly classified 50.0% of patients (5-fold cross-validated 52.5%, n = 40). CONCLUSIONS: Tongue advancement and upper airway enlargement with mandibular advancement in conjunction with baseline AHI improve treatment response categorization to a satisfactory level (69.2%, 5-fold cross-validated 62.5%).
Subject(s)
Mandibular Advancement , Sleep Apnea, Obstructive , Humans , Polysomnography , Sleep Apnea, Obstructive/pathology , Sleep Apnea, Obstructive/surgery , Tongue , Treatment OutcomeABSTRACT
Anatomical and imaging evidence suggests neural control of oblique and horizontal compartments of the genioglossus differs. However, neurophysiological evidence for differential control remains elusive. This study aimed to determine whether there are differences in neural drive to the oblique and horizontal regions of the genioglossus during swallowing and tongue protrusion. Adult participants (n = 63; 48 M) were recruited from a sleep clinic; 41 had obstructive sleep apnea (OSA: 34 M, 8 F). Electromyographic (EMG) was recorded at rest (awake, supine) using four intramuscular fine-wire electrodes inserted percutaneously into the anterior oblique, posterior oblique, anterior horizontal, and posterior horizontal genioglossus. Epiglottic pressure and nasal airflow were also measured. During swallowing, two distinct EMG patterns were observed - a monophasic response (single EMG peak) and a biphasic response (2 bursts of EMG). Peak EMG and timing of the peak relative to epiglottic pressure were significantly different between patterns (linear mixed models, P < 0.001). Monophasic activation was more likely in the horizontal than oblique region during swallowing (OR = 6.83, CI = 3.46-13.53, P < 0.001). In contrast, during tongue protrusion, activation patterns and EMG magnitude were not different between regions. There were no systematic differences in EMG patterns during swallowing or tongue protrusion between OSA and non-OSA groups. These findings provide evidence for functional differences in the motoneuronal output to the oblique and horizontal compartments, enabling differential task-specific drive. Given this, it is important to identify the compartment from which EMG is acquired. We propose that the EMG patterns during swallowing may be used to identify the compartment where a recording electrode is located.NEW & NOTEWORTHY During swallowing, we observed two distinct, stereotyped muscle activation patterns that define the horizontal (monophasic, maximal EMG) and oblique (biphasic, submaximal EMG) neuromuscular compartments of genioglossus. In contrast, volitional tongue protrusions produced uniform activation across compartments. This provides evidence for task-dependent, functionally discrete neuromuscular control of the oblique and horizontal compartments of genioglossus. The magnitude and temporal patterning of genioglossus EMG during swallowing may help guide electrode placement in tongue EMG studies.
Subject(s)
Sleep Apnea, Obstructive , Tongue , Adult , Electromyography , Facial Muscles , Humans , Tongue/physiology , WakefulnessABSTRACT
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.
Subject(s)
Spinal Cord Injuries , Spinal Cord Stimulation , Humans , Physical Therapy Modalities , Quality of Life , Randomized Controlled Trials as Topic , Spinal Cord Injuries/complications , Walking/physiologyABSTRACT
Genioglossus was stimulated intramuscularly to determine the effect of regional activation of the muscle on tongue movement in eight healthy adults. Stimulation at motor threshold was delivered with a needle electrode inserted to different depths in the anterior and posterior regions of genioglossus. The current amplitude that induced muscle contraction was â¼80% higher for anterior than posterior sites. Evoked tongue movements were determined from stimulus-triggered averages (150 pulses) of the outputs from an accelerometer fixed to the posterosuperior surface of the tongue. The median amplitude [95% confidence intervals] for the resultant acceleration was 0.0 m/s2 [0.0, 0.2] for anterior and 0.6 m/s2 [0.1, 2.8] for posterior sites. There was a positive relationship between acceleration amplitude and stimulation depth in the posterior of genioglossus (p < 0.001), but acceleration amplitude did not vary with stimulation depth in the anterior region (p = 0.83). This heterogeneity in acceleration responses between muscle regions may contribute to differences in collapsibility of the upper airway.
Subject(s)
Movement/physiology , Muscle Contraction/physiology , Muscle, Skeletal/physiology , Respiration , Tongue/physiology , Adult , Electric Stimulation , Humans , Ultrasonography , Young AdultABSTRACT
BACKGROUND: Swallowing disorders occur in COPD, but little is known about tongue strength and mastication. This is the first assessment in COPD of tongue strength and a test of mastication and swallowing solids (TOMASS). METHODS: Anterior tongue strength measures were obtained in 18 people with COPD, aged 73±11â years (mean±sd), and 19 healthy age-matched controls, aged 72±6â years. Swallowing dynamics were assessed using an eating assessment tool (EAT-10), timed water swallow test (TWST), and TOMASS. Swallowing measures were compared to an inhibitory reflex (IR) in the inspiratory muscles to airway occlusion (recorded previously in the same participants). RESULTS: Tongue strength was similar between COPD and controls (p=0.715). Self-assessed scores of dysphagia EAT-10 were higher (p=0.024) and swallowing times were prolonged for liquids (p=0.022) and solids (p=0.003) in the COPD group. During TWST, â¼30% of COPD group showed clinical signs of airway invasion (cough and wet voice), but none in the control group. For solids, the COPD group had â¼40% greater number of chews (p=0.004), and twofold-higher number of swallows (p=0.0496). Respiratory rate was 50% higher in COPD group than controls (p <0.001). The presence of an IR was not related to better swallowing outcomes, but signs of airway invasion were associated with a delayed IR. CONCLUSION: Dysphagia in stable COPD is not due to impaired anterior tongue strength, but rather swallowing-breathing discoordination. To address dysphagia, aspiration and acute exacerbations in COPD, therapeutic targets to improve swallowing dynamics could be investigated further.