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ABSTRACT: Patients with suboptimal asthma control often have nocturnal symptoms which wake them, causing sleep fragmentation.
It was hypothesised that symptomatic patients were more accurately identified by measuring respiratory effort using chest wall electromyography than by pulmonary function testing.
Nocturnal electrical activity of the parasternal intercostal muscles (EMG(para)) in the second intercostal space was measured in subjects with controlled (diurnal peak expiratory flow (PEF) variability <20%, n=12) and uncontrolled (diurnal PEF variability >20%, n=12) asthma, and it was compared with that in normal subjects (n=12).
Subjects with controlled and uncontrolled asthma did not differ significantly in age (mean (SD) 42 (17) vs 46 (17) years, p=0.64), body mass index (BMI; 26.6 (2.9) vs 27.5 (3.5) kg/m(2), p=0.48) or gender distribution (males:females, 6:6 vs 7:5, p=0.68); the normal subject group was younger (27 (11) years, p=0.011) and slimmer (BMI 21.1 (2.9) kg/m(2), p<0.001). An elevated respiratory disturbance index (RDI) was associated with poor asthma control (RDI in normals 0.5 (0.9), in controlled asthma 4.0 (1.9), p<0.001, and in poorly controlled asthma 7.4 (4.3) h(-1); p<0.021). Similarly, EMG(para)%max (normals 4.9 (3.2)%max evening, 4.9 (3.5)%max morning) was higher in controlled asthma (7.2 (2.3)%max evening, 8.1 (4.0)%max morning, p=0.049) and higher still in uncontrolled asthma (16.8 (14.2)%max in the evening, 18.4 (11.6)%max in the morning, p<0.008).
Nocturnal respiratory effort is increased in those with asthma and neural respiratory drive is more variable in patients with poorly controlled asthma. Changes in the EMG(para) inversely reflect changes in pulmonary function tests. Measuring the EMG(para) offers a method to monitor asthma breath-by-breath while subjects are asleep, which could be adapted for home use.
Thorax 07/2011; 66(7):609-14. · 6.84 Impact Factor
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ABSTRACT: Neural respiratory drive (NRD) measured from the diaphragm electromyogram (EMGdi) reflects the load/capacity balance of the respiratory muscle pump and is a marker of lung disease severity. EMGdi measurement is invasive, but recording the EMG from the parasternal intercostal muscles using surface electrodes (sEMGpara) could provide a non-invasive method of assessing NRD and disease severity. Objectives To test the hypothesis that NRD measured by sEMGpara correlates with EMGdi, to provide an index of disease severity in cystic fibrosis (CF) and to relate to exercise-induced breathlessness.
15 patients with CF (mean forced expiratory volume in 1 s (FEV(1)) 53.5% predicted) and 15 age-matched healthy controls were studied. sEMGpara and EMGdi were recorded at rest and during exercise. sEMGpara was recorded using surface electrodes and EMGdi using a multipair oesophageal electrode catheter. Signals were normalised using the peak EMG recorded during maximum respiratory manoeuvres and expressed as EMG%max. The respiratory pattern, metabolic data, oesophageal and gastric pressures and Borg scores were also recorded.
Mean (SD) resting sEMGpara%max and EMGdi%max were higher in patients with CF than in controls (13.1 (7)% and 18.5 (7.5)% vs 5.8 (3)% and 7.5 (2)%, respectively, p<0.001). In the patients with CF, resting sEMGpara%max and EMGdi%max were related to the degree of airways obstruction (FEV(1)) (r = -0.91 and r = -0.82, both p<0.001), hyperinflation (r = 0.63 and r = 0.56, both p<0.001) and dynamic lung compliance (r = -0.53 and r = -0.59, both p<0.001). During exercise, sEMGpara%max and EMGdi%max were strongly correlated with breathlessness in the patients with CF before (r = 0.906, p<0.001) and after (r = 0.975, p<0.001) the onset of neuromechanical dissociation.
sEMGpara%max provides a non-invasive marker of neural drive, which reflects disease severity and exercise-induced breathlessness in CF.
Thorax 03/2011; 66(3):240-6. · 6.84 Impact Factor
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ABSTRACT: The therapeutic value of transcutaneous electrical stimulation of the genioglossus muscle in patients with obstructive sleep apnea (OSA) to reduce sleep-disordered breathing is unclear.
Contraction of the genioglossus muscles during transcutaneous stimulation was investigated using ultrasonography in 11 healthy subjects (seven men, mean [SD] age 30 [6] years; BMI, 24.2 [3.5] kg/m(2)). Esophageal and gastric pressures were measured with balloon catheters, and transesophageal diaphragm electromyogram (EMGdi) was recorded during polysomnography in 11 patients with OSA (eight men, aged 51 [16] years; BMI, 42.0 [9.7] kg/m(2)) while transcutaneous electrical stimulation of the genioglossus was applied in non-rapid eye movement sleep (stage N2).
Ultrasonography measurements showed a significant increase in tongue diameter during stimulation (sagittal: 10.0% [2.8%]; coronal: 9.4 % [3.7%]). The measurements were reproducible and repeatable. In patients with OSA, snoring decreased during stimulation (P < .001) and oxygenation improved (P = .001); the respiratory disturbance index (RDI) fell from 28.1 (26.3) to 10.2 (10.2) events per hour during stimulation (P = .002), returning to 26.6 (26.0) events per hour after stimulation was stopped. Transdiaphragmatic pressure swing decreased from 24.1 (13.5) cm H(2)O to 19.7 (7.1) cm H(2)O (P = .022), increasing to 24.2 (10.8) cm H(2)O afterward, and EMGdi fell from 23.8% max (12.6% max) to 15.7% max (6.4% max) (P < .001), rising to 22.6% max (10.4% max) post stimulation.
Continuous transcutaneous electrical stimulation of the genioglossus contracts the genioglossus muscle and reduces ventilatory load and neural respiratory drive in patients with OSA.
Chest 03/2011; 140(4):998-1007. · 5.25 Impact Factor
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ABSTRACT: It is unknown whether efficiency of neural drive as expressed by a ratio of ventilation to the diaphragm electromyogram (EMGdi) in patients with COPD differs from that of healthy subjects during exercise and whether maximal neural drive is exhibited at the point of exercise termination.
We studied 12 male patients with COPD (mean ± SD age, 62.8 ± 10.3 years; FEV(1), 28.1 ± 10.2% predicted) and 12 age- and sex-matched healthy subjects (age, 61.1 ± 7.2 years, FEV(1), 101.5 ± 11.9% predicted). EMGdi was recorded from a multipair esophageal electrode during a constant work (80% of maximal oxygen consumption derived from a previous incremental exercise test) treadmill exercise. Minute ventilation and oxygen consumption were also measured.
Root mean square (RMS) of the EMGdi increased initially and reached a plateau at submaximal drive during constant load exercise in both patients with COPD and healthy subjects. The ratio of ventilation to EMGdi remained stable during exercise in healthy subjects from beginning to the end (100% ± 70% at the beginning and 100% ± 39% at the end, P > .05), whereas the ratio decreased gradually during exercise in patients with COPD (from 85% ± 66% to 42% ± 13%, P < .05).
Efficiency of neural drive decreases in patients with COPD during treadmill exercise. Neural respiratory drive reached a submaximal plateau during constant load exercise in both healthy subjects and patients with COPD, indicating that it may not be the only factor determining exercise capacity.
Chest 12/2010; 138(6):1309-15. · 5.25 Impact Factor
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ABSTRACT: We wished to quantify, in patients with obstructive sleep apnoea (OSA), the activity of the respiratory muscles in relation to upper airway occlusion and patency in sleep. We hypothesized that particular levels of neuromuscular activation are directly associated with upper airway patency. 21 patients with previously diagnosed OSA and 21 healthy control subjects underwent respiratory muscle testing and polysomnography. Neural respiratory drive, as measured by the electromyogram of the diaphragm (EMG(di)) was elevated in the obese OSA patients, awake and supine (13.1(5.6)%max), compared to normal subjects (mean (SD) 8.1(2.3)%max, p<0.01). During unobstructed breathing in sleep (stage N2) normal subjects had an EMG(di) of 7.7(3.9) compared to 22.8(19.2)%max in the OSA group (p<0.001). Prior to airway occlusion, EMG(submandibular) and EMG(di) dropped markedly, and then, following occlusion, increased progressively to their highest levels at airflow onset. Patients with OSA require specific and increased levels of neural respiratory drive to sustain ventilation in sleep.
Respiratory Physiology & Neurobiology 04/2010; 171(1):54-60. · 2.24 Impact Factor
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ABSTRACT: The load imposed on ventilation by increased body mass contributes to the respiratory symptoms caused by obesity. A study was conducted to quantify ventilatory load and respiratory drive in obesity in both the upright and supine postures.
Resting breathing when seated and supine was studied in 30 obese subjects (mean (SD) body mass index (BMI) 42.8 (8.6) kg/m(2)) and 30 normal subjects (mean (SD) BMI 23.6 (3.7) kg/m(2)), recording the electromyogram of the diaphragm (EMGdi, transoesophageal multipair electrode), gastric and oesophageal pressures.
Ventilatory load and neural drive were higher in the obese group as judged by the EMGdi (21.9 (9.0) vs 8.4 (4.0)%max, p<0.001) and oesophageal pressure swings (9.6 (2.9) vs 5.3 (2.2) cm H(2)O, p<0.001). The supine posture caused an increase in oesophageal pressure swings to 16.0 (5.0) cm H(2)O in obese subjects (p<0.001) and to 6.9 (2.0) cm H(2)O in non-obese subjects (p<0.001). The EMGdi increased in the obese group to 24.7 (8.2)%max (p<0.001) but remained the same in non-obese subjects (7.0 (3.4)%max, p = NS). Obese subjects developed intrinsic positive end-expiratory pressure (PEEPi) of 5.3 (3.6) cm H(2)O when supine. Applying continuous positive airway pressure (CPAP) in a subgroup of obese subjects when supine reduced the EMGdi by 40%, inspiratory pressure swings by 25% and largely abolished PEEPi (4.1 (2.7) vs 0.8 (0.4) cm H(2)O, p = 0.009).
Obese patients have substantially increased neural drive related to BMI and develop PEEPi when supine. CPAP abolishes PEEPi and reduces neural respiratory drive in these patients. These findings highlight the adverse respiratory consequences of obesity and have implications for the clinical management of patients, particularly where the supine posture is required.
Thorax 05/2009; 64(8):719-25. · 6.84 Impact Factor
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ABSTRACT: Distinguishing central sleep apnea (CSA) from obstructive sleep apnea (OSA) can be clinically important because different types of apnea may require different treatment approaches. Academically, this distinction is important for investigating the pathological mechanism of different types of sleep apnea. Conventional polysomnography (PSG) with recording of chest and abdominal movement may overestimate the frequency of CSA, leading to inappropriate treatment of sleep-disordered breathing. We hypothesized that diaphragm electromyogram (EMGdi) could be a useful technique to assess neural respiratory drive and respiratory effort and, therefore, to distinguish accurately CSA from OSA.
A multipair esophageal electrode catheter mounted with a balloon was used to record the EMGdi and esophageal pressure (Pes) during overnight PSG. Nineteen patients were included in the study, 12 of whom had previously been identified as having central apnea-hypopnea on a diagnostic PSG undertaken for symptoms that suggest OSA and 7 of whom were known to have heart failure.
A good relationship was found between the swing of Pes and the root mean (+/- SD) square of the EMGdi during OSA events (0.89 +/- 0.10). About one third of CSA events diagnosed by uncalibrated respiratory inductance plethysmography could not be confirmed by Pes or EMGdi. No difference was found in the number of CSAs diagnosed by Pes (1,319) vs EMGdi (1,293; p > 0.01).
We conclude that both Pes and EMGdi measurements are useful in accurately differentiating central from obstructive respiratory events. Conventional PSG with recording of chest and abdominal movement overestimates the frequency of CSA events.
Chest 01/2009; 135(5):1133-41. · 5.25 Impact Factor
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ABSTRACT: Quadriceps weakness and loss of muscle mass predict mortality in chronic obstructive pulmonary disease (COPD). It was hypothesised that a reduced quadriceps cross-sectional area could be detected by ultrasound in patients with COPD compared with healthy subjects, and that measurements relate to strength and fat-free mass (FFM).
Rectus femoris muscle cross-sectional area (RF(CSA)) was measured by ultrasound and whole-body FFM estimated using electrical bioimpedance. Quadriceps strength was measured by maximum voluntary contraction and twitch tension (TwQ) following magnetic femoral nerve stimulation.
26 healthy volunteers of mean (SD) age 63 (9) years and 30 patients with COPD of mean (SD) age 67 (9) years and percentage predicted forced expiratory volume in 1 s (FEV(1)) 48.0 (20.8)% with a similar FFM (46.9 (9.3) kg vs 46.1 (7.3) kg, p = 0.193) participated in the study. Mean RF(CSA) was reduced in patients with COPD by 25% of the mean value in healthy subjects(-115 mm(2); 95% CI -177 to -54, p = 0.001) and was related to MRC dyspnoea scale score, independent of FFM or sex. Maximum voluntary contraction strength was linearly related to RF(CSA) in patients with COPD (r = 0.78, p<0.001). TwQ force per unit of RF(CSA) was similar in both healthy individuals and those with COPD (mean (SD) 17 (4) g/mm(2) vs 18 (3) g/mm(2), p = 0.657). Voluntary contraction strength per unit of RF(CSA) was dependent on central quadriceps activation and peripheral oxygen saturation in COPD.
Ultrasound measurement of RF(CSA) is an effort-independent and radiation-free method of measuring quadriceps muscle cross-sectional area in patients with COPD that relates to strength.
Thorax 01/2009; 64(5):418-23. · 6.84 Impact Factor
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ABSTRACT: Respiratory muscle weakness is an important clinical problem. Tests of varying complexity and invasiveness are available to assess respiratory muscle strength. The relative precision of different tests in the detection of weakness is less clear, as is the value of multiple tests.
The respiratory muscle function tests of clinical referrals who had multiple tests assessed in our laboratories over a 6-year period were analysed. Thresholds for weakness for each test were determined from published and in-house laboratory data. The patients were divided into three groups: those who had all relevant measurements of global inspiratory muscle strength (group A, n = 182), those with full assessment of diaphragm strength (group B, n = 264) and those for whom expiratory muscle strength was fully evaluated (group C, n = 60). The diagnostic outcome of each inspiratory, diaphragm and expiratory muscle test, both singly and in combination, was studied and the impact of using more than one test to detect weakness was calculated.
The clinical referrals were primarily for the evaluation of neuromuscular diseases and dyspnoea of unknown cause. A low maximal inspiratory mouth pressure (Pimax) was recorded in 40.1% of referrals in group A, while a low sniff nasal pressure (Sniff Pnasal) was recorded in 41.8% and a low sniff oesophageal pressure (Sniff Poes) in 37.9%. When assessing inspiratory strength with the combination of all three tests, 29.6% of patients had weakness. Using the two non-invasive tests (Pimax and Sniff Pnasal) in combination, a similar result was obtained (low in 32.4%). Combining Sniff Pdi (low in 68.2%) and Twitch Pdi (low in 67.4%) reduced the diagnoses of patients with diaphragm weakness to 55.3% in group B. 38.3% of the patients in group C had expiratory muscle weakness as measured by maximum expiratory pressure (Pemax) compared with 36.7% when weakness was diagnosed by cough gastric pressure (Pgas), and 28.3% when assessed by Twitch T10. Combining all three expiratory muscle tests reduced the number of patients diagnosed as having expiratory muscle weakness to 16.7%.
The use of single tests such as Pimax, Pemax and other available individual tests of inspiratory, diaphragm and expiratory muscle strength tends to overdiagnose weakness. Combinations of tests increase diagnostic precision and, in the population studied, they reduced the diagnosis of inspiratory, specific diaphragm and expiratory muscle weakness by 19-56%. Measuring both Pimax and Sniff Pnasal resulted in a relative reduction of 19.2% of patients falsely diagnosed with inspiratory muscle weakness. The addition of Twitch Pdi to Sniff Pdi increased diagnostic precision by a smaller amount (18.9%). Having multiple tests of respiratory muscle function available both increases diagnostic precision and makes assessment possible in a range of clinical circumstances.
Thorax 12/2007; 62(11):975-80. · 6.84 Impact Factor
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ABSTRACT: Diaphragm paralysis may be the presenting feature of motor neuron disease (MND), but signs attributable to the disease are usually found at that time or within the following month.We present two patients who developed shortness of breath due to isolated diaphragm paralysis, which was confirmed by transdiaphragmatic pressure measurements and cervical magnetic stimulation of the phrenic nerves.A 65-year-old man developed hypercapnia and progressive muscle wasting 6 years after first symptoms of diaphragm paralysis. Dysarthria, common peroneal nerve palsy on the right and fasciculations of the tongue were found a year later and MND was diagnosed.A 47-year-old-man first presented with hypercapnic respiratory failure (PaCO2 18 kPa) and was intubated and ventilated. He had a 2-year history of dyspnoea and isolated bilateral diaphragm paralysis was confirmed. Other symptoms of MND developed 9 months later.These cases serve as a reminder that MND may be the underlying diagnosis of diaphragm paralysis and may occasionally take years to develop more typical features.
Respiratory Medicine Extra 2(3):98-100.
