Katie Ward

Outpatient pulmonary rehabilitation following acute exacerbations of COPD

Background Exacerbations of chronic obstructive pulmonary disease (COPD) are characterised by increased dyspnoea, reduced quality of life and muscle weakness. Re-exacerbation and hospital admission are common. Pulmonary rehabilitation (PR) administered after hospital admission for an exacerbation can improve quality of life and exercise capacity. Objective To determine whether outpatient post-exacerbation PR (PEPR) could reduce subsequent hospital admission episodes. Methods Patients admitted to hospital for an exacerbation of COPD were randomised to receive either usual follow-up care (UC) or PEPR after discharge. Hospital admission and emergency department attendances for COPD exacerbations were recorded over a 3-month period and analysed on an intention-to-treat basis. Secondary outcomes included exercise capacity and quadriceps strength. Results 60 patients underwent concealed randomisation at the time of their hospital discharge (UC: n=30, mean (SD) age 65 (10) years, forced expiratory volume in 1 s (FEV1) 52 (22)% predicted; PEPR: n=30, 67(10) years, 52 (20)% predicted). The proportion of patients re-admitted to hospital with an exacerbation was 33% in the UC group compared with 7% in those receiving PEPR (OR 0.15, 95% CI 0.03 to 0.72, p=0.02). The proportion of patients that experienced an exacerbation resulting in an unplanned hospital attendance (either admission or review and discharge from the emergency department) was 57% in the UC group and 27% in those receiving PEPR (OR 0.28, 95% CI 0.10 to 0.82, p=0.02). Conclusions Post-exacerbation rehabilitation in COPD can reduce re-exacerbation events that require admission or hospital attendance over a 3-month period. Clinical Trials Registration Number NCT00557115.

Ultrasound measurement of rectus femoris cross-sectional area and the relationship with quadriceps strength in COPD

Background: 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). Methods: Rectus femoris muscle cross-sectional area (RFCSA) 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. Results: 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 (FEV1) 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 RFCSA was reduced in patients with COPD by 25% of the mean value in healthy subjects(−115 mm2; 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 RFCSA in patients with COPD (r = 0.78, p<0.001). TwQ force per unit of RFCSA was similar in both healthy individuals and those with COPD (mean (SD) 17 (4) g/mm2 vs 18 (3) g/mm2, p = 0.657). Voluntary contraction strength per unit of RFCSA was dependent on central quadriceps activation and peripheral oxygen saturation in COPD. Conclusion: Ultrasound measurement of RFCSA is an effort-independent and radiation-free method of measuring quadriceps muscle cross-sectional area in patients with COPD that relates to strength.

Neural respiratory drive in healthy subjects and in COPD

The aim of the present study was to use the diaphragm electromyogram (EMGdi) to compare levels of neural respiratory drive (NRD) in a cohort of healthy subjects and chronic obstructive pulmonary disease (COPD) patients, and to investigate the relationship between NRD and pulmonary function in COPD. EMGdi was recorded at rest and normalised to peak EMGdi recorded during maximum inspiratory manoeuvres (EMGdi % max) in 100 healthy subjects and 30 patients with COPD, using a multipair oesophageal electrode. EMGdi was normalised to the amplitude of the diaphragm compound muscle action potential (CMAPdi,MS) in 64 healthy subjects. The mean±sd EMGdi % max was 9.0±3.4% in healthy subjects and 27.9±9.9% in COPD patients, and correlated with percentage predicted forced expiratory volume in one second, vital capacity and inspiratory capacity in patients. EMGdi % max was higher in healthy subjects aged 51–80 yrs than in those aged 18–50 yrs (11.4±3.4 versus 8.2±2.9%, respectively). Observations in the healthy group were similar when peak EMGdi or CMAPdi,MS were used to normalise EMGdi. Levels of neural respiratory drive were higher in chronic obstructive pulmonary disease patients than healthy subjects, and related to disease severity. Diaphragm compound muscle action potential could be used to normalise diaphragm electromyogram if volitional inspiratory manoeuvres could not be performed, allowing translation of the technique to critically ill and ventilated patients.

Neural respiratory drive, pulmonary mechanics and breathlessness in patients with cystic fibrosis

Background 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. Methods 15 patients with CF (mean forced expiratory volume in 1 s (FEV1) 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. Results 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 (FEV1) (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. Conclusion sEMGpara%max provides a non-invasive marker of neural drive, which reflects disease severity and exercise-induced breathlessness in CF.

Acute ischaemic hemispheric stroke is associated with impairment of reflex in addition to voluntary cough

Cough function is impaired after stroke; this may be important for protection against chest infection. Reflex cough (RC) intensity indices have not been described after stroke. RC, voluntary cough (VC) and respiratory muscle strength were studied in patients within 2 weeks of hemispheric infarct. The null hypotheses were that patients with cortical hemisphere stroke would show the same results as healthy controls on: 1) objective indices of RC and VC intensity; and 2) respiratory muscle strength tests. Peak cough flow rate (PCFR) and gastric pressure (Pga) were measured during maximum VC and RC. Participants also underwent volitional and nonvolitional respiratory muscle testing. Nonvolitional expiratory muscle strength was assessed by measuring Pga increase after magnetic stimulation over the T10 nerve roots (twitch T10 Pga). Stroke severity was scored using the National Institutes of Health Stroke Scale (NIHSS; maximum = 31). 18 patients (mean±sd age 62±15 yrs and NIHSS score 14±8) and 20 controls (56±16 yrs) participated. VC intensity was impaired in patients (PCFR 287±171 versus 497±122 L·min−1) as was VC Pga (98.5±61.6 versus 208.5±61.3 cmH2O; p<0.001 for both). RC PCFR was reduced in patients (204±111 versus 379±110 L·min−1; p<0.001), but RC Pga was not significantly different from that of controls (179.0±78.0 versus 208.0±77.4 cmH2O; p = 0.266). Patients exhibited impaired volitional respiratory muscle tests, but twitch T10 Pga was normal. VC and RC are both impaired in hemispheric stroke patients, despite preserved expiratory muscle strength. Cough coordination is probably cortically modulated and affected by hemispheric stroke.

Transcranial magnetic stimulation study of expiratory muscle weakness in acute ischemic stroke

Background: Expiratory muscle weakness due to cerebral infarction may contribute to reduced airway clearance in stroke patients. Methods: Transcranial magnetic stimulation (TMS) at the vertex and over each hemisphere and magnetic stimulation over the T10-11 spinal roots (Tw T10) and the phrenic nerves bilaterally (BAMPS) were performed in 15 acute ischemic stroke patients (age 68.9 ± 9.8 years) and 16 matched controls. Surface electrodes recorded motor evoked potentials (MEPs) in the rectus abdominis (RA) and external oblique (EO) muscles bilaterally. Respiratory muscle function was assessed by measuring maximum static expiratory pressure (PEmax) and changes in intragastric (Pgas) and transdiaphragmatic (Pdi) pressure after voluntary cough, TMS, TwT10, and BAMPS. Regression models were used to assess determinants of peak voluntary cough flow rates (PCFR). Results: PCFR, cough Pgas, and vertex TMS Pgas were decreased in stroke patients compared with controls (203.6 ± 151.1 vs 350.8 ± 111.7 L/min, p = 0.004; 72.7 ± 64.5 vs 163.4 ± 55.8 cm H2O, p = 0.0003 and 8.7 ± 3.3 vs 16.7 ± 11.5 cm H2O, p = 0.023, respectively). There were no differences in TwT10 Pgas (25.2 ± 7.8 vs 29.4 ± 12.4 cm H2O, p = 0.153) or BAMPS Pdi (21.6 ± 7.2 vs 19.2 ± 3.4 cm H2O, p = 0.163). TMS Pgas was lower (4.1 ± 2.8 vs 6.1 ± 1.9 cm H2O, p = 0.023) following TMS of the injured compared with the uninjured hemisphere in stroke patients. Age and gender adjusted PCFR correlated with Pgas (r = 0.51, p = 0.009) and PEmax (r = 0.46, p = 0.024). Stroke was an independent determinant of PCFR after adjusting for Pgas and PEmax (p = 0.031). Conclusion: Ischemic cortical injury is associated with expiratory muscle weakness and may contribute to cough impairment in stroke patients. BAMPS = bilateral anterolateral magnetic phrenic stimulation; EO = external oblique; MEP = motor evoked potential; NIHSS = NIH Stroke Scale; Pdi = transdiaphragmatic pressure; Pes = esophageal pressure; Pgas = intragastric pressure; PCFR = peak voluntary cough flow rates; PEmax = maximum static expiratory pressure; POE = point of optimal excitability; RA = rectus abdominis; TMS = transcranial magnetic stimulation.

Increased load on the respiratory muscles in obstructive sleep apnea

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.

Quadriceps and ankle dorsiflexor strength in chronic obstructive pulmonary disease

Introduction: Quadriceps strength and size are commonly reduced in chronic obstructive pulmonary disease (COPD). We wished to assess volitional and nonvolitional ankle dorsiflexor strength in COPD. Methods: Quadriceps and ankle dorsiflexor strength were measured by maximum voluntary contraction (MVC) and by twitch responses to supramaximal femoral and fibular nerve stimulation. Cross‐sectional areas of the tibialis anterior (TACSA) and rectus femoris muscles (RFCSA) were measured by ultrasound. Results: Eighteen elderly subjects and 20 COPD patients [mean(SD) %predictedFEV1 50(20)%] participated. No significant difference in fat‐free mass index, ankle dorsiflexor strength, or TACSA were observed in the presence of reduced quadriceps strength and size in COPD [mean MVC difference: −10.9 kg (95% confidence interval {CI}: −17.1 kg to −4.8 kg, P < 0.01; mean RFCSA difference −119 mm2, 95% CI: −180 mm2 to −58 mm2, P < 0.01)]. Conclusions: Ankle dorsiflexor strength is less attenuated than quadriceps strength in COPD patients with moderate airflow obstruction. Direct quadriceps assessment may be more relevant than measurement of lower limb fat‐free mass. Muscle Nerve 46: 548–554, 2012

Neural respiratory drive measured during inspiratory threshold loading and acute hypercapnia in healthy individuals

•  What is the central question of this study? The aim of this study was to examine the relationship between neural respiratory drive (NRD) measured as the electromyogram of the diaphragm (EMGdi%max) and parasternal intercostal muscles (sEMGpara%max) during two different ventilatory loading strategies, namely acute hypercapnia and inspiratory threshold loading. We hypothesized that, although agonist in nature, there would be a preferential increase in NRD to the diaphragm over the parasternal intercostal muscles during the two different loading conditions, given their different mechanical advantages and relative contributions to ventilation. •  What is the main finding and its importance? The sEMGpara%max provides a non‐invasive alternative to EMGdi%max recorded using an invasive oesophageal electrode catheter for the quantification of NRD. The EMGdi%max was, however, consistently greater than sEMGpara%max during both loading protocols, demonstrating that these two measures of NRD are not interchangeable.

The Intensity of Voluntary, Induced, and Spontaneous Cough

BACKGROUND The intensity of cough is an important determinant of cough severity. Few studies have quantified cough intensity in patients with chronic cough with objective measures. We investigated the intensity of voluntary, induced, and spontaneous cough in patients with chronic cough and healthy control subjects. METHODS Patients with chronic cough and control subjects underwent physiologic assessment of the intensity of maximum voluntary, capsaicin-induced, and spontaneous cough. Assessments included measurement of gastric pressure (Pga) and esophageal pressure (Pes) during cough, peak cough flow (PCF), expiratory muscle strength (twitch gastric pressure [TwPga]), and cough compression phase duration (CPD). Subjective perception of cough intensity was assessed using a visual analog scale (VAS). RESULTS Pes, Pga, and PCF during maximum voluntary cough were significantly greater in patients with chronic cough compared with control subjects (P = .003-.042). There was no difference in TwPga between patients and control subjects. CPD was increased in female patients compared with control subjects (mean ± SD, 0.50 ± 0.22 s vs 0.28 ± 0.17 s; P = .007). Mean ± SD Pes during spontaneous cough was comparable to induced cough (128 ± 28 cm H2O vs 122 ± 37 cm H2O, P = .686) but less than maximum voluntary cough (170 ± 46 cm H2O, P = .020). Median within-subject correlation coefficients between cough intensity VAS and Pes, Pga, and PCF were r = 0.82 to 0.86. CONCLUSIONS Maximum voluntary cough intensity was increased in patients with chronic cough compared with control subjects. There was no significant difference in expiratory muscle contractility. Further studies should evaluate the compressive phase of cough in more detail. Physiologic measures of cough intensity correlated strongly with subjective perception of intensity in patients with chronic cough and may be relevant objective outcome measures for clinical studies.