S82 CLINICAL USEFULNESS OF MEASURING NEURAL RESPIRATORY DRIVE FOR IDENTIFICATION OF DETERIORATION IN ACUTE EXACERBATIONS OF COPD

¹P. Murphy, ²A. Kumar, ³C. Reilly, ³C. Jolley, ¹K. Brignall, ⁴M. Polkey, ³J. Moxham, ⁵N. Hart. ¹Lane Fox Respiratory Unit, Guy’s & St Thomas’ NHS Foundation Trust, London, UK, ²King’s College London, London, UK, ³Thoracic Medicine, King’s College Hospital, London, UK, ⁴Sleep & Ventilation Unit, Royal Brompton & Harefield NHS Foundation Trust, London, UK, ⁵Guy’s & St Thomas’ NHS Foundation Trust and Kings College London NIHR Biomedical Research Centre, London, UK

Introduction Early discharge schemes and transfer of acute care into the community setting are strategic objectives for the National Health Service (NHS), with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) identified as a key area. The ability to predict accurately response to treatment and early detection of clinical deterioration are therefore essential. We hypothesised that neural respiratory drive (NRD), as represented by parasternal muscle electromyography (EMG_para), could be used as a novel clinical tool to identify clinical change in AECOPD.

Method Emergency admissions to the acute medicine ward with AECOPD were enrolled within 24 h of admission. Repeated measures of EMG_para were performed during their hospital admission and correlated with clinical course as assessed by the supervising clinician, blinded to the EMG_para data. EMG_para was normalised to EMG_para%max obtained during a maximal sniff manoeuvre performed at the time of readings, and data were analysed off-line as peak root mean squared per breath1 to produce an EMG_para%max.

Results 25 patients (27% male), mean age 74 (8.5) years and forced expiratory volume in 1 s (FEV₁) 0.57 (0.29) litres had baseline data recorded. All patients were able to tolerate EMG_para testing on study days, in contrast to 30% of patient unable or unwilling to complete FEV₁ testing. Repeat readings on consecutive days led to 30 pairs of data. On five occasions patients were deemed to have clinically deteriorated and on 25 occasions deemed to have improved. Changes in heart rate (HR), oxygen saturations (SpO₂), respiratory rate (RR), FEV₁, Medical Early Warning Score (MEWS) and NRD are shown in table 1.

Conclusion These data show the feasibility of measuring NRD in the acute care setting. There were no significant differences observed between “improvers” and “deteriorators” in the standard physiological measurements performed in the acute care setting. Although there was a significant difference in MEWS, the mean increase in the patients who deteriorated was <1 and thus insufficient to prompt a clinical response. However, both EMG_para and NRD showed discrimination between “mprovers” and “deteriorators”. Further work is currently ongoing to investigate the usefulness of NRD for identifying treatment failure and early deterioration in AECOPD.

S83 FACEMASK SPIROMETRY IN PATIENTS WITH BULBAR MOTOR NEURON DISEASE

A. A. Khaliq, I. E. Smith. Papworth Hospital NHS Foundation Trust, Cambridge, UK

Background Forced vital capacity (FVC) has predictive value for prognosis in motor neuron disease (MND) and is used as a decision aid when starting non-invasive ventilation (NIV). However, bulbar involvement makes it impossible for many people with MND to perform the manoeuvre due to mouth leaks or difficulty inserting and gripping a mouthpiece.

Aim To investigate the use of a facemask to measure FVC and compare it with spirometry using a conventional mouthpiece, in people with MND and bulbar symptoms.

Methods People with MND and bulbar symptoms (dysphagia, dysarthria or drooling with signs of increased jaw jerk, fasciculation or spasticity of tongue) attending a follow-up clinic had facemask spirometry if there was a suspicion that the results of mouthpiece measurement were suboptimal. The best of three attempts were recorded for each technique in the seated position.

Results In a 9-month period, 27 people (13 men), with a mean age of 64 (SD 13.6) years, had both methods of measuring spirometry attempted. Eleven of the 27 were using NIV. All managed with a facemask; 14 failed to record anything on the mouthpiece. Facemask FVC was 1.84 litres (SD 0.77, n = 27). Facemask FVC in those who failed with the mouthpiece was 1.63 litres (SD 0.70, n = 14). In those who were able to record FVC with the mouthpiece FVC was 1.42 litres (SD 0.65, n = 13). When FVC was recorded with both methods, FVC was greater using the facemask in all but one person (see fig 1). The mean difference was 0.65 litre (SD 0.43) p<0.001.

Conclusion In these patients facemask spirometry was acceptable to patients and none failed to record results, while 52% could not produce any result with a mouthpiece. The mean difference between the measures when both were available was clinically significant and could affect decision making regarding NIV. A formal study is required to confirm these findings, extend them to patients without obvious bulbar symptoms and exclude order effects.

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Abstract S83 Figure 1

Bland–Altman plot of forced vital capacity (FVC) using both the mouthpiece and facemask (n = 13).

S84 QUADRICEPS ENDURANCE IS REDUCED IN FIBROTIC IDIOPATHIC INTERSTITIAL PNEUMONIA

L. Mendoza, A. Gogali, D. Shrikrishna, S. V. Kemp, A. S. Jackson, Z. F. Shaikh, M. I. Polkey, A. U. Wells, N. S. Hopkinson. Royal Brompton Hospital, London, UK

Background Fibrotic idiopathic interstitial pneumonia is characterised by exertional dyspnoea and reduced exercise capacity, both attributed to pulmonary function deterioration. Little is known about the role of reduced peripheral skeletal muscle function as a factor in exercise capacity in this condition.

Aims To determine the presence of reduced quadriceps strength and/or endurance and its relationship to exercise capacity in patients with fibrotic idiopathic interstitial pneumonia.

Methods We studied 25 patients with fibrotic idiopathic interstitial pneumonia, forced vital capacity (FVC) mean (SD) 78.7 (14.0) % predicted, TL_CO mean (SD) 40.3 (10.9) % predicted, and 25 age-matched healthy controls. We measured fat-free mass, respiratory muscle strength, voluntary quadriceps strength (QMVC), twitch quadriceps force (TwQ) and quadriceps endurance with a protocol consisting of repetitive magnetic stimulation of the quadriceps using a special coil with 60 trains (2 s on, 3 s off) over 5 min. The 6 minute walking test (6MWT) was measured as an indicator of exercise capacity.

Results Both groups had comparable fat-free mass. There were no significant differences between patients and controls in respiratory muscle function (sniff nasal inspiratory pressure (SNIP), maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP)) and quadriceps strength measurements (QMVC mean (SD) 75.3 (18.3) vs 78.1 (16.5) % predicted and TwQ 8.0 (2.4) kg vs 9.8 (3.3) kg, patients vs controls). However, the force decline of the quadriceps during the endurance protocol was significantly greater in patients (fig 1). There was a significant difference in the 6MWD (489 (88.8) m vs 616 (74.6) m, patients vs controls, p<0.0001). The time to fall to 70% of baseline force (T_70%) in the endurance protocol correlated significantly with the 6MWD in controls (r² = 0.35 p = 0.016) but not in patients. In a stepwise multiple regression analysis, basal PaO₂ was the only significant predictor of the 6MWD in patients (r² = 0.2 p = 0.022).

Conclusion Fibrotic idiopathic interstitial pneumonia significantly affects quadriceps endurance.

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Abstract S84 Figure 1

S85 COMPARISON OF EAR AND FINGER OXIMETRY READINGS DURING AMBULATORY OXYGEN ASSESSMENTS

E. Barnett, R. Barraclough, A. Duck. Wythenshawe Hospital, Manchester, UK

Ambulatory oxygen requirements are routinely assessed and titrated using portable finger pulse oximetry (BTS 2006). In practice, we found that movement artefact or reduced circulation may adversely affect the measurement. Whilst using ear oximetry alongside finger oximetry on patients it was noted that the ear readings were often higher. These differences could potentially affect the prescription of ambulatory oxygen.

Objective To evaluate the use of portable oximetry measurements taken from the ear and finger during ambulatory assessments.

Method Over a period of 18 months 265 non-smoking patients referred for ambulatory oxygen assessment had ear and finger pulse oximetry measurements recorded before, during and after a 6 minute walking test using the Konica Minolta Pulsox. The finger oximeter was sited on the middle finger of the right hand; the ear probe on the right ear lobe after vasodilation with thurfyl nicotinate (Transvasin) cream. Patients were instructed to walk at a comfortable pace for up to 6 min. Pretest and post-test saturation and pulse were simultaneously recorded from the finger and ear oximeters.

Results There was a significant difference between ear and finger measurements both before and after exercise (p<0.001 for both). The mean difference before exercise was 1.9% (95% CI −1.75% to 5.5%), and postexercise was 2.8% (95% CI −3.5% to 9.1%). Earlobe measurements tended to be higher than finger measurements. There were no significant differences noted in pulse rate measurements. The observed differences in oxygen saturation could have altered the clinical outcome in 25% of the patients assessed (66 of 265).

Conclusion There are clinically and statistically significant differences in the ear and finger probe measurements. In our observational study, an extra 25% of patients met the criteria for ambulatory oxygen therapy using finger oximetry compared with earlobe readings. This may impact not only on the patient, but also on the national ambulatory oxygen budget.

S86 THE EFFECT OF ACUTE HYPOXIA ON QT INTERVAL IN RESPIRATORY PATIENTS UNDERGOING FITNESS TO FLY TESTS

¹J. R. A. Skipworth, ²D. A. Raptis, ¹Z. Puthucheary, ¹J. Rawal, ³D. Shrikrishna, ¹J. Windsor, ⁴D. Cramer, ³M. I. Polkey, ¹H. E. Montgomery, ³N. S. Hopkinson. ¹Institute of Human Health and Performance, University College London, London, UK, ²Department of Surgery and Interventional Science, University College London, London, UK, ³National Heart and Lung Institute, Imperial College, Royal Brompton Hospital, London, UK, ⁴Lung Function Department, Royal Brompton Hospital, London, UK

Background Previous studies have shown that acute exposure of healthy subjects to hypoxic conditions prolongs cardiac repolarisation (QT interval or QTc when corrected for heart rate) and that the magnitude of desaturation correlates with lengthening of the QTc interval. We aimed to assess whether this occurred in patients with chronic respiratory disease who were exposed acutely to hypoxic conditions.

Methods Patients with chronic respiratory disease undergoing “fitness to fly” tests, at a single centre, between April 2008 and February 2009, were retrospectively identified. Tests were performed by exposing patients to 15% O₂ for 20 min with assessment of blood gases and 12-lead ECG prior to and at the end of the hypoxic exposure period.

Results 101 patients were included (58 females and 43 males; median age 57 years). 40 (39.6%) patients had a diagnosis of interstitial lung disease, 12 (11.9%) bronchiectasis, 12 (11.9%) chronic obstructive pulmonary disease (COPD), 8 (7.9%) sarcoidosis, 7 (6.9%) cystic fibrosis, 6 (5.9%) systemic sclerosis, 5 (5.0%) asthma, 3 (3.0%) extrinsic allergic alveolitis and 8 (7.9%) suffered from other conditions. 15 (14.9%) also had pre-existing cardiac disease. Mean PaO₂/SaO₂ fell from 10.56 kPa/95.8% on air to 6.82 kPa/87.2% on 15%O₂ (p<0.001). ECG analysis revealed that the hypoxic challenge resulted in a significant increase in heart rate (from 83.2 to 86.9 bpm; p<0.001), a significant decrease in QT interval (from 357.8 to 348.8 ms; p<0.001) and a significant decrease in PR interval (from 161.2 to 158.0 ms; p = 0.01). However, there was no significant change in QTc (from 415.2 to 417.0 ms; p = 0.50). A significant correlation was noted between decrease in QT interval and decrease in PaO₂ (p = 0.01); however, there was no correlation between change in QTc and change in either PaO₂ or SaO₂. There was no difference in response between those with and without pre-existing cardiac disease.

Conclusion This cohort of 101 patients with chronic respiratory disease demonstrated a decrease in QT interval consistent with an increased heart rate in response to hypoxic challenge. This is different from the response in healthy subjects and may represent an effect of hypoxic preconditioning. Fitness to fly tests do not appear, on the basis of ECG evidence, to be hazardous for patients.

S87 SHALLOW BREATHING AND CYST-LIKE SPACES AUGMENT DEADSPACE VENTILATION IN COALWORKERS’ PNEUMOCONIOSIS

¹J. Cotes, ²J. Reed, ¹D. W. Wilson. ¹School of Medicine & Health, Durham University, UK, ²Medical School, Newcastle University, UK

Background Coalworkers’ pneumoconoisis (CWP) traditionally presents with breathlessness secondary to increased exercise ventilation. We examined the mechanisms and estimated their likely magnitudes in men referred for assessment by the local Pneumoconiosis Medical Panel.

Subjects, Methods and Underlying lung function Lung function and the ventilatory responses to progressive submaximal treadmill exercise were assessed in 54 ex-coalminers with radiographic pneumoconiosis and exertional dyspnoea, 9 men with presumed centrilobular emphysema (PCE) and 44 men with normal lung function, despite working in dusty occupations. The latter formed a comparison group (CG). Exercise ventilation was at an O₂ uptake of 1.0 l/min (45 mmol/min, designated V′ex_st). The breathing pattern was in terms of ventilation and respiratory frequency at a V′ex of 30 l/min (Vt₃₀ and fR₃₀, respectively). Ventilation was interpreted using a model with terms for alveolar ventilation, and airway and alveolar deadspace ventilation (V′aw.ds and V′alv.ds, respectively).1

Results The lung function of the men with CWP exhibited moderate airways obstruction and defective gas transfer, similar to that reported for coalworkers with irregular opacities.2 It differed significantly from that for the men with PCE. On exercise, the V′ex_st in CWP and in PCE was increased compared with CG (means 34.6, 33.6 and 23.4 l/min, respectively, p<0.05). In CWP the Vt₃₀ was reduced. From the model, in men with CWP 17% of the increase in exercise ventilation reflected additional alveolar ventilatory drive (possibly from the low transfer factor), 24% a shallow breathing pattern and 59% a significant V′alv.ds, possibly ventilation of cyst-like spaces (not PCE).

Conclusions Up to 41% of the increase in ventilation could be amenable to therapy. To this end, the functional assessment should include breathing pattern during treadmill exercise. The neuropharmacology of control of breathing pattern should be explored. The findings have implications for other chronic lung disorders.