Design Recommendations for Presenting Clinical Guidelines on Mobile Devices

Some areas of clinical practice are still required to access and utilise clinical information that is inefficient or restrictive. Therefore, mobile device information delivery is becoming a key factor. However, recommendations on presenting clinical information on mobile devices are limited or not optimised for modern mobile design. Results from user-centred design studies inform the creation of a set of recommendations to assist in creating and delivering clinical guidelines on mobile devices.

A case of successful pregnancy managed in a patient living with Motor Neurone Disease for more than 3 years

A woman in her 20s presented with progressive weakness of her left arm and leg, slurred speech and swallowing difficulties. The clinical presentation and neurophysiological tests were consistent with motor neuron disease. She was referred to the regional ventilation unit for respiratory muscle function testing. This confirmed restrictive spirometry and borderline sniff nasal inspiratory pressure and cough peak expiratory flow. Three years later, she presented with an unplanned pregnancy and expressed the wish to continue the pregnancy to term. She was monitored throughout pregnancy with interval respiratory muscle testing and was reviewed in the high-risk pregnancy anaesthetic clinic. She was also closely monitored by the obstetrics and gynaecology team. A multidisciplinary team meeting between all stakeholders agreed on caesarean section delivery at 34 weeks. The pregnancy and the delivery were without complications; the baby was healthy and both mother and baby remain well to date.

Impact of the COVID-19 pandemic on a respiratory physiology department and the patient’s perception of rapid service change

Background

Originating as a cluster of unexplained cases of pneumonia in Wuhan, China, a novel coronavirus disease, officially named as COVID-19 by WHO, has now reached a pandemic level. In the wake of this global health crisis, stringent public health measures were implemented to curtail the spread of COVID-19. At a local level, the University Hospitals of North Midlands National Health Service Trust suspended all elective and outpatient activity, primarily to address the current potential implications of the COVID-19 outbreak. Within respiratory physiology, all but urgent and emergency work was suspended.

Methods

In June 2020, the service commenced its restoration/recovery plan, which was based on national and international guidelines to ensure safe practice for patients and staff alike. The plan was a roadmap developed to upscale the respiratory physiology service to deliver urgent and routine care and to assist the service to undertake the essential task of managing the patient backlog as a consequence of the interruption of service. Patient concerns and anxieties due to the pandemic was a key aspect of the restoration/recovery plan. The service developed numerous initiatives along with a questionnaire to assess patient experience following attendance for investigations or assessment.

Results

The questionnaire confirmed that the initiatives put in place as part of the restoration/recovery plan achieve high levels of satisfaction in terms of communication, interaction within the service, professionalism and importantly patient safety.

Conclusion

COVID-19 had a significant impact on routine clinical care and out-patient activity. This brought about significant change in service delivery that required a strict regimen to ensure COVID-19 free status and minimise cross-contamination of service users. The systems and processes introduced demonstrated positive responses and confirmed the objective of patient safety, which translated to the service users.

Mechanical ventilation for amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease, is a fatal neurodegenerative disease. Neuromuscular respiratory failure is the most common cause of death, which usually occurs within two to five years of the disease onset. Supporting respiratory function with mechanical ventilation may improve survival and quality of life. This is the second update of a review first published in 2009.

OBJECTIVES

To assess the effects of mechanical ventilation (tracheostomy-assisted ventilation and non-invasive ventilation (NIV)) on survival, functional measures of disease progression, and quality of life in ALS, and to evaluate adverse events related to the intervention.

SEARCH METHODS

We searched the Cochrane Neuromuscular Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL Plus, and AMED on 30 January 2017. We also searched two clinical trials registries for ongoing studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs involving non-invasive or tracheostomy-assisted ventilation in participants with a clinical diagnosis of ALS, independent of the reported outcomes. We included comparisons with no intervention or the best standard care.

DATA COLLECTION AND ANALYSIS

For the original review, four review authors independently selected studies for assessment. Two review authors reviewed searches for this update. All review authors independently extracted data from the full text of selected studies and assessed the risk of bias in studies that met the inclusion criteria. We attempted to obtain missing data where possible. We planned to collect adverse event data from the included studies.

MAIN RESULTS

For the original Cochrane Review, the review authors identified two RCTs involving 54 participants with ALS receiving NIV. There were no new RCTs or quasi-RCTs at the first update. One new RCT was identified in the second update but was excluded for the reasons outlined below.Incomplete data were available for one published study comparing early and late initiation of NIV (13 participants). We contacted the trial authors, who were not able to provide the missing data. The conclusions of the review were therefore based on a single study of 41 participants comparing NIV with standard care. Lack of (or uncertain) blinding represented a risk of bias for participant- and clinician-assessed outcomes such as quality of life, but it was otherwise a well-conducted study with a low risk of bias.The study provided moderate-quality evidence that overall median survival was significantly different between the group treated with NIV and the standard care group. The median survival in the NIV group was 48 days longer (219 days compared to 171 days for the standard care group (estimated 95% confidence interval 12 to 91 days, P = 0.0062)). This survival benefit was accompanied by an enhanced quality of life. On subgroup analysis, in the subgroup with normal to moderately impaired bulbar function (20 participants), median survival was 205 days longer (216 days in the NIV group versus 11 days in the standard care group, P = 0.0059), and quality of life measures were better than with standard care (low-quality evidence). In the participants with poor bulbar function (21 participants), NIV did not prolong survival or improve quality of life, although there was significant improvement in the mean symptoms domain of the Sleep Apnea Quality of Life Index by some measures. Neither trial reported clinical data on intervention-related adverse effects.

AUTHORS' CONCLUSIONS

Moderate-quality evidence from a single RCT of NIV in 41 participants suggests that it significantly prolongs survival, and low-quality evidence indicates that it improves or maintains quality of life in people with ALS. Survival and quality of life were significantly improved in the subgroup of people with better bulbar function, but not in those with severe bulbar impairment. Adverse effects related to NIV should be systematically reported, as at present there is little information on this subject. More RCT evidence to support the use of NIV in ALS will be difficult to generate, as not offering NIV to the control group is no longer ethically justifiable. Future studies should examine the benefits of early intervention with NIV and establish the most appropriate timing for initiating NIV in order to obtain its maximum benefit. The effect of adding cough augmentation techniques to NIV also needs to be investigated in an RCT. Future studies should examine the health economics of NIV. Access to NIV remains restricted in many parts of the world, including Europe and North America. We need to understand the factors, personal and socioeconomic, that determine access to NIV.

Evaluation of the effectiveness of a home-based inspiratory muscle training programme in patients with chronic obstructive pulmonary disease using multiple inspiratory muscle tests

PURPOSE

To evaluate the effectiveness of a home-based inspiratory muscle training (IMT) programme using multiple inspiratory muscle tests.

METHOD

Sixty-eight patients (37 M) with moderate to severe chronic obstructive pulmonary disease (COPD) (Mean [SD], FEV1 36.1 [13.6]% pred.; FEV1/FVC 35.7 [11.2]%) were randomised into an experimental or control group and trained with a threshold loading device at intensity >30% maximum inspiratory pressure (PImax) or <15% PImax, respectively, for 7 weeks. Thirty-nine patients (23 M) completed the study. The following measures were assessed pre- and post-IMT: PImax, sniff inspiratory nasal pressure (SNIP), diaphragm contractility (Pdi,tw), incremental shuttle walk test (ISWT), respiratory muscle endurance (RME), chronic respiratory disease questionnaire (CRDQ), the hospital anxiety and depression scale (HADS) and the SF-36. Between-group changes were assessed using one-way analysis of variance (ANOVA).

RESULTS

PImax and perception of well-being improved significantly post-IMT [p = 0.04 and <0.05 in four domains, respectively]. This was not reflected in SNIP [p = 0.7], Pdi,tw [p = 0.8], RME [p = 0.9] or ISWT [p = 0.5].

CONCLUSIONS

A seven-week, community-based IMT programme, with realistic use of health-care resources, improves PImax and perception of well-being but a different design may be required for improvement in other measures. Multiple tests provide a more comprehensive evaluation of changes in muscle function post-IMT.

IMPLICATIONS FOR REHABILITATION

A seven-week, home-based inspiratory muscle training programme improves maximal inspiratory pressure and perception of well-being in patients with moderate to severe COPD but not sniff nasal inspiratory pressure or diaphragm contractility, respiratory muscle endurance and exercise capacity. Multiple tests are recommended for a more comprehensive assessment of changes in muscle function following inspiratory muscle training programmes. Therapists need to explore different community-based inspiratory muscle training regimes for COPD patients and identify the optimal exercise protocol that is likely to lead to improvements in diaphragm contractility and exercise capacity.

Sniff nasal inspiratory pressure in patients with moderate-to-severe chronic obstructive pulmonary disease: learning effect and short-term between-session repeatability

BACKGROUND

Sniff nasal inspiratory pressure (SNIP) is a non-invasive measure of inspiratory muscle function often used as an outcome measure in clinical studies. An initial period of familiarisation with the test is recommended to minimise the learning effect. The repeatability of SNIP in patients with chronic obstructive pulmonary disease (COPD) is currently unknown.

OBJECTIVES

The aim of this study was to assess the between-session repeatability of SNIP over a 3-week period in moderate-to-severe COPD patients and compare it with that of maximal inspiratory (PI max) and expiratory pressure (PE max).

METHODS

Twenty-one patients (13 males) with a mean forced expiratory volume in 1 s (FEV1) of 38% of predicted (SD: 15) and FEV1/forced vital capacity of 34.3% (SD: 10.4) performed SNIP and PI max and PE max manoeuvres on 3 different sessions (S1, S2 and S3) 3-7 days apart. SNIP was performed at functional residual capacity (FRC), and PI max was performed at FRC and at residual volume (RV) to explore volume-dependent differences in the learning effect between sessions and PE max from total lung capacity.

RESULTS

The intra-class correlation coefficient (ICC) for SNIP was the highest of the three measures: S1-S3 ICC (95% CI) SNIP: 0.96 (0.88-0.94); PI max at FRC 0.82 (0.63-0.92); PI max at RV: 0.89 (0.78-0.95), and PE max: 0.96 (0.92-0.98), and had the lowest mean change between sessions [mean S2 - S1: 2.1(p = 0.4) and S3 - S2: -0.3 (p = 0.9)].

CONCLUSIONS

SNIP is repeatable over a period of 3 weeks in medically stable, moderate-to-severe COPD patients. In our study, 2 sessions were adequate to learn how to perform the test.

Mechanical ventilation for amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis, also known as motor neuron disease, is a fatal neurodegenerative disease. Neuromuscular respiratory failure is the commonest cause of death, usually within two to five years of the disease onset. Supporting respiratory function with mechanical ventilation may improve survival and quality of life. This is the first update of a review first published in 2009.

OBJECTIVES

The primary objective of the review is to examine the efficacy of mechanical ventilation (tracheostomy and non-invasive ventilation) in improving survival in ALS. The secondary objectives are to examine the effect of mechanical ventilation on functional measures of disease progression and quality of life in people with ALS; and assess adverse events related to the intervention.

SEARCH METHODS

We searched The Cochrane Neuromuscular Disease Group Specialized Register (1 May 2012), CENTRAL (2012, Issue 4), MEDLINE (January 1966 to April 2012), EMBASE (January 1980 to April 2012), CINAHL Plus (January 1937 to April 2012), and AMED (January 1985 to April 2012). We also searched for ongoing studies on ClinicalTrials.gov.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials involving non-invasive or tracheostomy assisted ventilation in participants with a clinical diagnosis of amyotrophic lateral sclerosis, independent of the reported outcomes. We planned to include comparisons with no intervention or the best standard care.

DATA COLLECTION AND ANALYSIS

For the original review, four authors independently selected studies for assessment and two authors reviewed searches for this update. All authors extracted data independently from the full text of selected studies and assessed the risk of bias in studies that met the inclusion criteria. We attempted to obtain missing data where possible. We planned to collect adverse event data from included studies.

MAIN RESULTS

For the original Cochrane review, the review authors identified and included two randomised controlled trials involving 54 participants with ALS receiving non-invasive ventilation. There were no new randomised or quasi-randomised controlled trials at this first update.Incomplete data were published for one study and we contacted the trial authors who were not able to provide the missing data. Therefore, the results of the review were based on a single study of 41 participants that compared non-invasive ventilation with standard care. It was a well conducted study with low risk of bias.The study showed that the overall median survival was significantly different between the group treated with non-invasive ventilation and the standard care group. The median survival in the non-invasive ventilation group was 48 days longer (219 days compared to 171 days for the standard care group (estimated 95% CI 12 to 91 days, P = 0.0062)). This survival benefit was accompanied by an enhanced quality of life. On subgroup analysis, the survival and quality of life benefit was much more in the subgroup with normal to moderately impaired bulbar function (20 participants); median survival was 205 days longer (216 days in NIV group versus 11 days in the standard care group, P = 0.0059). Non-invasive ventilation did not prolong survival in participants with poor bulbar function (21 participants), although it showed significant improvement in the mean symptoms domain of the Sleep Apnoea Quality of Life Index but not in the Short Form-36 Health Survey Mental Component Summary score. Neither trial reported clinical data on intervention related adverse effects.

AUTHORS' CONCLUSIONS

Evidence from a single randomised trial of non-invasive ventilation in 41 participants suggests that it significantly prolongs survival and improves or maintains quality of life in people with ALS. Survival and some measures of quality of life were significantly improved in the subgroup of people with better bulbar function, but not in those with severe bulbar impairment. Future studies should examine the health economics of NIV and factors influencing access to NIV. We need to understand the factors, personal and socioeconomic, that determine access to NIV.

Protocol for diaphragm pacing in patients with respiratory muscle weakness due to motor neurone disease (DiPALS): a randomised controlled trial

Background

Motor neurone disease (MND) is a devastating illness which leads to muscle weakness and death, usually within 2-3 years of symptom onset. Respiratory insufficiency is a common cause of morbidity, particularly in later stages of MND and respiratory complications are the leading cause of mortality in MND patients. Non Invasive Ventilation (NIV) is the current standard therapy to manage respiratory insufficiency. Some MND patients however do not tolerate NIV due to a number of issues including mask interface problems and claustrophobia. In those that do tolerate NIV, eventually respiratory muscle weakness will progress to a point at which intermittent/overnight NIV is ineffective. The NeuRx RA/4 Diaphragm Pacing System was originally developed for patients with respiratory insufficiency and diaphragm paralysis secondary to stable high spinal cord injuries. The DiPALS study will assess the effect of diaphragm pacing (DP) when used to treat patients with MND and respiratory insufficiency.

Method/Design

108 patients will be recruited to the study at 5 sites in the UK. Patients will be randomised to either receive NIV (current standard care) or receive DP in addition to NIV. Study participants will be required to complete outcome measures at 5 follow up time points (2, 3, 6, 9 and 12 months) plus an additional surgery and 1 week post operative visit for those in the DP group. 12 patients (and their carers) from the DP group will also be asked to complete 2 qualitative interviews.

Discussion

The primary objective of this trial will be to evaluate the effect of Diaphragm Pacing (DP) on survival over the study duration in patients with MND with respiratory muscle weakness. The project is funded by the National Institute for Health Research, Health Technology Assessment (HTA) Programme (project number 09/55/33) and the Motor Neurone Disease Association and the Henry Smith Charity. Trial Registration: Current controlled trials ISRCTN53817913. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the HTA programme, NIHR, NHS or the Department of Health.

Mechanical ventilation for amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis, also known as motor neuron disease, is a fatal neurodegenerative disease. Without mechanical ventilation, death from respiratory failure usually follows within two to five years of the onset of symptoms.

OBJECTIVES

To examine the efficacy of mechanical ventilation (tracheostomy and non-invasive ventilation) in improving survival, on disease progression and quality of life in amyotrophic lateral sclerosis.

SEARCH STRATEGY

We searched The Cochrane Neuromuscular Disease Group Trials Specialized Register (December 8 2008), The Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 4, 2008), MEDLINE (January 1966 to December 2008), EMBASE (January 1947 to December 2008), CINAHL Plus (January 1937 to December 2008), and AMED (January 1985 to December 2008). We also searched for ongoing studies on clinicaltrials.gov.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials involving non-invasive or tracheostomy assisted ventilation in participants with a clinical diagnosis of amyotrophic lateral sclerosis.

DATA COLLECTION AND ANALYSIS

Four authors independently selected studies for assessment. All authors extracted data independently from the full text of selected studies and assessed the risk of bias in studies that met the inclusion criteria. We attempted to obtain missing data where possible.

MAIN RESULTS

Two randomised controlled trials involving 54 participants receiving non-invasive ventilation were identified and included. Incomplete data were published for one study and we contacted the trial authors who were not able to provide the missing data. Therefore the results of the review were based on a single study of 41 participants. The study showed that the overall median survival in the whole cohort after initiation of assisted ventilation was significantly different between the non-invasive ventilation and standard care groups (P = 0.0062) with a median survival for the non-invasive ventilation group patients of 48 days longer than the standard care group participants. Non-invasive ventilation significantly improved survival and quality of life in the subgroup with normal to moderately impaired bulbar function. Non-invasive ventilation did not prolong survival in patients with poor bulbar function although it showed significant improvement in the mean symptoms domain of the sleep apnoea quality-of-life index but not in the Short Form-36 quality of life mental component summary score .

AUTHORS' CONCLUSIONS

Evidence from a single randomised trial of non-invasive ventilation in 41 participants suggests that it significantly prolongs survival and improves or maintains quality of life in people with ALS. Survival and some measures of quality of life were significantly improved in the subgroup of people with better bulbar function, but not in those with severe bulbar impairment.

The effect of noninvasive ventilation on ALS patients and their caregivers

BACKGROUND

Noninvasive ventilation (NIV) reduces mortality and improves some aspects of quality of life (QoL) in ALS. However, concerns remain that progressive disability may negate these benefits and unnecessarily burden caregivers.

METHODS

Thirty-nine patients requiring NIV were offered treatment. Twenty-six were established on NIV, but 13 declined or could not tolerate NIV. Fifteen patients without respiratory muscle weakness (RMW) but with similar ALS severity and age were studied in parallel. Caregivers of 21 NIV, 7 untreated, and 10 patients without RMW participated. Patients and caregivers had detailed QoL measurements for 12 months. NIV patients underwent cognitive testing before and after treatment.

RESULTS

RMW correlated with lower QoL. The median survival of untreated patients (18 days; 95% CI 11 to 25 days) was shorter than for NIV patients (298 days; 95% CI 192 to 404 days) and non-RMW patients (370 days; 95% CI 278 to 462 days; log rank test [2 df] = 81, p = 0.00001). A wide range of QoL measures improved within 1 month of starting NIV, and improvements were maintained for 12 months. QoL of non-RMW patients declined as RMW progressed. Caregivers of NIV and non-RMW patients showed similar increases in burden, but NIV patient caregivers developed a deterioration in the Short Form-36 Vitality score. No improvements were found on measures of learning and recall in the NIV patients.

CONCLUSIONS

Respiratory muscle weakness has a greater impact on quality of life (QoL) than overall ALS severity. Noninvasive ventilation (NIV) improves QoL despite ALS progression. NIV has no impact on most aspects of caregiver QoL and does not significantly increase caregiver burden or stress.

Diaphragm electromyograms recorded from multiple surface electrodes following magnetic stimulation

The diaphragm compound-muscle action potential (CMAPdi), elicited by unilateral magnetic stimulation (UMS) of the phrenic nerve can be recorded using surface electrodes. However, there is no consensus on the best positioning of surface electrodes and there are no data on the reproducibility of the signal. Using 36 surface electrode pairs, in five healthy subjects, the CMAPdi elicited by UMS and electrical stimulation (ES) were compared and 12 pairs were identified as providing acceptable signals. The latency and amplitude were measured for each CMAPdi, following UMS at 60-100% of maximal stimulator output, in 12 healthy subjects, on two occasions. Latencies obtained using UMS and ES ranged between 6.1-7.33 and 6.25-7.17 ms, respectively. Optimum CMAPdi were not recorded from the same electrode pair in all subjects, or for both hemidiaphragms in each subject. However, the optimal recording site for a particular individual remained unchanged on subsequent testing. When recorded from the optimal site, latencies and amplitudes of CMAPdi elicited on the two occasions were not significantly different. The current study suggests that the use of multiple chest wall electrodes can identify an optimal electrode pair, from which it is possible to obtain reproducible compound-muscle action potential signals.

Twitch airway pressure elicited by magnetic phrenic nerve stimulation in anesthetized healthy children

Children with diaphragm dysfunction may be unable to maintain adequate ventilation. Accurate diagnosis is important, but can only be achieved using an appropriate test and reference range. The aim of this study, therefore, was to measure diaphragm contractility and examine the influence of age and maturation, using magnetic phrenic nerve stimulation in healthy children. Anterolateral magnetic stimulation (MS) of the phrenic nerves was performed using a 43-mm figure-eight coil in 23 children (14 male; mean age, 7.8 years; range, 1.8-15.7) anesthetized for minor surgery with sevoflurane gas. The airway was maintained with a cuffed laryngeal mask airway (LMA) which was briefly occluded during MS. Diaphragm contractility was assessed by measuring the airway pressure (TwPaw) elicited by MS. TwPaw responses were obtained in all subjects, with mean (SD) TwPaw 18.2 (6.8) cm H2O bilateral, 7.3 (3.2) cm H2O left unilateral, and 8.6 (3.1) cm H2O right unilateral. Subgroup analysis was performed in 17 of the children who were prepubertal. Their mean (SD) TwPaw was 17.3 (6.8) cm H2O bilateral, 7.1 (3.7) cm H2O left unilateral, and 8.3 (3.3) right unilateral. The mean (SD) intrapatient coefficients of variation for bilateral and left and right unilateral TwPaw were 8.4% (5.2), 6.7% (3.5), and 11.7% (10.3), respectively. Bilateral and left and right unilateral TwPaw were significantly related to age (P < 0.05). In healthy prepubertal children, diaphragm contractility is primarily influenced by age.

Effect of salmeterol on respiratory muscle activity during exercise in poorly reversible COPD

BACKGROUND

Some patients with irreversible chronic obstructive pulmonary disease (COPD) experience subjective benefit from long acting bronchodilators without change in forced expiratory volume in 1 second (FEV(1)). Dynamic hyperinflation is an important determinant of exercise induced dyspnoea in COPD. We hypothesised that long acting bronchodilators improve symptoms by reducing dynamic hyperinflation and work of breathing, as measured by respiratory muscle pressure-time products.

METHODS

Sixteen patients with "irreversible" COPD (<10% improvement in FEV(1) following a bronchodilator challenge; mean FEV(1) 31.1% predicted) were recruited into a randomised, double blind, placebo controlled, crossover study of salmeterol (50 micro g twice a day). Treatment periods were of 2 weeks duration with a 2 week washout period. Primary outcome measures were end exercise isotime transdiaphragmatic pressure-time product and dynamic hyperinflation as measured by inspiratory capacity.

RESULTS

Salmeterol significantly reduced the transdiaphragmatic pressure-time product (294.5 v 348.6 cm H(2)O/s/min; p = 0.03), dynamic hyperinflation (0.22 v 0.33 litres; p = 0.002), and Borg scores during endurance treadmill walk (3.78 v 4.62; p = 0.02). There was no significant change in exercise endurance time. Improvements in isotime Borg score were significantly correlated to changes in tidal volume/oesophageal pressure swings, end expiratory lung volume, and inspiratory capacity, but not pressure-time products.

CONCLUSIONS

Despite apparent "non-reversibility" in spirometric parameters, long acting bronchodilators can cause both symptomatic and physiological improvement during exercise in severe COPD.

Cough augmentation in amyotrophic lateral sclerosis

Cough flows and pressures were measured during cough augmentation in healthy subjects and patients with bulbar and nonbulbar amyotrophic lateral sclerosis. Manual assistance increased flow 11% in bulbar (p < 0.01) and 13% in nonbulbar (p < 0.001) patients. Mechanical insufflation-exsufflation increased flow 17% in healthy subjects (p < 0.05), 26% (p < 0.001) in bulbar, and 28% (p < 0.001) in nonbulbar patients. The greatest improvements were in patients with the weakest coughs. Patient group and level of weakness influenced the effect of augmentation.

Cough gastric pressure and maximum expiratory mouth pressure in humans

Maximal expiratory mouth pressure is a well established test that is used to assess expiratory muscle strength. However, low values are difficult to interpret, as they may result from technical difficulties in performing the test, particularly in patients with facial muscle weakness or bulbar dysfunction. We hypothesized that measuring the gastric pressure during a cough, a natural maneuver recruiting the expiratory muscles, might prove to be a useful additional test in the assessment of expiratory muscle function. Mouth expiratory and cough gastric pressures were measured in 99 healthy volunteers to obtain normal values and in 293 patients referred for respiratory muscle assessment to compare the two measurements. Between-occasion within-subject coefficient of variation, assessed in 24 healthy volunteers, was 10.3% for mouth pressure and 6.9% for cough. Mean +/- SD cough gastric pressure for normal males was 214.4 +/- 42.2 and 165.1 +/- 34.8 cm H2O for females. In 171 patients deemed weak by a low mouth expiratory pressure, 42% had a normal cough gastric pressure. In 105 patients deemed weak by a low cough gastric pressure, 5.7% had a normal expiratory mouth pressure. Low maximal expiratory mouth pressures do not always indicate expiratory muscle weakness. Cough gastric pressure provides a useful complementary test for the assessment of expiratory muscle strength.

Non-volitional assessment of skeletal muscle strength in patients with chronic obstructive pulmonary disease

BACKGROUND

Although quadriceps weakness is well recognised in chronic obstructive pulmonary disease (COPD), the aetiology remains unknown. In disabled patients the quadriceps is a particularly underused muscle and may not reflect skeletal muscle function as a whole. Loss of muscle function is likely to be equally distributed if the underlying pathology is a systemic abnormality. Conversely, if deconditioning and disuse are the principal aetiological factors, weakness would be most marked in the lower limb muscles.

METHODS

The non-volitional technique of supramaximal magnetic stimulation was used to assess twitch tensions of the adductor pollicis, quadriceps, and diaphragm muscles (TwAP, TwQ, and TwPdi) in 22 stable non-weight losing COPD patients and 18 elderly controls.

RESULTS

Mean (SD) TwQ tension was reduced in the COPD patients (7.1 (2.2) kg v 10.0 (2.7) kg; 95% confidence intervals (CI) -4.4 to -1.4; p<0.001). Neither TwAP nor TwPdi (when corrected for lung volume) differed significantly between patients and controls (mean (SD) TwAP 6.52 (1.90) N for COPD patients and 6.80 (1.99) N for controls (95% CI -1.5 to 0.97, p=0.65; TwPdi 23.0 (5.6) cm H(2)O for COPD patients and 23.5 (5.2) cm H(2)O for controls (95% CI -4.5 to 3.5, p=0.81).

CONCLUSIONS

The strength of the adductor pollicis muscle (and the diaphragm) is normal in patients with stable COPD whereas quadriceps strength is substantially reduced. Disuse may be the principal factor in the development of skeletal muscle weakness in COPD, but a systemic process preferentially affecting the proximal muscles cannot be excluded.

Extubation failure due to phrenic nerve injury

A 26 week gestation infant had an increasingly elevated right hemidiaphragm following drainage of bilateral pleural effusions and failed extubation on numerous occasions. Electric stimulation of the phrenic nerves revealed absent activity on the right, indicating phrenic nerve injury from chest tube drain insertion. Diaphragmatic plication was performed and the infant successfully extubated four days later.

Reproducibility of twitch and sniff transdiaphragmatic pressures

Twitch transdiaphragmatic pressure (Tw Pdi) measured with magnetic stimulation of the phrenic nerve is used to follow up patients and to assess the effect of clinical treatments on diaphragm function. However the reproducibility of Tw Pdi on different occasions has been little studied. We investigated 32 normal subjects, measuring Tw Pdi elicited by bilateral magnetic stimulation of the phrenic nerves on two to 14 occasions. Sniff transdiaphragmatic pressure (sniff Pdi) was also measured. The mean value of Tw Pdi and sniff Pdi were 28+/-5 and 134+/-24 cm H(2)O, respectively. The within subjects coefficient of variation was 11% for both Tw Pdi and sniff Pdi. We conclude that there is a variability of Tw Pdi and the variability of Tw Pdi is the same as that of sniff Pdi.

Postprandial effects on twitch transdiaphragmatic pressure

Twitch transdiaphragmatic pressure (Pdi,tw), measured following magnetic stimulation of the phrenic nerves, is used to assess diaphragm strength, contractility and fatigue. Although the effects of posture, lung volume and potentiation on Pdi,tw are well described, it is not known whether the degree of gastric filling affects the measurement. Pdi,tw was recorded in seven healthy volunteers on two occasions with antero-lateral magnetic stimulation of the phrenic nerves. On the first occasion, the subjects had fasted for at least 8 h, whilst on the second occasion, measurements were made after each subject had eaten a substantial meal sufficient to produce a feeling of satiation. Mean postprandial unpotentiated and potentiated Pdi,tw were significantly greater than corresponding fasting Pdi,tw in all seven volunteers (29.8 versus 25.7 cmH2O and 38.9 versus 34.4 cmH2O, respectively). This was due to a significantly increased gastric pressure component (1.10 versus 0.84 and 0.94 versus 0.78, respectively), and reduced abdominal compliance (36 versus 62 mL x cmH2O(-1)). Twitch oesophageal pressure was preserved (15.0 versus 15.4 cmH2O). The postprandial state increases twitch transdiaphragmatic pressure, and this should be taken into account when using twitch transdiaphragmatic pressure to follow-up patients or to assess the effects of interventions on diaphragm contractility.

Diaphragm compound muscle action potential measured with magnetic stimulation and chest wall surface electrodes

To seek a method to reliably measure phrenic nerve conduction time (PNCT) with magnetic stimulation we investigated two stimulus sites, placing the magnetic coil at the cricoid cartilage (high position) or close to the clavicle (low position). We also compared compound muscle action potential (CMAP) recorded from three different sites: in the sixth to eighth intercostal spaces in the anterior axillary line (Ant-a); in the 8th intercostal space close to the midclavicular line; and with one electrode at the lower sternum and the other at the costal margin. Fourteen normal subjects were studied. The PNCT measured by magnetic stimulation in the high position recorded from (Ant-a) was 7.6+/-0.6 on the left side and 8.4+/-0.7 on the right. The PNCT recorded from all three sites become much shorter when the magnetic coil was moved from the high to the low position. Our results show that PNCT can be accurately measured with magnetic stimulation when care is taken to avoid coactivation of the brachial plexus.

Effect of diaphragm fatigue on neural respiratory drive

To test the hypothesis that diaphragm fatigue leads to an increase in neural respiratory drive, we measured the esophageal diaphragm electromyogram (EMG) during CO(2) rebreathing before and after diaphragm fatigue in six normal subjects. The electrode catheter was positioned on the basis of the amplitude and polarity of the diaphragm compound muscle action potential recorded simultaneously from four pairs of electrodes during bilateral anterior magnetic phrenic nerve stimulation (BAMPS) at functional residual capacity. Two minutes of maximum isocapnic voluntary ventilation (MIVV) were performed in six subjects to induce diaphragm fatigue. A maximal voluntary breathing against an inspiratory resistive loading (IRL) was also performed in four subjects. The reduction of transdiaphragmatic pressure elicited by BAMPS was 22% (range 13-27%) after 2 min of MIVV and was similar, 20% (range 13-26%), after IRL. There was a linear relationship between minute ventilation (VE) and the root mean square (RMS) of the EMG during CO(2) rebreathing before and after fatigue. The mean slope of the linear regression of RMS on VE was similar before and after diaphragm fatigue: 2.80 +/- 1.31 vs. 3.29 +/- 1.40 for MIVV and 1.51 +/- 0.31 vs 1.55 +/- 0.31 for IRL, respectively. We conclude that the esophageal diaphragm EMG can be used to assess neural drive and that diaphragm fatigue of the intensity observed in this study does not affect respiratory drive.