Neuromuscular weakness in chronic obstructive pulmonary disease: chest wall, diaphragm, and peripheral muscle contributions.

PURPOSE OF REVIEW: Chronic obstructive lung disease affects the lung parenchyma and airways leading to well described effects in respiratory function. This review describes the current knowledge and advances regarding neuromuscular function and chest wall mechanics, which are affected in chronic obstructive pulmonary disease (COPD). RECENT FINDINGS: In COPD, progressive lung hyperinflation becomes constrained by a chest wall with decreasing capacity to expand, resulting in respiratory muscle inefficiency. There is evidence of neuromuscular uncoupling, that is, the respiratory muscle is unable to increase its output in proportion to increasing neural signals. COPD patients also have evidence of altered peripheral muscles function. The end effect of all these pathological changes is neuromuscular weakness. SUMMARY: Respiratory and peripheral muscles dysfunction is found in patients with COPD. This manifests clinically as dyspnea, poor exercise capacity, and decreased quality of life. We have clear evidence that rehabilitation helps several aspects of patients with COPD. Further understanding of the physiopathology is needed to improve our therapeutic and rehabilitation strategies.

[Use of pulmonary rehabilitation in the treatment of decreased respiratory muscle strength]. / Moznosti vyuzití technik plicní rehabilitace pro lécbu snízené síly dýchacích svalu.

Decreased respiratory muscle strength could lead to other health problems, which can decrease the quality of life of those patients. Ineffective expectoration and dyspnoea during physical activities and during activity of daily living are the most frequent disorders associated with decreased respiratory muscle strength. Multidisciplinary treatment including pulmonary rehabilitation programme is very important for those patients. Ventilatory muscle training (strength and endurance type of training), airway clearance techniques - active (e.g. autogenic drainage, instrumental techniques) and passive (e.g. manual thoracic compression, mechanical insufflator/exsufflator machine) and exercise training are the most frequent used techniques in these patients. Assessment of all respiratory muscles function - especially their respiratory and postural function - is important at the beginning of rehabilitation treatment.

Exercise therapy for a patient with persistent dyspnea after combined traumatic diaphragmatic rupture and phrenic nerve injury.

We present a case report of a patient with a history of diaphragmatic rupture who had persistent dyspnea for 9 months after primary surgical repair of a right diaphragmatic rupture caused by a car accident. A phrenic nerve conduction study was performed, which demonstrated a rare accompanying ipsilateral phrenic nerve injury with resultant hemidiaphragmatic paralysis. Aerobic exercise therapy for the purpose of improving endurance and dietary modification for weight reduction were prescribed and continued for 6 months. The exercise intensity was prescribed based on the percentage of maximum heart rate as confirmed by an exercise tolerance test. The duration of exercise was gradually increased. In this case, the long-persistent dyspnea was successfully alleviated via nonoperative management to the point that the patient could resume regular activities of daily living.

Parálisis diafragmática en el post operatorio de cirugía cardiovascular, trasplantes cardíaco y pulmonar / Diaphragmatic paralysis in the postoperative period after cardiovascular surgery, and heart and lung transplantation

Objetivo principal: Describir la incidencia, evolución y tratamiento de los pacientes con parálisis diafragmática (PD) en los postoperatorios (POP) de cardiopatías congénitas (CC), trasplante cardiaco (TC) y trasplante pulmonar (TP) en la Unidad de Cuidados Intensivos 35 (UCI 35) del Hospital de Pediatría Juan P. Garrahan. Método: Se estudiaron 43 pacientes POP de CC, TC y TP que cursaron con PD durante los años 2010 al 2013. Se estudiaron datos demográficos como edad expresada en meses, sexo, peso en kilos, la existencia de sindromes genéticos, internación prequirúrgica, mala condición previa presencia de cirugía, circulación extracorpórea (CEC), días en ARM, fracaso de extubación, plicatura diafragmática, defecto residual cardiaco, obstrucción de VAS post extubación, atelectasias (ATL), episodios en ventilación no invasiva (VNI), traqueotomía (TQT), entre otros días de internación, tipo de egreso y sobrevida. Resultados: La incidencia de PD fue del 2,35%, de los 43, 22 fueron niñas, la edad M = 9 meses (0,5-204), con un peso M = 6,8 (2,3-65); 34 pacientes POP de CC, 4 POP de TC y 5 de TP. El 95% de la cirugías fue con CEC, 18 pacientes tenían cirugía previa, 21 con mala condición preoperatoria, los días de ARM M = 10 (0-109), el 55% tuvo al menos un fracaso de extubación, se realizaron 21 plicaturas, dentro de los 5 días del diagnóstico de PD en un 50%, se practicaron 6 TQT, el 83% de los pacientes tuvo por lo menos un episodio en VNI, la sobrevida al alta, de 88%. Conclusiones: Si bien la PD es poco frecuente en nuestra población, aumenta considerablemente la morbilidad de estos pacientes.

Parálisis diafragmática en el post operatorio de cirugía cardiovascular, trasplantes cardíaco y pulmonar / Diaphragmatic paralysis in the postoperative period after cardiovascular surgery, and heart and lung transplantation

Objetivo principal: Describir la incidencia, evolución y tratamiento de los pacientes con parálisis diafragmática (PD) en los postoperatorios (POP) de cardiopatías congénitas (CC), trasplante cardiaco (TC) y trasplante pulmonar (TP) en la Unidad de Cuidados Intensivos 35 (UCI 35) del Hospital de Pediatría Juan P. Garrahan. Método: Se estudiaron 43 pacientes POP de CC, TC y TP que cursaron con PD durante los años 2010 al 2013. Se estudiaron datos demográficos como edad expresada en meses, sexo, peso en kilos, la existencia de sindromes genéticos, internación prequirúrgica, mala condición previa presencia de cirugía, circulación extracorpórea (CEC), días en ARM, fracaso de extubación, plicatura diafragmática, defecto residual cardiaco, obstrucción de VAS post extubación, atelectasias (ATL), episodios en ventilación no invasiva (VNI), traqueotomía (TQT), entre otros días de internación, tipo de egreso y sobrevida. Resultados: La incidencia de PD fue del 2,35%, de los 43, 22 fueron niñas, la edad M = 9 meses (0,5-204), con un peso M = 6,8 (2,3-65); 34 pacientes POP de CC, 4 POP de TC y 5 de TP. El 95% de la cirugías fue con CEC, 18 pacientes tenían cirugía previa, 21 con mala condición preoperatoria, los días de ARM M = 10 (0-109), el 55% tuvo al menos un fracaso de extubación, se realizaron 21 plicaturas, dentro de los 5 días del diagnóstico de PD en un 50%, se practicaron 6 TQT, el 83% de los pacientes tuvo por lo menos un episodio en VNI, la sobrevida al alta, de 88%. Conclusiones: Si bien la PD es poco frecuente en nuestra población, aumenta considerablemente la morbilidad de estos pacientes

Respiratory muscle training for cervical spinal cord injury.

BACKGROUND: Cervical spinal cord injury (SCI) severely comprises respiratory function due to paralysis and impairment of the respiratory muscles. Various types of respiratory muscle training (RMT) to improve respiratory function for people with cervical SCI have been described in the literature. A systematic review of this literature is needed to determine the effectiveness of RMT (either inspiratory or expiratory muscle training) on pulmonary function, dyspnoea, respiratory complications, respiratory muscle strength, and quality of life for people with cervical SCI. OBJECTIVES: To evaluate the efficacy of RMT versus standard care or sham treatments in people with cervical SCI. SEARCH METHODS: We searched the Cochrane Injuries and Cochrane Neuromuscular Disease Groups' Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (2012, Issue 1), MEDLINE, EMBASE, CINAHL, ISI Web of Science, PubMed, and clinical trials registries (Australian New Zealand Clinical Trials Registry, ClinicalTrials, Controlled Trials metaRegister) on 5 to 8 March 2013. We handsearched reference lists of relevant papers and literature reviews. We applied no date, language, or publication restrictions. SELECTION CRITERIA: All randomised controlled trials that involved an intervention described as RMT versus a control group using an alternative intervention, placebo, usual care, or no intervention for people with cervical SCI were considered for inclusion. DATA COLLECTION AND ANALYSIS: Two review authors independently selected articles for inclusion, evaluated the methodological quality of the studies, and extracted data. We sought additional information from the trial authors when necessary. We presented results using mean differences (MD) (using post-test scores) and 95% confidence intervals (CI) for outcomes measured using the same scale or standardised mean differences (SMD) and 95% CI for outcomes measured using different scales. MAIN RESULTS: We included 11 studies with 212 participants with cervical SCI. The meta-analysis revealed a statistically significant effect of RMT for three outcomes: vital capacity (MD mean end point 0.4 L, 95% CI 0.12 to 0.69), maximal inspiratory pressure (MD mean end point 10.50 cm/H2O, 95% CI 3.42 to 17.57), and maximal expiratory pressure (MD mean end point 10.31 cm/H2O, 95% CI 2.80 to 17.82). There was no effect on forced expiratory volume in one second or dyspnoea. We could not combine the results from quality of life assessment tools from three studies for meta-analysis. Respiratory complication outcomes were infrequently reported and thus we could not include them in the meta-analysis. Instead, we described the results narratively. We identified no adverse effects as a result of RMT in cervical SCI. AUTHORS' CONCLUSIONS: In spite of the relatively small number of studies included in this review, meta-analysis of the pooled data indicates that RMT is effective for increasing respiratory muscle strength and perhaps also lung volumes for people with cervical SCI. Further research is needed on functional outcomes following RMT, such as dyspnoea, cough efficacy, respiratory complications, hospital admissions, and quality of life. In addition, longer-term studies are needed to ascertain optimal dosage and determine any carryover effects of RMT on respiratory function, quality of life, respiratory morbidity, and mortality.

Diaphragm pacing and noninvasive respiratory management of amyotrophic lateral sclerosis/motor neuron disease.

INTRODUCTION: Although it is known that continuous noninvasive ventilation (CNIV) can prolong life in amyotrophic lateral sclerosis/motor neuron disease (ALS/MND), in this study we explore similar claims for diaphragm pacing (DP). METHODS: NIV and DP users' vital capacities (VCs) over time and duration of NIV and CNIV dependence were analyzed for 354 non-DP and 8 DP ALS/MND patients. RESULTS: Patients had a higher rate of monthly VC decline before NIV use (5.1 ± 7.6%) than during NIV use (2.5 ± 3.6%) (P < 0.01, 95% CI 0.84-4.5); the decline for 4 DP users was 3.7-20%. Fifty-five ALS/MND patients used part-time NIV for 19.9 ± 27.6 months until tracheostomy/death, whereas 113 others used it for 10.9 ± 10.5 months until CNIV dependence for another 12.8 ± 16.2 months. After placement, 7 DP users were CNIV dependent in 8.0 ± 7.0 months, whereas 6 underwent tracheostomy/died in 18.2 ± 13.7 months. CONCLUSIONS: CNIV prolonged the survival of 113 of the 354 non-DP and 6 DP ALS/MND patients by 12.8 and 10.2 months, respectively. DP provided no benefit on VC or mechanical ventilation-free survival.

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.

Posterolateral surface electrical stimulation of abdominal expiratory muscles to enhance cough in spinal cord injury.

BACKGROUND: Spinal cord injury (SCI) patients have respiratory complications because of abdominal muscle weakness and paralysis, which impair the ability to cough. OBJECTIVE: This study aims to enhance cough in high-level SCI subjects (n = 11, SCI at or above T6) using surface electrical stimulation of the abdominal muscles via 2 pairs of posterolaterally placed electrodes. METHODS: From total lung capacity, subjects performed maximum expiratory pressure (MEP) efforts against a closed airway and voluntary cough efforts. Both efforts were performed with and without superimposed trains of electrical stimulation (50 Hz, 1 second) at a submaximal intensity set to evoke a gastric pressure (P(ga)) of 40 cm H(2)O at functional residual capacity. RESULTS: In the MEP effort, stimulation increased the maximal P(ga) (from 21.4 ± 7.0 to 59.0 ± 5.7 cm H(2)O) and esophageal pressure (P(es); 47.2 ± 11.7 to 65.6 ± 13.6 cm H(2)O). During the cough efforts, stimulation increased P(ga) (19.5 ± 6.0 to 57.9 ± 7.0 cm H(2)O) and P(es) (31.2 ± 8.7 to 56.6 ± 10.5 cm H(2)O). The increased expiratory pressures during cough efforts with stimulation increased peak expiratory flow (PEF, by 36% ± 5%), mean expiratory flow (by 80% ± 8%), and expired lung volume (by 41% ± 16%). In every subject, superimposed electrical stimulation improved peak expiratory flow during cough efforts (by 0.99 ± 0.12 L/s; range, 0.41-1.80 L/s). Wearing an abdominal binder did not improve stimulated cough flows or pressures. CONCLUSIONS: The increases in P(ga) and PEF with electrical stimulation using the novel posterolateral electrode placement are 2 to 3 times greater than improvements reported in other studies. This suggests that posterolateral electrical stimulation of abdominal muscles is a simple noninvasive way to enhance cough in individuals with SCI.

Neonatal phrenic nerve injury due to traumatic delivery.

AIMS: To describe the clinical course of infants recovering spontaneously from diaphragmatic paralysis due to perinatal phrenic nerve injury as well as those that underwent plication of the diaphragm. METHODS: Between 1990 and 2006, 14 newborns admitted to the Neonatal Intensive Care Unit (NICU) of the Wilhelmina Children's Hospital in Utrecht, The Netherlands, were diagnosed with diaphragmatic paralysis due to obstetric phrenic nerve injury. The clinical and follow-up data were studied retrospectively. RESULTS: Four infants recovered spontaneously and could be weaned from mechanical ventilation within nine days without further treatment. Plication of the diaphragm was performed in 10 infants because of failure to wean from ventilatory support or serious persistent respiratory distress. Time between birth and plication ranged from 10 to 51 days, with a median of 19 days. Satisfactory respiratory outcome was achieved in 86% of the cases. CONCLUSIONS: The minority of infants suffering from diaphragmatic paralysis due to perinatal phrenic nerve injury recovers spontaneously. Infants who fail to wean from ventilatory support and undergo early plication have a quick recovery and can be extubated successfully within a few days.

Suspected statin-induced respiratory muscle myopathy during long-term inspiratory muscle training in a patient with diaphragmatic paralysis.

BACKGROUND AND PURPOSE: Abnormal lipids are associated with the development of coronary heart disease; for this reason, lipid-lowering agents have become a standard of care. The purposes of this case report are: (1) to highlight the association of impaired inspiratory muscle performance (IMP) with statin therapy and (2) to describe potentially useful methods of examining and treating people with known or suspected statin-induced skeletal myopathies (SISMs). CASE DESCRIPTION: The patient had breathlessness on exertion and a restrictive lung disorder from a right hemidiaphragmatic paralysis, for which he was prescribed high-intensity inspiratory muscle training (IMT). He had a secondary diagnosis of hyperlipidemia, which was treated with 40 mg of simvastatin after 5(1/2) months of IMT. OUTCOMES: The improvements in IMP, symptoms, and functional status obtained from almost 6 months of high-intensity IMT were lost after the commencement of simvastatin. However, 3 weeks after termination of simvastatin combined with high-intensity IMT, the patient's IMP, symptoms, and functional status exceeded pre-statin levels. DISCUSSION: This case report suggests that high-intensity IMT can be used effectively in a patient with impaired diaphragmatic function and during recovery from a respiratory SISM. The marked reduction in IMP and inability to perform IMT resolved with the cessation of statin therapy. The case report also highlights the potential effects of SISMs in all skeletal muscle groups. The clinical implications of this case report include the potential role of physical therapy in monitoring and possibly facilitating the spontaneous recovery of an SISM, as well as the need to investigate the IMP of a person with dyspnea and fatigue who is taking a statin.

Phrenic nerve stimulation in the evaluation of ventilator-dependent individuals with C4- and C5-level spinal cord injury.

Three individuals with C4 or C5 spinal cord injuries (SCI) were seen in follow-up for management of their late complications, which included impaired ventilation. Electrodiagnostic studies were performed on all three as part of the assessment of the function of their phrenic nerves and diaphragm muscles in relation to their need for mechanical ventilator support. Each patient had evidence of lower-motor neuron injury to the phrenic nerves. Two of the patients who initially displayed small-amplitude (<0.1 mV) compound muscle action potentials (CMAP) bilaterally were later reevaluated during the course of their observation in the outpatient rehabilitation clinic. The CMAP amplitude of the diaphragm increased in these two cases during the 3-11 mos after SCI. Evidence of nerve recovery occurred in parallel with improvements in pulmonary function testing and was followed by successful weaning from the ventilator. These individuals both gained ventilator independence after the CMAP amplitude of least one hemidiaphragm was >0.4 mV. In the third case, early failure of ventilator weaning was reported to the patient as a poor prognostic sign. At the time of our first evaluation 11 mos after injury, a CMAP of 1.0 mV was seen on the right, with an absent response on the left. In case 3, the needle electromyogram demonstrated voluntary active motor unit action potentials that provided additional electrophysiologic support for phrenic nerve function. Phrenic nerve-conduction studies can provide useful measures in assessing the recovery of lower-motor neuron diaphragm function in relation to impaired ventilation in individuals with C4- or C5-level SCI.

Inspiratory muscle pacing in spinal cord injury: case report and clinical commentary.

BACKGROUND/OBJECTIVE: A significant fraction of patients with cervical spinal cord injury suffer from respiratory muscle paralysis and dependence on chronic mechanical ventilation. In selected patients, diaphragm pacing (DP) through electrical stimulation of the phrenic nerves provides an alternative to mechanical ventilation with significant advantages in life quality. METHODS: A case report of an individual who successfully underwent DP using intramuscular diaphragm electrodes. A brief review of the state of the art of DP including the clinical benefits of DP, patient selection and evaluation, description of equipment, methods of transition from mechanical ventilation to DP, potential complications and side effects, long-term outcome, and potential future developments in this field is included. RESULTS: Several available DP systems are available, including conventional ones in which electrodes are positioned directly on the phrenic nerves through thoracotomy and less invasive systems in which electrodes are placed within the diaphragm through laparoscopy. For patients with only unilateral phrenic nerve function, a combined intercostal and unilateral diaphragm pacing system is under development. CONCLUSIONS: In patients with ventilator-dependent tetraplegia, there are alternative methods of ventilatory support, which offer substantial benefits compared to mechanical ventilation.

Relationship between inspiratory muscle strength and cough capacity in cervical spinal cord injured patients.

STUDY DESIGN: Prospective single centre study. OBJECTIVES: Pulmonary rehabilitation focuses on improving the expiratory muscle function in order to increase the reduced cough capacity in patients with cervical spinal cord injuries (SCI). However, an improvement in the inspiratory function is also important for coughing effectively. Therefore, this study was to examine the significance of the inspiratory muscle strength on the cough capacity in the patients with a cervical SCI. SETTING: SCI unit, Yonsei Rehabilitation Hospital, Seoul, Korea. METHODS: The vital capacity (VC), maximum inspiratory pressure (MIP), and maximum expiratory pressure (MEP) were measured. Moreover, the unassisted peak cough flow (PCF) and assisted PCF under three conditions were evaluated. RESULTS: All three assisted cough methods showed a significantly higher value than the unassisted method (P < 0.001). The VC correlated with the voluntary cough capacity and the MIP (R = 0.749) correlated more significantly with the VC than the MEP (R = 0.438) (P < 0.01). The MIP showed a higher correlation with both the unassisted PCF and all three assisted PCFs than the MEP (P < 0.001). CONCLUSIONS: The management of the inspiratory muscle strength should be considered in the pulmonary rehabilitation at cervical SCI patients.

Resistive inspiratory muscle training in sleep-disordered breathing of traumatic tetraplegia.

OBJECTIVE: To assess the effect of resistive inspiratory muscle training (RIMT) on the static pulmonary function and sleep-induced breathing disorder of individuals with chronic cervical cord injury. DESIGN: Before-after training. SETTING: Home-setting training program. PATIENTS: Fourteen complete traumatic tetraplegic patients (12 men, 2 women; mean age, 41.1 +/- 14y; range, 19-56y) injured for more than 6 months. INTERVENTION: Subjects participated in a 6-week RIMT program for 15 minutes twice daily at a training intensity of 60% of maximum inspiratory pressure (MIP). The participants were reevaluated at the end of 6-week training. MAIN OUTCOME MEASURES: Lung volume, peak expiratory flow (PEF), MIP, and maximum expiratory pressure (MEP) were measured by using a spirometry and inspiratory force meter, respectively. Capnography was used to monitor nocturnal pulse oxyhemoglobin saturation (SpO(2)) and end-tidal carbon dioxide tension level (ETCO(2)) of the patients. RESULTS: The maximum voluntary ventilation (MVV) and MIP of individuals with chronic cervical cord injury substantially improved after RIMT. MIP increased from -68.7 +/- 27.4cmH(2)O to -77.3 +/- 24.0cmH(2)O and MVV rose from 62.7 +/- 33.2L to 73.4 +/- 31.3L (P <.05). Despite increasing from 3.5 +/- 1.8L/s to 4.0 +/- 1.7L/s, PEF was statistically insignificant. For the individuals with improved MIP, the duration of ETCO(2) greater than 48mmHg reduced from 2.2% +/- 3.3% to 1.0% +/- 2.0% of total sleep time (P =.05) and that of SpO(2) less than 90% significantly declined from 1.8% +/- 2.8% to 1.3% +/- 2.4% of total sleep time (P <.05). CONCLUSION: These findings suggest that RIMT can enhance the respiratory muscle strength and endurance of chronic tetraplegia and further ameliorate the sleep-induced breathing disorder. Therefore, RIMT is suggested as a home program for patients with sleep-disordered breathing.

Neural prostheses in the respiratory system.

Approximately 5% of spinal cord-injured individuals suffer from respiratory muscle paralysis and require chronic mechanical ventilation. Unfortunately, this form of life support is associated with a number of undesirable side effects and discomforts. The only available alternative to mechanical ventilation is diaphragm pacing via bilateral phrenic nerve stimulation. This technique can provide patients with marked improvements in life quality and offers significant advantages compared to mechanical ventilation. Many patients, however, do not have bilateral phrenic function or are not willing to accept the risks inherent with phrenic nerve pacing and therefore are not candidates for this technique. Two alternative methods to ventilate patients with ventilator-dependent tetraplegia are reviewed in this paper. In patients with only a single functional phrenic nerve who are therefore not candidates for phrenic nerve pacing, combined intercostal muscle and unilateral phrenic nerve stimulation has recently been shown to maintain ventilatory support. In patients with bilateral phrenic nerve function, on-going studies suggest that intramuscular diaphragm pacing may be a useful alternative to direct phrenic nerve pacing. With the electrodes placed into the diaphragm laparoscopically, this method allows for the diaphragm to be activated without manipulation of the phrenic nerve, need for thoracotomy, or hospitalization. Both techniques provide benefits similar to that derived from bilateral phrenic nerve pacing and hold promise as alternative methods of ventilatory support in selected populations groups.

Respiratory response to exercise in postpolio patients with severe inspiratory muscle dysfunction.

OBJECTIVES: To evaluate the limiting factors of exercise performance and to analyze the respiratory strategies adopted during exercise in postpolio patients with severe inspiratory muscle dysfunction. PATIENTS: Five patients with prior poliomyelitis associated with scoliosis and with respiratory muscle dysfunction (mean vital capacity, 1.74L [range, 1.1 to 2.4]) were studied at rest and during leg or arm cycle exercise. METHODS: Gas exchange was examined by arterial blood gases and mass spectrometry of expired air. Ventilatory mechanics were studied by measurement of esophageal and gastric pressures. RESULTS: Blood gases at rest were normal, except for subnormal PO2 levels in three patients. In all but one patient, ventilatory insufficiency was the limiting factor for exercise. A compensatory breathing pattern with abdominal muscle recruitment during expiration was present already at rest in three of the patients. The pressures generated by the diaphragm were below fatiguing margins, ie, levels that in healthy subjects can be sustained for at least 45 minutes. CONCLUSIONS: The extent of ventilatory dysfunction was not evident in blood gas values at rest; however, it was revealed by blood gas values during the exercise test. Diaphragm fatigue seems to be avoided at the cost of impaired blood gases.

Respiratory response during arm elevation in isolated diaphragm weakness.

Upper extremity exercise is associated with a significant metabolic and ventilatory cost that is particularly evident in patients with severe chronic airflow obstruction. In these patients abnormal ventilatory muscle recruitment has been hypothesized to relate to impaired diaphragm function resulting from hyperinflation. Similar data have never been reported in patients with isolated diaphragm weakness but without airflow obstruction or hyperinflation, a group that would ideally define the role of diaphragm function during arm elevation (AE). We prospectively studied 15 patients with isolated diaphragm weakness of varying severity (Pdi(sniff), 31.74 +/- 3.75 cm H(2)O) as contrasted with eight normal subjects (Pdi(sniff), 111. 77 +/- 13.35 cm H(2)O) of similar age. Patients with diaphragm weakness demonstrated significant lung volume restriction with normal DL(CO)/VA. There was no difference in resting oxygen consumption (V O(2)), carbon dioxide production (V CO(2)), minute ventilation (V E), and tidal volume (VT) between the two groups; however, a borderline difference in resting breathing frequency (f(b)) (p = 0.056) was evident. Both groups demonstrated a rise in V O(2), V CO(2), and V E during 2 min of AE anteriorly. Normal subjects demonstrated a statistically significant rise in VT but a statistically insignificant rise in f(b) during AE. In contrast, patients with diaphragm weakness demonstrated a statistically significant rise in f(b) during AE but a statistically insignificant rise in VT. In patients the observed rise in VT directly correlated with baseline Pdi(sniff) (r = 0.59, p = 0.02) and Pdi(max) (r = 0.81, p = 0.002). Both groups demonstrated a rise in Pdi during AE. The rise in Pdi during AE directly correlated to Pdi(sniff) in the patients (r = 0.69, p = 0.004). Observed end-expiratory Ppl rose during arm elevation in both the patient group and in the normal control group, but no evidence of a differential response to AE was found. In those patients with greater diaphragm weakness (Pdi(sniff) < 30 cm H(2)O), abnormal respiratory muscle function (lesser rise in Pdi) and a lesser increase in VT during AE were more evident. These data highlight the importance of diaphragm function in determining the metabolic and respiratory muscle response to arm elevation.