The effect of acute non-invasive ventilation on corticospinal pathways to the respiratory muscles in chronic obstructive pulmonary disease

Ventilatory neural drive in chronically hypercapnic patients with COPD: effects of sleep and nocturnal noninvasive ventilation

Sleep brings major challenges for the control of ventilation in humans, particularly the regulation of arterial carbon dioxide pressure (P _aCO2 ). In patients with COPD, chronic hypercapnia is associated with increased mortality. Therefore, nocturnal high-level noninvasive positive-pressure ventilation (NIV) is recommended with the intention to reduce P _aCO2 down to normocapnia. However, the long-term physiological consequences of P _aCO2 "correction" on the mechanics of breathing, gas exchange efficiency and resulting symptoms (i.e. dyspnoea) remain poorly understood. Investigating the influence of sleep on the neural drive to breathe and its translation to the mechanical act of breathing is of foremost relevance to create a solid rationale for the use of nocturnal NIV. In this review, we critically discuss the mechanisms by which sleep influences ventilatory neural drive and mechanical consequences in healthy subjects and hypercapnic patients with advanced COPD. We then discuss the available literature on the effects of nocturnal NIV on ventilatory neural drive and respiratory mechanics, highlighting open avenues for further investigation.

Diaphragm dysfunction as a potential determinant of dyspnea on exertion in patients 1 year after COVID-19-related ARDS

Some COVID-19 patients experience dyspnea without objective impairment of pulmonary or cardiac function. This study determined diaphragm function and its central voluntary activation as a potential correlate with exertional dyspnea after COVID-19 acute respiratory distress syndrome (ARDS) in ten patients and matched controls. One year post discharge, both pulmonary function tests and echocardiography were normal. However, six patients with persisting dyspnea on exertion showed impaired volitional diaphragm function and control based on ultrasound, magnetic stimulation and balloon catheter-based recordings. Diaphragm dysfunction with impaired voluntary activation can be present 1 year after severe COVID-19 ARDS and may relate to exertional dyspnea.

This prospective case–control study was registered under the trial registration number NCT04854863 April, 22 2021

Diaphragmatic motor cortex hyperexcitability in patients with chronic obstructive pulmonary disease

Background and objectives

Respiratory muscles dysfunction has been reported in COPD. Transcranial magnetic stimulation (TMS) has been used for assessing the respiratory corticospinal pathways particularly of diaphragm. We aimed to study the cortico-diaphragmatic motor system changes in COPD using TMS and to correlate the findings with the pulmonary function.

Methods

A case control study recruited 30 stable COPD from the out-patient respiratory clinic of Main Alexandria University hospital- Egypt and 17 healthy control subjects who were subjected to spirometry. Cortical conduction of the diaphragm was performed by TMS to all participants followed by cervical magnetic stimulation of the phrenic nerve roots. Diaphragmatic resting motor threshold (DRMT), cortical motor evoked potential latency (CMEPL), CMEP amplitude (CMEPA), peripheral motor evoked potential latency (PMEPL), PMEP amplitude (PMEPA) and central motor conduction time (CMCT) were measured.

Results

66.7% of COPD patients had severe and very severe COPD with median age of 59 (55–63) years. There was statistically significant bilateral decrease in DRMT, CMEPA and PMEPA in COPD group versus healthy subjects and significant increase in CMEPL and PMEPL (p <0.01). Left CMCT was significantly prolonged in COPD group versus healthy subjects (p <0.0001) but not right CMCT. Further, there was significant increase in CMEPL and CMCT of left versus right diaphragm in COPD group (p = 0.003 and 0.001 respectively) that inversely correlated with FEV₁% and FVC% predicted. Right and left DRMT were insignificantly different in COPD group (p >0.05) but positively correlated with FEV₁/FVC, FEV₁% and FVC% predicted.

Conclusion

Central cortico-diaphragmatic motor system is affected in COPD patients with heterogeneity of both sides that is correlated with pulmonary function.

Significance

Coticospinal pathway affection could be a factor for development of diaphragmatic dysfunction in COPD patients accordingly its evaluation could help in personalization of COPD management especially pulmonary rehabilitation programs.

ERS statement on respiratory muscle testing at rest and during exercise

Assessing respiratory mechanics and muscle function is critical for both clinical practice and research purposes. Several methodological developments over the past two decades have enhanced our understanding of respiratory muscle function and responses to interventions across the spectrum of health and disease. They are especially useful in diagnosing, phenotyping and assessing treatment efficacy in patients with respiratory symptoms and neuromuscular diseases. Considerable research has been undertaken over the past 17 years, since the publication of the previous American Thoracic Society (ATS)/European Respiratory Society (ERS) statement on respiratory muscle testing in 2002. Key advances have been made in the field of mechanics of breathing, respiratory muscle neurophysiology (electromyography, electroencephalography and transcranial magnetic stimulation) and on respiratory muscle imaging (ultrasound, optoelectronic plethysmography and structured light plethysmography). Accordingly, this ERS task force reviewed the field of respiratory muscle testing in health and disease, with particular reference to data obtained since the previous ATS/ERS statement. It summarises the most recent scientific and methodological developments regarding respiratory mechanics and respiratory muscle assessment by addressing the validity, precision, reproducibility, prognostic value and responsiveness to interventions of various methods. A particular emphasis is placed on assessment during exercise, which is a useful condition to stress the respiratory system.

Is Inspiratory Muscle Weakness a Determinant of Endurance Exercise Tolerance During NIV-Supported Exercise in Patients With COPD?

PURPOSE

Previous research has reported that inspiratory muscle weakness is critical to decreased exercise tolerance and exercise tolerance improves with 10 cmH2O pressure support ventilation in patients with chronic obstructive pulmonary disease (COPD). The purpose of this study was to evaluate the effects of proportional assist ventilation (PAV) and continuous positive airway pressure (CPAP) compared with sham on exercise tolerance in patients with and without inspiratory muscle weakness.

METHODS

In a prospective design, 12 of 54 patients were eligible after clinical and comprehensive lung function evaluation, including maximum inspiratory pressure (MIP) measurement. Using baseline measures, participants were divided into 2 age-matched groups that differed in regard to MIP (Group 1, MIP <60 cmH2O, and Group 2, MIP ≥60 cmH2O). Each participant performed 3 constant work rate tests with noninvasive support (PAV, CPAP, sham) in random order on different days at 80% of maximal incremental power.

RESULTS

During the endurance tests, heart rate, peripheral oxygen saturation (SpO2), dyspnea perception scale, and exercise tolerance were measured. There were no significant differences between groups for heart rate, SpO2, dyspnea perception, or exercise tolerance during PAV, CPAP, or sham-supported exercise (P > .05 for all).

CONCLUSIONS

In this small representative group of patients with COPD, inspiratory muscle weakness was not a determining factor of performance during CPAP or PAV-supported aerobic exercise.

Neurophysiological Evidence for a Cortical Contribution to the Wakefulness-Related Drive to Breathe Explaining Hypocapnia-Resistant Ventilation in Humans

Spontaneous ventilation in mammals is driven by automatic brainstem networks that generate the respiratory rhythm and increase ventilation in the presence of increased carbon dioxide production. Hypocapnia decreases the drive to breathe and induces apnea. In humans, this occurs during sleep but not during wakefulness. We hypothesized that hypocapnic breathing would be associated with respiratory-related cortical activity similar to that observed during volitional breathing, inspiratory constraints, or in patients with defective automatic breathing (preinspiratory potentials). Nineteen healthy subjects were studied under passive (mechanical ventilation, n = 10) or active (voluntary hyperventilation, n = 9) profound hypocapnia. Ventilatory and electroencephalographic recordings were performed during voluntary sniff maneuvers, normocapnic breathing, hypocapnia, and after return to normocapnia. EEG recordings were analyzed with respect to the ventilatory flow signal to detect preinspiratory potentials in frontocentral electrodes and to construct time-frequency maps. After passive hyperventilation, hypocapnia was associated with apnea in 3 cases and ventilation persisted in 7 cases (3 and 6 after active hyperventilation, respectively). No respiratory-related EEG activity was observed in subjects with hypocapnia-related apneas. In contrast, preinspiratory potentials were present at vertex recording sites in 12 of the remaining 13 subjects (p < 0.001). This was corroborated by time-frequency maps. This study provides direct evidence of a cortical substrate to hypocapnic breathing in awake humans and fuels the notion of corticosubcortical cooperation to preserve human ventilation in a variety of situations. Of note, maintaining ventilatory activity at low carbon dioxide levels is among the prerequisites to speech production insofar as speech often induces hypocapnia.

SIGNIFICANCE STATEMENT

Human ventilatory activity persists, during wakefulness, even when hypocapnia makes it unnecessary. This peculiarity of human breathing control is important to speech and speech-breathing insofar as speech induces hypocapnia. This study evidences a specific respiratory-related cortical activity. This suggests that human hypocapnic breathing is driven, at least in part, by cortical mechanisms similar to those involved in volitional breathing, in breathing against mechanical constraints or with weak inspiratory muscle, and in patients with defective medullary breathing pattern generators. This fuels the notion that the human ventilatory drive during wakefulness often results from a corticosubcortical cooperation, and opens new avenues to study certain ventilatory and speech disorders.

Reduced survival in patients with ALS with upper airway obstructive events on non-invasive ventilation

INTRODUCTION

Non-invasive ventilation (NIV) is part of standard care in amyotrophic lateral sclerosis (ALS). Intolerance or unavailability of NIV, as well as the quality of correction of nocturnal hypoventilation, has a direct impact on prognosis.

OBJECTIVES

We describe the importance of NIV failure due to upper airway obstructive events, the clinical characteristics, as well as their impact on the prognosis of ALS.

METHODS

Retrospective analysis of the data of 190 patients with ALS and NIV in a single centre for the period 2011-2014. 179 patients tolerating NIV for more than 4 h per night without leaks were analysed.

RESULTS

Among the 179 patients, after correction of leaks, 73 remained inadequately ventilated at night (defined as more than 5% of the night spent at <90% of SpO2), as a result of obstructive events in 67% of cases (n=48). Patients who remained inadequately ventilated after optimal adjustment of ventilator settings presented with shorter survival than adequately ventilated patients. Unexpectedly, patients with upper airway obstructive events without nocturnal desaturation and in whom no adjustment of treatment was therefore performed also presented with shorter survival. On initiation of NIV, no difference was demonstrated between patients with and without upper airway obstructive events. In all patients, upper airway obstruction was concomitant with reduction of ventilatory drive.

CONCLUSIONS

This study shows that upper airway obstruction during NIV occurs in patients with ALS and is associated with poorer prognosis. Such events should be identified as they can be corrected by adjusting ventilator settings.

Cortical drive to breathe in amyotrophic lateral sclerosis: a dyspnoea-worsening defence?

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease causing diaphragm weakness that can be partially compensated by inspiratory neck muscle recruitment. This disappears during sleep, which is compatible with a cortical contribution to the drive to breathe. We hypothesised that ALS patients with respiratory failure exhibit respiratory-related cortical activity, relieved by noninvasive ventilation (NIV) and related to dyspnoea.

We studied 14 ALS patients with respiratory failure. Electroencephalographic recordings (EEGs) and electromyographic recordings of inspiratory neck muscles were performed during spontaneous breathing and NIV. Dyspnoea was evaluated using the Multidimensional Dyspnea Profile.

Eight patients exhibited slow EEG negativities preceding inspiration (pre-inspiratory potentials) during spontaneous breathing. Pre-inspiratory potentials were attenuated during NIV (p=0.04). Patients without pre-inspiratory potentials presented more advanced forms of ALS and more severe respiratory impairment, but less severe dyspnoea. Patients with pre-inspiratory potentials had stronger inspiratory neck muscle activation and more severe dyspnoea during spontaneous breathing.

ALS-related diaphragm weakness can engage cortical resources to augment the neural drive to breathe. This might reflect a compensatory mechanism, with the intensity of dyspnoea a negative consequence. Disease progression and the corresponding neural loss could abolish this phenomenon. A putative cognitive cost should be investigated.

Interactions Between Dyspnea and the Brain Processing of Nociceptive Stimuli: Experimental Air Hunger Attenuates Laser-Evoked Brain Potentials in Humans

Dyspnea and pain share several characteristics and certain neural networks and interact with each other. Dyspnea-pain counter-irritation consists of attenuation of preexisting pain by intercurrent dyspnea and has been shown to have neurophysiological correlates in the form of inhibition of the nociceptive spinal reflex RIII and laser-evoked potentials (LEPs). Experimentally induced exertional dyspnea inhibits RIII and LEPs, while “air hunger” dyspnea does not inhibit RIII despite its documented analgesic effects. We hypothesized that air hunger may act centrally and inhibit LEPs. LEPs were obtained in 12 healthy volunteers (age: 21–29) during spontaneous breathing (FB), ventilator-controlled breathing (VC) tailored to FB, after inducing air hunger by increasing the inspired fraction of carbon dioxide -FiCO₂- (VCCO₂), and during ventilator-controlled breathing recovery (VCR). VCCO₂ induced intense dyspnea (visual analog scale = 63% ± 6% of full scale, p < 0.001 vs. VC), predominantly of the air hunger type. VC alone reduced the amplitude of the N2-P2 component of LEPs (Δ = 24.0% ± 21.1%, p < 0.05, effect-size = 0.74) predominantly through a reduction in P2, and the amplitude of this inhibition was further reduced by inducting air hunger (Δ = 22.6% ± 17.9%, p < 0.05, effect-size = 0.53), predominantly through a reduction in N2. Somatosensory-evoked potentials (SEPs) were not affected by VC or VCCO₂, suggesting that the observed effects are specific to pain transmission. We conclude that air hunger interferes with the cortical mechanisms responsible for the cortical response to painful laser skin stimulation, which provides a neurophysiological substrate to the central nature of its otherwise documented analgesic effects.

Neural respiratory drive and breathlessness in COPD

The aim of this study was to test the hypothesis that neural respiratory drive, measured using diaphragm electromyogram (EMGdi) activity expressed as a percentage of maximum (EMGdi%max), is closely related to breathlessness in chronic obstructive pulmonary disease. We also investigated whether neuroventilatory uncoupling contributes significantly to breathlessness intensity over an awareness of levels of neural respiratory drive alone. EMGdi and ventilation were measured continuously during incremental cycle and treadmill exercise in 12 chronic obstructive pulmonary disease patients (forced expiratory volume in 1 s±sd was 38.7±14.5 % pred). EMGdi was expressed both as EMGdi%max and relative to tidal volume expressed as a percentage of predicted vital capacity to quantify neuroventilatory uncoupling. EMGdi%max was closely related to Borg breathlessness in both cycle (r=0.98, p=0.0001) and treadmill exercise (r=0.94, p=0.005), this relationship being similar to that between neuroventilatory uncoupling and breathlessness (cycling r=0.94, p=0.005; treadmill r=0.91, p=0.01). The relationship between breathlessness and ventilation was poor when expansion of tidal volume became limited. In chronic obstructive pulmonary disease the intensity of exertional breathlessness is closely related to EMGdi%max. These data suggest that breathlessness in chronic obstructive pulmonary disease can be largely explained by an awareness of levels of neural respiratory drive, rather than the degree of neuroventilatory uncoupling. EMGdi%max could provide a useful physiological biomarker for breathlessness in chronic obstructive pulmonary disease.

Unrecognized suffering in the ICU: addressing dyspnea in mechanically ventilated patients

BACKGROUND

Intensive care unit (ICU) patients are exposed to many sources of discomfort. Although increasing attention is being given to the detection and treatment of pain, very little is given to the detection and treatment of dyspnea (defined as "breathing discomfort").

METHODS

Published information on the prevalence, mechanisms, and potential negative impacts of dyspnea in mechanically ventilated patients are reviewed. The most appropriate tools to detect and quantify dyspnea in ICU patients are also assessed.

RESULTS/CONCLUSIONS

Growing evidence suggests that dyspnea is a frequent issue in mechanically ventilated ICU patients, is highly associated with anxiety and pain, and is improved in many patients by altering the ventilator settings.

CONCLUSIONS

Future studies are needed to better delineate the impact of dyspnea in the ICU and to define diagnostic, monitoring and therapeutic protocols.

Transcranial direct-current stimulation reduced the excitability of diaphragmatic corticospinal pathways whatever the polarity used

We investigated effects of transcranial direct-current stimulation (tDCS) on the diaphragmatic corticospinal pathways in healthy human. Anodal, cathodal, and sham tDCS were randomly applied upon the left diaphragmatic motor cortex in twelve healthy right-handed men. Corticospinal pathways excitability was assessed by means of transcranial magnetic stimulation (TMS) elicited motor-evoked-potential (MEP). For each tDCS condition, MEPs were recorded before (Pre) tDCS then after 10 min (Post1, at tDCS discontinuation in the anodal and cathodal sessions) and 20 min (Post2). As result, both anodal and cathodal tDCS significantly decreased MEP amplitude of the right hemidiaphragm at both Post1 and Post2, versus Pre. MEP amplitude was unchanged versus Pre during the sham condition. The effects of cathodal and anodal tDCS applied to the diaphragm motor cortex differ from those observed during tDCS of the limb motor cortex. These differences may be related to specific characteristics of the diaphragmatic corticospinal pathways as well as to the diaphragm's functional peculiarities compared with the limb muscles.

Singing classes for chronic obstructive pulmonary disease: a randomized controlled trial

BACKGROUND

There is some evidence that singing lessons may be of benefit to patients with chronic obstructive pulmonary disease (COPD). It is not clear how much of this benefit is specific to singing and how much relates to the classes being a group activity that addresses social isolation.

METHODS

Patients were randomised to either singing classes or a film club for eight weeks. Response was assessed quantitatively through health status questionnaires, measures of breathing control, exercise capacity and physical activity and qualitatively, through structured interviews with a clinical psychologist.

RESULTS

The singing group (n=13 mean(SD) FEV1 44.4(14.4)% predicted) and film group (n=11 FEV1 63.5(25.5)%predicted) did not differ significantly at baseline. There was a significant difference between the response of the physical component score of the SF-36, favouring the singing group +12.9(19.0) vs -0.25(11.9) (p=0.02), but no difference in response of the mental component score of the SF-36, breathing control measures, exercise capacity or daily physical activity. In the qualitative element, positive effects on physical well-being were reported in the singing group but not the film group.

CONCLUSION

Singing classes have an impact on health status distinct from that achieved simply by taking part in a group activity.

TRIALS REGISTRATION

Registration Current Controlled Trials - ISRCTN17544114.

Central and peripheral quadriceps fatigue in congestive heart failure

AIMS

The clinical syndrome of heart failure includes exercise limitation that is not directly linked to measures of cardiac function. Quadriceps fatigability may be an important component of this and this may arise from peripheral or central factors.

METHODS AND RESULTS

We studied 10 men with CHF and 10 healthy age-matched controls. Compared with a rest condition, 10 min after incremental maximal cycle exercise, twitch quadriceps force in response to supramaximal magnetic femoral nerve stimulation fell in both groups (CHF 14.1% ± 18.1%, p=0.037;

CONTROL

20.8 ± 11.0%, p<0.001; no significant difference between groups). There was no significant change in quadriceps maximum voluntary contraction voluntary force. The difference in the motor evoked potential (MEP) response to transcranial magnetic stimulation of the motor cortex between rest and exercise conditions at 10 min, normalised to the peripheral action potential, also fell significantly in both groups (CHF: 27.3 ± 38.7%, p=0.037;

CONTROL

41.1 ± 47.7%, p=0.024). However, the fall in MEP was sustained for a longer period in controls than in patients (p=0.048).

CONCLUSIONS

The quadriceps is more susceptible to fatigue, with a similar fall in TwQ occurring in CHF patients at lower levels of exercise. This is associated with no change in voluntary activation but a lesser degree of depression of quadriceps motor evoked potential.