Capucine Morélot-Panzini

Electroencephalographic evidence for pre-motor cortex activation during inspiratory loading in humans

Faced with mechanical inspiratory loading, awake animals and anaesthetized humans develop alveolar hypoventilation, whereas awake humans do defend ventilation. This points to a suprapontine compensatory mechanism instead of or in addition to the ‘traditional’ brainstem respiratory regulation. This study assesses the role of the cortical pre‐motor representation of inspiratory muscles in this behaviour. Ten healthy subjects (age 19–34 years, three men) were studied during quiet breathing, CO2‐stimulated breathing, inspiratory resistive loading, inspiratory threshold loading, and during self‐paced voluntary sniffs. Pre‐triggered ensemble averaging of Cz EEG epochs starting 2.5 s before the onset of inspiration was used to look for pre‐motor activity. Pre‐motor potentials were present during voluntary sniffs in all subjects (average latency (±s.d.): 1325 ± 521 ms), but also during inspiratory threshold loading (1427 ± 537 ms) and during inspiratory resistive loading (1109 ± 465 ms). Pre‐motor potentials were systematically followed by motor potentials during inspiratory loading. Pre‐motor potentials were lacking during quiet breathing (except in one case) and during CO2‐stimulated breathing (except in two cases). The same pattern was observed during repeated experiments at an interval of several weeks in a subset of three subjects. The behavioural component of inspiratory loading compensation in awake humans could thus depend on higher cortical motor areas. Demonstrating a similar role of the cerebral cortex in the compensation of disease‐related inspiratory loads (e.g. asthma attacks) would have important pathophysiological implications: it could for example contribute to explain why sleep is both altered and deleterious in such situations.

Dyspnea in mechanically ventilated critically ill patients.

Objectives:Ensuring the comfort of intensive care unit patients is crucial. Although control of pain has been extensively addressed in this setting, data on dyspnea in mechanically ventilated patients are scant. The objective of this study was to assess the prevalence of dyspnea in mechanically ventilated patients, identify its clinical correlates, and examine its impact on clinical outcomes. Design:Prospective 6-month observational study. Setting:Two medical intensive care units within university hospitals. Participants:Intubated or tracheotomized patients who were mechanically ventilated for >24 hrs. We enrolled 96 patients (age, 61 ± 18 yrs; Simplified Acute Physiology Score II 43 [interquartile range, 31–60]) as soon as they could answer symptom-related questions. Dyspnea was evaluated on a “yes–no” basis; if yes, it was followed by a visual analog scale and descriptor choice (“air hunger” and/or “respiratory effort”). Pain and anxiety were also assessed by visual analog scales. Interventions:Ventilator settings adjustment in dyspneic patients. Measurements and Main Results:Forty-five patients (47%) reported dyspnea (respiratory effort in seven cases, air hunger in 15, both in 16, and neither of these in seven). Dyspneic and nondyspneic patients did not differ in terms of age, Simplified Acute Physiology Score II, indication for mechanical ventilation, respiratory rate, clinical examination, chest radiograph, or blood gases. Dyspnea was significantly associated with anxiety (odd ratio [OR], 8.84; 95% confidence interval [CI], 3.26–24.0), assist-control ventilation (OR, 4.77; 95% CI, 1.60–4.3), and heart rate (OR, 1.33 per 10 beats/min; 95% CI, 1.02–1.75). Adjusting ventilator settings improved dyspnea in 35% of patients. Successful extubation within 3 days was significantly less frequent in patients whose dyspnea failed to recede after adjusting ventilator settings (five [17%] vs. 27 [40%]; p = .034). Conclusions:Dyspnea is frequent, intense, and strongly associated with anxiety in mechanically ventilated patients. It can be sensitive to ventilator settings and seems to be associated with delayed extubation.

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

BackgroundIntensive 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”).MethodsPublished 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/ConclusionsGrowing 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.ConclusionsFuture studies are needed to better delineate the impact of dyspnea in the ICU and to define diagnostic, monitoring and therapeutic protocols.

Diaphragm pacing restores olfaction in tetraplegia

High cervical spinal cord injuries induce extreme handicap and tactile isolation. Tracheotomised tetraplegic patients are also bound to be olfaction deprived. By restoring negative pressure inspiration, diaphragm pacing (DP) should improve olfaction. We tested olfaction in 10 consecutive tetraplegics during positive pressure mechanical ventilation and DP, using the University of Pennsylvania Smell Identification Test (UPSIT). Quality of life was assessed using the Satisfaction with Life Scale (SWLS). Self-perceived benefits of DP were studied using an in-house questionnaire. Olfaction was very poor during positive pressure mechanical ventilation (UPSIT, mean±sd 17.1±6.4, anosmia or severe microsmia). It improved during DP (35.2±1.9, normosmia or mild microsmia; p<0.0001) and SWLS was 18.5±4.2. Nine patients stated that DP had improved their quality of life. This was driven by better mobility (ranked first), improved self-image and relationships with others (ranked second), improved olfaction and better feeling of security (both ranked third). Improved olfaction is among the benefits of DP and should be mentioned to patients considered for this therapy. Furthermore, attention to olfaction is warranted in tracheotomised ventilator-dependent patients, as a putative path towards improvement of quality of life.

A comparison of assisted cough techniques in stable patients with severe respiratory insufficiency due to amyotrophic lateral sclerosis

Abstract Cough can be impaired in ALS. This can result in peak cough flows (PCFs) too low for an adequate airway clearance (<270 l/mn). There are several cough assistance techniques that aim at a better elimination of airway secretions, but which are effective, especially in bulbar patients, is not known. We designed the present investigation to compare the PCFs produced by a range of manual and mechanical techniques in patients with ALS, in non-bulbar but also in bulbar patients. In the whole study population, PCFs ranged from 84 (35–118) l/mn for the spontaneous cough manoeuvre to 488 (243–605) l/min for the in/exsufflator (p = 0.0005). In the bulbar group, these values were 42 (35–130) l/min versus 436 (244–630) l/min, respectively (p = 0.008), and 89 (40–106) l/min versus 491 (192–580) l/min, respectively, in the non-bulbar group (p = 0.019). There was no statistically significant difference between the bulbar and the non-bulbar groups. The in/exsufflator was not always the best tool. We conclude that capacity of coughing efforts to produce efficient peak cough flows can be dramatically improved with different tools, even in patients with very severe bulbar symptoms and that it appears useful to test an array of techniques to optimally tailor cough improvement techniques to individual patients.

Scalene muscle activity during progressive inspiratory loading under pressure support ventilation in normal humans

We hypothesized that (1) in healthy humans subjected to intermittent positive pressure non-invasive ventilation, changes in the ventilator trigger sensitivity would be associated with increased scalene activity, (2) if properly processed - through inspiratory phase-locked averaging - surface electromyograms (EMG) of the scalenes would reliably detect and quantify this, (3) there would be a correlation between dyspnea and scalene EMG. Surface and intramuscular EMG activity of scalene muscles were measured in 10 subjects. They breathed quietly through a face mask for 10min and then were connected to a mechanical ventilator. Recordings were performed during three 15-min epochs where the subjects breathed against an increasingly negative pressure trigger (-5%, -10% and -15% of maximal inspiratory pressure). With increasing values of the inspiratory trigger, inspiratory efforts, dyspnea and the scalene activity increased significantly. The scalene EMG activity level was correlated with the esophageal pressure time product and with dyspnea intensity. Inspiration-adjusted surface EMG averaging could be useful to detect small increases of the scalene muscles activity during mechanical ventilation.

Intrathoracic phrenic pacing: A 10-year experience in France

BACKGROUND Phrenic pacing is an alternative to positive-pressure ventilation in selected patients, mostly in cases of upper spinal cord injury. We evaluated results of phrenic pacing performed by video-assisted thoracic surgery (VATS). METHOD Between 1997 and 2007, after complete neuromuscular investigations, 20 patients requiring full-time ventilation were selected for phrenic pacing (19 with posttraumatic tetraplegia and 1 with congenital central hypoventilation syndrome). Quadripolar cuff electrodes were fixed around each intrathoracic phrenic nerve via bilateral VATS. They were connected to a subcutaneous radiofrequency receiver coupled to an external radiofrequency transmitter. All patients participated in a reconditioning program beginning 2 weeks after implantation and continued until ventilatory weaning. RESULTS Phrenic pacing was successful in all cases. No intraoperative complications or perioperative mortality were observed. Intraoperative testing detected stimulation thresholds in 19 patients (range, 0.05-2.9 mA). Ventilatory weaning was obtained in 18 patients. Median diaphragm reconditioning time was 6 weeks (2 weeks-11 months). Reconditioning was still in process in a young woman and was not achieved in an elderly woman with a 4-year history of tetraplegia. All the patients weaned from mechanical ventilation reported improved quality of life. Failure or delay in recovery of effective diaphragm contraction was due to nonreversible amyotrophy. CONCLUSIONS VATS implantation of 4-pole electrodes around the intrathoracic phrenic nerve is a safe procedure. Ventilatory weaning correlates with the degree of diaphragmatic amyotrophy. Phrenic pacing, performed as soon as neurologic and orthopedic stabilization is achieved, is the most important prognostic factor for successful weaning.

Diaphragm pacing improves sleep in patients with amyotrophic lateral sclerosis

Abstract In amyotrophic lateral sclerosis (ALS) patients, respiratory insufficiency is a major burden. Diaphragm conditioning by electrical stimulation could interfere with lung function decline by promoting the development of type 1 muscle fibres. We describe an ancillary study to a prospective, non-randomized trial (NCT00420719) assessing the effects of diaphragm pacing on forced vital capacity (FVC). Sleep-related disturbances being early clues to diaphragmatic dysfunction, we postulated that they would provide a sensitive marker. Stimulators were implanted laparoscopically in the diaphragm close to the phrenic motor point in 18 ALS patients for daily conditioning. ALS functioning score (ALSFRS), FVC, sniff nasal inspiratory pressure (SNIP), and polysomnographic recordings (PSG, performed with the stimulator turned off) were assessed before implantation and after four months of conditioning (n = 14). Sleep efficiency improved (69 ± 15% to 75 ± 11%, p = 0.0394) with fewer arousals and micro-arousals. This occurred against a background of deterioration as ALSFRS-R, FVC, and SNIP declined. There was, however, no change in NIV status or the ALSFRS respiratory subscore, and the FVC decline was mostly due to impaired expiration. Supporting a better diaphragm function, apnoeas and hypopnoeas during REM sleep decreased. In conclusion, in these severe patients not expected to experience spontaneous improvements, diaphragm conditioning improved sleep and there were hints at diaphragm function changes.

Functional magnetic resonance imaging suggests automatization of the cortical response to inspiratory threshold loading in humans

Inspiratory threshold loading (ITL) induces cortical activation. It is sustained over time and is resistant to distraction, suggesting automaticity. We hypothesized that ITL-induced changes in cerebral activation may differ between single-breath ITL and continuous ITL, with differences resembling those observed after cortical automatization of motor tasks. We analyzed the brain blood oxygen level dependent (BOLD) signal of 11 naive healthy volunteers during 5 min of random, single-breath ITL and 5 min of continuous ITL. Single-breath ITL increased BOLD in many areas (premotor cortices, bilateral insula, cerebellum, reticular formation of the lateral mesencephalon) and decreased BOLD in regions co-localizing with the default mode network. Continuous ITL induced signal changes in a limited number of areas (supplementary motor area). These differences are comparable to those observed before and after overlearning of motor tasks. We conclude that the respiratory-related cortical activation observed in response to ITL is likely due to automated, attention-independent mechanisms. Also, ITL activates cortical circuits right from the first breath.

Optimized analysis of surface electromyograms of the scalenes during quiet breathing in humans

Studying the inspiratory recruitment of the scalenes is clinically relevant, but the interpretation of surface electromyographic (EMG) recordings is difficult. The aim of this study was to optimize an averaging method to analyze the surface EMG activity of the scalenes. Ten healthy subjects were studied. Nasal flow and surface EMG of the right scalene were recorded during 15 min epochs of quiet breathing. In four subjects, needle scalene EMG was also recorded. The flow signal was used to trigger the ensemble averaging of the ventilatory wave forms from 80 consecutive breaths. In eight cases, this evidenced a phasic inspiratory activation of the scalenes and permitted the determination of the electromechanical inspiratory delay (134+/-55 ms) and post-inspiratory activity (811+/-233 ms). When simultaneously available, surface and intramuscular recordings provided identical results. An averaging method triggered from a respiratory flow signal can identify and characterize a low phasic inspiratory activity of the scalenes within a noisy surface signal.