Airway Pressure Generation Research Articles

Comparison of disc and wire electrodes to restore cough via lower thoracic spinal cord stimulation

Objective To compare the safety and effectiveness of wire (WE) vs. disc (DE) electrodes to restore cough in subjects with spinal cord injury (SCI). Design Clinical trials assessing the effectiveness and clinical outcomes associated with two electrode systems to activate the expiratory muscles. Setting Inpatient hospital setting for DE or WE electrode insertion; outpatient evaluation of cough efficacy and instructions for home use. Participants Twenty-nine subjects with SCI; 17 participants with DE and 12 with WE implants. Intervention Surgical implantation of WE or DE to restore cough. Daily application of spinal cord stimulation (SCS) at home. Main outcome measure(s) Airway pressure (P) and peak airflow (F) generation achieved with SCS; clinical parameters including ease in raising secretions, incidence of acute respiratory tract infections (RTI) and side effects. Results P and F achieved with DE and WE were not significantly different. For example, at total lung capacity (TLC) with participant effort, P was 128 ± 12 cmH2O and 118 ± 14 cmH2O, with DE and WE, respectively. The degree of difficulty in raising secretions improved markedly in both groups. The incidence of RTI per year fell from 1.3 ± 0.3 and 1.3 ± 0.5–0.3 ± 0.1 and 0.1 ± 0.1 for DE and WE groups, respectively (P < 0.01 for both when compared to pre-implant values and NS between DE and WE groups). The only significant side effect i.e. short-term autonomic dysreflexia was also similar between groups. Conclusions The results of this investigation indicate that both DE and WE result in comparable degrees of expiratory muscle activation, clinical benefits and side effects. Importantly, SCS to restore cough can be achieved with use of WE which can be placed using minimally invasive techniques and associated reduction in cost, surgical time and overall risk. Trial registration: ClinicalTrials.gov identifier: NCT00116337., NCT01659541, FDA IDE: G980267

Effects of nasal high flow on nocturnal hypercapnia, sleep, and sympathovagal balance in patients with neuromuscular disorders

PurposeIn neuromuscular disorders (NMD), inspiratory muscle weakness may cause sleep-related hypoventilation requiring non-invasive ventilation (NIV). Alternatively, nasal high flow therapy (NHF) may ameliorate mild nocturnal hypercapnia (NH) through washout of anatomical dead space and generation of positive airway pressure. Ventilatory support by NIV or NHF might have favourable short-term effects on sympathovagal balance (SVB). This study comparatively investigated the effects of NHF and NIV on sleep-related breathing and SVB in NMD patients with evolving NH.MethodsTranscutaneous CO2 (ptcCO2), peripheral oxygen saturation (SpO2), sleep outcomes and SVB (spectral analysis of heart rate, diastolic blood pressure variability) along with haemodynamic measures (cardiac index, total peripheral resistance index) were evaluated overnight in 17 patients. Polysomnographies (PSG) were randomly split into equal parts with no treatment, NIV and NHF at different flow rates (20 l/min vs. 50 l/min). In-depth analysis of SVB and haemodynamics was performed on 10-min segments of stable N2 sleep taken from each intervention.ResultsCompared with no treatment, NHF20 and NHF50 did not significantly change ptcCO2, SpO2 or the apnea hypopnea index (AHI). NHF50 was poorly tolerated. In contrast, NIV significantly improved both gas exchange and AHI without adversely affecting sleep. During daytime, NHF20 and NHF50 had neutral effects on ventilation and oxygenation whereas NIV improved ptcCO2 and SpO2. Effects of NIV and NHF on SVB and haemodynamics were neutral during both night and daytime.ConclusionsNHF does not correct sleep-disordered breathing in NMD patients with NH. Both NHF and NIV exert no immediate effects on SVB.

Effects of Lower Thoracic Spinal Cord Stimulation on Bowel Management in Individuals With Spinal Cord Injury

ObjectiveTo systematically determine whether use of the spinal cord stimulation (SCS) system to restore cough may improve bowel management (BM) in individuals with spinal cord injury (SCI). DesignExperimental studies (clinical trial). SettingInpatient hospital setting for electrode insertion; outpatient setting for measurement of respiratory pressures; home setting for application of SCS. ParticipantsParticipants (N=5) with cervical SCI. InterventionA fully implantable SCS cough system was surgically placed in each subject. SCS was applied at home, 2-3 times/d, on a chronic basis, every time bowel regimen was performed and as needed for secretion management. Stimulus parameters were set at values resulting in near maximum airway pressure generation, which was used as an index of expiratory muscle strength. Participants also used SCS during their bowel routine. Main Outcome MeasuresAirway pressure generation achieved with SCS. Weekly completion of Bowel Routine Log including BM time, mechanical measures, and medications used. ResultsMean pressure during spontaneous efforts was 30±8 cmH2O. After a period of reconditioning, SCS resulted in pressure of 146±21 cmH2O. The time required for BM routines was reduced from 118±34 minutes to 18±2 minutes (P<.05) and was directly related to the magnitude of pressure development during SCS. Mechanical methods for BM were completely eliminated in 4 patients. No patients experienced fecal incontinence as result of SCS. Each participant also reported marked overall improvement associated with BM. ConclusionsOur results of this pilot study suggest that SCS to restore cough may be a useful method to improve BM and life quality for both patients with SCI and their caregivers. Our results indicate that the improvement in BM is secondary to restoration of intra-abdominal pressure development.

Comparison of Wire and Disc Leads to Activate the Inspiratory Muscles in Dogs

ObjectiveHF‐SCS is a unique method of inspiratory muscle activation which results in coincident activation of the diaphragm and inspiratory intercostal muscles via spinal cord pathways and has the potential to provide respiratory support in ventilator dependent persons with spinal cord injury (SCI). The purpose of the present study was to examine the effectiveness of wire leads, which can be placed using minimally invasive techniques, to activate the inspiratory muscles.MethodsIn 5 anesthetized dogs, in separate trials, disc and wire leads were inserted onto the ventral epidural space at the T1–T4 spinal cord levels. The effects of electrical stimulation with disc, single wire, and two wire leads placed in parallel were compared.Outcome measuresAirway pressure generation following stimulation with disc and various configurations of wire leads were compared.ResultsSeveral different configurations of wire leads resulted in airway pressures that were similar to those generated with monopolar stimulation with disc leads (D). For example, monopolar stimulation (3mA, 300Hz, 0.2ms) with parallel wire leads in which each of the electrode contacts at the T2 were connected together and functioned as a common cathode (Y‐connection) and monopolar stimulation (separate cathode) at T2 both with a remote ground resulted in airway pressures that were 91±6 and 92±4%, respectively, of those achieved with D (NS for both). Bipolar stimulation (3mA, 300Hz, 0.2ms) with parallel wire leads using Y‐connection and with a separate cathode at the T2 and T3 level resulted in airway pressures that were 96 ± 4 and 94 ± 4%, respectively, of the pressures achieved with D (NS for both).ConclusionThese results suggest that specific configurations of wire leads, which can be placed via minimally invasive techniques, result in comparable activation of the inspiratory muscles compared to disc leads and may be a useful technique to restore ventilatory support in persons with SCI.Support or Funding InformationSupportNIH‐NINDS (R01NS064157)DisclosureDr. DiMarco is a founder of and has a significant financial interest in Synapse BioMedical, a manufacturer of diaphragm pacing systems and holds patents for spinal cord stimulation to restore cough and respiration (5,678,535; 5,911,218; 5,999,855; 8,751,004). Drs. DiMarco and Kowalski hold the U.S. patents for technology related to the content of this manuscript: Respiratory Muscle Activation by Spinal Cord Stimulation (8,352,036).

Diagnostic Accuracy of Positive Airway Pressure Device for Sleep Apnea Detection in Acute Stroke Patients.

Background and Purpose- Sleep apnea has been associated with a poor outcome in acute stroke patients. Polysomnography is the gold standard diagnostic method for sleep apnea, but it is not feasible as a routine in the acute stroke setting. The current generation of positive airway pressure (PAP) devices can detect the different types of respiratory events. This study aimed to compare the algorithms used in PAP device to manually scored events on polysomnography in patients with acute stroke. Methods- A sleep study was performed with standard polysomnography and PAP device, simultaneously, within the first 48 hours after acute stroke onset. Results- We prospectively evaluated 29 patients with acute stroke (59.5±12.1 years). The area under the receiver operating characteristic curve for each apnea-hypopnea index value was above 0.90 by PAP device. There was a good correlation of apnea-hypopnea index (rs=0.92; P<0.001), hypopnea index (rs=0.89; P<0.001), and apnea index (rs=0.70; P<0.001) between device-detected events and manually scored polysomnography. Conclusions- Given the high frequency of sleep apnea during the acute phase of stroke and the complexity of a full polysomnography study in this setting, PAP device on diagnostic mode can be used as an alternative tool for sleep apnea detection in acute stroke patients.

Inspiratory muscle activation via ventral lower thoracic high-frequency spinal cord stimulation.

In animals, high-frequency spinal cord stimulation (HF-SCS) applied on the ventral epidural surface at the T2 level results in negative airway pressure generation consistent with inspiratory muscle activation. In the present study, in anesthetized dogs, we found that ventral HF-SCS (500 Hz) applied at all thoracic levels resulted in negative airway pressure generation. In the region of the lower thoracic spinal cord, negative airway pressure generation was most pronounced at the T9 level. At this level, airway pressure generation was monitored: 1) during ventral HF-SCS over a wide range of stimulus amplitudes (0.5-15 mA) and frequencies (50-1,000 Hz) and 2) following spinal sections at C8 (to assess potential diaphragm activation) and subsequently at T6 (to assess potential intercostal muscle activation). The application of low stimulus currents between 1 and 2 mA and high stimulus frequencies (>300 Hz) resulted in the development of large negative airway pressure generation. Stimulation with 1 mA, 500 Hz resulted in a highest negative airway pressure generation of 47 ± 2 cmH2O. Increasing stimulus current was associated with progressive reductions in the magnitude of negative airway pressure generation. HF-SCS (500 Hz) with 15 mA resulted in a negative airway pressure generation of 7 ± 3 cmH2O. C8 section markedly reduced negative airway pressure generation, and subsequent T6 section resulted in positive airway pressure generation after HF-SCS. Our results indicate the existence of pathways with connections to both the phrenic and inspiratory intercostal motoneuron pools in the ventral part of the lower thoracic spinal cord. We speculate that the circuits mediating the previously described excitatory intercostal-to-phrenic reflex mediate the observed responses. NEW & NOTEWORTHY This study suggests that, in contrast to dorsal high-frequency spinal cord stimulation at the T9 spinal level, which results in positive pressure generation, ventral high-frequency spinal cord stimulation at the same spinal level results in large negative airway pressure generation with low stimulus currents. This method, therefore, may provide an alternative method to restore ventilation in ventilator-dependent spinal cord-injured patients.

Differential Activation of Respiratory Muscles during Lower Thoracic High Frequency Spinal Cord Stimulation (HF‐SCS)

ObjectiveLower thoracic HF‐SCS (500 Hz, 1 mA) applied via a single stimulating electrode located on the dorsal surface of the spinal cord at the T9 level results in large positive airway pressures consistent with marked expiratory muscle activation. The purpose of the present study was to evaluate the effects of lower thoracic HF‐SCS on the ventral surface at this spinal level.MethodsIn 4 anesthetized dogs, HF‐SCS was applied via a stimulating electrode (4 mm disc) positioned on the ventral surface of the spinal cord at the T9 level. Airway pressure generation was monitored before and following spinal sections at the C8 (to eliminate potential diaphragm activation) and subsequently at the T6 (to eliminate potential intercostal muscle activation) levels.ResultsHF‐SCS (500 Hz, 1 mA) on the ventral surface, results in inspiratory airway pressure generation of 40 ± 3 cmH2O. Following complete C8 spinal section, HF‐SCS results in a significant reduction in negative airway pressure generation to 14 ± 1 cmH2O (p&lt;0.05). Subsequent section at the T6 level, HF‐SCS results in a positive airway pressure of 10±1 cmH2O (p&lt;0.05 when compared to before either section).ConclusionIn contrast to dorsal stimulation, lower thoracic ventral HF‐SCS (500 Hz, 1 mA), at T9 results in activation of pathways with connections to both the phrenic and inspiratory intercostal motoneuron pools resulting in the generation of the large negative airway pressures and minimal expiratory muscle activation. Under the experimental conditions of this study, neuronal pathways with connections to the inspiratory and expiratory motoneuron pools are each limited anatomically to specific regions of the spinal cord. These anatomic differences allow for separate activation of the inspiratory and expiratory muscles to restore function.Support or Funding InformationSupport: Merit Review Award I01‐RX‐001488 from the U.S. Department of Veterans Affairs, Rehabilitation Research and Development Service.Disclosure: Dr. DiMarco holds two U.S. patents for technology related to the content of this abstract: Method and Apparatus for Electrical Activation of the Expiratory Muscles to Restore Cough (5,999,855) and Bipolar Spinal Cord Stimulation to Activate the Expiratory Muscles to Restore Cough (8,751,004).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract TMP88: High Accuracy of Auto-CPAP for Obstructive Sleep Apnea in Acute Stroke Patients

Background: Obstructive sleep apnea (OSA) is very common in acute stroke patients and has been associated with a poor short-term and long-term outcome. Polysomnography (PSG) is the gold standard diagnostic method for OSA, but it is not feasible as a routine for all acute stroke patients. Therefore, it is essential to validade alternative methods to accurately diagnose OSA in acute stroke patients. The newest generation of automatic continuous positive airway pressure (auto-CPAP) devices innovates by the possibility of detecting the different types of respiratory events. However, the accuracy of auto-CPAP devices for OSA diagnosis has never been tested in comparison to PSG in the acute stroke setting. The main objective of this study was to evaluate the accuracy of an auto-CPAP device to diagnose OSA and to validate its algorithm of respiratory events detection to diagnose OSA in patients during the acute phase of stroke. Methods: A sleep study was performed with PSG and auto-CPAP device, simultaneously, within the first 48 hours after the acute stroke onset. The Receiver Operating Characteristic Curve (ROC), C-statistics, Spearman correlation coefficient, and intraclass correlation coefficient were analyzed. Results: We prospectively evaluated 31 adult patients with acute stroke. The mean age was 59.7 ± 12 years and 60% were males. All patients used auto-CPAP for longer than 4 hours. The PSG revealed an apnea-hypopnea index (AHI) mean of 34 ± 41 events/h, and the auto-CPAP showed an AHI of 18 ± 16 events/h. The area under the ROC curve for OSA diagnosis by the auto-CPAP was above 0.90, with sensitivity and specificity above 80% for each AHI value. The Spearman correlation coefficients (rs) of the AHI, of the hypopnea index, of the obstructive apnea index and of the central apnea index were 0.92; 0.89; 0.63 and 0.62, respectively. The intraclass correlation coefficients between device-detected and PSG manually scored events were 0.60 for AHI, 0.64 for hypopnea index, and 0.45 for apnea index. Conclusion: The auto-CPAP showed an excellent accuracy for the diagnosis of OSA and it was well tolerated by acute stroke patients. Our results suggest that auto-CPAP should be considered as the preferred diagnostic tool for OSA diagnosis during the acute phase of stroke.

Effects of expiratory muscle activation via high-frequency spinal cord stimulation.

In persons with spinal cord injury, lower thoracic low-frequency spinal cord stimulation (LF-SCS; 50 Hz, 15 mA) is a useful method to restore an effective cough. Unfortunately, the high-stimulus-amplitude requirements and potential activation of pain fibers significantly limit this application in persons with intact sensation. In this study, the mechanism of the expiratory muscle activation, via high-frequency SCS (HF-SCS; 500 Hz, 1 mA) was evaluated in dogs. In group 1, the effects of electrode placement on airway pressure generation (P) was evaluated. Maximal P occurred at the T9-T10 level with progressive decrements in P at more rostral and caudal levels for both LF-SCS and HF-SCS. In group 2, electromyographic (EMG) latencies of internal intercostal muscle (II) activation were evaluated before and after spinal root section and during direct motor root stimulation. Onset time of II EMG activity during HF-SCS was significantly longer (3.84 ± 1.16 ms) than obtained during direct motor root activation (1.61 ± 0.10 ms). In group 3, P and external oblique (EO) EMG activity, before and after sequential spinal section at the T11-T12 level, were evaluated. Bilateral dorsal column section significantly reduced EO EMG activity below the section and resulted in a substantial fall in P. Subsequent lateral funiculi section completely abolished those activities and resulted in further reductions in P. We conclude that 1) activation of the expiratory muscles via HF-SCS is dependent entirely on synaptic spinal cord pathways, and 2) HF-SCS at the T9 level produces a comparable level of muscle activation with that achieved with LF-SCS but with much lower stimulus amplitudes. NEW & NOTEWORTHY The findings in the present study suggest that lower thoracic high-frequency spinal cord stimulation with low stimulus currents results in sufficient activation of the expiratory muscles via spinal circuitry to produce large positive airway pressures sufficient to generate an effective cough mechanism. This method, therefore, may be applied in patient populations with intact sensation such as stroke and amyotrophic lateral sclerosis to restore an effective cough.

Safety assessment of epidural wire electrodes for cough production in a chronic pig model of spinal cord injury

BackgroundIt is our hypothesis that high intensity spinal cord stimulation (SCS) to restore an effective cough mechanism using wire leads, will result in significant activation of target neurons without tissue injury or electrode corrosion. MethodsAdult mini-pigs underwent chronic spinal cord compression, followed by implantation of parallel wire leads on the dorsal epidural surface of the spinal cord, with stimulation contacts at the T9 and T12, and control electrode contacts at the T2 and T5 levels. After 3 months of daily SCS, airway pressure generation (P), tissue in the area of the stimulating and control electrodes and electrode leads were examined. P was also assessed in acute animals, which served as controls. ResultsMean P at FRC was 54±5cmH2O and 109±11cmH2O in the control and chronically stimulated animals, respectively (p<0.05). There was minimal tissue reaction in the area of the stimulating and control electrodes. All sets of leads revealed no evidence of electrode corrosion. Comparison with existing methodsPrevious porcine models of chronic spinal cord injury (SCI) were developed to study neurological and regenerative outcomes. Our method of chronic SCI porcine model was developed to evaluate the safety of electrical SCS to restore expiratory muscle function. ConclusionChronic SCS with wire lead electrodes results in significant increases in P without evidence of significant adverse tissue reaction, nor evidence of electrode corrosion. This method may be a safe and useful technique to restore a functional cough in spinal cord injured subjects.

Brachycephalic obstructive airway syndrome: a growing problem

Brachycephalic obstructive airway syndrome: a growing problem

Spinal pathways mediating phrenic activation during high frequency spinal cord stimulation

High frequency spinal cord stimulation (HF-SCS) is a method of inspiratory muscle activation resulting in phrenic motoneuron activation via stimulation of spinal cord pathways. The specific pathways mediating this response, however, are unknown. The aim of this study was to assess the potential role of upper cervical (C1–C4) pre-phrenic interneurons (UCI) and localize the pathways in the thoracic spinal cord mediating activation of phrenic motoneurons during HF-SCS. In 7 anesthetized, spinalized (C1 level) dogs, HF-SCS was applied at the T2 level. Diaphragm EMG, inspired volume and airway pressure generation were monitored before and following sequential spinal cord sections at the C4 and C8 levels. Section at the C4 level and dorsal columns at C8 resulted in no significant changes. However, lateral funiculi section (C8 level) resulted in significant reductions in each parameter. We conclude that during upper thoracic HF-SCS, the phrenic motoneuron pools are activated via spinal pathways located in the lateral funiculus but UCI are not involved.

Lateral versus anterior thoracic thrusts in the generation of airway pressure in anaesthetised pigs

ObjectiveAnterior chest thrusts (with the subject sitting or standing and thrusts applied to the lower sternum) are recommended by the Australian Resuscitation Council as part of the sequence for clearing upper airway obstruction by a foreign body. Lateral chest thrusts (with the victim lying on their side) are no longer recommended due to a lack of evidence. We compared anterior, lateral chest and abdominal thrusts in the generation of airway pressures using a suitable animal model. MethodsThis was a repeated-measures, cross-over, clinical trial of eight anaesthetised, intubated, adult pigs. For each animal, ten trials of each technique were undertaken with the upper airway obstructed. A chest/abdominal pressure transducer, a pneumotachograph and an intra-oesophageal balloon catheter recorded chest/abdominal thrust, expiratory air flows, airway and intrapleural pressures, respectively. ResultsThe mean (SD) thrust pressures generated for the anterior, lateral and abdominal techniques were 120.9 (11.0), 135.2 (20.0), and 142.4 (27.3)cmH2O, respectively (p<0.0001). The mean (SD) peak expiratory airway pressures were 6.5 (3.0), 18.0 (5.5) and 13.8 (6.7)cmH2O, respectively (p<0.0001). The mean (SD) peak expiratory intrapleural pressures were 5.4 (2.7), 13.5 (6.2) and 10.3 (8.5)cmH2O, respectively (p<0.0001). At autopsy, no rib, intra-abdominal or intra-thoracic injury was observed. ConclusionLateral chest and abdominal thrust techniques generated significantly greater airway and pleural pressures than the anterior thrust technique. We recommend further research to provide additional evidence that may inform management guidelines for clearing foreign body upper airway obstruction.

Expiratory Resistance Increases End-Expiratory Lung Volume during Sleep

A 37-year-old man with severe obstructive sleep apnea presented to our sleep disorders research laboratory and was instrumented with an epiglottic catheter, pneumotachograph, and magnetometers (to measure relative changes in lung volume) as part of an ongoing study. During the night there were periods of spontaneous, sustained increases in upper airway resistance during expiration (Figure 1A). During these periods, expiratory positive airway pressure developed at the level of the epiglottis (epiglottic pressure channel). Note that although epiglottic pressure increases during expiration, there is no corresponding increase in flow or mask pressure, suggesting a choke point between the epiglottis and airway opening. Expiratory positive airway pressure was associated with an increase in end-expiratory lung volume (rib cage, abdomen, and change in lung volume channels) according to the total respiratory system compliance (Figure 1B). Although other factors may be important, such as upper airway muscle activation, the increase in end-expiratory lung volume was generally associated with a decrease in upper airway resistance (increased flow despite less negative epiglottic pressure) (Figure 1C). Figure 1. Nasal expiratory resistance valves may improve obstructive sleep apnea in a subset of patients, but the mechanism of action is not known (1, 2). Expiratory resistance valves increase end-expiratory lung volume during wakefulness, which might stabilize the upper airway, but this phenomenon has not been clearly demonstrated during sleep. This spontaneously occurring example provides proof of concept that expiratory resistance acts to increase end-expiratory lung volume during sleep via generation of expiratory positive airway pressure. Furthermore, it suggests that such increased end-expiratory lung volume can stabilize the upper airway during inspiration. This image has not been previously published in any form.

Effects of Spinal Cord Section on Inspiratory Pressure Generation During High Frequency Spinal Cord Stimulation (HF‐SCS)

ObjectiveHF‐SCS is a novel and more physiologic method of inspiratory muscle activation which involves activation of spinal cord pathways. The specific pathways by which inspiratory motoneurons are activated by this method however are unknown. The aim of the present study was to evaluate the potential role of upper cervical inspiratory neurons on the observed responses.MethodsIn 6 anesthetized and spinalized (C1 level) dogs, HF‐SCS was applied at T2 level. Airway pressure generation (P) was monitored as an index of the degree of inspiratory muscle activation before and following sequential spinal sections at the C4 (to eliminate upper cervical propriospinal neurons) and subsequently the C8 level.ResultsDuring HF‐SCS, P at FRC was 68±6 cmH2O. Sequential bilateral dorsal columns (DC), lateral funiculi (LF) and complete section (CS) at C4, resulted in no significant changes in P (69±5, 67±5 and 65±7 cmH2O respectively, NS). While DC section at C8 resulted in no changes in P (63±5 cmH2O), LF section resulted in significant reduction in P to 18±3 cmH2O (p&lt;0.05). Subsequent CS resulted in no further reduction in P (14±1 cmH2O, NS).ConclusionDuring upper thoracic HF‐SCS, activation of the phrenic motoneuron pools does not involve upper cervical propriospinal inputs. The phrenic motoneuron pools are activated via spinal pathways located bilaterally in the lateral funiculi.Support: NIH‐NINDS (R01NS064157).

Lower Thoracic Spinal Cord Stimulation to Restore Cough in Patients With Spinal Cord Injury: Results of a National Institutes of Health–Sponsored Clinical Trial. Part I: Methodology and Effectiveness of Expiratory Muscle Activation

DiMarco AF, Kowalski KE, Geertman RT, Hromyak DR. Lower thoracic spinal cord stimulation to restore cough in patients with spinal cord injury: results of a National Institutes of Health–sponsored clinical trial. Part I: methodology and effectiveness of expiratory muscle activation. Objective Evaluation of the capacity of lower thoracic spinal cord stimulation (SCS) to activate the expiratory muscles and generate large airway pressures and high peak airflows characteristic of cough, in subjects with tetraplegia. Design Clinical trial. Setting Inpatient hospital setting for electrode insertion; outpatient setting for measurement of respiratory pressures; home setting for application of SCS. Participants Subjects (N=9; 8 men, 1 woman) with cervical spinal cord injury and weak cough. Interventions A fully implantable electrical stimulation system was surgically placed in each subject. Partial hemilaminectomies were made to place single-disk electrodes in the epidural space at the T9, T11, and L1 spinal levels. A radiofrequency receiver was placed in a subcutaneous pocket over the anterior portion of the chest wall. Electrode wires were tunneled subcutaneously and connected to the receiver. Stimulation was applied by activating a small portable external stimulus controller box powered by a rechargeable battery to each electrode lead alone and in combination. Main Outcome Measures Peak airflow and airway pressure generation achieved with SCS. Results Supramaximal SCS resulted in high peak airflow rates and large airway pressures during stimulation at each electrode lead. Maximum peak airflow rates and airway pressures were achieved with combined stimulation of any 2 leads. At total lung capacity, mean maximum peak airflow rates and airway pressure generation were 8.6±1.8 (mean ± SE) L/s and 137±30 cmH 2O (mean ± SE), respectively. Conclusions Lower thoracic SCS results in near maximum activation of the expiratory muscles and the generation of high peak airflow rates and positive airway pressures in the range of those observed with maximum cough efforts in healthy persons.

High flow nasal oxygen generates positive airway pressure in adult volunteers

The use of non-invasive ventilation (NIV) as an alternative to intubation in respiratory failure is associated with better outcomes in certain conditions. NIV is often poorly tolerated by patients hence precipitating the need for invasive ventilation. High flow nasal (HFN) oxygen delivery is a potential alternative to NIV as it delivers air and oxygen via a humidified circuit at flows greater than those traditionally used with a nasal interface. BODY: Studies of paediatric patient using high flow nasal oxygen therapy have been shown to have similar efficacy as nasal continuous positive airway pressure (CPAP). Although the degree of positive pressure and the effect of different flow rates on positive pressure generation have not been well defined or studied in the adult intensive care population. St. Vincent's Health Human Research and Ethics Committee granted approval to this study and also awarded a $3000 grant. Volunteers were fitted with the Fisher & Paykel high flow nasal interface (RT034) and pharyngeal pressures were recorded with flows from 0 to 60L/min. Expiratory pressures with the mouth closed were higher than those with the mouth open and this was statistically significant (<0.001). Expiratory pressures were higher with the mouth closed and were statistically different (p<0.001). EPPs were higher amongst female subjects compared to male subjects and were statistically different between genders for both open (p<0.05) and closed (p<0.001) measurements. This study has demonstrated that high flow nasal therapy is associated with the generation of significant positive airway pressure in volunteers. In conclusion there is a degree of CPAP generated with the HFN therapy, which is flow dependent and also dependent on whether the person is breathing with mouth open or closed.

Effects of diaphragm activation on airway pressure generation during lower thoracic spinal cord stimulation

Lower thoracic spinal cord stimulation (SCS) results in the generation of large positive airway pressures. The potential effects of diaphragm co-activation during SCS were investigated in 10 anesthetized dogs. Diaphragm compound action potentials (CMAPs) were present during SCS at the T10 and T12 levels. In group 1, airway (Paw) and trans-diaphragmatic (Pdi) pressures were monitored during supramaximal SCS before and after phrenicotomy. In group 2, pressures were monitored before and after C2 section to evaluate the potential influence of supraspinal centers. Following phrenicotomy in group 1, the reduction in Pdi during SCS was associated with increases in Paw. In group 2, diaphragm CMAPs and active Pdi increased following C2 section, while Paw fell. Following phrenicotomy, Paw increased significantly. In intact animals therefore, changes in Paw during SCS are affected by the interaction between inhibitory and excitatory influences on diaphragm activation. We conclude that lower thoracic SCS results in substantial diaphragm co-activation and secondary reductions in airway pressure generation.

Mechanism of Expiratory Muscle Activation During Upper Lumbar Spinal Cord Stimultion (SCS)

Combined lower thoracic (T9) and upper lumbar (L1) SCS may be a useful method to restore an effective cough mechanism in tetraplegic patients. In previous studies in dogs, we demonstrated that SCS at the T9 level resulted in direct activation of the spinal cord roots in the vicinity of the stimulating electrode and also more caudal roots via spinal pathways. The purpose of the present study was to investigate the mechanism of expiratory muscle activation during upper lumbar (L1) SCS. In 3 anesthetized dogs, expiratory muscle activation was monitored by evoked compound action potentials (CAP) from the intercostal muscles in the 7th and 9th interspaces (T7, T9) and portions of the external oblique innervated by the T13 and L2 motor roots. SCS applied with single shocks resulted in short latency CAP at T13 and L2 but not more rostrally. SCS resulted in long latency CAPs at T7 and T9, suggesting activation via spinal cord pathways. SCS at L1 was also applied before and after sequential section of the dorsal columns (DC), lateral (LF) and ventral funiculi (VF) at the T11 spinal cord level while monitoring airway pressure under conditions of airway occlusion. DC section did not affect short latency CAPs but abolished long latency CAPs at T9 and T7 and also resulted in a fall in airway pressure generation from 26 ± 6 cmH2O to 18 ± 5 cmH2O (NS). Section of the LF and VF resulted in further decrements in airway pressure (17 ± 6 and 11 ± 2 cmH2O respectively, NS). We conclude that SCS at the L1 level results in direct activation of the spinal roots in the vicinity of stimulating electrode and more rostral roots via spinal pathways. (HL34143).

A comparison of the continuous positive airway pressures produced by two systems

To compare the generation of continuous positive airway pressure using a hand-made device (underwater seal) or a ventilator (Inter 3). Two positive airway pressure generation systems were compared through laboratory simulations. Measurements were not considered if the mechanical ventilator required calibration or in the presence of gas flow variation (flowmeter sphere oscillation). Recordings were assessed in terms of the capacity to produce the desired pressure (3, 5 and 6 cmH2O) when submitted to three different flow values (8, 10 and 12 l/min). For that end, Student's t test for paired samples and the nonparametric Man-Whitney test for independent samples were employed. We verified that the systems behave in different manners under the same conditions of flow and positive end expiratory pressure. For the mechanical ventilator, the mean pressure behavior under continuous positive airway pressure at 3 cmH2O with flows of 8, 10 and 12 l/min were 2.26+/-0.41, 2.22+/-0.37, 2.04+/-0.41, respectively; under positive end-expiratory pressure at 5 cmH2O we found 3.96+/-0.41, 3.87+/-0.43 and 3.75+/-0.52; and under positive end-expiratory pressure at 6 cmH2O the values recorded were 4.94+/-0.40, 4.85+/-0.41 and 4.72+/-0.37. For the underwater seal, the mean pressure behavior under continuous positive airway pressure at 3 cmH2O with flows of 8, 10 and 12 l/min were 4.24+/-0.24, 4.46+/-0.26, 4.72+/-0.37, respectively; at 5 cmH2O the values were 5.97+/-0.17, 6.28+/-0.18, 6.47+/-0.31; and at 6 cmH2O we recorded 6.85+/-0.20, 7.17+/-0.29 and 7.53+/-0.31. All the comparisons were statistically significant (p = 0.000). Through our recordings it was possible to observe that the Inter 3 continuous positive airway pressure system was more stable than the underwater seal.