Electrical Activity Of Diaphragm Research Articles

High-Level Pressure Support Ventilation Attenuates Ventilator-Induced Diaphragm Dysfunction in Rabbits

BackgroundThe effects of different modes of mechanical ventilation in the same ventilatory support level on ventilator-induced diaphragm dysfunction onset were assessed in healthy rabbits. MethodsTwenty New Zealand rabbits were randomly assigned to 4 groups (n = 5 in each group). Group 1: no mechanical ventilation; group 2: controlled mechanical ventilation (CMV) for 24 hours; group 3: assist/ control ventilation (A/C) mode for 24 hours; group 4: high-level pressure support ventilation (PSV) mode for 24 hours. Heart rate, mean arterial blood pressure, PH, partial pressure of arterial oxygen/fraction of inspired oxygen and partial pressure of arterial carbon dioxide were monitored and diaphragm electrical activity was analyzed in the 4 groups. Caspase-3 was evaluated by protein analysis and diaphragm ultra structure was assessed by electron microscopy. ResultsThe centroid frequency and the ratio of high frequency to low frequency were significantly reduced in the CMV, A/C and PSV groups (P < 0.001). The percent change in centroid frequency was significantly lower in the PSV group than in the CMV and A/C groups (P = 0.001 andP =0.028, respectively). Electromyography of diaphragm integral amplitude decreased by 90% ± 1.48%, 67.8% ± 3.13% and 70.2% ± 4.72% in the CMV, A/C and PSV groups, respectively (P< 0.001). Caspase-3 protein activation was attenuated in the PSV group compared with the CMV and A/C groups (P = 0.035 andP= 0.033, respectively). Irregular swelling of mitochondria along with fractured and fuzzy cristae was observed in the CMV group, whereas mitochondrial cristae were dense and rich in the PSV group. The mitochondrial injury scores (Flameng scores) in the PSV group were the lowest among the 3 ventilatory groups (0.93 ± 0.09 in PSV versus 2.69 ± 0.05 in the CMV [P < 0.01] and PSV versus A/C groups [2.02 ± 0.08,P <0.01]). ConclusionsThe diaphragm myoelectric activity was reduced in the PSV group, although excessive oxidative stress and ultrastructural changes of diaphragm were found. However, partial diaphragm electrical activity was retained and diaphragm injury was minimized using the PSV mode.

The diaphragm has an expiratory braking effect in spontaneously breathing lung injured animals as shown by electrical diaphragmatic activity

Albeit defined as an inspiratory muscle, the diaphragm interacts with the respiratory system also during expiration. The expiratory load on the diaphragm derives from lung volume and hence, possibly from lung collapse. We hypothesized that the diaphragm has a braking effect during the whole expiration, preserving lung patency during SB in collapse prone lungs. We investigated this hypothesis by measuring the expiratory electrical diaphragmatic activity (EAdiexp) in the modulation of expiratory flow (V'exp) in a porcine model.

Feasibility of neurally adjusted positive end-expiratory pressure in rabbits with early experimental lung injury.

BackgroundDuring conventional Neurally Adjusted Ventilatory Assist (NAVA), the electrical activity of the diaphragm (EAdi) is used for triggering and cycling-off inspiratory assist, with a fixed PEEP (so called “Triggered Neurally Adjusted Ventilatory Assist” or “tNAVA”). However, significant post-inspiratory activity of the diaphragm can occur, believed to play a role in maintaining end-expiratory lung volume. Adjusting pressure continuously, in proportion to both inspiratory and expiratory EAdi (Continuous NAVA, or cNAVA), would not only offer inspiratory assist for tidal breathing, but also may aid in delivering a “neurally adjusted PEEP”, and more specific breath-by-breath unloading.MethodsNine adult New Zealand white rabbits were ventilated during independent conditions of: resistive loading (RES1 or RES2), CO2 load (CO2) and acute lung injury (ALI), either via tracheotomy (INV) or non-invasively (NIV). There were a total of six conditions, applied in a non-randomized fashion: INV-RES1, INV-CO2, NIV-CO2, NIV-RES2, NIV-ALI, INV-ALI. For each condition, tNAVA was applied first (3 min), followed by 3 min of cNAVA. This comparison was repeated 3 times (repeated cross-over design). The NAVA level was always the same for both modes, but was newly titrated for each condition. PEEP was manually set to zero during tNAVA. During cNAVA, the assist during expiration was proportional to the EAdi. During all runs and conditions, ventilator-delivered pressure (Pvent), esophageal pressure (Pes), and diaphragm electrical activity (EAdi) were measured continuously. The tracings were analyzed breath-by-breath to obtain peak inspiratory and mean expiratory values.ResultsFor the same peak Pvent, the distribution of inspiratory and expiratory pressure differed between tNAVA and cNAVA. For each condition, the mean expiratory Pvent was always higher (for all conditions 4.0 ± 1.1 vs. 1.1 ± 0.5 cmH2O, P < 0.01) in cNAVA than in tNAVA. Relative to tNAVA, mean inspiratory EAdi was reduced on average (for all conditions) by 19 % (range 14 %–25 %), p < 0.05. Mean expiratory EAdi was also lower during cNAVA (during INV-RES1, INV-CO2, INV-ALI, NIV-CO2 and NIV-ALI respectively, P < 0.05). The inspiratory Pes was reduced during cNAVA all 6 conditions (p < 0.05). Unlike tNAVA, during cNAVA the expiratory pressure was comparable with that predicted mathematically (mean difference of 0.2 ± 0.8 cmH2O).ConclusionContinuous NAVA was able to apply neurally adjusted PEEP, which led to a reduction in inspiratory effort compared to triggered NAVA.

The effect of caffeine citrate on neural breathing pattern in preterm infants

BackgroundCaffeine citrate is widely used to prevent and treat prematurity-associated apnea. AimsThe aim of this study was to characterize the effect of caffeine citrate on the neural control of breathing, especially central apnea, in premature infants. Study designPreterm infants were evaluated for 30min before and 30min after caffeine citrate loading (20mg/kg). A feeding tube including miniaturized sensors was used to measure the diaphragm electrical activity (Edi) waveform. Central apnea was defined as any period where the Edi waveform was flat for >5s. SubjectsSeventeen preterm infants with a mean age of three days and mean birth weight of 900 grams were evaluated. Outcome measuresIn addition to central apnea, several parameters including neural inspiratory time, neural respiratory rate, peak Edi, delta inspiratory change in Edi (phasic Edi) and minimum Edi on exhalation were measured. ResultsThe majority of the apnea were short (5 to 10s) and the number of apnea correlated with birth weight (p=0.039). Caffeine citrate reduced significantly the number of 5-to-10-second-long central apnea during the 30-minute periods (12±11 to 7±7; p=0.02). Caffeine citrate increased both peak and phasic Edi leading to a significant increase in the diaphragm energy expenditure. ConclusionsEdi signal can be reliably measured and processed to study changes in premature infants' neural breathing. The beneficial effect of caffeine citrate on the reduction of the number of apnea is mediated through stimulated neural breathing increasing the diaphragm energy expenditure.

Assisted Ventilation in Patients with Acute Respiratory Distress Syndrome: Lung-distending Pressure and Patient-Ventilator Interaction.

In patients with acute respiratory distress syndrome (ARDS), the use of assisted mechanical ventilation is a subject of debate. Assisted ventilation has benefits over controlled ventilation, such as preserved diaphragm function and improved oxygenation. Therefore, higher level of "patient control" of ventilator assist may be preferable in ARDS. However, assisted modes may also increase the risk of high tidal volumes and lung-distending pressures. The current study aims to quantify how differences in freedom to control the ventilator affect lung-protective ventilation, breathing pattern variability, and patient-ventilator interaction. Twelve patients with ARDS were ventilated in a randomized order with assist pressure control ventilation (PCV), pressure support ventilation (PSV), and neurally adjusted ventilatory assist (NAVA). Transpulmonary pressure, tidal volume, diaphragm electrical activity, and patient-ventilator interaction were measured. Respiratory variability was assessed using the coefficient of variation of tidal volume. During inspiration, transpulmonary pressure was slightly lower with NAVA (10.3 ± 0.7, 11.2 ± 0.7, and 9.4 ± 0.7 cm H2O for PCV, PSV, and NAVA, respectively; P < 0.01). Tidal volume was similar between modes (6.6 [5.7 to 7.0], 6.4 [5.8 to 7.0], and 6.0 [5.6 to 7.3] ml/kg for PCV, PSV, and NAVA, respectively), but respiratory variability was higher with NAVA (8.0 [6.4 to 10.0], 7.1 [5.9 to 9.0], and 17.0 [12.0 to 36.1] % for PCV, PSV, and NAVA, respectively; P < 0.001). Patient-ventilator interaction improved with NAVA (6 [5 to 8] % error) compared with PCV (29 [14 to 52] % error) and PSV (12 [9 to 27] % error); P < 0.0001. In patients with mild-to-moderate ARDS, increasing freedom to control the ventilator maintains lung-protective ventilation in terms of tidal volume and lung-distending pressure, but it improves patient-ventilator interaction and preserves respiratory variability.

Tonic diaphragmatic activity in critically ill children with and without ventilatory support.

Infants have to actively maintain their end expiratory lung volume (EELV). In mechanically ventilated infants, the diaphragm stays activated until the end of expiration (tonic activity), contributing to EELV maintenance. It is unclear whether tonic activity compensates for the lack of laryngeal braking due to intubation or if it is normally present. To determine if tonic diaphragm activity remains after extubation in infants, and if it can be observed in older children. Prospective observational study of pediatric patients ventilated for >24 hr. Diaphragm electrical activity (EAdi) was recorded using a specific nasogastric catheter during four periods: (i) the acute phase, (ii) pre-extubation, (iii) post-extubation, and (iv) at PICU discharge. Tonic EAdi was defined as the EAdi in the last quartile of expiration. Fifty-five patients, median age 10 months (Interquartile range: 1-48) were studied. In infants (<1 year, n = 28), tonic EAdi was always present, and represented 33% (22-43) of inspiratory EAdi at PICU discharge. No significant change was observed between pre- and post-extubation periods. In older patients (n = 27), tonic activity was negligible as a whole, but 10 patients exhibited significant tonic EAdi at one time-point during PICU stay. Bronchiolitis was the only independent factor associated with tonic EAdi. In infants, tonic EAdi remains involved in ventilatory control after extubation and restoration of laryngeal braking. Tonic EAdi may play a pathophysiological role in bronchiolitis and it can be reactivated in older patients. The interest of tonic EAdi as a tool to titrate mechanical ventilation warrants further evaluation.

Measuring diaphragm thickness with ultrasound in mechanically ventilated patients: feasibility, reproducibility and validity.

Ultrasound measurements of diaphragm thickness (T di) and thickening (TFdi) may be useful to monitor diaphragm activity and detect diaphragm atrophy in mechanically ventilated patients. We aimed to establish the reproducibility of measurements in ventilated patients and determine whether passive inflation by the ventilator might cause thickening apart from inspiratory effort. Five observers measured T di and TFdi in 96 mechanically ventilated patients. The probe site was marked in 66 of the 96 patients. TFdi was measured at peak and end-inspiration (airway occluded and diaphragm relaxed) in nine healthy volunteers inhaling to varying lung volumes. The association with diaphragm electrical activity was quantified. Right hemidiaphragm thickness was obtained on 95 % of attempts; left hemidiaphragm measurements could not be obtained consistently. Right hemidiaphragm thickness measurements were highly reproducible (mean ± SD 2.4 ± 0.8 mm, repeatability coefficient 0.2 mm, reproducibility coefficient 0.4 mm), particularly after marking the location of the probe. TFdi measurements were only moderately reproducible (median 11 %, IQR 3-17 %, repeatability coefficient 17 %, reproducibility coefficient 16 %). TFdi and diaphragm electrical activity were positively correlated, r² = 0.32, p < 0.01). At inspiratory volumes below 50 % of inspiratory capacity, passive inflation did not cause diaphragm thickening. TFdi was considerably lower in patients on either partially assisted or controlled ventilation compared to healthy subjects (median 11 vs. 35 %, p < 0.001). Ultrasound measurements of right hemidiaphragm thickness are feasible and highly reproducible in ventilated patients. At clinically relevant inspiratory volumes, diaphragm thickening reflects muscular contraction and not passive inflation. This technique can be reliably employed to monitor diaphragm thickness, activity, and function during mechanical ventilation.

Feasibility Study on Neurally Adjusted Ventilatory Assist in Noninvasive Ventilation After Cardiac Surgery in Infants.

Our objective was to evaluate the feasibility, the quality of synchronization, and the influence on respiratory parameters of the noninvasive neurally adjusted ventilatory assist (NIV-NAVA) mode in infants after cardiac bypass surgery. We conducted a prospective, randomized cross-over study in infants undergoing noninvasive ventilation (NIV) after cardiac surgery. Subjects were 10 infants < 5 kg. After extubation, subjects underwent 2 consecutive ventilatory modes after randomization into groups. In the CPAP first group, the subjects were ventilated first in nasal CPAP-1 and then in NIV-NAVA-2 for 30 min in each mode. In the NIV-NAVA first group, periods were reversed. All children were ventilated using the same interface. The analysis of curves showed a synchronization rate of 99.3% for all respiratory cycles. The rate of pneumatic inspiratory trigger was 3.4%. Asynchronies were infrequent. Some typical respiratory patterns (continuous effort and discontinuous inspiration) were found at rates of 10.9% and 31.1%, respectively. The respiratory trends showed a lower maximum diaphragmatic electrical activity (EAdi(max)) in NIV-NAVA periods compared with CPAP periods (P < .001 in the beginning of periods). The breathing frequency decreased significantly during the nasal CPAP-2 and NIV-NAVA-1 periods (P < .05). The inspiratory pressure increased significantly during the NIV-NAVA-1 and NIV-NAVA-2 periods (P < .05), but there was no significant difference for each parameter when comparing Δ values between the beginning and the end of each period. The EAdi signal was easy to obtain in all subjects, and no major side effects were associated with the use of NIV-NAVA. NIV-NAVA allows good synchronization in bi-level NIV in infant cardiac subjects weighing < 5 kg. The analysis of respiratory parameters shows that NIV NAVA decreases the work of breathing more effectively than nasal CPAP. The study shows some typical respiratory patterns in infants. (ClinicalTrials.gov registration NCT01570933.).

Effect of flumazenil on diaphragm electrical activation during weaning from mechanical ventilation after acute respiratory distress syndrome

Diaphragm electrical activation (EAdi) and the ratio of tidal volume to EAdi (VT/EAdi) may provide clinical information on neuroventilatory efficiency (NVE) in patients being weaned from mechanical ventilation. We tested the hypothesis that residual sedation could interfere with respiratory recovery, by assessing the effects of flumazenil on EAdi and VT/EAdi ratio. This observational study included 13 patients breathing with pressure-support ventilation (PSV) after a long period of controlled mechanical ventilation (i.e. >4 days) plus midazolam-based sedation for acute respiratory distress syndrome. EAdi and respiratory patterns were compared before and after a bolus of flumazenil, which was given because neurological status needed to be evaluated. Flumazenil induced a significant increase in EAdi [+71 (41-123)%, P=0.0002] and VT [+17 (8-32)%, P=0.0005], resulting in significantly decreased NVE [-34 (15-43)%]. The increased VT was significantly correlated with the increased EAdi (ρ=0.70, P=0.009). During weaning from mechanical ventilation, the diaphragmatic contribution to the breathing process may be reduced by residual midazolam-induced ventilatory depression. The increased EAdi with reversal of residual sedation was associated with a proportional increase in VT. These findings should be considered by the attending physician when interpreting daily EAdi and VT changes during weaning from mechanical ventilation.

Neurally adjusted ventilator assist in very low birth weight infants: Current status.

Continuous improvements in perinatal care have resulted in increased survival of premature infants. Their immature lungs are prone to injury with mechanical ventilation and this may develop into chronic lung disease (CLD) or bronchopulmonary dysplasia. Strategies to minimize the risk of lung injury have been developed and include improved antenatal management (education, regionalization, steroids, and antibiotics), exogenous surfactant administration and reduction of barotrauma by using exclusive or early noninvasive ventilatory support. The most frequently used mode of assisted ventilation is pressure support ventilation that may lead to patient-ventilator asynchrony that is associated with poor outcome. Ventilator-induced diaphragmatic dysfunction or disuse atrophy of diaphragm fibers may also occur. This has led to the development of new ventilation modes including neurally adjusted ventilatory assist (NAVA). This ventilation mode is controlled by electrodes embedded within a nasogastric catheter which detect the electrical diaphragmatic activity (Edi) and transmit it to trigger the ventilator in synchrony with the patient's own respiratory efforts. This permits the patient to control peak inspiratory pressure, mean airway pressure and tidal volume. Back up pressure control (PC) is provided when there is no Edi signal and no pneumatic trigger. Compared with standard conventional ventilation, NAVA improves blood gas regulation with lower peak inspiratory pressure and oxygen requirements in preterm infants. NAVA is safe mode of ventilation. The majority of studies have shown no significant adverse events in neonates ventilated with NAVA nor a difference in the rate of intraventricular hemorrhage, pneumothorax, or necrotizing enterocolitis when compared to conventional ventilation. Future large size randomized controlled trials should be established to compare NAVA with volume targeted and pressure controlled ventilation in newborns with mature respiratory drive. Most previous studies and trials were not sufficiently large and did not include long-term patient oriented outcomes. Multicenter, randomized, outcome trials are needed to determine whether NAVA is effective in avoiding intubation, facilitating extubation, decreasing time of ventilation, reducing the incidence of CLD, decreasing length of stay, and improving long-term outcomes such as the duration of ventilation, length of hospital stay, rate of pneumothorax, CLD and other major complications of prematurity. In order to prevent barotrauma, next generations of NAVA equipment for neonatal use should enable automatic setting of ventilator parameters in the backup PC mode based on the values generated by NAVA. They should also include an upper limit to the inspiratory time as in conventional ventilation. The manufacturers of Edi catheters should produce smaller sizes available for extreme low birth weight infants. Newly developed ventilators should also include leak compensation and high frequency ventilation. A peripheral flow sensor is also essential to the proper delivery of all modes of conventional ventilation as well as NAVA.

Neurally Adjusted Ventilatory Assist in Preterm Neonates with Acute Respiratory Failure

Background: Neurally adjusted ventilatory assist (NAVA) is a novel mode of ventilation that has been demonstrated to improve infant-ventilator interaction, compared to the conventional modes in retrospective and short-term studies. Objectives: To prospectively evaluate the physiologic effects of NAVA in comparison with pressure-regulated volume control (PRVC) in two nonrandomized 12-hour periods. Methods: We studied 14 consecutive intubated preterm neonates receiving mechanical ventilation for acute respiratory failure. Peak airway pressure (Paw_peak), diaphragm electrical activity (EAdi), tidal volume (V_T), mechanical (RR_mec) and neural (RR_neu) respiratory rates, neural apneas, and the capillary arterialized blood gases were measured. The RR_mec-to-RR_neu ratio (MNR) and the asynchrony index were also calculated. The amount of fentanyl administered was recorded. Results: Paw_peak and V_T were greater in PRVC (p < 0.01). Blood gases and RR_mec were not different between modes, while RR_neu and the EAdi swings were greater in NAVA (p = 0.02 and p < 0.001, respectively). MNR and the asynchrony index were remarkably lower in NAVA than in PRVC (p = 0.03 and p < 0.001, respectively). 1,841 neural apneas were observed during PRVC, with none in NAVA. Less fentanyl was administered during NAVA, as opposed to PRVC (p < 0.01). Conclusions: In acutely ill preterm neonates, NAVA can be safely and efficiently applied for 12 consecutive hours. Compared to PRVC, NAVA is well tolerated with fewer sedatives.

O-081 Non-invasive Ventilation In Severe Viral Bronchiolitis With Failure Of Ncpap: Neurally Adjusted Ventilatory Assist Versus Pressure Assist/control Ventilation

Background To determine the prevalence of main inspiratory asynchrony events during non-invasive intermittent positive-pressure ventilation (NIV) for severe bronchiolitis in infants who failed to respond to nasal continuous positive airway pressure (nCPAP). Ventilator response time and asynchrony were compared in neurally adjusted ventilator assist (NAVA) and in pressure assist/control (PAC) modes. Methods This prospective study in a university hospital’s paediatric intensive care unit included 11 children (aged 35.2 ± 23 days) with respiratory syncytial virus bronchiolitis with failure of nCPAP. Patients received NIV for 2 h in PAC mode followed by 2 h in NAVA mode. Diaphragm electrical activity and pressure curves were recorded for 10 min. Trigger delay, main asynchronies (auto-triggering, double triggering, or non-triggered breaths) were analysed, and the asynchrony index was calculated. Results The asynchrony index (fig. 1) was lower during NAVA than during PAC (3 ± 3% vs. 38 ± 21%, p 2 baselines values (8.6 ± 1.6 kPa vs. 8.1 ± 1.2 kPa during NAVA, p = 0.36) and their evolutions during the study period (-0.8 ± 1.4 kPa vs. -1.6 ± 2.3 kPa during NAVA, p = 0.36) did not differ. Conclusion Severe patient-ventilator inspiratory asynchronies and ventilator response times were much lower in NAVA mode than in PAC mode during NIV in infants with bronchiolitis.

Clinical assessment of auto-positive end-expiratory pressure by diaphragmatic electrical activity during pressure support and neurally adjusted ventilatory assist.

Auto-positive end-expiratory pressure (auto-PEEP) may substantially increase the inspiratory effort during assisted mechanical ventilation. Purpose of this study was to assess whether the electrical activity of the diaphragm (EAdi) signal can be reliably used to estimate auto-PEEP in patients undergoing pressure support ventilation and neurally adjusted ventilatory assist (NAVA) and whether NAVA was beneficial in comparison with pressure support ventilation in patients affected by auto-PEEP. In 10 patients with a clinical suspicion of auto-PEEP, the authors simultaneously recorded EAdi, airway, esophageal pressure, and flow during pressure support and NAVA, whereas external PEEP was increased from 2 to 14 cm H2O. Tracings were analyzed to measure apparent "dynamic" auto-PEEP (decrease in esophageal pressure to generate inspiratory flow), auto-EAdi (EAdi value at the onset of inspiratory flow), and IDEAdi (inspiratory delay between the onset of EAdi and the inspiratory flow). The pressure necessary to overcome auto-PEEP, auto-EAdi, and IDEAdi was significantly lower in NAVA as compared with pressure support ventilation, decreased with increase in external PEEP, although the effect of external PEEP was less pronounced in NAVA. Both auto-EAdi and IDEAdi were tightly correlated with auto-PEEP (r = 0.94 and r = 0.75, respectively). In the presence of auto-PEEP at lower external PEEP levels, NAVA was characterized by a characteristic shape of the airway pressure. In patients with auto-PEEP, NAVA, compared with pressure support ventilation, led to a decrease in the pressure necessary to overcome auto-PEEP, which could be reliably monitored by the electrical activity of the diaphragm before inspiratory flow onset (auto-EAdi).

Relation between peak and integral of the diaphragm electromyographic activity at different levels of support during weaning from mechanical ventilation: A physiologic study

PurposeTo investigate the relationship between peak (EAdipeak) and area under the curve (EAdiAUC) of diaphragm electrical activity, and to evaluate the validity of their ratio (P/I index) as a measure of the imbalance between drive and sustainability of effort demand at different support levels. MaterialsProspective physiological study on 18 ready-to-wean patients ventilated with neurally adjusted ventilatory assist (NAVA) undergoing 2 levels of NAVA (NAVA100% and NAVA50%) followed by a weaning trial with continuous positive airway pressure, according to which patients were classified as success or failure. Tidal volume (VT), respiratory rate, EAdipeak, EAdiAUC, rapid shallow breathing index (respiratory rate/VT), neuroventilatory index (VT/EAdipeak), and P/I index were obtained at the end of each step. ResultsThe slopes of regression line between EAdipeak and EAdiAUC (a mathematical equivalent of P/I index) and P/I index were significantly higher in failures. At variance with other variables, P/I index did not vary with level of support. P/I index was inversely correlated with inspiratory time at all support levels. ConclusionsThe relationship between EAdipeak and EAdiAUC and the P/I index may give important information on the balance between respiratory drive and inspiratory demand sustainability.

The effects of skin-to-skin care on the diaphragmatic electrical activity in preterm infants

BackgroundSkin-to-skin care (SSC) is widely used in neonatal intensive care units due to its positive effects on infant physiology and parent–infant interaction. AimsWe investigated the safety and the effect of SSC on the diaphragm electrical activity (EAdi) in premature infants recovering from respiratory distress syndrome treated on noninvasive neurally adjusted respiratory assist. Study designAn observational cross-over study design was used. The infants were evaluated during SSC and in both prone and supine positions before and after SSC during a 9-hour study period. The EAdi was measured via miniaturized sensors incorporated into a feeding tube. SubjectsSeventeen premature infants with a mean age of 20d (range, 2–43d) were studied. Their mean birth weight was 900g (490–1845g) and mean gestational age at birth 28wk (25–32wk). Outcome measuresUnder each condition, EAdi peak (representing tidal, neural inspiratory effort) and EAdi minimum (representing neural expiratory activity) were numerically quantified. Oxygen saturation, heart rate, and apnea were recorded. ResultsThe mean EAdi minimum values were lower during SSC and prone position. In addition, a tendency towards lower EAdi peak values was found during SSC. There were no differences in the occurrence of apnea between the study phases. ConclusionsSSC is safe and it is not associated with increased neural activity of the diaphragm. On the contrary, low EAdi minimum values were registered reflecting more complete diaphragmatic de-activation between respiratory cycles.

Diaphragmatic neuromechanical coupling and mechanisms of hypercapnia during inspiratory loading

We hypothesized that improved diaphragmatic neuromechanical coupling during inspiratory loading is not sufficient to prevent alveolar hypoventilation and task failure, and that the latter results primarily from central-output inhibition of the diaphragm and air hunger rather than contractile fatigue. Eighteen subjects underwent progressive inspiratory loading. By task failure all developed hypercapnia. Tidal transdiaphragmatic pressure (ΔPdi) and diaphragmatic electrical activity (ΔEAdi) increased during loading – the former more than the latter; thus, neuromechanical coupling (ΔPdi/ΔEAdi) increased during loading. Progressive increase in extra-diaphragmatic muscle contribution to tidal breathing, expiratory muscle recruitment, and decreased end-expiratory lung volume contributed to improved neuromechanical coupling. At task failure, subjects experienced intolerable breathing discomfort, at which point mean ΔEAdi was 74.9±4.9% of maximum, indicating that the primary mechanism of hypercapnia was submaximal diaphragmatic recruitment. Contractile fatigue was an inconsistent finding. In conclusion, hypercapnia during acute loading primarily resulted from central-output inhibition of the diaphragm suggesting that acute loading responses are controlled by the cortex rather than bulbopontine centers.

Physiological comparison of breathing patterns with neurally adjusted ventilatory assist (NAVA) and pressure-support ventilation to improve NAVA settings

Neurally adjusted ventilator assist (NAVA) assists spontaneous breathing in proportion to diaphragmatic electrical activity (EAdi). Here, we evaluate the effects of various levels of NAVA and PSV on the breathing pattern and, thereby, on PaCO2 homeostasis in 10 healthy volunteers. For each ventilation mode, four levels of support (delivered pressure 0 i.e. baseline, 5, 8, and 10cmH2O) were tested in random order. EAdi, flow, and airway pressure were recorded. Optoelectronic plethysmography was used to study lung volume distribution. During both PSV and NAVA, EAdi decreased with the level of assistance (P<0.01). Tidal volume (VT) increased and PtCO2 decreased with increased levels of PSV (P=0.044 and P=0.0004; respectively) while no change was observed with NAVA. Subject–ventilator synchronization was better with NAVA than with PSV. NAVA and PSV similarly decreased the abdominal contribution to VT. No airflow profile similarities were observed between baseline and mechanical ventilation. Diaphragmatic activity can decrease during NAVA without any change in VT and PaCO2. This suggests that NAVA adjustment cannot be based solely on VT and PCO2 criteria.Registered by Frédéric Lofaso and Nicolas Terzi on ClinicalTrials.gov, #NCT01614873.

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Introduction: Neurally Adjusted Ventilatory Assist (NAVA) is an emerging mode of mechanical ventilation that is aimed at optimizing patient-ventilator synchrony. The properties and initiation of each breath adjust based on the patient's current physiologic state and ventilatory demand. This dynamic approach to ventilation allows the patient to completely control each breath while also reducing fatigue and lung injury. NAVA accomplishes this by using a modified nasogastric tube with electrodes situated at the gastric end to measure electromyelogram (EMG) potentials generated by the diaphragm. The magnitude of each potential is used to formulate each breath delivered by the ventilator. There is no single strategy in managing mechanical ventilation in patients with a Congenital Diaphragmatic Hernia (CDH), but aims should be at protecting against lung injury. NAVA has only previously been described in post operative care of CDH. In this report, we demonstrate how NAVA mechanical ventilation was applied to a patient with a CDH both pre and post-operatively. Case Description: Our case index is a healthy 14 month old female who presented to the emergency department with acute respiratory distress. The patient required immediate intubation with mechanical ventilation. Chest x-ray demonstrated an Anderson Catheter tip projecting over the left upper quadrant of the abdomen suggestive of gastrothorax. During the first 24 hours, the patient had discomfort and asynchrony with synchronized intermittent mechanical ventilation (SIMV) and was requiring increased amounts of sedative medications. After having asynchrony with SIMV pressure control pressure support (PS), SIMV pressure regulated volume controlled PS, and SIMV volume controlled PS, the patient was switched to NAVA mechanical ventilation. The patient appeared more comfortable and sedative medication was weaned. NAVA was continued until the patient was transferred to the operating suite for surgical closure of the left anterior Bochdalek diaphragmatic hernia via a gortex patch. Once the patient recovered from general anesthesia, she was placed back on NAVA ventilation. On post-operative day one, the patient was extubated and successfully weaned to room air. Discussion: The diaphragm is the principle inspiratory muscle in humans. It is innervated by phrenic motor neurons found in the ventral horn of levels C3-C5 of the cervical spinal cord. The respiratory function and control of the diaphragm is dependent on these phrenic motor units. The number of units recruited to generate a given force is dependent on the contractility and fatigue of the diaphragmatic muscle fibers. This is the specific EMG activity that is detected by the NAVA catheter and transmitted as an electrical activity of diaphragm (Edi) signal to the ventilator. For instance, if a patient's central nervous system sends a signal to recruit more motor neurons, a greater EMG potential will be measured by the NAVA catheter. The catheter transmits an Edi signal to the ventilator which results in increased pressure delivered to the patient. NAVA mechanical ventilation requires intact respiratory drive and detection of EMG signal from the diaphragm. In this case, the patient had intact respiratory drive, but also had a known diaphragmatic defect. A trial of NAVA was chosen in efforts to optimize mechanical ventilation, reduce amount of sedation, and also reduce possible lung injury. After placement of the EMG recording catheter, a chest x-ray confirmed that the gastric end of the catheter was within the portion of the stomach herniating through the diaphragm. Conclusion: In this patient with diaphragm pathology, NAVA allowed the patient to self control for optimal ventilation. Despite the defect in this case of CDH, the diaphragmatic EMG potentials were transmitted successfully resulting in delivery of appropriately synchronized ventilation.

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Introduction: In contrast with adults, infants have to actively maintain their end expiratory lung volume because of the high compliance of their rib cage. In mechanically ventilated infants, we previously showed that the diaphragm stays activated until the end of expiration (tonic activity). We hypothesized that this tonic activity was present to compensate for the lack of laryngeal braking secondary to endotracheal intubation. We conducted a clinical study to determine if the tonic activity of the diaphragm remains after extubation in infants, and if it can be observed at all ages in children. Methods: This is a prospective longitudinal observational study. Patients 1 week to 18 year old admitted to the pediatric intensive care unit (PICU), mechanically ventilated for at least 24 hours and with parental consent were eligible. Diaphragm electrical activity was recorded using a specific nasogastric catheter at four different times during PICU stay: in acute phase, before and after extubation and at PICU discharge. Diaphragmatic activity was analyzed in a semi-automatic manner to determine inspiratory and expiratory times. Tonic diaphragmatic activity was defined as the activity during the last quartile of expiration. Results: 55 patients with a median age of 10 months (Interquartile range: 1–48) were studied. In infants (< 1 year-old, n=28), tonic activity expressed as a percentage of inspiratory activity was 48% (30–56) in acute phase, 38% (25–44) pre-extubation, 28% (17–42) post-extubation and 33% (22–43) at PICU discharge (p<0.05, ANOVA, with significant difference between recording 1 and recordings 3 and 4). No significant change in tonic activity was observed between before and after extubation. As expected from physiology, the tonic diaphragmatic activity in older patients (> 1 year-old) was negligible during normal breathing (Median: 0.6mcv). However, significant tonic activity (> 1mcv and >10% of inspiratory activity) was observed at one point during the stay of 10 patients (aged 13 months to 118 months) out of 27 patients > 1 year-old. Conclusions: In infants, tonic diaphragmatic activity remains important after extubation despite restoration of laryngeal braking. Older patients breathing normally don’t show significant tonic activity but it can be re-activated in pathological conditions. Tonic activity seems to be an indicator of patient’s efforts to maintain their end expiratory lung volume. Further studies should evaluate if this monitoring could facilitate the detection of situations of inappropriate ventilatory support.

Monitoring diaphragm electrical activity and the detection of congenital central hypoventilation syndrome in a newborn

A full-term newborn infant is described with recurrent episodes of oxygen desaturation and apnea on the day of birth. The apnea did not improve with continuous positive airway pressure (CPAP) and intermittent nasal ventilation, therefore intubation and mechanical ventilation were required. A preliminary diagnosis of congenital central hypoventilation syndrome (CCHS) was made with the use of simultaneous measurements of end-tidal CO2 (EtCO2) and a diaphragm electrical activity waveform that was detected using microsensors placed on the infant's feeding tube. It was observed that during deep sleep, the diaphragm electrical activity waveform was close to 0 μV (central apnea) and EtCO2 levels rose accordingly (central hypoventilation). Genetic testing subsequently revealed a Phox2b mutation, establishing the diagnosis of CCHS. Simultaneously measuring diaphragm electrical activity and EtCO2 is feasible and may be a valuable bedside diagnostic tool in cases of suspected CCHS before the diagnosis is confirmed with genetic testing.