Reverse Triggering Dyssynchrony 24 h after Initiation of Mechanical Ventilation.

BACKGROUND: Reverse triggering is a delayed asynchronous contraction of the diaphragm triggered by passive insufflation by the ventilator in sedated mechanically ventilated patients. The incidence of reverse triggering is unknown. This study aimed at determining the incidence of reverse triggering in critically ill patients under controlled ventilation. METHODS: In this ancillary study, patients were continuously monitored with a catheter measuring the electrical activity of the diaphragm. A method for automatic detection of reverse triggering using electrical activity of the diaphragm was developed in a derivation sample and validated in a subsequent sample. The authors assessed the predictive value of the software. In 39 recently intubated patients under assist-control ventilation, a 1-h recording obtained 24 h after intubation was used to determine the primary outcome of the study. The authors also compared patients' demographics, sedation depth, ventilation settings, and time to transition to assisted ventilation or extubation according to the median rate of reverse triggering. RESULTS: The positive and negative predictive value of the software for detecting reverse triggering were 0.74 (95% CI, 0.67 to 0.81) and 0.97 (95% CI, 0.96 to 0.98). Using a threshold of 1 µV of electrical activity to define diaphragm activation, median reverse triggering rate was 8% (range, 0.1 to 75), with 44% (17 of 39) of patients having greater than or equal to 10% of breaths with reverse triggering. Using a threshold of 3 µV, 26% (10 of 39) of patients had greater than or equal to 10% reverse triggering. Patients with more reverse triggering were more likely to progress to an assisted mode or extubation within the following 24 h (12 of 39 [68%]) vs. 7 of 20 [35%]; P = 0.039). CONCLUSIONS: Reverse triggering detection based on electrical activity of the diaphragm suggests that this asynchrony is highly prevalent at 24 h after intubation under assist-control ventilation. Reverse triggering seems to occur during the transition phase between deep sedation and the onset of patient triggering.

Work of Breathing in Premature Neonates: Noninvasive Neurally-Adjusted Ventilatory Assist versus Noninvasive Ventilation.

BACKGROUND: We tested whether work of breathing in premature newborns estimated by phase angle (θ) by using respiratory inductance plethysmography is decreased during neurally-adjusted ventilatory assist (NAVA) noninvasive ventilation (NIV) versus NIV alone. METHODS: NAVA NIV and NIV were applied in random order while using respiratory inductance plethysmography to measure the phase angle. RESULTS: Patient-ventilator asynchrony was decreased during NAVA NIV; however, the phase angle was not different between the modes. A large number of repeated assists with switches to backup were found when using NAVA NIV. Results of the analysis indicated these were due to the apnea alarm limit set during NAVA NIV. CONCLUSIONS: The improvement in patient-ventilator synchrony supports the hypothesis that work of breathing may be decreased with NAVA NIV; however, we were unable to demonstrate this with our study design. Short apnea time settings with NAVA NIV led to a large number of switches to backup and repeated assists during the same neural effort. (ClinicalTrials.gov registration NCT02788110.).

Tidal volume transmission during non-synchronized nasal intermittent positive pressure ventilation via RAM® cannula.

BACKGROUND: Nasal intermittent positive pressure ventilation (NIPPV) is a widely used mode of support in neonates, during which ventilator inflations may or may not coincide with spontaneous breathing. OBJECTIVE: We tested the hypothesis that inflations delivered with NIPPV via RAM® cannula and not accompanied by patient effort produce minimal tidal volume as measured by respiratory inductance plethysmography. DESIGN/METHODS: Fourteen subjects were monitored while receiving NIPPV. We compared tidal volumes during ventilator-supported breaths, unsupported breaths, and ventilator inflations not accompanied by patient effort (defined using electrical activity of the diaphragm). RESULTS: Mean tidal volumes in arbitrary units were 0.30 ± 0.22 in NIPPV inflations associated with patient effort and 0.27 ± 0.15 in spontaneous breaths without ventilator assistance (p = 0.82). Tidal volumes during ventilator-only inflations were 0.06 ± 0.04 (p < 0.005 vs. both ventilator-assisted and unassisted efforts). CONCLUSIONS: NIPPV via RAM cannula produces minimal, clinically insignificant tidal volumes during non-spontaneous inflations.

[Functional consequences of eccentric contractions of the diaphragm]. / Consecuencias de las contracciones excéntricas del diafragma sobre su función.

INTRODUCTION AND OBJECTIVES: Eccentric contractions are those that occur after a muscle has been stretched, and they can predispose the muscle to damage. Most previous studies have been performed on limb muscles, and the potential consequences of eccentric contractions on the respiratory muscles are therefore unknown. The aim of this study was to evaluate the effects of repeated eccentric contractions on diaphragmatic function. METHODS: In 6 dogs, the diaphragm was stretched by applying pressure on the abdominal wall, and consecutive series of eccentric contractions were induced by bilateral supramaximal stimulation. The effect of these contractions on the diaphragm was then evaluated by applying bilateral twitch and tetanic stimulation of the phrenic nerves and measuring the changes in abdominal pressure and the shortening of the right and left hemidiaphragms (by sonomicrometry). Structural study of the muscle was also performed in 4 animals. RESULTS: Eccentric contractions were successfully achieved in all cases. Stimulation-induced diaphragmatic pressures became lower immediately after these contractions: twitch pressure fell by 53% and tetanic pressure by 67% after the first 10 eccentric contractions (P<.001 in both cases). Tetanic stimulation also demonstrated an early deterioration in contractility, which fell by 29% in the right hemidiaphragm (P<.05) and by 14% in the left hemidiaphragm (P<.001). Functional impairment was persistent, lasting at least 12 hours, and was associated with sarcomeric and sarcolemmal damage. CONCLUSIONS: This experimental model, which enabled the effects of eccentric contractions to be studied in the diaphragm, revealed a deterioration of muscle function that persisted for hours and that appeared to be partly due to structural damage. In the clinical setting, physiologic or therapeutic maneuvers that increase the resting length of the diaphragm should be used with caution.

[Modifications of diaphragmatic activity induced by midline laparotomy and changes in abdominal wall compliance]. / Modificaciones en la actividad del diafragma inducidas por laparotomía media y cambios en la rigidez de la pared abdominal.

INTRODUCTION AND OBJECTIVE: Diaphragmatic activity varies with the initial length of the muscle. Our objective was to evaluate the influence of surgery and changes in abdominal wall compliance on diaphragmatic activity. METHODS: Both phrenic nerves in 7 mongrel dogs were stimulated electrically with single supramaximal pulses (twitch). The gastric (Pga) and transdiaphragmatic (Pdi) pressures generated and muscle shortening (sonomicrometry) were used to evaluate diaphragmatic activity, which was determined at baseline, after midline laparotomy, with an elastic abdominal bandage, and with a rigid circular cast. Abdominal pressure was then gradually increased in order to induce progressive lengthening of the diaphragm. RESULTS: After laparotomy, the pressures were somewhat lower (by 12%) than at baseline. The elastic bandage produced a slight increase in the pressure generated by the diaphragm (mean [SE] values: Pga, from 4.2 [0.3]cm H(2)O to 6.3 [0.9]cm H(2)O, P<.01; Pdi(tw), from 12.1 [2.0]cm H(2)O to 15.4 [1.8]cm H(2)O, P<.05]), and these values increased even further with the rigid cast (Pga, to 12.6 [1.5]cm H(2)O; Pdi, to 20.2 [2.3]cm H(2)O; P<.01 for both comparisons); this occurred despite smaller degrees of muscle shortening: by 57% [5%] of the initial length at functional residual capacity at baseline, by 49% [5%] with the bandage (P<.05), and by 39% [6%] with the cast (P<.01). With progressive lengthening of the muscle, its contractile efficacy increased up to a certain point (105% of the length at functional residual capacity), after which it began to decline. CONCLUSIONS: Abdominal wall compliance plays an important role in the diaphragmatic response to stimulation. This appears to be due mainly to changes in its length at rest.

Consecuencias de las contracciones excéntricas del diafragma sobre su función / Functional Consequences of Eccentric Contractions of the Diaphragm

Introducción y objetivos las contracciones excéntricas (CC.EE.) se caracterizan por producirse previa elongación muscular, lo que facilita la lesión. La mayoría de los estudios precedentes se han desarrollado en músculos de las extremidades, por lo que se desconoce la relevancia potencial de las CC.EE. en los músculos respiratorios. El objetivo del presente trabajo ha sido evaluar los efectos funcionales de series repetidas de CC.EE. sobre el diafragma. Métodose provocó la elongación del diafragma mediante presión externa abdominal en 6 perros y se indujeron CC.EE. mediante series consecutivas de pulsos supramáximos bilaterales. El efecto se valoró mediante la posterior respuesta del músculo ante estimulación frénica bilateral tanto de pulso único como tetánica, en términos de presión y acortamiento (sonomicrometría) de los hemidiafragmas derecho e izquierdo. En 4 casos se realizó estudio estructural. Resultadosse consiguió inducir CC.EE. en todos los casos. Las presiones diafragmáticas inducidas por estimulación disminuyeron inmediatamente después de la actividad excéntrica (pulso único: 53%; tetánica: 67%; p<0,001 en ambas, tras las primeras 10 CC.EE.), al igual que la propia contractilidad diafragmática (evidenciable con la estimulación tetánica; hemidiafragma derecho un HD 29%, p<0,05, e hemidiafragma izquierdo, un 14%, p<0,001). La disfunción fue persistente (duró al menos 12h) y se asoció a la presencia de daño sarcomérico y sarcolémico. Conclusióncon el modelo propuesto, que permite estudiar el efecto de las CC.EE. en el diafragma, se demuestra una pérdida funcional mantenida durante horas, que en parte parece debida a una lesión estructural. Clínicamente se debería ser cauto con las maniobras fisiológicas o terapéuticas que impliquen la elongación basal del diafragma(AU)

Introduction and Objectives Eccentric contractions are those that occur after a muscle has been stretched, and they can predispose the muscle to damage. Most previous studies have been performed on limb muscles, and the potential consequences of eccentric contractions on the respiratory muscles are therefore unknown. The aim of this study was to evaluate the effects of repeated eccentric contractions on diaphragmatic function. MethodsIn 6 dogs, the diaphragm was stretched by applying pressure on the abdominal wall, and consecutive series of eccentric contractions were induced by bilateral supramaximal stimulation. The effect of these contractions on the diaphragm was then evaluated by applying bilateral twitch and tetanic stimulation of the phrenic nerves and measuring the changes in abdominal pressure and the shortening of the right and left hemidiaphragms (by sonomicrometry). Structural study of the muscle was also performed in 4 animals. ResultsEccentric contractions were successfully achieved in all cases. Stimulation-induced diaphragmatic pressures became lower immediately after these contractions: twitch pressure fell by 53% and tetanic pressure by 67% after the first 10 eccentric contractions (P<.001 in both cases). Tetanic stimulation also demonstrated an early deterioration in contractility, which fell by 29% in the right hemidiaphragm (P<.05) and by 14% in the left hemidiaphragm (P<.001). Functional impairment was persistent, lasting at least 12 hours, and was associated with sarcomeric and sarcolemmal damage. ConclusionsThis experimental model, which enabled the effects of eccentric contractions to be studied in the diaphragm, revealed a deterioration of muscle function that persisted for hours and that appeared to be partly due to structural damage. In the clinical setting, physiologic or therapeutic maneuvers that increase the resting length of the diaphragm should be used with caution(AU)

Modificaciones en la actividad del diafragma inducidas por laparotomía media y cambios en la rigidez de la pared abdominal / Modifications of Diaphragmatic Activity Induced by Midline Laparotomy and Changes in Abdominal Wall Compliance

Introducción y objetivos la actividad del diafragma puede verse modificada por su longitud inicial. Nuestro objetivo ha sido evaluar la influencia de la cirugía y los cambios en la rigidez de la pared abdominal sobre la actividad del músculo.Métodoen 7 perros mestizos se estimularon eléctricamente ambos nervios frénicos con pulsos únicos supramáximos (twitch). Para evaluar la actividad del diafragma se determinaron las presiones generadas —gástrica (Pgatw) y transdiafragmática (Pditw)— y el acortamiento muscular (sonomicrometría). La respuesta diafragmática se obtuvo en situación basal, tras laparotomía media, con venda abdominal elástica y con prótesis rígida circular. A continuación se incrementó ligera y progresivamente la presión abdominal para conseguir el alargamiento sucesivo del diafragma.Resultadostras la laparotomía, las presiones fueron algo inferiores a las basales (12%). La banda elástica provocó un leve aumento de la presión generada por el diafragma (valores medios±error estándar. Pgatw: 4,2±0,3 a 6,3±0,9cmH2O, p<0,01; Pditw: 12,1±2,0 a 15,4±1,8cmH2O, p<0,05), que se incrementó aún más con la prótesis rígida (Pgatw: 12,6±1,5cmH2O; Pditw: 20,2±2,3cmH2O; p<0,01 para ambas), a pesar de valores de acortamiento inferiores —un 57±5% de la longitud inicial a capacidad funcional residual en situación basal, un 49±5% con banda (p<0,05) y un 39±6% con prótesis (p<0,01)—. Al alargar progresivamente el músculo, su efectividad contráctil aumentó hasta un punto (un 105% de la longitud a capacidad funcional residual) a partir del cual comenzó a declinar.Conclusiónla rigidez de la pared abdominal desempeña un papel importante en la respuesta del diafragma a la estimulación. Esto parece deberse fundamentalmente a cambios en su longitud de reposo(AU)

Introduction and Objective Diaphragmatic activity varies with the initial length of the muscle. Our objective was to evaluate the influence of surgery and changes in abdominal wall compliance on diaphragmatic activity.MethodsBoth phrenic nerves in 7 mongrel dogs were stimulated electrically with single supramaximal pulses (twitch). The gastric (Pga) and transdiaphragmatic (Pdi) pressures generated and muscle shortening (sonomicrometry) were used to evaluate diaphragmatic activity, which was determined at baseline, after midline laparotomy, with an elastic abdominal bandage, and with a rigid circular cast. Abdominal pressure was then gradually increased in order to induce progressive lengthening of the diaphragm.ResultsAfter laparotomy, the pressures were somewhat lower (by 12%) than at baseline. The elastic bandage produced a slight increase in the pressure generated by the diaphragm (mean [SE] values: Pga, from 4.2 [0.3]cm H2O to 6.3 [0.9]cm H2O, P<.01; Pditw, from 12.1 [2.0]cm H2O to 15.4 [1.8]cm H2O, P<.05]), and these values increased even further with the rigid cast (Pga, to 12.6 [1.5]cm H2O; Pdi, to 20.2 [2.3]cm H2O; P<.01 for both comparisons); this occurred despite smaller degrees of muscle shortening: by 57% [5%] of the initial length at functional residual capacity at baseline, by 49% [5%] with the bandage (P<.05), and by 39% [6%] with the cast (P<.01). With progressive lengthening of the muscle, its contractile efficacy increased up to a certain point (105% of the length at functional residual capacity), after which it began to decline.ConclusionsAbdominal wall compliance plays an important role in the diaphragmatic response to stimulation. This appears to be due mainly to changes in its length at rest(AU)

[Diaphragmatic response is influenced by previous muscle activity]. / Respuesta diafragmática en función de la actividad previa del músculo.

OBJECTIVE: Previous muscle activity can alter muscle contractility and lead to strength underestimation or overestimation in functional measurements. The objective of this study was to evaluate changes in the maximum pressure produced by the diaphragm after different series of spontaneous near-to-maximal isometric contractions. METHODS: Duplicate studies were performed on 6 dogs with a mean (SD) weight of 26 (7) kg. The supramaximal response of the diaphragm was achieved by simultaneous supramaximal stimulation of both phrenic nerves, both under basal conditions and after series of 5, 10, and 20 spontaneous inspiratory efforts against the occluded airway, performed before and after spinal anesthesia (which eliminates the ventilatory contribution of the intercostal muscles). The response was measured using the twitch gastric pressure (Pga) and twitch esophageal pressure (Pes) and by muscle shortening (sonomicrometry). RESULTS: The short series of 5 inspiratory efforts and, in particular, the medium series of 10 efforts produced potentiation of the contractile response, with a rise in the Pga from 3.2 (0.4) cm H(2)O to 3.7 (0.3) cm H(2)O, and from 3.5 (0.3) cm H(2)O to 3.9 (0.3) cm H(2)O, respectively (P=.05 in both cases). The potentiation was somewhat greater after subarachnoid anesthesia (an increase in the Pga of 21% after the medium series of 10 efforts with anesthesia vs 11% without anesthesia). However, the long series of 20 efforts produced a fall in the response, with a decrease in the Pga from 3.2 (0.4) cm H(2)O to 2.5 (0.3) cm H(2)O (P< .05), probably due to fatigue overcoming the effect of potentiation. CONCLUSIONS: Previous effort affects the contractile capacity of the diaphragm and it is difficult to predict the predominance of fatigue or potentiation in the response. This factor must be taken into account when determining the maximum respiratory pressures in daily clinical practice.

Respuesta diafragmática en función de la actividad previa del músculo / Diaphragmatic response is influenced by previous muscle activity

OBJETIVO: La actividad previa puede modificar la contractilidadmuscular, lo que puede conducir a la infra o supraestimaciónde la fuerza en las determinaciones funcionales.El presente trabajo se ha propuesto como objetivovalorar cambios en la presión máxima generada por el diafragmatras diferentes series de contracciones isométricasespontáneas y cuasi máximas.MÉTODOS: Se estudiaron por duplicado 6 perros con unpeso medio ± desviación estándar de 26 ± 7 kg. Se obtuvo larespuesta supramáxima del diafragma –presiones gástrica(Pgatw) y esofágica (Pestw) inducidas por estimulación frénicabilateral, y acortamiento muscular (sonomicrometría)— porestimulación simultánea supramáxima de ambos nervios frénicos,tanto en situación basal como tras series cortas(5), medianas (10) y largas (20) de esfuerzos inspiratorios espontáneoscontra la vía aérea ocluida, antes y después de administraranestesia subaracnoidea (elimina la contribuciónventilatoria de los músculos intercostales).RESULTADOS: La serie corta y, sobre todo, la serie medianaprovocaron la potenciación de la respuesta contráctil (Pgatwde 3,2 ± 0,4 a 3,7 ± 0,3, y de 3,5 ± 0,3 a 3,9 ± 0,3 cmH2O, respectivamente;p < 0,05 ambas). La potenciación fue algo superiorcon anestesia subaracnoidea (un 21 frente al 11% sinanestesia, para la Pgatw tras las series medianas). La serielarga provocó, sin embargo, una disminución de la respuesta(Pgatw: 3,2 ± 0,4 a 2,5 ± 0,3 cmH2O; p < 0,05), probablementepor predominio de la fatiga sobre la potenciación.CONCLUSIONES: Los esfuerzos previos determinan la capacidadcontráctil del diafragma y resulta difícil predecir elpredominio de fatiga o de potenciación en la respuesta. Estefactor debería tenerse en cuenta al determinar las presionesrespiratorias máximas en la clínica diaria

OBJECTIVE: Previous muscle activity can alter musclecontractility and lead to strength underestimation oroverestimation in functional measurements. The objectiveof this study was to evaluate changes in the maximumpressure produced by the diaphragm after different seriesof spontaneous near-to-maximal isometric contractions.METHODS: Duplicate studies were performed on 6 dogs witha mean (SD) weight of 26 (7) kg. The supramaximal responseof the diaphragm was achieved by simultaneous supramaximalstimulation of both phrenic nerves, both under basal conditionsand after series of 5, 10, and 20 spontaneous inspiratory effortsagainst the occluded airway, performed before and after spinalanesthesia (which eliminates the ventilatory contribution of theintercostal muscles). The response was measured using thetwitch gastric pressure (Pga) and twitch esophageal pressure(Pes) and by muscle shortening (sonomicrometry).RESULTS: The short series of 5 inspiratory efforts and, inparticular, the medium series of 10 efforts produced potentiationof the contractile response, with a rise in the Pga from 3.2 (0.4)cmH2O to 3.7 (0.3) cmH2O, and from 3.5 (0.3) cmH2O to 3.9 (0.3)cmH2O, respectively (P=.05 in both cases). The potentiation wassomewhat greater after subarachnoid anesthesia (an increase inthe Pga of 21% after the medium series of 10 efforts withanesthesia vs 11% without anesthesia). However, the long seriesof 20 efforts produced a fall in the response, with a decrease in thePga from 3.2 (0.4) cmH2O to 2.5 (0.3) cmH2O (P<.05), probablydue to fatigue overcoming the effect of potentiation.CONCLUSIONS: Previous effort affects the contractilecapacity of the diaphragm and it is difficult to predict thepredominance of fatigue or potentiation in the response. Thisfactor must be taken into account when determining themaximum respiratory pressures in daily clinical practice