[A pilot study of diaphragmatic function evaluated as predictors of weaning in chronic obstructive pulmonary disease patients].

OBJECTIVE: To evaluate the predictive performance of neuro-mechanical coupling (NMC) and neuro-ventilatory coupling (NVC) in the weaning outcome in patients with chronic obstructive pulmonary disease (COPD). METHODS: Sixteen patients were enrolled when the criteria for their first spontaneous breathing trial (SBT) was met. A 30-minute SBT was attempted, with the measurement of electrical activity of the diaphragm (Edi), NMC, NVC, NVC × NMC, index of rapid shallow breathing (f/Vt), airway occlusion pressure (P(0.1)) and f/Vt × P(0.1) at 0, 5 and 30 min. The receiver operating characteristic (ROC) curve was calculated to evaluate the predictive performance of each index. RESULTS: Successful weaning (S group) was observed in 6 patients while weaning failure (F group) in 10 patients. (1) The predictive capacity of Edi: at 30 min of SBT, Edi showed higher values in the F group (P < 0.05), the area under the ROC curves (AUC) was 0.817(P < 0.05). (2) The predictive capacity of NVC and NMC: at 5, 30 min of SBT, NVC and NMC showed higher values in the S group (P < 0.05); at 30 min of SBT NVC presented the largest AUC than any other time of SBT (0.822, P < 0.05), while the AUC of NMC was 0.800(P > 0.05). (3) The predictive capacity of NVC × NMC: at 30 min of SBT, the AUC of NVC × NMC was larger than NVC (0.864, P < 0.05), showing greater sensitivity (100.0%) and specificity (83.3%). (4) The predictive capacity of f/Vt and P(0.1): f/Vt and f/Vt × P(0.1) presented poor predictive performance in the failed patients. CONCLUSIONS: Edi, NVC and NVC × NMC were good predictor for the weaning outcome in patients with COPD.

[Effects of neurally adjusted ventilatory assist on subject-ventilator synchrony in rabbits with acute respiratory distress syndrome].

OBJECTIVE: To observe the effects of neurally adjusted ventilatory assist (NAVA) on subject-ventilator synchrony in rabbits with acute respiratory distress syndrome (ARDS). METHODS: The rabbit model of ARDS was induced by intratracheal infusion of hydrochloric acid. After sufficient recruitment, the rabbits were randomly divided into 2 groups: pressure support ventilation (PSV) group and NAVA group. The parameters of subject-ventilator synchrony such as ventilation trigger, ventilation switching and magnitude of assist were observed at 0, 1, 2, 3 h respectively. RESULTS: (1) Ventilation trigger: 1) trigger delay: the trigger delay in the NAVA group were markedly lower than the PSV group at 0, 1, 2, 3 h (P < 0.05); as ventilation time elapsed, the trigger delay changed neither in NAVA nor in PSV group (P > 0.05). 2) Ineffective trigger index: the ineffective trigger index was 17.7% ± 13.7% in the PSV group. While all neural efforts were trigger, there was no ineffective trigger observed in the NAVA group. (2) Off-cycle delay: the off-cycle delay were significantly lower in the PSV group than that in the NAVA group at 0, 1, 2, 3 h (P < 0.05); as the ventilation time elapsed, the off-cycle delay changed neither in the NAVA group nor in the PSV group (P > 0.05). (3) Magnitude of assist: in the NAVA group, peak EAdi and peak pressure were markedly correlated (determination coefficient 0.86 ± 0.07, P < 0.05). But pressure delivery during the PSV group was not correlated with EAdi (P > 0.05). CONCLUSION: As compared with PSV, NAVA can improve subject-ventilator synchrony in rabbits with ARDS.

[Effects of neurally adjusted ventilatory assist on prevention of ventilator-induced diaphragmatic dysfunction in acute respiratory distress syndrome rabbits].

OBJECTIVE: To evaluate the effect of neurally adjusted ventilatory assist (NAVA) on prevention of ventilator-induced diaphragmatic dysfunction (VIDD) in ARDS rabbits. METHODS: Twenty New Zealand white rabbits were randomly divided into 4 groups: (1) control group (n = 5); (2) Volume control (VC) group (n = 5); (3) Pressure support (PSV) group (n = 5); (4) NAVA group (n = 5). In VC, PSV and NAVA groups, the rabbits were killed and the diaphragm was removed after 4 hours of ventilation. Animals in the control group were not mechanically ventilated, and the diaphragm was also removed immediately after anesthetizing. In all rabbits, malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH) of diaphragm were measured. Structure of diaphragm was observed by light microscope, electron microscope, constituent ratio and mean cross-sectional area (CSA) of diaphragm fiber. RESULTS: (1) MDA: Compared with the control [(0.15 ± 0.06) nmol/mg], PSV group [(0.30 ± 0.11) nmol/mg], there was no significant difference in MDA of diaphragm in NAVA group [(0.28 ± 0.19) nmol/mg] (F = 2.730, P > 0.05). MDA in VC group [(0.40 ± 0.16) nmol/mg] was significantly higher than the control group (P < 0.05). (2) SOD: Compared with control [(111 ± 12) U/mg], PSV group [(93 ± 4) U/mg], there was no significant difference in SOD of diaphragm in NAVA group [(94 ± 9) U/mg] (F = 4.422, P > 0.05). SOD in VC group [(80 ± 21) U/mg] was significantly lower than the control group (P < 0.05). (3) GSH: Compared with control [(5.3 ± 1.0) mg/g] and PSV group [(4.5 ± 1.2) mg/g], there was no significant difference in GSH of diaphragm in NAVA group [(5.6 ± 1.0) mg/g] (F = 3.001, P > 0.05). GSH in VC group [(3.3 ± 1.7) mg/g] is significantly lower than control and NAVA groups (P < 0.05). (4) Light microscope: In VC group, many changes were observed in the muscle, such as myelofibrosis, necrosis, and some of muscle fibers became atrophy, but these were no obvious changes of pathological structure in control, PSV or NAVA groups. (5) Electron microscope: In control, PSV and NAVA groups, the ultrastructure of diaphragm was normal. Different from the above 3 groups, some abnormal ultrastructure was observed in VC group, including disrupted myofibrils, swollen mitochondria. (6) CSA of diaphragm fiber: Compared with control and PSV group, there was no significant difference in CSA of diaphragm fiber in NAVA group (P > 0.05); The CSA of type II fibers in VC group was markedly lower than control group (P < 0.05). CONCLUSIONS: Compared with volume control ventilation, NAVA may mitigate diaphragmatic oxidative stress, atrophy and injury, and prevent VIDD better than VC.

Effects of pulmonary stretch reflex on lung injury in rabbits with acute respiratory distress syndrome.

BACKGROUND: Pulmonary stretch reflex plays an important role in regulation of respiratory movement. This study aimed to evaluate the effect of pulmonary stretch reflex on lung injury in rabbits with acute respiratory distress syndrome (ARDS). METHODS: ARDS rabbits were given intratracheal infusion of hydrochloric acid and ventilated with neurally adjusted ventilatory assistance (NAVA) with a tidal volume (VT) of 6 mL/kg and the electrical activity of diaphragm (EAdi)-determined positive end expiratory pressure. After isolation of the bilateral vagus nerve trunk, the rabbits were randomized into two groups: sham operation (SHAM) group (n=5) and bilateral vagotomy (VAG) group (n=5). Gas exchange and respiratory mechanics were detected at baseline, after lung injury and 1, 2, and 3 hours after ventilation respectively. Pulmonary permeability index, pathological changes and inflammatory response were also measured. RESULTS: Compared with the SHAM group, PaO2/FiO2 in the VAG group decreased significantly 2 and 3 hours after ventilation (P<0.05). There was no significant difference in PaCO2 between the SHAM and VAG groups (P>0.05), and the VAG group had a high VT, peak pressure (Ppeak), and mean pressure (Pm) compared with the SHAM group 1, 2, 3 hours after ventilation (P<0.05). Compared to the SHAM group, dead space fraction (VD/VT) and respiratory system elastance (Ers) in the VAG group increased (P<0.05) and static pulmonary compliance (Cst) decreased markedly (P<0.05) after ventilation for 3 hours. Lung wet/dry weight ratio (W/D) (8.4±1.2 vs. 6.6±1.0), lung injury score (6.3±1.8 vs. 3.8±1.3), tumor necrosis factor-α (TNF-α) (779±372 pg/mL vs. 355±130 pg/mL) and interleukin-8 (IL-8) (169±21 pg/mL vs. 118±17 pg/mL) increased significantly in the VAG group compared with the SHAM group (P<0.05). CONCLUSION: Lung injury is aggravated after bilateral vagotomy, demonstrating that pulmonary stretch reflex may have protective effect on the lung.

[Effects of electrical activity of diaphragm on the titration of positive end-expiratory pressure in a model of acute respiratory distress syndrome].

OBJECTIVE: To explore the relationship of electrical activity of diaphragm (EAdi) and positive end-expiratory pressure (PEEP) in a rabbit model of acute respiratory distress syndrome (ARDS). METHODS: The rabbit model of ARDS was induced by an intratracheal infusion of hydrochloric acid. After a sufficient amount of recruitment maneuvers (RM), the level: the PEEP levels were (10.4 ± 1.0) cm H2O in EAdi group and (9.7 ± 2.1) cm H2O in rabbits were divided into 2 groups: (1) PEEP titration with EAdi (EAdi group); (2) PEEP titration with maximum oxygenation (maximum oxygenation group). The tidal volume was 6 ml/kg in 2 groups. Pulmonary mechanics, gas exchange and hemodynamic were observed in two groups at baseline, after lung injury and ventilation 1, 2, 3 h respectively. RESULTS: (1) PEEP maximum oxygenation group. There was no significant difference between two groups (P > 0.05). (2) Pulmonary mechanics:there was no significant difference in peak pressure (Ppeak) and mean pressure (Pm) between two groups at ventilation 1, 2, 3 h (P > 0.05). (3) Gas exchange: at ventilation 1, 2, 3 h, the oxygenation index (PaO2/FiO2) in EAdi group was higher than that of after lung injury (P < 0.05) and there was no significant difference in PaO2/FiO2 and partial pressure of arterial carbon dioxide (PaCO2) between two groups (P > 0.05). (4) Hemodynamic: at ventilation 1, 2, 3 h, the heart rate (HR) and mean artery pressure (MAP) in EAdi group had no significant differences with baseline, after lung injury and maximum oxygenation group (P > 0.05). CONCLUSION: EAdi may be an ideal method for PEEP titration at post-RM in an ARDS model.

[Effects of neurally adjusted ventilatory assist on patient-ventilator synchrony in patients with acute respiratory distress syndrome].

OBJECTIVE: To observe the effect of neurally adjusted ventilatory assist (NAVA) on patient-ventilator synchrony in patients with acute respiratory distress syndrome (ARDS). METHODS: Eighteen patients with ARDS were enrolled in the study. Each patient underwent both an incremental pressure support ventilation (PSV) and NAVA run randomly in 4 steps. The PSV level was gradually increased 5 cm H2O (1 cm H2O = 0.098 kPa) every 5 min from 5 cm H2O until to 20 cm H2O. Incremental NAVA was individually set in steps of 0.2 - 1.0 cm H2O/microV every 5 min to determine the NAVA level predicted to give an airway pressure in each step equivalent to that of PSV. Parameters in patient-ventilator synchrony such as ventilation trigger, ventilation switching and ventilation maintenance were observed at the same time during PSV(PSV1-PSV4) and NAVA(NAVA1-NAVA4). RESULTS: (1) Ventilation trigger:(1) trigger delay: with progressive increases in PSV, the trigger delays increased significantly (P < 0.05). With increasing NAVA, the trigger delay did not increase significantly (P > 0.05) and each of them was shorter than that of PSV in each corresponding step (P < 0.05). (2) Ineffective trigger: At PSV1, the ineffective triggers accounted for 2. 3% of the neural respiratory rate (NRR), but the ineffective triggers added up to 22% in PSV4 significantly (P < 0.05). All neural efforts were triggered and there were not ineffective triggers at all level in NAVA. (2) Off cycle delay: the off cycle delays in PSV2 - PSV4 increased significantly when compared with PSV1 (P < 0.05). With increasing NAVA, the off cycle delays did not increase significantly (P > 0.05) and each of them was shorter than that of PSV in each corresponding step (P < 0.05). (3) Magnitude of assist [tidal volume (VT)]: The VT [(361 +/- 69) ml] in NAVA1 was equivalent to the VT[(361 +/- 121) ml] in PSV1(P > 0.05). The VT [(417 +/- 71) ml, (427 +/- 80) ml, respectively] in NAVA3-NAVA4 was significantly lower than the VT[(604 +/- 141) ml, (675 +/- 108) ml, respectively] in PSV3-PSV4 (P < 0.05). (4)Respiratory muscle loading: Increasing NAVA and PSV level reduced the magnitude of diaphragm electrical activity (EAdi) and the pressure-time products of esophagus (PTPes) (P < 0.05), but there was no significant difference in each corresponding step of PSV and NAVA(P > 0.05). CONCLUSIONS: Compared with PSV, the ventilation cycle and the magnitude of assist in NAVA matched the patient's breathing pattern. NAVA improved patient-ventilator synchrony in patients with ARDS.