A mechanical ventilation trigger way is set forth and a technical analysis on the pressure trigger way and flow trigger way is made in this paper. And it is pointed out that the PEEPi's influence on the human organism is the reason for the latter two kinds of trigger ways' notable differences in the measured values of the inspiration time and breath work.
Humans ; Positive-Pressure Respiration ; Respiration, Artificial ; methods ; Work of Breathing

Without artificial airway though oral, nasal or airway incision, the bi-level positive airway pressure (Bi-PAP) has been widely employed for respiratory patients. In an effort to investigate the therapeutic effects and measures for the respiratory patients under the noninvasive Bi-PAP ventilation, a therapy system model was designed for virtual ventilation experiments. In this system model, it includes a sub-model of noninvasive Bi-PAP respirator, a sub-model of respiratory patient, and a sub-model of the breath circuit and mask. And based on the Matlab Simulink, a simulation platform for the noninvasive Bi-PAP therapy system was developed to conduct the virtual experiments in simulated respiratory patient with no spontaneous breathing (NSB), chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). The simulated outputs such as the respiratory flows, pressures, volumes, etc, were collected and compared to the outputs which were obtained in the physical experiments with the active servo lung. By statistically analyzed with SPSS, the results demonstrated that there was no significant difference ( P > 0.1) and was in high similarity ( R > 0.7) between the data collected in simulations and physical experiments. The therapy system model of noninvasive Bi-PAP is probably applied for simulating the practical clinical experiment, and maybe conveniently applied to study the technology of noninvasive Bi-PAP for clinicians.
Humans ; Respiration, Artificial/methods* ; Positive-Pressure Respiration/methods* ; Respiration ; Ventilators, Mechanical ; Lung

Neurocritical care (NCC) is not only generally guided by principles of general intensive care, but also directed by specific goals and methods. This review summarizes the common pulmonary diseases and pathophysiology affecting NCC patients and the progress made in strategies of respiratory support in NCC. This review highlights the possible interactions and pathways that have been revealed between neurological injuries and respiratory diseases, including the catecholamine pathway, systemic inflammatory reactions, adrenergic hypersensitivity, and dopaminergic signaling. Pulmonary complications of neurocritical patients include pneumonia, neurological pulmonary edema, and respiratory distress. Specific aspects of respiratory management include prioritizing the protection of the brain, and the goal of respiratory management is to avoid inappropriate blood gas composition levels and intracranial hypertension. Compared with the traditional mode of protective mechanical ventilation with low tidal volume (Vt), high positive end-expiratory pressure (PEEP), and recruitment maneuvers, low PEEP might yield a potential benefit in closing and protecting the lung tissue. Multimodal neuromonitoring can ensure the safety of respiratory maneuvers in clinical and scientific practice. Future studies are required to develop guidelines for respiratory management in NCC.
Humans ; Lung ; Lung Diseases/etiology* ; Positive-Pressure Respiration/methods* ; Respiration, Artificial/adverse effects* ; Tidal Volume

OBJECTIVE: To find out the circuit pressure and flow at the trigger point by observing the characteristics of the inspiratory trigger waveform of the ventilator, confirm the intra-alveolar pressure as the index to reflect the effort of the trigger according to the working principle of the ventilator combined with the laws of respiratory mechanics, establish the related mathematical formula, and analyze its influencing factors and logical relationship. METHODS: A test-lung was connected to the circuit in a PB840 ventilator and a SV600 ventilator set in pressure-support mode. The positive end-expiratory pressure (PEEP) was set at 5 cmH₂O (1 cmH₂O ≈ 0.098 kPa), and the wall of test-lung was pulled outwards till an inspiratory was effectively triggered separately in slow, medium, fast power, and separately in flow-trigger mode (sensitivity V_Trig 3 L/min, 5 L/min) and pressure-trigger mode (sensitivity P_Trig 2 cmH₂O, 4 cmH₂O). By adjusting the scale of the curve in the ventilator display, the loop pressure and flow corresponding to the trigger point under different triggering conditions were observed. Taking intraalveolar pressure (Pa) as the research object, the Pa (called P_a-T) needed to reach the effective trigger time (T_T) was analyzed in the method of respiratory mechanics, and the amplitude of pressure change (ΔP) and the time span (ΔT) of Pa during triggering were also analyzed. RESULTS: (1) Corresponding relationship between pressure and flow rate at TT time: in flow-trigger mode, in slow, medium and fast trigger, the inhalation flow rate was V_Trig, and the circuit pressure was separately PEEP, PEEP-Pn, and PEEP-Pn' (Pn, Pn', being the decline range, and Pn' > Pn). In pressure-trigger mode, the inhalation flow rate was 1 L/min (PB840 ventilator) or 2 L/min (SV600 ventilator), and the circuit pressure was PEEP-P_Trig. (2) Calculation of P_a-T: in flow-trigger mode, in slow trigger: P_a-T = PEEP-V_TrigR (R represented airway resistance). In medium trigger: P_a-T = PEEP-Pn-V_TrigR. In fast trigger: P_a-T = PEEP-Pn'-V_TrigR. In pressure-trigger mode: P_a-T = PEEP-P_Trig-1R. (3) Calculation of ΔP: in flow trigger mode, in flow trigger: without intrinsic PEEP (PEEPi), ΔP = V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+V_TrigR. In medium trigger: without PEEPi, ΔP = Pn+V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+Pn+V_TrigR. In fast trigger: without PEEPi, ΔP = Pn'+V_TrigR; with PEEPi, ΔP = PEEPi-PEEP+Pn'+V_TrigR. In pressure-trigger mode, without PEEPi, ΔP = P_Trig+1R; with PEEPi, ΔP = PEEPi-PEEP+P_Trig+1R. (4) Pressure time change rate of Pa (F_P): F_P = ΔP/ΔT. In the same ΔP, the shorter the ΔT, the greater the triggering ability. Similarly, in the same ΔT, the bigger the ΔP, the greater the triggering ability. The FP could better reflect the patient's triggering ability. CONCLUSIONS The patient's inspiratory effort is reflected by three indicators: the minimum intrapulmonary pressure required for triggering, the pressure span of intrapulmonary pressure, and the pressure time change rate of intrapulmonary pressure, and formula is established, which can intuitively present the logical relationship between inspiratory trigger related factors and facilitate clinical analysis.
Humans ; Respiration, Artificial/methods* ; Positive-Pressure Respiration ; Lung ; Ventilators, Mechanical ; Respiratory Mechanics

The goal of mechanically ventilating patients with acute respiratory distress syndrome (ARDS) is to ensure adequate oxygenation and minimal ventilator-associated lung injury. Non-invasive ventilation should be cautiously used in patients with ARDS. Protective ARDS mechanical ventilation strategies with low tidal volumes can reduce mortality. Driving pressure is the most reasonable parameter to optimize tidal volume. Available evidence does not support the routine use of higher positive end expiratory pressure (PEEP) in patients with ARDS. The optimal level of PEEP may be titrated by the inflection point obtained from static pressure-volume curve. Promising therapies include prone position ventilation, high frequency oscillatory ventilation and extracorporeal membrane oxygenation as salvage treatment. While mechanically ventilating, it is also important for ARDS patients to maintain spontaneous breathing via assisted ventilation mode such as bilevel positive airway pressure, pressure support ventilation and neurally adjusted ventilation assist. Exogenous surfactant, inhaled nitric oxide, bronchodilators, airway pressure release ventilation and partial liquid ventilation are not recommended therapies.
Humans ; Positive-Pressure Respiration ; Respiration, Artificial ; methods ; Respiratory Distress Syndrome, Adult ; therapy ; Tidal Volume

OBJECTIVETo evaluate the effects of different interventional strategies, namely controlled high-concentration oxygen therapy, continuous positive airway pressure (CPAP) and bi-level positive airway pressure (BiPAP) ventilation, on respiratory response and work of breathing (WOB) in canine models of early-stage acute lung injury (ALI).

METHODSAfter successful duplication of ALI models with oleic acid (diagnostic criteria: Pa(O2)/Fi(O2)

RESULTSBiPAP resulted in the most significant effects in reducing the respiratory rate (RR) and f/V(T) (P<0.001), followed by CPAP and O2 interventions (P<0.001). None of the 3 treatments showed obvious effects on V(E) (P>0.05), which maintained the level of early ALI/ARDS stage. BiPAP greatly improved V(T) and V(T)/Ti, showing better effects than CPAP and O2. No significant differences were noted among the 3 groups in T(I)/T(tot) (P>0.05). BiPAP showed superior effect to CPAP in lowering the peak transdiaphragmatic pressure (Pdi). CPAP and BiPAP both effectively counteracted intrinsic positive end expiratory pressure (PEEPi) (P<0.01), while O2 produced no obvious such effects (P>0.05). BiPAP showed the most evident effects, followed by CPAP, in reducing WOB, but oxygen therapy produced no obvious effects. CPAP (P<0.01) and BiPAP (P>0.05) both effectively reduced the proportion of ingredients in WOB related to PEEPi.

CONCLUSIONBiPAP and CPAP can produce favorable effects in relieving dyspnea, reducing WOB and improving respiratory response to control the deterioration of ARDS. BiPAP has more significant therapeutic effects than CPAP and oxygen therapy.

Acute Disease ; Animals ; Continuous Positive Airway Pressure ; Dogs ; Female ; Lung Diseases ; physiopathology ; therapy ; Male ; Oxygen Inhalation Therapy ; Positive-Pressure Respiration ; Respiration ; Respiration, Artificial ; methods ; Time Factors

Acute Disease ; Humans ; Intubation, Intratracheal ; methods ; Length of Stay ; Positive-Pressure Respiration ; methods ; Respiratory Insufficiency ; therapy

OBJECTIVETo evaluate the applicability of electrical impedance equipment in assessing local lung volume during different PEEP ventilation and at different respiratory rate in neonatal piglets.

METHODSElectrical impedance measurements (EIM) were performed on 6 healthy newborn piglets (age 4 +/- 1 d, weight 1.66 +/- 0.31 kg) using 8 electrodes distributed to 4 quadrants of the lung (left, right, upper, lower). Tidal impedance and functional residual impedance changes during PEEP levels of 2, 4, 6 and 8 cm H2O and frequencies ranging from 0.5 to 15 Hz were investigated.

RESULTSThe sum of regional tidal impedance obtained from four quadrants, significantly reflected tidal volume (VT) measured by a pneumotachograph during both frequency and PEEP changed (r2 = 0.98). A decrease of PEEP 4 to 2 cm H2O caused a significant increase in total tidal impedance (TTI) as well as in VT (P < 0.01 and P < 0.05); whereas an increase in frequency from 0.5 to 15 Hz was associated with a significant decrease in both TTI and VT (P < 0.05 and P < 0.01). Increased frequency had a balancing effect on air distribution, whereas higher PEEP did not result in more homogeneous ventilation. Minimal impedance values (FRI) (surrogate variable for FRC) showed that total FRI significantly decreased with increasing PEEP level.

CONCLUSIONSEIM demonstrated good applicability to assess changes in thoracic gas volume. It is highly suggested that this method could be considered and further studied as a non-invasive bedside method to monitor continuously regional lung ventilation of neonates under any mode of mechanical ventilation.

Animals ; Animals, Newborn ; Electric Impedance ; Lung Volume Measurements ; methods ; Positive-Pressure Respiration ; Respiratory Rate ; Swine

OBJECTIVETo study the effects of expiratory triggering sensitivity (ETS) on patient-ventilator expiratory synchrony and work of breathing in chronic obstructive pulmonary disease (COPD) patients during pressure support ventilation (PSV).

METHODSA total of 31 COPD patients were ventilated in PSV mode, and measured by a pulmonary monitor. Meanwhile, the electromyogram of the diaphragm (EMG(diaph)) was obtained with electromyography. Five levels of ETS, 1%, 15%, 25%, 35%, and 50% of peak inspiratory flow (PIF), were studied in random order. Each ETS level lasted 30 minutes and all the data were recorded simultaneously for 3 minutes at the end of each period. The effects of ETS on patient-ventilator expiratory synchrony were analyzed by measuring the phase angle of expiration between the EMG(diaph) and the flow wave curve, and the effects of ETS on work of breathing by calculating total work of breathing (Wtot), work of inspiration by patients (Wi, P) and expiratory work of breathing (Wex).

RESULTSTen patients were excluded from the study. At the 25% PIF level of ETS, patient-ventilator expiratory synchrony was the best, theta = (8 +/- 3) degrees, 16 patients - 15 degrees < or = theta < or = 15 degrees, and the amount of Wtot, Wi, p, Wex was the smallest among all the 5 levels of ETS, which was (1.86 +/- 0.53) J/L, (0.54 +/- 0.13) J/L, and (0.16 +/- 0.08) J/L respectively. When the level of ETS decreased, the occurrence of delayed termination of inspiration and the amount of Wex increased. At the level of 1% PIF, 18 patients theta > 15 degrees, and Wex was (0.48 +/- 0.10) J/L; at this level of ETS, Wi, p also increased significantly to (0.65 +/- 0.16 ) J/L. But when the level of ETS increased, the occurrence of premature termination of inspiration and the amount of Wi, p increased: at 50% PIF level of ETS, theta < - 15 degrees and Wi, p was (1.33 +/- 0.14) J/L in 19 patients.

CONCLUSIONThe proper adjustment of ETS during PSV improves patient-ventilator synchrony and decreases work of breathing in COPD patients.

Humans ; Intermittent Positive-Pressure Ventilation ; methods ; Pulmonary Disease, Chronic Obstructive ; physiopathology ; therapy ; Respiration

Cardiac Surgical Procedures ; adverse effects ; Humans ; Positive-Pressure Respiration ; methods ; Respiratory Insufficiency ; therapy