Traditionally, adequate tidal volume is considered to be a necessary condition to support respiratory patient breathing. But the high frequency ventilation (HFV) with a small tidal volume can still support the respiratory patient breathing well. In order to further explore the mechanisms of HFV, the pendelluft ventilation between left and right lungs was proposed in this paper. And a test platform by using two fresh sheep lungs was developed for investigating the pendelluft ventilation between the left and right lungs. Furthermore, considering the viscous resistance (R), inertance (I) and lung compliance (C) in the lung, a second-order lung ventilation model was designed to inspect and evaluate the pendelluft ventilation between left lung and right lungs. On referring to both results of experiments in practice and simulation in MATLAB Simulink, between the left and right lungs, the phase difference in their airflow happens during HFV at some frequencies. And the pendelluft ventilation between the left and right lungs is resulted by the phase difference, even if the total airflow entering a whole lung is 0. Under HFV, the pendelluft ventilation between left and right lungs will benefit the lungs being more adequately ventilated, and will be improve the utilization rate of oxygen in the lungs.
ObjectiveTo evaluate the accuracy of the new dynamic approach in the measurement of respiratory mechanics with different pressure support (PS) level during pressure support ventilation (PSV) via oral-nasal mask.MethodsThe Respironics V60 ventilator was connected to a ASL5000 lung simulator, which simulate lung mechanics in patients with chronic obstructive pulmonary disease ［system compliance (Crs)=50 mL/cm H2O, airway resistance (Raw)=20 cm H2O/(L·s), inspiratory time (TI)=1.6 s, breathing rate=15 beats per minute］. PSV were applied with different levels of PS ［positive end-expiratory pressure=5 cm H2O, PS=5/10/15/20/25 cm H2O) and back-up rate=10 beats per minute］. Measurements were conducted at system leaks with 25 – 28 L/min. The performance characteristics and patient-ventilator asynchrony were assessed, including flow, airway pressure, time and workload. Crs and Raw were calculated by using new dynamic approach.ResultsTidal volume (VT) was increased with increasing PS level ［(281.45±4.26)mL at PS 5 cm H2O vs. (456.81±1.91)mL at PS 10 cm H2O vs. (747.45±3.22)mL at PS 20 cm H2O, P<0.01］. Severe asynchronous was occurred frequently when PS is at 25 cm H2O. Inspiration cycling criterion (CC) was up-regulated accompanied by increasing PS level ［(15.62±3.11)% at 5 cm H2O, vs. (24.50±0.77)% at 20 cm H2O, P<0.01］. Premature cycling was always existed during PSV when PS < 20 cm H2O, which could be eliminated as PS level increasing. Delay cycling was found when PS was at 20 cm H2O, and cycling delay time was (33.60±15.91)ms (P<0.01). The measurement of Crs was (46.19±1.57)mL/cm H2O with PS at 10 cm H2O, which was closer to the preset values of simulated lung. The underestimate of Crs was observed during high level PS support. The calculation of inspiratory and expiratory resistance was approximate to 20 cm H2O/(L·s) when PS level was exceeded 15 cm H2O.ConclusionsThe new dynamic approach can continuously assess the respiratory mechanics during non-invasive ventilation, which is no need to interrupt the patient's spontaneous breathing. Higher inspiratory flow during PSV is beneficial for Raw measurement, whereas the accuracy of Crs was influenced by the value of actual VT.
The high frequency oscillatory ventilation (HFOV) is characterized with low tidal volume and low mean airway pressure, and can well support the breathing of the patients with respiratory diseases. Since the HFOV was proposed, it has been widely concerned by medical and scientific researchers. About the HFOV, this paper discussed its current research status and prospected its future development in technologies. The research status of ventilation model, mechanisms and ventilation mode were introduced in detail. In the next years, the technologies in developing HFOV will be focused on: to develop the branched high-order nonlinear or volume-depended resistance-inertance-compliance (RIC) ventilation model, to fully understand the mechanisms of HFOV and to achieve the noninvasive HFOV. The development in technologies of HFOV will be beneficial to the patients with respiratory diseases who failed with conventional mechanical ventilation as one of considerable ventilation methods.
Objective To evaluate the influence on the estimation of respiratory mechanics with dynamic signal analysis approach during noninvasive positive pressure ventilation (NPPV) under different inspiratory effort conditions. Methods The Respironics V60 ventilator was connected to a ASL5000 lung simulator, which simulate lung mechanics in healthy adults with body weight from 65 to 70 kg, and patients with chronic obstructive pulmonary disease (COPD) and acute respiratory distress (ARDS). Each lung models was subjected to 4 different muscle pressures (Pmus): 0, 5.0, 10.0, and 15.0 cm H2O. Inspiratory pressure support level was adjusted to maintain tidal volume (VT) achieving 7.0 mL/kg outputted by ventilator respectively. Positive end expiratory pressure was set at 5.0 cm H2O and back-up rate was 10 beats per minute. Measurements were conducted at system leaks with 25 to 28 L/min. The respiratory system compliance (Crs), inspiratory and expiratory resistance (Rinsp and Rexp) were estimated by special equations, which was derived from the exhaled VT, flow rate and airway pressure. Results The driving pressure (DP) was decreased with Pmus increasing, and was 1.0 cm H2O after Pmus exceeding 10.0 cm H2O and the VT was larger than 7.0 mL/kg in normal adult model. The estimated value of Crs was affected by the changes of Pmus in all three lung models. The significant underestimation of Raw and the overestimation of Crs were observed when Pmus level exceed 10.0 cm H2O. The measured errors of Crs and Rexp were within 10% in COPD and ARDS model when Pmus was at 5.0 cm H2O. The underestimation of Rinsp was always existed in all Pmus level (P<0.01). Conclusions Using dynamic signal analysis approach, the real-time estimation of respiratory mechanics (Crs and Raw) is no need to interrupt the spontaneous breathing during NPPV. Excessive effort will increase the patient’s inspiratory workload, which is not benefit to accurate estimation of respiratory mechanics.
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.