Dynamic and quasi-static lung mechanics system for gas-assisted and liquid-assisted ventilation

Our aim was to develop a computerized system for real-time monitoring of lung mechanics measurements during both gas and liquid ventilation. System accuracy was demonstrated by calculating regression and percent error of the following parameters compared to standard device: airway pressure difference (Delta P(aw)), respiratory frequency (f(R) ), tidal volume (V(T)), minute ventilation (V'(E)), inspiratory and expiratory maximum flows (V'(ins,max), V'(exp,max)), dynamic lung compliance (C(L,dyn) ), resistance of the respiratory system calculated by method of Mead-Whittenberger (R(rs,MW)) and by equivalence to electrical circuits (R(rs,ele)), work of breathing (W(OB)), and overdistension. Outcome measures were evaluated as function of gas exchange, cardiovascular parameters, and lung mechanics including mean airway pressure (mP(aw)). Delata P(aw), V(T), V'(ins,max), V'(exp,max), and V'(E) measurements had correlation coefficients r = 1.00, and %error < 0.5%. f(R), C(L,dyn), R(rs,MW), R(rs,ele), and W(OB) showed r > or = 0.98 and %error < 5%. Overdistension had r = 0.87 and %error < 15%. Also, resistance was accurately calculated by a new algorithm. The system was tested in rats in which lung lavage was used to induce acute respiratory failure. After lavage, both gas- and liquid-ventilated groups had increased mP(aw) and W(OB), with decreased V(T), V'(E), C(L,dyn), R(rs,MW), and R(rs,ele) compared to controls. After 1-h ventilation, both injured group had decreased V(T), V'(E) , and C(L,dyn), with increased mP(aw), R(rs,MW), R(rs,ele), and W(OB) . In lung-injured animals, liquid ventilation restored gas exchange, and cardiovascular and lung functions. Our lung mechanics system was able to closely monitor pulmonary function, including during transitions between gas and liquid phases.

Multicenter comparative study of conventional mechanical gas ventilation to tidal liquid ventilation in oleic acid injured sheep

We performed a multicenter study to test the hypothesis that tidal liquid ventilation (TLV) would improve cardiopulmonary, lung histomorphological, and inflammatory profiles compared with conventional mechanical gas ventilation (CMV). Sheep were studied using the same volume-controlled, pressure-limited ventilator systems, protocols, and treatment strategies in three independent laboratories. Following baseline measurements, oleic acid lung injury was induced and animals were randomized to 4 hours of CMV or TLV targeted to "best PaO2" and PaCO2 35 to 60 mm Hg. The following were significantly higher (p < 0.01) during TLV than CMV: PaO2, venous oxygen saturation, respiratory compliance, cardiac output, stroke volume, oxygen delivery, ventilatory efficiency index; alveolar area, lung % gas exchange space, and expansion index. The following were lower (p < 0.01) during TLV compared with CMV: inspiratory and expiratory pause pressures, mean airway pressure, minute ventilation, physiologic shunt, plasma lactate, lung interleukin-6, interleukin-8, myeloperoxidase, and composite total injury score. No significant laboratories by treatment group interactions were found. In summary, TLV resulted in improved cardiopulmonary physiology at lower ventilatory requirements with more favorable histological and inflammatory profiles than CMV. As such, TLV offers a feasible ventilatory alternative as a lung protective strategy in this model of acute lung injury.

A Prototype of Volume-Controlled Tidal Liquid Ventilator Using Independent Piston Pumps

Liquid ventilation using perfluorochemicals (PFC) offers clear theoretical advantages over gas ventilation, such as decreased lung damage, recruitment of collapsed lung regions, and lavage of inflammatory debris. We present a total liquid ventilator designed to ventilate patients with completely filled lungs with a tidal volume of PFC liquid. The two independent piston pumps are volume controlled and pressure limited. Measurable pumping errors are corrected by a programmed supervisor module, which modifies the inserted or withdrawn volume. Pump independence also allows easy functional residual capacity modifications during ventilation. The bubble gas exchanger is divided into two sections such that the PFC exiting the lungs is not in contact with the PFC entering the lungs. The heating system is incorporated into the metallic base of the gas exchanger, and a heat-sink-type condenser is placed on top of the exchanger to retrieve PFC vapors. The prototype was tested on 5 healthy term newborn lambs (<5 days old). The results demonstrate the efficiency and safety of the prototype in maintaining adequate gas exchange, normal acido-basis equilibrium, and cardiovascular stability during a short, 2-hour total liquid ventilator. Airway pressure, lung volume, and ventilation scheme were maintained in the targeted range.

Comparison of Static Airway Pressures During Total Liquid Ventilation While Applying Different Expiratory Modes and Time Patterns

To compare pump driven (active) and gravity-siphon (passive) expiration modes during perfluorocarbon total liquid ventilation (TLV), a liquid ventilator was developed capable of providing either expiration mode. In a prospective, controlled laboratory study, 90 rabbits (3.2 +/- 0.1 kg) were anesthetized, tracheotomized, killed. After prefill with 12 ml/kg perflubron and TLV for 90 minutes (tidal volume 12 ml/kg, I:E ratio 1:2), randomly using passive (height 40 or 80 cm) or active expiration, respiratory rates were 4, 8, or 12/min. Static peak inspiratory and end-expiratory intratracheal pressures were measured at 5 minute intervals. Peak inspiratory and end-expiratory were constant in active groups, and increases in all 40 cm and 80 cm passive groups were significant. Differences between groups were significant for expiratory mode but not for respiratory rates. Only passive groups showed significant increases in body weight after TLV. Percentage of fluorothoraces was 10% using active and 85% using passive expiration. Based upon the stability of intrapulmonary pressures and volumes and a reduced rate of fluorothoraces, active expiration is more efficient than passive drainage during TLV.