Assessment of Respiratory System Resistance during High-Frequency Oscillatory Ventilation Based on In Vitro Experiment

High-frequency oscillatory ventilation (HFOV) is a type of mechanical ventilation with a protective potential characterized by a small tidal volume. Unfortunately, HFOV has limited monitoring of ventilation parameters and mechanical parameters of the respiratory system, which makes it difficult to adjust the continuous distension pressure (CDP) according to the individual patient’s airway status. Airway resistance Raw is one of the important parameters describing the mechanics of the respiratory system. The aim of the presented study was to verify in vitro whether the resistance of the respiratory system Rrs can be reliably determined during HFOV to evaluate Raw in pediatric and adult patients. An experiment was performed with a 3100B high-frequency oscillator, a physical model of the respiratory system, and a pressure and flow measurement system. The physical model with different combinations of resistance and compliance was ventilated during the experiment. The resistance Rrs was calculated from the impedance of the physical model, which was determined from the spectral density of the pressure at airway opening and the spectral cross-density of the gas flow and pressure at airway opening. Rrs of the model increased with an added resistor and did not change significantly with a change in compliance. The method is feasible for monitoring respiratory system resistance during HFOV and has the potential to optimize CDP settings during HFOV in clinical practice.

Effect of nasal airway nonlinearities on oscillometric resistance measurements in infants

Oscillometric measurements of respiratory system resistance (Rrs) in infants are usually made via the nasal pathways, which not only significantly contribute to overall Rrs but also introduce marked flow acceleration-dependent distortions. Here, we propose a method for correcting flow acceleration-dependent nonlinearity error based on in vitro measurements in 3D-printed upper airway casts of infants as well as in vivo measurements. This correction can be adapted to estimate Rrs from a single intrabreath oscillometric measurement.

Respiratory mechanics during initial lung aeration at birth in the preterm lamb

Despite recent insights into the dynamic processes during lung aeration at birth, several aspects remain poorly understood. We aimed to characterize changes in lung mechanics during the first inflation at birth and their relationship to changes in lung volume. Intubated preterm lambs (gestational age, 124–127 days; n = 17) were studied at birth. Lung volume changes were measured by electrical impedance tomography (VL EIT). Respiratory system resistance (R5) and oscillatory compliance (Cx5) were monitored with the forced oscillation technique at 5 Hz. Lambs received 3–7 s of 8 cmH2O of continuous distending pressure (CDP) before delivery of a sustained inflation (SI) of 40 cmH2O. The SI was then applied until either Cx5 or the VL EIT or the airway opening volume was stable. CDP was resumed for 3–7 s before commencement of mechanical ventilation. The exponential increases with time of Cx5 and VL EIT from commencement of the SI were characterized by estimating their time constants (τCx5 and τVL EIT, respectively). During SI, a fast decrease in R5 and an exponential increase in Cx5 and VL EIT were observed. Cx5 and VL EIT provided comparable information on the dynamics of lung aeration in all lambs, with τCx5 and τVL EIT being highly linearly correlated ( r2 = 0.87, P < 0.001). Cx5 and VL EIT decreased immediately after SI. Despite the standardization of the animal model, changes in Cx5 and R5 both during and after SI were highly variable. Lung aeration at birth is characterized by a fast reduction in resistance and a slower increase in oscillatory compliance, the latter being a direct reflection of the amount of lung aeration.

2592. Lung Function as an Indicator of Vaccine Enhanced RSV Disease in Cotton Rats

Background Respiratory syncytial virus (RSV) infection is the leading cause of lower respiratory tract infections in infants and young children. Seronegative children previously vaccinated with formalin-inactivated live RSV formulated with aluminum (FIRSV) developed vaccine enhanced RSV disease (VERD), which is characterized by fever, wheezing, bronchopneumonia, and airway hyperresponsiveness (AHR). We investigated whether impaired lung function can serve as a marker for VERD in an animal model of RSV infection. Methods Uninfected and RSV-infected cotton rats intranasally challenged with 106 pfu of RSV A2 were anesthetized with pentobarbital and tracheostomized. A cannula was placed in the trachea and animals were connected to flexiVent™ (Scireq), which is a computer-controlled piston ventilator that analyzes pressure and volume signals in response to an oscillatory waveform applied at the animal’s airways. Vecuronium bromide was administered to ventilated animals to prevent independent breathing. To measure AHR, animals were exposed to increasing doses of inhaled methacholine, and methacholine-induced bronchoconstriction was measured. Results Two independent studies showed that RSV-infected cotton rats (n = 4) exhibited increased total respiratory system resistance (Rrs) and airway resistance (Rn) following methacholine challenge on days 4 and 6 post-infection compared with uninfected cotton rats (n = 4). Conclusion RSV-induced impairment in lung function can be exploited for the development of a more robust and objective method for assessing vaccine safety in a cotton rat model of respiratory disease compared with traditional histopathological analysis. Disclosures All authors: No reported disclosures.

Lung function in athletes and non-athletes aged 13-15 years

Background Regular sports or physical training contributes in increasing the body’s pulmonary function. The increase of pulmonary function is determined by the strength of respiratory muscle, thoracic compliance, upper respiratory system resistance, and pulmonary elasticity. Objective To compare pulmonary function between athletes and non-athletes aged 13-15 years. Methods This is a cross-sectional analytical study conducted onnior high school students aged 13-15 years throughout June to August 2017. Participants are classified as athletes from particular sports and non-athletes. Assessment of pulmonary function was done using a spirometry test, in which each subject was asked to inhale and exhale in a particular method. Parameters assessed include vital capacity (VC), forced vital capacity (FVC), expiratory volume in 1 second (FEV1), forced expiratory flow (FEF) and FEV1/FVC. Differences in lung function between athletes and non-athletes were analyzed using independent T-test. Results There were 60 athletes and 60 non-athletes included in this study. The mean age of athletes and non-athletes were 13.38 (SD 0.99) years old and 13.70 (SD 0.76) years old, respectively. The statistically significant differences in mean lung function parameters between athletes and non-athletes were as follows: VC: 85.03% vs. 79.41%, respectively (P=0.035); FVC: 95.66% vs. 88.43%, respectively (P=0.016); FEV1: 102.10% vs. 94.28%, respectively (P=0.016); and FEV1/FVC: 105.95% vs. 102.69%, respectively (P=0.011). However, there were no statistically significant differences in the means of FEF 25-75% between the two groups (P>0.05). Conclusions Parameters of lung function in athletes are in general significantly higher than in non-athletes.