Ventilation Waveforms Research Articles

Could dynamic ventilation waveforms bring about a paradigm shift in mechanical ventilation?

today, mechanical ventilators are the primary life-support systems routinely used in every intensive care unit around the world. Mechanical ventilators first reached widespread use in the United States during the poliomyelitis epidemic in the 1940–1950s. Initial devices, known as “iron lungs

Lagrangian transport properties of pulmonary interfacial flows

Disease states characterized by airway fluid occlusion and pulmonary surfactant insufficiency, such as respiratory distress syndrome, have a high mortality rate. Understanding the mechanics of airway reopening, particularly involving surfactant transport, may provide an avenue to increase patient survival via optimized mechanical ventilation waveforms. We model the occluded airway as a liquid-filled rigid tube with the fluid phase displaced by a finger of air that propagates with both mean and sinusoidal velocity components. Finite-time Lyapunov exponent (FTLE) fields are employed to analyse the convective transport characteristics, taking note of Lagrangian coherent structures (LCSs) and their effects on transport. The Lagrangian perspective of these techniques reveals flow characteristics that are not readily apparent by observing Eulerian measures. These analysis techniques are applied to surfactant-free velocity fields determined computationally, with the boundary element method, and measured experimentally with micro particle image velocimetry (μ-PIV). We find that the LCS divides the fluid into two regimes, one advected upstream (into the thin residual film) and the other downstream ahead of the advancing bubble. At higher oscillatory frequencies particles originating immediately inside the LCS experience long residence times at the air-liquid interface, which may be conducive to surfactant transport. At high frequencies a well-mixed attractor region is identified; this volume of fluid cyclically travels along the interface and into the bulk fluid. The Lagrangian analysis is applied to velocity data measured with 0.01 mg ml(-1) of the clinical pulmonary surfactant Infasurf in the bulk fluid, demonstrating flow field modifications with respect to the surfactant-free system that were not visible in the Eulerian frame.

Abstract P101: Comparison of Ventilation Rate Measured with Thoracic Bioimpedance and with Capnography during Out-of-Hospital Cardiopulmonary Resuscitation

Objective: To determine the ability of thoracic bioimpedance to measure ventilation rate during cardiac arrest and CPR. Methods: Philips MRx devices monitored 32 patients during out-of-hospital cardiac arrest and CPR. The devices recorded chest compressions with an accelerometer, continuous 1-lead EKG, thoracic bioimpedance, and continuous capnography. Of the 32 files, 4 were not used in this study because of incomplete recording. Two reviewers manually annotated ventilation waveforms independently using Laerdal QCPR software, which also automatically annotated ventilation through the bioimpedance channel. Reviewers manually measured ventilation rate (number of breaths/min) recorded with capnography for each 1 minute epoch, which were matched and compared with those measured through bioimpedance for each patient file (N = 28). A total of 585 1-minute epochs were measured and compared. We assessed intra-class correlation for 2 individual raters for ventilation rates measured with capnography and with annotated bioimpedance to establish inter-user reliability of measurements. Ventilation rate measured with capnography vs. bioimpedance was compared with simple regression. Results: The majority (60%) of ventilation rates measured with capnography and with automated software bioimpedance were within 2 breaths/min of each other. After manual annotation of the bioimpedance channel, 81% of 1-min epochs were within 2 breaths/min of rates measured with capnography. Ventilation rate measured with capnography had good correlation with bioimpedance (r = .82, p < .0001). Inter-rater agreement is estimated to be 0.96 for ventilation rate measured with capnography and 0.93 for rate measured with bioimpedance. Discussion: The software occasionally missed obvious ventilation waveforms and occasionally annotated waveforms obviously caused by chest compressions. Manual review and annotation improved the accuracy of ventilation rates measured with bioimpedance. Approximately 75% to 90% of recordings made with the Philips MRx device are expected to be useful for measurement. Conclusion: Ventilation rate measured with thoracic bioimpedance alone is acceptable using the Philips MRx device. Inter-rater agreement for measurements is excellent.

The experimental evaluation of asymmetric ventilation waveforms on surfactant transport during airway reopening

The experimental evaluation of asymmetric ventilation waveforms on surfactant transport during airway reopening

The effects of temperature on oxygen uptake, gill ventilation and ecg waveforms in the nile tilapia, Oreochromis niloticus

Oreochromis niloticus were acclimated to 35 (group I) and 15°C (group II). In group I, the temperature was decreased from 35 to 15°C, followed by return to 35°C, while in group II, the temperature rose to 35 and returned to 15°C. For each temperature, oxygen uptake ( V ̇ O 2), gill ventilation ( V ̇ G) and electrocardiograms were obtained. Curves were identical and for the two groups were without hysteresis. Increases of V ̇ G/ V ̇ O 2 with rising temperature kept O 2 extraction relatively constant. Heart rate increased with temperature. The QRS and the T wave amplitudes were constant, while QRS and ventricular action potential duration increased at low temperature.

Optimal ventilation waveforms for estimating low-frequency respiratory impedance.

We present a broad-band optimal ventilator waveform (OVW), the concept of which was to create a computer-driven ventilator waveform containing increased energy at specific frequencies (f). Values of f were chosen such that nonlinear harmonic distortion and intermodulation were minimized. The phases at each f were then optimized such that the resulting flow waveform delivered sufficient volume to maintain gas exchange while minimizing peak-to-peak airway opening pressure. Simulations with a linear anatomically consistent branching airway model and a nonlinear viscoelastic model showed that respiratory resistance (Rrs) and elastance (Ers) estimates at 0.1-2 Hz from the OVW are far superior to those from a standard step ventilator waveform (SVW) during healthy and obstructed conditions and that the OVW reduces the influences of harmonic interactions. Using a servo-controlled oscillator, we applied individual sine waves, an OVW containing energy at 0.15625-2.4 Hz, and an SVW to healthy humans and one symptomatic asthmatic subject before and after bronchodilation. The OVW was markedly superior to the SVW and always provided smooth estimates of Rrs and Ers. Before bronchodilation in the asthmatic subject Rrs was highly elevated and Ers was markedly increased with f; after bronchodilation the level of Rrs and the f dependence of Ers decreased. Although based on results from only one asthmatic subject, these data suggest a dominant influence of airway constriction and lung inhomogeneities during asthmatic bronchoconstriction that is alleviated by bronchodilators. These and other results indicate that the OVW approach has high potential for simultaneously probing f and amplitude dependence in the mechanical properties of clinical subjects during physiological breathing conditions and perhaps during dynamic bronchoconstriction.

Respiratory control of arterial pH as temperature changes in rainbow trout Salmo gairdneri.

Respiratory control of arterial pH as temperature changes in rainbow trout Salmo gairdneri.