Objective. In this paper, an automated stable tidal breathing period (STBP) identification method based on processing electrical impedance tomography (EIT) waveforms is proposed and the possibility of detecting and identifying such periods using EIT waveforms is analyzed. In wearable chest EIT, patients breathe spontaneously, and therefore, their breathing pattern might not be stable. Since most of the EIT feature extraction methods are applied to STBPs, this renders their automatic identification of central importance.Approach. The EIT frame sequence is reconstructed from the raw EIT recordings and the raw global impedance waveform (GIW) is computed. Next, the respiratory component of the raw GIW is extracted and processed for the automatic respiratory cycle (breath) extraction and their subsequent grouping into STBPs.Main results. We suggest three criteria for the identification of STBPs, namely, the coefficient of variation of (i) breath tidal volume, (ii) breath duration and (iii) end-expiratory impedance. The total number of true STBPs identified by the proposed method was 294 out of 318 identified by the expert corresponding to accuracy over 90%. Specific activities such as speaking, eating and arm elevation are identified as sources of false positives and their discrimination is discussed.Significance. Simple and computationally efficient STBP detection and identification is a highly desirable component in the EIT processing pipeline. Our study implies that it is feasible, however, the determination of its limits is necessary in order to consider the implementation of more advanced and computationally demanding approaches such as deep learning and fusion with data from other wearable sensors such as accelerometers and microphones.
Assessment of the temporal and spatial dynamics of hyperpolarized Helium-3 (3He) distribution in the lung with ultrafast gradient-echo magnetic-resonance imaging.Coronal images of the lung were acquired using ultrafast gradient-echo pulse sequences with TR/TE = 3.3 ms/1.3 ms (slice thickness, 40 mm) and TR/TE = 2.0 ms/0.7 ms (without slice selection). A series of 80 or 160 projection images was obtained with 210 ms or 130 ms temporal resolution, respectively. Imaging was performed during several respiratory cycles after application of a single bolus of 300 mL hyperpolarized 3He. Measurements were performed in six healthy volunteers (spontaneous breathing).Different phases of in- and expiration could be visualized. During the course of consecutive respiratory cycles the 3He signal decreased due to dilution of 3He in residual alveolar gas and by inspired air, relaxation due to oxygen and the RF pulses, and due to Helium-3 washout. The signal of a single bolus of 3He was detected in the lung for up to four respiratory cycles. Anatomical structures were better visualized on slice selective images than on images without slice selection.Distribution of inspired 3He within the tracheobronchial tree and alveolar space and its washout can be visualized by ultrafast imaging of a single bolus of hyperpolarized 3He gas. This method may allow for regional analysis of lung function with temporal and spatial resolution superior to conventional methods.
Platelet activating factor (PAF) induces vascular barrier breakdown and intestinal failure that contribute to the development of sepsis. The exact cellular mechanisms are not well understood.
Introduction: In the absence of lung disease, respiratory mechanics of ventilated patients may be described by a one-compartment model of the lung. In ARDS, perfused alveoli are to be recruited, as well as ventilated, in order to ensure adequate gas exchange. Lung aeration can be analyzed using fast dynamic multiscan CT, by following radiologic lung density during respiratory cycles. We studied the temporal behavior of radiologic lung density in- and deflation maneuvers, with the aim to identify the impact of ARDS upon dynamics of lung aeration. Methods: With IRB approval, five anesthetized pigs (27 +/- 1 kg) were imaged by dynamic multiscan CT (slice thickness = 1 mm, high resolution reconstruction, temporal resolution = 250ms). In one predefined transverse cross section of the lungs, fast repetitive imaging was performed before and after induction of saline lavage ARDS. Rectangular step-up and step-down maneuvers in airway pressures between 0 and 50 cm H2 O were performed during dynamic CT acquisitions (196 images). On consecutive images, the area of a density range of -910 to -300 Hounsfield Units was defined as aerated lung parenchyma, and determined planimetrically. The response of aerated lung area (A, % of total cross-sectional lung area at 50 cm H2 O) to pressure steps was plotted against time. Least-square fit procedures were used to describe two distinct time constants ("fast" or "slow", Tcfast, Tcslow) and their relative contribution to A (Afast, Aslow). Results: Prior to ARDS induction, a "fast" lung compartment dominated both inflation and also, although less so, deflation. In contrast, after establishment of lavage ARDS, a significantly larger portion of the lung responded to inflation as "slow compartment", and to deflation as "fast compartment (Table 1).Table 1Discussion: Dynamic multiscan CT allows to determine lung compartments whose aeration follows very distinct time constants prior to and after ARDS induction. The single, short Tc of healthy lungs may characterize ventilation of already aerated lung regions. In ARDS, the coexisting longer inspiratory Tc may represent alveolar recruitment, whereas, during expiration, a large compartment with short Tc reflects rapid alveolar collapse. Conventional ventilatory modes may not be able to recruit, and prevent collapse of, alveolar regions with this behavior. Thus, the detection of compartments with these characteristics could provide the rationale for the High Frequency Oscillatory Ventilation in severe ARDS. Funding: Deutsche Forschungsgemeinschaft (DFG TH 315/9)
