System and method for assessing real time pulmonary mechanics
Inventors
Al-Rawas, Nawar Nazar Yousif • Gabrielli, Andrea • Euliano, Neil Russell • Banner, Michael Joseph
Assignees
CONVERGENT ENGINEERING Inc • University of Florida Research Foundation Inc
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Publication Number
US-8728002-B2
Publication Date
2014-05-20
Expiration Date
Abstract
A system and method of calculating an accurate estimate of pulmonary mechanics of a patient, including but not limited to compliance, resistance, and plateau pressure without modification of ventilator flow pattern. The accurate estimation of pulmonary mechanics is derived from airway pressure and flow sensors attached to the patient using novel mathematical models. These estimated figures for pulmonary mechanics (respiratory system compliance and resistance) are important for monitoring patient treatment efficacy during mechanical ventilation and ensuring alveoli do not over distend to avoid baro- and/or volutrauma, especially in patients with restrictive lung diseases. The subject method of calculating these accurate estimated figures for pulmonary mechanics is based on linear or non-linear calculations using multiple parameters derived from the above-mentioned sensors.
Core Innovation
The disclosed invention provides a method for real time estimation of at least one selected from the group consisting of respiratory system compliance (CRS), patient airway resistance (RRS), and inspiratory plateau pressure Pplt. A device interfaces with the patient pulmonary system and measures respiratory parameters, which are received in real time and processed by a processor unit. The method calculates an expiratory time constant τE using at least one respiratory parameter from exhalation, and then calculates real time estimates of CRS, RRS, and/or Pplt using at least one respiratory parameter from inspiration together with τE.
The approach estimates τE from respiratory parameters derived from exhalation, using the more reliable middle portion of passive exhalation rather than an end-inspiratory pause. The method optionally corrects τE for ventilator exhalation valve resistance using parameters related to the ventilator and the patient. The disclosure further includes selection windows and exclusions for exhalation data, and constraints on which portions of the expiratory waveform and volume/flow regions are used for τE estimation.
The resulting τE, together with single-point measurements during inspiration at low patient effort, is used within mathematical models to compute Pplt, CRS, and RRS across ventilation modes. The mathematical models include linear and nonlinear formulations and may include neural networks. The disclosure states that the method includes downstream uses such as monitoring treatment efficacy, avoiding baro-/volutrauma, diagnosis, estimating effort and synchrony, and ventilator control.
Claims Coverage
The independent claim covers a real time method that computes expiratory time constant τE from exhalation-derived respiratory parameters and then estimates at least one of CRS, RRS, and Pplt using τE plus inspiration-derived respiratory parameters. Across dependent claims, the disclosed coverage specifies how τE is computed from selected exhalation portions, how τE is corrected, and what the computed CRS/RRS/Pplt estimates are used for, yielding multiple inventive features.
Real time τE estimation from exhalation and CRS/RRS/Pplt estimation using inspiration
A method for real time estimation of at least one selected from the group consisting of CRS, RRS, and Pplt by receiving respiratory parameters from a device that interfaces with a patient pulmonary system, calculating the patient's τE using at least one respiratory parameter from exhalation, and calculating at least one real time estimate selected from CRS, RRS, and Pplt using at least one respiratory parameter from inspiration together with τE.
τE correction using ventilator exhalation valve resistance
Applying a correction factor to a patient's τE calculated from exhalation, where the correction factor is derived using peak inspiratory flow and peak expiratory flow and an equation of the form τE(t)=τE total(t)−(Rvent(t)×C_est).
Using a median or average of multiple τE estimates
Calculating the patient's τE from a median or average of multiple τE estimates calculated during exhalation.
Excluding early exhalation time window for τE calculation
Excluding 0 to 0.1 seconds of a patient's exhalation when using at least one respiratory parameter to calculate the patient's τE.
Using volume-based selection between 80% and 20% of exhaled volume
Calculating multiple τE estimates during exhalation between 80% of exhaled volume and 20% of exhaled volume.
Using CRS/RRS/Pplt estimates for effort, diagnosis, efficacy, and ventilator control
Using calculated estimates of Pplt, CRS, or RRS in functions including estimating breathing effort and resistance/compliance, diagnosing pulmonary condition or disease, assessing ventilation/pharmaceutical efficacy, establishing ventilator settings, identifying ventilation obstructions, optimizing synchrony and ventilator triggering, and assessing health and treatment response.
Overall, the claim set focuses on real time computation of τE from exhalation-derived respiratory parameters and the use of inspiration-derived respiratory parameters together with τE to estimate CRS, RRS, and/or Pplt. Dependent refinements cover τE selection (median/average and specific exhalation windows), optional τE correction related to ventilator exhalation valve resistance, and explicit downstream clinical/control functions for the computed mechanics estimates.
Stated Advantages
Enables real time estimation of CRS, RRS, and inspiratory plateau pressure Pplt.
Avoids using an end-inspiratory pause by using exhalation-derived τE from passive exhalation for the estimation.
Improves safety by avoiding baro-/volutrauma (as stated in the provided content).
Supports monitoring treatment efficacy and health/treatment response.
Supports diagnosis of pulmonary condition or disease.
Supports estimation of patient breathing effort and assessment of synchrony.
Supports ventilator control including establishing ventilator settings and optimizing ventilator on-triggering and off-triggering.
Documented Applications
Monitoring treatment efficacy and assessing overall patient response to treatment.
Avoiding baro-/volutrauma.
Diagnosis of pulmonary condition or disease.
Assessing breathing effort and resistance/compliance, and assessing patient pulmonary mechanics during pharmaceuticals.
Establishing ventilator settings for patient treatment.
Identifying ventilation obstructions or obstacles affecting patient ventilation.
Determining and/or optimizing patient synchrony, including optimizing ventilator on-triggering and off-triggering.
Assessing overall patient health.
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