Parameterization of Respiratory Peripheral Drive in Spontaneously Breathing Patients with Central Drive Depression
Translated title
Parameterisering af respiratorisk perifert drive hos patienter med spontan vejrtrækning og centralt drive depression
Authors
Sørensen, Kasper ; Mark, Esben Bolvig
Term
4. term
Publication year
2015
Submitted on
2015-06-03
Abstract
Patientens respirationsdrive, dvs. kroppens automatiske styring af vejrtrækningen, er klinisk vigtig, fordi viden herom kan forbedre behandlingen. Kroppens respirationskontrol bygger især på to kemoreflekser, som reagerer på kuldioxid- og ilttryk i arterielt blod, kaldet den centrale og den perifere drive. At måle respirationsdrivet og adskille bidragene fra de to drivkræfter er ikke ligetil, men matematiske modeller kan hjælpe. Ved at kombinere en arteriel blodgasprøve med klinisk tilgængelige mål for gasudveksling i lungerne, målt med bedside-værktøjet ALPE, kan patientens respirationsdrive beskrives med få parametre, og ændringer i vejrtrækning ved ændrede ventilatorindstillinger kan estimeres. Den eksisterende model beskriver patientens centrale drive-tærskel og har ikke tidligere været afprøvet hos spontant vejrtrækkende patienter uden mekanisk ventilation. Denne afhandling introducerer en ny metode til at parametrisere og estimere den perifere drive hos spontant vejrtrækkende patienter. Testgruppen består af patienter med COPD (kronisk obstruktiv lungesygdom), som ofte har nedsat central drive. Et lavt centralt drive kan være risikabelt, fordi et øget arterielt ilttryk under iltbehandling, f.eks. postoperativt, kan føre til hypoventilation og hypoksæmi. Fire enkle metoder til parameterestimering af den perifere drive afprøves hos seks spontant vejrtrækkende patienter ved hjælp af en grid search-algoritme. Metoderne vurderes både ved visuel inspektion og ved beregning af middelkvadratfejl mellem målt og estimeret alveolær ventilation (den del af vejrtrækningen, der når lungenes alveoler). Parametrisering af den perifere drive kan bruges ved sengen til at beskrive og forudsige, hvordan ændringer i iltbehandling påvirker vejrtrækningen.
A patient’s respiratory drive—the body’s automatic control of breathing—is clinically important because it can guide better treatment. Breathing is regulated mainly by two chemoreflexes that respond to carbon dioxide and oxygen levels in arterial blood, known as the central and peripheral drives. Measuring respiratory drive and separating the contributions of these drives is not straightforward, but mathematical models can help. By combining an arterial blood gas sample with clinically available measures of pulmonary gas exchange obtained with the bedside tool ALPE, a patient’s respiratory drive can be described with a few parameters, and changes in breathing due to adjustments in ventilator settings can be estimated. The current model represents the patient’s central drive threshold and has not previously been tested in spontaneously breathing patients without mechanical ventilation. This thesis introduces a new method to parameterize and estimate the peripheral drive in spontaneously breathing patients. The test group comprises patients with COPD (chronic obstructive pulmonary disease), a group known to have reduced central drive. Reduced central drive is risky because an increase in arterial oxygen pressure during oxygen therapy, for example after surgery, may cause hypoventilation and hypoxemia. Four simple parameter estimation methods are tested to estimate the peripheral drive in six spontaneously breathing patients, using a grid search algorithm to fit different parameters. The methods are evaluated by visual inspection and by calculating the mean squared error between measured and estimated alveolar ventilation (the portion of ventilation that reaches the lungs’ gas-exchanging air sacs). Parameterizing the peripheral drive may help describe and predict the respiratory response to changes in oxygen treatment at the bedside.
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