Parameterization of Respiratory Peripheral Drive in Spontaneously Breathing Patients with Central Drive Depression

Abstract

Viden om en patients respiratoriske drive kan bidrage til en forbedret behandling. De fysiologiske teorier bag respirationskontrol beskriver, at respirationen hovedsageligt er styret af to kemoreflekser, der reagerer på ændringer i arterielle tryk af kuldioxid og oxygen. Den kuldioxidfølsomme refleks kaldes det centrale drive og den oxygenfølsomme refleks kaldes det perifere drive. Det er ikke trivielt at bestemme de to drives bidrag til den samlede ventilation, da de ikke kan måles direkte. Der er udviklet et sæt af matematiske modeller, der kan estimere ventilationsbidragene ud fra en arteriel blodgas-prøve og parametre for respiratorisk gasudveksling der er tilgængelig fra det kliniske måleudstyr ALPE. Det respiratoriske drive kan herved parametriseres for en patient, hvilket kan hjælpe til at give beslutningsstøtte i forhold til ændring af respiratorindstillinger. Den nuværende version af modellen kan parametrisere en patients centrale drive, men er ikke tidligere blevet testet på patienter med spontan vejrtrækning, der ikke er i respiratorbehandling. Denne specialeopgave introducerer en metode til parametrisering og estimering af perifert drive for patienter med spontan vejrtrækning. Den inkluderede patientgruppe består af patienter diagnosticeret med KOL. Denne patientgruppe er blandt andet karakteriseret ved nedsat centrale drive. Nedsat centralt drive kan være farligt, hvis patienten er under oxygenbehandling, da øget arterielt ilttryk kan medføre hypo-ventilation og hypoxæmi grundet. Fire simple parameterestimeringsmetoder er blevet testet for at es- timere det perifere drive i seks KOL-patienter med spontan vejrtrækning. Metoderne estimerer forskellige perifere drive-parametre, som kan beskrive hvordan ændringer i inspiratoriske iltfraktioner kan påvirke ventilationen. Metoderne er baseret på en grid-search algoritme. De tre metoder er vurderet ud fra visuel inspektion af resultater samt udregning af mean squared error imellem de målte og es- timerede værdier for alveolær ventilation. Parametrisering af det perifere drive kan være brugbart til at beskrive og forudsige respiratorisk respons til ændringer i oxygen behandling.

The respiratory drive of the individual patient is of clinical interest to the clinician as this parameter might contribute to an improved treatment. The physiological theories of the mechanisms of respiratory drive is well described. The respiratory control consists mainly of two chemoreflexes that respond to arterial carbon dioxide and oxygen pressure referred to as the central and the peripheral drive control respectively. Measuring the respiratory drive and determining the contributions of the different drives is not a trivial task. In order to do so a set of mathematical models can be used. Using a sample of arterial blood gas and clinically available parameters for pulmonary gas exchange obtained with the bedside tool ALPE, the respiratory drive of the patient can be parameterized and changes in the patient’s respiration due to change in ventilator settings can be estimated. The current version of the model of respiratory drive parameterizes the central drive threshold of the patient. The model have not previously been tested on patients with spontaneous breathing and with no mechanical ventilation. This thesis introduces a novel method for parameterization and es- timation of the peripheral drive of spontaneously breathing patients. The patients included in the selected test group are diagnosed with COPD. This patient group is known to have a reduced central drive. Reduction in central drive poses a threat to the patient, because an increased arterial oxygen pressure may then cause hypoventilation and hypoxemia. Patients submitted to oxygen treatment as in the post-operative period may experience increased arterial oxygen pressure. Four simple parameter estimation methods are tested in order to estimate the peripheral drive in six spontaneously breathing patients. The methods includes a parameter estimation of different peripheral drive parameters using a grid search algorithm. The four methods of parameter estimation are evaluated both by visually inspection and calculation of mean squared error between measured and estimated alveolar ventilation. Parameterization of the peripheral drive may be used to describe and predict respiratory response to changes in oxygen treatment at the bedside.

A master thesis from Aalborg University

Parameterization of Respiratory Peripheral Drive in Spontaneously Breathing Patients with Central Drive Depression

[Parameterisering af respiratorisk perifert drive hos patienter med spontan vejrtrækning og centralt drive depression]