Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA009

Poster Communications

The physiological effects of Nasal High Flow: a Theoretical Study

A. Ben-Tal1, J. Revie2, S. Tatkov2

1. Institute of Natural and Mathematical Sciences, Massey University, Auckland, New Zealand. 2. Fisher & Paykel Healthcare Limited, Auckland, New Zealand.

Nasal High Flow (NHF) is a therapy in which humidified, warm air is delivered through the nose to spontaneously breathing patients. It has been shown that NHF affects the amplitude and frequency of breathing and that this response varies between patients and between wakefulness and disease states (1). To help us understand these physiological effects of NHF, we have developed a mathematical model of the respiratory system that couples the upper airway with lung mechanics, gas exchange and gas transport. We conduct our study in open loop (i.e. without including the respiratory feedback mechanisms) and change the breathing pattern manually to maintain physiological levels of arterial partial pressures of oxygen (O2) and carbon dioxide (CO2). We simulate the model numerically under control conditions (no NHF) and under conditions that mimic NHF. When NHF is administrated, the nostrils are partially blocked while airflow is delivered; hence, the resistance to spontaneous breathing through the nose is increased. We study these two effects (pure flow and increased nasal resistance) independently as well as dependently. Our simulations show that when pure flow is administrated without taking into account the increased nasal resistance, it has the same effect as reducing the lung dead space, that is, it improves the delivery of O2 and the removal of CO2 from the blood. However, when changes to the nasal resistance are included, the effects on the blood levels of O2 and CO2 could be reversed, leading to either increase or decrease in blood O2 and CO2 levels. We hypothesize that these changes in blood gas levels trigger the respiratory control system to change the breathing pattern and we show that changing the breathing pattern under normal conditions can bring the blood levels of O2 and CO2 back to normal (however, we show that a variety of breathing patterns can achieve this). Our simulations also show that administrating NHF leads to an increase in baseline of airway pressure as well as an increase in pressure swings during breathing. These results are aligned with trends seen in previous experimental studies (1, 2, 3). Our theoretical study provides several new insights about the physiological effects of NHF and although it is still unclear why a particular combination of frequency and amplitude of breathing is selected by the neural system, our study demonstrates the potential of using NHF for studies of neural control of breathing.

Where applicable, experiments conform with Society ethical requirements