Respiratory load compensation and perception during 10‐breath sustained inspiratory resistive loading in normal subjects

Abstract

Increased load on the respiratory system is a key feature in various respiratory diseases, accompanied by ventilatory compensatory behavior and breathlessness. This increased inspiratory load is often prolonged, ranging from minutes to days, and requires the individual to adjust their breathing pattern to sustain alveolar ventilation and minimize the work of breathing, i.e. load compensation. Experimentally, this is often studied by breathing through resistive (R) loads. Most prior load compensation studies have used single breath loads within a range of adaptability for most individuals (0–40 cmH2O/l/s) to determine the load compensation mechanisms. However, during exacerbations of lung diseases, the individual must load compensate for multiple breaths against increasing load magnitudes that may exceed their ability to sustain alveolar ventilation. The aim of this study was to investigate load compensation in normal subjects when breathing for multiple breaths (10) through loads of increasing magnitudes greater than their expected ability to sustain alveolar ventilation. A threshold for load decompensation was hypothesized. Healthy participants were tested while breathing through a circuit with inspiratory flow‐resistive loads (R's: 0–100 cmH20/L/s). The loads were presented in random block order, each for 10 consecutive breaths and separated by unloaded breathing periods. The loads were presented in 2 trials, 2 times each per trial. Subjects estimated their perceived load intensity in one trial and unpleasantness in the other trial. A load compensation index (LCI) was calculated using breath phase duration and airflow. For R=0–25 cmH2O/L/s, respiratory load pattern was a load magnitude dependent increased maximum inspiratory pressure, decreased airflow, increased inspiratory duration and decreased expiratory duration. This resulted in a relatively constant total breath time, inspiratory volume, minute ventilation, PCO2, PO2 and LCI. However, decompensation was observed for R50 and R100 leading to declining minute ventilation and LCI. The results suggest, however, that increasing the duration of the R=50–100 load presentations would likely lead to hypoventilation and respiratory failure. The perception of inspiratory R load intensity and unpleasantness increased with load magnitude. The results suggest that high magnitude loads and/or long durations of loaded breathing result in increased affective response and decompensating respiratory pattern indicating that the individual is no longer able to sustain ventilation under these conditions.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.