DYSPNEA AND MECHANICAL VENTILATION: APPLYING PHYSIOLOGY TO GUIDE THERAPY

Abstract

While advances in our understanding of mechanical ventilation have improved mortality from acute respiratory distress syndrome, recent studies indicate a rising incidence of post-ventilation mental health sequelae, including post-traumatic stress disorder (PTSD). Concurrent research on the physiology of dyspnea provides insights about the role of multiple sources of sensory information underlying respiratory discomfort along with the contribution of efferent-afferent dissociation to dyspnea, and the subsequent relationship of dyspnea to a range of affective responses, including fear and anxiety. An understanding of the mechanisms of dyspnea may provide holistic approaches to managing acute respiratory failure that can achieve the best physical and emotional outcomes for patients requiring mechanical ventilation.

Fig. 1.

Mechanisms of dyspnea: Dyspnea arises from multiple sources including a corollary discharge from the motor to sensory cortex leading to a sense of effort or work of breathing; a sense of air hunger, linked closely to the drive to breathe, which is heightened due to stimulation of multiple receptors in the lungs and vasculature; and chest tightness, which develops in association with bronchospasm. In addition, the intensity of dyspnea is heightened by dissociation between the outgoing (efferent) neurological impulses to the ventilatory muscles and the incoming (afferent) messages from the lungs, airways, and rib cage that provide information on the mechanical consequences of the neurological command to breathe in a certain way. Adapted with permission from: Schwartzstein RM. Physiology of Dyspnea. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA (Accessed on March 28, 2023.) Copyright © 2023, UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.

Fig. 2.

Affective elements of dyspnea. In this study, healthy subjects were made breathless in a laboratory experiment under three conditions: (1) eucapnic hyperpnea while breathing with a resistive load, (2) hypercapnia with a moderate limit on the size of the tidal volume, and (3) hypercapnia with a severe tidal volume limit. Subjects were asked to rate five affective responses evoked by their breathing discomfort: depression, anxiety, frustration, anger, and fear. Severe limits on tidal volume with hypercapnia elicited the most intense emotional responses. From reference (24). Reprinted with permission of the American Thoracic Society. Copyright © 2023 American Thoracic Society. All rights reserved. Banzett RB, Pederson SH, Schwartzstein RM, Lansing RW. The affective dimension of dyspnea. American Journal of Respiratory and Critical Care Medicine 2008;177:1384–1390. The American Journal of Respiratory and Critical Care Medicine is an official journal of the American Thoracic Society.