TAILIEUCHUNG - Chapter 033. Dyspnea and Pulmonary Edema

Mechanisms of Dyspnea Respiratory sensations are the consequence of interactions between the efferent, or outgoing, motor output from the brain to the ventilatory muscles (feed-forward) and the afferent, or incoming, sensory input from receptors throughout the body (feedback), as well as the integrative processing of this information that we infer must be occurring in the brain (Fig. 33-1). A given disease state may lead to dyspnea by one or more mechanisms, some of which may be operative under some circumstances but not others. . | Chapter 033. Dyspnea and Pulmonary Edema Mechanisms of Dyspnea Respiratory sensations are the consequence of interactions between the efferent or outgoing motor output from the brain to the ventilatory muscles feed-forward and the afferent or incoming sensory input from receptors throughout the body feedback as well as the integrative processing of this information that we infer must be occurring in the brain Fig. 33-1 . A given disease state may lead to dyspnea by one or more mechanisms some of which may be operative under some circumstances but not others. Figure 33-1 Hypothetical model for integration of sensory inputs in the production of information from the receptors throughout the respiratory system projects directly to the sensory cortex to contribute to primary qualitative sensory experiences and provide feedback on the action of the ventilatory pump. Afferents also project to the areas of the brain responsible for control of ventilation. The motor cortex responding to input from the control centers sends neural messages to the ventilatory muscles and a corollary discharge to the sensory cortex feed-forward with respect to the instructions sent to the muscles . If the feed-forward and feedback messages do not match an error signal is generated and the intensity of dyspnea increases. Adapted from Gillette and Schwartzstein. Motor Efferents Disorders of the ventilatory pump are associated with increased work of breathing or a sense of an increased effort to breathe. When the muscles are weak or fatigued greater effort is required even though the mechanics of the system are normal. The increased neural output from the motor cortex is thought to be sensed due to a corollary discharge that is sent to the sensory cortex at the same time that signals are sent to the ventilatory muscles. Sensory Afferents Chemoreceptors in the carotid bodies and medulla are activated by hypoxemia acute hypercapnia and acidemia. Stimulation of these receptors as .

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