Breathlessness in Patients with Chronic Airflow Limitation: Dynamic Lung Hyperinflation in CAL
This result is in accordance with previous studies that have shown that breathlessness increases as the frequency (F) and extent of ventilatory muscle contraction (Vt/VC) increase. The study extended previous observations by underlining the important contribution of acute changes in operating lung volumes. Regression analysis selected change in end-inspiratory lung volume (or change in inspiratory reserve volume) from various dynamic ventilatory parameters as the strongest predictor of ABorg (r=0.63, p<0.001). Moreover, acute DH was shown to contribute importantly to intersubject variability in the perception of breathlessness for a given Ve: at a standardized Ve, EELVdyn predicted 31 percent of the variance in Borg ratings (p<0.01). These findings suggest that acute DH is an important dyspneogenic stimulus during exercise in CAL read generic allegra. The mechanisms by which this stimulus is transduced neurophysiologically into the conscious awareness of unpleasant respiratory sensation remain to be determined.
Neurophysiologic Basis of Breathlessness A detailed discussion of the neurophysiologic basis of breathlessness is beyond the scope of this review (excellent comprehensive reviews are available). The relative importance of peripheral respiratory mechanoreceptor activation, medullary activation, or central motor command output in the genesis of the global sensory experience of breathlessness is not precisely known and remains speculative. Current theories of the origin of breathlessness emphasize the central importance of motor output or neural activation of the ventilatory muscles.’ Certainly, there is considerable experimental evidence that breathlessness, under a variety of conditions, increases as a function of motor output as reflected by the pressures generated by the ventilatory muscles expressed as a fraction of their maximal pressure generation. The previously outlined correlation between breathlessness ratings and Ve/MBC supports this notion since this ratio also crudely reflects motor output relative to its maximum. It has been proposed that motor output can be consciously perceived as “sense of effort” via collateral discharge or efferent copy from respiratory-related neurons in the medulla to the sensory cortex. “Sense of effort” is a discrete respiratory sensation that is distinguishable from peripheral muscular sensations relating to muscle tension development or displacement.
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise