Breathlessness in Patients with Chronic Airflow Limitation: Physiologic Correlates
Breathlessness is a common and often incapacitating symptom in patients with advanced chronic airflow limitation (CAL) and may seriously curtail their ability to exercise. In its later stages, the disease is essentially irreversible and management strategies must necessarily be directed toward symptom alleviation. Currently, the effective management of breathlessness has remained an elusive goal, but our understanding of the source and mechanisms of this distressing symptom continues to grow. Canadian health&care mall itat on This review represents a pragmatic consideration of the pathophysiologic basis of breathlessness in CAL in an attempt to identify specific sources of this unpleasant sensation that might be amenable to treatment.
Although breathlessness generally intensifies as pulmonary function declines, there is wide overlap in the relationship between breathlessness and commonly measured resting physiologic parameters such as dynamic expiratory flow rates, static lung volumes, and arterial blood gases. The study of sensory-mechanical interrelationships in CAL is preferably undertaken in the setting of induced breathlessness during chemical loading, external mechanical loading, broncho-provocation, or exercise. Since breathlessness in CAL is primarily activity related, mechanistic studies of exertional breathlessness are particularly relevant.
Several studies that have used exercise as the dys-pneogenic stimulus in CAL have shown a close statistical correlation between intensity of breathlessness, measured by a semiquantitative scale (Borg Scale), and the ventilatory index (minute ventilation expressed as a fraction of maximal breathing capacity (Ve/MBC)). In a recent study of 23 patients with severe CAL (FEVi=36±13 percent predicted, mean±SD), we have shown that exertional breathlessness ratings (Borg) correlated strongly with the ventilatory index: ABorg=9.5XAVE/MBC—0.2 (r= 0.77, p<0.001; A=change from rest, MBC= 28.09 XFEVi+18.4). This important association between perceived breathlessness and ventilatory demand was confirmed in a second study that compared ventilatory responses with exercise in two groups of patients with CAL who differed significantly in their level of chronic activity-related breathlessness. The severely breathless (SB) group (n=17) could clearly be distinguished from the mildly breathless group (MB) (n=21) by having significantly higher slopes of Ve/MBC vs work rate.
Category: Respiratory Symptoms
Tags: breathlessness, chronic airflow limitation, copd, dynamic compression, dynamic hyperinflation, exercise