Dyspnea

• a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity

• derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioural responses

Mechanisms of Dyspnea

• respiratory sensations• 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 occurring in the brain

• given disease state may lead to dyspnea by one or more mechanisms, some may be operative under some circumstances

Association of Qualitative Descriptors and Pathophysiologic Mechanisms of Shortness of

BreathDescriptor PathophysiologyChest tightness or constriction Bronchoconstriction, interstitial edema

(asthma, myocardial ischemia)Increased work or effort of breathing Airway obstruction, neuromuscular disease

(COPD, moderate to severe asthma, myopathy, kyphoscoliosis)

Air hunger, need to breathe, urge to breathe

Increased drive to breathe (CHF, pulmonary embolism, moderate to severe airflow obstruction)

Cannot get a deep breath, unsatisfying breath

Hyperinflation (asthma, COPD) and restricted tidal volume (pulmonary fibrosis, chest wall restriction)

Heavy breathing, rapid breathing, breathing more

Deconditioning

Likely Mechanisms of Dyspnea in Selected ConditionsCondition MechanismAsthma Increased sense of effort

Stimulation of irritant receptors in airways

Neuromuscular disease Increased sense of effortCOPD Increased sense of effort

HypoxiaHypercapniaDynamic airway compression

Mechanical ventilation Afferent mismatchFactors associated with the underlying condition

Pulmonary embolism Stimulation of pressure receptors in pulmonary vasculature or right atrium(possible)

Approach to the

Patient: Dyspnea

Patterns of Abnormality in Cardiopulmonary Exercise Testing

Cardiovascular limitation Respiratory limitation•Heart rate 85% of predicted maximum•Low anaerobic threshold•Reduced maximal oxygen consumption•Drop in blood pressure with exercise•Arrhythmias or ischemic changes on ECG•Does not achieve maximal predicted ventilation•Does not have significant desaturation

•Achieves or exceeds maximal predicted ventilation•Significant desaturation (90%)•Stable or increase dead space–to–tidal volume ratio•Development or bronchospasm with falling FEV1•Does not achieve 85% of predicted maximal heart rate•No ischemic ECG changes