Chronic Obstructive Pulmonary Disease: Clinical Integrative Physiology

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Key points

  • COPD is characterized by heterogeneous physiologic abnormalities that are not adequately represented by simple spirometry.

  • Extensive peripheral airway dysfunction is often present in smokers with mild spirometric abnormalities and may have negative clinical consequences.

  • Activity-related dyspnea and exercise intolerance in patients with mild airway obstruction are linked to increased ventilatory inefficiency and dynamic gas trapping during exercise.

  • Progressive increases in dyspnea and activity

Clinical Relevance

It is well established that those with mild-to-moderate disease severity represent most patients with COPD, yet this subpopulation is understudied.1, 2 For the purpose of this review, mild COPD refers to spirometrically defined mild airway obstruction (ie, FEV1 80%–100 % predicted), which need not be synonymous with early COPD. There is evidence from several population studies that, compared with nonsmoking healthy populations, smokers with mild COPD show increased mortality (including

Moderate-to-severe COPD

Concepts of the natural history of COPD are strongly influenced by the seminal longitudinal population study of Fletcher and Peto80 who have charted the decline in FEV1 with time in susceptible smokers. Much less information is available on the temporal evolution of complex mechanical abnormalities and of pulmonary gas exchange abnormalities. Clearly, disease progression is characterized by worsening of the heterogeneous physiologic derangements already outlined in mild COPD. Recent short-term

Physiologic mechanisms of dyspnea in COPD

Most patients with COPD experience dyspnea during daily activities.117, 124, 167 As COPD progresses, dyspnea intensity ratings become progressively higher at any given V′E, power output, or metabolic load (Fig. 8).108 At the breakpoint of exercise healthy individuals report that their breathing requires more work or effort.104 However, patients with COPD additionally report the sense of unsatisfied inspiration (“can’t get enough air in”).97, 104, 110 These distinct qualitative dimensions of

Summary

COPD is characterized by diverse physiologic derangements that are not adequately represented by simple spirometry. The human respiratory system has enormous reserve and develops effective compensatory strategies to fulfill its primary function of maintaining blood gas homeostasis even in the face of extensive injury to the small airways, lung parenchyma, and its microvasculature. These physiologic adaptations together with behavioral modification (eg, activity avoidance) can result in a

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