Obstructive Disease In General

Question 1

Air Trapping

Answer 1

• when small airways collapse (w/ air in them) due to high resistance
• Inc RV and dec in VC

Question 2

Dynamic Hyperinflation

Answer 2

• when end-expiratory vol is inc b/c not enough time to fully expire and reach equilibrium SO elastic recoil remains pos (intrinsic or auto PEEP)
• Can make resistance worse b/c pos pleural pressure remains –> push down on airways –> airway collapse and compression

Question 3

How are respiratory muscles affected?

Answer 3

(inc energy expenditure)

• Must overcome more pressure to overcome viscous forces (resistance) - takes energy
• Air trapping and hyperinflation –> diaphragm loses dome shape –> less efficient –> more energy to do same work
• Intrinsic PEEP causes insp muscles to contract and then wait until equilibrium is actually reached to generate flow

Question 4

PFT Findings

Answer 4

• Dec in all expiratory flow rates (PEFR, FEF25-75, FEV1) - takes more total expiratory time
• FVC (volume) is normal or dec if air trapping; even if dec FVC, FEV1 is more dec so FEV1/FVC is low
• Vol-Time Curves - show vol cont to inc w/ time; do not reach plateau quickly like normal
• Flow-Vol Curves - show “scooped out” appearance

Question 5

Why is there exercise limitation and dyspnea?

Answer 5

• Max flow dec as disease progresses (so need more time to exhale - limits RR)
• Air trapping and hyperinflation –> dec max tidal volume (limits VT)
• SO … overall cannot inc minute ventilation b/c minute vent = Vt x RR

Question 6

Long Term Changes

Answer 6

• Cap destruction and hypoxia-induced vasoconstriction –> dec SA / inc resistance
• Intima thickening –> irreversible inc resistance
• Leads to pulmonary HTN –> R heart fail or “cor pulmonale” (inc JVP, hepatomegaly, peripheral edema)

Question 7

Examples of Obstructive Lung Disease

Answer 7

• COPD (chronic bronchitis and emphysema)
• Asthma
• Bronchiectasis
• Bronchiolitis