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17 Pulmonary: Airflow and Resistance


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conducting zone
- all bronchi and bronchioles to terminal bronchioles
- no alveoli so no gas exchange
- air movement by bulk flow
respiratory zone
- distal to terminal bronchiole --> Acinus
- largest volume (2.5 - 3 L)
- movement: diffusion b/c of large cross sectional area
air flow
- due to differences in pressure across airway
- rate: proportional to driving pressure, inverse to airway resistance
- V(. flowrate) = ΔP/R
- valid under laminar flow
Poiseuille's Law
R = 8nl/pi r^4

flowrate and pressure under laminar flow
- R = resistance
- n = viscosity of gas
- l = length of tube
- decrease in radius by half increases resistance by 16 fold
reynold's number
- effect of radius on resistance greater if flow is turbulent
- determines if laminar or turbulent
- Re= (vrd/n)
v = average velocity
d = density
r = radius
n = viscosity

Less than 2000 --> laminar
Airway tone
- airway antomy:
- brochi are airways til 9th generation, contain cartilage
- bronchioles at 10-15 generation no cartilage, airway maintained by surrounding tissue and smooth muscle tone
- stimulation (Ach, metacholine) --> bronchoconstriction
- atropine, ipatropium and bromide cause bronchodilation
- circulating catecholamines --> bronchodilation by stimulating β2 receptors on bronchial smooth muscle
Vital capacity maneuver
- performed under maximum expiratory flow (FVC)
- maximum inspiration followed by maximum expiration
- spirometer measures volume and flow
flow volume graphs
- beings exhaling at TLC and continues until RV is reached
- instantaneous maximum flow (peak expiratory flow) ↓ in conditions of increased Air resistance
- distinct patterns for dx compared to normal
- width of flow-volume graph = FVC
- height and shape of expiratory limb of loop = flow capabilities
Effort dependence
- expiratory flow through early airways effort and volume dependent
- through small airways, effort independent
dynamic airway compression
- closure of airways due to ↑ PIP
- in normal: PIP less than PB , PA starts higher than PB then --> 0
- PTM is + and acts on airway wall to keep it open
-on forced expiration:
- PIP > PB and PA>PB
- as long as pressure in airway > PIP airways remain open
- when airway pressure =PIP = Equal pressure point PTM= 0
- downstream from EPP, airway pressure < than PIP airway collapses
FVC maneuver tracings
- FEV1 (O-1 second) lowered means airway obstruction
- FEV1/FVC - ratio of amount expired in 1 sec to total expired (to peak of maximal inspiration to where graph peters out)
- FEF(25-75%) measured airflow through small to middle sized airways
- airflow reduction can be detected here, steeper slope in normal FVC x .25
Restrictive Dx
- volumes reduced
- "obstructive to flow, restrictive to volume"
Obstructive Dx
- flows are reduced
- "obstructive to flow, restrictive to volume"
Values in Flow/volume graphs

decreased in obstructive and restrictive
decreased in obstructive and restrictive
- decreased in obstructive
- normal or high in restrictive

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