Resp - Respiratory Mechanics Flashcards
muscles of inspiration
diaphragm (75%) external intercostals (25%)
accessory inspiration muscles
scalenes (raise rib 1/2)
sternocleidomastoid (raise sternum)
muscles of expiration (active)
abdominal wall
internal intercostals
causes for difficulty inspiring
scar tissue
reduced surfactant
mucous
fluid
causes for difficulty expiring
emphysema
point where laminar –> turbulent
reynolds # > 2000
conditions where turbulence likely occurs
velocity high
radius high
Reynold’s number
Re = 2rvd/n
Ohm’s law (airflow)
F = delta P/R
Poiseuille’s law
R = 8L(viscocity)/pi(radius^4)
Poiseulle’s law take away
smaller the airway, greater the R (reduce r by 50% increase R x 16)
site of most airway R (+why)
medium sized bronchi
smaller than large (up R) and in series rather than parallel (smaller ones in parallel)
factors increasing resistance
turbulent flow small radius lung volume decreasing bronchial SM contraction gas density elevated (SCUBA) forced expiration
causes of bronchoconstriction
allergy
mucous, airway collapse
PNS during relaxed state (Ach on muscarinic)
low CO2
causes of bronchodilation
SNS
- Epi (beta-2)
- CO2 up
forced exhalation
PA drives air out PA = Pip + P elastic recoil further from alveoli, less recoil exhaling air hits R, loses P EPP
equal pressure point
when Pairway = Pip
if Pip > Pairway –> collapse
(EPP @ cartilage for healthy people)
emphysema and forced expiration
alveoli have lost elastic recoil
PA is lower, EPP happens closer to alveoli, compression of airway
chronic obstructive pulmonary disease (diseases)
asthma
chronic bronchitis
emphysema
emphysema mech
- irritation –> many macs, release trypsin
usually alveoli release antitrypsin (but too many macs to fight) - breakdown of alveolar walls
- down recoil, collapse smaller airways
pulmonary function tests
spirometry
lung vol measurement
diffusion capacity for CO
arterial blood gases
tidal volume (TV)
V in or out in quiet resp
~500 ml
inspiratory reserve volume (IRV)
extra V can be inspired after quiet inspiration
expiratory reserve volume (ERV)
extra V can be expired after quiet expiration
inspiratory capacity (IC)
max V in after quiet expiration (TV + IRV)
vital capacity (VC)
max V in after max expiration (IRV + TV + ERV)
~ 4800 ml
residual volume (RV)
min air remaining in lungs after max expiration
functional residual capacity (FRC)
V in lungs after quiet expiration (ERV + RV)
total lung capacity (TLC)
max V lungs can hold (VC + RV) ~6000 ml
abnormal spirometry results (obstructive)
can’t get air out
RV up
up RV, FRC, TLC
–> slow flow, hyperinflation, down recoil
abnormal spirometry results (restricted)
cant get air in
TLC down
down VC, RV, FRC, VT
–> up recoil, down V
spirogram measurements
FVC: (V forcibly blown out after full breath)
FEV1: V forced out in 1 second
FEV1/FVC: proportion
normal FVC
80%
abnormal spirogram (obstructive)
FEV1 down (a lot) FVC down FEV1/FVC down (42%)
abnormal spirogram (restrictive)
FEV1 down
FVC down
FEV1/FVC normal or higher
flow volume loop action
- inhale to TLC
- exhale to RV as forcefully and quickly as possible
- forcefully inspire to TLC
flow volume loop: forced expiration
compression of airways from Pip up –> high flow then slow down
early = pt dependent
late = pt independent
flow volume loop: forced inspiration
muscle force down as V up
lung recoil up as V up
airway R down as V up
abnormal flow volume loop (obstructive)
scooped
peak is lower but quick
slow expiration flow
abnormal flow volume loop (restrictive)
witch’s hat
TLC, FVC is lower
Diffusion capacity action
- exhale to RV
- inhale gas (w/ small CO) to TLC
- hold breath 10 s
- measure exhaled gas for CO
diffusion capacity (obstructive)
hyperinflation and DLCO down –> emphysema
hyperinflation and DLCO normal –> asthma
normal lung volume and DLCO normal –>. chronic bronchitis
DLCO results
DLCO down in any condition affecting alveolar surface area
lung resection, emphysema
diffusion capacity (restrictive)
low RV and low DLCO –> scarring diseases
normal (or high) RV and normal DLCO = neuromuscular diseases, kyphosis, scoliosis
lung compliance
delta V/delta P
things that affect compliance
apex vs base
inspiration vs expiration (hysteresis)
disease
amount of CT
compliance (regional)
compliance greatest at base
gravity pulls on alveoli in apex, makes them more expanded
compliance (hysteresis)
PV curve diff for inspiration and expiration (not linear)
scoop for inspire, bump for expire
compliance (disease)
low compliance: stiff - pulmonary fibrosis - large transmural P needed to expand
high compliance: low recoil - emphysema
elastic recoil relations
directly related to stiffness (low compliance)
inversely related to distensibility (high compliance)
things affecting elastic recoil
elastin/collagen
*alveolar surface tension (2/3)
surface tension actions
increases recoil
decreases compliance
responsible for diffs in inspiration/expiration curves
surface tension relative to size
smaller alveoli more likely to collapse than larger
LaPlace’s Law
P = 2T/r T = surface tension
DPPC
dipalmitoyl phosphatidylchloline hydrophilic head (go in fluid) hydrophobic tail (go in air) attenuate cohesion (act as detergent)
surfactant and alveoli size
most effective when DPPC close together –>
small alveoli have lower ST
surfactant fxns
- lower surface tension (increase compliance)
- stabilize alveoli
- keep alveoli dry (avoid edema)
how surfactant keeps alveoli dry
ST usually lowers interstitial hydrostatic P (pulls fluid in)
surfactant reduces this
neonatal resp distress syndrome mech
abnormally low production of surfactant
up ST
collapse alveoli (atelectasis)
hypoxemia
neonatal resp distress syndrome Sx
cyanosis
pronounced hysteresis
high inflation P to ventilate
pulmonary edema
alveoli stabilizing factors
elastin/collagen (against overdistension)
surfactant
interdependence (tethering effect)
transmural pressure gradient
forces promoting alveolar collapse
elasticity (elastin)
alveolar surface tension
forces keeping alveoli open
transmural P gradient
pulmonary surfactant
alveolar interdependence
chest volume equilibrium
equilibrium @ ~70% TLC
< 70: recoil force out
> 70: recoil force in
lung/chest combined equilibrium volume
chest compressed below equilibrium
lung expanded above
chest force out is equal to lung force in
occurs @ FRC
