How does the diaphragm expand the thoracic cavity?
forces abdominal contents down and forward
What is the "bucket handle" movement of the ribs?
-external intercostals
-pull ribs upward and outward away from spinal column
How are lungs inflated? Deflated?
Active contraction of muscles inflates lungs by creating negative pressure in the thoracic cavity.
lungs are deflated by elastic recoil of lung tissue--reduces volume thoracic cavity passively
Active expiration occurs when ventilation is increased--the in
What is compliance? How is it affected by volume?
compliance=volume change per unit pressure change (big volume change w/small pressure change=stretchy=compliant)
At High volumes:
-tissues are unfolded and being stretched
-compliance is low
-flat part compliance curve
At Low volumes:
-tissues have a lot
How does elastic tissue affect compliance?
more elastic tissue=more stiffness=decreased compliance
What are diseases/situations that cause decreased compliance?
1. Pulmonary fibrosis (increased fibrous tissue in lungs)
2. Alveolar edema (harder to inflate alveoli)
3. Unventilated lung regions (due to atelectasis or increased surface tension)
4. Increased pulmonary venous pressure (engorge lung with blood, decreas
What is Pulmonary Fibrosis?
Diffuse interstitial pulmonary fibrosis:
-thickened interstitium of alveolar wall
-infiltration with lymphocytes and plasma cells
-fibroblasts lay down collagen bundles, surround alveoli
What is a disease with increased compliance? Describe its effects?
COPD (Pulmonary Emphysema/chronic bronchitis/mixture of the 2): change in elastic tissue of the lungs
-ill-defined disease
-anatomic enlargement of the airspaces distal to terminal bronchioles
-destruction alveolar walls
Describe the mechanism and properties of the elastic recoil of the lungs
Pleural pressure
-created in virtual space filled with small amount of fluid between visceral and parietal pleura that surround the lungs
-usually negative, balance between outward recoil of chest wall and inward recoil of lungs
*at all physiologically at
Look at graph on page 62
Look where 0 pressure is for each curve. For lung it always needs positive pressure to increase volume. For chest wall it isn't relaxed until 80% vital capacity so chest wall is almost always pulling outward--at near 100% chest AND alveoli pull inward, ot
When is compliance of the chest affected by disease?
*rarely--much less often than the lungs are affected
-ankylosing spondylitis (spinal joint inflammation)
-kyphosis (excessive spinal curvature)
-kyphoscoliosis (kyphosis plus side-to-side abnormal curvature spine)
-obesity
What is surface tension?
surface tension: force that acts on the plane of an interface between 2 phases (like water and gas) and attempts to minimize the surface area of the interface (why water forms into round drops on a solid surface)
What is the effect of surface tension on the lung?
*tends to collapse the lungs b/c of attractive forces btw liquid molecules lining the lungs
1. increases work lungs have to do to inflate and deflate
-saline inflation: easy b/c eliminates air-water interface and surface tension
-air inflation: requires 3
Why is it hard to reinflate a collapsed lung?
P=0
alveoli collapse (atelectasis), hard to oppose surface tension
small airways collapse as well
What equation explains atelectasis?
Atelectasis=tendency of alveoli to collapse
determined by 2 properties: surface tension and radius of sphere
in a thin walled space...
P=2T/r
P=pressure, T=tension in wall, r=radius sphere
1. Size of alveoli (r)
-large alveoli have small pressure trying t
What is surfactant?
*amphipathic organic compound, lines alveolar subphase (which is the thin layer of fluid that lines the alveolus)
-hydrophobic side faces air
-hydrophilic side faces water
*opposes intermolecular attractive forces btw liquid molecules that line the alveol
When does surfactant appear in the fetus? What happens to premature infants without it?
-appears gestational weeks 24-35
-Neonatal respiratory distress syndrome=premature infants lack surfactant, have atelectasis, hypoxemia
When is surfactant abnormally reduced?
-oxygen related abnormalities (hypoxia, anoxia, O2 toxicity)
-acidosis
-atelectasis (localized lung collapse)
-IRDS (infant respiratory distress syndrome)
-ARDS (adult respiratory distress syndrome)
-pulmonary embolus (deprives type II cells of nutrients)
When is surfactant increased?
-Secretagogues (substance that promotes secretion--beta-adrenergic agonists, experimental agents)
-mechanical stretch (yawns)
-birth (due to hormonal defects)
What is the critical opening pressure?
The large initial increase necessary to inflate an alveolus at low volume-->overcome maximum surface tension
*compliance is lowest at max inflation, but it is also low at minimum inflation--surface tension and elasticity are opposing forces
*like blowing
find a lamellar body on an electron micrograph
do it
What are the 2 types of airflow? describe them.
1. Laminar flow:
-streamlined flow, gas molecules move parallel to each other and walls
-high axial velocity
2. Turbulent flow
-chaotic movement, rapid irregular changes in velocity and pressure
-cannot be prevented
-often occurs in large airways
-less ef
What factors determine the airflow? What is the equation that shows this relationship?
1. Pressure difference between nose/mouth and alveoli (deltaP)
-greater difference=greater airflow
2. Airway resistance (R)
-more resistance=less airflow
Vdot=?P/Raw
Vdot=airflow (mL/min)
?P=pressure gradient (cmH2O)
Raw=resistance in the airway (cm H2O/l
What equation describes airway resistance in laminar flow?
R=(8?l)/(?r^2)
?=viscosity
l=length of tube
r=radius of tube
*this indicates that resistance decreases with increased radius
*however the total resistance of larger airways is greater than smaller ones b/c they have a smaller cross-sectional area (smaller
Why is most of the total resistance of the airways contributed by the largest airways?
1. airway diameter decrease only gradually with branching
2. total cross-sectional area is much smaller than the combined cross-sectional area of the smaller airways (cross-sectional area increases exponentially with branching)--forward velocity of gas is
What predicts a tendency toward turbulent flow?
Reynold's number:
Re=2rVdot(?/?)
Re=Reynold's number
r=radius tube
Vdot=flow rate
?=density
?=viscosity
*(?/?) is 20x greater for air than blood, so airflow is much more turbulent
*turbulence is normal in large airways
*in distal parts of tree (small airw
How does flow rate compare in laminar and turbulent flow?
laminar:
Vdot=?P/Raw
turbulent:
Vdot=??P/Raw (square root)
*laminar flow much more efficient than turbulent flow
Vdot=flow rate (function of driving pressure deltaP)
What are factors that increase airway resistance?
1. bronchoconstrictors
-parasympathetic nervous system (ACh)
-cholinergic agonists
-histamine (from mast cells in asthma)
-smoke/pollutants
-bronchitis (inflammation bronchi)
2. compression of airways
3. particles in airways
4. low lung volumes (less trac
What causes decreased airway resistance?
1. Brochodilation
-sympathetic nervous system (norepinephrine)
-Beta-adrenergic agonists
2. High lung volumes
-greater traction, decreased airway resistance
-breathing at higher volumes good way to decrease resistance in pts with asthma and other diseases