Respiratory Physiology Lecture 1 Flashcards
What is the difference between ventilation and respiration?
Ventilation refers to the entire process of breathing in and out
Respiration is strictly the events involved in gas exchange
What is the difference between external respiration and internal respiration?
External respiration: exchange of O2 and CO2 between the atmosphere and body tissues
Internal respiration: use of O2 in generation of ATP by ox-phos; CO2 is the waste product
What are some of the nonrespiratory functions of the respiratory system? (7)
- Filters thrombi (clots) and emboli (fat or air) from the blood
- Metabolism (AngI -> AngII; produces surfactant)
- Shock absorber for the heart & enhances venous return
- Alter blood pH
- Route for water loss and heat elimination
- Blood reservoir (10% of total blood volume)
- Provide airflow for speech, singing, and other vocalizations
What is the purpose of cartilaginous rings and plates along the trachea and bronchi?
Prevent collapse of airway during pressure changes, coughing (increased pressure), etc
If bronchioles contain no cartilage, what physical characteristics keep them open to allow for gas exchange? (2)
Lung tissue parenchyma
Elasticity
How is airway diameter regulated? (2)
Smooth muscle innervation (ANS)
Circulating hormones and local chemicals
What are the components of the conducting zone? Why is it considered “anatomical dead space”?
Trachea & first 16 generations of airways
No alveoli, so no gas exchange
~150 mL
What are the components of the respiratory zone?
Last 7 generations of airways (only a few mm long)
~300 milion alveoli
~3 L
What are the functions of the conducting zone? (3)
Distribution of air evenly to deeper parts of the lungs
Warms (37 ℃), humidifies, and filters air
Defense (mucociliary escalator; macrophages)
What is the total surface area of alveoli?
60-80 m2
What are the functions of Type I and Type II alveolar cells?
Type I: simple squamous epithelia that allow for gas exchange
Type II: secrete surfactant
What is the function of Pores of Kohn?
Permit airflow between adjacent alveoli and connect one alveolus to the next (collateral ventilation)
What are the components of lung tissue parenchyma (4)? Which components contain smooth muscle?
airways (SM)
alveoli
blood vessels (SM)
elastic connective tissue
Describe the pleural sac.
Double-walled, closed sac:
Visceral wall covers surface of the lung
Parietal wall interacts with the inside of the thoracic cavity
Secretes intrapleural fluid (~1.5 mL) to lubricate pleural surfaces to adhere together
Define atmospheric (barometric) pressure (PB).
Pressure exerted by the weight of the air in the atmosphere
~760 mm Hg at sea level
Define intrapulmonary (alveolar) pressure (PA).
Pressure inside the alveoli
~760 mm Hg (or 0 mm Hg)
Define intrapleural pressure (PIP).
Pressure in the pleural fluid; normally less than intrapulmonary pressure
~756 mm Hg (-4 mm Hg)
Define transmural pressure (PT). Formula?
Pressure difference across the wall
(transpulmonary = across the lung wall)
PT= PA - PIP
Neither the thoracic wall nor lungs are in their “natural positions.” Which directions do each of these structures tend to pull?
Stretched lungs tend to recoil in
Compressed thoracic wall tends to recoil out
What two forces keep the lung and chest from pulling away from each other?
Transmural pressure gradient
Intrapleural fluid cohesiveness
PIP tends to be ______ during quiet breathing and deep inspiration. PIP tends to be ______ during forced expiration.
Negative; positive
Explain what happens during a pneumothorax (4).
Air enters the pleural space
PIP equilibrates with PB
Transpulmonary pressure gradient is lost and IPF alone cannot hold lungs and wall
Lungs and thorax separate and assume their “natural positions”
Define atelectasis
Collapse of alveoli
What do the following primary symbols denote?
P
V
F
Q
C
Physical quantities:
P = pressure, tension or partial pressure of a gas
V = volume of a gas
F = fractional concentration of a gas
Q = Volume of blood
C = content
What do the following secondary symbols denote?
A
a
B
D
E
I
ip
v
Location of the gas:
A = alveolar
a = arterial
B = barometric
D = dead space
E = expiratory
I = inspiratory
ip = pleural
v = venous
What does “•” denote?
Rate
Define pleurisy.
Inflammation of the pleural sac
What must occur in order to alter lung volume (3)
Respiratory muscles must change the size of the thoracic cavity
Overcome tissue elastance
Overcome surface tension within alveoli
If air flows down a pressure gradient, which direction is air flowing when PA < PB?
Air enters the lungs
If air flows down a pressure gradient, which direction is air flowing when PA > PB?
Air exits the lungs
Define Boyle’s Law. What is the equation for it?
The pressure and volume of a gas are inversely related.
As volume increases, pressure exerted by gas decreases proportionally
P1 * V1 = P2 * V2
How much pressure is needed to create airflow? Why is this?
1 mm Hg
Resistance in the airway is low, so 1 mm Hg is sufficient to create airflow
Describe the pressure changes during inspiration.
Before inspiration:
PA = PB
Diaphragm contracts:
PA drops –> fresh air flows in until pressures equalize
PIP drops –> increased transpulmonary pressure gradient
How much does the diaphragm move during normal inspiration vs forced inspiration?
Normal: 1 cm
Forced: 10 cm
What nerve innervates the diaphragm? How does it contract?
Phrenic nerve
Increases thoracic cavity by descending downward
What nerves innervate the external intercostal muscles? How do they contract?
Intercostal nerves
Elevate ribs and thus sternum upward and forward (“bucket-handle” fashion)
What are the accessory muscles recruited during forced inspiration (2)? What are their functions?
Scalene muscles: elevate the first two ribs
Sternocleidomastoid: raises the sternum
What are the steps of expiration? (4)
Inspiratory muscles relax
Lungs recoil due to elastic properties
Pleural & alveolar pressures rise (PA = 761 mm Hg)
Gas flows passively out of the lungs due to elastic recoil
What muscles are involved in forced (active) expiration (“2”)? What pressure change occurs with contraction of these muscles?
Internal intercostals
Abdominal muscles (Transverse abdominis, external abdominal oblique, internal abdominal oblique)
Increases PA
What are some factors that make it difficult to expand the lungs and breathe in? (4)
Scar tissue
Reduced surfactant
Excess mucus
Fluid
What are the differences between laminar and turbulent flow?
Laminar:
Air flows in the same direction, parallel to walls, low flow rates, gas in center travels more rapidly
Turbulent:
As airflow increases, air moves more irregularly; creates resistance to flow which requires higher pressures
Renolds Number determines ______. What is the equation to calculate it?
Gas flow patterns
Re = (2rvd) / n
r = radius
v = velocity
d = density
n = viscosity
Laminar flow becomes turbulent when Reynold’s number_____
> 2000
Under what conditions is turbulence most likely to occur?
Average velocity is high and radius is large
Ex: in the trachea, large diameter (3 cm) and gas flow (1 L/sec)
*gas flow in larger airways is turbulent*
Which type of flow can be heard with a stethoscope (breath sounds) and which type cannot?
Laminar: silent
Turbulent: induce vibrations on the airway walls
Ohm’s law equation
F = ΔP/R
F = flow rate
ΔP = pressure difference
R = resistance
Poiseuille’s Law for resistance (for laminar air flow) equation. What is the biggest determinant for resistance?
R = (8 * L * η) / (π * r4)
R = resistance to flow in a tube
L = length of tube
η = viscosity of the fluid
π = 3.14
r = radius of the tube (biggest determinant)
The smaller the airway, the ______ the resistance
greater
Which of the following has the highest resistance to airflow? Explain:
Large airways (trachea and large bronchi)
Medium-sized bronchi
Small airways (terminal bronchioles and alveoli)
Large airways: has turbulent flow, but radius is too large
Medium-sized bronchi: tubes in series (R1 + R2….) have greater resistance than tubes in parallel (1/R1 + 1/R2….)
Small airways: small radius, but vast cross-sectional area, so they contribute little to resistance
What are some factors that affect resistance? (4)
Lung volume (diameter of airways)
Bronchial smooth muscle
Gas density
Forced expiration
What physiologic factors can cause bronchoconstriction? (2)
Neural control (PNS): acetylcholine acts on muscarinic receptors during quiet relaxed situations when demand is not high
Local control: when CO2 is low
What major physiological factors can cause bronchodilation? (2)
Hormones: Epi and nEpi when demand is high (β2 adrenergic agonists); ex: albuterol
Local control: high CO2
What is the equal pressure point (EPP)?
During forced expiration, where Pairway = PIP
*If PIP > Pairway, airway will collapse
Where does EPP occur normally in healthy lungs? Why?
Where cartilage is
Prevents closure of the airway
Using the provided diagram, describe what pathological changes happen in the lungs in someone with emphysema.
Loss of alveoli and thus elastic recoil; lowers PA further during forced expiration
EPP occurs closer to the alveoli where the cartilage cannot prevent airway collapse
EPP is influenced by lung elastic recoil. Describe the changes in elastic recoil of someone with emphysema and what it ultimately leads to.
Healthy: Recoil -> increases PA -> EPP established in larger airways; collapse is minimal
Emphysema: low recoil -> decreased PA -> EPP established in small airways; easily compressed
What is chronic obstructive pulmonary disease?
COPD
Umbrella term used to describe chronic lung diseases that cause limitations in lung airflow (increased resistance)
What are the two main forms of COPD and how are they different from each other?
Chronic bronchitis (bottom): airway walls become thickened & inflamed; airways become clogged with mucus
Emphysema (top): alveolar walls are destroyed; alveoli lose their ability to recoil
What does spirometry measure?
Pulmonary function test; measures lung volumes and capacities
Describe tidal volume (VT)
Volume of air entering or leaving lungs during a single breath
~500 mL
Describe inspiratory reserve volume (IRV)
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume
~3100 mL
Describe expiratory reserve volume (ERV)
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
~1200 mL
Describe inspiratory capacity (IC). How can it be calculated?
Maximum volume of air that can be inspired at the end of a normal quiet expiration (IC = IRV +VT)
~3600 mL
Describe residual volume (RV)
Minimal volume of air remaining in the lungs after maximal expiration
~1200 mL
Describe functional residual capacity (FRC). How can it be calculated?
Volume of air in lungs at the end of normal passive expiration (FRC = ERV +RV)
~2400 mL
Describe vital capacity (VC). How can it be calculated?
Maximum volume of air that can be moved out during a single breath following maximal inspiration (VC = IRV + VT + ERV)
~4800 mL
Describe total lung capacity (TLC). How can it be calculated?
Maximum volume of air that the lungs can hold (TLC = VC + RV)
~6000 mL
Label the following components of the volume-time curve:
Residual volume (RV), Expiratory reserve volume (ERV), Vital capacity (VC), Total lung capacity (TLC), Tidal volume (VT), Inspiratory reserve volume (IRV), Functional residual capacity (FRC), and Inspiratory capacity (IC)
Spirometry cannot provide any information about a patient’s RV, FRC, nor TLC. What techniques must be performed in order to measure them? (2)
gas dilution
body plethysmography
How do the lung volumes change in someone with an obstructive lung disorder? What factors cause this?
Increased RV, FRC, and TLC (static lung volumes)
Slow flow rates, hyperinflation, decreased recoil
Ex: COPD
How do the lung volumes change in someone with a restrictive lung disorder? What factors cause this?
Decreased TLC due to decreased VC, RV, FRC, and VT
Increased recoil, decreased volume
Ex: pulmonary fibrosis, scoliosis, ALS
What is FEV1?
Forced expiratory volume in 1 second
FEV1/FVC measures what?
proportion of FVC expired in 1st second of expiration
What is compliance? How is it calculated?
How easily the lung can be stretched (distensibility)
C = ΔV/ΔP
Is compliance greater at the apex or base of the lungs? Why?
Base
Gravity causes weight of lungs to pull down on alveoli
A lung that is more distensible has ____ elastic recoil
less
(the two are inversely related)
What two factors determine elastic behavior of the lungs?
Elastin & collagen fibers (1/3 of total force)
Alveolar surface tension (2/3 of total force)
Surfactant is secreted by Type II alveolar cells. What is this surfactant called and what is its function?
Dipalmitoyl phosphatidylcholine (DPPC)
Reduce surface tension in alveoli, thus increase compliance
DPPC/Sphingomyelin (L/S) ratio in amiotic fluid indicates lung maturity. In a ratio of 2:1 indicates ______ and a ratio <2:1 indicates _____.
mature enough lungs to survive outside of the womb
immature lungs that can develop into breathing problems
