Mechanics of Breathing Flashcards
What is ventilation?
movement of air between lungs and atmosphere
Airflow in and out of the respiratory system needs a…
pressure difference between atmosphere and the lungs
- air moves from high pressure to low pressure
- air gets pulled in and pushed out
What is inspiration?
- inward movement of air
- from atmosphere to lungs
- chest cavity expands to lower pressure within chest
- expends E
Inspiration requires which skeletal muscle contractions?
- diaphragm (major muscle here)
- external intercostals
- sternocleidomastoid
What happens to the diaphragm during inspiration?
- contraction signaled by phrenic nerves
- diaphragm flattens
- abdominal contents are forced downwards
What impairs the diaphragm?
- obesity
- pregnancy
- tight clothing
Which skeletal muscles are classified as accessory?
- external intercostals
- sternocleidomastoid
When are accessory muscles utilized for respiration?
deep respiration
What is expiration?
outward movement of air (from lungs to atmosphere)
- chest cavity decreases in size to increase pressure within chest
During normal expiration, there is an increase in ______ due to…
pressure gradient due to:
- passive elastic recoil of lung
- decrease in size of chest due to relaxation of muscles of inspiration
- no E expended
Forced expiration occurs when…
- exercising
- hyperventilation
- coughing
- sneezing
- vomiting
Which muscles are involved in forced expiration?
- abdominal wall muscles (most important)
- internal intercostals
- expends E
Contraction of abdominal wall muscles leads to…
abdominal contents being forced upward towards diaphragm
What is ambient air?
air we breathe
- 79% N
- 21% O
- <1 % CO2
Air at sea level is what atm?
760 mmHg
For comparison purposes, the atmospheric pressure is set at…
0
What is the pressure inside the alveolus during inspiration and expiration?
- inspiration: negative (less than ambient pressure)
- expiration: positive (greater than ambient pressure)
What is pleural pressure?
pressure associated with pleural fluid in between chest wall and lung
- usually negative compared to atm pressure
What is transairway pressure?
pressure in airway - pressure of pleural fluid
What happens to pleural pressure when expiration is forced?
turns positive and triggers airway collapse
- air gets trapped within lungs
What is alveolar pressure?
pressure inside alveolus
- 0 at rest
What is transpulmonary pressure?
pressure in alveolus - pressure of pleural fluid
- always positive to prevent collapse of lungs
What is a pneumothorax?
introduction of air into pleural space
- changes pleural pressure to 0 or positive
What happens during a pneumothorax?
- air enters via punctured chest wall or ruptured lung
- elastic recoil of lung causes lung to collapse
What are the pressure changes in normal breathing cycle?
- end of expiration: no airflow (Pa=Pb)
- mid inspiration: expansion of lung and chest cavity by muscle contraction and air flows in (Pa
- end of inspiration: no airflow (Pa=Pb)
- mid expiration: air flows out (Pa>Pb)
What are the pleural pressures during the normal breathing cycle?
- end of expiration: -5
- mid-inspiration: -7
- end of inspiration: -8
- mid-expiration: -6
Lung volumes and capacities are determined by…
balance between lungs elastic recoil properties and properties of muscles of chest wall
What is a spirogram?
graphs volume of air that’s moved into and out of lungs over time
What are the different types of lung volumes?
- tidal volume (VT)
- inspiratory reserve volume (IRV)
- expiratory reserve volume (ERV)
- residual volume (RV)
Definition of tidal volume:
volume of air moved in and out during quiet breathing
Definition of inspiratory reserve volume:
additional volume of air that can be inhaled during maximum inspiration
Definition of expiratory reserve volume:
additional volume of air that can be exhaled after normal expiration
Definition of residual volume:
volume of air left in the lungs after maximum expiration
Capacity is the sum of…
2 or more volumes
What are the types of capacity?
- inspiratory capacity (IC)
- vital capacity (VC)
- total lung capacity (TLC)
- functional residual capacity (FRC)
Definition of inspiratory capacity:
maximum volume that can move into lungs after normal expiration
- tidal volume + IRV
Definition of vital capacity:
volume of air moved out from maximum inspiration to maximum expiration
- IRV + VT + ERV = IC + ERV
Definition of total lung capacity:
total volume that can be in the lungs
- varies with height
- VC + RV
Definition of functional residual capacity:
volume left in lungs at end of normal expiration during quiet breathing
- RV + ERV
What is minute ventilation?
volume of air moved between lungs and air per minute
- measured by using amount of air expired per minute
T/F: all gas from minute ventilation participates in gas exchange
F because tidal volume is distributed between conducting airways and alveoli
- some areas in conducting airways don’t participate in gas exchange
What is the anatomical dead space?
air within conducting airways that doesn’t participate in gas exchange
What is the physiological dead space?
total volume of gas in each breath that doesn’t participate in gas exchange
- includes anatomical dead space and alveolar spaces that aren’t perfused
What is alveolar ventilation?
volume of air that participates in gas exchange
What is the most important variable in gas exchange?
alveolar ventilation
What is the relationship between minute and alveolar ventilation if expired ventilation is constant?
- inverse relationship with dead space volume and alveolar ventilation
- increase in frequency -> decrease in alveolar ventilation
- decrease in tidal volume -> decrease in alveolar ventilation
T/F: air going to exchange areas is uniformly distributed
F, gravity affects it by increasing air to alveoli in lower portion of the lungs
Lung function is determined by which 4 factors?
- strength of chest and abdominal muscles
- lung size
- airway resistance
- lung compliance
How does strength of chest and abdominal muscles affect lung function?
decrease in strength -> reduction of inspiratory capacity
How does lung size affect lung function?
decrease in areas involved in perfusion -> reduction of TLC
How does airway resistance affect lung function?
increase in resistance -> airflow impaired
How does lung compliance affect lung function?
stiffening of alveoli -> greater effort needed to inflate lungs
Where is the major site of airway resistance?
large and medium sized bronchi b/c air has more leeway in how it travels
Gas flow in larger airways is turbulent or calm?
turbulent
When does turbulence occur?
- at high flow rates
- diameters change
An increase in turbulence leads to…
- increase in resistance
- decrease in flow
Small airways contribute to airway resistance via…
- small diameter
- large number of them
- high airflow velocity
- laminar flow
T/F: there are no breath sounds in small airways
T, because they have laminar flow
Which factors contribute to airway resistance?
- diameter: smaller = higher resistance
- volume: higher the volume of airways = decrease in resistance
- airway mucus: increase = increase in resistance
- edema: increase in fluid = increase in resistance
Regulation of the diameter of airways are under…
ANS control
What happens during PNS innervation of bronchial and bronchiolar smooth muscle?
- contraction
- increase in mucus production
- Ach to M3 receptors associated with PLC
What happens during SNS innervation of bronchial and bronchiolar smooth muscle?
- relaxation
- decrease in mucus production
- norepi to beta 2 receptors
Examples of bronchoconstrictors:
- histamine
- thromboxane
- PGF2 alpha
- leukotrienes
Bronchoconstrictors are triggered by…
allergens and infections
Examples of bronchodilators:
- beta agonists: isoproterenol and epi (same effect as SNS)
- M antagonists: atropine (inhibit Ach)
What is distensibility of the lung?
how easily a lung can be stretched or inflated
What is the elastic recoil of lungs?
ability to return back to original shape after being stretched - inversely related to lung compliance
What happens if your lungs have a large lung compliance?
lung easily distensible, but difficult to deflate because of low elastic recoil
What happens if your lungs have a small lung compliance?
stiff lung
- difficult to inflate but easy to deflate because of high elastic recoil
Lung compliance is often affected by…
respiratory disorders
How do obstructive diseases affect lung compliance?
lung is more compliant due to loss of elastic recoil
- easy to inflate but needs effort to get air out
- high FRC because of high RV
Examples of obstructive diseases:
- emphysema
- chronic bronchitis
- cystic fibrosis
- asthma
How do restrictive diseases affect lung compliance?
lung is noncompliant
- difficult to inflate, but easily deflatable
- lower TLC but normal RV
Examples of restrictive diseases:
- scar tissue from infections
- pulmonary fibrosis
What is the relationship between surface tension and compliance?
increase in surface tension = decrease in compliance
Surface tension occurs at…
inner surface of alveoli because of moist surface and spherical shape
- smaller alveoli have greater pressure than larger alveoli
What happens to the alveoli when there is an increase in surface tension?
- air gets diverted to larger alveoli and causes them to overinflate
- smaller alveoli collapse
How do you reduce surface tension?
have type 2 cells produce surfactant
- gets stimulated by stretching of alveoli when tidal volume is high
What causes respiratory distress syndrome (RDS)?
inadequate surfactant production
What happens to compliance during exercise?
- compliance is higher
- tidal volume increases and stimulates surfactant release
What are some ways MDs can measure the efficiency of the respiratory system?
- RV/TLC
- forced vital capacity (FVC)
- forced vital capacity in 1 sec (FEV1)
- FEV1/FVC x 100
What is the purpose of RV/TLC?
ratio used to distinguish different types of pulmonary disease
What is the normal ratio for RV/TLC?
0.20
How do you know if you have an obstructive disease by looking at RV/TLC?
increase in RV because of air being trapped secondary to airway collapse
How do you know if you have a restrictive disease by looking at RV/TLC?
decrease in TLC
What is forced vital capacity (FVC)?
volume that’s exhaled forcefully and rapidly after max inhalation
- normally 5L
Which test is the most useful for testing lung function?
FVC
FVC for athletes?
> 7L
FVC for people with asthma?
< 5L because of collapse of small airways
FVC for people with bronchitis?
3 L because airways are swollen and inhibit air flow
What happens during forced vital capacity in 1 sec (FEV1)?
max flow occurs early and decreases progressively toward RV
Is FEV1 effort dependent or independent?
- dependent (proportional)
- independent at lower volumes
FEV1/FVC x 100 corrects for…
differences in lung size
What is the normal FEV1/FVC x 100 ratio?
80% is exhaled in a second
What is the FEV1/FVC x 100 during obstructive diseases?
all measurements are reduced (FEV1, FVC, FEV1/FVC)
What is the FEV1/FVC x 100 during restrictive diseases?
normal or slightly higher
- FEV1 and FVC decreased
- FEV1/FVC normal or high
When does work increase during breathing patterns?
- deeper breaths taken b/c has to overcome elastic properties of lung
- respiration rate increases b/c needs greater flow resistance to overcome elastic properties of lung
Label the red box:
Inspiratory reserve volume (IRV)
Label the purple box:
expiratory reserve volume (ERV)
Label the black box:
residual volume (RV)
Label the gray box:
tidal volume (Vt)
Label the orange box:
inspiratory capacity
Label the green box:
vital capacity (VC)
Label the yellow box:
functional residual capacity (FRC)
Label the blue box:
total lung capacity (TLC)
