Physical Aspects of Breathing Flashcards
Why does the amount of oxygen consumed differ from the CO2 produced?
It depends on the carbon source
ratio of CO2 produced to O2 consumed
respiratory quotient (R)
Value of respiratory quotient for a normal, mixed diet
0.8
Value of respiratory quotient for a pure fat diet
0.7
Value of respiratory quotient for a pure carb diet
1
used clinically to determine the composition of alveolar gas; by comparing alveolar gas to blood gas we can determine how well the lungs are working
Alveolar Gas Equation
The total pressure of a mixture of gases is the sum of the pressures exerted by each gas
Dalton’s Law of partial pressures
Which gases compose the majority of air
Nitrogen (78%) Oxygen (21%) CO2 (0.04%) H2O traces of other gases
Normal barometric pressure at sea level
760 mmHg
- assuming humidity is 0%
What is the partial pressure of O2 in the atmosphere?
160 mmHg
Why is the oxygen content of air “diluted” once it reaches the trachea and alveoli?
Trachea: water vapor (humidity) dilutes it
Alveoli: C02 leaving body dilutes it
Vapor pressure of H20
47mmHg
The amount of gas dissolved in the liquid is directly proportional to the partial pressure of the gas above the liquid
Henry’s Law
Partial pressure of oxygen and carbon dioxide in blood entering and leaving the alveolar capillaries
pO2: 104 mmHg
pCO2: 40 mmHg
How many “generations” (divisions) are there in your airway
23 (resulting in over 8 million airway segments and about 300 million alveoli)
parts of the airway that are considered “conducting”
Trachea
Bronchi
Bronchioles
Terminal bronchiole (last part of conducting zone)
last part of the conducting airway
terminal bronchiole
portion of airway where capillaries are not close enough to inspired air for gas exchange; contributes to anatomic dead space; trachea, bronchi, bronchiole and terminal bronchiole
Conducting zone
portion of airway where capillaries are close enough to inspired air for gas exchange; rich vascularization; respiratory bronchiole, alveolar duct and alveolar sac
Respiratory zone
When does the branching of the airways begin to result in an exponential increase cross-sectional area (after what “generation”)
Generation 10
Muscles involved with inspiration
- Diaphragm (contract to flatten/downward movement)
2. External intercostals (Elevate ribs 2-12 outward which widen thoracic cavity)
Muscles involved with expiration
- Usually none (passive and by lung elastic recoiling)
2. Active/forced is by contraction of abdominal and internal intercostal muscles (plus lung elastic recoil
1 mmHg = ??? cmH2O
1.36 cmH2O
As the inspiratory muscles contract and increase the volume of the thoracic cavity, alveolar pressure becomes more _____________ creating a driving force for the inward flow of air
negative (sub-atmospheric)
- -1 cmH2O
the space between the outer surface of the lung (visceral pleura) and the inner surface of the thoracic cavity (parietal pleura); usually filled with a small amount of fluid (10 mL)
Intrapleural space
Intrapleural pressures during inspiration vs. expiration
Expiration: -5 cmH2O
Inspiration: -8 cmH2O
Pleura that lines the lung
Visceral pleura
Pleura that lines the chest cavity
Parietal pleura
pressure difference across the surface of the lung relative to alveolar pressure; calculated as the alveolar pressure minus the intrapleural pressure
Transpulmonary pressure
Equation for transpulmonary pressure
Alveolar pressure - intrapleural pressure
highly (compliant/elastic) lung is considered floppy
Compliant
A highly (compliant/elastic) lung is considered stiff
Elastic
How does one develop sub-atmospheric alveolar pressure during inspiration?
Inspiratory muscles contract—> Thoracic cavity expands—> intrapleural pressure decreases—> transmural pressure gradient increases—> air flows inward
(expiration/inspiration) during a quiet tidal breath takes longer, since this is typically passive (elastic recoil)
Expiration
Volume of air in anatomic dead space
150 mL
Volume of air in the lungs when no active muscular force is being exerted
Functional residual capacity (FRC)
The amount of gas in the lung at the end of a maximal inspiration
Total lung capacity
Lung volumes are measured using a…
Spirometer
Volume of air during a single inspiration or expiration
Tidal volume (500ml per inspiration in a healthy person)
Maximal volume that can be inhaled following a normal inspiration
Inspiratory reserve volume
Volume that can be forcibly expired from a normal expiration
Expiratory reserve volume
Volume of air remaining after maximal expiration
Residual volume
Volume of air after a normal expiration; ERV + RV
Functional residual capacity
Maximal volume of gas that can be inspired following a normal expiration; TV + IRV
Inspiratory Capacity
Maximal volume of gas which can be expired following a maximal inspiration; IRV + TV + ERV
Vital Capacity
Major categories of lung disease (3 total)
- Developmental: anomalies, hypoplasia, chronic lung disease of newborn
- Obstructive: asthma, bronchitis, cystic fibrosis, emphysema
- Restrictive: fibrosis, sarcoidosis, chest wall disorders, hypersensitivity pneumonitis, neuromuscular diseases
What is the partial pressure of oxygen in alveoli (PAO2)?
104 mmHg
What is the partial pressure of CO2 in alveoli (PACO2)?
40 mmHg
Where does the air become humidified in the respiratory tract?
Trachea (100% humidified)
What is the partial pressure of O2 in trachea? Why?
- 21 * (760-47) = 150 mmHg or Torr
* Inhaled air become humidified in the trachea 100% and water vapor takes up 47 Torr at 37 celcius.
What is the partial pressure of O2 in alveoli?
104 mmHg or Torr
What is the partial pressure of O2 in arterial blood?
100 mmHg or Torr
As the airways branch, the individual units become ______ but the aggregate cross-sectional area of the airways _______ with each generation.
smaller
increases
What generation of branching denotes terminal bronchioles?
generation 16
- therefore marks the end of conducting zone and the beginning of respiratory zone
Where does visceral pleura and parietal pleura become contiguous?
at the root of the lung (hilum)
Pleural space (intrapleural space) is filled with a lubricating liquid and substances secreted by what cells?
mesothelial cells
what keeps the lung surface and the thoracic wall from separating?
subatomospheric intrapleural pressure
What is the pressure gradient across any particular barrier? It is represented by the pressure inside the structure minus the pressure outside the structure.
Transmural Pressure
Why is it important to have the positive transpulmonary pressure?
This positive transpulmonary pressure holds the lung open at end-expiration.
Transpulmonary pressure ______ during inspiration enough to overcome the elastane of the lung, resulting the lung to
increases
inflate
Describe Boyle’s Law
Pressure X Volume = Constant
Describe how air is drawn into the lungs during inspiration?
- Inspiratory muscles contract
- Thoracic cavity expands
- Intrapleural pressure becomes more subatmospheric
- Transmural pressure gradient increases, creating subatmospheric alveolar pressure
- Air flows inward inflating the lungs
Obesity ______ compliance
decreases
