Respiratory Week 1 Flashcards
Are accessory muscles sufficient for ventilation?
No, we need the diaphragm
Describe what the diaphragm is doing during inspiration
Contracting and moving downward
Describe what the diaphragm is doing during expiration
Relaxing and moving upward
What are the muscles of inspiration?
Diaphragm (duh)
Secondary accessory muscles: SCM, scalenus, parasternal intercartilaginous muscles, external intercostals
What are the muscles of expiration?
Internal intercostals (except the parasternal intercartilaginous muscles) and the abdominal muscles (rectus abdominus, external oblique, internal oblique, transversus abdominus)
Do we do work during inspiration or expiration?
Inspiration
Expiration is passive
What comprises the conducting airways? What Z levels correspond to this?
Nasal sinuses, pharynx, larynx, trachea, bronchi, bronchiole, terminal bronchioles
Z levels: 0 to 16
What volume of air is held in the conducting airways?
150 mls
What is the airflow like in the conducting airways?
Generally turbulent/transitional
Trachea is really where the turbulence is
What Z levels comprise the alveolar/respiratory airways?
17 to 23
What volume of air is in the alveolar/respiratory airways during normal breathing?
2500-3000 mls
What is the airflow like in the alveolar/respiratory airways?
Laminar flow
Where in the conducting airways does cartilage disappear? What Z level is this?
At the bronchiole level
Z4
In order for passive diffusion to be effective, we need to maximize the _________ across which gases move
surface area (and the vast majority of lung surface area is in the aveolar airways)
Define tidal volume (Vt). What is a normal Vt?
The amount of air inhaled/exhaled with a normal breath from the resting level
~0.5 L
Define Expiratory Reserve Volume (ERV). What is a normal ERV?
The volume of air that can be expelled after normal tidal volume expiration
~2 L
Define Residual Volume (RV). What is a normal RV?
The amount of air that remains after maximal expiration
~1.2 L
Define Forced Vital Capacity (FVC). What is a normal FVC?
The amount of air which can be forcibly exhaled from the lungs after taking the deepest breath possible and factoring in the time component (“ceiling to floor”)
~5 L (usually 5 L per 5 seconds)
**Note: similar to Vital Capacity (VC) but with the time component
Define Vital Capacity (VC). What is a normal VC?
The volume of air that is exhaled after maximal inspiration
~5 L
VC = ERV + IRV + Vt
Define Total Lung Capacity (TLC). What is a normal TLC?
The maximum volume to which the lungs can be expanded
~6 L
TLC = VC + RV
Define Functional Residual Capacity (FRC). What is a normal FRC?
The amount of air left in the lungs after a tidal volume breath
~2.5 L
FRC = RV + ERV
Define Inspiratory Reserve Volume (IRV). What is a normal IRV?
The volume of air that can be inhaled after a normal inhalation
~2.5 L
Define Inspiratory Capacity (IC). What is a normal IC?
The amount of air that can be drawn into the lungs after normal expiration
~3 L
What three things can spirometry NOT measure?
Residual volume, total lung capacity, functional residual capacity
If someone says, “At TLC….” what do they mean?
At maximal inhalation
If someone says, “At RV…” what do they mean?
At maximal exhalation
Under tidal volume breathing, we breathe out because of _____ ______
lung recoil
What is Trans-pulmonary Pressure?
The pressure difference between what is in the alveoli and what is in the pleural space
P(tp) = P(alveolar) - P(pleural)
What happens when the pleural pressure is -5cm H2O and the alveolar pressure is 0cm H2O?
P(tp) = 0 - (-5) = +5cm H2O
The negative pressure in the pleural space acts like a vacuum and pulls the lungs outward
What happens when the Trans-pulmonary pressure is 0 cm H2O?
The lungs collapse
This happens during a pneumothorax.
What is compliance?
A measure of how easily the lung can be stretched out (“elastic nature”)
Compliance = Change in volume/Change in pressure
What is a normal clinical value for lung compliance?
0.2 L per cm H2O
What does it mean to have low lung compliance? What is it characteristic of?
Low lung compliance is seen in someone with pulmonary fibrosis (elastin to collagen). They have “stiff lung” or “cement lung”
There is a relatively small change in lung volume for a given change in pressure. This person has to do more work
What does it mean to have high lung compliance? What is it characteristic of?
High lung compliance is characteristic of someone with emphysema. Their lungs have no elastic nature and no recoil
There is a relatively large change in lung volume for a given change in pressure
Compliance is directly or inversely proportional to lung recoil?
Inversely proportional
What is atmospheric pressure and alveolar pressure during inspiration?
Atmosphere: 0 cm H2O
Alveolar: -1 cm H2O
(thus air leaves the alveoli because the pressure is greater in the atmosphere)
What is the atmospheric pressure and alveolar pressure during expiration?
Atmosphere: 0 cm H20
Alveolar: +1 cm H2O
(thus air goes into the alveoli because the pressure is greater there)
When the volume increases (pleural space, alveoli, etc) what happens to the pressure?
Decreases
sorry, super basic thing I need to hammer
If the trans-pulmonary pressure decreases what happens to the force on the lungs?
It decreases too/the lungs begin to collapse
This is seen on expiration
If the trans-pulmonary pressure increases what happens to the force on the lungs?
It increases/the lungs are pulled outward
This is seen on inspiration
What type of pressure difference does the diaphragm generate?
Trans-pleural pressure differences
How do you calculate air flow (Poiseuille’s Law)?
Air flow (V with a dot) = Change in pressure * r^4/8nl
n = viscosity of the gas in the tube; essentially a constant
l = length of the tube, constant
r = radius of the tube
Change in pressure is between the two ends of the tube
What type of relationship do resistance and air flow have?
Inverse
This is good because when the resistance in the lungs becomes super high we stop air flow/stop the lungs from collapsing
What type of relationship do radius and resistance have?
Inverse
The smaller the radius, the greater the resistance
How do you calculate resistance?
R = n*l/r^4
What is the major site of airway resistance? What Z levels is this?
Segmental bronchi
Z3-Z7
Why does air flow through the alveolar airway system have very little resistance/laminar flow?
Because of the large numbers of alveoli (~500 million~)
Why are the segmental bronchi the “natural resistor”?
- Surface Area is low. While the radius is decreasing, there isn’t enough branching yet to make a difference (like in the alveoli)
- Smooth muscle has the inherent ability to constrict
What affect do epinephrine and norepinephrine (sympathetic nervous system) have on respiratory smooth muscle? What does this do to air flow and resistance?
Epi & norepi are bronchiodilators/cause smooth muscle relaxation (they act on B-receptors in the pulmonary system)
Bronchiodilation increases the radius and thus decreases resistance and increases air flow
What affect does acetylcholine (parasympathetic nervous system) have on respiratory smooth muscle? What does this do to air flow and resistance?
Ach is a broncho-constrictor. This will lead to decreased radius and thus increased resistance and decreased air flow
The relative balance of what two things determines airway resistance?
Parasympathetic and sympathetic tone (aka the level of smooth muscle relaxation or constriction)
Asthma is characterized by increased or decreased airway resistance?
Increased!
When airway resistance increases exponentially, what happens to air flow?
It decreases exponentially
Why don’t the alveoli collapse immediately when the pleural pressure reaches +30cm H2O?
The natural resistor, the segmental bronchi, get very small and build up high pressure behind them into the alveoli. This pressure (+40 cm H2O) helps keep the alveoli open longer so that we can blow out for ~5 seconds
Is work ever expended upon expiration?
Yes, in a pathologic state (like asthma or emphysema)
Examples of restrictive lung diseases?
Pulmonary fibrosis and pulmonary edema
**Lung inflation in restricted
Examples of obstructive lung diseases?
Emphysema and asthma
**lung expiration is obstructed
How do you differentiate between restrictive and obstructive lung diseases in the clinic?
measure the forced vital capacity (FVC)
What is FEV1? What is a normal FEV1 value?
Forced Expiratory Volume in 1 Second
The amount of air which can be forcefully exhaled during the first second of expiration
~4 L
What is the FEV1/FVC ratio? What is a normal value?
Forced Expiratory Volume in 1 Second/Forced Expiratory Capacity (5 seconds)
Normal: 80%
What four factors influence FVC?
- Strength of the chest and abdominal muscles
- Airway resistance
- Lung size
- Elastic properties of the lung
SALE
Why is vital capacity reduced in restrictive disease?
decreased total lung capacity (lung isn’t inflating)
“ceiling came down”
Why is vital capacity reduced in obstructive diseases?
Increased residual volume (air is trapped!)
“floor came up”
What airflow requires the least amount of energy? The most?
Least: laminar
Most: turbulent
Where do we find transitional air flow?
Throughout the tracheo-bronchial tree
Where do we find turbulent air flow?
Predominately in the trachea
How are changes in pressure and turbulent flow related?
Flow is proportional to the square root of the change in pressure
For example, for a 9-fold change in pressure we would see a 3-fold increase in flow. So an even greater change in pressure is required to generate the same amount of flow
Radius affects both flow and resistance in a(n) _______ manner
exponential
What does “limit of airway inflation” mean?
Making pleural pressure more negative (past -20 cm H2O) has diminishing returns because of decreased compliance
Pleural pressure beyond what will cause an opening of the airways?
-8cm H2O according to the pressure-volume curve
What is hysteresis?
The difference in the inflation and deflation lines on the pressure volume curve
It occurs because a greater pressure is required to open a previously closed airway than to keep an already-open airway from closing
How do you calculate work?
Force * distance
Force = change in pressure Work = change in volume
Is more or less work done to inspire with restrictive lung disease?
More work
What happens to compliance in restrictive lung disease? Recoil?
Compliance decreases. You can calculate this or look at the slope becoming flatter
Recoil increases (remember it has an inverse relationship with compliance)
Is more or less work required to inspire with obstructive lung disease?
Less work
BUT work is required to expire
What happens to compliance in obstructive lung disease? Recoil?
Increases (steep slope now!)
Recoil decreases (remember it has an inverse relationship with compliance)
How can you differentiate between obstructive asthma vs. emphysema?
Give the patient albuterol and see if that improves their function
Emphysema is abnormal compliance and asthma is abnormal airway resistance
The characteristics of the compliance curve are determined by what?
The elastic forces of the lung
The elastic forces of the lung are composed of what two things?
- Elastic forces of the lung tissue itself (i.e. elastin and collagen)
- Elastic forces caused by surface tension at the air:water interface that lines the alveoli
What builds at any air:water interface?
Surface tension
What is the net effect of the air:water interface?
It creates a large degree of surface tension at the interface
What are the relative contributions of the elastic tissue vs. the air:water interface to the elastic recoil properties of the lung?
1/3 tissue
2/3 air:water surface tension
What lowers the surface tension in the lungs?
Surfactant. It does this by disrupting the rigid structure of water
From ~50-70 dynes/cm to ~5-10 dynes/cm (50 to 90% reduction in surface tension)
Surfactant changes the interface from air:water to what?
Air:oil
This has significantly less surface tension
Type II pneumocytes constitute what percentage of the alveolar surface?
10-20% (depends on the lecturer)
What is surfactant composed of?
Lipids, proteins, ions
What is the main component of surfactant that is responsible for reducing surface tension?
Dipalmitoyl-phosphatidylcholine
What is LaPlaces Law? What is it related to?
The pressure that is required to keep an alveolus open. Surfactant reduces T and thus reduces the pressure needed to keep an alveolus open
P = 2T/r
T = surface tension in the wall of the sphere r = radius of the sphere
What is Acute Respiratory Distress Syndrome (ARDS)?
When a preemie is born before ~28 weeks and lacks surfactant
Tx: artificial surfactant or being placed on a positive pressure ventilator
What happens to the following when we lack surfactant? Surface tension, lung compliance, lung recoil
ST: Increases
Compliance: Decreases
Recoil: Increases
What happens to work on inspiration when we lack surfactant?
It increases
When we lack surfactant is this restrictive or obstructive disease?
Restrictive (which means decreased TLC!)
When elastic work increases (i.e. pulmonary fibrosis) what will happen to respiratory rate?
It will increase in order to find the point where total work is the lowest
When airway resistance increases (i.e. asthma) what will happen to respiratory rate?
It will decrease in order to find the point where total work is the lowest
Minute value equation?
Tidal volume * Respiratory rate
Amount of air that we breathe in and out each minute
= 500 mls * 12 breaths per min
= 6000 mls per min
What is alveolar ventilation? Equation?
The amount of air that makes it into the alveolar airways
Alveolar vent = (Tidal volume - anatomic dead space/conducting airways) * respiratory rate
= (500 mls - 150 mls) * 12 breaths per min
= 4200 mls per min
What percentage of air that we breathe in is available for gas exchange?
~70 %
What is more important for alveolar ventilation: tidal volume or respiratory rate?
Tidal volume
Deep breathing is better for alveolar ventilation than shallow, rapid breathing (tachypnea)
Total pressure at sea level in mmHg? Percentage of O2 in air?
760 mmHg
21% O2
Atmospheric O2 partial pressure?
160 mmHg
Inspired O2 partial pressure?
150 mmHg
Alveolar O2 (PAO2) partial pressure?
100 mmHg
Arterial O2 (PaO2) partial pressure?
100 mmHg
Arterial CO2 (PaCO2) partial pressure?
40 mmHg
Equation for calculating alveolar partial pressure of O2?
[P (inspired) O2] - [P (Alv) CO2/R)
where R = 0.8
How do you calculate P (inspired) O2?
P(inspired)O2 = (760 - 47)* FIO2
What is the problem with increased altitude? Barometric pressure or FIO2?
Decreased barometric pressure
FIO2 stays the same at 21% regardless of altitude