Respiratory Physiology I Flashcards
List the muscles of expiration
List the muscles of inspiration
Contraction of the inspiratory muscles reduces _____ and increases ______. What law is this an example of?
thoracic pressure
thoracic volume
Boyle’s Law
During inspiration, which muscle(s) increase A-P diameter?
Which muscle(s) increase superior-inferior dimension?
External intercostals
Diaphragm
What are the accessory muscles of inspiration?
Sternocleidomastoid
Scalenes
Active exhalation is carried out by:
What’s a good mnemonic for this?
the abdominal muscles
I let the air out of my TIREs:
Transverse Abdominus
Internal Oblique
Rectus Abdominus
External Oblique
What vital capacity is required in order to form a good cough?
15 ml/kg
The functional divisions of the airway can be divided into three zones:
Conducting
Transitional
Respiratory
The conducting zone begins at the ____ and ends at the ______
Nares
Terminal Bronchioles
______ is the last structure perfused by the bronchial circulation
Terminal bronchioles
The transitional zone contains:
the respiratory bronchioles
Dual function of air conduction and gas exchange
The respiratory zone consists of _____ and _____
Alveolar Ducts
Alveolar Sacs
List the levels of the airway, from the trachea down
- Trachea
- Bronchi
- Bronchioles
- Respiratory Bronchioles
- Alveolar Ducts
- Alveolar Sacs
What is the last are of the airway that contains cartilage?
Bronchi
Bronchioles DO NOT have cartilage
What is the last area of the airway containing smooth mucles?
The alveolar ducts
The alveolar sacs are the only structures that do not have any
Gas exchange occurs across ____ cells by ______
Type 1
Diffusion
Alveolar Pressure is the pressure _______
Intrapleural pressure is the pressure _______
inside the airway
outside the airway
Transpulmonary Pressure = ______ - ______
Alveolar Pressure - Intrapleural pressure
If TPP is positive, the airway _______
If TPP is negative, the airway _______
Opens
Closes
DURING TIDAL BREATHING
Transpulmonary Pressure is always ______
Intrapleural pressure is always ________
Positive (keeps airway open)
Negative (keeps lungs inflated)
Alveolar pressure becomes slightly ______ during inspiration
and slightly _____ during expiration
negative
positive
There are only two times when intrapleural pressure becomes positive:
Forced expiration
Pneumothorax
What is the transpulmonary pressure?
Is air moving in or out?
-1
You use the first area in the lungs to deflate
15 - (+16) = -1
Out - Forced Expiration
What is the TPP? Is air moving out or in?
-1 - (-8) = 7
Air is moving in (inspiration)
Minute ventilation = ______ x _______
Tidal Volume x RR
Alveolar Ventilation = ________ x _________
(TV - dead space) x RR
What is the VT?
What is a normal VT?
Tidal Volume is the amount of gas that is inhaled and exhaled during a breath
6-8 mlkg
What is the VT?
What is a normal VT?
Tidal Volume is the amount of gas that is inhaled and exhaled during a breath
6-8 ml/kg
What is Vd?
What is a normal VD?
Dead space
~ 2 ml/kg (150 ml)
Any condition that increases VD also increases:
The PaCO2 - EtCO2 gradient
Makes it harder to expire gases from the airway, causing CO2 retention
How can you predict PaO2 by age?
How do you calculate static compliance?
How do you calculate Dynamic Compliance?
What are some factors that increase dead space?
Anything that increases the volume of the conducting zone
OR
Reduces pulmonary blood flow
e.g. Hypotension (reduces pulmonary blood flow)
Atropine (bronchodilates, which increases the volume of the conducting zone)
PPV (increases ventilation relative to perfusion, which is another way of saying that dead space is increased)
What are some factors that decrease dead space?
Anything that reduces the volume of the conducting zone or increases pulmonary blood flow
e.g. ETT, LMA, neck flexion
What are the four types of dead space?
Anatomic
Alveolar
Physiologic
Apparatus
What are two examples of apparatus dead space?
Heat and Moisture Exchanger
Face Mask
What is physiologic dead space?
Anatomic dead space + alveolar dead space
What causes alveolar dead space?
Decreased pulmonary blood flow
What is the Vd/Vt ratio?
Ratio between dead space and ventilation
What is the Vd/Vt for a 65 kg woman with a Vt of 350 ml?
We assume adults have a Vd of 2 ml/kg, which would mean she has 130 ml dead space
130 ml/350ml = 0.37
How does mechanical ventilation effect Vd/Vt?
It increases it to about 50% (0.5)
BECAUSE
It increases the V/Q ratio, which essentially means it increases dead space
What is the most common cause of increased Vd/Vt under general anesthesia?
Decreased cardiac output
If etCO2 abruptly decreases, this should be your first suspicion before looking for other causes of increased dead space
What disease states cause increased Vd?
Decreased CO
COPD
PE
Neck flexion and extension have what effect on Vd?
Flexion: reduces the amount of hypopharynx open, and therefore reduces dead space
Extension: opens the hypopharynx, increasing dead space
In a circle system, dead space begins at:
the Y piece
How is physiologic dead space calculated?
The Bohr Equation
Many clinicians use ______ and ______ to estimate dead space
The difference between the PaCO2 and the etCO2
In the textbook patient:
V =
Q =
V/Q =
4 L/min
5 L/min
.8
What is compliance?
Change in Volume
_______________
Change in Pressure
When upright, blood flow predominantly to the lung bases. Why doesn’t the V/Q ratio get smaller?
Because alveoli in the base also have higher compliance:
for a set pressure, they take in more volume
more volume = more gas exchange
Which alveoli have the poorest compliance?
Which have the highest?
Apex
Base
Describe V/Q in the non-dependent portion of the lung
Describe V/Q in the dependent area of the lung
What determines how “ventilated” any particular alveoli is?
The alveoli with the greatest ventilation are the ones that undergo the greatest volumetric change
Better compliance = better ventilation
Is this dead space or shunting?
Dead Space
Is this dead space or shunting?
Shunt
What is the most common cause of hypoxemia in the PACU?
Atelectasis
Blood passing through an underventilated alveoli tends to ______ CO2
retain
and is unable to take in oxygen
Blood passing through an overventilated alveoli tends to ______ CO2
give off too much CO2 (more than the alveoli could empty out), but it can’t take up a proportional amount of oxygen
(just because you’re giving off more CO2 does not mean you’re getting more O2 because of the dissociation curve)
Which is usually effected by a V/Q mismatch: PAO2-PaO2 or PACO2-PaCO2
Why?
Usually just the O2 A-a gradient is effected
The lung compensates by overinflating alveoli. This works at eliminating CO2, but not at getting O2 in
How does the body combat shunt?
hypoxic pulmonary vasoconstriction reduces pulmonary blood flow to hypoventilated alveoli
How does the body combat dead space?
Bronchioles constrict to minimize airflow to poorly perfused alveoli
The law of Laplace regarding spheres states that:
As the radius of a sphere increases, the wall tension increases as well
The tendency of an alveolus to collapse is directly proportional to ______
and indirectly proportional to ______
more surface tension = more likely to collapse
smaller radius = more likely to collapse
Why are alveoli pressures constant, despite varying sizes?
Every alveolus has the same amount of surfactant
As the radius decreases, the concentration of surfactant increases
As the radius increases, the concentration of surfactant decreases
the surface tension therefore remains the same
Zone 1 =
Zone 2 =
Zone 3 =
Zone 4 =
Zone 1 is equivalent to a V/Q =
Infinity
Where does Zone 1 usually occur in the lung?
It doesn’t. Purely pathological.
Hypotension, PE, excessive airway pressure
Zone 3 is equivalent to a V/Q =
0
Shunting!
What West Zone should a PA cath be placed in?
Why?
Zone 3
The pressure in the capillary is always higher than the alveolus, and the vessel is always open
What causes Zone 4?
Interstitial edema, usually from:
- Increased hydrostatic pressure (fluid overload)
- Increased negative pressure (flash pulmonary edema)
What is the most common cause of increased dead space intraoperatively?
Decreased cardiac output
What is the Bohr equation?
Compares the partial pressure of CO2 in the blood to the partial pressure in exhaled gas. Allows us to calculate dead space.
Why does it matter that FRC is reduced by anesthesia?
FRC is the reservoir of oxygen that prevents hypoxemia during apnea
If the FRC is reduced, these patients will have very, very short tolerance of apneic episodes
What are the anesthesia-related causes of reduced FRC?
