Unit 1 (Respiratory) - Respiratory Physiology Flashcards
What are the muscles of inspiration?
- Sternocleidomastoid
- Scalene muscles
- External intercostals
- Diaphragm
What are the muscles of expiration?
- Internal intercostals
- Rectus abdominis
- External oblique
- Internal oblique
- Transversus abdominis
Contraction of the inspiratory muscles reduces thoracic pressure and increases thoracic volume… this is an example of what law?
Boyle’s Law
Which two muscles contract during normal inspiration?
Diaphragm and external intercostals
Sternocleidomastoid and scalene muscles are accessory
Exhalation is driven by what?
The recoil of the chest wall
The conducting zone consists of which structures?
Trachea, bronchi, and bronchioles
What is the function of the conducting zone and the transitional zone?
Bulk gas movement
The transitional zone consists of what structures?
Respiratory bronchioles
The respiratory zone consists of what structures and participates in what function?
Alveolar ducts and alveolar sacs
Participates in gas exchange
Another name for the conducting zone is what?
Anatomic dead space
The conducting zone begins at the ________ and ends with the ______________
Begins - Nares and mouth
Ends - Terminal bronchioles
Respiratory bronchioles serve a dual function of __________ and ___________
Air conduit and gas exchange
To prevent airway collapse, the pressure inside the airway must be (greater/less than) the pressure outside of the airway
Greater
Airway pressures for dummies
Alveolar pressure = Inside the airway
Intrapleural pressure = Outside the airway
Transpulmonary pressure = difference between those pressures
True/False: Transpulmonary pressure is always positive, keeping the airway open
TRUE
True/False: Intrapleural pressure is always positive
FALSE - Intrapleural pressure is always negative, keeping the lungs inflated
When would the intrapleural pressure become positive?
Pneumothorax and forced expiration
Formula for alveolar ventilation:
(Tidal volume - Dead space) x Respiratory rate
Increased dead space widens the PaCO2-EtCO2 gradient and causes ____________
CO2 retention
Tidal volume: 500 mL
Respiratory rate: 10 breaths/min
The patient is a normal, 70 kg adult. What is the patients minute ventilation? What about alveolar ventilation?
Minute Ventilation = 500 mL x 10 breaths/min = 5,000 mL/min
Alveolar Ventilation = (500 mL - 150 mL) x 10
- 350 mL x 10 = 3,500 mL/min
Alveolar ventilation is directly proportional to ______________
CO2 production (A higher CO2 production stimulates the body to breathe deeper and faster so it can eliminate more CO2)
Alveolar ventilation is inversely proportional to _______
PaCO2 (Faster and deeper breathing reduces PaCO2)
Air confined in the conducting airways
Example: Nose & mouth –> Terminal bronchioles
Anatomic dead space
Alveoli that are ventilated but not perfused
Example: Decreased pulmonary blood flow
Alveolar dead space
What is the most common cause of Vd/Vt under general anesthesia is a reduction in ____________
Cardiac output
How does Atropine increase Vd?
It’s bronchodilator action increases the volume of the conducting airway
If dead space increases, what must increase to maintain a constant PaCO2?
Minute ventilation
Compares the partial pressure of carbon dioxide in the blood vs. the partial pressure of carbon dioxide in exhaled gas
Bohr Equation
A change in alveolar volume for a given change in pressure
Alveolar compliance
Ventilation and perfusion are greatest at the lung ________ due to higher alveolar compliance and gravity
Base
Which alveoli have the poorest ventilation? Why?
The alveoli in the apex - They have the poorest compliance
Which alveoli have the greatest ventilation? Why?
Alveoli in the base - They have the greatest compliance
What two things affect the distribution of blood flow to the lung
Gravity and hydrostatic pressure
Blood passing through underventilated alveoli tends to _________________ and is unable to take in enough oxygen
Retain CO2
To combat dead space (zone 1), the bronchioles ________ to minimize ventilation of poorly perfused alveoli
Constriction
To combat shunt (zone 3), what reduces pulmonary blood flow to poorly ventilated alveoli
hypoxic pulmonary vasoconstriction
States that as the radius of a sphere or cylinder becomes larger, the wall tension increases as well
Variables include: tension, pressure, and radius
Law of LaPlace
What is the equation for the Law of Laplace?
Cylinder Shape - Tension = Pressure x Radius)
Spherical Shape - Tension = (Pressure x Radius)/2
The tendency of an alveolus to collapse is directly proportional to what?
Surface tension
More tension = more likely to collapse
The tendency of an alveolus to collapse is inversely proportional to what?
Alveolar radius
Smaller radius = more likely to collapse
Which cells produce surfactant?
Type 2 Pneumocytes
Type 2 pneumocytes begin producing surfactant between __________ weeks with peak production occurring at 35-36 weeks
22-26 weeks
If a fetus is going to be born prematurely, what can be used to hasten fetal lung maturity?
Corticosteroids (Betamethasone)
Name the West Zone:
- Ventilation, but no perfusion
- Does not occur in a normal lung
- PA > Pa > Pv
Zone 1
Zone 1 is increased by what factors?
- Hypotension
- Pulmonary embolus
- Excessive airway pressure
Name the West Zone:
- Ventilation and perfusion (V/Q = 1)
- Pa > PA > Pv
Zone 2
Name the West Zone:
- Blood flow is a function of pulmonary arteriovenous pressure difference (Pa-Pv)
- Blood flow in the absence of ventilation
- Pa > Pv > PV
Zone 3 (Shunt)
Why does the tip of the pulmonary artery catheter need to be placed in zone 3?
Because the pressure in the capillary is always higher than the alveolus, the vessel is always open, and blood is always moving through it
Describes any venous blood that empties directly into the left side of the heart
Anatomic shunt
Occurs when the rate of fluid entry into the pulmonary interstitial exceeds the rate of fluid removal by the lymphatic system
Zone 4
- Used to estimate the partial pressure of oxygen in the alveoli
- Tells us the maximal PAO2 that can be achieved at a given FiO2
Alveolar gas equation
The difference between alveolar oxygen (PAO2) and arterial oxygen (PaO2)
A-a gradient
What increases the A-a gradient?
- Aging (Closing capacity increases relative to FRC)
- Vasodilators (Decreased hypoxic pulmonary vasoconstriction)
- Right-to-left shunt (Atelectasis, pneumonia, bronchial intubation, intracardiac defect)
- Diffusion limitation (Alveolocapillary thickening hinders O2 diffusion)
We can estimate that shunt increases 1% for every ___________ of A-a gradient
20 mmHg
Volume that can be forcibly inhaled after a tidal inhalation
Inspiratory Reserve Volume (~3 L)
Volume of gas that can be forcibly exhaled after a tidal exhalation
Expiratory Reserve Volume (~1,100 mL)
Volume of gas that enters and exits the lungs during tidal breathing
Tidal Volume (~ 500 mL)
Volume of gas that remains in the lungs after a complete exhalation
This volume can not be exhaled from the lungs
Residual Volume (~1,200 mL)
What volume provides a “windbag” of alveolar gas that provides an oxygen reservoir during apnea?
Residual Volume
The volume above residual volume where the small airways begin to close
Closing Volume
What are the normal parameters for:
Tidal volume?
Vital capacity?
Functional residual capacity?
- Tidal Volume = 6-8 mL/kg
- Vital Capacity = 65-75 mL/kg
- FRC = 35 mL/kg
In patients with asthma, emphysema, and bronchitis, which lung volumes/capacities are increased?
- Residual Volume
- Closing Capacity
- Total Lung Capacity
Which dynamic measurements assess small airway closure?
Closing volume and capacity
Patient has an FRC of 2.3 L and oxygen consumption (VO2) of 250 mL/min… how long until they desaturate?
FRC / VO2
2,300/250 = 9.2 mins
True or False: When FRC is reduced, intrapulmonary shunt increases
TRUE
The point at which dynamic compression of the airways begins… it’s the volume above residual volume where the small airways begin to close during expiration
Closing volume
Factors that increase closing volume (CLOSE-P)
- COPD
- LV failure
- Obesity
- Surgery
- Extremes of age
- Pregnancy
When closing capacity is greater than FRC, airway closure occurs during tidal breathing. This contributes to what?
Intrapulmonary shunting and hypoxemia
A measure of how much oxygen is present in 1 deciliter of blood
Oxygen content
What is the formula for oxygen content (CaO2)?
CaO2 = (1.34 x Hgb x SaO2) + (PaO2 x 0.003)
Normal Hgb and Hct values:
Male: 15 g/dL and 45%
Female: 13 g/dL and 39%
What should be used to determine gas exchange in the lungs and not as a measure oxygen content in the blood
PaO2
Oxygen dissolves in the plasma according to which law?
Henry’s Law
- The concentration of gas in a solution is directly proportional to the partial pressure of the gas above the solution
What is the solubility coefficient for oxygen?
0.003 mL/dL/mmHg
What is the formula for oxygen delivery (DO2)?
CaO2 x CO x 10
10 is the conversion factor that converts all units to liters
What is the formula for oxygen consumption?
CO x (CaO2 - CvO2) x 10
Oxygen consumption numbers to know
2.5 mL/kg/min
~250 mL/min (Assumes 70 kg male)
The PaO2 where Hgb is 50% saturated by oxygen
P50
- Low P50 = Left shift
- High P50 = Right shift
Tissues with a high metabolic rate consume more oxygen and produce more CO2, hydrogen ions, and heat… this causes a _________ shift
Right shift
Right = Rise in temp, 2,3-DPG, CO2, and H+
What hemoglobinopathies cause a left shift?
Fetal hemoglobin, methemoglobin, and carboxyhemoglobin
When is 2,3-DPG produced?
During RBC glycolysis
Hypoxia _____________ 2,3-DPG production, which facilitates oxygen off loading
Increases
ATP is produced by ___________ of proteins, carbohydrates, and fats
Oxidation
What is the primary substrate used for ATP synthesis?
Glucose
What is the primary goal of glycolysis?
To convert 1 glucose to 2 pyruvic acid molecules
In the absence of oxygen, pyruvic acid is converted to what?
Lactate
What are three ways CO2 is transported in the blood?
- As bicarbonate (70%)
- Bound to Helpmeglobin as carbamino compounds (23%)
- Dissolved in plasma (7%)
What is the primary goal of the citric acid cycle?
To produce a large quantity of H+ ions in the form of NADH
What is the end product of oxidative phosphorylation?
34 ATP molecules and water
What is the enzyme that facilitates the formation of carbonic acid from H2O and CO2?
Carbonic Anhydrase
Carbonic acid dissociates into what two things?
H+ and HCO3-
Dissolved CO2 has a solubility coefficient of __________
0.067 mL/dL/mmHg
States that CO2 and decreased pH cause the erythrocyte to release oxygen
Bohr Effect
States that oxygen causes the erythrocyte to release CO2… deoxygenated blood can carry more CO2
Haldane Effect
In the presence of oxygenated hemoglobin, the CO2 dissociation curve shifts which way?
Right
- Blood has a decreased affinity for CO2
- Occurs in the lungs to facilitate unloading of CO2
In the presence of deoxygenated hemoglobin, the CO2 dissociation curve shifts which way?
Left
- Blood has an increased affinity for CO2
- Occurs in the systemic capillaries to facilitate loading of transport of CO2
What are the three main causes of hypercapnia?
- Increased CO2 Production
- Decreased CO2 Elimination
- Rebreathing
In acute respiratory acidosis, for every 10 mmHg increase above 40 mmHg pH decreases by __________
0.08
In chronic respiratory acidosis, for every 10 mmHg increase above 40 mmHg pH decreases by…
0.03 (Due to bicarb retention by the kidneys)
What is the primary monitor of PaCO2 in the brain?
The central chemoreceptor in the medulla
What plays a secondary role in monitoring PaCO2?
Peripheral chemoreceptors in the carotid bodies and transverse aortic arch
What is the MAC of CO2?
200 mmHg
A left shift and increased slope in the CO2 ventilatory response curve indicates that ventilation is __________ than expected and leads to __________________
Higher
Respiratory alkalosis
A right shift and decreased slope in the CO2 ventilatory response curve indicates that ventilation is __________ than expected and leads to __________________
Lower
Respiratory acidosis
The highest PaCO2 at which a person will not breathe
Apneic threshold
Where is the respiratory center located?
In the reticular activating system in the medulla and pons
What is the primary job of the respiratory center?
To determine how fast and deep you breathe
Pneumotaxic Center: Inhibits DRG
Location:
Function:
Location: Upper pons
Function: Triggers the end of inspiration
Apneustic Center: Stimulates DRG
Location:
Function:
Location: Lower pons
Function: Antagonizes the pneumotaxic center which causes inspiration (Action is inhibited by pulmonary stretch receptors, J receptors)
Dorsal Respiratory Group: Causes inspiration
Location:
Function:
Location: Medulla - Nucleus tractus solitarius
Function: Pacemaker for inspiration
Ventral Respiratory Group: Causes expiration
Location:
Function:
Location: Medulla (Nucleus ambiguous, nucleus retroambiguus)
Function: Has inspiration and expiration functions
Contains the pre-Botzinger complex
What is the most important stimulus for the central chemoreceptor?
Hydrogen ion concentration in the CSF
Describe the hypoxic ventilatory response:
- PaO2 < 60 mmHg closes K+ channels
- Membrane potential rates and calcium channels open, which increases NT release (Act and ATP)
- An action potential is sent along Hering’s nerve
- The afferent pathway terminates in the inspiratory center in the medulla
- Minute ventilation increases to restore PaO2
When lung inflation is > 1.5 L above FRC, this reflex turns off the dorsal respiratory center… stopping inspiration
Hering-Breuer Inflation Reflex
When lung volume is too small, this reflex helps prevent atelectasis by stimulating the patient to take a deep breath
Hering-Breuer Deflation Reflex
Stimulation of these receptors cause tachypnea, they are activated by things that Jam traffic in the pulmonary vasculature, such as PE or CHF
J Receptors
This is what causes a newborn baby to take their first breath
Paradoxical Reflex of Head
Occurs in response to a reduction in alveolar oxygen tension (NOT arterial PO2)
Hypoxic Pulmonary Vasoconstriction
True or False:
IV anesthetics do NOT affect HPV (Ketamine, propofol, fentanyl, etc.)
TRUE
