Respiratory Study Questions Flashcards
Describe the cell types found in the alveolus and name their function
- type 1 epithelial: majority of alveolar surface area
- type 2 epithelial: produces surfactant and repair epithelial damage
- brush cells: not known
- macrophages: immune defense
- PMNs (polymorphonuclear neutrophils): immune defense
- mast cells: immune defense
- clara cells: secretory functions
- endothelial cells: inner lining of alveolus
What is the symbol for partial pressure of oxygen in the mixed venous blood?
PvO2
- line above the v indicates mixed venous (mean venous)
What is the symbol for carbon dioxide production?
VCO2
What is the symbol for expired minute ventilation?
VE
What is the symbol for tidal volume?
VT
Name 3 functions of the nasal cavity
Warms, filters, humidifies inspired air
What is the contribution to resistance during normal breathing for the nasal cavity? Trachea?
- nasal cavity: 50%
- trachea: 20%
- bronchi: 20%
- bronchioles: 10%
Describe the histologic structure of the trachea
Mucosa is classified as pseudostratified ciliated columnar epithelium
- apocrine, or goblet cells are also present to secrete mucous
- basal cells on innermost lumen
- ciliated cells to participate in mucociliary elevator to move out foreign debris
Compare and contrast the structure of the trachea to the bronchioles
- carilage in trachea, but not in the bronchioles
- no gas exchange in either
- clara cells in bronchioles, not in trachea
- epithelium flattens down toward the alveolus, cuboidal in bronchioles and psuedo columnar in trachea
- smooth muscle in bronchioles
What is the major muscle responsible for quiet inspiration? Accessory muscles?
Diaphragm - triggered by action potential delivered by phrenic nerve
- accessory muscles - sternomastoids, scalene
What are the 2 muscles of inspiration?
Cricoarytenoideus dorsalis and dilator nasoapicalis
Be able to calculate dead space and alveolar gas tension, and know the different factors that are important to each
Dead space: alveoli that are ventilating, but not perfused so carbon dioxide is not exchanged
- VD/VT = (PaCO2-PECO2)/PaCO2
- PaCO2 = partial pressure of alveoli carbon dioxide
- PECO2 = partial pressure of expired carbon dioxide
- VD = volume of dead space
- VT = tidal volume
Name 2 tests that can be used to assess pulmonary function
Pulmonary function: - blood gas analysis - capnography - pulse oximetry Respiratory system: - radiography - bronchoscopy - cytology/biopsy
VT
Tidal volume
- volume of air that gets in and out of lungs in 1 normal ventilation
- body mass times 10/15 for average
FRC
Functional reserve (residual) capacity - 2 volumes responsible for gas exchange - ventilation mechanics need to match flow - normal decreases occur during pregnancy FRC = ERV + RV
IC
Inspiratory capacity
- one normal conscious inspiration (requires effort)
IC = IRV + VT
IRV
Inspiratory reserve volume
- inspiratory volume if you take out tidal volume
TLC
Total lung capacity
- max volume of air that lungs are able to take
TLC = IRV + VT + ERV + RV
VC
Vital capacity
- can change with pathological conditions or medically
VC = IRV + VT + ERV + RV
To have at least 1 capacity, you need at least ________
2 different volumes
What is expired minute ventilation? How can it be calculated?
Represents a volume (liter or ml) of lung gas per minute
VE = VT x f (frequency of breaths per min)
Pulmonary compliance
Change in volume per unit pressure (how easily the lungs will expand)
C = V/P
What is the most important determinant of compliance behavior of the lung?
Surface tension (2/3) - each alveolus is an air-water interface - surface tension promotes deflation (responsible for 2/3 of the compliance behavior) Elastic recoil (1/3)
Alveolar gas tension
- PIO2 = (PB-PH2O) x FIO2
- PaCO2 = 1:1 ratio with PACO2 at the alveoli level (can be used interchangeably)
What is the expected partial pressure of O2 in systemic arterial blood? In blood from the pulmonary artery? The alveolus?
- PO2 in systemic arterial blood = 85-100 mmHg
- PO2 in pulmonary artery blood = 40 mmHg
- PO2 in alveolus = 104 mmHg
What is the PO2 of moist inspired gas of a dog standing on the summit of Mount Everest (PB = 247 mmHg)?
PO2 = FIO2 x (PB-PH2O)
- PO2 = 0.21 x (247-47) = 42
What is hysteresis?
Term used to describe that there is a difference between the inflation and deflation curves of the lung
- takes slightly more pressure to inflate the lungs then to deflate (which is passive in most species)
What are the major components of surfactant?
- DPPC: dipalmitoyl phosphatidylcholine (major component with a hydrophobic and hydrophilic component)
- Ca++
- apoproteins SP-A, B, C, and D
What are the functions of surfactant?
- decreases work of breathing
- increases compliance
- stabilizes alveolar size
- has a drying effect on the alveoli
Describe what happens to the lung and chest wall when a pneumothorax is induced
- When atmospheric air is introduced into the intrapleural space, eliminating the negative pressure
- introduction of air into the intrapleural space can be via damage to the chest wall, the lungs, the mediastinum, etc
- net result = loss of tethering between the lungs and chest wall, allowing the lungs to collapse and the chest wall to expand without a net movement of air
What is the major difference between static and dynamic compliance of the respiratory system?
Dynamic compliance has additional factors of - airway resistance, tissue resistance, and inertia
* airway resistance is most important*
What components are common between static and dynamic compliance?
- elastic properties of chest wall
- elastic properties of lung
- surface tension
Static compliance
Compliance of each component (lung vs chest wall)
What is dynamic compliance and how does it limit expiratory flow?
Compliance of the components working together, which will define the work of breathing
- limits expiratory flow via tissue or airway resistance
What factors determine airway resistance?
Generation determines resistance
- -> earlier generations in the flow of air (nasal cavity, large and medium bronchi) offer greater resistance than those further into the lung
- -> resistance decreases when cross-sectional area increases!
Where does turbulent flow occur in the normal tracheobronchial tree?
Turbulent flow occurs in the upper respiratory airways
- due to high resistance and large volume of trachea
What type of flow occurs in the majority of the lung?
Transitional flow
What does interdependence of structure mean (i.e., mechanical tethering)?
Inflation of 1 alveoli tends to augment/increase the inflation of adjacent alveoli
Using Bohr’s equation determine physiologic dead space in a dog with PaCO2 = 40 mmHg and PECO2 = 30 mmHg
VD/VT = PaCO2-PECO2/PaCO2
= 40-30/40
= .25
With regard to the pulmonary circulation, describe what is meant by “shunting” of blood
A small percentage of pulmonary blood is not oxygenated correctly
List 5 differences between the pulmonary and systemic circulation
Pulmonary - uniform, not much change - low pressure - thin-walled arteries - less autonomic control influence Systemic - changes depending on organ system or body condition - high pressure - high vascular resistance - thick-walled arteries - tremendous autonomic control influence
What is the blood volume of the pulmonary circulation? What factors influence pulmonary blood volume?
Pulmonary blood volume = 10% Factors: - changes in posture - changes in systemic vasomotor tone (sleeping, exercising) - left heart failure
Describe the effect of gravity on pulmonary blood flow (zone 1)
Dorsal - blood perfusion is least
- PA>Pa>Pv
- alveolar ventilation is high, perfusion is low
- high V/Q
- dead space ventilation
Describe the effect of gravity on pulmonary blood flow (zone 2)
Middle - blood perfusion is uniform
- Pa>PA>Pv
- alveolar ventilation and pulmonary perfusion matched well
- good V/Q relationship
Describe the effect of gravity on pulmonary blood flow (zone 3)
Ventral - blood perfusion is most
- Pa>Pv>PA
- alveolar ventilation is low but perfusion is high
- low V/Q
- alveoli become atelectic
- zone of pulmonary shunting
Define hypoxic pulmonary vasoconstriction
Effect of altitude on pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP)
- altitude increases = PO2 decreases, PVR increases
- pulmonary vascular response to areas of hypoxia in the lungs
Describe the effect on lung volume on pulmonary vascular resistance
As lung volume increases, pulmonary vascular resistance will increase
- alveoli squeeze the thin-walled pulmonary vessels that line the alveoli
Write the Starling equation for fluid flux, define its variables, describe how changes in each will affect fluid flux from pulmonary capillaries
Flux = K[(Pc-Pi)-o(3.14c-3.14i)
- K = filtration coefficient/permeability of endothelial barrier
- o = reflection coefficient/how much water is returned
- Pc = capillary hydrostatic pressure (pushes fluid out)
- Pi = interstitial hydrostatic pressure (pushes fluid in)
- 3.14c = capillary oncotic pressure (fluid in capillary)
- 3.14i = interstitial oncotic pressure (fluid out capillary)
- edema results from increases in this equation*
Define pleural effusion and describe the factors that can contribute to it
Fluid between visceral and parietal pleural linings of the lungs
- fluid accumulation in the pulmonary interstitium, can result from failure of the lymphatic system properly drain the area
Diseases that can result in pulmonary edema
- left sided heart failure
- capillary endothelial damage
- severe exercise (race horses)
- pulmonary hypertension (abnormally high blood pressure in the arteries of the lungs)
Why does pulmonary vascular resistance fall during exercise?
Increases blood flow through lungs during exercise –> decreases pulmonary vascular resistance
What is Dalton’s Law?
The sum of all partial pressure of individual gases will equal the atmospheric pressure
What is Henry’s Law?
The pressure of gas in a liquid is determined by the concentration of the gas and its solubility
P = concentration/solubility
Solubility coefficients
CO2 > O2 > CO > N2 > He
What is the FIO2 on top of Mount Everest?
21%
List the factors that determine diffusion of oxygen across the alveolar barrier?
Thickness of alveolar membrane - alveolar edema - interstitial edema - pulmonary fibrosis Altered surface area - emphysema - exercise
Which step in the diffusion process is rate limiting?
Thickness of the alveolar membrane –> affects diffusion time across the membrane
Quiz answer:
- partial pressure difference
- diffusion distance thru tissue water
- cross sectional area
- molecular weight and gas solubility
Describe the oxygen tension gradient between the ambient air and the cell
Oxygen tension decreases from dry air to the cell
- dry air: 160 mmHg
- intracellular: 5-40 mmHg
What is normal arterial oxygen tension?
85-100 mmHg
What is the normal alveolar tension?
104 mmHg
Why is the arterial oxygen tension less than the alveolar oxygen tension?
Shunts allow blood to reach the arterial system without passing thru ventilated areas of the lungs
- when a small amount of shunted blood is added to arterial blood, O2 concentration is depressed = large fall in PaO2 because O22 dissociation curve is so flat in the upper range
What are the normal values for the following: PaO2 PvO2 PaCO2 PvCO2
- PaO2: 85-100 mmHg
- PvO2: 40
- PaCO2: 40
- PvCO2: 40-45
Write the alveolar gas equation
PAO2 = PIO2 - PaCO2/R
R = 0.8
PIO2 determined by FIO2
What is the D(A-a)O2?
Alveolar-arterial oxygen difference
- represents the amount of oxygen removed by metabolically active tissues throughout the body
- is normally 5-20 mmHg when FIO2 is 0.21
List the 4 causes of hypoxemia
- decreased alveolar volume over time (lung volume)
- decreased oxygen fraction (FIO2)
- diffusion impairment
- ventilation/perfusion inequalities
Define intrapulmonary shunt
Pulmonary shunt = venous admixture (blood that doesn’t pass thru functional pulmonary capillaries)
- is perfused, but not ventilated (does not undergo gas exchange)
- low V/Q
Describe the relationship between O2 content and O2 partial pressure for whole blood
Oxygen content is a function of both hemoglobin saturation with O2 and the partial pressure of dissolved oxygen.
- partial pressure only contributes a small amount to total oxygen content, but its important because oxygen must first dissolve in the blood in order to become saturated
Name the factors that will cause a shift in the oxygen-hemoglobin dissociation curve
- increased H ions
- increased CO2
- increased temperature
- increased BPG
What is the Bohr effect?
Shift in the oxygen-hemoglobin dissociation curve as a result of changes in PCO2
- high PCO2 –> high H+ –> decreased O2 affinity (enhanced O2 release to tissue)
- low PCO2 –> low H+ –> increased O2 affinity (enchanced O2 loading in lungs)
What is nitric oxide? How does it affect carriage of oxygen?
Produced by vascular endothelial cells
- has a high affinity for ferrous binding sites on hemoglobin
- is transported by hemoglobin to tissues, where it is released and reduces vascular resistance, while enhancing O2 transport (vasodilator)
How is CO2 carried in the blood?
Carried as a bicarbonate
- goes into RBC and is converted to bicarb via carbonic anhydrase
- bicarb exits RBC and is carried in plasma
List 4 ways to assess oxygenation in a patient
- mucous membrane color
- arterial blood gas analysis
- pulse oximetry
- co-oximetry
A normal dog is given propofol to induce anesthesia. It halves is alveolar ventilation, but does not affect his CO2 production. What would you predict is PaCO2 to be? Assume R=0.8, what will his PAO2 be?
PACO2 = PIO2 - (PaCO2/R)
= (760-47) x 0.21
= 150
PaCO is normally 40, but ventilation is cut in half while production remains the same, so it doubles to 80
PACO2 = 150 - (80/0.8)
= 150-100
= 50
A dog is anesthetized and has a pulmonary and systemic arterial catheter placed. The O2 content of the dog’s pulmonary arterial and systemic arterial blood are 14 and 16 mL. Assume that blood leaving a function alveolus has a content of 20 mL, what is this animal’s shunt fraction?
QS/QT = 20-16/20-14 = 4/6 = 0.67
Will oxygen supplementation improve arterial oxygenation in a patient with a right-to-left shunt?
No
- O2 supplementation may improve the oxygenation of the blood slightly, it will not have a significant impact
- to improve arterial oxygenation, blood will need to become perfused by the pulmonary system
Translate FIO2
Fraction of inspired oxygen
Your patient is on 1 L/min of 100% oxygen. What is the FIO2? if you increase the flowrate to 2L/min, what is the FIO2?
1 L/min of 100% O2 = 1
2 L/min = 1
What role does myoglobin play in oxygen transport?
Myoglobin acts as a facilitator for DO2 from blood to mitochondria
What is the function of the dorsal respiratory group?
Medullary center that controls ventilator muscles and ventilation
- responsible for ramping effect during inspiration
- sets the rate and depth of ventilation
- automatically begins ventilation regardless of input
- receives input from chemo/baroreceptors via vagus and glossopharyngeal nerves
- airway stretch receptors send info to DRG via vagus nerve, efferent info via phrenic nerve
What is the function of the ventral respiratory group?
Not active during normal breathing
- activated during exercise, fear, disease
- affects DRG to cause an increased ramping effect and directly affects the ventilator muscles to increase inspiratory volume
- causes an active expiration phase
- receives info thru vagus and glossopharyngeal nerves
- sends info thru phrenic nerve
How do the central chemoreceptors sense changes in O2?
Central chemoreceptors don’t sense changes in PO2, but they do sense PCO2 by sensing changes in the pH
- CO2 can cross the BBB where it diffuses into bicarb and H ions via carbonic anhydrase
- CO2 is responsible for changes in ventilation
Where are the peripheral chemoreceptors located
Carotid and aortic bodies
- can sense both PCO2 and PO2, but their primary influence is PO2
What is the primary stimulus for ventilation in a healthy patient?
PCO2
- carbonic acid equation is extremely important
At what PO2 does hypoxic drive become significant?
When PO2 drops below 60-70 mmHg
Where does gas exchange occur in the fetus?
Placenta
What is surfactant and why is it important?
Reduces work of breathing, dries alveoli, and reduces surface tension
- produced just prior to birth and is correlated with a surge in fetal corticosteroid production
Is systemic blood pressure lower or higher in the fetus than in the dam?
Lower
What is the PO2 of blood reaching the fetal brain?
17 mmHg
What changes occur during birth that alter the function of the respiratory system?
- placenta breaks away = decreased circulatory pressure
- fetus passes thru pelvis and expels fluid in lungs
- fetus meets cold environment and inhales O2 rich gas
- lungs fill with O2 = increases PO2 in blood, decreases PVR
- increased PO2 = ductus arteriosis constriction
- pressure shift from high RV and low LV to low RV and high LV
- foramen ovale closes
- circulation changes from left to right
What is unique about fetal hemoglobin?
Higher O2 affinity
What are the differences between avian and mammalian respiratory systems?
Avian is completely passive
- air fills posterior sac –> transferred thru lungs and into anterior sac –> expelled
Mammalian is active for inhalation and passive for exhalation
Describe the composition of airway fluid
Mucociliary apparatus - serous fluid within the cilia and a mucus layer on top that moves upward and out of the airways to be swallowed
Describe the different mechanisms that are utilized in the removal of inhaled particles
- filtration
- mucociliary elevator
- smallest particles can be phagocytized by pulmonary macrophages
List the filtration and anticoagulant functions of the pulmonary circulation
- blood clots, fat, and air that come thru can either be phagocytized or exhaled
- anticoagulants are activated or deactivated in the lungs
What is angiotensin I and how is it affected by the lung?
Involved in kidney function thru the renin-angiotensin system
- converted to angiotensin II in the lungs by way of angiotensin converting enzyme
Describe the role of the lung in temperature regulation
- heat: dead space ventilation is increased in order to utilize evaporative cooling
- cold: dead space ventilation is decreased to hold onto heat
What is the inspired PO2 at an atmospheric pressure of 155 mmHg?
0.21 x 155 = 32.55 mmHg
What would you predict would happen should an animal or human become exposed to this atmospheric pressure?
They would need oxygen since there would be limited amounts at this altitude
Why do stored RBCs not function as well as fresh RBCs? What is missing?
Stored RBCs scavenge and hold onto nitric oxide
Is breathing 100% O2 the same as hyperbaric oxygenation?
Yes
How does hyperbaric O2 improve tissue oxygenation?
Combines high pressure and pure oxygen increasing the concentration of oxygen in bloodstream, which permeates deep into body tissues to help promote healing
Are there any side effects or dangers associated with hyperbaric oxygen?
Some patients may develop changes in eyesight - temporary myopia caused by increased blood oxygen levels
What happens to mental function when PaCO2 is >80 mmHg?
Severe anxiety due to hypoxia
How do anesthetic drugs affect the response to CO2?
Sensitize the response to CO2
- pulmonary system becomes unresponsive
How do anesthetic drugs affect the response to O2?
Dull the response or eliminate it completely, even when PO2 is less than 60-70 mmHg
List 4 things that can lead to hypoxemia during anesthesia
- decreased minute ventilation
- increased shunt fraction
- increased dead space ventilation
- decreased FRC
Describe how positive pressure ventilation affects venous return
Forcing air into the alveoli in order to inhale
- decreases venous return because heart rate and systemic vascular resistance are increased, redistribution of systemic blood flow
What happens to pleural pressure during positive-pressure ventilation? Venous return?
Positive intrapleural pressure: air is being forced in, no longer being drawn in as with the negative pressure under normal physiologic conditions
How do whales stay active underwater for prolonged periods of time?
They have tons of myoglobin
- 30 x greater than terrestrial mammals
