Respiratory - High Yield Points Flashcards
The primary function of the lungs is…
gas exchange
What four processes must be functioning for optimal gas exchange?
Ventilation
Perfusion
Diffusion
Control of breathing
Optimal Gas Exchange
Ventilation
Getting gas to the alveoli
Optimal Gas Exchange
Perfusion
removing gas from the alveoli by the blood
Optimal Gas Exchange
Diffusion
Getting gas across alveolar walls
Optimal Gas Exchange
Control of Breathing
regulating gas exchange
What structures make up the conducting zone?
Trachea
Bronchi
Bronchioles
No alveoli
What structures make up the Respiratory Zone?
Respiratory Bronchioles
Alveolar Ducts
Alveolar Sacs
Alveoli
Characteristics of Alveoli
Small, thin walled inflatable air sacs encircled by pulmonary capillaries
Single layer of thin exchange epithelium
Air flows between alveoli via pores of Kohn
Where is the site of gas exchange in alveoli?
The single layer of thin exchange epithelium
Define
Type I Alveolar Cells
Very thin
allowing gas exchange
Define
Type II Alveolar Cells
Thicker
Secrete surfactant to ease lung expansion
Define
Alveolar Macrophages
Protect and Defend
Define
Atmospheric Pressure (PB)
What is it at sea level? How does it change?
760 mmHg at sea level
decreases as altitude increases
Define
Intra-alveolar pressure (PA)
What is its value?
Equilibriates with PB
Define
Intrapleural Pressure (Pip)
Value? What is it?
756 mmHg
Recoil forces create a vacuum (-4)
Closed cavity
Define
Transmural Pressure (PL)
Pressure across the lungs
Key to inflating the lungs
What is the purpose of the cohesiveness of Intrapleural Fluid and the transmural pressure gradient?
They hold the lungs and thoracic wall in tight position even though the lungs are smaller
PA = 760, pushes out vs. Pip of 756
PB = 760, pushes in vs. PIP
Why does the pleural space have a slightly negative pressure?
Because the chest is pulling out, the lungs are pulling in, and there’s no extra fluid to fill the expanded space
Pneumothorax
What causes it? What occurs with one?
Air enters pleural cavity
Pressure equalizes with atmospheric pressure
transmural pressure gradient is gone
Lungs collapse
Thoracic wall springs out
Define
Boyle’s Law
Volume and pressure are inversely related
↓V↑P
Changes in volume of chest cavity during ventilation cause…
Pressure gradients
↑Chest Volume ↓Pressure → air moves into body from atmosphere
Inspiration results from…
contraction of the diaphragm and intercostal muscles `
active process
During inspiration, the rib cage swings…
upwards and outwards
Expiration results from…
the relaxation of the diaphragm and intercostal muscles
passive process
During expiration, the rib cage moves…
inward and downwards
How is air forced out of the lungs during expiration?
The elastic recoil of the lungs creates a higher intra-alveolar pressure compared to atmospheric pressure that forces air out of the lungs
Define
Laminar Airflow
What is it? Where is it?
Low flow rate
usually in small airways
Define
Turbulent Airflow
What is it? Where is it?
Fast flow rate
usually in large airways
How much do terminal bronchioles contribute to total resistance?
Each terminal bronchiole has a high resistance to flow, but they have a large cross-sectional area and are in parallel
Their overall contriution to total R is low
Air flow in the respiratory system increases as…and decreases as…
increases as the pressure gradient increases
decreases as resistance increases
Airflow = ΔP/R
Where is airway resistance greatest? How is it measured?
Greatest in medium sized airways
Measured with Poiseuille’s Law R = (8nl)/3.14r^4
What is the relationship between airway radius and resistance?
Airway radius is a pimary determinant of resistance
Length and viscosity are virtually constant
Why is the diameter of the bronchiole adjustable?
No cartilage but has smooth muscle
Bronchioles
Bronchoconstriction
What causes it? What effect does it have on resistance and airflow?
Caused by low levels of CO2
increases resistance
decreases air flow
Bronchioles
Bronchodilation
What causes it? What effect does it have on airflow?
caused by increased CO2
increases airflow
Define
Equal Pressure Point (EPP)
When airway pressure is equal to intrapleural pressure
What is the purpose of Pulmonary Function Tests?
they measure lung volumes, lung capacities, and flow rate
They can detect abnormalities in lung function before diseases are symptomatic
Define
Tidal Volume (TV)
Air volume moving in a single normal inspiration or expiration
Define
Inspiratory Reserve Volume (IRV)
Additional volume inspired above tidal volume
Define
Expiratory Reserve Volume (ERV)
Air exhaled beyond the end of normal expiration
Define
Residual Volume (RV)
Air in respiratory system after maximal exhalation (not measured directly)
What are lung capacities?
The sums of 2 or more lung volumes
Define
Vital Capacity (VC)
Define; How do you calculate it?
Max volume of air voluntarily moved through respiratory system
VC = IRV + ERV + VT
Equation
Total Lung Capacity (TLC)
TLC = VC + RV
Equation
Inspiratory Capacity (IC)
IC = VT + IRV
Equation
Functional Residual Capacity (FRC)
FRC = ERV + RV
Obstructive lung disease is characterized by…
Increases in lung volumes and airway resistance and decreases in expiratory flow rates
Define
Emphysema
What is it? Characteristics?
Type of COPD
characterized by increasing lung compliance and decreased diffusion capacity for carbon monoxide
Obstructive Lung Disease
Restrictive Lung Diseases are characterized by…
decreases in lung volume
normal expiratory flow rates
normal resistance
marked decrease in lung compliance
Define
Compliance
The ability of the lungs to stretch
↑stretch↑compliance
Defined by slope of pressure volume curve for lungs
How does the slope of the pressure - volume curve for lungs change?
Steep slope is seen at low and normal lung volumes
Curve flattens at very high volumes
High compliance lungs are…
easily stretched
Low compliance lungs…
require more force to stretch (more work)
Hysteresis
Different compliance for expiration and inspiration because of surfactant
What is the purpose of elasticity in the lungs?
The lungs are able to return to its original shape after the force stretching it has been removed
Normal lungs are both compliant and elastic
What causes the differences in ventilation throughout an upright lung?
Gravity
How does gravity effect the apex and base of the lung?
Alveoli at the apex are larger and less compliant and receive less of each tidal volume breath than those at the base
What happens to the lungs in a patient with emphysema?
elastin fibers/lung tissue are destroyed
Lungs have high compliance and low elastance
poor recoil during expiration
hyper-inflated lung and “barrel-chest”
What effect do Restrictive Lung Diseases have on compliance?
They reduce compliance
More work must be expended to stretch a stiff lung
What are some possible causes of restrictive lung diseases/reduced lung compliance?
Inelastic scar tissue
insufficient surfactant production
Pulmonary elasticity is generated by…
Elastic fibers
Surface Tension
Why are elastic fibers important in respiratory system?
The natural tendency of these fibers to recoil facilitates passive expiration
What causes surface tension in the respiratory system? Why is it bad?
Surface tension on alveolar surfaces arise due to the strong attractive force that water has for itself
Surface tension tends to make alveoli collapse (especially smaller alveoli)
What is the purpose of surfactant?
To reduce surface tension around the alveoli
The chest wall and lung are in equilibrium at…
the FRC
Pulmonary circulation is a _ flow, _ pressure, _ resistance circuit
high flow
low pressure
low resistance
Where does RV CO go?
The lungs receive 100% of RV CO
Why is pressure so much lower in the pulmonary circulation vs. the systemic?
Only enough pressure is needed to lift blood to top of lung
Length of pulmonary blood vessels is shorter
RV doesn’t have to pump as hard to overcome peripheral resistance
This allows low pulmonic BP, low net hydrostatic BP
Work required of RV is much less than LV
Pulmonaries are _ compliant than the aorta and systemic arteries
much more compliant
The bronchial circulation supplies the _ and is part of the _ circulation
conducting portions of the lungs
systemic circulation
What happens to the deoxygenated blood found in the bronchial circulation?
It flows into the pulmonary veins along with freshly oxygenated blood from the alveoli
It doesn’t return to systemic circulation
What does the addition of deoxygenated blood from the bronchial circulation to pulmonary circulation do to blood O2 content?
Addition of deoxygenated blood slightly lowers the oxygen content of the blood before it reaches the left side of the heart
What do increases in CO or Pulmonary Arterial Pressure do to pulmonary vascular resistance (PVR) and Pulmonary blood flow? How?
pulmonary vascular resistance (PVR) decreases
pulmonary blood flow increases
due to recruitment and distension of capillaries
PVR is lowest at…
FRC
Why is PVR lowest at FRC?
extra-alveolar vessels are tethered to surrounding alveoli and compressed with low lung volumes
Alveolar vessels are located between alveoli and are compressed with high lung volumes
Hypoxia can alter pulmonary blood flow and PVR depending on…
whether it is regional or generalized
What occurs in Zone 1?
Pa < PA
Capillary collapses before it crosses alveolus
No flow
doesn’t exist in normal lungs
might exist with hemorrhage when BP and intravascular volume are low
What occurs in Zone 2?
Pa > PA > PV
Flow driven by difference between arterial and alveolar pressure
primary area of distension, recruitment of vessels during exercise
What occurs in Zone 3?
Pa > PV > PA
continuous forward flow through distended vessels
Pulmonary capillary fluid exchange is regulated by…
the same starling forces as systemic capillaries, but also has surface tension and alveolar pressure influences
The sum of partial pressures of a gas must be equal to…
total pressure
The partial pressure of a gas is equal to…
the fraction of gas in the gas mixture times the total pressure
What happens to inspired gas by the time it reaches the trachea?
It is fully saturated with water vapor, which exerts a pressure of 47 mmHg at body temp and dilutes the partial pressures of N2 and O2
What occurs because the conducting airways do not participate in gas exchange?
The partial pressures of O2, N2, and H2O vapor remain unchanged in the airways until the gas reaches the alveolus
Equation
Total (Minute) Ventilation (VE) =
VE = Tidal Volume (VT) x respiratory rate (f)
VT is more important than f when VE increases
At rest, total ventilation is approximately…
6,000 mL → 6L
Define
Anatomical Dead Space
~ 150 mL
volume of air filled in conductin airways incapable of gas exchange with blood
Equation
Alveolar Ventilation (VA)
VA = (Tidal Volume (VT) - VD (dead space)) x f
At rest, VA is approximately…
4200 mL → 4.2L
Breathing deeply and slowly…
What effect does it have on VE and VA?
VE is unchanged
VA increases
Breathing shallowly and rapidly…
What effect does it have on VE and VA?
VE is unchanged
VA decreases
The partial pressure of oxygen in the alveolus is given by…
The Alveolar Gas Equation
PAO2 = FIO2 (PB-PH2O) - (PACO2/R)
At sea level, R = 0.8; PAO2 = 0.21(760-47)-(40/0.8) = 100
Define
Respiratory Quotient
What is it?
The ratio of CO2 produced to O2 consumed
What is the relationship between CO2 production and Alveolar Ventilation (VA)?
defined by the PCO2 equation
Inverse relationship between PACO2 and VA
alveolar PACO2 is tightly regulated to remain constant (normally)
The V/Q ratio is the crucial factor in determining…
alveolar/arterial PO2 and PCO2
Why does the apex of the upright lung have a high V/Q with a high PO2 and low PCO2?
alveoli in the apex are poorly ventilated and perfused but better ventilated than perfused
What happens to alveolar gas pressure when there is poor perfusion but good ventlation?
alveolar gas pressure is similar to mixed venous blood
PAO2 = 40, PACO2 = 45
Define
A-a O2 gradient
What does it do? How do you determine it?
Measures gas exchange efficiency across the alveolar - capillary membrane and can point to the cause of hypoxemia
Can be determined using the alveolar gas equation and arterial blood gasses
What is a normal A-a O2 gradient and what causes it?
≤ 20 mmHg
Due to normal V/Q mismatch
Shunting of bronchial and cornary blood into Thesbian veins back to the left side of the heart
Normal A-a O2 gradient can be predicted by…
(your age/4) + 4
Increases with age
What are the 5 causes of hypoxemia?
Low inspired O2
Hypoventilation
Diffusion Limitation
Right-to-Left Shunt
Ventilation - Perfusion Mismatch
When would the A-a O2 gradient be normal during hypoxemia?
When hypoxemia is due to low inspired O2 and hypoventilation
What effect do diffusion defects, V/Q mismatching, and Right-to-Left Shunts have on the A-a O2 gradient?
the A-aO2 gradient is widened
Right-to-Left Shunt is the only cause of hypoxemia in which…
arterial PO2 fails to rise to the expected level when 100% O2 is administered
What two forms is O2 carried from the blood to the lungs to the tissues?
Physically dissolved in the blood
Chemically combined to Hb
What three forms is CO2 carried inthe blood?
Physically dissolved in blood
chemically bound to blood proteins (like carbamino compounds)
As bicarbonante
Define
Fick’s Law of Diffusion
the diffusion of a gas across a sheet of tissue is directly related to the surface area of the tissue, the diffusion constant of the specific gas, and the partial pressure difference of the gas on each of the tissues, and inversely related to tissue thickness
What is the relationship between O2 and CO2 loading and unloading?
They do not occur simultaneously but also facilitate each other
Which diffuses faster through the alveolar-capillary membrane, CO2 or O2?
CO2
How does O2 bind to the heme groups of the hemoglobin (Hb) molecule?
Quickley and reversibly
Which form of O2 is measured clinically in an arterial blood gas sample as the PaO2?
dissolved O2
it maintains its molecular structure and gaseous state
What affect does CO2 have on hemoglobin and O2 binding?
CO2 can alter hemoglobins affinity for O2 and enhance the delivery of O2 to tissues and uptake of O2 in the lungs
Tissue hypoxia occurs when…
insufficient amounts of O2 are supplied to the tissue to carry out normal levels of aerobic metabolism
The major source of CO2 production is…
the mitochondria during aerobic cellular metabolism
What is the major pathway for HCO3- generation?
The reversible reaction of CO2 with H2O to form carbonic acid (H2CO3) with its subsequent dissociation to HCO3- and H+ catalyzed by carbonic anhydrase within red blood cells
What shape is the O2 dissociation curve?
S
What occurs in the plateau phase of the O2 dissociation curve?
increasing/decreasing PO2 have minimal effect on Hb saturation
What is important about the plateau phase of the O2 dissociation curve?
It allows adequate Hb saturation over a large range of PO2
What does ths steep portion of the O2 dissociation curve show?
That during O2 deprivation (Low PO2) O2 is readily released fromHb with only small changes in PO2
This facilitates o2 diffusion to the tissue
Respiratory control is…
What type?
automatic and voluntary
Ventilatory control is composed of…
sensors
controllers
effectors
The primary respiratory control center providing output to respiratory muscles.
Medullary Respiratory Center
Define
Ventral Respiratory Group (VRG)
What is it? Whats it do?
Contains the rhythm generator whose output drives respiration
Sets eupena
Define
Dorsal Respiratory Group (DRG)
What does it do?
Integrates peripheral sensory input (from chemoreceptors and stretch receptors) and modifies the rhythm generated by the VRG based on physiological need
What do the apneutic pontine center and the penumotaxic pontine center do to the medullary center?
They exert a fine tuning effect on the medullary center to ensure smooth breathing and smooth transitions between inspiration and expiraiton
Define
Penumotaxic Center
What does it do besides fine tuning?
Sends impulses to DRG to turn off inspiratory neurons
Define
Apneustic Center
What does it do besides fine tuning?
Prevents inspiratory neurons from being turned off
Which pontine center is dominate?
Pneumotaxic Center
What do Central Chemoreceptors do? How?
They respond to PCO2 by sensing H+ in the medullary interstitial fluid
Located near the ventral surface of the medulla
What do Peripheral Chemoreceptors do?
respond primarily to decreases in PO2, minimally to decreases in pH and increases in PCO2
Mechanism of detection results in inhibition of a K+ channel
only chemoreceptors that respond to changes in PO2
A decrease in PaO2 below 60 mmHG has what effect on peripheral chemoreceptors?
Increased firing rate of peripheral chemoreceptors
Pulmonary receptors on the lungs are sensitive to…
Lung volumes, mechanics, and irritants
Define
Irritant Receptors
Where are they? What is their function? What stimulates it?
Located between airway epithelial cells
Stimulated by particles, cold air, touch, or noxious substances (dust, smoke, etc.)
Protect by inducing cough and hypernea
What stimulates Juxtacapillary (J receptors) in the alveolar-capillary membrane?
distortion of the alveolar wall
Lung congestion or edema
What is the most important regulator of ventilation at rest?
PCO2
