Respiratory High Yield Concepts Flashcards
The primary responsibility of the lungs is…
exchange gas
What processes must be functioning for optimal gas exchange?
Ventilation → getting gas to the alveoli
Perfusion → removing gas from the alveoli by the blood
Diffusion → getting gas across alveolar walls
Control of breathing → regulating gas exchange
The airways consist of…
a series of branching tubes which become narrower, shorter, and more numerous as they penetrate deeper into the lung
Conducting zone
no alveoli
trachea, bronchi, bronchioles
Respiratory Zone
alveoli
respiratory bronchioles. alveolar ducts and sacs
There are ___ alveoli in lungs creating a total surface area of about ___
300 million
75 m2
Define: Alveoli
small, thin-walled inflatable air sacs encircled by pulmonary capillaries
has a single layer of thin exchange epithelium and is the site of gas exchange
air flows between adjacent alveoli via pores of Kohn
What are the 3 types of cells in alveoli?
Type I alveolar cells
Type II alveolar cells
Alveolar macrophages
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
Atmospheric Pressure (PB)
760 mmHg at sea level
decreases as altitude increases
Intra-alveolar pressure (PA)
will equilibrate with atmospheric pressure
Intrapleural Pressure (Pip)
756 mmHg
recoil forces create a vacuum (“-4”)
closed cavity
Transmural Pressure (PL)
pressure across the lungs (PA - Pip)
key to inflating lungs
___ and __ hold the lungs and thoracic wall in tight apposition even though the lungs are smaller
Intrapleural fluid’s cohesiveness and the transmural pressure gradient (most important)
PA = 760 mmHg, pushes out vs. Pip of 756 mmHg
PB = 760 mmHg, pushes in vs. Pip
Why does the pleural space have slightly negative pressure?
because the chest is pulling out, lungs are pulling in, and there’s no extra fluid to fill expanded space
Pneumothorax
air enters pleural cavity, pressure equalizes with atmospheric pressure, transmural pressure gradient is gone, lungs collapse, thoracic wall springs out
Boyle’s Law
describes the relationship between the pressure and volume of a gas
as volume decreases, pressure increases
P1V1 = P2V2
changes in volume of chest cavity during ventilation cause pressure gradients
An increase in chest volume causes..
a decrease in pressure
air moves into the lungs from the atmosphere
A decrease in chest volume causes…
an increase in pressure, air moves out from body
Inspiration results from…
the contraction of the diaphragm and intercostal muscles (an active process)
the rib cage swings upwards and outwards
the enlarged cavity housing the lungs undergoes a pressure reduction with respect to the pressure existing outside the body
Expiration results from…
the relaxation of the diaphragm and intercostal muscles (a passive process)
The rib cage moves inward and downwards
The elastic recoil of the lungs creates a higher intra-alveolar pressure compared to atmospheric pressure that forces air out of the lungs
Laminar Airflow
low flow rate
usually in small airways
Turbulent airflow
fast flow rate
usually in large airways
Why is the overall contribution to total R of bronchioles low?
even though each terminal bronchiole has a high resistance to flow, their total cross-sectional area is large and the tubes are in parallel so their overall contribution to total R is less low
Air flow in the respiratory system obeys the same rules as blood flow, what are they?
Airflow = ΔP/R
Flow increases as the pressure gradient increases and decreases as resistance increases
Where is airway resistance the greatest and how can it be measured?
airway resistance is greatest in the medium sized airways
it can be measured using Poiseuille’s Law: R = 8nL/πr4
What is the primary determinant of resistance in airways?
airway radius
the length and viscosity are virtually constant in respiratory systems
Why is the diameter of the bronchiole adjustable?
no cartilage but has smooth muscle
Low CO2 in the bronchiole leads to…
bronchoconstriction → increases resistance and decreases airflow
Increased CO2 in the bronchiole leads to…
bronchodilation → increases airflow
Define: Equal Pressure Point (EPP)
when airway pressure is equal to intrapleural pressure
Pulmonary Function Tests
measure lung volumes, lung capacities and flow rates
these tests can detect abnormalities in lung function before diseases become symptomatic
Air moved during breathing is divided into 4 lung volumes…
Tidal volume (VT)
Inspiratory reserve volume (IRV)
Expiratory reserve volume (ERV)
Residual volume (RV)
Tidal Volume (VT)
air volume moving in a single normal inspiration or expiration
Inspiratory Reserve Volume (IRV)
Additional volume inspired above tidal volume
Expiratory Reserve Volume (ERV)
air exhaled beyond the end of normal expiration
Residual Volume (RV)
air in respiratory system after maximal exhalation (not measured directly)
Vital Capacity (VC)
Maximum volume of air voluntarily moved through the respiratory system
IRV + ERV + VT = VC
Total Lung Capacity (TLC)
VC + RV = TLC
Inspiratory Capacity
VT + IRV = Inspiratory Capacity
Functional Residual Capacity (FRC)
ERV + RV = FRC
Obstructive Lung Disease
characterized by increases in lung volumes and airway resistance and decreases in expiratory flow rates (FEV1/FVC)
Emphysema
type of COPD
obstructive lung disease
characterized by increased lung compliance and decreased diffusion capacity for CO
condition in which elastin fibers are destroyed
high compliance and low elastance
exhibit poor recoil during expiration
can result in hyper-inflated lungs and “barrel-chest”
Restrictive Lung Diseases
characterized by decreases in lung volume, normal expiratory flow rates and resistance, and a marked decrease in lung compliance
more work must be expanded to stretch stiff lung
Possible Causes: inelastic scar tissue, insufficient surfactant production
Compliance
the ability of the lungs to stretch
defined by slope of pressure-volume curve for lungs → curve is steep at low and normal lung volumes but flattens at very high volumes
High-compliance lungs…
easily stretch
Low-compliance lungs…
require more force to stretch lungs (more work)
Hysteresis
different compliance for expiration and inspiration because of surfactant
What does elasticity mean for the lungs?
the lung is able to return to its original shape after the force stretching it has been removed
the normal lung is both compliant and elastic
What causes the ventilation difference in an upright lung? what are they?
ventilation differences are caused by the effects of gravity
alveoli at the apex are larger and less compliant and receive less of each tidal volume breath than alveoli in the base
Pulmonary elasticity is generated by:
Elastic fibers → the natural tendency of these fibers to recoil facilitates passive expiration
Surface tension → surface tension on the alveolar surface arises due to the strong attractive force that water has for itself → tends to make alveoli collapse, particularly smaller alveoli
Surfactant molecules ___ surface tension
reduce
The chest wall and lung are in equilibrium at the…
FRC
Respiratory Control is….
both automatic and voluntary
Ventilatory control is composed of…
sensors, controllers, and effectors
The Medullary Respiratory Center
the primary respiratory control center providing output to respiratory muscles
Ventral Respiratory Group (VRG)
contains the rhythm generator whose output drives respiration
sets eupnea (12-15 breaths/min)
Dorsal Respiratory Group (DRG)
Integrates peripheral sensory input (from chemoreceptors and stretch receptors) and modifies the rhythm generated by the VRG based on physiological need
What are the two pontine centers? What do they do in general together?
Apneustic Center and pneumotaxic center exert a “fine tuning” effect on the medullary center to ensure smooth breathing and a smooth transition between inspiration and expiration
Pneumotaxic dominates
Pneumotaxic center
sends impulses to DRG to turn off inspiratory neurons
dominates
Apneustic Center
prevents inspiratory neurons from being turned off
Central Chemoreceptors
near ventral surface of medulla
respond to PCO2 by sensing H+ in the medullary interstitial fluid
Peripheral Chemoreceptors
carotid and aortic bodies
responds primarily to decreases in PO2, less so to decreases in pH and increases in PCO2
a drop in PaO2 below 60 mmHg results in an increased firing rate
only chemoreceptors to respond to changes in PO2
mechanism of detection ends in inhibition of a K+ channel
The lungs have pulmonary receptors that are sensitive to…
lung volumes, mechanics, and irritants
Pulmonary Stretch Receptors
located in airway smooth muscle
respond to mechanical stimulation and are activated by lung inflation
What are pulmonary stretch receptors responsible for?
The Hering - Breuer reflex
when VT > 1 L pulmonary stretch receptors activated → APs travel to medullary center and inhibit inspiratory neurons
Irritant Receptors
located between airway epithelial cells
stimulated by particles, cold air, touch or noxious substances (dust, smoke)
Protect by inducing cough or hypernea
Juxta-capillary (J receptors)
in the alveolar capillary membrane
stimulated by distortion of the alveolar wall (lung congestion or edema)
What is the most important regulator of ventilation at rest?
PCO2
The sensitivity of the ventilatory response to CO2 is enhanced by…
hypoxia
The sensitivity of the ventilatory response to O2 is enhanced by…
hypercapnia
How is O2 carried in the blood from the lungs to the tissues?
Physically dissolved in the blood
chemically bound to Hemoglobin
How is CO2 carried in the blood?
physically dissolved in the blood
chemically combined to blood proteins as carbamino compounds
as bicarbonate
Gases (NO) with a rapid rate of air-to-blood equilibration are…
perfusion limited
Gases (CO) with a slow air-to-blood equilibration rate are…
diffusion limited
Under normal conditions, O2 transport is ___ but can be ___ in certain conditions
perfusion-limited
diffusion-limited
Fick’s Law of Diffusion
The diffusion of 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 tissue and is inversely proportional to tissue thickness
Vgas ∝ (A*D*(P1-P2))/T
A = surface tension, D = diffsion constant (=Solubility/sqrtMW)
P1-P2 = partial pressure difference of gas one ach side of tissue
T = tissue thickness
What is the relationship between O2 and CO2 loading and unloading?
they occur simultaneously and facilitate each other
CO2 diffuses approximately __ times more rapidly through the alveolar-capillary membrane than O2
20X
O2 binds ___ and ___ to the heme groups of the hemoglobin molecule
quickly and reversibly
Dissolved form of O2
maintains its molecular structure and gaseous state
this is the form that is measured clinically in an arterial blood gas sample as the PaO2
The ability of CO2 to alter the affinity of hemoglobin for O2 (Bohr effect)….
enhances O2 delivery to tissue and O2 uptake 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…
in the mitochondria during aerobic cellular metabolism
The reversible reaction of CO2 with H2O to form carbonic acid (H2CO3) with its subsequent dissociation to HCO3- and H+ is catalyzed by…
the enzyme carbonic anhydrase within RBCs
major pathway for HCO3- generation
What is the shape of the O2 dissociation curve?
S - shaped
it is not linear
What happens during the Plateau portion of the O2 dissociation curve?
the plateau area is above 60 mmHg
increasing the PO2 has only minimal effect on hemoglobin saturation → the same is true if there is a decrease in PO2 from 100 to 60 mmHg → this assures adequate hemoglobin saturation over a large range of PO2
What does the steep portion of the O2 dissociation curve show?
20-60 mmHg
illustrates that during O2 deprivation (low PO2) O2 is readily released from hemoglobin with only small changes in PO2, which facilitates O2 diffusion to the tissue
Pulmonary circulation is a ___ flow, ___ pressure, ___ resistance circuit
high flow (5 L/min)
low pressure
low resistance (1-2 mmHg/L/min)
The lungs receive the entire volume of ___ cardiac output
Right ventricle (5 L/min)
The average pressure in the pulmonary circulation is ___ compared to ___ systemic blood pressure
25/8 mmHg
120/80 mmHg
only need enough pressure to lift blood to top of lung
work required by right ventricle is much less than left ventricle
Why doesn’t the right ventricle have to work as hard to overcome peripheral resistance?
the pulmonary arteries are much more compliant (distensible, easier to stretch) than the aorta and systemic arteries
the total length of pulmonary blood vessels is shorter
What is the result of the right ventricle not having to work as hard to overcome peripheral resistance?
it allows for low pulmonary blood pressure → results in low net hydrostatic pressure → yields low fluid flow into interstitial space → lymphatic system removed filtered fluid
Bronchial Circulation
supplies the conducting portions of the lungs
part of the systemic circulation → but the deoxygenated venous blood of the bronchial circulation does not return to the system circulation
Where does the deoxygenated venous blood of the bronchial circulation go?
it flows into the pulmonary veins along with freshly oxygenated blood from the alveoli → the addition of deoxygenated blood slightly lowers the oxygen content of the blood before it reaches the left side of the heart
Increases in CO or pulmonary artery pressure…
decrease pulmonary vascular resistance (PVR) and increase pulmonary blood flow by recruitment and distention of capillaries
___ affect PVR
Changes in lung volume
PVR is lowest…
at FRC
Where are extra-alveolar vessels? When are they compressed?
they are tethered to surrounding alveoli and compressed with low lung volumes
Where are alveolar vessels? When are they compressed?
they are located between alveoli and are compressed with high lung volumes
What effect does Hypoxia have on PCR and pulmonary blood flow? What does it depend on?
Hypoxia can alter pulmonary blood flow and PVR depending upon whether it is regional or generalized
The relationships among pulmonary artery, alveolar and pulmonary vein pressures divide the lung into 3 functional zones, what are they?
Zone 1: Pa< PA
Zone 2: Pa > PA > PV
Zone 3: Pa > PV > PA
Functional Zone 1
Pa< PA
capillary collapses before it crosses alveolus
no flow
doesn’t exist in normal lungs (might with hemorrhage when BP and intravascular volume are low)
Functional Zone 2
Pa > PA > PV
flow driven by difference between arterial and alveolar pressure
primary area of distention
recruitment of vessels during exercise
Functional 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
Pulmonary Capillary Wedge Pressure (PCWP) measures…
back pressure from left atrium
Normal PCWP is….
2-15 mmHg
Increased PCWP indicates…
hydrostatic pressure and filtration forces
The sum of the partial pressures of a gas must be equal to….
the total pressure
The partial pressure of a gas is equal to…
the fraction of gas in the gas mixture times the total pressure
By the time inspired gas 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
The conducting airways do not participate in gas exchange, and therefore….
the partial pressures of O2, N2, and H2O vapor remain unchanged in the airways until the gas reaches the alveolus
Minute (Total) Ventilation (VE)
Minute Ventilation (VE) = Tidal Volume (VT) (mL/breath) x respiratory rate (f) (breaths/min)
Minute (Total) Ventilation (VE) at rest
6,000 mL = 500 x 12
exercise can increase 25-fold to 150 L/min
When is VT more important than respiratory rate
when minute (total) ventilation increases
Anatomical Dead Space
150 mL
volume of air filled in conducting airways incapable of gas exchange with blood = 150 mL
Alveolar Ventilation (VA)
VA = (VT - VD) x f
VT = tidal volume, VD = dead space, f = respiratory rate
Alveolar Ventilation (VA) at rest
4,200 mL = (500 - 150) x 12
What effect does breathing deeply and slowly have on minute (total) ventilation (VE) and alveolar ventilation (VA)?
VE stays the same but VA increases
What effect does breathing shallowly and rapidly have on minute (total) ventilation (VE) and alveolar ventilation (VA)?
VE stays the same but VA decreases (even to zero)
Alveolar Gas equation
PAO2 = FIO2 (PB - PH2O) - (PACO2/R)
gives the partial pressure of oxygen in the alveolus
at sea level and when R = 0.8;
PAO2 = 0.21(760-47) - (40/0.8) = 100
The respiratory quotient
the ratio of CO2 produced to O2 consumed
Mixed diet: 0.8
The relationship between CO2 production and alveolar ventilation is defined by….
the PCO2 Equation
there is an inverse relationship between PACO2 and VA
In normal individuals, the alveolar PACO2 is…
tightly regulated to remain constant at about 40 mmHg
The V/Q ratio is the crucial factor in determining…
alveolar, and therefore, arterial PO2 and PCO2
At the apex of the upright lung, alveoli are…
poorly ventilated and perfused, but they are better ventilated than perfused leading to high V/Q with a high PO2 and low PCO2
When there is poor perfusion but good ventilation, alveolar gas pressure is…
similar to inspired air
PAO2 = 150
PACO2 = 0
At the base of the upright lung, alveoli are…
well ventilated and perfused, but they are better perfused than ventilated leading to a low V/Q with a low PO2 and high PCO2
When there is poor ventilation but good perfusion, alveolar gas pressure is….
similar to mixed venous blood
PAO2 = 40
PACO2 = 45
A-a O2 Gradient
can be determined using the alveolar gas equation and arterial blood gases
measures gas exchange efficiency across alveolar - capillary membrane and can point to the cause of hypoxemia
A normal A-a O2 Gradient is ___ and is due to…
≤20 mmHg
due to normal V/Q mismatch and shunting of bronchial and coronary blood into Thebesian veins back to left side of heart
Normal A-a O2 Gradient can be predicted by
age/4+4
A-a O2 Gradient increases with age
The five causes of hypoxemia are
low inspired O2
hypoventilation
diffusion limitation
right-to-left shunt
ventilation-perfusion mismatch
The A-a O2 Gradient is normal if hypoxemia is due to…
low inspired O2 and hypoventilation
The A-a O2 Gradient is widened if hypoxemia is due to…
diffusion defects, V/Q mismatch, and/or right-to-left shunt
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
