Respiratory Flashcards
Lung Functions
Gas exchange
pH maintenance
Warm/humidify air
Vocalization
Gas Laws & Equations
Ideal Gas Equation
Boyle’s Law
Dalton’s Law
Fick’s Law
Ideal Gas Equation
PV=nRT
P = 1/V
Boyle’s Law
P1V1= P2V2
Dalton’s Law
Partial pressure of gas = Patm * % of gas in atmosphere
Partial pressures of gases in atmosphere. Gases go down their partial pressure gradient.
In atm O2=21% N2= 79%
Fick’s Law of Diffusion
Diffusion = Area * ∆Pressure * Diffusion Coefficient
Distance
Diffusion Coefficient = Solubility
√MW
Pressures
Atmospheric pressure
Alveolar pressure
Intrapleural pressure
Transpulmonary pressure
Resistance
anything that opposes flow
R = 8lη or R ∝ lη r4 r4
Flow, Resistance, and Pressure
F ∝ ∆P
F ∝ 1/R
F ∝ ∆P/R
Describe the generation of a pressure gradient between the atmosphere and the alveoli.
During inspiration , the diaphragm contracts , flattens , and expands thoracic cavity.This increase in volume decreases pressure inside the lungs and encourages air to enter lungs because the Patm is higher. When Plungs and Patm equalize , no more air enters. The diaphragm relaxes , decreasing volume and
increasing pressure ,forcing air back out into the atmosphere until pressure is equalized
Define the pressures of various compartments of the respiratory system.
Alveolar pressure :pressure within the alveoli .
Cycles from 0 f- atm) to f) as air is forced out into blood or exhalation.
Intrapleural pressure : pressure within the pleural cavity between the visceral 1-parietal layers. Always (-)
Transpulmonary pressure : difference between alveolar pressure and intrapleural pressure.
Explain the importance of negative pressure in the pleural cavity.
The pleural cavity is considered a potential space because it is really 2 membranes with fluid in between them ( water between 2 microscope slides). This reduces friction but increases surface area to keep the lungs inflated however without a negative pleural pressure ,
the lungs would not stay inflated.
Describe how flow, resistance and pressure gradients are related and how changes in one will affect the others.
F ∝ ∆P
F ∝ 1/R
F ∝ ∆P/R
Increase Pressure increase flow
Increase resistance decrease flow
Compliance
Ability of lungs to expand/stretch
Extent of expansion for each unit increase in transpulmonary pressure
Determined by elastic forces
Compliance = ∆Volume ∆ Pressure
Elastance
Ability of lungs to “recoil”
Opposite of compliance
Both needed for efficient respiration
Elastic forces
Elastin and collagen fibers
Surface tension of fluid in lungs
Define compliance and elastic forces in the lungs.
compliance is the ability of the lungs to expand /stretch
Compliance = ∆Volume
∆ Pressure
Elastance is the opposite of compliance :
the ability of lungs to recoil
Surfactant
Reduces surface tension in aveoli
Surface tension
Attraction of water molecules at air/water interface
Will result in collapse of alveoi
Secreted by Type II alveolar cells
Contains phospholipids and proteins
Detergent-like
Law of LaPlace
T = P * r/2 or P = 2T/r
P = pressure required to prevent alveolar collapse (at rest)
T = surface tension
r = radius
The smaller the radius, the larger the pressure required to prevent collapse
P1
Pressure required to
prevent alveoli #1 from
collapsing.
P2
Pressure required to
prevent alveoli #2 from
collapsing.
Give the role of surfactant.
surfactant is a thin, soapy material that reduces surface tension in alveoli . It is secreted by type 2 alveolar cells .
Surfactant also helps to overcome the Law of Laplace ( smaller radius requires larger pressure to prevent collapse)
Pulmonary Ventilation
Ventilation: movement of air
Pulmonary ventilation:
TPV = VR * VT
Total pulmonary ventilation = ventilation rate * tidal volume
TPV is a measurement of effectiveness of ventilation
Dead Space
Volume of air inhaled, but that does not participate in gas exchange
Anatomical dead space
Air in trachea, bronchi (conducting airways)
~150ml
Alveolar dead space
Alveoli that are not well perfused
Alveolar Ventilation
Volume of fresh air that reaches exchange areas of blood
AV = VR * (VT - DS)
Alveolar Ventilation = Ventilation Rate * (Tidal Volume - Dead Space)
Define alveolar ventilation and compare it to pulmonary ventilation.
TPV = VR ✗ VT of ventilation (measures the effectiveness)
tidal volume
AV = VR ✗ (VT - DS) *
DS = 150mL
Define dead space and explain its effect on alveolar ventilation.
Dead space is volume of air not reaching alveoli for perfusion (doesnot participate in gas exchnage). increase DS decrease Alveolar space and decrease diffusion =150ML
The Lungs as a Blood Reservoir
Normally ~9% of blood (~450ml) is in lungs
Can range from ~225-900ml, depending on body’s needs/pathology
Ventilation/Perfusion Ratio
Normally, air coming into lungs contains enough O2 to fully oxygenate blood as it flows through
Ventilation/Perfusion ratio (V/Q) should be close to 1
To maintain this:
Blood vessels around poorly-oxygenated alveoli constrict (due to hypoxic conditions)
This sends blood to better-oxygenated areas
Hydrostatic Pressure
Causes lower portions of lungs to have higher arterial pressure
Can differ by 23mm Hg
Compare pulmonary circulation to systemic.
Blood enters the lungs from the right ventricle through the pulmonary artery. O2 from the alveoli enters capillaries while CO2 enters alveoli from capillaries . Blood then travels thru pulmonary vein back to heart into left atrium. Pulmonary system is at a much lower pressure
Describe how the pulmonary circuit acts as a blood reservoir
Normally the pulmonary circuit contains ~9% (450mL) of blood but can expand as work as a reservoir ventilation / Perfusion rate should be ~1 , so BV constrict due to decrease O2 or dilate increase O2
Contrast pulmonary capillary dynamics with systemic.
Outward Forces
PPc = 7
πif = 14
Pif = 8
Total = 29
Inward Forces
πPc = 28
29-28=1mmHg
Net Filtration Pressure
Intrapleural Fluid
Only a few ml
Excess fluid is edema (of pleural cavity) or effusion
Lymphatic blockage
Heart failure
Low plasma π
Inflammation
Explain the causes and effects of excess fluid in or around the lungs
The pleural fluid is only a few ML, any excess is edemas and could be due to a lymphatic blockage , heart failure , low plasma proteins ,
or inflammation
Principles of Gas Exchange/ Diffusion of O2 & CO2
Pressure differences cause net diffusion
Compositions of alveolar/atmospheric air
Diffusion of gases through respiratory membrane
Pressure Differences Cause Net Diffusion
Gas contributes to total pressure in direct proportion to concentration
Diffusion is in response to concentration gradient due to pressure gradient
Diffusion depends on partial pressure of gas
Diffusion of Gases Through Respiratory Membrane
Respiratory Membrane
Factors Affecting Diffusion
Diffusing Capacity
Describe the diffusion of gases and define partial pressure.
Diffusion of gases occurs in response to a concentration gradient due to a pressure gradient.
Diffusion depends on partial pressures (% total pressure an element contributes to total pressure in system)
Respiratory Membrane Layers
1.Fluid with surfactant that lines alveolus
2.Alveolar epithelium
3.Alveolar basement membrane
4.Interstitial “space”
5.Capillary basement membrane
6.Capillary endothelium membrane
Respiratory Membrane
Alveolar epithelium
Capillary endothelium
Fused basement membranes of both
Partial Pressures of Gases Determine Diffusion
Remember Dalton’s Law
Each gas in the mixture exerts part of the total pressure, or “partial pressure”
Gases move from an area of high partial pressure to low partial pressure
Po2 in alveolar air is ~149mm Hg
Po2 in blood entering the lungs is ~40mm Hg
O2 will move/diffuse from high (alveolar air) to low (blood)
Describe the respiratory membrane and explain the factors that affect the rate of gas diffusion across the membrane.
1.Fluid with surfactant that lines alveolus
2.Alveolar epithelium
3.Alveolar basement membrane
4.Interstitial “space”
5.Capillary basement membrane
6.Capillary endothelium membrane
Diffusion of Gas is based on:
Rate = A x P x Diffusion coefficent/distance
PO2 alveoli = ~ 149 O2 will move
PO2 blood = ~ 40
dependent directly on partial pressure of CO2
Diffusing Capacity (DL)
Defined as ml gas diffusing each minute for a
pressure difference of 1 mmHg
* Can change, as in exercise
* DL= Surface area*diffusion coefficient/thickness
* Units: ml/min/mm Hg
* Diffusion rate = DL * Pressure gradient
* Units: ml/min
Diffusion of O2
DL=21 ml/min/mmHg * gradient of 11 mmHg
=230 ml/min diffusion of oxygen
Diffusion of CO2
DL=400+ ml/min/mm Hg * gradient < 1 mmHg
=400+ ml/min diffusion of carbon dioxide
Describe the exchange of oxygen &
carbon dioxide with the atmosphere and
relate gas exchange to the metabolism of
body tissues.
O2 and CO2 follow pressure gradients into blood or into alveoli.
A higher metabolism = a higher O2 demand . Alveolar ventilation must increase or arterial CO2 will
↳ a cells O2 use is directly dependent on ADP levels
DL= Surface area*diffusion coefficient/thickness
O2: DL=21 Rate=230
CO2: DL= 400 Rate= 400
Dissolved oxygen
Solubility 0.003 ml O2/100 ml blood mmHg
* Normal blood 0.3 ml O2 / 100 ml blood
* Normal oxygen consumption 250 ml O2/min
* Would require 83 L/min blood flow
Hemoglobin
97% O2 transport (remainder dissolved in
plasma)
* O2 + HB HBO2
Normal blood flow
20 ml O2/ 100 ml blood * 5000 ml blood/min
1000 ml O2/min
Increased blood flow
20 ml O2/ 100 ml blood * 20000 ml blood/min
4000 ml O2/min
Increased Blood Flow To Tissues
O2 Uptake During Exercise
Increased cardiac output
* Decreased transit time
* Increased diffusing capacity
* Opening up of additional capillaries
* Better ventilation/perfusion match
* Equilibration even with shorter time
Describe how O2 is transported through the blood
Oxygen is not very soluble in 11-20 . A CO of 83 mL/min would be needed to keep up with normal O2 consumption of 250m mL/min.
Hemoglobin solves this problem by binding to 97% of blood O2 ,
the remaining 3° to dissolved in plasma. This is a reversible binding.
As blood flow increases , O2 delivery increases, increase in CO decreases transit time and increases diffusion capacity by opening capillaries. PO , is dependent only on plasma O2
Partial Pressure
Depends on percentage of gas
* Driving force for diffusion
Saturation
% Hb that has oxygen bound (
Content
Absolute quantity (ml O2/100 ml blood)
Right shift at tissue
increased carbon dioxide in blood
* decreased affinity for oxygen
* maintain partial pressure gradient
Left shift at lungs
loss of carbon dioxide at lungs
* increased affinity of oxygen
Explain the oxygen-hemoglobin curve
and predict how changing variables will
affect the curve.
As more O2 binds to hemoglobin , the affinity for O2 rises ,
increasing Oz binding . This happens in the lungs. As less O2 binds to hemoglobin, the affinity for O2 decreases, encouraging dissociation.
This happens at the tissues.
A shift to the right at the tissues increases CO2 and decreases affinity for O2 to maintain partial P.
A shift to the left at the causes decreases CO2 and increases affinity for O2
A decrease in pH requires a increase PO2 for % saturation
A increase in pH requires a decrease in PO2 for % saturation
Transport of CO2
HCO3-
* Serves as a buffer
* 70%
* Hb-CO2
* 23%
* Dissolved
* Solubility 20X oxygen
* 7%
Regulation of Respiration
Respiratory Center
* Chemical Control of Respiration
* Regulation of Respiration During Exercise
Dorsal Respiratory
Group (DRG
Inspiration
* Instrinsic nerve activity
* ramp signal
Pontine Respiratory
Group
(PRG)/Pneumotaxic
Center
Limits inspiration duration
* Increases respiratory rate
Ventral Respiratory
Group
Inactive during quiet
respiration
* Active when need
increased ventilation
* Expiration
* Inspiration
Stretch Receptors
Located in smooth muscle of large and small airways
* Prevent over-inflation (protective mechanism)
* Hering-Breuer reflex
* Receptors send signals through vagus nerve to DRG, stops
ramp
Irritant receptors
Nasal mucosa, upper airways, possibly alveoli
* Bronchoconstriction
* Coughing, sneezing
Chemical Control of Respiration
Carbon Dioxide
* Central & peripheral
* Hydrogen Ions
* Central & peripheral
* Oxygen
* Peripheral only
Describe how CO2 is transported thru the blood.
CO2 diffuses out of cells ( alveoli or other) and enters blood vessels where it enters RBCs when exchanged with CI -.
Carbonic anhydrase converts
CO2 and H2O → HC05 (bicarb) which travels as a buffer in the blood.
7% dissolved in plasma as O2 (20 ✗more soluble than O2)
23% bound to hemoglobin
70% as bicarb
Peripheral Chemoreceptors
Sensors: chemoreceptors in carotids, aorta, and
throughout thoracic cavity
* Afferent signal: Hering’s nerves to glossopharyngeal
nerves (from carotids); vagus nerves (from aorta)
* Integrating center: DRG
* Efferent signal: somatic motor neurons
* Targets: skeletal muscles: diaphragm, intercostals
* Response: increased rate and depth of breathing
Peripheral Chemoreceptors
Respiration During Exercise
Linear increase in ventilation with increasing
O2 consumption
* Arterial PO2, PCO2 and pH levels do not
change much
* Increased respiration happens before arterial
PO2, PCO2 and pH levels could change
* Conclusion: not sure the exact mechanism
responsible for increased ventilation
Respiration During Exercise
Other Factors that
Influence Respiration
Voluntary control
* Activity from vasomotor center
* Body temperature
* Irritants
* Anesthesia
