Lung Physiology Flashcards
Tidal Volume (TV)
Volume exchanged during normal breathing
Inspiratory Reserve Volume
Volume Maximally inspired above TV
Expiratory Reserve Volume
Volume maximally expired below TV
Residual Volume
Volume remaining in lungs that cannot be exhaled
Total Lung Capacity
Sum of All volumes
Functional Reserve Capacity
Volume remaining in lungs after tidal exhalation
Vital Capacity
Sum of TV, IRV, and ERV
Forced Vital Capacity
Volume of air forcibly expelled
Elastic Structure
a structure whose volume is directly proportional to the pressure difference across the wall of the structure
Transmural pressure
internal surface pressure - external surface pressure
Compliance
dV/dP
Slope of the graph of volume vs pressure
Flattens out at the elastic limit
Greater compliance = greater change in volume with change in pressure
Do the lungs have linear compliance?
No, curvilinear
At low volume lung is difficult to inflate
At midrange the lung is highly compliant
A high volume the lung is stiff (elastic maximum)
Hysteresis
Different compliance for inflation and deflation of the lung
Airway pressure
Pressure within the trachea
Pressure at the body surface
Usually atmospheric pressure
May change under special conditions (diving)
Alveolar pressure
Difference between pressure in the alveoli and atmospheric pressure
Pleural pressure
Difference between pressure in the pleural space and atmospheric pressure
Also called transthoracic pressure
Esophageal pressure can be used as surrogate
What is the most important pressure differential?
Transpulmonary pressure
Pairway - Pplueral or
Palveoli - Pplueral
What happens to transpulmonary pressure on inspiration and expiration?
On inspiration transpulmonary pressure increases, on expiration transpulmonary pressure decreases.
What happens to alveolar pressure on inspiration?
Alveolar pressure increases on inspiration and decreases on expiration
What happens to pleural pressure on inspiration?
Pleural pressure decreases on inspiration and increases on expiration
What is the importance of pleura and pleural fluid
Maintains pressure
Lubricates movement
Helps the lungs stick to the chest wall
At a transmural pressure of 0 what is going on with the volume of the lungs and chest wall?
The chest wall is half expanded but the lungs are mimimally full (not collapsed)
How is the does the compliance of the chest wall change the pressure flow diagram during inspiration and expiration?
It shifts it to the right during inspiration and to the left during expiration.
What factors influence compliance of the lung?
Gravity (alveoli at top are more stretched out)
Presence of surfactant (reduces surface tension)
Small vs. Large Alveoli
What is surfactant?
Located at the gas/liquid interface
Surface area decreases as surfactant becomes more concentrated
it is 85% dipalmitoylphosphatidylcholine
What is the law of LaPlace?
P=2T/r
When surface tension is equal, pressure is greater with smaller radius, therefore more pressure is required to inflate small alveoli and air flows from smaller to larger alveoli
Why don’t alveoli collapse on themselves?
Surfactant reduces surface tension so less inward pressure is maintained in the alveoli
What happens with surfactant in smaller alveoli?
Surfactant is concentrated so surface tension is lower and pressure expands them, in larger alveoli surfact is dilute so surface tension is high and the alveolus collapses
What happens to surfactant during birth?
Fluid that filled the lungs and alveoli is absorbed and coughed up requiring 40-100 cmH20 of pressure
Surfactant on the surface of the lungs decreaces the surface tension from 50 to 5 dynes
Tenfold decrease in negative pressure (2cmH2o) is necessary to inflate the lungs
How does the total airway cross section change with each generation?
Total airway cross section (surface area for exchange) increases dramatically with each terminal generation
What is resistance?
Change is pressure/flow
How does airway resistance change?
It is greatest in the midsized airway, as cross sectional area increases resistance decreases.
How do oxygen molecules reach the alveoli?
Through combined mass flow and diffusion
Diffusion becomes more important toward the periphery
On inspiration what does pressure look like?
Plueral Pressure (-20)
Ptp (5)
PA (-15)
On expiration what does pressure look like?
Ptp (5)
Ppl (10)
PA (15)
What prevents collapse of the trachea on expiration?
Collagenous tracheal rings
What is the relationship between resistance and lung volume.
Resistance decreases with lung volumes above FRC and increases with lung volumes below FRc
On expiration why does flow slow down
At volumes below FRC resistance increases slowing flow
What is the equal pressure point concept?
Large airways with cartilage only partially collapse
Smaller airways without support collapse when high pressure is exerted
Higher pressures during exhalation move air at great velocities at larger lung volumes
How does Flow vs Volume change with COPD?
Decrease in elastic recoil
Increase in TLC and RV
Decrease in expiratory flow
How does flow vs volume change with Fibrotic Lung Disease?
Increase in elastic recoil
Decrease in TLC and RV
Increase in Expiratory flow
What are the parts of the conducting respiratory system?
Nasal cavity
Nasopharynx
Larynx
Trachea and Bronchi
What are the parts of the respiratory respiratory system?
Broncioles
Alveoli
What are the components of the pump?
Chest wall skeleton
Chest wall muscles
Diaphragm
Elastic connective tissue
What are the major functions of the respiratory system?
Facilitate gas exchange in and out of tissues
Maintain acid-base balance in the body
What are the minor functions of the respiratory system?
Vocalization
Removal of irritants
Temperature control
Trace Oxygen from air to tissues
Air to Alveoli, Alveoli to Hemoglobin, Hemoglobin to tissues
How does oxygen get across the alveoli?
Simple diffusion, no mechanical force is required.
What is the p=PO2 is alveolar space? In alveolar capillaries?
100 in space, 40 in capillaries
How is partial pressure calculated?
Partial pressure = total pressure x fractional gas concentration
What is atmospheric pressure at sea level?
760 mm Hg
What are the percentages of gas in normal air?
N 78.62%
O 20.84%
CO2 0.04%
H20 0.50%
Why is alveolar air not the same composition as room air?
Dry air is moistened by nasal passages to 6.2% H20
Alveolar air is not completely replaced so PCO2 increases to 5.3%
Oxygen is constantly exiting alveolar air so Po2 decreases to 13.6%
PCO2 of alveolar capillaries
PCO2 = 45mmHg
PCO2 in alveolar space = 40mmHg (760 x 5.3%)
What is the equation for partial pressure of gas in a liquid?
partial pressure = concentration/solubility
For any given partial pressure something that is more soluble with have a much higher concentration
This is Henry’s law
What are the solubility coefficients for different gases?
Oxygen 0.024 CO2 0.57 CO 0.018 N 0.012 Helium 0.008
How does solubility affect diffusion rate?
The greater the solubility the higher the diffusion rate becuase more molecules are present to diffuse
What are the factors that are proportional to diffusion?
Solubility in fluid
Difference in partial pressure
Cross sectional area for diffusion
Temperature
What are the factors that negatively affect diffusion?
Square root of MW of gas
Distance of diffusion
What are the diffusion coefficients for CO2, O2, and N
- 3 Co2
- 0 O2
- 53 N
Why is the diffusion of oxygen in the lungs so rapid?
There is a large surface area for diffusion and a short distance of diffusion
What are the reason for massive surface area for diffusion?
300-500 million alveoli
Each alveoli may have 1000 capillaries
Total surface area of membranes is about 70-100m2
What is the normal pulmonary capillary blood volume?
65-100ml (1/3 or a tall cup of starbuck coffee)
How thick on average are the respiratory membranes?
0.6 microns (as thin as .2 microns)
How long does it take pulmonary capillary blood to equal partial pressure in the alveolus?
About 1/3 of the capillary length. This is important because during exercise as blood is pumped faster there is a buffer zone for normal oxygenation of the blood.
How much 02 is transported dissolved in plasma or cytoplasm?
3%, the rest is bound to hemoglobin. The solubility of 02 in plasma is significantly lower than that of CO2.
There are 280 million molecules of hemoglobin in each RBC
Describe the composition of hemoglobin.
2 alpha and 2 beta chains, one heme group, each heme group binds one oxygen.
Binding of one oxygen causes conformational change allowing for easier binding of next oxygen to unoccupied heme
How does hemoglobin buffer oxygen delivery to tissues during exercise?
At rest hemoglobin only delivers around 5% of it’s oxygen to tissues, when PO2 decreases hemoglobin more freely gives up oxygen so it can supply 80% of it’s bound oxygen during activity.
What factors shift the oxygen-hemoglobin curve to the right, decreasing it’s affinity for O2
Hydrogen Ions CO2 (from metabolism) Temperature 2,3 BPG (from glycolysis) (All of these increase with exercise)
What cause issues with oxygen supply?
Altitude (even commercial planes)
Fires
Anemia (no change in PaO2, no change in saturation, just change in carrying capacity)
What does CO poisoning do?
Competitively binds to Heme with 200x the affinity, causes change is carrying capacity with no change in PAO2, must rely on plasma O2 which is low.
What is the difference between diffusion rates of O2 and CO2
CO2 is 20x more soluble so less difference in partial pressure is required for the same rate of diffusion.
How is CO2 transported?
about 4 mL of CO2 is transported per 100ml of blood
Transported as: dissolved CO2 (7%), bicarbonate (70%), and carbamino compounds (23%).
(there is no dedicated carrier for CO2)
What is the Chloride Shift?
RBCs in venous blood have more Cl in them than RBCs in arterial blood because the PCO2 is higher and therefore when it is converted to bicarb and exchanged for chloride the concentration increases in the cell.
What buffers the H+ made during HCO3 formation in the RBCs?
Primarily Deoxy-Hb
Why does more CO2 form carbamino compounds in RBCs than outside them?
Hb is more concentrated inside the cell
Hb binds CO2 more readily than other proteins
Hb is a buffer for acid production during formation
What is the haldane effect?
O2 binding to hemoglobin causes CO2 to be released from the blood more effectively.
Oxyhemoglobin is stronger acid than deoxyhemoglobin, released hydrogen binds bicarb and dissociates into h20 and co2, O2 binding carbaminohemoglobin displaces Co2 as well
Hyperventilation
breathing increased more than normal lowering PCO2
Hypoventilation
breathing decreased increasing PCO2
Hyperpnea
increased breathing to match metabolic needs (like during exercise)
Tachypnea and Bradypnea
Increased and decreased rates of breathing respectively
Brachypnea
Shortness of breath (dyspnea)
What factors influence breathing?
Changes in arterial levels of O2, CO2, and pH sensed by central and peripheral chemoreceptors and by mechanoreceptors.
What part of the brain is responsible for regulating autonomic breating?
The pons and the medulla
Central Pattern generator lies in the medulla
What are the different respiratory groups that control breathing?
Pontine respiratory group, dorsal respiratory group, ventral respiratory group (consisting of caudal and rostral VRGs)
What is the function of the dorsal respiratory group?
Has the nucleas of the solitary tract (bilateral)
Receives blood gas information from the thorax and abdomen and integrates with the VRG to drive inspiration.
What is the function of the ventral respiratory group?
Usually quiescent during normal breathing, conducts powerful expiratory signals during exercise and controls dilation of the airway
VRG is influenced by Cortex during fear, excitement, anger, etc.
What is the pre-botzinger complex
Has pacemaker activity that is easily overridden by conscious control and DRG input. Is located in the VRG
Probably not the only site of pacemaker activity
Affected by hormones like thyrotropin releasing hormone
Pneumotaxic center
Located in the pons
Off switch for the inspiratory center
Stimulated by medullary inspiratory neurons
Stimulation shortens inspiration and increases breathing rate
Apneustic center
Located in lower pons
May control depth of breath
Transection above this site leads to prolonged inspirations with short expirations (apneustic breathing)
How is breathing regulated?
Glosspharyngeal and vagus nerves give signals to the DRG and VRG, DRG gives signals to the phrenic and intercostal nerves as well as the VRG.
Neurons of the Pre-bot in the VRG fire at a particular rate and are modified by information that is received.
Where are the peripheral chemoreceptors located?
Carotid bodies (signal through GP nerve) Aortic bodies (signal through vagus nerve)
How are gas changes sensed in the chemoreceptors?
Increases in CO2 diffuse into type 1 glomus cells where they are converted into CO2 and H2O by glomus cells.These two chemicals block the K+ channel causing an influx of calcium which allows vacuoles to move to the membrane and secrete neurotransmitters.
How does sympathetic activity control breathing peripherally?
innervation constricts arterioles causing blood flow to be decreased and mimicking an increase in PCO2.
