Respiratory pressures Flashcards
Type 1 pneumocyte
Simple squamous epithelium on the alveoli that contributes to gas exchange
Shares a BM with endothelial cells
Type 2 pneumocyte
Cuboidal epithelium with lamellar bodies
Produce surfactant
Surfactant
Reduces surface tension in alveoli and prevents collapsing during exhalation
Located in alveoli up to the respiratory bronchioles
What would happen without surfactant
Alveolar surface tension would be so high that they would collapse, making it difficult to re-expand during the lungs during the next inhalation
Why is surfactant crucial
Maintains lung compliance (ability of lungs to expand and recoil with ease
Law of LaPlace
If two circles have the same surface tension, the smaller bubble will have higher pressure (Decrease volume = increase pressure)
Law of LaPlace equation
Pressure = 2 times surface tension / radius of circle
What happens in different size alveoli without surfactant
With equal surface tension and a difference in volume (and pressure), the air is going to go towards the area with a decrease in pressure (goes down the pressure gradient)
Surfactant’s role in breathing
Inhalation, diaphragm and intercostal mm contract expanding the thoracic cavity
* This expansion lowers the intrapulmonary pressure, causing air to flow into the lungs.
* Surfactant ensures alveoli remain open, preventing collapse and facilitating the
entry of air.
* During exhalation, diaphragm and intercostal muscles relax, elastic recoil of the lungs naturally causes them to decrease in volume.
* Surfactant helps to reduce the work required to overcome surface tension during exhalation
and maintains the alveoli’s ability to stay open.
* This ensures that the lung tissue can efficiently and completely recoil to expel air
Alveolar macrophages
Dust cells
Phagocytize microbes and particulate matter
Derived from monocytes
Pulmonary capillary
Lined with endothelial cells (simple squamous)
Aid in gas exchange
Basement membrane in alveoli
Connects type I pneumocytes and simple squamous of the capillary (share the BM)
Perfusion
The blood that enters the lungs to be oxygenated
Transmural pressure
Difference in pressure between alveolar and pleural pressure
Transpulmonary pressure
Natural state of lungs with no outside forces
Collapse because of the elastic tissue
Natural state of the chest wall with no outside forces
Expanding out to its natural state that was formed during fetal development without any lung pressure
Contraction of the inspiratory muscles expands chest wall and _____ transmural pressure
increases
Contraction of expiratory muscles compresses chest wall _____ transmural pressure
decreases
Functional residual capacity
The volume remaining in the lungs after a normal, passive exhalation
At FRC
Diaphragm relaxed, elastic recoil of lungs is equal and opposite to the elastic recoil of the chest
Intrapleural pressure is -5
No airflow and no pressure gradient
What needs to happen to draw air into the lungs
A difference in the pressure in the alveoli and atmosphere needs to be created by contraction of the inspiratory muscles
Intrapleural pressure at rest
-5 cmH20
Elastic recoil of the lungs is ________ to the elastic recoil of the chest wall
equal in magnitude but opposite in direction
Parietal space impact on lung pressure system
When it changes in volume creates a suction that won’t allow the lungs to collapse any further
Step 1 of breathing
Lungs at FRC, glottis is open, alveolar pressure is equal to atmospheric pressure
No air flow
Step 2 of breathing
Diaphragm contracts, airways stretch, ribs move up and out
Increases volume of the lungs and alveoli increases
Alveolar pressure decreases below atmospheric pressure
Air flows in
Step 3 of breathing
Volume of the lungs and alveoli increased, alveolar pressure is equal to atmospheric pressure
No air is flowing
Step 4 of breathing
Diaphragm relaxes and airways recoil, ribs fall
Volume of lungs and alveoli decreases, alveolar pressure increases above atmospheric and air flows out
Step 5 of breathing
Repeat step 1
Pleural pressure
Less than atmospheric pressure
Negative pressure keeps lungs inflated
Pneumothorax
Air in pleural space that causes an equalization to atm pressure
Lung collapses
Spirometry
Shows air moving in and out/how much
Tidal volume
Amount of air that moves in and out the lungs during quiet breathing
Inspiratory reserve volume
Extra volume of air inspired with maximal effort at end of normal inspiration
Expiratory reserve volume
Extra volume of air expired with maximal effort beyond level reached at end of normal respiration
Residual volume
Amount of air that remains in lungs after fully exhaling
Total lung capacity
Sum of all lung volumes
Vital capactiy
Sum of IRV, TV, ERV
Functional residual capacity =
Expiratory reserve volume and residual volume
Arterial O2 Pressure (PaO2)
The amount of O2 gas molecules in the blood plasma
How oxygen is moved throughout the body
2% is dissolved in the plasma
98% is bound to HB in RBCs
Oxygen dissociation curve
Shows relationship between percentage saturation of hem. with O2 and partial pressure of oxygen
Sequential binding of O2 to Hb
Binding of first molecule is hard, but once one is bind, becomes easier to bind another (like this until all 4 subunits bound)
Because of confirmational change in structure once O2 binds
Cooperativity
O2 affinity of Hb increases with each progressive oxygen molecule binding
(same concept with loosing, hard to loose 1 but then easier as you loose more)
Hemoglobin
Complex protein in RBCs that transports O2 from lungs to tissues
Contains 4 subunits with iron bound heme group that binds the O2
Factors that impact Hb affinity for O2
Temp, pH, H+ ions, CO2
Hb saturation with low PaO2 and location
Low
Small concentration of O2 so harder to bind with Hb
Tissues
Hb saturation with high PaO2
High
High concentration of O2 so once bind easier to fill
Lungs
PaO2 percentage in the lungs
100% or 100 mmHg - will be until it reaches systemic capillaries
PaO2 percentage in the tissues
40% or 40mmHg
O2 saturation % in the systemic veins
75%, don’t loose all the O2 at the tissues, only some is unloaded in the tissues
How O2 moves to Hb or tissues
Wants to move down its concentration gradient
In lungs higher than in the blood
In blood higher than in tissues
Hb saturation in the aorta
98%, remains until hits systemic capillaries
P50
Partial pressure of O2 in the blood equals 50% saturation of Hb (~27mmHg)
What causes shifting O2-Hb dissociation curve to the right
Increase in temp (exercise)
Increase in CO2 amount
Decrease in pH
Increase in H+ ions
Result of shifting O2-Hb dissociation curve to the right
Decrease O2 affinity, results in increase O2 unloading
The p50 has a higher PO2 to get to the same amount of O2 saturation in Hb
Why exercise shits O2 Hb curve
Your muscles need more O2, so want to decrease affinity so more O2 is sent to the tissues
What causes shifting O2-Hb dissociation curve to the left
Decrease in temperature
Decrease in H+ ions
Increase in pH
Bohr effect
Excess H+ bind to hemoglobin which creates confirmational change that decreases affinity of Hb for O2
Result of increase in H+ ions
Changes Hb formation so decrease affinity for O2 and results in O2 unloading (shift to the right)
Haldane effect
Affinity of Hb for CO2 decreases in high O2 environment
So increase in O2 kicks of the H+, confirmational change so CO2 loses affinity and O2 can bind
Ways to transport CO2
Hb transports to lungs
CO2 dissolves in plasma
CO2 diffuses in RBC and turned to bicarb
CO2 to bicarb
In RBC, carbonic anhydrase turns CO2 and water into carbonic acid, which is a weak acid so it dissociates into bicarb and H+, so more acidic
Equilibrium for increase in CO2
With an increase in CO2, convert with H20 to create bicarb and H+
Equilibrium for increase in H+ ions
When H+ ions get kicked off hemoglobin bicarb combines with the H+ to form CO2 and H20
A-a gradient
Difference between O2 concentration in alveoli and arterial system
PAO2 - PaO2
Measuring PaO2
Via blood gas
Measuring PAO2
Calculation is used
How is the A-a equation helpful
Shows how well Hb can grab and let go of O2
Want a low gradient
Respiration
Entire breathing process that includes ventilation and oxygenation
Ventilation
Exchange of gases in the lungs on a molecular level
O2 in and CO2 out
Oxygenation
Diffusion of oxygen from the air into the RBCs where it is then delivered to the tissues
O2 from lungs to the tissues via RBCs
Perfusion
Delivery aspect of tissue oxygenation
Increase in CO2 down chain equation
Combines with what
To carbonic acid
Dissociates into H+ and bicarbonate ion
Chemoreceptors
Monitor levels of CO2 which then can increase or decrease ventilation
Ventilation CO2 impact
Increases CO2 (decreases pH)
Primary stimuli to initiate breathing
Primary stimuli to breathing
CO2
Increasing minute ventilation can change _____
pH rapidy
Minute ventilation =
Respiratory rate x tidal volume
Normal range of pH
7.35- 7.45
Increase in minute ventilation causes an increase in CO2 elimination. Would this increase or decrease pH?
Increase
Less conversion to bicarb and H+
So more basic
Decreases in minute ventilation cause a/an ______ in CO2 elimination and results in _____ CO2 and ______ pH
decrease
increased retention of
decreased (conversion to bicarb and H+)
Hypercapnia (hypercarbia)
CO2 retention
PaCO2 over 45 mmHg
Hypocapnia
Decrease in PaCO2
Below 35 mmHg
CO2 and bicarb equation controls
Left side is controlled by respiratory system
By changing RR and TV can change the amount of CO2 in the system
Can take seconds to minutes
Right side is controlled by the kidneys by retaining or secreting bicarb and H+ into the urine
Days to weeks
Chronic CO2 elevelation
Down regulates chemoreceptors response to a reduced pH
So much CO2 that is bombarding the chemoreceptors that it now takes even more of a change to activate them
Creates a new baseline
Stimulus for breathing with hypoventilation
With chronic hypercapnia, hypoxia becomes the primary stimulus for ventilation
A-a gradient in hypoventilation
Normal
Decrease in PAO2 which means that the PaO2 is also decreased, so both is smaller but gradient is the same
Hypoxemia
When the partial pressure of oxygen in blood is low (under 75 mmHg)
How to measure hypoxemia
Blood gas (ABG)
Oxygen saturation
How much oxygen is currently bound to hemoglobin
How to measure oxygen saturation
Pulse oximetry
Hypoxia
When tissue oxygen level is impaired
Anoxic
No oxygen delivery to a tissue
Infarction
Tissue death
Causes of hypoxemia without hypoxia
Without hypoxia: Increase in O2 delivery to compensate for low PaO2, more O2 in tissues, less in the blood
CO increased to maintain perfusion or a decrease in O2 consumption (hypothermia)
Causes of hypoxemia with hypoxia
Low arterial O2 content
Most common cause of hypoxia
Low oxygen available in the blood
Causes of hypoxia without hypoxemia
Tissues unable to use O2 effectively or delivery system is impaired
No perfusion, poisoning, shunting
Causes of hypoxia with hypoxemia
Low arterial O2 content
V/Q mismatch
During hypoxemia events, looking at the amount of air entering the alveoli and the blood flow passing by the alveoli
Can see where the problem is
V = (mismatch)
Alveolar ventilation
Air entering the lungs into the alveoli
Q= (mismatch)
Perfusion
Blood flow in capillary past alveolus
Access to blood flow
Goal of normal pulmonary ventilation
Match blood flow to areas of gas exchange
Hypoxic pulmonary vasoconstriction
If there is an area that is damage lungs will cut off that section so oxygen goes to somewhere that will use it
Vasoconstrict pulmonary blood flow to poorly functioning areas
Common causes of V/Q mismatch
Asthma
COPD
Pulmonary embolism
Cystic fibrosis
Interstitial lung disease
Right to left shunt (V/Q mismatch)
Blood travels from RV to LA without ever being oxygenated
No air flow into the lungs so blood can’t pick up O2
Diffusion impairment
Getting oxygen from the alveolus to the capillary
Can be due to scaring or fibrosis of the membrane or to reduction in surface area
Carbon monoxide
Has much stronger binding ability for Hb, competitive antagonism
Also changes shape of Hb making it harder to unload O2 into tissues
