Test 2 (Lectures 1-4) Flashcards
P (indicates)
- Partial pressure of a gar: must specify which gas you are referring to. The units are mm Hg
PO2= Partial pressure of Oxygen
PCO2= Partial pressure of Carbon Dioxide
Q or a Q with a dot over it (indicates)
- Blood Flow
V (indicates)
- Volume of Gas
V with a dot over it named “V Dot” (indicates)
- Airflow or Volume per unit time
F (indicates)
- Fractional concentration of gas (again you specify what gas you are referring to). There are no units
FO2: Partial Pressure of Oxygen (100% Oxygen = 1.0; 21% = 0.21)
FCO2: Partial pressure of Carbon Dioxide
A (indicates)
- ALVEOLAR Gas
- Conventional use: PAO2
a (indicates)
- ARTERIAL Gas
- Conventional use: PaO2
E (indicates)
- EXPIRED Gas
- Can indicate that the volume in question was measured during Expiration
I (indicates)
- INSPIRED Gas
- FIO2: Fraction of Inspired Oxygen
Muscles of Inspiration
1) The DIAPHRAGM
- Innervated by the PHRENIC NERVE
- When contracting, flattens or moves down in Abdomen
- INCREASES VOLUME of the Thorax as a result
2) EXTERNAL Intercostal Muscles
- Between ribs
- Slope DOWN and FORWARD
- When CONTRACTION, they RAISE the ribs
- INCREASING the ANTEROPOSTERIOR Diameter of the Thorax (BUCKET HANDLE MOTION)
3) There are additional muscles that participate in Inspiration under certain CIRCUMSTANCES (Ex: Exercise)
- SCALENE: Raise 1st and 2nd Ribs
- STERNOMASTOIDS: Raise Sternum
- Some muscles in Head and Neck
What are the Pros and Cons of the Respiratory muscle being Skeletal (and therefore dependent on the Brain for Activation)?
PROS:
- For talking because we can control this since its under Central Control
- RAPID Uniform ACTIVATION
- Respond rapidly to different conditions
CONS:
- Brain or Spinal cord damage can STOP BREATHING
- Length/ Tension Curve: If the lungs get too big, can stretch the Muscle
**The LENGTH TENSION DIAGRAM can start working against me in the Diaphragm during something that causes HYPERINFLATION, which causes the Diaphragm to MVOE TO SHORTER LENGTHS!
Events in Inspiration
STEP 1:
- CONTRACTION of the Inspiratory Muscles
- INCREASE in the THORACIC Volume
- ***Under NORMAL Conditions, the LUNGS and the MUSCLES/ RIBS are NOT PHYSICALLY CONNECTED to one another!!!!!
- Parietal Pleura and Ribs are NOT CONNECTED
- ***In between the VISCERAL and PARIETAL Pleura there is FLUID
- This fluid effectively CONNECTS the two Pleura together!!!
Side Note: The Intrapleural Pressure
- Because of their Anatomy and Physical characteristics, the LUNGS and the CHEST Wall are CONSTANTLY trying to PULL AWAY from Each Other (Even at Rest)
- This results in an INTRAPLEURAL PRESSURE that is BELOW ATMOSPHERIC PRESSURE
**Because these two are pulling away from each other, this means that the Intrapleural Space is NEGATIVE!!!!
Conventions in Respiratory Physiology
- Because the pressure we are dealing with are Relatively Small (and due to some history), the pressures we will all about are measure in CM H2O, not mm Hg!!!
- A 1 cm H2O change in Pressure is almost exactly the same as a 1 mm Hg due to the DENSITY of Hg
- We also NORMALIZE Atmospheric Pressure to 0 cm H2O (so a Pb of 760 mm Hg becomes 0 cm H20 in Respiratory Physiology)
- If you are in a place with a different Barometric Pressure, it is still 0 cm H2O
Side Note: The Intrapleural Pressure
- At REST, the Intrapleural Pressure is generally near -5 cm H2O!!!!!!
Events in Inspiration
- As the Thorax INCREASES Volume, the Intrapleural Pressure will DECREASE (as Volume Increases, Pressure DECREASES) to about -8 cm H2O!!!
Events in Inspiration
- Because of the Coupling of the Lungs and the Chest Wall, the lungs will EXPAND as the Thorax Expands
Events in Inspiration
- As the Lungs INCREASE in SIZE, the ALVEOLAR PRESSURE (Pressure within the Alveoli) DECREASES!!!!
A) At rest, Alveolar Pressure is the same as Atmospheric (0 cm H2O)B) During a NORMAL INSPIRATION, it will go to -1 cm H2OC) Due to the INCREASE in ALVEOLAR SIZE
***Make the ALVEOLAR PRESSURE LOWER than the Atmospheric Pressure and then the Air will flow in
Events in Inspiration
- When the ALVEOLAR PRESSURE drops BELOW the Atmospheric pressure, AIR FLOWS INTO THE LUNGS
The Respiratory Cycle
As Inspiration Proceds:
- Intrapleural Pressure will reach its lowest point at the end of Inspiration (in a normal breath, about -8cm H2O)
- Airflow into the lungs will Decrease as Alveolar Pressure returns back to 0 cm H2O
- The amount of air inhaled in a given breath is known as the TIDAL VOLUME and abbreviated VT. In a typical breath, VT is about 500 mL!!!
1) VOLUME CHANGE (Liters)
- Volume increases from 0 to +0.5 at the END of INSPIRATION
2) ALVEOLAR PRESSURE (cm H2O)
- Starts off at 0 then goes down to -1 half way through Inspiration and then finishes off at 0 at the END of INSPIRATION
3) INTRAPLEURAL PRESSURE (cm H2O)
- Starts off at -5 at the beginning of Inspiration and then proceeds to -8 at the END of INSPIRATION
4) AIR FLOW (L/sec)
- Starts off at 0 and then drops to -1 half way through Inspiration and then off at o at the END of INSPIRATION
The Expiratory Muscles
1) Abdominal Muscles
- Action: to PUSH into the abdomen displace the Diaphragm UPWARDS
2) INTERNAL INTERCOSTALS
- Orientated at (more or less) a RIGHT ANGLE to the External Intercostals
- DECREASES the AP Diameter of the Thorax
3) There are also ACCESSORY Muscles of Expiration
IMPORTANT: In a NORMAL BREATH, we don’t have to use these Muscles. EXPIRATION IS PASSIVE because the Lungs “WANT” to be Smaller (Like a balloon)
**The ELASTIC RECOIL od the lungs will be sufficient so the the expiration muscles will not be needed unless we are exercising
Events in Expiration
- As the Inspiratory Muscles Relax, the VOLUME of the THORAX DECREASES as the Diaphragm and rib cage RETURN to their STARTING POSITIONS
Events in Expiration
- The DECREASING VOLUME causes the Intrapleural Pressure to return to its STARTING POINT (-5)
Events in Expiration
- The Alveolar Pressure also INCREASES due to the Action of the Rib Cage
- It will reach a PEAK of about +1 cm H2O at MID-EXPIRATION