Pulmonary 4 - Lecture 26 Flashcards
What is the combined gas law?
PV/T1 = PV/T2
- Pressure is proportional to temp
- volume is proportional to temp
- volume & pressure are inversely related
What does the sum of the partial pressures & partial volumes of a gas equal?
Equals the total pressure & total volume
What airways do not participate in gas exchange?
O2, N2, and Water vapor in humidified air remains unchanged until gas reaches what?
CONDUCTING AIRWAYS!
Unchanged until it reaches the ALVEOLUS
respiratory zone
What kind of relationship exists between CO2 and ventilation?
As ventilation increases, what happens to CO2 content?
INVERSE
As ventilation increases, CO2 content decreases
What are the regional differences in ventilation? What are the 2 reasons?
The base has higher ventilation than the apex
- Gravitational Effects
- Variable Resistance/Compliance of alveolar units
What is the PO2 equation?
The PAO2 equation?
PIO2 = (Patm - Pwater)x FO2
PAO2 = PIO2 - PACO2 / R
What is a normal PA02?
95-100 cmH20
1.What is the PAO2 if you breathe 100% oxygen and the PACO2 is 45 mmHg (R=0.8)
PIO2 = (760 -47 mmhg) X 1.0
= 713 mmHG
PAO2 = 713 mmHg – 45 mmHg / 0.8 PAO2 = 657 mmHg
- What is the PAO2 if you breath 40% oxygen and the PACO2 is 60 mmHG (R=0.8)
PIO2 = (760 mmHG – 47 mmHg) X 0.4
= 285 mmHg
PAO2 = 285 mmHg – 60 mmHg / 0.8
= 210 mmHg
expect this in the arterial blood
What determines the fraction of Alveolar CO2 (partial pressure)?
2 things
- Metabolism
2. Rate of elimination (ventilation)
If alveolar CO2 is high, is ventilation high or low?
LOW
If you increase ventilation by 2, how does CO2 change?
Decreases by 2
What did radioactive Xenon studies determine about inspired air?
Showed that air is distributed more to the base of the lung
Why does the base of the lung receive the most air?
- 5 lobes form a triangular structure so widest part is at the BASE - anatomically more alveoli
- at FRC the base of the lung is MORE COMPLIANT than apex
Because the Pleural Pressure & Translung pressure is greater at the APEX in an upright position, why is there still LESS air into the apex?
The Alveoli units at the apex are LESS COMPLIANT
-AT the top:
the alveoli are already slightly open since they are in a more negative pleural pressure, but because they are LOWER in compliance
they receive LESS VOLUME of the ventilation as compared to the base of the lung
When are the Base Alveoli completely collapsed and thus the units of airflow at the APEX are higher than those at the base?
LOW VOLUMES
The time constant is determined by what? What does a longer time constant represent?
T = R * C
Resistance & Compliance
Longer Time constant = slow emptying/filling
What are normal inspiratory & expiratory times?
Normal inspiratory time: 2 s
Normal expiratory time: 3s
If Resistance increases how does the Time Constant change?
If compliance decreases?
- SLOWER FILLING, incomplete filling at 2 s
- Incomplete filling in 2s
- fills FASTER but incompletely filled (since it is stiffer) so a smaller portion ventilated
If you decrease compliance and keep resistance constant, what happens to the time constant/ filling and ventilation?
FILLS FASTER! BUT INCOMPLETELY filled so a smaller proportion of the ventilation!!!
- affects whether the lung is evenly ventilated
What does the single nitrogen test show?
State the 4 events
At uniform ventilation, N2 and lung volume is constant
- N2 fixed at zero as dead spaces full of O2 empty
- Rapid Upswing in N2 as alveolar regions in the BASE OF THE LUNG empty
- Aveolar Plateau - equal emptying of all lung zones from base to apex
- 2nd increase in N2 due to slow emptying alveoli!!!
What is the equation for ventilation?
Ventilation = Frequency * Tidal Volume
The tidal volume first fills what space?
Dead space filled first (VD) then the alveolar space (VA)
Vtotal = f * (VD + VA) = f * VT
What is the first air to reach the deep alveoli during inspiration?
Dirty air from previous exhalation
What ventilation does not contribute to gas exchange?
Dead space ventilation
D= f*VD
What is the alveolar ventilation equation?
VA = f*VA
OR
VA = f * (Vt - VD)
What does the single breath Nitrogen washout determine?
Anatomical Dead Space
“Fowler’s Method”
What measures Anatomic Dead Space? Physiological dead space?
- Anatomic = Fowler’s Nitrogen Washout
2. Bohr’s method
What is physiological dead space?
Total volume that does not participate in gas exchange =
Anatomical Dead Space + ventilated Alveoli that are not perfused (ex: lung emboli –> vessels are obstructed and alveolar regions not perfused)
When do physiologically dead spaces become larger than anatomical dead spaces? Are these usually equal?
DISEASES
- usually equal
What is the normal ratio of VD/Vt?
0.2 - 0.35
What does the expired fraction of CO2 X the exhaled tidal volume equal?
Vt * Fe = (Vt - VD) * FA
VD/Vt = PaCO2 - PCO2 / PaCO2
PaCO2 = arterial CO2 FA = alveolar CO2 fraction Fe = expired fraction of CO2
What are the two components of tidal volume?
- Dead space
2. Alveolar Ventilation
How does one increase alveolar ventilation?
1. Increase Frequency of breathing
OR
2. Increase Tidal Volume
Increasing Tidal Volume is more effective than an increase in the frequency of breathing
