Waters IV Flashcards
For ideal gas exchange, ventilation should be matched to _____.
perfusion
For the whole lung, the ventilation-perfusion ratio is given by:
Va/Q, Where Va= total alveolar ventilation and Q= total pulmonary blood flow (aka cardiac output)
Why is there less ventilation at the apical end of the lung compared to the base?
Intrapleural pressure is more negative, so transmural gradient is larger.. Thus, alveoli are larger and less compliant and less ventilation occurs
Why is there less perfusion at the apical end of the lung compared to the base?
lower intravascular pressures increase resistance
T or F. Blood flow and ventilation decrease moving upward in the lung at the same rate
F. Blood flow decreases faster
Where is the Va/Q ratio highest?
At the apex because perfusion drops faster than ventilation
Would the Va/Q be increased or decreased in a COPD patient?
increased in some regions and decreased in others
What is a normal Va/Q?
0.8
How does the Va/Q change in pulmonary embolus?
drastically increased
What is a shunt?
A situation where there is plenty of perfusion but an airway obstruction (Va/Q is 0)
Where is PaO2 highest in the vertical lung? What is it? What is it at the base?
at the apex - 130 mm Hg
base- 89 mm Hg
Where is Paco2 highest in the vertical lung? What is it? What is it at the base?
the base- 42 mm Hg
the apex- 28 mm Hg
Where in the vertical lung would ventilation be considered “wasted” in relation to perfusion
the apex
What is a pathologic consequence of PaO2 being higher in the apex?
organisms that use O2 as a nutrient source flourish in the apex
The A-a gradient is roughly 100:105 mm Hg for Po2
This can change in disease states
T or F. The A-a gradient of a shunt can be normalized using 100% O2
F.
T or F. The A-a gradient decreases in ventilation-perfusion mismatch
F. It increases (but CAN be normalized with 100% O2)
What happens in acute respiratory distress syndrome?
loss of barrier function causes fluid to leak into the air spaces and air diffusion is worse
How is pulmonary edema fluid cleared by the body?
edema fluid contains Na+ and type I and II pneumocytes move sodium from the alveoli into themselves via ENaC channels on the apical side and use a NaKATPase on the other side to remove it, and then water follows
How is oxygen carried?
- dissolved
- bound to hemoglobin
T or F. Pao2 is a measure of O2 bound to hemoglobin
F. It is DISSOLVED O2
Only 1.5% of all O2 in the blood is dissolved, the rest is bound to hemoglobin
How many molecules of O2 are bound by hemoglobin?
4
What is the O2 content of blood?
amount bound to hemoglobin + amount dissolved
= (O2 binding capacity * %saturation) + dissolved O2
Which of the following does decreased Hb affect:
a) O2 content of blood
b) O2 saturation
c) arterial Po2
only A
What is the eqn. for O2 delivery to tissues?
(Cardiac Output)* O2 content in blood
Where specifically does O2 bind to Hb?
central Fe2+ (ferrous) in each subunit
Iron in the ferric (Fe3+) state does not bind O2. What is this called?
Methemoglobin
T or F. Fetal hemoglobin (HbF) has a higher affinity for O2
T.
Define Co-operativity
the reactions of four the subunits occur sequentially, with each combination facilitating the next binding reaction
Oxygen diffusion is governed only by what?
the dissolved portion in blood
How does the oxygen gradient that exists from the alveoli to blood maintain itself?
Hemoglobin binds it so the dissolved O2 conc. in blood remains low AF (in the capillaries HB dumps O2 and a new gradient is established that promotes diffusion into tissue)
What is %saturation defined as?
O2 bound to Hb/max capacity of Hb to bind O2
What things decrease binding affinity for O2 (shift to right)
Increased temp, 2,3-DPG, and Co2 (aka decreased pH)
Why would increased co2 decrease Hb binding affinity?
both Co2 and H+ can bind to Hb (this is called the Bohr effect)
Why would increased temp decrease binding affinity?
heat changes the structure of Hb
What is the role of 2,3-DPG?
it helps oxygen dissociate from Hb (unregulated in hypoxia conditions)
What factors affect oxygen content of blood?
- CO poisoning
- Anemia
How is Co2 transported?
- dissolved in blood
- can bind to Hb (or any amino group of a protein) (accounts for 10-20% of co2 in blood). Called protein carbamylation
- formation of HCO3- (major form 80-90%)
How is Co2 transported out tissue?
mostly transformed to H2CO3 first by carbonic anhydrase (rate limiting) than to HCO3- (and H+) within RBCs
What is Hamburger;s phenomenon?
When HCO3- enters back into plasma from the cell it is charge compensated by adding a Cl- into the cell which drags H2O causing the cell to swell
The Cl- shift is driven by ____
band 3 protein
What happens to the H+ in the RBCs when HCO3- exits?
it remains and is buffered by deoxyhemoglobin to prevent acidification and is carried in venous blood this way
What is the Bohr effect?
When CO2 is produced by tissues, HCO3-and H+ are produced in the
blood. Due to H+ production, pH becomes lower. The higher H+ concentration
causes increased binding to Hb causing it to bind O2 with less affinity. The
position of the O2 dissociation curve shifts to the right facilitating O2 unloading.
