Respiratory Physiology

Front 1

What is the thickness and the surface area of the blood gas barrier?

Back 1

~.3 uM thick with 50-100 square meters of surface area.

Front 2

What happens if pressure rises to unphysiological levels?

Back 2

Capillaries can rupture.

Front 3

What is the barometric pressure at sea level? At high altitudes? Below sea level?

Back 3

At sea level the barometric pressure is 760 mm Hg. At high altitudes the barometric pressure decreases and when going under sea level the pressure increases 760 mm Hg every 33 feet.

Front 4

How do you calculate partial pressure? What is the PO2 in room air?

Back 4

Partial pressure = barometric pressure x fractional concentration
PO2 = .21 x 760 = 160 mm Hg

Front 5

What is a normal PaO2 and normal PaCO2? What are they measuring with an ABG?

Back 5

PaO2 = 100 mm Hg and PaCO2 = 40 mm Hg. These are measuring the amount of oxygen and CO2 dissolved in blood (not Hb bound!)

Front 6

How do you calculate the oxygen content in the blood?

Back 6

Oxygen content = Hb bound O2 + dissolved O2 = [Hb (g/dl) x 1.4 mL O2/g x O2 sat] + [.003 mL O2/dl x PaO2]

Front 7

What is the normal oxygen content? Normal amount Hb bound and dissolved?

Back 7

Normal oxygen content is 20.3 mL O2/dl. Hb bound is 20 mL O2/dl and dissolved is .3 mL O2/dl.

Front 8

What is the difference between the O2 and CO2 dissociation curve?

Back 8

The O2 curve flattens out but the CO2 curve doesn't - it is much steeper and linear.

Front 9

At what pressure does the O2 dissociation curve fall?

Back 9

When PaO2 drops below 60 mm Hg the Hb bound O2 drops.

Front 10

Why is it that the y-axis numbers on an O2 dissociation curve can only be used in normal condition?

Back 10

Because they rely on the fact that Hb= 15 g/dl - anything more or less than that you must change the y-axis numbers.

Front 11

What are the ways that O2 and CO2 are carried in the blood?

Back 11

O2 is carried on Hb and dissolved in blood (PaO2). CO2 is carried mostly as HCO3 but also bound to Hb and dissolved (PaCO2).

Front 12

How do you calculate oxygen delivery?

Back 12

DO2 = CO x O2 content (x 10)

Front 13

Which has a higher O2 content and which has a higher CO2 content - mixed venous or arterial blood?

Back 13

Mixed venous blood has a higher CO2 content and a lower O2 content than arterial blood.

Front 14

What is a normal PvO2 and Venous O2 saturation? How does this compare to arterial blood?

Back 14

PvO2 = 40 mm Hg (compared with 100 mm Hg PaO2) and venous saturation is 70% (compared with ~95% in arterial blood)

Front 15

How do you calculate R? What is a normal value and what does this value imply?

Back 15

R = VCO2/VO2. A normal value is 0.8 (or about 1). This implies that the amount of CO2 made is the same amount as O2 consumed.

Front 16

What is the definition of anemia? What values are changed?

Back 16

Anemia is a reduced Hb content (and therefore Hb bound O2 content) in both arterial and mixed venous blood. There is a normal PaO2 but a reduced PvO2. There is a normal arterial O2 saturation and a reduced venous O2 saturation. Make sure you change the values on the O2 dissociation curve to reflect the reduced Hb value.

Front 17

Why is there a reduced PvO2 and venous O2 saturation in anemic patients but the PaO2 and arterial O2 saturation is normal?

Back 17

The mixed venous values reflect O2 delivery.

Front 18

How can you measure O2 saturation in a patient with CO toxicity?

Back 18

Finger pulse ox does not work because it cannot distinguish between OxyHb and CO bound Hb. O2 dissociation curve cannot be used because the relationship between PaO2 and O2 saturation is invalid. You must use mass spec.

Front 19

What values are normal and what changes in a patient with CO toxicity?

Back 19

Decreased O2 content and O2 saturation but with normal PaO2.

Front 20

How do you treat a patient with CO toxicity and how does it work?

Back 20

Give 100% oxygen which increases fractional concentration to compete with CO. Hyperbaric chamber increases the barometric pressure. Remember that partial pressure = barometric pressure x fractional concentration. Therefore these treatments increase the partial pressure of O2.

Front 21

How do you shift the O2 dissociation curve to the left and to the right? What does this mean?

Back 21

Shifting the curve to the left means there is an increase in Hb affinity for O2. This can be done by increasing pH (alkalosis) and CO binding to Hb. A right shift means that Hb has less affinity for O2. This can be done by increasing temp, decreasing pH (acidosis), increasing PCO2 or increasing DPG.

Front 22

What are the similarities and differences between emphysema and pulmonary fibrosis?

Back 22

Emphysema is the destruction of ECM and alveoli. Pulmonary fibrosis is ECM deposition in the lung. Both cause impaired gas exchange, dyspnea.

Front 23

What are the differences between inhaled air and exhaled air?

Back 23

Inhaled air has lots of O2 but no CO2. Exhaled air has CO2 and less O2.

Front 24

What is the dead space? What is a normal value?

Back 24

Dead space is area in the lungs in which there is no gas exchange. To get total physiologic dead space you must add the anatomic dead space (trachea and bronchi) and any lung disease dead space (if applicable). A normal value is 30% (150/500 mL)

Front 25

What is a normal value for tidal volume? How do you calculate it?

Back 25

A normal value for tidal volume is 500 mL. It can be calculated by adding alveolar ventilation volume and dead space volume.

Front 26

What is the minute ventilation? How do you calculate it?

Back 26

Minute ventilation is the total amount of air moving in and out of the chest per minute. This can be calculated by multiplying the tidal volume by the respiratory rate.

Front 27

What happens when there is decreased alveolar ventilation?

Back 27

The PAO2 drops leading to hypoxemia (low PaO2).

Front 28

VCO2 =
PaCO2 =
PACO2 =

Back 28

VCO2 = VA x FACO2 = alveolar ventilation volume x alveolar fractional concentration of CO2.
PaCO2 = K(VCO2/VA) = FACO2 x Pb.

Front 29

Does PACO2 = PaCO2? Does PAO2 = PaO2?
Why?

Back 29

PACO2 does equal PaCO2. But PAO2 does not equal PaO2. This is because the CO2 dissociation curve is linear which means it is less likely to be diffusion limited compared to the O2 curve which flattens out and can be diffusion limited.

Front 30

What happens if you double alveolar ventilation?

Back 30

When you double the alveolar ventilation, half the PaCO2.

Front 31

What is hypercapnea? What is the normal value? What does this lead to?

Back 31

Hypercapnea is a PaCO2 > 40 mm Hg. This leads to acidemia, unconsciousness, and respiratory arrest.

Front 32

How do you measure the dead space fraction?

Back 32

Vd/Vt = (PaCO2 - PECO2)/PaCO2

Front 33

What is FECO2?

Back 33

The mixed expired CO2 - the fractional concentration of CO2 in the entire tidal volume breath.

Front 34

Which part of the lung gets more perfusion and ventilation? Why?

Back 34

The base of the lung - because of gravity. If you were standing on your head, this would be reversed.

Front 35

What is a normal Pulmonary circulation pressure? Wedge Pressure?

Back 35

20-25 mm Hg/ 10
6-12 mm Hg

Front 36

How do you calculate PVR? What is normal?

Back 36

PVR = (PPa - PLa)/CO ~ 2 mm Hg
PPa = 25, PLa = wedge pressure 12

Front 37

Why is there a low pressure circulation in the lungs?

Back 37

Less work fo rthe heart, protects capillaries from rupturing, low starling forces prevent edema, redundancy in underused/unused vessels.

Front 38

Are the lung capillaries compliant? What happens when you increase BP?

Back 38

Yes, the lung capillaries are compliant. If you increase the BP, decrease PVR - capillaries can change diameter and resistance.

Front 39

When you inhale what happens to the alveolar and extra-alveolar capillaries?

Back 39

Inhaling compresses the alveolar capillaries (increased PVR) and stretches the extra-alveolar capillaries (decreased PVR). There is an overall increase in PVR.

Front 40

Describe the lung zones and where they are in a normal lung and on a ventilator?

Back 40

Zone 1: collapsed when Palv>PPc. There is no blood flow or gas exchange.
Zone 2: Palv ~ PPc. Indeterminate flow determined by upstream flow.
Zone 3: Distended Palv>Ppc - high blood flow
In the normal lung in the top 1/3 is zone 2 and bottom 2/3 is zone 3.
On a ventilator top 1/3 is zone 1, middle 1/3 is zone 2, and bottom 1/3 is zone 3.

Front 41

Why does a ventilator create zone 1?

Back 41

Normally the lungs create a negative pressure to fill the lungs with air. The ventilator creates a positive pressure which increases the alveolar pressure therefore compressing the capillaries.

Front 42

What is recruitment in the lung?

Back 42

Increased CO and BP (like during exercise) can increase the number of high flow capillaries and decrease the PVR. This increases the surface area for gas exchange.

Front 43

How does Fick's law of diffusion apply to the lung?

Back 43

The flow rate of a gas is directly proportional to the surface area, diffusion constant (D = solubility/sqrt MW), and difference between P1 and P2. This is inversely proportional to the thickness of the barrier.

Front 44

Are these gases diffusion limited or perfusion limited? Why?
Nitrous oxide, carbon monoxide, oxygen.

Back 44

Nitrous oxide is perfusion limited because it only dissolved in plasma so the amount taken up depends on blood flow. P2 (arterial) rises rapidly to equilibrate with P1 (alveolar.
Carbon monoxide is diffusion limited because the P2 (arterial) doesn't rise much because it binds to Hb so fast after dissolving in the blood. P2 will never equal P1.
Oxygen is normally perfusion limited but can be diffusion limited in patients with lung disease.
In the normal lung, it takes 0.25 seconds for the P2 (arterial) to equilibrate with P1 (alveolar). In lung disease, P2 may or may not reach P1 depending on severity.

Front 45

Explain dyspnea on exertion

Back 45

In the normal lung, the RBC spends 0.75 s in the capillary. It takes 0.25 seconds for PaO2 to equal PAO2 - this is perfusion limited. In a patient with lung disease, it may take longer for P1 and P2 to equilibrate. During exercise the RBC may only spend 0.25 sec in the capillary which in a patient with diffusion limitation may not be enough for PaO2 to equal PAO2.

Front 46

What happens to DLCO in a patient with pulmonary fibrosis? Anemia? Why?

Back 46

DLCO would decrease in both patients. For patient with pulmonary fibrosis, the blood gas barrier has thickened. For the patient with anemia, decreased Hb increases the resistance to diffusion and decreases the conductance.

Front 47

What factors affect diffusing capacity of the lung?

Back 47

Diffusion process (Dm) and the time needed for O2 or Co to reach Hb (blood). 50% contribution for each.

Front 48

What happens to DLCO if you increase the partial pressure of O2 in the air? (Put patient on 100% O2)

Back 48

The increase in partial pressure of O2 will decrease the DLCO.

Front 49

What causes hypoxemia?

Back 49

Low PaO2 is caused by hypoventilation, diffusion limitation, shunt, and ventilation perfusion inequality.

Front 50

When can a normal lung have diffusion impairment?

Back 50

At high altitudes.