Breathing Mechanics & Gas Exchange

Question 1

Boyles Law

Answer 1

At a constant temp,

P & V are inversely related.

Question 2

Transpulmonary pressure

Answer 2

Alveolar Pressure - Intrapleural Pressure.

At rest (end-insp & end-exp) alveolar pressure is ~ 1ATM (relative 0). End expiration intrapleural pressure is -5 and gets more negative with inspiration (as volume decreases). Transpulmonary pressure is never negative because you are subtracting from 0.

Question 3

Compliance

Answer 3

the change in volume divided by the change in pressure. relates to the elastic recoil of the lungs. Normal is ~ 200ml/cm H2O. At very high or very low lung volumes compliance is reduced.

Question 4

Static Compliance

Answer 4

Tidal volume / (plateau pressure -PIP) : describes the pressure volume relationship when air is not moving.

Question 5

Dynamic Compliance

Answer 5

tidal volume / (PIP-PEEP) : describes the p/V relationship when air is moving.

Question 6

Daltons Law of Partial Pressure

Answer 6

The sum of a gas mixture is the result of each individual gas independently exerting its partial pressure. Is directly proportional to its concentration.

Question 7

Vapor Pressure

Answer 7

The maximum pressure by a gas that can also exist as a liquid under standard conditions
• If sevo is 157 mmHg then the max it can be under standard conditions is (157/760mmHg) = 21%
Dependent on temperature and the specific agent - increase temp = increase vapor pressure
•

Question 8

Volatile Liquids

Answer 8

have a high vapor pressure at room temp. they go freely from liquid to gas.

Question 9

Vapor Pressure of:
Isoflurane
Sevoflurane
Desflurance

Answer 9

238mmHg
160mmHg
660mmHg

Question 10

Henrys Law

Answer 10

the number of dissolved molecules of a gas is proportional to its partial pressure. it is indicative of solubility.
Gas Conc = a x partial pressure, where a is the gas solubility coefficient(ex: O2s is 0.003ml/dL/mmHg)

Question 11

Formula for concentration of dissolved O2 in blood:

Answer 11

CdO2=aO2 x PO2

aO2: solubility, PO2: arterial O2

Question 12

Oxygens Solubility in Blood

Answer 12

0.003ml of O2/dL/mmHg

Question 13

Arterial Oxygen Content Formula:

Answer 13

CaO2=SaO2 (hgb x 1.36) + 0.003 x PaO2

CaO2: arterial oxygen content
Hbg: hemoglobin level
1.36: the capacity of hemoglobin for oxygen
0.003: the solubility of oxygen per dL of blood
SaO2: arterial oxyhemoglobin saturation
PaO2: partial pressure of Oxygen in arterial blood

Question 14

Oxyhemoglobin Dissociation Curve

Answer 14

Right Shift: O2 has a decreased affinity for hgb, more is released to the tissues.
- exercise, acidosis, increased temp, increased CO2

Left Shift: O2 has an increased affinity for hgb, less is released to tissues

Question 15

Formula for the Partial Pressure of Alveolar Oxygen

Answer 15

account for water vapor from humidifying and for the mixing of gases in the airway (expelled CO2)

PAO2= FiO2 x (Pb-PH2O) - (PaCO2/RQ)

RQ: 0.8 - the ratio of CO2 production to oxygen consumption

Question 16

A-a Gradient

Answer 16

the difference between alveolar and arterial oxygen content. normal is 5-10mmHg, increasing 1mmHg with each decade

Question 17

Carbon Dioxide

Answer 17

produced by tissues, removed by lungs. production ~ 250ml/min. carried in blood as dissolved gas, bicarbonate, and a small amount bound to hgb. PaCO2 of 200 mmHg = 1MAC. PaCO2 > 80mmHg can delay wakening from anesthesia.