Resp Cycle & Lung Volumes

Question 1

Residual Volume (RV)

Answer 1

Volume of air that cannot be forced out, no matter how hard you try

Question 2

Tidal Volume (VT)

Answer 2

Amount of air inspired/expired in a single breath. Varies under circumstances, normal resting is 500mL

Question 3

Inspiratory Reserve Volume (IRV)

Answer 3

Volume of air you breathe above tidal volume (VT)

Question 4

Expiratory Reserve Volume (ERV)

Answer 4

Volume of air that can be forced out, in addition to VT. Does not include residual volume. Requires activation of expiratory muscles.

Question 5

Vital Capacity (VC)

Answer 5

The amount of air that can be maximally inspired following maximal expiration.

VC = IRV + VT + ERV

VC can be influenced by posture, ability of diaphragm to contract/expand, strength of respiratory muscles, lung elasticity, etc.

Question 6

Inspiratory Capacity (IC)

Answer 6

Capacity of air that can be maximally inspired following a NORMAL exhale.

IC = VT + IRV

Question 7

Functional Residual Capacity (FRC)

Answer 7

Amount of air that remains in the lungs following a normal exhalation.

FRC = ERV + RV

Helps prevent lung collapse, reduces workload, dilutes toxic inhaled gases

Question 8

Total Lung Capacity (TLC)

Answer 8

Maximal volume to which lungs can be expanded with greatest effort.

TLC = IC + FRC = VC + RV = IRV + VT + ERV + RV

Question 9

What does a low Forced Vital Capacity (FVC) value indicate?

Answer 9

Indicates a restrictive pattern

Question 10

Forced Expiratory Reserve Volume (FEV)

Answer 10

The amount of air exhaled during the first second of the FVC maneuver via spirometry (tends to be lower in diseases that obstruct the airway, such as asthma)

Question 11

What does a low FEV/FVC ratio indicate?

Answer 11

Indicates an obstructive pattern, whereas a normal value indicates a normal pattern

Question 12

What does pseudorestriction due to air trapping look like on a graph compared to normal TLC?

Answer 12

TLC overall is increased, with a larger RV and a smaller FVC. The smaller FVC is due to air trapping resulting in an increased residual volume

Question 13

What are 4 extra-parenchymal causes of restriction?

Answer 13

Obesity, neuromuscular disease, chest wall deformities, large pleural effusions

Question 14

What do anemia, pulmonary arterial hypertension and chronic thomboemboic disease have in common?

Answer 14

They can all potentially reduce the diffusing capacity in the lungs, leading to progressive dyspnea, even though FVC and TLC are normal

Question 15

Minute ventilation equation

Answer 15

V(dot) = Vt x freq (respiratory rate)

Question 16

Alveolar ventilation equation

Answer 16

Valv = Vt - Vds (dead space)

Question 17

Minute alveolar ventilation equation

Answer 17

V(dot)A = Valv x freq

Question 18

Airway resistance equation

Answer 18

R = 8nL / r^4

n = viscosity
L = tube length
r = radius

Question 19

Alveolar diffusion rate equation

Answer 19

J = (SA) x (D) x (P1-P2) / d

J = diffusion rate
SA = surface area
D = diffusion coefficient
P1-P2 = pressure gradient across alveolar membrane
d = diffusion distance (thickness of barrier)

Question 20

What are the normal J values for O2 and CO2?

Answer 20

J (O2) = 250 mL/min

J (CO2) = 200 mL/min

Question 21

What are normal PAO2 and PACO2 levels?

Answer 21

PAO2 = 100 mmHg
PACO2 = 40 mmHg

Question 22

What are normal PvO2 and PvCO2 levels?

Answer 22

PvO2 = 40 mmHg
PvCO2 = 45 mmHg

Question 23

What are normal PaO2 and PaCO2 levels?

Answer 23

PaO2 = 60 mmHg
PaCO2 = -5 mmHg

Question 24

What is the diffusion capacity of the lung for O2?

Answer 24

DlO2 = 21 mL O2/min/mmHg

Question 25

What is the diffusion capacity of carbon monoxide?

Answer 25

DlO2 = 1.23 x DlCO

Question 26

What is LaPlace’s Law?

Answer 26

Pressure = 2T / r

T = tension
r = radius

Question 27

Respiratory quotient equation

Answer 27

RQ = V(dot) CO2 / V (dot) O2

Question 28

Alveolar gas equation

Answer 28

PAO2 = PiO2 - V(dot)O2
= PiO2 - PaCO2 / RQ
= O2 inspired - O2 consumed

Question 29

Oxygen inspired equation

Answer 29

PiO2 = [P(atm) - P(h2o)] FiO2

P(atm) = 760 mmHg
P(h20) = 47 mmHg
FiO2 = 21%

Question 30

Oxygen consumed equation

Answer 30

V(dot)O2 = PaCO2 / RQ

RQ will either be 0.8 (mixed fuel), 1 (glucose), 0.7 (fatty acids-hypoglycemia, diabetic starvation, etc)