SM 155a - Ventilation

Question 1

What portions of the airway make up the anatomic dead space?

Answer 1

The space between the nose/mouth and gas exchange surfaces of the alvioli -

The conducting portion fo the ariway

Question 2

What portions of the airway make up the alveolar dead space?

Answer 2

Alveoli that are not adequately perfused; even when ventilated, these alveoli cannot participate in gas exchange

Should be very small or 0 in healthy people

Question 3

What makes up the physiologic dead space?

Answer 3

Anatomic dead space + Alveolar dead space

(In a healthy individual, physiologic dead space is about equal to anatomic dead space)

Question 4

Normally, V_T is about ___* V_D

Answer 4

Normally, V_T is about 3 * V_D​

Question 5

What is the equation for alveolar ventilation (V̇_A)?

Answer 5

V̇_A = f * (V_T - V_D)

f = Breaths per minute

V_T = Tidal volume

V_D = Anatomic dead space

Question 6

What is equation for P_iO2?

Answer 6

P_iO2 = F_iO2 * (P_B - P_H2O)

P_B = P_atm = atmospheric pressure, 760mm Hg at sea level

P_H20= water vapor pressure, 47 mmHg

F_iO2: fraction of oxygen, .21 for room air

Question 7

What is the alveolar gas equation?

Answer 7

Question 8

How is the composition of alveolar air different from ambient air?

Answer 8

• Alveolar air is saturated with water vapor
• Alveolar air contains CO₂ that returns from the circulation

Question 9

What is the equation for minute ventilation (V̇)?

Answer 9

V̇ = V_T * f

V_T = Tidal volume

f = breaths/minute

Question 10

If metabolic rate increases, what respiratory parameter must change to maintain homeostasis?

Answer 10

V̇_A must increase to maintain constant arterial P_CO2

Question 11

What is the equation for RQ?

Answer 11

RQ = V̇_CO2/V̇_O2

Normal RQ = 0.8

Question 12

During expiration, when in P_CO2​ in expired air the highest?

When is it the lowest?

Answer 12

P_CO2 in expired air is close to zero at first, because this is when air in the anatomic dead space is expelled

As soon as air from the alveoli is expelled, P_CO2 increases to the level of P_ACO2 (~40 mmHg)

Question 13

List 4 causes of alveolar dead space

Answer 13

• Hydrostatic failure of alveolar perfusion
  
  • Hypotension
• Pulmonary embolus
• Ventilationof non-vascular air space
  
  • Lung injury
• Obstruction of pulmonary circulation by external forces
  
  • Tumor
  • Vasoconstriction

Question 14

What is the alveolar ventilation equation for CO₂?

Answer 14

V̇_A = RTV̇_CO2/P_ACO2

or

P_ACO2= RTV̇_CO2/V̇_A

RT = 863

V̇_CO2 = The CO2 produced per minute by tissues

Question 15

What is exercise hyperpnea?

What is its physiologic purpose?

Answer 15

Increased ventilation due to moderate intensity physical exercise

Its purpose its ot maintain P_aCO2 by increasing V̇_A