B4.051 Acid Base Balance and Regulation of Ventilation

Question 1

how is minute ventilation calculated

Answer 1

tidal volume * resp rate

Question 2

if minute ventilation is constant, will arterial blood gases also remain the same?

Answer 2

yes

Question 3

what does minute ventilation include?

Answer 3

air going into alveoli and air going into dead space

Question 4

what is the equation for alveolar ventilation?

Answer 4

(tidal volume - dead space) * resp rate

Question 5

how can dead space be estimated?

Answer 5

1/3 of NORMAL tidal volume

Question 6

can alveolar ventilation change if minute ventilation remains constant?

Answer 6

yes
if a person reduced tidal volume and increases resp rate, alveolar ventilation can still decrease due to the constant dead space

Question 7

what is a decrease in alveolar ventilation synonymous with

Answer 7

hypoventilation

Question 8

why does hypoxia cause constriction of pulm arteries

Answer 8

tries to shift blood flow from poorly ventilated areas to well ventilated areas of the lung
important mechanism for V/Q mismatching

Question 9

what happens if there is hypoxia throughout the lungs (high altitude, pulm edema)

Answer 9

generalized pulmonary arteriolar constriction
increases pulm vascular resistance and elevates pulm artery pressure
chronic increase in afterload to RV will result in RVH

Question 10

how does going to high altitude impact chemoreceptors?

Answer 10

decreased PaO2 increases firing of peripheral chemoreceptors
alveolar ventilation increases
increase in ventilation decreases PaCO2, which will decrease H+ levels in blood
these changes will decrease firing of central chemoreceptors

Question 11

how can you estimate PaO2 from alveolar ventilation?

Answer 11

arterial gas equation

PAO2 = PIO2 - (PaCO2 * 1.2)

Question 12

what is a persons acid base status after being at high altitude for a short time?

Answer 12

non compensated respiratory alkalosis

Question 13

what would cause a decrease in PaO2 and PaCO2 after prolonged period at altitude?

Answer 13

high altitude pulmonary edema

Question 14

what is high altitude pulmonary edema?

Answer 14

1. heterogeneous constriction of pulm arterioles

2. increased vascular permeability

Question 15

what is the mechanism behind HAPE?

Answer 15

constriction of pulmonary arterioles in response to hypoxia will increase pressure in the pulm artery
if some arterioles do not constrict, cap pressure will be increased downstream of these arterioles
this increases filtration and causes pulmonary edema

Question 16

discuss differences in alveolar ventilation on day 1 at altitude vs day 10

Answer 16

2 opposing influences: low PaO2 attempting to increase vent, low H+ and low CO2 attempting to increase it
day 1: low PaO2 stimulated chemoreceptor firing and large decrease in H+ opposed chemoreceptor firing, small increase in ventilation
day 10: H+ closer to normal due to metabolic compensation, less opposition to increased chemoreceptor firing, alveolar vent increases even higher than day 1

Question 17

after 28 weeks at altitude how can body compensate for low PIO2 levels?

Answer 17

increased RBC production due to EPO release from kidneys

increased hematocrit increased O2 content despite low PO2

Question 18

are there negative consequences to EPO compensations?

Answer 18

increased blood viscosity
can contribute to increased pulm vascular resistance (already elevated due to constriction bc of hypoxemia)
RVH can occur over months