week 11

Question 1

CaO2 vs CvO2?

Answer 1

CaO2: how much O2 is in arterial blood
CvO2: how much O2 is in venous blood

Question 2

how do we increase VO2 during exercise

Answer 2

to increase VO2 during exercise you need to increase the a-VO2 difference
- could increase CaO2
- could decrease CvO2
- could do both

Question 3

what are legit ways to describe how much O2 is in arterial blood?

Answer 3

1. CaO2
2. PaO
3. SaO2

Question 4

How much O2 is in arterial blood?

Answer 4

there is a small amount of O2 dissolved in the plasma
- 0.0031 mL O2 for every 1 mmHg of PO2
- oxygen content depends on PaO2

most O2 is bound to Hb
- every gram of Hb binds 1.36 mL of O2 when fully saturated with O2
- oxygen content depends on [Hb] and %SaO2

Question 5

define CaO2, PaO2, and SaO2

Answer 5

CaO2: arterial O2 content - TOTAL amount of O2 in blood (mL O2/dL blood)

PaO2: arterial partial pressure of O2 - reflects amount of O2 DISSOLVED in blood (mmHg)

SaO2: arterial O2 saturation - percentage of Hb binding sites that are saturated with O2 (%)

Question 6

how do we calculate arterial O2 content and venous O2 content?

Answer 6

CaO2 = (PaO2 x 0.0031 mL O2/mmHg/dL) + ([Hb] (in g/dL) x 1.36 mL O2/g x SaO2 (in %)/100)

CvO2 = (PvO2 x 0.0031 mL O2/mmHg/dL) + ([Hb] (in g/dL) x 1.36 mL O2/g x SvO2 (in %)/100)

Question 7

how much O2 is in venous blood?

Answer 7

small amount of blood is dissolved in plasma
- 0.0031 mL O2 of every 1 mmHg PO2
- oxygen content depends on PvO2

most O2 in blood is bound to Hb
- every gram of Hb binds 1.36 mL O2 when fully saturated with O2
- oxygen content depends on [Hb} and %SvO2

Question 8

what does the oxygen cascade describe?

Answer 8

the flow of O2 through the body

air -> alveoli -> arteries -> tissue

Question 9

quick outline of the 4 steps that gas goes through when entering bod

Answer 9

1. ventilation - VA is what matters
2. gas exchange - diffusion
3. gas transport - carried in blood pumped by heart
4. gas exchange - diffusion

Question 10

how does O2 enter the blood?

Answer 10

via diffusion

diffusion happens down a gradient (high to low pressure)

Question 11

what is diffusion rate affected by?

Answer 11

• pressure gradient - high pressure = faster
• diffusion area = more area = faster
• membrane thickness - less thick = faster

DIFFUSION TAKES TIME

Question 12

what is O2 diffusion into tissue driven by

Answer 12

it is driven by the gradient between PaO2 and PtO2

Question 13

what is O2 diffusion into blood driven by?

Answer 13

the gradient between PAO2 and PvO2

Question 14

why is Palveolar lower than PIO2?

Answer 14

because of the dilution by CO2 and water vapour

Question 15

what factors influence CaO2?

Answer 15

PaO2 - partial pressure of O2 in arterial blood
- reflects diffusion from alveoli
depends on:
- pressure gradient (PA-VO2)
- PA depends on VA
- diffusion area
- membrane thickness
- time

[Hb] - concentration of a blood protein that combines reversibly with O2
- oxyhemoglobin (HbO2)
- deoxyhemoglobin (HHb)
depends on: genetics, nutrition, and health status

%SaO2 - percentage of possible Hb binding sites that are carrying O2
depends on:
- PaO2
- temp, pH, CO2

Question 16

what is the primary determinant of SaO2

Answer 16

PaO2

Question 17

what is exercise-induced arterial hypoxemia (EIAH)

Answer 17

a drop in arterial O2 levels as a result of exercise

EIAH happens at very high exercise intensities in ~50% of highly-trained males - the body is so well trained that it exceeds the respiratory system’s capacity to supply O2

EIAH happens in ~67% of all females (not just highly-trained ones)

in females, EIAH happens at moderate intensities (not just near-maximal efforts)

Question 18

what does hyperpnea do in moderate/heavy exercise

Answer 18

hyperpnea in moderate/heavy exercise keeps PAO2 constant at resting levels

Question 19

what is the hyper-ventilatory response at max exercise?

Answer 19

• increases PAO2
• widens alveolar to arterial O2 gradient
• facilitates diffusion
  this is critical since blood is flowing very quickly past the alveoli

the result is no change in PaO2 (and therefore SaO2) during exercise - except in ppl with EIAH

Question 20

what factors influence CvO2?

Answer 20

PvO2 - partial pressure of O2 in venous blood
- reflects how much O2 has been extracted from arterial blood by tissues
- reflects diffusion from blood
- depends on:
- diffusion area
- membrane thickness
- time
- pressure gradient (Pa-tO2)
- Pt depends on tissue oxygen consumption

[Hb] - concentration of a blood protein that combines reversibly with O2
- arterial [Hb] = venous [Hb]
- not really influenced by acute exercise

%SvO2 - percentage of possible Hb binding sites that are carrying O2
- depends on:
- PvO2
- temp, pH, CO2

Question 21

how low can we get PvO2 during exercise? How much O2 can we EXTRACT from arterial blood?

Answer 21

as VO2 in exercise goes up, tissue PO2 goes down

at max exercise, blood leaving the capillary bed of working muscles will have PO2 of ~2-5 mmHg

BUT blood returning to heart is mixed venous blood which means it is a mixture of blood returning from ALL capillary beds

makes diffusion at the lung faster

Question 22

what happens when we widen the arterial to tissue PO2 gradient?

Answer 22

• big decrease in PvO2
• big increase in a-vO2 diff

Question 23

what causes the oxyhemoglobin saturation curve to get right shifted?

Answer 23

increased temp
increased CO2
decreased pH

bigger environmental change = bigger effect on the relationship between %SO2 and PO2

Question 24

what does it mean to have a right shifted curve:

for a given PO2, SO2 will be ___

it takes a ___ PO2 to achieve the same SO2

Hb has a ___ affinity for O2

It is ___ for Hb to load O2 at the lungs

it is ___ for Hb to unload O2 at the tissues

Answer 24

lower
higher
lower
about the same
easier

Question 25

what changes in the body during exercise?

Answer 25

increase in temp
increase in PvCO2
decrease in pH

• very little effect on SaO2 and CaO2
• big decrease in SvO2 and therefore PvO2 and CvO2
• big increase in a-vO2 diff
• these lead to a right-shifted oxyhemoglobin curve

there is no meaningful change in PaO2, SaO2, or CaO2 during exercise