week 11 Flashcards
CaO2 vs CvO2?
CaO2: how much O2 is in arterial blood
CvO2: how much O2 is in venous blood
how do we increase VO2 during exercise
to increase VO2 during exercise you need to increase the a-VO2 difference
- could increase CaO2
- could decrease CvO2
- could do both
what are legit ways to describe how much O2 is in arterial blood?
- CaO2
- PaO
- SaO2
How much O2 is in arterial blood?
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
define CaO2, PaO2, and SaO2
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 (%)
how do we calculate arterial O2 content and venous O2 content?
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)
how much O2 is in venous blood?
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
what does the oxygen cascade describe?
the flow of O2 through the body
air -> alveoli -> arteries -> tissue
quick outline of the 4 steps that gas goes through when entering bod
- ventilation - VA is what matters
- gas exchange - diffusion
- gas transport - carried in blood pumped by heart
- gas exchange - diffusion
how does O2 enter the blood?
via diffusion
diffusion happens down a gradient (high to low pressure)
what is diffusion rate affected by?
- pressure gradient - high pressure = faster
- diffusion area = more area = faster
- membrane thickness - less thick = faster
DIFFUSION TAKES TIME
what is O2 diffusion into tissue driven by
it is driven by the gradient between PaO2 and PtO2
what is O2 diffusion into blood driven by?
the gradient between PAO2 and PvO2
why is Palveolar lower than PIO2?
because of the dilution by CO2 and water vapour
what factors influence CaO2?
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
what is the primary determinant of SaO2
PaO2
what is exercise-induced arterial hypoxemia (EIAH)
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)
what does hyperpnea do in moderate/heavy exercise
hyperpnea in moderate/heavy exercise keeps PAO2 constant at resting levels
what is the hyper-ventilatory response at max exercise?
- 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
what factors influence CvO2?
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
how low can we get PvO2 during exercise? How much O2 can we EXTRACT from arterial blood?
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
what happens when we widen the arterial to tissue PO2 gradient?
- big decrease in PvO2
- big increase in a-vO2 diff
what causes the oxyhemoglobin saturation curve to get right shifted?
increased temp
increased CO2
decreased pH
bigger environmental change = bigger effect on the relationship between %SO2 and PO2
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
lower
higher
lower
about the same
easier
what changes in the body during exercise?
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
