Lecture 25 - Gas Transport Flashcards
What is the waterfall theory? Relation to CO2?
PO2 decreases at each 4 steps of respiration from the air to the mitochondria in peripheral tissues:
- From room air to trachea, PO2 drops as we warm and humidify the air with water vapor (160 to 150 mmHg)
- In the alveoli, PO2 droops again as we make room for the CO2 and O2 diffuses (160 to 100 mmHg)
- PO2 drops in systemic arterial blood due to anatomical circulatory shunts (100 to 90-95 mmHg)
- PO2 drops from artery to mean capillary PO2 and from interstium to cytoplasm and from cytoplasm to mitochondria
Complete opposite for CO2
What is Henry’s Law?
Amount of gas dissolved in water is directly proportional to its partial pressure in the gas phase
PCO2 in air?
0.3 mmHg
Concentration of dissolved O2 in blood with per 1 mmHg of PaO2? Therefore, what is the concentration of dissolve O2 in blood if PaO2 = 100 mmHg?
0.003 mL O2 per 100 mL blood
Normal arterial blood at PaO2 of 100 mmHg contains 0.3 mL/O2/100 mL of blood
Volume of O2 dissolved in blood per minute?
Dissolved O2 x CO = 0.3 mL/O2/100 mL x 5,000 mL/min = 15 mL O2/min
Volume of O2 binding for every gram of Hb?
1.34 mL
Volume of O2 binding to Hb per minute?
1 L/min
Tissue requirements of O2 in extreme situations?
300 mL O2/min
Ideal amount of Hb in healthy person?
15 g/dL
Ideal amount of O2 bound to Hb in a healthy person?
15 g/dL x 1.34 mL O2/g = 20 mL O2/dL of blood
Ideal amount of O2 delivered to tissues via Hb per minute?
5,000 mL/min x 20 mL O2/dL of blood bound to Hb = 1 L/min O2 delivered/min
2 ways of delivering O2 to tissues? Which one is most important?
- Dissolved O2 in blood
2. Via Hb***
How does Hb affect blood viscosity?
More Hb = more viscous
How does an increase in Hb content of the blood affect the heart? What does this mean?
Increased viscosity = increase work of the heart to pump the blood, so it needs more O2
Increased O2 delivered via O2 to tissues AND to the heart
=> tradeoff! Optimal Hb blood content for the heart is 10 g/dL because if you raise it higher the heart does not gain any more O2 that it does not consume
What is the arterio-venous difference?
Difference in O2 content of blood in arteries vs veins due to tissues consuming O2 from blood
What is VO2 max?
Overall O2 consumption of the body = a-v difference of CO
Saturation of Hb with O2 in venous blood? What is this used for?
SO2 = 75%
Used as a marker for cardiac function for patients who are not in shock
Saturation of Hb with O2 in arterial blood?
SO2 = 97%
VO2 max in healthy individual?
VO2 max = 1L O2/min - (1 L x 75%) = 1 L - 750 mL = 250 mL O2 consumed/min
Arterio-venous difference for O2 per dL of blood?
5 mL O2/dL
Arterio-venous difference for CO2 per dL of blood?
4 mL CO2/dL
VCO2 max in healthy individual?
VCO2 max = 5 L/min x 10 x 4 mL CO2/dL = 200 mL CO2/min
How to calculate respiratory quotient?
= VCO2 max / VO2 max = 200/250 = 0.8
Equation for O2 delivery to tissues? Unit?
DO2 = CaO2 x CO
Unit = mL O2/min
Equation for O2 consumption? Unit?
VO2 = CO x (CaO2 – CvO2)
Unit = mL O2/min
Equation for O2 content of blood? Unit?
CaO2 = (Hb x SaO2 x 1.34) + (PaO2 x 0.003)
Unit = mL O2/dL
What is the capacity of blood?
Max possible amount of O2 that can be carried in the blood, which occurs at 100% Hb O2 saturation
What is the extraction ratio? Best possible ER?
Fraction of O2 delivered in the blood that is actually consumed by a tissue: VO2/DO2
Best possible ER = 66%
Normal CaO2?
CaO2 = 20 mL O2/dL blood
TBD
Normal Hb saturation in arterial blood?
97%
Do some organs extract more O2 than others?
YUP! Like the brain for example
What is shock due to hemorrhage? What happens at this stage? Treatment?
Supply of O2 to tissues does not meet their O2 demand as DO2 decreases below 400 mL O2/min => VO2 of tissues decreases => tissues conduct anaerobic metabolism to meet energy needs => lactic acid accumulates
Raise DO2 by transfusing blood
Normal extraction ratio when DO2 greatly exceeds VO2 max?
25%
From shock to out of shock, how do DO2 and VO2 change?
They both increase
What happens during septic shock when the Hb content of blood is unchanged? Treatment?
- Sepsis = blood vessels dilate + VO2 max is increased due to body fighting infection + normal DO2 + low ER because blood is not being efficiently distributed
- Over time DO2 decreases below 1L O2/min due to the vasodilation + VO2 decreases + lactic acid accumulates = septic shock
Treatment =
1. Increase DO2 by transfusing blood to increase Hb content + inotropes
- Decrease VO2 by treating the fever, sedating, and intubating
- Make sure to keep CO high to maintain higher DO2
Hallmark of shock?
Lactic acidosis
Adequate Hb (aka no need to transfuse more blood)?
7 g/dL
What is the Fick principle?
Amount of substance added or removed to or from an organ = blood flow x (a-v)
(a-v) = difference in O2 content across the organ between arteries and veins
How to calculate CO via the Fick principle?
CO = Q = blood flow across the lungs = VO2 / CaO2-CvO2
a = systemic arterial oxygen concentration (sampled from any artery) v = pulmonary arterial oxygen concentration
SO2 when PO2 = 40 mmHg?
75%
SO2 when PO2 = 100 mmHg?
97%
SO2 when PO2 = 26.5 mmHg?
50%
Describe the O2 saturation of Hb curve? 2 advantages?
- X-axis = O2 tension in mmHg or kPa (or any other measure of O2 blood content)
- Y axis = SaO2 of Hb
- Plateau: when O2 pressures are high (aka in the lung), fluctuations in O2 content of the environment or in diffusion capabilities of the lungs do not impact saturation of Hb
- Steep slope: when O2 pressures are low (aka at the tissues) Hb can unload O2 cooperatively with small fluctuations of O2 pressure, allowing the tissues to withdraw large O2 amounts
What does a right shift of the O2 saturation Hb curve mean?
Means Hb is unloading O2 more (affinity decreased) = more O2 delivered to tissues (and a little less O2 uptook at alveolar capillaries)
4 causes of right shift of Hb saturation curve? Why?
- Increase in temperature
- Decrease in pH
- Increase in PaCO2
- Presence of 2,3-DPG (BPG)
First 3 mean increased activity (e.g. exercise) so increased O2 needs
DPG is compound present in Sherpas or other peeps living at high altitudes where to O2 pressure in air is lower
What does a left shift of the O2 saturation Hb curve mean?
Means Hb is unloading O2 less (affinity increased)
5 causes of left shift of Hb saturation curve?
- Decrease in temperature
- Increase in pH
- Decrease in PaCO2
- Presence of CO
- Absence of 2,3-DPG
Why does CO interfere with O2 transport?
- It has a much higher affinity to Hb than O2 does so Hb is not available to bind O2 => forms carboxyhemoglobin => Hb saturation curve maximum O2 content decreases
- It causes a left shift of the Hb dissociation curve making it harder for Hb to unload O2 at the tissues
Clinical presentation of carbon monoxide poisoning patients?
- Pink due to carboxyhemoglobin
- Normal PaO2
- Normal PAO2
- Normal SaO2 because cannot tell difference between Hb bound to O2 and CO
- Normal Hb content in blood
- Lactic acidosis
Treatment for carbon monoxide poisoning? What law does this employ?
Employing Henry’s Law by using a hyperbaric chamber: patient breathes pure O2 in a pressurized room and the partial pressure of O2 is so high that we can dissolve enough in the blood to oxygenate the tissues and enough to overcome the CO bound to the Hb
Why are not all fever and lactic acidoses treated?
Because they help unload O2 to the tissues (right shift of the Hb saturation curve)
How does blood change after it is removed from body? What does this mean?
Loses 2,3-DPG = left shift of Hb saturation curve
SO fresh blood should be sent to community hospitals that use blood slowly and older blood should be sent to big hospital that uses blood very fast
When will CO and O2 bind the same amount of Hb?
When the PaCO is 240 times less than PaO2
HbCO of 33% would correspond to what % blood loss?
33%
What are capillaries surrounded by at the tissues?
Interstitial fluid = milieu
PO2 of interstitial fluid at tissues?
= 40 mmHg
PCO2 of interstitial fluid at tissues?
= 45 mmHg
What drives diffusion of O2 from capillaries to tissues and CO2 from tissues to capillaries?
Concentration gradients between blood and interstitial fluid
2 possible limitations of diffusion of gases at the tissues? Examples?
- Perfusion limited: vascular disease or increased tissue demand
- Diffusion limited: thickened membrane or decreased PaO2
Composition of capillary blood?
Same as arterial blood
Composition of interstitial fluid of tissue?
Same as venous blood draining tissue
3 ways of carrying CO2 in blood? % for each?
- Dissolved in blood: 10%
- Bound to proteins like Hb: 30%
- As bicarbonate: 60%
Which is more soluble in blood: O2 or CO2? By how much?
CO2: 20 x more
What is the Haldane effect?
CO2 dissolves in blood via these reaction:
- CO2 + H2O <=> H2CO3
- H2CO3 <=> HCO3- + H+
Reaction 1 is fast in RBC due to carbonic anhydrase and slow in plasma
Reaction 2 is fast without any enzymes in both plasma and blood
HCO3- in the RBC diffuses out but H+ ion does not (RBC impermeability to cations) so the cell uptakes Cl- to compensate = chloride shift
SOME H+ ions do diffuse out and bind Hb => Hb reduction => Hb less acidic and binds H+ better than O2 => H+ + HbO2 = H+ + Hb + O2 => PRESENCE OF REDUCED HB IN PERIPHERY HELPS LOADING OF CO2 AND OXYGENATING OF HB IN LUNGS PROMOTES UNLOADING OF CO2
What is the end product of aerobic metabolism?
CO2
Where is CO2 concentration highest?
Mitochondria
Form of CO2 when bound to blood proteins? How is it formed? Most important protein bound?
Carbamino compound formed with binding of CO2 to terminal amine groups in blood proteins
Most important = globin of Hb = carbamo-hemoglobin
Dissociation curve of Hb to CO2 compared to O2?
More linear
How does oxygenation affect CO2 content?
Decreases it because less CO2 can bind to Hb
PaO2 of blood during anemia? Hypoxemia?
NORMAL so NOT hypoxemic BUT tissue is hypoxic because low CaO2 of blood
Difference between hypoxia and hypoxemia?
Hypoxia = low CaO2
Hypoxemia = low PaO2
Does CO gas have a distinct odor?
NOPE
What does it mean for DO2 and VO2 to be coupled?
This happens during shock when VO2 is less than 250: body is in O2 debt and is making ATP anaerobically but if it had more O2, it would use it => if DO2 goes up, VO2 will go up as well so they are said to be coupled
Does hypoxemia always lead to hypoxia?
YES
By how much does the presence of Hb increase the blood concentration of O2?
70 times
Will anemia cause low CaO2 of mixed venous blood?
YUP
Will CO poisoning cause low CaO2 of mixed venous and arterial blood?
YUP
