Gas Exchange and Transport Quiz 3.txt

• Blood carries oxygen in two forms:
• 1. dissolved in the plasma and erythrocyte intracellular fluid
• 2. combined with hemoglobin in the red blood cell (RBC): MAJORITY IS CARRIED HERE!

• Gaseous oxygen diffuses into the blood and dissolves in the plasma and erythrocyte fluid
• Most blood oxygen is transported in chemical combination with hemoglobin (Hb) in the erythrocytes

• Dissolved oxygen (ml/dl) = PO2 X 0.003
• 0.003 is the solubility coefficient of oxygen at 1 mmHg in 100ml of plasma

• In whole blood, each gram of Hb can carry about 1.34 ml of oxygen.
• Average Hb is about 15 g/dl
• To compute the oxygen-carrying capacity of the blood we use the following formula:
• 1.34 ml/g X Hb = Hb O2 carrying capacity
• 1.34 ml/g X 15 g/dl = 20.1ml/dl

• Saturation is a measure of the amount of available hemoglobin that is actually carrying oxygen.
• It is content (HbO2) divided by capacity (total hemoglobin) expressed as a percentage.
• SaO2 = [HbO2]___ x 100
• Total Hb

• Example: Total Hb = 15 g/dl and HbO2 = 7.5g/dl
• SaO2 (%) = 7.5____ X 100 = 50%
• 15
• This hemoglobin is 50% saturated so it is only carrying half its oxygen

• Hb saturation with oxygen varies with changes in PO2
• Below 60mmHg, the curve steepens. Here, a small drop in PO2 causes a large drop in SaO2 indicating a lessening affinity for oxygen

• Must have three variables; (1) PO2, (2) total hemoglobin content (g/dl), and (3) hemoglobin saturation.
• CxO2 = (0.003 X PxO2) + (Hbtot x 1.34 X SxO2)
• CaO2 = (0.003 X 100) + 15 X 1.34 X 0.97
• CaO2 = (0.3) + (19.5)
• CaO2 = 19.8 ml/dl

97 %

75%

PaO2 of 100 mmHg and SaO2 of 97%

PvO2 of 40 mmHg and SvO2 of 73%

• 4-8, or 5 ml/dl and is the amount of oxygen given up by every 100 mls of blood on each pass through the tissues
• The C(a-v)O2 indicates the amount of oxygen removed in relation to blood flow

• Combined O2 (1.34 x 15 X SO2) 19.5 14.7
• Dissolved O2(PO2 X 0.003) 0.3 0.1
• Total O2 content 19.8 14.8 (difference of 5)

• Qt = VO2______
• C(a-v)O2 X 10

• Qt is cardiac output (L/min)
• VO2 is whole-body consumption (ml/min)
• C(a-v)O2 is the arteriovenous oxygen contents difference (ml/dl)
• 10 converts ml/dl to ml/L

• Using a normal VO2 of 250 ml/min and a normal C(a-v)O2 of 5 ml/dl you can calculate the cardiac output:
• Qt = VO2___
• C(a-v)O2 X 10
• Qt = 250 ml/min________
• 5 ml/dl X 10
• Qt = 250 ml/min________
• 50 ml/L
• Qt = 5.0 L/min

250 ml/min; 5 ml/dl

If the oxygen consumption remains constant, a decrease in cardiac output will increase the C(a-v)O2 and if the cardiac output rises, the C(a-v)O2 will fall proportionately.

• blood pH,
• body temperature,
• erythrocyte concentration of certain organic phosphates (2,3 DPG),
• Hb structure variations
• Other substances combining with Hb (ex. carboxyhemoglobin)

• Right;
• When the curve shifts to the right, the % Hb sat for a given PO2 falls (decreased affinity for oxygen)

• Left;
• As the curve shifts to the left, the % Hb sat for a given PO2 rises (increased affinity of Hb for oxygen).

alters the position of the HbO2 dissociation curve due to changes in blood pH. These changes enhance oxygen loading in the lungs and oxygen unloading in the tissues. As blood in the tissues picks up CO2, pH falls, the curve shifts to the right. With lower affinity for oxygen, Hb more readily gives up its oxygen to the tissues. Venous blood returning to the lungs, pH goes up to 7.40 and shifts the HbO2 curve back to the left to aid loading at the lungs.

Left; increases affinity; decreased unloading

Right; decreases affinity; increased unloading

• the partial pressure of oxygen at which the Hb is 50% saturated, at 7.40 pH
• Normal P50 is about 27 (26.6)mmHg

found in the red blood cells. It stabilizes the deoxygenated Hb molecule, reducing its affinity for oxygen. Without 2,3-DPG normal oxygen unloading would be impossible

• shifts the HbO2 curve to the right, increased oxygen unloading or decreased affinity of Hb for oxygen
• Things that cause it:
• alkalosis
• chronic hypoxemia
• anemia

• shift the curve to the left, increased affinity of Hb for oxygen (loading)
• What causes this:
• acidosis
• banked blood-(stored blood)

the curve is shifted to the right, increased unloading, decreased affinity of Hb for O2.

the curve is shifted to the left, increased affinity of Hb for O2 and decreased unloading

120; 15-40%

nitrite poisioning; Blood looks brownish in color, and skin color is grayish

200 times

• Left (harder unloading);
• increasing oxygen concentration to decrease the half life of CO and to supersaturate the plasma to keep oxygen going to the tissues. Hyperbaric oxygen (HBO) is recommended for use, usually with patients of 25% or greater HbCO

• low pH (acidity)
• increase in body temperature
• increased 2,3-DPG
• increased P50

• high pH (alkalinity)
• decrease in body temperature
• decrease 2,3-DPG
• decreased P50
• HbCO

• low pH (acidity)
• increase in body temperature
• increased 2,3-DPG
• increased P50

• high pH (alkalinity)
• decrease in body temperature
• decrease 2,3-DPG
• decreased P50

Opposite, if one is increase, the other will be decreased