Chapter 6 Oxygen Transport 1307
Normal CaO2 is
20 mL/dL
The quantity of oxygen that dissolves in plasma is determined by the
PAO2 to which plasma is exposed.
Mixed Venous Oxygen Saturation (SvO2)
Saturation of venous blood in RA
Hyperthermia (exercise or fever)
Shift to the RIGHT Enhances release of O2 at the cellular level
CaO2=
[(Hb x 1.34)(SaO2)] + (PaO2 x 0.003)
Increase in SvO2 indicates that C(a-v)O2, VO2, and O2ER are ____
decreasing
> 30 % is ____
life threatening
A small amount of CO ties up a lot of hemoglobin and
prevents oxygen molecules from binding to hemoglobin
At normal body temperature:
0.003 mL of O2 will dissolve in 100 mL (deciliter) of blood for every 1 torr of PO2
Each gram of Hb is capable of carrying ___ mL of oxygen
1.34
Steep part of curve
10-60 torr, O2 combines rapidly with Hb as the PaO2 increases
5 mL of O2 are needed from each ___mL blood for normal tissue metabolism
100
Total Oxygen Delivery average
1000 mL O2 / min
0.3 mL of O2 is dissolved in every ____ of blood plasma
100mL
Hb F is gradually replaced with Hb A during the first ___ months of life
12
Normal Hb for an Adult Female
12-15 g/dL
Normal Hb for an Adult Male
14-16 g/dL
Normal CvO2 is
15 mL/dL
What is the normal CaO2 value?
16-20 mL/dL, vol% or mL/100 mL of blood
Hemoglobin's affinity for CO is ___ greater than O2
210
Normal Oxygen Concentration Ratio (O2ER)
25%
Normal Oxygen Consumption is
250 mL/min
Each red blood cell contains ___ million hemoglobin molecules
280
Normal Anatomic Shunt is ___% of Cardiac Output
3
Moderate Hypoxemia
40-59 torr
Normal C(a-v)O2 is
5 mL/dL
Flat part of curve
60-100 torr; increases in PaO2 have little effect on SaO2
Mild Hypoxemia
60-79 torr
Under normal circumstances a person's hemoglobin returns to the alveoli ~____% saturated with oxygen
75
Normal Mixed Venous Oxygen Saturation (SvO2)
75% is normal (65% is acceptable)
The PaO2 can drop from 100 to 60 torr and Hb will still be ___% saturated with O2 (____)
90;suggests a strong affinity
Hypoxemia
Abnormally low arterial oxygen tension (Low PaO2)
Absolute Shunt is caused by
Alveolar collapse or atelectasis Alveolar fluid accumulation Alveolar consolidation (fluid, blood, infection)
Relative Shunts are caused by
Alveolar hypoventilation Ventilation/Perfusion mismatch: Chronic emphysema, bronchitis, asthma and excessive airway secretions Alveolar-capillary diffusion defects Pulmonary fibrosis, pulmonary edema
Total Oxygen Delivery (Do2)
Amount of oxygen delivered (or transported) to peripheral tissues is dependent upon: Body's ability to oxygenate the blood Hemoglobin concentration Cardiac output (QT)
Oxygen delivery to the tissue cells decreases if there is decline in:
Blood oxygenation (PaO2) Cardiac output Hb concentration
The impact of changes in blood pH on hemoglobin's affinity for oxygen is called the
Bohr effect
How is a Mixed Venous Oxygen Saturation (SvO2) obtained?
By an indwelling (Swan-Ganz) pulmonary artery catheter
O2ER=
C(a-v)O2/CaO2
PaO2 falls below 60 torr
Decrease in amount of oxygen bound to hemoglobin Quantity of O2 delivered to tissue cells may be significantly reduced
Factors that Increase Oxygen Concentration Ratio
Decreased cardiac output Increased oxygen consumption Anemia Decreased arterial oxygenation
Hemoglobin S or "Sickle Cell Anemia"
Deoxygenated Hb changes RBC shape to crescent or sickle form; tendency to form thrombi
Arterial-Venous Oxygen Content Difference C(A-V)O2
Difference between CaO2 and CvO2
Oxygen is transported in blood in two forms:
Dissolved oxygen molecules in blood plasma Chemically bound to hemoglobin (Hb) within the erythrocyte (RBC)
Methemoglobin
Drugs and chemicals (nitric oxide) change iron molecule from ferrous state to ferric state, so it cannot combine with O2 for transport
Factors that increase Arterial-Venous Oxygen Content Difference C(A-V)O2
Exercise Seizures Shivering Hyperthermia
Factors that increase Oxygen Consumption
Exercise Seizures Shivering Hyperthermia
Four heme (iron) groups on each Hb molecule, bonded and enfolded in:
Globin (complex protein) made of four linked amino acid chains
Shift to the Right: Oxyhemoglobin Dissociation Curve
Hb affinity for O2 decreases (Hb is less saturated at a given PO2) and oxygen unloading at the cellular level is enhanced
Shift to the Left: Oxyhemoglobin Dissociation Curve
Hb affinity for O2 increases (Hb is more saturated at a given PO2) and oxygen loading onto Hb molecule in the lungs is enhanced
If all 4 Heme groups on a hemoglobin molecule bind with four O2 molecules,
Hb is considered to be 100% saturated with O2 "Oxyhemoglobin"
Deoxyhemoglobin
Hemoglobin not bound to O2
Oxyhemoglobin Dissociation Curve
Illustrates the percentage of Hb that is chemically bound to O2 (saturation) at any specific PaO2
Factors the decrease Arterial-Venous Oxygen Content Difference C(A-V)O2
Increased QT Skeletal muscle relaxation Peripheral shunting (sepsis, trauma) Certain poisons (cyanide, prevents cellular metabolism) Hypothermia
Factors that decrease Oxygen Concentration Ratio
Increased cardiac output Skeletal muscle relaxation Peripheral shunting Poisons Hypothermia Increased Hb Increased arterial oxygenation
Fetal Hb (Hb F)
Increases hemoglobin's affinity for O2 allowing for better transfer of maternal O2 across placenta to the fetus
What happens with a Left Shift on the Oxyhemoglobin Dissociation Curve?
Loading of O2 at the lungs is enhanced and Unloading of O2 at the Tissues
Is the Oxyhemoglobin Dissociation Curve a linear relationship?
No it is an S Curve
2,3-BIPHOSPHOGLYCERATE (BPG)
Organic phosphate and by-product of anaerobic glycolysis found in the RBC
Total O2 content (CaO2) in 100 mL of blood consists of:
Oxygen dissolved in the plasma + Oxygen bound to hemoglobin
P50 ON Oxyhemoglobin Dissociation Curve
Partial pressure at which the Hb is 50% saturated with O2 (2 oxygen molecules on each Hb molecule) (Normal P50 is 27 torr)
Shunt Equation
Percent of shunted blood when compared to Cardiac Output
Absolute Shunt responds ____to oxygen therapy (refractory)
Poorly
Pulmonary Shunt
Portion of the cardiac output that moves from the RIGHT side of heart to LEFT side of heart without being exposed to alveolar oxygen
Relative Shunt
Pulmonary capillary perfusion exceeds alveolar ventilation
Hypothermia
Shift to the LEFT O2 demand at the cold tissues sites is decreased
Factors that decrease Oxygen Consumption
Skeletal muscle relaxation Peripheral shunting Certain poisons Hypothermia
Blood pH fluctuations cause variations in the shape of the hemoglobin molecule (what specific part?)
The Globin Portion
Henry's Law:
The amount of gas that dissolves in a liquid (blood plasma) is proportional to its partial pressure.
Oxygen Consumption
The amount of oxygen consumed by the peripheral tissues in 1 min (VO2)
Oxygen Concentration Ratio (O2ER)
The amount of oxygen extracted by the peripheral tissues divided by the amount of oxygen delivered to the peripheral cells
When PaO2 is within normal limits (80 to 100 torr), a shift of the oxyhemoglobin dissociation curve to the right or left does NOT significantly affect hemoglobin's ability to transport oxygen to the peripheral tissues, because shifts in this pressure range occur where on the curve?
The flat part/safe space
Venous Admixture
The mixing of shunted, non-reoxygenated blood with re-oxygenated blood in the pulmonary venous system
When PaO2 falls below the normal range (60 or 80), a shift to the right or left can have a remarkable effect on hemoglobin's ability to pick up and release oxygen, because shifts in this pressure range occur where on the curve?
The steep part
Normal Physiologic Shunts(all deoxygenated):
Thebesian venous drainage into the LA Bronchial venous drainage Underventilated alveoli relative to pulmonary blood flow (zone 1)
Anatomic Shunts
When blood flows from Right side of heart to Left side of the heart without coming into contact w/alveolus
Abnormal Hemoglobin
When the number, sequence, or spatial arrangement of globin chains is altered, hemoglobin will be abnormal
In a normal Anatomical Shunt deoxygenated blood bypasses the alveoli and enters the pulmonary vascular system via ___and Coronary blood enters LA via ____
bronchial venous drainage; Thebesian veins
Most O2 that diffuses from the alveoli into pulmonary capillary blood moves rapidly into erythrocytes and
chemically binds to hemoglobin (Hb) molecules
Examples of Abnormal Anatomic Shunts:
congenital heart disease, intrapulmonary fistula, vascular lung tumors
Most pulse oximeter measurements below 70% are considered
inaccurate and unreliable
Hypoxia ___ 2,3 BPG levels
increases
Decrease in SvO2 indicate that C(a-v)O2, VO2, and O2ER are ___
increasing
10-20 % indicates ___
intrapulmonary abnormality
20-30 % indicates significant ___
intrapulmonary disease
Oxygen transport between the lungs and body tissue cells
is a function of the blood and the heart
COHb impedes oxygen delivered to body tissues by shifting the curve to the ____
left
Shunt % < 10 is___
normal
If PaO2 within normal range----small right to left shift on Oxyhemoglobin Dissociation Curve is
not clinically significant.
At center of each of the four heme groups, the iron molecule can combine with one O2 molecule in an easily reversible reaction to form
oxyhemoglobin
Factors that Shift the Oxyhemoglobin Dissociation Curve
pH H+ CO2 levels Body Temperature 2,3 DPG Hb F COHb
As hydrogen ion concentration increases:
pH decreases (acidotic) Shifts curve to the RIGHT Hb affinity for O2 Enhances the unloading of O2 at cellular level
As hydrogen ion concentration decreases
pH increases (alkalotic) Shifts curve to the LEFT Hb affinity for O2 Enhances the loading of O2 onto Hb
At a normal PaO2 of 100, Hb is 97% saturated due to
physiologic shunts
Physiologic shunt
portion of venous blood that travels from the R heart to the L heart without participating in gas exchange
As 2,3 BPG level increases, curve shifts to the ___, decreasing Hb affinity for oxygen
right
The amount of oxygen bound to Hb is directly related to
the partial pressure of oxygen
Hb is highly specialized in structure to
transport O2 and CO2
Hemoglobin saturation with oxygen ___ with changes in PaO2
varies
Relative Shunts responds ____ to oxygen therapy
well
