120 quiz 4 ch 8

In what ways does blood carry oxygen? 

Oxygen dissolved in plasma 

Oxygen combined with hemoglobin (Hb transports most of the O2) 

What equation expresses mL of oxygen dissolved in 100mL of plasma?

PO2 × 0.003 = mL/dL dissolved oxygen

Approximately 0.003 mL of O2 will dissolve in 100 mL of blood for every 1 torr of PO2. Thus, PaO2 of 100 = ____mL

0.3 mL

If PaO2 = 100 mmHg and Hb concentration = 15 g/dL, Hb carries ____ mL/dL 

20

Normal cardiac output (Q) of 5 L/min:

O2 delivery to all body tissues = 1000 mL O2/min

O2 consumption by tissues = ____ mL/min

250 mL/min

O2 delivery is 4x body’s resting requirement; in other words, tissues consume about ___% of the O2 delivered to them

25%

Oxyhemoglobin (HbO2)

Hb combined with oxygen

Deoxyhemoglobin 

Hb not bound with oxygen 

Cooperative binding

Each molecule of oxygen bound to Hb makes the next molecule bind more quickly

Most oxygen that diffuses into pulmonary capillary blood rapidly moves into ____s and chemically attaches to ____.

RBCs, hemoglobin

approximately how many Hb molecules does each RBC contain?

280 million Hb molecules

Normal adult hemoglobin (Hb A) consists of: 

• Four heme groups 

  • pigmented, iron-containing nonprotein portions of hemoglobin molecule

• Four amino acid chains (polypeptide chains) that collectively constitute globin (protein)

Hemoglobin saturation normal values:

Normal SaO2 = _____ %

• Occurs at PaO2 of ____ mmHg

97.5%

100 mmHg

Hemoglobin saturation normal values:

Normal SvO2 = ____%

• Occurs at PvO2 of ____ mmHg

75%

40 mmHg

% saturation is NOT equal to O2 or Hb concentration.

This means that an SaO2 of 100% does not necessarily mean the O2 content is ____

normal

When hemoglobin is 100% saturated with O2, each gram of hemoglobin (g% Hb) can carry ____ mL of O2 

1.34 mL of O2

What is the normal Hb level range?

12 to 15 g/dL

At 15 g/dL and 100% saturation, Hb carries ____ mL of oxygen 

20.1 mL

Mixed venous blood at 75% saturation carries 0.75 × 20.1 (mL O2 at 100%) = ____ mL/dL

15.1 mL/dL

At 100% saturation Hb carries 20.1 mL oxygen

At 75% saturation mixed venous blood carries 15.1 mL oxygen

This makes the arterial-venous content difference = ~ ____ mL/dL

5 mL/dL 

Each g% Hb can carry 1.34 mL of oxygen. Thus if Hb level is 15 g%, and if Hb is fully saturated, approximately ____ vol% of O2 will be bound to Hb 

20.1 vol% of O2 

Found by: 

1.34 mL O2 × 15 g% Hb = 20.1 vol% of O2

At normal PaO2 of 100 mmHg, however, Hb saturation (SaO2) is only ~ 97% due to the following three normal physiologic shunts:

• Thebesian venous drainage into left atrium

• bronchial venous drainage into pulmonary veins

• alveoli that are under-ventilated

Thus, amount of arterial oxygen in preceding equation must be adjusted to 97%:

20.1 vol% O2 × 0.97 = 19.5 vol% O2

To determine total amount of oxygen in 100 mL of blood, the following must be added together:

dissolved oxygen in plasma

oxygen bound to hemoglobin

What is the equation for total oxygen content of arterial blood (CaO2)?

CaO2 = (PaO2 × 0.003) + (SaO2 × 1.34 x Hb)

CaO2 = oxygen content of arterial blood, mL/dL

PaO2 = partial pressure of oxygen

0.003 = dissolved O2 factor

SaO2 = percentage Hb fully saturated with O2, %

1.34 = volume of O2 bound to Hb at 100% saturation

Hb = concentration of hemoglobin 

Normal CaO2 (O2 content of arterial blood)?

about 20 mL/dL

What is the equation for total oxygen content of mixed venous blood (CvO2)?

CvO2 = (PvO x 0.003) + (SvO2 × 1.34 x Hb) 

Normal CvO2 (O2 content of mixed venous blood)?

about 15 mL/dL

Normal C(a-v)O2 (arterial-venous O2 content difference)? (range)

Range is 3.5 to 5 mL/dL 

What is the equation for total oxygen content of pulmonary capillary blood (CcO2)? 

CcO2 = (PAO2 × 0.003) + (1.34 x Hb) 

What does the Oxyhemoglobin Dissociation Curve graphically illustrate?

The percentage of Hb chemically bound to oxygen at each oxygen pressure PO2

What is the clinical significance of the flat portion of the HbO2 dissociation curve?

PO2 can fall from 60 to 100 torr and Hb will still be 90% saturated with O2.

• excellent safety zone

As Hb moves through AC system, significant partial pressure difference continues to exist between alveolar gas and blood, even after most O2 has transferred. Why?

It enhances diffusion of O2

What is the effect of increasing PO2 beyond 100 torr? 

doing so adds very little O2 to blood 

• dissolved O2 only (PO2 × 0.003) 

What is the clinical significance of the steep portion of the HbO2 dissociation curve? 

Reduction of PO2 below 60 torr causes rapid decrease in the amount of O2 bound to Hb. 

• however, diffusion of oxygen from Hb to tissue cells in enhanced 

The flat portion of the HbO2 equilibrium curve shows that large changes in PO2 between 60 and 100 mmHg lead to what?

small changes in SO2 and CaO2

The steep portion of the HbO2 equilibrium curve shows that small changes in PO2 between 20 and 60 mmHg lead to what?

large changes in SO2 and CaO2

P50 is the point of reference on the HbO2 dissociation curve.

It is ~ = ____ torr

What does it represent?

27 torr

It represents partial pressure at which hemoglobin is 50 percent saturated with oxygen

What factors affect the HbO2 dissociation curve? 

pH 

Temperature 

CO2 

2,3-bisphosphoglycerate (BPG) 

When the curve shifts to the right, P50 _____

increases

Factors that shift HbO2 curve to the RIGHT:

↓ pH,

↑ PCO2, ↑ Temperature, ↑ DPG

A shift to the RIGHT means that Hb affinity for oxygen has decreased. What does this mean?

Hb releases additional O2 into the plasma, which incrases the pressure gradient for O2 diffusion into the tissues

When curve shifts to the left, P50 _____ 

decreases 

Factors that shift HbO2 curve to the LEFT:

↑ pH,

↓ PCO2, ↓ Temperature, ↓ BPG

A shift to the LEFT means that Hb affinity for oxygen has increased. What does this mean?  

Hb releases less O2 into plasma, so less O2 is available to tissues. 

O2 and CO2 pressure gradients in the lungs are _____ in the systemic tissues. 

reversed

At lungs, curve shifts left

At tissue level, curve shifts right

Total oxygen delivery (DO2) 

What  is it and what is it dependent on? 

Total amount of oxygen delivered or transported to peripheral tissues 

Dependent on: 

• Body’s ability to oxygenate blood

• Hemoglobin concentration

• Cardiac output

What is the equation for total oxygen delivery (DO2)?

DO₂ = QT x (CaO₂ × 10)

QT = cardiact output (L/min)

CaO2 = oxygen content (vol%)

What is the normal DO2?

about 1000 mL/min

DO2 decreases in response to:

Low blood oxygenation

• low PaO2

• low SaO2

• low Hb concentration

• low cardiac output

DO2 increases in response to:

Increased blood oxygenation

• increased PaO2

• increased SaO2

• increased Hb concentration

• increased cardiac output

What is the normal value of C(a-v)O₂?

Normally, CaO2 is ~ 20 vol% and CvO2 is 15 vol%

thus, normal C(a-v)O2 is ~5 vol%

What is oxygen consumption (VO2)? 

Equation? 

Amount of oxygen extracted by peripheral tissues during period of one minute

VO₂ = QT [C(a-v)O₂ × 10]

What is oxygen consumption (VO2) normally?

about 250 mL O2/min

What is oxygen extraction ration (O2ER)?

Equation?

Amount of oxygen extracted by perippheral tissues divided by amount of oxygen delivered to peripheral cells

O2ER = C(a-v)O2 / CaO2

The oxygen extraction ratio (O2ER) is also called the ____.

Oxygen utilization coefficient

What is the normal value of O2ER?

In considering normla CaO2 of 20 vol% and normal CvO2 of 15 vol%, 

O2ER = ~25% 

Changes in the mixed venous saturation, or SvO2, can be used to detect changes in:

• C(a-v)O2

• VO2

• O2ER

Pulmonary shunting

Portion of cardiac output that moves from right side to left side of heart without being exposed to PaO2 (oxygenation via alveolar oxygen)

Clinically, pulmonary shunting can be subdivided into:

Absolute shunt (true shunt)

Relative shunt (shunt-like effects)

Absolute shunts can be grouped under two major categories: 

Anatomic shunts 

Capillary shunts 

Anatomic vs capillary shunts

Anatomic

• exist when blood flows from right side of heart to left side without coming in contact with alveolus for gas exchange

Capillary

• caused by alveolar collapse or atelectasis, alveolar fluid accumulation, alveolar consolidation

In healthy lung, normal anatomic shunt is approximately ___% of cardiac output

3%

Normal shunting is caused by nonoxygenated blood completely bypassing alveoli and entering:

• pulmonary vascular system by means of bronchial venous drainage 

• left atrium by way of thebesian veins 

Common causes of absolute shunting 

Congenital heart disease 

Intrapulmonary fistula

Vascular lung tumors 

Relative shunt, or shunt-like effect, exists when pulmonary capillary perfusion is in excess of _____

alveolar ventilation

What are common causes of relative shunting?

• hypoventilation

• ventilation/perfusion mismatches

  • chronic emphysema, bronchitis, asthma

• alveolar-capillary diffusion defects

  • alveolar fibrosis or alveolar edema

The end result of pulmonary shunting is venous admixture. What is this? 

Mixing of shunted, non-reoxygenated blood with reoxygenated blood distal to alveoli

Downstream in pulmonary venous system 

When venous admixture occurs, shunted, non-reoxygenated blood gains oxygen molecules while, simultaneously, reoxygenated blood loses oxygen molecules.

Process continues until:

PO2 throughout all plasma of newly mixed blood is in equilibrium

All Hb molecules carry the same number of oxygen molecules

Shunt equation and information needed

Pb, PaO2, PaCO2, PvO2, Hb, PAO2, FIO2

Steps for solving shunt equation

1. Calculate PAO2

2. Calculate CcO2

3. Calculate CaO2

4. Calculate CvO2

5. Plug into shunt equation 

Interpreting pulmonary shunting percentages

<10% - normal status

10-20% - indicated intrapulmonary abnormality

20-30% - significant intrapulmonary diseases

>30% - potentially life-threatening

hypoxemia

abnormally low arterial oxygen tension

frequently assoiciated with hypoxia

Although presence of hypoxemia strongly suggests tissue hypoxia, does not necessary mean _____ existence of tissue hypoxia

absolute

Hypoxia 

low or inadequate oxygen for aerobic cellular metabolism

hypoxia is characterized by:

tachycardia, hypertension, peripheral vasoconstriction, dizziness, and mental confusion

What are the four main types of hypoxia?

• hypoxic hypoxia

• anemic hypoxia

• circulatory hypoxia

• histotoxic hypoxia

hypoxic hypoxia and causes

Inadequate oxygen at the tissue cells  caused by low arterial oxygen tension (PaO2) 

Common causes: 

• Low PaO2 caused by: 

  • hypoventilation, high altitude

• Diffusion impairment

  • interstitial fibrosis, interstitial lung disease, pulmonary edema, pneumoconiosis

• Ventilation-perfusion mismatch

• Pulmonary shunting

anemix hypoxia and causes

PaO2 is normal, but the oxygen-carring capacity of hemoglobin is inadequate

Common causes:

• decreased Hb concentration

  • anemia, hemorrhage

• abnormal hemoglobin

  • carboxyhemoglobin

  • methemoglobin

circulatory hypoxia and causes

blood flow to the tissue cells is inadequate; thus, oxygen is not adequate to meet tissue needs

Common causes:

• slow or stagnant (pooling) peripheral blood flow

• arterial venous shunts

histotoxic hypoxia and causes

Impaired ability of the tissue cells to metabolize oxygen

Cause:

• cyanide poisoning

cyanosis

Blue-gray or purplish discoloration seen on mucous membranes, fingertips, and toes

May appear whenever blood contains at least 5 g% of deoxyHb

Peripheral vs Central cyanosis

peripheral

• Low SvO2 (SaO2 may be normal), low blood flow states - tissues extract more O2, affects skin and nail beds 

central 

• Low SaO2, more profound hypoxemia than peripheral, affects mucous membranes 

Anemia vs polycythemia

Anemia

• low # of RBCs, so Hb levels are lower than normal

Polycythemia

• high # of RBCs, so Hb levels are higher than normal

Carboxyheoglobin (HbCO) - CO inhalation 

Hb has ____x greater affinity for CO than for O2

210x

Treating CO inhalation - competitive binding

High FiO2 - decreases half-life of HbCO

Hyperbaric oxygen therapy

Methemoglobin (metHb) characteristics & cause

Hb with Fe++ oxidized to Fe+++

Cannot bind with oxygen

Caused by nitrate poisoning or toxic reactions to oxidant drugs.

Normal <1% total Hb, value is on ABG