Pulmonary Physiology 3 Flashcards by Joel Glotfelty

Diffuses much quicker than O2 but has a lower arteriole to vein gradient

CO2

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Intense exercise reduces the time available for

Oxygenation

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Exercise increases blood flow and thus decreases

Capillary transit time

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In a healthy person with a normal environment, exercise will not change

PaO2

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Exercise increases blood flow and reduces capillary transit time, normally this is not a problem unless there is a

Diffusion barrier or low PAO2 (hypoxia)

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Under normal circumstances, PaO2 within the alveolar capillary reaches its maximum within approximately

0.25 seconds

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This is explained by the fact that deoxy-Hb,sucha as what exists in venous RBCs has a high affinity for

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Once the O2 binding sites on Hb are saturated, we see an increase in

PaO2 (because PaO2 represents dissolved O2)

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The alveolar-to-blood gas pressure gradient is the driving force for O2 diffusion from the

Alveolus

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Once PaO2 is near 100 mmHg, a significant pressure gradient no longer exists and we see no further diffusion of O2 from the alveolus to the

Capillaries

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During periods of increased cardiac output, blood moves through the capillaries more rapidly. This results in reduced

Perfusion limitation of O2 transfer

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Because the rate of O2 diffusion is really fast and the formation of oxyhemoglobin occurs within 100ths of a second, the only limitation to oxygenation is the

Rate of capillary blood flow

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The number of RBCs passing through a capillary per unit time

Rate of capillary blood flow

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Keep in mind that in a healthy lung, total O2 transfer is elevated with increased cardiac output due to recruitment of previously non-perfused capillaries which augments the surface area for

O2 diffusion

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Oxygen is carried in the blood in which two forms?

) Dissolved in plasma

2. ) Bound to Hb (SaO2)

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Incorporates these variables plus the amount of Hb

Total blood O2 (CaO2)

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The amount of gas dissolved in liquid is proportional to its partial pressure and temperature in equilibrium with

Gas

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The higher the partial pressure of alveolar O2, the higher the

O2 in solution in blood

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At normal body temperature (37 C) for each mmHg of PO2, there is

0.003 ml O2 / dl Blood

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Thus at normal conditions, what is the mL O2 / dL blood?

0.3mL O2 / dL blood (dissolved O2)

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Dissolved O2 can only meet a small portion of O2 demand, this is why it is critical that we have

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A complex of Heme (iron porphyrin) with a protein globin

Hemoglobin

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The oxygen binding capacity of Hb is

1.39 mL O2 / g Hb

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Therefore under normal conditions, how much O2 can be carried in the arterial blood in the form of HbO2?

20.7 mL O2 / dL blood

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Under normal conditions, the Hb is completely

Saturated

Oxygen saturation (SaO2) is commonly determined in the clinic with a pulse oximeter, which detects the color of

Hemoglobin

Non oxygenated Hb conformation appears

Purple (thus cyanosis is purple-blue)

Oxygenated Hb has which color?

Red

Saturation can also be used to determine concentration if you also know the

Concentration of Hb (usully 15g/dL)

If you know the O2 binding capacity and the concentration of Hb, PO2, and SaO2, you can calculate

O2 concentration

O2 concentration is proportional to PO2 in blood until

Hb binding sites are saturated

Upon saturation, the curve basically

Plateaus

In an O2 dissociation curve total CaO2 is primarily due to that complexed to

Hb -dissolved O2 makes up only a small fraction

In an O2 dissociation curve at exceedingly low PO2, the O2 dissociation curve is

Less steep

In an O2 dissociation curve with increased PO2, the plot becomes steeper as

More O2 is bound to Hb (thus increasing the binding capacity)

In an O2 dissociation curve the steep portion of the curve represents

The ability of Hb to off-load O2 at the tissue level as well as up-load O2 at alveolar capillary level

In an O2 dissociation curve at normal PaO2, Hb is

100% saturated with O2. Increasing PO2 can not augment saturation

Note that normal arterial blood is represented on the

Upper, flat portion of the O2 dissociation curve

On the O2 dissociation curve, we can see that lowering PO2 to approximately 60-70 mmHg will

Not effect CaO2 (SaO2)

This phenomenon enables us to go to reasonably high altitudes and be exposed to other moderate hypoxic conditions without a significant loss in the ability to

Deliver O2 to tissues

The sigmoidal shape of the oxygen dissociation curve shows a rapid increase in blood O2 (oxyhemoglobin) with increased

PO2 (up to approximately 70 mmHg)

After 70 mmHg, further increase in PO2 will not appreciably increase

O2 content

The steep central portion of the sigmoidal curve shows that Hb will readily unload O2 at the level of peripheral tissues in response to a small drop in

Capillary PO2

Moderate hypoxia or small decreases in ventilation and/or diffusion will not dramatically reduce

Oxygenation

At a constant PO2, a shift in the O2 dissociation curve to the RIGHT shows that

Increased unloaidng of O2 from Hb will occur

What 4 things will cause a rightward shift in the O2 dissociation curve, indicating a change of affinity of O2 for Hb?

1. ) Reduced pH 2. ) Increased PCO2 3. ) Increased DPG (increased with hypoxia) 4. ) Increased temperature

At a constant PO2, a leftward shift in the dissociation curve signifies that

O2 has higher affinity for Hb (like in fetal circulation)

CO2 is transported in the blood in which 3 forms?

1. ) Dissolved 2. ) Bicarbonate (HCO3-) 3. ) Carbamino compounds

Accounts for 10% of total CO2 expired by the lungs -20x more soluble than O2

Dissolved CO2

The reaction of H2O with CO2 to form H2CO3 and eventually HCO3- and H+ occurs in the

RBCs

What percentage of CO2 blown off at the lungs is transported as HCO3-? -Converted to CO2 upon reaching the lungs

60%

Carbon dioxide that is combined with terminal amino groups of proteins, particularly Hb, are known as

Carbamino compounds

Readily form in RBCs in the presence of CO2 and protonated deoxy-Hb

Carbamino compounds

Carbamino compounds account for what percentage of expired CO2?

30%

The dissociation of CO2 form Hb is affected by -due to competitive binding sites on Hb

O2 sat

The lower the PO2 and Hb binding, the greater the binding of

CO2 to Hb

At the level of the alveolar-capillary unit, high PO2 induces

Dissociation of CO2 from Hb for expiration

Enzymes, ligands, receptors, ion channels, transporters, and structural proteins are examples of molecules, the functions of which, will be affected by

Alterations in molecular charge

The principal chemoreceptors

Carotid chemoreceptors

Together, the peripheral chemoreceptors sense changes in

PCO2, pH, and PO2, with increased PCO2 as the main driving force

As PCO2 rises even a couple of mm Hg above the normal range, receptor activity is increased sending afferent signals from the 1. ) Aortic receptors via? 2. ) Carotid receptors via?

1. ) CN X | 2. ) Hering's Nerve

Hering's nerve essentially runs as a branch along

CN IX

These afferents are wired into ventilatory regulatory centers within the

Medulla

The peripheral chemoreceptors are more or less insensitive to changes in PO2 above approximately

50-60 mmHg

Thus, the predominant driving force to increase ventilation is

Hypercapnia as opposed to hypoxemia

Moderate decrease in PO2 will in fact induce an elevation in

Ventilation

However, this effect is transient since the rapid expulsion of CO2 via increased ventilation raises -counteracts increase in ventilation

Central chemoreceptors do not respond to

Hypoxemia

Instead, these receptors are exclusively designed to sense elevated

PCO2 within CSF (most likely as increase [H+])

The largest organ, the function of which is affected by fairly robust hydrostatic and pleural pressure gradients

The lung

In order for gas exchange to occur, the alveoli must be sufficiently

Ventilated

Importantly, alveoli ventilation (4-6 L/min) must also be matched with

Perfusion of alveoli

In general, pulmonry blood flow (perfusion) is set by which 3 things?

1. ) Local hydrostatic pressures 2. ) Alveolar pressures 3. ) Vascular resistance

In general, ventilation is dependent on which 3 things?

1. ) Pleural hydrostatic gradients 2. ) Airway geometry 3. ) Regional tissue compliances

Equals the entire output of the right ventricle, which matches cardiac output

Pulmonry blood flow

Consist of relatively thin walls when compared to those comprising the systemic vasculature

Pulmonary blood vessels

This histologic feature is largely due to a low compliment of

Vascular smooth muscle

Because of this, pulmonary vessels offer less resistance to

Flow

Highly distensible and under relatively low pressure

Pulmonary Vessels

The primary determinants of mean pulmonary artery pressure are

LA pressure, pulmonary blood flow, and pulmonary vascular resistance (PVR)

Itself is affected by lung volume, alveolar and interpleural pressures, right ventricular output, and gravity

PVR

The difference between the inside and outside pressures of a vessel

Transmural pressure gradient

If there is a large pressure gradient, pulmonary vessel diameter will

Increase

Will cause compression or collapse of a vessel

A negative transmural pressure

With inspiration, the alveoli expand, this is combined with an elongation and reduction in diameter of

Alveolar capillaries

This reduction in diameter causes an increased resistance to

Blood flow

With expiration, alveoli collapse, this is combined with a shortening and increased in diameter of

Alveolar capillaries

This increased diameter causes a decrease in resistance to

Blood flow

Actually distend with inspiration and compress with exhalation

Large pulmonary arteries and veins

An interesting phenomenon occurs during physical exertion whereby cardiac output can increase as much as 5-7x yet we do not see a correspondingly large increase in

Mean pulmonary arterial pressure

This trait enables pulmonary vascular resistance to decrease with elevations in -thus providing a greater matching of ventilation and perfusion

Pulmonary blood flow

Pulmonary capillaries posses a high

Critical opening pressure

That is, at resting cardiac output, when less ventilation is required, many of these vessels which surround less ventilated alveoli are

Constricted and relatively non-perfused

However, with increased metabolic demand, increased flow due to increased cardiac output forces these vessels to

Open

There is a regional distribution of

Pulmonary blood flow

Pulmonary blood pressure increases towards the

Base of the lung

This increased pressure recruits more vessels in this region to distend, allowing for

Disproportionately greater flow to base of the lung

Lower blood pressures are present towards the

Apex of the lung

Lower blood pressures are present outwards the apex of the lung, such that at rest, the critical opening pressure for these vessels is

Not achieved

There are several factors which actively regulate

PVR