57: Ventilation Perfusion Flashcards by Deleted Deleted

Alveolar Ventilation (VA)

4L/min at rest

How well did you know this?

Not at all

Perfectly

Perfusion (Q)

cardiac output 5L/min

How well did you know this?

Not at all

Perfectly

Alveolar- arterial oxygen (A-a O2) gradient

5 to 15 mm

Hg is due to venous admixture

How well did you know this?

Not at all

Perfectly

Hypoxemia

PaO2 below 85 mm Hg

Increased venous admixture results in low O2 tension in
the blood

How well did you know this?

Not at all

Perfectly

Dead Space

V(D)

Volume of inhaled air that does not
participate in gas exchange

How well did you know this?

Not at all

Perfectly

Anatomic dead

space

Conducting airways

150 mL

How well did you know this?

Not at all

Perfectly

Alveolar dead

space

Alveoli with no perfusion

How well did you know this?

Not at all

Perfectly

Physiologic Shunt

total venous

admixture

How well did you know this?

Not at all

Perfectly

Cause 1 of Physiologic Shunt?

Anatomic shunt

right –to –left shunt

ex: bronchial circulation

How well did you know this?

Not at all

Perfectly

Cause 2 of Physiologic Shunt?

50% from low VA/Q

ex: partially obstructed airway

How well did you know this?

Not at all

Perfectly

“wasted air”

all inspired air
does not participate
in gas exchange

anatomic + alveolar = physiologic dead
space

How well did you know this?

Not at all

Perfectly

“wasted blood”

all blood entering the lung is not fully oxygenated

anatomic + low (VA/Q) ratio = physiologic shunt

How well did you know this?

Not at all

Perfectly

Lung is slinky

top: coils are pulled apart, weight pulling down on it
middle: coils tighter than the top, half of weight pulling down on it
bottom: coils are tighter, little weight pulling down on it
* lungs rest on abdomen

How well did you know this?

Not at all

Perfectly

Pressure Volume at FRC

apex less compliant than base

at rest: apex 70% and base 15% distended

How well did you know this?

Not at all

Perfectly

What is the change in volume at apex during inspiration?

Significantly less than base

ventilation gradient aligned with gravity

How well did you know this?

Not at all

Perfectly

Pulmonary circulation

high-flow,

low-pressure, low-resistance system

How well did you know this?

Not at all

Perfectly

Is the base or apex of the lung more compliant?

The base of the lung

How well did you know this?

Not at all

Perfectly

There is more resistance to blood flow toward the apex of the lung b/c upward flow runs against…….

Hydrostatic pressure

How well did you know this?

Not at all

Perfectly

High alveolar volume in the apex reduces ,,,,,,,,

Blood flow (this restriction is not present when alveolar pressure falls below pulmonary arterial pressure)

How well did you know this?

Not at all

Perfectly

Apex of Lung: Ventilation

Intrapleural pressure more………..
Greater transmural pressure gradient
Alveoli ………….
Less ventilation

Negative

Larger, Less compliant

How well did you know this?

Not at all

Perfectly

Apex of Lung; Perfusion

Low Intravascular pressures
…….. Recruitment and Distention
…….. Resistance
Less blood Flow

Less Recruitment

Higher Resistance

Base of Lung: Ventilation

Intrapleural pressure less negative
……….. Transmural Pressure Gradient
Alveoli…………
More Ventilation

Smaller Transmural Pressure Gradient

Alveoli smaller, more compliant

Base of Lung: Perfusion:

………. Vascular Pressures
……….. Recruitment and Distention
Lower resistance
Greater Blood Flow

Greater vascular pressures

More Recruitment

………….. and ……… are both gravity dependent

Ventilation and Blood Flow

Ventilation-perfusion ratio ........down the lung

Decreases

........... is more efficient at the apex of the lung as compared to the base.

Gas Exchange

For low V/Q ratio (lots of blood or too little ventilation); causes the blood coming into the area to be directed to other parts of the lung.

Hypoxic vasoconstriction

for high V/Q ratio, the bronchi will constrict slightly to increase the resistance and decrease the amount of ventilation coming into an area that is not well perfused thus limiting the amount of alveolar dead space

Bronchoconstriction

The patient with a V/Q = 0 may most likely not benefit from supplemental oxygen because there is .........

No ventilation

Regional low VA/Q ratio causes A-a O2 gradient to .....

Increase

An Anatomic shunt causes A-a O2 gradient to .....

Increase

Diffusion block causes A-a O2 gradient to .....

Increase

How does hypoventilation effect A-a O2 gradient?

No Change

If the patient has hypoxemia and PaCO2 is less than 40 and A-a is outside of the 5-20 mmHg points to .......

Hypoventilation

........ has high alveolar pressure –which increases resistance in pulmonary circulation

Apex of lung

V/Q = 0 means

Perfusion of an area with no ventilation i.e. a shunt

V/Q = infinity means

Dead space –ventilation with no perfusion

The healthy lung has ....... the majority of respiratory segments blood flow (by controlling pulmonary capillary flow) to ventilation –and therefore have a V/Q of ~1

Matched

V/Q mismatch always ......the oxygen content of the venous admixture and increases the A-a gradient.

Lowers | not necessarily hypercapnia though

↑V/Q = >1 =

↑PO2 ↓PCO2

V/Q = 1 =

PO2 100, PCO2 40

↓V/Q = <1 =

↓PO2 ↑PCO2

With high altitude, alveolar PO2 ......... which results in decreased arterial PO2 (hypoxemia)

Decreases

.......... is stimulated by the hypoxemia experienced by carotid/aortic bodies

Ventilation

Minute alveolar ventilation ..........in an attempt to restore blood oxygen levels

Increases

During a rapid Altitude Increase, leads to:

* Hypoxemia –stimulated ventilation * PCO2 declines producing resp. alkalosis * These tend to counter the increase in ventilation due to hypoxia * Over 2-3 days –blood pH is corrected (acidified) by renal excretion of HCO3-. CSF also returns to normal with HCO3excretion. * Full hypoxic ventilatory drive is then restored

How can polycythemia be caused by hypoxemia?

Low PO2 of kidney stimulates the release of erythropoietin –which in turn stimulates bone marrow to increase RBC production

During mountain sickness, the pulmonary hypoxic vasoconstriction ....... pulmonary vascular resistance –......... hydrostatic pressure in the pulmonary circulation

Increases | Increasing

During mountain sickness, .........sympathetic stimulation and cardiac output due to arterial chemoreceptor stimulation

Increase

........ is sensitive to hypocapnea –it is a strong cerebral vasoconstrictor

Cerebral Circulation

Common symptom of altitude sickness

Headaches, mental confusion

Low PO2 leads to cerebral vessel ........... and hyperperfusionof the vessels. Increases the likelihood of cerebral edema

Vasodilation