V: Ventilation and Perfusion Flashcards
Total volume mobilized during the total number of exhalations
Ventilation
Ventilation equation
Tidal V x Respiratory Rate
Standard tidal volume
500mL
Standard breathings per minute
15 breaths per minute
Normal ventilation is
7500 mL per minute
Current volume is made up of
Alveolar volume and physiologically dead space volume VD
Subtypes of physiologically dead volume
Anatomically dead space
Alveolar dead space
Of the air inspired how much remains in anatomically dead space and how much is actually entering the respiratory zone
Total = 7500mL/min
Air in anatomically dead space = 150mL/min
Air into respiratory zone = 5250mL/min
Of the air inspired how much remains in anatomically dead space and how much is actually entering the respiratory zone
Total = 7500mL/min
Air in anatomically dead space = 150mL/min
Air into respiratory zone = 5250mL/min
Air entering into respiratory zone =
Alveolar ventilation
How is alveolar ventilation measured
CO2 expired, Bohr’s method
Is there diffusion in anatomically dead spaces
No
How is anatomically dead space measured (Procedure)
Fowler method, where you breath in N2 (measured), then a single O2 breath taken.
O2 will be mixed with N2 in anatomically dead space therefore [N2] exhaled will increase
How much air inside alveolar dead space
0 in normal conditions, but relevant in pathology
Normal ratio of dead space/tidal volume
0.2 - 0.3
PCO2 in alveolar and arterial blood are
IDENTICAL
Differences between Fowler and Bohr method
Fowler measured the volume in conduction airways
Bohr measured the volume of the lung that does not clear up CO2
In normal conditions, measurements of Fowler and Bohr should be
Equal
Does the entire cardiac output pass through pulmonary circulation
Yes, except bronchial and coronary circulation
Cardiac output is measured through which method
Thermoregulation method
How is the process of thermoregulation
Cold serum administered to right atrium
Travels through circulatory system
When it reached RA again –> drop in venous blood
Normal cardiac output
5L
How does fluid express different gravities
Through hydrostatic pressure
Does perfusion increase down the lung
Yes
Does ventilation increase down the lung
Yes
Which increases more going down the lung, perfusion or ventilation
Perfusion
Is hydrostatic pressure greater or lower at the base of the lung
Greater, it increases going down the lung
Consequences of increased hydrostatic pressure at base of lung
Greater perfusion and ventilation
What is the ratio of air reaching tissues
V / Q
Is ventilation at apex greater than perfusion
Yes
If V>Q then
Dead space in APEX
If V/Q = 1 then
At middle of lung
If V < Q
Shunt at base of lung
Pulmonary diffusion at APEX
V/Q > 1
Alveolar P > Arterial P > Venous P
Pulmonary diffusion at MIDDLE LUNG
V/Q = 1
Arterial P > Alveolar P > Venous P
Pulmonary diffusion at BASE
V/Q < 1
Arterial P > Venous P > Alveolar P
Flow at APEX determined by
Atriovenous pressure
Flow at MIDDLE determined by
Arterio-alveolar pressure
Flow at BASE determined by
Arteriovenous pressure
Ventilation perfusion ratio =
0.8
If V/Q > 0.8…
Apical zone, dead space
If V/Q < 0.8…
Basal space, shunt
Is alveolar PO2 smaller than atmospheric PO2
Yes
PO2 alveolar
104mmHHg
PO2 atmospheric
160mmHg
Why does PO2 drop from 160mmHg to 150mmHg entering the airways
Because due to humidification
Blood ENTERING alveolar capillary PO2 and PCO2
PO2 = 40mmHg PCO2 = 45mmHg
Blood LEAVING alveolar capillary PO2 and PCO2
PO2 < 100mmHg
PCO2 = 40mmHg
In alveolar obstruction what accumulates in the blood
CO2, because there cannot be an effective gas exchange
Reaction of organism in blockage situation
Vasodilate to increase perfusion so blood of poorly ventilated capillaries mixed with blood of well ventilated capillaries
Result in blood from vasodilation and mixing blood of well and poorly ventilated areas
Decrease in blood [O2]
Does vasodilation actually happen then in the organism
No
What does ACTUALLY occur in the organism as a response to a shunt
There is vasoconstriction of poorly ventilated areas to prevent a drop in O2
What is hypoxia
Decreased O2 in blood
How does the organism react to hypoxia
By vasoconstricting vessels of poorly ventilating areas to redirect blood to the good ventilated areas
EX. Mountaneers
Decreased barometric pressure –> decreased alveolar O2 –> body reacts by vasoconstricting poorly ventilated areas
EX. COPD
Alveoli are obstructed so no gas exchange –> PO2 decreases in alveoli –> vasoconstriction of poorly ventilated areas
IN COPD, vasoconstriction of poorly ventilated areas can lead to
Pulmonary hypertension
Alveolar obstruction occurs when
Alveoli are obstructed so the blood passing through the capillaries of these alveoli do not carry out the process of gas diffusion
Perfusion obstruction occurs when
Alveolar capillaries are obstructed so air enters during respiration but not able to diffuse into blood
Airway obstruction equals to
Shunt (at base of lung) because V/Q < 0.8
Because there is little ventilation and great perfusion due to alvoelar obstruction
Perfusion obstruction equals to
Anatomical dead space (Apex) because V/Q > 0.8
Since ventilation is much greater than perfusion due alveolar capillary obstruction
What would be the consequence of perfusion obstruction
Thrombus, clot that forms on the wall of a blood vessel
What would a thrombus cause
Hypertension
Why is PO2 exiting the lung not equal to alveolar 104mmHg
Because the PO2 exiting the lung is a mixture of all exchanges happening at different levels –> 98mmHg