Resp 2 Flashcards
“It takes a red blood cell about --- seconds to travel through the pulmonary circulation at resting cardiac output; about --- of a second of this time is spent in pulmonary capillaries.”
4 to 5
0.75
pulmonary circulation sequence
Vena Cava Right Atrium Tricuspid Valve Right Ventricle Pulmonary Valve Pulmonary Artery Pulmonary Capillaries Pulmonary Vein Left Atrium Bicuspid Valve Left Ventricle Aortic Valve Aorta
Pulmonary circulation has
(4) than the
systemic circulation.
lower pressures,
lower resistance,
higher compliance,
& lower volume (~450 ml of 5oo ml)
Pulmonary Arteries & Arterioles (2)
– Diameters are larger than systemic arteries and
arterioles
– Walls are thin and distensible–large compliance
Pulmonary Capillaries (2)
– More distensible than systemic capillaries
– There is a population that is closed at rest
About 280 billion pulmonary capillaries supply approximately
300 million alveoli, resulting in a
potential surface area for
gas exchange estimated to be 50 to 100 m2.
Pulmonary Veins (1)
– Much shorter than systemic veins
Bronchial Circulation (Part of Systemic Circuit) Supplies
oxygen and nutrients to the tracheobronchial tree down to the
terminal bronchioles and also pulmonary blood vessels, visceral pleura,
nerves and hilar lymph nodes.
Bronchial flow is about -% of
cardiac output of the left
ventricle.
2
Bronchial flow is about 2% of
cardiac output of the left
ventricle.
This means that blood in the
LA has slightly
lower O2 concentration than blood in the pulmonary capillaries (PaO2 = 95 mmHg (not 100)) since some deoxygenated blood from the bronchial veins mixes with oxygenated blood in the pulmonary veins.
Structures in the Respiratory Zone receive
oxygen directly by — and receive —
diffusion from the
alveolar air
nutrients from the
mixed venous blood in pulmonary
circulation.
The Pulmonary Circulation has Low
2
Pressure & Resistance
Pulmonary capillary pressure: ~–mmHg
7
Pulmonary venous/Left Atrial pressure: ~–mmHg
2
Pulmonary blood volume accounts for ~—% of blood volume
(450ml) but is is highly —.
9
variable
Pulmonary blood volume accounts for ~9% of blood volume
450ml) but is is highly variable. (3
– Volume increases during inspiration
– Lying down increases the blood volume
– Disease states (ex. heart failure) can increase volume
Pulmonary vessels are far more
distensible (compliant)
and able to alter their size and adjust to changing
pulmonary volumes.
Pulmonary vessels are far more distensible (compliant)
and able to alter their size and adjust to changing
pulmonary volumes. (2)
– Even though Cardiac Output increases 4-7 times with heavy
exercise, there is only a small increase in pulmonary artery
pressure.
– At rest, multiple pulmonary capillary networks are closed but are
capable of opening if necessary.
The Pulmonary Circulation is not as Prone to
— as the Systemic Circulation.
Hypertension
During exercise, CO (flow) may increase 7-fold...but MAP in the pulmonary circulation will only increase 1-2 mmHg. How is that possible?
An increase in Flow (CO) to lungs
will decrease pulmonary
Resistance through: (2)
- Recruitment of pulmonary
capillaries - Distension of pulmonary
capillaries
An increase in blood flow leads to a decrease in pulmonary vascular resistance. What is the mechanism that produces this response?
When PAO2 (Alveolar concentration of O2) drops 70% below normal,
adjacent blood vessels constrict. The resistance can
increase more than 5X.
If instead PAO2 is high, adjacent vessels will dilate.
The functional result is that blood is delivered to alveoli where
it will be most effective at gas exchange.
This matches perfusion (blood flow) with ventilation (air flow).
What then would happen throughout the pulmonary
circulation at a high altitude where PAO2 is reduced?
Does the same response happen in the systemic circulation
when PaO2 levels drop?
Vasoactive Substances for the Pulmonary Arterioles:
Vasodilators (7)
- High O2 in alveoli
- Dopamine
- Bradykinin
- Prostacyclin
- Nitric Oxide
- Histamine (H2)
- Acetylcholine
Vasoactive Substances for the Pulmonary Arterioles:
Vasoconstrictors (7)
- Low O2 in alveoli
- High CO2 in alveoli
- Norepinephrine
- Angiotensin II
- Endothelin
- Vasopressin
- Thromboxane A2
— response than what is produced in systemic
arterioles with the same changes in gas concentration.
Opposite
Lung Volumes have a — Effect on
Pulmonary Vascular Resistance (PVR)
Passive
Alveolar Vessels:
Pulmonary capillaries, smallest arterioles &
venules
Extra-alveolar Vessels:
All other vessels
PVR is the the total of
Alveolar Vessels + Extra-alveolar Vessel Resistance
When the alveoli expand
during INSPIRATION….. (2)
(1) Alveolar vessels are compressed/elongated and their resistance increases (2) Extra-alveolar vessels have decreased resistance
Resistance in the pulmonary circulation is
lowest when lung volume is equal to —
FRC
At low lung volumes, extraalveolar vessel resistance ---, which --- total PVR.
increases
increases
At high lung volumes, alveolar vessel resistance --- which --- total PVR.
increases
increases
FRC (Functional
Residual Capacity):
The volume of air in
the lungs after a
normal (TV) expiration.
