Pulmonary circulation Flashcards
bronchial circulation characteristics
- )high pressure, low flow
- )supplies arterial blood to the tissues of the respiratory system (1-2% of CO)
- )branches off the thoracic aorta and delivers oxygenated blood to lungs
- )returns venous blood to pulmonary veins
pulmonary circulation characteristics
- )low-pressure, high flow
- )supplies deoxygenated venous blood to pulmonary capillaries for gas exchange
- ) returns oxygenated arterial blood to LA
- )Pulmonary arteries have large compliance (7ml/mmhg) because of shorter, thinner, larger diameter (less branching)
Pulmonary blood pressures
right ventricular diastolic / RA: 0-1 mmHg
right ventricular systolic / PA Systolic: 25mmHg
mean- 15mm Hg
PA diastolic: 8 mmHg
pulmonary caps: 7 mmHg
PWCP:5 mmHg
LA: 2mmHg
total blood volume of lungs
9% of total blood volume. 450mls. 70 mls in the pulmonary caps.
changes in blood volume of lungs
can change from 1/2 normal - 2 times normal.
Left heart failure or mitral valve problems can create increased resistance to flow leaving pulmonary caps. This is very bad and can cause 100% increase in volume and increases in pressure. ( not a good kid)
Alveolar pressure that causes constriction of surrounding arterioles to poorly oxygenated alveoli (opposite of what happens at a systemic level) why is this an advantage?
73 mmHg. Increases ventilation perfusion ratio which makes lungs more efficient because they are not supplying blood to alveoli that are not receiving ventilation.
pascal’s hydrostatic law
pressure at surface is equal to atmosphere. Pressure in bucket will increase 1 mmHg for every 13.6 mm (weight of water) due to gravity.
total pressure diference of lungs
about 23mm Hg
pressure difference at top of lungs compared to heart
about 15 mmHg lower
pressure difference at bottom of lungs compared to heart
about 8 mmHg higher
why is flow different at top of lungs than bottom
because there is a higher driving pressure (23 mmHg higher) Q= delta P/ R
zone 1 blood flow
no blood flow at any time. alveolar pressure is greater than pulmonary cap. pressure. This causes collapsing of lungs. Zone 1 does not occur in healthy lungs!!!
zone 2 blood flow
intermittent blood flow due to fluctuating pressure. systolic pulmonary cap. pressure will be higher than alveolar pressure. little or no flow during diastole
zone 3
continuous blood flow. pulmonary cap pressure is always higher than alveolar pressure. as blood pressure increases due to increases in CO zone 2 can convert to zone 3
perfusion no ventilation
only venous blood so PO2 and PCO2 equilibrate at venous blood pressures. PO2=40 PC02=45 V/Q=0
normal alveolar pressure
V/Q=normal PO2=104 PCO2=40
ventilation no perfusion
alveoli continually refreshed. both reach max O2 and min. CO2 possible in alveoli V/Q equals infiniti. Po2=149 PCO2=0
cardiac output increases …. times during heavy exercise
4-7
lungs handle increased flow during exercise by…
tripling number of open capillaries. doubling distension of open caps. allowing increased flow by decreased resistance. increasing pulmonary arterial pressure
affect of increased CO on pulmonary arterial pressure
increases in pressure small compared to increases in blood flow. This reduces work on RV and pulmonary edema
pulmonary response high LA pressure
slight increase in LA pressure cause dilation of pulmonary veins which reduces overall resistance to flow
left side heart failure LA pressure can go as high as
40 - 50 mmHg
pulmonary circ. can accommodate LA pressure up to
7 mmHG. Above this there will be in increase in pulmonary pressure all the way back to RV. LA pressure above 30 mmHg will result in formation of pulmonary edema
flow in capillaries of alveoli is also known as
sheet flow
Time it takes blood to travel through pulmonary caps during normal CO
.8 sec. can go as low as .3 sec with high CO
DIFFERENCES BETWEEN SYSTEMIC AND PULMONARY CAPILLARIES
- )pulmonary caps lower (7 vs. 17)
- )pulmonary caps interstitial fluid more neg (-5 to -8 vs.-3)
- )pulmonary caps are more leaky allowing protein to escape interstitial fluid which makes interstitial oncotic pressure higher (14 vs. 8)
- ) alveolar wall are thin are friable- can be broken if interstitial pressure is greater than alveolar pressure (i.e. if interstitial pressure is greater than 0) makes it relatively easy to move interstitial fluid into the alveoli
forces moving in and out in pulmonary caps
forces moving in :plasma colloid osmotic pressure (28) forces moving out: cap pressure (7) neg. interstitial pressure (8) interstitial fluid oncotic pressure (14) balance: net force outward (1)
causes of pulmonary edema
anything that increases rate of capillary filtration or decreases lymphatic removal.
most common causes: left side heart failure or mitral valve disease. damage to pulmonary cap membranes (pneumonia, toxic gases)
lethal pulmonary edema
25 -30 mmHg higher than safety level of 28 mmHg. Patient dead in less than 30
lungs can compensate for increases in pulmonary capillary pressure if it remains elevated for more than 2 weeks by…
large expansion in lymphatic blood vessels which increase capacity by 10 fold. allows patients with chronic cap. pressure greater than 40mmHg to live without developing pulmonary edema. Has to occur slowly over time!!!
pleural cavity fluid
lubricates, kept at a minimum by lymphatics, provides negative pressure (-4) to keep lungs expanded to normal resting size
pleural effusion caused by
blockage of lymphs, cardiac failure with high pulmonary pressures, greatly reduced plasma colloid pressure, infection/inflammation which changes permeability
Alveolar surface area
770-1076 ft ^2
Shunt unit
No ventilation so alveolar unit collapses. Perfusion continues. Examples include atelectasis and pneumonia .
Dead space unit.
Ventilation without perfusion. Example pulmonary embolus preventing blood flow through capillaries.
