Lecture 23: Pulmonary circulation Flashcards
Lung blood volume
450 mL blood within pulmonary circulation (9% of total blood volume in body)
Failure of left side of heart can cause pressure buildup in pulmonary circulation: increases blood volume as much as 100%, increases BP, mild systemic effect because systemic blood volume is 9 times that of the pulmonary system
Physiologic shunt of blood distribution
2% of blood in the systemic arteries is blood that has bypassed the pulmonary capillaries
It is blood coming from the lung parenchyma and left side of the heart
Contains less oxygen than expected
Blood distribution through lungs
When [O2] in alveoli is 70% or more below normal –>adjacent blood vessels constrict due to an unknown vasoconstrictor
In standing position there is little blood flow to the top of the lungs but about 5 times as much to bottom of lungs.
Lungs can be divide into 3 zones
Zones of lungs
Zone 1: No blood flow;local alveolar capillary pressure never rises higher than alveolar air pressure
Zone 2: Intermittent blood low. only during systole
Zone 3: continuous blood flow
Normally apices have zone 2 flow and lower areas have zone 3 flow.
Exercise can convert apices from zone 2 to zone 3 flow
Importance of pulmonary veins as blood reservoir
Due to distensibility pulmonary blood volume can increase by up to 400 mL which is released to general circulation when person stands up
Obstruction to normal lung causes blood flow through other lung to double, pulmonary pressure in the other lung only slightly increases due to passive dilation of pulmonary vessels
Pulmonary arterioles constrictors
Norepinephrine
Epinephrine
Angiotensin II
Some prostaglandins
Pulmonary arterioles dilators
Isoproterenol
Acetylcholine
Pulmonary venules constrictors
Serotonin
Histamine
E. coli endotoxin
Sympathetic vasoconstrictor nerve fibers
Outflow from cervical sympathetic ganglia
Decrease pulmonary blood flow by as much as 30%
Mobilize blood from pulmonary reserve
Physiology during heavy exercise
Blood flow through lungs increases by 4 to 7 times due to an increase number of open capillaries up to 3 times, distension of all capillaries increases flow rate up to 2 times==>Increase pulmonary arterial pressure
Increase number of open capillaries and distension pulmonary arterial pressure rises little even during maximum exercise by conserving energy of right side of heart and preventing significant rise in pulmonary capillary pressure
Left side heart failure
Left atrial pressure normally never above +6 mm Hg. In left heart failure:
- Blood begins to dam up in left atrium
- Left atrial pressure rises from 1-5 mm Hg to 40-50 mm Hg
- Increase above 8 mm Hg causes equal increase in pulmonary arterial pressure
- Above 30 mm Hg pulmonary edema is likely to develop
Pulmonary edema
Occurs when pulmonary capillary pressure is above 25 mm Hg.
Most common causes:
-Left sided heart failure or mitral valve disease
-Damage to pulmonary blood capillary membranes (infections, breathing noxious substances)
Lethal pulmonary edema can occur within hours or minutes
Pleural effusion
Edema of the pleural cavity.
Pumping of fluid from the pleural space by the lymphatics creates a normal pressure in the pleuyral space o -7 mm Hg,if the pressure becomes more positive(-4 mm Hg) lungs tend to collapse
Causes of pleural effusion
Blockage of lymphatic drainage from pleural cavity
Cardiac failure
Considerably reduced plasma colloid osmotic pressure
Infection/Inflammation
Hypoxia and pulmonary blood flow
Hypoxia increases pressure in the pulmonary artery possibly because of the release of a prostaglandin
Results of bronchial obstruction due to low alveolar pressure O2 effect, drop in pH due to accumulation of CO2 which produces vasoconstriction in pulmonary vessels and vasodilation in other tissues
Reduction of blood flow to a portion of the lung
