Pulmonary Blood Flow Gas Exchange And Transport 1 Flashcards
What does A stand for
Alveolar
What does a stand for
Arterial blood
What does ṽ stand for
Mixed venous blood (e.g. in pulmonary artery)
What does PaO2 stand for
Partial pressure of oxygen in arterial blood
What does PACO2 stand for
Partial pressure of carbon dioxide in alveolar air
What types of circulation are there
Bronchial circulation (nutritive) Pulmonary circulation (gas exchange)
What supplies bronchial circulation
The bronchial arteries that arise from systemic circulation
What type of blood does bronchial circulation supply and to where
Supply oxygenated blood to the airway smooth muscle, nerves and lung tissues
What does pulmonary circulation consist of
Left and right pulmonary arteries that originated from the right ventricle
What does pulmonary circulation carry
The entire cardiac output from the right ventricle
What does pulmonary circulation supply
The dense capillary network surrounding the alveoli and returns oxygenated blood to the left atrium through the pulmonary vein
What type of system is pulmonary circulation
High flow, low pressure system
What does air diffuse across
Membranes down partial pressure gradient
What obeys the rules for simple diffusion
The diffusion of gases between the alveoli and the blood
Gases will move across a membrane which is permeable to that gas down its partial pressure gradient and shall continue to do so until equilibrium is reached
State 5 features about the rate of diffusion across the membrane
Directly proportional to the partial pressure gradient.
Directly proportional to gas solubility
Directly proportional to the available surface area
Inversely proportional to the thickness of the membrane
Most rapid over short distances
Why are alveoli efficient in gas exchange
They have a large surface area and a thin membrane with a short diffusion distance
What is emphysema
The destruction of alveoli which reduces the surface area for gas exchange
What are the Po2 levels in patients with emphysema
Normal or low Po2 in the alveoli and a low Po2 in the capillaries
What is fibrotic lung disease
A thickened alveolar membrane which slows gas exchange
There is a loss of lung compliance which may decrease alveolar ventilation
What are the Po2 levels in patients with fibrotic lung disease
Low Po2 in alveoli and a low Po2 in the capillaries
What is pulmonary edema
When the fluid in the interstital space increases the diffusion distance
Describe the Pco2 and Po2 levels
Arterial Pco2 could be normal due to a higher CO2 solubility in water
Po2 in alveoli = normal
Po2 in alveoli normal while Po2 in capillaries kow
What does asthma cause
Increased airway resistance and decreases airway ventilation
Describe the Po2 levels in asthma
Bronchioles are constricted which cause a low Po2 in the alveoli and capillaries.
What is ventilation
Air getting to alveoli L/min
What is perfusion
Local blood flow L/min
What is the most optimal condition in the ventilation-perfusion releationship
When the ventilation in alveoli is matched to perfusion through the pulmonary capillaries
What is blood flow distribution in the lung influenced by
Hydrostatic (blood) pressure (Pa) and alveolar pressure
What is blood flow inverserly proportional to
Vascular resistance and declines with height across the lung.
At the base of the lungs is blood flow high or low and why
High
The arterial pressure exceeds the alveolar pressure so vascular resistance is low
At the apex of the lungs is blood flow high or low and why
Low
The arterial pressure is less than the alveolar pressure which will compress the arterioles and vascular resistance is increased
From what rib does ventilation exceed blood flow
About rib 3 upwards
Why does the ratio of ventilation to perfusion in the upright position within the lung change from the base to apex
Gravity
What are the 3 types of ratios which can occur
Perfectly matched Ventilation:Perfusion ratio = 1.0
Mismatch 1 Ventilation>Perfusion ratio > 1.0
Mismatch 2 Ventilation
Where does most mismatching occur
Apex and then autoregulated to keep the ventilation perfusion ration close to 1.0
What happens if ventilation decreases in a group of alveoli
Pco2 will increase and Po2 will decrease
The blood flowing past those alveoli will not be oxygenated
What is a shunt
The dilution of oxygenated blood from better ventilated areas
What does a decreased tissue Po2 around under-ventilated alveoli cause
Constriction of their arterioles, diverting the blood to better-ventilated alveoli
What is the constriction in response to hypoxia specific to
Pulmonary vessels (systemic vessels will dilate)
What will increased Pco2 cause
Mild bronchodilation
When does autoregulation occur
When ventilation is greater than blood flow creating an alveolar dead space
What happens when the alveolar Po2 increases in the alveolar dead space
Pulmonary vasodilation
What happens when the alveolar Pco2 decreases in the alveolar dead space
Bronchial constriction
What is a shunt
The passage of blood through areas of the lung that are poorly ventilated
What is a shunt opposite to
Alveolar dead space
What is the alveolar dead space
Alveoli that are ventilated but not perfused
What is the anatomical dead space
Air in the conducting zone of the respiratory tract unable to participate in gas exchange as walls of airways in this region (nasal cavities, trachea, bronchi and upper bronchioles) are too thick
Physiological dead space =
Alveolar DS + anatomical DS
