Pulmonary 2 Flashcards
HIGH PRESSURE
LOW FLOW
Branches of thoracic aorta
Systemic arterial blood
Trachea, bronchial tree, supporting tissues of the lungs
1-2% of total cardiac output
Bronchial arteries
LOW PRESSURE HIGH FLOW Venous blood from the right ventricle Pulmonary capillaries for gas exchange 5cm Thin walls, large diameter -> large compliance 7 ml/mmHg
Pulmonary artery
Blood volume in the lungs
450 ml 9% of total blood volume
70ml is in the pulmonary capillaries
Decreased alveolar oxygen reduces local alveolar blood flow and regulates pulmonary blood flow distribution
Alveolar O2 below 70 percent of normal (73mmHg)
Alveolar hypoxia -> vasoconstriction of adjacent pulmonary vessels
To redistribute blood flow where it is most effective
Hypoxic vasoconstriction
In the upright position, when the effects of gravity are apparent, the lung apices are relatively
underperfused owing to low arterial hydrostatic pressure at lung apices
Whereas in the upright position, the lung bases are relatively
overperfused
for this reason, pulmonary blood flow is often described as being divided into three different zones
Palveoli > Partery > P vein
Zone:
Zone 1
Lung apices are relatively underperfused
Partery > Palveoli > Pvein
Zone 2
Partery> P vein> Palveoli
Zone 3
Lung bases are relatively overperfused
No blood flow during the cardiac cycle
A pathologic condition that does not normally occur in the healthy lung
The lack of perfusion in this zone pulmonary blood flow quickly leads to tissue necrosis and lung damage
Occur when hydrostatic arterial and venous pressures are lower than alveolar pressure
Zone 1
Seen with severe hemorrhage and positive-pressure ventilation
Occur in lung apices, where arterial hydrostatic pressure are reduced relative to the pressures in arteries supplying the lower lung fields
Under these conditions, the blood vessel is completely collapsed and there is no blood flow during either systole or diastole
Zone 1 blood flow
This zone has intermittent blood flow during the cardiac cycle
No blood flow during diastole
This is typically exhibited by the upper 2/3 of the lungs
Alveolar pressures cause collapse of pulmonary capillaries during diastole, but pulmonary capillary pressures during systole exceed alveolar pressures, resulting in perfusion during systole
No blood flow during diastole because of collapse of pulmonary capillaries
Zone 2 blood flow
This zone has continuous blood flow during the cardiac cycle
This pattern of blood flow is characteristic of the lung bases which are situated below the heart
Pulmonary capillary pressures are greater than alveolar pressures during systole and diastole, which means that the pulmonary capillaries remain patent throughout the cardiac cycle.
Zone 3 blood flow
Causes by any factor that increases fluid filtration out of the pulmonary capillaries or impede pulmonary lymphatic function
Most common causes:
LSHF of mitral valve disease
Damage to the pulmonary blood capillary membranes
Pulmonary edema
Normal pleural fluid
50 ml
Excess fluid is pumped away by lymphatics:
Mediastinum
Lateral surface of parietal pleura
Superior surface of the diaphragm
This comes from the pumping of fluids out of the pleural space by the lymphatics
Negative pressure
Blockade of lymphatic drainage from the pleural cavity
Cardiac failure
Greatly reduced plasma colloid osmotic pressure
Infection or any other cause of inflammation
Pleural effusion
Important for efficient gas exchange
For gas exchange to occur efficiently at the pulmonary membrane, pulmonary ventilation and perfusion should be well matched
Optimal matching minimizes unnecessary ventilation of nonperfused regions and perfusion of nonventilated areas
Inefficient to perfuse unventilated alveoli or ventilate nonperfused alveoli
V/Q matching
V/Q at rest
0.8 with alveolar ventilation of about 4L/m and cardiac output of 5L/minute
The lung apices at rest are
underperfused and relatively overventilated (V/Q ratio = 3.3) but compared with the lung bases, they do not receive as much perfusion
The high V/Q ratio indicated discrepancy between the
amount of blood flow and ventilation
Conversely, the lung bases at rest are relatively
overperfused (V/Q ratio, 0.6)
Optimal matching of pulmonary ventilation and perfusion is achieved by
hypoxia-induced vasoconstriction and by changes in response to exercises
Mechanisms of Maintaining V/Q Matching
Hypoxia-induced vasoconstriction
Changes during exercise
Shunts blood to better-ventilated lung segments
Hypoxia-Induced Vasoconstriction
Recruitment
Distention
Changes during exercise
In most capillary beds, hypoxia stimulates vasodilation (eg. myogenic response of autoregulation)
In pulmonary vasculature, hypoxia stimulated
vasoconstriction of pulmonary arterioles, essentially preventing the perfusion of poorly ventilated lung segments (eg. as might occur in pulmonary disease)
This allows the lungs to optimize V/Q matching for more efficient gas exchange
Only about 1/3 of the pulmonary capillaries are open at rest.
Recruitment: opening of previously closed pulmonary capillaries because of increased pulmonary arterial pressures as may occur with exercise.
During exercise, additional capillaries are
Capillaries that are already open dilate to accomodate more blood
Open (recruitment) because of increased pulmonary artery blood pressure
Distention
During exercise, ventilation and perfusion (and hence gas exchange) occur more frequently efficiently because
With increased cardiac output, blood flow is increased to the relatively underperfused lung apices
Ventilation is increased to the relatively underventilated lung bases.
V/Q matching occurs more efficiently during exercise.
Blood that bypasses the lungs or for another reason does not participate in gas exchange
Shunt
Two types of shunts:
Anatomic shunt
Physiologic shunt
Blood flow bypasses lungs
Ex
Fetal blood flow
Intracardiac shunting (L->R, R->L)
Anatomic shunt
Blood flow to unventilated portions of lungs
Ex
Bronchial artery circulation
Pneumonia
Pulmo edema
Physiologic shunt
Oxygen content of systemic arterial blood at sea level
200 ml O2
197 ml from O2 bound to hemoglobin (98.5%)
3 ml from O2 physically dissolved (1.5%)
Cardiac output = 5L/min
O2 carried to tissues/min = 5L/min x 200 ml O2/L
= 1000 ml O2/min
SpO2 of 90% = pO2
pO2 60 mmHg
Any increase in pO2 will cause minimal increase in spO2
Shift to the right
A slight decrease in pO2 causes a profound change in SpO2
Shift to the left
Onset of cyanosis
SpO2 85%
Bohr Effect
Increased O2 delivery to tissues when CO2 and H+ shift O2-Hgb dissociation curve
Shift to the right
EPO is produced in the
peritubular capillaries of the kidneys
Strongest stimulus of EPO
Hypoxia
Composition of air:
79% nitrogen
21% oxygen
0% CO2
In a mixture of gases, each gas exerts a partial pressure proportional to its mole fraction
Total pressure =
sum of the partial pressures of each gas
760 mmHg
Oxygen binding curve is
sigmoidal for both Hb-F and Hb-A
Has higher affinity for oxygen because it binds to DPG less strongly
Hb-F
Factors that lower oxygen bindng to hemoglobin
Dec pH Inc CO2 Inc H ion concentration Inc BPG/DPG Inc temperature
Conditions where oxygen is low, O2-Hgb curve shifts to the right such that
Type of effect
more oxygen is readily available for distribution to the peripheral tissues
Bohr Effect
Shift to the right
HCO3 leaves the RBCs into the plasma
HCO3 is replaced by chloride
Chloride shift
Chloride shift
Partial pressure of CO2
Effect of allosteric factor to oxygen-binding curve
Increase in temperature increases O2 release
Shift to the right
Hypothermia causes shift to the
Left because it reduces oxygen requirements due to slow cellular metabolism
Increase 2,3 DPG decreases O2-Hb affinity leading to a shift to the
right
One DPG molecule binds to each Hb and stabilizes T form promoting
O2 release
Relaxed form Hgb
Binds better to O2
Tense/taut form
Decreased binding with O2
Shift to the right
Has an affinity for Hb 200 times that of oxygen
Once bound, does not readily dissociate
Affects O2 transport
Carbon monoxide
ETC happens in
Inner mitochondria
Oxidative phosphorylation
Complex IV involves
Cytochrome oxidase
Inhibits cytochrome oxidase
carbon monoxide
Cyanide
Final acceptor in ETC
oxygen
Binds only to metHb
Prevents reduction to active form
Impairs ability of blood to transport O2
Cyanide
Drug associated with cyanide poisoning
sodium nitroprusside
Antidote for cyanide poisoning
Thiosulfate
Hydroxocobalamin
Amyl nitrite
Describes the relationship between the rate of diffusion and the three factors that affect diffusion
The rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane
Fick’s Law of Diffusion
Receives entire cardiac output
Has markedly lower pressures
Smaller pressure drop across the pulmonary bed
Pulmonary circulation
Mean = 15
Most perfused area of the lung
Base
Zone 3
Most ventilated area of the lung
Apex
Increased hydrostatic pressure leads to
Edema
Secretion in pulmonary edema
Frothy
Blood tinged/pinkish secretion
First line drug for pulmonary edema
Furosemide
Transudative pleural fluid
Low albumin hypoalbuminemia
Liver cirrhosis
Nephrotic syndrome
Most common cause of V/Q mismatching
Hypoxia
