Respiratory - Physiology Flashcards
What are the effects of surfactant secretion in the lungs?
Decreased alveolar surface tension, increased compliance, and decreased work of inspiration
Name five important molecules produced by the lungs.
Surfactant, prostaglandins, histamine, angiotensin-converting enzyme, and kallikrein
In addition to inactivating bradykinin, what other reaction does angiotensin-converting enzyme catalyze?
The conversion of angiotensin I to angiotensin II
Angiotensin-converting enzyme inhibitors increase bradykinin, which leads to which two common adverse effects?
Cough and angioedema
A deficiency of surfactant leads to what neonatal condition?
Respiratory distress syndrome
Give the equation for calculating collapsing pressure.
Collapsing pressure = 2 × tension / radius
What is the effect of histamine on the airways in the lung?
Increases bronchoconstriction
In the lung, _____ (angiotensin-converting enzyme/kallikrein) inactivates bradykinin, _____ (angiotensin-converting enzyme/kallikrein) activates bradykinin.
Angiotensive converting enzyme; kallikrein
What is the term for the volume of air in the lungs after maximal expiration?
Residual volume
What is the term for the volume of air that can still be breathed out after normal expiration?
Expiratory reserve volume
What is the term for the volume of air that moves into the lungs with each quiet inspiration?
Tidal volume
How much is the typical tidal volume?
500 mL
What is the term for the volume of air in excess of tidal volume that moves into the lung on maximum inspiration?
Inspiratory reserve volume
What is the term for the maximum volume of air that can be inhaled and exhaled?
Vital capacity
Vital capacity equals the sum of what three lung volumes?
Tidal volume, inspiratory reserve volume, and expiratory reserve volume
The residual volume plus the expiratory reserve volume equals what?
The functional reserve capacity
Describe the functional reserve capacity.
The volume left in the lungs after normal expiration
The inspiratory reserve volume plus the tidal volume equals what?
Inspiratory capacity
The inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume plus the residual volume equals what?
Total lung capacity
What is the term for the lung volume that includes all capacity except the residual volume?
Vital capacity
Which lung volume cannot be measured on spirometry: inspiratory reserve volume, tidal volume, expiratory reserve volume, or residual volume?
Residual volume
What is the formula for calculating dead space volume given an arterial blood gas and a measurement of exhaled carbon dioxide?
Dead space volume = tidal volume × [(partial arterial pressure of carbon dioxide - partial expiratory pressure of carbon dioxide) / partial arterial pressure of carbon dioxide]
Physiological dead space includes the anatomical dead space of the _____ (conducting/respiratory) airways plus the functional dead space in _____ (alveoli/bronchioles).
Conducting; alveoli
Which section of the healthy lung contributes more to functional dead space: the apex or the base?
The apex
Describe the natural tendency of movement of the lung and chest wall.
The lungs tend to collapse inward and chest wall springs outward
At the point of functional residual capacity (i.e., at the end of a normal expiration), what is the value of the air pressure within the lungs?
At functional residual capacity, the pressure within the lungs is equal to atmospheric pressure
What balances the inward elastic pull of the lung at the point of functional residual capacity (i.e. at the end of a normal expiration)?
The outward pull of the chest wall
How many polypeptide subunits make up hemoglobin?
Four
Adult hemoglobin is formed from two _____ subunits and two _____ subunits.
α; β
What are the two conformational forms of hemoglobin?
Relaxed and taut
Which form of hemoglobin has a low affinity for oxygen, relaxed or taut?
Taut
Which form of hemoglobin has a high affinity for oxygen, relaxed or taut?
Relaxed
Fetal hemoglobin is composed of two ____ subunits and two ____ subunits.
α; γ
Does hemoglobin have positive or negative cooperativity with respect to oxygen binding and affinity?
Positive; the more oxygen molecules bind, the more affinity hemoglobin has for additional oxygen molecules
Does fetal hemoglobin have a higher or lower affinity for oxygen compared with adult hemoglobin?
Higher; as a result, fetal blood can draw oxygen across the placenta
Does fetal hemoglobin have a higher or lower affinity for 2,3-biphosphoglycerate compared with adult hemoglobin and what is the result?
Lower; increased affinity for oxygen
An increase in which five factors will favor the taut form of hemoglobin over the relaxed form and decrease affinity for oxygen?
Chloride, hydron, carbon dioxide, 2,3-bisphosphoglycerate, and temperature
Which form of hemoglobin will lead to decreased oxygen unloading?
The relaxed form (remember: “When you’re Relaxed, you do your job better [carry oxygen]”)
With respect to cooperativity and affinity for oxygen, what are the differences between hemoglobin and myoglobin?
Myoglobin has high affinity for oxygen but does not display cooperativity of oxygen binding because it has only a single subunit
Does hemoglobin contain iron in the oxidized state or in the reduced state; Fe2+ or Fe3+; ferric iron or ferrous iron?
The reduced state; Fe2+; ferrous iron
Does methemoglobin contain iron in the oxidized state or the reduced state; Fe2+ or Fe3+; ferric iron or ferrous iron?
The oxidized state; Fe3+; ferric iron
Hemoglobin contains _____ (ferric/ferrous) iron, whereas methemoglobin contains _____ (ferric/ferrous) iron.
Ferrous; ferric
What are the mechanisms of action of nitrites and thiosulfate in the treatment of cyanide poisoning?
Nitrites oxidize the iron in hemoglobin to form methemoglobin; methemoglobin then binds to cyanide ions, which in turn allows cytochrome oxidase to function; after administering nitrites, thiosulfate is used to bind to the cyanide-methemoglobin complexes, to form thiocyanate, which is renally excreted
When another molecule, such as CO, binds to hemoglobin in place of oxygen, what are the systemic effects?
This leads to tissue hypoxia from decreased oxygen saturation and decreased oxygen content in the blood
Which has a higher affinity for oxygen, hemoglobin or methemoglobin?
Hemoglobin
What is the treatment for toxic levels of methemoglobin?
Methylene blue (remember: METHemoglobinemia can be treated with METHylene blue)
Which has a higher affinity for cyanide, hemoglobin or methemoglobin?
Methemoglobin
What is the name of a form of hemoglobin in which carbon monoxide is bound instead of oxygen?
Carboxyhemoglobin
In treating cyanide poisoning, ______ is the compound used to bind cyanide, forming _____ which is a renally excretable compound.
Thiosulfate; thiocyanate
What is the treatment for cyanide poisoning?
Nitrites, and subsequently thiosulfate
Does carbon monoxide or oxygen have a greater affinity for hemoglobin?
Carbon monoxide has 200 times the affinity of oxygen
What is the shape of the oxygen-hemoglobin dissociation curve?
Sigmoidal
When the oxygen-hemoglobin dissociation curve shifts to the right, what happens to the affinity of hemoglobin for oxygen?
A right shift decreases the affinity of hemoglobin for oxygen
When the oxygen-hemoglobin dissociation curve shifts to the right, what happens to the P50?
A right shift increases the P50, indicating that higher oxygen pressure is required to saturate hemoglobin
A shift of the oxygen-hemoglobin dissociation curve to the right facilitates what process in tissue?
The unloading of oxygen to tissue
When the oxygen-hemoglobin dissociation curve shifts to the left, what happens to the affinity of hemoglobin for oxygen?
A left shift increases the affinity of hemoglobin for oxygen
When the oxygen-hemoglobin dissociation curve shifts to the left, what happens to the P50?
A left shift decreases the P50; hemoglobin is saturated at lower pressures of oxygen
A decrease in the partial pressure of carbon dioxide causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Left
A decrease in temperature causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Left
A decrease in pH causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Right
A decrease in 2,3-diphosphoglycerate causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Left
The oxygen-hemoglobin dissociation curve for fetal hemoglobin is shifted in what direction?
Left; fetal hemoglobin has higher affinity for oxygen than adult hemoglobin
An increase in the partial pressure of carbon dioxide causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Right
An increase in temperature causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Right
An increase in pH causes a ______ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Left
High altitude induces what change in the oxygen-hemoglobin dissociation curve?
A right shift
An increase in 2,3-diphosphoglycerate causes a _____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Right
In the oxygen-hemoglobin dissociation curve, what values are represented by the x and y axes?
The partial pressure of oxygen represents the x axis, while hemoglobin saturation represents the y-axis
Hemoglobin can bind four oxygen molecules and has a higher affinity for each subsequent oxygen molecule bound. What is the term for this phenomenon?
Positive cooperativity
An increase in the amounts of which six factors causes a right shift of the oxygen-hemoglobin dissociation curve?
CO2, hydrogen ions (therefore acidity), altitude, 2,3-DPG, metabolic needs (eg, exercise), and temperature
(remember: CADET face right: CO2, Acid/Altitude, DPG [2,3-DPG], Exercise, Temperature)
Normally, pulmonary circulation is a _____ (high/low) resistance, _____ (high/low) compliance system.
Low; high
Within the lungs, a decrease in the partial pressure of oxygen in arterial blood causes what process to occur within the vasculature in the area?
Hypoxic vasoconstriction; in the rest of the body hypoxia causes vasodilation
Within the lungs, hypoxic vasoconstriction serves what physiologic function?
It shifts blood away from the poorly ventilated regions of the lung to the well-ventilated regions of the lung
Under normal, healthy conditions, is oxygen a perfusion-limited gas or a diffusion-limited gas?
Perfusion-limited gas
Is carbon dioxide a perfusion-limited gas or a diffusion-limited gas?
Perfusion-limited gas
Is nitrous oxide a perfusion-limited gas or a diffusion-limited gas?
Perfusion-limited gas
Is carbon monoxide a perfusion-limited gas or a diffusion-limited gas?
Diffusion-limited gas
Under conditions of strenuous exercise, is oxygen a perfusion-limited gas or a diffusion-limited gas?
Diffusion-limited gas
Under perfusion-limited conditions, where along the length of the pulmonary capillary do the partial pressures of a gas equilibrate?
Early; gas exchange is not limited by its ability to cross the membrane, only by the supply of blood
Under perfusion-limited conditions, how can gas exchange be increased?
By increasing blood flow
Under what three conditions is oxygen a diffusion-limited gas?
Exercise, emphysema, and fibrosis
Under diffusion-limited conditions, where along the length of the pulmonary capillary does the gas equilibrate?
It does not equilibrate; the characteristics of the gas cause it to diffuse slowly across the alveolar membrane
What are the cardiac complications of pulmonary hypertension?
Cor pulmonale and right ventricular failure
What are three signs of right ventricular heart failure due to cor pulmonale?
Jugular venous distention, edema, and hepatomegaly
What is the equation for diffusion of a gas across a membrane?
Vgas = A/T × Dk(P1- P2), where A = area, T = thickness, and Dk(P1 - P2) = difference in partial pressures
In the equation for gas diffusion, which variable is affected by emphysema and how?
Area of membranes available for gas transfer is decreased in emphysema, causing a decrease in diffusion
In the equation for gas diffusion, which variable is affected by pulmonary fibrosis and how?
Thickness of the membrane is increased in pulmonary fibrosis, causing a decrease in diffusion
What is normal pulmonary arterial pressure?
10-14 mm Hg
What pulmonary artery pressures define pulmonary hypertension?
25 mm Hg or greater during rest and >35 mm Hg during exercise
Primary pulmonary hypertension is caused by what?
An inactivating mutation in the BMPR2 gene, which normally functions to inhibit vascular smooth muscle proliferation
What is the prognosis for a patient diagnosed with primary pulmonary hypertension?
Very poor; the disease is progressive and fatal
What are some of the potential causes of secondary pulmonary hypertension?
Chronic obstructive pulmonary disease, left-to-right shunt, mitral stenosis, recurrent thromboemboli, autoimmune disease (ie, systemic sclerosis), sleep apnea, or living at high altitudes
What are three pathological changes in the vasculature are caused by pulmonary hypertension?
Atherosclerosis, medial hypertrophy, and intimal fibrosis of the pulmonary arteries
How does chronic obstructive pulmonary disease cause pulmonary hypertension?
By the destruction of lung parenchyma and subsequent vasoconstriction due to hypoxia
How does mitral stenosis cause pulmonary hypertension?
By increasing resistance to blood flow in the left heart; thus causing a build-up of pressure starting in the left atrium and backing up to the pulmonary vasculature
How do recurrent thromboemboli cause pulmonary hypertension?
By decreasing the total cross-sectional area of the pulmonary vascular bed
How can autoimmune disease cause pulmonary hypertension?
Processes such as systemic sclerosis lead to inflammation, then to intimal fibrosis, which in turn leads to medial hypertrophy in the pulmonary vasculature
How does left-to-right shunt cause pulmonary hypertension?
By causing increased shear stress (due to increased blood volume in the pulmonary vasculature) and thus endothelial injury
How do sleep apnea or living at high altitudes cause pulmonary hypertension?
Sleep apnea and living at high altitudes cause hypoxia, which in turn causes pulmonary vasoconstriction
What are the sequelae of pulmonary hypertension if left untreated?
Severe respiratory distress, causing right ventricular hypertrophy and cyanosis . This results in decompensated cor pulmonale which leads to death
How is pulmonary vascular resistance calculated?
Pulmonary vascular resistance = (pressure in the pulmonary artery minus pressure in the left atrium) divided by the cardiac output
How is left atrial pressure measured?
It is approximated by wedge pressure
Pulmonary vascular resistance is _____ (directly/inversely) related to vessel length and _____ (directly/inversely) related to vessel radius.
Directly; inversely
What is the equation for resistance, given vessel length, diameter, and blood viscosity?
R = (8ηl) / (πr4), where η = viscosity of blood, l = vessel length, and r = vessel radius
How is the oxygen content of the blood calculated?
Oxygen content of the blood = (oxygen-binding capacity × percent saturation) + dissolved oxygen
How much oxygen can 1 g of hemoglobin bind?
1.34 mL
What is the average amount of hemoglobin in normal blood?
Approximately 15 g/dL
What is the normal oxygen-binding capacity of the blood?
Approximately 20.1 mL oxygen/dL of blood
When the hemoglobin level rises, the oxygen content of the blood _____ (rises/falls).
Rises, because oxygen-binding capacity depends on the total amount of hemoglobin
When the hemoglobin level falls, the percent oxygen saturation of the blood ______ (rises/falls/remains stable).
Remains stable; the blood can still be 100% saturated but there will be less oxygen-binding capacity and therefore lower total oxygen content
A decrease in hemoglobin will have what effect on partial oxygen pressure: decrease, increase, or no change?
No change
Visible cyanosis typically results when deoxygenated hemoglobin is at what level?
> 5 g/dL
Why does arterial partial pressure of oxygen decrease with chronic lung disease?
Physiologic shunt decreases the oxygen extraction ratio
What is the formula for oxygen delivery to tissues?
Oxygen delivery to tissues = cardiac output × oxygen content of blood
Will a patient with anemia become cyanotic at a higher or lower oxygen saturation than a normal patient?
An anemic patient will have a lower oxygen saturation by the time she appears cyanotic; the blue coloration of cyanosis is proportional to the concentration of deoxyhemoglobin, which is lower in anemic patients (as are the concentrations of all types of hemoglobin)
What is the alveolar gas equation?
Alveolar partial pressure of oxygen (in mm Hg) = the partial pressure of oxygen in inspired air minus (alveolar partial carbon dioxide pressure divided by the respiratory quotient); or, PAO2 = PIO2 - (PACO2/R)
How can the alveolar gas equation be simplified and approximated (assuming that the patient is breathing ambient air)?
Alveolar partial pressure of oxygen = 150 - (arterial partial pressure of carbon dioxide / 0.8)
By using the alveolar gas equation, what important measure of pulmonary function can be determined?
The alveolar-arterial gradient (the A-a gradient)
What is the normal alveolar-arterial gradient?
10-15 mmHg
What three pathological processes can lead to increased A-a gradient?
Shunting, ventilation/perfusion mismatch, and fibrosis of the lungs
Name five processes that can lead to hypoxemia (ie, decreased arterial oxygen).
High altitude, hypoventilation, ventilation/perfusion mismatch, diffusion limitation, and right-to-left shunt
Name five processes that can lead to hypoxia (ie, decreased oxygen delivery to tissue).
Decreased cardiac output, hypoxemia, anemia, cyanide poisoning, and carbon monoxide poisoning
Name two processes that can lead to ischemia (i.e. loss of blood flow).
Impeded arterial flow, and reduced venous drainage
What is the difference between hypoxemia and hypoxia?
Hypoxemia refers to decreased arterial partial pressure of oxygen and can lead to hypoxia, which is defined as decreased oxygen delivery to tissue
Which 2 processes lead to hypoxemia with a normal A-a gradient?
High altitude and hypoventilation
Which 3 processes can lead to hypoxemia with an increased A-a gradient?
Ventilation/perfusion mismatch, diffusion limitation, and right-to-left shunt
What is the ideal ratio of ventilation to perfusion to maximize gas exchange?
1 to 1
Within what part of the lung does ventilation/perfusion equal approximately 3?
The apex of the lung
In the apex of the lung, there is wasted _____ (perfusion/ventilation).
Ventilation
Within what part of the lung does ventilation/perfusion equal approximately 0.6?
The base of the lung
In the base of the lung, there is wasted _____ (perfusion/ventilation).
Perfusion
Is ventilation greater at the base of the lung or the apex of the lung?
The base of the lung
Is perfusion greater at the base of the lung or the apex of the lung?
The base of the lung
The vasodilation of the apical capillaries of the lung that occurs with exercise results in what change to the ventilation/perfusion ratio?
The ventilation/perfusion ratio approaches 1, maximizing gas exchange to meet the metabolic demands of exercise
Microorganisms that thrive in high-oxygen environments, such as tuberculosis, flourish in which part of the lungs?
The apex
A ventilation/perfusion ratio that approaches 0 for a given area of lung indicates that what is occurring in that area?
Airway obstruction, creating a shunt of blood flow that does not participate in gas exchange
What is the name for the process whereby airway obstruction leads to perfusion with no ventilation within an area of the lungs?
Shunt
A ventilation/perfusion ratio that approaches infinity for a given area of lung indicates that what is occurring in that area?
Blood flow obstruction (ie, pulmonary embolus)
When blood flow (but not airflow) into an area of the lungs is obstructed such that the ventilation/perfusion ratio approaches infinity, the area can be considered what type of space?
Physiologic dead space
Which zone of the lung is associated with wasted ventilation?
Zone 1
Which zone of the lung is associated with wasted perfusion?
Zone 3
In hypoxia due to _____ (dead space/shunting), 100% oxygen does not improve the partial pressure of oxygen in the blood; while in hypoxia due to increased _____ (dead space/shunting), there is an improvement in the partial pressure of oxygen in the blood.
Shunting; dead space
In the lung apex (zone 1), arrange the following in order of increasing pressure: artery, vein, alveolus.
Vein < artery< alveolus
In zone 2 of the lung, arrange the following in order of increasing pressure: artery, vein , alveolus.
Vein < alveolus < artery
In the lung base (zone 3), arrange the following in order of increasing pressure: artery, vein, alveolus.
Alveolus < vein < artery
What process causes the ventilation at the apex of the lungs to be considered “wasted?”
The high alveolar pressure at the apex causes compression of the capillaries, and thus an inability to undertake gas exchange with the blood vessels
In which forms is carbon dioxide transported from the tissues to the lungs?
Three forms: (1) as bicarbonate, (2) bound to hemoglobin as carbaminohemoglobin, and (3) dissolved
Ninety percent of the carbon dioxide transported from the tissues to the lungs is in what form?
Bicarbonate, the creation of which is catalyzed by carbonic anhydrase
Other than as bicarbonate, in what two other ways is carbon dioxide transported from the tissues to the lungs?
Bound to hemoglobin as carbaminohemoglobin and dissolved in blood
What percentage of carbon dioxide gets transported from the tissues to the lungs as carbaminohemoglobin; as dissolved carbon dioxide?
Approximately 5%; approximately 5%
After it is inside a red blood cell, each carbon dioxide molecule combines with which molecule in a reaction catalyzed by carbonic anhydrase?
Water
What enzyme catalyzes the conversion of carbon dioxide and water into carbonic acid?
Carbonic anhydrase
Within a red blood cell, the carbonic acid formed from the combination of carbon dioxide and water dissociates into what two compounds?
Hydrogen and bicarbonate ions
What is the fate of the bicarbonate that results from the deprotonation of carbonic acid within an red blood cell?
It gets exchanged out of the red blood cell for a chloride molecule that enters the red blood cell
In the lungs, the oxygenation of hemoglobin promotes what?
The dissociation of a proton from hemoglobin and therefore a decrease in pH, which favors formation of carbon dioxide from bicarbonate
What is the name for the effect in which the oxygenation of hemoglobin within the lungs promotes the dissociation of carbon dioxide from hemoglobin?
The Haldane effect
Regarding carbon dioxide transport, in which direction will the lower pH of peripheral tissues (compared to the lungs) shift the oxygen dissociation curve?
To the right, favoring dissociation of oxygen from hemoglobin
In peripheral tissues, the right shift of the oxygen dissociation curve that results from decreased pH causes an unloading of oxygen. What is this effect called?
The Bohr effect
What happens to ventilation as a response to high altitude in acute situations; chronic situations?
Ventilation is increased in both cases
What happens to erythropoietin levels as a response to high altitude?
Erythropoietin levels are increased as are hematocrit and hemoglobin
What happens to the level of 2,3-diphosphoglycerate in response to high altitude?
The 2,3-diphosphoglycerate level increases
What substance binds to hemoglobin so that hemoglobin releases more oxygen as a physiologic response to high altitude?
2,3-Diphosphoglycerate; increased concentrations shift the hemoglobin dissociation curve to the right
What cellular changes occur in response to high altitude?
There is an increase in mitochondria
Increased renal excretion of what substance occurs in response to high altitude?
Bicarbonate
The increased renal excretion of bicarbonate that is seen in response to high altitude compensates for what?
The respiratory alkalosis that occurs as a result of increased ventilation
The increased renal excretion of bicarbonate that is seen in response to high altitude can be augmented using what?
Acetazolamide; the drug is a carbonic anhydrase inhibitor that makes the urine more basic
In response to high altitude, chronic hypoxic pulmonary vasoconstriction results in what condition?
Right ventricular hypertrophy
As a result of exercise, what happens to carbon dioxide production in muscles; oxygen consumption?
Both are increased
What happens to the V/Q ratio as a response to exercise?
It becomes more uniform from apex to base; hence gas exchange is more efficient
What happens to pulmonary blood flow as a response to exercise?
It increases due to increased cardiac output
How does the pH of the body change during strenuous exercise?
pH decreases during strenuous exercise due to lactic acidosis
PaO2 and PaCO2_____ (increase/decrease/remain stable) in response to exercise, whereas venous CO2 content _____ (increases/decreases/remains stable).
PaO2 and PaCO2do not change in response to exercise but venous CO2content increases
