[USMLE] Respiratory Physiology Flashcards
the volume inspired or expired with each normal breath
Tidal volume (TV)
the volume that can be inspired over and above the tidal volume; used during exercise
Inspiratory reserve volume (IRV)
the volume that can be expired after the expiration of a tidal volume
Expiratory reserve volume (ERV)
the volume that remains in the lungs after a maximal expiration; cannot be measured by spirometry
Residual volume (RV)
the volume of the conducting airways
Anatomic dead space
Anatomic dead space is normally approximately
150 mL
the volume of the lungs that does not participate in gas exchange
Physiologic dead space
Physiologic dead space is approximately equal to the anatomic dead space in
normal lungs
Physiologic dead space may be greater than the anatomic dead space in lung diseases in which there are
ventilation/perfusion (V/Q) defects
Physiologic dead space equation
In words, the equation states that physiologic dead space is tidal volume multiplied by a fraction. The fraction represents the dilution of alveolar PCO2 by dead-space air, which does not participate in gas exchange and does not therefore contribute CO2 to expired air.
Minute ventilation is expressed as
Minute ventilation = Tidal volume × Breaths min
Alveolar ventilation is expressed as
Alveolar ventilation = (Tidal volume − Dead space) × Breaths min
is the sum of tidal volume and IRV
Inspiratory capacity
is the sum of ERV and RV
Functional residual capacity (FRC)
the volume remaining in the lungs after a tidal volume is expired; includes the RV; cannot be measured by spirometry
FRC
sum of tidal volume, IRV, and ERV;
volume of air that can be forcibly expired after a maximal inspiration
Vital capacity (VC), or forced vital capacity (FVC)
sum of all four lung volumes;
volume in the lungs after a maximal inspiration;
includes RV, so it cannot be measured by spirometry
Total lung capacity (TLC)
volume of air that can be expired in the first second of a forced maximal expiration
FEV1
FEV1 is normally
80% of the forced vital capacity
FEV1 / FVC =
0.8
In obstructive lung disease, such as asthma, what happens to FEV1 and FVC
FEV1 is reduced more than FVC so that
FEV1/FVC is decreased
In restrictive lung disease, such as fibrosis, what happens to FEV1 and FVC
oth FEV1 and FVC are reduced and FEV1/FVC
is either normal or is increased
most important muscle for inspiration.
diaphragm
When the diaphragm contracts, the abdominal contents are
pushed downward
the ribs are lifted ____________
upward and outward
what happens to its volume
increases the volume of the thoracic cavity
are not used for inspiration during normal quiet breathing;
used during exercise and in respiratory distress
External intercostals and accessory muscles
Expiration is normally
passive
the lung-chest wall system is
elastic
it returns to its resting position after
inspiration
expiratory muscles are used during
exercise or when airway resistance in increased because of disease (asthma)
compress the abdominal cavity, push the diaphragm up, and push air out of the lungs
Abdominal muscles
Internal intercostal muscles pull the ribs
downward and inward
distensibility of the lungs and chest wall;
slope of the pressure–volume curve
Compliance of the respiratory system
Compliance of the respiratory system equation
C= V/P
Compliance of the respiratory system is inversely related to
elastance and stiffness
elastance depends on the amount of
elastic tissue
When the pressure outside of the lungs (i.e., intrapleural pressure) is negative,
the lungs expand and lung volume increases
When the pressure outside of the lungs is positive,
the lungs collapse and lung volume
decreases
the difference in the inflation of the lungs (inspiration) and the deflation of the lungs (expiration)
hysteresis
In the middle range of pressures, compliance is
greatest
In the middle range of pressures, lungs are
most distensible
At high expanding pressures, compliance is
lowest
At high expanding pressures, the lungs are
least distensible
At high expanding pressures, curve
flattens
at rest, lung volume is
at FRC
at rest, the pressure in the airways and lungs is
equal to atmospheric pressure (i.e. zero)
at equilibrium conditions, there is
a collapsing force on the lungs and an
expanding force on the chest wall
at FRC, these two forces are
equal and opposite
intrapleural pressure is negative
subatmospheric
intrapleural space
pneumothorax
If air is introduced into the intrapleural space (pneumothorax), the intrapleural pressure
becomes equal to atmospheric pressure
In a patient with emphysema, what happens to lung compliance and the tendency of the lungs
lung compliance is increased and the tendency of the
lungs to collapse is decreased
In a patient with fibrosis, what happens to lung compliance and the tendency of the lungs
lung compliance is decreased and the tendency of the lungs to collapse is increased
results from the attractive forces between liquid molecules lining the alveoli
Surface tension of the alveoli
collapsing pressure that is directly proportional to surface tension and inversely
proportional to alveolar radius
Laplace’s Law
Laplace’s Law equation
P= 2T / r
Large alveoli (large radii) have
low collapsing pressures and are easy to keep open
Small alveoli (small radii) have
high collapsing pressures and are more difficult to keep
open
In the absence of surfactant, the small alveoli have a tendency to
collapse (atelactasis)
lines the alveoli
surfactant
by disrupting the intermolecular forces between liquid molecules
surface tension is reduced
This reduction in surface tension prevents small alveoli from
collapsing and increases compliance
surfactant is synthesized by
type II alveolar cells
surfactant consists primarily of the phospholipid
dipalmitoyl phosphatidylcholine (DPPC)
Surfactant may be present as early as gestational
week 24 and is almost always present by
week 35
can occur in premature infants because of the
lack of surfactant
Neonatal respiratory distress syndrome
atelectasis
lung collapse
difficulty reinflating the lungs
decreased compliance
hypoxemia
decreased V/Q
Airflow is driven by, and is directly proportional to the
pressure difference between the mouth
(or nose) and the alveoli
Airflow is inversely proportional to
airway resistance
airflow equation
Q= (delta P) / R
is described by Poiseuille’s law
Resistance of the airways
Resistance of the airways equation
R = (8nl) / (pi*r^4)
major site of airway resistance
medium-sized bronchi
smallest airways would seem to offer the
highest resistance, but they do not because of their parallel arrangement
changes airway resistance by altering the radius of the airways
Contraction or relaxation of bronchial smooth muscle
Parasympathetic stimulation relationship to airways, radius and resistance to flow
Parasympathetic stimulation, irritants, and the slow-reacting substance of anaphylaxis (asthma) constrict the airways, decrease the radius, and increase the
resistance to airflow
Sympathetic stimulation and sympathetic agonists (isoproterenol) relationship to airways, radius and resistance to flow
Sympathetic stimulation and sympathetic agonists (isoproterenol) dilate the airways via a2 receptors, increase the radius, and decrease the resistance to
airflow.
alters airway resistance because of the radial traction exerted on the airways by surrounding lung tissue
lung volume
High lung volumes are associated with
greater traction and decreased airway
resistance
Patients with increased airway resistance (e.g., asthma)
“learn” to breathe at higher lung volumes to offset the high airway resistance associated with their disease
Low lung volumes are associated with
less traction and increased airway resistance even to the point of airway collapse
During a deep-sea dive, what happens to air density and resistance to airflow
both increased
Breathing a low-density gas what happens to the resistance to airflow
reduced
At rest (before inspiration begins), alveolar pressure
equals atmospheric pressure
at rest, intrapleural pressure
negative
lung volume is the
FRC
during inspiration inspiratory muscles _____ and the volume of the thorax _____
contract;
increase
As lung volume increases, what happens to alveolar pressure
alveolar pressure decreases to less than atmospheric
pressure (i.e., becomes negative)
what causes air to flow into the lungs
pressure gradient between the atmosphere and the alveoli
during inspiration, intrapleural pressure becomes
more negative
Because lung volume increases during inspiration, the what happens to the elastic recoil strength
also increases
At the peak of inspiration, lung volume is the
FRC plus one TV
during expiiration, Alveolar pressure becomes
greater than atmospheric pressure
alveolar gas is compressed by the
elastic forces of the lung
during a forced expiration, intrapleural pressure actually becomes
positive
positive intrapleural pressure
compresses the airways and makes expiration
more difficult
In COPD, airway resistance is
increased
during expiration, lung volume
returns to FRC
is characterized by decreased FVC, decreased FEV1, and decreased FEV1/FVC
Asthma; COPD
in asthma, air that should have been expired is not, leading to
air trapping and increased FRC
COPD
obstructive disease; increased lung compliance
in COPD, air that should have been expired is not, leading to
air trapping, increased FRC, and a
barrel-shaped chest
“Pink puffers” (primarily emphysema)
mild hypoxemia and normocapnia (normal PCO2)
“Blue bloaters” (primarily bronchitis)
severe hypoxemia with cyanosis and hypercapnia (increased PCO2)
is characterized by a decrease in all lung volumes. Because FEV1 is decreased less than
FVC, FEV1/FVC is increased (or may be normal).
fibrosis
Dalton’s law of partial pressures
Partialpressure = Totalpressure × Fractionalgas concentration
In dry inspired air, the partial pressure of O2 can be calculated as
760 mmHg * 0.21
In humidified tracheal air at 37°C, the calculation is modified to correct for the partial pressure of H2O, which is
47 mm Hg
The amount of gas dissolved in a solution (such as blood) is
proportional to its partial pressure
The diffusion rates of O2 and CO2 depend on the
partial pressure differences across the membrane and the area available for diffusion
is illustrated by N2O and by O2 under normal conditions.
Perfusion-limited exchange
In perfusion-limited exchange, the gas equilibrates early along the
length of the pulmonary capillary
The partial pressure of the gas in arterial blood becomes
equal to the
partial pressure in alveolar air
diffusion of the gas can be increased only if
blood flow increases
Diffusion-limited exchange is illustrated by CO and by O2 during
strenuous exercise
O2 is carried in blood in two forms:
dissolved or bound to hemoglobin (most important)
Hemoglobin, at its normal concentration,
increases the O2-carrying capacity of blood 70-fold
Each subunit of the hemoglobin contains a
heme moiety, which is iron-containing porphyrin
normal adult hemoglobin
α2β2
In fetal hemoglobin, the β chains are replaced by
gamma chains
fetal hemoglobin is called
α2 gamma 2
O2 affinity in adult and fetal
The O2 affinity of fetal hemoglobin is higher than the O2 affinity of adult hemoglobin (left-shift) because 2,3-diphosphoglycerate (DPG) binds less avidly
causes sickle cell disease
Hemoglobin S
maximum amount of O2 that can be bound to hemoglobin in blood
O2-binding capacity of blood
total amount of O2 carried in blood, including bound and dissolved O2
O2 content of blood
O2 content of blood equation
O2 content = (O2 binding capacity * % saturation) + Dissolved O2
Hemoglobin combines rapidly and reversibly with O2 to form
xyhemoglobin
the result of a change in the affinity of hemoglobin as
each successive O2 molecule binds to a heme site (called positive cooperativity)
sigmoid shape of the curve
affinity for the fourth O2 molecule
highest
Alveolar gas has a PO2 of
100 mmHg
The very high affinity of hemoglobin for O2 at a PO2 of 100 mm Hg facilitates the
diffusion process
The curve is almost flat when
PO2 is between 60 and 100 mm Hg
when the affinity of hemoglobin for O2 is decreased
Shifts to the right
during exercise, the tissues produce
CO2, which decreases tissue pH and, through the Bohr effect, stimulates O2 delivery to the exercising muscle
Increases in temperature (e.g., during exercise)
shift the curve to the right
Increases in 2,3-DPG concentration
shift the curve to the right by binding to the β chains of deoxyhemoglobin and decreasing the affinity of hemoglobin for O2
affinity of hemoglobin for O2 is increased
shift to the left
shift to the left causes
decreased PCO2, increased pH, decreased temperature, and decreased 2,3-DPG concentration
Decreased binding of 2,3-DPG results in
ncreased affinity of HbF for O2, decreased P50, and a shift of the curve to the left
decrease in arterial PO2
hypoxemia
alveolar gas equation
PAO2 = P_I_O_{2} - (P_A_C_{O} / R)
normal A–a gradient is
< 10 mm Hg
A–a gradient is increased (>10 mm Hg) if
O2 does not equilibrate between alveolar gas and arterial blood (e.g., diffusion defect, V/Q defect, and right-to-left shunt)
decreased O2 delivery to the tissues.
Hypoxia
O2 delivery equation
O2 delivery = Cardiac output * O2 content of blood
hypoxia can be caused by
decreased cardiac output, decreased O2-binding
capacity of hemoglobin, or decreased arterial PO2
CO2 is produced in the tissues and carried to the lungs in the venous blood in three forms:
Dissolved CO2, Carbaminohemoglobin, HCO3
site where CO2 is being added
capillaries
transport of HCO3 as CO2 in the lungs
In the lungs, all of the above reactions occur in reverse. HCO3 – enters the RBCs in exchange for Cl–. HCO3 – recombines with H+ to form H2CO3, which decomposes into CO2 and H2O. Thus, CO2, originally generated in the tissues, is expired.
H+ is buffered inside the RBCs by
deoxyhemoglobin
pressure in pulmonary vs systemic circulation
Pressures are much lower in the pulmonary circulation than in the systemic circulation.
resistance in pulmonary vs systemic circulation
Resistance is also much lower in the pulmonary circulation than in the systemic circulation
Cardiac output of the right ventricle is
pulmonary blood flow.
Cardiac output of the right ventricle =
cardiac output of the left ventricle
When a person is supine, blood flow is
nearly uniform throughout the lung
When a person is standing, blood flow is
unevenly distributed because of the effect of gravity
Blood flow is lowest at
the apex of the lung (zone 1)
Blood flow is highest at
the base of the lung (zone 3)
why is blood flow lowest in zone 1?
Alveolar pressure > arterial pressure > venous pressure
The high alveolar pressure may compress the capillaries and reduce blood flow in zone. 1. This situation can occur if arterial blood pressure is decreased as a result of hemorrhage or if alveolar pressure is increased because of positive pressure ventilation.
why is blood flow medium in zone 2?
Arterial pressure > alveolar pressure > venous pressure
Moving down the lung, arterial pressure progressively increases because of gravitational effects on hydrostatic pressure.
also, blood flow is driven by the difference between arterial pressure and alveolar pressure
why is blood flow highest in zone 3?
Arterial pressure > venous pressure > alveolar pressure
Moving down toward the base of the lung, arterial pressure is highest because of gravitational effects, and venous pressure finally increases to the point where it exceeds alveolar pressure.
In zone 3, blood flow is driven by the difference between arterial and venous pressures, as in most vascular beds.
In the lungs, hypoxia causes
vasoconstriction
in other organs, hypoxia causes
vasodilation
Fetal pulmonary vascular resistance is very high because of
generalized hypoxic vasoconstriction; as a result, blood flow through the fetal lungs is low.
With the first breath, the alveoli of the neonate are oxygenated, pulmonary vascular resistance decreases, and pulmonary blood flow increases and becomes equal to cardiac output (as occurs in the adult).
Right-to-left shunts results in
a decrease in arterial PO2 because of the admixture of venous blood with arterial blood
pressure are higher on which side of the heart
left
is lowest at the apex and highest at the base because of gravitational effects
blood flow
V/Q ratio is
higher at the apex of the lung and lower at the base of the lung
At the apex (higher V/Q), PO2 is highest and PCO2 is lower because
gas exchange is more efficient
At the base (lower V/Q), PO2 is lowest and PCO2 is higher because
gas exchange is less efficient
If the airways are completely blocked (e.g., by a piece of steak caught in the trachea), then ventilation is
zero
If blood flow is normal, then V/Q is
zero, which is called a shunt
If blood flow to a lung is completely blocked (e.g., by an embolism occluding a pulmonary artery), then blood flow to that lung is
zero
If ventilation is normal, then V/Q is
infinite, which is called dead space
The PO2 and PCO2 of alveolar gas will approach their values in
inspired air
Sensory information (PCO2, lung stretch, irritants, muscle spindles, tendons, and joints) is coordinated in the
brain stem
Medullary respiratory center is located in the
retricular formation
is primarily responsible for inspiration and generates the basic rhythm for breathing
Dorsal respiratory group
Input to the dorsal respiratory group comes from what nerves
vagus and glossopharyngeal nerves
The vagus nerve relays information from
peripheral chemoreceptors and mechanoreceptors in the lung
The glossopharyngeal nerve relays information
from
peripheral chemoreceptors
Output from the dorsal respiratory group travels, via the ____ to the diaphragm
phrenic nerve
is primarily responsible for expiration
Ventral respiratory group
Ventral respiratory group is not active during
normal, quiet breathing, when expiration is passive
Ventral respiratory group is activated during
exercise, when expiration becomes an active
process
is located in the lower pons
Apneustic center
Apneustic center stimulates
inspiration
Apneustic center produces
a deep and prolonged inspiratory gasp (apneusis)
is located in the upper pons
Pneumotaxic center
Pneumotaxic center inhibits
inspiration
Pneumotaxic center regulates
inspiratory volume and respiratory rate
is limited by the resulting increase in PCO2 and
decrease in PO2
Hypoventilation (breath-holding)
Central chemoreceptors in the medulla are sensitive to the
pH of the cerebrospinal fluid (CSF)
CO2 diffuses from arterial blood into the
CSF because CO2 is lipid-soluble and readily
crosses the blood–brain barrier
The aortic bodies are located
above and below the aortic arch
Decreases in arterial PO2 stimulate the peripheral chemoreceptors and
increase breathing rate
Increases in arterial PCO2 stimulate peripheral chemoreceptors and
increase breathing rate
In metabolic acidosis, breathing rate is
increased (hyperventilation) because arterial
[H+] is increased and pH is decreased
When lung stretch receptors are stimulated by distention of the lungs, they produce a
reflex
decrease in breathing frequency (Hering–Breuer reflex)
During exercise, what happens to the ventilatory rate?
increases
what happens to the mean values for arterial PO2 and PCO2
do not change
Arterial pH does not change during moderate exercise, although it may decrease during
strenuous exercise because of
lactic acidosis
what happend to PCO2 during exercise?
increases; because the excess CO2 produced by the exercising muscle is carried to the lungs in venous blood
Pulmonary blood flow increases because
cardiac output increases during exercise
what happens to alveolar PO2 at high altitude
decreased; because the barometric pressure is decreased
stimulates the peripheral chemoreceptors and increases the ventilation rate (hyperventilation) at high altitude
hypoxemia
at high altitude, hyperventilation produces
respiratory alkalosis
at high altitude, 2,3-DPG concentrations are
increased
when 2,3-DPG concentrations are increased, the hemoglobin–O2 dissociation curve shifts
to the right
an increase in pulmonary arterial pressure, increased work of the right side of the heart against the higher resistance, and hypertrophy of the right ventricle
Pulmonary vasoconstriction
