Respiratory Physiology Flashcards
What are the two critical functions of ventilation?
- 02 is delivered to hemoglobin to support aerobic metabolism.
- C02 is eliminated from the blood
Contraction of the inspiratory muscles reduces thoracic pressure and increases thoracic volume, this is an example of what law?
Boyle’s law
The diaphragm lowers and thoracic pressure is reduced during which part of the respiratory cycle?
Inspiration
Which part of the respiratory cycle is passive?
Exhalation
The Mnemonic “I let the air out of my TIREs” is used to name the muscles involved in exhalation, name them.
Transverse abdominis
Internal oblique
Rectus abdominis
External oblique
A vital capacity of at least what amount is required for an effective cough?
15ml/kg
What two situations can cause exhalation to become an active process?
+ when minute ventilation is increased
+ with lung diseases such as COPD
Which part of the respiratory cycle is driven by the recoil of the chest wall?
Exhalation
True or False
Air will always follow the pressure gradient?
True
The airway can be divided into three zones, name them.
conducting zone
respiratory zone
transitional zone
Which zone of the airway does not participate in gas exchange?
conducting zone
Which zone is where gas exchange takes place?
Respiratory zone
Which zone is anatomic dead space?
conducting zone
which zone begins at the nares and mouth and ends with the terminal bronchioles?
conducting zone
Which zone serves the dual function of air conduit and gas exchange?
Transitional zone
The respiratory bronchioles and alveolar ducts are considered part of which zone?
Transitional zone
Which zone begins at the respiratory bronchioles and also includes the alveolar ducts and alveolar sacs?
Respiratory zone
What is the last structure perfused by the bronchial circulation?
terminal bronchioles
True or False
Gas exchange can not occur across a flat epithelium?
False,
gas exchange can ONLY occur across the flat epithelium
In what zone is cilia most prevalent?
conducting zone
In what zone does the bulk of gas movement occur?
conducting zone
In the airway, most cartilage is present where?
Trachea (patchy in the bronchi)
Can you name the structures of the airway from Trachea to alveolar sacs?
Trachea Bronchi Bronchioles respiratory bronchioles alveolar ducts alveolar sacs
alveolar ducts and alveolar sacs belong to which zone?
Respiratory zone
Respiratory bronchioles belong to which zone?
Transitional zone
what is alveolar pressure?
pressure inside the airway
what is intrapleural pressure?
pressure outside the airway
What is Transpulmonary pulmonary pressure?
The difference between the pressure inside the airway and the pressure outside the airway.
What happens if TPP is a positive value vs a negative value?
positive value then the airway stays open
negative value then the airway collapses
intrapleural pressure is always positive or negative during tidal breathing?
negative (this keeps the lungs inflated)
Transpulmonary pressure is always positive or negative during tidal breathing?
always positive (keeps airway open)
alveolar pressure becomes slightly negative during which phase of the respiratory cycle and slightly positive during which phase of the respiratory cycle?
slightly negative during inspiration and slightly positive during expiration
At what two states of tidal breathing is there NO airflow?
no airflow during FRC or end-inspiration
What is the only breathing situation in which intrapleural pressure becomes positive?
during forced expiration
would be positive during pneumothorax but this is not a normal state
What is your TPP at FRC?
+5
What is your TPP during normal inspiration?
+7
What is your TPP at end-inspiration?
+8
What is your TPP during quite expiration?
+6
What is your TPP during forced expiration?
-1
Define tidal volume?
The amount of gas that is inhaled and exhaled during the breath
Normal dead space is?
2ml/kg
When a patient exhales which zone of gas is removed first?
conducting zone (dead space) gas is removed first.
Is gas from the respiratory zone removed first or last during exhalation?
removed last
Any condition that increases what makes it more difficult to eliminate expiratory gases from the lungs?
any condition that increases tidal volume
increased tidal volume widens what gradient and causes CO2 retention.
increased tidal volume widens the PaC02-EtC02 gradient and causes CO2 retention
What is minute ventilation?
the amount of air in a single breath (Vt) multiplied by the number of breaths per minute.
What is ventilation rate?
the volume of air moved into and out of the lungs in a given period of time.
what is the formula for minute ventilation?
Minute ventilation = Tidal volume x Respiratory rate
or
VE = Vt x RR
What is the minute ventilation of a patient with a Vt of 500ml who has a RR of 10?
500ml x 10 RR = 5,000mL/min
What is Alveolar Ventilation?
VA only measures the fraction of VE that is available for gas exchange. It removes dead space gas from the minute ventilation equation.
What is the formula for alveolar ventilation?
alveolar ventilation = (tidal volume - dead space) x RR
You can also relate Alveolar ventilation to PaC02, what is the formula when you do this?
alveolar ventilation = C02 production / Pac02
VA is directly proportional to carbon dioxide production.
VA is inversely proportional to PaC02
What is the primary determinant of carbon dioxide elimination?
alveolar ventilation
this is bc VA takes out dead space which does not contribute to gas exchange
What is the most common cause of Vd/Vt under general anesthesia?
reduction in cardiac output
If the Etc02 in the general anesthesia patient acutely decreases you should first rule out what?
hypotension
How does atropine increase Vd (dead space)?
bronchodilator action increases the volume of the conducting airway
Does COPD increase or decrease Vd?
increases
Does PPV increase or decrease Vd?
increases
If dead space increases then what else must increase to maintain a constant PaCO2?
Minute ventilation (RR, Vt, or both)
What equation can calculate physiologic dead space?
Bohr equation
What equation compares the partial pressure of carbon dioxide in the blood vs. the partial pressure of carbon dioxide in exhaled gas?
Bohr’s equation used to determine physiologic dead space
In what region of the lung is the PA02 and V/Q ratio higher?
non-dependent region
In what region of the lung is the PAC02 higher but the V/O ratio is lower?
dependent region
What is the formula for compliance?
compliance = change in volume / change in pressure
Does non-dependent or dependent region of a lung have a greater V/Q ratio?
non-dependent region
Is there increased or decreased vascular resistance in the non-dependent region of a lung?
vascular resistance is increased in the non-dependent region of the lung.
Does V/Q mismatch usually increase or decrease the A-a gradient?
usually increases
What does hypoxic pulmonary vasoconstriction minimize?
shunt (NOT dead space)
Bronchioles constrict to minimize which zone?
Zone 1
Blood passing through the under ventilated alveoli tends to give up or retain CO2?
retain C02
In the sitting position is ventilation greater than perfusion at the apex or base?
apex
What is the most common cause of hypoxemia in the PACU ?
atelectasis which is V/Q mismatch
Blood passing through the under ventilated tends to do what with CO2?
retain C02, and is unable to take in enough oxygen
How many times faster does C02 diffuse compared to 02?
20 x faster
In an overventilated lung the blood passing through the alveoli tends to give off an excessive amount of C02, what happens to 02?
even though an excessive amount of CO2 is being eliminated from the blood, it can not take up a proportionate amount of 02. The alveolus can transfer much more CO2 than it can 02.
Why is the PAO2-PaO2 gradient large with V/Q mismatch?
The lung with V/Q mismatch cannot absorb more oxygen from overventilated alveoli to compensate for under ventilated alveoli.
How does the body combat/compensate for a shunt in the lungs?
hypoxic pulmonary vasoconstriction reduces pulmonary blood flow to poorly ventilated alveoli.
What do type 2 pneumocytes produce and how does it help the alveoli to stay open?
They produce surfactant which lowers surface tension and prevents alveolar collapse
Do alveoli of different sizes contain different amounts of surfactant?
No, every alveoli regardless of size contains the same amount of surfactant
Fetal lung maturity can be hastened by what?
corticosteroids (betamethasone)
Type 2 pneumocytes begin producing surfactant between what weeks of fetal development? When does it peak?
production between 22-26 weeks and it peaks around 25-36 weeks
closing capacity is what two lung volumes?
RV + CV
How is a pressure gradient created in the lungs to transfer gas into and out of the lungs?
By changing the lung volumes (respiration)
What two things can hypoventilation cause?
hypercarbia
hypoxemia
increasing the concentration of oxygen in a patient who has hypoxemia and hypercarbia will fix the hypoxemia but not the hypercarbia, what can you do to fix the hypercarbia?
increase the alveolar ventilation that would remedy both the hypoxemia and the hypercarbia.
what is the equation for respiratory quotient?
carbon dioxide production divided by oxygen consumption
What does a respiratory quotient (RQ) OVER 1 suggest?
What does a respiratory quotient of 0.7 suggest?
over 1 = lipogenesis and this occurs with overfeeding.
0.7 suggests lipolysis, this occurs with starvation
What are the components of the A-a gradient?
difference between alveolar oxygen and arterial oxygen.
What cause of hypoxemia can not be fixed with supplemental oxygen?
Shunt (pulmonary blood bypassing the alveoli)
When breathing room air the normal A-a difference is less than?
15 mmHg
What three veins bypass the alveolar-capillary interface and deliver deoxygenated blood to the left heart? (contributing to a small physiologic shunt)
Thesbesian, bronchiolar, and pleural
What does a wide variation between PA02 and PaO2 imply?
significant degree of shunt, V/Q mismatch, or diffusion defect across the alveolar-capillary membrane
Aging increases the A-a gradient, why?
closing capacity increases relative to FRC
Why do vasodilators increase A-a gradient?
decreased hypoxic pulmonary vasoconstriction
atelectasis, pneumonia, bronchial intubation, and intracardiac defect are what kind of shunt? (L-R or R-L)
Right to Left shunt
True or False
right to left shunt increases A-a gradient?
True
Why does diffusion limitation increase the A-a gradient?
alveolocapillary thickening hinders 02 diffusion
What is the formula to find alveolar ventilation? (PA02)
PA02 = Fi02 x (Pb - H20) - PaC02/RQ
Pb is barometric pressure which is normally 760mmHg
H20 is usually 47 mmHg
RQ is usually 0.8
What is the formula for A-a gradient?
You first may have to find your alveolar ventilation which is the formula for PA02.
Your Pa02 should be given to you?
A-a gradient = PA02-Pa02
final answer is in mmHg
How many mmHg of A-a gradient causes a 1% increase in shunt?
20mmHg
if your A-a gradient is 218 mmHg then what percentage shunt do you have?
11% roughly
every 20 mmHg = 1%
Amount of gas that can be forcibly inhaled after a tidal inhalation is known as?
Inspiratory reserve volume
Volume of gas that can be forcibly exhaled after a tidal exhalation?
Expiratory Reserve Volume
Volume of alveolar gas that serves as oxygen reservoir during apnea?
Residual volume
Volume of gas that remains in the lungs after complete exhalation.
Cannot be exhaled from the lungs
Residual volume
The volume above residual volume where the small airways begin to close is known as?
closing volume
Total lung capacity definition?
IRV + TV + ERV + RV
Vital capacity definition?
IRV + TV + ERV
Inspiratory capacity definition?
IRV + TV
Functional Residual Capacity definition?
RV + ERV
Closing capacity definition?
RV + CV
tidal volume is x-x ml/kg?
6-8 mL/kg
vital capacity is x-x mL/kg?
65-75 mL/kg
Functional residual capacity is xx ml/kg?
35 mL/kg
all lung volumes are calculated on what type of body weight?
ideal body weight NOT total
lung volumes are what % smaller in women?
25%
obstructive lung diseases tend to cause air trapping, what disorders would fall under this?
asthma
emphysema
bronchitis
if you have an obstructive lung disease what lung volumes will be increased?
increased residual volume
closing capacity
total lung capacity
(due to air trapping)
What volumes can NOT be measured with spirometry?
residual volume (total lung capacity and functional residual capacity have residual volume as part of them)
closing volume
capacity
What lung volume is the reservoir of oxygen that prevents hypoxemia during apnea?
FRC
What are some conditions that decrease FRC?
general anesthesia obesity pregnancy neonates supine lithotomy Trendelenburg paralysis inadequate anesthesia excessive IV fluid High Fi02 Reduced pulmonary compliance
In what region of the lung is pleural pressure higher and thus the airways in this region close first?
dependent region of the lung
what is closing volume?
the point at which dynamic compression of the airways begins.
Said another way, it is the volume above residual volume where the small airways begin to close during expiration.
Factors that increase closing volume (CLOSE-P)?
COPD Left ventricular failure Obesity Supine position Extremes of age Pregnancy
What is closing capacity?
closing volume + residual volume = CC
absolute volume of gas contained in the lungs when the small airways begin to collapse
FRC is greater than closing capacity when?
under normal circumstances
When does airway closure occur during tidal breathing?
when closing capacity is greater than FRC
what tactic can we use to increase FRC relative to CC?
PEEP
What are some consequences of aging related to the lungs?
increased FRC
Increased closing capacity
increased residual volume
decreased vital capacity
On average how much oxygen is dissolved in the blood and how much is reversibly bound with hemoglobin?
3% dissolved in plasma
97% reversibly binds with hemoglobin
each gram of hemoglobin molecule can carry a theoretical maximum of how many mL of molecular oxygen?
1.39 mL
Oxygen bound to hemoglobin formula?
(1.34 x Hgb x Sa02)
Ca02 formula?
(1.34 x Hgb x Sa02) + (Pa02 x 0.003) = 20 mL 02 per dL
Normal Hgb and Hct values for Male and Female?
Male 15g/dL and 45%
Female 13g/dL and 39%
Oxygen dissolved in plasma formula?
(Pa02 x 0.003)
solubility coefficient for oxygen is?
0.003 mL/dL/mmHg
What is Henrys law?
concentration of gas in a solution is directly proportional to the partial pressure of the gas above the solution
is oxygen more or less soluble than C02 in the blood?
20 x less soluble than C02
What does Ca02 tell you?
HOW MUCH 02 is contained in the blood (bound to hgb + dissolved in the blood)
What does DO2 tell you? ( oxygen delivery)
HOW FAST a quantity of 02 is delivered to the tissues
Ca02 stands for?
Oxygen content
formula for oxygen delivery? (DO2)
DO2 = Ca02 x cardiac output x 10
V02 is what?
oxygen consumption
Numbers you must know, what is VO2 in mL/kg/min and ml/min assuming a 70kg male?
V02 = 3.5mL/kg/min
V02 is approx. 250mL for a 70 kg male
formula for VO2?
VO2 = cardiac output x (Ca02 - Cv02) x 10
increased affinity for 02 is what kind of shift?
left shift
What is P50?
P50 is the Pao2 where hgb is 50% saturated by oxygen
What shifts the oxyhgb curve to the left?
decreased temp.
decreased 2,3-DPG
decreased CO2
decreased H+
increased pH
increased HgbMet
increased HgbCO
increased Hgb F
What shifts the oxyhgb curve to the right?
increased temp
increased 2,3-DPG
increased CO2
increased H+
decreased pH
What is the partial pressure of oxygen at P50?
26.5
What two molecules cause Hgb to release oxygen?
CO2 and hydrogen ions
When is 2,3-DPG produced?
During RBC glycolysis
Tell me the difference between the Bohr effect and the Haldane effect?
Bohr describes oxygen carriage and Haldane is just the opposite.
Bohr says that C02 and decreased pH cause the erythrocyte to release oxygen while Haldane says that oxygen causes the erythrocyte to release CO2.
deoxygenated hemoglobin can carry more CO2, what effect is that?
Haldane effect
The more oxygen carried by hemoglobin the less CO2 that can be carried, is this a left or right shift on the carbon dioxide dissociation curve?
left is a love for oxygen just like the oxyhemoglobin curve.
The carbon dioxide dissociation curve explains what?
When hemoglobin is oxygenated in the lungs it has a decreased affinity for C02 and this allows for unloading of CO2 and CO2 to be excreted from the body.
If the hemoglobin is deoxygenated then it has an affinity for CO2 and in the systemic capillaries CO2 is picked up and transported.
What value = hypercapnia?
PaCO2 > 45 mmHg
CO2 production / alveolar ventilation describes what formula?
PaCO2 formula
What can cause hypercapnia?
increased CO2 production or decreased CO2 elimination
