Physiology - Pulmonary / Renal Block (I) Flashcards
Describe some of the functions of the lungs and respiratory system.
(1) To transport / warm / humidify / filter air for gas exchange
(2) To filter the blood for particles, clots, or tumors
(3) To metabolize compounds (e.g. peptides, amines, arachidonic acid metabolites)
(4) To provide a reservoir for blood for the left ventricle
(5) To facilitate speech / vocalization
In what organ system is angiotensin I converted to angiotensin II?
In what organ system is bradykinin removed from the blood?
The lungs;
the lungs
How thick is the alveolar-capillary membrane?
0.3 μm
True/False.
Large increases in pulmonary capillary pressure can damage the thin alveolar-capillary interface (0.3 μm).
True.
Identify the labeled structures in this scanning electron micrograph.
What structures will an O2 molecule in the alveolar air cross to reach a passing RBC and bind to hemoglobin?
A surfactant layer –>
A type I pneumocyte –>
The pneumocyte basement membrane –>
The interstitial space –>
The capillary basement membrane –>
The capillary endothelial cell –>
Plasma –>
The RBC membrane –>
Hemoglobin
True/False.
Fibroblasts impair gas exchange in the alveoli.
True.
(due to fibrosis and increased collagen / fiber deposition)
Describe the epithelium type of a type I and type II pneumocyte.
Type I - simple squamous (less abundant but make up 95% of surface area)
Type II - simple cuboidal (more abundant)
Which section of the respiratory system has the smallest cross-sectional area?
Which section of the respiratory system has the largest cross-sectional area?
The smallest bronchi;
the alveoli
How much volume (on average) is in the conducting zone?
How much volume (on average) is in the alveoli?
150 mL
(~1 mL per lb. ideal body weight)
2 - 3 L
Which zone of the respiratory tract is synonymous with dead space?
How much volume is typically in this space?
The conducting zone;
150 mL
(~1 mL per lb. ideal body weight)
What is the purpose of nasal turbinates?
To increase surface area and warm/humidify the air
What is Dalton’s law?
(In relation to atmospheric pressure)
Total gas pressure = the sum of the partial pressures of its constituent gasses
(e.g. Patm = pH2O +pCO2 + pO2 + pN2)
What gas partial pressures contribute to atmospheric air pressure (Patm)?
pH2O +pCO2 + pO2 + pN2
What is Henry’s law?
(In relation to atmospheric pressure)
The amount of gas dissolved is proportional to its partial pressure
(e.g. Pgas = Fgas x Patm)
What is the partial pressure of oxygen in inspired air (dry, ambient, and at sea level)?
150 mmHg
- (PO2 * (Patm - PH2O))*
- (0.21 * (760 - 47))*
What is the partial pressure of H2O in dry, ambient air at seal level that has just been inhaled into the nose?
What will the partial pressure be by the time it has passed through the trachea?
0 mmHg;
47 mmHg
Describe the changes in partial pressure of O2 as air travels from the environment through the nose, trachea, and alveoli.
(Note: assume dry, ambient air at sea level.)
Describe the changes in partial pressure of CO2 as air travels from the environment through the nose, trachea, and alveoli.
(Note: assume dry, ambient air at sea level.)
Describe the changes in partial pressure of H2O as air travels from the environment through the nose, trachea, and alveoli.
(Note: assume dry, ambient air at sea level.)
What is the water pressure in dry, sea level air that has been inspired, humidified, and warmed?
47 mmHg
How long does blood normally remain in contact with the pulmonary capillaries before moving on (assume at rest and not in a disease state)?
0.75 seconds
When does surfactant production begin in utero?
~25 weeks
Which alveoli will collapse first in cases of surfactant deficiency, the small or the large?
The small
(Due to the law of LaPlace, the pressure in the small is greater and so they flow into the large. Surfactant is meant to counter this pressure differential.)
After ingesting foreign particles, what do alveolar macrophages usually do next?
Travel either:
(1) out the mucociliary escalator to be swallowed and digested,
(2) to bronchial lymph nodes for antigen presentation
Identify each of these lung volumes.
(From top to bottom for each column)
Column 1: IRV, TV, ERV, RV
Column 2: IC, FRC
Column 3: VC
Column 4: TLC
What is an average tidal volume?
What is an average total lung capacity?
500 mL;
6 L
The inspiratory capacity (usually ~3 L)
+
the _______________________
=
total lung capacity.
Functional residual capacity
(usually ~3 L)
How much is the average inspiratory capacity?
How much is the average expiratory reserve volume?
How much is the average residual volume?
3 L;
- 5 L;
- 5 L
How is total ventilation calculated?
How is alveolar ventilation calculated?
Tidal volume * respiratory rate
(e.g. 500 mL * 15 breaths/min)
(Tidal volume - dead space) * respiratory rate
(e.g. (500 mL - 150 mL) * 15 breaths/min)
What effect will cutting a patient’s respiration rate in half have on their blood pCO2?
It will ~double
Which organ system has primary control over CO2 levels in the blood?
The lungs
What is alveolar dead space?
The air that makes it into non-perfused alveoli
(e.g. at the very top of the lungs)
What is anatomic dead space?
What is alveolar dead space?
What is physiologic dead space?
The conducting zone (~150 mL);
non-perfused alveoli;
the anatomic DS + the alveolar DS
What effect does lung disease have on physiological dead space?
An increase
Where does more ventilation occur, the lower or upper lung?
Why?
The lower
(gravity effects + lower alveoli are smaller and expand more)
Where does more perfusion occur, the lower or upper lung?
The lower lung
Describe gas movement in the respiratory system using the terms ‘bulk flow’ and ‘diffusion.’
Bulk flow is the collective movement of gas into the body and down the trachea;
diffusion is the alveolar-arterial movement of individual gasses due to partial pressures down their concentration gradient from otherwise stationary collective gas
Do bulk flow pressures push oxygen into the arteries?
No, diffusion down partial pressure gradients
Which diffuses more easily through biological membranes, CO2 or O2?
CO2
Explain, according to Fick’s law, what factors are proportional to the diffusion rate across the alverolar-arterial membrane.
Explain, according to Fick’s law, what factors are inversely proportional to the diffusion rate across the alverolar-arterial membrane.
Cross-sectional area (A), partial pressure difference (P1 - P2)
Thickness (T)
Which ‘a’ is which in the A-a gradient?
Big A = alveolar partial pressure (PA)
Little a = arterial partial pressure (Pa)
What gas is diffusion limited?
What does this mean for its alveolar-arterial differences in partial pressure?
Carbon monoxide (CO);
its arterial pressure (Pa) will always be lower than its alveolar pressure (PA)
What gas is used for measuring DLCO?
Why?
What is this measurement?
Carbon monoxide,
it is diffusion-limited;
diffusion capacity
Is nitrous oxide (N2O) diffusion- or perfusion-limited? Will it equilibrate quickly or slowly?
Is carbon monoxide (CO) diffusion- or perfusion-limited? Will it equilibrate quickly or slowly?
Is oxygen (O2) diffusion- or perfusion-limited? Will it equilibrate quickly or slowly?
Perfusion; quickly.
Diffusion; it never does.
Perfusion; quickly.
True/False.
Transfer of O2 into the blood is always a perfusion-limited process.
False.
It becomes diffusion-limited under abnormal circumstances.
What is Fick’s law?
What effect will a decreased hematocrit have on a patient’s diffusion capacity (DL) in the lungs?
It will decrease
(because there is less Hgb for O2 to bind, less O2 gets through)
How much oxygen is carried by 1 g of hemoglobin?
1.34 mL
How can the oxygen content of the blood be calculated?
(1.34 mL * Hgb * (oxyHgb - Hgb)/100) + 0.003(pO2)
How many mL of O2 are dissolved in one dL of blood?
How many mL of O2 are bound to one g/dL of Hgb?
- 3
* (0.003 for each mm of air pressure)* - 34
* (Takeaway: much more bound than dissolved)*
What is the usual value for parteryO2? And pveinO2?
What is the usual value for parteryCO2? And pveinCO2?
PaO2: 90 mmHg; PvO2: 40 mmHg
PaCO2: 40 mmHg; PvCO2: 45 mmHg
Under normal conditions, which of the following (or both or neither) are perfusion-limited, O2 or CO2?
Under abnormal conditions, which of the following (or both or neither) are diffusion-limited, O2 or CO2?
Both;
both
Describe the pressures within the pulmonary and bronchial arterial systems, respectively.
Pulmonary arteries: low pressure, high compliance system
25/8 mmHg
Bronchial arteries: normal, systemic pressures
120/80 mmHg
What equation can be used to calculate pulmonary vascular resistance?
Ohm’s Law: R = (Input pressure - output pressure) / blood flow
(R = V / I)
The pressure drop across pulmonary circulation is about 10 mmHg. Blood flow is about 6 L/min.
What is the pulmonary vascular resistance?
- 7 mmHg/L
* (Input pressure - output pressure) / blood flow = 10 / 6*
What will happen to pulmonary vascular resistance if cardiac output increases?
It will decrease
(V = IR; if I increases, R must decrease to maintain V)
Via what two structural mechanisms can pulmonary vascular resistance be decreased?
Recruitment;
vessel distention
Describe the effects of lung volume on pulmonary vascular resistance.
At what point is the PVR lowest?
See image.
The functional reserve capacity.
Which lung volume cannot be directly measured?
Residual volume
Name a few examples of substances/factors that increase pulmonary vascular tone, thus increasing resistance.
Histamine
Hypoxia
Norepinephrine
Endothelin
Serotonin
Name a few examples of substances/factors that decrease pulmonary vascular tone, thus decreasing resistance.
Acetylcholine
Phosphodiesterse inhibitors
Prostacyclin (PGI2)
Ca2+ channel blockers
What are the two organs in which phosphodiesterase inhibitors function? What is the effect?
What are some example drugs in this class?
The lungs and penis –> smooth muscle relaxation;
sildenafil, vardenafil
What test can be used to see if pulmonary hypertension is being caused by left-sided heart failure or by pulmonary disease?
Get the ‘wedge’ pressure (left ventricular filling pressure)
via a Swan-Ganz catheter
Describe the differences in pressures in West Zone 1.
PAlveolus > PArtery > PVein
Describe the differences in pressures in West Zone 2.
PArtery > PAlveolus > PVein
Describe the differences in pressures in West Zone 3.
PArtery > PVein > PAlveolus
In which West Zone is there no pulmonary blood flow?
What are two examples of situations that might increase the size of this zone?
West Zone 1;
hemorrhage, positive pressure ventilation
Describe where West Zones 1, 2, and 3 are, respectively, in the lungs.
Are there any capillary beds in the body that respond to hypoxemia by vasoconstricting?
Yes;
the pulmonary capillary beds
(pulmonary hypoxic vasoconstriction)
What about high altitudes can cause pulmonary hypertension?
Widespread hypoxic vasoconstriction
How does hypoxic vasoconstriction factor into birth and newborn respiration?
Before birth: the infant’s pulmonary arterioles are uniformly vasoconstricted.
At first breath: the hypoxic vasoconstriction is reversed by the incoming oxygen, and the alveoli all pop open.
What is the point of hypoxic pulmonary vasoconstriction?
To shunt blood to more oxygen-rich alveoli
What are some basic causes of pulmonary edema?
Pulmonary hypertension
Infection (i.e. pneumonia)
Nephrotic syndrome (loss of oncotic pressure)
Liver failure (loss of oncotic pressure)
What other primary function does ACE have besides converting angiotensin I to angiotensin II?
Inactivating bradykinin
Name a few substances that are inactivated in the lungs.
Serotonin
Bradykinin
Prostaglandins E1, E2, and F2α
True/False.
IgE is secreted into the respiratory mucus and mucopolysaccharides are secreted into the bronchial mucus.
False.
IgA is secreted into the respiratory mucus and mucopolysaccharides are secreted into the bronchial mucus.
What role do the lungs play in serotonin management?
What role do the lungs play in heparin management?
Inactivation and storage;
production via mast cells
1. How is the partial pressure of oxygen in the trachea (pO2) calculated?
2. How is the partial pressure of oxygen in an alveolus (pAO2) calculated?
1. 0.21 * (760 - 47) = 150 mmHg
2. Now, just subtract out the pCO2 (~40 mmHg) –>
150 mmHg - pCO2/0.8
(~100 mmHg)
In the equation for alveolar partial pressure of oxygen (pAO2 = pIO2 - pCO2/R), what value do we give to the constant, R?
0.8
Why do pAlveolarO2 levels drop in cases of hypoventilation?
The pCO2 rises
(remember Dalton and Henrys’ laws)
D.
What are the four physiologic causes of hypoxemia?
- Hypoventilation
- Diffusion limitation
- Shunt
- V/Q mismatch
What effect does hypoventilation have on arterial and alveolar pCO2?
Both increase
What are some example causes of hypoventilation?
Drugs: e.g. alcohol, benzodiazepenes, opiates, etc.
Morbid obesity, airway obstruction
Nerve conduction diseases: e.g. myasthenia gravis
Spinal cord damage
Chest wall damage
Paralysis
Describe the effect (increase or decrease) of each of the following on the paO2:
Hypoventilation
Diffusion limitation
Shunt
V/Q mismatch
Decrease
Decrease
Decrease
Decrease
What is a shunt?
Any case where blood traverses the lungs without being ventilated
What effect does an increase in the fraction of inspired O2 (FiO2) have on a shunt?
Very little
(the shunt bypasses the air, so changes in O2 are irrelevant)
Explain the shunt fraction equation (attached).
Qs = Blood flow through shunt
QT = Total blood flow past alveolus
Cc’O2 = Ideal blood oxygen levels (if all extracted at 1.34 mL per dL)
CaO2 = measured arterial pO2
CaO2 = measured pO2 after mixing of shunt and non-shunt blood
Why is the shunt fraction equation (attached) useful?
It allows for determining what proportion of pulmonary blood flow is being shunted
True/False.
Supplemental oxygen can be used to treat the effects of hypoventilation but not usually those of a shunt.
True.
Which is essentially a shunt, a V/Q of infinity or a V/Q of 0?
V/Q of 0
(ventilation blocked)
What is a normal V/Q relationship?
Does it increase or decrease from West Zone 1 to 2 to 3?
1:1
Decrease (perfusion increasing)
B.
A patient’s pCO2 is 80 mmHg (normal 40 mmHg). What is their pAO2?
What percentage supplemental oxygen (FiO2) do you need to give to get them back to 100 mmHg pAO2?
pAO2 = FiO2 - pCO2/R = 150 - 80/0.8 = 50 mmHg
pAO2 = FiO2 - pCO2/R
100 = (x)(760-47) - 80/0.8
x = 0.28
28%
What effect will a V/Q mismatch approaching 0 have on arterial and venous CO2/O2 levels?
Normal:
Arterial O2 — 90 mmHg
Arterial CO2 — 40 mmHg
Venous O2 — 40 mmHg
Venous CO2 — 45 mmHg
Arterial O2 — 40 mmHg
Arterial CO2 — 40 mmHg
Venous O2 — 45 mmHg
Venous CO2 — 45 mmHg
What effect will a V/Q mismatch approaching infinity have on alveolar O2 and CO2 levels?
Normal:
Alveolar O2 — 90 mmHg
Alveolar CO2 — 40 mmHg
Alveolar O2 — 150 mmHg
Alveolar CO2 — 0 mmHg
(no more CO2 driving down the O2:CO2 ratio)
Identify which V/Q mismatch is a shunt and which is dead space:
Increasing V/Q (from normal)
Decreasing V/Q (from normal)
Increasing — Dead space
(virtually no blood flow –> cannot be a shunt)
Decreasing — Shunt
(i.e. blood flowing past blocked alveoli)
Is the V/Q relationship higher or lower than 1 at the top of the lung?
Is the V/Q relationship higher or lower than 1 at the bottom of the lung?
Higher;
lower
Explain why tuberculosis favors the upper lobes of the lungs. Use V/Q relationship terminology.
The upper portions of the lung have a higher V/Q relationship than the lower lobes. TB loves O2.
Higher V/Q –> more ventilation than blood flow –> less CO2 to blow off and more ventilation to do it –> the fraction of O2 in the alveolus increases as CO2 decreases (maybe even approaching 150 mmHg pO2 and 0 mmHg pCO2)
Does ventilation change much from the top to the bottom of the lungs?
Does perfusion change much from the top to the bottom of the lungs?
A little, not much (it increases).
Yes (it increases drastically).
A higher V/Q relationship leads to a(n) ____________ in CO2 and a(n) ______________ in O2. (Increase/Decrease)
A lower V/Q relationship leads to a(n) ____________ in CO2 and a(n) ______________ in O2. (Increase/Decrease)
Decrease, increase;
increase, decrease
B.
True/False.
The blood passing through the pulmonary arteries has a higher O2 content than mixed venous blood.
False.
It is mixed venous blood (i.e. the blood returning to the heart from all the organs pooled together. I.e. what is found in the vena cava.).
What would it mean for V/Q to equal 3.3 at the top of the lungs?
What would it mean for V/Q to equal 0.63 at the bottom of the lungs?
Relatively more ventilation than perfusion
Relatively more perfusion than ventilation
Will blood pH be lower at the top or the bottom of the lungs?
The bottom
(due to the decreased V/Q)
When will paO2 be higher than pAO2?
Never!
Arterial pO2 is a function of alveolar pO2 and is always slightly less.
(Hence, the A-a gradient is always positive.)
Given paO2 in an arterial blood gas (ABG) reading, what else do you need to calculate the A-a gradient?
Just pAO2 (alveolar pO2)
pAO2 = PiO2 - pCO2/R
A normal A-a gradient should be:
< age/4 + 4
OR
< age/3
(both methods work)
What is the patient’s A-a gradient?
What does this indicate about the patient’s condition?
25 (normal for his age: ~16);
the hypoxemia is not due to hypoventilation (otherwise, the A-a gradient would have been normal)
How can you differentiate between a patient’s shunt or another V/Q mismatch?
Give 100% O2.
If the paO2 improves, it’s not a shunt.
Describe the changes in capillary bed engorgement/stretching/perfusion/recruitment in the top of the lungs vs. the bottom of the lungs.
How many alveoli are in the body?
~500,000,000
Surfactant is especially important in keeping the _______ (small/large) alveoli patent.
Small
(remember the law of LaPlace)
What are the three measurement categories that are typically taken in a pulmonary function testing lab?
- Spirometry (rate + volumes)
- Lung volumes (static)
- Diffusion capacity (DLCO)
What is another name for total ventilation?
Is this the same as alveolar ventilation?
Minute ventilation;
no
Will a 2000 mL breath have a larger dead space, as opposed to the 150 mL of dead space in a normal tidal volume of 500 mL?
No, the dead space volume remains constant
True/False.
A wedge pressure is measured using a Swan-Ganz catheter which temporarily occludes a portion of the lung (using a balloon) and measures the right ventricular filling pressure on the proximal portion of the occlusion.
False.
A wedge pressure is measured using a Swan-Ganz catheter which temporarily occludes a portion of the lung (using a balloon) and measures the left* ventricular filling pressure on the *distal portion of the occlusion.
What is a normal left ventricular filling pressure?
How can this be measured?
< 12 mmHg (pulmonary edema occurs at ≥ 18);
a Swan-Ganz catheter
Blood that flows through the lungs without being oxygenated is known as:
Shunt.
True/False.
The paCO2 and pACO2 can be assumed to be virtually identical.
True.
What is the typical V/Q at the very top of the lungs?
What is the typical V/Q at the very bottom of the lungs?
~3;
~0.7
Why is there a higher oxygen tension at the top of the lungs vs. the bottom?
The V/Q relationship is higher at the top
How much O2 is dissolved in a dL of blood?
0.003 mL for each mm of air pressure
(so, at 100 mmHg pO2, 0.3 mL)
At what partial pressure of oxygen (pO2) will the hemoglobin dissociation curve be at about the P50 (50% of Hgb bound)?
At what partial pressure of oxygen (pO2) will the hemoglobin dissociation curve be at about full saturation?
~27 mmHg
~55 mmHg
D.
What are some factors that might shift the oxygen dissociation curve to the right?
Increased temperature
Increased pCO2
Decreased pH
Increased 2,3-BPG
What are some factors that might shift the oxygen dissociation curve to the left?
Decreased temperature
Decreased pCO2
Increased pH
Decreased 2,3-BPG
What happens to ventilation at altitude?
It increases
(increased respiratory rate to blow off CO2)
How can high altitude directly affect the heart?
Right-sided hypertrophy due to pulmonary vasoconstriction
What effect do right-shifting factors have on the P50 for the oxyhemoglobin disassociation curve?
The P50 increases
If one gram of hemoglobin can carry 1.34 mL of O2, how much O2 can be carried in a dL?
20.1 mL
(1.34 mL/g * 15 g/dL)
What is the oxygen saturation of arterial blood at pO2 of 100 mmHg?
What is the oxygen saturation of mixed venous blood at pO2 of 40 mmHg?
97.5%
75%
What is an example condition where oxygen saturation might be low, but no cyanosis will be seen?
What is an example condition where oxygen saturation might be normal, but cyanosis can be seen?
Anemia
Polycythemia
Which is better at buffering H+, deoxyhemoglobin or oxyhemoglobin?
Deoxyhemoglobin
(this explains the Haldane effect –> blood is oxygenated at the lungs –> acidity increases –> more CO2 is formed from bicarbonate to be released)
D.
- (C. is incorrect because H+ and HCO3- are produced in equal amounts.*
- D. describes the Haldane effect.)*
Explain the Haldane effect.
Blood is oxygenated at the lungs –> *[H+] increases –> more CO2 is formed from bicarbonate (LeChatlier)
*deoxyhemoglobin carries H+ better than oxyhemoglobin
When a patient is given O2, their CO2 levels will instantly rise. Why is this?
The Haldane effect
(deoxyhemoglobin carries H+ better than oxyhemoglobin)
What would cause a person to move from point A to point B on the graph?
How will the body try to correct the pH if the problem is not fixed?
Respiratory acidosis (hypoventilation);
renal compensation (bicarbonate reabsorption)
What would cause a person to move from point A to point C on the graph?
How will the body try to correct the pH if the problem is not fixed?
Respiratory alkalosis (hyperventilation);
renal compensation (bicarbonate secretion)
What would cause a person to move from point A up the CO2 line (along the same line but further towards the top of the graph)?
How will the body try to correct the pH if the problem is not fixed?
Metabolic alkalosis;
respiratory compensation (hypoventilation)
What would cause a person to move from point A down the CO2 line (along the same line but further towards the bottom of the graph)?
How will the body try to correct the pH if the problem is not fixed?
Metabolic acidosis;
respiratory compensation (hyperventilation)
What is the Henderson-Hasselbalch equation in terms of blood pH (give it without numbers)?
pH = a constant + log(kidneyFunction/LungFunction)
A patient presents with the following ABG.
What is your analysis?
pH 7.24
pCO2 60
pO2 50
HCO3- 26
Acute respiratory acidosis
(acidemia, elevated CO2, normal HCO3-)
A patient presents with the following ABG.
What is your analysis?
pH 7.35
pCO2 60
pO2 50
HCO3- 32
Respiratory acidosis with partial metabolic compensation
(slight acidemia, elevated CO2, elevated HCO3-)
A patient presents with the following ABG.
What is your analysis?
pH 7.6
pCO2 20
pO2 60
HCO3- 22
Acute respiratory alkalosis
(alkalemia, decreased CO2, normal HCO3-)
A patient presents with the following ABG.
What is your analysis?
pH 7.1
pCO2 40
pO2 90
HCO3- 12
Acute metabolic acidosis
(alkalemia, normal CO2, decreased HCO3-)
A patient presents with the following ABG.
What is your analysis?
pH 7.20
pCO2 20
pO2 90
HCO3- 8
Metabolic acidosis with partial respiratory compensation
(acidemia, decreased CO2, decreased HCO3-)
A patient presents with the following ABG.
What is your analysis?
pH 7.55
pCO2 46
pO2 88
HCO3- 36
Metabolic alkalosis with some respiratory compensation
(alkalemia, slightly increased CO2, increased HCO3-)
In general terms, describe the changes in pCO2 and HCO3- seen in respiratory acidosis.
pCO2 — Elevated (hypoventilation)
HCO3- — Elevated (compensation)
In general terms, describe the changes in pCO2 and HCO3- seen in metabolic acidosis.
HCO3- — Decreased
pCO2 — Decreased (compensation)
In general terms, describe the changes in pCO2 and HCO3- seen in respiratory alkalosis.
pCO2 — Decreased (hyperventilation)
HCO3- — Decreased (compensation)
In general terms, describe the changes in pCO2 and HCO3- seen in metabolic alkalosis.
HCO3- — Increased
pCO2 — Variable
What is the Henderson-Hasselbalch equation in terms of blood pH (with numbers)?
Without numbers = pH = constant + kidney function / lung function
pH = 6.1 + log [HCO3-] / (0.03 * pCO2)
What will happen to bicarbonate levels in sustained respiratory acidosis?
They will increase (renal compensation)
E.
D.
Where is the functional residual capacity in this lung compliance graph?
The dashed line
Where is the primary site of airway resistance in the respiratory system?
The medium-sized bronchi
D.
What is the FEV1/FVC in a patient with restrictive lung disease?
What is the FEV1/FVC in a patient with obstructive lung disease?
Normal to elevated (both values decrease);
decreased
Which disease category is categorized by air trapping, obstructive or restrictive lung disease?
Obstructive
E.
D.
What is a normal bicarbonate level?
24 mEq/L
(22 - 26)
Below what pO2 are peripheral chemoreceptors most active?
Below 50 mmHg
(only a slight response from 90 - 50 mmHg)
Which diffuses faster, CO2 or O2?
CO2 (~20x faster)
Why is it important to check lactate levels in a patient with a severe infection?
To make sure the tissues are getting the oxygen they need
What are the four types of hypoxia?
Hypoxic
Anemic
Circulatory
Histotoxic
Define each of the following types of hypoxia:
Hypoxic
Anemic
Circulatory
Histotoxic
Hypoxic - caused by pulmonary disease
Anemic - low oxygen-carrying capacity
Circulatory - poor blood flow
Histotoxic - inability to use oxygen (e.g. cyanide poisoning)
Is supplemental oxygen ever not a useful treatment for hypoxia (Hypoxic, Anemic, Circulatory, Histotoxic)?
No. It can benefit all of these
What does this equation describe?
PA = Pip + Pelastic
The alveolar pressure is equal to the intrapulmonary pressure plus the elastic
What equation describes the mechanical pressures affecting alveolar pressure?
PA = Pip + Pelastic
(Note: Pip is often a negative value)
How is compliance defined?
ΔV/ΔP
How will a pneumothorax affect the chest wall - lung relationship?
The lung collapses inwards;
the chest flares out
A.
What effect does fibrosis have on lung compliance?
What effect does emphysema have on lung compliance?
It decreases;
it increases
True/False.
When the lungs are contracting during exhalation, some small airways close early, trapping air in the alveoli.
True.
This is called air trapping and happens more as we age but may be present to a small degree in youth.
C.
A.
(Note: ‘capacity’ is a weird word here. The ‘capacity’ for oxygen-carrying hasn’t changed, even if the affinity has.)
What is a normal FEV1/FVC?
80%
What is indicated by these results from patients B and C?
(Hint: Which parts of the graph are effort-dependent and which are effort-independent?)
They took sub-maximal measurements (potential malingering)
Can either H+ or HCO3- cross the blood-brain barrier?
What does this mean for respiratory control?
No;
central chemoreceptors respond to changes in CO2 only
Describe the central chemoreceptors.
CO2-sensitive and pH-sensitive receptors on the ventral medulla that control minute-to-minute ventilation
Which chemoreceptors are CO2-sensitive and pH-sensitive receptors on the ventral medulla that control minute-to-minute ventilation?
The central chemoreceptors
Where are central chemoreceptors?
Where are peripheral chemoreceptors?
What does each sense?
The ventral medulla — CO2, pH
carotid and aortic bodies — O2, CO2, and pH
Name some of the sensory receptors within the lungs.
Pulmonary stretch r.
irritant r.
Pulmonary J r.
Bronchial C r.
Which is faster, peripheral or central chemoreceptor responses?
Which is stronger?
Peripheral;
central
When is the activity of central and peripheral chemoreceptors magnified?
When paO2 is low
Of the peripheral chemoreceptors, which is more important?
The carotid
(vs. the aortic)
True/False.
Most of a patient’s respiratory rate is controlled by their FiO2.
False.
Most RR control comes from CO2 levels — O2 levels matter most once a patient drops below 100 mmHg paCO2
Why should some patients with severe lung disease not be given supplemental O2?
They may be depending on hypoxic drive for their ventilation
(their CSF has normalized despite the chronically elevated CO2)
Low blood pH is detected primarily by:
Peripheral chemoreceptors
What is the typical resting minute ventilation?
What is the typical resting cardiac output?
5 - 6 L/min
5 L/min
What type of abnormal breathing can be seen at high altitudes (especially during sleep) and also in CHF and brain damage?
Cheyne-Stokes respiration
(10-20 second periods of apnea and hyperventilation)
Describe Cheyne-Stokes respiration.
10 - 20 second periods of apnea and hyperventilation
(can be seen in CHF, brain damage, at high altitudes, etc.)
During exercise, CO can change from 5 L/min to 25 L/min.
How does oxygen consumption change during exercise?
From 300 mL/min to anywhere from 3,000 to 6,000 mL/min
What happens to pulmonary capillaries when cardiac output increases?
Recruitment and distention
How does the body acclimitize to higher elevations?
Hyperventilation (immediate)
Erythrocytosis (takes 2 - 3 days)
Increased mitochondrial density
Increased 2,3-BPG
Describe absorption atelectasis.
A small pulmonary duct gets blocked (e.g. by mucus) –> if the person has been receiving 100% supplemental oxygen, the gas keeps diffusing into the blood –> the alveoli collapse
(Note: this only happens with supplemental oxygen. Nitrogen partial pressures counteract the effects because the nitrogen won’t all diffuse through.)
Describe ‘the bends’.
Deep diving puts the body under increased pressure
–> nitrogen is forced out into the tissues
–> while ascending, the nitrogen returns to the blood and forms expanding bubbles
How extended are fetal lungs?
How is this changed at first breath?
40% of total lung capacity;
reversal of hypoxic vasoconstriction
What is the oxygen content of the blood in a person with a 98% SpO2 and 15 g/dL hemoglobin?
(1.34 mL/g * 15 g/dL * 0.98 SpO2) + 0.003 (90 mmHg)
= 19.7 + 0.27
= ~20
True/False.
Forceful exhalation (as often seen in cases of COPD) can actually cause premature airway closure proximal to the air being expelled due to higher pressures within the thoracic cavity.
True.
(Think of emphysematous ‘pink puffers’ pursing their lips to increase intrapulmonary pressures.)
True/False.
Positive pressure ventilation is the same method our bodies always use for respiration.
False.
Our bodies normally use negative pressure ventilation.
Why is there typically a greater residual volume in patients with COPD?
Air trapping due to airway closure
What is the diving reflex?
What cardiac presentation can it be used to disrupt?
When the face is immersed in cold water and the patient holds their breath, heart rate slows dramatically;
supraventricular tachycardia
Which has better buffering capabilities, the blood or CSF?
Blood, due to presence of hemoglobin
(meaning CSF is more sensitive to changes in pH)
True/False.
The ventilation response to changes in CO2 can differ dramatically from person to person based on age, fitness, race, personality, genetics, etc.
True.
VO2 max is essentially a measurement of maximal:
Oxygen consumption
Duing moderate exercise, describe what will happen to each of the following:
pAO2
paO2
paCO2
Arterial pH
No significant change
During prolonged, strenuous exercise, describe what will happen to each of the following:
pAO2
paO2
paCO2
Arterial pH
pAO2 — increases
paO2 — decreases
paCO2 —decreases
Arterial pH — decreases (lactic acidosis)
For what calculation is this equation used?
Describe the terms.
The shunt equation: the percentage of shunted pulmonary blood
Cc’O2 — the ideal oxygen amount extracted into the blood
CaO2 — the amount in the pulmonary venous blood
CvO2 — the amount in the mixed venous blood
For what calculation is this equation used?
Describe the terms.
The alveolar gas equation: to calculate the pO2 in the alvelous (or the FiO2 to get it back to a certain paO2).
PAO2 — Alveolar partial pressure of oxygen
FiO2 — Inspired fraction of oxygen (0.21)
PB — atmospheric pressure (760 mmHg)
PH2O — water pressure (47 mmHg)
PACO2 — Alveolar partial pressure of carbon dioxide
R — a constant (0.8)
For what calculation is this equation used?
Describe the terms.
The Bohr Equation (dead space ratio): Deadspace : total ventilation
VD / VT — ratio being solved
PaCO2 — arterial partial pressure of CO2
PECO2 — expired partial pressure of CO2
Given a PaO2, what else can be calculated using the equation below?
The A-a gradient
(by calculating PAO2)
For what calculation is this equation used?
Describe the terms.
Fick’s Law: the rate of diffusion.
VX (with a dot above the V) — volume flow being solved
A — surface area of alveoli
D — diffusion constant
T — thickness of alveolar-capillary interface
(Px1 - Px2) — pressure differential
Which pulmonary equation can be rearranged to give the DLCO equation?
Fick
Which equation is this?
The DLCO equation
What equation is this?
Rewrite it in the pulmonary format.
The Henderson-Hasselbalch equation
For what calculation is this equation used?
Describe the terms.
PA = Pip + Pelastic
Intraalveolar pressure: external pressure acting on the alveolus
PA — total pressure on the alveolar wall
Pip — intrapleural pressure (often a negative value)
Pelastic — pressure created by elastic recoil of the lung
What equation would you use to calculate this patient’s GFR?
GFR = Urine flow * UrineCreatinine / PlasmaCreatinine
(1440 mL/day / 24 hours/day / 60 min/hour) * 100 mg/dL / 1 mg% = 100 mL /min
What equation would you use to calculate this patient’s filtered load of urea?
Filtered Load of urea = GFR * PlasmaUrea
100 mL/min * 0.005 mM/mL = 0.5 mM/min
What equation would you use to calculate this patient’s urea excretion?
Urea excretion = Urine flow * UrineUrea
1 mL/min * 0.220 mM/mL = 0.22 mM/min
What equation would you use to calculate this patient’s net urea reabsorption?
Net urea reabsorption = Filtered - Excreted
0.5 mM/min - 0.22 mM/min = 0.28 mM/min
What equation would you use to calculate this patient’s fractional excretion of urea?
Fractional excretion of urea = Excreted / Filtered
0.22 mM/min / 0.5 mM/min = 0.44 = 44%
Fill in the blank for oxygen bound to hemoglobin:
___ mL O2 / g hemoglobin
1.34
Fill in the blank for oxygen dissolved in the blood:
___ mL O2 / 100 mL blood / mmHg pO2
0.003
How much oxygen is found bound to hemoglobin in one dL?
How much oxygen is found dissolved in one dL of blood?
20.1 mL / dL
1.34 mL O2 / g hgb * 15 g hgb / dL blood
0.3 mL / dL
0.003 mL O2 per 100 mL blood / mmHg pO2 * 100 mmHg paO2
What equation is used to calculate total ventilation?
What equation is used to calculate alveolar ventilation?
Respiratory rate * tidal volume
Respiratory rate * (tidal volume - dead space)
What equation is used to calculate an anion gap?
Anion gap = (Na+ + K+) - (Cl- + HCO3-)
Via what equation is renal clearance measured?
Clearancex = Urine flow * Urinex / Plasmax
When calculating GFR via renal plasma flow, what equation should be used?
Renal plasma flow = (Urine flow * Urinex) / (Pa(x) - Pv(x))
What is the equation for filtered load at the glomerulus?
GFR * plasma concentration
