fisiologia Flashcards
What is the term for the volume of air in excess of tidal volume that moves into the lung on inspiration?
Inspiratory reserve volume
A man breathes calmly and quietly. He takes in a normal breath and then lets it out without any forcing. What volume of air is being moved?
Tidal volume, which is approximately 500 mL
What is the term for the volume of air that can still be breathed out after a normal expiration?
Expiratory reserve volume
What is the term for the volume of air in the lungs after maximal expiration?
Residual volume
What is unmeasurable on spirometry: inspiratory reserve volume, tidal volume, expiratory reserve volume, residual volume?
Residual volume
The inspiratory reserve volume plus the tidal volume equals what?
Inspiratory capacity
The residual volume plus the expiratory reserve volume equals what?
The functional reserve capacity
Describe the functional reserve capacity. What are its two components?
FRC = the total volume left in the lungs after normal expiration; residual volume + expiratory reserve volume = FRC
Vital capacity equals the sum of what three lung volumes?
Tidal volume, inspiratory reserve volume, and expiratory reserve volume
What is the term for the maximum volume of air that can be inhaled and exhaled?
Vital capacity
A patient exhales as much as he can, inhales as much as he can, and then exhales as much as he can again. What volume of air has he moved?
His vital capacity (VC)
Inspiratory reserve volume plus tidal volume plus expiratory reserve volume plus residual volume equals what?
Total lung capacity
Name the four lung volumes.
Lung volumes (LITER) = Inspiratory reserve (IRV), Tidal (TV), Expiratory reserve (ERV), Residual (RV)
What is the definition of a capacity?
The sum of greater than or equal to two physiologic volumes
What is the equation for determining the volume of dead space in the lungs, where PaCO2 = arterial and PECO2 = expired air?
VD = VT × ([PaCO2 - PECO2]/PaCO2) (Taco, Paco, PEco, Paco, as the order of variables)
You know a patient’s physiologic dead space, expired air CO2, and arterial CO2. Can you calculate their tidal volume (VT)?
Yes, as VD = VT × ([PaCO2 - PECO2]/PaCO2), where PaCO2 = arterial, and PECO2 = expired air
A patient’s tidal volume is 500 mL, PaCO2 is 50 mmHg, and PECO2 is 35 mmHg. What is the physiologic dead space?
150 mL; VD = 500 mL × ([50 mmHg - 35 mmHg]/50 mmHg)
Describe the parts of the airway that contribute to the physiologic dead space.
Conducting airways that contribute to anatomic dead space, and alveolar dead space
Which alveolar section of the healthy lung contributes more to physiologic dead space: the apex or the base?
Apex
What is the volume of inspired air that does not contribute to gas exchange?
Physiologic dead space, VD
What is minute ventilation (VE)? How do you calculate it?
The total volume of gas entering the lungs each minute; VE = VT × respiratory rate
A patient with a tidal volume of 400 mL is breathing 20 times per minute. What is his minute ventilation?
8000 mL/min, as minute ventilation (VE) = 400 mL × 20 breaths/min
What is alveolar ventilation (VA)? How do you calculate it?
The volume of gas per unit time that reaches the alveoli; VA = (VT - VD) × respiratory rate
A patient with a tidal volume of 650 mL is breathing 10 times per minute. His dead space is 150 mL. What is his alveolar ventilation?
5000 mL/min, as alveolar ventilation (VA) = (650 mL - 150 mL) × 10 breaths/min
A patient is breathing naturally. Describe the natural tendency of movement of the lung and chest wall.
The lungs tend to collapse inward, and chest wall springs outward
At what point in the respiratory cycle is the inward pull of the lung equal to the outward pull of the chest wall?
At functional residual capacity
At the point of functional residual capacity, what is the value of the air pressure within the lungs?
At FRC, the pressure within the lungs is equal to atmospheric pressure
A patient takes in a deep breath. What determines the combined volume of the chest wall and lungs?
Elastic properties of both
• In terms of lung pressures, explain how a pneumothorax is prevented.
At FRC, lung pressures are atmospheric, and opposing forces of the lung and chest wall create negative pressure in the intrapleural space
• When is pulmonary vascular resistance at a minimum?
At functional residual capacity
What is compliance?
The change in lung volume for a given change in pressure
• A 43-y/o woman has pulmonary fibrosis. How does this affect her lung compliance? Other conditions that would affect compliance similarly?
Lung compliance decreases with pulmonary fibrosis, and in pulmonary edema and pneumonia
Lung compliance ____ (increases/decreases) in a patient with emphysema, and with natural aging.
Increases
• How many polypeptide subunits make up hemoglobin?
Four
What are the two conformational forms of hemoglobin?
Relaxed (oxygenated) and taut (deoxygenated)
Of the two forms of hemoglobin, the taut (T) form has ____ (high/low) affinity for oxygen. The relaxed (R) form has ____ (high/low) affinity.
Low; high (300 times more affinity in R form) (Taut in Tissues, Relaxed in Respiratory tract)
Does hemoglobin have positive or negative cooperativity with respect to oxygen binding and affinity?
Positive
Does hemoglobin have positive or negative allostery with respect to oxygen binding and affinity?
Negative
An increase in which five factors will favor the taut form of hemoglobin over the relaxed form and will decrease affinity for oxygen?
Chloride (Cl-), protons (H+), carbon dioxide, 2,3-bisphosphoglycerate, and temperature
A patient is exercising in the freezing cold. He is otherwise healthy. Is his hemoglobin more likely to be taut or relaxed?
Taut, as exercise (generating CO2) favors the taut form (the outside temperatures are meaningless, as body temperature is what matters)
Fetal hemoglobin has ____ (higher/lower) affinity for 2,3-BPG than does adult hemoglobin, causing ____ a (higher/lower) affinity for oxygen.
Lower, higher
Hemoglobin can act as a buffer for which ions?
H+
Changes to hemoglobin can lead to decreased O2 ____ and ____, causing hypoxia in tissues.
• Saturation, content
Normal Hb iron is ____(reduced/oxidized), or ____(ferric/ferrous). Methemoglobin iron is ____(reduced/oxidized), or ____(ferric/ferrous).
Reduced, ferrous (just the 2 of us: ferrous is Fe2+); oxidized, ferric (Fe3+)
A man suffers from cyanide poisoning. What property of methemoglobin makes it useful for treatment?
The ferric (Fe3+) state of methemoglobin decreases the affinity for O2 but increases the affinity for cyanide
A cyanotic patient is found to have chocolate-colored blood. Treatment?
Methylene blue (this patient has methemoglobinemia)
• A child has cyanide poisoning. What is the mechanism of action of nitrites used in the treatment?
Nitrites oxidize iron to form methemoglobin, which readily binds cyanide, restoring function to cytochrome oxidase
A patient has cyanide poisoning. What two treatments do you give?
Nitrites and subsequently thiosulfate
A patient looks blue and has blood that has turned brown. What caused this?
Poisoning by nitrites or benzocaine
What is the name of a form of hemoglobin in which carbon monoxide is bound instead of oxygen?
Carboxyhemoglobin
When another molecule, such as carbon monoxide, binds to hemoglobin in place of oxygen, what are the systemic effects?
CO causes a left shift in the oxygen-hemoglobin curve, resulting in tissue hypoxia from decreased oxygen unloading
Does carbon monoxide or oxygen have a greater affinity for hemoglobin?
CO has 200 times the affinity of oxygen for hemoglobin
What is the shape of the oxygen-hemoglobin dissociation curve? Explain.
Sigmoidal due to positive cooperativity, as Hb can bind four O2 molecules—O2 binding is easier when more O2 is bound
How does the structure of myoglobin affect its function?
It is monomeric and thus has no positive cooperativity as seen in hemoglobin, and it lacks the sigmoidal curve
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 O2 saturation (%) at a PO2 of 50 mmHg?
• A right shift decreases oxygen saturation (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
Increases in the amount of which six factors cause a right shift of the oxygen-hemoglobin dissociation curve?
Right = ACE BATs right handed (Acid [H+], CO2, Exercise, 2,3-BPG, Altitude, Temperature)
When the oxygen-hemoglobin dissociation curve shifts to the left, what happens to the O2 saturation (%) at a PO2 of 50 mmHg?
A left shift increases oxygen saturation (less oxygen pressure is required to saturate hemoglobin)
Decreases in the amount of which factors cause a left shift of the oxygen-hemoglobin dissociation curve?
Acid (H+), CO2, exercise, 2,3-BPG, altitude, temperature
A fetus’s oxygen-hemoglobin dissociation curve is investigated. How does it compare to an adult’s oxygen-hemoglobin dissociation curve?
It is shifted to the left (fetal hemoglobin has higher affinity for oxygen than has adult hemoglobin)
A patient in shock develops a lactic acidosis. This decrease in pH causes what kind of shift in the oxygen-hemoglobin dissociation curve?
Right shift (due to increased acid [or H+] lowering the pH)
A patient’s chest is injured and her partial pressure of CO2 is increased. How does this affect her oxygen-hemoglobin dissociation curve?
Shifts it to the right
A patient is exercising. What effect would this have on his oxygen-hemoglobin dissociation curve?
• A right shift
An increase in 2,3-bisphosphoglycerate (2,3-BPG) causes a ____ (left/right) shift in the oxygen-hemoglobin dissociation curve.
Right
A hiker scales an extremely tall mountain. High altitude induces what change in the oxygen-hemoglobin dissociation curve?
A right shift
A patient develops a fever. An increase in temperature causes what kind of shift in the oxygen-hemoglobin dissociation curve?
A right shift
What is the equation for oxygen content in the blood?
O2 content = (O2 binding capacity × percent saturation) + dissolved O2
What is the normal level of hemoglobin in the blood. How many milliliters of oxygen can it bind?
Normal Hb amount = 15 g/dL; each gram can bind 1.34 mL of oxygen
A previously healthy patient develops blue lips and fingertips. What does this say about the value of her deoxygenated hemoglobin level?
Her deoxygenated hemoglobin must be >5 g/dL (this is cyanosis)
What is the normal value of the O2 binding capacity?
• 20.1 mL O2/dL
As Hb falls, what happens to each parameter (increase/decrease/unchanged): O2 content of arterial blood, O2 saturation, arterial PO2?
O2 content of arterial blood decreases, O2 saturation and arterial PO2 remain unchanged
How do you calculate oxygen delivery to the tissues?
O2 delivery to tissues = cardiac output × O2 content of blood
A woman has CO poisoning. What are the likely levels of her Hb, %O2 saturation of Hb, dissolved O2 (PaO22 content?
• Hb is normal, %O2 saturation of Hb is decreased (CO competes with O2), PaO2 is normal, and total O2 content is decreased
A woman has fatigue and pallor. What are the likely levels of her Hb, %O2 saturation of Hb, dissolved O2 (PaO2), and total O2 content?
Hb is decreased, %O2 saturation of Hb is normal, PaO2 is normal, and total O2 content is decreased (she has anemia)
A man has polycythemia. What are the likely levels of his Hb, %O2 saturation of Hb, dissolved O2 (PaO2), and total O2 content?
Hb is increased, %O2 saturation of Hb is normal, PaO2 is normal, and total O2 is content increased
