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Questions and Answers

The most common cause of cyanide poisoning is smoke inhalation.

True

Cyanide inhibits aerobic metabolism, resulting in hypoxia unresponsive to supplemental O2.

True

What distinct breath odor do patients with cyanide poisoning present?

almond

What skin discoloration is associated with cyanide poisoning?

<p>cherry-red</p> Signup and view all the answers

Exercise alone can make healthy patients hypoxemic.

<p>False</p> Signup and view all the answers

What causes the narrowing of the venous-arterial PO2 gradient in cyanide poisoning?

<p>Cyanide poisoning</p> Signup and view all the answers

Increased lung volumes result in increased pulmonary vascular resistance.

<p>True</p> Signup and view all the answers

Pulmonary vascular resistance is lowest near the functional residual capacity (FRC).

<p>True</p> Signup and view all the answers

Cyanide poisoning may occur through the ingestion of ______, which is found in apricot seeds.

<p>amygdalin</p> Signup and view all the answers

Carbon monoxide poisoning is classically associated with bilateral globus pallidus hyperintensities on MRI.

<p>True</p> Signup and view all the answers

What drives O2 diffusion across the placenta from mother to fetus?

<p>O2 diffusion is driven by concentration gradients.</p> Signup and view all the answers

The increased O2 binding affinity of fetal hemoglobin results from decreased affinity of HbF for 2,3-BPG.

<p>True</p> Signup and view all the answers

Hemoglobin exists in two forms: ______ and ______.

<p>taut, relaxed</p> Signup and view all the answers

What type of hemoglobin is found in most tissues?

<p>Taut form of hemoglobin.</p> Signup and view all the answers

What equation is used to calculate the O2 content of blood?

<p>O2 content = (1.34 × Hb × SaO2) + (0.003 × PaO2)</p> Signup and view all the answers

What is the effect of increased pCO2 on hemoglobin?

<p>Decreased affinity for O2</p> Signup and view all the answers

Shifts of the O2-Hb dissociation curve to the right occur when there is a decreased affinity of hemoglobin for O2.

<p>True</p> Signup and view all the answers

What is the effect of increased 2,3-BPG on the O2-hemoglobin dissociation curve?

<p>It causes the curve to shift to the right.</p> Signup and view all the answers

What is the management of carbon monoxide poisoning?

<p>All of the above</p> Signup and view all the answers

How does the hemoglobin concentration change in polycythemia?

<p>Increased</p> Signup and view all the answers

Hypoxia is defined as a decrease of O2 delivery to tissues.

<p>True</p> Signup and view all the answers

Which poisonous substance is characterized by a 'bitter almond' odor?

<p>Cyanide</p> Signup and view all the answers

What happens to the A-a gradient in response to high altitude?

<p>Normal</p> Signup and view all the answers

Ischemia occurs due to a loss of blood flow, such as ______.

<p>impaired arterial flow</p> Signup and view all the answers

What is the effect of normal aging on total lung capacity (TLC)?

<p>No change</p> Signup and view all the answers

Pulmonary blood flow is equal to the cardiac output of the right heart.

<p>True</p> Signup and view all the answers

When a person is standing, pulmonary blood flow is lowest at the apex of the lungs.

<p>True</p> Signup and view all the answers

The volume that moves into the lung with each quiet inspiration is known as the tidal volume.

<p>True</p> Signup and view all the answers

What is the typical normal value for tidal volume (mL)?

<p>500 mL</p> Signup and view all the answers

What is the additional volume that can be inspired above tidal volume called?

<p>Inspiratory reserve volume (IRV)</p> Signup and view all the answers

What is the additional volume that can be expired below tidal volume called?

<p>Expiratory reserve volume (ERV)</p> Signup and view all the answers

What volume remains in the lungs after maximal forced expiration?

<p>Residual volume</p> Signup and view all the answers

Residual volume can be measured on spirometry.

<p>False</p> Signup and view all the answers

What is the sum of tidal volume and inspiratory reserve volume known as?

<p>Inspiratory capacity</p> Signup and view all the answers

What is the sum of residual volume and expiratory reserve volume known as?

<p>Functional residual capacity (FRC)</p> Signup and view all the answers

Which lung capacities cannot be measured on spirometry?

<p>Total lung capacity (TLC)</p> Signup and view all the answers

What is the typical normal value for anatomic dead space (mL)?

<p>150 mL</p> Signup and view all the answers

What equation may be used to determine the physiologic dead space (VD)?

<p>$VD = VT \times \frac{P_{aCO_2} - P_{ECO_2}}{P_{aCO_2}}$</p> Signup and view all the answers

What is minute ventilation?

<p>Total volume of gas that enters the lungs per minute</p> Signup and view all the answers

How is minute ventilation calculated?

<p>Minute Ventilation (VE) = VT × RR</p> Signup and view all the answers

What is the normal range of respiratory rates for a healthy adult (breaths/min)?

<p>12-20 breaths/min</p> Signup and view all the answers

What is the effect of increased alveolar ventilation on arterial and alveolar Pco2?

<p>Decreased Pco2</p> Signup and view all the answers

What equation describes the alveolar gas equation?

<p>PAO2 = PIO2 - (PaCO2/R)</p> Signup and view all the answers

What is the normal value for the ratio of FEV1/FVC?

<p>0.7</p> Signup and view all the answers

What describes lung compliance?

<p>Change in lung volume for a given change in lung pressure</p> Signup and view all the answers

What is the equation for calculating lung compliance?

<p>C = ΔV/ΔP</p> Signup and view all the answers

The compliance of the lungs and chest wall is directly proportional to their elastance.

<p>False</p> Signup and view all the answers

A lung with high compliance is easier to fill.

<p>True</p> Signup and view all the answers

The law of Laplace states that the collapsing pressure of an alveolus (P) can be determined by the equation: P = 2T / ______

<p>r</p> Signup and view all the answers

What is the effect of emphysema on lung compliance?

<p>Increased compliance</p> Signup and view all the answers

What is the effect of pulmonary fibrosis on lung compliance?

<p>Decreased compliance</p> Signup and view all the answers

What three drug classes and singular drug are commonly associated with methemoglobinemia?

<p>All of the above</p> Signup and view all the answers

What is induced-methemoglobinemia used for?

<p>Treat cyanide poisoning</p> Signup and view all the answers

What happens to the partial pressure of oxygen in arteriolar blood compared to alveolar air due to the physiologic shunt?

<p>Slightly lower</p> Signup and view all the answers

What is fetal hemoglobin known for?

<p>Higher binding affinity for O2 than adult hemoglobin</p> Signup and view all the answers

Study Notes

Pulmonary Blood Flow

  • Pulmonary blood flow is equal to the right heart's cardiac output
  • When a person stands, blood flow is lower at the lungs' apex and higher at the base

Lung Volumes

  • The volume inhaled during quiet breathing is the tidal volume (TV)
  • Typical Tidal Volume (TV) is 500 mL
  • Inspiratory Reserve Volume (IRV) is the extra volume inhaled above TV
  • Expiratory Reserve Volume (ERV) is the extra volume exhaled below TV
  • Residual Volume (RV) is the volume remaining in the lungs after maximal exhalation
  • Residual volume (RV) cannot be measured with spirometry
  • Inspiratory Capacity (IC) is the sum of TV and IRV
  • Functional Residual Capacity (FRC) is the sum of RV and ERV
  • Functional Residual Capacity (FRC) is the volume remaining after a normal exhale
  • Vital Capacity (VC) is the sum of TV, IRV, and ERV
  • Forced Vital Capacity (FVC) is the maximum volume exhaled after maximal inhalation
  • Total Lung Capacity (TLC) is the sum of TV, IRV, ERV, and RV
  • FRC and TLC are not measurable with spirometry
  • FRC can be measured with helium dilution or body plethysmography

Dead Space

  • Anatomic dead space is the volume of air that does not participate in gas exchange
  • Typical anatomic dead space is 150 mL
  • Alveolar dead space is the volume of alveoli that are ventilated but not perfused
  • Physiologic dead space is the total volume of non-gas exchange air (anatomic + alveolar)
  • The apex of a healthy lung is the largest contributor to alveolar dead space
  • In healthy lungs, physiologic dead space is close to anatomic dead space
  • In unhealthy lungs, physiologic dead space can be greater than anatomic, indicating a ventilation/perfusion mismatch
  • Pathologic dead space occurs when an area of the respiratory zone is ventilated but not perfused

Ventilation

  • Minute ventilation is the total volume of air entering the lungs per minute
  • Minute Ventilation (VE) = VT × RR
  • Alveolar ventilation is the volume of air reaching the alveoli per minute (accounting for physiologic dead space)
  • Alveolar Ventilation (VA) = (VT - VD) × RR
  • Normal respiratory rate for an adult is 12-20 breaths/minute

Carbon Dioxide Regulation

  • With constant CO2 production, arterial and alveolar Pco2 is determined by alveolar ventilation
  • Increased alveolar ventilation reduces arteriolar and alveolar Pco2
  • Decreased alveolar ventilation increases arteriolar and alveolar Pco2

Alveolar Gas Equation

  • Alveolar gas equation: PAO2 = PIO2 - (PaCO2/R)
  • Respiratory Quotient (R) is CO2 production rate / O2 consumption rate
  • In the steady state, R is normally 0.8
  • PIO2 at sea level is 150 mmHg
  • The alveolar-arterial (A-a) gradient is the difference between PAO2 − PaO2
  • Normal (A-a) gradient in a non-smoking young adult is 5-10 mmHg

Lung Mechanics

  • FEV1 is the volume forcibly exhaled after maximal inhalation in one second
  • Normal FEV1/FVC ratio is ≥0.7
  • Lung compliance is the change in lung volume for a given change in lung pressure (ΔV / ΔP)
  • Lung compliance can be calculated by C = ΔV/ΔP
  • Compliance of the lungs and chest wall is inversely proportional to elastance
  • Elastance is the force generated by the lungs collapsing inward and the chest wall expanding outward
  • Compliance is inversely proportional to elastance and directly proportional to recoil
  • High compliance means easy filling, low compliance means harder filling
  • The slope of a respiratory system pressure-volume curve represents lung compliance
  • Hysteresis is the difference in pressure-volume loop slopes for inspiration and expiration
  • Hysteresis is due to surface tension forces overcome during lung inflation

Intrapleural Pressure

  • At FRC, intrapleural pressure is negative relative to the atmosphere
  • At FRC, the lung's inward pull is balanced by the chest wall's outward pull
  • A pneumothorax occurs when intrapleural pressure equals atmospheric pressure
  • Lung-chest wall system compliance is less than individual components
  • At FRC, airway and alveolar pressures equal atmospheric pressure
  • At lung volumes below FRC, there is a net expanding force on the lung-chest wall system
  • At lung volumes above FRC, there is a net collapsing force on the lung-chest wall system

Compliance Factors

  • Emphysema increases lung compliance, causing increased FRC
  • Normal aging increases lung compliance
  • Pulmonary fibrosis decreases lung compliance, causing decreased FRC
  • Pulmonary edema decreases lung compliance
  • Pneumonia decreases lung compliance
  • Surfactant increases lung compliance

Lung Volume Changes

  • Increased lung volume decreases airway resistance
  • Decreased lung volume increases airway resistance

Airway Resistance

  • The law of Laplace states that the collapsing pressure of an alveolus (P) is: P = 2T / r
  • A large alveolus has a lower collapsing pressure, a small alveolus has a higher collapsing pressure
  • Alveoli are more prone to collapse during expiration
  • Airflow (Q) can be calculated as Q = ΔP/R
  • Airflow is inversely proportional to airway resistance, and directly proportional to the pressure gradient
  • Airway resistance can be calculated using Poiseuille's equation: R = 8ηl/πr4
  • Resistance is inversely proportional to the fourth power of the airway radius
  • The medium-sized bronchi are the main site of airway resistance
  • Parasympathetic innervation increases airway resistance
  • Sympathetic innervation decreases airway resistance
  • Increased viscosity (i.e. deep-sea diving) increases resistance
  • Decreased viscosity (i.e. helium inhalation) decreases resistance

Pulmonary Vascular Resistance (PVR)

  • PVR = (Ppulm artery - PL atrium) / cardiac output

Breathing Mechanics

  • Transpulmonary pressure is alveolar pressure minus intrapleural pressure
  • Lung volume increases during inspiration
  • Intrapleural pressure becomes more negative during inspiration
  • Alveolar pressure becomes more negative during mid-inspiration, causing air to flow inwards
  • Lung volume decreases, intrapleural pressure becomes less negative, and alveolar pressure becomes more positive during expiration, causing air to flow outwards
  • Forced expiration can cause intrapleural pressure to become positive

Gas Exchange

  • Partial pressure of a gas in humidified tracheal air is (PB - PH2O) * F
  • Partial pressure in dry expired air is PB * F
  • Concentration of a dissolved gas (Cx) is Px * Solubility
  • Transfer of gases across membranes occurs by simple diffusion
  • Fick's law states: V̇ x = DAΔP / Δx
  • CO2 has about 20x higher diffusion coefficient than O2
  • Lung diffusing capacity (DL) is the permeability of the alveolar-pulmonary capillary barrier
  • DL can be assessed using carbon monoxide (CO) as it is diffusion-limited
  • DLCO estimates oxygen transfer from lungs to blood
  • DL is proportional to surface area and diffusion coefficient, and inversely proportional to wall thickness
  • DL decreases in emphysema due to decreased surface area
  • DL decreases in pulmonary fibrosis due to increased wall thickness
  • DL increases during exercise due to increased surface area

Gas Pressures

  • Dry inspired air Po2 is 160 mmHg
  • Humidified tracheal air Po2 is 150 mmHg
  • PAO2 and PaO2 are normally around 100 mmHg
  • PACO2 and PaCO2 are normally 40 mmHg
  • PvO2 is around 40 mmHg
  • PvCO2 is 46 mmHg
  • PaO2 is slightly lower than PAO2 because of the physiologic shunt
  • The physiologic shunt comes from bronchial and a portion of coronary venous blood
  • The total gas concentration is dissolved gas + bound gas + chemically modified gas
  • Only the free, dissolved gas contributes to the partial pressure
  • In diffusion-limited exchange, gas doesn't equilibrate by the end of the capillary
  • In perfusion-limited exchange, gas equilibrates early in the capillary
  • Increased blood flow is the only way to increase diffusion in perfusion-limited scenarios
  • In normal health, O2, CO2, and N2O are perfusion-limited; CO is diffusion-limited
  • In diseased lungs, O2 transfer becomes diffusion-limited
  • Reduced O2 pressure gradient at high altitude slows equilibration

Hemoglobin

  • O2 is carried in blood dissolved (2%) or bound to hemoglobin (98%)
  • Hemoglobin is a protein with 4 subunits
  • Each subunit has a heme moiety (iron-binding porphyrin) and a polypeptide chain
  • Hemoglobin iron is normally in the ferrous (Fe2+) state
  • Methemoglobin is hemoglobin with iron in the ferric (Fe3+) state
  • Methemoglobin binds O2 less readily than hemoglobin
  • Methemoglobin has higher affinity for cyanide than hemoglobin
  • Methemoglobinemia causes cyanosis and chocolate-colored blood
  • Methemoglobinemia is treated with methylene blue or vitamin C
  • Nitrates, sulfa drugs, topical anesthetics, and dapsone are associated with methemoglobinemia
  • Polluted water can contain nitrites, causing methemoglobinemia
  • Methemoglobinemia parameters: decreased SaO2 (usually to 85%), decreased O2 content, normal PaO2, decreased PaCO2
  • HbA is the most common adult hemoglobin, with 2 α and 2 β subunits
  • HbF, fetal hemoglobin, has higher O2 binding affinity than HbA
  • HbF has higher affinity for O2 because of decreased affinity for 2,3-BPG
  • Hemoglobin exists in taut (deoxygenated) and relaxed (oxygenated) forms
  • The taut form has low O2 affinity and is found in most tissues
  • The relaxed form has high O2 affinity and is found in the lungs
  • 1 g of hemoglobin binds 1.34 mL of O2
  • Blood normally has 15 g/dL of hemoglobin
  • Blood's O2 binding capacity is 20.1 mL O2 / 100 mL blood
  • O2 content of blood = (1.34 × Hb × SaO2) + (0.003 × PaO2)
  • Anemia (decreased hemoglobin) has normal SaO2, decreased O2 content, and normal PaO2
  • O2 delivery to tissues = CO × O2 content of blood
  • The oxygen-hemoglobin dissociation curve has a sigmoidal shape due to positive cooperativity
  • Myoglobin binds 1 O2 molecule
  • P50 is the Po2 where hemoglobin is 50% saturated
  • The oxygen-hemoglobin curve flattens between 60 and 100 mmHg
  • The oxygen-myoglobin dissociation curve is not sigmoidal, as it has a higher O2 affinity at lower pressures### Myoglobin
  • Myoglobin is a monomeric protein, meaning it does not exhibit positive cooperativity like hemoglobin.

Oxygen-Hemoglobin Dissociation Curve

  • Shifts to the right indicate decreased hemoglobin affinity for oxygen.
  • Shifts to the right cause increased oxygen unloading at tissues.

Bohr Effect

  • Increased pCO2 and resulting decrease in pH enhance oxygen release from hemoglobin.

Factors Affecting Oxygen-Hemoglobin Dissociation Curve

  • Increased temperature shifts the curve to the right.
  • Increased 2,3-BPG shifts the curve to the right.
  • 2,3-BPG decreases hemoglobin affinity for oxygen by binding to beta chains.
  • Increased 2,3-BPG occurs under hypoxic conditions, such as at high altitudes.
  • High altitudes indirectly cause the curve to shift to the right.
  • Increased pH shifts the curve to the left.
  • Decreased temperature shifts the curve to the left.
  • Increased HbF shifts the curve to the left.

Carboxyhemoglobin

  • Carboxyhemoglobin is hemoglobin bound to carbon monoxide (CO) instead of oxygen.
  • Carbon monoxide binds to hemoglobin competitively with 200-250 times greater affinity than oxygen.
  • Carboxyhemoglobin shifts the oxygen-hemoglobin dissociation curve to the left, increasing hemoglobin affinity for oxygen, and decreasing oxygen unloading at tissues.
  • Carboxyhemoglobin causes decreased oxygen-binding capacity
  • Management of carbon monoxide poisoning (carboxyhemoglobinemia) includes 100% oxygen, hyperbaric oxygen therapy,& endotracheal intubation.
  • Carboxyhemoglobinemia is associated with decreased SaO2, decreased oxygen content, and normal PaO2.
  • Hemoglobin concentration remains normal in carboxyhemoglobinemia.

Anemia

  • Hemoglobin concentration decreases in anemia.

Polycythemia

  • Polycythemia is associated with normal SaO2, increased oxygen content, and normal PaO2.
  • Hemoglobin concentration increases in polycythemia.

Erythropoietin (EPO)

  • Erythropoietin is a hormone synthesized in the kidneys in response to hypoxia.
  • Decreased oxygen delivery to the kidneys due to hypoxia increases production of hypoxia-inducible factor 1α, which stimulates EPO synthesis.
  • Hypoxia-inducible factor 1α acts in renal fibroblasts to cause synthesis of erythropoietin mRNA.
  • EPO causes differentiation of proerythroblasts, which develop into mature erythrocytes.

Carbon Dioxide Transport

  • Deoxygenated hemoglobin acts as a buffer for H+ ions.
  • Carbon dioxide is transported in the blood in three forms: dissolved CO2 (5%), bound to hemoglobin as carbaminohemoglobin (HbCO2) (25%), and as bicarbonate (HCO3-) (70%).
  • CO2 binds to hemoglobin at the N-terminus of globin.
  • The Haldane effect states that decreased oxygen binding to hemoglobin increases affinity for CO2 and H+, while increased oxygen binding to hemoglobin decreases affinity for CO2.
  • In red blood cells, CO2 combines with water via carbonic anhydrase, forming H2CO3 (carbonic acid).
  • The H+ from H2CO3 is buffered by deoxyhemoglobin.
  • HCO3- is transported from red blood cells into the plasma in exchange for Cl-.
  • HCO3- is carried to the lungs in the plasma of venous blood.
  • In the lungs, oxygenation of hemoglobin promotes H+ release from its buffering sites.
  • HCO3- enters red blood cells in exchange for Cl-.
  • H2CO3 is reconverted to CO2 and H2O and expired.
  • The Cl--HCO3- exchange across the red blood cell membrane is facilitated by band 3 protein.

Pulmonary Circulation

  • The pulmonary circulation is normally characterized as a low resistance, high compliance system.
  • Hypoxic vasoconstriction, which shunts blood away from poorly ventilated regions of the lung, occurs when PAO2 decreases.
  • Fetal pulmonary vascular resistance is high due to generalized hypoxic vasoconstriction.
  • Decreased Po2 (hypoxia) causes vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation.
  • Increased Pco2 (hypercapnia) causes vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation.

Pulmonary Zones

  • Blood flow (Q) is lowest in zone 1 (apex) and highest in zone 3 (base) of the lung.
  • Zone 1: PA ≥ Pa > Pv
  • Zone 2: Pa > PA > Pv
  • Zone 3: Pa > Pv > PA
  • In zone 1, high alveolar pressure may compress capillaries.
  • In zone 2, blood flow is driven by the difference between arteriolar and alveolar pressure.
  • In zone 3, blood flow is driven by the difference between arteriolar and venous pressure.

Right-to-Left Shunts & Hypoxemia

  • Right-to-left shunts cause hypoxemia because a portion of cardiac output bypasses the lungs.
  • Hypoxemia caused by right-to-left shunts cannot be corrected with high oxygen gas.
  • Left-to-right shunts do not result in hypoxemia.

Ventilation/Perfusion (V/Q) Ratio

  • The V/Q ratio is the ratio of alveolar ventilation to pulmonary blood flow.
  • The normal average V/Q is 0.8.
  • Ventilation and perfusion are greater at the base of the lung than at the apex.
  • The V/Q is highest in zone 1 (apex) and lowest in zone 3 (base).
  • The ideal V/Q for adequate gas exchange is 1 (ventilation matches perfusion).
  • Blood flow obstruction results in a V/Q of ∞ (dead space).
  • Airway obstruction results in a V/Q of 0 (shunt).

V/Q Mismatch

  • Pulmonary embolus causes dead space (V/Q = ∞).
  • Airway obstruction causes shunt (V/Q =0).
  • 100% oxygen improves PaO2 in V/Q mismatch due to dead space, but not in shunt.
  • Organisms that thrive in high oxygen (e.g., Mycobacterium tuberculosis) flourish in the apex of the lung.
  • Exercise increases cardiac output and causes vasodilation of apical capillaries, making the V/Q ratio approach 1.
  • Exercise increases oxygen consumption, ventilation rate, and pulmonary blood flow.
  • Pulmonary resistance decreases with increased perfusion.
  • Strenuous exercise causes decreased pH due to lactic acidosis.
  • PaCO2 does not change with exercise.
  • PaO2 does not change with exercise.
  • Exercise increases venous CO2 content and decreases venous O2 content.

High Altitude Physiology

  • Decreased atmospheric oxygen at high altitude causes decreased PaO2.
  • Response to high altitude includes increased ventilation, which decreases PaCO2.
  • High altitude initially causes respiratory alkalosis and hypoxia, which may cause acute altitude sickness.
  • Chronic high altitude causes increased ventilation, polycythemia ( due to increased erythropoietin), increased 2,3-BPG, and intracellular changes like increased mitochondria.
  • Respiratory alkalosis at high altitude may be treated with carbonic anhydrase inhibitors.
  • High altitude causes chronic hypoxic pulmonary vasoconstriction, resulting in pulmonary hypertension and right ventricular hypertrophy.

Hypoxemia & Hypoxia

  • Hypoxemia is defined as decreased PaO2.
  • The A-a gradient is normal in high altitude, hypoventilation, and diffusion defects.
  • The A-a gradient is increased in V/Q mismatch and right-to-left shunts.
  • Right-to-left shunts are not helped by supplemental oxygen.
  • Hypoxia is decreased oxygen delivery to tissues.
  • Hypoxia can be caused by decreased cardiac output, hypoxemia, anemia, and carbon monoxide poisoning.
  • Ischemia is oxygen deprivation due to loss of blood flow.

Cellular Respiration & Toxic Inhibitors

  • Carbon monoxide, cyanide, and sodium azide inhibit complex IV of the electron transport chain.
  • Cyanide inhibits the ETC by binding Fe3+, preventing electron transfer to oxygen.
  • Carbon monoxide inhibits the ETC by binding Fe2+, preventing electron transfer to oxygen.
  • Sodium nitrite is a treatment for cyanide poisoning by inducing methemoglobinemia.
  • Sodium thiosulfate helps restore rhodanese-mediated metabolism of cyanide to thiocyanate.
  • The first-line antidote for cyanide poisoning is vitamin B12 (hydroxocobalamin), which binds to cyanide and promotes its excretion in urine.
  • Cyanide is characterized by a "bitter almond" odor.

Hemoglobins

  • HbF: two alpha and two gamma chains
  • HbA: two alpha and two beta chains
  • HbA2: two alpha and two delta chains
  • Carbon monoxide poisoning is associated with a cherry-red skin appearance and myocarditis.

Ischemia

  • Ischemia occurs due to inadequate blood supply.
  • Causes of ischemia include decreased arterial perfusion, decreased venous drainage, and hypoperfusion (e.g., shock).

Normal Aging & Respiratory System

  • Decreased chest wall compliance.
  • Increased residual volume (RV).
  • Decreased forced vital capacity (FVC).
  • Decreased FEV1.
  • No change in total lung capacity (TLC).
  • Normal aging can cause ventilation/perfusion mismatch.
  • Increased A-a gradient.
  • Decreased respiratory muscle strength.

Cyanide Poisoning

  • Most common cause is smoke inhalation.
  • Cyanide inhibits aerobic metabolism, resulting in hypoxia unresponsive to supplemental oxygen.
  • Patients with cyanide poisoning present with an "almond" breath odor and cherry-red skin discoloration.

Exercise & Gas Exchange

  • In exercise, O2 exhibits mixed-limited gas exchange.
  • Blood flows faster through pulmonary capillaries, increasing the time needed to maximize O2 concentration.
  • Healthy individuals do not become hypoxemic solely due to exercise.

Inhalation Injury

  • Inhalation injury may occur due to burns, carbon monoxide inhalation, or cyanide or arsenic poisoning.

Pulmonary Vascular Resistance

  • Increased lung volumes increase pulmonary vascular resistance.
  • Decreased lung volumes during expiration increase extra-alveolar vessel resistance.
  • Pulmonary vascular resistance is lowest near the functional residual capacity (FRC).

Cyanide Poisoning Sources

  • Cyanide poisoning may occur through ingestion of amygdalin, a glucoside found in apricot seeds.

Carbon Monoxide Poisoning & Imaging

  • Carbon monoxide poisoning is associated with bilateral globus pallidus hyperintensities on MRI.
  • Decreasing V/Q may be due to a pulmonary shunt.
  • Increased V/Q results in alveolar dead space.

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