Pulmonary II Flashcards
Graham’s Law
Diffusion is proportional to solubility and 1/sqrt(MW)
Which gas is diffusion limited?
Carbon monoxide
Which gases are perfusion limited?
nitrous oxide, oxygen, and carbon dioxide
- however, CO2 may be diffusion-limited in a person with an abnormal alveolar-capillary barrier
What determines the amount of gas taken up in perfusion-limited gases?
blood flow
What determines the amount of gas taken up in diffusion-limited gases?
diffusion
(alveolar-capillary membrane)
When will oxygen act as a diffusion-limited gas?
- during high cardiac output
- decrease inhaled partial pressure of O2
- thickened alveolar-capillary membrane
What (4) conditions decrease the diffusion capacity?
- thickened barrier
- interstital/alveolar edema or fibrosis
- scleroderma
- interstital/alveolar edema or fibrosis
- decreased surface area
- emphysema
- low cardiac output
- decreased uptake by erythrocytes
- anemia
- ventilation-perfusion mismatch
(4) Factors that increase diffusion
- increased pulmonary capillary blood volume
- polycythemia
- supine position
- exercise
Diffusion Capacity of Lung Equation
- V is the amount of gas transferred (diffused)
- P1 & P2 are partial pressures for alveolar & capillary blood (∆P)
- Since there is no CO in capillary blood, Carbon Monoxide is the volume transferred in ml/min/mmHg of alveolar partial pressure
- DLCO is used clinically to evaluate the alveolar-capillary membrane
Normal PFT Tests for 40 y.o. male
- VC
- 5
- RV
- 1.8
- TLC
- 6.8
- FRC
- 3.4
- FEV-1
- 4
- MVV
- 168 L/min
- DLCO
- 33 mL/min/mmHg
PFT are compared based on what factors?
height, weight, age, sex, and race
What tests measure lung volumes?
spirometry, He or Xe dilution, and body plethysmography
Flow volume loop for forced and normal breathing
Flow-Volume Loop for Obstructive Disorder
- prolongation of expiration
- MEF < MIF
- Examples: emphysema and asthma
Flow-Volume Loop for Restrictive Disorder
- narrowed loop due to diminished lung volumes
- greater airflow due to increased elastic recoil
- Ex: interstital lung disease and Kyphoscholiosis
Flow-Volume Loop for Fixed Obstruction of Upper Airway
- top and bottom of loops are flattened
- fixed obstruction limits flow equally during inspration and expiration
- MEF = MIF
- Ex: tracheal stenosis and goiter
Flow-Volume Loop for Variable Extrathoracic Obstruction
unilateral vocal cord paralysis or vocal cord dysfunction
Flow-Volume Loop for Variable Intrathoracic Obstruction
- during forced inspiration, negative pleural pressure holds trachea open
- Ex: tracheomalacia
FEV-1
- % of the vital capacity
- standard index for assessing airflow limitation
Normal FEV-1
> 80%
FEV-1 graph
(normal vs restrictive vs obstructive)
Changes in respiratory variables in Obstructive Disease
- decrease
- VC
- FEV-1/FVC
- maximal expiratory flow
- maximal breathing capacity
- DLCO (especially with COPD)
- Increase
- Total lung capacity
Chances in respiratory variables in Restrictive diseases
- decrease
- vital capacity
- total lung capacity
- FEV-1/FVC ratio
- DLCO (very large decrease)
A patient reports SOB and fatigue during exercise. The pulmonary function test reveals a normal FEV1/FRC ratio and decreased DLCOSB. What is the most likely diagnosis?
pulmonary fibrosis
Overall pulmonary vascular resistance is increased by _____
hypoxemia
(due to HPV)
Henry’s Law
Vgas = Cs * Pgas
Dissolved O2 in Blood
- 1% of total O2 is dissolved
- 0.003 mL/dL/mmHg
- Normally 0.25 mL/dL
- Only dissolved oxygen in plasma exerts a partial pressure
Chemical theor predicts that ____ mL of O2 binds wtih 1g of Hb
1.39
Mixed venous blood has an O2 saturation of ____
75%
- PO2 40 mmHg
At what pressure does 90% saturation occur?
60 mmHg
What factors cause a shift in the OxyHb Curve?
- temperature
- pH
- 2,3-DPG
- PCO2
What shifts the OxyHb curve to the right?
- decrease pH
- Increase:
- PCO2
- temperature
- 2,3-DPG
A shift to the right has a better unloading of oxygen off of hemoglobin
Oxygen Content equation
CO2 = (0.0031 * PO2) + (1.31 * Hb * SO2)
- PaO2 predicted by age:
- 102 - Age/3
Effects of Carboxyhemoglobin
left-ward shift of OxyHb curve and decreased oxygen utilization
At what %COHb will a patient become unconscious?
40-60%
At what %COHb will a patient have impaired vision and temporal discrimination?
5%
Half-Life of CO on 100% Oxygen
1-2 hours
Half-Life of CO in Hyperbaric Chamber
22 minutes
Methemoglobin - Mechanism of Action
Fe2+ is oxidized to Fe3+
- cannot bind O2
- causes the other 3 Fe2+ molecules to increase their binding affinity for oxygen
- will not release into tissues
Common Sources of Methemoglobin
- Benzocaine
- Primaquine
- Dapsone
- Nitrates and Nitrities
- Smoke inhalation
What % Methemoglobin is first diagonsed with cyanosis?
10-15%
Treatment of Methemoglobin
Methylene Blue
- 1-2 mg/kg over 3-5 minutes
- use carefully in patients with G6PD deficiency
- total dose of 15 mg/kg may induce hemolysis
Sulfhemoglobin - Mechanism of Action
sulfur atom incorporated into the porphyrin ring
- incapable of binding oxygen
- green pigmentation
- favors sickling in HbS
Common Sources of Sulfhemoglobin
- Sulfonamides
- Phenacetin
- Dapsone
- Metoclopromide (in repeated doses)
- sulfur dioxide and hydrogen sulfide
Sulfhemoglobin - Signs and Symptoms
- Cyanosis without respiratory distress
- 7-10% SulfHb produces obcious cyanosis
- reduces affinity of unaffected Hb molecules for oxygen
- unlike MetHb
Treatment of Sulfhemoglobin
no effective therapy
- possible to RBC transfusion
deoxygenated blood that bypasses the pulmonary circulation is called:
shunt
(venous admixture)
What drug may cause sulfhemoglobinemia and turn the patient’s blood green?
Sumatriptan
(imitrex)
Sickle Cell Anemia (HbS)
Valine replaces Glutamic Acid on position 6 of Beta chain
- decrease solubility of deoxyHb
- more prone to hemolysis
- Sickling at PaO2 < 40 mmHg
How long do Sickle Cell RBCs usually last?
10-20 days
Considerations for Sickle Cell
- avoid dehyration
- keep Hb below 11g/dL
- avoid acidosis and hypothermia
- treat pain promptly
Fetal Hb
- leftward shift of O2 dissociation curve
- greater affinity enhances loading of oxygen into fetal blood
- P50 of 19-20 mmHg
- adult P50 = 27
Oxyhemoglobin Dissociation Curve Comparison
How is CO2 transported in the blood
- Dissolved 10%
- Bicarbonate 60%
- Carbamino compounds 30%
What catalyzes the reaction of CO2 and H2O into H2CO3?
Carbonic Anhydrase
- none available in plasma
- reaction is very slow
What inhibits Carbonic Anhydrase?
- thiazide diuretics
- acetazolamide
What %CA must be blocked to alter CO2 transport?
98%