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USMLE STEP 1 EXAM WITH COMPLETE QUESTIONS AND CORRECT ANSWERS RATED A+
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USMLE STEP 1 EXAM WITH COMPLETEQUESTIONS AND CORRECT ANSWERS
RATED A+
Asthma Correct Answer Dec FEV1/ FVC
Exp wheeze
Caused by env and genetics
Chr Eosinophil Bronch: IL-5 by TH2 cells
MPB= bronch epith dmg- mc in exercise induced asthma
Cause of LVHF shortness of breath Correct Answer Impaired
diastolic return of Pul v. because high end diastolic pressure
causes an increase in hydrostatic pressure and transudate leaks
out into the interstitium--> causes affected tissue to swell and
increased resistance of movement due to decreased lung
compliance
= the neg pressure generated normally from inspiration isnt
enough to distend the lungs, causing poor gas exchange and sob
Reduced pulmonary compliance Correct Answer -LV Heart
Failure + Pul Congestion
-Pul Fibrosis
-Insuff Surfactant
decreased compliance= decreased FRC
Surfactant Correct Answer -cortisol/ thyroxine ↑synthesis
-insulin ↓ synthesis
Pulmonary infarction Correct Answer -Pulmonary infarction: MC
site lower lobes
-Saddle embolus: sudden death
-dyspnea/tachypnea MC symptom/sign
-respiratory alkalosis; hypoxemia; ↑D-dimers
,Caplan syndrome Correct Answer pneumoconiosis + cavitating
rheumatoid nodules
Perfusion-limited gas exchange Correct Answer -diffusion can
increase only if blood flow increases
-examples: N2O and O2 under normal conditions
Diffusion-limited gas exchange Correct Answer -diffusion
continues as long as pressure gradient exists across pulmonary
membrane
-examples: O2 during vigorous exercise at high altitude and CO
pathophysiologic mechanisms that reduce diffusing capacity
Correct Answer (1) increased thickness of the pulmonary
membrane in restrictive diseases (the primary factor in silicosis
and idiopathic pulmonary fibrosis)
(2) collapse of alveoli and lung segments (atelectasis), which
contributes to a decreased surface area available for gas
exchange (e.g., with bed rest after surgery)
(3) poor lung compliance, resulting in insufficient ventilation (e.g.,
silicosis)
(4) destruction of alveolar units, which also decreases surface
area (e.g., emphysema)
Physiologic shunt Correct Answer -This occurs when blood is
appropriately directed to the lungs but is not involved in gas
exchange
-EX bronchial arterial circulation= The bronchial arteries supply
the bronchi and supporting lung parenchyma but
are not involved in gas exchange at the level of the alveoli
Physiological Shunts in Pathological Cases (Disease states)
Correct Answer -pneumonia or pulmonary edema
-impaired ventilation may result in perfusion of unventilated alveoli
,Anatomic Shunt Correct Answer -Blood flow bypasses lungs
-Increased perfusion of bronchial arteries in chronic inflammatory
lung disease
Left-to-Right Shunt Correct Answer -Bypasses systemic
circulation
-May cause pulmonary hypertension and
eventual right-to-left shunt
-Patent ductus arteriosus, ventricular septal defect
Right-to-left Shunt Correct Answer -Bypasses pulmonary
circulation
-Tetralogy of Fallot, truncus arteriosus, transposition of great
vessels, atrial septal defect
Compromised airways in Obstructive Airway Diseases Correct
Answer -Residual volume increases because inspiratory volumes
are always slightly greater than expiratory volumes, leading to an
increase in the AP diameter or the chest
-This explains the "barrel-chested" appearance of patients with
emphysema
-Dynamic air trapping during exercise is a major limitation to
rigorous activity in patients with chronic obstructive pulmonary
disease (COPD)
-Air trapping results in an elevated FRC at which tidal breaths
occur--> airways are more patent, which reduces airflow
resistance particularly during expiration; this decreases the work
of breathing
Restrictive Lung Disease Correct Answer -do not have difficulty
emptying their lungs, FVC typically decreases because they are
unable to adequately fill their lungs during inspiration
-inspiration is limited by noncompliance of the lungs, which limits
expiratory volumes
, -elastic recoil of the lungs is largely preserved (if not increased),
the FVC is typically reduced more than is the FEV1, resulting in
an FEV1/FVC ratio that is normal or increased
-decreased TLC
Obstructive Lung Capacity Correct Answer -expiratory volumes
are reduced because of airway narrowing and sometimes a loss
of elastic recoil in the lungs
-Total expiratory volumes are largely preserved, but the ability to
exhale rapidly is substantially reduced
-FEV1 is reduced more than is FVC, and the FEV1/FVC ratio is
reduced
-increased TLC
Mechanically Ventilated Patients Correct Answer -The amount of
anatomic dead space increases considerably b/c the volume of
space occupied by the respiratory apparatus from the patient's
mouth to the ventilator must be considered to be anatomic dead
space
-Alveolar ventilation is altered, and care must be taken to ensure
adequate oxygenation
Decreased Alv Ventilation Correct Answer -falls to a level too low
to provide sufficient oxygen to the tissue, patients must
compensate by increasing the rate of breathing (tachypnea) or by
taking larger-volume tidal breaths
-taking larger tidal breaths would be better because it minimizes
the effect of dead space on alveolar ventilation
Elevated Alveolar-Arterial Gradient: V/Q Mismatch Correct
Answer -Pulmonary embolism
-Airway obstruction
-Interstitial lung disease
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