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Old 12-15-2012
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Arrow A 25-year-old man with SOB

A 25-year-old man is recovering in the hospital from an open repair of his broken femur, which he suffered during an automobile accident. On postoperative day 3, he develops sudden-onset shortness of breath and vague chest discomfort. His temperature is 37.6C (99.6F), heart rate is 108/min, blood pressure is 95/62 mm Hg, respiratory rate is 42/min, and oxygen saturation is 89% on room air. Physical examination is significant for jugular venous distention to 9 cm and an accentuated pulmonic component of the second heart sound. A quantitative plasma D-dimer enzyme-linked immunosorbent assay is elevated at 900 ng/mL. . Which of the following is most likely to be decreased?

(A) Airway resistance
(B) Alveolar dead space
(C) Alveolar ventilation
(D) Pulmonary compliance
(E) Pulmonary vascular resistance
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pulmonary embolism (E) Pulmonary vascular resistance ?
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C) Alveolar ventilation.
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Originally Posted by aknz View Post
pulmonary embolism (E) Pulmonary vascular resistance ?

PVR increases due to vasoconstrictive hypoxia.
alveolar ventilation decreases, due to shifting of the blood to other well-perfused lung areas.
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Default (E) Pulmonary vascular resistance

(E) Pulmonary vascular resistance
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Originally Posted by heartbeat View Post
A 25-year-old man is recovering in the hospital from an open repair of his broken femur, which he suffered during an automobile accident. On postoperative day 3, he develops sudden-onset shortness of breath and vague chest discomfort. His temperature is 37.6C (99.6F), heart rate is 108/min, blood pressure is 95/62 mm Hg, respiratory rate is 42/min, and oxygen saturation is 89% on room air. Physical examination is significant for jugular venous distention to 9 cm and an accentuated pulmonic component of the second heart sound. A quantitative plasma D-dimer enzyme-linked immunosorbent assay is elevated at 900 ng/mL. . Which of the following is most likely to be decreased?
(C) Alveolar ventilation- due to increased dead space

Alveolar ventilation= (TV-Dead space) x RR

(A) Airway resistance

(B) Alveolar dead space-increases as the affected alveoli are not being perfused.

(D) Pulmonary compliance--increases

(E) Pulmonary vascular resistance--increases (causes right heart strain)
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(C) Alveolar ventilation- due to increased dead space

Alveolar ventilation= (TV-Dead space) x RR

(A) Airway resistance

(B) Alveolar dead space-increases as the affected alveoli are not being perfused.

(D) Pulmonary compliance--increases

(E) Pulmonary vascular resistance--increases (causes right heart strain)
I think that alveolar perfusion decreases not ventilation as a result of an embolus ??There is no obstruction to inflow of air so alveolar ventilation will be unchanged ?
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I think that alveolar perfusion decreases not ventilation as a result of an embolus ??There is no obstruction to inflow of air so alveolar ventilation will be unchanged ?

alveolar ventilation represents the amount of air inhaled utilized for the exchange at the level of alveoli....even though the person might suck in more air than usual but the due to reduced perfusion, the net amount of air used for exchange is decreased.......
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Here the question has asked for which of the option will be DECREASED............as there is an embolus DECREASING d perfusion of affected alveoli.........so that alveoli will act as a dead space with no exchange of gases through it so this dead space will be add to the total dead space resulting an increased alveolar dead space.
Alveolar ventilation which by definition describes total amount of gas exchange through d alveolar membrane will be DECREASED. Whereas pulmonary ventilation means total amount of air comes in and out through the lung will have no change as there is no airway resistance which is option A).
Pulmonary embolism will obviously INCREASE pulmonary vascular resistance from hypoxia induced vasoconstriction which is option E)
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Thanks for discussion frnds. I am remembering similar Q in the STEP 1 UW and i got it wrong and did same mistake when took it again yesterday
Quote:
Originally Posted by aknz View Post
pulmonary embolism (E) Pulmonary vascular resistance ?
Quote:
Originally Posted by fadi551 View Post
(E) Pulmonary vascular resistance
PVR = (input pressure − output pressure)/blood flow. If an embolus blocks one or several lobes of the lung then blood flow will decrease, so pulmonary vascular resistance rises--> increase PV pressure--> Rt heart strain.

Quote:
Originally Posted by Master shifu View Post
C) Alveolar ventilation.
Quote:
Originally Posted by Dr.Lacune View Post
alveolar ventilation decreases, due to shifting of the blood to other well-perfused lung areas.
Quote:
Originally Posted by Novobiocin View Post
(C) Alveolar ventilation- due to increased dead space
Alveolar ventilation= (TV-Dead space) x RR
Quote:
Originally Posted by aknz View Post
I think that alveolar perfusion decreases not ventilation as a result of an embolus ??There is no obstruction to inflow of air so alveolar ventilation will be unchanged ?
Quote:
Originally Posted by anomali View Post
alveolar ventilation represents the amount of air inhaled utilized for the exchange at the level of alveoli....even though the person might suck in more air than usual but the due to reduced perfusion, the net amount of air used for exchange is decreased.......
Quote:
Originally Posted by Master shifu View Post
Here the question has asked for which of the option will be DECREASED............as there is an embolus DECREASING d perfusion of affected alveoli.........so that alveoli will act as a dead space with no exchange of gases through it so this dead space will be add to the total dead space resulting an increased alveolar dead space.
In pulmonary embolus (PE), alveolar ventilation increases, rather than decreases, due to stimulation of irritant receptors. Alveolar ventilation is defined as the volume of fresh air reaching the alveoli per minute. Mathematically it is expressed asVA = (tidal volume − anatomic dead space) respiratory rate. In PE, the increase in respiratory rate causes an increase in alveolar ventilation.
Alveolar dead space is defined as an area of the lung that is ventilated but not perfused.Anatomically, this usually represents the area at the top of the lung. In pulmonary embolus, alveolar dead space increases, rather than decreases, due to vascular obstruction.
As i see from formula the effect of increasing RR is more than effect of increasing Dead space ,So VA is increase.


Finally the correct answer is D.
Pulmonary embolism has many effects on pulmonary physiology. The compliance of the lungs, which is defined as the volume change per unit pressure change, decreases. The decrease occurs for a number of reasons, such as lung edema, lung hemorrhage, and loss of surfactant.
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