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  #1  
Old 10-20-2012
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Question CVS physiology

1. An electrocardiogram(ECG) on a person shows ventricular extrasystoles. The extrasystolic beat would produce which of the following change?

(a) increased pulse pressure because heart rate is increased.

(b) increased pulse pressure because contractility is increased.

(c) decreased pulse pressure because ventricular filling time is increased.

(d) decreased pulse pressure because stroke volume is decreased.

(e) decreased pulse pressure because PR interval is increased.



2. A 24 year old woman presents to the emergency department with severe diarrhea. When she is supine,her blood pressure is 90/60 mm Hg and her heart rate is 100 beats/min. When she is moved to a standing position, her heart rate further increases to 120 beats/min. Which of the following accounts for further increase in heart rate upon standing?

(a) Decreased total peripheral resistance.

(b) Increased vasoconstriction.

(c) Increased contractility.

(d) Increased afterload.

(e) Decreased venous return.


Explanation favoring u'r answer would be better
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  #2  
Old 10-21-2012
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Quote:
Originally Posted by Master shifu View Post
1. An electrocardiogram(ECG) on a person shows ventricular extrasystoles. The extrasystolic beat would produce which of the following change?

(a) increased pulse pressure because heart rate is increased.

(b) increased pulse pressure because contractility is increased.

(c) decreased pulse pressure because ventricular filling time is increased.

(d) decreased pulse pressure because stroke volume is decreased.

(e) decreased pulse pressure because PR interval is increased.



2. A 24 year old woman presents to the emergency department with severe diarrhea. When she is supine,her blood pressure is 90/60 mm Hg and her heart rate is 100 beats/min. When she is moved to a standing position, her heart rate further increases to 120 beats/min. Which of the following accounts for further increase in heart rate upon standing?

(a) Decreased total peripheral resistance.

(b) Increased vasoconstriction.

(c) Increased contractility.

(d) Increased afterload.

(e) Decreased venous return.


Explanation favoring u'r answer would be better
Hey there, so ur second question. See the thing is Mean Arterial Pressure is a product of Cardiac Output times Total Peripheral Resistance. When the old lady is in a recumbent position her heart is beating at 100 beats per minute. Ok? Now as she stands up, the heart beating rate goes from 100 to 120.

MAP= CO x TPR

Now the pooling of blood in the veins of leg (systemic veins. And having highest compliance, even higher than pulmonary veins. Source: kaplan physiology) causes a decrease in the circulating volume. Now to counter the effect of decreased perfusing voulme to organs and to maintain the the blood flow, you have to throw more blood out of the heart. We know that:

Cardiac Output = Heart Rate x Stroke Volume

If the volume returning to the heart is decreased, the only other way you are going to increase the cardiac output is by increasing the heart rate.

Seeing you options in the questions, I will most likely go with C


Other guys: can you please let me know if the logic seems good enough to you. Help me help Shifu
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  #3  
Old 10-21-2012
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Post

would also go with @nooranimm for 2nd one

for the 1st one i would like to go with D..

i'm thinking that extrasystoles cause heart to pump fast with incomplete volume ejection and also incomplete filling due to ventricular diastole interrupted(coz extrasystoles are not depolarized by SA node)...so end systolic volume increases and stroke volume decreases.. and decrease in stroke volume causes decreased pulse pressure

thanks
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I m going with 1.D 2.E
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Old 10-21-2012
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1)b
But confused c options
2)E
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Old 10-21-2012
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D ..decreased PP because SV reduces ( seconadary to decreased ventricular filling time) and next answer is E (decreased venous return !)
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Old 10-21-2012
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my ans is 1>>b 2>>>c
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Old 10-21-2012
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Default Here is the correct answer

1) D

Explanation: On the extrasystolic beat, pulse pressure decreases because there is inadequate ventricular filling time---the ventricles beats too soon. As a result stroke volume decreases.

2) E

Explanation: Diarrhea causes a loss of extracellular fluid volume,which produces decrease in arterial pressure. The decrease in arterial pressure activates baroreceptor feedback mechanism,which produces an increase in heart rate when the patient is supine. When she stands up, blood pools in her leg veins and produces decrease in venous return, a decrease in cardiac output (by frank starling law) and a further decrease in arterial pressure causes further activation of the baroreceptor mechanism and a further increase in heart rate.
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  #9  
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Quote:
Originally Posted by nooranimm View Post
Hey there, so ur second question. See the thing is Mean Arterial Pressure is a product of Cardiac Output times Total Peripheral Resistance. When the old lady is in a recumbent position her heart is beating at 100 beats per minute. Ok? Now as she stands up, the heart beating rate goes from 100 to 120.

MAP= CO x TPR

Now the pooling of blood in the veins of leg (systemic veins. And having highest compliance, even higher than pulmonary veins. Source: kaplan physiology) causes a decrease in the circulating volume. Now to counter the effect of decreased perfusing voulme to organs and to maintain the the blood flow, you have to throw more blood out of the heart. We know that:

Cardiac Output = Heart Rate x Stroke Volume

If the volume returning to the heart is decreased, the only other way you are going to increase the cardiac output is by increasing the heart rate.

Seeing you options in the questions, I will most likely go with C


Other guys: can you please let me know if the logic seems good enough to you. Help me help Shifu


Look at the question again it asked for the reason of increased heart rate upon standing not the way it would increase heart rate.
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  #10  
Old 10-22-2012
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Default D? E

1. D -I believe but I am not quite sure. Extrasystolic beats increase the heart rate leading to a decrease in filling time. Decrease filling time means decreased blood in heart and therefore decreased stroke volume.

2. E -when you stand up gravity causes your blood to pool, this pooling is most significant in veins and venules, leading to a decrease of venous return to the right heart and a reflex tachycardia.
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