MSP PHYSIO PROBLEM SET #1
1) a. As capacitance vessels, veins contain the majority of blood volume at rest.
How does venular structure contribute to this property?
b. During stress/exercise, autonomic regulation constricts veins. How does this
affect central venous pressure and the relative distribution of blood in the
vascular tree (i.e. relative volume in arterial vs. venous system)?
2) One day while in his office, your preceptor (an internist) decides to test your
knowledge of cardiac physiology. He hands you a copy of the “wigger’s
diagram” and asks the followinga. “Immediately following S1, which valve opens first and why?”
b. “A distinction is made between electrical systole and mechanical systole. Can
you show me which points on the diagram indicate the beginning of each? Also,
why don’t the electrical and mechanical events occur simultaneously?”
c. “You’re doing very well, so this is the last question.” Suppose that a patient
presents with tricuspid insufficiency [due to strep endocarditis ]. Briefly describe
changes (if any) which would occur in the right atrial pressure trace?”
3) Refer to the P-V loop in your notes for the following questions.
a. Write the equation for ejection fraction using letters on the diagram (e.g. E.F.
= cxa/b-d).
b. According to the diagram, what is this person’s systolic and diastolic pressure?
c. Which letter is closest to the region of aortic valve closure?
3.
You’re talking to a patient who has recently had a heart transplant. The
patient relates, “I was warming up to go running during my lunch break when I
saw a group of devastatingly good looking students walking down the hall -I think their shirts and jackets said class of 2001 on them. So I notice that a
little later my heart starts beating faster, and things get worse when I start
running. My heart gets beating super fast, and I start feeling light-headed so I
have to stop. I can’t approach those second-year medical students, I get so
nervous, so I figured that you might know what’s going on.”
4.
On your first preceptor visit after Christmas break, your preceptor’s office is
busier than the return/exchange lines the day after Christmas. While running
down the halls and almost out of breath, your preceptor quickly asks, “Are you
taking cardiac physiology yet?” You nod your head, and your preceptor says,
“Good. I gotta go to the bathroom – gotta cut back on the coffee -- but if you
could figure out this patient’s stroke volume before I get back, that’d be great.
All the information you need should be on the front page of the chart. Use the
Fick, Luke!” Before you can confess how little you’ve studied, your preceptor
is gone. You look at the patient’s chart and see:
Hb: 15 gm/dl x 1.36 ml O2 / gm Hb x 10 = 204 mL O2 / L blood
Pulmonary Vein O2 saturation:
95%
Pulmonary Artery O2 saturation: 60%
VO2 = 250 mL/min (Vo2 is a measure of O2 consumption)
HR = 100
You concentrate and hear “Use the Fick, Luke…” echoing in your head.
Your preceptor returns and says, “Well, my young jedi student doctor, what is
the patient’s stroke volume? You respond in your best Yoda voice:
Dissecting a pressure-volume curve
D
C
B
A
6) a. What sets the upper boundary of these loops (the upper dotted line)?
b. What sets the lower border of the loops (lower dotted line)?
c. Which of the four loops (A,B,C,D) represents the greatest stroke volume?
d. What happened physically between loop A (the control state) and loop B?
e. What can cause the loop to change from B to C?
f. How can you explain “loop” D?
7) Considering all the free time you have in med school, you decide you want to
start marathon training. On one of those long training runs you start thinking
about your heart. You remember from physiology that your heart more efficient,
and the "muscle pump" increase the return of the blood to your heart. Describe
the mechanism and effect of this increase .
8) At your preceptor's office you encounter a heavy set middle aged man who
complains that he loses his breath after climbing one flight of stairs, and it seems
to be getting worse. During the course of HEADS, you find that he smokes 50
pack years (2 packs a day for 25 years). In addition you find out that he enjoys
drinking a "couple" beers with his buddies after work, and then goes home and
has a "couple" more while eating fried chicken and watching TV. In addition, he
does not like doctors, and has not seen a physician since his discharge from the
Navy 15 years ago. After taking blood pressures all first semester, you expertly
find that his blood pressure is 200/120. Illustrate how this history will affect the
output of the heart.
Why is this guy short of breath?
9) Your good friend at USC medical school brags to you about his discovery of a
novel heart that lacks outer membrane calcium channels. He explains to you
how this definitively proves that all of the calcium needed for heart function is
present in the sarcoplasm reticulum. Defend or counter the credibility of such a
heart.
10) Explain how digoxin works in treating heart failure, given that it inhibits the
Na/K pump. Feel free to use diagrams and mention all the channels involved.
11) Draw the force curve for isometric contraction and explain the events
occurring between the actin and the myosin.