Download Key to PS 4 - Napa Valley College

Problem Set #4 - Cardiovascular System - Answer Key
Fill in your answers on the answer sheet. Show your calculations and include proper units.
1. Maria’s heart rate is 90 beats/min and her cardiac output is 5,400 mL/min. What is Maria’s
stroke volume?
C.O. = HR x SV
SV = C.O. / HR
(5,400 mL/min) = 60 mL / beat
(90 beats/min)
2. Joe’s systolic blood pressure is 155 mm Hg and his diastolic pressure is 95 mm Hg.
a) What is Joe’s pulse pressure?
Pulse P = Systolic P – Diastolic P
(155 mm Hg) – (95 mm Hg) = 60 mm Hg
b) What is Joe’s mean arterial pressure?
MAP = Diastolic P + 1/3 (Pulse P)
(95 mm Hg) + ⅓ (60 mm Hg) = 115 mm Hg
c) What is Joe’s condition?
hypertension (stage 1)
3. The graph below shows Alice’s left ventricular volume during a cardiac cycle.
A
B
a) What is the name of the specific phase marked “A”? isovolumic contraction
b) What is the name of the phase marked “B”?
ventricular ejection
c) Is the blood pressure in the left ventricle higher in phase A or phase B? phase B
Blood pressure reaches its highest point during ventricular ejection.
d) What is Alice’s stroke volume?
SV = EDV – ESV
(130 mL) – (70 mL) = 60 mL
e) If Alice’s heart rate is 80 beats/min, what is her cardiac output?
C.O. = HR X SV
(80 beats/min) x (60 mL/beat) = 4,800 mL/min
4. Dave’s resting heart rate is 50 beats/min and his stroke volume is 100 mL. When Dave runs
up the Skyline Trail, his heart rate increases to 160 beats per minute and his stroke volume
increases to 150 mL. By what factor (how many times) does his cardiac output increase during
running relative to rest?
Resting C.O. = (50 beats/min) x (100 mL/beat) = 5,000 mL/min
Exercise C.O. = (160 beats/min) x (150 mL/beat) = 24,000 mL/min
Factor of increase = (24,000 mL/min) / (5,000 mL/min) = 4.8 times
5. Dave’s resting blood pressure is 120/75 mm Hg (systolic/diastolic) When he is running up the
Skyline Trail, his blood pressure increases to 145/85.
a) Calculate Dave’s mean arterial pressure during rest and during running.
Resting MAP = 75 mm Hg + ⅓ (45 mm Hg) = 90 mm Hg
Exercise MAP = 85 mm Hg + ⅓ (60 mm Hg) = 105 mm Hg
b) By what factor (how many times) does his MAP increase during exercise?
Factor of increase = (105 mm Hg) / (90 mm Hg) = 1.2 times
6. Given the results for questions 4 and 5 above,
a) How do you explain the discrepancy between the large increase in Dave’s cardiac output and
the relatively small change in his MAP? (Hint: MAP = CO X TPR). Does Dave’s total peripheral
resistance increase or decrease during exercise?
Since C.O. increases by a large factor and MAP changes relatively little, this must mean that
total peripheral resistance decreases during exercise.
b) What specific physiological mechanism causes this change in peripheral resistance during
exercise?
Resistance decreases due to vasodilation of arterioles in the skeletal muscles during
exercise. This vasodilation results from: (1) local metabolic effects on vascular smooth
muscle (autoregulation); and (2) autonomic (sympathetic) effects on the blood vessels, via
binding of epinephrine and NE to beta-2 receptors in muscle.
Bonus Problem (Recall: concentration (C) = amount of solute (S) ; for dilutions: C1V1 = C2V2.)
volume of solution (V)
7. Lisa has a plasma volume of 3 liters and a plasma glucose concentration of 50 mg/dL.
a) How many grams of glucose are contained in Lisa’s plasma?
S=CxV
(50 mg/dL) x (10 dL/L) x (3 L) = 1,500 mg = 1.5 g
b) Suppose a doctor determines that Lisa needs 3 more grams of glucose in her plasma.
What volume of a 5 g/dL (5%) glucose solution would be needed to deliver 3 grams of glucose?
Rearranging the equation to solve for volume:
V=S/C
(3 g) / (5 g/dL) = 0.6 dL = 60 mL
c) Suppose Lisa receives an intravenous (IV) infusion of 50 mL of 5% glucose solution (5 g/dL).
How many grams of glucose has she received in this IV infusion?
S=CxV
(5 g/dL) x (50 mL) x (1 dL/100 mL) = 2.5 g
d) Suppose you have 1 mL of a 20 g/dL glucose solution and you dilute it by adding 4 mL of
distilled water. What is the final volume and final concentration of your dilution?
Final volume (V2) = 1 mL + 4 mL = 5 mL
Rearrange the dilution equation to solve for the final concentration, C2 = C1V1 / V2
= (20 g/dL) x (1 mL) / (5 mL) = 4 g/dL