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Chapter 4. Cardiovascular Physiology

A 14-year-old boy with sickle cell disease received a blood transfusion that caused his blood volume to increase significantly above normal. What changes in cardiac contractility and total peripheral resistance (TPR) would occur within a few minutes of receiving this transfusion?

A Increased contractility and increased TPR

B Increased contractility and decreased TPR

C Decreased contractility and increased TPR

D Decreased contractility and decreased TPR

D. The baroreceptor reflex would cause a decrease in sympathetic nervous tone as a result of this sudden blood volume expansion. The intrinsic contractility of the heart would decrease due to less norepinephrinergic stimulation (note: “contractility” refers to intrinsic contraction strength for a given preload; in this case, SV may be increased due to high preload but contractility is reduced). Reduced vasoconstrictor tone causes decreased TPR.

A 29-year-old elite endurance athlete completes a medical examination as part of her registration for a triathlon event. Her resting HR is measured at 36 beats/min. Compared with untrained individuals, what change in the cardiac conduction system or autonomic nervous tone is most responsible for this woman's low resting HR?

A Decreased automatic rate of (SA) node discharge

B Decreased sympathetic neural tone

C Decreased vagal tone

D Increased automatic rate of SA node discharge

E Increased sympathetic neural tone

F Increased vagal tone

F. A decrease in resting HR and an increase in SV is a characteristic of endurance training that allows a greater increase in cardiac output during exercise. This adaptation of training results from increased vagal tone to the SA node.

Paramedics were called to attend to a 74-year-old man who fainted while watching a baseball game. When they arrived, the man was conscious but confused. He was noticeably short of breath, had profound bradycardia (HR 25 beats/min) and appeared to be complaining of chest pain. An ECG showed normal P waves that were regularly spaced. QRS complexes were wide and regularly spaced but were dissociated from P waves. What is the most likely origin for electrical stimulation of this patient's ventricles?

A (SA) node

B Atrial internodal conduction pathways

C AV node

D Bundle of His


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