CVS Physiology Guyton Qs & Ans 2022

A 60-year-old woman has a resting heart rate of 70 beats/min, arterial pressure is 130/85 mm Hg, and body temperature is normal. Her pressure-volume diagram of the left ventricle is shown above. What is her cardiac output in milliliters per minute? A) 2000 B) 3000 C) 4000 D) 6000 E) 7000 E) 7000 FROM PREVIOUS DIAGRAM When does the second heart sound occur in the ventricular pressure-volume relationship? A) At point D B) Between point A and point B C) Between point B and point C D) Between point C and point D E) Between point D and point A A) At point D During the ejection phase, the aortic and pulmonary valves open and blood flows into the aorta and pulmonary artery. The ejection phase is between C and D, so the aortic and pulmonary valves open at C and then close at D. The closing of these valves causes the second heart sound When does the third heart sound occur in the ventricular pressure-volume relationship? A) At point D B) Between point A and point B C) Between point B and point C D) Between point C and point D E) Between point D and point A B) Between points A and B is the period of ventricular filling. The vibration of the ventricular walls makes this sound after sufficient blood has entered the ventricular chambers. What is her ventricular ejection fraction? A) 33% B) 50% C) 60% D) 67% E) 80% D) The ejection fraction is the stroke volume/end diastolic volume. Stroke volume is 100 ml, and the end systolic volume at point D is 150 ml. This gives you an ejection fraction of 0.667 or in terms of percentage 66.7%. In which phase of the ventricular muscle action potential is the potassium permeability the highest? A) 0 B) 1 C) 2 D) 3 E) 4 D) During phase 3 of the ventricular muscle action potential, the potassium permeability of ventricular muscle greatly increases, which causes a more negative membrane potential. In a resting adult, the typical ventricular ejection fraction has what value? A) 20% B) 30% C) 40% D) 60% E) 80% D) The typical ejection fraction is 60%, and lower values are indicative of a weakened heart. A 30-year-old man has an ejection fraction of 0.25 and an end systolic volume of 150 ml. What is his end diastolic volume? A) 50 ml B) 100 ml C) 125 ml D) 200 ml E) 250 ml D) The end diastolic volume is always greater than the end systolic volume. Multiplication of the ejection fraction by the end diastolic volume gives you the stroke volume, which is 50 ml in this problem. Therefore, the end diastolic volume is 50 ml greater than the end systolic volume and has a value of 200 ml. Which of the following statements about cardiac muscle is most accurate? A) The T-tubules of cardiac muscle can store much less calcium than T-tubules in skeletal muscle B) The strength and contraction of cardiac muscle depends on the amount of calcium surrounding cardiac myocytes C) In cardiac muscle the initiation of the action potential causes an immediate opening of slow calcium channels D) Cardiac muscle repolarization is caused by opening of sodium channels E) Mucopolysaccharides inside the T-tubules bind chloride ions B) The cardiac muscle stores much more calcium in its tubular system than skeletal muscle and is much more dependent on extracellular calcium than the skeletal muscle. An abundance of calcium is bound by the mucopolysaccharides inside the T-tubule. Calcium is necessary for contraction of cardiac muscle, and its strength of contraction depends on the calcium concentration surrounding the cardiac myocytes. At the initiation of the action potential, the fast sodium channels open first, followed later by the opening of the slow calcium channels. A 60-year-old man's EKG shows that he has an R-R interval of 0.55 sec. Which of the following best explains his condition? A) He has fever B) He has a normal heart rate C) He has excess parasympathetic stimulation of the S-A node D) He is a trained athlete at rest E) He has hyperpolarization of the S-A node A) Heart rate is determined by the formula 60/R-R interval, and the heart rate for this patient is 109 beats/min. This is a fast heart rate, which would occur during fever. A trained athlete has a low heart rate. Excess parasympathetic stimulation and hyperpolarization of the S-A node both decrease heart rate. Which of the following is most likely to cause the heart to go into spastic contraction? A) Increased body temperature B) Increased sympathetic activity C) Decreased extracellular fluid potassium ions D) Excess extracellular fluid potassium ions E) Excess extracellular fluid calcium ions E) The heart goes into spastic contraction following a large increase in the calcium ion concentration surrounding the cardiac myofibrils, and this occurs if extracellular fluid calcium ion concentration increases too much. An excess potassium concentration in the extracellular fluids causes the heart to become dilated because of the more positive resting membrane potential of the cardiac muscle fibers. Which of the following events occurs at the end of the period of ventricular ejection? A) A-V valves close B) Aortic valve opens C) Aortic valve remains open D) A-V valves open E) Pulmonary valve closes E) At the end of ventricular ejection, both the aortic valves and the pulmonary valves close. This is followed by the period of isovolumic relaxation. Which of the following phases of the cardiac cycle follows immediately after the beginning of the QRS wave? A) Isovolumic relaxation B) Ventricular ejection C) Atrial systole D) Diastasis E) Isovolumic contraction E) Immediately after the QRS wave, the ventricles begin to contract and the first phase that occurs is isovolumic contraction. This occurs before the ejection phase and increases the ventricular pressure enough to mechanically open the aortic and pulmonary valves. Which of the following conditions will result in a dilated, flaccid heart? A) Excess calcium ions in the blood B) Excess potassium ions in the blood C) Excess sodium ions in the blood D) Increased sympathetic stimulation E) Increased norepinephrine concentration in the blood B) Excess potassium ions in the blood Excess potassium ions in the blood and extracellular fluid cause the heart to become dilated and flaccid as well as slowing the heart. This effect is important due to a more positive resting membrane potential in the cardiac muscle fibers. As the membrane potential becomes more positive, the intensity of the action potential decreases, which makes the contraction of the heart progressively weaker. Excess calcium ions in the blood and sympathetic stimulation and increased norepinephrine concentration of the blood all cause the heart to contract vigorously. A 25-year-old, well-conditioned athlete weighs 80 kg (176 lb). During maximal sympathetic stimulation, what is the plateau level of his cardiac output function curve? A) 3 L/min B) 5 L/min C) 10 L/min D) 13 L/min E) 25 L/min E) The normal plateau level of the cardiac output function curve is 13 L/min. This level decreases in any kind of cardiac failure and increases markedly during sympathetic stimulation. Which of the following events is associated with the first heart sound? A) Closing of the aortic valve B) Inrushing of blood into the ventricles during diastole C) Beginning of diastole D) Opening of the A-V valves E) Closing of the A-V valves E) Closing of the A-V valves The first heart sound by definition occurs just after the ventricular pressure exceeds the atrial pressure. This causes the A-V valves to mechanically close. The second heart sound occurs when the aortic and pulmonary valves close. Which of the following conditions at the A-V node will cause a decrease in heart rate? A) Increased sodium permeability B) Decreased acetylcholine levels C) Increased norepinephrine levels D) Increased potassium permeability E) Increased calcium permeability D) Increased potassium permeability The increase in potassium permeability causes a hyperpolarization of the A-V node, and this will decrease the heart rate. Increases in sodium permeability will actually partially depolarize the A-V node, and an increase in norepinephrine levels increases the heart rate. Sympathetic stimulation of the heart A) Releases acetylcholine at the sympathetic endings B) Decreases sinus nodal discharge rate C) Decreases excitability of the heart D) Releases norepinephrine at the sympathetic endings E) Decreases cardiac contractility D) Increased sympathetic stimulation of the heart increases heart rate, atrial contractility, and ventricular contractility and also increases norepinephrine release at the ventricular sympathetic nerve endings. It does not release acetylcholine. It does cause an increased sodium permeability of the A-V node, which increases the rate of upward drift of the membrane potential to the threshold level for self-excitation, thus increasing heart rate. What is the normal total delay of the cardiac impulse in the A-V node plus bundle? A) 0.22 sec B) 0.18 sec C) 0.16 sec D) 0.13 sec E) 0.09 sec D) 0.13 sec The impulse from the S-A node travels rapidly through the internodal pathways and arrives at the A-V node at 0.03 sec, at the A-V bundle at 0.12 sec and at the ventricular septum at 0.16 sec. The total delay is thus 0.13 sec. Which of the following best explains how sympathetic stimulation affects the heart? A) Permeability of the S-A node to sodium decreases B) Permeability of the A-V node to sodium decreases C) Permeability of the S-A node to potassium increases D) There is an increased rate of upward drift of the resting membrane potential of the S-A node E) Permeability of the cardiac muscle to calcium decreases D) During sympathetic stimulation, the permeabilities of the S-A node and the A-V node increase. Also, the permeability of cardiac muscle to calcium increases resulting in an increased contractile strength. In addition, there is an upward drift of the resting membrane potential of the S-A node. Increased permeability of the S-A node to potassium does not occur during sympathetic stimulation. Which of the following structures will have the slowest rate of conduction of the cardiac action potential? A) Atrial muscle B) Anterior internodal pathway C) A-V bundle fibers D) Purkinje fibers E) Ventricular muscle C) The atrial and ventricular muscles have a relatively rapid rate of conduction of the cardiac action potential, and the anterior internodal pathway also has fairly rapid conduction of the impulse. However, the A-V bundle myofibrils have a slow rate of conduction because their sizes are considerably smaller than the sizes of the normal atrial and ventricular muscle. Also, their slow conduction is partly caused by diminished numbers of gap junctions between successive muscle cells in the conducting pathway, causing a great resistance to conduction of the excitatory ions from one cell to the next. If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the epicardial surface at the base of the left ventricle? A) 0.22 sec B) 0.18 sec C) 0.16 sec D) 0.12 sec E) 0.09 sec A) After the S-A node discharges, the action potential travels through the atria, through the A-V bundle system and finally to the ventricular septum and throughout the ventricle. The last place that the impulse arrives is at the epicardial surface at the base of the left ventricle, which requires a transit time of 0.22 sec. If the S-A node discharges at 0.00 seconds, when will the action potential normally arrive at the A-V bundle (bundle of His)? A) 0.22 sec B) 0.18 sec C) 0.16 sec D) 0.12 sec E) 0.09 sec D) The action potential arrives at the A-V bundle at 0.12 sec. It arrives at the A-V node at 0.03 sec and is delayed 0.09 sec in the A-V node, which results in an arrival time at the bundle of His of 0.12 sec. Which of the following conditions at the S-A node will cause heart rate to decrease? A) Increased norepinephrine levels B) Increased sodium permeability C) Increased calcium permeability D) Increased potassium permeability E) Decreased acetylcholine levels D) Increases in sodium and calcium permeability at the S-A node result in an increased heart rate. An increased potassium permeability causes a hyperpolarization of the S-A node, which causes the heart rate to decrease. Which of the following are caused by acetylcholine? A) Hyperpolarization of the S-A node B) Depolarization of the A-V node C) Decreased permeability of the S-A node to potassium ions D) Increased heart rate E) Increased permeability of the cardiac muscle to calcium ions A) Acetylcholine does not depolarize the A-V node or increase permeability of the cardiac muscle to calcium ions but causes hyperpolarization of the S-A node and the A-V node by increasing permeability to potassium ions. This results in a decreased heart rate. What is the membrane potential (threshold level) at which the S-A node discharges? A) 240 mV B) 255 mV C) 265 mV D) 285 mV E) 2105 mV A) The normal resting membrane potential of the S-A node is 255 mV. As the sodium leaks into the membrane an upward drift of the membrane potential occurs until it reaches 240 mV. This is the threshold level that initiates the action potential at the S-A node. Which of the following conditions at the A-V node will cause a decrease in heart rate? A) Increased sodium permeability B) Decreased acetylcholine levels C) Increased norepinephrine levels D) Increased potassium permeability E) Increased calcium permeability ) An increase in potassium permeability causes a decrease in the membrane potential of the A-V node. Thus, it will be extremely hyperpolarized, making it much more difficult for the membrane potential to reach its threshold level for conduction. This results in a decrease in heart rate. Increases in sodium and calcium permeability and norepinephrine levels increase the membrane potential, causing a tendency to increase the heart rate. If the ventricular Purkinje fibers become the pacemaker of the heart, what is the expected heart rate? A) 30/min B) 50/min C) 65/min D) 75/min E) 85/min A) If there is a failure in conduction of the S-A nodal impulse to the A-V node or if the S-A node stops firing, the A-V node will take over as the pacemaker of the heart. The intrinsic rhythmical rate of the A-V node is 40 to 60 times per minute. If the Purkinje fibers take over as pacemakers, the heart rate will be between 15 and 40 beats/min. 28. What is the normal total delay of the cardiac impulse in the A-V node and the A-V bundle system? A) 0.03 sec B) 0.06 sec C) 0.09 sec D) 0.13 sec E) 0.17 sec D) The impulse coming from the S-A node to the A-V node arrives at 0.03 sec. Then there is a total delay of 0.13 sec in the A-V node and bundle system allowing the impulse to arrive at the ventricular septum at 0.16 sec. What is the resting membrane potential of the sinus nodal fibers? A) -100 mV B) -90 mV C) -80 mV D) -55 mV E) -20 mV D) The resting membrane potential of the sinus nodal fibers is 255 mV, and this is in contrast with the 285 to 290 mV membrane potential of cardiac muscle. Other major differences between the sinus nodal fibers and ventricular muscle fibers are that the sinus fibers exhibit self-excitation from inward leaking of sodium ions. If the Purkinje fibers, situated distal to the A-V junction, become the pacemaker of the heart, what is the expected heart rate? A) 30/min B) 50/min C) 60/min D) 70/min E) 80/min A) If the Purkinje fibers are the pacemaker of the heart, the heart rate ranges between 15 and 40 beats/min. In contrast, the rate of firing of the A-V nodal fibers are 40 to 60 times a minute, and the sinus node fires at 70 to 80 times per minute. If the sinus node is blocked for some reason, the A-V node will take over as the pacemaker; and if the A-V node is blocked, the Purkinje fibers will take over as the pacemaker of the heart. Sympathetic stimulation of the heart normally causes which of the following conditions? A) Acetylcholine release at the sympathetic endings B) Decreased heart rate C) Decreased rate of conduction of the cardiac impulse D) Decreased force of contraction of the atria E) Increased force of contraction of the ventricles E) Sympathetic stimulation of the heart normally causes an increased heart rate, increased rate of conduction of the cardiac impulse and increased force of contraction in the atria and ventricles. However, it does not cause acetylcholine release at the sympathetic endings because they contain norepinephrine. Parasympathetic stimulation causes acetylcholine release. The sympathetic nervous system firing increases the permeability of the cardiac muscle fibers, the S-A node, and the A-V node to sodium and calcium. When recording lead I on an EKG, the right arm is the negative electrode, and the positive electrode is the A) left arm B) left leg C) right leg D) left arm 1 left leg E) right arm 1 left leg A) By convention, the left arm is the positive electrode for lead I of an EKG. When recording lead aVL on an EKG, the positive electrode is the A) left arm B) left leg C) right leg D) left arm 1 left leg E) right arm 1 left leg A) By convention, the left arm is the positive electrode for lead aVL of an EKG. A 70-year-old man was had the following EKG during his annual physical exam. What is his Q-T interval? A) 0.12 sec B) 0.16 sec C) 0.22 sec D) 0.30 sec E) 0.40 sec E) The contraction of the ventricles lasts almost from the beginning of the Q wave and continues to the end of the T wave. This interval is called the Q-T interval and ordinarily lasts about 0.35 sec. In this particular example the Q-T interval is a little bit longer than average and equals 0.40 sec. What is the heart rate in the pervious EKG? A) 64 B) 70 C) 88 D) 94 E) 104 B) The heart rate can be calculated by 60 divided by the R-R interval, which is 0.86 sec. This results in a heart rate of 70 beats/min. What is the normal QT interval? A) 0.03 seconds B) 0.13 seconds C) 0.16 seconds D) 0.20 seconds E) 0.35 seconds E) The contraction of the ventricles lasts almost from the beginning of the Q wave and continues to the end of the T wave. This interval is called the Q-T interval and ordinarily lasts about 0.35 sec. When recording lead II on an EKG, the positive electrode is the A) left arm B) left leg C) right leg D) left arm 1 left leg E) right arm 1 left leg B) By convention, the left leg is the positive electrode for lead II of an EKG. When recording lead III on an EKG, the negative electrode is the A) left arm B) left leg C) right leg D) left arm 1 left leg E) right arm 1 left leg A) By convention, the left arm is the negative electrode for lead III of an EKG. A 65-year-old man had an EKG recorded at a local emergency room following a biking accident. His weight was 80 kg and his aortic blood pressure was 160/90 mm Hg. The QRS voltage was 0.5 mV in lead I and 1.5 mV in lead III. What is the QRS voltage in lead II? A) 0.5 mV B) 1.0 mV C) 1.5 mV D) 2.0 mV E) 2.5 mV D) Einthoven's law states that the voltage in lead I plus the voltage in lead III is equal to the voltage in lead II, which in this case is 2.0 mV. A ventricular depolarization wave when traveling 290° in the frontal plane will cause a large negative deflection in which lead? A) aVR B) aVL C) Lead II D) Lead III E) aVF E) aVF The positive portion of lead aVF has an axis of 90° and the negative part of this lead has an axis of 290°. Note the difference between the positive and the negative ends of this vector is 180° Use Fig. for Questions 41-43 A 60-year-old woman had the following EKG recorded at a local emergency room following an automobile accident. Her weight was 70 kg and her aortic blood pressure was 140/80 mm Hg. What is the mean electrical axis calculated from standard leads I, II, and III shown in her EKG? A) -90° B) -50° C) -12° D) +100° E) +170° B) The mean electrical axis can be determined plotting the resultant voltage of the QRS for leads I, II, and III. The result is as is shown above and has a value of -50°. What is the heart rate using lead I for the calculation? A) 70 B) 88 C) 100 D) 112 E) 148 A) The heart rate can be calculated by 60 divided by the R-R interval, which is 0.68 sec. This results in a heart rate of 88 beats/min. What is her likely diagnosis? A) Mitral valve stenosis B) Left bundle branch block C) Pulmonary valve stenosis D) Right bundle branch block E) Left ventricular hypertrophy B) Left bundle branch block There is a QRS width greater than 0.12 sec. This indicates a bundle branch block. There is also a left axis deviation, which is consistent with a left bundle branch block. Which of the following conditions will usually result in right axis deviation in an EKG? A) Systemic hypertension B) Aortic valve stenosis C) Aortic valve regurgitation D) Excess abdominal fat E) Pulmonary hypertension E) Systemic hypertension results in a left axis deviation because of the enlargement of the left ventricle. Aortic valve stenosis and aortic valve regurgitation also result in a large left ventricle and left axis deviation. Excessive abdominal fat, because of the mechanical pressure of the fat, causes a rotation of the heart to the left resulting in a leftward shift of the mean electrical axis. Pulmonary hypertension causes enlargement of the right heart and thus causes right axis deviation. A ventricular depolarization wave when traveling 60° in the frontal plane will cause a large positive deflection in which of the following leads? A) aVR B) aVL C) Lead I D) Lead II E) aVF D) Lead II has a positive vector at the 60° angle. The positive end of lead II is at -120°. Questions 46 and 47 A male long-term smoker who is 62 years old weighs 250 lb. He had the following EKG recorded at his local hospital. Which of the following is the mean electrical axis calculated from standard leads I, II, and III shown in his EKG? A) -110° B) -20° C) +90° D) +105° E) +180° D) Note that lead III has the strongest vector, therefore the mean electrical axis will be closer to this lead than to leads I or II. The angle of lead III is 120°, and the resultant vector (mean electrical axis) is close to that lead and has a value of +105°.