📌 Professor’s Notes: Quick Revision
High-yield revision notes for rapid review before university examinations.
- Heart rate (HR) is the number of heartbeats per minute and normally ranges from 60–100 beats/min in adults. It reflects the discharge rate of the sinoatrial (SA) node. Bradycardia is HR <60 beats/min, and tachycardia is HR >100 beats/min. Under normal conditions, pulse rate equals heart rate because each ventricular contraction produces one arterial pulse.
- Heart rate varies physiologically with age, sex, sleep, respiration, body temperature, posture, exercise, emotions, and environmental temperature. It increases during inspiration (respiratory sinus arrhythmia), exercise, fever, emotional excitement, and standing, while it decreases during sleep and with increased vagal activity.
- Regulation of heart rate is mainly by the autonomic nervous system.
- Parasympathetic (vagal) stimulation decreases heart rate by releasing acetylcholine, which increases potassium permeability and slows SA nodal depolarization. Resting heart rate is primarily determined by vagal tone.
- Sympathetic stimulation increases heart rate through β₁-adrenergic receptors by the action of norepinephrine. The intrinsic heart rate of a denervated heart is about 100–110 beats/min.
- Important cardiovascular reflexes regulating heart rate are:
- Baroreceptor reflex: Increased arterial pressure causes reflex bradycardia.
- Chemoreceptor reflex: Activated by hypoxia, hypercapnia, and acidosis.
- Bainbridge reflex: Increased venous return causes tachycardia.
- Cushing reflex: Raised intracranial pressure produces hypertension followed by reflex bradycardia.
Higher brain centers, emotions, catecholamines, and thyroxine also increase heart rate.
- Arterial pulse is the rhythmic expansion and recoil of an artery produced by the pressure wave generated during ventricular systole. The radial artery is the commonest site for pulse examination. Pulse assessment provides information about heart rate, rhythm, stroke volume, arterial compliance, and circulatory status.
- A normal pulse tracing has:
- Percussion (tidal) wave: Produced by ventricular ejection.
- Dicrotic notch: Indicates aortic valve closure.
- Dicrotic wave: Produced by elastic recoil of arteries after valve closure.
Pulse deficit occurs when heart rate exceeds pulse rate, commonly in atrial fibrillation.
- Common abnormal pulses include:
- Anacrotic pulse: Slow-rising pulse seen in severe aortic stenosis.
- Dicrotic pulse: Prominent dicrotic wave seen in low cardiac output, septic states, and heart failure.
- Water-hammer (collapsing) pulse: Rapid upstroke and rapid collapse due to aortic regurgitation and other high-output states; associated with wide pulse pressure.
- Pulsus bisferiens: Two systolic peaks; seen in combined aortic stenosis with aortic regurgitation and hypertrophic obstructive cardiomyopathy.
- Pulsus paradoxus: Inspiratory fall in systolic blood pressure >10 mmHg; occurs in cardiac tamponade, constrictive pericarditis, and severe bronchial asthma.
📝 Practice MCQs
🎙️ Frequently Asked Viva Questions
High-yield viva questions with concise answers for rapid university examination preparation.
Q1. Why is the normal resting heart rate lower than the intrinsic heart rate of the SA node?
Answer: Continuous vagal (parasympathetic) tone suppresses SA nodal firing. Therefore, the resting heart rate is lower than the intrinsic rate of about 100–110 beats/min.
Q2. Why are the effects of vagal stimulation on heart rate rapid and short-lived?
Answer: Acetylcholine released from vagal nerves is rapidly broken down by cholinesterase, allowing quick, beat-to-beat regulation of heart rate.
Q3. Why are the effects of sympathetic stimulation longer lasting than vagal effects?
Answer: Norepinephrine is not rapidly destroyed at the neuroeffector junction and acts through the cAMP pathway, producing a slower but more prolonged increase in heart rate.
Q4. Explain the baroreceptor reflex in regulating heart rate.
Answer: Increased arterial pressure stimulates carotid sinus and aortic arch baroreceptors, increasing vagal activity and reducing sympathetic activity, leading to bradycardia.
Q5. What is the Bainbridge reflex?
Answer: Increased venous return stretches receptors at the venoatrial junctions, causing reflex tachycardia to accommodate the increased blood volume.
Q6. How does respiratory sinus arrhythmia occur?
Answer: Heart rate increases during inspiration and decreases during expiration due to normal changes in vagal activity with respiration.
Q7. What is pulse deficit and what does it indicate?
Answer: Pulse deficit is the difference between heart rate and pulse rate. It suggests that some ventricular contractions fail to produce an effective peripheral pulse, commonly in atrial fibrillation.
Q8. What produces the percussion wave, dicrotic notch, and dicrotic wave in a normal pulse tracing?
Answer: Percussion wave: ventricular ejection; dicrotic notch: aortic valve closure; dicrotic wave: elastic recoil of arteries during diastole.
Q9. Why is the radial artery commonly used for pulse examination?
Answer: The radial artery is superficial, easily accessible, and provides a reliable assessment of arterial pulse.
Q10. What is a water-hammer pulse and what is its common cause?
Answer: It is a rapidly rising and rapidly collapsing pulse, classically seen in severe aortic regurgitation.
Q11. Why does aortic regurgitation produce a water-hammer pulse?
Answer: Increased stroke volume causes a rapid upstroke, while blood flows back into the left ventricle during diastole, causing a rapid collapse of the pulse.
Q12. What is pulsus paradoxus?
Answer: It is an inspiratory fall in systolic blood pressure greater than 10 mmHg, causing marked weakening of the peripheral pulse during inspiration.
Q13. Why does cardiac tamponade produce pulsus paradoxus?
Answer: Increased pericardial pressure restricts ventricular filling. During inspiration, the septum shifts toward the left ventricle, reducing left ventricular filling and stroke volume.
Q14. What is pulsus alternans and what does it indicate?
Answer: Pulsus alternans is a regular rhythm with alternating strong and weak pulse volumes. It usually indicates severe left ventricular failure.
Q15. What is pulsus bisferiens and when is it seen?
Answer: Pulsus bisferiens is a pulse with two systolic peaks in one cardiac cycle, commonly seen in combined aortic stenosis with aortic regurgitation or hypertrophic obstructive cardiomyopathy.
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