L5 physiology

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Questions and Answers

What is the normal duration of the P wave in an ECG?

  • 0.16 sec
  • 0.06 sec
  • 0.10 sec (correct)
  • 0.25 sec

Which component of the ECG is primarily associated with ventricular depolarization?

  • T wave
  • QRS complex (correct)
  • U wave
  • P wave

What is the amplitude of a normal T wave in an ECG?

  • 0.4 mV
  • 0.2 mV (correct)
  • 1 mV
  • 0.1 mV

How is the heart rate calculated using the number of large boxes between two consecutive beats?

<p>Heart rate = 300 / number of large boxes (A)</p> Signup and view all the answers

In which condition is the PR interval most likely prolonged?

<p>Atrial hypertrophy (C)</p> Signup and view all the answers

What does a prolonged PR interval indicate?

<p>Delayed conduction through the AV node (A)</p> Signup and view all the answers

What does the U wave in an ECG typically indicate?

<p>Repolarization of papillary muscle or Purkinje fibers (C)</p> Signup and view all the answers

What does Lead II in an ECG record?

<p>Potential difference between the left leg and the right arm (B)</p> Signup and view all the answers

What is the standard speed of ECG paper?

<p>25 mm/sec (D)</p> Signup and view all the answers

Which unipolar lead is assigned to the left leg?

<p>aVF (D)</p> Signup and view all the answers

Where is the exploring electrode placed for lead V1?

<p>In the fourth intercostal space at the right sternal border (C)</p> Signup and view all the answers

Which leads are used to assess the inferior surface of the heart?

<p>Leads II, III, and aVF (A)</p> Signup and view all the answers

What does lead aVR primarily examine?

<p>The right atrium (D)</p> Signup and view all the answers

What is the purpose of checking voltage calibration in ECG interpretation?

<p>To ensure accurate measurements of the electrical signals (C)</p> Signup and view all the answers

Which leads look at the right ventricle?

<p>V1 and V2 (D)</p> Signup and view all the answers

Which of the following is NOT a step in the commonly followed sequence of ECG interpretation?

<p>Analyze the patient's background (D)</p> Signup and view all the answers

What is the role of capillaries in the circulatory system?

<p>Connect arterioles to venules (C)</p> Signup and view all the answers

Which property of cardiac muscle allows it to initiate beats independently of nervous signals?

<p>Rhythmicity (C)</p> Signup and view all the answers

What is the formula for calculating Stroke Volume (SV)?

<p>SV = EDV - ESV (C)</p> Signup and view all the answers

How much blood is typically pumped by each ventricle per beat at rest?

<p>70-80 ml/beat (C)</p> Signup and view all the answers

What is the primary function of the cardiovascular system?

<p>Removing metabolic byproducts (A)</p> Signup and view all the answers

What characteristic of cardiac muscle allows it to spread electrical impulses throughout the heart?

<p>Conductivity (C)</p> Signup and view all the answers

During which phase do all four chambers of the heart relax?

<p>Diastole (A)</p> Signup and view all the answers

What is considered the steady-state volume of blood pumped by the heart per minute at rest?

<p>5-5.5 L/min (A)</p> Signup and view all the answers

What does the equation CO = HR X SV represent?

<p>The calculation of cardiac output (D)</p> Signup and view all the answers

What does preload represent in cardiac function?

<p>Load acting on the ventricle before contraction (A)</p> Signup and view all the answers

Which statement regarding electrocardiography (ECG) is correct?

<p>ECG captures the algebraic sum of electrical activity during the cardiac cycle (B)</p> Signup and view all the answers

What is the normal range for ejection fraction?

<p>55-80% (D)</p> Signup and view all the answers

Einthoven's Triangle is used to illustrate what concept in ECG?

<p>The placement of electrodes for recording electrical activity (C)</p> Signup and view all the answers

Which process occurs first in the cardiac cycle?

<p>Atrial systole (D)</p> Signup and view all the answers

What is the primary function of the left ventricle in the cardiovascular system?

<p>Pumps oxygenated blood to the body (C)</p> Signup and view all the answers

What does afterload signify in the context of heart function?

<p>Load acting on the ventricle during contraction (C)</p> Signup and view all the answers

The electrical activity that precedes cardiac contraction is primarily due to what ion influx?

<p>Na+ (A)</p> Signup and view all the answers

Which component of the heart controls blood flow from the atrium to the ventricle?

<p>Atrioventricular valve (D)</p> Signup and view all the answers

Which sequence accurately describes the systemic circulation pathway?

<p>Left ventricle → Aorta → Arteries → Capillaries → Veins → Right atrium (D)</p> Signup and view all the answers

What is the role of the right ventricle in the cardiovascular system?

<p>Pumps deoxygenated blood to the lungs (B)</p> Signup and view all the answers

In the context of blood vessels, which statement is correct?

<p>Capillaries are responsible for gas exchange (A)</p> Signup and view all the answers

What term describes the two circuits of blood flow in the cardiovascular system?

<p>Pulmonary and systemic circulation (C)</p> Signup and view all the answers

Which statement accurately describes the function of semilunar valves?

<p>Regulates the flow between the heart and major arteries (B)</p> Signup and view all the answers

What does the term 'Einthoven triangle' refer to?

<p>The configuration of standard ECG leads (B)</p> Signup and view all the answers

Flashcards

Cardiovascular System

The heart, the main pressure pump, and the blood vessels, including arteries, arterioles, capillaries, venules, and veins.

Heart Chambers

The right and left sides of the heart, each containing an atrium and a ventricle. The atrium receives blood, and the ventricle pumps it out.

Atrioventricular Valves

Valves in the heart that control the direction of blood flow from the atria to the ventricles.

Semilunar Valves

Valves that control the direction of blood flow from the ventricles to the arteries.

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Aorta

The large blood vessel that carries oxygenated blood from the left ventricle to the rest of the body.

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Systemic Circulation

The circulation of blood from the left ventricle to the body and back to the right atrium.

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Pulmonary Circulation

The circulation of blood from the right ventricle to the lungs and back to the left atrium.

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Arteries

Blood vessels that carry blood away from the heart.

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Cardiac Muscle Excitability

The ability of cardiac muscle to respond to a stimulus by generating an electrical impulse.

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Cardiac Muscle Rhythmicity

The ability of cardiac muscle to initiate its own rhythmic contractions without external stimulation.

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Cardiac Muscle Conductivity

The ability of cardiac muscle to conduct electrical impulses efficiently throughout the heart.

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Cardiac Muscle Contractility

The ability of cardiac muscle to contract in response to electrical stimulation.

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Stroke Volume (SV)

The volume of blood pumped out by each ventricle with every heartbeat.

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End Diastolic Volume (EDV)

The volume of blood remaining in the ventricle at the end of diastole (relaxation).

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End Systolic Volume (ESV)

The volume of blood remaining in the ventricle at the end of systole (contraction).

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Cardiac Output (CO)

The volume of blood pumped out by each ventricle per minute.

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What is Cardiac Output (CO)?

Cardiac output (CO) is the amount of blood pumped by the heart per minute. It is calculated by multiplying heart rate (HR) by stroke volume (SV).

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What is Cardiac Index?

Cardiac index (CI) is a better measure of CO than CO alone, as it takes into account the surface area of the body. It's calculated by dividing CO by body surface area.

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What is Ejection Fraction (EF)?

Ejection fraction (EF) is the percentage of blood ejected from the left ventricle with each beat. It's calculated by dividing stroke volume (SV) by end-diastolic volume (EDV).

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What is Preload?

Preload is the amount of stretch on the heart muscle fibers before contraction. It is represented by end-diastolic volume (EDV) or venous return.

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What is Afterload?

Afterload is the resistance the heart muscle faces during contraction. It is represented by arterial resistance or total peripheral resistance (TPR).

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What is Electrocardiography (ECG)?

Electrocardiography (ECG) measures the electrical activity of the heart muscles during the cardiac cycle. It records the depolarization and repolarization of the heart muscle cells, which precedes cardiac contraction.

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How is ECG Recorded?

The heart's electrical activity spreads through the heart muscle, creating potential differences that can be detected on the body's surface using electrodes.

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What is Einthoven's Triangle?

Einthoven's triangle refers to the placement of three electrodes (on the right arm, left arm, and left leg) to record the electrical activity of the heart. It is based on the principle that the sum of the potentials at the points of an equilateral triangle with a current source in the center is zero.

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Standard Limb Leads

The standard limb leads used in electrocardiography are Lead I, Lead II, and Lead III. They record the electrical activity of the heart using two active electrodes placed on specific limbs.

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Lead I

Lead I records the potential difference between the left arm and the right arm (LA-RA).

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Lead II

Lead II records the potential difference between the left leg and the right arm (LL-RA).

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Lead III

Lead III records the potential difference between the left leg and the left arm (LL-LA).

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Unipolar Leads

Unipolar leads use a single active electrode to record the electrical potential difference between the electrode and a neutral reference point.

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Unipolar Limb Leads

Unipolar limb leads are aVR, aVL, and aVF. They use the right arm, left arm, and left leg respectively for the active electrode, with the neutral reference point on the chest.

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Unipolar Chest Leads

Unipolar chest leads (V1-V6) use an active electrode placed on different chest locations to record electrical activity from various areas of the heart.

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Importance of Different ECG Leads

Different ECG leads provide views of different areas of the heart, allowing for a more comprehensive assessment of its electrical activity.

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PR interval

The time interval between the beginning of the P wave to the beginning of the R wave in an ECG recording.

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QRS complex

Represents the duration of ventricular depolarization, meaning the electrical activation of the ventricular muscle causing contraction.

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T wave

The electrical activity associated with the repolarization of the ventricle, which is when the heart muscle relaxes and prepares for the next heartbeat.

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U wave

A slight positive deflection after the T wave, sometimes observed in ECGs. Usually related to the repolarization of the papillary muscles or Purkinje fibers.

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Large and small boxes on ECG

Used to measure the heart rate on an ECG. Each large box represents 0.2 seconds, while each small box represents 0.04 seconds.

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RR interval

The interval between two consecutive R waves on an ECG, reflecting the time between heartbeats.

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P wave

A positive wave on the ECG caused by atrial depolarization, indicating electrical activation of the atria.

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T wave

A positive wave that occurs during the repolarization of the ventricles, meaning as the ventricles relax.

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Study Notes

Introduction to CVS and ECG

  • The cardiovascular system is composed of the heart and blood vessels (arteries, arterioles, capillaries, venules, and veins)
  • The heart has two halves (right and left), each with an atrium and a ventricle
  • Atrioventricular (AV) valves ensure one-way blood flow from atrium to ventricle
  • Left ventricle pumps blood to the systemic circulation at high pressure
  • Right ventricle pumps blood to the pulmonary circulation at lower pressure
  • Semilunar valves control blood flow between ventricles and major arteries

Learning Objectives

  • Describe heart chambers, valves, and blood flow direction
  • Describe systemic and pulmonary circulation
  • Define ECG
  • Describe the Einthoven triangle
  • List ECG leads used in recordings
  • Describe ECG waves and their relation to the cardiac cycle
  • Interpret ECG findings
  • Discuss ECG applications

Circulation

  • Systemic circulation carries oxygenated blood to body tissues
  • Pulmonary circulation carries deoxygenated blood to the lungs for gas exchange

Pressures in the Circulation

  • Right ventricle: 25/0 mm Hg
  • Pulmonary artery: 25/8 mm Hg
  • Mean pulmonary artery: 15 mm Hg
  • Capillary: 7-9 mm Hg
  • Pulmonary venous: 5 mm Hg
  • Left atrium: 5-10 mm Hg
  • Left ventricle: 120/0 mm Hg
  • Aorta: 120/80 mm Hg
  • Mean arterial blood pressure: 93 mm Hg
  • Capillary (skeletal, renal, glomerular): 30 mm Hg, 45-50 mm Hg
  • Peripheral veins: 15 mm Hg
  • Right atrium (central venous): 0 mm Hg

Blood Vessels

  • Form a closed system, beginning and ending at the heart
  • Arteries carry blood away from the heart
  • Veins carry blood towards the heart
  • Capillaries connect arterioles and venules, allowing gas and nutrient exchange

Vessel Types and Function

  • Arteries: Transport high-pressure blood from heart to smaller arteries/arterioles
  • Arterioles: Connect arteries and capillaries, act as resistance vessels
  • Veins: Connect capillaries and venules, transport low-pressure blood to heart
  • Venules: Connect capillaries to veins
  • Capillaries: Allow gas exchange, nutrient transfer, and waste removal between blood and tissues

Function of CVS

  • Transport and distribute essential substances to tissues
  • Remove metabolic byproducts
  • Adjust oxygen and nutrient supply in different physiological states
  • Regulate body temperature
  • Facilitate humoral communication

How Does the Heart Function?

  • Heart parts beat in an orderly sequence (atrial systole, ventricular systole, diastole)
  • Contraction preceded by electrical stimulation (action potential)
  • Heartbeat originates in specialized cardiac conduction system and spreads to myocardium

Properties of Cardiac Muscle

  • Excitability
  • Rhythmicity
  • Conductivity
  • Contractility

What is Pumped Out of the Heart?

  • Stroke Volume (SV): Volume of blood pumped per ventricle beat (70-80 ml/beat)
  • End Diastolic Volume (EDV): Blood volume remaining in the ventricle at end of diastole (135 ml)
  • End Systolic Volume (ESV): Blood volume remaining in the ventricle at end of systole (65-70 ml)

Cardiac Output (CO)

  • Volume of blood pumped by each ventricle per minute (5-5.5 L/min)
  • CO = Heart Rate (HR) x Stroke Volume (SV)
  • Cardiac Index = CO/surface area

Important Terms

  • Preload: Load on the ventricle before contraction (venous return, end-diastolic volume)
  • Afterload: Load on the ventricle during contraction (arterial resistance, TPR)

What is ECG?

  • Electrocardiography (ECG): Algebraic summation of electrical activity in cardiac muscle during cardiac cycle
  • Recording of cardiac muscle's electrical activity (depolarization & repolarization)
  • Depolarization (due to Na+ influx), Repolarization (due to K+ efflux)

ECG Recording

  • Body fluids conduct electrical signals
  • Metal electrodes on extremities & chest wall detect signals
  • Signals amplified & recorded
  • ECG can be unipolar (using one active electrode) or bipolar (using two active electrodes)

Einthoven's Triangle

  • A triangle with electrodes on arms and left leg, center represents zero potential
  • Used for reference point for unipolar leads
  • Lead II = Lead I + Lead III

Leads used in ECG Recording

  • Standard Bipolar Limb Leads (using 2 electrodes): Lead I, Lead II, Lead III
  • Unipolar Leads (aVR, aVL, aVF)
    • aVR: Exploring electrode on right arm
    • aVL: Exploring electrode on left arm
    • aVF: Exploring electrode on left leg
  • Unipolar Chest Leads (V1-V6)

The value of different ECG leads

  • Leads I and aVL: Left lateral wall
  • Leads II, III, and aVF: Inferior surface
  • Lead aVR: Atrial activity
  • V1 and V2: Right ventricle
  • V3 and V4: Anterior and lateral walls of left ventricle

Normal ECG

  • P wave: Atrial depolarization
  • QRS complex: Ventricular depolarization
  • T wave: Ventricular repolarization
  • PR interval: Atrial depolarization to ventricular depolarization
  • QRS duration: Ventricular depolarization time
  • QT interval: Ventricular depolarization and repolarization

Interpretation of ECG

  • Voltage calibration
  • Heart rhythm
  • Heart rate
  • Intervals (PR, QRS, QT)
  • Mean QRS axis
  • Abnormalities of P wave
  • Abnormalities of QRS
  • ST segment and T wave abnormalities

Heart rate by RR interval

  • Heart rate (bpm) = 1500 / number of small boxes between two consecutive R waves
  • Heart rate (bpm) = 300 / number of large boxes between two consecutive R waves

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