Curriculum

17 Sections
1548 Lessons
100 Days

Expand all sectionsCollapse all sections

U01.01 Biochemistry
This biochemistry review for USMLE Step 1 covers essential topics including metabolism, enzymology, and molecular biology.
126
U01.02 Immunology
Prepare for USMLE Step 1 Immunology with a comprehensive review covering foundational concepts, immune system mechanisms, and key disorders to solidify your understanding and boost exam readiness.
42
U01.03 Microbiology
Review essential microbiology topics for the USMLE Step 1, covering key pathogens, mechanisms of disease, and antimicrobial principles critical for mastering infectious disease concepts.
172
U01.04 General Pathology
Explore key concepts in general pathology essential for the USMLE Step 1. This review covers fundamental principles, disease mechanisms, and clinical correlations to help you excel in your medical exam.
35
U01.05 Pharmacology
Master key pharmacology concepts for the USMLE Step 1 with a focus on drug mechanisms, therapeutic uses, adverse effects, and interactions essential for high-yield exam performance.
43
U01.06 Public Health Sciences
Review essential Public Health Sciences topics for the USMLE Step 1, covering epidemiology, biostatistics, health policy, and ethics to strengthen your understanding of foundational public health principles.
53
U01.07 Cardiovascular system
Comprehensive review of essential cardiovascular system topics to help you excel in the USMLE Step 1 exam, covering key concepts from anatomy to pathology.
73
U01.08 Endocrine system
Master essential concepts of the endocrine system for USMLE Step 1, covering hormone regulation, feedback mechanisms, and key disorders to boost your exam readiness.
51
U01.09 Gastrointestinal system
Review key topics in the gastrointestinal system for the USMLE Step 1, covering essential concepts in anatomy, physiology, pathology, and pharmacology to reinforce your understanding and test readiness.
131
U01.10 Hematology and Oncology
This review covers essential Hematology and Oncology topics for the USMLE Step 1, including hematopoiesis, coagulation, anemias, leukemias, lymphomas, and neoplastic syndromes.
148
U01.11 Musculoskeletal, Skin, and Connective Tissue
Review essential topics for the USMLE Step 1 Musculoskeletal, Skin, and Connective Tissue systems, covering anatomy, physiology, pathology, and pharmacology fundamentals critical for exam success.
178
U01.12 Neurology and Special Senses
Master the foundational concepts of Neurology and Special Senses with our USMLE Step 1 review, covering essential topics like neuroanatomy, neurophysiology, and sensory pathways.
143
U01.13 Psychiatry
Psychiatry for the USMLE Step 1 focuses on understanding the pathophysiology, diagnosis, and treatment of psychiatric disorders, with an emphasis on key concepts like neurotransmitter imbalances, mental health disorders, and pharmacology.
83
U01.14 Renal System
The Renal System review for USMLE Step 1 covers key concepts including renal physiology, nephron function, acid-base balance, electrolyte regulation, and renal pathology, crucial for understanding both normal and abnormal kidney functions.
81
U01.15 Reproductive System
The USMLE Step 1 Reproductive System review covers key concepts in human reproduction, including anatomy, physiology, endocrinology, and common pathologies affecting both male and female reproductive health.
124
U01.16 Respiratory System
The Respiratory System review for the USMLE Step 1 covers key concepts in anatomy, physiology, pathophysiology, and pharmacology essential for understanding respiratory diseases and treatments.
61
U01.17 Rapid Review
he USMLE Step 1 Rapid Review covers essential topics across multiple disciplines, providing a concise, high-yield overview to reinforce key concepts and optimize your exam preparation.
5

U01.07.007 Cardiac output variables

Cardiac Output Variables for USMLE Step 1

1. Stroke Volume (SV)

Stroke Volume is the volume of blood ejected by the heart with each contraction and is influenced by contractility, afterload, and preload.

Factors Affecting Stroke Volume:

Contractility:
- Increased contractility increases stroke volume.
- Examples: Anxiety, exercise.
Preload:
- Increased preload increases stroke volume.
- Example: Early pregnancy.
Afterload:
- Increased afterload decreases stroke volume.
- Example: Increased systemic vascular resistance (SVR).

Clinical Relevance:

A failing heart (e.g., heart failure) has a decreased stroke volume, whether due to systolic or diastolic dysfunction.

2. Contractility

Contractility refers to the heart’s ability to contract. It’s influenced by various factors such as catecholamines, digitalis, and calcium handling.

Factors that Increase Contractility:

Catecholamine Stimulation (via β1 receptors):
- Activation of protein kinase A increases phospholamban phosphorylation, promoting Ca2+ ATPase activity.
- Increased Ca2+ storage in the sarcoplasmic reticulum.
- Increased Ca2+ entry via Ca2+ channels.
- Enhanced Ca2+-induced Ca2+ release.
- Increased intracellular Ca2+.
Digitalis:
- Inhibits the Na+/K+ ATPase pump, causing increased intracellular Na+.
- Decreased Na+/Ca2+ exchanger activity, leading to increased intracellular Ca2+ and improved contractility.

Factors that Decrease Contractility:

β1-blockade (decreases cAMP).
Heart failure (HF) with systolic dysfunction.
Acidosis (decreases contractility).
Hypoxia/Hypercapnia (low Po2 and high Pco2 decrease contractility).
Non-dihydropyridine calcium channel blockers (e.g., verapamil, diltiazem).

3. Preload

Preload is approximated by ventricular end-diastolic volume (EDV) and depends on venous tone and circulating blood volume.

Factors Affecting Preload:

Increased Preload: Higher EDV increases preload.
Vasodilators (e.g., nitroglycerin) decrease preload by reducing venous return.

4. Afterload

Afterload is approximated by mean arterial pressure (MAP) and represents the load against which the heart has to pump.

Effects of Afterload on the Heart:

Increased Afterload increases wall tension and decreases stroke volume.
- According to Laplace’s Law, wall tension is proportional to pressure and radius of the ventricle.

Compensation Mechanism:

The left ventricle (LV) compensates for increased afterload by thickening (hypertrophy) to reduce wall stress.

Factors Affecting Afterload:

Arterial Vasodilators (e.g., hydralazine) decrease afterload.
ACE inhibitors and ARBs reduce both preload and afterload.
Chronic Hypertension: Increased MAP leads to LV hypertrophy as the heart compensates for the increased workload.

5. Myocardial Oxygen Demand

Myocardial oxygen demand (MVO2) reflects the heart’s need for oxygen and is influenced by several factors.

Factors that Increase Myocardial Oxygen Demand:

Increased Contractility.
Increased Afterload (proportional to arterial pressure).
Increased Heart Rate.
Increased Diameter of the Ventricle (due to increased wall tension).

Wall Tension and Laplace’s Law:

Wall Tension = Pressure × Radius
Wall Stress = (Pressure × Radius) / (2 × Wall Thickness)

Key Points to Remember for USMLE Step 1:

Stroke Volume (SV) is influenced by contractility, preload, and afterload.
Contractility is increased by catecholamines (β1 activation), digitalis, and increased intracellular Ca2+. It is decreased by β-blockers, acidosis, hypoxia, and non-dihydropyridine calcium channel blockers.
Preload is determined by ventricular EDV, venous tone, and circulating blood volume. Vasodilators decrease preload.
Afterload is determined by MAP and increases wall tension. Arterial vasodilators decrease afterload.
Myocardial O2 demand increases with contractility, afterload, heart rate, and ventricular diameter.

Your voice matters – comment below!Cancel reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

USMLE Step 1 Review Series