Cardiac Mechanics

Overview of Cardiac Output

Definitions

• Cardiac output (CO):
  • Amount of blood the heart pumps per minute
  • CO = stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle x HR
    • Stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle: the amount of blood ejected during ventricular systole Systole Period of contraction of the heart, especially of the heart ventricles. Cardiac Cycle
    • Heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology: number of contractions per minute
• CO affected by:
  • Preload: how much the ventricles can stretch prior to contraction → determines how much blood fills the ventricles (i.e., end-diastolic volume End-diastolic volume Cardiac Cycle ( EDV EDV Cardiac Cycle))
  • Afterload: force the ventricle needs to overcome to pump Pump ACES and RUSH: Resuscitation Ultrasound Protocols blood out to the body (i.e., aortic pressure)
  • Inotropy (also called contractility): how hard the heart contracts
• These factors are regulated by:
  • Autonomic nerves
  • Hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview and Types
  • Frank-Starling law: 
    • Intrinsic properties of actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction and myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction filaments in the cardiomyocytes that allow the cells to contract more the more they are stretched.
    • As left ventricular end-diastolic pressure (LVEDP) increases owing to increased ventricular filling Ventricular filling Cardiac Cycle, stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle increases as well.
• Preload, afterload, and inotropy are typically discussed in association with the left ventricle (LV); however, the atria and right ventricles respond in similar ways.

Pressure volume loops

Overview:

• A graphical demonstration of how the volumes and pressures change in the LV throughout the cardiac cycle Cardiac cycle The cardiac cycle describes a complete contraction and relaxation of all 4 chambers of the heart during a standard heartbeat. The cardiac cycle includes 7 phases, which together describe the cycle of ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. Cardiac Cycle:
  • Removes variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables of time from the cardiac cycle Cardiac cycle The cardiac cycle describes a complete contraction and relaxation of all 4 chambers of the heart during a standard heartbeat. The cardiac cycle includes 7 phases, which together describe the cycle of ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. Cardiac Cycle graphs below
  • Results in a diagram appearing as a loop
• X-axis: LV volume
• Y-axis: LV pressure
• Point A: Mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy opens.
• Point B: Mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy closes.
• Point C: Aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy opens.
• Point D: Aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy closes.

Phases:

• Ventricular filling Ventricular filling Cardiac Cycle: 
  • Segment A → segment B
  • Seen as the somewhat flat line across the bottom of the graph, moving from left to right
  • The volume is increasing, but because the mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy is open, the increase in pressure is minimal.
• Isovolumetric contraction Isovolumetric contraction Cardiac Cycle: 
  • Segment B → segment C
  • Seen as the vertical line going straight up
  • Mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy closes at B
  • Aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy does not open until C; with both valves closed, no volume change is possible.
  • Ventricular contraction causes an increase in LV pressure without a change in volume.
• Ventricular ejection Ventricular ejection Cardiac Cycle: 
  • Segment C → segment D
  • Seen as the curved line along the top, moving from right to left
  • Aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy opens, allowing blood to leave → volume falls
  • Ventricles are contracting, so initially pressure increases, until volume falls so much that pressure starts falling as well.
• Isovolumetric relaxation Isovolumetric relaxation Cardiac Cycle: 
  • Segment D → segment A
  • Seen as the vertical line going straight down
  • Aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy closes
  • Mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy does not open until A; with both valves closed, no volume change is possible.
  • Ventricular relaxation causes a drop in LV pressure without a change in volume.

Preload

Definition

Preload is a measure of how much the cardiomyocytes have stretched by the end of diastole Diastole Post-systolic relaxation of the heart, especially the heart ventricles. Cardiac Cycle. The Frank-Starling law is associated with preload effects on SV: ↑ preload = ↑ SV.

Length–tension relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship

The length–tension relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship explains how the Frank-Starling law works. This law applies to striated muscle Striated muscle One of two types of muscle in the body, characterized by the array of bands observed under microscope. Striated muscles can be divided into two subtypes: the cardiac muscle and the skeletal muscle. Muscle Tissue: Histology: skeletal and cardiac muscles.

• The more muscle filaments (i.e., actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction and myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction) are stretched apart, the more force they can generate during contraction.
• If Z bands are close together (minimal stretch at rest), there is little room for the fibers to move closer together → weaker contraction
• Therefore, the EDV EDV Cardiac Cycle is higher when:
  • Myocardial muscle filaments are stretched more at the end of diastole Diastole Post-systolic relaxation of the heart, especially the heart ventricles. Cardiac Cycle.
  • Ventricular contraction is stronger.
  • Pressure in the ventricles during contraction is stronger.
• Also known as length-dependent activation

Factors that ↑ preload

• ↑ Venous pressure → ↑ venous return → more blood returned to the heart, which occurs with:
  • ↓ Venous compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology (ability to stretch)
  • ↑ Venous volume
• ↑ Ventricular compliance Compliance Distensibility measure of a chamber such as the lungs (lung compliance) or bladder. Compliance is expressed as a change in volume per unit change in pressure. Veins: Histology
• ↑ Atrial inotropy (how strongly the atria contract)
• ↑ Afterload: if cannot push out as much blood per stroke → ↑ end-systolic volume End-systolic volume Cardiac Cycle ( ESV ESV Cardiac Cycle) → ↑ preload for the next contraction
• ↓ Ventricular inotropy: weaker ventricular contraction → ↑ ESV ESV Cardiac Cycle → ↑ preload for the next contraction
• ↓ HR: more time for the heart to fill

Effects of preload on pressure–volume loops

• ↑ EDV EDV Cardiac Cycle (e.g., increasing blood volume via IV fluids IV fluids Intravenous fluids are one of the most common interventions administered in medicine to approximate physiologic bodily fluids. Intravenous fluids are divided into 2 categories: crystalloid and colloid solutions. Intravenous fluids have a wide variety of indications, including intravascular volume expansion, electrolyte manipulation, and maintenance fluids. Intravenous Fluids) = ↑ stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle
• ↓ EDV EDV Cardiac Cycle (e.g., hemorrhage) = ↓ stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle

Afterload

Definition

Afterload is the resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing in the aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy that prevents blood from leaving the heart. Afterload represents the pressure the LV needs to overcome to eject blood into the aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy.

Effects of afterload on ventricular function

↑ Afterload:

• ↑ Aortic pressure→ higher pressures are required during isovolumetric contraction Isovolumetric contraction Cardiac Cycle to open the aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy: 
  • Energy is “wasted” on isovolumetric contraction Isovolumetric contraction Cardiac Cycle rather than on ejection
  • Results in ↓ stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle 
• ↑ Preload for the next contraction
• Flattens the Frank-Starling curve: ↓ rate of ventricular pressure development
•  ↑ Contraction velocity:
  • Myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction fibers can quickly move along the actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction fibers → rapid shortening of sarcomeres
  • If you have to lift something light, you can do so quickly and easily.

↓ Afterload:

• ↓ Aortic pressure → lower pressures are required during isovolumetric contraction Isovolumetric contraction Cardiac Cycle to open the aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy
  • More of the contraction is used for ejection 
  • Results in ↑ stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle 
• ↓ Preload for the next contraction
• Steepens the Frank-Starling curve: ↑ rate of ventricular pressure development
• ↓ Contraction velocity:
  • More difficult for myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction fibers to move along actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction fibers → slower shortening of sarcomeres
  • If you have to lift something much heavier, you will lift it more slowly and with more difficulty.

Inotropy

Definition

Inotropy is a measure of the force of contraction, independent of changes in preload.

• Unrelated to the Frank-Starling law
• Known as length-independent activation 
• Ultimately controlled by levels of intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺: 
  • Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ allows the myofilaments Myofilaments Refers to individual proteins that together cause muscle contraction. Muscle Tissue: Histology actin Actin Filamentous proteins that are the main constituent of the thin filaments of muscle fibers. The filaments (known also as filamentous or f-actin) can be dissociated into their globular subunits; each subunit is composed of a single polypeptide 375 amino acids long. This is known as globular or g-actin. In conjunction with myosins, actin is responsible for the contraction and relaxation of muscle. Skeletal Muscle Contraction and myosin Myosin A diverse superfamily of proteins that function as translocating proteins. They share the common characteristics of being able to bind actins and hydrolyze mgATP. Myosins generally consist of heavy chains which are involved in locomotion, and light chains which are involved in regulation. Within the structure of myosin heavy chain are three domains: the head, the neck and the tail. The head region of the heavy chain contains the actin binding domain and mgATPase domain which provides energy for locomotion. The neck region is involved in binding the light-chains. The tail region provides the anchoring point that maintains the position of the heavy chain. The superfamily of myosins is organized into structural classes based upon the type and arrangement of the subunits they contain. Skeletal Muscle Contraction to make contact and move along one another.
  • ↑ Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ = ↑ strength of contraction

Factors affecting inotropy

Inotropy is increased as a result of:

• Sympathetic activation:
  • Impulses coming from the ANS ANS The ans is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ans consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System: Anatomy
  • Causes ↑ intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ via:
    • Activation of L-type Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ channels Channels The Cell: Cell Membrane 
    • Release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology of Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ from the sarcoplasmic reticulum Sarcoplasmic Reticulum A network of tubules and sacs in the cytoplasm of skeletal muscle fibers that assist with muscle contraction and relaxation by releasing and storing calcium ions. Muscle Tissue: Histology (SR) 
  • Activates phospholamban: pumps additional Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ back into the SR so that the next contraction can release Release Release of a virus from the host cell following virus assembly and maturation. Egress can occur by host cell lysis, exocytosis, or budding through the plasma membrane. Virology even more Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺ and be even stronger
• ↑ Circulating catecholamines Catecholamines A general class of ortho-dihydroxyphenylalkylamines derived from tyrosine. Adrenal Hormones: 
  • Epinephrine Epinephrine The active sympathomimetic hormone from the adrenal medulla. It stimulates both the alpha- and beta- adrenergic systems, causes systemic vasoconstriction and gastrointestinal relaxation, stimulates the heart, and dilates bronchi and cerebral vessels. Sympathomimetic Drugs and norepinephrine Norepinephrine Precursor of epinephrine that is secreted by the adrenal medulla and is a widespread central and autonomic neurotransmitter. Norepinephrine is the principal transmitter of most postganglionic sympathetic fibers, and of the diffuse projection system in the brain that arises from the locus ceruleus. Receptors and Neurotransmitters of the CNS in the blood secreted by the adrenal medulla Adrenal Medulla The inner portion of the adrenal gland. Derived from ectoderm, adrenal medulla consists mainly of chromaffin cells that produces and stores a number of neurotransmitters, mainly adrenaline (epinephrine) and norepinephrine. The activity of the adrenal medulla is regulated by the sympathetic nervous system. Adrenal Glands: Anatomy
  • Also cause ↑ intracellular Ca CA Condylomata acuminata are a clinical manifestation of genital HPV infection. Condylomata acuminata are described as raised, pearly, flesh-colored, papular, cauliflower-like lesions seen in the anogenital region that may cause itching, pain, or bleeding. Condylomata Acuminata (Genital Warts)²⁺
• ↑ HR (Bowditch effect: the faster the heart beats, the stronger the contractions)
• ↑ Afterload (Anrep effect: The heart will increase contraction strength if it has to overcome higher afterloads.)

Effects of inotropy on ventricular function

↑ Inotropy:

• ↑ Stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle
• Steepens the Frank-Starling curve: ↑ rate of ventricular pressure development
• Steepens the end-systolic pressure–volume relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship (ESPVR) line on pressure–volume loops: contractions are stronger
• ↑ Ejection fraction Ejection fraction Cardiac Cycle
• ↓ Preload for next contraction

↓ Inotropy:

• ↓ Stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle
• Flattens the Frank-Starling curve: ↓ rate of ventricular pressure development
• Flattens the ESPVR line on pressure–volume loops: contractions are weaker
• ↓ Ejection fraction Ejection fraction Cardiac Cycle
• ↑ Preload for next contraction

Clinical Relevance

The following are common conditions that affect Affect The feeling-tone accompaniment of an idea or mental representation. It is the most direct psychic derivative of instinct and the psychic representative of the various bodily changes by means of which instincts manifest themselves. Psychiatric Assessment cardiac mechanics.

• Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension: condition of increased pressure in the arterial system. Hypertension Hypertension Hypertension, or high blood pressure, is a common disease that manifests as elevated systemic arterial pressures. Hypertension is most often asymptomatic and is found incidentally as part of a routine physical examination or during triage for an unrelated medical encounter. Hypertension is a state of persistently increased afterload, which puts increased strain on the heart. 
• Heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR) (HF): congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure ( CHF CHF Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure) is the inability of the heart to supply the body with the normal CO required to meet metabolic needs. This condition may result in chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain, exertional dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, and episodes of hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension, dizziness Dizziness An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness. Lateral Medullary Syndrome (Wallenberg Syndrome), and/or syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope. EF EF Cardiac Cycle of the left ventricle is used to clinically categorize HF into HF with preserved EF EF Cardiac Cycle (≥ 50%) and HF with reduced EF EF Cardiac Cycle (≤ 40%), each with their own severity, prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas, and treatment regimens. 
• Cardiomyopathies Cardiomyopathies A group of diseases in which the dominant feature is the involvement of the cardiac muscle itself. Cardiomyopathies are classified according to their predominant pathophysiological features (dilated cardiomyopathy; hypertrophic cardiomyopathy; restrictive cardiomyopathy) or their etiological/pathological factors (cardiomyopathy, alcoholic; endocardial fibroelastosis). Cardiomyopathy: Overview and Types: group of myocardial diseases associated with structural changes of the myocardium Myocardium The muscle tissue of the heart. It is composed of striated, involuntary muscle cells connected to form the contractile pump to generate blood flow. Heart: Anatomy and impaired systolic and/or diastolic function, in the absence of other heart disorders. Cardiomyopathies Cardiomyopathies A group of diseases in which the dominant feature is the involvement of the cardiac muscle itself. Cardiomyopathies are classified according to their predominant pathophysiological features (dilated cardiomyopathy; hypertrophic cardiomyopathy; restrictive cardiomyopathy) or their etiological/pathological factors (cardiomyopathy, alcoholic; endocardial fibroelastosis). Cardiomyopathy: Overview and Types can be classified as dilated, restrictive, hypertrophic, or arrhythmogenic. With abnormal ventricular structure, the pumping action of the ventricles can be severely impaired, resulting in HF and/or volume overload.
• Fight-or-flight response: activation of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. Nervous System: Anatomy, Structure, and Classification (SNS), which affects several aspects of the cardiac cycle Cardiac cycle The cardiac cycle describes a complete contraction and relaxation of all 4 chambers of the heart during a standard heartbeat. The cardiac cycle includes 7 phases, which together describe the cycle of ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. Cardiac Cycle simultaneously. Activation of the SNS increases contractility (moving the ESPVR line up and to the left), while also increasing venous return (↑ EDV EDV Cardiac Cycle). This results in synergistic effects, increasing stroke volume Stroke volume The amount of blood pumped out of the heart per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume. Cardiac Cycle owing to effects on both ↑ preload and ↑ inotropy.