last cardiac cycle and cardiac output 2_17

Basic Heart Anatomy and Physiology

• Heart Structure: The heart has several layers crucial for its function.

  • Lumen: Refers to the inside of a hollow organ (e.g., heart, blood vessels). This is where blood flows.

  • Endocardium: A thin layer of connective tissue that separates the lumen from the myocardium; it is impermeable.

  • Myocardium: The cardiac muscle layer responsible for contracting and creating pressure within the heart.

  • Pericardium: The outer covering of the heart with two layers: visceral and fibrous; includes a serous cavity filled with serous fluid for lubrication.

  • Coronary Circulation: Blood vessels supplying the myocardium; they branch out to form capillary networks that deliver oxygen and nutrients while removing waste products.

Importance of Coronary Circulation

• Myocardial Infarction (Heart Attack):

  • Definition: Acute myocardial infarction (AMI) refers to tissue death due to a lack of blood supply.

  • Cause: Often results from blockages in coronary arteries (e.g., due to atherosclerosis) which restrict blood flow, leading to tissue damage.

  • Critical Nature: Heart tissues rapidly die due to high blood flow demand as they utilize a significant percentage of the available blood flow.

Cardiac Output Overview

• Definition: Cardiac output is the volume of blood the heart pumps per minute, indicating the heart's performance.

• Formula: Cardiac output = Heart Rate (HR) × Stroke Volume (SV)

  • Heart Rate: Number of beats per minute; generally ranges from 50 to 90 beats per minute at rest.

  • Stroke Volume: The volume of blood ejected by the heart per beat; typically around 70 mL per beat in a healthy adult.

Stroke Volume

• End Diastolic Volume (EDV): The volume of blood in the heart at the end of filling (relaxation phase); usually around 135 mL.

• End Systolic Volume (ESV): The volume of blood remaining in the heart at the end of contraction; often around 65 mL.

• Calculation of Stroke Volume: SV = EDV - ESV. With an example: SV = 135 mL - 65 mL = 70 mL.

• Ejection Fraction: Percentage of blood ejected during each contraction; typically ranges from 45% to 60% or higher during exercise.

Heart Function and Blood Circulation

• At rest, cardiac output is about 5L/min, indicating the heart efficiently circulates the entire blood volume through the body.

• Variability in Blood Volume: An average adult has approximately 4-6 liters of blood. Thus, cardiac output adequately maintains blood flow in all tissues, especially during varying physical states (rest vs. exercise).

EKG Basics

• Normal EKG: Consists of a P-wave, QRS complex, and T-wave, indicating healthy electrical conduction in the heart.

• Junctional Rhythm: Affects heart rate, usually resulting from malfunctioning SA nodes, leading to slower heartbeats and reduced efficiency in blood pumping.

• Second-Degree Heart Block: Characterized by P waves without accompanying QRS complexes, implying a disconnect between the SA and AV nodes, potentially due to ischemia or damage.

• Ventricular Fibrillation: A life-threatening condition where the ventricles contract in a disorganized fashion. Requires immediate intervention (e.g., AED).

• Other abnormalities can indicate temporary or permanent issues with the heart's electrical conduction system.