Cardiac Hemodynamics - Biophysics of Blood Flow

Introduction

The function of the cardiovascular system is primarily to transport nutrients and oxygen to the tissues and take the waste products out from the tissues to the organ of disposal. The cardiovascular system is responsible for taking oxygen from the lungs, glucose, amino acids, and other gastrointestinal tract nutrients and distributing these nutrients to the peripheral tissues. The peripheral tissues remove waste such as carbon dioxide, urea, and creatinine, and the blood takes the carbon dioxide from the lungs and other waste products to the kidney so that they are expelled from the body. Blood is also responsible for carrying the hormones from the endocrine organs to the target tissue.

The blood mainly acts as a transport mechanism by carrying and supplying nutrients and oxygen. Hemo describes blood, and dynamics means the mechanism by which it flows.

What Is Hemodynamics?

• Hemodynamics explains the biophysics of blood flow to the organs. The main organ involved is the heart because it provides the driving force for blood flow to all body parts. Blood vasculature has an arterial system, the venous system, and microcirculation.

• The arterial system is the blood vessels in the circulatory system that bring oxygen-rich blood from your heart to all of the body’s cells.

• The venous system consists of veins that drain the blood back to your heart from other organs. The primary function of the heart is to move blood. Hemodynamics is important because it predicts the overall performance of the heart and determines the condition of the circulatory or cardiovascular system.

• The aorta is the primary artery or main outflow to the circulation responsible for supplying blood to the system. The main artery divides into smaller arteries (smaller blood vessels), and the smaller arteries break down into arterioles. The arterioles break into very small vessels called capillaries. The arterial tree feeds the capillaries. In this manner, blood is supplied to many tissues like skin, GIT (gastrointestinal tract), renal, skeletal, and central nervous systems. Aorta and the arterial system supply all the blood to the entire body. The organs extract the oxygen, and the blood returns to the heart through veins. The heart again pumps the blood to the lungs for oxygen, and the cycle restarts.

Physiologic Anatomy of the Heart

• The coronary arteries (blood vessels to the heart) are present on the surface of the heart, and small arteries are present in the cardiac muscle.

• The myocardium (muscle of the heart) receives blood supply through the arteries.

• The left coronary artery supplies the anterior and lateral parts of the left ventricle.

• The right coronary artery supplies the posterior part of the left ventricle and the right ventricle.

What Are the Factors That Affect Hemodynamics?

The Frictional Force Offered by the Blood Vessel: The blood flows fast where there’s no friction with blood vessel walls. The blood swirls (turbulent) in your ventricles (lower heart chambers) wherever the diameter changes or the vessel divides into branches. The turbulent blood flow is inefficient because the heart has to pump blood with extra force to help the blood flow back to the organs efficiently.

Blood Vessel Compliance to the Pressure: When the pressure rises, the force of blood flow is more, and if the wall of the blood vessel is rigid or does not expand to accommodate the flow, then the pressure increases in the artery. Blood vessel compliance depends on age. Usually, younger individuals have more elastic vessels, whereas elders have rigidity in the blood vessels because of aging.

The Diameter of the Blood Vessels: Obesity can build up excess fat in the blood vessels leading to the formation of fibrofatty tissue. This plaque (fibrofatty tissue) obstructs normal blood flow. As a result, it’s harder for the blood to flow through an obstructed blood vessel.

Ventricular Functioning: If the person has cardiovascular disease, the ventricles become weak, and the heart is unable to pump blood efficiently, which affects the overall circulation of the body.

Blood Pressure: In hypertensive individuals, the high blood glucose and plaque build-up constantly injures the endothelium of the heart and causes vascular inflammation that results in coronary artery disease and stroke. The heart might have to work harder by pumping harder against the resistance offered by the blood vessels.

Blood Viscosity: The thickness of the blood affects the flow.

Peripheral Resistance: The resistance offered by the circulatory system to create pressure. Resistance is created when the blood vessels constrict, which increases the pressure.

Oxygen Demand and Local Metabolism: The oxygen demand of the organ or tissue is the major factor for blood flow through a region. Local needs regulate blood flow to the entire coronary system. The oxygen consumption depends upon the work performed by the heart.

What Is Hemodynamic Instability?

In this condition, the person doesn’t have sufficient pressure for the blood flow to all parts of the body. The condition is referred to as shock. It is also a dangerous condition characterized by circulatory failure that causes insufficient oxygen supply leading to cellular and tissue hypoxia.

The types of shock are:

• Cardiogenic shock.

• Anaphylactic shock.

• Cardiomyopathic shock.

• Hypovolemic shock.

• Distributive shock.

• Neurogenic shock.

What Are the Signs of Hemodynamic Instability?

• Chest pain.

• Cold hands, legs, feet, arms, peripheral cyanosis (bluish discoloration).

• Shortness of breath.

• Restlessness.

• Hypotension (low blood pressure).

• Unconsciousness.

• Tiredness.

• Confusion.

• Decreased urine output.

What Are the Diseases and Conditions That Affect Hemodynamics?

• Myocardial infarction (a blockage in the heart’s blood vessels).

• Heart failure (the heart cannot pump sufficient blood to meet the body’s requirements).

• Arrhythmia (irregular, fast heartbeat due to abnormalities in impulse generation).

• Coronary artery disease (oxygen supply is less than the demand).

• Cardiovascular interventions such as angioplasty (a procedure to widen the blocked blood vessels).

• Coronary artery bypass surgery (It is a procedure to treat coronary artery disease and helps to restore blood flow to the heart by creating a new route around the blockage for the blood to pass).

• Valvular surgery.

• Heart transplantation.

• Chronic stable angina.

• Congenital heart disease.

How Can We Measure Hemodynamics?

• Use cardiac catheterization to measure the pressure of the valve.

• A catheter or ultrasound is used to check the central venous pressure.

• Echocardiogram to check the lower chambers.

• Sphygmomanometer to measure blood pressure.

• Measure cardiac output using a transthoracic echocardiogram.

• Electrocardiogram (EKG) to check for an abnormal heart rhythm.

• A catheter can be used to do invasive blood pressure monitoring in an artery.

Conclusion:

Consult a physician or doctor when someone has the above-mentioned signs and symptoms. For improved blood flow to the tissues, it is very important to treat the issue so that fresh oxygen supply is retained in the body and to avoid further complications such as heart disease and stroke.