Regulation and Disorders of the Cardiovascular System

Cardiovascular System Regulation

Cardiac Output and Blood Pressure

The cardiovascular system is responsible for delivering blood to every cell, ensuring their metabolic needs are met. Cardiac output is the volume of blood pumped by the heart into the aorta each minute, and maintaining a constant arterial blood pressure is essential for proper organ function. This is achieved by regulating cardiac output and the diameter of arterioles, which adjusts resistance to blood flow.

Baroreceptors and Blood Pressure Regulation

Baroreceptors are specialized sensory receptors located in the walls of certain blood vessels. They detect changes in blood pressure and initiate a negative feedback loop to maintain homeostasis:

• Step 1: Increased blood pressure stretches baroreceptors.

• Step 2: Sensory neurons innervating baroreceptors fire when stretched.

• Step 3: The signal travels to the cardiovascular center in the brain.

• Step 4: The brain responds by altering nerve stimulation to the heart and blood vessels.

• Step 5: Heart rate and force of contraction decrease, lowering cardiac output.

• Step 6: Blood vessels reduce vascular resistance, increasing blood flow.

This negative feedback loop restores blood pressure to normal levels.

Local Regulation of Blood Flow

Blood flow to tissues is regulated locally based on metabolic needs. Precapillary sphincters control blood flow into capillary beds, adjusting according to the tissue's requirements:

• Increased metabolism (e.g., contracting muscles) leads to greater consumption of oxygen and nutrients, and increased production of waste (CO2).

• Vasodilating substances are produced, causing arterioles and precapillary sphincters to dilate and increase blood flow.

• At rest, minimal vasodilating substances are produced, resulting in reduced blood flow.

Exercise and Cardiac Output

Effects of Exercise

During exercise, metabolic activity increases, causing local oxygen concentrations to drop. Blood vessels dilate to increase blood flow to skeletal muscles. This triggers a baroreceptor-mediated reflex that increases cardiac output:

• Sensory input from moving muscles and joints signals the cardiovascular center to stimulate the heart.

• Cardiac output increases before blood pressure changes significantly.

Target Heart Rate

Target heart rate zones are used to guide exercise intensity. The table below shows recommended heart rate zones for different age groups:

Age	Target HR zone (50–70% of max HR)	Target HR zone (70–85% of max HR)	Average max HR
20	100–140 bpm	140–170 bpm	200 bpm
25	98–137 bpm	137–166 bpm	195 bpm
30	95–133 bpm	133–162 bpm	190 bpm
35	93–130 bpm	130–157 bpm	185 bpm
40	90–126 bpm	126–153 bpm	180 bpm
45	88–123 bpm	123–149 bpm	175 bpm
50	85–119 bpm	119–145 bpm	170 bpm
55	83–116 bpm	116–140 bpm	165 bpm
60	80–112 bpm	112–136 bpm	160 bpm
65	78–109 bpm	109–132 bpm	155 bpm
70	75–105 bpm	105–128 bpm	150 bpm

Cardiovascular Disorders

Overview

Cardiovascular disorders are a major health concern in Western countries, causing more than 740,000 deaths per year in the U.S. They are the leading cause of death, far surpassing cancer. Common causes include hypertension, aneurysms, and atherosclerosis.

Angina

Angina is chest pain resulting from impaired blood flow to the heart, usually due to narrowed coronary arteries. Symptoms include chest pain, tightness, shortness of breath, and a sensation of choking. Angina is often triggered by physical activity, emotional stress, cold weather, or heavy meals. It is usually temporary and relieved by rest or deep breaths.

• Diagnosis: Angiography visualizes blood vessels after filling them with contrast.

• Treatment: Medications to increase blood flow, balloon angioplasty to open blocked areas.

Heart Attack (Myocardial Infarction)

A heart attack occurs when blood flow to an area of the heart stops long enough to cause sudden death of heart tissue (myocardial infarction). This results in permanent damage and impairs the heart's ability to function. Immediate ECG is required for diagnosis and treatment. Many patients have a history of angina.

• Classic symptoms: Intense chest pain, tightness or pressure, shortness of breath, pain radiating down the left arm.

• Women: More likely to experience nausea, jaw pain, and back pain.

Coronary Artery Bypass Graft (CABG)

CABG is a surgical procedure used to treat blocked coronary arteries. Vein grafts are used to bypass the blocked area, restoring blood flow to the heart muscle.

Heart Failure

Heart failure occurs when the heart becomes less efficient at pumping blood, often due to damage to the heart muscle. This leads to fluid congestion, as blood backs up into veins and capillaries, causing increased capillary pressure and leakage of fluid into the interstitial space. Congestive heart failure is characterized by a buildup of interstitial fluid.

• Symptoms: Trouble breathing while lying down, shortness of breath, swollen ankles or legs, swollen neck veins, weight gain in the abdomen due to fluid retention.

• Treatment: Mild exercise, diuretics, vasodilating drugs, drugs to strengthen heart contractions.

Embolism

An embolus is a sudden blockage of a blood vessel caused by material floating in the bloodstream, such as a blood clot that has broken off and traveled to another location. Embolisms are named based on their location (e.g., pulmonary embolism, cerebral embolism, cardiac embolism).

Stroke (Cerebrovascular Accident, CVA)

A stroke is damage to blood vessels in the brain, resulting in interruption of blood supply. It is the brain equivalent of a heart attack and is the most common brain injury. Causes include embolism (blockage) and rupture (bleeding) of cerebral arteries. Immediate medical care is crucial.

Reducing Risk of Cardiovascular Disease

Risk Factors

• Non-modifiable: Sex, race, age, genetics.

• Modifiable: Lifestyle choices such as smoking, diet, salt intake, exercise, blood pressure management, body weight, diabetes control, stress management, and certain medications.

Prevention Strategies

• Do not smoke – smokers have more than twice the risk of heart attack.

• Monitor cholesterol and salt intake.

• Engage in regular moderate exercise (20–30 minutes, 3 times per week).

• Seek treatment for high blood pressure.

• Maintain a healthy weight.

• Control diabetes mellitus.

• Avoid chronic stress.

Summary: Understanding the regulation of the cardiovascular system and recognizing the signs, symptoms, and risk factors of cardiovascular disorders is essential for prevention and management. Lifestyle modifications play a significant role in reducing the risk of heart disease.