Pharmacology of Drugs Acting on Cardio Vascular System / Cardio Vascular System notes / Pharmacology Notes PDF / KDT Notes / Short Notes

 

 Pharmacology of Drugs Acting on Cardio Vascular System.........

INDEX .. 

 Introduction to hemodynamic and electrophysiology of heart.

 Drugs used in congestive heart failure

 Anti-hypertensive drugs.

 Anti-anginal drugs.

 Anti-arrhythmic drugs.

 Anti-hyperlipidemic drugs

CARDIOVASCULAR SYSTEM 

 Introduction

Cardiovascular system comprises of the heart and an extensively branched

structure of blood vessels that transports oxygen, nutrients , heat, and other

substances throughout the body.

Cardiac or heart muscles are involuntary striated muscles found in the heart and

its walls, especially in the myocardium (the muscle tissue forming a thick

middle layer amid the outer epicardium and the inner endocardium ). For

delivering oxygen and nutr ients, and removing waste products such as carbon

dioxide, the cardiac muscle cells depend on the available blood and e lectrical

supply.

The myocardial tissue is made up of contracting cells and conducting cells .

The pumping action of the heart involves the contracting cells. The

conducting tissues of the heart include SA node (acts as the pacemaker), AV

node, and His -Purkinje system. Various parts of the conducting tissue exhibit

automaticity. Cardiac muscles being specialised tissues have distinct

properties of:

1) Excitability: It is the ability of cardiac cells to depolarise in response to a

stimulus.

2) Contractility: It is the ability of myocardium to contract and pump blood out

of the heart.

3) Automaticity: It is the ability of cardiac cells to generate electrical impulses

spontaneously.

1.1.2. Hemodynamics

The study of the dynamic behaviour of blood is termed hemodynamics.

Pressures are generated in the various parts of heart (cardiovascular pressures)

when blood flows from one chamber to another, when valves open and close, and

when the myocardium contracts and relaxes. Catheters are used to measure and

monitor these pressures by placing their tips in the atria, pulmonary artery , or

systemic arteries; these are called the hemodynamic lines.

Hemodynamic lines have multiple uses:

1) They allow the sampling of venous and arterial blood without having to stick

a patient frequently.

2) They help in monitoring different waveforms, thus providing evidences to

patient’s status.

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Pharmacology of Drugs

Acting on CVS

3) The cardiac output can be calculated with the combination of pulmonary,

arterial, and systemic arterial lines.

4) They allow direct monitoring of various cardiac pressures, and a nalysis of

these pressures helps in planning and assessing therapy in shock, cardiac

failure, fluid overload or deficit, and other conditions.

1.1.3. Electrophysiology of Heart

The cardiac cell is a polarised membrane . It has a resting membrane potential of

–80 to –90mV, and a high Na+ ion concentration outside the membrane and K +

ion concentration inside the membrane. Upon excitation, depolarisation occurs as

the cell membrane permeability to Na + ions increases, the negativity of resting

potential is lost, and a positive current is gen erated inside the cell. The

characteristics of action potential rely on the type of the cell -myocardial

contractile cell, or pacemaker, or potential pacemaker cell. There are five phases

of the action potential of cardiac cells (figure 1.1):

1) Phase 0: In t his phase, rapid

depolarisation of the cell membrane

is observed as the sodium ions

rapidly enter the cell through sodium

channels. This phase is followed by

re-polarisation.

2) Phase 1: In this short and initial phase, rapid re-polarisation is observed as the potassium ions move out of the cell.

3) Phase 2: This prolonged plateau phase is observed as the calcium ions enter the cell slowly through the calcium channels . This phase of action potential is present only in the

cardiac cells.

4) Phase 3: This phase is th e second period of rapid re -polarisation as the potassium ions move out of the cell.

5) Phase 4: This is the resting phase as the resting membrane potential is re - established when the potassium ions return into the cell and sodium and calcium ions move out of it.

The cell s do not depolarise in response to another impulse during the phases 1

and 2; and this is called the absolute refractory period. The cells depolarise in

response to a powerful impulse d uring the phases 3 and 4 ; and this is called the

relative refractory period.

The heart rate and stroke volume are used for determining the cardiac output. The

stroke volume depends on the preload (which itself depends on venous return) ,

afterload, and contractility. The load on the heart due to the blood volume

reaching the left ventricle is called preload; while the resistance to the left

ventricular ejection, i.e., the total peripheral resistance is called afterload.