II MBBS CBC

1. Introduction 2021
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Demonstrate the effects of drugs on blood pressure
S. No Competency Name of Competency Level Suggested
teaching method
1 PH 4.2 Demonstrate the effects of drugs on blood pressure
(vasopressor and vaso-depressors with appropriate
blockers) using computer aided learning
SH Skill Lab- EP Lab
Learning Objectives
At the end of the learning session, the students should be able to:
1. Demonstrate the effects of various drugs on different haemodynamic parameters in a pithed rat
computer simulation.
2. Understand the underlying mechanism of action of these drugs.
3. Compare drugs belonging to either the same or different pharmacological groups.
Introduction
The aim of these practical classes is to provide an opportunity to observe the effects of various drugs on the
cardiovascular system.
In order to reduce to a minimum the number of animals used in teaching, a computer simulation [Computer
assisted learning (CAL)] of this experiment will be used. This programme can simulate the effects of drugs on
arterial and central venous blood pressures, heart rate and force of contraction of the ventricles. The
anaesthetised rat (or alternatively the pithed rat) is a standard preparation to determine the actions of drugs on
the cardiovascular system in pharmacological research. (Download: https://doctoru.weebly.com/)
Drugs, administered intravenously, can be studied over a wide concentration range. Measurements of systolic
and diastolic arterial blood pressure (mmHg), force of contraction, central venous pressure (mmHg) and heart
rate (beats min-1
), are shown. The trace below gives an example of what you will see on your computer
screen.
During the CAL practical classes students will be required to measure the appropriate haemodynamic
variables (using the measurement cursor) and enter the results in the table to allow them to reach a final
conclusion.

2. Introduction 2021
2 CVSSimulationforPHASEIIMBBS PHARMACOLOGYSTUDENTS (https://doctoru.weebly.com/)
ABP = Arterial blood pressure
LVP = Left ventricular pressure
VBP = Venous blood pressure
Con = Force of contraction of heart
HR = Heart rate

3. Introduction 2021
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4. Introduction 2021
4 CVSSimulationforPHASEIIMBBS PHARMACOLOGYSTUDENTS (https://doctoru.weebly.com/)
The pithed rat
This kind of experiment would be performed using a rat which has been anaesthetised prior to destruction of
the brain and spinal cord (pithed). Despite the loss of the central nervous system, by placing the animal on a
respirator, the heart will continue to beat. The lack of CNS means that any drug effects observed will not be
complicated by baroreceptor reflex-induced changes.
In a pithed rat, the blood pressure is highly dependent upon the amount of the vasoconstrictor angiotensin-II
(A-II) circulating in the plasma. Angiotensin-I( A-I) is converted to active A-II by angiotensin converting enzyme
(ACE). A-I in turn, is generated from angiotensinogen by the action of renin, which is released from the kidney.
1. Catheter into a main artery, heart rate and arterial blood pressure can be measured directly. 2. Catheter
inserted into the lumen of the left ventricle allows indirect measurement of the force of contraction of the
heart. A catheter in a vein allows both measurement of central venous pressure and administration of drugs.
REFERENCE
Dempster J. Strathclyde Pharmacology Simulations Software. 2021. University of Strathclyde.