Cardiovascular physiology involves the study of the circulatory system. It addresses more specifically the physiology of the heart and blood vessels hence the name cardio and vascular. Rabbits are generally nervous and non-aggressive and sociable with each other. In this laboratory, the primary experimental variables were the heart rate and arterial blood pressure. The main goal of this laboratory was to investigate the effects of different hormones on the rabbit’s blood pressure and heart rate by means of intravenous injections, nerve stimulation and respiratory alterations. We hypothesized that the catecholamines would increase the heart rate and blood pressure while the chilonergic drugs would have a decreasing effect on the heart rate and the blood pressure. We also hypothesized that nerve stimulation would have a decreasing effect on heart rate and blood pressure. We predicted that epinephrine would result into an increase in heart rate, systolic and diastolic pressure. We also predicted that the stimulation of the vagus nerve would have the same response on both the left and right sides and that increasing the dead air space would increase the respiration rate, which would increase the heart rate and the blood pressure.
The arterial blood pressure is exerted by the blood on the walls of the carotid artery and depends on the cardiac output; this is why it is important to the heart rate, stroke volume and blood volume. Arteriolar vasoconstriction is the limit to which the blood pressure is altered. Hormonal regulation is important to the blood flow and the blood pressure of the artery.
We measured systolic pressure and diastolic pressure. The cardiovascular system has some anatomical structural aspects for example the tricuspid valve of the heart which has only 2 cusps. The rabbit’s heart also has a small group of peacemakers. A rabbit’s heart has been used in the recent past for a series of lab experiments because of its structure. The test conducted was to establish how a rabbit’s heart functions, the similarities between a rabbit’s heart and that of a human being. It is expected that the rabbit’s heart pumps faster than a human being’s heart and these were some of the things that were to be established. Some of the things that we wanted to find out about the rabbit’s heart included; the effects of decreasing blood pressure in the carotid sinus, how a rabbit compensates for an increase in blood volume and effects of epinephrine, acetylcholine, nerepinephrine serine and atropine in the cardiovascular system. We also wanted to find out how the cardiovacularsystem is affected when the vagus nerve is stimulated and the effects of severing the vagus nerves. The arterial blood which was measured in the lab was the pressure exerted by blodd on the walls of the carotid artery. The rate of the heart beat is primarily determined by the balance between the sympathetic and parasympathetic output of the heart. The release of the acetylcholine from the parasympathetic fibers slows down the hear rate. The sympathetic and parasympathetic outflow to the heart can be affected by general levels of excitement and activity, input from the baroreceptors and chemoreceptors. On the other hand, an increase in sympathetic outflow of circulating epinephrine increased the contractility of the heart which resulted to an increase in stroke volume which also increased arterial blood pressure. We carried out a surgery to determine the effects of different hormones on heart rate and the arterial blood pressure.
1. We set up the computer and the transducer and started the BSL software. We then opened the mammaliansurgery.gtl so as to change the settings of the force transducer, blood pressure and the heart rate. We also changed the output settings so that they could be visible at the top of the screen.
2. We then connected and calibrated the blood pressure transducer after which we prepared the consumables and cannulae.
3. We prepared the animal by ensuring that it was in good health and then anesthetized it with a 4 ml intramuscular injection of anesthetic.
4. We shaved the rabbit with the clippers through the entire neck region and then we started the dissection
5. We were able to identify the jugular veins and cleaned the connective tissue and fascia from the vein surface
6. We isolated the arteries by placing a ligature under each of the arteries and then identified the left and right vagus nerves
7. We set the second ligature under the right jugular vein. We used a fine scissors to nick the jugular vein below the high ligature. We then inserted a cannula into the hole cannulating toward the heart.
8. We started a flow of saline into the rabbit. We then flushed arterial blood from the cannula with Heparin –Saline from the pressure transducer setup
9. We recorded the arterial blood pressure on LabScribe and computed the following parameters from the blood pressure record.
Mammals have baroreceptors which respond to the pressure in the carotid artery by stretching in the carotid artery wall. The baroreceptors have an afferent nerve tract which runs through the glossopharyngeal nerve to the brain. By reducing carotid sinus pressure the heart rate will decrease.
Blood Volume Expansion - By increasing the rate of saline infusion, it is possible to transiently increase blood volume. An increase in saline infusion rate resulted into a reduction on arterial blood pressure.
Increased infusion rate – we opened the infusion line and realized that the blood pressure also increased.
Effects of Epinephrine – the epinephrine had the largest effect on increasing the heart rate. It actually increased the heart rate to 285 bits per minute.
Effects of Acetylcholine – the acetylcholine had the greatest effect on decreasing the heart rate at 184 bits per minute.
Effects of Norepinephrine – we realized that the norepinephrine also resulted into a corresponding increase in blood pressure and hear rate. Norepinephrine is sometimes used as a stress prevention hormone.
Vagal stimulation – we realized that the Vagal stimulation resulted into a decrease in hear rate and blood pressure.
Effects of Cholinergic Agent – we realized that the Norepinephrine increased heart rate, blood pressure and ventilatory rate.
Respiratory Effects - When we forced the rabbit to breath through a long tube, blood carbon dioxide levels rise and oxygen levels fall (the effect is similar to when you hold your breath).
This resulted into a corresponding increase in the heart rate immediately the rabbit was let to breathe freely.
Vagotomy – we realized that sectioning each vagus nerve resulted into an increase on heart rate and blood pressure. When we stimulated the caudal (toward the heart) section of each vagus nerve, heart rate and blood pressure also increased significantly.
From the results obtained above, we concluded that epinephrine was the hormone to have the largest effect on increasing the heart rate at 285 bpm. This is because the epinephrine acts upon adrenergic receptors which contain the alpha and beta receptors. There are two beta receptors which are used for stimulating and inhibiting smooth muscle contraction especially in the heart and in the lungs. Since the heart contractions are stimulated with the beta receptors, blood pressure will therefore increase through the epinephrine stimulation.
We also realized that the acetylcholine had the largest effect on decreasing the heart rate at 184 bpm. We also observed that stimulating the left vagus nerve decreased blood pressure and heart rate more than stimulating the right. The nerve stimulation also had a decreasing effect on the heart rate and the blood pressure.
The results obtained from the above experiment may not be very accurate. The inaccuracy can be caused by but not limited to the following reasons: during Jugular Vein Isolation, we tied off the jugular veins before the carotid arteries and vagus nerves had been isolated which led to inaccurate results. During Carotid Artery Isolation we were not very careful not to injure the vagus nerve. When we were Cannulate the right Jugular Vein there were leaks, (saline filling the body cavity) which must have also resulted into inaccurate results.
From the results we confirmed that the catecholamines would increase the heart rate and blood pressure, while the cholinergic drugs would have decreasing effects on the heart rate and blood pressure. We also confirmed that nerve stimulation had a decreasing effect on the heart rate and the blood pressure.
Work cited list
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Fedriani, J.M., Palomares, F., M. Delibes. Niche relations among three sympatric Mediterranean carnivores. Oecologia 121: 138-148 1999
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Susan E. Davis and Margo DeMello, Stories Rabbits Tell: A Natural And Cultural History of A Misunderstood Creature. Lantern Books, 2003, p.27