The experiment needed to be able to produce results on equal grounds for the arteries and veins, showing how the elastic recoil could be shown after a significant force had been applied, and removed, from the vessels. The method below shows how the experiment was carried out.
Method:
A retort stand and clamp were taken. The clamp was positioned at approximately 60cm from the base of the stand. A hook was then attached to the clamp. The ring of artery or vein, cut to approximately 2-3mm in thickness, was then placed at the end of the hook. To the ring of artery a mass carrier was placed, to which the force was then applied. A ruler was used to measure the distance the vessel had stretched after this force had been applied. The sketch below reiterates this method.
The first experiment that had to be carried out was to test the elasticity of the artery by adding weight. This was done by setting up the apparatus as described above. The length of the artery, before any force had been applied, was then recorded (this involved removing the mass carrier). After this a 10g weight was added to the mass carrier (which weighed 10g, therefore making an addition of 20g of weight). The length of the artery was then measured and recorded. Following this, a 20g mass was added to the mass carrier, making a total of 40g of force being applied to the artery. This was then measure and recorded. From here on, 20g weight were added, each time being measured and recorded, until the amount of force applied on the artery reached 300g.
Once this was completed, the weights had to be removed, again in 20g increments (from 300g to 0g), so that it was finally possible to calculate the elasticity of the artery.
The above method was repeated in exactly the same way for the vein, each time with increments of 20g until the mass carrier held 290g (+ 10g of its own weight equaling 300g) and then removing, giving elastic recoil results.
Safety:
As the experiment was dealing with non-sterilized organic material it was important to clear and clean the work surfaces before and after the experiment was carried out. This minimalised the spread of bacteria found on the blood vessels. It was also important to wash any skin (especially hands) that came into contact with the blood vessels. Lab coats were also worn whilst the experiment was undertaken.
Fair Testing:
For the results to be of the highest accuracy, fair test conditions needed to be implemented. As already stated the same equipment was used for both of the experiments, this included the measurements. All measurements were in millimeters (mm), all being measured with the same ruler, as accurately as possible. Without this accuracy it would create inaccurate results, thus creating percentage errors. Also, when the force was applied to the ring of blood vessel, it was important that the hook used to hang the vessel from the clamp was thick enough so that it would not cut through the vessel (the thinner the less surface area the higher the pressure causing the vessel to sever). Another factor that had to be controlled was the placement of weights on the mass carrier, as if the weights were dropped onto the mass carrier without precision it would cause shock loading, in turn stretching the vessel instead of giving a fair representation of elastic recoil. The only thing that was hard to keep constant, and was not maintained in this experiment was the thickness of the vessels, which was only an approximate. Because of this, there was no replication for the experiments, as each cutting of blood vessel had a different cross-sectional area, causing variation in results.
Calculations for results:
As the results table was rather extensive, it was important to make sure that the calculations for the results were accurate.
Percentage change in length:
The most important calculation used was to find the percentage change in length of the tissue after a mass had been applied, or removed. The equation was as follows:
((new length – original length) ÷ original length) x 100
Overall Elasticity:
This was calculated by subtracting the length after removal of force from the length after application of force.
Table of results:
Arteries:
Veins:
Graphs:
See attached papers.
Conclusions:
As stated earlier on in this paper, due to the thicknesses of the artery and vein not being exactly the same, the results can only depict a trend, as opposed to an exact calculation, this aside, based on the graphs, it is quite clear to see that arteries have more elasticity than veins. When force was applied to the arteries, they stretched a lot more than that of the veins. This is seen by the largest percentage change on application for the arteries, which was 23.68% (9mm difference), compared to the relatively lower 17.14% (6mm difference) for the veins. Looking at the elastic recoil of the vessels, it is also clear to see that both vessels finished with a difference of -3mm. However, because the arteries stretched 3mm more than the veins, it is seen that there is more elastic recoil in the arteries than the veins.
Discussion:
Due to veins having a thinner layer of elastic fibres, smooth muscle and a larger lumen to that of the artery, it is expected that the structure of the vein does not allow it to have high strength and elasticity. Therefore, the thickness in layer of elastic fibres is directly proportional to the outcome of vessel elasticity relative to its size. Also, the thinner muscular walls of the vein are proportional to its strength, as seen by the experiment results. However, the vessel strength is not entirely dependant on the thickness in muscular walls. The arteries however, have a much thicker layer of elastic fibres and smooth muscle, as well as a smaller lumen. This explains why it has much higher elasticity, recoil and strength, all seen by the results in the graphs.
From this experiment, it was noted that it if arteries were to have more elastic fibres, it would increase the amount of elastic recoil, thus enabling the arteries to return to their original size, reducing the risk of elastic damage in their high pressure (80-120 mm Hg) environments. This would not be so important for the veins, which not only have a lower pressure (10 mm Hg) environment, but valves along the vessels, which in turn reduce the risk of elastic damage.
