Arterioles have an essential role in regulating blood flow into capillaries by regulating the resistance; the mechanism used for opposing blood flow. Resistance is achieved by friction between the blood and the walls of the blood vessel. When relaxation of the smooth muscle occurs, the diameter of the blood vessel is greater and resistance is reduced as friction has also been reduced. This is known as vasodilation. In contrast when contraction of the smooth muscle occurs, the diameter of the blood vessel has been reduced and there is an increase in both friction and resistance. This is known as vasoconstriction. During exercise there is a high demand for oxygen therefore as a result blood flow needs to be increased and resistance decreased. The relaxation of the smooth muscle in the local arterioles allows this happens. The process of vasodilation also causes a reduction in the Total Peripheral Resistance (TPR) which further caused a reduction in blood pressure.
Blood pressure (BP) is the force that drives the blood around the body. The greater the pressure exerted means that the flow of blood will also be greater. When the TPR causes a reduction in blood pressure, pressure sensitive receptors known as baroreceptors detect the change and set in motion a series of events to increase it. These receptors can be found in the walls of the aortic arch and internal carotid arteries. They send impulses to the cardiovascular system in the medulla of the brain to assist in the regulation of blood pressure. The two reflexes that are important in the regulation of blood flow are the carotid sinus reflex and the aortic reflex.
The carotid sinus reflex is initiated by baroreceptors in the walls of carotid sinuses which are located in the arteries of the neck. This reflex assists in regulating blood pressure around the brain. Nerve impulses are then projected from the carotid sinus baroreceptors to the cardiovascular centre in the medulla oblongata in the brain. The aortic reflex is initiated by baroreceptors in the aortic arch which regulates systemic blood pressure. Nerve impulses are projected to the cardiovascular centre by sensory neurons.
The cardiovascular centre then works to increase blood flow and pressure by increasing heart rate and the force of the hearts contractions by the means on the sympathetic innervation of the heart.
An additional effect of physical activity is an increased amount of venous return to the heart which further increases the force of the hearts contractions. During isotonic exercise an increased affect on systolic blood pressure occurs whilst diastolic blood pressure remains relatively normal due to the fact TPR has been reduced. Systolic blood pressure is the force exerted on the artery walls during ventricular contraction and is normally 120mmHg in an adult. It is the highest pressure found in artery walls whilst diastolic blood pressure is the lowest. Diastolic blood pressure occurs during ventricular relaxation and is normally about 80mmHg in an adult.
The aim of this practical is to investigate the effect upon which isotonic exercise has on heart rate and blood pressure.
Method
Within this practical ECG recordings will be used to determine the heart rate of the subject and an electronic sphygmomanometer to establish the blood pressure readings. The three levels of exercise that will be performed are 40, 80 and 120 Watts.
Before getting started on the bike the subject needs to secure the ECG electrodes in the correct positioning on the body. The electrodes should be placed in the lead II arrangement.
When the subject is ready they should get positioned on the bicycle and acclimatise until their heart rate and blood pressure return to baseline levels. The subject then should start exercising on the bicycle for 5 minutes at each workload. Heart rate and blood pressure should be recorded at rest and at each workload, moving to a higher workload as soon as the time is up and each set of data has been recorded.
At the end of the highest workload the subject should be allowed to rest and recordings of the heart rate and blood pressure should be taken until they reach baseline levels.
Results
The results obtained from this practical were as follows:
Table 1: Heart Rate and Blood Pressure at varying workloads
Figure 1: Graph showing the effect of recovery heart rate against time
Figure 2: Graph showing log heart against time
Discussion
From the results obtained from this practical it is clear to distinguish that the effect upon which exercise has on the heart rate and blood pressure is increased as the workload increases and exercise is continued for a longer time.
Although a psychological effect should occur before the onset of exercise, as a means for the body to prepare itself for the physical activity ahead, the heart rates recorded for both rest and anticipation didn’t show any variance for either subject but remained at similar rates. This could have been due to the fact the subjects were already aware of the exercise they would be undertaking beforehand therefore there wasn’t really much anticipation being felt.
As the weight load increases there is a significant difference in the increase from each level for both heart rate and blood pressure. The rate in which the heart rate and blood pressure begin to increase gives an indication on how fit the subject is and how fast their body is able in coping with exercise and adjusting itself each time as a heavier workload was placed on the machine. The increase venous return to the heart causes the force of the hearts contraction to increase immensely which then gives rise to the systolic blood pressure. Within the practical by the time the heaviest load of the weights was applied each of the subjects systolic readings were ranged between 160-200+.
During the recovery phase the heart rates for each subject still remained high and had not reached back to baseline levels within the time given. This indicates a lack of fitness within the subjects as their bodies needed a longer recovery time in which to restore their heart rate and blood pressure back to normal. Professional athletes are able to recover much quicker and restore their heart rate and blood pressure back to normal as their bodies and hearts are adapted to demanding physical exercise. They don’t have as high heart rates because their hearts have been adapted to coping with regular vigorous exercise. This is due to the fact their hearts are able to exert a greater amount of blood within just one heartbeat than a person who does little exercise can. Therefore their heart rates don’t need to be as high in order to deliver the body the essentials nutrients it requires.
In contrast the heart rates of the subject remained comparatively high which suggests they needed a much longer recovery time in order from them to return back to baseline levels.