Background to the study, aims, and hypotheses

Homeostatic imbalance of the blood pressure results in pathological conditions such as hypertension. It is characterized by rapid, irregular heart rates and periodically elevated blood pressure with diastolic pressure above 90 mmHg and an equally raised systolic pressure above 140mmHg (Amitrano & Tortora 2006). According to Battegay, Lip & Bakris (2005) in about ninety percent of the patients, the causes of hypertension are not known (primary/benign hypertension). The remaining ten percent of the cases (secondary hypertension) are known to be caused by other underlying conditions such as renal disease, Cushing’s syndrome, Conn’s syndrome, atherosclerosis, pregnancy, estrogen therapy and oral contraceptives (Battlegay, Lip & Bakris 2005). Patients with primary hypertension are considered to be exaggerated responses to some physiological stimuli like cold or excitement. The main cause of sustained increase in blood pressure is attributed to peripheral resistance i.e. the resistance to blood flow offered by the gradual decrease in the diameter of the blood vessels. The peripheral resistance is profoundly affected by hormone-mediated changes in blood vessels such as vasodilatation and vasoconstriction. An increased dietary intake of salts will favor water retention in the blood and raises blood volume causing hypertension (Harrison et al. 2011).

Harrison et al. (2011) explains the effects of hypertension on the body; it causes damage to the heart, kidneys and brain. High blood pressure increases the workload of heart and consequently the heart becomes enlarged and the muscles are thickened. This causes angina pectoris (chest pain) and myocardial infarction (heart attack). High blood pressure may weaken the cerebral arteries supplying the brain producing aneurysm which may finally rupture causing cerebral hemorrhage which results in stroke (Moser & Riegel 2009). According to Pickering et al. (2005) continued high blood pressure may cause thickening of the arterioles of the kidneys, thus, narrowing the lumen; the blood supply to the kidneys is, therefore, reduced. In response to this, the kidneys produce renin, a hormone for accelerating the blood flow. This further raises the blood pressure and compounds hypertension-related reduced blood supply to the kidneys. This may result to kidney failure due to death of cells.

Aims:

Experiment 1: the aim of the first experiment was to investigate if there are any diurnal changes of the heart rate.

Experiment 2: it aimed at investigating the effects of change of posture on the heart rate.

Experiment 3: it aimed at investigating the thermoregulation of heart rate i.e. how it changes on exposure to heat and cold

Hypotheses:

Experiment 1: that there will be diurnal variation of the rates of heart beat; the evening heart rates will be higher than the morning heart rates.

Experiment 2: that there will be an increase in the heart rate when in the upright position as compared to when in the supine or prone position.

Experiment 3: that there will be an increase in the heart rate when the feet and legs are placed in warm water (heat) and lowering of the heart rate when the feet and legs are exposed to cold water (cold).

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