BLOOD PRESSURE CHANGES DURING THE MENSTRUAL CYCLE
The blood pressures of one hundred and twenty girls were measured during the four different phases of the menstrual cycle. The subjects whose ages range from seventeen to twenty five years (17 – 25 yrs), and a single subject of thirty six years (36yrs), were randomly selected from among students of the University of Port Harcourt. Records were made of the subjects’ height (m), weight (kg) age at menarche (years), length of cycle (days), and length of menstruation (days). The mean arterial blood pressures was found to vary in the different phases of the menstrual cycle, being highest at phase 2, followed by phase 3 then 4, and lowest at phase 1 (menstruation). It was also observed that subjects on oral contraceptive had a lower mean arterial pressure per phase of cycle than subjects not on oral contraceptive. A positive correlation was also found to exist between the weight of the subjects and their diastolic blood pressures in respect of phase 1 and 2 (P<0.05). diurnal rhythm was not observed in the blood pressure values in any of the phases of the cycle. There was also no relationship between the parity, and gravidity of the subject, and the phase of the menstrual cycle.
TABLE OF CONTENTS
Title Page – – – – – – – – – – i
Declaration – – – – – – – – – ii
Dedication – – – – – – – – – iii
Acknowledgement – – – – – – – – iv
Abstract – – – – – – – – – – v
Table of Contents – – – – – – – – vi
List of Abbreviations – – – – – – – – vii
Chapter One Introduction
Chapter Two Materials
Chapter Three Results
Chapter Four Discussion
LIST OF ABBREVIATIONS
Phase 1 Menstruation
Phase 2 Follicular (Pre-ovulatory) Phase
Phase 3 Luteal Phase
Phase 4 Pre-menstrual Phase
BP Arterial Blood Pressure
SBP Systolic Blood Pressure
DBP Diastolic Blood Pressure
MAP 1 Mean Arterial Pressure in Phase 1 of Menstrual Cycle.
MAP 2 Mean Arterial Pressures in Phase 2 of Menstrual Cycle.
MAP 3 Mean Arterial Pressure in Phase 3 of Menstrual Cycle.
MAP 4 Mean Arterial Pressure in Phase 4 of Menstrual Cycle.
M Subject on Medication
A Subject takes Alcohol
C Subject Smokes Cigarettes
INTRODUCTION AND LITERATURE REVIEW
Blood is a highly complex fluid, in which solid elements are suspended; these are the corpuscles or blood cells. It has a specific gravity of 1.050, and its viscosity is three times that of water. The fluid portion of blood is called the plasma, which contain proteins, organic and inorganic substances in solution, nutritive and excretory materials, antibodies and hormones. Plasma has a specific gravity of approximately 1.027, but this varies with the protein concentration. The corpuscles constitute 46% of the volume of human blood, and the plasma 54%. The blood serves respiratory, nutritive, excretory and maintenance functions. Its other functions include regulatory and protective functions. The constituents of blood include;
- Cells: Erythrocytes, leucocytes and thrombocytes
- Plasma: Water, proteins, electrocutes, non-protein nitrogenous substances, antibodies and enzymes.
About three quarters of all the blood volume in the circulatory system is in the veins. When a person bleeds severely, the veins can constrict causing adequate amount of blood still to fill the other vessels of the body. Therefore the veins act as a conduit for return of blood from the peripheral tissues, and also as a blood reservoir of the body. The total blood flow through the entire systemic circulation is called the cardiac output, and is about five liters per minute (5L/min). Under certain conditions, this can , increase to as much as twenty five to thirty fiver liters per minute, (25 – 35 L/min), during the most extreme exercise in athlete or it can decrease following severe hemorrhage to as low as one point five liters per minute (1.5L/min); without causing immediate death.
BLOOD PRESSURE: The term “Blood Pressure” unless otherwise indicated means arterial blood pressure. During the contraction of the left ventricle, the pressure exerted upon the blood it contains is greater than the blood in the aorta; hence the blood flows from the heart into the aorta. All the systemic arteries are kept in a condition of tension, and this tension is produced by the elastic walls of the vessels being put on the stretch by the blood which has been forced into them by the heart, and forces the blood out of the larger arteries into arterioles and from these through the capillaries into the veins. The force that the blood exerts against the walls of the vessel, at any point is termed the BLOOD PRESSURE. The importance of blood pressure then, is that it is the force that makes the blood flow through the circulation.
- Pumping action of the heart
- Peripheral resistance in the blood vessels especially the arterioles.
Other factors combining to maintain the normal arterial pressure include the:
iii. Quantity of blood in the arterial system
- Viscosity of blood
- Elasticity and thus dispensability of the arterial walls.
Normal blood pressure according to the World Health Organization (WHO), is said to be 110/70mmHg they also found it to vary with age, sex and build. The period during the cardiac cycle when the ventricles are contracting is called SYSTOLE, and the period of relaxation is called DIASTOLE. It is quite important to distinguish between systole and diastole.
At birth, the systole pressure measures from 20 – 60 mmHg, (twenty to sixty millimeter mercury). It rises rapidly for a month. From a slow steady rise occurs, until about the twelfth year. With the onset of puberty, a more sudden rise occurs. In girls, there is an increase in systolic pressure, up to the fifteenth year, then a decline to the eighteenth, it remains steady from then, or shows a gradual rise. In women, up to the time of menopause, the systolic pressure is lower than for males of the same age, by about 4 – 5 mm.
Van der Brouke and Haar (1982) claim that body build is correlated with blood pressure level, they found in a survey that in sny weight group, broad chested persons on the average had a higher systolic and diastolic blood pressure than those of slender build.
The systolic pressure is influenced to a small but definite extent by meals. This lasts for about an hour only. There is little change in diastolic pressure presumably as a result of vasodilatation in the digestive organs and skin.
Emotional influences such as fear, fright, worry, markedly affect the arterial blood pressure, especially the systolic due to an increased cadiac action and changes in the state of the vessels.
Quiet restful sleep, according to Adams and Victor (1985) is accompanied by a fall of 15 – 30 mmHg in the systolic pressure. They observed that if the sleep was disturbed and accompanied by imaginary motor activities there might not be a depression of pressure, but rather an elevation to as high as 200/105 mmHg in some cases.
Strenuous exercise has a most powerful effect on arterial blood pressure. During muscular effort or immediately preceding it, the pressure commences to rise, and reaches a heigh of 180 or 200 mmHg. The diastolic pressure shows a less pronounced rise, so that the pulse pressure is increased. This work was documented by Van der Brouke and Haar (1982).
The diastolic pressure is somewhat higher in the standing than in the sitting position, and lowest at recumbence. This change occurs whether the postural change is brought about activity or passively and is evidently an over-compensation for the effect of gravity. Systolic pressure rises to a lesser extent than the diastolic.
Blood pressure may be persistently below or above the normal range. These departures from normal are termed “hypotension” and “hypertension”, respectively, by the layman. It is difficult to separate the normal from the abnormal, but the WHO considers pressures above 160/95 mmHg to be definitely hypertensive, for that individual. Hypertension functions by preventing normal excretion of salt and water. It may also be due to excess sympathetic activity, excess hormone secretion by the adrenal cortex, and excess secretion of renin by the kidneys. About 95% of patients however, have hypertension of unknown origin called essential hypertension (Guyton, 1984).
MENSTRUAL CYCLE: The reproductive system of the female shows regular cyclic changes that teleological may be regarded as periodic preparation for possible fertilization and pregnancy. In the adult human female, the cycle is a menstrual cycle, and its most conspicuous feature is the periodic vaginal bleeding that occurs with the shedding of the uterine mucosa called menstruation. The length of a normal cycle is notoriously invariable in women, but an average figure is twenty eight days from the start of one menstrual period to the start of the next.
During the reparative and resting stages – FOLLICULAR PHASE (10 days), a Graaafian follicle is in the process of developing and reaches maturity fourteen to fifteen days after the beginning of the last menstrual period. The ovum is now shed on the fourteenth day, a process called OVULATION, and at this stage the glands in the uterine mucosa enlarge and secrete mucus; concurrently, the formation and development of the corpus luteum is proceeding LUTEAL PHASE. Gradually, the underlying layers lining the uterus becomes suffused with blood stained lymph and fourteen days following ovulation there is a breakdown of superficial epithelium, blood and mucus then escapes from the uterine cavity, and constitutes the menstrual flow-MENSTRUATION which lasts on average for five days, signifies the beginning of a new cycle. If the ovum is not fertilized, the corpus luteum atrophies, another Graafian follicle ripens and the cycle is repeated.
Although this relationship holds true, it must be noted that menstruation may occur in the absence of ovulation. In ovulatory cycles, in which ovulation fails to occur during the menstrual cycle, no corpus luteum is formed, and the progesterone effects on the endometrium are absent.
Of marked importance in the regulation of the menstrual cycle are hormones from the anterior pituitary called anterior pituitary gonadotropins, these are the Follicle Stimulating Hormone (FSH), and Luteinizing Hormone (LH). Also involved are two ovarian hormones, estrogen and progesterone.
In ovulatory cycles, estrogens continue to cause growth, however, and the proliferative endometrium becomes thick enough to slough. The time for bleeding to occur is variable, but usually occurs in less than twenty eight days from the last menstrual period. The flow also ranges from scanty to profuse. Such cycles are common for the first twelve to eighteen month after menarche, and again before the onset of menopause.
Estrogens cause an increased secretion of angiotensinogen, the precursor of angiotensin II. Angiotensin II previously called hypertension produces arteriolar constriction and a rise in systolic and diastolic pressure. Another action of angiotensin II is facilitation of the release of non-epinephrine by a direct action on post ganglionic sympathetic neurons (Hill, 1970).
Adams and Victor 1986, wrote that during a normal menstrual cycle, the use of hormones to prevent pregnancy has increased the severity and frequency of migraine, and in a number of the cases studied, resulted in an elevated blood pressure. In the same year, they stated that as to the biochemical and physiologic changes occurring during lassitude and fatigue, including an increase in the rate of breathing, quickening of the pulse, increase in blood pressure, widening of the pulse pressure, increase in white blood cell count and basal metabolic rate.
Wood in 1967 suspected that hypertension may be aggravated in some cases of women on oral contraceptives, and postulates a change in the renin-angiotensin-aldosterone system. Estrogen caused retention of salt and water, or an effect on the vascular smooth muscle as possible causes. He reported six cases showing a rise in blood pressure on “orthonovum”, and a fall when this was withdrawn. In more recent years, this relationship between oral contraceptives and the incidence of hypertension has been well proven clinically.
From the foregoing, it could be said that much has already been done on blood pressure changes in differing physiological states. However, the variation in blood pressure during the menstrual cycle has yet enjoyed little attention. It is the aim of this work, therefore, to provide a comprehensive analysis of blood pressure changes in the menstrual cycle for a sub population of females in the University of Port Harcourt, NIGERIA.
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