Systole in the context of Orthostatic hypotension

The atrium (Latin: ātrium, lit. 'entry hall'; pl.: atria) is one of the two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular mitral and tricuspid heart valves.

There are two atria in the human heart – the left atrium receives blood from the pulmonary circulation, and the right atrium receives blood from the venae cavae of the systemic circulation. During the cardiac cycle, the atria receive blood while relaxed in diastole, then contract in systole to move blood to the ventricles. Each atrium is roughly cube-shaped except for an ear-shaped projection called an atrial appendage, previously known as an auricle. All animals with a closed circulatory system have at least one atrium.

The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. After emptying, the heart relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting.

Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 second to complete the cycle. Duration of the cardiac cycle is inversely proportional to the heart rate.

Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is indicated by two numbers, the systolic blood pressure (the top number) and the diastolic blood pressure (the bottom number), which are the maximum and minimum blood pressures within the cardiac cycle, respectively. A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension. Different numbers apply to children. However, in practice, blood pressure is considered too low only if noticeable symptoms are present.

Symptoms may include dizziness, lightheadedness, confusion, feeling tired, weakness, headache, blurred vision, nausea, neck or back pain, an irregular heartbeat or feeling that the heart is skipping beats or fluttering, and fainting. Hypotension is the opposite of hypertension, which is high blood pressure. It is best understood as a physiological state rather than a disease. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock. Shock is classified based on the underlying cause, including hypovolemic shock, cardiogenic shock, distributive shock, and obstructive shock.

Calcium channel blockers (CCB), calcium channel antagonists or calcium antagonists are a group of medications that disrupt the movement of calcium (Ca) through calcium channels. Calcium channel blockers are used as antihypertensive drugs, i.e., as medications to decrease blood pressure in patients with hypertension. CCBs are particularly effective against large vessel stiffness, one of the common causes of elevated systolic blood pressure in elderly patients. Calcium channel blockers are also frequently used to alter heart rate (especially from atrial fibrillation), to prevent peripheral and cerebral vasospasm, and to reduce chest pain caused by angina pectoris.

N-type, L-type, and T-type voltage-dependent calcium channels are present in the zona glomerulosa of the human adrenal gland, and CCBs can directly influence the biosynthesis of aldosterone in adrenocortical cells, with consequent impact on the clinical treatment of hypertension with these agents.

Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Healthy pulse pressure is around 40 mmHg. A pulse pressure that is consistently 60 mmHg or greater is likely to be associated with disease, and a pulse pressure of 50 mmHg or more increases the risk of cardiovascular disease. Pulse pressure is considered low if it is less than 25% of the systolic. (For example, if the systolic pressure is 120 mmHg, then the pulse pressure would be considered low if it were less than 30 mmHg, since 30 is 25% of 120.) A very low pulse pressure can be a symptom of disorders such as congestive heart failure.

Cardiac rhythmicity is the spontaneous depolarization and repolarization event that occurs in a repetitive and stable manner within the cardiac muscle. Rhythmicity is often abnormal or lost in cases of cardiac dysfunction or cardiac failure. It is the ability of the heart to maintain a relatively stable relation between its systole and diastole. Not increasing one on the expense of the other. However, external factors may lead to the disruption of the heart's rhythmicity.

The mitral valve (/ˈmaɪtrəl/ MY-trəl), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-way valves allowing blood flow in just one direction. The mitral valve and the tricuspid valve are known as the atrioventricular valves because they lie between the atria and the ventricles.

In normal conditions, blood flows through an open mitral valve during diastole with contraction of the left atrium, and the mitral valve closes during systole with contraction of the left ventricle. The valve opens and closes because of pressure differences, opening when there is greater pressure in the left atrium than ventricle and closing when there is greater pressure in the left ventricle than atrium.

The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ventricle during diastole, and to close to prevent backflow (regurgitation) from the right ventricle into the right atrium during right ventricular contraction (systole).

Diastole (/daɪˈæstəli/ dy-AST-ə-lee) is the relaxed phase of the cardiac cycle when the chambers of the heart are refilling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricular diastole the relaxing of the ventricles.

The term originates from the Greek word διαστολή (diastolē), meaning "dilation", from διά (diá, "apart") + στέλλειν (stéllein, "to send").