Starting with A for "ACE inhibitor" and continuing through to Y for "Yolk Sac Tumour", we give you succinct explanations for scientific and medical terms in clear and simple words.
- Blood pressurePressure in the blood vessels and heart chambers. Strictly speaking, blood pressure is the arterial blood pressure measured in or on a peripheral artery in mm Hg (mm mercury) or kPa (Kilopascal, 1 mm Hg = 133.322 Pa) and which causes blood circulation. Blood pressure depends on the power of the heart and the resistance of the blood vessels and is subject to blood pressure regulation.
Systolic blood pressure
Blood pressure when the heart muscle contracts and develops tension. The heart systole is the highest point of the pressure curve during direct measurement of blood pressure.
Diastolic blood pressure
Blood pressure during relaxation and reduction in tension of cardiac muscle. The heart diastole is the lowest point in the pressure curve.
Blood pressure is given in the sequence systolic /diastolic blood pressure. Blood pressure is very different in different sections of the circulation. The pulsed fluctuations in pressure which are produced by the left heart ventricle (ca. 16/1.6 kPa or 120/12 mm Hg) are damped by the elastic so-called windkessel function of the aorta (ca. 16/10.7 kPa or 120/80 mm Hg). In the peripheral arteries, the amplitude of the pulses is large, as the systolic pressure rises as a result of wave reflection. When the arteries divide to form arterioles (arteries of small diameter) there is an increase in total cross-section, which results in a sharp drop in pressure, which continues in the capillaries, the so-called hair vessels. There is a further reduction in blood pressure in the large veins. In the right atrium there is the so-called central venous pressure. The pressure in the right heart ventricle is ca. 2.9/0.7 kPa or 22/5 mm Hg. The contraction of the right heart drives the blood through the pulmonary artery. This is the main artery of the lung and the pressure here is ca. 2.9/1.3 kPa or 22/10 mm Hg. The blood then passes through the vascular bed of the lungs into the left atrium, where the filling pressure for the left ventricle (the main chamber of the left heart) is ca. 1.1 kPa or 8 mm Hg. Cf. circulation of the blood.
Glossary entries: Roche and Walter de Gruyter, Berlin