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Transmural pressure is the difference in pressure between two sides of a wall or equivalent separator. According to myogenic theory smooth muscle contract in response to increased transmural pressure and relax to decreased transmural pressure For body vasculature or other hollow organs, see Smooth muscle#External substances
However, transmural pressure across the wall of the blood vessels increases down this zone due to gravity. Consequently the vessels wall are more stretched so the caliber of the vessels increases causing an increase in flow due to lower resistance. Zone 4 can be seen at the lung bases at low lung volumes or in pulmonary edema.
Arterial compliance is an important cardiovascular risk factor. Compliance diminishes with age and menopause. Arterial compliance is measured by ultrasound as a pressure (carotid artery) and volume (outflow into aorta) relationship. [5] Compliance, in simple terms, is the degree to which a container experiences pressure or force without disruption.
structures of the cardiovascular system, including the heart and great vessels, which include the thoracic aorta, the pulmonary artery and all its branches, the superior and inferior vena cava, the pulmonary veins, and the azygos vein; structures of the respiratory system, including the diaphragm, trachea, bronchi and lungs [1]
Pulse pressure is quantified using a blood pressure cuff and stethoscope (Korotkoff sounds), by measuring the variation of the systolic pressure during expiration and inspiration. [8] To measure the pulsus paradoxus, place a blood pressure cuff on the patient's arm and very slowly deflate the cuff while listening for brachial pulsations.
The azygos vein is unpaired in that there is only one in the body, mostly on the right side. While there is the hemiazygos vein and its accessory on the left side of the body, they are considered tributaries of the azygos vein rather than its left-side equivalent. This terminology is only accurate in some species, such as the human, dog, and cat.
The venous valves serve to prevent regurgitation (backflow) due to the low pressure of veins, and the pull of gravity. [1] They also serve to prevent the over-widening of the vein. [20] [21] A venous valve is bicuspid (having two leaflets) and is formed by an infolding of part of the tunica intima on either side of the lumen of the veins.
The low-pressure baroreceptors, are found in large systemic veins, in pulmonary vessels, and in the walls of the right atrium and ventricles of the heart (the atrial volume receptors). [4] The low-pressure baroreceptors are involved with the regulation of blood volume.