A text-book of physiology, for medical students and physicians . hed as the outside pressure is increased, and when this pres-sure is equal to the diastolic blood-pressure within the artery one will neu-i ralize I he ol her, and the diameter of the artery will be equal to that assumedwhen the vessel contains Mood under no pressure and is kept, patent only bythe stiffness of its walls (b). Under this condition the pulse wave? when ittraverses this portion of the vessel finds its walls completely relaxed, as itand the force of the heart wave will consequently cause a greater dis- * Archives ital
A text-book of physiology, for medical students and physicians . hed as the outside pressure is increased, and when this pres-sure is equal to the diastolic blood-pressure within the artery one will neu-i ralize I he ol her, and the diameter of the artery will be equal to that assumedwhen the vessel contains Mood under no pressure and is kept, patent only bythe stiffness of its walls (b). Under this condition the pulse wave? when ittraverses this portion of the vessel finds its walls completely relaxed, as itand the force of the heart wave will consequently cause a greater dis- * Archives italiennes de biologic, 23, 177, L895. VELOCITY AND PRESSURE OF BLOOD-FLOW. 487 tension of the arterial walls and a larger pulse wave in the recording ap-paratus. If the outside pressure is increased beyond the amount of diastolicpressure it will not only neutralize this latter, but will tend to overcome thestiffness of the arterial wall. When the pulse wave passes through this stretchit will be forced not only to distend the walls, but also to overcome the excess. Fig. 199.—Record {Erlanger) to show the maximum size of the recorded pulsewave when the outside or extra vascular pressure is equal to the internal diastolic artery is compressed first with a pressure above systolic, sufficient to obliterate thelumen. As this pressure is lowered in steps of 5 mms. the recorded pulse wave increases insize to a maximum and then again becomes smaller. The outside pressure with which themaximum pulse is obtained measures the amount of the internal diastolic pressure (Mareysprinciple). of pressure on the outside. The movement of the walls with the pulse wavewill be less extensive in proportion to the excess of pressure on the , therefore, one starts with an outside pressure sufficient to obliterate theartery completely the recorded pulse wave will be small. As this pressure
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