File:A text-book of physiology (1893) (14783920245).jpg

Identifier: textbookofphysio18931fost (find matches)
Title: A text-book of physiology
Year: 1893 (1890s)
Authors: Foster, M. (Michael), Sir, 1836-1907 Lea, Arthur Sheridan. Chemical basis ..
Subjects: Physiology
Publisher: New York, London, Macmillan and Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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the curvedepends on the relative amounts which are entering the arterialsystem from the heart, and leaving it by the peripheral vessels. It is possible that under some circumstances the whole of the Chap, iv.) THE VASCULAR MECHANISM. 259 contents may be discharged before the actual systole ends; butthe observations and arguments which we have just related,shew that such an event must be regarded as of exceptional, andnot, as has been contended, of normal occurrence. Of the smaller secondary variations visible on the systolicplateau, conspicuous in some curves (4, 5, 6, 7 in Fig. 47), variousexplanations have been given. Into the discussion of these wecannot enter here ; we may however say that in many observations,which we may probably regard as correct, these secondary markingsare identical in the curves of ventricular pressure, of aortic pressureand of the cardiac impulse, or of the change in the outward formof the heart; the events which cause them tell in the same wayon all three.
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Systole Diastole Fig 55 Diagram of Ventricular and Aortic Pressure and of theCardiac Impulse. Huktiile. We give in Fig. 55 a diagram of the cardiac events accordingto the exposition which we have just made. The curves previouslygiven were copies of actual curves obtained by experiment; thisis a constructed diagram. The upper curve is the curve of thecardiac impulse. The middle curve is the curve of pressure in the 260 NEGATIVE PRESSUEE. (Book i. left ventricle ; the unbroken line represents the course of the curvewhen, the peripheral resistance being small, the pressure neededto drive onward the blood is not very high, in the figure less than150 mm. Hg. The dotted line represents the course of the curvewhen, the peripheral resistance being great, the pressure is high,in the figure nearly 200 mm. Hg. The lower curve is the curve ofpressure at the root of the aorta, the unbroken and the dottedlines having the same significance as in the ventricular curve.The line 0 marks the commencemen

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