. An introductionto physiology. ready shut,and the mitral not yet open. 256 THE CIRCULATION OF THE BLOOD The Period of Outflow from the Ventricle. — Tie a rubber membrane over the smaller thistle-tubeof the sphygmograph (Fig. 54) and cement a bonebutton in the centre. Prepare a second receiv-ing tambour in the same way. Bring the writingpoints of the recording tambours into the samevertical line against a smoked drum. Let the drum revolve atits fastest thebutton of one re-ceiving tambouron the aortajthe other on themembrane of thetube which re-cords the intra-ventricularpressure. L
. An introductionto physiology. ready shut,and the mitral not yet open. 256 THE CIRCULATION OF THE BLOOD The Period of Outflow from the Ventricle. — Tie a rubber membrane over the smaller thistle-tubeof the sphygmograph (Fig. 54) and cement a bonebutton in the centre. Prepare a second receiv-ing tambour in the same way. Bring the writingpoints of the recording tambours into the samevertical line against a smoked drum. Let the drum revolve atits fastest thebutton of one re-ceiving tambouron the aortajthe other on themembrane of thetube which re-cords the intra-ventricularpressure. Letthe ventricle pump with the usual force and fre-quency. When the two curves have been written,stop the clock-work and turn back the drum untilthe point of the lever recording the ventricularpressure lies at the exact beginning of the upstrokein the aortic pulse curve. Cause each lever towrite an ordinate on the stationary drum. Theseordinates will indicate synchronous points andwill mark the beginning of the outflow Pig. 64. The sphygmograph. THE MECHANICS OF THE CIKCULATION 257 Now turn the drum until the point of theaortic lever lies beneath the notch seen in thedown stroke of the pulse curve (the dicroticnotch, see page 274). Describe synchronousordinates. It is known that the dicrotic notchin the aortic pulse curve corresponds closely tothe moment of closure of the aortic valves. Itmarks, therefore, the end of the outflow that this point is reached soon after theventricle begins to relax. Thus the period dur-ing which the intraventricular pressure is higherthan the pressure in the aorta embraces part ofthe relaxation as well as part of the contractionof the ventricle. It includes approximately thehighest third of the intraventricular pressurecurve. Observe also the considerable interval betweenthe beginning of ventricular contraction and theopening of the aortic valve, as shown by theupstroke in the pulse curve consequent uponthe entrance of liquid
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