GABE, I. T., J. KARNELL, I. G. P O R J~ and B. RUDEWALD. The measurement of input impedance and apparent phase velocity in the human aorta. Acta physiol. scand. 1964. 61. 73-84. Measurement of the input impedance in the

PORJE, I. G. and B. RUDEWALD. Hemodynamic studies with d&erential pressure technique. Acta physiol. scand. 1961. 51. 116-135. -A theoretical analysis of the fluid motion in a circular elastic tube is presented. The formulae for computation of pulsatile flow and other hydrodynamic data are discussed. Apparatus and technique for recording differential pressure are, described. Results of studies of the hydrodynamics in a model circulation system show that the theory is valid. For kinematic viscosities ranging from 1-9 cst the differential pressure is in the main unaltered. Original differential pressure records from the ascending aorta in cases with normal aortic valves are presented and their features described. Blood velocity curves computed from such curves are presented. To illustrate the use of the method the effect of the Valsalva manoeuvre and a nitrite (Etrynit, Bofors) upon the aortic blood motion are demonstrated.Heart catheterization has opened possibilities for quantitative determination of the cardiac output per minute a n d the stroke volume according to the Fick or the Hamilton principles. Thereby valuable clinical and physiological data about the circulation in intact m a n is obtained. These methods give mean values for the flow during a certain interval of time b u t no information about the dynamics of a particular heart stroke. For the direct measurement of the flow there a r e several types of flowmeters b u t as yet none c a n be used safely to measure the instantaneous aortic blood flow i n intact man. Our work has been devoted to the development of a method for the study of the dynamics of the aortic blood motion, based upon differential-pressure curves recorded from the aorta. 116

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Theoretical Part.:Frank-Broemser's manometer theory for oscillations in the aorta is based on an analogy which makes it possible to treat these oscillations mathematically in the same way as a damped linear oscillator is treated in mechanics. The aorta is an elastic tube ("manometer"). At a point, near the heart, acts a pressure (the central pulse pressure) which is periodical with the time period T = the pulse time. This pressure can be mathematically expressed in a Fourier series. M P == A , + C A,, cos (notpn), 1L = 1 1) 2n T where o = ~ and t = the time in seconds. At a point on the aorta lying near its lower end, the likewise periodical, peripheral pulse pressure is measured. P' = A', + C A ' , cos (notp',). M n = l 2)

PORJB, I. G. and B. RUDEWALD. Studies on the eject of a nitrate compound on arterial hernodynamics in human beings. Acta physiol. scand.1962. 55. 270-275. -The effect of 1 hydroxy-2,2 bis (hydroxymethyl) butantrinitrate (Etrynit, Bofors), on arterial blood pressure, aortic blood flow and left ventricular external work (power) in human beings has been studied with a pressure gradient method. An unsteady state is induced with rapid changes, which cannot be studied with methods based on observations of mean flow over an appreciable time. A transient increase of cardiac output and left ventricular work may be observed during the first 3-4 min and then fluctuating decrease of these modalities may follow. The effect of the drug on blood acceleration and arterial blood pressure is discussed.