Mean circulatory filling pressure measured immediately after cessation of heart pumping.

W HEN the heart stops, the arterial pressure falls and the venous pressure rises until aftes 30-50 seconds the two pressures almost reach equilibrium. This equilibrium pressure, which presumably is equal to the pressure in all portions of the circulatory system, has in previous studies from this laboratory (1-3) and in this present study been called the ‘mean circulatory filling pressure.’ The term ‘mean systemic pressure’ as used by Starling (4) has not been used because the word ‘systemic’ now has the connotation of applying to the peripheral circulatory system alone rather than the entire circulatory system. Also, the terms ‘hydrostatic mean pressure’ as used by Bolton (5) and ‘static blood pressure’ as used by Starr (6) have not been employed in this discussion because to many physiologists the word ‘static’ means ‘unchanging’ and it has been shown many times that the autonomic reflexes continue to cause marked changes in pressures throughout the circulatory system even after the heart stops pumping (1-7). Another reason for using the term ‘mean circulatory filling pressure’ is that, even though the pressures throughout the circulatory system under dynamic conditions are widely variant, there is a mean integrated pressure in the circulatory system all of the time, If one takes into consideration the different elasticity coefficients of the different blood vessels and also takes into consideration the different volumes of the different beds, then the mean integrated pressure of the circulatory system at any given instant can be shown mathematically to be exactly equal to the mean circulatory filling pressure should the heart stop _~~ ____Received for publication May IO, I#+ 1 This investigation was supported by a research grant from the National Heart Institute, Public Health Service. 2 Student Fellow, National Foundation for Infantile Paralysis. beating and all pressures come to equilibrium instantaneously. Therefore, use of a term which implies that there is a continuously present mean pressure in the circulatory system has many advantages in emphasizing the importance of this pressure. The mean circulatory filling pressure as it exists in the body at any given instant cannot possibly be measured because life is dependent on dynamic circulatory conditions. On the other hand, it has been pointed out by all investigators who have measured the mean circulatory filling pressure that shortly after the heart stops beating, intense vasoconstriction begins throughout the circulatory system (4, 6, 7). Consequently, in order to estimate accurately the mean circulatory filling pressure as it exists at any given moment, it is essential that measurement of this value be made within a few seconds after the heart stops beating or, in other words, before significant changes in vasomotor tone can take place as a result of reflexes. In order to make such rapid measurements it is necessary to establish rapidly equilibrium of the circulatory pressures by artificial means, for the rate of blood flow from the arteries to the veins is too slight for rapid equilibrium to occur. Except for the preliminary measurements reported from this laboratory (1-3, 7), the mean circulatory filling pressure has never been determined within the short interval of time after the heart stops beating and before reflex vasomotor constriction begins. In the present study, attempts which are believed to have been successful have been made to make such measurements under a number of different conditions.