at each ventricular ejection contraction , a volume of blood , the stroke volume is injected into the aorta . the aorta stretches to accommodate the stroke volume and an accompanying pressure pulse launches down the aorta into the main arteries . fig2 shows a plot 200 of the velocity of a pulse along the major arteries as a function of the age of an individual . the pulse can travel at speeds of between about 5 - 10 meters / sec — the lower speeds typically applying at lower ages and the higher speeds applying at higher ages . since a typical pulse rate is of the order of one pulse per second , the high pulse velocity indicates that to a first approximation , the entire arterial tree feels the same pressure practically simultaneously . the pressure in the arterial tree is related to the distension of the arteries . as shown in fig3 , over a wide range of pressures , the plot 302 of the relation between the blood volume ( distension ) and the pressure is linear as contrasted with the plot 304 representing low - pressure veins . accordingly : where δv i denotes the change in volume in the i th artery due to a pressure change δp , and d i denotes the distensibility of the i th artery . the pressure in the arterial tree does not remain elevated after injection of a stroke volume of blood , because the pressure drives the blood from the arterial tree into the microvasculature . as shown in fig4 , the time course of the pressure in the arterial tree changes slightly from the aorta plot 402 to the plot 404 of the outlying main arteries . the change in the time course has been ascribed to reflections from branching points , selective damping of higher frequency components , and dispersion due to frequency - dependent phase velocities . the rise time of the pulse is so much shorter than the decay time that in the lowest approximation it can be assumed that the stroke volume is injected instantaneously into the arterial tree . after injection , the blood volume v in the arterial tree is assumed to decrease at a rate proportional to the pressure in the tree , since it is this pressure that causes the blood to flow from the tree . here , z denotes the resistance to flow presented by the microvasculature fed by the arteries . this gives an exponential pressure decline — a smoothed version of the arterial pressure decline seen in fig4 . at any instant , the pressure p is equal to the pressure that exists just before the stroke volume is injected into the tree — i . e . the diastolic pressure p d , plus the pressure δp of eq . [ 1 ] similarly , the instantaneous volume of the arterial tree is equal to the sum of the volume just before a stroke volume is injected , v d , plus the sum of the volumes δv i of eq . [ 1 ] the sum being over the body arteries . the general solution to equation [ 5 ] is the constant c can be evaluated at t = 0 where it is known that by definition the increment in pressure is equal to the difference between the systolic pressure p s and the diastolic pressure p d if the pulse rate , f , is some number of pulses per minute , then the end of the period , t , occurs when t = 1 / f . at that time , the pressure must once again be the diastolic pressure p d . thus , the relationship can be shown as : since the arterial distensibility d , peripheral resistance z , and pulse rate f , all enter into the exponent in this relationship , the ratio of systolic to diastolic pressure can depend sensitively on these parameters . at t = 0 , the total change in volume from the diastolic volume ( the volume just before injection of the stroke volume ) must be equal to the stroke volume v s . equation [ 1 ] then shows ( on using eq . [ 8 ]) that : the cardiac output & lt ; dv / dt & gt ; is the product of the pulse rate and the stroke volume . then arterial distensibility : d =& lt ; dv / dt & gt ;[ f ( p s − p d )] − 1 [ 14 ] peripheral resistance z =( p s − p d )[& lt ; dv / dt & gt ; ln ( p s / p d )] − 1 [ 15 ] d n = d /& lt ; dv / dt & gt ;=[ f ( p s − p d )] − 1 [ 16 ] r n = z & lt ; dv / dt & gt ;= ( p s − p d )[ ln ( p s / p d )] − 1 [ 17 ] the left sides of [ 16 ] and [ 17 ] are respectively , normalized distensibility , d n , and normalized peripheral resistance , r n . as shown , these terms are expressible solely in terms of quantities routinely and easily measured in local medical offices and represent parameters which are normalized by cardiac output . the product of these values dr = d n r n , is independent of cardiac output . the significance and utility of eqs . [ 16 ] and [ 17 ] derives from records of their values in association with several medical conditions . the normal reference values of blood pressures for typical subjects are shown in fig1 . if the values of diastolic pressure and systolic pressure at the boundaries of the normal range are taken , then the corresponding normal values for d n and r n are as shown in fig1 - 16 . the r n is independent of pulse rate , while the d n depends on pulse rate . fig1 shows the values of d n for a pulse rate of 70 per minute and fig1 shows the values for d n for a pulse rate of 90 per minute . also shown on each plot are two double - ended arrows , indicating the range of values for the morning and evening readings for a subject . fig1 shows that the normal values of d n and r n fall within in a narrow range . this is in contrast to the values obtained on one hypertensive subject over the time period of several months which were found to vary widely about the reference values . fig1 shows the entry and processing of blood pressure numeric data 102 and pulse rate numeric data 104 into a computer 106 . a wide variety of analog or digital computers may be used , such as hand - held , laptop , or desktop computers , the selection turning mostly on clinical convenience . the blood pressure data 102 can be gathered from a standard inflatable cuff and sphygmomanometer . the pulse rate data 104 can be gathered by manual timing of the pulse or from automatic equipment that can deliver the data electronically to computer 106 . the systolic and diastolic pressures , expressed numerically in a consistent set of units , for example , torr , are entered into computer 106 . the difference between these pressure numbers is produced and then divided by the natural logarithm of their ratio . the result is the r n . in the embodiment shown in fig1 , unity gain amplifiers 108 and 110 , produce differences of input numbers , indicated by arrowheads 112 . conventional logarithmic elements 114 and 116 produce natural logarithms of their input numbers . conventional multipliers , 118 , 120 , 122 , and 124 , produce the products of two input numbers each . amplifiers 126 and 128 , each of gain g & gt ;& gt ; 1 , produce division of input numbers . the output of amplifier 126 , co for instance , is co = g ·( p s − p d )− g ·[ ln ( p s )− ln ( p d )]· co . solving for co gives co = g ·( p s − p d )/{ 1 + g ·[ ln ( p s )− ln ( p d )]} which , because g & gt ;& gt ; 1 gives co ≈( p s − p d )/[ ln ( p s )− ln ( p d )]=( p s − p d )/ ln ( p s / p d )= r n , normalized peripheral resistance . in like manner , the output of amplifier 128 is do = 1 /[( p s − p d )· f ]= d n , normalized arterial distensibility , where f is in units of beats per minute , for example . these two outputs and their product d n r n are applied to a standard display device 130 , which includes analog to digital converters producing called out numbers on the appropriate abscissa , as indicated in fig1 . the three histograms 132 , 134 and 136 shown in fig1 display statistical data taken from a collection of similar individuals . for example , the statistical data can be taken from the first month of the patient &# 39 ; s examinations ( 21 exams during this period ), the idea being to substitute the ensemble average by a time average , the ergotic hypothesis of statistical mechanics . the utility of these normalized measures is given in an example of a hypertensive scleroderma patient for whom values for blood pressure readings , heart rate , d n , and r n obtained over a four month period are displayed in fig7 - 12 . in this patient , before adequate treatment , the value for dr was below normal , the value for r n was within normal limits and the value for d n was below normal . the patient &# 39 ; s range of these values is displayed with reference to normal values in fig1 - 15 . it can be inferred from these values that his hypertension was due to a decrease in normalized artery distensibility rather than to scieroderma - related increase in normalized peripheral resistance . these results would guide a clinician to select those drugs which inhibit vasoconstriction rather than those which address increased cardiac output such as beta - blockers and diuretics . routine and automatic recording of the parameters , thus building a statistical database , would be a useful diagnostic adjunct to individual blood pressure and pulse rate readings thereby improving monitoring for therapeutic efficacy . fig1 shows the correlation between d n and r n in the first 24 exams . unlike these data , the single points indicated by the arrows in the peripheral resistance and arterial resistance histograms of fig1 were taken near the end of the four - month examination period where hypertension was under control . arterial distensibility , d n , increased and peripheral resistance , r n , decreased because of the correlation between them . although the present invention is described with reference to the presently preferred embodiments , it is understood that the invention as defined by the claims is not limited to these described embodiments . various other changes and modifications to the invention will be recognized by those skilled in this art and will still fall within the scope and spirit of the invention , as defined by the accompanying claims .
a medical diagnostic method using systolic and diastolic blood pressures , and pulse frequency of a patient is provided to compute a normalized diastolic distensibility value and a normalized peripheral resistance value , and to automatically compute the product of the normalized diastolic distensibility value and the normalized peripheral resistance value to generate a first product value . the first product value is compared to a stored distribution of normalized diastolic distensibility and a normalized peripheral resistance values for comparable individuals to determine if the first product value is equivalent to a value determined to indicate an abnormal condition . particular values of the computed parameters aid in determining the etiology of hypertension and direct selection of pharmacotherapy .