Abstract:
According to the invention a sphygmomanometer for continuous plethysmographic measurement of blood pressure includes at least one inflatable pressure pad which is attachable to a body part containing an artery, arterial signal sensors for determining arterial blood flow, and a valve-controlled pressure chamber connected to a gas source and to the inflatable pressure pad and including a pressure sensor for measuring the pressure in the pressure chamber or in the pressure pad. The pressure chamber has separate inlet and outlet valves which are controlled dependent on signals of the arterial signal sensors.

Description:
BACKGROUND OF THE INVENTION 
     In medicine there is a need to frequently, and possibly, continuously take blood pressure. Novel devices have been created In recent times for this purpose, The method devised by Panaz contributed an essential novelty (Digest of the 10 th  International Conference on Medical and Biological Engineering 1973 Dresden), wherein light is shone through a finger and the registered flow Is kept constant by a booster control. 
     This photoplethysmographic method was taken up by several others also (Yamakoshi, Wesseling, TNO). EP 537 383 (TNO) Apr. 21, 1993 (21.04.93) discloses an inflatable finger cuff used for non-invasive continuous monitoring of blood pressure. The inflatable cylindrical space is connected pneumatically to a fluid source. An infrared light source and a detector are positioned on both sides of the finger inside the fixed cylinder. A valve is provided for filling the cylinder with gas. Electrical cables for the infrared light source and the detector are threaded through. U.S. Pat. No. 4,510,940 A (WESSELING) Apr. 16, 1985 (16.04.85) and U.S. Pat. No. 4,539,997 A (WESSELING) Sep. 10, 1985 (10.09.85) disclose a device for continuous non-invasive measuring of blood pressure. A fluid-filled cuff, a light source, a light detector and a differential pressure booster are provided. U.S. Pat. No. 4,406,289 A (WESSELING) Sep. 27, 1983 (27.09.83) also discloses such a device according to the prior art. 
     The cited documents all show prior art only, especially so when it is considered that features essential to the invention are missing in the main claim. 
     A major problem of these methods is on the one hand in the cuffs being used which have to be placed very precisely, are very interference-prone and not very durable, and on the other hand is with the proportional valves used which are very expensive to manufacture (U.S. Pat. No. 4,406,289) and also in the calibrating of the device which can very precisely indicate the relative fluctuations in blood pressure, wherein absolute measuring however deviates considerably from the actual intra-arterial values. Usually, with the proportional valves used to date either a) a toggle flapper is used, which can be moved alternately in one or the other direction by an electromagnet, or b) an electromagnetic shaker is used. With both these proportional valves there is a constant gas flow through the pressure chamber, as there is a part of the valve always open. Either the outlet opening is released into the open, or the inlet opening is released by the gas supply. There is no position of the valves, in which both inlet and outlet opening are simultaneously closed. 
     This results in very high gas consumption, of little relevance in fixed apparatus, but clearly significant in the case of portable units. A further drawback is the use of pressure generation systems (usually pumps and compressors) which must generate a pressure flow without ripple, since any such ripple would influence the measuring signal. Pumps or compressors generating a constant and even air flow are generally more expensive and consume more power than pressure generation systems delivering a pressure which may not be under a specific threshold. The weight or the power consumption of the unit is clearly increased. 
     Yet another disadvantage of the methods utilised is that such methods used to date are employed exclusively on fingers, and the finger arteries belong to the small arteries which are regulated in the flow from the body for example by the temperature of the fingers, so that the pressure in these arteries no longer corresponds to the pressure in the large arteries, in which doctors are primarily interested. For this reason the devices used hitherto (for example the Finapres marketed by Ohmeda) very clearly give the relative fluctuations in blood pressure but not in absolute values of the pressure, so that the Finapres unit was also removed from the market. 
     Another existing sphygmomanometer essentially uses planartonometry. An array of very small pressure receivers, which are embedded in silicon, is applied to the artery by means of compressed air bellows, whereby a computer searches out the pressure sensor outputting the clearest signal. The pressure in the bellows is no longer altered after a clear signal has been found, while the pressure curve is calibrated by one-off or multiple measuring of the oscillometric blood pressure which can be measured intermittently on the same upper arm. When a hard object is applied, namely the array onto the artery, the former deforms in an uncontrollable manner, so that the pressure values output by this unit deviate very strongly from the intra-arterial values. (Zorn et al, Blood Pressure Monitoring 2: 185, 1997). Precise analysis of the pressure curves can additionally be employed by means of an expanded Windkessel model in known fashion to evaluate compliance of the large and small vessels, as demonstrated by Waft and Burrus. Furthermore, the pressure in the central aorta can also be calculated by computer, for example with frequency analyses, or a so-called augmentation index can also be calculated which clearly reflects the actual mechanical strain on the heart and vascular system. To date the so-called aplanation tonometry, wherein a hard pressure sensor was applied by hand or per micrometer screw to the artery, has been used to relieve arterial wall. The disadvantage of this so far has been that the pressure lying on the artery because of the pressure sensor was not known, and that it was exceedingly troublesome to accurately find the artery by hand. 
     The object of the present invention is to prevent these known difficulties by developing a new sphygmomanometer. 
     SUMMARY OF THE INVENTION 
     According to the invention a sphygmomanometer for continuous plethysmographic measurement of blood pressure includes at least one inflatable pressure pad which is attachable to a body part containing an artery, arterial signal sensors for determining arterial blood flow, and a valve-controlled pressure chamber connected to a gas source and to the inflatable pressure pad and including a pressure sensor for measuring the pressure in the pressure chamber or in the pressure pad. The pressure chamber has separate inlet and outlet valves which are controlled dependent on signals of the arterial signal sensors. 
     The sphygmomanometer according to the invention is described in greater detail with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the new blood pressure measuring system according to the invention; 
     FIG. 2 shows the new finger cuff in greater detail; 
     FIG. 3 illustrates an embodiment of the blood pressure measuring system, wherein pressure sensors are used as arterial signal sensors 
     FIG. 4 illustrates an embodiment of the blood pressure measuring system, wherein several signal sensors are used as arterial signal receivers; and 
     FIGS. 5,  6  and  7  are detailed illustrations of the arterial signal receivers, 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 the gas source is designated by reference numeral  1 , which could refer to an air pump or also to a gas cartridge. An attenuator pad is designated by  2 , for example a gas filter, which would equilise high-frequency irregularities of the gas supply, for example when a membrane pump is being used as a gas source and at the same time serves as dust filter. The pressure chamber is designated by  3 , whereby the connection to gas source  1  is established by an inlet valve  4 . The outlet valve is designated by  5 . The valves could be conventional proportional valves, while the use of valves with very short response times is particularly beneficial, as given for example by piezoelectric elements. Response times for these piezoelectric valves of around a millisecond can give rise to pressure changes here which can be in a frequency range of up to 50 Hz. With the use of piezoelectric valves the valves can be controlled digitally and especially easily by a computer  10 , so that characteristics can be imparted to the valves by way of this digital control, not attainable or only with difficulty so with conventional proportional valves or with forced coupling of outlet and inlet valve (such as for example in U.S. Pat. No. 4,406,289 Wesseling). Each desired pressure cycle can thus be adjusted in pressure chamber  3  with an upper limit frequency of ˜50 Hz and gas consumption can also be kept low. 
     Pressure chamber  3  can be connected via another reversing valve  6  for example with two or more pressure pads  7  by way of lines  3   a  and  3   b  of pressure chamber  3 , which serve as artery compression. If only one pressure pad is used reversing valve  6  can be omitted. The relatively rigid outer wall is designated by  8 . Its purpose is to keep the compliance of pressure pad  7  low. Reference numeral  9  designates a mouldable membrane which serves as artery compression. In a special case pressure pads  7  are distinguished as annular in cross-section, because they are designed for use on fingers, by which pressure pad  7  is attached. Reference numeral  11  designates a rigid positioning component, by means of which both pressure pads  7  can be connected. The advantage here is that the position of pressure pads  7  on the fingers is guaranteed in relatively constant alignment. A constant position of arterial signal sensors  12  applied to the limit of pressure pads  7  relative to the artery lying beneath mouldable membrane  9  is guaranteed. With arterial signal sensors  12  it could be a matter of, for example, light sources and light sensors (arterial signal receivers  12   a  and arterial signal senders  12   b ) which measure the flow of the artery, or also ultrasound sensors or lasers or even pressure sensors. Therefore, controlled by arterial signal receivers  12 , which are likewise attached to computer  10 , the desired pressure can be produced any time in pressure pad  7 . Instead of pressure pads  7  illustrated here as annular in shape, any other shape adapted to the body part in use could be used in this instance. Should the sphygmomanometer be used for example on the skull above the arteria temporalis, flat pressure pads  7  would be suitable. 
     Moreover, anywhere in the vicinity of the communicating interstice, formed by pressure chamber  3  and pressure pad  7 , a pressure sensor  13  is attached which measures the pressure in the pressure chamber and forwards the results to computer  10 . The pressure measured in the pressure chamber with appropriate control by means of arterial signal sensors  12  corresponds to the arterial pressure. By way of advantage with the illustrated pressure sensor  13  it could well be a matter of a differential pressure sensors. The advantage of this would be that pressure measuring can be corrected any time to the artery height difference, relative to the heart. For this a fluid-filled line would have to be available which reaches the level of the heart (symbolically illustrated in FIG. 1 with a heart). By way of advantage fluid-filled line  14  is filled with a fluid which corresponds to the density of blood. The fluid, with which line  14  is filled, should exhibit a slight output coefficient (for example oily fluids). The hose can be attached by means of a fastening mechanism  14   a  (such as a locking band, pressure knob, clamp and the like) to the extremity (for example upper arm or article of clothing) at heart level. A free-floating membrane  14   b , which prevents the fluid from escaping, but which allows the fluid column to move, could be attached at the heart end of line  14 . Another air-permeable but hard-wearing membrane  14   c  or a fine-mesh grille  14   c , which prevents free-floating membrane  14   b  from being damaged, could be attached via free-floating membrane  14   b.    
     Another pressure pad  15  can also be added, which comes to rest via another artery, preferably a major artery, which can be connected to another gas source  16  to measure the blood pressure there conventionally, for example oscillometrically or auscultatorically. In the same way and with adequate capacity gas source  1  could be used, effectively necessitating more valves (not illustrated). It is known that conventional blood pressure measuring, such as auscultatoric or oscillometric measuring, works intermittently, that is, normally at intervals of minimum half a minute to a minute. The other pressure pad is likewise connected to computer  10 , so that calculation and display of the continuous arterial pressure, as determined in the small artery by pressure pad  7 , is automatically corrected to the true value of the blood pressure in the major artery, as is measured by pressure pad  15 . 
     The added advantage of the second pressure measuring via a major artery by pressure pad  15 : for continuous measuring of pressure by pressure pad  7  the pressure in pressure pad  7  must constantly track the average arterial pressure, that is, the operating point must be readjusted. To readjust the operating point the continuous blood pressure measuring must be briefly interrupted by pressure pad  7 . Major changes in the average arterial pressure can now be discovered by measuring pressure in another artery by pressure pad  15  discontinuously, and the operating point can be continually adapted automatically and without interruption to the continuous measuring of pressure by pressure pad  7 . In this way continuous, unbroken recording of the true intra-arterial pressure curve is possible using the abovedescribed sphygmomanometer. By changing automatically from one pressure pad  7  to the other pressure pad  7   a  via reversing valve  6  measuring of pressure is not interrupted, since the patient does not experience any discomfort from continuous measuring on the same spot. 
     FIG. 2 illustrates an advantageous embodiment of pressure pad  7  which comprises a relatively rigid outer wall  8  which on the one hand gives pressure pad  7  beneficial minimal compliance, and on the other hand allows rigid connection  11  to adjacent pressure pad  7   a  which is designed similarly. Located inside relatively rigid outer wall  8  is mouldable membrane  9 , on which in the illustrated case arterial signal sensors  12  rest. There is thus no interfering membrane between arterial signal receivers (flow sensors)  12  and arteries  17  which might impair measurement of the blood flow. As mentioned, these flow sensors could be LED&#39;s combined with light detectors, (for example photodiodes), lasers (or laser diodes) and photodiodes or ultrasound emitters and receivers (arterial signal receivers  12   a  and arterial signal receivers  12   b ). Using other pressure sensors (see FIG. 3) is also feasible. Recesses  18 , into which arterial signal sensors  12  can disappear, are realised advantageously in the relatively rigid outer wall for arterial signal sensors  12  when mouldable membrane  9  is close to rigid outer wall  8 . This close fit is accordingly meaningful to keep the compliance of pressure pad  7  to a minimum. In the illustrated example two arterial signal receivers  12   a  and  12   b  are attached to one another at an angle of 120° to ensure an optimum signal, arteries  17  lie relative to finger bone  19  in finger  20 , corresponding to an angle of 180° in illustrated pressure pad  7 , and the clearest signal is emitted, when arterial signal receivers  12   a  and arterial signal receivers  12   b  are positioned at ca. 120° to one another, as already mentioned, since at the same time an even better and more homogeneous pressure can be exerted on the artery. This is therefore the case because then only mouldable membrane  9 , and not arterial signal receivers  12   a  and  12   b , which are not mouldable, which comes to rest on artery  17 . 
     In the illustrated example mouldable membrane  9  consists of gas-tight and fluid-tight synthetic material. In order to make measuring more pleasant for the patient, a skin-friendly tissue  21  is additionally applied between mouldable membrane  9  and the body, which for example could comprise nylon or other synthetic tissues, cotton or similar. In the process the skin-friendly tissue releases arterial signal receivers  12   a  and  12   b , so that the signal is not impaired. Of particular benefit are those materials which can readily be cleaned or disinfected. Electrical shielding  22  is also provided which keeps electrical interference away from arterial signal receivers  12 . In the illustrated example electrical shielding  22  is applied externally on rigid outer wall  8 , but could also be placed inside rigid outer wall  8 . 
     To ensure correct positioning of arterial signal sensors  12  above artery  17 , if only one pressure pad  7  is present, it can be beneficial to also mount rigid positioning component  11  on rigid outer wall  8 , if only one pressure pad is used. Rigid positioning component  11  is then formed to the adjacent body structures (in the case of a finger for example the adjoining fingers, back of hand, palm; in the case of the thumb the ball of the thumb, not illustrated) and could thus also take on a ring shape or form parts of a ring. 
     As illustrated in FIG. 3, it can be beneficial to mount pressure sensors as arterial signal sensors  12  in rigid outer wall  8 . In this illustrated example it can be beneficial to divide the communicating system, comprising pressure chamber  3  and pressure pad  7 , by additional easily mouldable septums  23  which create separate areas  24   a  and  24   b  in the pressure chamber. Area  24   a  located in the vicinity of the arterial signal receivers could then be filled with another medium, namely with fluid, to better transmit the signals emitted by the artery to the arterial signal receivers. Reference numeral  25  designates a filling or ventilating aperture which can be sealed and which is located in relatively rigid outer wall  8 , by way of which sector  24   a  can be filled with a fluid. The advantage of this embodiment is that in the concrete example arterial signal sensor  12  can also be a high-resolution pressure receiver which can absorb the pure, unattenuated signals from artery  17  lying on bone  26 , without impairing these mechanically. In this way the continuous pulse curve can be recorded ongoing in high resolution, while a precisely known pressure of artery  17  can be applied via flexible septums  23 . The arterial wall can thus be relieved, and a pure pulse curve can be recorded continuously. 
     In the embodiment used here blood pressure can be measured using pressure sensor  13 , which is connected to sector  24   b  of pressure pad  7 , also oscillometrically in known fashion, and then with knowledge of the systolic, diastolic and average arterial pressure, any desired pressure in relation to the systolic, diastolic and average arterial pressure in pressure pad  7  and thus also in fluid-filled area  24   a  can be created in order to thus record the pulse curve with precisely defined pressure ratios and thus to enable continuous bloodless recording of blood pressure. It is understood that other arterial signal sensors  12  (receiver  12   a  and sender  12   b ), as for example light-sensitive sensors and LED&#39;s can be installed in the rigid outer wall. 
     As illustrated in FIG. 4, several arterial signal receivers ( 12   a-d ) may be present, whereby a multiplex switch  27  and computer  10  carry out the choice of the optimally placed arterial signal receivers  12   a-d  in order to receive an optimum arterial signal. This is particularly beneficial for enabling interference-free recording of signals when the artery is in a position altered from individual to individual. It would be ideal, instead of localizing pressure pad  7  above a small artery, for example the finger artery, with the necessity of recalibrating the measuring by another pressure pad  15  which lies above a large artery, to utilise just one pressure pad  7  from now on over a major artery, which allows continuous measuring of pressure and at the same time the absolute values can be correctly determined. An example of such an artery is the arteria radialis or temporalis, which is on the one hand large enough to be representative of the major arteries, but on the other hand still allows recording of arterial signals, such as flow metering by irradiation or reflection on underlying bone  26  (for example, the radius or skull bones) by waves emitted to arterial signal senders  12   b . The additional advantage of the arteria radialis for example is that yet another artery, namely other artery  17   a  in this instance the arteria ulnaris, is available. For measuring only artery  17  has to be compressed by pressure pad  7 , and not other artery  17   a  and the blood flow to the extremity is consequently not interrupted. In addition, only mouldable membrane  9  has to be inflatably connected to a sector  28  of rigid outer wall  8  in that area which lies above artery  17  being examined, while other artery  17   a  is not compressed by mouldable membrane  9 . 
     FIG. 5 illustrates a practical realisation of the device, as it is advantageous if the arterial signal receivers (receiver  12   a  and sender  12   b ) are supported on mouldable membrane  9 . In this case the mouldable membrane, which may comprise latex, for example, is not interrupted, rather arterial signal sensor  12  is cast in a mouldable lens  29 , preferably from the same material as mouldable membrane  9 , which is attached to membrane  9  (for example stuck or vulcanised). At the same time electrical wires  30  are guided between mouldable membrane  9  and skin-friendly tissue  21 , so that these wires can also be guided to computer  10  while shielded mechanically and insulated. 
     FIG. 6 illustrates another embodiment of the planned device, wherein arterial signal sensors  12  are applied to a strip  31 , whereby strip  31  represents a part of septum  23  which separates gas-filled area  24   b  from fluid-filled area  24   a . Gas-filled area  24   b  is drawn through on the side turned away from the body, so that when the pressure in pressure chamber  3  is raised (and thus in gas-filled area  24   a ) the arterial signal receivers cannot or can only slightly alter their position to artery  17  and in any case cannot be lifted from the body. An optimum signal is always obtained from arterial signal sensors  12  independently of the pressure in pressure chamber  3 . So that arterial signal sensors  12  in strip  31  cannot tilt, an additional one, preferably two stayers  32  are solidly connected to strip  31 , and are mounted movably in relatively rigid outer wall  8 , in guide openings  33 , for example. And so that optimum pressure transmission without loss of pressure from area  24   b  to area  24   a  is possible, strip  31  is narrow so that septum  23  can transmit the pressure from area  24   b  to area  24   a  from several sides. 
     As FIG. 7 illustrates stayers  32  are passed by outside gas-filled area  24   b  of pressure pad  7  so that pressure pad  7  does not have to be interrupted. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Legend 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 gas source 
               
               
                   
                  2 
                 attenuator 
               
               
                   
                  3 
                 pressure chamber 
               
               
                   
                  4 
                 inlet valve 
               
               
                   
                  5 
                 outlet valve 
               
               
                   
                  6 
                 reversing valve 
               
               
                   
                  7 
                 pressure pad 
               
               
                   
                  8 
                 rigid outer wall 
               
               
                   
                  9 
                 mouldable membrane 
               
               
                   
                 10 
                 computer 
               
               
                   
                 11 
                 rigid positioning component 
               
               
                   
                 12 
                 arterial signal sensors 
               
               
                   
                 12a 
                 arterial signal receiver 
               
               
                   
                 12b 
                 arterial signal sender 
               
               
                   
                 13 
                 pressure sensor 
               
               
                   
                 14 
                 fluid-filled line 
               
               
                   
                 14a 
                 fastening device 
               
               
                   
                 14b 
                 easily mouldable floating membrane 
               
               
                   
                 14c 
                 hard-wearing, air-permeable membrane 
               
               
                   
                 15 
                 other pressure pad 
               
               
                   
                 16 
                 additional gas source 
               
               
                   
                 17 
                 artery 
               
               
                   
                 17 
                 another artery 
               
               
                   
                 18 
                 depressions 
               
               
                   
                 19 
                 finger bones 
               
               
                   
                 20 
                 finger 
               
               
                   
                 21 
                 skin-friendly tissue 
               
               
                   
                 22 
                 electrical shielding 
               
               
                   
                 23 
                 septums 
               
               
                   
                 24a 
                 24b separate areas 
               
               
                   
                 25 
                 ventilating apertures 
               
               
                   
                 26 
                 bones 
               
               
                   
                 27 
                 multiplex switch 
               
               
                   
                 28 
                 outer wall sector 
               
               
                   
                 29 
                 mouldable lens 
               
               
                   
                 30 
                 electrical wires 
               
               
                   
                 31 
                 strip 
               
               
                   
                 32 
                 stayer 
               
               
                   
                 33 
                 guide openings