AU2003265729A1 - Physiological demand responsive control system - Google Patents

Description

WO 2004/028593 PCT/AU2003/001281 PHYSIOLOGICAL DEMAND RESPONSIVE CONTROL SYSTEM The present invention relates to a demand responsive physiological control system and, more particularly, to such a system particularly suited for use with blood pumps 5 and, even more particularly, those used to assist heart function such as, for example, ventricular assist devices. BACKGROUND With particular reference to physiological control 10 systems in mammals and more particularly those of the human body it has been noted that the control systems which the body itself uses to control various organs are complex. For example, the heart of a mammal may cause the amount of blood that is to be circulated through the body 15 to change not just for what might be termed obvious reasons such as an increase in physical exertion by a person, but may also occur for example, as a result of anticipation of exertion. Furthermore the triggers which can cause changes in heart rate and pumped blood volume may derive from the 20 nervous system directly or may derive from the action of hormones or other chemical releases within the body. It follows, where mechanical aids are introduced into the body to assist the body's functions such as, for example, implantable rotary blood pumps used as ventricular WO 2004/028593 PCT/AU2003/001281 -2 assist devices that simplistic control mechanisms for these mechanical aids cannot hope to anticipate or mimic the commands which the body may pass to the heart. For example,~ in early applications of ventricular 5 assist devices the control mechanisms simply set the ventricular assist device to pump at a constant volume per unit time, adjusted at the time of initial installation to best suit the patient in whom the device has been installed. 10 Such systems use pump speed as the controlled variable. Unfortunately, a set pump speed bears no relation to actual physiological demand. It is an object- of the present invention to address or ameliorate one or more of the above mentioned 15 disadvantages. BRIEF DESCRIPTION OF INVENTION Accordingly, in one broad form the invention there is provided a demand responsive physiological control system for use with a rotary blood pump; said system including a 20 pump controller which is capable of controlling pump speed of said pump; said system further including a physiological controller, and wherein said physiological controller is adapted to analyse input data relating to physiological condition of a user of said pump; and wherein WO 2004/028593 PCT/AU2003/001281 -3 said physiological controller determines appropriate pumping speed and sends a speed control signal to said pump controller -to adjust pump speed; said system further including a physiological state detector which provides 5 said input data indicative of at least one physiological state of said user ,in use, to said physiological controller. Preferably said the physiological state detector includes an accelerometer to sense motion of the user, when 10 in use. Preferably said the accelerometer senses motiori in at least one axis. Preferably said the accelerometer senses motion in three orthogonal axes. 15 Preferably said system includes a pump monitor that detects information relating to voltage and current of the pump and delivers this information to said physiological controller. Preferably said pump monitor detects an instantaneous 20 pump impeller speed of the rotary blood pump through measurements. Preferably said pump monitor detects non-invasively.

WO 2004/028593 PCT/AU2003/001281 -4 Preferably said physiological controller uses. said information received from the pump monitor to 'derive .mathematically an appropriate pump speed. Preferably said physiological controller assesses flow 5. dynamics and an average flow estimate developed from speed and input power supplied to the pump by the pump controller. Preferably said physiological controller mathematically. determines a pumping state and if a 10 deleterious state is determined the speed control signal is changed accordingly. In a further broad form of the invention there is provided a physiological detector includes a means of detecting and quantifying a heart rate of the user, when in 15 use. Preferably said physiological detector includes a means of non-invasively detecting and quantifying a heart rate of the user, in use. Preferably said physiological controller can determine 20 a heart rate of the user by sensing speed of the pump. Preferably said physiological controller can determine a heart rate of the user using power inputted to the pump. Preferably said pump is internally implantable within the user.

WO 2004/028593 PCT/AU2003/001281 Preferably said the pump is a ventricle assist device. Preferably said the pump has a hydrodynamic. bearing that produces a relatively flat pump head versus pump flow curve. 5 Preferably said physiological controller is capable of manual manipulation by the user. Preferably said manual manipulation is within adjustable predefined limits. Preferably said physiological controller is adapted 10 for communication with a computer and wherein the .physiological controller is adapted for manipulation by a software user interface. Preferably said physiological controller includes an alarm. 15 In a further broad form of the invention there is provided a process for using physiological demand data to optimize pump speed of a rotary blood pump wherein the process comprises of the following steps: a heart rate of the user is non-invasively determined; a level of 20 physiological exertion of the user is determined through non invasive means; an instantaneous pump speed and input power 'is used to calculate instantaneous blood flow rate; a pumping state is mathematically determined; the heart rate, pumping state and level of physical exertion are compared WO 2004/028593 PCT/AU2003/001281 to the blood flow rate; and the pumping speed of the rotary blood pump is changed to appropriately supply the user with the correct blood flow rate. In yet a further broad form of the invention there is S provided a pump control system for a pump for use in a heart assist device; said system comprising data processing means which receives body motion information and heart rate information thereby to derive a speed control signal for impeller speed of an impeller of said pump. 10 'preferably . said body motion information is derived from an accelerometer. Preferably said accelerometer senses motion in a single axis. Preferably said accelerometer senses motion in three is orthogonal axes. Preferably said heart rate information is derived from a non-invasive sensor. Preferably said heart rate information is derived from voltage and current applied to an electric motor driving 20 said impeller. In yet a further broad form of the invention there is provided a method of control of pump speed of a blood pump; said method comprising establishing a base set point speed; said method further comprising establishing one or more WO 2004/028593 PCT/AU2003/001281 7 criteria which, if satisfied, cause establishment of at least a second set point speed; said second set point speed higher than that of said base set point speed. 5 BRIEF DESCAIPTIN OF DRAWINGS Embodiments of the present invention will .now be described with reference to the accompanying. drawings wherein: Fig.. 1 is a diagram of a ~ventricular assist device. 10 installation within a human body suitable for control by embodiments of the present invention; Fig. 2 is a block diagram of a physiological demand responsive of control system applicable to the system of Fig. 1 in accordance with a first preferred embodiment of 15 the present invention; Fig. 3 illustrates graphically the behaviour of the control system of Fig. 2 under specified physiological conditions; Fig. 4 is a graph of accelerometer behaviour utilised 20 as a basis for an input to the control algorithm of the first preferred embodiment; Fig. 5 is a block diagram of a control system in accordance with a second preferred embodiment of the present invention; WO 2004/028593 PCT/AU2003/001281 Fig. 6 is a block diagram of a pumping state detection module for use with the second embodiment; Fig.- 7 is a flowchart for 'determining pump drive set point for the arrangement of the second embodiment; 5 Fig. 8 illustrates graphically an HQ curve for a preferred pump type particularly suited for use with the control system of Fig. 2 or Fig. 5; and Fig. 9 is a diagram of a preferred embodiment of the present invention wherein said diagram shows preferred 10 inputs and outputs. DETAILED DESCRIPTION OF PREFERRED EMBODIl4flTS With initial reference to Fig. 1 there is illustrated in diagrammatic form a blood pump 10 installed within a 15 human body 11 and arranged. to function as a left ventricular assist device. The pump 10 is arranged to operate in parallel with blood flow passing through left ventricle 12. This is effected by inserting an inlet cannula 13 into left ventricle 12 and directing blood flow 20 through the inlet cannula into an inlet of blood pump 10. Blood pump 10, in operational modern pumps the blood thus received into aorta 14 via outlet cannula 15, as illustrated in Fig. 1.

WO 2004/028593 PCT/AU2003/001281 -9 The blood pump 20 can take a number of forms and rely on a number -of different pumping and drive technologies. Broadly, the pump technology can be based on axial or centrifugal rotary pump arrangements or on positive 5 displacement technologies. In particular, although not limiting forms, preferred pumping technologies for the control system to be'described below include r6tary pump technologies which rely on an impeller supported for rotation within a casing and which 10 causes blood to be urged between an inlet and outlet of the casing as the impeller rotates therein. In more particular preferred forms a centrifugal form of pump can be utilised with the control system with the characteristics of the pump tailored to compliment or otherwise work particularly 15 advantageously with the control system according to various embodiments of the present invention. Typically the pump 10 is driven by an electrical power source, in this instance a battery pack 16 mounted externally of the body. Electrical power from the battery 20 pack 16 is controlled by a controller unit 17 also mounted externally of the body. In addition to communicating electrical power to the pump 10 the controller 17 can also communicate with an external programming source, in this case a personal computer 18 for the purposes of initial WO 2004/028593 PCT/AU2003/001281 - 10 setup and ongoing periodic monitoring and recalibration of the pump and controller as customised for a specific patient. Embodiments of a control system suited for use, 5 although not exclusively, with the controlled 17 of the arrangement described above and with reference to Fig. 1 will now be described. DEFINITIONS 10 In the description which follows, the following definitions of various terms as referenced therein are to be utilised: "non-invasive" i.s applied to the derivation of various 15 physiological parameters of body 11 (including blood flow rates and.the like) by means which do not require sensors to be placed (invasively) within the body. "IRBP" - implantable rotary blood pump. "LVAD" - left ventricular assist device. 20 'LVP" - left ventricular pressure. "RMS" or 'rms" - route mean square. "V" - volts applied to pump motor. "I" - current consumed by pump motor. "SVR." Systemic Vascular Resistance WO 2004/028593 PCT/AU2003/001281 -11 "VR"- Venous Resistance "H" - pump head pressure. "N" - pump impeller rotation speed. - flow rate of blood through pump. 5 "P" or "PWR" - pump power consumption. "C" - angular velocity of impeller. "t" -time. Pumping States 10. "TVC" - total ventricular collapse. "PR" -. pump regurgitation. "PVC" - partial ventricular collapse. "AC" - aortic valve closed. "VE" - ventricle ejecting 15 )FIlST EMBODIMENT With initial reference to Figs. 1-4 a first preferred embodiment of a control algorithm and control system is described below and by way of example. 20 In this embodiment the aim is to provide a pUmp controller which utilises a control algorithm which takes as its two primary inputs for decision making firstly an indication of the degree of movement of body 11 per unit time as a coarse measure of exertion and hence pumping load WO 2004/028593 PCT/AU2003/001281 - 12 required of the heart and particularly left ventricle 12 and secondly an indication of heart rate derived, in this instance, non-invasively by monitoring of electrical parameters driving pump 10. 5 The system described with reference to Figs. 1-4 exhibits the following characteristics: 1. Allowing motor speed to vary and deriving control information from those time varying signals; and 2. Concept of using control of power input or speed 10 to the motor/pump. The block diagram shown in figure 2 shows the signals that are derived (non-invasively) from pump motor power and speed. To detect these conditions the strategy is to 15 measure speed instantaneously every revolution of the impeller as a digital signal from the motor commutation electronics. . The haemo-dynamic controller electronics measure the frequency of this signal which is proportional to impeller speed. Using speed is an advantage since it is 20 a digital signal, which in practice has been found to be an inherently less electrically noisy signal than that derived from measuring motor current or power. Both instantaneous speed and root mean square (rms) of speed are calculated.

WO 2004/028593 PCT/AU2003/001281 - 13 Also instantaneous pump input power and rms of pump input power are calculated. Many researchers only discuss constant speed or speed set point. However the present control strategy allows 5 impeller speed and pump input power to be freely modulated by ventricular contractions and uses the resulting dynamic information as feedback to the control system. The characteristics of centrifugal IRBPs mean that impeller speed is more sensitive to hydraulic load variations than 10 for -axial IRBPs. Furthermore, allowing impeller speed to vary in magnetically suspended IRBPs may affect suspension control. A preferred pump uses a hydro dynamically suspended impeller and therefore suspension controls are not needed. 15 Calculation of instantaneous impeller speed N(t) and rms of -mpeller speed Nzms (t) Each pulse from the commutation controller represents 20 1

/

6 th of a rotation of the impeller and is time stamped relative to a reference time base. Therefore the angular velocity cs of the impeller for each 60* of rotation is described by equation 1.

WO 2004/028593 PCT/AU2003/001281 - 14 21(T) equation 1 6[(Tn+1) -Tn] where Tn+1 - Tn is the time difference between pulses (interrupts) in seconds- e(t) is converted to speed N(t) in 5 rpm by multiplying by 60/21 as in equation 2 N(=0(t)= equation 2 2.V Rms speed is calculated in equation 3 from a moving window 10 of samples of N (t), the sample rate dependent on impeller speed. Each instantaneous speed sample is time stamped at ti to t,. 2[N(t)] 2 Nrms t) = 0 equation 3 n 15 Calculation of instantaneous and rms electrical input power Pin(t). 20 Calculation of pump electrical power is a direct way to monitor the power consumption of the pump. Since the pump power and speed is modulated by the heart which is an asymetrical modulation (due to the ejection fraction not WO 2004/028593 PCT/AU2003/001281 - 25 being 50% rms) calculation of both instantaneous power and speed is implemented. Power -is calculated using equation 4. 5 Pin(Q) = Vn().n(t) equation 4 Where Vm(t) and Im(t) are the "instantaneous" motor coil voltage and summed phase current respectively, sampled. A moving window of samples of Pin(t) is used to calculate 10 Prms(t) using equation 5. [Pin ()]2 rUs () ~ equation 5 SECOND EMBODIMENT 15 With reference to Figs. 5 to 7 inclusive there will now be described a control system in accordance with a second preferred embodiment: In relation to this second embodiment the control 20 strategy is similar to that described with respect to the first embodiment but, in addition, includes as a further control input derived from non-invasively determined parameters the "pumping state" of pump 10. This feature provides a safety-override nechanisni as illustrated in the 25 flowchart of Fig. 7 thereby to ensure that the basic control strategy described with reference to the first WO 2004/028593 PCT/AU2003/001281 - 16 embodiment is less likely to put the patient at risk. Initially in the description which follows invasively derived parameters are discussed showing how the various pumping states have been defined and come to be identified. 5 A method of non-invasively deriving the same parameters and pumping state determinations is then described with both forms of derivation being summarised in table 1. With reference to Fig. 4 experimental data suggests that there is a correlation between heart rate and 10 accelerometer output where at least a single axis accelerometer is attached to a patient and used as a measure of physical activity of the patient. This observation is used for the control algorithm now to be described. 15 Fig. 5 is a block diagram of the control arrangement wherein, in addition to the input variables described with reference to example 1 there is a "physical motion" input which can be derived from. an accelerometer associated with a patient. In the simplest form the accelerometer can be a 20 single axis accelerometer. In alternative forms multiple axes of accelerometer sensing can be utilised. DETECTION OF PHYSIOLOGICALLY SIGNIFICANT PUMPING STATES Physiologically critical pumping state detection methods are used based on the non-invasive system observers WO 2004/028593 PCT/AU2003/001281 - 17 pump speed and electrical input power. Activity level is detected using heart rate (detected from pump impeller instantaneous speed) and motion by using an accelerometer although other measuring devices may -be used without 5 departing from the scope of the present invention. These non-invasive observers are utilised as inputs to a control algorithm for a rotary blood pump to seek to ensure that pump output is better adapted to patient rest and exercise states. 10 Identifying Pumping States Methods were developed to detect pumping states based on instantaneous measured pump power and speed. The methods developed allow impeller speed and pump input power to be 15 freely modulated by ventricular contractions. This dynamic information is utilised as feedback to the control system. Data from in-vitro and in-vivo experiments shows that states TVC (total ventricular collapse) and PR (pump regurgitation) produce low flow through the pump. State TVC 20 produces non-pulsatile low flow while state PR produces pulsatile low flow less than 1L/min. States PVC (Partial Ventricular Collapse)r AC (Aortic valve Closed) and. VE (Ventricle Ejecting) produce normal pump flows greater than IL/min. States PVC and PR can be differentiated from state WO 2004/028593 PCT/AU2003/001281 - 18 AC since flow -pulsatility is more evident. State PVC can be differentiated from state VE since the dynamic flow synaetry is different from all other states. The dynamic nature of the flow is reflected by pump speed and power. 5 Instantaneous measured pump speed is used to indicate flow dynamics. Detecting of state TVC, ventricle totally collapsed occluding the inlet cannula. 10 Examining the in-vitro and in-vivo data it has been found that state TVC can be consistently detected by fall in pump flow to near OL/min accompanied by a reduction of flow pulsatility. It has been observed Flow waveform 15 symmetry may not be relevant for detection of this state. Detecting state PVC, ventricle not ejecting and beginning to collapse onto the cannula 20 The state PVC is indicated by a variation in symmetry of the instantaneous speed waveform given a level of pulsatility. Given that normal flow rates can still be observed during this state and that flow pulsatility is large, the only parameter distinguishing this state from 25 the VE state is the flow symmetry. State AC ventricle not ejecting and positive pump flow.

WO 2004/028593 PCT/AU2003/001281 - 19 By analysing the cardiac cycle with the pump it has been was found that there may be a portion of state AC where the aortic valve remains closed, whilst however the pump flow is still pulsatile. Assistance beyond this point 5 causes pump flow pulsatility to reduce. At high perfusion demands, as in exercise, the failed ventricle may be supplemented to such an extent that the flow through the pump is pulseless Theoretically if no left ventricle contraction occurs then implantable rotary blood pump flow 10 will be non pulsatile. Contraction of the left ventricle with the pump connected means that pump head is proportional to the difference between the aortic pressure and the left ventricular pressure (LVP) . If the pump power is increased beyond the -point that the left ventricle is 15 doing no work (the aortic valve no longer opens) maximum LVP begins to decrease. This means that minimum instantaneous pump differential pressure will begin to rise. relative to the RMS of the pump differential pressure over the cardiac cycle- If the- ventricle is weakened through 20 hegrt failure this will occur at relatively lower pump speeds and the mitral valve will still continue to open and LVP maximum will decrease towards zero with increasing speeds. During this interval the mitral valve will open and close. Steady flow occurs when there is no pulsatility in WO 2004/028593 PCT/AU2003/001281 - 20 the speed signal and the mitral valve never closes. The target speed at which this occurs will increase with .SVR or VR and cardiac contractility. Continuing to increase the pump power will cause the transition from pulsatile to non 5 pulsatile flow. This mearis detection of the state VE and state AC can- only be achieved dynamically by considering the maximum instantaneous speed NTnax(t) and the rms of instantaneous speed Nrms(t) f or the nth -and (n-1)th cardiac cycle. A significant change occurrs only if there is a 10 change in average pump speed set point, after load or pre load. A method of detecting the AC state without relying on transitions has been chosen which uses peak to peak flow rate given that pump flow is greater than 1L/min.

WO 2004/028593 PCT/AU2003/001281 - 21 Detecting State VE, ventricle ejecting with positive pump flow 5 State VE may be identified non invasively by pump flow rate being larger than iL/min and peak to peak instantaneous voltage (flow) being greater than a threshold value and the flow symmetry being greater than that for the PVC state. J0 Detecting State PR: The point at which Pump flow rate is less than zero The PR state may be indicated when the pump flow falls 15 below the lower flow limits Qmin which is set to be 1L/min. This level of Qmin is set at iL/min although not "0 L/min" may be was considered a safe limit to be classed as retrograde flow. 20 Pumping state detection using non-invasive pump parameters By analysing pump parameters deriving from invasive derived parameters it is postulated that flow, flow amplitude and waveform symmetry appear to be good 25 indicators of pumping state -using only non-invasively derived pump parameters. These variables can be detected non-invasively using estimated pump flow (Qest,), peak to peak instantaneous speed Npp (n) and symmetry Nsym (n) . Table 1 shows the relationship of physiological parameters to WO 2004/028593 PCT/AU2003/001281 - 22 non-invasive pump parameters for- each of the physiologically identified pumping states which have been taken from iri-vitro and in-vivo data sets (n= 3). Identifying Parameters Invasion (Physiological) Non-invasive via pump (from s peed and powe , Puse LVP Qav Q s 11 M{t Qy,(n) Npp(n) State mmHg prem. max (/mm ) (rpm) (mmHg)(mg (L,/min) TVC <40 <10 <40 < 1 <1 <30 PVC 60-180 > 10 60-180 <'I >1 < 0.4 >30 AC 60-180 < 10 <AoP < I >'I <30 VE 60-180 > 10 >AoP > I >1 >0.4 >30 PR__ 60-180 >10 >AoP > 1 <1 >0.4 >30 5 Table I : A summary of physiological (invasive) and pump (non-invasive) parameters used as the criteria to identify pumping states. Estimated pump flow Qat is derived from Nrffl 5 (t) and 10 PWRm,(L).- The RMS of instantaneous pump speed N.,(t) and power PfRrx (t) are derived from instantaneous speed N(t) and power PWR(t). The haemo-dynamic controller electronics measure the frequency of the speed signal, which is proportional to impeller speed. Using speed rather than 15 power as an observer for dynamic changes is an advantage since it is a digital signals substantially free from electrical noise which may contribute to error.

WO 2004/028593 PCT/AU2003/001281 - 23 Detecting low flow Equation 6 is used to model low and normal flow rate through the pump based on RMS impeller speed and electrical input power. Qet c K + speed + Pwr + (Pwr) 2 + (Pwr)3 equation 6 A flow Index, QIndex, shown in equation 7 is developed 10 to distinguish between low flow rates and normal flow rates. by incorporating Qest- If Opndex > 50 this corresponds in this example to a flow rate greater than 1L/min. A Qplndex < 50 means that flow is less than 11/min or "low flow" 15 Q,, Index = 5O.Q, equation 7 Both the TVC and the PR pumping states defined and discussed' produce low pump flow rates. States PVC, AC and VE produce "normal" flow rates where the circulation is not 20 compromised. Detecting pulsatile flow States TVC and AC produce near non pulsatile pump 25 flow. The difference between these states is that state AC occurs when the circulation is supported and state TVC when it- is not. These states can be differentiated by comparing QestIndex . States PVC, VE and PR produces pulsatile flow. States PVC and VE produce flow which supports the WO 2004/028593 PCT/AU2003/001281 -24 circulation whereas state PR compromises the circulation due to back flow through the pump. It has been shown that instantaneous speed amplitude is proportional to pump flow amplitude. The flow pulsatility index Q.p. Index (equation 5 9) is' developed based on instantaneous speed amplitude N p., (n) (equation 8) which is equal to the difference between the -maximum and the minimum instantaneous impeller speed N max (n) and N min (n). for the nth cardiac cycle. The index outputs a value greater than 50 for pulsatile flow and less 10 than 50 for non fpulsatile flow. ,(n) = N. (n) - NlT, (n) equation 8 Q(,Index = 50, N'~' equation 9 15 Detecting Variations Ln flow symmetry The in-vitro and in-vivo data show that instantaneous speed reflects the inverse symmetry of pump flow whilst 20 current reflects the same symmetry, although speed exhibits less electrical noise. Thus it is postulated that the symmetry of flow can be estimated by using the inverted symmetry of instantaneous speed. States PVC and VE both produce flow rates which 25 support the circulation and a degree of pulsatility. Differentiating between states can be achieved by WO 2004/028593 PCT/AU2003/001281 - 25 considering the symmetry of the flow wave form which is reflected in instantaneous speed. The symmetry of flow rate is an inversion of the instantaneous speed signal. The flow symmetry index Q.ymIndex (equation 11) is developed by 5 using the inverted speed waveform symmetry defined by equation 10 with the symmetry threshold Qy.hMAX set at 0. The :index is set so that if the flow symmetry falls below 0.3 (speed symmetry rises above 0.7) its output is less than 50. 10a (N,,. (n) -Nmin(n) N,,. . (n) equation 10 N,_,(n) QQ aMAX. yYJndex = 50 "" equation 11 15 Determining the current pumping state from non-invasive indicators The block diagram shown in figure 5 shows the module that combines the detection methods discussed above derived 20 from instantaneous power and speed. The current state is determined by the logic table shown in figure 10 where flow, flow pulsatility and symmetry are used to decide the present pumping state.

WO 2004/028593 PCT/AU2003/001281 -_26 Deteotion of heart rate using pump speed While pulsatile flow is detected, the heart rate is 5 calculated by using the array of speed samples. For the entire speed array N[tI-tn] of samples the frequency of speed is calculated by using the derivative of speed and detecting the time of the speed maxima and minim'a. The derivative of speed is defined in equation 12. 10 IN(i.) = N(t,) -Nft,_) equation 12 dt At HR is then calculated by time stamping the maxima and minima of the speed signal given by HRa and HRb in 15 equations 13 and 14. The average is then computed and used as HR using equation 15. Speed maxima are detected by dN(t,)/dt changing from a positive, to a negative value. Speed minima are detected by dN(t,)/dt changing from a negative to a positive value. T tsxl-1), tminrn), Cmin(n-2) 20 are th'e time stamps for the maximum and minimum values of instantaneous speed. 60 H-Ra = equation 13 I [tmax(n) - tmax(nt 1)] 25 60 HRb= equation 74 [tmin(n) - tmin(n -1)} WO 2004/028593 PCT/AU2003/001281 - 27 HR = + 2Rb equation 15 2 Detection of physical motion 5 An accelerometer is mounted in the controller electronics and used to detect physical motion. The accelerometer output is amplified by a differential amplifier and integrated to provide a signal level 10 indicating continuous physical motion. A preferred embodiment of the present invention of the physiological demand responsive controller is suited for used with implantable third generation LVASs. Also, a further embodiment of the present invention is designed to 15 cooperate with a Ventrassistm left ventricle assist system (LVAS). One of the preferred embodiments may automatically adjust the pumping speed of an implanted third generation blood pump to an optimal level for the varying physiological 20 needs of the implanted patient. The preferred embodiment ma achieve this by periodically iteratively changing the speed setpoint of the pump. When the control system detects increased physiological demand by the patient (e.g. by physical exertion) the controller will increase the pumping 25 speed accordingly. The pumping state of the patient's heart and physiological demand of the patient will be computed by WO 2004/028593 PCT/AU2003/001281 - 28 the control system in real time as functions of the pump's motor power and speed setpoint of the, pump., Additionally, the physiological demand of the patient may also be detected by the use of a three axis accelerometer. 5 This accelerometer may be able to detect the instantaneous motion of the patient. Preferably, this instantaneous motion may also be indicative of the relative motion of the patient. The, output of the accelerometer may preferably be directed into a conditioning circuit to 10 digitise and filter the output signal of said accelerometer. This signal will then be passed from the conditioning circuit to - a computational . module which derives a physiological demand state (eg. resting, sleeping, exercising, or patient collapse) as a numerically 15 represented version of the state (eg. 1=resting; 2=sleeping etc). The numerically represented Version of the physiological demand state may then be inputted into the control system for a pumping device or medical device. The pumping speed of the implantable blood pump may then be 20 altered in respect of the predetermined rangE for physiological demand for a particular patient.. Preferably, the predetermined ranges of pumping speeds will be 'set by a specialist doctor at the time of implantation of the blood pump. Additionally, it may be WO 2004/028593 PCT/AU2003/001281 - 29 preferable to allow doctors to amend the predetermined range as they see fit. Preferably in an embodiment of the present invention the control system may include a specialised algorithm. This 5 algorithm may include a mathematical model of ideal pumping speed of an implantable blood pump for suitable physiological conditions of the patient. This algorithm may receive input or data included within three broad areas of data. These areas of data may include pump power, 10 instantaneous pump speed and physical motion. The algorithm within the controller system (see Figure 9) may use these areas of data to predict certain patient data. This patient data may include blood flow rate, heart rate, flow profile, pulsatility and physiological demand. The algorithm will 15 then output. the preferred pump speed and the remainder of the controller system will use this information to set a speed setpoint for the blood pump. Preferably, an embodiment of the present invention will be such that iterative changes will be able to be made 20 in timely manner. In a further embodiment of the present invention, a preferred physiological demand responsive controller system may be adapted for use with a radial -off flow type centrifugal blood pump.

WO 2004/028593 PCT/AU2003/001281 - 30 The above describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing 5 from the scope and spirit of the present invention. The system is particularly suited for use with pumps which exhibit a relatively flat HQ curve as described with reference to Pig. 8. In particular, but not-exclusively, pumps of the radial off flow type as, for example, 10 described in International Patent Application PCT/AU98/00725 can exhibit this relatively flat characteristic. The description of PCT/AU98/00725 is incorporated herein by cross-reference

Claims (23)

1. A demand responsive physiological control system for use with a rotary blood pump; said system including 5 a pump controller which is capable of controlling pump speed of said pump; said system further including a physiological controller, and wherein said physiological controller is adapted to analyse input data relating to physiological condition of a 10 user of said pump; and wherein said physiological controller determines appropriate pumping speed and sends a speed control signal to said pump controller to adjust pump speed; said system further including a physiological state detector which provides said 15 input data indicative of at least one physiological state of said user ,in use, to said physiological controller.

2. The system as in claim 1 wherein the physiological state detector includes an accelerometer to sense 20 motion of the user, when in use.

3. The system as in claim 2 wherein the accelerometer senses motion in at least one axis.

4. The system as in claim 3 wherein the accelerometer senses motion in three orthogonal axes. WO 2004/028593 PCT/AU2003/001281 - 32 5. The system as in any preceding claim, wherein said system includes a pump monitor that detects information relating to voltage and current of the pump and delivers this information to said 5 physiological controller. (. The system as in claim 5 wherein the ptimp monitor detects an instantaneous pump impeller speed of the rotary blood pump through measurements.

7. The system as in claim 6 wherein the pump monitor 10 detects non-invasively.

8. The system as in claim 6 wherein said physiological controller uses said information received from the pump monitor to derive mathematically an appropriate pump speed. 15 9. The system as in claim 8 wherein the physiological controller assesses flow dynamics and an average flow estimate developed from speed and input power supplied to the pump by the pump controller.

10. The system as in claims 8 wherein the physiological 20 controller mathematically determines a pumping state and if a deleterious state is determined the speed control signal is changed accordingly.

11. The system as in' any preceding claim wherein the physiological detector includes a means of detecting WO 2004/028593 PCT/AU2003/001281 - 33 and quantifying a heart rate of the user, when in use.

12. The system as in claim '11 wherein the physiological detector includes a means of non-invasively 5 detecting and quantifying a heart rate of the user, in use.

13. The system as in any preceding claim wherein the physiological controller can determine a heart rate of the user by sensing speed of the pump. 10 14.. The system as in any preceding claim wherein the physiological controller can determine a heart rate of the user using power inputted to the pump.

15. The system as in any preceding claim wherein the pump is internally implantable within the user. 15 16. The system as in claim 15 wherein the pump is a ventricle assist device.

17. The system as in claims 15 or 16 wherein the pump has a hydrodynamic bearing that produces a relatively flat pump head versus pump flow curve. 20 18. The system as in any preceding claim wherein the physiological controller is capable of manual manipulation by the user.

19. The -system as in claim 18 wherein the manual manipulation is within adjustable predefined limits. WO 2004/028593 PCT/AU2003/001281 34

20. The -system as in any preceding claim wherein the physiological controller is adapted for communication with a computer and wherein the physiological controller is adapted for manipulation 5 by a software user interface.

21. The system as in any preceding claim wherein the physiological controller includes an alarm.

22. A process for using physiological demand data to optimize pump speed of a rotary blood pump wherein 10 the process comprises of the following steps: a heart rate of the user is non-invasively determined; a level of physiological exertion of the user is determined through non invasive means; an instantaneous pump speed and input power is used to 15 calculate instantaneous blood flow rate; a pumping state is mathematically determined; the heart rate, pumping state and level of physical exertion are compared to the blood flow rate; and the pumping speed of the rotary blood. pump is changed to 20 appropriately supply the user with the correct blood flow rate.

23. A pump control system for a pump for use in a heart assist device; said system comprising data processing means which receives body motion WO 2004/028593 PCT/AU2003/001281 - 35 information and heart rate information thereby to derive a speed control signal for impeller speed of an impeller of said pump.

24. The. system of Claim 23 wherein said body. motion 5 information is derived from an accelerometer.

25. The system of Claim 24 wherein said accelerometer senses motion in a single axis.

26. The system of Claim 24 wherein said accelerometer senses motion in three orthogonal axes. 10 27. The system of. Claim 23 wherein said heart rate information is derived from a non-invasive sensor.

28. The system of Claim 27 wherein said heart rate information is derived from voltage and current applied to an electric motor driving said impeller. 15 29. A method of control of pump speed of a blood pump; said method comprising establishing a base set point speed; said method further comprising, establishing 'one or more criteria which, if satisfied, cause establishment of at least a second set point speed; 20 said second set point speed higher than that of said base set point speed.

30. A physiological demand responsive controller for use with a blood pump implanted within a patient, wherein said controller includes: an accelerometer, WO 2004/028593 PCT/AU2003/001281 36 which produces an output signal as an analogue of a patient's physical motion; wherein said accelerometer provides an output signal to the circuits of the controller; and wherein said 5 controller controls pumping speed setpoints of blood pump using said output signal.

31. The controller of claim 30 wherein said controller determines pumping speed setpoint by use a mathematical model or algorithm. 10 32. The controller of claim 30 wherein said circuits of the controller include at least one conditioning circuit.