Patent Description:
Blood pressure (BP) or, more precisely, arterial blood pressure, is the pressure exerted by circulating blood on the arterial vessel walls. It is one of the key vital signs to establish patient well-being and therefore needs to be monitored for patients at risk. Blood pressure is a periodic signal, which rises at each contraction of the heart and decreases in between heart beats. It is typically described by systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial blood pressure (MAP), where systolic blood pressure is the maximum blood pressure during heart cycle, diastolic blood pressure is the minimum blood pressure during heart cycle, and mean arterial blood pressure is the average blood pressure during a heart cycle.

Different techniques exist by which blood pressure can be determined and these can be classified as invasive or non-invasive blood pressure measurement techniques. Typically, non-invasive blood pressure (NIBP) measurement techniques are cuff-based, which require an inflatable cuff to be placed around a limb (which is usually the upper arm) of a subject. The pressure in the cuff is then changed to infer blood pressure. There are two common methods that use a cuff in this way, which are referred to in the art as the auscultatory method and the oscillometric method respectively.

The auscultatory method for NIBP measurement is based on the appearance and disappearance of sounds created by the artery under the cuff during the period that the cuff pressure is changed. These sounds are referred to in the art as Korotkoff sounds. The pressures at which the Korotkoff sounds appear and vanish are indicative of DBP and SBP with Korotkoff sounds appearing at each heart beat between DBP and SBP. The measurement of sound can be performed manually with a stethoscope that is placed over the artery just below the cuff, or in an automated way with a microphone under the cuff.

In the oscillometric method for NIBP measurement, the systolic and diastolic blood pressure values are based on small volume oscillations or pressure oscillations that are induced in the cuff by each heart beat. The amplitude of these volume or pressure oscillations depends on the difference between the cuff pressure and the actual arterial blood pressure. Systolic blood pressure and diastolic blood pressure are then determined as the cuff pressure where the volume or pressure oscillations have amplitudes of a certain fraction of the maximum oscillation amplitude. These fractions are typically heuristically determined.

In both the auscultatory and oscillometric method, the mean arterial pressure is typically calculated as: MAP = <NUM>/<NUM>*DBP + <NUM>/<NUM>*SBP.

The oscillometric and auscultatory measurement methods can be performed either during inflation of the cuff or during deflation of the cuff. Conventionally, measurements during deflation are used, in which the cuff is rapidly inflated to a level above the SBP where the blood flow in the artery under the cuff is blocked, after which cuff pressure is decreased gradually or in a stepwise manner. During deflation, the volume or pressure oscillations or the Korotkoff sounds are measured. While deflation stage NIBP measurement is well-established, an issue exists in the discomfort it introduces to the subject. In particular, the subject is exposed to a relatively high cuff pressure for a certain amount of time and pressures above a certain level can be uncomfortable and even painful, either due to the pressure exerted by the cuff itself or due to a build-up of venous blood in the clamped extremity (namely, venous pooling). The longer these pressures are applied to the subject, the higher the discomfort level is for the subject.

Another issue with utilizing the deflation based NIBP measurement is that the process of inflating the cuff and then deflating the cuff can be considerably long, where each NIBP measurement during deflation typically takes <NUM> seconds to complete. Also, since a defined maximum pressure level needs to be achieved before the deflation procedure can be initiated, the subject is exposed to a maximum cuff pressure that is higher than that required for the blood pressure measurement itself. Furthermore, the inherent variability of blood pressure over time can distort a single blood pressure measurement.

Due to these issues, apparatus have been developed that modify cuff-based NIBP measurements to determine the arterial volume (or pressure) oscillations during (e.g. continuous) inflation of the cuff. An example of such apparatus are inflation based NIBP (iNIBP) apparatus that use a fixed flow (mL/s) and variable speed (mmHg/s) or a fixed speed (mmHg/s) and a variable flow (mL/s) to inflate the cuff. However, the fixed flow technique results in the iNIBP measurement apparatus only functioning for a small range of cuffs as, for smaller cuffs, the inflation is too fast (which results in there being too few pressure oscillations to have an accurate estimate of systolic and diastolic blood pressure) and, for larger cuffs, the iNIBP measurement becomes slow. The fixed speed technique overcomes these problems by changing the flow for a certain desired speed. However, there still exists an issue with this implementation in that a wide range of flows has to be generated and thus a wide range of cuffs have to be available for use with the iNIBP measurement apparatus.

The pump of the iNIBP measurement apparatus can be used to generate a range of flows. However, it is difficult to span a complete flow range from the smallest of cuffs (e.g. cuffs for neonatal subjects) to the largest of cuffs (e.g. thigh cuffs for an adult) with a normal pump. Moreover, currently, the only techniques aimed at addressing this require additional hardware components to be added to the iNIBP measurement apparatus, which can be complex. Exemplary cuffs for use with iNIBP measurement apparatus are known from documents <CIT> and <CIT>.

As noted above, the limitations associated with existing techniques are that the range of flows that can be generated to inflate a cuff for use in inflation-based non-invasive blood pressure (iNIBP) measurement is limited and the limited range of flows that are possible also require complex hardware modifications to an iNIBP measurement apparatus for use with the cuff. It would thus be valuable to address these limitations.

Therefore, according to a first aspect, there is provided a cuff for use with an inflation-based non-invasive blood pressure, NIBP, measurement apparatus. The cuff comprises an inlet configured to be coupled to an outlet of the inflation-based NIBP measurement apparatus to receive a flow of fluid and a bladder coupled to the inlet and inflatable to pressurize a measurement site of a subject by receiving the flow of fluid. The cuff also comprises a valve disposed along a flow path between the inlet and the bladder or disposed on the bladder. The valve is configured to pass part of the flow of fluid received in the bladder to the atmosphere during inflation of the bladder and the valve is sized to have a flow resistance that causes the bladder to inflate at a required flow rate for inflating the cuff.

In some embodiments, the flow resistance of the valve may be defined based on a physical property of the cuff. In some embodiments, the physical property of the cuff may comprise any one or more of a size of the cuff, an elasticity of the cuff, and a compliance of the cuff. In some embodiments, the flow resistance of the valve may be defined based on a flow range of a pump configured to output the flow of fluid. In some embodiments, the flow resistance of the valve may be defined based on a target inflation rate for the cuff to reach for determining a blood pressure measurement for the subject. In some embodiments, the valve may have a diameter that defines the flow resistance of the valve. In some embodiments, the valve may be a needle valve, a globe valve, a butterfly valve, or a poppet valve. In some embodiments, the cuff may comprise a deflation valve controllable to deflate the bladder.

According to a second aspect, there is provided a system comprising at least one cuff as described earlier. In some embodiments, the system may comprise the inflation-based NIBP measurement apparatus. In some embodiments, the inflation-based NIBP measurement apparatus may comprise a deflation valve controllable to deflate the bladder. In some embodiments, the inflation-based NIBP measurement apparatus may comprise a pump configured to output the flow of fluid. In some embodiments, the system may comprise a processor configured to acquire a signal indicative of pressure oscillations detected in the cuff during inflation of the cuff and determine a blood pressure measurement for the subject based on the acquired signal. In some embodiments, the system may comprise a plurality of cuffs as described above. In some embodiments, at least two cuffs of the plurality of cuffs may be of different sizes and the flow resistance of the valve of each of the at least two cuffs may be different.

According to the aspects and embodiments described above, the limitations of existing techniques are addressed. In particular, the above-described aspects and embodiments enable a wider range of flows to be generated to inflate the bladder of the cuff without requiring the hardware configuration of an inflation-based NIBP measurement apparatus to be modified for use with the cuff. In this way, the above-described aspects and embodiments enable inflation-based NIBP measurement for a wider range of cuffs. As a desired fluid (e.g. gas) flow is to a large extent determined by the size of the cuff, the valve disposed along a flow path between the inlet and the bladder or on the bladder according to the above-described aspects and embodiments can be used to optimize the flow range to be supported by a particular size of cuff (e.g. an infant, a child cuff, or any other size cuff). This allows for improved control of the flow range as it can, for example, allow a pump of the inflation-based NIBP measurement apparatus to be operated at a high-flow condition in order to avoid artifacts.

The limitations associated with the existing techniques discussed earlier are therefore addressed by way of the above-described aspects and embodiments.

There is provided herein a cuff (or clamp unit) for use with a non-invasive blood pressure (NIBP) measurement apparatus or, more specifically, an inflation-based non-invasive blood pressure (iNIBP) measurement apparatus, which overcomes the limitations with existing techniques.

The cuff described herein can be a wearable cuff. That is, the cuff described herein can be configured to be worn on or around (e.g. wrapped around, attached to, or fastened to) a measurement site of the subject (e.g. a patient). The measurement site of the subject referred to herein can be any site on the body of the subject that is suitable for use in measuring a blood pressure of the subject, such as any site on the body of the subject that comprises an artery. For example, the measurement site of the subject referred to herein may be located on a limb of the subject, such as an arm (e.g. an upper arm or a forearm) of the subject or the leg (e.g. a thigh) of the subject. Thus, the cuff described herein can be configured to be worn on or around (e.g. wrapped around, attached to, or fastened to) a limb of the subject. The subject referred to herein can be, for example, an adult or a pediatric subject, e.g. an infant, a child or an adolescent. An infant can, for example, be a neonate, such as a pre-term or premature infant, a full-term infant or a post-term infant.

<FIG> illustrate the cuff <NUM>, <NUM> described herein. Briefly, with reference to <FIG>, the cuff <NUM>, <NUM> described herein comprises an inlet <NUM>, <NUM> configured to be coupled to an outlet of the inflation-based NIBP measurement apparatus (not illustrated in <FIG>) to receive a flow of fluid.

The cuff <NUM>, <NUM> described herein also comprises a bladder <NUM>, <NUM> coupled to the inlet <NUM>, <NUM> and inflatable to pressurize a measurement site of a subject (not illustrated in <FIG>) by receiving the flow of fluid. In this way, the bladder <NUM>, <NUM> can pressurize an artery in the measurement site of the subject. Typically, the bladder <NUM>, <NUM> can be supplied with a fluid (e.g. a gas, such as air, or any other fluid) suitable for inflating the bladder <NUM>, <NUM>. The bladder <NUM>, <NUM> can be inflatable to pressurize the measurement site of a subject (and thus an artery in the measurement site of the subject) at the pressure of the fluid in the bladder <NUM>, <NUM>. Thus, the bladder <NUM> can hold (or store) at least part of the received fluid.

The cuff <NUM>, <NUM> described herein also comprises a valve <NUM>, <NUM>. The valve <NUM>, <NUM> is either disposed along a flow path between the inlet <NUM> and the bladder <NUM> (as illustrated in <FIG>) or disposed on the bladder <NUM> (as illustrated in <FIG>). In some embodiments where the valve <NUM> is disposed along a flow path between the inlet <NUM> and the bladder <NUM>, such as that illustrated in <FIG>, the valve <NUM> may be disposed on a tube (or hose) that is connected to or is part of the bladder <NUM>. The flow resistance of the valve <NUM>, <NUM> described herein is such that the valve <NUM>, <NUM> passes (or releases) part of the flow of fluid received in the bladder <NUM>, <NUM> to the atmosphere in order to inflate the bladder <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>. That is, the valve <NUM>, <NUM> has a flow resistance such that the valve <NUM>, <NUM> passes (or releases) part of the flow of fluid received in the bladder <NUM>, <NUM> to the atmosphere to inflate the bladder <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>. The flow resistance referred to herein can be defined as a pressure drop over the valve <NUM>, <NUM> divided by a flow rate through the valve <NUM>, <NUM>.

In some embodiments, the flow resistance of the valve <NUM>, <NUM> can be defined based on a physical property of the cuff <NUM>, <NUM>. For example, in some embodiments, the physical property of the cuff <NUM>, <NUM> may comprise any one or more of a size of the cuff <NUM>, <NUM> (e.g. an inner circumference of the cuff <NUM>, <NUM>), an elasticity of the cuff <NUM>, <NUM>, and a compliance of the cuff <NUM>, <NUM>. The compliance of the cuff <NUM>, <NUM> may also be referred to in the art as the "cuff compliance" for the cuff <NUM>, <NUM>. The cuff compliance for the cuff <NUM>, <NUM> can be defined as a value that relates a pressure change in the cuff <NUM>, <NUM> due to a volume change of the cuff <NUM>, <NUM>.

Alternatively or in addition, in some embodiments, the flow resistance of the valve <NUM>, <NUM> may be defined based on one or more properties of a system (or components of the system) comprising the cuff <NUM>, <NUM>. For example, in some embodiments, the flow resistance of the valve <NUM>, <NUM> may be defined based on a flow range of a pump configured to output the flow of fluid. For example, the pump configured to output the flow of fluid may have a certain flow range that can be provided. The flow range of the pump referred to herein is the range of flow rates that the pump can provide. In embodiments where a pump is configured to output the flow of fluid, the pump can act as a fluid flow source. As the valve <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM> to the atmosphere, in effect, the valve <NUM>, <NUM> passes part of the fluid flow output of the pump to the atmosphere in order to inflate the bladder <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM> according to these embodiments.

Alternatively or in addition, in some embodiments, the flow resistance of the valve <NUM>, <NUM> may be defined based on a target inflation rate for the cuff <NUM>, <NUM> to reach (or achieve) for determining a blood pressure measurement for the subject or, more specifically, an inflation-based blood pressure measurement.

In some embodiments, the flow resistance of the valve <NUM>, <NUM> may be defined by the size of the valve <NUM>, <NUM>. For example, the valve <NUM>, <NUM> may have a diameter that defines the flow resistance of the valve <NUM>, <NUM>. In some embodiments, the valve <NUM>, <NUM> can be a needle valve, a globe valve, a butterfly valve, a poppet valve or any other valve suitable to pass part of the flow of fluid received in the bladder <NUM>, <NUM> to the atmosphere.

In some embodiments, the cuff <NUM>, <NUM> may comprise a deflation valve (not illustrated in <FIG>). The deflation valve of the cuff <NUM>, <NUM> can be controllable to deflate the bladder <NUM>, <NUM> of the cuff <NUM>, <NUM>. The deflation valve of the cuff <NUM>, <NUM> can thus be any valve that is controllable to deflate the bladder <NUM>, <NUM> of the cuff <NUM>, <NUM>. The deflation valve may also be referred to as a release valve.

<FIG> illustrates a system <NUM> comprising a cuff <NUM> according to an embodiment. The system <NUM> may also be referred to as an inflation-based NIBP measurement system. Although only one cuff <NUM> is illustrated in <FIG>, the system <NUM> can comprise at least one cuff <NUM>, i.e. one or a plurality of cuffs <NUM>. The at least one cuff <NUM> can comprise at least one cuff <NUM> as described earlier with reference to <FIG>. Alternatively or in addition, the at least one cuff <NUM> can comprise at least one cuff <NUM> described earlier with reference to <FIG>. Thus, the at least one cuff <NUM> comprises an inlet <NUM> (such as the inlet <NUM> illustrated in and described earlier with reference to <FIG> or the inlet <NUM> illustrated in and described earlier with reference to <FIG>), a bladder <NUM> (such as the bladder <NUM> illustrated in and described earlier with reference to <FIG> or the bladder <NUM> illustrated in and described earlier with reference to <FIG>), and a valve (not illustrated in <FIG>, such as the valve <NUM> illustrated in and described earlier with reference to <FIG> or the valve <NUM> illustrated in and described earlier with reference to <FIG>).

In some embodiments where the system <NUM> comprises a plurality of cuffs <NUM>, at least two cuffs of the plurality of cuffs <NUM> may be of different sizes. In these embodiments, the flow resistance of the valve of each of the at least two cuffs can be different.

As illustrated in <FIG>, in some embodiments, the system <NUM> can comprise the inflation-based NIBP measurement apparatus <NUM>. The inflation-based NIBP measurement apparatus <NUM> can be for use with the cuff <NUM> in measuring blood pressure. As illustrated in <FIG>, the inflation-based NIBP measurement apparatus <NUM> comprises an outlet <NUM>. The outlet <NUM> is configured to be coupled to the inlet <NUM> of at least one cuff <NUM> (such as the inlet <NUM> of the cuff <NUM> illustrated in <FIG> and/or the inlet <NUM> of the cuff <NUM> illustrated in <FIG>).

As illustrated in <FIG>, in some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise at least one supply line (or at least one supply tube) <NUM>, which may also be referred to as at least one pressure supply line (or at least one pressure supply tube) <NUM>. In these embodiments, the at least one supply line <NUM> can comprise the outlet <NUM>. Thus, the cuff <NUM> may be coupled to the inflation-based NIBP measurement apparatus <NUM> via at least one supply line <NUM> according to some embodiments. The at least one supply line <NUM> can be arranged for pressurizing the bladder of the cuff <NUM> (such as the bladder <NUM> of the cuff <NUM> illustrated in <FIG> or the bladder <NUM> of the cuff <NUM> illustrated in <FIG>) and, consequently, the measurement site of the subject. The at least one supply line <NUM> may be provided for inflating and/or deflating the bladder of the cuff <NUM>. As an alternative to the at least one supply line <NUM>, in other embodiments (not illustrated), the inflation-based NIBP measurement apparatus <NUM> can be coupled directly to (e.g. mounted directly on) the cuff <NUM>. As mentioned earlier, the cuff <NUM> can be supplied with any fluid suitable for inflating the bladder of the cuff <NUM>.

In some embodiments, as illustrated in <FIG>, the inflation-based NIBP measurement apparatus <NUM> may comprise a deflation valve <NUM>. The deflation valve <NUM> may also be referred to as a release valve. The deflation valve <NUM> of the inflation-based NIBP measurement apparatus <NUM> can be controllable to deflate the bladder of the cuff <NUM> (such as the bladder <NUM> of the cuff <NUM> illustrated in <FIG> or the bladder <NUM> of the cuff <NUM> illustrated in <FIG>). The deflation valve <NUM> can thus be any valve that is controllable to deflate the bladder of the cuff <NUM>. The inflation-based NIBP measurement apparatus <NUM> may comprise the deflation valve <NUM> instead of or in addition to a deflation valve of at least one the cuff <NUM>. In some embodiments, the deflation valve <NUM> can be controllable by the inflation-based NIBP measurement apparatus <NUM> (or, more specifically, by a processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) to deflate the bladder of the cuff <NUM>. The inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) may communicate with and/or connect to the deflation valve <NUM> in any suitable way to control the deflation valve <NUM>.

As illustrated in <FIG>, in some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise a pump <NUM>. Alternatively or in addition, the pump <NUM> may be external to (e.g. separate to or remote from) the inflation-based NIBP measurement apparatus <NUM>. The pump <NUM> can be configured to output a flow of fluid. That is, the pump <NUM> can be configured to output a flow of fluid via the outlet <NUM> of the inflation-based NIBP measurement apparatus <NUM> to the inlet <NUM> of a cuff <NUM> to which the outlet <NUM> is coupled (such as the inlet <NUM> of the cuff <NUM> illustrated in <FIG> and/or the inlet <NUM> of the cuff <NUM> illustrated in <FIG>).

As described earlier with reference to <FIG>, the inlet of the cuff <NUM> is configured to receive the flow of fluid. Thus, the pump <NUM> can be controllable to inflate the bladder <NUM> of the cuff <NUM> according to some embodiments. The pump <NUM> can thus be any pump that is controllable to inflate the bladder <NUM> of the cuff <NUM>. In particular, the pump <NUM> can be controllable to provide a flow of fluid to inflate the bladder <NUM> of the cuff <NUM>. In some embodiments, the pump <NUM> can be controllable by the inflation-based NIBP measurement apparatus <NUM> (or, more specifically, by a processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor). The inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) may communicate with and/or connect to the pump <NUM> in any suitable way to control the pump <NUM>.

In some embodiments, the pump <NUM> may be configured to provide a flow of fluid at a predetermined margin from a minimum fluid flow limit. By operating the pump <NUM> at the predetermined margin from the minimum fluid flow limit, noise from the pump <NUM> that can produce artifacts (which may interfere with inflation-based NIBP measurements) can be prevented from affecting inflation-based NIBP measurements. It can be the case that the artifacts are more of an issue when the pump <NUM> is operated to provide a flow of fluid at a minimum fluid flow limit of approximately <NUM>/s. Thus, in some embodiments, the pump <NUM> may be configured to provide a flow of fluid that is greater than <NUM>/s, e.g. greater than <NUM>/s.

The inflation-based NIBP measurement apparatus <NUM> described herein can be implemented in numerous ways, with software and/or hardware, to perform the various functions described herein. In particular implementations, the inflation-based NIBP measurement apparatus <NUM> can comprise a plurality of software and/or hardware modules, each configured to perform, or that are for performing, individual or multiple functions described herein.

In some embodiments, the system <NUM> may comprise a processor <NUM>. As illustrated in <FIG>, in some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise the processor <NUM>. However, in other embodiments, the processor <NUM> may be external to (e.g. separate to or remote from) the inflation-based NIBP measurement apparatus <NUM>. The processor <NUM> may comprise one or more processors (such as one or more microprocessors, one or more multi-core processors and/or one or more digital signal processors (DSPs)), one or more processing units, and/or one or more controllers (such as one or more microcontrollers) that may be configured or programmed (e.g. using software or computer program code) to perform the various functions described herein.

The inflation-based NIBP measurement apparatus <NUM> may be implemented as a combination of dedicated hardware (e.g. amplifiers, pre-amplifiers, analog-to-digital convertors (ADCs) and/or digital-to-analog convertors (DACs)) to perform some functions and the processor (e.g. one or more programmed microprocessors, DSPs and associated circuitry) <NUM> to perform other functions.

In some embodiments, the processor <NUM> can be configured to acquire a signal indicative of pressure oscillations detected in the cuff <NUM> during inflation of the cuff <NUM>. In some of these embodiments, the processor <NUM> can also be configured to determine a blood pressure measurement for the subject based on the acquired signal. Any existing techniques for determining a blood pressure measurement for a subject based on an acquire signal indicative of pressure oscillations can be used and a person skilled in the art will be aware of such existing techniques that may be used.

Although not illustrated in <FIG>, in some embodiments, the system <NUM> may comprise at least one pressure sensor. The at least one pressure sensor can be configured to measure the pressure in the bladder of the cuff <NUM> (such as the bladder <NUM> of the cuff <NUM> illustrated in <FIG> or the bladder <NUM> of the cuff <NUM> illustrated in <FIG>). In some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise the at least one pressure sensor configured to measure the pressure in the bladder of the cuff <NUM>. Alternatively or in addition, the cuff <NUM> may comprise the at least one pressure sensor configured to measure the pressure in the bladder of the cuff <NUM>. Alternatively or in addition, at least one pressure sensor external to (e.g. separate to or remote from) the inflation-based NIBP measurement apparatus <NUM> and/or the cuff <NUM> may be configured to measure the pressure in the bladder of the cuff <NUM>.

In some embodiments, the at least one pressure sensor can be controllable by the inflation-based NIBP measurement apparatus <NUM> or, more specifically, the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor to measure the pressure in the bladder of the cuff <NUM>. The inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) may communicate with and/or connect to the at least one pressure sensor in any suitable way to control the at least one pressure sensor.

Although also not illustrated in <FIG>, in some embodiments, the system <NUM> may comprise a communications interface (or communications circuitry). In some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise a communications interface. Alternatively or in addition, the communications interface may be external to (e.g. separate to or remote from) inflation-based NIBP measurement apparatus <NUM>. The communications interface can be for enabling the inflation-based NIBP measurement apparatus <NUM>, or components of the inflation-based NIBP measurement apparatus <NUM>, to communicate with and/or connect to one or more other components, sensors, interfaces, devices, or memories (such as any of those described herein).

For example, the communications interface can be for enabling the inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) to communicate with and/or connect to any one or more of the deflation valve <NUM>, the pump <NUM>, and the at least one pressure sensor described earlier. The communications interface may enable the inflation-based NIBP measurement apparatus <NUM>, or components of the inflation-based NIBP measurement apparatus <NUM>, to communicate and/or connect in any suitable way. For example, the communications interface may enable the inflation-based NIBP measurement apparatus <NUM>, or components of the inflation-based NIBP measurement apparatus <NUM>, to communicate and/or connect wirelessly, via a wired connection, or via any other communication (or data transfer) mechanism. In some wireless embodiments, for example, the communications interface may enable the inflation-based NIBP measurement apparatus <NUM>, or components of the inflation-based NIBP measurement apparatus <NUM>, to use radio frequency (RF), Bluetooth, or any other wireless communication technology to communicate and/or connect.

Although also not illustrated in <FIG>, in some embodiments, the system <NUM> may comprise a memory. In some embodiments, inflation-based NIBP measurement apparatus <NUM> may comprise the memory. Alternatively or in addition, the memory may be external to (e.g. separate to or remote from) inflation-based NIBP measurement apparatus <NUM>. The inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) may be configured to communicate with and/or connect to the memory. The memory may comprise any type of non-transitory machine-readable medium, such as cache or system memory including volatile and non-volatile computer memory such as random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), and electrically erasable PROM (EEPROM). In some embodiments, the memory can be configured to store program code that can be executed by a processor (e.g. the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) to cause the inflation-based NIBP measurement apparatus <NUM> to operate in the manner described herein.

Alternatively or in addition, in some embodiments, the memory can be configured to store information required by or resulting from implementations of the functions described herein. For example, in some embodiments, the memory may be configured to store any one or more of a measure of a pressure in the bladder of the cuff <NUM>, a determined blood pressure measurement for a subject, or any other information, or any combination of information, required by or resulting from the implementation of the functions described herein. In some embodiments, the inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) can be configured to control the memory to store information required by or resulting from the implementation of the functions described herein.

Although also not illustrated in <FIG>, the system <NUM> may comprise a user interface. In some embodiments, the inflation-based NIBP measurement apparatus <NUM> may comprise the user interface. Alternatively or in addition, the user interface may be external to (e.g. separate to or remote from) the inflation-based NIBP measurement apparatus <NUM>. The inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) may be configured to communicate with and/or connect to a user interface. The user interface can be configured to render (or output, display, or provide) information required by or resulting from the implementation of the functions described herein. For example, in some embodiments, the user interface may be configured to render (or output, display, or provide) one or more of a measure of a pressure in the bladder of the cuff <NUM>, a determined blood pressure measurement for a subject, or any other information, or any combination of information, required by or resulting from the implementation of the functions described herein. Alternatively or in addition, the user interface can be configured to receive a user input. For example, the user interface may allow a user to manually enter information or instructions, interact with and/or control the inflation-based NIBP measurement apparatus <NUM>.

Thus, the user interface may be any user interface that enables the rendering (or outputting, displaying, or providing) of information and, alternatively or in addition, enables a user to provide a user input. For example, the user interface may comprise one or more switches, one or more buttons, a keypad, a keyboard, a mouse, a touch screen or an application (for example, on a smart device such as a tablet, a smartphone, or any other smart device), a display or display screen, a graphical user interface (GUI) such as a touch screen, or any other visual component, one or more speakers, one or more microphones or any other audio component, one or more lights (such as light emitting diode LED lights), a component for providing tactile or haptic feedback (such as a vibration function, or any other tactile feedback component), an augmented reality device (such as augmented reality glasses, or any other augmented reality device), a smart device (such as a smart mirror, a tablet, a smart phone, a smart watch, or any other smart device), or any other user interface, or combination of user interfaces. In some embodiments, the user interface that is controlled to render information may be the same user interface as that which enables the user to provide a user input. In some embodiments, the inflation-based NIBP measurement apparatus <NUM> (or the processor <NUM> of the inflation-based NIBP measurement apparatus <NUM> or any other processor) can be configured to control the user interface to operate in the manner described herein.

Although also not illustrated in <FIG>, the inflation-based NIBP measurement apparatus <NUM> may comprise a battery or other power supply for powering the inflation-based NIBP measurement apparatus <NUM> or means for connecting the inflation-based NIBP measurement apparatus <NUM> to a mains power supply. It will also be understood that the inflation-based NIBP measurement apparatus <NUM> may comprise any other component to those described herein or any combination of components.

<FIG> is a circuit diagram representation of an implementation of a system <NUM> comprising the cuff <NUM> described herein according to an example embodiment. The cuff <NUM> can comprise the cuff <NUM> described earlier with reference to <FIG>, the cuff <NUM> described earlier with reference to <FIG>, or the cuff <NUM> described earlier with reference to <FIG>.

Thus, the cuff <NUM> illustrated in <FIG> comprises an inlet <NUM> (such as the inlet <NUM> illustrated in and described earlier with reference to <FIG>, the inlet <NUM> illustrated in and described earlier with reference to <FIG>, or the inlet <NUM> illustrated in and described earlier with reference to <FIG>), a bladder <NUM> (such as the bladder <NUM> illustrated in and described earlier with reference to <FIG>, the bladder <NUM> illustrated in and described earlier with reference to <FIG>, or the bladder <NUM> illustrated in and described earlier with reference to <FIG>), and a valve <NUM> (such as the valve <NUM> illustrated in and described earlier with reference to <FIG>, the valve <NUM> illustrated in and described earlier with reference to <FIG>, or the valve <NUM> illustrated in and described earlier with reference to <FIG>).

In <FIG>, the layout of the implementation of system <NUM> is shown as a circuit diagram comprising connections between a pump <NUM> of the inflation-based NIBP measurement apparatus <NUM>, a deflation valve <NUM> of the inflation-based NIBP measurement apparatus <NUM>, a supply line <NUM> of the inflation-based NIBP measurement apparatus <NUM>, an outlet <NUM> of the inflation-based NIBP measurement apparatus <NUM>, the inlet <NUM> of the cuff <NUM>, the bladder <NUM> of the cuff <NUM> and the valve <NUM>, which is illustrated as being disposed along a flow path between the inlet <NUM> of the cuff <NUM> and the bladder <NUM> of the cuff <NUM> in the illustrated example of <FIG>. The inlet <NUM> of the cuff <NUM> is coupled to the outlet <NUM> of the inflation-based NIBP measurement apparatus <NUM> to allow the inlet <NUM> of the cuff <NUM> to receive a flow of fluid from the pump <NUM> of the inflation-based NIBP measurement apparatus <NUM>.

In the circuit diagram, the supply line <NUM> of the inflation-based NIBP measurement apparatus <NUM>, the deflation valve <NUM> of the inflation-based NIBP measurement apparatus <NUM> and the valve <NUM> disposed along a flow path between the inlet <NUM> of the cuff <NUM> and a bladder <NUM> of the cuff <NUM> are modelled as resistors. More specifically, the supply line <NUM> of the inflation-based NIBP measurement apparatus <NUM> is modelled as a series resistance between the outlet <NUM> of the inflation-based NIBP measurement apparatus <NUM> and the inlet <NUM> of the cuff <NUM>. The deflation valve <NUM> of the inflation-based NIBP measurement apparatus <NUM> is modelled as a resistor connected to ground (where ground represents the atmosphere) via a switch. This illustrates that the deflation valve <NUM> of the inflation-based NIBP measurement apparatus <NUM> can allow a flow of fluid therethrough when the switch is closed. The valve <NUM> disposed along a flow path between the inlet <NUM> of the cuff <NUM> and a bladder <NUM> of the cuff <NUM> is modelled as a resistor connected to ground (where ground represents the atmosphere). The valve <NUM> is modelled as a resistor in parallel to the bladder <NUM> of the cuff <NUM>. The bladder <NUM> of the cuff <NUM> is modelled as a capacitor (as, in effect, the bladder <NUM> of the cuff <NUM> stores at least part of the received fluid). The pump <NUM> is modelled as a current source (as it provides the fluid).

It will be appreciated that the arrangement of components of the system <NUM> is exemplary and may be different to that show according to other embodiments. For example, the arrangement of the valve <NUM> and the deflation valve <NUM> shown in <FIG> is exemplary and can be different to that shown according to other embodiments (e.g. any one or more of the valve <NUM> and the deflation valve <NUM> may be located nearer to, or be disposed on, the bladder <NUM> of the cuff <NUM> according to other embodiments).

The flow of fluid into the bladder <NUM> of the cuff <NUM> (via the inlet <NUM> of the cuff <NUM>) can be defined according to the following equation: <MAT> where qprovided denotes the flow of fluid provided to the inlet <NUM> of the cuff <NUM> (e.g. the flow of fluid provided by the pump <NUM> of the inflation-based NIBP measurement apparatus <NUM>), qbladder denotes the flow of fluid into the bladder <NUM> of the cuff <NUM>, and qvalve denotes the part of the flow of fluid received in the bladder <NUM> that is passed to the atmosphere by the valve <NUM>.

The flow of fluid qbladder into the bladder <NUM> of the cuff <NUM> can be specified by the required inflation rate and the cuff <NUM> itself. For some cuffs, this flow of fluid qbladder into the bladder <NUM> of the cuff <NUM> is too low to be realized by the flow of fluid qprovided provided to the inlet <NUM> of the cuff <NUM> (e.g. the flow of fluid provided by the pump <NUM> of the inflation-based NIBP measurement apparatus <NUM>). However, the flow resistance of the valve <NUM> described herein is such that the valve <NUM> passes part of the flow of fluid received in the bladder <NUM> to the atmosphere in order to inflate the bladder <NUM> at a required flow rate for inflating the cuff <NUM>. That is, the valve <NUM> has a flow resistance such that the valve <NUM> passes part of the flow of fluid received in the bladder <NUM> to the atmosphere to inflate the bladder <NUM> at a required flow rate for inflating the cuff <NUM>. Thus, the part of the flow of fluid qvalve received in the bladder <NUM> that is passed to the atmosphere by the valve <NUM> can ensure that it is possible to provide the total flow of fluid (qbladder + qvalve) required to inflate the bladder <NUM> at the required flow rate for inflating the cuff <NUM> (e.g. by the pump <NUM> of the inflation-based NIBP measurement apparatus <NUM>).

Thus, as described earlier, the cuff <NUM>, <NUM>, <NUM> described herein comprises a valve <NUM>, <NUM>, <NUM> (disposed along a flow path between the inlet <NUM>, <NUM>, <NUM> and the bladder <NUM>, <NUM>, <NUM> or disposed on the bladder <NUM>, <NUM>, <NUM>) and the flow resistance of the valve <NUM>, <NUM>, <NUM> is such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere in order to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. That is, the valve <NUM>, <NUM>, <NUM> has a flow resistance such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. As the flow resistance of the valve <NUM>, <NUM>, <NUM> ensures that a sufficient part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> is passed to the atmosphere to enable the bladder <NUM>, <NUM>, <NUM> to be inflated at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>, a valve <NUM>, <NUM>, <NUM> with optimal flow resistance is provided for the cuff <NUM>, <NUM>, <NUM>. This enables a wide range of fluid flows into the cuff <NUM>, <NUM>, <NUM> while a pump <NUM> providing the flow of fluid to the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> can be operated in its usual (e.g. ideal) operating range of fluid flows.

<FIG> is a graphical illustration of a flow rate through a valve <NUM>, <NUM>, <NUM> (measured in mL/s) as a function of pressure in a bladder <NUM>, <NUM>, <NUM> of a cuff <NUM>, <NUM>, <NUM> (measured in mmHg). The flow rate through the valve <NUM>, <NUM>, <NUM> is illustrated on the y-axis and the pressure in the bladder <NUM>, <NUM>, <NUM> is illustrated on the x-axis. The flow rate through the valve as a function of pressure is illustrated for different flow resistances of the valve <NUM>, <NUM>, <NUM> (measured in mmHg·s/mL), which are listed in the legend of <FIG>. The area under the curve <NUM> is representative of the flow range of the pump <NUM> that provides the flow of fluid to the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM>. The flow range of the pump <NUM> is a range from a minimum flow rate that can be provided by a pump <NUM> to a minimum flow rate that can be provided by a pump <NUM>. Thus, the curve <NUM> itself in <FIG> represents the maximum flow rate that can be provided by the pump <NUM>.

As illustrated in <FIG>, if the flow resistance of the valve <NUM>, <NUM>, <NUM> is too low, the flow rate through the valve <NUM>, <NUM>, <NUM> to the atmosphere may exceed the maximum flow rate that can be provided by a pump <NUM> at some pressure level. This can be seen by way of the example illustrated in <FIG> where the flow resistance of the valve <NUM>, <NUM>, <NUM> is <NUM> mmHg·s/mL. In particular, it can be seen from <FIG> that this flow resistance of <NUM> mmHg·s/mL intersects the maximum flow rate that can be provided by the pump <NUM> at around <NUM> mmHg. Consequently, it is not possible to inflate the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> to pressures beyond <NUM> mmHg, since all of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> will be passed to the atmosphere. Thus, it is not possible to further inflate the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> and the pressure in the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> will not increase. On the other hand, if the flow resistance of the valve <NUM>, <NUM>, <NUM> is too high (e.g. greater than <NUM> mmHg·s/mL), the flow resistance may not be sufficient to allow the pump to be operated beyond a minimum flow rate that can be provided by a pump <NUM>.

As can be seen in <FIG>, where the flow resistance of the valve <NUM>, <NUM>, <NUM> is within the flow range of the pump <NUM> (around <NUM> mmHg·s/mL in this illustrated example), the flow rate through the valve <NUM>, <NUM>, <NUM> to the atmosphere is still close to the maximum flow rate that can be provided by a pump <NUM> at high pressures. This means that the range of fluid flows that can be provided by the pump <NUM> is limited. In <FIG>, this range of fluid flows is represented by the difference between the maximum flow rate that can be provided by the pump <NUM> and the flow rate through the valve <NUM>, <NUM>, <NUM>. As illustrated in <FIG>, at <NUM> mmHg·s/mL and <NUM> mmHg, this range of fluid flows is limited between <NUM> and <NUM>/s.

Although this maximum inflation flow restriction is generally not an issue for small cuffs (e.g. for an infant or a smaller subject) as the required inflation flows are also small, it can reduce the inflation speeds that can be achieved in intermediate or larger cuffs (e.g. for a child or adult subject), which in turn can slow down a NIBP measurement and increase the discomfort experienced by the subject.

Therefore, as described herein, the flow resistance of the valve <NUM>, <NUM>, <NUM> is such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere in order to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. That is, the valve <NUM>, <NUM>, <NUM> has a flow resistance such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. As the flow resistance of the valve <NUM>, <NUM>, <NUM> ensures that a sufficient part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> is passed to the atmosphere to enable the bladder <NUM>, <NUM>, <NUM> to be inflated at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>, a valve <NUM>, <NUM>, <NUM> with optimal flow resistance is provided for the cuff <NUM>, <NUM>, <NUM>. This enables a wide range of fluid flows into the cuff <NUM>, <NUM>, <NUM> while a pump <NUM> providing the flow of fluid to the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> can be operated in its usual (e.g. ideal) operating range of fluid flows. In this way, the limitations described earlier can be addressed.

<FIG> illustrates results of a simulation of the flow requirements for an example cuff <NUM>, <NUM>, <NUM>. The results of the simulation illustrated in <FIG> allow an analysis of the required flow rate for inflating a variety of cuffs <NUM>, <NUM>, <NUM>. <FIG> illustrate the case when the cuff is worn on (or, more specifically, wrapped around) a rigid cylinder and <FIG> illustrate the case when the cuff is worn on (or, more specifically, wrapped around) an arm of a subject.

In more detail, <FIG> illustrate a flow rate provided by a pump <NUM> (measured in mL/s) as a function of pressure in a bladder <NUM>, <NUM>, <NUM> of a cuff <NUM>, <NUM>, <NUM> (measured in mmHg) according to an example. The flow rate provided by the pump ("pump flow") is illustrated on the y-axis and the pressure in the bladder <NUM>, <NUM>, <NUM> is illustrated on the x-axis in <FIG>. The area under the curve <NUM> in <FIG> and the area under the curve <NUM> in <FIG> are representative of the flow range of the pump <NUM> that provides the flow of fluid to the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM>. <FIG> illustrate a flow rate in the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> (measured in mL/s) as a function of pressure in the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> (measured in mmHg) according to the example. The flow rate in the bladder <NUM>, <NUM>, <NUM> ("cuff inflation flow") is illustrated on the y-axis and the pressure in the bladder <NUM>, <NUM>, <NUM> is illustrated on the x-axis in <FIG>.

The flow rate provided by the pump as a function of the pressure in the bladder <NUM>, <NUM>, <NUM> in <FIG> and the flow rate in the bladder <NUM>, <NUM>, <NUM> as a function of the pressure in the bladder <NUM>, <NUM>, <NUM> in <FIG> are illustrated for different flow resistances ("Rflow") of valve <NUM>, <NUM>, <NUM> (measured in mmHg·s/mL), which are listed in the legend of <FIG>. The two dashed lines for the flow resistances in <FIG> indicate the maximum and minimum flow rates required to inflate the cuff <NUM>, <NUM>, <NUM>.

For infinite resistance (i.e. without a valve <NUM>, <NUM>, <NUM>), the minimum flow rate required to inflate the cuff <NUM>, <NUM>, <NUM> cannot be provided by the pump <NUM> for pressures above <NUM> mmHg. By adding the valve <NUM>, <NUM>, <NUM> described herein with optimal flow resistance (which in this example is a flow resistance up to <NUM> mmHg·s/mL), it is possible to achieve the minimum flow rate required to inflate the cuff <NUM>, <NUM>, <NUM> when the cuff <NUM>, <NUM>, <NUM> is worn on (or, more specifically, wrapped around) the arm of the subject. With an even lower flow resistance, the minimum flow rate required to inflate the cuff <NUM>, <NUM>, <NUM> can also be achieved if the cuff <NUM>, <NUM>, <NUM> is worn on (or, more specifically, wrapped around) the rigid cylinder.

However, if the flow resistance of the valve <NUM>, <NUM>, <NUM> becomes too low, the desired maximum flow rate required to inflate the cuff <NUM>, <NUM>, <NUM> can no longer be reached and a maximum inflation pressure limits the system <NUM>. For example, for a valve <NUM>, <NUM>, <NUM> having a flow resistance of <NUM> mmHg·s/mL, the cuff <NUM>, <NUM>, <NUM> cannot be inflated beyond a pressure of <NUM> mmHg. At this point, all of fluid flow received in the bladder <NUM>, <NUM>, <NUM> is passed to the atmosphere via the valve <NUM>, <NUM>, <NUM>, such that it is not possible to further inflate the cuff <NUM>, <NUM>, <NUM>. Thus, as described herein, the flow resistance of the valve <NUM>, <NUM>, <NUM> is such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere in order to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. That is, the valve <NUM>, <NUM>, <NUM> has a flow resistance such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>. In the example described with reference to <FIG>, this means that the flow resistance of the valve <NUM>, <NUM>, <NUM> may, for example, be <NUM> mmHg·s/mL.

<FIG> illustrates a graphical illustration of a predicted flow rate through three different valves <NUM>, <NUM>, <NUM> (measured in mL/s) as a function of pressure in a bladder <NUM>, <NUM>, <NUM> of a cuff <NUM>, <NUM>, <NUM> (measured in mmHg) according to an example. In the example illustrated in <FIG>, the different valves <NUM>, <NUM>, <NUM> comprise different needle valves. Each of the valves <NUM>, <NUM>, <NUM> in this example has a different diameter to define different flow resistances. The flow rate is predicted based on a look-up table previously designed to measure pump flow output as function of pressure, duty cycle, and supply voltage. As illustrated in <FIG>, it can be seen that different flow resistances of the valves <NUM>, <NUM>, <NUM> described herein (which are defined by different diameters of valve <NUM>, <NUM>, <NUM> in this example) result in different flow rates to the atmosphere.

<FIG> each illustrate an inflation rate (or pressurization rate, measured in mmHg/s) that can be achieved for a cuff <NUM>, <NUM>, <NUM> comprising a valve <NUM>, <NUM>, <NUM> as a function of pressure in a bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> (measured in mmHg) according to an example. The pressure is illustrated on the x-axis and the inflation rate ("rate") is illustrated on the y-axis in <FIG> illustrates the inflation rate that can be achieved as a function of pressure using an infant cuff <NUM>, <NUM>, <NUM>, <FIG> illustrates the inflation rate that can be achieved as a function of pressure using a child cuff <NUM>, <NUM>, <NUM>, and <FIG> illustrates the inflation rate that can be achieved as a function of pressure using a (small) adult cuff <NUM>, <NUM>, <NUM>. The different lines <NUM>, <NUM>, <NUM> in <FIG> represent the inflation rate that can be achieved as a function of pressure using those cuffs <NUM>, <NUM>, <NUM> comprising different valves <NUM>, <NUM>, <NUM>. Two target inflation rates of <NUM> mmHg and <NUM> mmHg are illustrated by the lines <NUM> and <NUM> respectively in <FIG>.

<FIG> illustrate the corresponding predicted flow rate through the different valves <NUM>, <NUM>, <NUM> (measured in mL/s) as a function of pressure in the bladder <NUM>, <NUM>, <NUM> of the cuffs <NUM>, <NUM>, <NUM> (measured in mmHg). The predicted flow rate ("predicted flow") is illustrated on the y-axis and the pressure in the bladder <NUM>, <NUM>, <NUM> is illustrated on the x-axis in <FIG>. As before, the different valves <NUM>, <NUM>, <NUM> are represented by the different lines <NUM>, <NUM>, <NUM> in each of <FIG>. In the example of <FIG>, the different cuffs <NUM>, <NUM>, <NUM> were wrapped around a rigid cylinder to illustrate the results that can be obtained and the different valves <NUM>, <NUM>, <NUM> comprised different needle valves.

It can be seen from <FIG> that the predicted flow rate through the valve <NUM>, <NUM>, <NUM> illustrated by the line <NUM> is too large, leading to a maximum pressure in the cuff <NUM>, <NUM>, <NUM> of about <NUM> mmHg. The valve <NUM>, <NUM>, <NUM> illustrated by the line <NUM> provides adequate results. However, at high pressures, the maximum flow rate is limited and, in some instances, the pressure in a bladder <NUM>, <NUM>, <NUM> of a cuff <NUM>, <NUM>, <NUM> does not reach <NUM> mmHg. This may be acceptable for the infant and child cuffs <NUM>, <NUM>, <NUM>. The valve <NUM>, <NUM>, <NUM> illustrated by the line <NUM> provides the optimum results, in particular for the adult cuff <NUM>, <NUM>, <NUM> comprising the valve <NUM>, <NUM>, <NUM> illustrated in <FIG>.

Thus, optimum results can be achieved using this valve <NUM>, <NUM>, <NUM> disposed along a flow path between the inlet <NUM>, <NUM>, <NUM> and the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> or disposed on the bladder <NUM>, <NUM>, <NUM> of the cuff <NUM>, <NUM>, <NUM> as the flow resistance of the valve <NUM>, <NUM>, <NUM> is such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere in order to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM> as described herein. That is, the valve <NUM>, <NUM>, <NUM> has a flow resistance such that the valve <NUM>, <NUM>, <NUM> passes part of the flow of fluid received in the bladder <NUM>, <NUM>, <NUM> to the atmosphere to inflate the bladder <NUM>, <NUM>, <NUM> at a required flow rate for inflating the cuff <NUM>, <NUM>, <NUM>.

There is thus provided herein a cuff <NUM>, <NUM>, <NUM> and a system <NUM> that address the limitations associated with the existing techniques.

Claim 1:
A cuff (<NUM>, <NUM>, <NUM>) for use with an inflation-based non-invasive blood pressure, NIBP, measurement apparatus (<NUM>), the cuff (<NUM>, <NUM>, <NUM>) comprising:
an inlet (<NUM>, <NUM>, <NUM>) configured to be coupled to an outlet (<NUM>) of the inflation-based NIBP measurement apparatus (<NUM>) to receive a flow of fluid;
a bladder (<NUM>, <NUM>, <NUM>) coupled to the inlet (<NUM>, <NUM>, <NUM>) and inflatable to pressurize a measurement site of a subject by receiving the flow of fluid; and
a valve (<NUM>, <NUM>, <NUM>) disposed along a flow path between the inlet (<NUM>, <NUM>, <NUM>) and the bladder (<NUM>, <NUM>, <NUM>) or disposed on the bladder (<NUM>, <NUM>, <NUM>), characterized in that
the valve (<NUM>, <NUM>, <NUM>) is configured to pass part of the flow of fluid received in the bladder (<NUM>, <NUM>, <NUM>) to the atmosphere during inflation of the bladder (<NUM>, <NUM>, <NUM>) and the valve (<NUM>, <NUM>, <NUM>) is sized to have a flow resistance that causes the bladder (<NUM>, <NUM>, <NUM>) to inflate at a required flow rate for inflating the cuff (<NUM>, <NUM>, <NUM>).