Patent Publication Number: US-2019167195-A1

Title: Systems and methods for performing diagnostic procedures for a volume clamp finger cuff

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 62/594,111, filed Dec. 4, 2017, the contents of which are incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the invention relate generally to non-invasive blood pressure measurement. More particularly, embodiments of the invention relate to the performance of diagnostic procedures for a volume clamp finger cuff. 
     Relevant Background 
     Volume clamping is a technique for non-invasively measuring blood pressure in which pressure is applied to a patient&#39;s finger in such a manner that arterial pressure may be balanced by a time varying pressure to maintain a constant arterial volume. In a properly fitted and calibrated system, the applied time varying pressure is equal to the arterial blood pressure in the finger. The applied time varying pressure may be measured to provide a reading of the patient&#39;s arterial blood pressure. 
     This may be accomplished by a finger cuff that is arranged or wrapped around a finger of a patient. The finger cuff may include an infrared light source, an infrared sensor, and an inflatable bladder. The infrared light may be sent through the finger in which a finger artery is present. The infrared sensor picks up the infrared light and the amount of infrared light registered by the sensor may be inversely proportional to the artery diameter and indicative of the pressure in the artery. 
     In the finger cuff implementation, by inflating the bladder in the finger cuff, a pressure is exerted on the finger artery. If the pressure is high enough, it will compress the artery and the amount of light registered by the sensor will increase. The amount of pressure necessary in the inflatable bladder to compress the artery is dependent on the blood pressure. By controlling the pressure of the inflatable bladder such that the diameter of the finger artery is kept constant, the blood pressure may be monitored in very precise detail as the pressure in the inflatable bladder is directly linked to the blood pressure. In a typical present day finger cuff implementation, a volume clamp system is used with the finger cuff. The volume clamp system typically includes a pressure generating system and a regulating system that includes: a pump, a valve, and a pressure sensor in a closed loop feedback system that are used in the measurement of the arterial volume. To accurately measure blood pressure, the feedback loop provides sufficient pressure generating and releasing capabilities to match the pressure oscillations of the patient&#39;s blood pressure. 
     Today, finger cuff based blood pressure monitoring devices generally use the same technology (e.g., photoplethysmography or similar technologies) to measure blood pressure. Unfortunately, such finger cuff devices may not be easily attachable to a patient&#39;s finger and may not be that accurate due to the finger cuff&#39;s positioning on the patient&#39;s finger. That is, attaching the finger cuff in a suboptimal way may negatively influence the measurement reliability and accuracy of the volume clamp system. For example, a loose finger cuff on the patient&#39;s finger may require the bladder to stretch in order to reach the finger. Therefore, this may lead to the additional consumption of energy and a reading of an artificially high blood pressure. 
     SUMMARY 
     Embodiments of the invention may relate to a system to monitor a finger cuff connectable to a patient&#39;s finger to be used in measuring the patient&#39;s blood pressure by a blood pressure measurement system utilizing the volume clamp method and to measure the plethysmogram of the finger cuff. The system comprises the finger cuff that includes an enclosing portion that encloses a patient&#39;s finger. The enclosing portion includes a bladder and a light emitting diode (LED) and photodiode (PD) pair. The system further comprises a processor to: command applying pneumatic pressure to the bladder of the finger cuff from a low pressure to a high pressure; measure the plethysmogram of the finger cuff as the pressure increases from the low pressure to the high pressure; and determine the fitness of the finger cuff on the patient&#39;s finger based on the measured plethysmogram. When the finger cuff is placed around the patient&#39;s finger, the bladder and the LED-PD pair aid the processor in measuring the plethysmogram. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example of a blood pressure measurement system according to one embodiment. 
         FIG. 2  is a block diagram illustrating a finger cuff and a pressure generating and regulating system. 
         FIGS. 3A-3C  are diagrams illustrating the measured plethysmograms of a finger cuff according to embodiments of the invention. 
         FIGS. 4A-4C  are diagrams illustrating additional measured plethysmograms of the finger cuff according to embodiments of the invention. 
         FIGS. 5A-5C  are diagrams illustrating additional measured plethysmograms of the finger cuff according to embodiments of the invention. 
         FIG. 6  a flow diagram of a method for measuring the pulsatility of a finger cuff according to embodiments of the invention. 
         FIG. 7  is a flow diagram of a method for determining whether a finger cuff is properly fitted on a patient&#39;s finger according to embodiments of the invention. 
         FIG. 8  is a flow diagram of another method for determining whether the finger cuff is properly fitted on the patient&#39;s finger according to embodiments of the invention. 
         FIG. 9  is a block diagram illustrating example control circuitry. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , which illustrates an example of a blood pressure measurement system according to one embodiment, a blood pressure measurement system  102  that includes a finger cuff  104  that may be attached to a patient&#39;s finger and a blood pressure measurement controller  120 , which may be attached to the patient&#39;s body (e.g., a patient&#39;s wrist or hand) is shown. 
     The blood pressure measurement system  102  may further be connected to a patient monitoring device  130 , and, in some embodiments, a pump  134 . Further, finger cuff  104  may include a bladder (not shown) and an LED-PD pair (not shown), which are conventional for finger cuffs. 
     In one embodiment, the blood pressure measurement system  102  may include a pressure measurement controller  120  that includes: a small internal pump, a small internal valve, a pressure sensor, and control circuity. In this embodiment, the control circuitry may be configured to: control the pneumatic pressure applied by the internal pump to the bladder of the finger cuff  104  to replicate the patient&#39;s blood pressure based upon measuring the pleth signal received from the LED-PD pair of the finger cuff  104 . Further, the control circuitry may be configured to: control the opening of the internal valve to release pneumatic pressure from the bladder; or the internal valve may simply be an orifice that is not controlled. Additionally, the control circuitry may be configured to: measure the patient&#39;s blood pressure by monitoring the pressure of the bladder based upon the input from a pressure sensor, which should be the same as patient&#39;s blood pressure, and may display the patient&#39;s blood pressure on the patient monitoring device  130 . 
     In another embodiment, a conventional pressure generating and regulating system may be utilized, in which, a pump  134  is located remotely from the body of the patient. In this embodiment, the blood pressure measurement controller  120  receives pneumatic pressure from remote pump  134  through tube  136  and passes on the pneumatic pressure through tube  123  to the bladder of finger cuff  104 . Blood pressure measurement device controller  120  may also control the pneumatic pressure (e.g., utilizing a controllable valve) applied to the finger cuff  104  as well as other functions. In this example, the pneumatic pressure applied by the pump  134  to the bladder of finger cuff  104  to replicate the patient&#39;s blood pressure based upon measuring the pleth signal received from the LED-PD pair of the finger cuff  104  (e.g., to keep the pleth signal constant) and measuring the patient&#39;s blood pressure by monitoring the pressure of the bladder may be controlled by the blood pressure measurement controller  120  and/or a remote computing device and/or the pump  134  and/or the patient monitoring device  130  to implement the volume clamping method. In some embodiments, a blood pressure measurement controller  120  is not used at all and there is simply a connection from tube  136  from a remote pump  134  including a remote pressure regulatory system to finger cuff  104 , and all processing for the pressure generating and regulatory system, data processing, and display is performed by a remote computing device. 
     Continuing with this example, as shown in  FIG. 1 , a patient&#39;s hand may be placed on the face  110  of an arm rest  112  for measuring a patient&#39;s blood pressure with the blood pressure measurement system  102 . The blood pressure measurement controller  120  of the blood pressure measurement system  102  may be coupled to a bladder of the finger cuff  104  in order to provide pneumatic pressure to the bladder for use in blood pressure measurement. Blood pressure measurement controller  120  may be coupled to the patient monitoring device  130  through a power/data cable  132 . Also, in one embodiment, as previously described, in a remote implementation, blood pressure measurement controller  120  may be coupled to a remote pump  134  through tube  136  to receive pneumatic pressure for the bladder of the finger cuff  104 . The patient monitoring device  130  may be any type of medical electronic device that may read, collect, process, display, etc., physiological readings/data of a patient including blood pressure, as well as any other suitable physiological patient readings. Accordingly, power/data cable  132  may transmit data to and from patient monitoring device  130  and also may provide power from the patient monitoring device  130  to the blood pressure measurement controller  120  and finger cuff  104 . 
     As can be seen in  FIG. 1 , in one example, the finger cuff  104  may be attached to a patient&#39;s finger and the blood pressure measurement controller  120  may be attached on the patient&#39;s hand or wrist with an attachment bracelet  121  that wraps around the patient&#39;s wrist or hand. The attachment bracelet  121  may be metal, plastic, Velcro, etc. It should be appreciated that this is just one example of attaching a blood pressure measurement controller  120  and that any suitable way of attaching a blood pressure measurement controller to a patient&#39;s body or in close proximity to a patient&#39;s body may be utilized and that, in some embodiments, a blood pressure measurement controller  120  may not be used at all. It should further be appreciated that the finger cuff  104  may be connected to a blood pressure measurement controller described herein, or a pressure generating and regulating system of any other kind, such as a pressure generating and regulating system that is located remotely from the body of the patient. Any kind of pressure generating and regulating system can be used, including but not limited to the blood pressure measurement controller, and may be described simply as a pressure generating and regulating system that may be used with a finger cuff  104  including an LED-PD pair and a bladder to implement the volume clamping method. 
       FIG. 2  is a block diagram illustrating a finger cuff and a pressure generating and regulating system. As an example, as shown in  FIG. 2 , finger cuff  202  may include an enclosing portion  210 , an inflatable bladder  212  and an LED-PD pair  214 . The enclosing portion  210  may encircle or enclose a patient&#39;s finger and include inflatable bladder  212  and LED-PD pair  214 . The inflatable bladder  212  may be pneumatically connected to a pressure generating and regulating system  220 . The LED may be used to illuminate the finger skin and light absorption or reflection may be detected with the PD. The pressure generating and regulating system  220  and control circuitry (e.g., including a processor)  230  may generate, measure, and regulate pneumatic pressure that inflates or deflates the inflatable bladder  212 , and may further comprise such elements as a pump, a valve, a pressure sensor, and/or other suitable elements, as previously described. In particular, pressure generating and regulating system  220  in cooperation with control circuitry  230  may be configured to implement a volume clamp method with the finger cuff  202  by: applying pneumatic pressure to the inflatable bladder  212  of the finger cuff  202  to replicate the patient&#39;s blood pressure based upon measuring the pleth signal received from the LED-PD pair  214  of the finger cuff  202  (e.g., to keep the pleth signal constant); and measuring the patient&#39;s blood pressure by monitoring the pressure of the inflatable bladder  212  based upon input from a pressure sensor, which should be the same as patient&#39;s blood pressure, and may further command the display of the patient&#39;s blood pressure on the patient monitoring device. 
     In one embodiment, pressure generating and regulating system  220  and control circuitry  230  may automatically perform diagnostic procedures (e.g., a series of tests) to assess equipment statuses (e.g., pump performance, valve performance), finger cuff fitness (e.g., tightness, location and fit), and/or patient suitability (e.g., patient&#39;s perfusion) for the volume clamp method. In some embodiments, the diagnostic procedures may be performed at system start-up and/or during system run time of the pressure generating and regulating system  220  and/or control circuitry  230  to obtain and assess various metrics associated with the equipment statuses, finger cuff fitness, and patient suitability. 
     A plethysmogram, or pleth signal, obtained by the bladder  212  and LED-PD pair  214  contains two parts. The finger pulsatility, also known as the AC pleth, is the pulsation due to the subject&#39;s heart beats. The pulsatility can be changed by applying pressure to the finger, for example by the bladder  212 , that confine the artery&#39;s movement within the finger. The finger blood volume, also known as the DC pleth, excludes changes due to the subject&#39;s heart beats. Rather, it is the steady background level of light absorbing blood and tissue in the finger. The finger blood volume can be changed by applying pressure to the finger, for example by the bladder  212 , which squeezes blood, both arterial and venous, out of the finger. Both pulsatility and blood volume can be characterized as functions of external pressure applied by the bladder  212 .  FIG. 3A  shows the plethysmogram as a function of pressure applied by a bladder, including both pulsatility and blood volume, for a typical finger.  FIG. 3B  separates out just the steady state blood volume from  3 A, as pressure increases light absorbing blood is pushed out of the finger and the DC Pleth increases.  FIG. 3C  separates out just the pulsatility from  3 A, at low pressures the artery is fully stretched by the subject&#39;s blood pressure resulting in low pulsatility, as the pressure increases the artery is compressed into a highly elastic state that yields large pulsations with each heartbeat, and at high pressure the artery is fully compressed and very little blood is able to enter the finger at each heartbeat. Thus both portions of the plethysmogram contain information relating to the interaction between subject&#39;s finger and the bladder. 
     In particular, pressure generating and regulating system  220  in cooperation with control circuitry  230  may apply pneumatic pressure to bladder  212  from a low pressure, e.g., 20-40 millimeter of mercury (mmHg), to a high pressure (e.g., 200 mmHg) and measure the plethysmogram of finger cuff  202  as the pressure increases from the low pressure to the high pressure. That is, in one embodiment, the pressure generating and regulating system  220  and control circuitry  230  (by way of bladder  212  and LED-PD pair  214 ) may make continuous volumetric measurements (or plethysmogram) of arterial blood flows within the patient&#39;s finger as the pressure increases from the low pressure to the high pressure. Thus, pulsatility and blood volume in the finger may be detected based on the plethysmogram, which may be generated based on the pleth signal received from the PD of LED-PD pair  214 . Based on the measured pulsatility and/or blood volume of finger cuff  202 , the control circuitry  230  may determine the fitness of finger cuff  202  on the patient&#39;s finger. For example, the control circuitry  230  may determine whether finger cuff  202  is loose, properly fitted, or too tight on the patient&#39;s finger. 
     In some embodiments, in determining the fitness of finger cuff  202 , the pressure generating and regulating system  220  and control circuitry  230  may apply multiple pressure sequences to the finger cuff  202 , and the pleth signal received from LED-PD pair  214  may be acquired and analyzed. For example, a low pressure (e.g., 20-40 mmHg) may be applied to bladder  212 , and the pleth signal may be measured as the pressure of the bladder increases to the low pressure. A high pressure (200 mmHg) may then be applied to bladder  212  and held for a time period (e.g., 1 second), and during such time period, the pleth signal may again be measured. Subsequently, the pressure from bladder  212  may be released (e.g., by turning off the pump) and the pressure decay may be observed. The pleth signal may be measured throughout the pressure decay, and in some embodiments, for an additional time period (e.g., 3 seconds or any suitable amount of time) after the pump has been turned off. Based on the various measurements of the pleth signal, as previously described, the control circuitry  230  may determine whether finger cuff  202  is loose, properly fitted, or too tight on the patient&#39;s finger (as described in more detail with respect to  FIGS. 3A-3C, 4A -C and  5 A- 5 C herein below). Further, based on the various measurements of the pleth signal, as previously described, the control circuitry  230  may perform various equipment status checks, as described below. 
     In some embodiments, with respect to equipment statuses, control circuitry  230  may check pump performance of the pressure generating and regulating system  220 . For example, control circuitry  230  may control a designated pneumatic pressure applied by the pump to the bladder  212  of the finger cuff  202 . Control circuitry  230  may then determine whether the pump has reached the designated pressure. If the pump does not reach the designated pressure, control circuitry  230  may determine that the pump is inoperable. Otherwise, control circuitry  230  may then determine whether the ratio of the designated pressure to the power of the pump during pressure impulse is within a desired ratio. If the ratio is not within the desired ratio, control circuitry  230  may determine that the pump is inoperable. In this case, an operator (e.g., healthcare provider) may be instructed to replace parts of the pump (e.g., servo unit). 
     In some embodiments, if a valve is present in pressure generating and regulating system  220 , the valve may be utilized to release pneumatic pressure from bladder  212 . In this case, control circuitry  230  may determine whether a leakage rate with the pump off and the valve closed is above a leakage threshold. If the leakage rate is not above the leakage threshold, control circuitry  230  may determine that a leakage exists in pressure generating and regulating system  220 . In this scenario, the operator may be instructed to check one or more connections between the servo and finger cuff  202 . If such condition occurs for a number of times (e.g., three times), the operator may be instructed to replace finger cuff  202 . If the condition continues to occur after the replacement of finger cuff  202 , control circuitry  230  may determine that the valve is inoperable and instruct the operator to replace, for example a servo unit associated with the valve. 
     In some embodiments, with respect to patient suitability, control circuitry  230  may check the patient&#39;s perfusion, which is the volume of blood flow through the finger. For example, control circuitry  230  may determine whether the blood volume measured at the end of recovery time, for example a DC Pleth magnitude, has returned to an initial value measured at the low pressure, thereby indicating that blood has returned to the finger. If the blood volume measured at the end of the recovery time has not returned to the initial value (i.e., the blood has not fully returned), control circuitry  230  may determine that the patient&#39;s perfusion is too low for the volume clamp system to operate properly. In this case, the operator may be instructed to increase the patient&#39;s perfusion by warming the hand or to select a different pressure monitoring technology. 
     Referring to  FIGS. 3A-3C , diagrams illustrating measured plethysmogram of finger cuff  202  according to embodiments of the invention are shown. In some embodiments,  FIGS. 3A-3C  illustrate the plethysmogram and its components, the finger pulsatility and finger blood volume, obtained by pressure generating and regulating system  220  and control circuitry  230 , as previously described, applying pressure to finger cuff  202  and measuring pleth signals. With reference to  FIG. 3A , the diagram illustrates a gradual pressure ramp response, and particularly, an example of the changing pleth signal as a function of pressure. As shown in the diagram, a trace  310  shows the measured plethysmogram in arbitrary units (a.u.) that corresponds to the pneumatic pressures (which may be measured in mmHg) applied to the patient&#39;s finger. 
     As can be seen on  FIGS. 3A-3C and 4A-4C , diagrams illustrating additional measured plethysmogram of finger cuff  202  according to embodiments of the invention are shown. With reference to  FIG. 3A , the diagram illustrates a pressure ramp response, and particularly, an example of a changing pleth signal as a function of pressure. As shown in the diagram, trace  310  shows the plethysmogram that corresponds to the pneumatic pressures applied to the patient&#39;s finger. In this case, as can be seen on trace  310 , at a low end  315  of the pressure (e.g., approximately 50-80 mmHg), pulsatility  317  is low relative to the maximum pulsatility  318 , which may indicate that finger cuff  202  is properly fitted ( FIG. 3C ). Similarly, with reference to  FIG. 3B , the diagram illustrates the finger blood volume, and particularly, another example of the changing pleth signal as a function of pressure. As shown, a trace  320  shows a finger blood volume at every pneumatic pressure level applied to the patient&#39;s finger. As can be seen on trace  320 , at a low end  325  of the pressure (e.g., approximately 30-60 mmHg), increase in DC pleth is gradual, whereas in the mid-range  327  of the pressure (e.g. approximately 80-120 mm Hg) the increase in DC Pleth is noticeably higher. The transition from gradual increase at low end  325  to rapid increase at mid-range  327  occurs between the low end of the pressure (approximately 30-60 mmHg) and the mid-range of the pressure (approximately 80-120 mmHg), which again may indicate that finger cuff  202  is properly fitted. 
     In contrast, referring to trace  410  of  FIG. 4A , at a low end  415  of the pressure (e.g., approximately 30-60 mmHg), pulsatility  417 , for example AC Pleth, is high compared to the peak pulsatility  418 , which may indicate that finger cuff  202  is too tight ( FIG. 4C ). Similarly, with reference to  FIG. 4B , the diagram illustrates the blood volume, and particularly, the DC pleth signal as a function of pressure. As shown, a trace  420  shows a finger blood volume at every pneumatic pressure level applied to the patient&#39;s finger. As can be seen on trace  420  of  FIG. 4B , the increase in DC Pleth with pressure is roughly constant, that is, the trace  420  does not contain separate regions of low and rapid increase, in contrast to  FIG. 3B , which again may indicate that finger cuff  202  is too tight. 
     In another embodiment of the invention, referring to trace  510  in  FIG. 5A , at the low end  515  of the pressure (e.g. approximately 30-60 mmHg), the pulsatility  517  is low compared to peak pulsatility  518 , and furthermore, the pulsatility remains low well into the mid-range of the pressure (e.g. above 80 mm Hg), which may indicate the finger cuff  202  is too loose ( FIG. 5C ). Similarly, with reference to  5 B, a region  525  of gradual increase in DC Pleth as a function of pressure and a separate region  527  of rapid increase in DC Pleth as a function of pressure are both present, similar to  FIG. 3B . Unlike  FIG. 3B , the transition from gradual increase of region  525  to rapid increase of region  527  occurs at a higher pressure (approximately 100 mm Hg), which may indicate the finger cuff  202  is too loose. 
     While  FIGS. 3A-3C, 4A-4C, and 5A-5C  illustrate a gradual pressure ramp response for the observations of the plethysmogram change, in some embodiments, a stepped increase (or “staircase”) and/or a large step response may be used for the observations of the plethysmogram change as a function of pressure. 
       FIG. 6  is a flow diagram of a method for measuring the pulsatility of a finger cuff according to embodiments of the invention. Process  600  may be performed by processing logic that includes hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination thereof. For example, process  600  may be performed by pressure generating and regulating system  220 , control circuitry  230 , or a combination thereof. 
     Referring to  FIG. 6 , at block  610 , the processing logic applies a low pressure (e.g., 20-40 mmHg) to a bladder (e.g., inflatable bladder  212 ) of a finger cuff (e.g., finger cuff  202 ). At block  620 , the processing logic measures plethysmogram of the finger cuff as pressure of the bladder increases to the low pressure. At block  630 , the processing logic applies a high pressure (e.g., 200 mmHg) to the bladder of the finger cuff. At block  640 , the processing logic measures the plethysmogram, observing both the finger blood volume, or DC pleth, and the finger pulsatility, or AC pleth, of the finger cuff as the pressure of the bladder increases to the high pressure. At block  650 , the processing logic releases the pressure from the bladder and observes pressure decay. At block  660 , the processing logic measures the plethysmogram, observing both the finger blood volume, or DC pleth, and the finger pulsatility, or AC pleth, of the finger cuff throughout the pressure decay. 
       FIG. 7  is a flow diagram of a method for determining whether a finger cuff is properly fitted on a patient&#39;s finger according to embodiments of the invention. Process  700  may be performed by processing logic that includes hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination thereof. For example, process  700  may be performed by pressure generating and regulating system  220 , control circuitry  230 , or a combination thereof. 
     Referring to  FIG. 7 , at block  710 , the processing logic determines whether pulsatility of a low end of the pressure (e.g., low end  315  of  FIG. 3A ) is at least a predetermined percentage lower than a peak pulsatility (or AC pleth level). At block  720 , if the pulsatility at the low end of the pressure is not at least a predetermined percentage lower than the peak pulsatility (e.g., as shown in pulsatility  417  and  418  and in pulsatility  517  and  518 ), the processing logic determines that the finger cuff (e.g., finger cuff  202 ) is incorrectly attached (e.g., too tight, rotated or offset from the phalanx center). In this case, an operator (e.g., healthcare provider) may be instructed, via patient monitoring device  130  for example, to remove and reapply (e.g., loosen) the finger cuff. In some embodiments, if the incorrect attachment of the finger cuff occurs for a predetermined number of times (e.g., three times), the operator may be instructed to select a larger finger cuff. Otherwise, at block  730 , the processing logic determines that the finger cuff is properly fitted if the pulsatility at the low end of the pressure is at least a predetermined percentage lower than the peak pulsatility (e.g., as shown in pulsatility  317  and  318 ). 
       FIG. 8  is a flow diagram of another method for determining whether a finger cuff is properly fitted on a patient&#39;s finger according to embodiments of the invention. Process  800  may be performed by processing logic that includes hardware (e.g. circuitry, dedicated logic, etc.), software (e.g., embodied on a non-transitory computer readable medium), or a combination thereof. For example, process  800  may be performed by pressure generating and regulating system  220 , control circuitry  230 , or a combination thereof. 
     Referring to  FIG. 8 , at block  810 , the processing logic determines whether pulsatility of a high end of the pressure is at least a predetermined percentage lower than a peak pulsatility (or pleth level). At block  820 , if the pulsatility at the high end of the pressure is not at least a predetermined percentage lower than the peak pulsatility, the processing logic determines that the finger cuff (e.g., finger cuff  202 ) is incorrectly attached (e.g., too loose, rotated or offset from the phalanx center). In this case, the operator may be instructed, via patient monitoring device  130  for example, to remove and reapply the finger cuff (e.g., to reapply the finger cuff more tightly). In some embodiments, if the incorrect attachment of the finger cuff occurs for a predetermined number of times (e.g., three times), the operator may be instructed to select a smaller finger cuff. Otherwise, at block  830 , the processing logic determines that the finger cuff is properly fitted if the pulsatility at the high end of the pressure is at least a predetermined percentage lower than the peak pulsatility. 
     Referring to  FIG. 9 , a block diagram illustrating example control circuitry  230  is shown. It should be appreciated that  FIG. 9  illustrates a non-limiting example of a control circuitry  230  implementation. Other implementations of the control circuitry  230  not shown in  FIG. 9  are also possible. The control circuitry  230  may comprise a processor  910 , a memory  920 , and an input/output interface  930  connected with a bus  940 . Under the control of the processor  910 , data may be received from an external source through the input/output interface  930  and stored in the memory  920 , and/or may be transmitted from the memory  920  to an external destination through the input/output interface  930 . The processor  910  may process, add, remove, change, or otherwise manipulate data stored in the memory  920 . Further, code may be stored in the memory  920 . The code, when executed by the processor  910 , may cause the processor  910  to perform operations relating to data manipulation and/or transmission and/or any other possible operations. 
     It should be appreciated that aspects of the invention previously described may be implemented in conjunction with the execution of instructions by processors, circuitry, controllers, control circuitry, etc. As an example, control circuity may operate under the control of a program, algorithm, routine, or the execution of instructions to execute methods or processes in accordance with embodiments of the invention previously described. For example, such a program may be implemented in firmware or software (e.g. stored in memory and/or other locations) and may be implemented by processors, control circuitry, and/or other circuitry, these terms being utilized interchangeably. Further, it should be appreciated that the terms processor, microprocessor, circuitry, control circuitry, circuit board, controller, microcontroller, etc., refer to any type of logic or circuitry capable of executing logic, commands, instructions, software, firmware, functionality, etc., which may be utilized to execute embodiments of the invention. 
     The various illustrative logical blocks, processors, modules, and circuitry described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a specialized processor, circuitry, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor or any conventional processor, controller, microcontroller, circuitry, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module/firmware executed by a processor, or any combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.