Parameter disturbance response apparatus

This invention provides apparatus for collecting parameter disturbance information from each connected apparatus which can disturb measuring vital signs, and broadcasting a message regarding the disturbance and a coordinating clock signal to all apparatus. Connected sensors susceptible to parameter disturbances identify them from the message and suppress their audible alarm during an interval given in the message. This eliminates false audible alarms caused by such disturbances. The disturbance interval can be extended for later disturbances unless it is a new source or disturbance type and the alarm is already suppressed. A brickwall timer limits the total maximum suppressed interval to a safe maximum. A recovery timer allows a sensor to recover from a parameter disturbance before responding to a subsequent one.

FIELD OF THE INVENTION 
The present invention relates to suppression of false audible alarms in any 
number of patient vital sign sensing apparatus interconnected with any 
number of devices which cause a disturbance and resulting false alarm. 
DESCRIPTION OF RELATED ART 
The problem of a patient monitoring system which includes a pulse oximeter 
sensor and a blood pressure module which inflates a cuff during its active 
cycle resulting in a false audible alarm by the pulse oximeter was 
addressed in Friedman et al. U.S. Pat. No. 5,309,908. Friedman et al., 
which is typical of the prior art, provides fixed interconnected logic 
elements which suppress the audible alarm of the pulse oximeter sensor and 
only during the time that the cuff inflation affects the pulse readings. 
As with the prior art, this apparatus is severely limited in scope. In the 
actual clinical environment, a number of devices can cause disturbances in 
reading a given body vital sign during their operation. Similarly, a 
number of sensors may each be susceptible to various disturbances 
resulting in false indications. An example of equipment which can cause 
such disturbances and resulting errors in vital sign sensors includes 
electrocauterization and transcutaneous electrical nerve stimulation 
(TENS) apparatus. These produce intense electrical fields which can cause 
read-out errors in susceptible sensors. 
Further, Friedman et al. does not address problems which may be presented 
in the future by additional apparatus which can produce disturbances 
resulting in reading errors in new vital sign sensing apparatus. 
SUMMARY OF THE INVENTION 
The instant invention addresses the problems of interconnection and 
interaction between any number of sensors and any number of devices which 
can produce an erroneous indication resulting in a false audible alarm in 
any one or more of these sensors. Further, the instant invention is open 
ended to permit adding new apparatus in the future, while still providing 
the protocol to eliminate false alarms caused by interaction between any 
of the previous or new devices. 
Operation of certain equipment used in patient procedures create 
disturbances which can cause an error in the sensing of a vital sign by a 
sensor susceptible to the disturbance. Such a disturbance is hereafter 
herein referred to as a Patient Parameter Disturbance (PPD). A typical PPD 
results when a blood pressure monitor inflates a cuff for detecting blood 
pressure. A cuff inflation will cause a pulse or oxygen saturation 
detection sensor attached to the same limb to indicate a false pulse 
missing error. Other PPD generators include such devices as 
electrocauterization and TENS excitation apparatus. These produce intense 
electrical fields which can cause read-out errors in susceptible sensors. 
A key feature of the present invention involves providing a common 
communication protocol for notifying each of the sensors concerning the 
occurrence, the timing, and the nature of each PPD event. In the preferred 
mode of practicing the present invention, a generalized PPD message format 
is defined, which can specify both timing and nature of any anticipated 
PDD event. A suitable PPD message is generated and transmitted to each 
sensor to provide notification of an approaching PPD event. If the proper 
PPD message is transmitted to each potentially effected sensor, the degree 
of centralization or decentralization of the communication functions may 
vary from one embodiment to another. 
In a first, highly centralized approach, the instant invention may use a 
communication timing (CT) unit to interconnect all equipment which 
includes such devices as: sensors which are susceptible to a PPD, sensors 
which are not susceptible to a PPD but which create a PPD themselves, and 
non-sensing apparatus which create PPDs. The CT unit may provide a master 
timing signal for synchronous communication or the individual devices may 
communicate asynchronously using separate clocks. In the preferred mode, 
asynchronous communication operates effectively assuming a delivery delay 
of less than one second. 
For this centralized approach, the Communicator Timer (CT) unit 
incorporates a communication network arranged to collect a PPD message 
from all PPD generating equipment, and broadcast this message to all 
connected apparatus. If synchronous communication is preferred, a time 
signal generated in the CT unit is also broadcast to all connected 
equipment to coordinate all PPD timing and any other data collected by any 
attached equipment. 
Each connected device, which can produce a PPD, generates a PPD message 
describing the PPD characteristics, an estimate of the PPD duration, and a 
PPD identifier. Each PPD generating device also creates another message 
which identifies the PPD and signifies the termination of the event. These 
PPD messages are obtained, encoded and transmitted from each PPD 
generating apparatus over the CT network to the CT unit. 
All of the PPD messages (plus a CT generated master time base, if 
synchronous transmission mode is used) are broadcast back over the same CT 
network to all connected equipment. These PPD messages provide information 
from all PPD generators to all susceptible sensors of all pertinent data 
regarding any PPD. 
All sensors susceptible to a PPD, upon receiving a PPD message use the PPD 
identifier to identify the PPDs to which they are susceptible, and if 
susceptible, take appropriate action through the estimated duration of the 
PPD event. 
The audible alarm signal of a susceptible sensor may be suppressed during a 
parameter disturbance interval, however, the visual alarm need not be 
suppressed to permit continual visual monitoring of all out-of-range 
conditions. The alarm suppression interval can be extended by later 
messages from the same apparatus or a new PPD message from a different 
apparatus which resets the parameter disturbance interval to the longest 
time interval. Because successive PPD messages could extend a PPD interval 
indefinitely, the maximum suppression time is preferably limited by a 
Brick Wall Timer (BWT). The BWT limits the maximum alarm suppression 
interval time to a predetermined length. This maximum alarm suppression 
time length, regardless of the number of successive PPD messages, though 
dependent upon the technology used and physiology involved, is preferably 
limited to 120 seconds, less a recovery timer interval of six seconds 
which will be described later, for adult or pediatric patient monitoring, 
and to 60 seconds, less six seconds for the Recovery Timer (RT) interval, 
for neonate monitoring. This ensures that audible alarms are not 
suppressed beyond a safe time interval. 
The PPD interval ends either at the end of the PPD time interval after the 
indication, or earlier, if a stop message for that particular PPD 
generating apparatus is received at any time during the PPD interval. In 
either event, when the time of a PPD termination is determined, a Recovery 
Timer is started, which extends the alarm suppression interval six seconds 
beyond the PPD termination time. This avoids sounding an alarm before a 
disturbed parameter can return to normal. 
The RT is also started by the BWT counting through its limit of 54 or 114 
seconds to end the alarm suppression six seconds after the BW timer counts 
through zero. The BWT timer has 6 seconds subtracted from its total count 
to account for the amount of RT time. 
In addition the above the PPD message is ignored if the sensor is 
out-of-range at the time of the receipt of any PPD start message when no 
alarm suppression has yet occurred. 
The CT unit, used to collect the PPD messages from all PPD producers and 
broadcast the PPD messages and time to all attached devices, interconnects 
any number of PPD generators and sensors susceptible to PPD disturbances 
into a single system. This permits informing all susceptible sensing 
apparatus of any potential parameter disturbances and provides a time 
reference for all units. Sensors, whether or not they are affected by 
PPDs, and non-sensor apparatus, whether or not they create a PPD, can be 
added initially or later to the CT unit merely by incorporating the 
capabilities required to communicate with the unit. This open ended 
capability permits expanding the system to incorporate present or future 
apparatus, whatever its function, whenever the interchange of PPD or time 
information is deemed useful. 
A second, highly decentralized approach distributes the functions of the CT 
unit amongst the PPD generators and suspectable sensors. In a preferred 
mode, all such devices are coupled via a token ring using a standard 
protocol such as ANSI 878.1. Each PPD generator broadcasts a PPD message 
as appropriate during its assigned time slot. Each susceptible sensor 
device reviews the PDD messages transmitted for those PDD events to which 
it is susceptible. According to this approach, each device is 
synchronously timed. In the most general case, a given PPD generator may 
also be a susceptible sensor device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A block diagram of the Parameter Disturbance Response 10 apparatus is shown 
in FIG. 1. Communication Timing unit (CT) 12 incorporates a clock 14 which 
generates a Master Time (MT) base. Sensor 16 will generate a patient 
parameter disturbance (PPD) in sensing a patient parameter but is not 
susceptible to any PPDs. Sensor 18 senses a patient parameter and is 
susceptible to PPDs but does not generate a PPD. Non-sensor apparatus 20 
does not sense a patient parameter, and is therefore not susceptible to a 
PPD, but generates a PPD. Sensor 21 both generates and is susceptible to 
PPD events. This equipment is representative of the types of equipment 
which are connected to a CT unit 12. The CT unit 12 also includes input 22 
and output 24. A Master time (MT) base derived from clock 14 is included 
in output 24. This MT base is used by all PPD susceptible equipment to 
coordinate timing information contained in the PPD message. 
FIG. 2 shows the organization of the PPD message generated from either 
sensor 16, or any other PPD generator, or non-sensor 20 or 21 through 
input 22 and broadcast by output 24 of CT unit 12. The PPD message has an 
upper byte 26 and a lower byte 30 with a MSB 32. The upper byte 26 gives 
the parameter disturbance interval in seconds. The beginning of a PPD is 
indicated by a MSB of one in the lower byte 30, and the end of a PPD is 
indicated by a MSB of zero in the lower byte 30. The remaining bits of 
lower byte 30 gives the identifier of the disturbed parameter. 
FIGS. 3A, 3B and 3C, which show logic flow charts and related timing, give 
the response of sensor 18, or any other susceptible sensor, to a PPD. In 
FIG. 3C, PPD interval timer 34 stores and then decrements the PPD 
estimated time interval in PPD message 25 in regular intervals through 
zero, and its register 36 stores the associated PPD identifier. PPD ID 
register 37 and PPD interval timer 35 provide for a second simultaneous 
PPD message. The outputs are or-ed and inverted by OR 40. Note that 
additional simultaneous PPD messages may be accommodated in this fashion. 
Brick Wall Timer (BWT) 38 and Recovery Timer (RT) 42 also decrement time 
in regular intervals from their respective initial values through zero. 
Upon reaching zero, RT 42 sets flip-flop 44 via line 46 enabling an alarm 
signal from alarm source 49 via AND 47 to generate an alarm via alarm 
output 50. The alarm is disabled by the clearing of flip-flop 44 via line 
48 from transition detector 45. The transition of the output of AND 41 
from 0 to 1 signifies that a PPD event has been signaled by a PPD start 
message. This transition occurs upon the output of BWT 38 and OR 40 both 
becoming 1. Similarly, transition detector 43 starts RT 42 upon a 
transition from 1 to 0 signifying the end of the PPD event or time-out via 
BWT 38. 
Referring to FIGS. 3A and 3B and operating simultaneously with the 
circuitry of FIG. 3C, sensor 18 is initialized by block 53 and has an 
input 54 which receives PPD messages 25 from output 24 of CT unit 12 and 
stores them in FIFO 56. Block 53 sets BWT=0, PPDT=0, and RT=0. Messages 25 
are entered into the top of FIFO 56 and are read from the bottom of the 
FIFO on a First In/First Out basis into a two byte storage register 57. 
FIFO 56 retains messages 25 until read, but while retained in the FIFO the 
PPD interval in all stored PPD messages are decremented by timer 55 at 
regular intervals. This ensures that if a PPD message is not read 
immediately, the PPD interval will not be effectively and inadvertently 
increased by the amount of time it remained in FIFO 56. Messages 25 are 
cleared from FIFO 56 as they are read into register 57. Register 57 does 
not need a timing capability because it is read and responded to in 
micro-seconds by a microprocessor used to generate the operations shown in 
FIGS. 3A, 3B and 3C. 
When any of the following described tests require information about message 
25, that information is obtained from register 57. Other data are obtained 
as implied from prestored data in other registers or from timer registers. 
As an example, test 60 requires information regarding to which PPD 
disturbances a particular sensor is susceptible. These identifiers are 
prestored in as many registers as required and all compared successively 
with the PPD identifier from the PPD message in this test. While the tests 
and various other operations, as shown in FIGS. 3A and 3B, are being 
performed in the sequence shown, the various timers and logic of FIG. 3C 
are operating independently. 
The system is arranged such that until a PPD message 25 is received the 
system waits for a word to be entered into FIFO 56. When a message 25 is 
entered into FIFO 56 that message is then read from the FIFO into register 
57. 
Test 58 determines whether RT is greater than zero. If yes, control is 
maintained. If not, control is given to test 60 which uses the PPD 
identification information of message 25 loaded into register 57 to 
determine whether the sensor reading the message is susceptible to a 
disturbance from the identified disturbance source. The question of Test 
60 is: Is this sensor susceptible to the identified PPD? If the answer is 
no, the next word in FIFO 56 is read. If FIFO 56 is empty the process is 
again halted until another message 25 is received, at which time the next 
PPD message in the FIFO is stored in register 57 and the above described 
sequence repeated. 
Test 62 asks the question: Is the MSB of the lower byte one? A no indicates 
a PPD stop message and control is transferred to test 68. If the answer is 
yes, the PPD message is a start message and control is given to test 63 
which determines whether BWT is zero. 
When test 63 results in a yes, test 64 determines whether the sensor is 
within range before the PPD disturbance is entered into the system. Test 
64 asks the question: Is this sensor in range? If the answer is no, 
control is returned to process the next PPD message. If the answer is yes, 
process 65 sets the PPD ID 36 or 37 from register 57, starts BWT at the 
maximum suppression time, and transfers the PPD event duration from 
register 57 to timer 34 or 35. If the answer to test 62 is yes (i.e. stop 
message), test 68 is performed. The question of Test 68 is: Is the PPD 
interval timer greater than zero? If the answer is yes, this is a normal 
termination and control is given to process 69 before returning to 
accommodate the next PPD message. Process 69 starts RT, sets BWT 38 to 
zero, and sets the PPD timer 34 or 35 to zero. If the answer is no, the 
next available word in FIFO 56 is read. 
Test 66 asks the question: Is the PPD interval in register 57 greater than 
the current PPD interval timer 34 or 35 value? If the answer is no the 
interval stated is smaller than that currently in the PPD interval timer 
34 and the next available word in FIFO 56 is read. If the answer is yes, 
then block 67 is executed where PPD interval timer 34 or 35 is set to the 
PPD interval stored in register 57 to extend the PPD interval, the PPD 
identifier stored in register 57 is read into PPD identification register 
36 or 37 of PPD interval timer 34 or 35, and the next available word in 
FIFO 56 is read. 
As shown in FIG. 3C, if during the above operations either all PPD interval 
timers (34 and 35), or BWT timer 38 decrement through zero from their 
initial value then Recovery Timer (RT) timer 42 will be started. When RT 
timer 42 decrements through zero from its initial value then Flip/Flop 44 
is set which will enable Alarm 50 and permit it to sound. 
This sequence of operations, while expressed as a series of test questions 
plus timing sequences, covers the necessary operations for this equipment. 
Any appropriate microprocessor can be coded with instructions to 
accomplish the operations described above by one skilled in the computer 
art. 
This apparatus and procedure for operating the same describes a complete 
structure and apparatus for sensors, whose accuracy is susceptible to 
certain PPD disturbances, to mute their alarms during those particular PPD 
disturbances in order to avoid false alarms. Additional important features 
include means to extend the disturbance interval limit for repeat or new 
disturbances, means to limit the total disturbance interval to avoid 
muting the alarm beyond a safe interval, and recovery timer means which 
extends the disturbance interval to allow the sensor to recover from a 
disturbance to improve its performance. These features are important for 
certain patient procedures using a variety of devices. A number of the 
additional features described above can be eliminated under certain 
conditions, for example, when there is only one PPD generator or type of 
PPD generator PPD identification can be eliminated, or if successive and 
different PPDs can not occur within a given PPD disturbance interval then 
the extension of the PPD disturbance interval is unnecessary. 
As described above, the functions of the Communications Timing (CT) unit 
may be highly centralized as in the embodiment of FIG. 1. FIG. 4 shows a 
system 60 wherein these functions are highly decentralized. System 60 
contains a number of devices consisting of susceptible sensors and PPD 
generators as in the above centralized example. For clarity, only devices 
62, 64, 66, and 68 are shown. 
System 60 has each of the devices (i.e. devices 62, 64, 66, and 68) coupled 
in a token ring employing a standard interface protocol (e.g. ANSI 878.1). 
This is most easily implemented using a "daisy-chain" approach as shown. 
As it is added to system 60, device 62 is coupled into the daisy-chain via 
cable 70 to an existing device (not shown). Similarly, device 64 is 
coupled via cable 72, device 66 is coupled via cable 74, and device 68 is 
coupled via 76 through devices not shown and through cable 80. 
Interface circuitry 82 of device 62 provides the electrical and functional 
interface between device 62 and the ANSI standard token ring. This 
circuitry is readily known in the art and enables device 62 to transmit 
PPD messages if it is a PPD generator and to receive and decode PPD 
messages if device 62 is a susceptible sensor. The other devices of system 
60 are similarly equipped with appropriate interface circuitry. 
While this invention has been described with respect to specific 
embodiments, this description is not intended to be construed in a 
limiting sense. Various modifications of the illustrative embodiments, as 
well as other embodiments of the invention, will be apparent to persons 
skilled in the art upon reference to this description within the scope of 
the appended claims.