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`problem. Other applications are to provide feedback to an input from the
`operator, and in some units to codify the patient pulse strength by changing the
`sound pitch accordingly to the strength as defined in the Standards (ASTM 1992).
`Despite these acoustical outputs, the primary output of a pulse oximeter is
`visual. Pulse oximeters can be primarily classified based on the technique used to
`present visual information into two categories:
`
`1. Graphical displays that present analog and digital information.
`2. Numerical displays that only present digital information.
`
`12.2.1 Graphical displays
`
`It is common knowledge that 'a picture is worth thousand words', and pulse
`oximeters are not an exception. Graphs produce a spatial presentation to
`communicate quantitative information to the exterior world, making them very
`flexible (Gillan and Lewis 1994). The displays used in pulse oximeters are
`normally liquid crystal displays (LCDs), although some models from Protocol
`Systems Inc. (Propaq 102/104/106) also have versions with an electroluminescent
`display (ELD). ELD displays perform better when it is necessary to view them
`from long distances. They are aimed toward bedside monitoring, where the units
`can be plugged to a power line source, because of the higher power that these
`displays require. On the other hand, LCD displays are better in direct sunlight
`and require much less power, which increases both the display life and the battery
`discharge cycle (Bosman 1989). Most of the commercially available LCD units
`have a backlight that increases display readability but also dramatically decreases
`the battery operating time. For example, Criticare specifies for its 503 model, a
`battery use time of 20 h when the backlight is turned off, while it decreases to 10
`h when the backlight is turned on.
`Graphical displays present one or more real-time waveforms. Normally, the
`units that incorporate graphical displays are also the ones that acquire more
`physiological signals, so there are more choices for display. All the units with
`graphical displays can simultaneously present different waveforms, although for
`readability it is not convenient to present more than two. The most common
`waveforms are the plethysmographic waveform and the ECG. The model POET
`TE Plus from Criticare also monitors CO2 and can display the capnographic
`waveform. The Propaq models from Protocol Systems, Inc., have different
`modular systems that can measure oxygen saturation, ECG, CO2 consumption,
`and invasive and noninvasive blood pressure. The units from Medical Research
`Laboratories, Inc. can be used as stand-alone systems or as a part of an integrated
`monitoring system as previously described. The model 9500 from Magnetic
`Resonance Equipment Co. is a multigas monitoring system that measures oxygen
`saturation, CO2, N02.02 and invasive and noninvasive blood pressure. The
`model BIOX 3700 from Ohmeda, shown in figure 12.2 has two separated LCD
`displays with different functions for each one. One displays different waveforms,
`while the other displays the values of oxygen saturation and pulse rate.
`In addition to real-time waveforms, displays can also present the trend from
`a past period of time. This feature does not involve a major increase in the
`complexity of the electronic design because it only requires storage of the already
`digitized values and further processing. The length of time that is available for
`display depends on the amount of the memory used in the design, but also on the
`sampling frequency, which is normally user selectable. There is a large variation
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`among the length of time that different models store trend display. In the Biox
`3700 from Ohmeda, the length of the trend can be selected between 20 and 60
`min, by pressing a key in the front panel. as shown in figure 12.2. The model N-
`3000 from Nellcor has three different ways of recording data for trend analysis.
`In the first two modes, the unit stores the average of oxygen saturation and heart
`rate measured over a period of 5 or 10 s. with a total duration of I 2 or 24 h
`respectively. In the third mode, the unit stores the maximum and minimum values
`obtained over a period of 20 s, with a total duration of 32 h. The length of the
`recording also changes with presentation. The Propaq models from Proti,col
`Systems, Inc. can display a total of 5 h on the screen and 8 h on a printer with a
`rexolution of 2 min. The data can be presented in graphical or tabular forni.
`
`Wik-r
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`9t
`ames 9 0000
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`O-1
`Jt
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`1
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`Figure 12.2 Front panel of Ohmeda B iox 3700 pulse oximeter (Courtesy of Ohmeda). The
`display at the left side shows mal-time waveforms and pulse strength, while the display at the right
`side is used for alann settings
`
`In some units, for example the model 504 from Criticare, the memory in
`which the trend data are being stored is not erasable on power-off. When trend
`data that contain periods of time in which the unit was turned off are displayed,
`the time during which the unit was turned off is shown as special characters so
`that the operator can be aware of this situation. This feature allows us to follow a
`patient during a long duration in which constant monitoring is not required. The
`drawback of this feature is that it can acquire the trend from the wrong patient if
`the previous data are not erased before starting to monitor a new patient. The
`trend display also marks times during which alarm set points have been exceeded
`or the pulse has been lost.
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`Trend graphs incorporate cursors that can be scrolled through the display
`with numeric readouts that normally show the values of the waveform and the
`time. This feature is particularly useful when the screen displays different
`waveforms because they do not incorporate a numerical vertical axis and it is not
`possible to distinguish magnitude by only reading the screen. It is also very
`important to properly label the different waveforms, as the most commonly
`displayed waveforms (pulse rate versus time, and oxygen saturation versus time)
`can present numerical values very similar to each other and confuse the system
`operator. It is also important that the trend display have the capability to use the
`dynamic range available in the screen to more clearly show small changes. For
`example, the model 504 from Criticare displays the trend in oxygen saturation
`between 75% and 100%. Although large changes in oxygen saturation can be
`easily recognized, it is difficult to notice small changes at a glance because most
`of the monitored patients will not have such a large oxygen saturation change.
`A series of menus that appear on the screen normally permit the operator to
`select between the displayed waveforms, cursor displacement, and other function
`controls. The selection keys are placed under the display screen or at its sides,
`and the function of a particular key is automatically changed depending on the
`displayed screen mode.
`The display of pulse strength is mandatory for those pulse oximeters that
`display a normalized pulse waveform (ASTM 1992). The reason for this feature
`is because the amplitude of the plethysmographic signal can be changed by the
`operator in order to achieve a good dynamic range on the screen, and it is
`desirable to have an indication of pulse strength regardless of the operator
`settings. In units with graphical displays, it is commonly done by a graphic bar
`whose amplitude is proportional to the pulse strength, situated on one side of the
`screen, as for example the unit shown in figure 12.2. The display of the pulse
`strength must be accompanied by acoustical signals.
`Other information commonly found in graphical display units is the values at
`which alarms have been set, their status, low battery indication, system
`malfunctions, and other messages of interest to operators.
`
`12.2.2 Numerical displays
`
`1
`
`The majority of the marketed pulse oximeters use only a numerical display made
`of red LED segments. In all the units examined, information on oxygen
`saturation and heart rate is presented. In addition to these variables, the models
`507 and 5070 from Criticare Systems, Inc., that are complex monitoring units,
`also display the values of systolic, diastolic, and mean blood pressure. POET TE
`Plus from Protocol Systems, Inc. displays the values of oxygen saturation and
`C02· Because in some patients, oxygen saturation and heart rate can reach the
`same numerical values, it is highly desirable that the displays incorporate a fast
`and reliable way for the operator to associate the number on the panel with the
`physiological variable of interest. However, only a few units have this feature.
`For example, the model POET TE Plus from Criticare Systems, Inc. uses
`different colors for LED segments to display oxygen saturation and CO2. The
`model 3500 from Magnetic Resonance Equipment Co. and the models 504 and
`504S from Criticare Systems, use different size LED segments to display oxygen
`saturation and pulse rate, and Medical Research Laboratories, Inc. uses larger
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`Design of pulse oximeters
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`green LEDs for oxygen saturation display and smaller red LEDs for heart rate
`display. The pulse strength in all the units with numerical output is displayed
`using a LED bargraph
`
`12.3 FUNCTION CONTROLS
`
`Function controls carry out communication from the healthcare professionals to
`the pulse oximeter to achieve the proper monitoring and care for the patient.
`Function controls are basically used to operate alarms (set alarm values, activate,
`deactivate and silence alarms) and displace the cursors along the graphical screen
`in those units with this feature.
`It is possible to distinguish three different function controls: switches,
`turning knobs and keys. They do not all need to exist in the same unit.
`The main function of switches is to turn tile device on or off. In some units
`switches are replaced by keys. Since this is the most basic function in a pulse
`oximeter, it is important that it cannot be turned off accidentally. For this reason.
`some units have the main power switch or key in a lateral panel where it is
`unlikely to turn the power off by accident.
`There are few units that incorporate turning knobs. The model N-200 shown
`in figure 12.3 and model N-3()00 from Nellcor use turning knobs as an intuitive
`and quick way to increase or decrease the alarm settings. The turning knobs are
`placed on the front panel or on the top of the unit, where they are large and thus
`are easier to manipulate without affecting other controls. A function thal uses
`turning knobs for control has to be designed so that a movement upwards, to the
`right or in a clockwise direction increases the control function (ASTM 1992).
`
`e
`
`Figure 12.3 Nellcor Puritan Bennett N-200 pulse oximeter (Reprinted by permission of Nellcor
`Puritan Bennett, Pleasanton, California).
`
`The majority of pulse oximeters use keys as input devices to control the
`instrument. We can distinguish between units that use touch panel keys and units
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`that use push buttons. Touch panel keys have the advantage that they are cheaper
`to manufacture and insert during the manufacturing process and can
`accommodate LEDs to indicate thal the function is active. They also contribute to
`a better seal of the unit's front panel. thus making it more suitable for use in
`hostile environments. Figure 12.2 shows a unit that uses these kind of keys for
`front panel functions. On the other hand, push buttons have a better feel and
`require lower pressure to activate. However, they have open spaces around them,
`can permit dust, humidity and other chemical agents to shorten the life of their
`electrical contacts.
`For any kind of keys used, it is desirable that the operator has a feedback
`that the key has been pressed successfully, either by a visual stimulus such as
`turning on a LED in a touch panel key, an audio stimulus by emitting a
`characteristic sound, or tactile feedback from the release of the pressed key
`pressing on the operator's finger (Cakir et al 1980).
`It is important to consider the number of different keys that are available in
`a pulse oximeter. In general, it is best to have as few keys as possible to simplify
`the access to the most common and critical functions. such as setting the alarm
`values. For example, the model N-200 from Nellcor has a very intuitive way of
`setting the alarm values (low oxygen saluralion, high oxygen saturation, low
`pulse rate, and high pulse rate) that consists of pressing a single key to select the
`alarm, and modify the actual value by rotating the turning knob as can be seen in
`figure 12.3. However, this device has only five different keys, so the operator
`needs to press two different keys simultaneously to activate other functions.
`Because the key labeling only refers to the basic function, it can become difficult
`to remember which keys need to be pressed in order to activate the desired
`function, and it is therefore harder to perform. In this particular unit, the
`manufacturer supplies a quick reference card to be placed on the bottom of the
`unit. It provides a helpful reminder to the operator if the operator knows where
`to look.
`On the other hand, the model 504US from Criticare uses the dynamic key
`function and labeling that has been described in previous sections. Wilh only
`lhrce touch panel keys for menu purposes, the operator enters a series of menus
`and submenus, changing the function of the keys according to the menu that is
`active. Allhough this way of controlling the functions has the advantage that the
`operator always knows lhe function of the set of keys, it is very easy to forget the
`depth of the menu entered, in which submenu a particular function of interest is
`located. It can also be time consuming to move between functions located in
`different submenus.
`In the same way that the operator needs feedback to indicate that a particular
`key has been pressed successfully, the operator also needs some feedback that
`indicates that the key, or combination of pressed keys, is valid, and a control
`funclion has been executed. The most common way to produce this feedback is by
`turning on a visual indicator that is related to the function executed, or by
`emitting a characteristic sound in the case of invalid keys.
`11 is also important to pay attention to the layout of displays and indicators
`and their control keys, selecting the position of the controls in a place that is
`consistent with the display. Figure 12.4 shows di fferent examples of good and
`poor relative positions between displays or indicators and controls, based on the
`idea that they have to be laid out in such a way that the relationship between
`controls and their indicators is obvious.
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`2 1.711-3.1
`8 1-31 III
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`Poor
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`D-1 Fil 4-1
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`Poor
`
`00 ~~
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`O0 1-5-1 ~
`
`Good
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`m Fill-31
`000
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`Good
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`Figure 12.4 Layout of controls and indicators to ensure good operator interaction. From
`Salvendy (1987).
`
`12.4 ALARM CONTROLS
`
`The alarms communicate the patient to the healthcare professionals, alerting of a
`potentially dangerous situation, Because the alanns are I he most critical functions
`in a pulse oximeter, it is absolutely necessary to be sure of their proper working
`condition, as well as to take extra effort to design them in such a way that they
`cannot be disconnected accidentally.
`The design of alarms and their controls section is by far the most regulated
`by the standards. The most common type of pulse oximeters, the units that display
`the oxygen saturation and heart rate, provide alarms for the following situations:
`
`1. High oxygen saturation.
`2. Low oxygen saturation.
`3. High pulse rate.
`4. Low pulse rate.
`
`Other sections in the ASTM Standard regarding the operation of alarms
`require that the alarm set points be operator adjustable, that the default limits on
`low oxygen saturation be 80% saturation or greater, and the difference between
`the alarm set point and the actual value of arterial oxygen saturation when the
`alarm is activated not exceed 2% of oxygen saturation (ASTM 1992).
`In most of the units, it is possible to deactivate at least the alarm for high
`oxygen saturation, except in the case when the pulse oximeter is configured for
`neonatal monitoring. The pulse oximeter shown in figure 12.2 has deactivated the
`alarms fur high oxygen saturation and high puse rate.
`From these alarms, only the low oxygen saturation alarm is required for the
`pulse oximeter to be qualified as a monitoring device. Those devices without low
`oxygen saturation the alarm shall be marked as 'NOT FOR MONITORING'
`(ASTM 1992). All tile marketed units examined provide these four alarm
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`situations, except the models 8500 and 9500 from Nonin Medical, Inc. These
`units have been designed not for a bedside monitoring situation in a hospital
`where the alarms are used to attract the operator's attention, but in a one-on-one
`working situation where a healthcare professional is always present with the
`patient, using the pulse oximeter to measure the oxygen saturation, for example,
`during ambulance transport.
`The 9500 unit, shown in figure 12.5, is the smallest available in the market.
`With a weight of only 36 g without batteries and an extremely small size, just
`slightly larger than most of the reusable finger probes, it displays heart rate and
`oxygen saturation. The unit 8500 is a hand-held pulse oximeter that has been
`designed to provide 100 h of continuous operation with batteries. Both units have
`been designed for evacuation situations. They both comply with the USAF
`vibration standards for helicopter tlight use, can operate at temperatures below
`freezing, and the manufacturer stresses their use in helicopter evacuation.
`
`. i
`
`Figure 12.5 A small Nonin model 9500 pulse oximeter designed for emergency evacuation
`purposes (courtesy of Nonin Medical Inc.).
`
`The visual and acoustic characteristics of the alarms are also regulated by the
`ASTM Standards, as shown in table 12.1. The ASTM differentiates three kinds of
`alarms based on their priority, assigning different colors and flashing frequency
`to each one.
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`Table 12.1 Aim·m characteristics for pulse oximeters (ASTM 1992).
`
`11
`
`R.ishing
`Alarm category Operator response Audible indicators Indicator color frequency (Hz)
`Red
`immediate
`High priority
`Not medium or
`1.4 to 2.8
`low prioi-ity
`Not high or low Yellow
`priority
`Not high or
`medium priority
`
`Medium priorily Prompt
`
`Low pi·iority
`
`Awareness
`
`Yellow
`
`0.4 to 0.8
`
`Constant
`
`The current ASTM Standard specifies neither the frequency nor the volume
`of the acoustic alarm sounds. Good practice suggests that the frequency of
`warning sounds should be between 150 Hz and 1000 Hz. It should have at least
`four frequency components in order to avoid masking from environmental noise.
`The acoustic level recommended is 15 dB to 16 d B above the masked threshold
`for signals that are triggered by situations that require a rapid response, and
`levels between 6 dB and I O dB above the masked threshold for all other kinds of
`signals, to achieve 100% detectability in controlled situations. In all cases, the
`level should be less than 30 dB above the masked threshold to minimize operator
`annoyance and disruption of communications (Salvendy 1987).
`The alarms in a pulse oximeter can be disconnected or silenced. Temporary
`silencing should be used when the operator has been alerted of the potentially
`dangerous situation and has taken steps in order to solve the problem, The
`Standard specifies that if this feature is provided in the pulse oximeter, it should
`not exceed 120 s, and a visual condition of the alarm has to remain on until the
`condition that triggered the alarm is corrected (ASTM 1992). The reason pulse
`oximeters incorporate a permanent silencing alarm is to avoid nuisance noise
`when the device and probe are being connected to the patient. The permanent
`alarm silencing activation must be designed in such a way that it requires a
`deliberate action for deactivation by the operator to be sure that it is not done in '
`error. It also requires a visual indication of this condition.
`As most of the pulse oximeters monitor heart rate from the
`plethysmographic waveform, they also incorporate alarms in case the pulse is
`lost. This increases security for the patient by monitoring more vital signs. but it
`also triggers false alarms, i n particular due to motion artifacts. To avoid this
`problem, Nellcor has developed what they call Oxismart, which, for loss of pulse,
`aims to distinguish between a real clinical condition and a motion artifact. This
`feature is incorporated in the latest models, such as the N-3000.
`Motion artifacts are detected by processing the plethysmographic waveform
`and before validating a pulse, requiring three different steps. Only the signals that
`pass all the steps are used to calculate Sp02 (Nellcor 1995). To differentiate
`between a loss of pulse due to motion artifact from a loss of pulse due to a
`clinical condition, the system assumes that if the pulse is lost, but the patient is
`moving, the patient has pulse and the loss is due to a motion artifact. Figure 12.6
`illustrates this fact. If the pulse oximeter fails to detect at least one pulse in 10 s,
`it enters into pulse search mode. The operator is aware of this situation because
`the PULSE SEARCH indicator lights, and the display alternates between data and
`dashes. In this condition, the pulse oximeter enters an evaluation period of 50 s.
`[f the patient is moving, each time that the pulse oximeter detects a valid pulse,
`readings for heart rate and oxygen saturation are validated. The device returns to
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`its normal operation after detecting an adequate sequence of validated pulses. If
`during the 50 s evaluation period, an adequate pulse sequence is not detected, a
`low-priority alarm sounds, and there is a visual indication of this condition as
`shown in table 12.1. On the other hand, if the pulse oximeter does not detect
`motion after 60 s in pulse search mode, a high-priority alarm sounds, and there is
`also a visual indication of this condition. With this feature, it is possible to track
`the oxygen saturation even in patients that produce signals of poor quality, and at
`the same time warning can be given of a potentially dangerous condition.
`
`Lost pulse WITH
`continuous motion
`1
`1
`I PULSE SEARCH indicator lights continuously i
`1
`1
`Sp02 and pulse r~te
`1 zeros
`alternate between previous display
`I and dashes
`
`1 Low-priority
`i alarm sounds
`PULSE SEARCH
`flashes
`
`11
`
` Data displays
`
`11
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`60
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`Time (s)
`
`MOTION indicator lights continuously
`
`1
`10
`
`16
`
`1
`
`1 1
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`Lost pulse WITHOUT
`motion
`
`1i
`
` HIGH-priority alarm sounds
`1
`1 PULSE SEARCH 1
`I indicator lights 1
`I continuously
`
`PULSE SEARCH indicator flashes
`
`1 Sp02 and pulse rate 1
`1
`1 alternate between
`previous values and
`1
`1 flashes
`16
`10
`
`Sp02 and pulse rate flashes zeros
`1
`60
`
`Time (s)
`
`0
`
`0
`
`Figure 12.6 Oxismart© alarm detectors used in some Nellcor units to reduce false alarms due to
`motion artifacts (Nellcor 1995).
`
`12.5 COMMUNICATION FUNCTIONS
`
`Communication functions are not a primary function, but an added value feature
`for a pulse oximeter. Communication functions can be found in all types of
`devices, but they provide a great improvement to the units with only numerical
`display, because it gives them the graphical features that otherwise are missing.
`They are used to send data to a printer or plotter. The most common use is to
`print the trend for both oxygen saturation and heart rate for a patient. This
`feature converts the most simple units into units that act like solid state Holter
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`monitors, with the clinical advantage associated with the knowledge of trend over
`time. There are few units that incorporate an internal printer, normally a thermal
`one, thus eliminating the need for extra connectors and cables.
`The most common method of communication is using the RS-232 protocol.
`It is also possible to obtain analog signals proportional to the plethysmographic
`and pulse rate waveforms. The voltage output is normally selectable between a
`range of 0 to I V dc and I to 10 V dc.
`
`12.6 CABLES AND CONNECTORS
`
`The cables and connectors are used to transmit power and signals between the
`device and the surrounding accessories and power supplies. We can roughly
`distinguish three levels of communication:
`
`1. Interface with the power source.
`2. Interface with the lead and probe.
`3. Interface with auxiliary equipment.
`
`The power connector is used to transfer Ihe energy required from the power
`source to the unit for its operation. The Standard requires that it should be
`designed so that it protects the patient from human errors (ASTM I 992). This
`means that it has to be clearly different from the connectors that will be attached
`to the patient. Power connectors are used to operate the units when it is turned
`on, and to recharge the battery when the unit is turned off.
`The connector for the lead and probe is usually placed on the front panel,
`and it is usually mechanically incompatible between different manufacturers,
`unless they specify that the probe is compatible. For example, Protocol Systems
`advertises that their Propaq models can use probes l'rom Nellcor. The most
`common types of probe connectors are DB9 and DIN. in all cases, the connectors
`are mechanically designed with physical alignment aids and visual indicators to be
`sure Ihat the lead is inserted the correct way into the connector. It is important
`that the connectors be constructed robustly, because the unit can be subjected to
`severe mechanical stress and vibration. Because most of the units can be
`synchronized with the ECG signal, obtained through a separate module, it is
`common to have an ECG connector.
`The auxiliary connectors are normally located on the side or the back panels,
`and they are normally used for communication functions. The most common ones
`are the transfer of digital data to a printer or analog data for further recording
`or to a graphical plotter. For these auxiliary functions almost every manufacturer
`uses their own set of connectors, voltage levels, and conlmunication protocols that
`make them work only with their own peripheral units.
`
`12.7 OTHER FEATURES
`
`Other indications that need to be displayed in a pulse oximeter are those
`regarding the correct labeling of all inputs, outputs, control knobs, and keys.
`Some models of pulse oximeters are manufactured in different levels of electrical
`isolation. For example, Criticare manufactures the unit 504/504US in BF (body
`floating) and CF (cardiac floating) versions. Because they look externally very
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`similar, if not the same, it is very important to carefully mark its application on
`the front panel to avoid connecting a patient that needs a CF unit to a BF unit.
`For those units that can be operated using an internal rechargeable battery,
`or disposable batteries, it is important to have an external indication of the
`approximate level of charge of the batteries and the remaining operating time, to
`control their replacement. The units from Medical Research Laboratories, Inc.
`display the charge level on an indicator. Most other units display a low-battery
`warning signal.
`
`12.8 COMPLIANCE REQUIREMENTS
`
`The Electromagnetic Compliance (EMC) requirements for electrical equipment
`in general, and biomedical equipment in particular, are changing at a fast pace.
`Because most of the new regulations have long transition periods during which
`they are not mandatory, it is wise to design products for future compliance with
`those regulations. We do not describe the current applicable regulations and
`standards, but describe their existence and probably future evolution.
`The basic idea behind the set of EMC regulations is to ensure the safety of
`operation of electrical equipment during normal circumstances. This means that a
`particular device should not cause harmful interference to other devices and this
`device should not be affected by interference from other devices. Figure 12.7
`illustrates these effects. They can be summarized as conducted emissions, radiated
`emissions, and immunity from interference generated by other equipment that
`can be either radiated or conducted to the device in question (Gerke and Kimmel
`1994a). For the interference generated in the unit, most o f the problems are
`caused by the radiated emissions, because the use of microprocessors running at
`high clock frequencies is becoming more common in medical devices and these
`generate radiated interference.
`
`Radio frequency
`
`interference 1
`
`Electrostatic
`discharges
`
`1
`
`Radlated
`~-r Interference
`
`Medical device -
`
`Microprocessor
`
`Eiectronics
`
`1
`1
`
`Power -
`disturbances
`
`- Conducted
`interference
`
`Figure 12.7 Different sources of disturbances and interferences for EMC purposes.
`
`The ASTM Standard refers to the IEC 601-1 and IEC 801-2 Standards for
`electromagnetic compatibility requirements in pulse oximeters (IEC 1988, 1990).
`The IEC 601-1 Standard describes a general set of requirements for the safety of
`electrical equipment for medical use. The unit only needs to be tested against
`electrostatic discharges (ESD) for its accessible parts, rather than in the interior
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`Design Of pulse oximeters
`
`of the device. The Standard justifies this procedure based on the fact that pulse
`oximeters are not life-support devices. but vigilance adjuncts. Therefore. the cost
`to provide immunity against ESD in the interior of the system is not justified
`(ISO 9919, annex L). The same Standard, however, serves as a reminder to
`exercise common sense and provides acceptable work procedures for maintenance
`personnel that require them to open the device.
`However, many times the manufacturers try to expand their market by
`exporting their products to other countries. Therefore the designers must be
`aware of the existence of other EMC regulations, which are generally less strict
`in the US and more strict in European, Asian and most other countries. As a rule
`of thumb, the European Economic Community (EEC) countries have more
`regulations and fewer exceptions to those regulations than the US, where most of
`the regulations are voluntary for most of the medical equipment. However,
`medical regulations are undergoing significant changes, and we may expect
`mandatory EMI regulations in the future, regarding ESD, RF fields and power
`disturbances, driven by the Food and Drug Administration (FDA) and the
`regulations in the EEC. At the present time, there are no mandatory regulations
`in the US, as medical devices are exempted from Federal Communications
`Commission (FCC) emission regulations, and they are covered only by voluntary
`susceptibility requirements. On the other hand, in the EEC countries, the
`equipment is required to be tested for emissions but not for immunity (Gerke and
`Kimmel 1994b). This situation is expected to change soon, and in the future we
`may expect mandatory regulations for RFI, ESD, and power disturbances in the
`US. Because of the need to be competitive in international markets, designers
`should consider that the best way to avoid unnecessary delays, and to lower the
`economic impact of changing a design, is to design for compliance from the first
`stages, without overdesign that implies an increment of cost with no additional
`value.
`
`REFERENCES
`ASTM \991 Standard Specijication for Pulse Oximeters, F!-1!5-1992 (Philade\phia, PA:
`American Society for Testing und Matenals)
`10% \991 Pulse oximeters for medical use-Requirements, ISO 99]9:!992 (E) CGeneva.·
`International Organi