cell phones affect monitors???

Discussion in 'Medical Students - MD' started by diente, May 13, 2002.

  1. diente

    diente Junior Member

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    Question for all you:
    Do cell phones actually affect monitoring equipment in hospitals or is this just an old wife's tale? I work in an emergency room and there is a rule against them but most of the doctors ignore it saying it dosen't affect anything. Anybody know? :confused:
     
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  3. docuw

    docuw Senior Member

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    The signals from the phone can interfere with monitoring equipment (like EKGs etc). This is not permanent damage, and is not a big deal.
     
  4. oldman

    oldman Senior Citizen
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    some patients are on heart monitors that are transmitted to nurses stations. supposedly the cell phones will interfere. i'm not sure how big of a deal it is, but heck i'd rather be safe than dead.
     
  5. Hopkins2010

    Hopkins2010 Banned
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    well... generally the electromagnetic spectrum that cell phones use is not in the same range that hospital monitoring equipment uses (i.e. pacemaker telemetry, heart monitors, etc)

    So i think its probably safe most of the time, however, there is always a small chance that interference could occur, so I think thats what they are basing theh safety standards on.

    For regular heart monitors, my guess is that its not that big of deal. The cell phones could possibly interrupt the wireless telemetry between the monitor and the base station temporarily, but usually communications would be restored as soon as the cell phone is cut off. So, the only real situation I can imagine there is if a patient goes asystole while someone is using a cell phone in the area that is interfering with the telemetry path to the nurses' station. In that situation, the nurses' wouldnt be aware that the patient was in trouble unless they were standing right by the patient.

    For pacemakers/defibrillators, most recent models have special analog circuitry and microprocessor design that prevents any interference with the telemetry system.

    My guess is that these precautions originated at a time before medical device design incorporated the safety features that exist nowadays.
     
  6. oldman

    oldman Senior Citizen
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    In these days of lawsuit happy people, I'm sure they want to be on the safe-side.
     
  7. droliver

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    The original concerns were with the first generation analog phones & should not apply to digital phones of today. Some traditions die hard & some nurses cannot understand this distinction & will say something
     
  8. ckent

    ckent Banned
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    Actually, I thought that the cell phone thing was a real big deal. I know that in some hospitals, they are looking for ways to install walkie-talkie systems or non-cell phone ways of communicating because cell phones aren't allowed on the hospital floors. Some of the systems that they have been looking at have been very expensive too. If cell phones were really alright, then you would think that everyone would just carry a cell phone instead of a beeper so that you wouldn't have to go looking for a phone every time you were paged.
     
  9. UHS2002

    UHS2002 Senior Member

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    Like droliver said, the issue was only with the analog phones. I got the info straight from an Intensivist...if anyone whould be concerned they should be the ones <img border="0" title="" alt="[Wink]" src="wink.gif" />
     
  10. diente

    diente Junior Member

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    Thank you all for your replys. The hospital I work at did install a whole new non-cell phone based portable phone system. It was a total waste of money. Then system is usually down or the phones don't work. I don't personally even have a cell phone, but I never even bother to tell the patients, or their visitors, to not use their cell phones. Saves me the time of calling for them on our phones.
     
  11. MacGyver

    MacGyver Banned
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    when you say analog phones, i'm assuming you mean analog cell phones?

    this doesnt make any sense to me. analog vs digital usually refers to the internal electronics, not the transmission medium.

    how can you have a digital transmission medium? I dont think its possible to transmit 0s and 1s thru space, you have to transmit electromagnetic waves and have the electronics in the phone interpret it based on analog or digital technology.
     
  12. Kirk

    Kirk Senior Member

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    </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by MacGyver:
    <strong>when you say analog phones, i'm assuming you mean analog cell phones?

    this doesnt make any sense to me. analog vs digital usually refers to the internal electronics, not the transmission medium.

    how can you have a digital transmission medium? I dont think its possible to transmit 0s and 1s thru space, you have to transmit electromagnetic waves and have the electronics in the phone interpret it based on analog or digital technology.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Well, you are partially wrong here. Analog vs. digital does indeed refer to the transmission of the radio waves. An analog phone sends the data as a ?wave? which rides on a much higher carrier frequency. This uses a much larger section of the frequency spectrum and hence it causes more distortion of other electronics.

    A digital phone converts the sound into a stream of signals (1 and 0) and transmits them on a carrier frequency. This combined frequency is much smaller then an analog signal (since you are sending a stream of bits instead of a large wave); therefore there is a much smaller chance of interference. However, since you are still sending out a signal, there will always be some chance of interfering with other electronics.
     
  13. wanderbray

    wanderbray Junior Member

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    There is just one more little point:
    1) Telemetry data is almost always digitally encoded.

    As Kirk said, there is a narrower bandwidth for digital transmitions, however, when two digital signals do collide one or both signals is obliterated. If the telemitry signal is strong enough to confuse the phone, the phone will drop the connection. But, since telemetry signals are intensionaly weak, this is not likely to happen, and only the telemetry signal will be obliterated.

    I personally don't know if there is band overlap or if this is an old wives tale, but if we can take a hint from the FAA: Your cell phone ***MAY*** cause the automatic landing & guidance mechanisms on an airplane to fail, so they ask you not to use your cell phones while we're in the air.

    Similarly, if the hospital asks you not to use your cell phone. Why not just go along with it until they say otherwise?
     
  14. intern in waiting

    intern in waiting Junior Member

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    I remember reading somewhere (prob NEJM or JAMA) that turning a cell phone on within 5 cm of certian ventilators caused it to reset the vent settings...I'll try and find that article
     
  15. Hopkins2010

    Hopkins2010 Banned
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    Well, actually analog cell phones work almost exactly like standard FM radio, except the carrier spectrum used for analog technology is in the 800-900 MHz range. With the older analog technology cell phones, its possible with a little ingenuity to modify your FM radio to pick up someone's phone conversation.

    Both analog and digital use carrier waves in the same spectral region (i.e. 800-900 MHz). However, the difference lies within the signal waves propagating on top of the carrier waves. Digital systems use FSK (frequency shift keying) which is a series of alternating high and low frequency sets used to represent 0s and 1s. Analog phones just convert sound waves directly into an electrical signal without using A/D or D/A converters.

    The bandwidth savings that digital phones enjoy is due to the pre-processing of the bit stream that occurs before the digital data inside the phone is transmitted via the RF antenna. Most cell phones use digital signal processors (DSPs) that use fancy mathematics to encode and compress the bit stream. Compressing the bit stream before transmission means that it takes less bandwidth to transmit the same data compared to an analog phone. Therefore, unlike analog phones, unless you know the exact compression and encoding scheme, you cant hack into a digital phone conversation.
     
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  17. UHS2002

    UHS2002 Senior Member

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    </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by wanderbray:
    <strong>I personally don't know if there is band overlap or if this is an old wives tale, but if we can take a hint from the FAA: Your cell phone ***MAY*** cause the automatic landing & guidance mechanisms on an airplane to fail, so they ask you not to use your cell phones while we're in the air.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">To be honest with you, if you knew how the FAA works, you would not be taking too many hints from them :rolleyes:

    There are cell phones on commercial airliners and you pay handsomely to use them, even though you could call on your own cell for a 10th of the cost. Yep, you cannot use them during takeoff and landing but you can use them during cruise and, if they were really that dangerous to navigational equipment, you would not be able to use them during cruise either. Additionally, you can fork about $7,000 to have a special cell phone installed in your private plane, because the FAA says you should not use your personal cell phone on your own plane either. They are concerned about:
    1.interference within a fairly narrow range of frequencies and want to make sure nobody uses equipment that perhaps operates within that range (which your cell phone doesn't use by the way, otherwise you would be picking up the VOR signal down the road <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" /> )
    2. people who KNOW their equipment will interfere with navigational equipment (which I think is the most valid and important reason)

    For the 2nd reason, it is imperative that people not be allowed to use their cell phones aboard a commercial flight. Now, I don't know many people who would intentionally rig their cell phones so they could interfere with telemetry/vents/pumps in a hospital...Actually, the people I saw most inconvenienced by not being able to use their cell phones in the hospital were the physicians.
     
  18. wanderbray

    wanderbray Junior Member

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    </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by UHS2002:
    <strong>To be honest with you, if you knew how the FAA works, you would not be taking too many hints from them :rolleyes:
    </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">:D Good point. I retract the comment. :)

    Never take any hints about how to do things from government agencies. <img border="0" alt="[Laughy]" title="" src="graemlins/laughy.gif" />
     
  19. tonem

    tonem Senior Member

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    I have a question for all those of you who obviously have a great deal of expertise in this area. This is something I started thinking about one night when I forgot to turn off my cell phone in the hospital and it started ringing.

    How is my phone going to have any more effect on anything in the hospital than the thousands or millions of electromagnetic transmissions that are obviously passing through the hospital at any given moment? The hospital doesn't have lead lined walls (otherwise my phone wouldn't have rung).
     
  20. Hopkins2010

    Hopkins2010 Banned
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    </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by tonem:
    <strong>I have a question for all those of you who obviously have a great deal of expertise in this area. This is something I started thinking about one night when I forgot to turn off my cell phone in the hospital and it started ringing.

    How is my phone going to have any more effect on anything in the hospital than the thousands or millions of electromagnetic transmissions that are obviously passing through the hospital at any given moment? The hospital doesn't have lead lined walls (otherwise my phone wouldn't have rung).</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You raise a good question. Its all about power and frequency ranges.

    Either the EM waves that pass thru the hospital lie in spectral ranges which hospital equipment does not use, or the transmitted power of the signals is so low that it doesnt cause any distortion in the hospital electronics.

    The most prominent EM interference is radio waves. All medical equipment is designed not to use frequencies within the FM range (i.e. 80 - 110 MHz)

    So, although those frequencies are definitely passing thru the hospital equipment, the analog circuitry inside the equipment (i.e. mainly inductors and capacitors) are tuned not to pick up those frequencies.

    In addition, most hospital equipment has modest EMI (electromagnetic interference) shielding, and the ASICs (integrated circuits) used inside the devices also have some EMI protection.

    In order to answer the more specific question of how cell phones interact with hospital equipment, I would need to know the specific frequency ranges and power levels used by telemetry circuits. This data is highly dependant on a given manufacturer, and its probably considered proprietary and semi-confidential material.

    If you had an antenna hooked up to an amplifier and oscilloscope, you could experimentally determine the frequency range used by such hospital equipment. But I dont know if there is any standard "hospital frequency range" that is set by the FCC or some other standardizing body. Perhaps someone else knows more specifics on if/how the hospital equipment broadcast range is regulated.
     
  21. Neuronix

    Neuronix Total nerd
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    I worked as an ER volunteer for three years at the local trauma center (Christiana Hospital). It started out with cell phones not banned, then they banned them for some length of time (a few months?), and then they unbanned them again. All they say now is not to use cell phones in the rooms, but I've seen docs do it several times.

    Not that this is at all scientific, but it doesn't seem like there's ever been any effect on equipment or anything.
     
  22. Rads

    Rads Member

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    ALL medical devices certified for use by the FDA must have shielding to prevent interference to other devices malfunction when exposed to near-field RF. Regardless of what the nurses tell you, your cell phone will NOT cause a 25,000 HP monitor to crash. First off, most cell phones these days put out milliwatts of power, hardly enough to cause major equipment interference. Secondly, you notice how nobody bothers hospital security when they are transmitting in the ED with their 4 watt UHF portable radios, or the police and EMS with their radios. Basically, not using your cell phone in a hospital is a courtesy, you aren't going to kill anyone.
     
  23. Chris_P

    Chris_P Senior Member

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    Hi

    Found a study which may be of interest:
    <a href="http://www.mayo.edu/proceedings/2001/jan/jan2001.html" target="_blank">Cellular Phone Interference With External Cardiopulmonary Monitoring Devices </a> The most severe interference related to cell phone use: A mechanical ventilator shut down and restarted when a cell phone was held within two inches of a communication port on the ventilator.

    Anyone know of any other articles about this?

    Chris
     
  24. Hopkins2010

    Hopkins2010 Banned
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    Very interesting read, thanks for the link.

    I think they should have tested for magnetic field in addition to electric field measurements. Capacitors store energy in the surrounding electric field, while inductors store energy in a magnetic field. Therefore, external magnetic fields can couple into inductors and affect the analog circuitry inside the medical equipment just like electric fields.

    They should probably have also done testing with transmission of voice data in addition to the rudimentary "ring" test they performed. EMI interference is highly dependent on the exact mode of operation, especially for digital cell phones. Most cell phones use DSP chips which periodically shut down the transmission link if a long silence is detected (in order to conserve battery power). In addition, the RF power output changes depending on if the phone is just ringing or if you are actually holding a conversation over the unit.

    I would have liked to have gotten more details and seen more analysis of the stand alone spectrum that the hospital equipment uses. It states in the article that there are maximum electric field interference requirements in the 450 MHz to 1 GHz spectrum, but thats the only inside look we have at how these devices communicate. I'm confident that if they had explored this deeper, they would be able to more conclusively analyze the conditions under which dangerous EMI problems could occur.

    As for the clinical relevance of the findings, I dont understand one of their claims. If you look at the last page of the article, it shows a minimal ECG baseline noise disturbance and the maximal case. For the baseline shift phenomena, its obvious that its not a clinically relevant difference. However, for the baseline noise maximal case, it appears to me that its very clinically relevant (yet they argue that its not, with no explanation). Its illegible to a cardiologist. Now its true that a microprocessor/DSP could extract the noise and get the true ECG waveform, but to human eyes its unusable. Doesnt that imply clinical significance?
     

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