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Thread: Is Breathlessness a manifestation of "delay with overshoot"

  1. #1

    Is Breathlessness a manifestation of "delay with overshoot"

    One of the common components of Central Pain is "delay with overshoot". What this means is that since there is decreased sensation, sharpness or other noxious stimuli may not be recognized at the ordinary threshold. But when it is perceived, there is overshoot. Which is to say that a pin or needle is not only sharp it is unbearably sharp. Excruciating. "Delay with Overshoot" is classically defined as a manifestation of injury to the spinothalamic tract. Some feel that it is the most accurate and important clinical sign of injury to the spinothalamic tract (carries pain signal to the brain). It is usually tested for by applying a safety pin to the skin. Artfully, an examiner can also test for this using Von Frey filaments.

    Most spinal injury is incomplete. Quadriparetics are much more common than quadriplegics, but for some reason, are not as interesting to examiners. Testing for intermediate injury to sensation is a definite art for an examiner.

    European doctors who do this sophisticated testing have indicated CP patients cannot detect temperature change as well as normals, (CP often requiring up to 4 degrees C before they detect a temp difference--normals can sometimes detect change at 1.5 degree change) but when a temp is finally at the painful level, CP subjects feel the painful temp much more dramatically, particularly if the probe is cold (cold test tubes are also used instead of probes).

    Temp sensation deficiency is almost never done in the U.S. because of the time involved. The skin must be brought to a given temperature before comparisons can be made between what is hot or cold. Perceived pain is relative to skin temp. Hardy's work in the Journal of Clinical Investigation in 1949 showed that despite other differences in pain susceptibility, humans are remarkably uniform in the temperature at which they perceive pain, so temperature perception changes are very significant.

    Graded points of sharpness can virtually always demonstrate delay with overshoot in quadriparetics, but the availability of such graded points of sharpness is very limited. Instead, the examiner usually uses his own idea of how hard he is pressing with the point of a safety pin. If he pushes very hard at all, he is already past the threshold and cannot really use the test. Graded sharpness is done more in Canada than the U.S.

    Now, quadriparetics and quadriplegics commonly have respiratory problems, particularly with high cervical lesions especially early after the injury. With time, there is increased serotonin released in the supply to the phrenic nerve (supplies diaphragm), which may alleviate the breathlessness to some degree. It is not clear whether this improvement is due to increased neural excitability or to increased synaptic strength.

    Some with CP have reported an instantaneous hesitation in inspiration (maybe a millisecond) followed by immediate involuntary strong inspiration to complete the respiratory movement. It occurs when at the start of inspiration, that a person has a hitch or pause and then completes the inspiration with a heavy breathing movement. The question is whether this represents hypoxia, which is missed at first until some threshold is reached, at which point the person suddenly completes the inspiratory movement with increased force.

    "Delay with Overshoot" is very very common in interviews with Central Pain patients, but oddly they almost never have heard the term. It means that in areas of decreased sensation, when something painful is finally perceived, it is dramatically increased.

    Just as a SCI patient can have decreased sensation without developing Central Pain (most SCI do not in fact develop CP), most (the vast majority) with respiratory impairment do not experience the inspiratory event described above.

    reprinted with permission from painonline.com
    Last edited by dejerine; 03-17-2014 at 10:01 PM.

  2. #2
    Hi Dej,
    For a moment I thought I needed to transfer the 'delay with overshoot' to a different forum - relationships and sexuality. But I didn't have to.

    Thanks, that is interesting.

    The phenomena is so familiar to me and I like to ignore the inevitable , such as the consequences of sitting on a hard surface - 'just for a minute' - I say to myself. Then 15 minutes later, I highly regret this as I end up with more than the usual 'seat' pain.

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