On Sensor Size

"Some of my older patients complain that the vaginal sensor is too big and feels uncomfortable. Why don't you make a smaller size than the vaginal sensor? Can I use the rectal size sensor if they complain?"

Many conscientious continence therapists are concerned about their patient's comfort level, and recognize that patients must feel relaxed in order to utilize biofeedback and learn internal muscular control and sensation. Since as many as 20 percent of patients comment about the "size" of the vaginal sensor, a careful analysis of the subject seems in order. Our observations are based on over 10 years experience with hundreds of patients, and feedback from therapists of thousands more.

(Fig. 1)

The Vaginal EMG Perineometer fits comfortably in the vaginal entrance, adjacent to the Pubococcycgeus muscle for highly reliable measurement.

The design of the EMG Perineometer has evolved over time to its present size and shape, which is under constant review. We continue to experiment with new materials, dimensions, and designs. The following considerations are part of that assessment.

Objective Considerations

The original vaginal myograph shape was copied from a 1973 research sensor, the vaginal photoplethysmograph, which was itself designed to look as much as possible like a tampon, to encourage easy acceptance by research subjects. But a tampon absorbs moisture, and soon swells to fill the much larger vaginal barrel. The new tampon-shaped device got "lost" in the available space, and it became impossible to know exactly where it was in relation to the muscles whose activity it was supposed to monitor. Measurement was unpredictable. It quickly became apparent that for reliable, repeatable measurement some automatic means of correctly positioning the sensor was essential.

The anatomical drawings of the "orgasmic platform" by Masters and Johnson provided a clue. The sensor was redesigned to include (l) an external restraining bulb, which would prevent it from being inserted too far, and (2) an internal restraining bulb, which would prevent it from falling out. Working together, these two bulbs served to balance the electrodes of the center portion over the narrow vaginal entrance. In principle, the device works like the cork of a champagne bottle and not like an ordinary wine bottle cork! Our objective was to enable the patient to insert the device herself, while allowing the therapist to know where the device was situated, without having to personally inspect it. Finally, a key (off-set cable or arrow) was added to provide the correct rotational positioning.

The present dimensions of the vaginal sensor are a delicate balance between a number of considerations. On the one hand, it is a characteristic of surface EMG electrodes that the depth of pickup in the tissue is proportional to the distance between electrodes; therefore, the electrodes need to be as far apart as possible. On the other hand, the sensor should be as small as possible to be comfortable.

The vagina and uterus are often described as the most marvelous organs of the human body for their capacity to stretch to many times their normal size to accommodate the heavy requirements of childbirth. Because its outer third is surrounded by muscle fibers, the normal vagina can expand or contract to accommodate almost any diameter of penis for intercourse; a distinct advantage for human beings. The vagina itself is like a deflated party balloon; Masters and Johnson called it a "potential space".

In normal, healthy women the vaginal entrance is smaller and tighter, due to the active exercise and physical bulk of the surrounding PC muscle. Normally the muscle must relax somewhat and stretch in order to accommodate the penis for intercourse. Then it tightens again to provide physical stimulation to both partners. (In vaginismus the woman is unable to relax these muscles enough to allow penetration. EMG Perineometry is the treatment of choice here.)

Generally, incontinent women (and men) have the opposite problem: Kegel called it "genital relaxation". -The pelvic muscles are weak, lax, and atrophied (without bulk), thus leaving the vaginal entrance relaxed, large, and gaping. When incontinence is coupled with a lack of vaginal activity and sexual arousal, vaginal shape becomes more "funnel" like, and less balloon-like. For this reason (apparently), Dr. Arnold Kegel designed his original perineometer with a complementary cone-shaped vaginal barrel.

Unfortunately, the cone shape is at once an advantage and a drawback; the Kegel Perineometer was readily expelled from the vagina by the slightest inter-abdominal pressure, and therefore had to be physically held in place with a guaze strip when in use (see Fig. 2). But the relatively unsteady pressure of the supporting band introduced considerable measurement inaccuracy, which may be one reason for its lack of wide acceptance. In any case the Kegel Perineometer could only be used in a supine, knees-up position. The modem EMG perineometer was designed to remain in place even when walking. In fact, walking back from the toilet area is actually recommended, in order to help the sensor position itself naturally in the vaginal entrance.

Fig. 2

In the 1940s, a gauze strip was recommended to hold the Kegel Perineometer in place without touching one's genitals. The modern PerryMeter(TM) EMG Perineometer was designed to automatically position it self in the vaginal entrance without touching.

The size of the restraining bulb that keeps the EMG Perineometer from falling out is a delicate balance between patient discomfort and effective therapy. Smaller bulbs were found to lead to more frequent expulsion during Kegel exercise, thus disrupting the therapy process. Even now, it is not uncommon to have the sensor expelled, leading to erratic and misleading displays on the computer graphics screen. Since most incontinent patients have been using absorbent pads, many have developed a "learned anesthesia" for the constantly irritated vaginal-urethral entrance, and thus are least able to detect even a slight dislodgement of the sensor. If the sensor is twisted or partially expelled, so that even one of the three silver pads fails to make good contact with the vaginal skin, erratic readings will result.

Finally, as a consequence of hysterectomy and sexual inactivity, the vaginal tissue itself often becomes dry, thin and atrophied, leading to local irritability and even bleeding. Gradually, as a direct result of pelvic muscle exercise, this tissue is regenerated and becomes healthier. In the early stages of exercise (the first month) daily or every other day applications of Premarin(TM) (estrogen) cream are often prescribed. Since the PC muscle is "estrogen dependent", this probably has a beneficial effect on exercise itself, as well as the vaginal surface.

If the vaginal entrance is itself dry (and it usually is in elderly and/or sexually inactive women), local application of a water-soluble lubricant such as KY(TM) Jelly is usually recommended to enhance the ease of insertion. A 1/4" dab of lubricant spread on the tip of the sensor is usually enough. Alternatively, it is therapeutically advantageous to have the patient apply the lubricant directly to the tissues, to increase sensory awareness and appreciation. This aids directly in facilitating mental imagery about the area, which greatly enhances the speed and effectiveness of the therapy. (It is difficult to remember to exercise a part of the body if you are trying to forget that it is there!) The only danger of direct application of the lubricant is the temptation to use too much, which leads to easier expulsion of the sensor.

Fig. 3

A rectal size sensor cannot make good contact with vaginal walls.

Using Smaller Sensors. It is tempting to offer patients the option of selecting the smaller "rectal" size EMG Perineometer sensor. Except in unusual circumstances (an objectively determined abnormally small vagina) this is not good therapeutic practice, since it leads to erratic readings. Since the rectal size sensor does not fill the potential space, (see Fig. 3 above) it must shift to one side or the other (and you don't know which!) leading to differences in daily or weekly measurement that are merely artifacts of sensor placement.

Subjective Considerations

Comments by patients about sensor size and comfort provide as much information about the patient as they do about the sensor. Such issues need to be viewed in a broader perspective of nursing and counseling considerations. A patient's remarks often provide valuable insights into their emotional problems and concerns.

It is a well-known axiom in the field of sex therapy that the greatest and most universal difference between males and females in our society is that almost all men have strong positive attitudes and feelings about their genitalia, whereas almost all women have strong negative attitudes about their own. These attitude differences are gradually softening, but they remain strong in the older generations which are more likely to be represented in Continence Clinics. Indeed, many elderly women have never used tampons (which were considered invasive and perhaps immoral when first introduced. As late as the 1950s, popular folklore debated whether a young woman could be considered a true virgin if she had ever used a tampon!) Finally, there are religious barriers. Some people have been raised to believe that any manual contact with their genitalia (other than through toilet paper) constitutes masturbation, a sin.

These sex, generational and religious differences need to be remembered when treating elderly women for urinary incontinence. It is normal for any woman (or man, for that matter) to feel anxiety about exposure of or medical contact with their genitals. Gynecologists formerly coped with this by the use of drapes, and by encouraging their patients' (and their own) mental disassociation in vaginal examinations (and this is what our patients are familiar with.) Unfortunately, such disassociation is antithetical to the goals of pelvic muscle rehabilitation, which cannot proceed effectively without clear mental contact with these organs.

Expressions of concern over sensor size, therefore, must be viewed as likely manifestations of personal anxiety, rather than informed opinion about specifications of medical devices. Insofar as they constitute what psychologists call "resistance", they should be handled with appropriate clinical counseling skills. For example, it is never appropriate to deny the patient's feelings by asserting that "it isn't really that big ". The therapist should acknowledge the patient's fears, and add objective information: "Yes, it certainly looks big, but it's actually smaller than a small-size speculum. Have you ever had a vaginal examination using a speculum?

Many patients need to be taught to relax, especially prior to beginning their home biofeedback practice. One suggestion is to have patients take a warm bath before attempting to insert the pelvic muscle sensor. Patients who report persistent irritation, or minor vaginal bleeding (i.e., an occasional spot of blood on the sensor when removed) should be encouraged to take a day off from at-home biofeedback practice before resuming sensor use.

More serious complaints should, of course, be referred back to the gynecologist or urologist who conducted the initial evaluation and made the referral to the Continence Clinic. Premarin cream is often prescribed for them. Often it is enough to simply acknowledge that some people find the sensor uncomfortable at first. The therapist might even anticipate such reactions among patients who are no longer sexually active, although one should should not create anxiety where it doesn't exist.

Among patients who are able to engage in rational informed consent, the therapist might point out that any temporary discomfort from the sensor is trivial compared with the alternative of surgery. Every surgical procedure will result in the formation of some scar tissue. The pain of minor scar tissue is dealt with by learned local anesthesia (choosing to ignore it, by closing down sensory awareness of the area). Although the tactic diminishes sexual pleasure, it works for most people. The alternative is life-long irritation, which also leads to loss of sexual enjoyment.

Many patients are under the mistaken impression that modern surgical techniques for treatment of incontinence are "simple, quick and painless" office procedures. Genuine "informed consent" should include viewing a film about vaginal surgery, which would quickly dispel that myth.

Alternatives

It is important that the clinician understand the significance of the placement of the longitudinal electrodes on the patented Perry brand vaginal EMG sensors. Three pads are located at 120 degrees around the sensor barrel. The "reference" (or "ground") electrode, indicated by an arrow embossed on the bell, should be pointed towards the anus. This positions the two "active" electrodes at 2 and 10 o'clock. Since the distance between the 2 and 10 o'clock positions is shorter over the top side (120 degrees) than under the bottom side (around past 6 o'clock, or 240 degrees), it follows the electrical sensitivity is greater on the top, or urethral, side of the vagina than on the bottom, or anal sphincter, side. In other words, the Perry sensor is intentionally "directional", and has its greatest sensitivity to muscles in the area of the urethra, and less sensitivity to the anal area, which would be misleading.

This directionality is a major advantage to the Perry design. A common application is the assessment of unilaterial damage to the pubococegeus muscle. A therapist licensed to treat naked patients can position the sensor manually during the 10-second computerized evaluation. Since the "active" electrodes pick up more signals from the side opposite the reference electrode, which is marked by an arrow, simple rotate the arrow from 6 o'clock (first trial), to 10 o'clock (second) and 2 o'clock (third); then repeat for the last three contractions. The first and fourth intervals will show the "top" strength, the second and fifth show "left side" and the remaining intervals are averaged together to show the "right side" strength. (Obviously, the rest period data will be only an artifact and should be crossed out to avoid confusion.) Such top-left-right comparisons are often useful in evaluating and confirming the impact of episiotomoty damage. One patient with a serious left-side deficiency suddenly remembered that her entire left leg had been in a cast during the first 6 months of puberty. (The PC muscle is often described as "estrogen dependent" and apparently did not develop uniformly.)

If a patient proves unsuitable for the vaginal sensor placement, a rectal placement (of a rectal-size sensor!) can be considered. Patients seem much more accepting of minor pain in the rectum, and the electromyographic results are almost as good. Diagnostics are slightly compromised, since most people (except the fecally incontinent) have better developed rectal sphincters which could be misleadingly strong. In assessing the progress of a patient using a rectal sensor, the clinician should expect 50 to 100% higher readings than in vaginal placements because of this. Nevertheless, the course of therapy with the rectal sensor is virtually identical, since most patients cannot isolate the several components of the PC muscle even if they try.

The main disadvantage of rectal placements is a slight increase in the risk of inducing germs. The lining of the rectum and colon has the opposite function of the vagina; it is designed to absorb from its contents (which many experts say is why AIDS spreads so quickly among male homosexuals.) In contrast, the vagina was clearly designed to accommodate and protect the body from foreign objects, so that vaginal lubrication actually cleanses the pores and flushes out germs. And the directionality of the sensor ensures that the top, or urethral, side of the vagina is contributing more to the readings; it is the inter-digitating fibers in the area of the urethra that contribute most to the sphincteric function. Thus the vaginal placement is definately superior whenever possible.

The use of anal measurements to treat urinary incontinence is an unfortunate artifact of the history of research at the National Institute on Aging labs in Baltimore. Having demonstrated the effectiveness of anorectal manometry in treating fecal incontinence, the lab's director hired a young psychology graduate to apply the same instruments to the treatment of urinary incontinence. Dr. Burgio was relatively successful (typically, 85% symptom reduction), but it is important to remember that her research only showed an average CURE rate of about 29% -- far lower than the cure rate with EMG biofeedback. Most observers would blame the painful intrusion of the anorectal balloons, which typically limits their application to only 3 or 4 biofeedback sessions. In contrast, there is no pain associated with EMG biofeedback sensors. In addition, because of the cost and invasiveness of the manometric devices, home training is out of the question.

External surface placement of traditional EMG or EKG patch electrodes should never be used. Except for a study of urinary retention (where precise measurement is not important because any contraction during relaxation is bad), there are no pubished studies supporting this practice, which is sometimes used when vaginal and rectal sensors are unavailable. O'Donnell used Dantec vaginal sponge sensors taped over the anal orifice, but they were so prone to poor contact that he was forced to constantly monitor the EMG signal for 60-cycle interferance. Patch surface electrodes are subject to more noise than EMG Perineometers due to their far greater distance from the muscles under study.

The disadvantages of external placement are that sometimes it is necessary to shave pubic hair to approximate the desired location, and repositioning from day to day is compromised. Since the sensors usually have to be carefully applied, they usually result in exposure of the patient's genitals, which compromises the non-invasive advantages of self-inserted sensors. Finally, repeated exposure to the electrode's adhesive may cause allergic reactions, and conventional electrode paste (or more expensive pre-gelled electrodes) must be used.

Conventional electrodes are also more expensive, if a full course of biofeedback therapy is compared. The most effective algorithms for EMG perineometry include at least twice or thrice daily applications of the sensor over a period of one to three months, or an average of 180 separate applications of the sensor per patient. At an average retail cost of $0.90 for three pre-gelled electrodes, the average patient will pay $162 for the single-use surface electrodes, compared with only $59.95 (1995 price) for the Single Patient EMG Sensor. Difficult patients could easily end up spending $300 or more for disposable patch electrodes to accomplish the same results. The alternative is that long-term goals of therapy may be compromised in the interest of short-term cost containment, resulting in fewer "100% dry" patients and more "greatly improved" ones. This topic is discussed at greater length in the essay "The Rationale of the Single User Sensor", which is also available on this site.

Fig. 4

Single-User Vaginal Sensor

A major advantage of the Single-Patient Sensors is that the patient gets to keep the device, even after returning the (rental) EMG instrument. Thus the patient can continue to use it weekly or more often as a passive exercise device, at no additional cost, for the rest of their lives.

In our clinics, we offered our "graduating" incontinence patients a double "guarantee". First, we guaranteed them that if they stopped doing a maintenance level of exercise, their incontinence would return. Second, we guaranteed them a FREE followup visit, at 3, 6, 9, or 12 months, if they felt they needed a "refresher" course to maintain their skills. About 20 percent of patients took advantage of this offer, and they were divided equally between those who had gotten BETTER with practice, and those who had failed to practice and gotten worse, in strength and symptoms. (A repeated course of training, while not free, was usually only one or two visits.)

"On Sensor Size" was first published in 1988, in response to clinician questions, and was slightly revised in 1996 for publication on IncontiNet.com. Copyright 1988 and 1996 by John D. Perry, PhD. Comments and questions are always welcome: click here for our feedback form.