Although Cole no longer employs the multiple strip technique, he has used it successfully in the past for what is now commonly referred to as "micro-minigrafting" and total follicular unit transplantation. His multi-FU grafts consisted of up to six hairs (rarely seven hairs) while his FU consisted of predominantly one to three hairs with an occasional four-hair graft. With multiple strip excisions, he produced the results shown in Table 7 with minimal waste.

TABLE 79

Unger routinely records the number of different types of grafts produced from the strips obtained during the first session of transplanting – the details of which are described later in this chapter. This record, which is kept in the patient’s file, then serves as a guide as to what size strips, both length and width, are necessary to achieve the objectives of later sessions. Most of his patients are treated with micro-minigrafting, and neither he nor they, are as concerned with the ability to very accurately anticipate the number of grafts created and transplanted per session as it appears most physicians employing exclusively FU seem to be. If too few are obtained from the initial harvest, he simply goes back and excises a small extra donor area, or makes up for the "shortfall" in a subsequent session. If more than the desired number of grafts is obtained, he treats a slightly larger area of the present or future areas of hair loss. With experience, neither of the above occurs with any significant frequency. There are, in his opinion, too many variables in technique and staff skill, to provide any consistently accurate estimating mechanism for all surgical teams.

Finally, all of the preceding discussion has dealt with various concepts of estimating the number of hairs that are being transplanted, but hair "bulk" or "mass", and therefore the apparent fullness of hair, is due not only to the number of hairs transplanted, but also the diameters of the hair shafts. This is discussed in the following section.

HAIR SHAFT DIAMETER

The importance of the hair shaft diameter cannot be overstated. It is the most important predictor of "coverage" in hair restoration surgery. To understand its effect, we must first define "coverage". "Full coverage" may be defined as reflection of light waves corresponding to the wavelength of the hair. Thinning may be defined as reflection of light waves corresponding to the wavelength of both the scalp and the hair. Alopecia is defined as reflection of light waves corresponding predominately to the color of the skin. The greater the surface area of the transplanted hair, the greater the coverage resulting from the transfer of a specific amount of hair.

Surface area of a hair is defined by the formula:

Area = 2 p r² + 2 p rh

Where r is the radius of the hair shaft and h is the length of the hair.

Since only approximately one half of the hair shaft reflects light, the formula may be simplified to:

Area = p r² + p rh

Variations in surface area are smaller than variations in volume. For this reason, it is easier to mathematically appreciate see the significant changes in volume from slight changes in hair diameter.

Volume (V) of a hair is defined by the formula:

V = p r²h

Where r is the radius of the hair shaft and h is the length of the hair.

The total hair volume, resulting from a specific amount of hair transferred, would by defined by the formula:

V = (THT) p ` r² h

Where THT is the total hair transferred and ` r² is the mean radius squared.

Notice that by doubling the mean diameter you quadruple the hair volume. By doubling the length or the number of hairs transferred, you merely double the hair volume transferred. Therefore, diameter is far more important than any other factor in predicting coverage from any given amount of hair transferred. Hair length, however, is a variable controlled by the patient, unlike his hair diameter and total donor hair "bank". Hair length can be hextuppled or even grown longer, which offers the patient a means to significantly increase his/her hair volume. Hair length is the second most important factor in predicting coverage, but only as long as the added length is within the bald surface area (see later in chapter).

Hair shaft diameter can be measured with a number of commercially available micrometers. The Starret Digital Micrometer (Sears and Roebuck Catalog), which Cole began using in 1996, is useful for rough estimates, and the Mitutoyo Digital Micrometer for more accurate measurements (Micro Enterprises, Norcross, GA). It is also possible to use a micrometer attached to a microscope. Fine-textured hairs generally allow for more dense packing and smaller recipient sites. As a result, they may or may not result in less coverage. More coarse hairs usually require larger recipient sites, possibly fewer grafts in a given recipient area, and produce better coverage per hair but if planted more sparsely than fine hair, may not produce better overall coverage.

Scalp "compliance" plays a role in the choice of how closely grafts can be placed, as well. Inserting grafts into the scalp always increases the tissue volume. If the scalp has minimal "compliance", the increased volume of each graft exerts pressure laterally, thereby decreasing circulation somewhat and also making the insertion of grafts into adjacent recipient sites more difficult. As scalp compliance increases, the size graft or the number of grafts a given recipient site will accept increases. Scalp compliance is subjective, and understanding it only results from experience. A clue to scalp compliance is derived at the time the donor strip is excised. If you notice that the skin has a tough, leather-like nature during excision and/or that donor area closure seems surprisingly tighter than you expected, it is important to perform test sites and insert some grafts prior to making all the recipient sites. If you undermine the donor strip with a scalpel blade and the blade becomes relatively dull during the excision, this is also a good indicator that the tissue is "harder" than average and the scalp may have a lower compliance.

According to Bernstein, scalp hair diameters range from 60 to 140 micrometers. ** Cole has found a much wider range of scalp hair diameter: 20 micrometers to 128 micrometers. He rarely sees scalp hairs greater than 110 micrometers and the largest mean diameter of donor hair measured to 2001 was 105 micrometers. In a study of 40 patients, using 45x magnification, Cole looked at the regional variation in hair diameter at the three reference points described in the section on hair density in this chapter. He found the following mean diameters: left supra-auricular area 73.5 micrometers, left mastoid area 78.5 micrometers, mid-occipital area 72 micrometers, right mastoid area 76.6 micrometers and right super-auricular area 73.5 micrometers.

This regional variation suggests there is a predominance of finer textured hairs in the mid-occipital and supra-auricular regions, and a predominance of coarser hairs in the mid-mastoid area. Unfortunately, the mid-occipital area contains not only the finest hairs, but also often contains the highest number of hairs per FU. (It also tends to contain the highest FU density and thus the highest calculated density). It therefore becomes more difficult to isolate single hairs for the hairline when the follicular unit densities and calculated densities are higher. Hair caliber also tends to decrease as one moves anteriorly towards the supra-auricular region and inferiorly in both parietal and occipital areas.

Hair in these latter areas may become finer with the passage of time, but usually there are some finer textured hairs in both sites that one can be reasonably sure will not do so to any significant degree. Unger has recommended such hairs, for many years, for transplanting the frontal hairline. * In the days before micrografting, excellent hairlines could be constructed with grafts taken from such sites because of their somewhat sparser and finer hair. (Fig.#7) These hairlines only improved with age. IF the hairs in these areas became progressively finer, and/or some were lost entirely, the hairline became more ragged and natural looking.

From the preceding discussion, it should be obvious that you cannot determine mean hair diameter by looking at a single hair. One must look at a minimum of 10 hairs and preferably 20 or more hairs in making this determination. (The more hairs, the more accurate the figure.) In determining mean diameter, Cole also does not include any hairs that are less than 50 micrometers in diameter unless they are the predominate type of hair in the group. If, for example, he were looking at 20 hairs, he would not include a single hair measuring 42 micrometers. Furthermore, he disregards hairs that are well over the prevailing measured diameter, unless there are a significant number of them (for instance greater than 25% of the sample). If the majority of hairs measured were between 55 micrometers and 72 micrometer, he would, for example, discard a measurement of 95 micrometers. In this way, the predominate width of hairs is measured and a measurement closer to the true mean is determined.

Cohen argues that the variability in hair diameters makes it difficult if not impossible to determine an "average" or "mean" diameter. * Cole disagrees with this assessment and believes that if the sampling of hairs is large enough it is possible to arrive at a meaningful mean hair diameter for that individual. Furthermore, while it is impossible to identify a person by a single hair, it is often possible to rule out a person if sufficient hairs are sampled. Some people, for example, have generally finer hair, while other people have generally coarser hair. Therefore, mean hair diameter assessments must have some predictive value. Seager, on the other hand, feels the mean diameter is the same regardless of the donor area location.* Cole again firmly disagrees but, of course, the measurement of multiple hair samples is necessary to most accurately determine the mean hair diameter. Furthermore, he claims that the variability in diameter is so striking that it is possible to visualize the differences between individuals with only a Rassman densitometer.

Vellus hairs have been defined as being less than 30 m m in diameter, of limited length, and reduced color. *¹⁵ The effect of these hairs on total hair surface area and volume is so limited that it seems to make little sense to include them in calculations of the mean hair diameter. For the same reasons, as noted above, one should probably not routinely include hairs that are less than 50 m m in diameter. Generally, the proportion of these hairs in the overall number of hairs moved is small. It would be of value to quantify these hairs to reinforce these or modify these suggested principals of calculation, because their exclusion does not mean that they have no impact on the illusion of coverage. Rather, the finer ones have a more limited impact, while the larger ones have a more marked impact on volume. In addition, both because of their size and lesser pigmentation, the smaller hairs are much more difficult to count during the graft production phase. As a result, they are often not included in the final hair count. This is particularly true when the epithelium is removed from the grafts.

According to Whiting, there are seven terminal hairs for every one vellus hair in the normal crown. * This represents14.3% of hair at that site or 143 vellus hairs for every 1000 terminal hairs. If this trend held true in the donor area, it is likely that most technicians would not see or count 14.3% of the hairs present in the donor tissue. There are, of course, other hairs whose diameters are greater than 30 m m and less than 50 m m, which also are less pigmented than average. These hairs would have a reduced probability of being included in a technician’s hair count. In studies Cole has performed in his office, technicians did not include as many as 20% of the hairs that he had originally counted in the donor area. Some of the missed hairs may not have been counted due to trans-section, however, he believes that the majority were not counted as a result of their limited size and pigmentation. Of course, it is more difficult to count miniaturized hair in Cole’s office because he prefers to remove the epithelium from his grafts. Thus, in a patient with non-pigmented hair, the disparity in true hair count and technician count would almost certainly widen.