Courtesy of Dr. John P. Cole
www.forhair.com 

OBJECTIVES
   
Comparative results between patients are typically assessed by the number of grafts transferred. Other times they involve the density of grafts in the recipient area. In fact, we know that individual hair characteristics are not the same. Therefore, traditional methods of assessment are flawed by these inaccurate assumptions and therefore, we impugn them. We all know that individual hair characteristics more precisely predict coverage. Not withstanding, a standardized method to evaluate results based on a more precise method of predictive values is essential. We feel that measurement of Hair Mass Transferred (HMT) for each surgery is indicated and offer a method to measure this value. Furthermore, HMT allows us to evaluate the efficiency of our procedure at multiple levels, the time of surgery and at the time of the final result. 

BACKGROUND
  
Dr. Bob Limmer noted that the density following hair transplant passes in his patients averaged as follows:

– one session 41 hairs / cm2
– two sessions 50 hairs/ cm2
– three sessions 63 hairs/ cm2
– four sessions 81 hairs/ cm2

It is interesting that the densities created by hair transplantation noted by Limmer are far less than the average hair density in the average donor area or non-bald recipient area. The following table is a table of observed average donor densities in 100 patients by Cole:

Manyy Marritt studied hair removal and the illusion of coverage by plucking hair from 1 sq. cm. After he removed over 50% of the original hair, the patient had the illusion of full coverage or the illusion that nothing had been removed. These methods assume that all hair characteristics are alike. It assumes that all hair diameters, all follicular densities, all hair densities, and all calculated densities (average number of hairs per follicular unit) are the same.

PREDICTION OF COVERAGE

Coverage may be defined as reflection of light waves corresponding wavelength particular to the color of the hair. Thinning may be defined as reflection of light waves corresponding to the color of both the hair and the skin. Baldness is defined as reflection of light waves the color of the scalp. To obtain the illusion of coverage it is necessary to move enough hair mass to the bald or thin areas of the scalp so that only light waves corresponding to the color of hair are reflected. There are several ways to look at this mathematically. Hair is a cylinder. As such we can determine its surface area and its volume. Volume is defined by the formula V = pr² h and this equates to the individual hair mass. Small changes in diameter result in significant changes in volume. Doubling the diameter results in a quadrupling of the volume. By the same token, decreasing the diameter through miniaturization of androgenic alopecia by ½ results in 1/4^th the volume of hair. The use of the term volume is useful because minor changes in hair radius result in significant changes in volume. Dramatic changes in values help both the physician and patient understand how important minor changes in hair diameter affect coverage. Coverage results when enough hair mass is moved to the scalp such that no light waves are able to penetrate to the scalp. If all hairs lay perfectly side-by-side rather than some entirely or partially stacked on top of other hairs, coverage would be easier to achieve. Hair stacking is more common with wet hair, when the covalent bonds of water molecules result in clumping of hairs together. This is why hair always looks its thinnest when the hair is wet. Hair surface area is defined by the formula Area = 2 p r + 2 pr h, where r is the hair radius and h is the length of the hair.  If the bald surface area is known, it is possible to accurately predict coverage provided the total number of hairs transferred is known, the mean hair diameter is known, the bald surface area you desire to cover is known, and the hair length is known. It is possible to vary the hair length. The reflective surface area of hair for any hair length is predictable.

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Courtesy of Dr. John P. Cole
www.forhair.com 

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