Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Light application
Reexamination Certificate
2000-04-19
2003-07-22
Shay, David M. (Department: 3739)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Light application
C607S091000, C002S906000, C600S310000, C600S315000, C128S903000, C128S904000
Reexamination Certificate
active
06596016
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to treatment of neonatal hyperbilirubinemia (jaundice). More particularly, it relates to phototherapy methods and devices containing light-emitting diodes.
BACKGROUND ART
Approximately 60% of the four million infants born in the United States each year become clinically jaundiced. Jaundice, or hyperbilirubinemia, results from increased production and transiently impaired elimination of the pigment bilirubin. While most affected neonates recover rapidly, some infants show persistent high levels of unconjugated bilirubin. Such high levels can lead to kernicterus, a condition involving deposition of bilirubin in the brain, which leads to deficits in cognition, neuromuscular tone and control, and hearing, and even death. The most common therapy for neonatal hyperbilirubinemia is phototherapy. It is estimated that as many as 400,000 neonates in the United States receive phototherapy every year.
Phototherapy facilitates the transformation of unconjugated bilirubin to compounds that are more easily excreted. Bilirubin undergoes in parallel three reactions: photooxidation, configurational isomerization, and structural isomerization. Structural isomerization is the predominant mechanism leading to bilirubin elimination from the bloodstream. Structural isomerization transforms bilirubin instantaneously and continuously into the more polar non-toxic pigment lumirubin, which is presumably the major bilirubin product excreted in newborns undergoing phototherapy. The wavelength range generally effective for facilitating bilirubin photoisomerization is approximately 400-550 nm (violet to green), with light of a wavelength between 450 and 460 nm (blue) yielding maximal photoisomerization. For general information on hyperbilirubinemia and phototherapy, see for example the articles by the Provisional Committee for Quality Improvement and Subcommittee on Hyperbilirubinemia (American Academy of Pediatrics) in
Pediatrics
94:558-565 (1994), Ennever in
Clin. Perinatol.
17:467-481 (1990), and Maisels in
Neonatology: Pathophysiology and Management of the Newborn,
4th Edition, J. B. Lippincott Co., Philadelphia, p. 630-735, as well as the books by Volpe,
Neurology of the Newborn
, W. B. Saunders Co., Philadelphia, 1995, and Brown and McDonagh,
Phototherapy for Neonatal Hyperbilirubinemia: Efficacy, Mechanism, and Toxicity
, Year-Book Medical Publishers, 1980.
The efficacy of phototherapy depends on four main factors: irradiance (light intensity), spectral range (wavelength or color), exposed skin surface area, and duration of exposure. Irradiance is a measurement of the light energy incident on the skin, in units of &mgr;W/cm
2
m (power per surface area per wavelength). For a given light source power, the irradiance can be increased by decreasing the distance between the light source and the newborn. Lumirubin formation is not only wavelength-dependent, but is also stimulated by higher light intensities, as discussed in the article by G. Agati et al. in
J. Photochem. Photobiol., B: Biol.
17:173-180 (1993). Proper evaluation of phototherapy devices and techniques requires assessment of each of these four factors, as well as consideration of potential side effects.
Phototherapy for treating hyperbilirubinemia is commonly delivered using fluorescent lamps suspended above the neonate. However, these conventional phototherapy devices have substantial drawbacks. While fluorescent lamps output high-intensity light, they also generate significant heat (infrared radiation), which prevents their placement close to the infant, thereby decreasing the irradiance. Fluorescent light is of a broad spectral range, and cannot be produced in only the narrow wavelength range desired. Conventional phototherapy devices typically illuminate the newborn only from above, and do not therefore make optimal use of the available skin area. U.S. Pat. No. 3,877,437 to Maitan et al. describes an apparatus for simultaneous bilateral phototherapy of neonates, from both above and below, thus effectively doubling the exposed surface area of the infant. The apparatus uses fluorescent lamps and thus subjects the neonate to side effects discussed below.
The use of fluorescent lamps for phototherapy leads to adverse side effects in many newborns. Such side effects include increased insensible water loss, hypothermia, loose and frequent bowel movements, tanning, and potential nasal obstruction by the eye pads required for preventing retinal damage. Furthermore, there are concerns that phototherapy using fluorescent lamps has potentially harmful effects on biological rhythms, and may increase the incidence of skin cancer in neonates subject to repeated treatment. For information on potential side effects of conventional phototherapy treatment see the articles by Wu and Moosa in
Pediatrics
61:193-198 (1978), Oh and Karecki in
Am. J. Dis. Child
124:230-232 (1972), Bell et al. in
J. Pediatr.
94:810-813 (1979), Woody and Brodkey in
J. Pediatr.
82:1042-1043 (1973), Messner in
Ped. Res.
(Abstr.) 12:530 (1978), Kemper et al. in
Pediatrics
84:773-778 (1989), and Garden et al. in
Arch. Dermatol.
121:1415-1420 (1985). In addition, overhead illumination with AC-powered blue light leads to discomfort and vertigo in nursery staff, as explained for example in the article by Wanamaker et al. in
Lighting, Research, and Technology
7:19 (1975).
Further drawbacks are introduced by the practical design of fluorescent lamps used for phototherapy. The bulky overhead lamps prevent unimpeded access to the baby and interfere with maternal-infant bonding. There is abundant literature regarding possible long-term harm stemming from disturbed maternal-infant bonding. For example, see
Monogr. Soc. Res Child Dev.
64(3):67-96 (1999) and discussion on pages 213-220; and
J. Child Psychol. Psychiatry
40(6):929-939 (1999). In the past, newborns typically remained in the hospital for at least three days, and hyperbilirubinemia was treated aggressively during this time. Now, however, most newborns are discharged within 24 or 36 hours, and bilirubin concentrations reach much higher levels before the problem is noticed. Such infants must be readmitted to the hospital for conventional phototherapy treatment, because phototherapy devices are not suitable for home use. Changing conditions demand phototherapy devices that are less expensive and more flexible to use, and particularly those that can be used at home by parents.
Several manufacturers have recently introduced fiberoptic phototherapy systems. Such manufacturers include Ohmeda (Columbia, Md.) and Fiberoptic Medical Products, Inc. (Allentown, Pa.). Typically, light from an incandescent ~150 W tungsten-halogen bulb is delivered to a fiberoptic pad containing interwoven optical fibers having multiple scattering centers. The ends of all of the fibers are bundled together to form a cable into which the light source is directed. When the cable becomes too large in diameter, it is no longer convenient or feasible to use; thus the total optical power delivered to the pad is limited by the cable size. While the fiberoptic pads can be placed adjacent to the neonate (e.g. directly around the infant), the pad sizes and light intensities available with such systems are limited. For a given light source, enlarging the pad requires distributing the light over a greater area, thus reducing the irradiance. To achieve high levels of irradiance, manufacturers must compromise the surface area by reducing the size of the pad, thereby exposing a relatively small surface area of the newborn to the light. Descriptions of fiberoptic phototherapy systems are provided in U.S. Pat. No. 4,234,907 to Daniel and U.S. Pat. No. 5,339,223 to Kremenchugsky et al. For a comparative analysis of two commonly used fiberoptic phototherapy devices, see the article by George and Lynch in
Clinical Pediatrics
, Mar. 1994: 178-180. The authors note the desirability of higher light intensities, and conclude that “in the past, perhaps too much attention has been paid to color and not
Seidman Daniel S.
Stevenson David K.
Vreman Hendrik J.
Lumen Intellectual Property Services Inc.
Shay David M.
The Board of Trustees of the Leland Stanford Junior University
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