The U.S. Court of Appeals for the Federal Circuit, finding the district court erred in its construction of two critical claim terms, vacated the district court’s summary judgment ruling of non-infringement and remanded the case. Nellcor Puritan Bennett, Inc., et al. v. Masimo Corp., Case No. 04-1247 (Fed. Cir. Apr. 8, 2005) (Bryson, J.).
This case involved pulse oximeters, medical devices that measure the level of oxygen saturation in a patient’s blood. Nellcor sued Masimo alleging that numerous Masimo pulse oximeter products infringe selected claims of its patent. Nellcor’s patent covers a method and apparatus for digitizing the signals received by a photodetector, processing those signals, separating much of the aperiodic noise from the signal variations caused by the pulsing of the patient’s blood and calculating the oxygen saturation from the processed signal using a well-known formula.
The claims recited processing of periodic information so that it becomes "attenuated and filtered." The first issue on appeal was whether the district court correctly construed the phrase "attenuated and filtered" to mean "reduced and removed." The Federal Circuit agreed with Nellcor that the district court interpretation was not supported by the plain meaning of the claim language, the patent specification or the prosecution history. The Court, citing Vitronics Corp. v. Conceptronic, Inc., also concluded that "construing the term ‘filtered’ to require removal of the aperiodic noise would have the effect of excluding all the embodiments described in the specification," a construction that is "rarely if ever correct." To the contrary, the Court found that such a finding in this case is "powerful evidence that the court’s construction is incorrect." In addition, the Court found no support within the prosecution history for the district court’s construction. Accordingly, the Federal Circuit held that "attenuated and filtered from the composite waveform" means "reduced in comparison to the desired information."
The claims also required a calculation based on a relative maximum and minimum amplitude of a composite waveform. The second issue on appeal was whether the district court’s ruling that the claimed "minimum amplitude" must be part of the composite and that it must be determined and used only after the composite waveform is generated. The district court found that the placement of the word "thereafter" (prior to the step of calculating) supported its conclusion that the minimum value could be used only after the composite signal was generated. The Federal Circuit disagreed: "the district court added a limitation that is not present in the claim language and is not supported by the specification or prosecution history. We have stated that we ‘cannot construe the claim to add a limitation not present in the claim itself’" (citing, Hewlett-Packard Co. v. Mustek Sys.). The Court held that the claim only required that both the "relative maximum" and "relative minimum" amplitudes must be used in the calculation.
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