United States Court of Appeals for the Federal Circuit 

04-1247 

NELLCOR PURITAN BENNETT, INC. 

and MALLINCKRODT INC., 

Plaintiffs-Appellants, 

v. 

MASIMO CORPORATION, 

Defendant-Appellee. 

Robert C. Morgan, Fish & Neave, of New York, New York, argued for plaintiffsappellants. With him on the brief was Anthony A. Pastor. Of counsel on the brief was 

Craig N. Hentschel, Dykema Gossett LLP, of Pasadena, California. Of counsel was 

Kevin P.B. Johnson, Fish & Neave, of Palo Alto, California. 

Joseph R. Re, Knobbe, Martens, Olson & Bear, LLP, of Irvine, California, argued 

for defendant-appellee. With him on the brief were James F. Lesniak, Joseph S. 

Cianfrani, Irfan A. Lateef, and Perry D. Oldham. Of counsel were Stephen C. Jensen

and Jon W. Gurka. 

Appealed from: United States District Court for the Central District of California 

Senior Judge Mariana R. Pfaelzer 
United States Court of Appeals for the Federal Circuit

04-1247 

NELLCOR PURITAN BENNETT, INC., 

and MALLINCKRODT INC., 

Plaintiffs-Appellants, 

v. 

MASIMO CORPORATION, 

 Defendant-Appellee. 

___________________________ 

DECIDED: April 8, 2005 

___________________________ 

Before NEWMAN, BRYSON, and DYK, Circuit Judges. 

BRYSON, Circuit Judge. 

 Appellants Nellcor Puritan Bennett, Inc., and Mallinckrodt Inc. (collectively, 

“Nellcor”) produce pulse oximeters, medical devices that measure the level of oxygen 

saturation in a patient’s blood. Nellcor owns U.S. Patent No. 4,934,372 (“the ’372 

patent”), which covers a method and apparatus for using red light, infrared light, and 

signal processing techniques to measure oxygen saturation noninvasively. Appellee 

Masimo Corporation makes pulse oximeters that also use red light, infrared light, and 

signal processing techniques to calculate the patient’s arterial blood oxygen level. 

Nellcor filed suit in the United States District Court for the Central District of California 

alleging that numerous Masimo products, including the Radical and Rad-9 pulse 

oximeters and MS circuit boards, infringe claims 1, 2, 20, and 21 of the ’372 patent. 
04-1247 2 

The district court granted summary judgment of noninfringement as to all the asserted 

claims. Nellcor Puritan Bennett, Inc. v. Masimo Corp., 300 F. Supp. 2d 923 (C.D. Cal. 

2004). We conclude that the district court made errors in claim construction that 

affected the judgment. We therefore vacate the judgment and remand for further 

proceedings. 

I 

 A commonly configured pulse oximeter contains a sensor that is attached to a 

portion of a patient’s body where there is strong blood flow, such as a finger. The pulse 

oximeter includes one light emitting diode (“LED”) that emits red light, another that emits 

infrared light, and a photodetector that detects the emitted light that passes through the 

patient’s finger from both LEDs. The red light and the infrared light are absorbed in 

different amounts, respectively, by oxygenated and deoxygenated hemoglobin, so the 

degree of oxygen saturation of the blood can be calculated based on the differences 

between the amounts of light detected at the red and the infrared wavelengths. 

In addition to differences in the levels of light detection attributable to the degree 

of oxygen saturation, the amount of light detected by the photodetector in both the red 

and infrared wavelengths changes in a periodic manner, because as blood pulses 

through the patient’s finger with each heartbeat, more light is detected when there is 

less blood in the finger and less light is detected when there is more blood in the finger. 

The detected signals may also contain additional, aperiodic noise caused by the 

patient’s movements or other artifacts unrelated to arterial blood flow. That aperiodic 

noise, if not suppressed, can interfere with the accuracy of the oximeter’s 

measurements. 
04-1247 3 

Nellcor’s ’372 patent covers a method and apparatus for digitizing the signals 

received by the 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. Claim 1 of the ’372 patent claims the method as follows (emphasis added): 

 1. A method for calculating the amount of a blood constituent from the blood flow 

characteristics of a patient comprising: 

detecting an absorption signal corresponding to the absorption of light 

measured at two or more wavelengths in the patient’s tissue including 

periodic changes in amplitude caused by periodic arterial pulses in the 

blood flow characteristics related to the patient’s heartbeat and aperiodic 

changes in amplitude unrelated to the patient’s heartbeat, and, for each of 

the measured wavelengths; 

obtaining a time-measure of the absorption signal including 

periodic information and aperiodic information; 

processing the time-measure collectively to determine a composite 

waveform having a relative maximum and minimum amplitude 

corresponding to a composite periodic waveform of the periodic 

information in the time-measure so that the aperiodic information present 

in the time-measure is attenuated and filtered from the composite; and 

thereafter 

calculating the amount of blood constituent from the relative maximum and 

minimum amplitude of the composite periodic waveforms of the detected 

wavelengths. 

Claim 2 depends from claim 1; claim 20 is an apparatus claim corresponding to the 

method of claim 1; and claim 21 depends from claim 20. 

The district court construed the phrase “attenuated and filtered” to mean 

“reduced and removed.” The court also ruled that the minimum amplitude of the 

composite periodic waveform must be part of the composite and that it must be 

determined and used only after the composite waveform is generated. Based on its 

claim construction, the court granted summary judgment of noninfringement. 
04-1247 4 

II 

 Nellcor first contends that the trial court improperly interpreted “attenuated and 

filtered” to mean “reduced and removed.” We agree with Nellcor that the district court’s 

interpretation is incorrect. 

The ’372 patent describes two embodiments of the invention in detail. The 

patent first describes a time domain method, which it characterizes as the preferred 

embodiment of the invention. The time domain method begins with a trigger that is 

related to the patient’s heartbeat and thus indicates the beginning of an arterial pulse. 

The device then detects optical data from the photodetector for both the red and 

infrared sources throughout the duration of the pulse. That data is digitized and then 

moved to a buffer that collects data for the red and infrared signals over time. With 

each subsequent pulse, new data is gathered and stored in a “new data” buffer. In the 

preferred embodiment, the value of each data point in the new data buffer is divided by 

6, and the values for each of those data points are added to 5/6 of the value of the 

corresponding data points in the data collection buffer. The sum of those two values is 

then stored in the data collection buffer, replacing the data previously stored in that 

buffer. ’372 patent, col. 6, line 20, to col. 8, line 49. 

Each set of new data contains information from the pulse of interest, together 

with aperiodic noise. Because the data in the data collection buffer is weighted five 

times as heavily as the new data that is introduced with each pulse, and because the 

aperiodic data does not share the same characteristics for each pulse (and thus does 

not accumulate over time), the effect of using this method of data accumulation is to 

reduce the effect of the aperiodic data in each pulse by 5/6. Additionally, the effect of 
04-1247 5 

older aperiodic data on the cumulative data is reduced at each triggering event by 1/6. 

Thus, the aperiodic data is not eliminated altogether, but it is continuously reduced in 

magnitude in comparison to the desired, periodic data. 

 A second embodiment of the invention described in the ’372 patent is a 

frequency domain method that can be used with or without a separate pulse-identifying 

event. ’372 patent, col. 11, line 12, to col. 12, line 60. In that embodiment, the output of 

the photodetector for each of the red and infrared signals is digitized at a rate of 57 

samples per second for about nine seconds. In the time domain, the amplitude of that 

data is represented as a function of the time at which the data was sampled. The 

resulting 512 data points for each wavelength are then averaged; the resulting value 

represents the average background intensity for each wavelength. That average value 

is then subtracted from each of the 512 data points for each wavelength. The resulting 

data is then transformed to the frequency domain using a mathematical operation 

known as a Fourier transform. The transformation of the data to the frequency domain 

produces a value for each of a number of frequencies above zero for both the red and 

infrared wavelengths. The average background intensity of the detected optical signals 

at the red wavelength and at the infrared wavelength is the amplitude at zero frequency 

for each of those wavelengths. When the data is transformed to the frequency domain, 

the amplitude of the pulse data for each wavelength can easily be detected because it is 

the value located at the pulse frequency. 

 Because the aperiodic noise has components at many frequencies, the aperiodic 

noise “appears spread across the frequency domain spectrum.” ’372 patent, col. 11, ll. 

53-54. The frequency domain embodiment, however, uses data at only two of the 512 
04-1247 6 

frequencies for each wavelength—the heartbeat frequency (which contains the most 

useful data for determining blood constituents) and zero frequency (which contains the 

background level of the optical signals). Accordingly, while some noise still remains at 

those two frequencies, the noise is not concentrated at those frequencies. The relative 

impact on the selected data is therefore considerably reduced. 

 Nellcor contends that the district court erred by construing the term “filtered” to 

require that the aperiodic signal data be removed rather than simply reduced in 

comparison to the desired periodic signals. Nellcor submits that the district court’s 

interpretation is not supported by the ordinary meaning of the claim language to one of 

skill in the art, and that it is not supported by the specification or the prosecution history 

of the ’372 patent. 

A standard dictionary prepared by the Institute of Electrical and Electronics 

Engineers (“IEEE”) provides eight different meanings for the noun “filter.” Those 

definitions include a device “that separates data, signals, or material in accordance with 

specified criteria” and a circuit “that eliminates certain portions of a signal, by frequency, 

voltage, or some other parameter.” IEEE, Authoritative Dictionary of IEEE Standard 

Terms 435 (7th ed. 2000). It is reasonable to characterize the disclosed processes as 

involving the separation of signals “in accordance with specified critieria,” including their 

frequency, and it is fair to characterize the process of reducing the relative magnitude of 

aperiodic noise as the elimination of “certain portions of a signal, by frequency . . . or 

some other parameter.” Thus, two of the definitions of the term “filter” given in the 

standard dictionary of electrical engineering and electronics are consistent with the 
04-1247 7 

definition proposed by Nellcor; in any event, the IEEE definition certainly does not 

compel rejection of Nellcor’s proposed construction of the term. 

The meaning that the patentees intended to accord to the claim phrase 

“attenuated and filtered” is made clear from an examination of the specification of the 

’372 patent. In the Background of the Invention portion of the specification, the patent 

describes one of the objects of the invention as being to “provide enhanced periodic 

information from which the patient’s blood constituent can be accurately determined” by 

“collecting successive portions of detected optical signals encompassing periodic 

information for more than one heartbeat and processing the collected portions to 

attenuate and filter therefrom aperiodic signal waveforms.” ’372 patent, col. 4, ll. 28-35. 

That passage summarizes the cumulation technique described in more detail later in the 

patent as resulting in the attenuation and filtering of aperiodic signals. As such, it 

indicates that the words attenuated and filtered are used to describe the relative 

reduction in the significance of aperiodic noise that results from the cumulation 

technique described in the patent. 

The same is true of the more detailed description of the invention in the 

Summary of the Invention portion of the specification. There, the patent describes the 

relative reduction of the impact of aperiodic noise on the composite signal through nonsynchronous (and thus canceling) addition and through the spreading of noise signals 

across the relative time frame of the composite signal. ’372 patent, col. 7, ll. 3-9. The 

patent describes that effect, and in particular the small relative weight given to new 

information as compared to the prior composite, as resulting in new aperiodic 

information being “quickly and effectively attenuated, and thus filtered out of the 
04-1247 8 

resultant additive portions.” Id., col. 7, ll. 21-22. The patent then summarizes the 

process as follows: “The collective additive sum having synchronized periodic 

information waveforms thus presents enhanced periodic information that is a composite 

data set that corresponds to a composite optical pulse from which noise, spurious 

signals, and motion artifact, have been filtered out.” Id., col. 7, ll. 33-38. Because the 

disclosed process does not actually remove data, but merely results in the suppression 

of aperiodic noise relative to the periodic signal, it is clear from those passages that the 

patent uses the terms “attenuated and filtered” to refer to the process of reducing the 

effect of the aperiodic noise as compared to the periodic signal. Thus, the specification 

confirms that the claim phrase “attenuated and filtered from the composite” is used to 

refer to what the patent at one point calls “effective removal” of data, id., col. 8, line 28, 

rather than the absolute removal of unwanted data, as held by the district court. 

Apart from the manner in which the term “filtered” is used in the patent, 

construing the term “filtered” to require removal of the aperiodic noise would have the 

effect of excluding all the embodiments described in the specification. That is because 

none of the embodiments actually “remove” the aperiodic noise from the data used for 

calculations, as opposed to reducing its relative impact on that data. As this court has 

explained, a construction that excludes all of the embodiments of an invention is “rarely, 

if ever, correct.” Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1583 (Fed. Cir. 

1996). The fact that the construction adopted by the district court and advocated by 

Masimo would have the effect of placing all the embodiments of the invention outside 

the scope of the claims is powerful evidence that the court’s construction is incorrect. 
04-1247 9 

Masimo argues that the district court’s construction would not mean that the 

claims would fail to read on all the embodiments set forth in the written description, but 

we disagree with that contention. The claim language in question provides for 

“obtaining a time-measure of the absorption signal including periodic information and 

aperiodic information,” and processing that data “to determine a composite waveform” 

so that “the aperiodic information present in the time-measure is attenuated and filtered 

from the composite.” The portions of the specification that describe that claimed 

process disclose the use of various means to reduce the impact of the aperiodic data on 

the resulting composite waveform. In each instance, the aperiodic data is reduced in 

impact but is not altogether removed from the composite. Thus, in the time domain 

embodiments of the invention the data is manipulated so that the periodic data 

cumulates, while the aperiodic data does not. As a result, the relative impact of the 

aperiodic data is constantly reduced in comparison with the impact of the periodic data. 

Similarly, in the frequency domain embodiment the selection of only the zero frequency 

and the heartbeat frequency as the frequencies from which data is obtained has the 

effect of substantially reducing the effect of aperiodic noise, which is spread across 

many frequencies, but it does not remove the noise altogether. From the context of the 

patent, it is clear that those processes are what the patent refers to as attenuation and 

filtering. See ’372 patent, col. 11, ll. 43-58. While it may be that, in hindsight, the 

patentees would have been wise to choose a word other than “filtered,” it is clear that 

they meant for that term to describe the “relative reduction” processes set forth in the 

specification. The use of the term in that fashion is not at odds with the understanding 

of the term “filtered” in the pertinent art, and in the absence of a clear contrary directive 
04-1247 10 

in the patent, we decline to give that term a definition that would exclude the preferred 

embodiments from inclusion within the language of the claims. 

In construing the phrase “attenuated and filtered from the composite,” the district 

court relied heavily on the prosecution history of the ’372 patent. The portion of the 

prosecution history on which the court relied was the applicant’s discussion of a prior art 

patent to New (U.S. Patent No. 4,653,498), which the examiner had cited against the 

application in an office action. The New patent disclosed a pulse oximeter in which the 

instrument tested each pulse-like signal against certain parameters to determine 

whether the signal was related to a heartbeat and therefore should be used in making 

the blood constituent measurement. The applicants argued that the method used to 

identify the proper source of meaningful data in New was quite different from the 

method set forth in the application. In particular, the applicants noted that the New 

patent disclosed a method consisting of “detecting an absorption signal and determining 

a related maximum and minimum value in the absorption signal corresponding to a 

pulse.” New’s method then evaluated each maximum and minimum “using preselected 

confidence criteria to determine whether or not they correspond” to a periodic pulse or 

an aperiodic event unrelated to the patient’s heartbeat. In New, the applicants 

explained, “[a] pulse history is formed based on accepted maximum and minimum 

signal values that are averaged to smooth out small deviations in pulse rate and oxygen 

saturation due to physiologic and artifactual noise variations.” 

The applicants argued to the examiner that the New patent described calculating 

blood constituents “in a manner that is fundamentally different from, and which does not 

teach or suggest applicants’ claimed invention.” In contrast to the New patent, the 
04-1247 11 

applicants claimed that their invention “teaches that by collecting and collectively 

processing time-measures to obtain a composite waveform from which aperiodic 

information is removed, and which yields a composite relative maximum and minimum, 

one does not need to examine each pulse against confidence criteria or to determine 

whether that pulse is [a] periodic or aperiodic pulse before the blood constituent can be 

reliably and accurately determined.” 

The district court seized on the applicants’ characterization of their invention as 

one in which “aperiodic information is removed” from the composite waveform, and 

concluded from that statement that the reference to aperiodic information being 

“attenuated and filtered” should be construed to mean that aperiodic information is 

removed altogether. In context, however, the prosecution history does not support that 

interpretation. The distinction that the applicants sought to draw between the method 

described in the New patent and the method used in their invention was between (1) 

testing each pulse-like event to determine whether it was related to the patient’s 

heartbeat, and (2) using a cumulation technique to separate synchronous pulse events 

from aperiodic events unrelated to the patient’s heartbeat. Their method, the applicants 

pointed out, reduced the relative amplitude of the aperiodic events through processing 

and thus effectively removed those events from consideration in the blood constituent 

measurements. The applicants’ reference to the “removal” of aperiodic noise thus must 

be interpreted to refer to a reduction in the aperiodic noise relative to the desired signal, 

so that the aperiodic noise does not materially affect the composite waveform generated 

by the patented method. Accordingly, we do not regard the prosecution history as 

providing support for the district court’s construction of the claim phrase “attenuated and 
04-1247 12 

filtered from the composite waveform.” For that reason, and because Nellcor’s 

proposed construction of that phrase as meaning “reduced in comparison to the desired 

information” is consistent with the written description of each embodiment of the 

invention, we hold that the district court erred in its construction of that critical claim 

language and that “attenuated and filtered from the composite waveform” means 

“reduced in comparison to the desired information.” 

III 

Nellcor next contends that the trial court erred when it ruled that “calculating . . . 

from the relative maximum and minimum” requires that any calculation using the relative 

minimum must be made only after formation of the composite signal. We agree with 

Nellcor that the district court’s claim construction is incorrect. The composite signal in 

the frequency domain embodiment of the ’372 patent consists of data for each of 512 

frequencies starting at zero frequency. The Fourier transform at zero frequency is equal 

to the average value of the signal in the time domain and represents the average 

background intensity of that signal. ’372 patent, col. 11, ll. 54-58 & Fig. 10. 

In the frequency domain embodiment of the ’372 patent, the zero frequency 

component of the composite signal is computed when the average value of the signal is 

determined, which is before the transformation for the other frequencies that make up 

the composite signal. That average value is then subtracted from each of the 512 data 

points before the Fourier transform is computed for the rest of the 511 frequencies that 

make up the composite signal. 

The district court was correct when it stated that the relative minimum value must 

be part of the composite signal, but it was incorrect in concluding that the minimum 
04-1247 13 

value may be determined only after the composite waveform is generated. Experience 

with oximeters has shown that infrared light has a different average detected 

background intensity than does red light. The detected background intensities for the 

red and infrared light are represented by the average value of the signal for each of 

those two wavelengths. Calculating the oxygen saturation of blood requires a 

determination of the ratio of the difference in absorbance level at those two 

wavelengths, with the detected average background intensities removed from each. 

Accordingly, in order to make that calculation, the infrared and red signals have to be 

normalized relative to one another. In the invention of the ’372 patent, the relative 

maximum values of the infrared and red signals are divided by their respective relative 

minimum, or zero frequency, components to normalize each relative to the other. This 

division produces the same result regardless of whether it is performed before or after 

the transformation of the data to the frequency domain. 

The district court found that the placement of the word “thereafter” in claim 1 

supported its conclusion that the minimum value could be used only after the composite 

signal was generated. We disagree. “Thereafter” refers to the time when the amount of 

blood constituent is calculated, not to the time when the relative minimum is used. By 

requiring that the relative minimum value be used in any calculation of the oxygen 

saturation only after the composite signal has been formed, 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.” Hewlett-Packard Co. v. Mustek Sys., 

340 F.3d 1314, 1325 (Fed. Cir. 2003). In light of our analysis, we believe that 
04-1247 14 

“calculating the amount of blood constituent from the relative maximum and minimum 

amplitude of the composite periodic waveforms of the detected wavelengths” means 

only that both the relative maximum and the relative minimum of the red and infrared 

waveforms must be mathematically used in the oxygen saturation calculation. 

On remand, the district court should reassess Nellcor’s claim of infringement 

against Masimo based on the claim construction that we have adopted with respect to 

the claim term “attenuated and filtered” and the reference to the “relative minimum” 

value in claim 1 of the ’372 patent. While we express no opinion with respect to the 

ultimate issue of infringement, the changes in claim construction that we have ordered 

require that the district court reexamine the infringement question. Accordingly, we 

vacate the district court’s summary judgment ruling of noninfringement, and we remand 

for further consideration based on our construction of the two critical claim terms 

discussed above. 

VACATED and REMANDED.