The recent Federal Circuit decision in ERBE Elektromedizin GMBH v. Canady Technology LLC serves as a reminder that the doctrine of claim differentiation generally will not be useful to support a claim interpretation that is contradicted by other claim construction tools.

The Claims At Issue

The technology at issue in ERBE relates to medical devices for argon gas-enhanced electrosurgery. Patent owner ERBE challenged the district court’s construction of independent claims 1 and 35 of U.S. 5,720,745, arguing that the court’s interpretation violated the doctrine of claim differentiation.

These claims recite, in relevant part:

1. An electrosurgical unit for achieving coagulation of tissue, comprising:
an endoscope . . .
a flexible, hollow tube . . . positioned within the endoscope . . . such that a gas stream exits from the opening at the distal end of the tube in order to establish an inert gas atmosphere between the distal end of the tube and the region of the tissue to be coagulated, and
an electrode for ionizing the inert gas . . .
a source of pressurized ionizable, inert gas . . . such that a stream of gas flows from the source, through the tube and exits through the opening at the distal end of the tube at a low flow rate of less than about 1 liter/minute . . . .

35. A method for coagulating tissue during endoscopic surgery comprising the following steps:
providing a surgical endoscope . . . having a flexible, hollow tube . . . connected to a source of ionizable, inert gas . . . and an electrode . . .
supplying the inert gas . . . with such a low flow rate, that gas exiting through said distal end opening is a not directed, non laminar stream but forms an inert gas atmosphere between the distal end of the tube and the region of the tissue to be coagulated . . .
ionizing said inert gas atmosphere . . . and
supplying an electric . . . and coagulating an area of the tissue . . . while the ionized gas is being supplied through the distal end opening of the tube as a not directed, non laminar stream with a low flow rate

Dependent claim 38 depends from claim 35 and recites:

38. The method as claimed in claim 35, whereby the stream of gas exits through said distal end opening with a flow rate of less than about one liter per minute

The District Court’s Claim Construction

The district court construed “low flow rate” to mean

a rate of flow less than about 1 liter/minute and producing flow velocities less than 19 km/hour such that the gas exiting through the distal end opening forms a non-laminar inert gas temperature.

It based this interpretation largely on prosecution history, and arguments that were used to overcome prior art rejections.

The Claim Differentiation Argument

ERBE challenged the district court’s claim construction on several grounds, including claim differentiation. In particular, ERBE argued that the district court’s interpretation of claim 35 rendered claim 38 redundant, "in violation of the canon of claim differentiation."

The Federal Circuit’s Analysis

The Federal Circuit approached claim construction as it usually does, considering the claim language, specification and prosecution history.

With regard to the specification, the Federal Circuit noted:

The specification explains that directed gas flow could injure the patient. The invention sought to overcome this problem by disclosing and claiming low argon gas flows that produce a low, not directed, non-laminar stream of gas exiting the tube. The specification further provides an exemplary flow rate of about less than 1 liter per minute.

With regard to the prosecution history, the Federal Circuit noted:

The inventors distinguished its low flow rate from the Canady ’675 patent prior art reference in order to obtain its invention. . . .

Applicants explained that the claimed flow rate avoids the production of laminar jets to prevent patient injuries. . . . Specifically, they stated:

This flow rate avoids the production of laminar jets of ionized gas directed with high impact onto the tissue. The problems of laminar jets are to be avoided, since the ionized gas can enter the blood-stream and have toxic effects on the patient. According to Canady [the ’675 patent], column 4 lines 3-5, a flow rate of 1 to 12 litres per minute is foreseen there. . . . A flow rate of 1 litre per minute leads to a flow velocity of 19 m/h. Taking the higher value of 12 litres per minute gives an outlet gas speed of 229 km/h. Such velocities in Canady would certainly be classified as laminar jets and would likely lead to the above problems.

The Federal Circuit also pointed out that after these arguments were submitted, "the examiner issued its notice of allowance." 

The Federal Circuit concluded that "the prosecution history clearly and unambiguously demonstrates that the applicants unequivocally disclaimed flow rates from 1 to 12 liters per minute that lead to ‘such velocities’ of 19 through 229 km/h disclosed in the ‘675 patent prior art reference, referred to by applicants as laminar jets." 

With regard to the doctrine of claim differentiation, the Federal Circuit generally agreed that “[a]ll the limitations of a claim must be considered meaningful,” but cautioned:

Claim differentiation may be helpful in some cases, but it is just one of many tools used by courts in the analysis of claim terms.

(This is not a quote you want to see in a decision if you advocated application of the doctrine to support a broad claim interpretation!)

In the case before it, the unambiguous disclaimer in the prosecution history trumped any general principles that might have supported a broader claim construction. Thus, the Federal Circuit agreed with the district court’s interpretation.

When Can Claims Differentiate?

There are Federal Circuit decisions that cite the doctrine of claim differentiation to support a claim broad interpretation. So, when does this doctrine apply?

Without undertaking a comprehensive review of case law on this issue, I think the following factors may be pertinent:

  • does the specification indicate that the limitation at issue is an optional feature, a possible variation, or one example among many?
  • does the specification disclose embodiments outside the scope of the narrower claim? 
  • does another claim recite embodiments outside the scope of the narrower claim? 
     
  • does the specification describe the invention in terms that suggest that the limitation is an essential feature of the invention?
  • does the prosecution history include any arguments or evidence that suggest that the limitation is an essential feature of the invention?
  • does the prosecution history include arguments that rely on the limitation at issue to distinguish prior art or satisfy the enablement requirement?  

(These factors are not exhaustive and may not apply in all cases.)

Whether you want to use the doctrine of claim differentiation to support a broad interpretation or are reviewing claims and considering whether the doctrine applies, you should keep in mind that the doctrine is usually treated as the "weakest link" among claim construction tools. As illustrated by ERBE, claim differentiation usually will not support an interpretation that is at odds with the plain meaning of the claims, any express definitions included in the specification, or any disclaimers made during prosecution.