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The firefly™ T-1 device is intended for the stimulation of healthy muscles in order to improve or facilitate muscle performance. The firefly™ T-1 device is not intended to be used in conjunction with therapy or treatment diseases of medical conditions of any kind.

The firefly™ T-1 device is a disposable, fully integrated neuromuscular stimulator for muscle conditioning composed of a constant current pulse generator with embedded software and battery enclosed in an over-molded plastic casing, and a silver electrode with a hydrogel coating which provides a means of attachment of the device and electrical contact with the patient. A single button controls the On/Off function and the intensity level of the device, which is achieved through changes in the delivered pulse width. The firefly™ T-1 is applied so that the electrodes lie over the common peroneal nerve behind the knee. Stimulation of the common peroneal nerve causes contraction of the calf muscles through the direct activation of the motor neurons, resulting in increased blood flow.

Here's an analysis of the acceptance criteria and supporting studies for the firefly™ T-1 device, based on the provided 510(k) summary:

This device is a Powered Muscle Stimulator, which typically focuses on performance characteristics rather than diagnostic accuracy like AI-powered imaging devices. Therefore, the traditional metrics of sensitivity, specificity, AUC, and multi-reader multi-case studies are not applicable in this context. Instead, the acceptance criteria relate to its functionality, safety, and effectiveness in stimulating muscles as intended.

1. Table of Acceptance Criteria and Reported Device Performance

Given the nature of a powered muscle stimulator, acceptance criteria are generally based on meeting industry standards for electrical safety, biocompatibility, and demonstrating the intended physiological effect. The document focuses on demonstrating substantial equivalence to a predicate device and proving its safety and effectiveness through non-clinical and limited clinical studies.

2. Sample Size Used for the Test Set and Data Provenance

Since this is not an AI/algorithm-only diagnostic device, the concept of a single "test set" for performance metrics like sensitivity/specificity doesn't apply directly. Instead, studies involved human subjects for physiological and subjective outcomes.

• Tucker et al.: The sample size is not explicitly stated in the summary, but it refers to "subjects." Data provenance is likely prospective clinical study.
• Warwick et al.: The sample size is not explicitly stated in the summary, but it involved "healthy volunteers." Data provenance is likely prospective clinical study.
• Jawad et al.: The sample size is not explicitly stated in the summary, but it involved "healthy subjects." Data provenance is likely prospective clinical study.
• Ferguson et al.: 21 healthy males. Data provenance is likely a prospective clinical study.

The specific country of origin for these studies is not provided in the 510(k) summary, but given the submitter's address (UK), it's plausible they were conducted in the UK or internationally.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

For medical devices that do not involve interpretation (like diagnostic imaging), the concept of "ground truth" established by experts in the typical sense does not apply. Instead, the studies measure objective physiological parameters (blood flow, muscle soreness scores) and subjective experiences (comfort levels). The researchers conducting these studies are the "experts" in their respective fields (e.g., physiology, sports medicine) who designed the studies, collected data, and analyzed results. Their qualifications are inherent in their authorship of scientific publications.

4. Adjudication Method for the Test Set

Adjudication methods (like 2+1, 3+1) are typically used in studies where multiple human readers interpret data to resolve discrepancies and establish a consensus ground truth. This is not applicable to the firefly™ T-1 device, as its studies involve direct physiological measurements or subjective reports from participants, not interpretive tasks.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done

No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not done. MRMC studies are specific to diagnostic tasks involving human interpretation of medical images or data. The firefly™ T-1 is a therapeutic/performance-enhancing device.

6. If a Standalone (i.e. algorithm only without human-in-the-loop performance) was done

This question is not applicable. The firefly™ T-1 is a medical device that directly interacts with the human body through electrical stimulation. Its performance is always "human-in-the-loop" in the sense that it is applied to a human subject. There is no independent "algorithm-only" performance to assess outside of its intended use on a person. Electrical safety and engineering bench testing could be considered "standalone" in a technical sense, but they assess instrumental characteristics, not clinical performance.

7. The Type of Ground Truth Used

The ground truth or outcome measures used in the studies were:

• Physiological Measurements:
  • Venous volume flow
  • Blood flow velocity
  • Microcirculatory flux
• Subjective Outcomes:
  • Perceived muscle soreness (measured using a scoring scale)
  • Comfort level (verbal rating scale)
• Safety Outcomes:
  • Monitorization for adverse events or safety concerns.

These directly measured or reported outcomes served as the "ground truth" for the device's performance in achieving its intended effects.

8. The Sample Size for the Training Set

This concept is not applicable to the firefly™ T-1 device. "Training set" refers to data used to develop and optimize an algorithm, typically in machine learning or AI applications. The firefly™ T-1 is a hardware-based electrical stimulator with embedded software, not an AI or machine learning model that requires a training set. Its design is based on established biomedical engineering principles and physiological understanding of neuromuscular stimulation.

9. How the Ground Truth for the Training Set Was Established

As explained above, the concept of a "training set" and associated ground truth establishment is not relevant for this type of medical device. The device's design and parameters (like the 1 Hz frequency) were informed by prior scientific research into effective and tolerable neuromuscular stimulation to promote blood flow (e.g., the early work of Tucker et al.) rather than being 'trained' on a dataset.

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