(29 days)
A bioimpedance spectroscopy device for use on adult human patients, utilizing impedance ratios that are displayed as an L-Dex ratio that supports the measurement of extracellular fluid volume differences between the limbs and is presented to the clinician on an L-Dex scale as an aid to their clinical assessment of unilateral lymphedema of the arm and leg in women and the leg in men.
The device is only indicated for patients who will have or who have had lymph nodes, from the axillary and pelvic regions, either removed, damaged or irradiated.
SOZOhub PC software - a PC software package that is intended to be used only with the ImpediMed SOZO device for uploading data on to the PC from the SOZO device, processing and analyzing of bioimpedance measurements.
The SOZO system consists of a connected hand and footplate with built-in stainless steel electrodes, paired with an Android tablet over Bluetooth connection. An app ("SOZOapp"), supplied with the tablet, controls the functionality of the hardware and supplies the bioimpedance measurement data to a database ("SOZOhub") contained within the hospital/facility network.
Measurements require the patient to make contact with bare hands and feet on stainless steel electrodes. The measurement takes about 30 seconds, during which the SOZO system measures small quantities of electrical energy (200ua RMS) across 256 frequencies, spaced logarithmically from 3kHz to 1000kHz. Established algorithms are used to analyze data and calculate extracellular fluid impedance levels for left and right limbs, and present the impedance ratio as an L-Dex® score for the clinician to review. This score facilitates their clinical assessment of unilateral lymphedema of the arm and leg in woman, and the leg in men.
Here's an analysis of the provided text regarding the acceptance criteria and study proving the device meets those criteria, formatted to address your specific points.
First, it's important to note that the provided documentation is a 510(k) premarket notification letter and summary for the SOZO™ device, which is an Impedance Plethysmograph (specifically, a bioimpedance spectroscopy device for assessing lymphedema). This type of submission primarily focuses on demonstrating substantial equivalence to a legally marketed predicate device, rather than proving efficacy through clinical trials with defined acceptance criteria and effect sizes as might be required for a PMA (Premarket Approval). Therefore, some of your requested information (e.g., effect size of human readers improving with AI, specific acceptance criteria for a clinical outcome, detailed ground truth establishment for a large test set) may not be present or applicable in this context.
The document emphasizes design changes to an existing technology (the L-Dex® U400) and the SOZO system's equivalence to that predicate. The "performance data" section primarily covers engineering and non-clinical testing.
Acceptance Criteria and Device Performance Study Analysis
1. Table of Acceptance Criteria and Reported Device Performance
The document does not present a formal table of "acceptance criteria" for clinical performance in the sense of a clinical trial. Instead, the performance data focuses on demonstrating that the new design of the SOZO system functions reliably and maintains characteristics similar to its predicate device. The "acceptance criteria" are implied by the successful completion of various engineering and non-clinical tests.
| Acceptance Criteria (Implied) | Reported Device Performance |
|---|---|
| Electrical Safety/EMC Compliance (e.g., IEC 60601 standards) | Met electrical safety and EMC requirements; CB certificate granted. |
| Software Verification & Validation (e.g., ISO 62304) | Software verified and validated to meet acceptance criteria and perform as intended. |
| Biocompatibility (e.g., ISO 10993 standards) | Passed biocompatibility testing with no failures reported. |
| Correlation with Predicate Device (L-Dex Readings) | Very strong correlation (r > 0.99) with the cleared U400 system. |
| Functional Performance/Design Reliability | Expected to remain functional throughout its intended life (tested with repeated weights). |
2. Sample Size Used for the Test Set and Data Provenance
The provided text does not specify a sample size for a clinical "test set" involving human subjects for performance evaluation. The "comparative performance vs. predicate device" was conducted using a "test fixture to create multiple fixed impedance loads representing different 'humans'." This is a laboratory-based, non-clinical test.
- Sample Size for Test Set: Not applicable for a human clinical test set. The comparative test used a "test fixture" with "multiple fixed impedance loads."
- Data Provenance: The testing appears to be primarily laboratory-based, likely conducted by the manufacturer (ImpediMed Limited, Australia) or accredited third-party labs. It is not described as involving retrospective or prospective human clinical data.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Qualifications
This information is not applicable as the "test set" was not a human clinical dataset requiring expert interpretation. The ground truth for the device's measurements is based on the physical properties of the "fixed impedance loads" used in the test fixture.
4. Adjudication Method for the Test Set
Not applicable, as there was no human-interpreted test set requiring adjudication.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and Effect Size
No, an MRMC comparative effectiveness study was not done. The device (SOZO) provides an L-Dex ratio, which is then used by a clinician as an "aid to their clinical assessment." This submission demonstrates the fidelity of the SOZO device's measurements compared to its predicate, not the impact on human reader performance. Therefore, there's no mention of an effect size for human readers improving with AI vs. without AI assistance because this is not an AI-based diagnostic tool in the sense that it provides an assessment directly to the clinician that then gets compared to human performance. It is a measurement device.
6. If a Standalone (i.e., Algorithm Only Without Human-in-the-Loop Performance) Was Done
The device's core functionality is its standalone measurement capability. The "L-Dex ratio" is a direct output of the device's algorithms based on bioimpedance spectroscopy data. The comparative test against the predicate device using a test fixture effectively evaluates this "standalone" measurement performance in a controlled environment. The "very strong correlation (r > 0.99)" reported indicates its standalone performance similarity to the predicate.
7. The Type of Ground Truth Used
The "ground truth" for the comparative performance study was the known, "fixed impedance loads" created by the test fixture. This serves as a known standard against which the measurements of both the SOZO device and the predicate U400 system were compared.
8. The Sample Size for the Training Set
The document does not specify a sample size for a "training set." This is likely because the device is based on "established algorithms" (Section 3: Device Description) and bioimpedance spectroscopy principles, rather than a machine learning model that would typically require a distinct training dataset to learn patterns. The focus is on the hardware and software's ability to accurately apply these existing algorithms and measure bioimpedance correctly.
9. How the Ground Truth for the Training Set Was Established
As there's no mention of a traditional "training set" for a machine learning model, the concept of establishing ground truth for it is not applicable in this document. The device relies on established scientific principles and algorithms for bioimpedance analysis, which were presumably developed and validated over time, but not detailed as a "training set" here.
§ 870.2770 Impedance plethysmograph.
(a)
Identification. An impedance plethysmograph is a device used to estimate peripheral blood flow by measuring electrical impedance changes in a region of the body such as the arms and legs.(b)
Classification. Class II (special controls). The device, when it is a body composition analyzer which is not intended to diagnose or treat any medical condition, is exempt from the premarket notification procedures in subpart E of part 807 of this chapter subject to the limitations in § 870.9.