(90 days)
For adult human patients at risk of lymphedema:
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 volume differences between the limbs and is presented to the clinician on an L-Dex scale as an aid to their clinical assessment of lymphedema.
The use of the device to obtain an L-Dex score is only indicated for patients who will have or who have had lymph nodes, from the axillary and/or pelvic regions, either removed, damaged or irradiated.
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 applies small levels of electrical energy (200µA RMS) to the body across 256 frequencies spaced logarithmically from 3kHz to 1000kHz and measures the resulting voltage levels. 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 lymphedema in adult human patients.
The SOZO® device is a bioimpedance spectroscopy device intended for adult human patients at risk of lymphedema. It uses impedance ratios to display an L-Dex ratio, aiding clinicians in assessing lymphedema by measuring extracellular volume differences between limbs.
Here's an overview of the acceptance criteria and the study proving the device meets them:
1. Acceptance Criteria and Reported Device Performance:
| Acceptance Criteria | Reported Device Performance |
|---|---|
| Electrical Safety/EMC: Meet requirements of IEC 60601 (-1, -1-2, -1-6). | The SOZO device meets electrical safety and EMC requirements. A CB certificate was granted for the system. |
| Software Verification & Validation (V&V): Meet acceptance criteria and perform as intended; ISO 62304 compliance. | The software documentation had the same level of concern as the predicate device. Testing was performed in accordance with ISO 62304. The software was verified and validated to meet acceptance criteria and perform as intended. |
| Biocompatibility: Meet requirements of ISO 10993 for a low-risk, limited-contact device. | Testing performed by an accredited third party. The SOZO system passed biocompatibility testing with no failures reported. |
| Functional Performance: Maintain functionality throughout its intended life under physical stress. | Multiple SOZO systems were tested for design reliability by repeatedly placing weights on components with high physical stress. Testing showed the system is expected to remain functional throughout its intended life. |
| Clinical Performance: Demonstrate strong correlation of extracellular fluid levels between at-risk and ipsilateral limbs to aid in clinical assessment of bilateral lymphedema. | Studies have identified the applicability of ImpediMed's BIS technology to act as an aid in the clinical assessment of bilateral lymphedema, by demonstrating strong correlation of extracellular fluid levels between at-risk and ipsilateral limbs (e.g., left leg vs. left arm). |
| Comparative Performance vs. Predicate Device: Strong correlation (r > 0.99) in outputs when compared to predicate devices. | Using a test fixture with multiple fixed impedance loads representing different 'humans', a SOZO system was compared against ImpediMed U400 and SFB7 systems. The SOZO system showed a very strong correlation (r > 0.99) compared to both systems. |
2. Sample Size Used for the Test Set and Data Provenance:
The document does not explicitly state a specific sample size for the "clinical testing" mentioned, nor does it detail the provenance (country of origin, retrospective or prospective) of the data used for establishing the strong correlation of extracellular fluid levels. For the "comparative performance vs. predicate device" test, the "test set" consisted of a test fixture creating "multiple fixed impedance loads representing different 'humans'".
3. Number of Experts and Qualifications:
The document does not specify the number or qualifications of experts used to establish ground truth for any of the tests. For "clinical testing," it refers to "studies" that identified the applicability of the BIS technology, implying clinical expertise was involved in those studies, but no details are provided here.
4. Adjudication Method:
The document does not mention any adjudication method for establishing ground truth within the context of the provided performance data.
5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study:
The document does not describe an MRMC comparative effectiveness study involving human readers with and without AI assistance. The device is presented as an "aid to their clinical assessment," suggesting a human-in-the-loop scenario, but no comparative effectiveness study of this nature is detailed.
6. Standalone (Algorithm Only) Performance Study:
A standalone performance study was conducted for the device. The comparative performance against the predicate device using a test fixture and the "clinical testing" demonstrating correlation of extracellular fluid levels support the algorithm's standalone performance in producing the L-Dex ratio.
7. Type of Ground Truth Used:
- For Electrical Safety/EMC, Software V&V, Biocompatibility, and Functional Performance, the ground truth was based on adherence to international standards and internal design specifications/requirements.
- For Clinical Performance, the ground truth seems to be implicitly derived from established clinical understanding of lymphedema and extracellular fluid levels, as evidenced by "studies (that) have identified the applicability of ImpediMed's BIS technology." While not explicitly stated as "expert consensus," the nature of clinical assessment of lymphedema often relies on expert judgment integrated with objective measures.
- For Comparative Performance vs. Predicate Device, the ground truth was established by comparing the SOZO system's outputs against the outputs of already established predicate devices (ImpediMed U400 and SFB7) when presented with the same "fixed impedance loads." This implies the predicate devices' outputs served as the reference or "ground truth" for correlation.
8. Sample Size for the Training Set:
The document does not explicitly mention a separate "training set" or its sample size. The "Established algorithms are used to analyze data" implies algorithms were developed and likely trained, but details about the training process are not provided in this summary.
9. How the Ground Truth for the Training Set Was Established:
This information is not provided in the document.
§ 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.