(266 days)
The SOZO system may be used as an adjunct to existing methods by aiding clinicians who are using Subjective Global Assessment (SGA) tools to assess patients at risk of protein-calorie malnutrition (PCM).
The SOZO system may be further used to estimate the following body composition parameters in humans to track clinically relevant body composition parameters over time:
- Fat mass
- Fat-free mass
- Total body water
- Intracellular fluid
- Extracellular fluid
- Skeletal muscle mass
The following outputs are also presented:
- Body Mass Index (BMI)
- Basal metabolic rate (BMR; based on Mifflin - St. Jeor's algorithm) displayed in calories per day
- Protein and mineral (also known as 'dry lean mass') represents the content of a body that is not fat or fluid; calculated by subtracting total body water weight from fat-free mass weight.
The SOZO device measures current (I), voltage (V) and phase angle (Phi), and from these values calculates resistance (R), reactance (Xc), and impedance (Z), which are used to estimate the above body composition parameters. The device/software will also display the Cole plot, subject height, weight, age and sex.
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 current (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 various body composition parameters and present the outputs for the clinician to review.
Here's an analysis of the acceptance criteria and study information provided in the document:
1. Table of Acceptance Criteria and Reported Device Performance
| Acceptance Criteria Category | Reported Device Performance |
|---|---|
| Electrical Safety/EMC | Meets requirements set forth in IEC 60601 (subparts -1, -1-2, and -1-6). CB certificate granted. |
| Software V&V | Meets acceptance criteria and performs as intended, tested in accordance with ISO 62304. |
| Biocompatibility | Passed testing according to ISO 10993 for a low-risk, limited-contact device; no failures reported. |
| Functional Performance | System expected to remain functional throughout its intended life; tested for design reliability by repeatedly placing weights on components. |
| Comparative Performance vs. Predicate Device (SFB7) | Very strong correlation (r > 0.99) with outputs from the SFB7 device when tested using a fixture with multiple fixed impedance loads representing different "humans." |
2. Sample Sizes Used for the Test Set and Data Provenance
The document does not explicitly state a specific "test set" sample size for a clinical study to directly prove the new indications for use. Instead, it states: "Clinical testing: clinical studies have identified the applicability of ImpediMed's BIS technology to act as an aid in body composition." This general statement implies that the underlying Bioimpedance Spectroscopy (BIS) technology has been validated through clinical studies, but it doesn't provide details about studies specific to the SOZO system's new indications or a dedicated test set with sample size.
For the comparative performance with the predicate device, a "test fixture" was used with "multiple fixed impedance loads," which isn't a human sample size but rather an engineering test.
Data Provenance: Not explicitly stated for specific clinical studies, only generally refers to "clinical studies."
3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications
This information is not provided in the document. The document refers to "clinical studies" for the applicability of BIS technology but does not detail how ground truth was established for these studies, nor the number or qualifications of experts involved.
4. Adjudication Method for the Test Set
This information is not provided in the document.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, and the Effect Size of Improvement with AI vs. Without AI Assistance
No MRMC study is mentioned in the document. The SOZO system is a device for measuring body composition parameters, not an AI-assisted diagnostic tool for human readers in the traditional sense of an MRMC study. Its use is described as "an adjunct to existing methods by aiding clinicians who are using Subjective Global Assessment (SGA) tools," but no study comparing human performance with and without SOZO assistance is described.
6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done
The device itself is a standalone measurement system that takes raw electrical measurements and processes them using "established algorithms" to calculate body composition parameters. The "comparative performance vs. predicate device" test (r > 0.99 correlation) can be considered a standalone performance assessment against a validated reference.
7. The Type of Ground Truth Used
- For Body Composition Parameters: The document states that "established algorithms are used to analyze data and calculate various body composition parameters." For the "comparative performance vs. predicate device," the predicate device (SFB7) is essentially the reference standard (ground truth surrogate). However, for the initial validation of the BIS technology to derive these parameters, it is generally understood that such systems are validated against gold standard body composition assessment methods (e.g., DEXA, isotope dilution, direct chemical analysis), though this specific detail is not provided for the SOZO system in this document. The document refers to "clinical studies have identified the applicability of ImpediMed's BIS technology to act as an aid in body composition," implying prior validation work.
- For Protein-Calorie Malnutrition (PCM) Assessment: The device is used as an adjunct to Subjective Global Assessment (SGA) tools, implying that SGA is the primary assessment method clinicians use.
8. The Sample Size for the Training Set
No training set sample size is explicitly mentioned. The device uses "established algorithms," suggesting that the algorithms were developed and potentially trained on datasets prior to this submission. This document focuses on the performance and equivalence of the SOZO device itself, not the detailed development of its underlying algorithms.
9. How the Ground Truth for the Training Set Was Established
This information is not provided in the document. As with the training set size, the document does not delve into the historical development and validation of the "established algorithms" that process the bioimpedance data.
§ 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.