A Wearable Internet of Things Device for Noninvasive Remote Monitoring of Vital Signs Related to Heart Failure

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Author Response

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper introduces a new heart-failure (HF) monitoring system utilizing body-mounted wearable sensors to capture thoracic impedance, blood oxygen saturation, heart rate, and activity status. The development of the body-mounted wearable device was presented comprehensively, including a user-friendly system with a skin patch on a flexible PCB. Having a detailed description on how to identify activity status using the wearable system would be highly beneficial.

 

The primary weakness of the paper lies in the evaluation of the proposed system:

- The experimental scenarios, involving 20 minutes of sitting, 20 minutes of standing, and 20 minutes of walking, are overly simplistic and may not accurately represent daily activities in a real-life setting.

- The study included only 10 subjects (6 female and 4 male), suggesting that the sample size might be insufficient for drawing meaningful conclusions.

- The experiments were conducted on healthy subjects, raising uncertainties about the system's ability to capture sudden changes in heart failure parameters.

- During the experimental study, all outliers were disregarded, such as impedance values falling outside the thoracic impedance range of 70-1120, which could affect the robustness of the findings.

 

Additionally, certain figures in the manuscript lack clarity. Please improve the resolution of selected figures, such as Figure 3(c) and Figure 3(d), or enlarge their size for better visibility.

Author Response

Response: We thank the reviewer for providing suggestions to improve the content of our manuscript. Following the reviewer’s comments/recommendations, we have added content and revised the manuscript. Please see our response to specific comments below

 

1. The paper introduces a new heart-failure (HF) monitoring system utilizing bodymounted wearable sensors to capture thoracic impedance, blood oxygen saturation, heart rate, and activity status. The development of the body-mounted wearable device was presented comprehensively, including a user-friendly system with a skin patch on a flexible PCB. Having a detailed description on how to identify activity status using the wearable system would be highly beneficial.

 

We thank the Reviewer for highlighting this. We have included the details of the activity detection in lines 144-151:

 

ADXL 362 can be programmed with activity and inactivity thresholds in terms of codes for the purpose of defining the activity. Whenever the acceleration of the subject is higher than the activity threshold the accelerometer will register it as an activity. For this purpose, we have defined our activity threshold with 300 codes at default Output Data Rate (ODR) of 100 Hz. This activity threshold was found sensitive enough to detect the transition of the subject from resting to active condition. In the wearable sensor we have used binary states for activity, where 1 indicates the active state and 0 indicates inactive state. Code

 

2. The primary weakness of the paper lies in the evaluation of the proposed system. The experimental scenarios, involving 20 minutes of sitting, 20 minutes of standing, and 20 minutes of walking, are overly simplistic and may not accurately represent daily activities in a real-life setting. The study included only 10 subjects (6 female and 4 male), suggesting that the sample size might be insufficient for drawing meaningful conclusions.

The experiments were conducted on healthy subjects, raising uncertainties about the system's ability to capture sudden changes in heart failure parameters.

 

 

We agree with the reviewer that we are using 10 subjects to test the developed system, we are not drawing any diagnostic conclusion from this project. For diagnostic use, the system has to be tested will a large patient population and that will be the goal of future work. Moreover, as discussed in the article thoracic impedance decreases due to the retention of the fluid in the thoracic impedance at the onset of heart failure therefore a device capable of measuring transthoracic impedance, validated over healthy subjects, will potentially measure the transthoracic impedance of heart failure patients and can detect the decrease in it due to the retention of the fluid, as it is detecting changes in transthoracic impedance due to respiration beats in healthy subjects. Similarly, for heart rate, SPO2 and activity status. The difference would be that, for heart failure patients the respective values of these parameters would be outside the healthy range but still will not be negligible that cannot be detected by the sensor. Furthermore, it is important to highlight that for heart failure patients changes in these parameters are not sudden but happen over a period of time with the gradual accumulation of the fluid that effects the ability of the heart to pump effectively.

 

For the initial validation study that we presented in this paper, we observed that the device gave reliable results when tested for 1 hour. We agree that longer monitoring will be required for the clinical study. We plan to use the device for 5 hours a day in a future clinical study on HF patients. 

 

 

3. During the experimental study, all outliers were disregarded, such as impedance values falling outside the thoracic impedance range of 70-1120, which could affect the robustness of the findings.

 

This was done for the reduction of the noise such as the thoracic impedance value cannot be outside this range. Any impedance value outside the range is either because of a short circuit where two electrodes are attached together highlighting impedances lower than 70 ohms or an open circuit due to the unconnected electrodes on the thoracic region highlighting values higher than the upper range.

 

4. Additionally, certain figures in the manuscript lack clarity. Please improve the resolution of selected figures, such as Figure 3(c) and Figure 3(d), or enlarge their size for better visibility.

 

We thank the reviewer for highlighting this. We have addressed this and have improved the Fig.3 visibility.

  

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper presents a promising technological/device advancement in heart failure management. I like the approach combining digital technologies details. I have a few concerns as follows:

 

Evaluation of System Errors, Cross Comparison with Other Devices or Wearables: The paper seems to lack providing a detailed evaluation of system errors or a direct comparison with other devices or wearables. This is an important aspect that could enhance the paper's value by providing context on how this device performs against existing solutions in the market.

 

Evaluation of the System Overhead of the Wearable and App: The paper mentions the device's power consumption, stating it consumes 72.35 mA and can run on a battery for around 18 hours. However, a comprehensive evaluation of the system overhead, including aspects like processing power, memory usage, and the impact on either the wearables and/or mobile app's performance, seems not detailed in the paper. As these devices aim for wearables and everyday usage, this information would be important for understanding the practicality and efficiency of the device in real-world scenarios.

 

Variation in Height and Weight of Subjects: The paper includes a range of subjects with varying heights and weights. While Subjects 4 and 8 present notable deviations in their biometric data, the biometric data range exhibited by the other subjects appears relatively constrained. Expanding the subject pool to include a broader range of heights and weights, as well as potentially other variables such as age and underlying health conditions, would strengthen the study.

Author Response

Response: We thank the reviewer for providing suggestions to improve the content of our manuscript. Following the reviewer’s comments/recommendations, we have added content and revised the manuscript. Please see our response to specific comments below

 

 

1. Evaluation of System Errors, Cross Comparison with Other Devices or Wearables: The paper seems to lack providing a detailed evaluation of system errors or a direct comparison with other devices or wearables. This is an important aspect that could enhance the paper's value by providing context on how this device performs against existing solutions in the market.

 

In accordance with the Reviewer’s suggestion we have discussed some of the recent efforts towards the monitoring of heart failure (HF) using wearable devices and have also discussed how our device is addresses the shortcoming of these efforts. This can be found in lines 57-76:

 

“Recently, efforts have been made for using wearable devices for various applications. Some efforts have also been made for the use of wearable devices specifically for HF management and monitoring^16–19. Notable examples include a wearable vest for HF monitoring, a hemotag and a wearable belt for monitoring vital cardiovascular parameters^20–22. The wearable belt by Svagard et al. is a chest-based belt that measures transthoracic impedance (TTI) and weight to monitor HF²⁰. They have found TTI to be 76% sensitive enough to HF and 33% sensitive to body weight. However, this device is not only bulky for the patient but is not a real-time continuous monitor, as it is only required to be used for 10 mins to extract parameters. Moreover, it is not fully wearable in nature that can be used at all times and in all conditions as it is only required to be used for resting conditions. Similarly, hemotag can only be used for resting position²¹. It monitors the HF using time-synchronized vibrations from the chest for only 30 secs. Moreover, the wearable belt by Svagard et al. is a multiparametric belt for monitoring different vital cardiovascular parameters such as heart rate and activity level along with other vital parameters such as skin temperature but does not include the most specific HF parameter, thoracic impedance²². Thoracic impedance is a vital indicator for measuring fluid accumulation and is a specific diagnostic indicator for HF.   Herein we report a wearable device that can monitor the vitals related to HF in different real-time conditions at all times. “

2. Evaluation of the System Overhead of the Wearable and App: The paper mentions the device's power consumption, stating it consumes 72.35 mA and can run on a battery for around 18 hours. However, a comprehensive evaluation of the system overhead, including aspects like processing power, memory usage, and the impact on either the wearables and/or mobile app's performance, seems not detailed in the paper. As these devices aim for wearables and everyday usage, this information would be important for understanding the practicality and efficiency of the device in real-world scenarios.

 

We are thankful to the Reviewer for highlighting this. In order to address this we have included the software performance of our wearable device highlighting the low memory consumption of the program. This can be found in lines 156-158:

 

The program for the wearable is an effective program that consumes only 62100 bytes that constitutes only 23% of the total flash memory of the microcontroller with 32 kilobytes (KB) of Static RAM (SRAM)

 

3. Variation in Height and Weight of Subjects: The paper includes a range of subjects with varying heights and weights. While Subjects 4 and 8 present notable deviations in their biometric data, the biometric data range exhibited by the other subjects appears relatively constrained. Expanding the subject pool to include a broader range of heights and weights, as well as potentially other variables such as age and underlying health conditions, would strengthen the study.

 

We thank the Reviewer for suggesting this. We do intend to scale the experimentation in next phase of our device. The purpose of this paper is to demonstrate the application of the wearable device and its ability to measure parameters in real time. Moreover, we agree that other biometric information such as age and underlying health conditions are effective indicators and for this purpose, the average age of participants is mentioned in lines 234-235 in following words:

 

The biometric information of the subjects is shown in Table2. All the subjects were in the age range of 24-31 years.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

As in the previous comments, I would suggest the authors expand the subject pool to include a broader range of heights and weights and potentially other variables such as age and different health conditions.

Author Response

We thank the reviewer for providing suggestions to improve the content of our manuscript. Following the reviewer’s comments/recommendations, we have added content and revised the manuscript. Please see our response to specific comments below

 

 

As in the previous comments, I would suggest the authors expand the subject pool to include a broader range of heights and weights and potentially other variables such as age and different health conditions.

 

 

We thank the Reviewer for suggesting this. The purpose of this paper is to demonstrate the application of the wearable device and its ability to measure parameters in real time. In accordance with the Reviewer’s comment, we have included the Ages of all subjects in the Table 2 as shown below.

Subject	Gender	Age	Height (cm)	Weight (lb)
1	M	29	165.1	137
2	M	28	168	120
3	M	31	168	130
4	M	32	167.64	176
5	F	29	161.5	92.59
6	F	31	164	110.231
7	F	30	156	117
8	F	31	171	171.9
9	F	29	158	112
10	F	24	160	105

Table:2 Biometric information of subjects

 

As mentioned, we do intend to scale the experimentation in the next phase of our device. Moreover, we agree that other biometric information such as age and underlying health conditions are effective indicators, and we intend to include heart failure patients along with healthy patients in the larger cohort.

Author Response File: Author Response.docx