Blood Pressure Estimation Algorithm Based on Photoplethysmography Pulse Analyses

Round 1

Reviewer 1 Report

The paper proposes an innovative algorithm for the estimation of blood pressure (BP) from photoplethysmography (PPG). The paper is very interesting since it provides an alternative method for BP estimation, avoiding the supra-systolic pressure cuff insufflation and the arteries occlusion. However, the paper is not completely clear and sometimes is confusive. I recommend to the Authors to address the following concerns:

MAJOR:

• I suggest to further stress the importance of the findings comparing the performances of the proposed algorithm with other methods known in literature to estimate BP from PPG. Moreover, I would highlight the advantages of using PPG instead of BP measurements to assess vascular stiffness in clinical practice, in order to confirm the importance of the findings.

           For instance, the Authors can refer to:

Lazazzera, R., Belhaj, Y., & Carrault, G. (2019). A New Wearable Device for Blood Pressure Estimation Using Photoplethysmogram. Sensors, 19(11), 2557.

Marzorati, D., Bovio, D., Salito, C., Mainardi, L., & Cerveri, P. (2020). Chest Wearable Apparatus for Cuffless Continuous Blood Pressure Measurements Based on PPG and PCG Signals. IEEE Access, 8, 55424-55437.

Perpetuini, D., Chiarelli, A. M., Cardone, D., Rinella, S., Massimino, S., Bianco, F., ... & Gallina, S. (2020). Photoplethysmographic Prediction of the Ankle-Brachial Pressure Index through a Machine Learning Approach. Applied Sciences, 10(6), 2137.

Pilt, K., Meigas, K., Kööts, K., & Viigimaa, M. (2014). Photoplethysmographic signal rising front analysis for the discrimination of subjects with increased arterial ageing. Proceedings of the Estonian Academy of Sciences, 63(3), 221.

 

• The presentation of the algorithm is not clear to me. It is not clear to me if the goal of the model is to estimate in a continuous manner the BP, or to evaluate the SBP of DBP. Is a preliminary ECG recording needed for the algorithm? Is a preliminary pressure measurement needed? Moreover, the acronym PP is not defined, but it is essential for the constants a and b estimation. Please, better describe the algorithm, in particular specify the variables to estimate (the output of the algorithm), the parameters of the model (and how these parameters are evaluated) and the equations used.

 

• Concerning the results, figure 4a and 4b are equal. Please check it, because they are fundamental to understand the performances of the algorithm. Moreover, please specify how the error of the estimation of SBP and DBP is evaluated.

Minors:

• Line 95: change “can can” with “can”
• Line 109: “PT is the pulse rate”, please correct.
• Line 128 “eight men and 12 women” please change in “8 men and 12 women”
• In Table 1 and 2, please report not only the mean value of the parameters, but also their standard deviation.

Author Response

We attached a reply to reviewer.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper aims at proposing a method to estimate blood pressure using PPG devices. The topic is quite interesting but the paper has several critical aspects that the authors must tackle.

The document must be deeply rearranged. The work should be much more contextualized within the reference literature. Methods section must be improved in order to clarify the experimental protocols used. The algorithm must be better explained and justified. The results are partial and confusing. The discussion must be more accurate.

Below the authors can find some comments that can help, hopefully, to improve the paper.

Title:

It should be more explicative of the content fo the paper. I would suggest including the word Photoplethysmography to give a better focus also on the methodology.

Abstract:

It is too much focused on the background, however, it should be balanced introducing the methodology, quantitative results and a conclusion. The authors state that a measurement device was developed. This doesn't appear in the paper. Please check this part.

Introduction:

lines 29-30. The sentence doesn't seem to be physiologically correct. Are the authors sure that pressure and blood flow velocity are maintained constant? What happens when a subject is, for example, doing sport? Please check the literature and provide a reference.

line 32. please list some of the chronic illnesses that can be related to blood pressure.

line 41. Reference 4 doesn't seem to be appropriate since it doesn't focus on blood pressure measurement devices. Please check and correct.

lines 42-43. The sentence is not clear. It must be re-written.

lines 47-48. What do you mean with "correlation between the measurement sensor and PPG distance"? What do you mean with impact factors?

line 58. What is blood flow wavelength?

Materials and Methods

It is not clear how the PPG signal was processed to extract the maxima P1 and P2. This aspect should be clarified.

A section regarding the technical properties of the instrumentation used is missing. What kind of PPG did you use? What about the automatic blood pressure measurement device? This part must be included in order to replicate the results.

A reference for equation 3 is missing. Please add it.

line 109. Are you sure PT is the pulse rate?

It is not clear how the parameters a and b were derived. Equation 6 must be derived from other equations or referenced appropriately. What is PP for?

line 119. What do you mean with "the measurement time was minimized"?

The measurement protocol must be better explained. Was the blood pressure measured at rest? Was it measured at the same time using PPG and Automatic device? How can you be sure that the subject condition was comparable? Please include all the aspects that can be useful to fully describe the experimental protocol.

How ECG was measured?

A Bland-Altman plot can be more appropriate than just a correlation. Please include it in the paper.

Results:

lines 143-144. It is not true that the PPG peak is the same as the PTT. In fact, in figure 1 it is the time difference between the peak of the R wave and the peak of PPG. It is confusing.

figure 3. It is not clear how PT can be estimated without ECG. Please clarify.

Table 1. What is PP? What are the units of the variables? The standard deviation is missing. The authors should also take into consideration to include a table with all the subjects values to show the variability of the measurements.

Figure 4b is the same as figure 4a. Please correct.

Table 2. The variability of the measurements must be considered.

Discussion:

A critical and quantitative comparison with other PPG methods is missing. What is the novelty of the proposed approach? What are the limitations? Did you select a gold standard device to compare your method?

Author Response

We attached a reply to the reviewer.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The Authors addressed all the concerns and the paper is significantly improved. It can be accepted in the present form.

Author Response

Reply) Thank you very much for your review.

Reviewer 2 Report

The authors significantly improved the paper following most of the suggestions.

Few minor issues still remain:

• The quality of the figures should be improved
• Figure 4. Please include the units on the axis

Author Response

We attached the file.

Author Response File: Author Response.docx