Research Papers

A Novel Modular Tonometry-Based Device to Measure Pulse Pressure Waveforms in Radial Artery

[+] Author and Article Information
Mohammad Ikbal Choudhury

Department of Applied Mechanics,
Indian Institute of Technology Delhi,
Block 4, Academic Building,
New Delhi 110016, India
e-mail: ikbal.choudhury.nits@gmail.com

Pranjal Singh

Department of Applied Mechanics,
Indian Institute of Technology Delhi,
Block 4, Academic Building,
New Delhi 110016, India
e-mail: pranjalnewton@gmail.com

Rajneesh Juneja

Department of Cardiology,
All India Institute of Medical Science,
Neurosurgery and Cardiac Surgery Building,
New Delhi 110016, India
e-mail: rjuneja2@gmail.com

Suneet Tuli

Center for Applied Research in Electronics,
Indian Institute of Technology Delhi,
Block 3, Academic Building,
New Delhi 110016, India
e-mail: suneet@care.iitd.ac.in

K. K. Deepak

Department of Physiology,
All India Institute of Medical Science,
New Delhi 110016, India
e-mail: kkdeepak@gmail.com

Anamika Prasad

Mechanical Engineering Department,
South Dakota State University,
Brookings, SD 57007
e-mail: Anamika.Prasad@sdstate.edu

Sitikantha Roy

Department of Applied Mechanics,
Indian Institute of Technology Delhi,
Block 4, Academic Building,
New Delhi 110016, India
e-mail: sroy@am.iitd.ac

1A. Prasad and S. Roy equally contributed to this work.

2Corresponding author.

Manuscript received February 10, 2017; final manuscript received December 14, 2017; published online January 31, 2018. Editor: William Durfee.

J. Med. Devices 12(1), 011011 (Jan 31, 2018) (10 pages) Paper No: MED-17-1032; doi: 10.1115/1.4039010 History: Received February 10, 2017; Revised December 14, 2017

The paper presents the development of a new device for measuring continuous pulse pressure waveforms (PPW) from the radial artery via applanation tonometry. The development focuses on improved accuracy, open and affordable design using off-the-shelf components, and greater user control in setting operational and calibration parameters to address user variability. The device design parameters are optimized through a tissue device interaction study based on a computational model. The design incorporates modular components and includes a sensor module for arterial flattening and pressure pick-up, a differential screw mechanism and a related algorithm for controlled stepwise motion and data collection during flattening, and a brace for wrist-flexion adjustment. Maximum pulse amplitude (PA) was used as an indicator of the optimum level of arterial flattening for recording the PPW. The PPW was observed to distort due to changes in parameters like gel-head placement, hold-down pressure (HDP), and wrist extension. The pressure waveforms collected using the device were validated using limited data against established products and showed good correlation within ±1.96 standard deviation of the mean difference in a Bland–Altman plot. This paper thus details the development of a simple and validated mechanical design to measure PPW using arterial tonometry.

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Fig. 1

(a) The device is placed on the wrist showing the main unit and the flex-lock brace, (b) details of the main unit and its components, and (c) details of the sensor module and its components. The main device consists of (1) differential screw, (2) device enclosure, and (3) a sensor module. The sensor module consists of (a) base plate, (b) tactile sensor, (c) gel layer, (d) gel head, and (e) top cover. The flex-lock brace is used to control and fix the angle of wrist flexion θ, and differential screw is used to sequentially apply and control the HDP for arterial flattening.

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Fig. 2

Computational analysis for sensor design, showing (a) idealized model of human wrist, (b) meshed computational domain near the aorta showing placement of tonometer plunger, (c) plot showing average contact pressure versus arterial flattening for three tonometer geometries, and (d) plot showing circumferential stress variation in artery wall versus applied hold down level during tonometry. Details of the simulation and materials parameters are provided elsewhere [25].

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Fig. 3

(a) Sensor calibration plot showing applied pressure versus voltage relationship and (b) schematic of experimental setup of sensor calibration where universal testing machine or UTM(1) with a load cell (2), was used to apply pressure on the sensor module (3), and pressure–voltage data captured and recorded via electronic circuit (4) and NI (National Instruments) data acquisition card (5)

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Fig. 4

Plot showing voltage versus time data during complete arterial loading (S1 to S7) and unloading (S8 to S12) steps. The top plot comes from the static voltage component (due to mean BP and hold down pressure) and fluctuating voltage component (pulse pressure variation). The bottom plot corresponds to the data after filtering of the static component, thus showing only the fluctuating component (pulse pressure changes) having a mean of zero for each step.

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Fig. 5

(a) Bland–Altman plot of PA measured using a sphygmomanometer and the new device. (b) Typical pulse waveform in time domain with the key points of the waveform marked namely crest time (T1), dicrotic wave time (T2), TPT, Systolic amplitude (A1), and dicrotic wave amplitude (A2), (c) Bland–Altman plot of ΔT = T2–T1 measured from the new device and CT, and (d) Bland–Altman plot of TPT values measured from the new device and CT. Data were recorded for five different subjects using the protocol defined. On all the Bland–Altman plots, ±1.96 SD and 95% CI lines are also marked. The CI line is fairly large due to limited subject cases, and is expected to decrease with increasing subject number and subject variability (gender, age group, health conditions).

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Fig. 6

(a) Variation of PA with shifting of a module over and away from the artery and (b) variation of PA with the angle of wrist extension (θ) where the markers indicate different subjects

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Fig. 7

Variation of PPW with the location of the gel head on the radial artery of five different subjects

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Fig. 8

Variation of PPW with the angle of extension of the wrist (Θ) for five different subjects

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Fig. 9

(a) Variation of PA with the screw steps in a loading and unloading cycle, (b) variation of PPW with the screw steps during loading, and (c) calibrated PPW at the right hold down pressure




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