Scale to Measure Nighttime Weight Change Kyle Herzog Team Leader Joe Ferris BWIG Ben Engel Communications Eric Printz BSAC Advisor Wally F Block Professor of Biomedical Engineering Client Timothy Juergens M D Geriatric psychiatrist sleep specialist December 10 2006 Table of Contents TABLE OF CONTENTS 2 ABSTRACT 3 MOTIVATION 4 PROBLEM STATEMENT 4 CLIENT REQUIREMENTS 4 BACKGROUND INFORMATION 5 Correlation between Obesity and Weight Gain Before Bed 5 Correlation between Obesity and Insomnia 7 DESIGN ALTERNATIVES 7 Load Cell 7 Pad Design 10 Tension Meter 11 DESIGN EVALUATIONS 13 FINAL DESIGN COMPONENTS 15 Analog Digital Converter 15 Amplifier 16 Load Cell 17 Test Stand 18 Data Interpretation 19 COST ANALYSIS 20 FUTURE WORK 21 ETHICAL CONSIDERATIONS 22 REFERENCES 24 APPENDIX 25 2 Abstract It has been proposed to design a weighing device that can measure weight change of a patient in a hospital bed over the course of a night A patient s weight can fluctuate as much as 700 g in one night Studies recently performed at Yale and the University of Japan have shown a direct connection between sleep and long term weight change Our client believes that there is a connection between the pattern of this weight change and sleep stage changes Due to the minute weight changes the device would have to read at an accuracy of about 0 05 lbs but the more accurate the device the more useful it will be The weight of the patient should be recorded every ten to fifteen minutes throughout the night The device would likely have to support a hospital bed supported by four legs The device should be capable of being moved between beds with minimal difficulty and without any complex recalibration required We considered three separate design alternatives a weighing pad to be placed under the mattress a load cell placed under each leg of the bed and a tension meter design After analyzing each option we decided to proceed with our load cell design Our prototype consists of a load cell that sends its signal through an amplifier and then to an analog digital converter This signal is then read by a computer and the weight readings are exported to an excel file using a program that we specially wrote 3 Problem Statement For most people weight fluctuates throughout the day and night As a result one can lose as much as 700 grams over the course of the night even if they do not eat or go to the bathroom Much of this is related to metabolism as well as water loss We would like to be able to measure this weight change accurately on people who are in hospital beds This will require that our device record the patient s weight every fifteen minutes The device would likely have to support a hospital bed which sits on four legs and read at an accuracy between 0 02 0 05 lbs Ideally the device could be moved to a different bed without too much difficulty one to two hours time and without complex recalibration Motivation Tracking weight change over the course of a night may be important from a research perspective There are a number of potential variables that may affect this weight change such as medications and sleep stage changes Another potential use would be to track and eventually predict those at higher risk of developing obesity correlate with body fat measurements activity and assess for metabolic changes when we do things to improve or correct sleep problems There is popular concern in recent sleep literature regarding various sleep stages insomnia and their impact on obesity Client Requirements One of the device s important client requirements is that it output weight readings to a computer at chosen time intervals The user should be able to choose the frequency of readings and have the data values imported to a program that is as universal as possible such as Microsoft 4 Excel This will allow for easy analysis and manipulation of the data The more accurate the scale the more useful the readings will be An accuracy of 0 02 to 0 05 lbs is desired but a slightly less precise scale would still be very useful Achieving accuracy this high with materials that are of reasonable cost will be very difficult and a lower accuracy may be used in the prototype designed this semester Another important client requirement is that the scale not be fixed to one bed It should be capable of being moved from one bed to another without the need for many hours of labor or complex recalibration Background Information Correlation between obesity and weight gain before bed A recent study performed at Nakamura Gauken University in Japan 4 proved that there is a direct correlation between the daily fluctuation in body weight immediately before going to bed weight regain and accompanying visceral fat accumulation in obese patients The study consisted of a 16 month weight reduction program with an initial four month education program The 16 month weight reduction program that the study focused on was completed by ninetyeight women in a charting group recorded weights at four different times of day and seventeen women in a noncharting group no weight measurements Consequently ninety eight obese women who ranged in age from 23 to 66 years who had no history of major diseases or medications known to influence the parameters examined in the study were assessed Weight recordings were made using a standard hospital grade scale at four separate times during the day immediately after waking up after eating breakfast after dinner and before going to bed Abdominal fat areas and blood samples were assessed at 0 4 and 16 months To ensure the comparability of the charts between days adherence to the exact times and weighing instructions 5 was critical The study found that plotting the daily body weight measured at four critical times each day is effective in weight reduction maintaining weight loss and preventing subjects from dropping out of a weight loss program Based on the rate of attrition the performance of subjects in the charting group was clearly superior to that in the noncharting group which confirms previous findings The results also revealed that the standard deviations of the difference in body weight between after waking up and before going to bed predicted the rebound increase in body weight Patients who had an inconsistent weight before going to bed higher than the weight after dinner quickly regained their lost weight by the end of the 16 months study Obese patients have the distinct characteristic of excessive snacking during the period
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