511730DSTXXX10.1177/1932296813511730Journal of Diabetes Science and TechnologyFinan et al research-article2014 Original Article Closed-Loop Control Performance of the Hypoglycemia-Hyperglycemia Minimizer (HHM) System in a Feasibility Study Journal of Diabetes Science and Technology 2014, Vol. 8(1) 35 42 2014 Diabetes Technology Society Reprints and permissions: sagepub.com/journalspermissions.nav DOI: 10.1177/1932296813511730 dst.sagepub.com Daniel A. Finan, PhD 1, Thomas W. McCann Jr, MBA 1, Linda Mackowiak, MS 1, Eyal Dassau, PhD 2,3, Stephen D. Patek, PhD 4, Boris P. Kovatchev, PhD 4, Francis J. Doyle III, PhD 2,3, Howard Zisser, MD 2,3, Henry Anhalt, DO 1, and Ramakrishna Venugopalan, PhD 1 Abstract Background: This feasibility study investigated the insulin-delivery characteristics of the Hypoglycemia-Hyperglycemia Minimizer (HHM) System an automated insulin delivery device in participants with type 1 diabetes. Methods: Thirteen adults with type 1 diabetes were enrolled in this nonrandomized, uncontrolled, clinical-research-centerbased feasibility study. The HHM System comprised a continuous subcutaneous insulin infusion pump, a continuous glucose monitor (CGM), and a model predictive control algorithm with a safety module, run on a laptop platform. Closed-loop control lasted approximately 20 hours, including an overnight period and two meals. Results: When attempting to minimize glucose excursions outside of a prespecified target zone, the predictive HHM System decreased insulin infusion rates below the participants preset basal rates in advance of below-zone excursions (CGM < 90 mg/dl), and delivered 80.4% less insulin than basal during those excursions. Similarly, the HHM System increased infusion rates above basal during above-zone excursions (CGM > 140 mg/dl), delivering 39.9% more insulin than basal during those excursions. Based on YSI, participants spent a mean ± standard deviation (SD) of 0.2 ± 0.5% of the closed-loop control time at glucose levels < 70 mg/dl, including 0.3 ± 0.9% for the overnight period. The mean ± SD glucose based on YSI for all participants was 164.5 ± 23.5 mg/dl. There were nine instances of algorithm-recommended supplemental carbohydrate administrations, and there was no severe hypoglycemia or diabetic ketoacidosis. Conclusions: Results of this study indicate that the current HHM System is a feasible foundation for development of a closed-loop insulin delivery device. Keywords algorithm, artificial pancreas, closed-loop control, model predictive control, type 1 diabetes Developing a closed-loop insulin delivery system has the potential to transform diabetes management and improve the lives of those living with the disease. Since JDRF (formerly the Juvenile Diabetes Research Foundation) launched the Artificial Pancreas Project in 2006, 1 various studies have reported the feasibility of different closed-loop algorithms to control blood glucose levels in patients with type 1 diabetes. 2-6 Although much technical progress has been made, patients with type 1 diabetes carry a significant burden in the completion of day-to-day diabetes care tasks, and run the continual risk of hypoglycemia and hyperglycemia in their attempts to achieve optimal glucose control. 7 Preliminary data from the Hypoglycemia-Hyperglycemia Minimizer (HHM) System, an automated insulin delivery device, are presented in this article. The control algorithm of the HHM System is designed to take action to reduce if not prevent glucose excursions outside of a prespecified target zone by adjusting insulin delivery based on predictions of near-future glucose trends. Following US Food and Drug Administration (FDA) guidance in preparation for human clinical trials, realistic aspects of the HHM System were investigated in silico, including protocol specifications and system characteristics. 8 The virtual cohort investigated comprised 100 adult patients, and has been accepted by the FDA as suitable replacement for animal studies. 9 1 Animas Corporation, West Chester, PA, USA 2 University of California, Santa Barbara, Santa Barbara, CA, USA 3 Sansum Diabetes Research Institute, Santa Barbara, CA, USA 4 University of Virginia, Charlottesville, VA, USA Corresponding Author: Daniel A. Finan, Animas Corporation, 965 Chesterbrook Blvd, Wayne, PA 19087, USA. Email: dfinan@its.jnj.com
36 Journal of Diabetes Science and Technology 8(1) The design of the simulation study approximated the clinical study design as closely as possible, from both system and protocol perspectives. 10 From a system perspective, the algorithm used in the simulation study was identical to that planned for the clinical study. From a protocol perspective, two key parameters were intended to be adjustable throughout the clinical study to glean more targeted information: the ratios of prandial insulin boluses to the breakfast and lunch carbohydrate (CHO) quantities, relative to the nominal matched amounts based on the subject s insulinto-cho ratios. The stated values of mismatch planned for the study were: (a) for breakfast, a matched bolus or 30% underbolus; and (b) for lunch, a matched bolus or 30% overbolus. The rationale for this bolus mismatch stipulation was to ensure adequate glucose fluctuations and thereby investigate the algorithm s insulin-dosing characteristics in response to potential hypoglycemic and hyperglycemic excursions. All stated values for these boluses were investigated in silico to demonstrate safety in the clinical study. The results from the simulations did not indicate any safety concerns, regardless of the bolus mismatch parameters, and provided sufficient justification for moving forward with the clinical (feasibility) study. 11,12 The feasibility study was executed to evaluate the performance of the HHM System in participants with type 1 diabetes in a clinical research center (CRC) setting. The primary objective of this study was to investigate the insulin delivery characteristics of the HHM System before and during glucose excursions below and above a prespecified target zone of 90-140 mg/dl. As the study was unpowered, targeted metrics were designed and used to assess the potential of the HHM System to safely maintain glucose levels by adjusting insulin infusion amounts in quiescent times (including overnight) as well as in response to meal challenges. Methods Clinical Study Design This was a nonrandomized, uncontrolled, CRC-based feasibility study. The study was conducted in accordance with the Declaration of Helsinki, International Conference on Harmonisation, Good Clinical Practice guidelines, and relevant local laws and regulations. The protocol and informed consent form were approved by Compass Independent Review Board, LLC (Mesa, AZ), and all participants provided written informed consent. The study objectives were to evaluate the performance of the HHM System in participants with type 1 diabetes in a CRC setting; investigate the insulin delivery characteristics of the HHM System in anticipation of, and during, glucose excursions below and above a prespecified target zone (90-140 mg/dl); and assess the ability of the system to safely maintain glucose levels by adjusting insulin infusion amounts in response to challenges of food and insulin boluses. Table 1. Main Inclusion and Exclusion Criteria for Participation. Inclusion criteria Age 21-65 years Diagnosed with type 1 diabetes for 1 year Using an insulin infusion pump for 6 months with commercially available rapid-acting insulin Hemoglobin A1c < 10% Exclusion criteria Pregnant/nursing Skin conditions that would preclude wearing study devices Diabetic ketoacidosis requiring an emergency room visit or hospitalization in the previous 6 months Severe hypoglycemia resulting in seizure or loss of consciousness in the previous 6 months History of a seizure disorder Use of oral prednisone or a beta-blocker Intolerant of or unable to receive glucagon Hematocrit level < 30% or > 55% Abnormal renal function (creatinine > 1.5 mg/dl) Subjects. The target cohort of this feasibility study was adults with type 1 diabetes using insulin pumps. Main inclusion and exclusion criteria are listed in Table 1. In addition, subjects with any other condition that, in the opinion of the investigator, would preclude successful participation in the clinical trial were excluded. Investigational device. In this study the investigational device, the HHM System, comprised a continuous glucose monitor (CGM), insulin pump, automatic control algorithm, and central laptop (Figure 1). 13 The algorithm of the HHM System had two modular components the Zone Model Predictive Controller (Zone- MPC) and the Safety Supervision Module (SSM) which worked to automatically and continuously dose insulin in response to changing CGM levels. The Zone-MPC algorithm used a mathematical approximation of insulin-glucose dynamics to predict near-future glucose trends from recent CGM measurements and insulin dosage amounts. CGM values are automatically input to the algorithm every 5 minutes. The algorithm was designed to deliver insulin as needed to maintain glucose levels within the target zone (90-140 mg/ dl). 14 The SSM used mathematical approximations of the insulin-glucose dynamics to continually assess and mitigate the risk of near-future hypoglycemia. 15 It acted on the Zone- MPC s recommended insulin infusion amount, and was designed to provide an additional safeguard against predicted near-future hypoglycemia. The action of the SSM was constrained to approving or reducing (but not increasing) the insulin amount recommended by the Zone-MPC. Procedure. During the week before the CRC visit, individual participants basal rates were assessed and optimized by
Finan et al 37 The breakfast meal on day 2 was administered at approximately 07:00, and included 1 g CHO per kg body weight, up to a maximum of 100 g CHO. Coincident with the breakfast meal, an insulin bolus was administered, which in some cases was an underbolus by 30% relative to their insulin-to- CHO ratio. The purpose for this deliberate underinsulinization was to ensure adequate algorithm activity in mitigating the subsequent (potential) hyperglycemia. The lunch meal on day 2 was administered at approximately 13:00, and also included 1 g CHO per kg body weight, up to a maximum of 100 g CHO. Coincident with the lunch meal, an insulin bolus was administered, which in some cases was an overbolus by 30%. Similar to the rationale for the underbolus at the breakfast meal, the purpose for the deliberate overinsulinization at lunchtime was to ensure adequate algorithm activity in mitigating the subsequent (potential) hypoglycemia. The participant was discharged in the evening of day 2. Figure 1. The investigational device comprised a continuous subcutaneous insulin infusion pump (OneTouch Ping Glucose Management System; Animas Corporation, West Chester, PA), a continuous glucose monitoring system (Dexcom SEVEN PLUS Continuous Glucose Monitor; Dexcom, Inc, San Diego, CA), and the Hypoglycemia-Hyperglycemia Minimizer algorithm run on the University of California, Santa Barbara/Sansum Diabetes Research Institute Artificial Pancreas System (APS ) laptop platform. 11 RF, radiofrequency. the investigative staff. The individual basal rates were used by the algorithm of the HHM System as the default insulin delivery rates when CGM values were predicted to be within the target zone; by extension, when CGM values were (or were predicted to be) outside the target zone, these basal rates served as the basis insulin delivery rate from which the algorithm might increase or decrease insulin delivery. CGM sensor insertion occurred 2-3 days prior to the CRC visit and was calibrated by meter throughout the study per the manufacturer s instructions. The CRC visit lasted approximately 24 hours for each participant, including approximately 20 hours of closedloop control during which the HHM System was assessed. The sequence of events during the CRC visit was as follows: The participant arrived during the early evening of day 1. Closed-loop control was initiated at approximately 00:00 (midnight), and lasted until approximately 20:00. Glucose monitoring was performed using YSI 2300 STAT Plus (YSI Inc, Yellow Springs, OH) at the following time points: before meals and every 2 hours prior to enabling closed-loop control mode; every 30 minutes during closedloop control mode; every 20 minutes for 80 minutes following meals; every 15 minutes if hypoglycemic, until glucose rose > 80 mg/dl; and every 30 minutes if hyperglycemic until glucose fell < 300 mg/dl. All diabetes care in the CRC was performed by study staff. A follow-up telephone call was conducted 24 hours after the CRC visit. Data Analysis The ability of the HHM System to anticipate and to preemptively respond to predicted below-zone and above-zone excursions based on CGM values was assessed, as was its ability to respond during below-zone and above-zone excursions. These metrics quantified differences in the HHM System delivered insulin rates compared to the corresponding basal rates in the 15 minutes prior to an out-of-zone breach (defined as when the CGM tracing exited the glucose target zone), as well as any time during an out-of-zone excursion. Glucose control metrics were calculated, but should be considered with the caveat that the primary objective of the study was not to obtain optimal glucose control, but rather to investigate the insulin-delivery characteristics of the HHM System including during periods of over- and underinsulinization. Glucose metrics based on YSI and CGM were calculated for four time ranges: overall, overnight (approximately 00:00-07:00), post-breakfast (approximately 07:00-13:00),
38 Journal of Diabetes Science and Technology 8(1) Table 2. Patient Characteristics (N = 13). Parameter Value Age, years, mean ± SD 42.5 ± 12.7 Female, n (%) 11 (84.6) Body mass index, kg/m 2, mean ± SD 24.7 ± 5.1 Duration of diabetes, years, mean ± SD 27.2 ± 13.3 Duration of pump use, years, mean ± SD 9.6 ± 3.8 Hemoglobin A1c, %, mean ± SD 7.4 ± 0.8 Type of insulin used, % Humalog 53.8 Novolog 38.5 Apidra 7.7 SD, standard deviation. and post-lunch (approximately 13:00-20:00). Glucose metrics were assessed as the percentage of time spent in an approximately normoglycemic range (70-180 mg/dl), a hyperglycemic range (> 180 mg/dl), and a hypoglycemic range (< 70 mg/dl) while in closed-loop control. Other calculated metrics included the mean glucose for all participants. Results Participant Characteristics The characteristics of the 13 participants who completed the study are summarized in Table 2. Insulin Infusion Characteristics of the HHM System The HHM System took significant preemptive, mitigating action prior to below-zone excursions (defined as the 15 minutes prior to a below-zone CGM breach) by delivering, on average, 77.2% less insulin than basal during these times (Table 3). The HHM System did not significantly increase dosing relative to basal in the times prior to above-zone excursions. During below-zone excursions, an average decrease of 80.4% in HHM System insulin infusion rates was observed compared with basal rates. During above-zone excursions an average increase of 39.9% in HHM System insulin infusion rates was observed compared with basal rates. 11 The algorithm response did not result in a significant increase or decrease in overall total daily dose relative to the participants basal/bolus therapy regimens, but rather in a redistribution of insulin delivery based on CGM data. There was a 10.6% increase in the average HHM System insulin infusion rate compared with the average basal rate. During the overnight period, the post-breakfast period, and the postlunch period the average HHM System infusion rate was 6.6%, 18.8%, and 3.8% greater than the average basal rate, respectively. The HHM System s insulin infusion rates stayed at approximately basal-level rates for 9.7% of the total time spent in closed-loop control, were higher than basal rates 47.4% of the time, and were lower 42.9% of the time. Overall, the average HHM System insulin infusion rate was 27% lower than that recommended by the Zone-MPC, reflecting the ability of the SSM to attenuate the insulin dose recommendations to mitigate the risk of hypoglycemia. The reductions in infusion rates by the SSM were 33.1% in the overnight period, 22.6% in the post-breakfast period, and 20.6% in the post-lunch period. Glucose Metrics Glucose metrics were calculated including the periods of deliberate underinsulinization and overinsulinization. Based on YSI measurements, participants spent on average 0.2 ± 0.5% of the closed-loop control time at glucose levels < 70 mg/dl and 69.6 ± 24.7% of the closed-loop control time at glucose levels 70-180 mg/dl (Table 4). During the overnight period, participants spent 0.3 ± 0.9% of the time < 70 mg/dl and 81.8 ± 35.6% of the time between 70 and 180 mg/dl. During the post-breakfast and post-lunch periods, participants spent 0.3 ± 1.1% and 0% of the time < 70 mg/dl, respectively. 11 Based on CGM measurements, participants spent on average 0.5 ± 1.2% of the closed-loop control time at glucose levels < 70 mg/dl and 62.2 ± 20.2% of the closedloop control time at glucose levels 70-180 mg/dl (Table 5). During the overnight period, participants spent 0.1 ± 0.3% of the time < 70 mg/dl and 80.0 ± 27.5% of the time between 70 and 180 mg/dl. During the post-breakfast and post-lunch periods, participants spent 1.5 ± 3.8% and 0% of the time < 70 mg/dl, respectively. 11 The mean ± SD glucose value based on YSI was 164.5 ± 23.5 mg/dl; the mean ± SD based on CGM was 175.1 ± 27.3 mg/dl. 12 For CGM excursions < 70 mg/dl (n = 3), the average area between the CGM curve and the threshold of 70 mg/dl was 0.35 mg/dl day overall and 1.69 mg/dl day for the postbreakfast period. 12 For excursions > 180 mg/dl, the average area between the CGM curve and the threshold of 180 mg/dl was 19.5 mg/dl day overall, 12.5 mg/dl day for the overnight period, 30.0 mg/dl day for the post-breakfast period, and 25.1 mg/dl day for the post-lunch period. Following initiation of closed-loop control, and leading up to the breakfast meal, there was an evident narrowing of the ± 1 SD band in the CGM tracings (Figure 2), indicating the HHM System s ability to control glucose to near-normoglycemic values during the overnight period. Based on YSI, the mean ± SD meal peaks for the breakfast and lunch meals were 241 ± 47 mg/dl and 200 ± 50 mg/dl, respectively, and based on CGM they were 265 ± 63 mg/dl and 224 ± 51 mg/ dl, respectively. Safety Events Under closed-loop control, there were a total of nine instances when the investigator administered algorithm-recommended CHO, which was 15 g of juice or glucose tablets (Table 6). Four of these instances occurred in one participant (participant 12). There were no instances of investigator-initiated
Finan et al 39 Table 3. Ability of the Hypoglycemia-Hyperglycemia Minimizer (HHM) System Algorithm to Modulate Insulin Delivery, Relative to the Participants Corresponding Basal Rates, Both Prior to and During Out-of-Zone Glucose Excursions. Below-zone excursions (n = 10) Above-zone excursions a (n = 27) Basal rate (mean ± SD; U/h) HHM rate (mean ± SD; U/h) % change from basal (mean) Basal rate (mean ± SD; U/h) HHM rate (mean ± SD; U/h) % change from basal (mean) Before excursions 0.77 ± 0.09 0.18 ± 0.33 77.2 0.70 ± 0.21 0.71 ± 0.79 +1.6 During excursions 0.84 ± 0.19 0.16 ± 0.36 80.4 0.90 ± 0.35 1.26 ± 1.14 +39.9 SD, standard deviation. a These metrics exclude the 60-minute period after meals due to the confounding effects of the meals and corresponding insulin boluses. Table 4. YSI Metrics While Under Closed-Loop Control: Percentage of Time Spent in Glucose Ranges of < 70 mg/dl, 70-180 mg/dl, and > 180 mg/dl. % of time spent Overall Overnight, 00:00-07:00 Postbreakfast, 07:00-13:00 Postlunch, 13:00-20:00 Participant <70 70-180 >180 <70 70-180 >180 <70 70-180 >180 <70 70-180 >180 1 a 0 95.3 4.7 0 100 0 0 85.7 14.3 0 100 0 2 a 0 41.8 58.2 0 75.6 24.4 0 12.3 87.7 0 28.8 71.2 3 a 0 72.6 27.4 0 100 0 0 63.4 36.6 0 46.5 53.5 4 a 0 68.4 31.6 0 94.4 5.6 0 68.1 31.9 0 23.1 76.9 5 1.3 78.2 20.5 3.4 96.6 0 0 76.7 23.3 0 56.3 43.7 6 0 21.5 78.5 0 1.6 98.4 0 38 62 0 21.3 78.7 7 0 72.5 27.5 0 98.9 1.1 0 48.6 51.4 0 63.9 36.1 8 0 26.2 73.8 0 4.4 95.6 0 58.3 41.7 0 20 80 9 0 89.9 10.1 0 100 0 0 67.1 32.9 0 100 0 10 0 88.7 11.3 0 91.8 8.2 0 63.6 36.4 NA NA NA 11 0 73.5 26.5 0 100 0 0 12.5 87.5 0 100 0 12 1.3 81.5 17.2 0 100 0 4.1 39.7 56.2 0 100 0 13 a 0 95.3 4.7 0 100 0 0 84.5 15.5 0 100 0 Average 0.2 69.6 30.2 0.3 81.8 17.9 0.3 55.3 44.4 0 63.3 36.7 Standard deviation 0.5 24.7 24.8 0.9 35.6 35.7 1.1 24.1 23.9 0 35.0 35.0 NA, not applicable. a Indicates subjects who were deliberately under- and overbolused by 30% for breakfast and lunch, respectively. CHO administration (i.e., when the algorithm was not recommending CHO administration). There was one instance of investigator-initiated treatment for hyperglycemia, per protocol requirement (glucose level >300 mg/dl for 1 hour by YSI). At the time of this insulin dose, CGM glucose was decreasing, ketones were 0.1 mmol/l, and the participant was asymptomatic. Protocol-defined glucose-related safety events (severe hypoglycemia or diabetic ketoacidosis) did not occur in any study participants. There was one adverse device effect related to bruising and bleeding at sensor insertion site (an expected event), which occurred prior to the CRC visit. Continuous-Glucose-Monitoring-Related Issues There were 128 total instances of missed CGM samples (on average, 9.8 samples per participant). These missed CGM samples were due to radiofrequency communication issues or other communication issues related to the investigational setup, or due to display of??? on the CGM receiver, indicating that the sensor is sending glucose readings but the receiver does not understand. The longest consecutive string of 10 missed CGM samples was due to device communication malfunction. For many participants, the longest string of missed samples was only 1 or 2 samples (corresponding to 5 or 10 minutes real time), indicating that the algorithm is able to cope with some missing data and carry on safely. Discussion This feasibility study evaluated the performance of the HHM System in participants with type 1 diabetes in a CRC setting. This study demonstrated that the HHM System was able to
40 Journal of Diabetes Science and Technology 8(1) Table 5. Continuous Glucose Monitor Metrics While Under Closed-Loop Control: Percentage of Time Spent in Glucose Ranges of < 70 mg/dl, 70-180 mg/dl, and > 180 mg/dl. % of time spent Overall Overnight, 00:00-07:00 Postbreakfast, 07:00-13:00 Postlunch, 13:00-20:00 Participant <70 70-180 >180 <70 70-180 >180 <70 70-180 >180 <70 70-180 >180 1 a 0 76.6 23.4 0 100 0 0 63.6 36.4 0 61.4 38.6 2 a 0 30.8 69.2 0 56.7 43.3 0 8.2 91.8 0 20.5 79.5 3 a 0 69.7 30.3 0 98.9 1.1 0 59.2 40.8 0 42.3 57.7 4 a 2.3 56.7 40.9 0 75.6 24.4 6.9 59.7 33.3 0 19.2 80.8 5 0 74.8 25.2 0 100 0 0 64.4 35.6 0 53.5 46.5 6 0 53.1 46.9 0 82.3 17.7 0 70.4 29.6 0 12.0 88.0 7 0 51.9 48.1 0 77.3 22.7 0 36.1 63.9 0 36.1 63.9 8 0 20.2 79.8 0 0 100 0 51.4 48.6 0 12.9 87.1 9 0 85.7 14.3 0 100 0 0 75.3 24.7 0 77.8 22.2 10 1.0 81.4 17.5 1.2 78.8 20.0 0 100 0 NA NA NA 11 0 53.4 46.6 0 94.6 5.4 0 6.9 93.1 0 45.8 54.2 12 3.8 72.3 23.9 0 97.8 2.2 12.3 27.4 60.3 0 84.5 15.5 13 a 0 82.0 18.0 0 78.0 22.0 0 71.8 28.2 0 97.1 2.9 Average 0.5 62.2 37.2 0.1 80.0 19.9 1.5 53.4 45.1 0 46.9 53.1 Standard deviation 1.2 20.2 20.4 0.3 27.5 27.5 3.8 27.0 26.4 0 28.8 28.8 NA, not applicable. a Indicates subjects who were deliberately under- and overbolused by 30% for breakfast and lunch, respectively. Table 6. Administrations of Algorithm-Recommended Supplemental Carbohydrates. Instance (sequentially) Participant YSI value at administration (mg/dl) CGM value at administration (mg/dl) 1 3 100.3 83 2 3 99.6 102 3 4 110.4 93 4 5 67.3 85 5 11 105.0 102 6 12 77.0 93 7 12 73.7 84 8 12 76.1 52 9 12 66.7 39 Mean ± SD 86.2 ± 17.3 81.4 ± 21.8 Figure 2. Average Hypoglycemia-Hyperglycemia Minimizer (HHM) System results for all participants (n = 13). Upper plot: Glucose levels (mean ± standard deviation) based on continuous glucose monitoring (CGM). Also shown are the nominal meal times. The shaded area is the approximately normoglycemic range (70-180 mg/dl). Lower plot: HHM System determined insulin delivered during closed-loop control, as a percentage difference from the participants respective basal rates (mean ± standard deviation). modulate insulin delivery based on CGM readings, and was effective in taking preemptive action to mitigate near-future Each administration was 15 g of juice or glucose tablets. CGM, continuous glucose monitor; SD, standard deviation. below-zone excursions by delivering less insulin than the corresponding preprogrammed basal rates. The algorithm appeared to redistribute insulin delivery based on CGM data, without significantly altering the overall total daily basal dose. To mitigate out-of-zone excursions, the HHM System decreased insulin infusion rates by an average of 80.4% during below-zone excursions and increased infusion rates by an average of 39.9% during above-zone excursions.
Finan et al 41 The efficacy of the HHM System is further supported by the glucose data, which demonstrate that the system was able to maintain participants glucose in the approximately normoglycemic range (70-180 mg/dl) most of the time (an average of 69.6% overall and 81.8% overnight, as measured by YSI) with very little time spent in the hypoglycemic range (< 1% of time with glucose levels < 70 mg/dl, as measured by both YSI and CGM). The safety data also support the feasibility of the HHM System. During the study, there were no instances of severe hypoglycemia or diabetic ketoacidosis, no instances of investigator-initiated CHO administration, and only one instance of investigator-initiated treatment for hyperglycemia. The nine instances of investigator-administered algorithmrecommended CHO served as a preliminary evaluation of the algorithm s warning capabilities, which will unquestionably be an important part of the overall HHM System. Although there were 128 instances of missed CGM samples (due to device communication or display issues, including related to investigational set-up), the algorithm was able to cope with the missing data and carry on safely. Recent studies have also demonstrated feasibility of overnight closed-loop control systems in clinical settings. 2,3,16,17 As in the current study, these studies demonstrate the feasibility of maintaining a majority of patients in (near) normoglycemia while mitigating the risk of hypoglycemia during defined periods of closed-loop control. Limitations of this research are inherent in a feasibility study and include the small sample size, the relatively short term of observation, and the artificial, sedentary CRC-based environment. As the study design included adjustment of food and insulin variables, the glucose outcomes need to be interpreted with caution. Conclusions The results of this study indicate that the HHM System is a feasible foundation for development of a closed-loop control insulin delivery device; further studies are under way. Abbreviations CGM, continuous glucose monitor; CHO, carbohydrate; CRC, clinical research center; FDA, Food and Drug Administration; HHM, Hypoglycemia-Hyperglycemia Minimizer; SD, standard deviation; SSM, Safety Supervision Module; Zone-MPC, Zone Model Predictive Controller. Authors Note ClinicalTrials.gov identifier: NCT01401751. Acknowledgments The authors would like to thank JDRF and the staff of Sansum Diabetes Research Institute for their participation in this study. The authors received editorial support from Excerpta Medica for preparation of this article. Parts of the study were presented as poster presentations at the 72nd Scientific Sessions of the American Diabetes Association (ADA), Philadelphia, PA (June 8-12, 2012) and at the 48th Annual Meeting of the European Association for the Study of Diabetes (EASD), Berlin, Germany (October 1-5, 2012). Declaration of Conflicting Interests The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Daniel A. Finan, Thomas W. McCann Jr, and Ramakrishna Venugopalan are employees of Animas Corporation. Linda Mackowiak and Henry Anhalt were employees of Animas Corporation at the time of execution of the study. Henry Anhalt is currently employed by Sanofi. Linda Mackowiak is a limited stockholder of Medtronic, Abbott, and Edwards Lifesciences. Eyal Dassau has received product support from Insulet Corporation. Stephen D. Patek and Francis J. Doyle III have no conflict of interest. Boris P. Kovatchev has acted on the advisory board/consulted for Animas Corporation and Sanofi-Aventis; and has received research grant and product support from Animas Corporation, Insulet Corporation, Roche Diagnostics, Sanofi-Aventis, and Tandem Diabetes Care. Howard Zisser has received honoraria for scientific lectures and travel reimbursement from Animas Corporation, Cellnovo, Insulet Corporation, MannKind Corporation, and Roche; and research grant and product support from Animas Corporation, Abbott Laboratories, Dexcom Inc, Eli Lilly and Co, GluMetrics Inc, Insulet Corporation, LifeScan Inc, Medtronic Inc, Novo Nordisk, Roche, and Sanofi; and is a board member of Artificial Pancreas Technologies. Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by JDRF and Animas Corporation. References 1. Kowalski AJ. Can we really close the loop and how soon? 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