Evaluation of CGMS during
Pressure changes
Johan Jendle, MD, PHD
Peter Adolfsson, MD
Hans Örnhagen, MD, PHD
Page reference
Introduction 3-4
Aim 4
Hypothesis 4
Resources 5
Protocol 5-6
Method 6
Method statistics 7
Responsibility 7
Meetings 7
Financial plan 8
Strategy presentation and publication 8
References 9
Introduction
Risk of hypoglycemia is a major concern for divers with diabetes. A severe hypoglycemic event could lead to reduced consciousness and subsequent risk of drowning which also could be fatal and cause severe problems for the diving partner. In many countries, recreational diving is an absolute contraindication for type 1 and type 2 diabetes requiring insulin treatment. A fair estimation is that at least 100.000 out of 10 million active divers are on insulin treatment.
The observational data that have been published speak in favour of the safety of divers with type 1 diabetes. The Divers Alert Network (DAN) conducted a voluntary survey where 48,663 dives by 110 divers with diabetes were reported (1). The Diving Diseases Research Centre (DDRC) in the UK performed a study collecting data from 230 divers with diabetes with 5348 logged dives (2). No deaths and no episodes of decompression illness (DCI) were the results. Hypoglycaemic events were present in very small numbers.
A repetitive monitoring schedule pre-dive assessing glucose levels via finger pricking at planned times of 60, 30 and 10 min pre-dive and immediately post-dive was developed by George Burghen, Camp DAVI (Diabetes Association of the Virgin Islands), and these guidelines were tested by Lerch et al. (3).
This monitoring schedule is recommended for all divers with diabetes.
However it only tells the result at a specific time, not the rate or direction of the glucose values
The Continuous Glucose Monitoring System (CGMS, Medtronic, Minneapolis, MN, US) offers an opportunity to assess the glucose levels in different contexts. The value of continuous glucose monitoring (CGM) in the management of type 1 diabetes was recently evaluated and this evaluation revealed that the use of CGM was associated with improved metabolic control in motivated adults (4).
In a recently published article (5), we reported that the use of downloaded SMBG, CGMS and repetitive PG in a monitoring schedule, has been shown to be a useful tool to identify those subjects who are suitable for diving.
In a later submitted article (6) we show that CGMS can be used with a high degree of accuracy in diving conditions. The signals provided by the CGMS were not interrupted during any of the 117 dives.
All the monitors used in this study were tested in a pressure chamber prior to the study. All the monitors displayed good function and no mechanical damage during the safety test, performed to a depth of 24 m.
Another application for CGMS which is in sharp contrast to diving is the use at lower atmospheric pressure – during flying.
Ageing cabin personnel has increased risk of having type 2 diabetes. The method of treatment is often either oral medicine or insulin. Some of the oral antidiabetic drugs used increases the risk of hypoglycaemia and some do not. The rules and regulations for cabinpersonal with diabetes is not updated to the modern antidiabetic drugs with low risk of hypoglycaemia ie. DPP-4 inhibitors, GLP-1 analogues and metformin. There is also a large individual variation regarding the frequency of hypoglycaemia when being treated with sulfonylurea or insulin.
In summary, hypoglycaemia is a risk factor during diving as well as during flying. An event of hypoglycaemia during such circumstances could be dangerous for the individual as well as other people.
By using CGMS events of hypoglycaemia could be detected but also decreased with the introduction of preventing strategies.
By using real time CGM even more hypoglycaemic events could be avoided.
However, at this point, paired values during diving or during increased pressure have not been evaluated. This kind of evaluation is necessary in order to use the CGM-technique for the development of strategies to achieve safer diving for those individuals with diabetes.
Aim
A test in a pressure chamber will be performed.
The performance of sensors and sensors together with monitors will be evaluated.
This test will show if the CGMS could be used to show reliable glucose values in conditions with changes in ambient pressure.
Producing glucose values accurately, the CGMS could be used in order to measure glucose variability in diving conditions as well as in a situation with at fall in pressure such as under flight conditions.
The use of a real-time monitor in the same conditions could lead to further improvements. Glucose values as well as the rate of glucose changes could then be presented. Alarms could be used to alert the individual to impending hypoglycaemia or actual hypoglycaemia prior to the planned activity, as well as during diving/flying. The aim of improved diving safety for people with type 1 diabetes could then be realised, also cabin personnel with diabetes could be evaluated with respect of the risk of hypoglycaemia during flying.
Hypothesis
Sensors produce reliable results during increased pressure whether or not the sensors are pre-wetted or not before insertion performed prior to increased pressure.
Sensors used together with monitors produce and shows reliable results before, during and after increased pressure.
Resources
The acquired resources are;
- Responsible for the project
- Medical doctors
- Nurse
- Physician at the pressure chamber
- Statistician
- Economy
- Graphic designer
- Sensors and monitors
- Calibration probes
- Glucose solution
- Pressure chamber
Protocol
The study is performed during two days.
First, all monitors (24) are tested together with calibration probes during decreased pressure corresponding to 5500 m followed by increased pressure until max depth corresponding to 30 m.
The calibration probes are to be set on three different levels corresponding to glucose levels representing hypo-, eu- and hyperglycaemia.
Secondly, all monitors (24) are tested together with sensors in a glucose solution. The same change of pressure is planned as above.
Thirdly, half of the sensors are pre-wetted while the other half is not, before insertion. Four individuals wear 6 sensors and monitors each. The test will be preformed in the pre-prandial state. The same change of pressure is planned as above.
All values are downloaded with CGMS software and then transferred to excel.
Statistics is performed with SPSS software.
Method
The study is prospective and performed in two different sections.
First at technical part and secondly a part including test on individuals.
Comparisons are made between fixed glucose levels (hypo-, eu- and hyperglycaemia), and those shown by the monitors during moment one (see protocol).
Comparisons are made between fixed glucose levels (glucose solution) and those glucose levels produced by sensors together with monitors during moment two.
During moment three comparisons are made between glucose levels produced by the CGMS and corresponding glucose levels produced by HemoCue – capillary measurements.
The study is performed during the first quarter of 2009.
Statistical Methods
Statistical comparisons are made between each type of glucose values.
A t-test is used for overall comparison.
A paired t-test is used for comparison between pre-wetted and not pre-wetted sensor surface.
The ANOVA-test is used for comparisons between each of the three parts as well as the results during increased and decreased pressure.
Responsibility
Johan Jendle, MD PhD, is responsible for the project.
Peter Adolfsson, MD, is assisting the project.
Hans Örnhagen, MD PhD, is responsible for the technical procedures as well as the procedures in the pressure chamber.
Meetings
Meeting occasions;
· Project planing
· Before start of Project
· Project
· After Project – results, statistics, presentation
Financial plan
Strategy presentation and publication
The aim is to present the results at an international conference and in an international journal.
The aim is to present and publish the results during 2009.
References
1 Dear G de L, Pollock NW, Ugguccioni DM, Dovenbarger J, Feinglos MN, Moon RE: Plasma glucose response to recreational diving in divers with insulin-requiring diabetes. Undersea Hyperb Med. 31:291-301, 2004
2 Edge C, St Ledger-Dowse M, Bryson P: Scuba diving with diabetes mellitus. The UK experience 1991-2001. UHMS. 32:27-37, 2005
3 Lerch M, Lutrop C. Thurm U: Diabetes and diving: can the risk of hypoglycemia be banned? SPUMS J. 26:62-66, 1996
4 The Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group. Continuous Glucose Monitoring and Intensive Treatment of Type 1 diabetes. N Engl J Med. 2008;359:1464-1476
5 Adolfsson P, Örnhagen H, Jendle J. The Benefits of Continuous Glucose Monitoring and a Glucose Monitoring Schedule in Individuals with Type 1 Diabetes during Recreational Diving. Journal of Science and Technology 2008;2:778-784
6 Adolfsson P, Örnhagen H, Jendle J. Accuracy and Functionality of Continuous Glucose Monitoring in individuals with Type 1 Diabetes during Recreational Diving
Submitted to Diabetes Technology & Therapeutics Jan. 2009
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