The impact of passive heat treatment on glycaemic response during an oral glucose tolerance test in diabetic patients

Type 2 diabetes mellitus (T2DM) is a metabolic disease with a rapidly
increasing incidence world-wide. The disease is characterized by a decreased
glucose tolerance as a result of insulin resistance, resulting in poor blood
glycaemic control. Blood glucose lowering medications are widely available, but
their effect stagnates as T2DM progresses. New treatment regimens are required
to combat the disease. Although therapies such as physical exercise have been
shown to induce beneficial effects on glycaemic control in T2DM patients, not
all patients are able to perform exercise. Passive heating treatment (PHT)
might be an alternative strategy to reduce insulin resistance, as it has been
postulated to have comparable effects on the cardiovascular system as exercise.
PHT has been linked to numerous health benefits, including improved
cardiovascular- and pulmonary function, pain alleviation and metabolic health.
In addition, long term use of PHT shows promising effects on glycaemic control
in T2DM patients. However, the acute effects of PHT on glucoregulation are yet
to be determined.

To assess the acute impact of passive heat treatment on the post-prandial
glycaemic response during an OGTT in T2DM patients.

Crossover, randomized, controlled trial

Participants will be subjected to two infrared sauna bathing (heated and
non-heated) sessions. Glycaemic control will be assessed during following both
sessions by performing an OGTT. Body mass, body temperature, blood pressure,
and heart rate will be monitored during the sessions. Blood samples will be
collected throughout the sessions to assess glucose and insulin concentrations,
and plasma volume.

The risks associated with participation are minimal. The burden can be
considered as low, considering the time investment of the participants and test
day procedures involved. Participants will visit the University for one
screening and two test days (1 week interval). The first visit will involve a
screening visit (~2 h), during which the eligibility of the participant will be
assessed. During the screening visit, a medical questionnaire is filled out and
a bioelectrical impedance (BIA) scan will be performed to assess body
composition, which does not cause any discomfort for the participant.
Participants will not be allowed to eat, drink (except water in small amounts),
perform strenuous exercise for 8 hours prior to the screening session.
Participants will participate in two *PHT test days* of ~4-5h. Insertion of the
catheters during test days is comparable to a normal blood draw and the only
risk is a small local hematoma. During each experimental test day, 8 blood
samples (~80mL/day) will be obtained. The total amount of blood collected
during this study (~160 mL) is far less than the amount of a blood donation
(500 mL) and will be completely restored in less than 1 month.
For each *PHT test day* visit participants are required to come to the
university in a fasted state, not having consumed any food or beverages (except
for water) as from 22:00 the evening before. Participants are required to eat a
standardized meal the evenings preceding each test days. Also, 2 days prior to
the experimental test days participants need to record their food intake and
activities performed. During these 2 days participants are not allowed to
perform heavy physical exercise or drink alcohol.
A commercially available infrared sauna will be used for the PHT-intervention.
Participants will perform 2 PHT session (heated and non-heated). Each session
will last 40 minutes. For diabetic older adults, there is a minor risk of being
exposed to this PHT-protocol. Dehydration and excessive sweating might
influence blood pressure and could cause hyper- or hypoglycemia. To monitor
this risk, finger prick equipment will be available to assess glucose levels in
case a participant indicates not feeling well. In addition, blood pressure
measurement will be performed. Subjects will be provided with a rehydration
protocol to replace the fluid that was lost during the PHT session after the
OGTT. PHT is known to be associated with many different health benefits
including improved blood pressure, metabolic profile, relaxation, reduced pain
sensation and reduced cardiovascular risk.
Core body will be monitored using an ear thermometer. This is safe,
non-invasive and easy to use. Skin temperature will be measured using iButton,
a peripheral thermometry device applied on the skin, which is also non-invasive
and safe to use.