CHECK-NIRS2D-Study

The study is a prospective, monocentric, controlled experimental study in healthy volunteers. It examines how external conditions, physiological states, and everyday behaviors influence measurements obtained with two-dimensional near-infrared spectroscopy (2D-NIRS). The imaging method is intended to assess local tissue oxygenation and microvascular perfusion non-invasively.

Detailed study description

1. General purpose The CHECK-NIRS2D study is a prospective, monocentric, controlled experimental study conducted at the University Hospital Düsseldorf. It investigates how external conditions, physiological states, and behavioral factors influence measurements of local tissue oxygenation obtained using two-dimensional near-infrared spectroscopy (2D-NIRS). The study uses the SnapshotNIR camera system (KD203, Kent Imaging Inc., Calgary, Canada). This non-invasive method produces spatially resolved images of tissue oxygenation, allowing the investigators to examine not only the overall oxygenation of a tissue region but also possible differences in perfusion between individual areas. The study is intended as physiological and methodological research. It does not evaluate the therapeutic efficacy or safety of the device and does not provide a direct medical benefit to participants. Its longer-term objective is to develop a standardized protocol for future studies involving patients with acute or chronic diseases, particularly in emergency and intensive-care medicine.
2. Participants The study plans to include healthy adults:

• Age: 20-40 years
• Male and female participants
• Voluntary written informed consent after detailed explanation
• No acute illness at the time of examination
• No relevant cardiovascular, pulmonary, renal, vascular, or neurological history
• No relevant disease, previous surgery, or acute pathology affecting the examined upper limb
• Resting oxygen saturation of at least 95%
• No relevant resting hypotension or hypertension Participants who regularly use medication affecting the cardiovascular system or blood coagulation, as well as pregnant or breastfeeding participants, are excluded. Five substudies, designated A-E, are planned. Approximately 20 participants per experimental group are intended. Participants may take part in more than one substudy, but this is voluntary. The order of experimental protocols is randomized, and a recovery period of at least 60 minutes is planned between measurements of the same extremity, except where the caffeine- and nicotine-specific protocols require a different arrangement.

1. General examination procedure

The examinations generally take place with the participant sitting upright. The arm to be examined is positioned beside the body, with the palm facing upwards and the elbow approximately at the level of the lower end of the sternum.

The following measurements are generally performed:

• 2D-NIRS imaging of the hand or upper extremity
• Measurement of regional and microvascular tissue oxygenation.
• Repeated imaging during baseline, temporary ischemia, and reperfusion.
• Vascular occlusion test (VOT)
• A pneumatic blood-pressure cuff is inflated to 200 mmHg.
• The radial pulse is checked at one-minute intervals to confirm interruption of arterial blood flow.
• Depending on the protocol, the occlusion lasts three, five, or six minutes.
• The cuff is then deflated, allowing reperfusion of the extremity.
• Blood-pressure measurement
• Systolic blood pressure
• Diastolic blood pressure
• Mean arterial pressure
• Pulse oximetry
• Measurement of peripheral oxygen saturation, or SpO₂.
• Heart-rate measuremen
• Capillary reperfusion time
• Assessment of the time required for capillary perfusion to return.
• Subjective pain assessment
• Pain or discomfort during the vascular occlusion test is recorded using a Numeric Rating Scale (NRS).
• Confocal retinal funduscopy
• In specified experimental groups, the retinal microcirculation is examined using fully automated, confocal funduscopy.

Depending on the substudy, this is performed at baseline and at the end of the experiment or repeatedly during control measurements.

During the standard VOT protocols, heart rate, blood pressure, SpO₂, and pain are generally recorded at one-minute intervals. NIRS imaging and capillary reperfusion measurements are performed at shorter intervals during ischemia and early reperfusion, including every 30 seconds during ischemia and during the first five minutes after reperfusion begins.

The protocol includes:

• Smokers and non-smokers
• VOT and control conditions
• Measurements after abstinence
• A specific acute nicotine-exposure condition in smokers
• NIRS imaging, VOT-related measurements, blood pressure, heart rate, SpO₂, pain assessment, and capillary reperfusion measurements are performed. In selected groups, retinal funduscopy is conducted at the beginning and end of the experiment.