Pain is an unpleasant sensory and emotional phenomenon that can be caused by tissue damage or potentially harmful stimuli. Pain is by definition a subjective phenomenon, and everyone experiences it differently, which creates problems in its assessment and treatment. There are many ways to measure pain, both through patient self-report (scales) and objective physiological indicators. However, there is no single, universal tool for measuring pain intensity that is simultaneously reliable, valid, and easy to use. Moreover, there are reports showing that not only the intensity of the unpleasant experience but also the nature of the stimulus can cause different levels of changes in the used indicators and scales. In this project, we will compare two devices used for pain monitoring based on physiological parameters: PainMonitor (Med-Storm, Oslo, Norway) and ANI Monitor (MetroDoloris, Loos, France). PainMonitor is a device that records skin conductance (SC) as an indicator of pain intensity. SC reflects the level of autonomic nervous system arousal. The device automatically analyzes these parameters and provides a numerical indicator of pain intensity/anesthesia level. The ANI Monitor is a device based on the analysis of parasympathetic nervous system activity through heart rate variability analysis. Based on this, the device also assesses the degree of pain intensity and presents it in numerical form. The aim of the project is to investigate the correlation between PainMonitor and ANI as tools for measuring pain intensity in situations where healthy volunteers are exposed to various unpleasant stimuli.

The study will involve approximately 100 healthy adult participants who will be exposed to three types of standardized stimuli: thermal (hot and cold), mechanical (pressure from a blood pressure cuff, pressure on a skin fold), chemical (spicy taste), and visual. Simultaneously, they will be monitored by PainMonitor, ANI, ECG, and peripheral perfusion index (using pulse oximetry). This data will then be compared and subjected to statistical analysis to determine if there is a relationship between the nature of the stimuli used and the objective and subjective indicators of pain intensity.

Stimuli (the order of stimuli 1-4 will be electronically randomized), with a break time between stimuli of 5-10 minutes:

1. NON-INVASIVE BLOOD PRESSURE MEASUREMENT: Non-invasive blood pressure measurement (NIBP) (single automatic blood pressure measurement using a Phillips IntelliVue Monitor).
2. HEAT: A metal cube with a temperature of 45 degrees Celsius will be used for heat stimulation. The cube will be applied for 60 seconds to the inner side of the forearm of the participant's dominant hand. The appropriate temperature of the cube will be maintained by keeping it in a water bath.
3. ALGOMETER: For mechanical stimulation, the researcher will apply pressure to the skin fold between the second and third fingers of the dominant hand using an algometer. The pressure will gradually increase from 0 to 250-300 kilo Pascal (kPa) and be maintained for 60 seconds.
4. VISUAL STIMULUS: For visual stimulation, a video will be shown on a display in front of the participant, depicting a model having a short intravenous cannula inserted. Participants will be asked to imagine that the hand on the screen is their own.
5. COLD: "Cold pressor test" - The participant's forearm will be immersed in water at a temperature of 2 degrees Celsius for 60 seconds or until discomfort causes the participant to withdraw their hand.
6. SPICY TASTE: 0.5 ml of spicy sauce with a specified amount of Scoville units will be applied to the participant's tongue using a syringe.

Inclusion Criteria:

• American Society of Anesthesiology (ASA) general condition assessment 1 or 2
• age 18 - 40 yrs

Exclusion Criteria:

• any arrhythmia,
• taking medications from the groups of beta-blockers, gabapentinoids, benzodiazepines, painkillers within the last 12 hours,
• chronic pain conditions,
• pregnancy,
• trypanophobia (fear of needles)