The objective of this observational study is to explore microcirculation in healthy volunteers and in ventilated patients in the operating room and in critical care.

The general objective of this study is to evaluate microcirculation with photoplethysmography (PPG) in different pathophysiological situations and to compare PPG with available standard methods. Specifically, evaluate the correlation between the determinations of AC-DC waves obtained by Photoplethysmography (PPG) and those obtained in different dynamic tests in healthy volunteers.

To compare microcirculation assessments [capillary refill time (CRT), perfusion index (PI), perfusion index variability (PIV)] with measurements obtained by PPG in the context of critically ill patients.

To compare microcirculation assessments (CRT, PI PVI) with measurements obtained by PPG in the context of patients on invasive mechanical ventilation (IMV) in the operating room and in critical care.

An attempt is made to explore different physiological aspects that affect microcirculation such as vascular tone and blood volume.

Photoplethysmography usually examines the AC wave equivalent to the pulsatile wave, however the DC component has been less explored and can account for the microcirculation and volemia status of the subjects.

Since there is no gold standard, it will be compared against different validated methods.

Healthy Volunteers:

Inclusion Criteria:

• Written informed consent.
• Age > 18 years.

Exclusion Criteria:

• Pregnancy.
• Smokers.
• Respiratory and/or cardiovascular pathologies.
• Peripheral vascular disease.

Operation room or Critical care Unit patients

Inclusion criteria:

• Written informed consent.
• Age > 18 years.
• Critical patients ventilated in the ICU of any origin.

Exclusion criteria:

• Known peripheral vascular disease.
• Burns on both upper limbs.
• Trauma to both upper limbs.

healthy volunteers or operating room or intensive care patients- See inclusion and exclusion criteria