Phase 2: Inclusion criteria: Patients admitted to acute hospitalization, with risk of skin integrity deterioration assessed by Braden scale (punctuation lower than 16) without pressure ulcers, who agree to participate in the study. Exclusion criteria: presence infusion of vasoactive drugs at the time of the study (dopamine, epinephrine, norepinephrine, dobutamine, nitroprusside, nitroglycerin, calcium channel blockers, ACE inhibitors). Regular oral treatment of alpha and beta-blockers and/or agonists or calcium channel blockers, nitrates, ACE inhibitors, angiotensin, renin inhibitors, diuretics, SSRIs, NSAIDs, will be accepted. Also patients with pacemakers and/or implanted defibrillator, fever, anemia with Hb <10g/dl, hypotension with systolic blood pressure <80 mmHg, presence of transfusions in the past 4 weeks, consumption and derivatives of erythropoietin, iron supplements, oral or parenteral anticoagulants will be excluded.