title: Autonomic activity and biomarker behavior in supine position and after passive postural stress in different orthostatic intolerance syndromes.
abstract: OBJECTIVE
  Orthostatic intolerance (OI) syndromes are a confusing topic and determining a specific diagnosis to achieve optimal treatment can be troublesome. We sought to assess biomarker, hemodynamic and autonomic variables in OI patients (autonomic dysfunction [AD], postural orthostatic tachycardia syndrome [POTS] and neurally mediated syncope [NMS]) and healthy controls during supine and head-up tilt position in order to achieve a better diagnosis.
  
  
  RESULTS
  In response to head-up tilt, patients with AD presented a marked decrease in systolic blood pressure (SBP) (p=0.002), and a blunted increase in heart rate (HR) (p=0.04). Baroreceptor gain was almost absent in supine position and did not change in response to tilt. Patients with POTS had lower values of atrial natriuretic peptide (p=0.03) but similar neurohormonal biomarkers and hemodynamic and baroreceptor function in supine position compared to healthy subjects. However, in response to head-up tilting greater reductions in stroke volume (p=0.008) and baroreceptor gain (p=0.002) and greater rises in HR (p=0.001), total peripheral resistance (p=0.008), low frequency component of SBP variability (LF-SBP) (p=0.003) and plasma noradrenaline (p=0.03) were observed. Patients with NCS had similar biomarkers and autonomic indices to healthy subjects in supine position, but a larger decrease in baroreceptor gain (p=0.007) and a greater rise in LF-SBP (p=0.004) and plasma adrenaline (p=0.003) response to head-up tilting.
  
  
  CONCLUSIONS
  Although different OI syndromes share similar symptoms, including blurred vision, syncope and dizziness particularly during orthostatism, they differ markedly regarding biochemical, autonomic and hemodynamic parameters. Assessment of these differences may be helpful for better diagnosis and management.
authors: Serviço de Cardiologia, Centro Hospitalar São João, Porto, Portugal; Universidade do Porto, Faculdade de Medicina, Porto, Portugal. Electronic address: jppafreitas@gmail.com.
authors: João
authors: J
authors: Freitas
authors: Serviço de Neurologia, Centro Hospitalar São João, Porto, Portugal.
authors: Elsa
authors: E
authors: Azevedo
authors: Universidade do Porto, Faculdade de Medicina, Porto, Portugal.
authors: Rosa
authors: R
authors: Santos
authors: Serviço de Cardiologia, Centro Hospitalar São João, Porto, Portugal.
authors: Maria Júlia
authors: MJ
authors: Maciel
authors: Universidade do Porto, Faculdade de Medicina, Porto, Portugal.
authors: Francisco
authors: F
authors: Rocha-Gonçalves
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000503:physiopathology*; D015415:Biomarkers / Q000097:blood; D002395:Catecholamines / Q000097:blood; D006439:Hemodynamics; D006801:Humans; D045265:Natriuretic Peptides / Q000097:blood; D054972:Postural Orthostatic Tachycardia Syndrome / Q000097:blood / Q000503:physiopathology*; D013312:Stress, Physiological; D016683:Supine Position / Q000502:physiology*; D019462:Syncope, Vasovagal / Q000097:blood / Q000503:physiopathology*; D018667:Tilt-Table Test
chemical_list: D015415:Biomarkers; D002395:Catecholamines; D045265:Natriuretic Peptides
keywords: Autonomic nervous system; Biomarcadores; Biomarkers; Intolerância ortostática; Orthostatic intolerance; Sistema nervoso autónomo; Teste de tilt; Tilt test