title: Circulating N-terminal brain natriuretic peptide and cardiac function in response to acute systemic hypoxia in healthy humans.
abstract: BACKGROUND
  As it remains unclear whether hypoxia of cardiomyocytes could trigger the release of brain natriuretic peptide (BNP) in humans, we investigated whether breathing normobaric hypoxic gas mixture increases the circulating NT-proBNP in healthy male subjects.
  
  
  METHODS
  Ten healthy young men (age 29 ± 5 yrs, BMI 24.7 ± 2.8 kg/m2) breathed normobaric hypoxic gas mixture (11% O2/89% N2) for one hour. Venous blood samples were obtained immediately before, during, and 2 and 24 hours after hypoxic exposure. Cardiac function and flow velocity profile in the middle left anterior descending coronary artery (LAD) were measured by Doppler echocardiography.
  
  
  RESULTS
  Arterial oxygen saturation decreased steadily from baseline value of 99 ± 1% after the initiation hypoxia challenge and reached steady-state level of 73 ± 6% within 20-30 minutes. Cardiac output increased from 6.0 ± 1.2 to 8.1 ± 1.6 L/min and ejection fraction from 67 ± 4% to 75 ± 6% (both p < 0.001). Peak diastolic flow velocity in the LAD increased from 0.16 ± 0.04 to 0.28 ± 0.07 m/s, while its diameter remained unchanged. In the whole study group, NT-proBNP was similar to baseline (60 ± 32 pmol/ml) at all time points. However, at 24 h, concentration of NT-proBNP was higher (34 ± 18%) in five subjects and lower (17 ± 17%), p = 0.002 between the groups) in five subjects than at baseline.
  
  
  CONCLUSIONS
  In conclusion, there is no consistent increase in circulating NT-proBNP in response to breathing severely hypoxic normobaric gas mixture in healthy humans, a possible reason being that the oxygen flux to cardiac myocytes does not decrease because of increased coronary blood flow. However, the divergent individual responses as well as responses in different cardiac diseases warrant further investigations.
authors.affiliation: Turku PET Centre, University of Turku and Turku University Hospital, PO Box 52, FI-20521 Turku, Finland. ilkka.heinonen@utu.fi.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Heinonen
authors.forename: Matti
authors.initials: M
authors.lastname: Luotolahti
authors.forename: Olli
authors.initials: O
authors.lastname: Vuolteenaho
authors.forename: Mikko
authors.initials: M
authors.lastname: Nikinmaa
authors.forename: Antti
authors.initials: A
authors.lastname: Saraste
authors.forename: Jaakko
authors.initials: J
authors.lastname: Hartiala
authors.forename: Juha
authors.initials: J
authors.lastname: Koskenvuo
authors.forename: Juhani
authors.initials: J
authors.lastname: Knuuti
authors.forename: Olli
authors.initials: O
authors.lastname: Arjamaa
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D006334:Heart Function Tests; D006801:Humans; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism; D020097:Natriuretic Peptide, Brain / Q000097:blood*
chemical_list: D015415:Biomarkers; D020097:Natriuretic Peptide, Brain