title: Cardiovascular and hormonal responses to bicycle exercise during lower body negative pressure.
abstract: The purpose was to combine bicycle exercise and LBNP as a model to investigate the mechanisms regulating circulation during gravitational stresses.
  
  
  METHODS
  Cardiac Output (CO) by acetylene-, argon-, oxygen rebreathing; Heart Rate (HR) from ECG; Mean Arterial Pressure (MAP) by arm cuff; Plasma Nor-Epinephrine (NE), Epinephrine (E), and Lactate (HLa) by isotope and enzymatic techniques respectively. Total Peripheral Resistance (TPR) = MAP/CO and stroke volume (SV) = CO/HR. Six subjects exercised at 180-200 Watts in the upright position on a mechanically braked computer controlled small bicycle ergometer placed in a LBNP box. The above parameters were measured at rest and at 5 and 9 min of exercise without and with LBNP at -30 or -40 mmHg (depending on LBNP tolerance).
  
  
  CONCLUSIONS
  In the face of an increased sympathetic nervous activity (NE+E,TPR, and HR increased) during exercise in LBNP, there was a decrease in CO and SV indicating that the venous return was insufficient. However, HLa was unchanged demonstrating that the blood flow to the working muscles did not suffer.
authors.affiliation: August Krogh Institute, University of Copenhagen, Denmark.
authors.forename: F
authors.initials: F
authors.lastname: Bonde-Petersen
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: N J
authors.initials: NJ
authors.lastname: Christensen
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D004837:Epinephrine / Q000097:blood / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008150:Lower Body Negative Pressure; D008297:Male; D009638:Norepinephrine / Q000097:blood / Q000378:metabolism; D013318:Stroke Volume / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*
chemical_list: D019344:Lactic Acid; D009638:Norepinephrine; D004837:Epinephrine