title: Forearm vascular and neuroendocrine responses to graded water immersion in humans.
abstract: The hypothesis that graded expansion of central blood volume by water immersion to the xiphoid process and neck would elicit a graded decrease in forearm vascular resistance was tested. Central venous pressure increased (P < 0.05) by 4.2 +/- 0.4 mmHg (mean +/- SEM) during xiphoid immersion and by 10.4 +/- 0.5 mmHg during neck immersion. Plasma noradrenaline was gradually suppressed (P < 0.05) by 62 +/- 8 and 104 +/- 11 pg mL-1 during xiphoid and neck immersion, respectively, indicating a graded suppression of sympathetic nervous activity. Plasma concentrations of arginine vasopressin were suppressed by 1.5 +/- 0.5 pg mL-1 (P < 0.05) during xiphoid immersion and by 2.0 +/- 0.5 pg mL-1 during neck immersion (P < 0.05 vs. xiphoid immersion). Forearm subcutaneous vascular resistance decreased to the same extent by 26 +/- 9 and 28 +/- 4% (P < 0.05), respectively, during both immersion procedures, whereas forearm skeletal muscle vascular resistance declined only during neck immersion by 27 +/- 6% (P < 0.05). In conclusion, graded central blood volume expansion initiated a graded decrease in sympathetic nervous activity and AVP-release. Changes in forearm subcutaneous vascular resistance, however, were not related to the gradual withdrawal of the sympathetic and neuroendocrine vasoconstrictor activity. Forearm skeletal muscle vasodilatation exhibited a more graded response with a detectable decrease only during immersion to the neck. Therefore, the forearm subcutaneous vasodilator response reaches saturation at a lower degree of central volume expansion than that of forearm skeletal muscle.
authors.affiliation: Danish Aerospace Medical Centre of Research, National University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: A
authors.initials: A
authors.lastname: Gabrielsen
authors.forename: R
authors.initials: R
authors.lastname: Videbaek
authors.forename: L B
authors.initials: LB
authors.lastname: Johansen
authors.forename: J
authors.initials: J
authors.lastname: Warberg
authors.forename: N J
authors.initials: NJ
authors.lastname: Christensen
authors.forename: B
authors.initials: B
authors.lastname: Pump
authors.forename: P
authors.initials: P
authors.lastname: Norsk
mesh_terms: D000328:Adult; D001127:Arginine Vasopressin / Q000097:blood; D001794:Blood Pressure / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D005542:Forearm / Q000098:blood supply / Q000294:innervation; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D009490:Neurosecretory Systems / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D012039:Regional Blood Flow / Q000502:physiology; D012083:Renin / Q000097:blood; D012084:Renin-Angiotensin System / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology; D014867:Water
chemical_list: D014867:Water; D001127:Arginine Vasopressin; D012083:Renin; D009638:Norepinephrine; D004837:Epinephrine