A diminished aortic-cardiac reflex during hypotension in aerobically fit young men.
We compared the aortic-cardiac baroreflex sensitivity in eight average fit (AF: VO2max = 44.7 +/- 1.3 ml.kg-1 x min-1) and seven high fit (HF: VO2max = 64.1 +/- 1.7 ml.min-1 x kg-1) healthy young men during hypotension elicited by steady state sodium nitroprusside (SN) infusion. During SN mean arterial pressure (MAP) was similarly decreased in AF (-12.6 +/- 1.0 mm Hg) and HF (-12.1 +/- 1.1 mm Hg). However, the increases in heart rate (HR) were less (P < 0.023) in HF (15 +/- 3 bpm) than AF (25 +/- 1 bpm). When sustained neck suction (NS, -22 +/- 1 torr in AF and -20 +/- 1 torr in HF, P > 0.05) was applied to counteract the decreased carotid sinus transmural pressure during SN, thereby isolating the aortic baroreceptors, the increased HR remained less (P < 0.021) in HF (8 +/- 2 bpm) than AF (16 +/- 2 bpm). During both SN infusion and SN+NS, the calculated gains (i.e., delta HR/delta MAP) were significantly greater in AF (2.1 +/- 0.3 and 1.3 +/- 0.2 bpm.mm Hg-1) than HF (1.2 +/- 0.2 and 0.6 +/- 0.2 bpm.mm Hg-1). However, the estimated carotid-cardiac baroreflex sensitivity (i.e., the gain difference between the stage SN and SN + NS) was not different between AF (0.7 +/- 0.2 bpm.mm Hg-1) and HF (0.6 +/- 0.1 bpm.mm Hg-1). These data indicated that the aortic-cardiac baroreflex sensitivity during hypotension was significantly diminished with endurance exercise training.
Shi
X
X
Department of Physiology, Texas College of Osteopathic Medicine, Fort Worth 76107-2699.
Crandall
C G
CG
Potts
J T
JT
Williamson
J W
JW
Foresman
B H
BH
Raven
P B
PB
D000328:Adult; D001011:Aorta / Q000187:drug effects / Q000502:physiology*; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002346:Carotid Sinus / Q000187:drug effects / Q000502:physiology; D002496:Central Venous Pressure / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007022:Hypotension / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D008297:Male; D009333:Neck; D009599:Nitroprusside / Q000008:administration & dosage / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology*; D011312:Pressure; D012146:Rest / Q000502:physiology
D009599:Nitroprusside