| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 School of Kinesiology, University of Western Ontario, London, Ontario N6A 3K7; and 2 Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
Arterial hypocapnia has been associated with
orthostatic intolerance. Therefore, we tested the hypothesis that
hypocapnia may be detrimental to increases in muscle sympathetic nerve
activity (MSNA) and total peripheral resistance (TPR) during head-up
tilt (HUT). Ventilation was increased ~1.5 times above baseline for each of three conditions, whereas end-tidal
PCO2 (PETCO2) was clamped at normocapnic (Normo), hypercapnic (Hyper; +5 mmHg relative to
Normo), and hypocapnic (Hypo; 
5 mmHg relative to Normo) conditions. MSNA (microneurography), heart rate, blood pressure (BP, Finapres), and
cardiac output (Q, Doppler) were measured continuously during supine
rest and 45° HUT. The increase in heart rate when changing from
supine to HUT (P < 0.001) was not different across
PETCO2 conditions. MSNA burst
frequency increased similarly with HUT in all conditions
(P < 0.05). However, total MSNA and the increase in
total amplitude relative to baseline (%
MSNA) increased more when
changing to HUT during Hypo compared with Hyper (P < 0.05). Both BP and Q were higher during Hyper than both Normo and Hypo (main effect; P < 0.05). Therefore, the MSNA response
to HUT varied inversely with levels of
PETCO2. The combined data suggest that augmented cardiac output with hypercapnia sustained blood pressure during HUT leading to a diminished sympathetic response.
muscle sympathetic nerve activity; head-up tilt; end tidal CO2; cardiac output; total peripheral vascular resistance
This article has been cited by other articles:
|
|
 |
|
  R. D. Thijs, J. G. van den Aardweg, R. H. A. M. Reijntjes, J. G. van Dijk, and J. J. van Lieshout Contrasting effects of isocapnic and hypocapnic hyperventilation on orthostatic circulatory control J Appl Physiol, October 1, 2008; 105(4): 1069 - 1075. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. H. Simmons, J. M. Manson, and J. R. Halliwill Mild central chemoreflex activation does not alter arterial baroreflex function in healthy humans J. Physiol., September 15, 2007; 583(3): 1155 - 1163. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. C. Tzeng, P. D. Larsen, and D. C. Galletly Effects of hypercapnia and hypoxemia on respiratory sinus arrhythmia in conscious humans during spontaneous respiration Am J Physiol Heart Circ Physiol, May 1, 2007; 292(5): H2397 - H2407. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. M. Stewart, M. S. Medow, N. S. Cherniack, and B. H. Natelson Postural hypocapnic hyperventilation is associated with enhanced peripheral vasoconstriction in postural tachycardia syndrome with normal supine blood flow Am J Physiol Heart Circ Physiol, August 1, 2006; 291(2): H904 - H913. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Kitano, J. K. Shoemaker, M. Ichinose, H. Wada, and T. Nishiyasu Comparison of cardiovascular responses between lower body negative pressure and head-up tilt J Appl Physiol, June 1, 2005; 98(6): 2081 - 2086. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Howden, J. T. Lightfoot, S. J. Brown, and I. L. Swaine The effects of breathing 5% CO2 on human cardiovascular responses and tolerance to orthostatic stress Exp Physiol, July 1, 2004; 89(4): 465 - 471. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Laitinen, L. Niskanen, G. Geelen, E. Lansimies, and J. Hartikainen Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects J Appl Physiol, June 1, 2004; 96(6): 2333 - 2340. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
