TY - JOUR
T1 - Mechanisms of orthostatic intolerance following very prolonged exercise
AU - Lucas, S.J.E.
AU - Cotter, J.D.
AU - Anson, J.G.
AU - Murrell, C.
AU - Wilson, L.
AU - Ainslie, P.N.
AU - Gaze, D.
AU - George, K.P.
PY - 2008/7/1
Y1 - 2008/7/1
N2 - Nine men completed a 24-h exercise trial, with physiological testing sessions before (T1, ∼0630), during (T2, ∼1640; T3, ∼0045; T4, ∼0630), and 48-h afterwards (T5, ∼0650). Participants cycled and ran/trekked continuously between test sessions. A 24-h sedentary control trial was undertaken in crossover order. Within testing sessions, participants lay supine and then stood for 6 min, while heart rate variability (spectral analysis of ECG), middle cerebral artery perfusion velocity (MCAv), mean arterial pressure (MAP; Finometer), and end-tidal PCO (PETCO ) were measured, and venous blood was sampled for cardiac troponin I. During the exercise trial: 1) two, six, and four participants were orthostatically intolerant at T2, T3, and T4, respectively; 2) changes in heart rate variability were only observed at T2; 3) supine MAP (baseline = 81 ± 6 mmHg) was lower (P <0.05) by 14% at T3 and 8% at T4, whereas standing MAP (75 ± 7 mmHg) was lower by 16% at T2, 37% at T3, and 15% at T4; 4) PET was reduced (P <0.05) at all times while supine (-3-4 Torr) and standing (-4-5 Torr) during exercise trial; 5) standing MCAv was reduced (P <0.05) by 23% at T3 and 30% at T4 during the exercise trial; 6) changes in MCAv with standing always correlated (P <0.01) with changes in PET (r = 0.78-0.93), but only with changes in MAP at T1, T2, and T3 (P <0.05; r = 0.62- 0.84); and 7) only two individuals showed minor elevations in cardiac troponin I. Recovery was complete within 48 h. During prolonged exercise, postural-induced hypotension and hypocapnia exacerbate cerebral hypoperfusion and facilitate syncope.
AB - Nine men completed a 24-h exercise trial, with physiological testing sessions before (T1, ∼0630), during (T2, ∼1640; T3, ∼0045; T4, ∼0630), and 48-h afterwards (T5, ∼0650). Participants cycled and ran/trekked continuously between test sessions. A 24-h sedentary control trial was undertaken in crossover order. Within testing sessions, participants lay supine and then stood for 6 min, while heart rate variability (spectral analysis of ECG), middle cerebral artery perfusion velocity (MCAv), mean arterial pressure (MAP; Finometer), and end-tidal PCO (PETCO ) were measured, and venous blood was sampled for cardiac troponin I. During the exercise trial: 1) two, six, and four participants were orthostatically intolerant at T2, T3, and T4, respectively; 2) changes in heart rate variability were only observed at T2; 3) supine MAP (baseline = 81 ± 6 mmHg) was lower (P <0.05) by 14% at T3 and 8% at T4, whereas standing MAP (75 ± 7 mmHg) was lower by 16% at T2, 37% at T3, and 15% at T4; 4) PET was reduced (P <0.05) at all times while supine (-3-4 Torr) and standing (-4-5 Torr) during exercise trial; 5) standing MCAv was reduced (P <0.05) by 23% at T3 and 30% at T4 during the exercise trial; 6) changes in MCAv with standing always correlated (P <0.01) with changes in PET (r = 0.78-0.93), but only with changes in MAP at T1, T2, and T3 (P <0.05; r = 0.62- 0.84); and 7) only two individuals showed minor elevations in cardiac troponin I. Recovery was complete within 48 h. During prolonged exercise, postural-induced hypotension and hypocapnia exacerbate cerebral hypoperfusion and facilitate syncope.
UR - http://www.scopus.com/inward/record.url?partnerID=yv4JPVwI&eid=2-s2.0-50649084362&md5=43553b724fa9e9eb031f6028f00427f7
U2 - 10.1152/japplphysiol.00175.2008
DO - 10.1152/japplphysiol.00175.2008
M3 - Article
AN - SCOPUS:50649084362
SN - 8750-7587
VL - 105
SP - 213
EP - 225
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 1
ER -