Influence of age on syncope following prolonged exercise: differential responses but similar orthostatic intolerance
Author
Murrell, Carissa J.
Cotter, James D.
George, Keith
Shave, Rob
Wilson, Luke
Thomas, Kate
Williams, Michael J.
Lowe, Tim
Ainslie, Philip N.
Date
2009Type
Article
Publisher
Wiley
ISSN
0022-3751
Metadata
Show full item recordAbstract
Orthostatic tolerance is reduced with increasing age and following prolonged exercise. The aim of this study was to determine the effect of age on cardiovascular and cerebrovascular responses to orthostatic stress following prolonged exercise. Measurements were obtained before, and within 45 min after, 4 h of continuous running at 70–80% of maximal heart rate in nine young (Y; 27 ± 4 years; inline image 59 ± 10 ml kg−1 min−1) and twelve older (O; 65 ± 5 years; inline image 46 ± 8 ml kg−1 min−1) athletes. Middle cerebral artery blood flow velocity (MCAv; transcranial Doppler ultrasound), blood pressure (BP; Finometer) and stroke volume (SV) were measured continuously whilst supine and during 60 deg head-up tilt for 15 min or to pre-syncope. Orthostatic tolerance was reduced post-exercise (tilt completed (min:s, mean ±s.d.): Pre, 14:39 ± 0:55; Post, 5:59 ± 4:53; P < 0.05), but did not differ with age (P > 0.05). Despite a 25% higher supine MCAv in the young, MCAv at syncope was the same in both groups (Y: 34 ± 10 cm s−1; O: 32 ± 13; P > 0.05). Although the hypotensive response to syncope did not differ with age, the components of BP did; SV was lowered more in the young (Y: –57 ± 16%; O: –34 ± 13%; P < 0.05); and total peripheral resistance was lowered in the older athletes but was unchanged in the young (Y: +8 ± 10%; O: –21 ± 12%; (at 10 s pre-syncope) P < 0.05). Despite a lower MCAv in the older athletes, time to syncope was similar between groups; however, the integrative mechanisms responsible for syncope did differ with age. The similar MCAv at pre-syncope indicates there is an age-independent critical cerebral blood flow threshold at which syncope occurs.
Journal/conference proceeding
The Journal of Physiology;
Citation
Murrell, C., Cotter, J.D., George, K., Shave, R., Wilson, L., Thomas, K., Williams, M.J., Lowe, T. and Ainslie, P.N. (2009) 'Influence of age on syncope following prolonged exercise: differential responses but similar orthostatic intolerance', The Journal of Physiology, 587(24), pp.5959-5969.
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