ISSN:
1439-6327
Keywords:
Transcranial Doppler ultrasound
;
Endtidal carbon dioxide tension
;
Dynamic exercise
;
Oxygen uptake
;
Anaerobic threshold
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary Cerebral blood flow has been reported to increase during dynamic exercise, but whether this occurs in proportion to the intensity remains unsettled. We measured middle cerebral artery blood flow velocity (νm) by transcranial Doppler ultrasound in 14 healthy young adults, at rest and during dynamic exercise performed on a cycle ergometer at a intensity progressively increasing, by 50 W every 4 min until exhaustion. Arterial blood pressure, heart rate, end-tidal, partial pressure of carbon dioxide (P ETCO2), oxygen uptake ( $$\dot V$$ O2) and carbon dioxide output were determined at exercise intensity. Mean vM increased from 53 (SEM 2) cm · s−1 at rest to a maximum of 75 (SEM 4) cm · s−1 at 57% of the maximal attained $$\dot V$$ O2( $$\dot V$$ O2max), and thereafter progressively decreased to 59 (SEM 4) cm · s−1 at $$\dot V$$ O2max. The respiratory exchange ratio (R) was 0.97 (SEM 0.01) at 57% of $$\dot V$$ O2maxand 1.10 (SEM 0.01) at $$\dot V$$ O2max. The P ETCO2 increased from 5.9 (SEM 0.2) kPa at rest to 7.4 (SEM 0.2) kPa at 57% of $$\dot V$$ O2maxand thereafter decreased to 5.9 (SEM 0.2) kPa at $$\dot V$$ O2max. Mean arterial pressure increased from 98 (SEM 1) mmHg (13.1 kPa) at rest to 116 (SEM 1) mmHg (15.5 kPa) at 90% of $$\dot V$$ O2max, and decreased slightly to 108 (SEM 1) mmHg (14.4 kPa) at $$\dot V$$ O2max. In all the subjects, the maximal value of v m was recorded at the highest attained exercise intensity below the anaerobic threshold (defined by R greater than 1). We concluded that cerebral blood flow as evaluated by middle cerebral artery flow velocity increased during dynamic exercise as a function of exercise intensity below the anaerobic threshold. At higher intensities, cerebral blood flow decreased, without however a complete return to baseline values, and it is suggested that this may have been at least in part explained by concomitant changes in arterial PCO2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00377701
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