SLIDE 1
Brunel University London
Brunel University London
Brain or leg level
Perfusion pressurebrain/leg = VO2 brain/leg= Blood flowbrain/leg x a-vO2 diff X Vascular Resistancebrain/leg
- Ohm’s law
Cerebral and leg blood flow during exercise: influence of hydration - - PowerPoint PPT Presentation
Cerebral and leg blood flow during exercise: influence of hydration - - PowerPoint PPT Presentation
Cerebral and leg blood flow during exercise: influence of hydration and heat stress Jos Gonzlez-Alonso Physiological demand influences the brain and leg blood flow responses to dehydration, hyperthermia and combined
SLIDE 2
SLIDE 3
Brunel University London
Water losses from different compartments – example 4% body weight loss or 2.8 kg
2.8 L sweat loss
~0.3 L ~1.1 L ~1.5 L
Plasma Interstitial Intracellular 4%
DECREASE IN BODY WEIGHT (70 kg person)
SLIDE 4
Brunel University London
Impact of exercise-induced dehydration
≈ 4 l/min ≈ 2 l/min
González-Alonso et al. J Physiol 513: 895-905, 1998
SLIDE 5
Brunel University London
Trangmar et al. Am J Physiol Heart Circ Physiol 309:H1598-H1607, 2015
Dehydration also reduces cerebral blood flow
36±6%
≈ 120 min at 55% VO2max Ta = 35ºC; rh = 50%; fan cooling Internal Carotid Artery Blood Flow (L/min) Control euhydration Progressive dehydration
CMRO2 = CBF x a-vO2 diff ?
SLIDE 6
Brunel University London
Leg a-vO2 diff (ml/l) Legs VO2 (l/min) Time (min)
- Time (min)
Brain a-vO2 diff (ml/l) CMRO2 (ml/min)
Trangmar et al. Am J Physiol Heart Circ Physiol 309:H1598-H1607, 2015 González-Alonso et al. J Physiol 513: 895-905, 1998
Leg VO2 = LBF x (CaO2- CfvO2)
- ≈
CMRO2 = CBF x a-vO2 diff ≈
Leg and cerebral O2 extraction and O2uptake
SLIDE 7
Brunel University London
Determinants of leg and brain blood flow
BF = Vascular Conductance x Perfusion Pressure ? ?
SLIDE 8
Brunel University London
Mechanisms reducing leg blood flow with dehydration
Noradrenaline (nmol/L) Adrenaline (nmol/L) Time (min) Time (min) Mean Arterial Pressure (mmHg) Leg Vascular Conductance (U) Time (min)
*† *†
González-Alonso et al. J Physiol 513: 895-905, 1998
SLIDE 9
Brunel University London
Mechanisms of leg blood flow decline ?
LBF = Leg Vascular Conductance ≈ x MAP
Arterial O2 content (ml/l) Time (min)
SLIDE 10
Brunel University London
Mechanisms of cerebral blood flow decline?
Cerebral blood flow (l/min) Trangmar et al. Am J Physiol Heart Circ Physiol 309:H1598-H1607, 2015
SLIDE 11
Brunel University London
Systemic level
VO2 = Q x a-vO2 diff
- ?
?
SLIDE 12
Brunel University London
VO2 = Q x a-vO2 diff
- ≈
Systemic response to submaximal exercise
González-Alonso et al. J Physiol 513: 895-905, 1998
SLIDE 13
Brunel University London
Dehydration at rest and low intensity exercise
SLIDE 14
Brunel University London
Effects of dehydration at rest and small muscle mass exercise
3 4
Rest Exercise
Pearson et al. Eur J Appl Physiol 113:1499–1509, 2013
Rest Knee-extensor exercise
SLIDE 15
Brunel University London
Mechanisms controlling perfusion
Vasoconstrictor Activity Vasodilator Activity
SLIDE 16
Brunel University London
Much greater vasoconstrictor activity during whole body exercise – cycling
Pearson et al. Eur J Appl Physiol 113:1499–1509, 2013 González-Alonso et al. J Physiol 513: 895-905, 1998
SLIDE 17
Brunel University London
MSNA and circulating NA increase exponentially with increasing exercise intensity
Ichinose et al. J Physiol 586: 2753-2766, 2008 Rosenmeir et al. J Physiol 558:351-365, 2004
SLIDE 18
Brunel University London
Mechanisms reducing stroke volume with dehydration?
Cardiac output Heart rate End-diastolic volume
?
End-systolic volume
?
≈
- r
Stroke volume
- r
SLIDE 19
Brunel University London
Dehydration reduces SV by diminishing cardiac filling
SV = EDV - ESV
Stöhr et al. J Appl Physiol 111: 891-897, 2011
- Fig. 2. Comparison of the effect of dehydration and rehydration on left
3 4
Rest Exercise
Trangmar & González-Alonso Exerc Sports Sci Rev 45(3): 146– 153, 2017
SLIDE 20
Brunel University London
Dehydration and submaximal cardiovascular capacity
Trangmar & González-Alonso. Sports Med 49 (Suppl 1):S69–S85, 2019
SLIDE 21
Brunel University London
Heat stress exercise and exercise-induced dehydration
SLIDE 22
Brunel University London
Heat stress during incremental cycling
Rowell et al. J Clin Invest 1966
26°C 43°C
SLIDE 23
Brunel University London
Whole body heat stress
Passive heat stress and limbs and head perfusion
Chiesa et al. Integrative human cardiovascular responses to hyperthermia, In: Périard JD & Racinais S (eds.) Heat Stress in Sport and Exercise. Springer, Cham. p. 45-65, 2019
SLIDE 24
Brunel University London
Combined small vs. large muscle mass (incremental) exercise heat stress and leg blood flow
Chiesa et al. Am J Physiol Heart Circ 2015 Trangmar et al. Physiol Rep 2017
SLIDE 25
Brunel University London
Dehydration and whole-body hyperthermia can drastically reduce VO2max
- Nybo et al. J Appl Physiol 90: 1057–1064, 2001
Cycling ≈ 400 W
- 15% VO2max
- 50% endurance
performance
- 0.7 l/min
SLIDE 26
Brunel University London
Heat stress and maximal whole body exercise
González-Alonso & Calbet. Circulation 107:824-830.2003
Leg VO2 = LBF x (CaO2- CfvO2)
SLIDE 27
Brunel University London
Dehydration impact on the brain
Trangmar et al. J Physiol 592: 3143–3160, 2014
CMRO2 = CBF x a-vO2 diff
SLIDE 28
Brunel University London
Maintained cerebral aerobic metabolism
Trangmar et al. J Physiol 592: 3143–3160, 2014
SLIDE 29
Brunel University London
Impact of dehydration and heat stress on maximal cardiovascular and aerobic capacity
Trangmar & González-Alonso. Sports Med 49 (Suppl 1):S69–S85, 2019
SLIDE 30
Brunel University London