การออกก าล งก บภาวะขาดน าในม า

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1 การออกก าล งก บภาวะขาดน าในม า (Exercise & Dehydration in the Horse) Prawit Butudom ประว ทย บ ตรอ ดม สพ.บ. (เก ยรต น ยม), MS, PhD ภาคว ชาอาย รศาสตร คณะส ตวแพทยศาสตร มหาว ทยาล ยขอนแก น

2 Racing & Equestrian Disciplines

3 Factors affecting performance Musculoskeletal/Cardio vascular/respiratory Fluid/Electrolyte loss & Acid base imbalance Thermoregulation Exhausted Horse Syndrome Heat retention Fluid & electrolyte loss Acid base imbalance Intramuscular glycogen depletion

4 Fluid, Electrolyte and Acid base Response to Exercise Racehorses/Polo/Jumping Three Day Event Endurance horses Intensity and duration of exercise have a major impact on physiologic changes Influenced by training, diet, medications and climate (hot/humid)

5 Thoroughbred Racing

6 Thoroughbred Racing Maximal Supramaximal exercise (VO 2 max 100%), m (1 2 min) 20 30% anaerobic metabolism (Eaton, 1994) Body fluid loss is not critical. (Hodgson et al. 1993; Scott et al. 1999) 20 C, 50% RH BW loss = 0.8% Sweat rate ~ 6 10 ml/m 2 /min K +, Ca 2+, Phosphate, Na +, Cl Acid base disturbance is likely a problem. FATIGUE

7 Intramuscular Acidosis & Fatigue (Hyppa & Poso 1993) Fuel + O 2 work + acid + heat + CO 2 + H 2 O

8 Thoroughbred Racing Acid base disturbance Blood lactate mmol/l (~ 1 mmol/l at rest) (Bayly et al. 1987; Harris & Snow, 1988) Intramuscular acidosis (Lovell et al. 1987) Metabolic acidosis (Carlson, 1995) A key determinant of sprint performance Buffer capacity The extrudtion of H + from muscle cells

9 Thoroughbred Racing Treatments affecting fluid, electrolyte, and acid base Dietary cation anion anion balance (DCAB) Sodium Bicarbonate Milk Shake Furosemide Under hot and high humidity, BW fluid & electrolyte lose could be a factor that may limit sprint performance.

10 2 nd Equestrian Disciplines nd day Three day event Speed & Endurance test km distance 20 60% VO 2 max Aerobic+Anaerobic Endurance ride Endurance ride > 20 km Prolonged low intensity < 50%VO 2 max aerobic metabolism

11 Physiological changes w/ prolonged low/moderate intensity exercise metabolic rate & heat production Fuel + O 2 work + acid + heat + CO 2 + H 2 O 70 80% of metabolic heat is dissipated. evaporation (sweat) ~ 70% respiration ( RR) ~ 20 25% (Hodgson et al. 1993)

12 Mechanism of Heat transfer (McConaghy 1993)

13 Sweat Composition Human sweat hypotonic to plasma [Na + ] = mmol/l (Convertino et al. 1996) Equine Sweat nearly isotonic to plasma [Na + ] = mmol/l, [K + ] ~ 28 mmol/l, [Cl ] ~ 160 mmol/l (McCutcheon and Goer, 1996) Horses lose more electrolytes with each liter of sweat produced. Attenuates Posm&[Na + ] less thirst

14 Fluid & electrolyte changes w/ prolonged low/moderate intensity exercise Sweating rate : L/hr (Carlson, 1983) Fluid & electrolyte depletion CCI**** 3 day event w/ C, RH 50 55% ~ 2 hr (McCutcheon & Goer, 1996) Fluid loss (sweat) ~ 19 liters Na + & Cl loss ~ 6500 mmol Hypochloremic metabolic alkalosis (Schott and Hinchcliff, 1993) Respiratory alkalosis (Bayly et al. 1995)

15 Dehydration and Bwt Loss Horses competing in 3 day events and endurance rides lose 3 7% BW (Lawrence et al. 1992; Ecker and Lindinger, 1993; Andrews et al. 1994: Schott et al. 1996, 1997). 3 4% BW loss persisted after overnight recovery period (Schott et al. 1996, 1997). BW loss is an accurate estimate of fluid loss in exercising horses (Kingston et al. 1998)

16 Factors limiting endurance performance Fluid & electrolyte depletion (Dehydration) Thermoregulation (Heat load) Energy depletion

17 Dehydration: What are the real danger?

18 What if human athletes dehydrated? Physiological consequences of hypohydration (Sawka, M.N. 1992) exercise performance ( aerobic power, critical value = 3% BW lost (temperate), 2 4% BW lost (hot climate) thermoregulation function (Hypohydration sweating rate as Tc, linearly Tc by 0.15 C for each 1% BW)

19 What if a horse is dehydrated? The metabolic heat load of an endurance horse (speed 8 m/s) would increase Tc ~ 21 C/hr if no heat were dissipated (Guthrie and lund, 1998) Endurance horses lost L/hr (Carlson, 1983) Hypohydration sweating & heat dissipation Fatigue occurs in horses when Tc ~ 42 C & Trectal ~ 40 C (Hodgson et al, 1993, 1994) exercise performance (aerobic power)???

20 Dehydrated horses Limitation to continued performance during prolonged endurance exercise (Schott & Hinchcliff, 1993; Schott et al., 1997) hyperthermia exhaustion, blood flow metabolic disorders Medical problems associated with dehydration Exhaustive Horse Syndrome (Carlson, 1983,1985) Exhaustion & SDF (Schott et al., 1997) Colic, Laminitis, SDF (Fowler, 1979) Postexertional Ileus (Schott&Charlton, 1996) Death (2 horses) WEG, France Sept, 2002????

21 Dehydration associated medical problems Dehydration is an important risk factor for heat exhaustion and associated medical problems during and after prolonged exercise (Carlson, 1985; Goer&McCutcheon, 1996; Schott&Charlton, 1996). Estimated that horses annually suffer from heat related exhaustion or illness (1996 endurance rides (AERC) & day events (USCTA) (Dr. Harold Schott II, Michigan State University, Personal communication, 2002)

22 Exercise under hot & humid conditions? Hodgson et al. (1993) (~20 C, 50% RH) Metabolic heat Tc 38.5 C sweating 40%VO 2 max sweating rate ~ 20 ml/m 2 /min Sweat must be evaporated to heat High ambient tempt & RH (>30 C, >90% RH)???? Sweating rate ~ 50% ( sweat production ~ 100%) (Schott, 2002) increase fluid & electrolyte loss, increase Thermal load Significant problem to a horse???

23 Hot & humid conditions Contributions of equine exercise physiology research to the success of the 1996 Equestrian Olympic Games (Jeffcott & Kohn, High ambient tempt & RH (>30 C, >90% RH) fluid, electrolyte loss & Bwt loss (Harris et al. 1995; McCutcheon et al. 1995) heat production & thermal load Slow recovery (Jones & Carlson, 1995; Kohn & Hinchcliff, 1995) run time ~ 56% (Goer et al. 1995)

24 Effect of Ta and RH on Tc & cooling during endurance test, 3 day event (Kohn & Hinchcliff 1995) Rectal Temp Respiratory rate

25 Atlanta, Goergia,, USA July, C, >90% RH Equestrian Olympic Games 1996

26 Strategies to risk of heat related problems under hot & humid conditions Acclimatisation Modification of the endurance test test severity mandatory halt Environmental monitoring Heat index Wet bulb globe temp index (WBGT) Preventative fluid loading/rehydration Aggressive cooling to heat dissipation Shading and multiple misting fans

27 Environmental Monitoring Heat Index Ta(F) + % RH >150 evaporative cooling > 180 = ineffective cooling (Mackay Smith & Cohen 1982) WBGT < 28 > 33 not a safe competition (Schroter & Marlin 1995)

28 Misting Fans & Shading, Atlanta 1996

29 Aggressive Cooling Stand quitely 15 C C water Bathing w/ cold/ice water (Khon et al. 1995, 1999b) (Marlin et al. 1998) Whole body cooling ( water 9 C) 9 Vs Regional cooling (31 C) 9 C C water decrease 10, 15, 20, 25 min after exercise (P<0.05) (Williamson et al. 1995) No deleterious effects of cooling No myopathy

30 Clinical observation at the 1996 Atlanta Olympic Games 2 of 99 horses were stopped on course or immediately after Phase D for excessive fatigue. No horse experienced heat related problems during the competition. The 1996 Olympic Games were a veterinary success. Dr. Jon Foreman FEI & Olympic Vet Vet Med, U of Illinois, (Personal communication, 1996)

31 Exercise & fluid replacement

32 Humans: Water & Performance Current recommendation: forced drinking prior to onset of thirst to minimize dehydration (Sawka & Pandolf, 1990)

33 Horses: Water & Performance "You can lead a horse to water, but cannot make it drink Forced drinking: not a practical solution Management myths: common practice to limit water intake by hot horses (Hinton, 1978)

34 Strategies to increase voluntary drinking following exercise Drinking is a consequence of thirst Primary stimulus for thirst increase Posm, increase P[Na + ]; secondary stimulus hypovolemia (Anderson, 1978; Fitzsimmons, 1998) Human athletes consume sports drinks containing CHO and Na + (20 40 mmol/l) (Maughan&Shirreffs, 1994; Shirreffs et al. 1996)

35 Exercise & fluid replacement (Equine Athletes) Forced rehydration Hyperhydration 90 min before exercise (17.5L hypotonic fluid) (Leon et al. 1995) Na + containing solutions via NG tube (Hyyppä et al. 1996; Marlin et al. 1998; Geor and McCuthceon 1998) Hypertonic oral electrolyte pastes (Coenen et al. 1995; Dusterdieck et al. 1999) Voluntary drinking during & following exercise 20 C, 0.9% NaCl (Nyman et al. 1996; Butudom et al. 2002, 2003)

36 Experimental Protocol Instrumentation Start Finish End km R1 15 km R2 15 km 60 Post Exercise Furosemide 1mg/kg IV B/BW B/BW B B/BW B B B/BW B/BW initial drink (0.45% NaCl, 0.9% NaCl, water) HR

37 fluid intake (l) Fluid Intake During Recovery * WI 20 60' FI W 0.45% 0.9%

38 Bodyweight Changes bodyweight (%) * * * Furos bout 1 R1 bout 2 R2 bout 3 recovery time in hours * * + * 18 + W 0.45% 0.9% * sign diff from pre (all 3) + sign diff from 0.45% & 0.9%

39 Experimental Protocol Instrumentation Start Finish End km R1 15 km 60 Post Exercise Furosemide 1mg/kg IV B/BW B/BW B B B/BW B/BW initial drink (10 o, 20 o, or 30 o C 0.9% NaCl) HR and core temperature

40 fluid intake (l) Fluid Intake During Recovery a 14.7 a b 20.0 ab 16.3 b b a a a WI 20 60' FI C NaCl 20C NaCl 30C NaCl

41 Bodyweight Changes bodyweight (%) * * Furos bout 1 R1 bout 2 recovery time in hours * * 10 and 30 o C * sign diff from pre 10 o C 20 o C 30 o C

42 Suggested strategies for fluid & electrolyte replacement during and following exercise (Butudom 2002; Schott & Butudom 2003) An initial drink of salt water (0.9% NaCl) at near ambient tempt after exericse or at rest breaks during competition Allow horses for free access to rehydration fluids after exercise Add salts in the grain (30 g of an equal mix of table salt & lite salt) Salt water is effective for rehydration. (Dr. Davies, Vet Med, U of Melbourne, Australian Three Day Event Team Vet; Personal communication, 2002)

43 Asia ม าแข ง/ม าน กก ฬา World Equestrian Games (WEG), France, Sept 2002: 2 horses died (Drs. Robert & Lars, FEI vet, Personal communication, 2002) Is it too much for the horse? Veterinary standard? 2008 Summer Olympic Games, Beijing, China Speed & Endurance Test modification? or no competition? 6 th Int Conf. Equine Exercise Physiology, Sept, 2002, Lexington, Kentucky, USA

44 ประเทศไทย-ม าแข ง/ม าน กก ฬา BW fluid & electrolyte lose could be a factor that may limit sprint performance. fluid electrolyte disturbance in event horse Management Myth: water restriction cold water Colic/Laminitis Force Rehydration?? CCI* or CCI**, not CCI**** Veterinary standard??