Cardiovascular Physiology and Response to Exercise

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Cardiovascular Physiology and Response to Exercise

• AVS 435 Equine Exercise Physiology

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• http//video.csupomona.edu/REBray/435.htm

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• Muscles youneed to know
• Medial gluteal
• Vastus lateralis

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• Semimenbranosus
• Semitendinosus
• Biceps femoris
• Gracilis

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• Required reading
• EEP Marlin
• Chapter 6, pgs 55-72
• Chapter 10, pgs 113 126
• EEP Hinchcliff
• Chapter 4.1 pgs 212 -

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• Review of heart anatomy
• Flow of blood RA gt RV gtlungs gtLA gt LV
  gtsystemiccirculation

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• Ventricles
• Majority oftissue mass
• Providesprimarypropulsion
• LV wallsthicker thanRV

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• TB heart average 4 -5 kg
• Phar Lap (1926) 6.4 kgs (14 lbs)
• Eclipse (1764) 6.4 kgs (14 lbs)
• Secretariat (1970) 10 kgs (22 lbs)
• 1 kg 2.2 lbs 1 lb .454 kgs, or 454 g
• There will be a metric conversion question on the
  exam, no calculators!

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• Heart tissue 0.9 of body mass in TBs
• 0.76 in Arabians
• 0.67 stock horses
• 0.62 in draft breeds

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• Left ventricle
• More musclemass
• Thicker walls
• Generatesmore force/pressure
• Mm Hg
• Systemiccirculation

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• Right ventricle
• Less musclemass
• Thinner walls
• Generatesless force/pressure
• Pulmoniccirculation

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• Atria
• Thin walls
• Collectiondepot
• Only needs togenerateenough forceto pump
  bloodfrom atrium tocorrespondingventricle

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• Ultrasound to evaluate heart
• Structure, function
• Absolute/relative measurement of walls, chamber
  size, septum
• Abnormalities, defects
• Integrity/function valves
• Vessels
• Stenosis, dilatation, defects

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• Ultrasound
• Transducerproducessound wavethatpenetratessof
  t tissue
• Producesreflection at fluid/tissue interfaces to
  produce image

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• Fluidconductssoundwithoutcausingreflectiongt
  black
• hypoechoic

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• Softtissueis denser,reflectsmoresoundgt
  whiter,echogenic
• Muscle,membrane,connective tissue, organ tissue
• Not bone

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• Doppler measures sound conduction
• Used toevaluateblood flow,velocity,direction,
  turbulence
• Ex. valvedisease,murmur

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• LV gt aorta gt arteries gt arterioles
• Arterioles, level of BP regulation via smooth
  muscle, autonomic control
• Relaxation vasodilation, decrease in pressures,
  increase in blood flow
• Tighten vasoconstriction, increase pressure,
  decrease blood flow

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• Capillaries
• Virtually no muscle or CT
• Single cell wall thickness
• Facilitates exchange of products
• Gas exchange, substrates, by-products

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• Venules gt veins gt vena cava gt RA
• Blood pressures regulated on venous side of
  circulatory system
• Venodilation, venoconstriction

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• Carotid arterybranches offaorta
• Supplies headand neck
• Also distributesvia arterioles,capillaries,venu
  les, veins

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• Primary venous return from the head is via
  jugular vein
• Easily located,superficial,bilateral
• Bloodchemistries viavenipuncture

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• Carotid arterylocated deep tojugular vein
• Use tomeasurerespiratorygases
• May be raised closer to skin surface in research
  animals
• Can also use facial artery

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• How is blood reoxygenated?
• Blood leaves RV gt pulmonary artery supplying
  lungs gt arterioles gtcapillaries at level of
  alveoli
• Alveoli site of oxygen/CO2 exchange
• Venules gt veins gt pulmonary veingt LA gt LV gt
  systemic circulation

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• Cardiac muscle is electrogenic
• Generates its own electrical impulses
• Autorhythmic
• Electrical impulses arise spontaneously and
  propagate throughout tissue to stimulate
  contraction

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• Electricalimpulseoriginatesin RA inSA
  (sinoatrialnode)
• Pacemaker

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• Electricalimpulse fromSA nodetravels
  acrossboth atria,both contractsimultan-eously
• Blood ispumped fromatria intoventricles

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• Atrialcontractionmust beisolated
  fromventricularcontractionto allow forfilling

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• AV nodeisolates/delayselectrical
  impulsebetweenatria andventricles
• Purkinjefibers

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• Measurement of electrical activity via
  electrocardiogram (ECG)
• Assess electricalactivity
• Derive someassessment offunctionality
• Correlate to tissuemass for heart score

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• Humans 18 20 electrical leads
• Assessment of heart disease
• Horses 3 leads
• Rt limb lead rt jugular furrow
• Left limb lead left thorax near apex of heart
• Ground to left limb

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• ECG
• P wave
• Assocd with atrialcontraction
• Small becausenot much tissue
• QRS complex
• Ventricular contraction
• Much larger becausemore tissue mass

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• ECG
• T wave
• Repolarization ofventricles
• Repolarizationof atria hiddenin QRS complex

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• ECG
• Interval betweenatria-ventricularactivity is
  P-R interval
• Assocd withdelay in electricalimpulse
  betweenatria and ventricles

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• ECGs used clinically to identify electrical
  abnormalities
• Very common in human medicine
• Also small animal medicine
• Cardiac disease not common in horses, but does
  occur

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• AV block
• Two P waves w/o a corresponding QRS
• NOT abnormal in resting horses
• Increase exercise, increase sympathetic tone,
  take another ECG
• If AV block still present, may be potential
  problem

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• Can also evaluate with stethoscope
• Normal heart sounds lub-dub
• AV block lublub-dub
• Manual evaluation of pulse
• Mandibular artery
• Digital artery
• Wont feel lub-dub, but feel irregularity in pulse

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• Heart Score
• Time for electrical impulse to travel through
  ventricular tissue
• Longer time larger QRS more tissue mass
• Correlated to performance?
• Larger tissue mass does not necessarily correlate
  to increased functional mass or stroke volume

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• Heart rate
• Normal resting 30 40 bpm
• May decrease 10-20 with conditioning, difficult
  to accurately measure, debated
• Rest is a relative term
• Good measure of anxiety
• In humans, resting HR good measure of fitness
• Average 70 bpm
• Unfit 80 bpm
• Athlete lt 60 bpm

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• HR recovery following exercise
• Better benchmark of fitness
• Fit, conditioned recovers rapidly
• Unconditioned stressed slower recovery
• Many events, horses must recover to pulse
  criteria before continuing in competition
• Endurance, cross country, polo

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• As exercise intensity increases, HR increases
• HRmax young, healthy racehorse 240 bpm
• Consider 9 14 lb heart contracting 4 times/sec
• Decreases 190 bpm in older horses
• Humans max HR 220 minus age

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• HRmax varies with breed, does NOT correlate to
  performance
• Horse with higher HRmax not necessarily faster
  runner
• Measurement HR
• Stethoscope (hard to do during exercise)
• Manually palpate

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• Heart rate monitors
• First developed forhuman sports,adaptedfor use
  in horses
• lt 100 very expensive
• HRs tend to be very repeatable if using
  consistent SET

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• Use of V200 and V180
• V velocity (speed)
• Note earlier V referred to volume, ie VO2max
• V180, V200 velocity required to produce a HR of
  180 (or 200)
• Why use V180 or V200 instead of max HR?

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• Use V180 (or V200) to quantify conditioning
• As fitness progresses, V180 increases
• Horse can run faster with less cardiovascular
  effort
• OR, over time, horse can perform sameSETs at
  progressively lower HR
• Works in humans, too

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• V180/V200 canbe used to detectproblems
• Ex Horsein training,V180 has
  beenincreasing,then suddenly decreases
• Injury? Disease? Attitude?
• May be as minor as thrush

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• Can be used field settings w/ practice
• Repeatable with SETs
• SET can be flat track, trail loop, etc

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• Cessation of exercise, HR should return to
  resting rate rapidly
• Cardiac Recovery Index
• Base HR
• Trot horse 40 m (125) out and back
• 2nd HR at 1 min
• Is HR higher, lower, same?
• Compare 48/42 vs 48/60

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• Used in endurance as criteria for Fit To Continue
  or BC judging
• Fit horses recoverltltlt 10 min
• Must recoverlt 30 min
• gt 30 min DQ,metabolicallystressed

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• Cardiac output
• Heart rate x Stroke Volume
• HR contractions per minute
• SV volume of blood ejected from heart with each
  contraction
• CO volume/unit time gt liters/min

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• With increasing intensity of exercise
• HR 40 gt gt gt 240 bpm (6-fold)
• SV increases somewhat
• At rest, TB SV 800 ml/min
• Max SV 1500 ml/min (2-fold increase)
• CO at rest 25 L/min
• CO max 300 L/min
• Majority of increase in CO is due to increase in
  HR, not SV

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• SV doesnt seem to increase much with
  conditioning
• Some studies 10 increase
• Other studies, little or none
• Hard to measure directly
• Human catheterization kits available
• Human CO 10 of TBs

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• Fick principle
• VO2 CO (O2 arterial O2 venous),
• Where VO2 is Volume O2 in ml/kg/min
• Oxygen uptake
• CO is cardiac output (HR x SV)

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• Measure O2 content in blood samples collected
  fromcarotid/facialartery, jugularvein
  duringtreadmill exercise
• Expensive,specialized equipment
• Not a backyard project
• Can potentially correlate CO to performance, but
  logistically difficult

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• Blood pressure
• At rest, similar to humans 120/80
• Systole ventricular contraction
• Pressure measured in artery as blood ejected from
  heart
• QRS complex

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• Diastole between contractions
• T wave, ventricular repolarization
• Ventricle relaxed, filling
• Pressure maintained by arterial elasticity
• Cardiac dz in humans/small animals
• Increased BP hypertension
• Rare in horses

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• MAP 100 mm Hg (120/80 100)
• Increases slightly during exercise (140 mm Hg),
  despite ten-fold increase in CO
• Resistance in vessels decreases
• Same pressure, more blood flow

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• CO from LV CO from RV
• Closed system
• No addition orsubtraction offluid to system

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• Pressures between loops differ
• Systemic loop
• 100 140 mm Hg
• Pulmonic loop
• 25 mm at rest
• 70-80 mm Hgduring exercise
• 3-fold increase
• EIPH

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• Q flow (ie, cardiac output)
• Qheart (P1 - P2)/R
• Where P1 is pressure in aorta at systolic
  ejection
• P2 is pressure in right atrium as blood re-enters
  the heart
• R is resistance in system

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• Net equation is Q ? P/R
• To increase Q, you can
• Increase pressure of blood as it leaves the heart
  via aorta (P1)
• Decrease the backpressure as blood re-enters the
  heart (P2)
• Decrease resistance throughout the system

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• Resistance is a function of
• Length of tube youre trying to move fluid
  through
• This doesnt change in a vascular system
• Viscosity of fluid
• Soda vs milkshake
• Doesnt change significantly under normal
  conditions
• Specific gravity distilled water 1.000
• Specific gravity of blood 1.003

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• Radius of tube
• Primary means of decreasing resistance in
  physiologic system

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• Resistance 1/r4 where r is radius
• 1 cm
• R 1/14 gt 1
• 2 cm
• R 1/24
• R 1/16
• Sixteen times less resistance created by doubling
  radius of blood vessel
• Back to the milkshake

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• How do we change blood vessel diameter?
• Function of smooth muscle at level of arterioles
• Vasoconstriction gt tighten gt decrease diameter
  gt increase resistance
• Vasodilation gt relax gt increase diameter gt
  decrease resistance

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• Q ? P/R
• In order to facilitate a ten-fold increase in
  cardiac output, there must be a huge decrease in
  peripheral resistance via vasodilation

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• What cardiovascular and muscle functions change
  significantly with conditioning?
• HR recovery following cessation of exercise
• More rapid recovery
• V180, V200
• Increases (can go faster at lower HR)

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• Increases in muscle hypertrophy
• Increase in contractile proteins, not of muscle
  cells
• Includes cardiac muscle, but not a significant
  increase in function
• OBLA (onset blood lactic acid) 4 mMol/L
• Also described as VLA4
• Velocity required to produce blood LA
  concentrations of 4 mMol/liter
• Increase or decrease?

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• Increased capillaries
• Better substrate delivery to tissue
• Oxygen, glucose, lipids, endocrine
• Faster removal of by-products
• H ions, CO2, lactic acid, NH4
• Increased efficiency of thermoregulation

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• What cardiovascular functions are NOT
  significantly affected by conditioning?
• HRmax
• Resting HR (maybe 10, but hard to accurately
  measure)
• SV (only increases 10)