Ventilatory and Cardiovascular Dynamics

1
Ventilatory and Cardiovascular Dynamics

• Brooks Chapts 13 and 16
• Outline
• Ventilation as limiting factor in aerobic
  performance
• Cardiovascular responses to exercise
• Limits of CV performance
• VO2 max criteria
• CV function and training

2
Ventilation as a Limiting Factor in Aerobic
Performance at Sea Level (Chapt 13)

• Ventilation not thought to limit aerobic
  performance at sea level.
• capacity to ? ventilation (35x) with exercise is
  greater than the capacity to ? Cardiac Output
  (6x)
• considerable ventilatory reserve exists to
  oxygenate blood passing through the lungs

3
Ventilation Perfusion Ratio - VE/CO

• Linear ? in ventilation with ? in exercise
  intensity.
• As exercise intensity reaches maximal levels
  there can be a non-linear increase in
  ventilation.
• Ventilation at rest 5 L/min
• Maximal levels 190 L/min (35x)
• Linear ? in cardiac output with ? in exercise
  intensity.
• Cardiac Output at rest 5 L/min
• Maximal levels 30 L/min (6x)
• Pulmonary minute ventilation (VE) to Cardiac
  Output is 1 at rest and ? 5 - 6 fold during
  maximal exercise.
• One reason why pulmonary ventilation is not
  thought to limit aerobic performance.

4

• Ventilatory Equivalent VE/VO2
• VO2 at rest 0.25 L/min, VE/VO2 20
• VO2 max 5 L/min, VE/VO2 35
• the ability to ? ventilation is greater than the
  ability to expand oxidative metabolism
• VEmax vs. MVV during exercise
• MVV- maximum voluntary ventilatory capacity
• the maximum VE during exercise is less than the
  MVV
• another reason why pulmonary ventilation is not
  thought to limit aerobic performance

5

• PAO2(alveolar) and PaO2(arterial)
• O2 moves from areas of high conc to areas of low
  conc
• during exercise maintain or ? PAO2
• PaO2 in blood is also well maintained
• Alveolar surface area is massive (50m2).
• only 200ml of blood (4) is in the pulmonary
  system during maximal exercise
• Fatigue of ventilatory muscules.
• the diaphragm and ventilatory muscles can fatigue
• during MVV test fatigue at end of the test
• repeat trials - decreased performance
• fatigue yes - is it relevant -NO (ultra
  endurance)
• athletes post ex can raise VE to MVV

6
Pulmonary Limits in Elite Athletes

• Fig 13-2 decline in PaO2 with maximal exercise
  in some elite athletes (individual variability)
• may be due to compliance in the ventilatory
  system
• may be due to economy (energy cost of breathing)
• athletes may learn to tolerate hypoxemia to ?
  energy cost of breathing during maximal exercise
• Altitude
• experienced climbers breathe more and maintain
  PaO2 when climbing at altitude

7
Cardiovascular Dynamics During Exercise

• Brooks, Chapt 16
• O2 to the working muscles ? with exercise
  intensity
• Principal Cardiovascular Responses to Exercise
• Increased cardiac output
• ? HR (60 to 200bpm)
• ? SV (80 to 200ml/beat)
• ? O2 and substrate delivery to muscle
• remove CO2 and metabolites
• ? skin blood flow
• regulate temperature

8

• ? blood flow to the kidneys
• maintain blood volume
• ? blood flow to viscera
• reduced gastrointestinal activity
• vasoconstriction in the spleen
• ? blood volume
• maintain blood flow to the brain
• ? blood flow to coronary arteries of the heart
• ? blood flow to working skeletal muscle

9

• Cardiovascular regulation is directed toward
  maintaining blood pressure.
• During exercise CV regulation balances the need
  for more blood to the active tissue with the need
  to maintain BP and blood flow to the brain and
  heart.
• Although maximum CO may limit O2 transport
  capacity, maximal exercise may be terminated by
  the threat of ischemia to the heart (Noakes).

10

• Table 16-1 Cardiovascular changes with endurance
  training.
• Rest Submax Ex Max Ex
• HR ? ? NC
• SV ? ? ?
• CO NC NC ?
• O2up - ? ?
• SBP ? ? NC
• TPR NC NC ?

11

• CV response depends on type and intensity of
  activity.
• dynamic ex large ? in HR, CO, SBP (not
  diastolic)
• volume load on the heart
• strength ex large ? in SBP and DBP, mod ? in
  HR, CO
• pressure load on the heart

12
Oxygen Consumption

• Oxygen consumption is proportional to exercise
  intensity.
• Determinants
• rate of O2 transport
• O2 carrying capacity of blood
• amount of O2 extracted
• VO2 HR x SV x (a-v)O2

13
Heart Rate

• HR accounts for 75 of O2 uptake at maximal
  exercise (most important factor)
• ? with intensity, levels off at VO2max (Fig 16-1)
• Range 70 - 210 bpm
• ? due to withdrawal of PNS and SNS stimulation
• intrinsic HR 100 bpm
• Estimated max HR 220 - age (/- 12)
• influenced by anxiety, dehydration, temp,
  altitude, digestion, genetics

14

• HR response with strength exercise
• lower than endurance training
• ? with muscle mass used
• higher with upper body
• ? intrathoracic pressure, smaller muscle mass
• less effective muscle pump - venous return
• Cardiovascular drift
• during prolonged exercise HR gradually ? at the
  same work rate
• ? venous return (? blood volume)
• Rate Pressure Produce - RPP
• HR X SBP
• rough index of coronary blood flow

15
Stroke Volume

• SV has major impact on CO (2 x SV 2 x CO).
• SV ? during exercise to 25 - 50 of max then
  levels off.
• Fig 16-2 SV ? from 75ml to 110ml/beat
• SV ? as exercise intensity ? toward max
  (variable).
• SV is perhaps the most important factor
  influencing individual differences in VO2max.
• max SV sedentary 90ml, athlete 180ml
• Supine exercise
• SV does not increase - starts high
• EDV remains unchanged

16
(a-v)O2 difference

• Difference increases with exercise intensity
• Fig 16-3 rest 5.6 - max 16 (vol)
• always some oxygenated blood returning to the
  heart
• non active tissue does not extract much O2
• (a-v)O2 can approach 100 in maximally working
  muscle

17
Blood Pressure

• BP must ? during exercise to maintain blood flow
  to the heart, brain and working muscle (Fig
  16-4).
• TPR ? with exercise to 1/3 resting (due to ? in
  CO).
• SBP ? steadily during exercise (120 - 180mmHg).
• MAP 1/3 (systolic-diastolic) diastolic
• DBP is relatively constant

18
Cardiovascular Triage

• CT protective mechanisms that prevent coronary
  and CNS ischemia and maintain central blood
  volume.
• During exercise these mechanisms limit blood flow
  to muscles when the the body cannot meet the
  needs of the heart and CNS
• With exercise blood is redistributed from
  inactive to active tissue
• brain and heart spared vasoconstriction
• SNS stimulation ? steadily with exercise
  intensity
• At altitude the circulatory system appears to
  protect the heart by ? blood flow to the muscles
  and reduce the work of the heart (Fig 16-5).

19

• Skin blood flow ? during submaximal exercise but
  ? to resting values during maximal exercise.
• Coronary blood flow ? during exercise from 260
  -900 ml/min
• flow occurs mainly during diastole
• coronary artery disease may restrict blood flow
  and cause ischemia
• a good warm up facilitates an ? in coronary
  circulation

20
Limits of CV Performance

• VO2 max has long been considered the best measure
  of CV capacity and aerobic performance (Fig
  16-6).
• VO2max HRmax x SVmax x (a-v)O2max
• VO2max is the point at which O2 consumption fails
  to rise, despite an ? power output or intensity.
• VO2PEAK

21
VO2max Anaerobic Hypothesis

• After reaching VO2max exercise intensity is ? by
  anaerobic metabolism.
• max CO and anaerobic metabolism will limit VO2
  max
• best predictor of performance in endurance sports
• Tim Noakes - South Africa
• re-analyzed data from classic studies
• found that most subjects did not plateau

22
Inconsistencies with Anaerobic hypothesis

• Blood transfusion and O2 breathing have been
  shown to ? performance.
• was it a CO limitation?
• Blood doping studies
• VO2max improved for longer time period than
  performance measures
• There is a discrepancy between VO2max and running
  performance in elite athletes.
• At altitude CO ?
• indicative of protective mechanism

23

• Lower VO2max for cycling compared with running.
• Running performance can improve without an ? in
  VO2max.
• ? VO2max through running does not improve
  swimming.
• Local muscle factors often appear to be more
  closely related to fatigue than a limitation in
  CO.
• CO is dependant upon and determined by coronary
  blood flow.
• Max CO implies cardiac fatigue, coronary ischemia
  and angina pectoris?

24
Protection of Heart and Muscle During Exercise

• Noakes (1998) alternative to anaerobic
  hypothesis.
• CV regulation and muscle recruitment are
  regulated by neural and chemical control
  mechanisms
• prevent damage to heart, CNS and muscle
• by regulating force and power output and
  controlling tissue blood flow
• Research by Noakes suggests that peak treadmill
  velocity is a good predictor of aerobic
  performance.
• high cross bridge cycling and respiratory
  adaptations
• biochemical factors such as mito volume and O2
  enzyme capacity are also good predictors of
  endurance capacity

25
Practical Basis of the Noakes Hypothesis

• Primary regulatory mechanism of the CV and
  neuromuscular systems facilitate intense exercise
  until it perceives risk of ischemic injury to the
  heart, CNS and muscles.
• Fitness should be improved by
• muscle power output capacity
• substrate utilization
• thermoregulatory capacity
• reduce work of breathing
• The CV system develops at the same time that
  other adaptations occur from training.

26
Criteria for Measuring VO2max

• Exercise must use at least 50 of the total
  muscle mass (do not use upper body exercise).
• The exercise must be continuous and rhythmical
  and done for at least 10 minutes.
• The test should try to eliminate motivation and
  skill.
• The subject must reach maximum capacity.
• The measurement must be made in a controlled
  environment.
• VO2max on a bicycle is usually 10 to 15 less
  than running on a treadmill.

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VO2 max and Performance

• For the general population VO2max will predict
  performance in an endurance event.
• For elite athletes VO2max is a poor predictor of
  performance in an endurance event.
• male 69, female 73 ml/kg/min male 15 min faster
• Other performance factors
• speed
• ability to continue at high of capacity
• lactate clearance capacity
• performance economy

28
Cardiovascular Adaptations with Endurance
Training

• Rest Submax Ex Max Ex
• HR ? ? NC
• SV ? ? ?
• (a-v)O2 NC ? ?
• CO NC NC ?
• VO2 - - ?
• SBP ? ? NC
• CorBF ? ? ?
• BloodVol ?
• HeartVol ?

29
Changes in CV Parameters with Training

• Heart ? ability to pump blood by ? SV (? EDV).
• Small ? in ventricular mass (volume load) with
  endurance training.
• Strength training produces a pressure load that
  will ? LV mass.
• Adaptation to endurance training is sport
  specific.
• Interval training
• acts as an overload
• improve speed and CV functioning
• combine with endurance training

30
CV Adaptations

• Improvements in VO2max depend on prior fitness,
  type of training, age.
• can ? VO2max by 20
• Endurance performance can ? by much more than 20
  by improving mitochondrial density, speed,
  running economy, and body composition.

31
Heart Rate

• Endurance training ? resting and submax HR by
  increasing PNS activity to the SA node.
• may ? intrinsic HR
• athlete 40bpm
• may be a genetic influence
• ? resting HR may be due to disease (sick sinus
  syndrome)
• Max HR may ? 3 bpm with training.

32
Stroke Volume

• Endurance training can ? resting and submax SV by
  20.
• ? SV due to ? in heart volume and contractility.
• ? HR will ? SV
• ? HR allows for ? filling time (Frank-Starling)
• ? LV compliance allows ventricle to stretch more.
• ? contractility due to ? in release and transport
  of Ca from SR.

33
(a-v)O2 difference

• (a-v)O2 ? slightly with training difference
• right shift of OxyHb dissociation curve
• mitochondrial adaptation
• ? Hb and myoglobin conc
• ? muscle capillary density
• ? capillarization around muscle fibres is thought
  to facilitate diffusion during exercise.
• Blood Pressure
• Endurance training ? resting and submax SBP, DBP
  and MAP (no change during max ex).

34
Blood Flow

• With endurance training coronary blood flow ?
  slightly at rest and during submax exercise.
• ? SV and ? HR reduce myocardial O2 consumption
• coronary blood flow ? at max ex with training
• supports higher metabolic requirements with ? CO
• Skeletal muscle vascularity ? with endurance
  training.
• ? peripheral resistance
• The trained muscle has an ? O2 extraction
  capacity.
• There is no change in skin blood flow with
  training.