Transcript Blood flow
Ventilation and Cardiovascular Dynamics Brooks Ch 13 and 16 1 Outline • Is Ventilation a limiting factor in aerobic performance? • Cardiovascular responses to exercise • Limits of CV performance – Anaerobic hypothesis – Noakes protection hypothesis • CV function and training 2 3 Ventilation as a limiting Factor to performance • Ventilation does not limit sea level aerobic performance – capacity to inc ventilation is greater than that to inc Q • Ventilation perfusion Ratio - VE/Q – Fig 12-15 - linear increase in vent with intensity to vent threshold then non linear – VE rest 5 L/min -exercise 190 L/min 4 Ventilation as a limiting Factor to performance • Fig 13-2 • Q rest 5L/min - ex 25 L/min • VO2/Q ratio ~ .2 at rest and max – VE/Q ratio • ~1 at rest - inc 5-6 fold to max exercise – Capacity to inc VE much greater • Ventilatory Equivalent VE/VO2 – rest 20 (5/.25) ; max 35(190/5) 5 VE max vs. MVV • MVV - max voluntary ventilatory capacity • 1.max VE often less than MVV • 2.PAO2(alveolar) and PaO2 (arterial) – Fig 11-4 , 12-12 – maintain PAO2 or rises – PaO2 also well maintained 6 VE max vs. MVV • 3. Alveolar surface area - is very large • 4. Fatigue of Vent musculature – MVV tests - reduce rate at end of test – repeat trials - shows decreased performance – Yes, fatigue is possible in these muscles - is it relevant NO – VE does not reach MVV during exercise, so fatigue less likely – Further, athletes post ex can raise VE to MVV, illustrating reserve capacity for ventilation 7 Elite Athletes • Fig 13-3 - observe decline in PaO2 with maximal exercise in some elite athletes 8 Elite Athletes • may see vent response blunted, even with dec in PaO2 – may be due to economy – extremely high pulmonary flow, inc cost of breathing, any extra O2 used to maintain this cost – ? Rise in PAO2 - was pulmonary vent a limitation, or is it diffusion due to very high Q ? • Altitude – experienced climbers - breathe more - maintain Pa O2 when climbing – Elite - may be more susceptible to impairments at altitude 9 CV Responses to Exercise • Increase flow to active areas • decrease flow to less critical areas • Principle responses – Inc Q - HR, SV – Inc Skin blood flow – dec flow to viscera and liver – vasoconstriction in spleen – maintain brain blood flow – inc coronary blood flow – inc muscle blood flow 10 CV Responses to Exercise • Table 16-1 - Rest vs acute exercise • CV response - depends on type and intensity of activity – dynamic - inc systolic BP; not Diastolic • Volume load – strength - in systolic and diastolic • Pressure load 11 Cardiovascular System Rest vs Maximal Exercise Table 16.1 (untrained vs trained) Rest UT T HR(bpm) 70 63 SV(ml/beat) 72 80 (a-v)O2(vol%) 5.6 5.6 Q(L/min) 5 5 VO2 ml/kg/min 3.7 3.7 SBP(mmHg) 120 114 Vent(L/min) 10.2 10.3 Ms BF(A)ml/min 600 555 CorBFml/min 260 250 Max Ex UT 185 90 16.2 16.6 35.8 200 129 13760 900 T 182 105 16.5 19.1 42 200 145 16220 940 12 Oxygen Consumption • Cardiovascular Determinants – rate of O2 transport – amount of O2 extracted – O2 carrying capacity of blood • VO2 = Q * (a-v)O2 • Exercise of increasing intensity • Fig 16-2,3,4 – Q and (a-v)O2 increases equally important at low intensities – high intensity HR more important – (a-v)O2 - depends on capacity of mito to use O2 - rate of diffusion-blood flow • O2 carrying capacity - influenced by Hb content 13 14 Heart Rate • Most important factor in responding to acute demand • inc with intensity due to Sympathetic stimulation and withdrawal of Parasympathetic – estimated Max HR 220-age (+/- 12) – influenced by anxiety, dehydration, temperature, altitude, digestion • Steady state - leveling off of heart rate to match oxygen requirement of exercise (+/- 5bpm) – Takes longer as intensity of exercise increases, may not occur at very high intensities • Cardiovascular drift - heart rate increases steadily during prolonged exercise due to decreased stroke volume 15 Heart Rate • HR response : – Is higher with upper body - at same power requirement • Due to : smaller muscle mass, increased intra-thoracic pressure, less effective muscle pump – Is lower in strength training • Inc with ms mass used • Inc with percentage of MVC (maximum voluntary contraction) • estimate the workload on heart , myocardial oxygen consumption, with • Rate Pressure Produce - RPP – HR X Systolic BP 16 Stroke volume • Stroke Volume - volume of blood per heart beat – Rest - 70 - 80 ml – Max - 80-175 ml • Fig 16-2 - increases with intensity to ~ 25-50% max - levels off – inc EDV (end diastolic volume) – high HR may dec ventricular filling – athletes high Co due to high SV • supine exercise – SV does not increase - starts high • SV has major impact on Q when comparing athletes with sedentary 17 – ~ same max HR - double the SV and Q for athletes (a-v)O2 difference • Difference between arterial and venous oxygen content across a capillary bed – (ml O2/dl blood -units of %volume also used) • Difference increases with intensity – fig 16-4 - rest 5.6 - max 16 (vol %) – always some oxygenated blood returning to heart - non active tissue – (a-v)O2 can approach 100% in maximally working muscle 18 Blood Pressure • Blood Pressure fig 16-5 – – – – – BP = Q * peripheral resistance (TPR) dec TPR with exercise to 1/3 resting Q rises from 5 to 25 L/min systolic BP goes up steadily MAP - mean arterial pressure • 1/3 (systolic-diastolic) + diastolic – diastolic relatively constant • Rise over 110 mmHg - associated with CAD 19 Cardiovascular Triage • With exercise - blood is redistributed from inactive to active tissue beds - priority for brain and heart maintained – sympathetic stimulation increases with intensity – Causes general vasoconstriction – brain and heart spared vasoconstriction – Active hyperemia directs blood to working muscle adenosine, NO - vasodilators • maintenance of BP priority – Near maximum, working ms vasculature can be constricted – protective mechanism to maintain flow to heart and CNS – May limit exercise intensity so max Q can be achieved without resorting to anaerobic metabolism in the heart • Eg - easier breathing - inc flow to ms 20 – harder breathing - dec flow to ms 21 22 Cardiovascular Triage • Eg. Altitude study fig 16-6 - observe a reduction in maximum HR and Q with altitude even though we know a higher value is possible - illustrates protection is in effect 23 Coronary blood flow • Large capacity for increase – (260-900ml/min) – due to metabolic regulation – flow occurs mainly during diastole • warm up - facilitates inc in coronary circulation 24 CV Performance Limitation • VO2max - long thought to be best measure of CV capacity and endurance performance – Fig 16-7 – VO2 max - maximum capacity for aerobic ATP synthesis – Endurance performance - ability to perform in endurance events 25 CV Performance Limitation • Criteria for identifying if actual VO2 max has been reached – – – – – – – Exercise uses minimum 50% of ms mass Results are independent of motivation or skill Assessed under standard conditions Perceived exhaustion (RPE) R of at least 1.1 Blood lactate of 8mM (rest ~.5mM) Peak HR near predicted max 26 VO2 max and Performance • General population - VO2 max will predict endurance performance - due to large range in values • elite - ability of VO2 to predict performance is not as accurate - all have values in 65-70 + ml/kg/min – world record holders for marathon – male 69 ml/kg/min female 73 ml/kg/min - VO2 max – male ~15 min faster with similar VO2max • other factors in addition to VO2 max that impact performance – – – – Sustained speed ability to continue at high % of capacity lactate clearance capacity performance economy 27 Capacity vs Performance • Local muscle factors more closely related to fatigue than Q limitation – Table 6-3 correlations between ox capacity, VO2 and endurance • Lower VO2 max for cycling compared to running • Running performance can improve without an inc in VO2 max • Inc VO2 max through running does not improve swimming performance 28 What limits VO2 max ? • Traditional Anaerobic hypothesis for VO2max – After max point - anaerobic metabolism is needed to continue exercise - plateau – max Q and anaerobic metabolism will limit VO2 max – this determines fitness and performance • Tim Noakes,Phd - South Africa – re-analyzed data creating Alternate hypothesis for VO2max – most subjects did not show plateau bringing anaerobic hypothesis into question – Says Q not a limitation – Rather - neural and endocrine control factors reduce output before damage occurs in heart 29 – Still very controversial - not accepted by most scholars Inconsistencies in Anaerobic hypothesis • Q dependant upon and determined by coronary blood flow – Max Q implies cardiac fatigue - ischemia -? Angina pectoris? – this does not occur in most subjects • Blood transfusion and O2 breathing – inc performance - many says this indicates Q limitation – But still no plateau – was it a Q limitation? • Blood doping studies – VO2 max improved for longer time period than performance measures (eg 10 km time trial) • altitude - observe decrease in Q – Yet we know it has greater capacity – This is indicative of a protective mechanism 30 Protection Hypothesis • 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 • Noakes research suggests peak treadmill velocity as a good predictor of aerobic performance – high cross bridge cycling and respiratory adaptations – Biochemical factors - mito volume, ox enzyme capacity 31 are also good predictors of performance Practical Aspects of Noakes Hypothesis • Primary regulatory mechanisms of Cardio Resp and neuromuscular systems facilitate intense exercise – until it perceives risk of ischemic injury – Then prevents muscle from over working and potentially damaging these tissues • Therefore, improve fitness by; – – – – muscle power output capacity substrate utilization thermoregulatory capacity reducing work of breathing • These changes will reduce load on heart – And allow more intense exercise before protection is instigated • CV system will also develop with training 32 Changes in CV with Training • Tables 16-1,2 - training impacts • Heart - inc ability to pump blood-SV - inc end diastolic volume-EDV • Endurance training – small inc in ventricular mass – triggered by volume load • resistance training – pressure load - larger inc in heart mass • adaptation is specific to form – swimming improves swimming • Interval training - repeated short to medium duration bouts – improve speed and CV functioning 33 – combine with over-distance training Cardiovascular Adaptations with Endurance Training Table 16.2 Rest Submax Ex (absolute) HR SV (a-v)O2 0 Q 0 0 VO2 0 0 SBP 0 0 CorBFlow Ms Bflow(A) 0 0 BloodVol HeartVol Max Ex 0 0 34 • 0 = no change CV Adaptations • O2 consumption • improvements depend on – prior fitness, type of training, age – can inc VO2 max ~20% – Performance can improve > than 20% • Heart Rate – training-dec resting and submax HR – inc Psymp tone to SA node • Max HR-dec ~3 bpm with training – progressive overload for continued adaptation • Stroke volume - 20% inc - rest, sub and max with training – slower heart rate - inc filling time 35 – inc volume - inc contractility - SV CV Adaptations • Stroke volume - cont. – EDV inc with training - due to inc left vent vol and compliance, inc blood vol, – Myocardial contractility increased • Better release and reuptake of calcium at Sarcoplasmic Reticulum • Shift in isoform of myosin ATPase – increased ejection fraction • (a-v)O2 difference – – – – – inc slightly with training due to ; right shift of Hb saturation curve mitochondrial adaptation Hb and Mb [ ] muscle capillary density 36 CV Adaptations • Blood pressure - decreased resting and submax BP • Blood flow – training - dec coronary blood flow rest and submax (slight) • inc SV and dec HR - dec O2 demand – inc coronary flow at max – no inc in myocardial vascularity • inc in muscle vascularity – dec peripheral resistance - inc Q – dec muscle blood flow at sub max – inc extraction - more blood for skin... – 10 % inc in muscle flow at max • no change in skin blood flow - though adaptation to exercise 37 in heat does occur