Ventilatory and Cardiovascular Dynamics

1. Ventilatory and Cardiovascular Dynamics • Brooks Ch 13 and 16 • OUTLINE • Ventilation as limiting factor in aerobic performance • Cardiovascular responses to exercise • Limits of CV performance • anaerobic hypothesis • protection of heart and muscle • Vo2 max criteria • CV function and training

2. Ventilation as a limiting Factor to performance • Ventilation not thought to limit aerobic performance at sea level • capacity to inc ventilation with ex • relatively greater than that to inc CO • Ventilation perfusion Ratio - VE/CO • Fig 12-14 • linear increase in ventilation with intensity-to vent threshold - non linear • Fig 13-1 rest 5 L/min - 190 L/min • ~1 at rest - inc 5-6 fold to max exercise • Ventilatory Equivalent VE/VO2 • rest 20 ; max 35

3. VE max vs. MVV • MVV - max voluntary ventilatory capacity • max VE often less than MVV • PAO2(alveolar) and PaO2(arterial) • Fig 11-3 , 12-11 • maintain PAO2 - or rises • PaO2 also well maintained • Alveolar surface area - massive • Fatigue of Vent musculature • MVV tests - reduce rate at end of test • repeat trials - decreased performance • fatigue yes - is it relevant -NO • VE does not reach MVV • athletes post ex can raise VE to MVV

4. Elite Athletes • Fig 13-2 - observe decline in PaO2 with maximal exercise in some elite • 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 CO ? • Altitude • experienced climbers - breathe more - maintain Pa O2 when climbing • Elite - may be more susceptible

5. CV Responses to Exercise • Increase flow to active areas • decrease flow to less critical areas • Principle responses • Inc CO - HR, SV • Inc Skin blood flow • dec flow to kidneys, viscera • vasoconstriction in spleen • maintain brain blood flow • inc coronary blood flow • inc muscle blood flow • Table 16-1 • CV response - depends on type and intensity of activity • dynamic - inc systolic BP; not Diastolic • strength - in syst and diastolic

6. Oxygen Consumption • Determinants - rate of O2 transport • O2 carrying capacity of blood • amount of O2 extracted • VO2 = Q * (a-v)O2 • Exercise of increasing intensity • Fig 16-1,2,3 • CO 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 - Hb content

7. Heart Rate • Most important factor • inc with intensity, levels off at VO2max range 70 - 200 bpm • increase due to withdrawal of Psymp and symp stimulation • estimated Max HR 220-age (+/- 12) • influenced by anxiety, dehydration, temp, altitude, digestion • Less HR response with strength exer • increases with muscle mass used • higher with upper body - at same power • inc MAP, peripheral resistance, intrathoracic pressure • less effective muscle pump - venous return

8. HR and Stroke volume • Rate Pressure Produce - RPP • HR X Systolic BP • estimate of cardiac load - O2 • Stroke Volume • Fig 16-2 - increase 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 CO • same max HR - double the SV and CO

9. (a-v)O2 difference • Difference increases with intensity • fig 16-3 - rest 5.6 - max 16 • always some oxygenated blood returning to heart - non active tissue • (a-v)O2 can approach 100% in maximally working muscle • Blood Pressure fig 16-4 • = CO * peripheral resistance (TPR) • dec TPR with exercise to 1/3 resting • CO rises 5-20 L/min • systolic BP goes up steadily • MAP - mean arterial pressure • 1/3 (systolic-diastolic) + diastolic • diastolic relatively constant • rise - associated with CAD

10. Cardiovascular Triage • With exercise - blood redistributed from inactive to active tissue • brain and heart spared vasoconstriction • symp stim inc with intensity • maintenance of BP priority • working ms can be constricted • protective mechanism - maintain flow to heart and CNS • limits exercise intensity - max Co can be achieved with out resorting to anaerobic metabolism • Eg - easier breathing - inc flow to ms • harder breathing - dec flow to ms • Eg. Altitude study fig 16-5

11. 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 • Limits of CV performance • VO2 max - long considered best measure of capacity of CV system and aerobic performance (fig 16-6) • VO2 max anaerobic hypothesis • = Q max * (a-v)O2 max • VO2 max indicated by point at which O2 consumption fails to rise despite an increased power output or intensity

12. CV Performance Limitation • VO2max - long thought to be best measure of CV and endurance capacity • VO2 max - maximum capacity for aerobic ATP synthesis • Endurance performance - ability to perform in endurance events • Anaerobic hypothesis • After max point - anaerobic metabolism to continue exercise- plateau • max CO and anaerobic metabolism will limit VO2 max • and determine fitness and performance • Tim Noakes - South Africa • re-analyzed data from classic studies • most subjects did not plateau

13. Inconsistencies with Anaerobic hypothesis • CO dependant upon and determined by coronary blood flow • Max CO implies cardiac fatigue - coronary ischemia -? Angina pectoris? • Blood transfusion and O2 breathing • inc performance - still no plateau • was it a CO limitation? • Blood doping studies • VO2 max improved for longer time period than performance measures • altitude - observe decrease in CO • indicative of protective mechanism

14. Protection of Heart and Muscle • Noakes (1998) • 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 • suggest peak treadmill velocity as predictor of aerobic performance • high cross bridge cycling and respiratory adaptations • Biochemical factors - mito volume, ox enzyme capacity

15. Practical Aspects • Primary reg mech of Cardio Resp and neuromuscular systems facilitate intense exercise • until it perceives risk of ischemic injury • prevents muscle from over working • Programs and Techniques for fitness • muscle power output capacity • substrate utilization • thermoregulatory capacity • reduce work of breathing • above reduce load on heart - allows more intense exercise before protection instigated

16. VO2 max and Performance • General population - VO2 max will predict performance in endurance • elite athletes - not as accurate • world records for marathon • male 69 female 73 ml/kg/min • male 15 min faster • other factors in addition to VO2 max • speed • ability to continue at high % of capacity • lactate clearance capacity • performance economy • in general high VO2 max pre req for elite performance - 65-70 ml/kg/min • represents capacity to exercise at high intensity before system limits itself

17. Changes in CV with Training • Tables 16-1,2 • 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 mass • adaptation is specific to form • swimming improves swimming • Interval training - repeated bouts of short to medium duration • improve speed and CV functioning • combine with overdistance training

18. 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 • inc volume - inc contractility - SV

19. CV Adaptations • Stroke volume - cont. • EDV also inc with training - inc left vent vol and compliance, blood vol, • Myocardial contractility increased • release and tx of calcium from SR • isoform of myosin ATPase • inc ejection fraction • (a-v)O2 difference • inc slightly with training • right shift of Hb saturation curve • mitochondrial adaptation • Hb and Mb [ ] • muscle capillary density

20. CV Adaptations • Blood pressure - dec resting and submax • 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 CO • dec musc blood flow at sub max • inc extraction - more blood for skin... • Max - 10 % inc in musc flow • no change in skin blood flow