2Ventilation in Steady Rate Exercise During light & moderate steady rate exercise, VE:VO2 linear relationship.Ventilatory equivalent for oxygen (VE:VO2): ratio of minute ventilation to oxygen uptake.Usually 25 : 1 during submaximal exercise up to 55% max.
3Ventilation in Steady Rate Exercise Ventilatory response to fixed level of submaximal exercise can be divided into 4 phases.Sudden increase at onset.Ventilation gradually increases to higher steady-rate level.Steady state level of ventilation maintained.Recovery period gradual return to resting levels.Phase IV higher than resting levels coincide with EPOC.
4Ventilation in Steady Rate Exercise Ventilatory equivalent for carbon dioxide (VE:VO2): ratio of minute ventilation to carbon dioxide produced.Remains constant during steady rate exercise because pulmonary ventilation eliminates CO2 .
5Ventilation in Non-Steady-Rate Exercise Minute ventilation (VE) increases in proportion to oxygen consumption over range from rest to moderate exercise.VE increases dispropor-tionately to oxygen consumption over range from moderate to strenuous.
6Ventilation in Non-Steady-Rate Exercise The point at which ventilation increases disproportionately with oxygen uptake during incremental exercise is termed: ventilatory threshold (VT).
7Ventilation in Non-Steady-Rate Exercise Lactic acid generated during anaerobic glycolysis is buffered in blood by sodium bicarbonate.Lactic acid + NaHCO3 →Na Lactate + H2CO3 → H20 + CO2
8Ventilation in Non-Steady-Rate Exercise The excess, non-metabolic CO2 stimulates ventilation.Recall that metabolic CO2 is produced in Krebs Cycle in oxidation of acetyl CoA.
9Ventilation in Non-Steady-Rate Exercise The non-metabolic CO2 from buffering HLa drives increased VE to eliminate it, so VE: VCO2 remains constant.The increased in VE exceeds increase in VO2 disproportionately.The point at which VEO2 breaks with linearity is the ventilatory threshold.RER = 1 where two lines intersect. R values > 1 indicate CO2 production exceeds O2 consumption, evidence of non-metabolic CO2 production.
10Ventilation in Non-Steady-Rate Exercise As exercise intensity increases, blood lactate begins to systematically increase over a baseline value of 4 mM/L termed onset of blood lactate.Blood lactate accumulation associated with changes in CO2 production, blood pH, bicarbonate, [H+], RER.
11Ventilation in Non-Steady-Rate Exercise Although variables (CO2 production, blood pH, bicarbonate, [H+], RER) are related to OBLA, doubtful that VT can be used to denote onset of anaerobic metabolism.OBLA directly assessed by measuring lactate level in blood.
12Ventilation in Non-Steady-Rate Exercise Common practice to use “bloodless” techniques e.g. R >1, or break in ventilatory equivalent for oxygen to denote anaerobic threshold.
13Does Ventilation Limit Aerobic Capacity for Average Person? If inadequate breathing capacity limited aerobic capacity, ventilatory equivalent for oxygen would decrease.Actually, healthy person tends to over-breathe in relation to VO2.In strenuous exercise, decreases arterial PCO2 & increase Alveolar PO2.
14Work of BreathingTwo major factors determine energy requirements of breathingCompliance of lungsResistance of airways to smooth flow of airAs rate & depth of breathing increase during exercise, energy cost of breathing increases too.At maximal exercise when VE= 100 L/m, oxygen cost of breathing represents 10-20% of total VO2.
15Work of BreathingAcute effects of 15 puffs on a cigarette during a 5-minute period3 fold increase in airway resistanceLasts an average 35 minutesSmokers exercising at 80%Energy requirement of breathing after smoking was 14% of oxygen uptakeEnergy requirement of breathing no cigarettes was only 9%.
16ReferencesAxen and Axen Illustrated Principles of Exercise Physiology. Prentice Hall.Kapit, Macey, Meisami Physiology Coloring Book. Harper & Row.McArdle, Katch, Katch Image Collection Essentials of Exercise Physiology, 3rd ed. Lippincott William & Wilkens.