Respiratory system changes during exercises
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- During exercise, oxygen uptake and carbon dioxide production increase greatly. Large amounts of oxygen diffuse into the blood in the lungs, while carbon dioxide moves from the blood into the alveoli. Increased pulmonary ventilation maintains stable alveolar gas concentrations to allow for efficient oxygen and carbon dioxide exchange. - As exercise intensity increases, minute ventilation increases disproportionately to the rise in oxygen uptake at a point called the ventilatory threshold. This is due to non-metabolic carbon dioxide production from lactate buffering, which stimulates further ventilation. - The onset of blood lactate accumulation occurs when blood lactate levels begin to rise above baseline, typically between 55-65% of maximum oxygen uptake in untrained individuals. This
Respiratory system changes during exercises
- 2. ◦ Physical activity increases oxygen uptake and carbon dioxide production more than any other physiologic stress. Large amounts of oxygen diffuse from the alveoli into the blood returning to the lungs during exercise. Conversely, considerable carbon dioxide moves from the blood into the alveoli. Concurrently, increases in pulmonary ventilation maintain stable alveolar gas concentrations, so oxygen and carbon dioxide exchange proceeds unimpeded. ◦ Fig- the relationship between minute ventilation and oxygen uptake through the range of steady-rate and non–steady-rate exercise levels up to VO2max.
- 4. Ventilation in Steady-Rate Exercise ◦ During light and moderate exercise (VO2 2.5 L/min in this example), pulmonary ventilation increases linearly with oxygen uptake; ventilation mainly increases by increases in TV. The ventilatory equivalent for oxygen (V. E / VO2) represents the ratio of minute ventilation to oxygen uptake. ◦ This index indicates breathing economy because it reflects the quantity of air breathed per amount of oxygen consumed. ◦ Healthy young adults usually maintain V.E / VO2 at about 25 (i.e., 25 L air breathed per L oxygen consumed) during submaximal exercise up to about 55% of VO2max. ◦ Higher ventilatory equivalents occur in children, averaging about 32 in 6-year- old children.
- 5. ◦ Despite individual differences in the ventilatory equivalent for oxygen of healthy children and adults during steady-rate exercise, complete aeration of blood takes place because of two factors: 1. Alveolar PO2 and PCO2 remain at near-resting values 2. Transit time for blood flowing through the pulmonary capillaries proceeds slowly enough to permit complete gas exchange ◦ During steady-rate exercise, the ventilatory equivalent for carbon dioxide (V.E. / V.CO2) also remains relatively constant because pulmonary ventilation eliminates the carbon dioxide produced during cellular respiration.
- 6. Ventilation in Non–Steady-Rate Exercise ◦ Ventilatory Threshold Note in Figure 9.15 that as exercise oxygen uptake increases, minute ventilation eventually increases disproportionately to the increase in oxygen uptake. ◦ This increases the ventilatory equivalent above the steady-rate exercise value; it may reach as high as 35 or 40 in maximal exercise. The point at which pulmonary ventilation increases disproportionately with oxygen uptake during graded exercise has been termed ventilatory threshold (VT). ◦ At this exercise intensity, pulmonary ventilation no longer links tightly to oxygen demand at the cellular level. Rather, the “excess” ventilation relates directly to carbon dioxide’s increased output from the buffering of lactate that begins to accumulate from anaerobic metabolism.
- 7. ◦ Sodium bicarbonate in the blood buffers the lactate generated during anaerobic metabolism in the following reaction: ◦ Lactate + NaHCO3 Na lactate + H2CO3 H2O + CO2 ◦ Excess, non-metabolic carbon dioxide liberated in this buffering reaction stimulates pulmonary ventilation that disproportionately increases V.E / V.O2. The respiratory exchange ratio (V.CO2 / V.O2) exceeds 1.00 when additional carbon dioxide is exhaled because of acid buffering.
- 8. ◦ The term anaerobic threshold originally defined the abrupt increase in ventilatory equivalent caused by non-metabolic carbon dioxide production from lactate buffering. Some researchers believed this point signaled the body’s shift to anaerobic metabolism (lactate formation). The researchers proposed the anaerobic threshold as a noninvasive ventilatory measure of the onset of anaerobiosis. ◦ Subsequent research showed that the ratios of V.E / V.O2 or V .CO2 / V.O2 did not necessarily link in a causal manner with lactate production (or accumulation) in exercise. Even if the association between ventilatory dynamics and cellular metabolic events remains noncausal, useful information can be obtained about exercise performance by applying these indirect procedures. Figure 9.16 outlines possible underlying factors that relate to anaerobic threshold detected from pulmonary gas exchange dynamics during graded exercise.
- 10. ◦ Onset of Blood Lactate Accumulation Steady rate exercise indicates that oxygen supply and utilization satisfy the energy requirements of muscular effort. When this occurs, lactate production does not exceed its removal, and blood lactate does not accumulate. ◦ Figure 9.15 showed that exercise intensity or oxygen uptake where blood lactate begins to increase above a baseline level of about 4 mML1 indicates the point of onset of blood lactate accumulation (OBLA). OBLA normally occurs between 55% and 65% of V.O2max in healthy, untrained subjects and often equals more than 80% V.O2max in highly trained endurance athletes.
- 11. Causes of OBLA ◦ The exact cause of the OBLA remains controversial. Many believe it represents the point of muscle hypoxia (inadequate oxygen) and therefore anaerobiosis. Muscle lactate accumulation does not necessarily coincide with hypoxia because lactate forms even in the presence of adequate muscle oxygenation. The OBLA does imply an imbalance between the rate of blood lactate appearance and disappearance. The imbalance may not result from muscle hypoxia; rather, it may result from decreased lactate clearance in total or increased lactate production only in specific muscle fibers. Practitioners should cautiously interpret the specific metabolic significance of the OBLA and its possible relationship to tissue hypoxia.
- 12. ◦ OBLA and Endurance Performance ◦ The point of OBLA often increases with aerobic training without an accompanying increase in V.O2max. This suggests that separate factors influence OBLA and V.O2max. Traditionally, exercise physiologists have applied V.O2max as the main yardstick to gauge capacity. ◦ For endurance exercise. This measure generally relates to long-duration exercise performance but does not fully explain all aspects of success. Experienced distance athletes generally compete at an exercise intensity slightly above the point of OBLA. Exercise intensity at the OBLA has emerged as a consistent and powerful predictor of aerobic exercise performance. Changes in endurance performance with training often relate more closely to traininginduced changes in the exercise level for OBLA than to changes in V.O2max.
- 13. Stitch In The Side ◦ During intense exercise, individuals frequently experience a severe, sharp pain in the lower, lateral aspects of the chest wall. This pain, called a “stitch in the side,” has no universally accepted explanation nor has it been possible to duplicate its occurrence in the laboratory. It usually occurs during adjustment to new metabolic demands and occurs most frequently in untrained individuals, it seems reasonable to speculate insufficient blood flow (ischemia) to either the diaphragm or intercostal muscles as the cause.
- 14. Second Wind ◦ Second wind, experienced as a changeover from dyspnea (labored breathing, shortness of breath) to eupnea (normal breathing) as exercise progresses, probably reflects a change in skeletal muscular efficiency brought about by respiratory adjustments to a new workload. ◦ Second wind may also relate to the adjustments brought about by increasing muscle temperature and adjustments in sweat output associated with a new level of energy expenditure.
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