Pulmonary Ventilation during Pulmonary Ventilation during Exercise Exercise

Ventilation in Steady Rate Ventilation in Steady Rate ExerciseExercise

During light & moderate steady rate exercise, During light & moderate steady rate exercise, VVEE:VO:VO2 2 linear relationship.linear relationship.

Ventilatory equivalent for oxygenVentilatory equivalent for oxygen (V(VEE:VO:VO22): ): ratio of minute ventilation to oxygen uptake.ratio of minute ventilation to oxygen uptake.– Usually 25 : 1 during submaximal exercise up to Usually 25 : 1 during submaximal exercise up to

55% max.55% max.

Ventilation in Steady Rate Ventilation in Steady Rate ExerciseExercise

Ventilatory response to Ventilatory response to fixed level of submaximal fixed level of submaximal exercise can be divided exercise can be divided into 4 phases.into 4 phases.

1.1. Sudden increase at onset.Sudden increase at onset.

2.2. Ventilation gradually Ventilation gradually increases to higher steady-increases to higher steady-rate level.rate level.

3.3. Steady state level of Steady state level of ventilation maintained.ventilation maintained.

4.4. Recovery period gradual Recovery period gradual return to resting levels.return to resting levels.

Phase IV higher than Phase IV higher than resting levels coincide with resting levels coincide with EPOC.EPOC.

Ventilation in Steady Rate Ventilation in Steady Rate ExerciseExercise

Ventilatory equivalent for carbon dioxideVentilatory equivalent for carbon dioxide (V(VEE:VO:VO22): ratio of minute ventilation to ): ratio of minute ventilation to carbon dioxide produced.carbon dioxide produced.– Remains constant during steady rate exercise Remains constant during steady rate exercise

because pulmonary ventilation eliminates CObecause pulmonary ventilation eliminates CO22 . .

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

Minute ventilation Minute ventilation (V(VEE) increases in ) increases in proportion to oxygen proportion to oxygen consumption over consumption over range from rest to range from rest to moderate exercise.moderate exercise.

VVEE increases increases dispropor-tionately dispropor-tionately to oxygen to oxygen consumption over consumption over range from moderate range from moderate to strenuous.to strenuous.

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

The point at which The point at which ventilation ventilation increases increases disproportionately disproportionately with oxygen with oxygen uptake during uptake during incremental incremental exercise is termed: exercise is termed: ventilatory ventilatory thresholdthreshold ( (VTVT).).

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

Lactic acid Lactic acid generated during generated during anaerobic glycolysis anaerobic glycolysis is buffered in blood is buffered in blood by sodium by sodium bicarbonate.bicarbonate.

Lactic acid + NaHCOLactic acid + NaHCO33 →→

Na Lactate + HNa Lactate + H22COCO33 → →

HH220 + 0 + COCO22

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

The excess, non-The excess, non-metabolic metabolic COCO22 stimulates stimulates ventilation.ventilation.

Recall that Recall that metabolic COmetabolic CO22 is is produced in Krebs produced in Krebs Cycle in oxidation Cycle in oxidation of acetyl CoA.of acetyl CoA.

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

The non-metabolic COThe non-metabolic CO22 from buffering HLa from buffering HLa drives increased Vdrives increased VEE to to eliminate it, so eliminate it, so VVEE: VCO: VCO22 remains constant.remains constant.

The increased in VThe increased in VEE exceeds increase in VOexceeds increase in VO22 disproportionately.disproportionately.

The point at which VThe point at which VEEOO2 2

breaks with linearity is breaks with linearity is the the ventilatory ventilatory thresholdthreshold..RER = 1 where two lines intersect. R values > 1 indicate CO2 production exceeds O2 consumption, evidence of non-metabolic CO2 production.

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

As exercise intensity As exercise intensity increases, blood lactate increases, blood lactate begins to systematically begins to systematically increase over a baseline increase over a baseline value of 4 mM/L termed value of 4 mM/L termed onset of blood lactate.onset of blood lactate.

Blood lactate Blood lactate accumulation associated accumulation associated with changes in COwith changes in CO22 production, blood pH, production, blood pH, bicarbonate, [Hbicarbonate, [H++], RER.], RER.

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

Although variablesAlthough variables (CO(CO22 production, blood pH, production, blood pH,

bicarbonate, [Hbicarbonate, [H++], RER)], RER) are are related to OBLA, related to OBLA, doubtful that VT can doubtful that VT can be used to denote be used to denote onset of anaerobic onset of anaerobic metabolism.metabolism.

OBLA directly OBLA directly assessed by assessed by measuring lactate measuring lactate level in blood.level in blood.

Ventilation in Non-Steady-Rate Ventilation in Non-Steady-Rate ExerciseExercise

Common practice Common practice to use “bloodless” to use “bloodless” techniques e.g. R techniques e.g. R >1, or break in >1, or break in ventilatory ventilatory equivalent for equivalent for oxygen to denote oxygen to denote anaerobic anaerobic threshold.threshold.

Does Ventilation Limit Aerobic Does Ventilation Limit Aerobic Capacity for Average Person?Capacity for Average Person?

If inadequate breathing If inadequate breathing capacity limited aerobic capacity limited aerobic capacity, ventilatory capacity, ventilatory equivalent for oxygen equivalent for oxygen would decrease.would decrease.

Actually, healthy person Actually, healthy person tends to over-breathe in tends to over-breathe in relation to VOrelation to VO22..

In strenuous exercise, In strenuous exercise, decreases arterial PCOdecreases arterial PCO22 & increase Alveolar PO& increase Alveolar PO22..

Work of BreathingWork of Breathing Two major factors Two major factors

determine energy determine energy requirements of breathingrequirements of breathing

1.1. Compliance of lungsCompliance of lungs

2.2. Resistance of airways to Resistance of airways to smooth flow of airsmooth flow of air

As rate & depth of As rate & depth of breathing increase during breathing increase during exercise, energy cost of exercise, energy cost of breathing increases too.breathing increases too.

At maximal exercise when At maximal exercise when VVEE= 100 L/m, oxygen cost = 100 L/m, oxygen cost of breathing represents of breathing represents 10-20% of total VO10-20% of total VO22..

Work of BreathingWork of Breathing Acute effects of 15 puffs Acute effects of 15 puffs

on a cigarette during a 5-on a cigarette during a 5-minute periodminute period– 3 fold increase in airway 3 fold increase in airway

resistanceresistance– Lasts an average 35 minutesLasts an average 35 minutes

Smokers exercising at Smokers exercising at 80%80%– Energy requirement of Energy requirement of

breathing after smoking was breathing after smoking was 14% of oxygen uptake14% of oxygen uptake

– Energy requirement of Energy requirement of breathing no cigarettes was breathing no cigarettes was only 9%.only 9%.

ReferencesReferences

Axen and Axen. 2001. Axen and Axen. 2001. Illustrated Illustrated Principles of Exercise PhysiologyPrinciples of Exercise Physiology. . Prentice Hall.Prentice Hall.

Kapit, Macey, Meisami. 1987. Kapit, Macey, Meisami. 1987. Physiology Physiology Coloring BookColoring Book. Harper & Row. . Harper & Row.

McArdle, Katch, Katch. 2006. Image McArdle, Katch, Katch. 2006. Image Collection Collection Essentials of Exercise Essentials of Exercise PhysiologyPhysiology, 3, 3rdrd ed. Lippincott William & ed. Lippincott William & Wilkens.Wilkens.