• Respiratory control center
– Receives neural and humoral input
• Feedback from muscles
• CO
2 level in the blood
– Regulates respiratory rate

Location of Respiratory Control Centers

• motor cortex - impulses from cortex may
“spill over” when passing through medulla on way to heart and muscles
• afferent - from GTO, muscle spindles or joint pressure receptors
• mechanoreceptors in the heart relay changes in Q

• central chemoreceptors - respond to changes in CO2 or H+ in CSF
• peripheral chemoreceptors - aortic bodies and carotid bodies
– both similar to central receptors, carotids also respond to increases in K+ and decreases in
PO2

Ventilation vs. Increasing PCO2

Ventilation vs. Decreasing PO2

• Submaximal exercise
– Linear increase due to:
• Central command
• Humoral chemoreceptors
• Neural feedback
• Heavy exercise
– Exponential rise above T vent
• Increasing blood H +

Respiration Control during Submaximal
Exercise

• Central commmand initially responsible for increase in V
E at onset
• combination of neural and humoral feedback from muscles and circulatory system fine-tune V
E
• Ventilatory threshold may be result of lactate or CO
2 accumulation (H+) as well as
K+ and other minor contributors

• Ventilation is lower at same work rate following training
– May be due to lower blood acidity
– Results in less feedback to stimulate breathing

Training Reduces Ventilatory Response to Exercise

• the pulmonary system is not thought to be a limiting factor to exercise in healthy individuals
• the exception is elite endurance athletes who can succumb to hypoxemia during intense near maximal exercise

Acid-Base Balance

• Acid - compound that can loose an H+ and lower the pH of a solution
– lactic acid, sulphuric acid
• Base - compound that can accept free H+ and raise the pH of a solution
– bicarbonate (HCO
3
)
• Buffer - compound that resists changes in pH
– bicarbonate (sorry)

• pH = -log
10
[H+]
– pH goes up, acidity goes down
• pH of pure water = 7.0 (neutral)
• pH of blood = 7.4 (slightly basic)
• pH of muscle = 7.0

Acidosis and Alkalosis

• CO2 - volatile because gas can be eliminated by lungs
– CO
2
+ H
2
O <--> H
2
CO
3
<--> H + + HCO
3
-
• The next point is erroneous
• Lactic acid and acetoacetic acid - CHO and fat metabolism respectively
– termed organic acids
– at rest converted to CO2 and eliminated, but during intense exercise major load on acid-base balance

• Sulphuric and Phosphoric acids - produced by oxidation of proteins and membranes or
DNA
– called fixed because not easily eliminated
– minor contribution to acid accumulation

• maintain pH of blood and tissues
• accept H+ when they accumulate
• release H+ when pH increases

• proteins
• phosphates
• PC
• bicarbonate

• bicarbonate - most important buffer in body remember the reaction hemoglobin - important buffer when deoxygenated picks up H+ when CO2 is being dumped into blood proteins - not important due to low conc.

Buffering Capacity of Muscles vs. Blood

• CO
2 has a strong influence on blood pH
• as CO
2 increases pH decreases (acidosis)
CO2 + H
2
O > H + + HCO
3
-
• as CO2 decreases pH increases (alkalosis)
• so, by blowing off excess CO2 can reduce acidity of blood

Changes in Lactate, Bicarb and pH vs.
Work Rate

Lines of Defense against pH Change during
Intense Exercise