Control of Ventilation

1
Control of Ventilation

• Respiratory control center
• Receives neural and humoral input
• Feedback from muscles
• CO2 level in the blood
• Regulates respiratory rate

2
Location of Respiratory Control Centers
3
Neural Input to the Respiratory Control Center

• 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

4
Humoral Input to the Respiratory Control Center

• 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

5
Ventilation vs. Increasing PCO2
6
Ventilation vs. Decreasing PO2
7
Ventilatory Control During Exercise

• Submaximal exercise
• Linear increase due to
• Central command
• Humoral chemoreceptors
• Neural feedback
• Heavy exercise
• Exponential rise above Tvent
• Increasing blood H

8
Respiration Control during Submaximal Exercise
9
Respiratory Control during Exercise

• Central commmand initially responsible for
  increase in VE at onset
• combination of neural and humoral feedback from
  muscles and circulatory system fine-tune VE
• Ventilatory threshold may be result of lactate or
  CO2 accumulation (H) as well as K and other
  minor contributors

10
Effect of Training on Ventilation

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

11
Training Reduces Ventilatory Response to Exercise
12
Final Note

• 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

13
Acid-Base Balance
14
Acids and Bases

• 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 (HCO3-)
• Buffer - compound that resists changes in pH
• bicarbonate (sorry)

15
pH

• pH -log10 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

16
Acidosis and Alkalosis
17
Acid Production during Exercise

• CO2 - volatile because gas can be eliminated by
  lungs
• CO2 H2O lt--gt H2CO3 lt--gt H HCO3-
• 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

18

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

19
Sources of H
20
Buffers

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

21
Intracellular Buffers

• proteins
• phosphates
• PC
• bicarbonate

22
Insert table 11.1
23
Extracellular Buffers

• bicarbonate - most important buffer in
  bodyremember the reactionhemoglobin - important
  buffer when deoxygenatedpicks up H when CO2 is
  being dumped into bloodproteins - not important
  due to low conc.

24
Buffering Capacity of Muscles vs. Blood
25
Respiration and Acid-Base Balance

• CO2 has a strong influence on blood pH
• as CO2 increases pH decreases (acidosis) CO2
  H2O gt H HCO3-
• as CO2 decreases pH increases (alkalosis)
• so, by blowing off excess CO2 can reduce acidity
  of blood

26
Changes in Lactate, Bicarb and pH vs. Work Rate
27
Lines of Defense against pH Change during Intense
Exercise