L8 Acid Base Balance and Control of Breathing

how is o2 tranported in blood

98.5% to Hb

1.5 % plasma

How is CO2 transported in the blood?

7-10% plasma

20-23% carbaminohemoglobin

70% bicarbonate

what chemical factors influence the rate and depth of breathing

hypercapnia and hypoxia

central chemoreceptors

Receptors in the central nervous system that monitor the PCO2 pH of CSF to help regulate ventilation rate.

peripheral chemoreceptors

Receptors in the carotid arteries and the aorta that monitor blood pH to help regulate ventilation rate.

how does training influence VE during exercise

- increased VE efficiency

- higher tolerance for high CO2 levels

- better adaptation

Organs involved in acid production and regulation

lungs, kidneys, liver

O2-Hb disassociation with decreased pH

right shift, weakened bonds (Bohr effect)

O2-Hb disassociation with decreased temp

right shift, weakened bonds

CO2 transport in blood

1. Dissolves in plasma

2. Combines with Hb

3. Combines with water, releasing H+ and HCO3-, which exits RBC, and Cl- enters to balance charge

how is Co2 released at lungs

1. Diffuses from plasma

2. Carbaminohb dissociates and CO2 diffuses

3. HCO3- reenters and forms Co2 is formed, diffusing out

what happens to pulmonary ventilation in rest to work transition

increases abruptly, then rises gradually to SS

what happens to arterial pressures of O2 and CO2 in rest to work transition

PO2 slightly decreases, PCO slightly increases, but remain relatively unchanged

what happens to pulmonary ventilation in incremental exercise

linear increase with O2 uptake to 50-75% Vo2max, beyond this point is Tvent

difference between untrained and trainer person's change in pulmonary ventilation in incremental exercise

trained increases more gradually and Tvent is at a higher threshold

what happens to arterial PO2 in incremental exercise untrained

maintain arterial Po2 within 10-12 mmHg of normal

what happens to arterial PO2 in incremental exercise trained

drop in arterial PO2 of 30-40mmHg

exericse induced hypoxemia

location of respiratory control center

medulla oblongata

preBotzinger complex

sets basic rhythm of breathing

Retrotrapezoid nucleus (RTN)

site of integration of central command and exercise pressor reflex signals that increase ventilation during exercise

parafacial respiratory group

Group of neurons within the ventral respiratory group important for generation of active contraction of abdominal muscles

Pons function in breathing

fine tune breathing

Types of Input to Respiratory Control Center

- neural (higher brain centers, afferent signal from mechanoreceptors)

- humoral (blood borne stimuli, chemoreceptors)

pFRG/RTN central chemoreceptors respond to what

increased PCO2, and H+ in CSF

aortic peripheral chemoreceptors respond to what

pH, PCO2

carotid peripheral chemoreceptors respond to what

PH, PCO2, PO2

a 1 mmHG rise in arterial PCO2 can increase ventilation by

2L/min

what happens to VE following training

lower VE at similar relative intensities due to enhanced efficiency of bioenergetic pathways

afferent feedback to respiratory center

mechanoreceptors in muscles and joints

what is the fine tuning mechanism of ventilation during exercise

afferent feedback from muscles and chemoreceptors

what causes the alinear rise in ventialtion associated with lactate threshold

rising H+ levels from lactic acid

3 main contributors to muscle acidosis

1. production of CO2/carbonic acid

2. production of lactic acid

3. ATP breakdown, releasing H+

4 types of intracellular buffers

1. cellular proteins

2. histidine dipeptide (carnosine)

3. phosphate groups

4. bicarbonate

3 extracellular buffers

1. bicarbonate

2. Hb

3. Blood proteins

2 main H+ transporters on the sarcolemma

sodium hydrogen exchanger (NHE)

MCT1 & MCT4

what muscle fiber type has a higher buffering capacity

fast twitch T2

Effect of Exercise Training on Buffering Capacity

increases muscle buffering capacity, and level of carnosine and MCT transporters

Henderson-Hasselbalch equation

pH = pKa + log [base]/[acid]

What % of H+ is buffered by each intracellular buffer type

60% cellular proteins

20-30% bicarbonate

10-20% phosphate groups

muscle and blood pH during exercise

- muscle and blood pH decrease, muscle pH is 0.4-0.6 units lower than blood pH

factors influencing H+ production

- exercise intensity

- amount of muscle mass involved

- duration

what happens when supplementing with sodium citrate

improved extracellular buffering capacity and high intensity exercise performance

what happens when supplementing with beta alanine (precursor to carnosine)

intracellular buffer, buffer and increase time to exhaustion

Do the lungs adapt to exercise training?

not really: lung structure and pulmonary function remain relatively unchanged, and pulmonary gas exchange does not improve.

why is the lung "overbuilt"

it's capacity for gas exchange is far greater than the needs for O2 and CO2 during exercise.

exercise induced hypoxemia

is probably caused by a red blood cell transit time through the pulmonary circuit that is too fast to allow for adequate diffusion and the achievement of gas equilibrium.

does the pulmonary system limit exercise performance

no at prolonged submax exercise, put potentially near VO2max

how does breathing low density air (heliox) affect exercise performance

can improve exercise performance by reducing WOB

what are the mechanical components of breathing that implicate WOB

elastic and resistive properties

do females have a greater or lower WOB

greater

how does breathing through a smaller tube during exercise affect WOB

increases SCM EMG activity, and metabolic demand, increasing overall WOB and VO2 needs

considering WOB is particularily important when working with what type of demographic

people with COPD, since they will have increased expiratory flow resistance

what V/Q ratio is considered ideal and why

1 because it means that the ventilation into the lungs is equally to the blood being perfused, no extra air or flow.

How do kidneys play a role in long term acid base balance

only contribute at rest because they talk a long time to exert their effects:

regualte bicarb concentration in blood