Lecture Notes of a Knowledgeable Respiratory Specialist
HM 273 Lectures 7 & 8 Outline
I chose these because they made the most sense to me based on the way I think of breathing. mgw
Overview:
1. External vs. internal respiration
2. Pulmonary ventilation
3. Pulmonary diffusion
4. Transport of O2 and CO2
5. Gas exchange at the muscles
6. Regulation of pulmonary ventilation
7. Ventilation & Energy metabolism
8. Respiratory regulation of acid-base balance
9. Respiratory adaptations during exercise and training
1. External vs. Internal Respiration
External Respiration
® processes that move gases from outside body to the lungs and into the bloodi) Pulmonary ventilation - breathing
ii) Pulmonary diffusion - exchange of O2 and CO2 between lungs and blood
Internal Respiration
® process of gas exchange between blood and tissuesi) Capillary gas exchange - exchange of O2 and CO2 between capillaries and metabolically active tissues
* NOTE: internal and external respiration
Figure 8.1 pg. 247 Wilmore & Costill (Ed.2)
(Figure 9.1 pg. 192 " (Ed.1))
2. Pulmonary Ventilation
Inspiration
® active process; requires external intercostal muscles and diaphragm®
during heavy exercise additional muscles involvedExpiration
® a passive process in resting state®
during forced breathing or heavy exercise an active process is involved requiring internal intercostal muscles** NOTE:
work of breathing during exerciseTERMS:
VV = VI or VE / min
Vt =
VC =
FVC =
FEV1 =
MVV =
3. Pulmonary Diffusion
2 Major Functions:
1. replenish blood’s O2 supply
2. remove CO2 returning from tissues
Respiratory Membrane: where gas exchanges between the air in alveoli and blood in pulmonary capillaries
3 components:
1. alveolar wall
2. capillary wall
3. basement membranes
Figure 8.3 pg. 250 Wilmore & Costill (Ed.2)
(Figure 9.4 pg. 196 " (Ed.1))
FICK’S Law of Diffusion: amount of gas that moves across a membrane is proportional to the surface area but inversely proportional to the thickness
\
blood gas barrier at alveoli is very thin and has a total area ~ 50-100 m2Partial Pressure of Gases
Þ
individual pressure from each gas in a mixtureDALTON’S LAW: the total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases in the mixture
air we breathe:
Table 1. Partial Pressures in Room Air
|
Gas |
% |
Standard Atmospheric Pressure |
Partial Pressure |
|
PO2 |
20.93% |
760 mmHg |
159.1 mmHg |
|
PCO2 |
0.03% |
760 mmHg |
0.2 mmHg |
|
PN2 |
79.04% |
760 mmHg |
600.7 mmHg |
Gas Exchange in Alveoli
Fig. 8.4 pg. 252 Wilmore & Costill (Ed.2)
(Fig. 9.5 pg.197 " (ED.1))
4. Transport of O2 and CO2
O2 Transport
O2 is transported in blood by Hb (98%) or dissolved in plasma (2%)
®
only 3 ml O2 dissolved per L plasmax 3-5 L plasma = 9-15 ml dissolved O2
®
at rest we need 250 ml O2/minrequire O2 bound to Hb
Table 2. Hemoglobin O2 binding
|
Male |
Female |
|
|
[Hb] (g/100ml blood) |
15-16 |
~14 |
|
O2 content of blood (100% sat.) |
20 |
18.8 |
|
O2 content of blood (98% sat.) |
19.6 |
18.4 |
Note: Hb binds 1.34 ml O2/g Hb, therefore
15 g Hb/100ml blood x 1.34 ml O2/g Hb
= 20 ml O2/100 ml blood
Oxygen-Hb dissociation curve
Figure 8.5 pg. 254 Wilmore & Costill (Ed.2)
(Figure 9.6 pg. 199 " (Ed.1))
Summary:
® both result in greater offloading of O2 in muscle during exercisecurvilinear relationship between PO2 and %Hb saturation
rightshift of curve at low pH and high temperature
CO2 Transport
CO2 released from cells is carried in blood in 3 forms:
i) dissolved in plasma (10%)
ii) as bicarbonate ion (60-80%)
iii) bound to Hb (20%)
in Muscle in RBC
CO2 + H2O ----------> H2CO3 -----------> H+ + HCO3-
\
carbonic H+ buffered by Hb
anhydrase
in Lungs (alveolar capillaries)
H+ + HCO3- ---------> H2CO3 -----------> CO2 + H2O
\
carbonic CO2 expired
anhydrase
Note: direction of the CA reaction is determined by the PCO2 gradient:
PCO2 muscle > PCO2 venous blood > PCO2 alveolar
\
ventilation (to keep alveoli PCO2 low) drives removal of CO2 from tissues5. Gas Exchange at the Muscles
Review:
® a-vO2 diff = 4-5 ml/100ml blood at rest= amount of O2 taken up by tissues at rest
= proportional to O2 use for oxidative ATP regeneration
Fig. 8.6 pg. 256 Wilmore & Costill (Ed.2)
(Fig. 9.8 pg. 201 " (Ed.1))
Factors influencing O2 delivery and uptake:
O2 content of blood
®
not altered by exercise but ¯ by anemic conditionsamount of blood flow
by exerciselocal cellular conditions
¯
muscle pH during exercise will muscle O2 supply
temperature during exercise will muscle O2 supply
muscle CO2 will O2 unloading in muscleSummary of Respiration
Fig. 8.7 pg. 258 Wilmore & Costill (Ed.2)
(Fig. 9.9 pg. 202 " (Ed.1))
6. Regulation of Pulmonary Ventilation
Goal: to maintain homeostatic balance in blood PO2, PCO2 and pH
Mechanisms of Regulation:
in CO2 and H+ in blood going to brain activate neural input to rate and depth of breathingrespiratory muscles regulated by motor neurons from respiratory centers in medulla oblongata and pons (FEEDFORWARD)
respiration also regulated by changes in chemical environment (FEEDBACK)
i.e.
in PCO2, H+ and ¯ PO2 sensed by chemoreceptors in aortic arch and in carotid arterychange in PCO2 is strongest stimulus for regulating breathing
stretch receptors in pleurae, bronchioles and alveoli stimulate expiratory centers to shorten duration of inspiration (Hering-Breuer reflex)
see Fig. 8.8 pg. 260 Wilmore & Costill (Ed.2)
(Fig. 9.10 pg. 203 " (Ed.1))
Regulation of Pulmonary Ventilation During Exercise
Start of Exercise: Two Phase Increase in Ventilation
1. immediate
® feedforward regulation, produced by mechanics of body movement®
motor cortex activated & stimulates inspiratory center®
proprioceptive feedback from skeletal muscle and joints provides input about movement2. second, gradual phase
® feedback regulation from change in temperature and blood PO2, PCO2 and pH®
stimulation of inspiratory centers by chemoreceptors?? chemoreceptors in muscle and LV
see Fig. 8.9 pg. 261 Wilmore & Costill (Ed.2)
(Fig. 9.11 pg. 204 " (Ed.1))
Following Exercise:
1. energy demand drops immediately but pulmonary ventilation decreases at a relatively slow rate
2. slow recovery suggests post-exercise breathing regulated by acid-base balance (H+), PCO2 and temperature
3. recall: EPOC
Breathing Abnormalities During Exercise
DYSPNEA
CO2 and H+ which rate & depth of breathingshortness of breath
due to
also due to poor conditioning of respiratory muscles
\ respiratory muscles fatigue easilyHYPERVENTILATION
¯ CO2 and ¯ H+overbreathing
due to increase in breathing >> metabolic need for oxygen
results in decreased stimulus to breathe due to
swimmers
® hyperventilate before competitionADV
® improved mechanics during 1st 8-10s underwaterDISADV.
® alveolar & arterial PO2 ¯®
may impair muscle oxidation & delivery of O2 to CNS®
¯ O2 delivery AND drive to breatheValsalva Maneuver
during lifting of heavy objects; common in weight lifters
due to: 1. closing of glottis
2.
intra-abdominal pressure (forcibly contracting diaphragm & abdominal muscles)3.
intrathoracic pressure (forcibly contracting respiratory muscles)results in: 1. air trapped and pressurised in lungs
2. restriction of venous due to collapse of great veins
3. if over extended periods of time will
¯ cardiac output7. Ventilation & Energy Metabolism
Ventilatory Equivalent for Oxygen
= ratio between volume of ventilation (VE) and amount of O2 consumed (VO2)
= VE/VO2 (L air/ L O2/min)
®
rest values ~ 23-28 L air/ L O2/min®
mild exercise: no change®
near max. intensity: to ~ 30 L air/ L O2/min** Note: overall VE and VO2 well matched
\
breathing control systems match body’s need for O2Ventilatory Breakpoint
= point where VE
disproportionately to VO2= breakpoint in the VE vs. WL curve
see Fig. 8.10 pg. 264 Wilmore & Costill (Ed.2)
(Fig. 9.12 pg. 206 " (Ed.1))
Summary:
requirement for glycolytic energythought to occur when O2 requirements > O2 delivery (> VO2max)
thought to reflect
Lac- + H+ + NaHCO3 --------> NaLac + H2CO3H20 + CO2
\
inspiratory drive due to VCO2Anaerobic Threshold
thought to be the threshold at which glycolytic metabolism
results in an
VCO2:VO2 and \ RERsee Fig. 8.11 pg. 265 Wilmore & Costill (Ed.2)
Fig. 9.13 pg. 207 " (Ed.1))
Criteria for Defining Anaerobic Threshold:
1.
in VE/VO22.
® in VE/VCO2\
ventilation to remove CO2 but is disproportionate to need for O2** Note: anaerobic threshold occurs ~ at lactate threshold BUT NOT ALWAYS THE SAME since they reflect different processes
(Hint: Review notes on Lactate threshold)
8. Respiratory Regulation Acid-Base Balance
Buffering Capacity of Blood
see Table 8.2 pg. 267 Wilmore & Costill (Ed.2)
(Table 9.3 pg. 209 " (Ed.1))
Major regulators of Blood pH
1. chemical buffers
2. pulmonary ventilation
3. kidney function
see Table 8.3 pg. 268 Wilmore & Costill (Ed.2)
(Table 9.4 pg. 211 " (Ed.1)
9. Respiratory Limitations to Performance
to 15% total energyat rest respiratory muscles consume ~2% total energy
during heavy exercise energy cost of breathing
respiratory muscles show glycogen sparing and are fatigue resistant
\
do not likely "fatigue" during high intensity exercise¯ alveolar PO2 or hypoxemiain average individuals, no
BUT in some elite athletes hypoxemia observed near exhaustion
Q. Does the ventilation system limit exercise capacity??*
HM273, 1999 Lectures 7-8 Respiration and Ventilation
Wilmore & Costill Ed.2 pg. 245-270
Ed.1 pg. 191-211
*The bigger question is: Does exercise limit the ventilation system?
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