OUTLINE 17

I. DIVISIONS OF RESPIRATORY AIR
A. Tidal volume (TV)
500 ml
B. Inspiratory Reserve Volume(IRV)
Fem: 1900ml Male: 3300ml
C. Expiratory Reserve Volume(ERV)
Fem: 700 ml Male: 1000 ml
D. Residual Volume (RV)
1000 ml
E. Expiratory Capacity =
TV + ERV
F. Inspiratory Capacity =
TV + IRV
G. Functional Residual Capacity =
ERV + RV
H. Vital Capacity = IRV + TV + ERV
Fem: 3100 ml Male: 4800 ml

1. VC decreases with aging
a. IRV decreases as lung CL decreases
b. ERV decreases as lung elasticity decreases
2. VC is reduced with restrictive disorders
I. Total lung capacity = IRV + TV + ERV + RV

II. ALVEOLAR VENTILATION
A. Alveolar Ventilation vs. Pulmonary Ventilation
1. Computations:
a. Pulmonary Ventilation = TV x RR
TV tidal volume; RR respiratory rate
500 ml x 13 cpm = 6500 ml/min

b. Alveolar Ventilation (AV) = (TV-ADS) x RR
ADS: anatomical dead space
(500 ml - 150 ml) 13 cpm = 4550 ml/min

B. Rate of Turnover of Alveolar Gas
1. During inspiration and expiration, volume change is not great in the alveoli.

2. Gas exchange is constant during inspiration and expiration.

3. It takes 90 sec to replace all the air in an alveolus

III. PULMONARY DIFFUSION

A. Structure of the alveolar-capillary membrane: 4 layers
1. Surfactant
2. Type I cell
3. Fused Basement membranes
4. Capillary endothelial cell

B. Influencing factors on the rate of gas diffusion
(.75 sec for diffusion; complete within .25 sec)

1. Partial pressure of gases: increase, increase rate

2. Surface area: increase, increase rate
a. Increased during maximal activity because increase in blood pressure and air flow throughout lung

3. Thickness of the membrane: increase, decrease rate

4. Solubility of Gas; increased, increase rate
a. CO2, increased solubility

IV. VENTILATION/PERFUSION RATIOS (VA/Q)
A. Definition: Ratio between alveolar ventilation and blood flow
1. VA : alveolar ventilation
2. Q: Blood flow

B. Ideal Value and Normal Ratios

1. Ideal 1:1; VA = Q (Air flow matches blood flow)

2. Real: About .9

a. Alveolar ventilation = (TV - ADS) x RR

(500 - 150) X 13 = 4550 ml
Blood flow = 5000 ml/min
4550/5000 = .91

b. Assumes all parts of the lungs are equally ventilated and perfused
1. Although this is not the case, regional airflow matches regional bloodflow in the base of the lung

C. Influencing Factors For Ventilation-Perfusion Ratio:
AIR FLOW TO THE BASE
1. Ventilation: Transpulmonary Pressures

a. Lungs are pyramid shaped
b. Thoracic cage expands
furthest at the base
c. Pressure gradient is
greatest to the base
d. Air flows to the base

2. Ventilation: Airway Resistance

a. Root of lung to the base
is not tortuous
1. Little turbulence,
air flows to the base

b. Root of lung to apex is tortuous
1. Air flow is turbulent
2. Increased resistance so
decreased air flow

BLOOD FLOW TO THE BASE
3. Perfusion: Gravity

a. The pulmonary blood pressure at rest (25 mm Hg) allows for blood to flow to capillaries in the largely in the base of the lung, due to the force of gravity

b. Capillaries in the apex of the lung receive minimal blood flow and therefore collapse, temporarily

c. With increased activity, blood pressure increases and respiration increases
1. More air reaches alveoli in the apex
2. More blood flows through the capillaries in the apex
3. This increases gas exchange in accord with the increased demand


4. Perfusion: Alveolar O2 and CO2 levels
Unlike other tissues in the body:
a. Blood flow is greatest to alveoli with high O2 levels
b. Blood flow is lowest to alveoli with high CO2 levels
c. Because air flow is greatest to the base, O2 levels are highest at the base, and blood flow to the base is greatest

5. *Note: Airflow is 2-3 higher than blood flow in the apex of the lung. Some air flows to the apex but most of the blood does not, instead heading to the base due to gravity and vascular reflexes (vasodilation to areas of highest O2).

D. Clinical Applications: