IPHY 3430 9-27-11

Review:During inhalation/exhalation at rest:pressure differential of about 1 mm

759mmHg

760

Inhalation at rest

761

760

Exhalation at rest

Review:

During exercise, pressure differentials greater than 1 mm generated due to greater numbers of muscles contracting with greater force, resulting in larger expansion of thoracic cavity and lungs.

750

760mmHg 770

760ExhalationInhalation

So,…..

Quiet breathing: 500 ml x 12 b/m = 6 L/min

Exercise: 2300 ml x 40-50 b/m = 100-120 L/ min

Factors that can affect gas exchange by influencing flow and lung volume

Ventilation: Air Flow = P/ resistance

SNS --bronchodilationPNS--bronchoconstriction

Chronic obstructive pulmonary disease (COPD)Asthma,emphysema, chronic bronchitis

Factors that reduce lung volume: pneumonia, cancer, tuberculosis

Gas exchange

Between outside air and lungs= ventilation

Between alveolar air and blood = diffusion

Diffusion rate = P x surface area x solubility coefficient distance x M.W.1/2

Physical principles governing diffusion1. Gases diffuse down partial pressure gradient (PO2, PCO2, PN2, etc)2. Diffusion of one gas unaffected by diffusion of another3. In lungs, all gases diffuse through water 4. The bigger the partial pressure gradient, the faster the rate of diffusion.

Partial pressures of gases (mm Hg)

Gas Air AlveolarN2 597 (78.6%) 569 (74.9%)O2 159 (20.8%) 104 (13.6%)CO2 0.3 ( 0.04%) 40 (5.3%)H20 3.7 (0.5%) 47 (6.2%)

760 760

Oxygen Diffusion at rest

Air--> alveoli-->arteriolar blood--> cells(159) (100) (100) (40)

lungs

venous

arteriolar

cells100

100

40 40 PO2 = 60

PO2 = 60

Oxygen Diffusion during exercise

Air--> alveoli-->arteriolar blood--> cells(159) (100) (100) (20)

lungs

venous

arteriolar

cells100

100

20 20 PO2 = 80

PO2 = 80

CO2 Diffusion during rest

Air<-- alveoli <--venous blood <-- cells (.3) (40) (46) (46)

lungs

venous

arteriolar

cells40

40

46 46 PCO2 = 6

PCO2 = 6

CO2 Diffusion during exercise

Air<-- alveoli <--venous blood <-- cells (.3) (40) (55) (55)

lungs

venous

arteriolar

cells40

40

55 55 PCO2 = 15

PCO2 = 15

During exercise: Alveolar PO2 (104) and PCO2 (40) MUSTbe maintained at those levels by increased rate and depth of ventilation in order to ensure that partial pressure gradients are as large as possible.Air<-- alveoli <--venous blood <-- cells (.3) (40) (55) (55)

lungs

venous

arteriolar

cells40

40

55 55 PCO2 = 15

PCO2 = 15

CO2 mustrise

High AltitudeAltitude Pb PO2 Alveolar PO2sea level 760 159 104 10,000 523 110 67 20,000 349 73 40

At 10,000 ftAir--> alveoli --> arteriolar blood --> cells (110) (67) (67) (40)

lungs

venous

arteriolar

cells67

67

40 40 PO2 = 27

PO2 = 27

At 20,000 ftAir--> alveoli --> arteriolar blood --> cells (73) (40) (40) (must be >40)

lungs

venous

arteriolar

cells40

40

20 20 PO2 = 20

PO2 = 20