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