Respiratory Physiology

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Respiratory Physiology – outline notes
By at September 15, 2011 | 6:43 am | Print
Respiratory System
I. Functions:
A. Provides area for gas exchange between air and blood
B. Moves air to and from area of gas exchange
C. Protects gas exchange surfaces
D. Sound production
E. Provides olfactory sensations to the CNS
F. Capillaries in lungs produce angiotensin converting enzyme (ACE) II. 4 Respiratory processes
A. Pulmonary ventilation (breathing)
1. Move air in and out of lungs
B. External respiration
1. Gas diffusion across respiratory membrane
2. O2 loading / CO2 unloading
C. Internal respiration
1. Gas diffusion to tissues of the body
2. O2 unloading / CO2 loading
D. Transport of O2 and CO2
III. Pulmonary ventilation
A. Movement of air in/out to maintain alveolar ventilation
B. Boyle’s Law
1. Inverse relationship b/t Pressure and Volume
2. P1V1=P2V2
3. P = 1/V
4. If you double the external pressure on a flexible container, its volume will drop by half : If you reduce the external pressure by half, the volume of the container will double
C. Air flows from high to low Pressure
D. Mechanisms of Pulmonary Ventilation
1. Inhalation
a. Diaphragm contracts, rib cage in elevated
b. Pressure in lungs decreases due to increase volume
c. Air flows in from high to low pressure
2. Exhalation
a. Pressure in lungs increases due to volume decrease
b. Air moves out from high to low pressure
E. Compliance
1. Expandability of lungs
2. Anything decreasing lung compliance will make it more difficult to fill and empty them
a. Increased alveolar surface tension
b. Decreased mobility of thoracic cage
F. Resistance to gas flow – friction in airways
1. Gas Flow = ∆P / resistance
2. Asthma
G. Pressure changes during breathing
1. Atmospheric pressure = 760 mm Hg
2. Intrapulmonary pressure (intra-alveolar)
a. Pressure inside alveoli
b. 759 mm Hg during inhalation (-1 mm Hg)
c. 761 mm Hg during exhalation (+1 mm Hg)
d. Valsalva maneuver
3. Intrapleural pressure
a. Pressure in pleural cavity
1) Between visceral and parietal pleurae
b. Averages –4 mm Hg
c. Negative pressure due to:
1) Elastic fibers pulling lungs away from chest wall
4. Pneumothorax – entry of air into pleural cavity
a. breaks fluid bond of pleurae
b. atelectasis – lung collapse
H. Modes of Breathing
1. Quiet breathing
a. Inhalation – muscle contraction
b. Exhalation – passive (elastic rebound)
c. Deep breathing – use diaphragm
d. Shallow breathing – external intercostals
1) Pregnancy – due to pressure on diaphragm
2. Forced breathing
a. Accessory muscles
IV. Respiratory Rates and Volumes
A. Respiratory minute volume (VE) – ml / min
1. VE = Respiratory rate (f) x Tidal volume (VT)
2. 6.0 L = 12 breaths/min x 500 ml
B. Alveolar ventilation (VA)
1. VD – anatomic dead space
a. 150 ml of tidal volume never reaches alveoli
2. VA = f x (VT – VD)
3. 4.2 L = 12 x (500 – 150)
C. Overhead of Volumes and Capacities
V. Gas Laws
A. Partial Pressure (Dalton’s Law)
1. Total pressure exerted by a mixture of gases is the sum of individual pressures exerted by each gas.
2. Sum of partial pressures = total pressure
.21 x 760 mmHg = 159 mmHg3. O2 = 21% ——
pp = 5974. N2 = 78.6% ——–
B. Henry’s Law
1. Amount of gas in solution is proportional to pp of that gas 2. At gas and liquid contact – gas under pressure will force gas into liquid until equilibrium
3. Ex) soda under pressure in can until opened
4. At given pp and temp – gas solubility determines am’t of gas in solution
5. CO2 is 20 times as soluble as O2
* In a pulmonary vein
-2.62 ml/dl of CO2 (pCO2 = 40 mmHg)
-0.29 ml/dl of O2 (pO2 = 100 mmHg)
-1.25 ml/dl of N2 ( pN2 = 573 mmHg)
6. Pressure = [dissolved gas] / Solubility coefficient
7. Solubility coefficients
a. O2 = 0.024
b. CO2 = 0.57
c. N2 = 0.012
C. Diffusion (D) of gases
D = ∆P x A x S / d x √MW
∆P – pressure difference
A – cross-sectional area
S – solubility of gas
D –...
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