lecture 11 Flashcards
(20 cards)
basic concept of air flow
air flow:
- flow of air or any other fluid is caused by a pressure differential between two points
- flow will originte from an area of high pressure, and proceed to area(s) of lower pressure
pulmonary structures
nasal cavity - pharynx - larynx - trachea - lungs - primary bronchi - bronchiole - pulmonary cappillaries - alveolus - pulmonary artery and vein
mechanics of ventilation
-creating “pressure differentials” to manipulate airflow
inspiration
- diaphragm contracts, flattens out, moves downward
- air in lungs expands, reducing its pressure
- pressure differential between lungs and ambient air sucks air in to inflate lungs
- ribs rise
expiration
- sternum and ribs swing down, while diaphragm moves toward thoracic cavity
- air in lungs compresses, increasing its pressure
- pressure differential between lungs and ambient air draws air out of lungs
- ribs lower
pressure changes across the respiratory cycle
thoracic wall —> parietal pleura —> pleural cavity —> visceral pleura —> intrapleural presure (756 mmHg (-4 mmHg)) —> intrapulmonary pressure 760 mmHg (0mmHg) —> transpulmonary pressure (760 mmHg - 756 mmHg = 4 mmHg) —> lung —> daphragm
resting lung volume
intrapleural pssure —> is always lower than atomspheric pressure and intrapulmonary pressure
flow and pressure vs volume
flow increases and volume increases because its not fully at max yet
lungs are meant for exercising
max flow-volume loop
- inspire is negative on the graph
- expire is positive on the graph (as well as fast increase at the beginning of expiration)
ventilation (Ve)
- the movement of iron in and out of the lungs
- minute ventilation (Ve) - total volume of expired gas p minute
Ve = respiratory rate (RR) x tidal volume (Vt)
if
Vt = 0.5 L/breath
RR = 12 breaths/min (6 breaths in 30s)
Ve = 0.5 x 12 = 6L/min (which is the normal resting ventilation)
Ve rises with metabolic demand
Ve at rest = 5L/min versus Ve at VO2max = 180L/min (36 x higher)
ventilation (Ve) during incremental exercise
Ve = respiratory rate (RR) x tidal volume (Vt)
Ve @ VO2 of 2.0L/min = 2.2L/breath x 19 breaths/min = 42L/min
Ve @ VO2 of 4.0L/min = 3.5L/breath x 31 breaths/min = 108L/min
alveolar ventilation (Va)
alveolar ventilation (Va)
- volume of gas per minute that participates in gas exchange (i.e. only air that reaches alveoli)
- represents a large fraction of Ve
dead space ventilation (Vd)
- fraction of minute ventilation that does not contribute to gas exchange
- made up of respiratory passages and non-perfused alveoli passages
- increase Vd means a increase Ve is needed to maintain Va for adequate Co2 removal and O2 uptake
- bronchioles, trachea, mouth, etc.
alveolar ventilation:
- Va = Ve - Vd
- Va = respiratory rate (RR) x [tidal volume (Vt) - dead space (Vd)]
- Va = RR x [Vt - Vd]
distribution of Vt in healhy person t rest
alveolar air —> takes up most of the space
physiologic dead space —> barely takes up anything
anatomic dead space —> takes up the rest of the space
effect of RR and Vt on Ve and Va
Va = RR x [Vt - Vd] = Ve - Vd
Vd = 150 always
shallow breathing —> Vt = 150, RR = 40, Ve = 6000, Vd x RR = (150x40) = 6000, Va = 0
normal breathing —> Vt = 500, RR = 12, Ve = 6000, Vd x RR = (150x12) = 1800, Va = 4200
deep breathing —> Vt = 1000, RR = 6, Ve = 6000, Vd x RR = (150x6) = 900, Va = 5100
alveolar ventilation calculations
rest
- Vt = 500mL
- Vd = 150mL (30% of Vt)
- RR = 14breaths/min
- Ve = 0.5 x 14 = 7L/min
- Va = [0.5 - 0.15] x 14 = 4.9L/min
maximal exercise
- Vt = 3600mL
- Vd = 720mL (20% of Vt)
- RR = 45breaths/min
- Ve = 3600 x 45 = 162L/min
- Va = [3.6-0.72] x 45 = 130L/min
changes in breathing during exercise
spirometry of a person at rest showing:
1. tidal volume
- only use half lung capacity
2. max expiration of residual volume
3. max inspiration of total lung capacity
with moderate to heavy exercise increase Ve achieved by increase in Vt and increase in RR
- increase Vt by encroaching on inspiratory and expiratory reserve volumes
- reduced end-expiratory lung volume (EELV) is maintained at max exercise in normally fit person
heavy exercise
- increase in volume and frequency
- generate larger inspiratory volume
gas exchange
- why do we breathe?
- to take up oxygen and eliminate carbon dioxide based on the metabolic requirements of the body - where does this exchange occur?
- at the alveolar - pulmonary capillary interface - how does this occur?
- through the process of pulmonary diffusion - how do we know that gases are exchanging properly?
- by the partil pressure of oxygen and carbon dioxide in arterial blood - what determines proper gas exchange?
- Va/Q matching and diffusion capacity
basic concepts of diffusion
dalton’s law of partial pressure
- individual gases in a mixture exert pressure proportional to their abundance
- more molecules in a given space = greater partial pressure
- sum of partial pressures = total pressure
henry’s law of diffusion between gases and liquids
- amount of gas dissolved in fluid depends on:
- pressure differential betwen gas above fluid and dissolved in it
- solubility of gas in fluid
- without gradient, gases are in equilibrium — no diffusion
oxygen —> pressure = 159mmHg
nitrogen —> pressure = 593mmHg
oxygen + nitrogen —> pressure = 752mmHg
gas concentration and pressures
- partial pressure difference is what allows diffusion
gas concentration
- amount of gas in a given volume determined by product of gas partialpressure and solubility
gas pressure
- force exerted by gas molecules against surfaces they encounter (mmHg)
partial pressure
- percentage concentration (F) x total pressure of gas mixture (P)
- ambient dry air (total pressure ~760mmHg)
- FO2 = 20.9%; FCO2 = 0.03% —> PO2 = 159mmHg; PCO2 = 0mmHg
- tracheal humidified air (total pressure ~760mmHg - 47mmHg [vaporized water] = 713mmHg)
- FO2 = 20.9%; FCO2 = 0.03% —> PO2 = 149mmHg; PCO2 = 0mmHg
- alveolar air (percentages, partial pressures, and gas volumes)
- in 1-L at sea level (37 degrees celcius)
resting and exercise individual Va
- gas - percentage - partial pressure (at 760 - 47mmHg) - volume of gas (mL/L)
- oxygen - 14.5% - 103mmHg - 145mL/L
- carbon dioxide - 5.5% - 39mmHg - 55mL/L
- nitrgen - 80.00% - 571mmHg - 800mL/L
- water vapour - 0 - 47mmHg - 0
alveolar-cailary interface
- site of pulmonary diffusion
- alveolar wall + capillary wall + respective basement membranes
- surface across which gases are exchaned
- large surface area: 300 million alveoli
- very thin: 0.5 to 4 um
- maximiation of gas exchange - gas exchange between alveoli and capillaries
- air inflow: bronchial tree —> alveoli
- blood inflow: right ventricle —> pulmonary arteries —> pulmonary capillaries (deoxygenated blood)
- alveoli surrounded by capillaries - 2 major functions
- replenishes blood oxygen supply
- removes carbon dioxide from blood
oxygen exchange in the alveoli
- gases diffuse from high to low pressure
- atomospheric PO2 (PiO2) = 150mmHg
- alveolar PO2 (PaO2) = 100mmHg
- pulmonary artery PO2 (PvO2) = 40mmHg
- PO2 gradient across respiratory membrane
- 60mmHg (i.e. 100mmHg - 40mmHg)
- as blood flows through pulmonary capillaries, equilibrium is rapidly established and pulmonay vein or end-capillary PO2 (PecO2) is ~100mmHg
time required for gas exchange. at rest, blood remains in pulmonary and tisue caillaries for about 0.75sec. pulmonary disease impairs rate of gas transfer across the alveolar-capillary membrane and prolongs gas equilibrium time
fick’s law of diffusion
the rate of diffusion through the respiratory membrane (Vgas) is:
- directly proportional to:
- surface area (A ~85 m2 per lung)
- differential in partial pressure of gas on both sides of membrane (P = P1 - P2)
- diffuion constant (D) - determined by gas solubility and molecular weight
- inversely proportional to:
- thickness of tissue thru which gas must diffuse (T, 0.5um)
edema, pulmonary hypertension
ventilation (Va) - perfusion (Q) relationship
- in most healthy individual air flow to alveoli (Va) ~ blood flow to that alveoli (Q)
- example: 1mL/min ir for 1mL/min blood flow; Va/Q = 1.0 - some alveoli may be well ventilated but poorly perfused (Va/Q >1.0, ex. 10)
- “wasted ventilation”; increase Vd (pulmonary hypertension) - some alveoli may be poorly ventilated bt well perfused (Va/Q <1.0, ex. 0.1)
- “wasted blood flow” or venous admixture (pulmonary disease)
- decrease O2, increase CO2, lack of pressure differential for gas exchange - in general, having a Va/Q mismatch mill mean you need to increase Ve to satisfy gas exchange requirements
