Physio Ventilation (26)

• getting air from the atmosphere INTO the alveoli
• aka transport of gas from the atmosphere to the alveolar surface

• a arterial
• c capillary
• v venous

• P pressure
• V volume (gas)
• Q volume (blood)
• C content
• F fractional concentration
• S saturation
• eg. P_aO₂ = partial pressure of O₂ in arterial blood

• A alveolar
• I inspired
• D dead space
• E expired
• T tidal
• eg. V_A = alveolar ventilation (volume of air/gas flow per unit time)

• the total pressure (P_total) exerted by a mixture of gasses is the sum of the partial pressures (P₁, P₂, etc) exerted independently by each gas in
• the mixture
• P_total = P₁ + P₂ + P₃ + ...
• the pressure of e/a gas contributes proportionally to its relative amount (if P₁ = 25% of the total gas in a mixture, then P₁ = Ptotal x 0.25)

• a mixture of gases: chiefly nitrogen, oxygen, water vapor, & carbon dioxide
• total pressure is the sum of e/a pressure contribution from the components of the mixture
• CO₂ in atmosphere is actually low (doesn't take much of it to have adverse effects)

multiply it's percentage (eg. 20.9 for O₂) by the TOTAL pressure (760 mmHg)

• is ~79% nitrogen & 21% oxygen →
• P_N2 = 597 mmHg & P_O2 = 159 mmHg

• it passes over nasal turbinate → through the sinuses
• by the time it arrives in the trachea (then called tracheal or inspired air), the air has been HUMIDIFIED, P_H2O = 47 mmHg (dilutes other gases)
• do this so air sent down to alveoli doesn't dry them out
• air is also warmed to body temperature at this point

• b/c that increase in P_H2O to 47 mmHg DILUTES the other components

• P_O2 (tracheal) = P_IO2 (inspired)
• = (P_total - P_H2O) x 0.21
• atmospheric air - water component * .21 (b/c the partial pressure of O₂ = 20.9)

• is FURTHER modified by the diffusion of O₂ into the blood & CO₂ from the blood into the alveoli
• O₂ & CO₂ numbers are CONSTANT
• P_O2: 104 mmHg*
• P_CO2: 40 mmHg*
• (eg. during exercise, you don't get TIRED from alveolar P_O2 dropping)
• these values are only changes in disease

• blood comes into alveolar capillary from the R side of the heart DEoxygenated: has low O₂ (40) & elevated CO₂ (46)
• passing through the capillaries O₂ is picked up in exchange for CO₂ - diffuse down their CONCENTRATION gradients
• blood leaving capillary has high O₂ (100) & lower CO₂ (40)

• alveolar P_O2: 105 mmHg
• blood exiting caps. P_O2: 100 mmHg
• b/c the blood returning to the L atrium has some contribution from the venous blood of the BRONCHIOLE circulation - it has not been oxygenated in the lung
• the addition of bronchiole venous blood to this blood lowers the P_O2

• systemic artery P_O2: 100 mmHg
• systemic artery P_CO2: 40 mmHg
• average cell P_O2 < 40 (mt P_O2 < 5!)
• average cell P_CO2 > 46
• these are STEADY STATE VALUES
• as blood passes through capillaries surrounding normal cells, it emerges on the other side as venous blood (P_O2 40, P_CO2 46)

• VENOUS blood flows through pulmonary arteries
• ARTERIAL blood flows through pulmonary veins
• it's the P_O2/P_CO2 composition that determines the TYPE of blood

• measured in (mL/min)
• is defined as:
• respiratory rate (breaths/min) * tidal volume (mL/breath)
• [conceptually analogous to C.O.; product of a rate * a volume]

amount of air you breath in & out in one breath

• respiratory rate * tidal volume
• respiratory rate at rest: ~12 breaths/min
• tidal volume: ~ 500 mL/breath
• = 12 bpm * 500 mLpb = 6000 mL/min (6 L/min)
• this is the typical amount of ventilation we supply our lungs w/

• NOT ALL OF IT
• about 150 mL of inspired air DOESN'T reach the alveoli - it fills the conducting airways/bronchial tree
• it fills Anatomic Dead Space, aka where NO gas exchange occurs
• of the 500 mL tidal volume, only ~350 mL reaches the alveoli

• 12 bpm * 350 mLpb = 4200 mL/min (4.2 L/min)
• (breaths per min) (mL per breath)
• as opposed to the 6000 mL/min calculated using the entire tidal volume

• the tidal volume & alveolar ventilation are equal, but the air entering the alveoli contains the DEAD SPACE GAS from a previous breath + newly inspired air
• the air derived from the anatomic dead space does NOT contribute to gas exchange ("wasted")

• @ end of expiration ~150 mL of used up alveolar gas sits in airways
• in next inspiration, 500 mL (tidal volume) of gas is inhaled
• sitting airways gas is returned to alveoli + ~350 mL of fresh air!
• the last 150 mL of inhaled gas sits in conducting airways & is exhaled in the NEXT breath w/o change
• 150 mL of inspired air filling conducting airways ~ filling anatomic dead space

• an experiment that measures the anatomic dead space
• subject breathes pure 100% oxygen, then expires into a rapid nitrogen gas analyzer (analyzes N₂ in expired air)
• 1st air blown out = pure O₂ (N₂ content will be 0)
• N₂ concentration rises as the dead space gas is washed out by alveolar gas
• pure alveolar gas is indicated by a CONSTANT level of N₂
• dead space volume is determined from a vertical line drawn such that areas A & B are equal
• dotted line ~1.5 L aka 150 mL (corresponds to anatomic dead space)

• results from alveoli that are ventilated but NOT perfused (gas entering such alveoli does NOT exchange w/ blood - same thing as in airways)
• healthy lungs have a very small amount of alveolar dead space
• it can be significant in pathologies such as Pulmonary Embolism

• can do so if you know alveolar CO₂ (P_ACO₂) & expired CO₂ (P_ECO₂) & use this eqn
• V_D/V_E = (P_ACO₂- P_ECO₂) / P_ACO₂
• V_E = volume of expired air
• *won't ask about on test

• the proportion of dead space in each breath
• actual values:
• V_D/V_E = (40-28) / 40 = 0.3
• ~30% in this case

• the flow of air into alveoli taking part in gas exchange
• of the 500 mL tidal volume, only ~350 mL of fresh air reaches the alveoli per resting breath, assuming NO alveolar dead space in a healthy individual
• therefore V_A = resp rate * (tidal vol - anatomic dead space vol)
• V_A = 12 bpm * 350 mLpb = 4200 mL/min

• the removal of CO₂ produced by cellular metabolism
• otherwise alveolar P_CO2 & P_ACO₂, will rise.
• therefore P_ACO₂ at any point reflects the balance between CO₂ production & removal by ventilation

• means alveolar P_ACO₂ is proportional to the rate at which you produce CO₂ by metabolism divided by alveolar ventilation
• V_CO2: the rate at of metabolic CO₂ production

• alveolar CO₂ (P_ACO₂) will increase [based on the above relationship]
• this is what happens when certain disease processes negatively affect (suppress) alveolar ventilation
• high V_CO2 (eg. in hyperthyroidism → elevated metabolic rate) will also result in ↑ P_ACO₂

• P_aCO₂: arterial CO₂ (~ 40 mmHg)
• clinically, the partial pressures of CO₂ in alveoli & arterial blood are assumed to be equal
• the partial pressures of CO₂ in arterial blood is easier to measure therefore is used to estimate P_ACO₂

• V_A = 0.863 * (V_CO2 / P_ACO₂)
• VA = 0.863 * (200 / 40) = 4.3 L/min (almost 4.2!)
• a change in P_ACO₂ produces a compensatory change in V_A

a proportionality constant that corrects for differences in the conditions for measuring V_A, V_CO2, & P_ACO₂

top: decrease breathing rate increase breathing rate → ↑ alveolar CO₂ (doubles! - morphine)

middle: normal P_ACO₂ (40 mmHg)

bottom: increase breathing rate → ↓ alveolar CO₂

• an airway's RADIUS - a decrease of only 5% in bronchial radius reduces airflow by 20% (b/c there's an ↑ in Resistance)
• remember, Flow = ΔPπr⁴ / 8ηL

• terminal airways have the LARGEST cross-sectional area
• this results in a DECREASE in airflow velocity
• the greatest resistance is actually in airways > 2 mm in diameter

• laminar in straight sections of the bronchial tree but turbulent at branch points, where eddies occur
• laminar can also become turbulent at high velocities of airflow (rapid breathing)
• Transitional Flow: alternation between laminar and turbulent flows

a larger ΔP

• they may collapse, particularly w/ increased intrapleural pressures during FORCED expiration
• small airways have no cartilage supporting their walls (only larger bronchi & bronchioles have cartilage supporting their branching)
• they're easily distended or compressed as the lungs inflate & deflate
• the distension during inspiration REDUCES resistance

• PSNS: bronchoconstriction
• SNS: bronchodilation

1. chemical irritants (eg. ammonia, smoke, dust) - cause a reflex constriction involving neuropeptides (substance P)

2. immediate hypersensitivity response (histamine mediated)

3. inflammatory mediators: arachidonic acid metabolites (prostaglandins & leukotrienes)

• reduce radius
• increase resistance
• limit airflow

• using open-circuit Spirometry
• basically have an inverted drum in a volume of water
• person holds a tube in their mouth that passes through fluid into the air in the drum
• inspiration: drum goes down
• expiration: drum goes up
• hooked up to pulley system that draws a picture of that breathing

• FRC: functional residual capacity
• RV: residual volume
• TLC: total lung capacity
• VC: vital capacity
• VT: tidal volume

• 1st part: normal resting breathing; change in vol. = 500 mL
• 1st dip: occurs when person's instructed to blow out all the air they can (~1 L); called the Expiratory Reserve Volume
• 1st peak: difference between normal inspiration & maximum inspiration = Inspiratory Reserve Volume

• Vital Capacity
• when you inhale maximally then exhale maximally
• in above graph, individual is moving ~5 L of air

• amount of air left in the lung after a normal breath (inhale → exhale)
• FRC = Expiratory Reserve Volume + Residual Volume

• the Residual Volume (RV)
• even if you maximally expire, you can't expire the volume down to 0 [can't reduce lung volume to 0 - chest wall/thoracic cavity is too big]

• using the Helium Dilution Method
• know volume of spirometer
• can add He to it - know the amount of He in spirometer drum is drum vol * He concentration
• open spicket - person breathes in air from tube
• this is started at the end of a normal exhalation - meaning air in lung corresponds to Functional Residual Capacity
• person breathes in & out air that contains He
• this dilutes He into total volume
• total volume is not original (V1) + lung volume (V2)
• …solve for V2
• I don't know
• C1 * V1 = C2 * V2 = C2 * (V1 + FRC)