Review Lung VolumesReview Lung Volumes

Tidal Volume (VTidal Volume (Vtt))

volume moved during either an inspiratory volume moved during either an inspiratory or expiratory phase of each breath (L)or expiratory phase of each breath (L)

Inspiratory Reserve Volume (IRV)Inspiratory Reserve Volume (IRV)

Reserve ability for inspiration (L)Reserve ability for inspiration (L) Volume of extra air that can be inhaled after Volume of extra air that can be inhaled after

a normal inhalation (L)a normal inhalation (L)

Expiratory Reserve Volume (ERV)Expiratory Reserve Volume (ERV)

Volume of extra air that can be exhaled after Volume of extra air that can be exhaled after a normal exhalation (L)a normal exhalation (L)

Forced Vital Capacity (FVC or VC)Forced Vital Capacity (FVC or VC)

Maximal volume of air that can be moved in Maximal volume of air that can be moved in one breath, from full inspiration to full one breath, from full inspiration to full expiration (L)expiration (L)

SVC may be greater due to air trappingSVC may be greater due to air trapping

Residual Volume (RV)Residual Volume (RV)

Volume of air remaining in lungs following a Volume of air remaining in lungs following a maximal exhalation (L)maximal exhalation (L)

Usually increases with ageUsually increases with age Allows for uninterrupted exchange of gasesAllows for uninterrupted exchange of gases

Functional Residual Capacity (FRC)Functional Residual Capacity (FRC)

Volume of air in the lungs at the end of Volume of air in the lungs at the end of a normal tidal exhalation (end tidal) (L)a normal tidal exhalation (end tidal) (L)

Important for maintaining gas pressures Important for maintaining gas pressures in the alveoliin the alveoli

Total Lung Capacity (TLC)Total Lung Capacity (TLC)

Maximal amount of air in the lungsMaximal amount of air in the lungs RV + VC = TLC (L)RV + VC = TLC (L)

Maximal Ventilatory Volume (MVV or Maximal Ventilatory Volume (MVV or MBC)MBC)

Maximal amount of air that can be moved in Maximal amount of air that can be moved in one minute (L/min)one minute (L/min)

Pulmonary VentilationPulmonary Ventilation

@ rest, usually ~ 6 l/min@ rest, usually ~ 6 l/min Increase due to increases in rate and depthIncrease due to increases in rate and depth Rate: inc. 35-45 breaths/min, elite athletes: Rate: inc. 35-45 breaths/min, elite athletes:

60-70 breaths/min, max. ex.60-70 breaths/min, max. ex. VVtt 2 lit, Ve > 100 lit/min 2 lit, Ve > 100 lit/min VVtt may reach 2 lit, still 55-65% if VC (Tr and may reach 2 lit, still 55-65% if VC (Tr and

UNTr)UNTr)

Anatomic Dead SpaceAnatomic Dead Space

Volume of air that is in conducting Volume of air that is in conducting airways, not in alveoli, not involved in airways, not in alveoli, not involved in gas exchangegas exchange

Nose, mouth, trachea, other non-Nose, mouth, trachea, other non-diffusible conducting portions of the diffusible conducting portions of the respiratory tractrespiratory tract

Air is identical to ambient air, but Air is identical to ambient air, but warmed, fully saturated with water warmed, fully saturated with water vaporvapor

350 ml of 500 ml tidal volume will enter into 350 ml of 500 ml tidal volume will enter into and mix with existing alveolar airand mix with existing alveolar air– 500 ml will enter alveoli, but only 350 ml is fresh 500 ml will enter alveoli, but only 350 ml is fresh

airair– 350 ml is about 1/7 of air in alveoli350 ml is about 1/7 of air in alveoli– This allows for maintenance of composition of This allows for maintenance of composition of

alveolar air (concentration of gases)alveolar air (concentration of gases)

Dead space versus tidal volumeDead space versus tidal volume

Anatomic dead space increases with Anatomic dead space increases with increases in tidal volumeincreases in tidal volume

Increase in dead space is still less than Increase in dead space is still less than increase in tidal volumeincrease in tidal volume

Therefore, deeper breathing allows for more Therefore, deeper breathing allows for more effective alveolar ventilation, rather than an effective alveolar ventilation, rather than an increase in breathing rateincrease in breathing rate

Physiologic Dead SpacePhysiologic Dead Space Gas exchange between the alveoli and Gas exchange between the alveoli and

blood requires ventilation and perfusion blood requires ventilation and perfusion matching: V/Qmatching: V/Q

@ rest, 4.2 l of air for 5 l of blood each @ rest, 4.2 l of air for 5 l of blood each minute in alveoli, ratio ~.8minute in alveoli, ratio ~.8

With light exercise, V/Q ratio is With light exercise, V/Q ratio is maintainedmaintained

Heavy exercise: disproportionate Heavy exercise: disproportionate increase in alveolar ventilationincrease in alveolar ventilation

When alveoli do not work adequately during When alveoli do not work adequately during gas exchange, it is due to gas exchange, it is due to – Under perfusion of bloodUnder perfusion of blood– Inadequate ventilation relative to the size of the Inadequate ventilation relative to the size of the

alveolialveoli

This portion of alveolar volume with poor V/Q This portion of alveolar volume with poor V/Q ratio is physiologic dead space ratio is physiologic dead space

Small in healthy lungSmall in healthy lung If physiologic dead space >60% of lung If physiologic dead space >60% of lung

volume, adequate gas exchange is volume, adequate gas exchange is impossibleimpossible

Techniques of assessing lung Techniques of assessing lung volumes:volumes:

Spirometry (cannot determine RV and FRC)Spirometry (cannot determine RV and FRC) Helium dilutionHelium dilution Oxygen washoutOxygen washout Plethysmograph (what we have)Plethysmograph (what we have)

– based on Boyle’s Law: PV = Pbased on Boyle’s Law: PV = P11VV11

Alveolar VentilationAlveolar Ventilation

> 300 million alveoli> 300 million alveoli elastic, thin-walled membranous sacselastic, thin-walled membranous sacs surface for gas exchangesurface for gas exchange blood supply to alveolar tissue is greatest to blood supply to alveolar tissue is greatest to

any organ in bodyany organ in body are connect to each other via small poresare connect to each other via small pores

capillaries and alveoli are side by sidecapillaries and alveoli are side by side at rest, 250 ml of Oat rest, 250 ml of O22 leave alveoli to blood, leave alveoli to blood,

and 200 ml of COand 200 ml of CO22 diffuse into alveoli diffuse into alveoli

during heavy exercise, (TR athletes) 25X during heavy exercise, (TR athletes) 25X increase in quantity of Oincrease in quantity of O22 transfer transfer

Gas exchange in the lungsGas exchange in the lungs

molecules of gas exert their own partial molecules of gas exert their own partial pressurepressure

total pressure = mixture of the sum of the total pressure = mixture of the sum of the partial pressurespartial pressures

Partial pressure = % concentration X total Partial pressure = % concentration X total pressure of the gas mixturepressure of the gas mixture

Ambient Air @ sea levelAmbient Air @ sea level

Oxygen: 20.93% X 760 mm Hg = 159 mm Oxygen: 20.93% X 760 mm Hg = 159 mm HgHg

Carbon Dioxide: 0.03% X 760 mm Hg = 0.2 Carbon Dioxide: 0.03% X 760 mm Hg = 0.2 mm Hgmm Hg

Nitrogen: 79.04% X 760 mm Hg = 600 mm Nitrogen: 79.04% X 760 mm Hg = 600 mm HgHg

Partial pressure is noted by P in front, e.g., Partial pressure is noted by P in front, e.g., POPO22 = 159 = 159

Tracheal AirTracheal Air

as air enters respiratory tract, it is as air enters respiratory tract, it is completely saturated with water vaporcompletely saturated with water vapor

water vapor will dilute the inspired air water vapor will dilute the inspired air mixturemixture

@ 37 degrees C, water exerts 47 mm @ 37 degrees C, water exerts 47 mm HgHg

760 - 47 = 713760 - 47 = 713 Recalculate pressures, PORecalculate pressures, PO22 = 149 = 149

Alveolar AirAlveolar Air

different composition than tracheal airdifferent composition than tracheal air b/c of COb/c of CO22 entering alveoli from blood entering alveoli from blood

and Oand O22 leaving alveoli leaving alveoli

average POaverage PO22 in alveoli ~103 mm Hg in alveoli ~103 mm Hg

PCOPCO22 = 39 = 39

these are average pressures, it varies these are average pressures, it varies with the ventilatory cycle, and the with the ventilatory cycle, and the ventilation of a portion of the lungventilation of a portion of the lung

FRC is present so that incoming breath has FRC is present so that incoming breath has minimal influence on composition of alveolar minimal influence on composition of alveolar airair

therefore, partial pressures in alveoli therefore, partial pressures in alveoli remains stableremains stable

Gas Transfer in lungsGas Transfer in lungs

POPO22 is about 60 mm Hg higher in alveoli than is about 60 mm Hg higher in alveoli than

capillariescapillaries b/c of diffusion gradient, oxygen will dissolve b/c of diffusion gradient, oxygen will dissolve

and diffuse through alveolar membrane into and diffuse through alveolar membrane into capillarycapillary

COCO2 2 pressure gradient is smaller, ~ 6 mm Hgpressure gradient is smaller, ~ 6 mm Hg

adequate exchange still occurs b/c of high adequate exchange still occurs b/c of high solubility of COsolubility of CO22

Nitrogen is not used nor produced, PN Nitrogen is not used nor produced, PN is relatively unchangedis relatively unchanged

Equilibrium is rapid, ~ 1 sec, the Equilibrium is rapid, ~ 1 sec, the midpoint of blood’s transit through the midpoint of blood’s transit through the lungslungs

during exercise, transit time decreases during exercise, transit time decreases ~ 1/2 of that seen at rest~ 1/2 of that seen at rest

during exercise, pulmonary capillaries during exercise, pulmonary capillaries can increase in blood volume 3X restingcan increase in blood volume 3X resting

this maintains the pressures of oxygen this maintains the pressures of oxygen and carbon dioxideand carbon dioxide

Gas Transfer in the TissuesGas Transfer in the Tissues

Partial pressures can be very different than Partial pressures can be very different than those seen in the lungthose seen in the lung

@ rest, PO@ rest, PO22 in fluid outside a muscle cell in fluid outside a muscle cell

are rarely less than 40 mm Hgare rarely less than 40 mm Hg PCOPCO22 is about 46 mm Hg is about 46 mm Hg

During exercise, PODuring exercise, PO22 may drop to 3 mm Hg, may drop to 3 mm Hg,

and PCOand PCO22 rise to 90 mm Hg rise to 90 mm Hg

OO22 and CO and CO2 2 diffuse into capillaries, carried to diffuse into capillaries, carried to heart and lungs, where exchange occursheart and lungs, where exchange occurs

body does not try to completely eliminate CObody does not try to completely eliminate CO22

blood leaves lungs with POblood leaves lungs with PO22 of 40 mm Hg, of 40 mm Hg, this is about 50 ml of carbon dioxide/100ml of this is about 50 ml of carbon dioxide/100ml of bloodblood

PCOPCO22 is critical for chemical input for control is critical for chemical input for control of breathing (respiratory center in brain)of breathing (respiratory center in brain)

By adjusting alveolar ventilation to metabolic By adjusting alveolar ventilation to metabolic demands, the composition of alveolar gas will demands, the composition of alveolar gas will stay constant, even during strenuous stay constant, even during strenuous exercise (which can increase VOexercise (which can increase VO22 and CO and CO22 production by 25X)production by 25X)