II. Background

  1. At rest
    1. Tidal Volume (TV) represents basal respiratory flow, in and out (similar to gentle ocean tides)
  2. With exertion
    1. Vital Capacity (IRV and ERV, in addition to TV) is recruited to allow for deeper breaths
      1. Analogous to Cardiac Stroke Volume, which increases with exertion
      2. May increase with Exercise from 500 ml to 4200 ml per breath (TV+IRV +ERV) in 70 kg adult
      3. In Obstructive Lung Disease (Asthma, COPD), taking deep breaths is primary compensation
        1. Increasing Tidal Volume with deep breaths is less work than increasing Respiratory Rate
    2. When Vital Capacity is insufficient to support exertion, Respiratory Rate (RR) increases
      1. Respiratory Rate is analogous to Heart Rate in compensation for exertion
      2. May increase with Exercise, from 12 to 36 breaths per minute with strenuous Exercise
      3. Increased Respiratory Rate is primary compensation in high lung elastic rebound
        1. Increasing Respiratory Rate is less energy for these patients, then taking deep breaths
    3. Minute Ventilation may increase with Exercise from 6 L/min to over 150 L/min
  3. Images
    1. lungVolumes.png

III. Interpretation: Overall Lung Volumes

  1. Vital Capacity (VC)
    1. Maximal volume expelled after maximal inspiration
    2. VC = ERV + TV + IRV
    3. VC = TLC - RV
    4. Decreased with low Lung Compliance, high elastic rebound (e.g. Restrictive Lung Disease, pulmonary fibrosis)
    5. Also low in Obstructive Lung Disease (e.g. Asthma, COPD), due to limited expiration (high Residual Volume)
  2. Total Lung Capacity (TLC)
    1. Volume in lungs at end of maximal inspiration
    2. Calculation: VC + RV
    3. Normal adult: 4-6 Liters
  3. Minute Ventilation (MV, Respiratory Minute Volume)
    1. Volume of breath inspired (and expired) per minute
    2. MV = TidalVolume x RespiratoryRate
    3. Typical resting Minute Ventilation in a 70 kg male is 6 liters/min = 500 ml TV x 12 breaths/min
  4. Alveolar Ventilation
    1. Volume of inspired air entering the alveoli per minute
    2. Similar to Minute Ventilation but subtracts alveolar dead space
      1. Aveolar dead space is 30-33% of Minute Ventilation in normal lungs (primarily Anatomic Dead Space)
      2. In a healthy lung, alveolar ventilation is typically two thirds of Minute Ventilation
      3. In very severe, end-stage COPD, alveolar ventilation may be as low as 20% of Minute Ventilation
    3. AV = (TidalVolume - AnatomicDeadSpace) x RespiratoryRate
      1. Normal adult example = (500-150) * 16 = 5600 ml

IV. Interpretation: Inspiratory Volumes

  1. Inspiratory Reserve Volume (IRV)
    1. Additional volume that could be inspired above normal inspiration (or Tidal Volume)
    2. Maximal inspired volume from end-tidal inspiration
    3. IRV may be as high as 40-43 ml/kg or 2800 ml in a 70 kg adult)
  2. Tidal Volume (Vt)
    1. Volume inspired and expired with each normal breath
    2. Tidal Volume is approximately one third of Vital Capacity
    3. Analogous to Cardiac Stroke Volume at Rest
    4. Minimum volume: 3 ml/kg
    5. Normal volume: 6-7 ml/kg (e.g. 500 ml in a 70 kg adult at rest)
    6. Typical ventilator Tidal Volume settings: 6-8 ml/kg
  3. Inspiratory Capacity (IC)
    1. Maximal volume inspired from resting expiratory level
    2. Calculation: IRV + Vt

V. Interpretation: Expiratory Volumes

  1. Expiratory Reserve Volume (ERV)
    1. Additional volume that could be expired in addition to normal exhalation (or Tidal Volume)
    2. Maximal expired volume from end-tidal inspiration
    3. Normal: 25% of Vital Capacity (up to 15 ml/kg or 1050 ml in a 70 kg adult)
  2. Functional Residual Capacity (FRC)
    1. Volume remaining in lungs at resting expiratory level
    2. Resting position of the respiratory Muscles
      1. Balance between the opposing recoil forces of lung and chest wall
    3. Functional Residual Capacity (FRC) is a key point from which other Lung Volumes are measured
      1. Inspiratory Capacity (IC) is measured from FRC to Total Lung Capacity (TLC)
      2. Expiratory Reserve Volume (ERV) is measured from FRC to Residual Volume (RV)
    4. FRC Measurements
      1. Body Plethysmography or body box
        1. Based on Boyle's law (Product of Pressure and Volume is constant, at constant Temperature)
        2. Technique
          1. Initial pressures are measured at mouth and in airtight box at rest (volume = FRC)
          2. Patient pants against a closed shutter and pressures are re-measured
            1. Volume has decreased from FRC to Residual Volume
            2. Pressure has increased
        3. FRC = Patm x dPb/dPm
          1. Where Patm = atmospheric or barometric pressure
          2. Where dPb = change in airtight box pressure
          3. Where dPm = change in mouth pressure
      2. Nitrogen Washout
        1. Start by rest breathing with normal Tidal Volumes
        2. At, end expiration, inhaled gas changed from room air to 100% oxygen
        3. Total exhaled nitrogen is measured over subsequent exhalations
        4. Volume of gas required to contain expired nitrogen is calculated (air is 78% nitrogen)
      3. Helium Dilution in Closed Circuit
        1. Start by rest breathing with normal Tidal Volumes
        2. At, end expiration, inhaled gas changed from room air to 10% helium in air
        3. Breathing and measurements continue until measured helium concentration reaches steady state
        4. Expired Carbon dioxide is absorbed by soda lime
        5. Used oxygen is replaced in the inspired air
        6. Helium concentration before and after steady state are used to calculate volume of replaced gas
  3. Forced Expiratory Volume in One Second (FEV1)
    1. Expiratory rate (FEV1) slowed by Obstructive Lung Disease (Asthma, COPD, chest masses)
  4. Residual Volume (RV)
    1. Volume remaining in lungs after maximal expiration
    2. Normal adult: 1.0 to 2.4 Liters
    3. Includes Respiratory Dead Space (anatomic and physiologic)
    4. Also includes healthy respiratory zone (alveoli to Bronchioles) that contribute to gas exchange
      1. Allows for passive CO2 and O2 diffusion in gas remaining in aveoli and Bronchioles between breaths
      2. Contrast with Physiologic Dead Space in diseased respiratory zone that cannot gas exchange
    5. RV is not measureable with standard Spirometry/PFTs
      1. Requires advanced testing (e.g. nitrogen washout, helium dilution, body plethysmography)
      2. Increased Residual Volume may also be suggested by barrel chest, hyperexpansion on CXR

VI. Interpretation: Dead Space

  1. Total Dead Space (Physiologic Dead Space)
    1. PhysiologicDeadSpace = AnatomicDeadSpace + AlveolarDeadSpace
  2. Anatomic Dead Space
    1. Volume of air within the nose, trachea and Bronchi that does not contribute to gas exchange
    2. Present in all patients regardless of health, representing 30-33% of Tidal Volume (e.g. 150 ml in 70 kg adult)
  3. Alveolar Dead Space
    1. Volume of air within the respiratory zone (alveoli to Bronchioles) that does not contribute to gas exchange
    2. In healthy patients, alveolar dead space is minimal (<5 ml)
    3. In diseased lung (e.g. COPD) or edematous lung (e.g. CHF, ARDS), alveolar dead space may be large
      1. Severe disease total dead space may be as large as 50-80% of Tidal Volume
    4. Ventilation-Perfusion mismatch results in some regions of lung that are over-ventilated and other underventilated
      1. Over-ventilated alveoli (V/Q>1) waste ventilation as blood is saturated with oxygen at a fixed maximum
      2. Alveolar dead space is the total excess ventilation to over-ventilated alveoli (V/Q>1)
  4. Measured Dead Space
    1. Vd/Vt = (PaCO2 - PeCO2)/PaCO2
    2. Where
      1. Vd = Physiologic Dead Space Volume
      2. Vt = Tidal Volume
      3. PaCO2 = arterial pCO2
      4. PeCO2 = expired CO2 (collected gas from several expired breaths)
        1. Expired CO2 is diluted by Ambient air and regions of excessive ventilation (V/Q>1)
          1. In these cases, PeCO2 will be much lower than PaCO2
    3. Interpretation
      1. Vd/Vt = 0.33 in normal lungs (resulting in ~150 ml in a 70 kg adult with TV 450-500 ml)
      2. Vd/Vt may increase to high fractions (0.6 to 0.8) in severe lung disease with V/Q>>1

VII. Resources

  1. Intagliata (2020) Lung Dead Space, StatPearls, Accessed 3/30/2021
    1. https://www.ncbi.nlm.nih.gov/books/NBK482501/

VIII. References

  1. Rollings (1984) Facts and Formulas, McNaughton & Gunn
  2. Marini (1987) Respiratory Medicine, Williams & Wilkins

Images: Related links to external sites (from Bing)

Related Studies

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Definition (NCI_CDISC) The maximum volume of air a subject can exhale from the lungs after a tidal exhalation.
Definition (NCI) The maximum volume of air a subject can exhale from the lungs after a tidal exhalation.
Definition (MSH) The extra volume of air that can be expired with maximum effort beyond the level reached at the end of a normal, quiet expiration. Common abbreviation is ERV.
Concepts Laboratory or Test Result (T034) , Organ or Tissue Function (T042)
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English Expiratory Reserve Volumes, Reserve Volume, Expiratory, Reserve Volumes, Expiratory, Volume, Expiratory Reserve, Volumes, Expiratory Reserve, expiratory reserve volume, ERV-Expiratory reserve volume, erv, expiratory reserve volume (ERV) of lung, ERV, Expiratory reserve volume, ERV - Expiratory reserve volume, Expiratory reserve volume (observable entity), Expiratory Reserve Volume
Japanese 予備呼気量, ヨビコキリョウ
Swedish Utandningsreservvolym
Czech ERV, exspirační rezervní objem, Exspirační rezervní objem
Finnish Uloshengityksen varatila
French Volume de réserve expiratoire, VRE (Volume de Réserve Expiratoire)
Italian Volume di riserva espiratoria
Polish Objętość wydechowa zapasowa
Hungarian Kilégzési tartalék térfogat
Portuguese Volume de Reserva Expiratória, Volume Expiratório de Reserva, Volume de reserva expiratória
Spanish Volumen de Reserva Espiratoria, Volumen Espiratorio de Reserva, VRE, volumen de reserva espiratorio (entidad observable), volumen de reserva espiratorio, Volumen espiratorio de reserva
Norwegian Utåndingsreservevolum, Ekspiratorisk reservevolum, ERV
Dutch expiratoir reservevolume, Reservevolume, respiratoir
German expiratorisches Reservevolumen, Exspiratorisches Reservevolumen

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Definition (CHV) The maximum volume of air that can be inspired after reaching the end of a normal, quiet expiration
Definition (NCI_CDISC) The maximum volume of air a subject can inhale into the lungs after a tidal exhalation (IRV plus TV).
Definition (NCI) The maximum volume of air a subject can inhale into the lungs after a tidal exhalation (IRV plus TV).
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Japanese 深吸気量, シンキュウキリョウ
Swedish Inandningskapacitet
Czech inspirační kapacita, Inspirační kapacita
Finnish Sisäänhengityskapasiteetti
French Capacité vitale inspiratoire, CI (Capacité Inspiratoire), Capacité inspiratoire
Polish Pojemność wdechowa, IC
Hungarian Belégzési kapacitás
Norwegian Inspiratorisk kapasitet
Spanish CI, capacidad inspiratoria (entidad observable), capacidad inspiratoria, Capacidad inspiratoria, Capacidad Inspiratoria
Portuguese Capacidade inspiratória, Capacidade Inspiratória
Dutch inspiratoire capaciteit, Capaciteit, inspiratoire, Inspiratoire capaciteit
German inspiratorische Kapazitaet, Inspirationskapazität, Kapazität, inspiratorische
Italian Capacità inspiratoria

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Czech inspirační rezervní objem, IRV
Finnish Sisäänhengityksen varatila
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Polish IRV, Objętość wdechowa zapasowa
Portuguese Volume de Reserva Inspiratória, Volume Inspiratório de Reserva
Spanish Volumen de Reserva Inspiratoria, Volumen Inspiratorio de Reserva, VRI, volumen de reserva inspiratoria (entidad observable), volumen de reserva inspiratoria
Norwegian Inspiratorisk reservevolum, IRV, Innåndingsreservevolum
German Inspiratorisches Reservevolumen
Italian Volume della riserva inspiratoria
Dutch Inspiratoir reservevolume, Reservevolume, inspiratoir

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Concepts Organ or Tissue Function (T042)
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SnomedCT 251916001
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Swedish Andning, dead space
Czech dýchání - mrtvý prostor
Finnish Kuollut tila
Polish Przestrzeń martwa
Norwegian Respiratorisk dødrom, Alveolært dødrom, Anatomisk dødrom, Fysiologisk alveolært dødrom
Spanish espacio muerto respiratorio (entidad observable), espacio muerto respiratorio, Espacio Muerto Respiratorio
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German Respiratorischer Totraum
Italian Spazio morto respiratorio
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Concepts Finding (T033)
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SnomedCT 13621006, 142202008, 165029006
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French TV, VT (Volume Courant), Volume courant
German VT, Atemhubvolumen, Atemzugvolumen
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Portuguese Taquicardia ventricular, Volume de Ventilação Pulmonar
Spanish TV, volumen corriente pulmonar (entidad observable), volumen corriente pulmonar, Volumen de Ventilación Pulmonar
Japanese 心室性頻脈, シンシツセイヒンミャク
Swedish Andetagsvolym
Czech dechový objem, Komorová tachykardie
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French CPT (capacité pulmonaire totale), CPT (Capacité Pulmonaire Totale), Capacité pulmonaire totale
German TLC, Totalkapazitaet der Lunge, Lungenkapazität, totale, Totale Lungenkapazität
Japanese TLC, ソウハイキリョウ, TLC, 全肺気量, 総肺容量, 総肺気量, 肺容量-総, 肺気量-全
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Hungarian TLC, Teljes tüdő kapacitás
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SnomedCT 88265002
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