Pulmonary Ventilation: Physiology, Spirometry, Lung Volumes and Capacities

Pulmonary Ventilation Physiology

PULMONARY VENTILATION Pulmonary system physiology Dra. Torres / Dra. Romo 2025-1 UAG. SCHOOL OF MEDICINE Breathe easy! You can't control EVERYthing! the AwkwardYeti.com

Objectives of Pulmonary Study

• Draw a normal spirogram, labeling the four lung volumes and four capacities. List the volumes that comprise each of the four capacities.
• Identify which volume and capacities cannot be measured by spirometry
• Define the mechanisms that determine the clinically important boundaries of lung volume (i.e., TLC, FRC, and RV).
• Define and contrast the following terms: anatomic dead space, physiologic dead space, wasted ventilation, total ventilation per minute and alveolar minute ventilation.
• Regional differences in ventilation in the lung
• Contrast the proportional relationship between alveolar ventilation and the arterial blood gases PCO2 and PO2.

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Ventilation Process and Normal Ranges

Ventilation: V'E = fx VT Process by which air moves in and out of the lungs. Incoming air is composed of a volume that fills the conducting airways (dead space ventilation) and a portion that fills the alveoli (alveolar ventilation).

Normal Range for Adults

Variable	Lower limit	Higher limit
Tidal volume (Vt)	400 mL	600 mL
Respiratory rate (RR)	10 resp/min	16 resp/min
Minute Ventilation (VE)	4000 mL/min	8000 mL/min

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Spirometry: Pulmonary Function Test

• Pulmonary function test
• Measure inhalation and exhalation volumes of air as a function of time
• For assessment and management of lung diseases

Mouthpiece Floating drum Counterbalance weight Airway Recorder Lung -Water Chest wall

• Volume-displacement spirometers
• Flow sensing spirometers

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Spirometry Measurement Process

• Patient breath through a tube. As patient exhale, bells moves up and the pen down
• Then patient takes a maximal inspiration, followed by maximal expiration

Floating drum Oxygen chamber -Recording drum Water Mouthpiece Counterbalancing weight UAG SCHOOL OF MEDICINE

Lung Volumes and Capacities Overview

LOOK WHAT I CAN DO! Lung volumes and capacities UAG SCHOOL OF MEDICINE

Lung Volume Measurement Example

80 Volume (ml/kg) 37 30 N 15 0 UAG. SCHOOL OF MEDICINE Label the four lung volumes and four capacities

Spirometry: Volumes and Capacities Explained

Spirometry: volumes & capacities 8 + Paper 1 6 Total lung capacity Spirometer Vital capacity Liters 4 Tidal volume Pen 2 T Functional residual Residual capacity volume 0 UAG. SCHOOL OF MEDICINE West, John. (2015). Respiratory Physiology. (10th Ed.): Lippincott. Williams & Wilkins

Lung Volumes vs. Lung Capacities

Lung volumes What is the difference between lung volume and lung capacity?

Calculating Lung Capacities

Lung capacities How can we calculate the four lung capacities? VC = IRV + VT + ERV VC = 3000 + 500 + 1200 VC = IC + ERV Inspiratory reserve volume (3000 mL) Inspiratory capacity Vital capacity Tidal volume (500 mL) N IC = IRV + VT IC = 3000 + 500 Total lung capacity Expiratory reserve volume (1200 mL) Functional residual capacity Residual volume (1200 mL) FRC = ERV + RV FRC = 1200 + 1200 Costanzo, Linda (2018). Physiology. (6th Ed.) Elsevier. Clinical Key UAG. SCHOOL OF MEDICINE Spirometry: volumes & capacities

Factors Affecting Lung Volumes and Capacities

Volumes & capacities

• Are affected by:
• Gender
• Total body surface area
• Body position
• Force of respiratory muscles

Volumes and Capacities Not Measurable by Spirometry

• V & C that can't be measured by spirometry
• Residual volume (RV) and all the capacities that include RV
• TLC
• FRC

UAG. SCHOOL OF MEDICINE Plethysmography Helium dilution method lung volume vs height 5 - 4 00 lungvol 00 3 000000 0 2 1 O 45 50 55 60 65 70 75 height

Dead Space in Respiration

Dead space

• Is the volume of the airways and lungs that does NOT participate in gas exchange
• About 30% of total ventilation in a respiratory cycle is wasted ventilation VT = VD + VA VT x n = (VD X n) + (VA X 2) VE=VD+VA

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Anatomical Dead Space

Anatomical Dead space 150 - Anatomic dead space Tidal volume = 500 mL 350 Conducting airways Alveolar air from previous breath Inspired air that fills conducting airways Inspired air that participates in gas exchange Alveoli Alveolar air from previous breath Inspire one VT End-expiration End-inspiration Costanzo, Linda (2018). Physiology. (6th Ed.) Elsevier. Clinical Key Volume of conducting airways: . Nose and mouth · Trachea · Bronchi · Bronchioles UAG. SCHOOL OF MEDICINE The first air expired is dead space air that has not undergone gas exchange. To sample alveolar air, one must sample end - expiratory air

Physiological Dead Space Definition

Physiological dead space Total volume of the lung that does NOT participate in gas exchange VD = VTX Paco, - PECO2 Pacoz

• Includes: anatomical dead space (conducting airways air) + functional dead space in the alveoli
• Ventilation/perfusion defect
• Calculated using Bohr equation
• Normal individual = nearly equal to Anatomical Dead Space
• VD/VT at rest is 0.2 to 0.36
• In Certain pathological conditions the physiological VD becomes larger than the anatomical VD (ventilation/perfusion mismatch)

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Physiological Dead Space Gas Exchange

Physiological dead space PIO2 = 150 Venous mix blood PvO2 = 40 PvCO2 = 46 PAO2 = 100 PACO2 = 40 PO2 = 100 PCO2 = 40 Venous mix blood PvO2 = 40 PvCO2 = 46 PAO2 = 150 PCO2 = 0 UAG. PaO2 = 40 PaCO2 = 46 SCHOOL OF MEDICINE

Bohr's Method for Physiological Dead Space

Physiological dead space Bohr's method Paco, - PECo2 VD = VTX .CO2 Paco2 UAG SCHOOL OF MEDICINE

• All CO2 in mixed expired gas comes from alveoli that are well-ventilated and perfused
• There is no CO2 in inspired gas
• Un-perfused alveoli do not contribute to CO2

Physiological Dead Space Calculation Example

Physiological dead space Paco2 - PECO2 PaCO2 = 40 mmHg PECO2 = 30 mmHg VT = 500 ml VD = VT Paco2 VD = 500 40 - 30 10 -20 VD = 125 ml UAG SCHOOL OF MEDICINE This is in one breath ... So, how can we know it per minute?

Ventilation Rates

Minute Ventilation

Minute ventilation (Minute respiration) VE = VT x n 500×12 6000 ml/min

Alveolar Ventilation

Alveolar ventilation . VA = VA x n VA = (VT-VD) x n (500-150) × 12

Dead Space Ventilation

Dead space ventilation VD = VD x n VD = (VT-VA) x n (500-350) x 12 UAG SCHOOL OF MEDICINE

Regional Differences in Lung Ventilation

Regional differences in ventilation .The lower regions of the lung are better ventilated than the upper regions due to the effect of gravity on the lung ·Ventilation decreases from the lower to the upper regions of the lung UAG SCHOOL OF MEDICINE

Regional Distribution of Ventilation

A DETECTION OF INSPIRED 133Xe 133Xenon in O2 Radioactivity counters Apex Apex Middle Base Base Lungs B REGIONAL DISTRIBUTION OF VENTILATION 100 VA 80 60 40 20 0 Base Middle Apex Location in lung C INTRAPLEURAL PRESSURES 0 Absolute pressures: mm Hg Relative pressures: cm H2O D STATIC PRESSURE-VOLUME DIAGRAM Barometric pressure 760 0 Barometric pressure 753 -10 Regional volume Unit mass 756 -5 For the same change in PIP, the AV (ventilation) is greater at the base than apex. 0 -10 -20 -30 758 -2.5 PIP (cm H2O) Unit volume (arbitrary units)

Alveolar Ventilation and Carbon Dioxide

Alveolar ventilation and Carbon Dioxide BEST parameter to evaluate adequate breathing: PaCO2 = 40 mmHg VCO2 PaCO2 PACO2 = VA PACO2 = PaCO2 UAG SCHOOL OF MEDICINE PaCO2 > 40 hypoventilation PaCO2 < 40 hyperventilation

Normal Ventilation

Normal Ventilation PO2 = 150 mm Hg PCO2 = 0 mm Hg inspired air PCO2 = CO2 production alveolar ventilation PO2 = 100 mm Hg Pco2 = 40 mm Hg Mixed venous blood Arterial blood Alveolus PO2 = 40 mm Hg PCO2 = 46 mm Hg PO2 = 100 mm Hg PCo2 = 40 mm Hg CO2 O2 CO2 O2 = Tissues CO2 O2 1 Normal Ventilation UAG SCHOOL OF MEDICINE I Netter .M.D. I

Alveolar Hypoventilation

Alveolar Hypoventilation PO2 = 150 mm Hg PCO2 = 0 mm Hg inspired air CO2 production (constant) PCO2 (elevated) alveolar ventilation (decreased) PO2 = 80 mm Hg Pco2 = 60 mm Hg Mixed venous blood Arterial blood Alveolus PO2 = 36 mm Hg PCO2 = 66 mm Hg PO2 = 80 mm Hg PCO2 = 60 mm Hg CO2 O2 C CO2 O2 Tissues CO2 O2 7 Netter - M.D. Hypercapnia îPaCO2 +VCO 2 IVA = ĮVE - VD Decreased Alveolar Ventilation due to Decreased Minute Ventilation (VE= [VT X ĮRR) Sedative drug overdose Respiratory muscle paralysis Central hypoventilation Middle East Critical Care Assembly UAG. SCHOOL OF MEDICINE Alveolar hypoventilation

Summary of Pulmonary Ventilation

Summary

• Normal Spirometry
• Volumes and capacities
• Anatomic & physiologic dead space volumes
• Bohr's equation
• Ventilation rates
• Regional differences in ventilation
• Normal ventilation - Hypoventilation

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Bibliography

• "Lung volumes and capacities" Respiratory physiology. Costanzo, Linda (2022). Physiology. (7th Ed.) Elsevier. Clinical Key. Chapter 5. Pages 197-203
• Boron, W., Boulpaep, E. (2022). Medical Physiology. (2nd Ed.). Philadelphia: Mosby-Elsevier.
• Guyton, A., Hall, J. (2021). Textbook of Medical Physiology. (14th Ed.). Philadelphia: Elsevier-Saunders. Clinical key
• West, John. (2015). Respiratory Physiology. (10th Ed.): Lippincott. Williams & Wilkins

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Images References

• Costanzo, Linda (2018). Physiology. (6th Ed.) Elsevier.
• Levitzky. Pulmonary Physiology. 2004
• Mulroney, S.Myers, A .. Netter's Essential Physiology. (2nd Ed.). Elsevier
• West, John. (2015). Respiratory Physiology. (10th Ed.): Lippincott. Williams & Wilkins

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