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Home , Alveolar gas equation, Bronchodilatation, Closing capacity, Pulmonary surfactant

Respiratory Physiology

Manuel Otero Lopez Department of Anaesthetics and Intensive Care Hôpital Européen Georges Pompidou, Paris, France Conflict of interest declaration

I do not have conflict of interest

www.esahq.org Programme • Functional respiratory anatomy • Ventilation • Mechanics of (compliance & ) • The inefficiency of respiratory (Respiratory and Shunt) • Ventilation- relationship • Gas transport •

www.esahq.org Functional respiratory anatomy

• Upper (from nostrils to vocal cords)

• Lower respiratory tract (from vocal cords to alveoli)

www.esahq.org Functional respiratory anatomy

Muscles of Innervation Diaphragm => Phrenic nerves (C3-C5 nerve roots) Intercostal muscles => by their respective thoracic nerves roots Vagus => provide sensory innervation to the tracheobronchial tree (, bronchial secretions). Sympathetic activity (T1-T4) causes and secretions via β2 –receptors. α1 receptors cause bronchoconstriction α1 and β2 receptors are also present in the pulmonary vessels.

www.esahq.org Weibel classification of airways

Ewald Weibel

Weibel ER. Morphometry of the human . Heidelberg: Springer-Verlag, New York: Academic Press; 1963

www.esahq.org Functional respiratory anatomy

 Each alveolar sac contains, on average, 17 alveoli. An estimated 300 million alveoli provide a membrane of 50 to 100 m2 for gas exchange.

 Pulmonary epithelium: - Type 1 pneumocytes - Type 2 pneumocytes ()

www.esahq.org Increase in total cross-sectional area of the airways in the respiratory zone

www.esahq.org Ventilation

www.esahq.org . Total ventilation = (VT) x respiratory frequency • Minute volume of ventilation

. Anatomic dead space = the volume of the conducting airways, which does not take part in gas exchange (VD)

. Alveolar ventilation = (VT - VD) x respiratory frequency • the amount of fresh inspired air available for gas exchange

. Physiologic dead space = the volume of gas that does not eliminate CO2

• VD / VT = 0.3 in spontaneous ventilation

• VD / VT = 0.5 in

www.esahq.org www.esahq.org and capacities

Volume vs. Capacity

Volume is the amount of 3D space taken up by an object, e.g. a solid, a liquid or a gas. Capacity is the measure of an object’s ability to hold a substance, e.g. a solid, a liquid or a gas.

Morgan and Mikhail’s Clinical Anesthesiology, 5th ed.

www.esahq.org Expiratory spirogram

Morgan and Mikhail’s Clinical Anesthesiology, 5th ed.

www.esahq.org Peak flowmeter, PEFR Measurement of the rate which is sustained for 10 ms

www.esahq.org Respiratory failure

 An obstructive pattern (COAD) will show :

Low FEV1.0 / FVC ratio, low PEFR, low VC and high RV.

 A restrictive pattern will show :

Normal FEV1.0 / FVC ratio, low VC, low PEFR and low RV. (after resection of the lung, kyphoscoliosis,…)

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• The lung volume present after a maximum expiratory effort is called RV (residual volume). At this minimum volume some of the dependent alveoli are close off.

• The closing capacity is the lung volume at which this closure is first recorded using a marker gas expirogram such as helium.

• Closing capacity is independent of body position but increases with age. If it exceeds FRC, there is some degree of airway closure during respiration (intrapulmonary shunt). Responsible for the normal age-related decline in arterial O2 tension.

www.esahq.org Closing capacity

(Morgan and Mikhail’s Clinical Anesthesiology, 5th ed.)

www.esahq.org Mechanics of breathing

www.esahq.org Pressure volume relationship and compliance

Compliance is an index of distensibility of elastic organs and defined as the change in volume per unit change in pressure (ΔV/ΔP).

Compliance Elastance

www.esahq.org Factors which modifie compliance • Body size • Posture • Volume history of the • Pulmonary volume • Fibrosis

Normal ~ 0.2-0.3 L/cm H2O (2-3 L/kPa)

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www.esahq.org Surface Tension and Surfactant

www.esahq.org Surface Tension

www.esahq.org Type II pneumocyte

Start to develop at about 24 weeks of gestation secreting small amounts of surfactant

Adequate amounts are not secreted until about 35 weeks of gestation

Electron micrograph of type II epithelial cell (x 10 000)

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• Reduces the surface tension of the alveolar lining layer

• Increases lung compliance

• Increases the stability of alveoli

• Prevents

• Has a short half-life

Absence

• Low lung compliance, alveolar , tendency to pulmonary edema

www.esahq.org Airway Resistance

Derived from Hagen–Poiseuille equation

Jean Louis Marie Poiseuille

www.esahq.org Main site of airway resistance

www.esahq.org Laminar versus turbulent flow

Laminar flow Turbulent flow

  Hagen-Poiseuille equation In tubulent flow the resistance to flow is greater and increases more rapidly when the flow increases.

 Reynolds’ number:

V x diameter x gas density gas viscosity

www.esahq.org The inefficiency of respiratory gas exchange (Respiratory Dead space and Shunt) Ventilation-perfusion relationship

www.esahq.org John B. West

Video Lectures in Respiratory Physiology http://meded.ucsd.edu/ifp/jwest/resp_phys/index.html

www.esahq.org www.esahq.org Gravitational Distribution of Blood Flow in the Lung

 The uneven distribution of blood flow can be explained by the hydrostatic pressure differences within the blood vessels (« 30 cm H2O pressure from top to bottom »)

 On exercise these regional differences become less.

John B. West

www.esahq.org VENTILATION-PERFUSION RELATIONSHIP

Distribution of V, Q and V/Q ratio in the normal, upright lung

www.esahq.org Ventilation /perfusion ratios in an erect subject. (Textbook of Anaesthesia, AR Aitkenhead & G Smith, 2nd ed. 1990)

www.esahq.org Dead space

The amount of ventilation not taking part in the gas exchange

www.esahq.org Ventilation-Perfusion Relationship

www.esahq.org Shunt

 Cc’ O2 can be calculated from the :

 Clinically, the alveolar – arterial difference is often used as an approximation for « shunt »

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Hypoxic Pulmonary Vasoconstriction

• alveolar constricts small pulmonary arteries • a compensatory mechanism aimed at reducing blood flow in hypoxic lung regions • the precise mechanism is not known • occurs in excised isolated lung

• probably a direct effect of the low PO2 on vascular smooth muscle

www.esahq.org DIFFUSION

www.esahq.org DIFFUSION Fick's Law of Diffusion

Adolf Fick, 1855

www.esahq.org DIFFUSION

www.esahq.org DIFFUSION Diffusion of Oxygen Across the Blood-Gas Barrier

• At rest PaO2 virtually reaches PAO2 after about 1/3 of its time in capillary

• The diffusion process is challenged by exercise, alveolar hypoxia, and thickening of the blood-gas barrier

• True diffusion defects that create arterial are rare

www.esahq.org GAS TRANSPORT

O2

• dissolved

• combined with Hb

www.esahq.org GAS TRANSPORT

Dissolved O2

-1 . For each mmHg of PO2 0.003 ml O2 · 100 ml of blood or 0.003 vol. %

-1 . In normal arterial blood PO2 of 100 mmHg 0.3 ml O2 · 100 ml

www.esahq.org GAS TRANSPORT

O2 capacity: 1 g Hb - 1.39 ml O2

O2 combined with Hb O2 saturation of Hb = X 100

O2 capacity

CO2 = 1.39 x Hb x SO2 (%)/100 + 0.003 PO2

Oxygen carrying capacity of Hb = Hüfner’s constant (1,39 ml/gr)

www.esahq.org O2 dissociation curve

www.esahq.org Shifts of the O2 dissociation curve

www.esahq.org GAS TRANSPORT

CO2

• dissolved

• as bicarbonate

• in combination with as carbamino compounds

www.esahq.org CO2 carriage in the blood

www.esahq.org www.esahq.org CONTROL OF RESPIRATION

www.esahq.org Basic elements of the respiratory control system

West, John B. Respiratory Physiology: The Essentials, 9th Edition Copyright © 2012 Lippincott Williams & Wilkins, a Wolters Kluwer business

www.esahq.org www.esahq.org www.esahq.org Carotid bodies

• respond to PO2, PCO2, pH • little response to normoxia • very high blood flow

• respond to arterial, not venous PO2

• response to PCO2, pH is < important • fast response

www.esahq.org Lung receptors

• pulmonary stretch receptors (slowly adapting pulmonary stretch receptors)

• Hering-Breuer inflation reflex

• irritant receptors (rapidly adapting pulmonary stretch receptors)

• J receptors (juxtacapillary) • bronchial C fibers

www.esahq.org Mechanisms of hypoxemia

Morgan and Mikhail’s Clinical Anesthesiology, 5th ed.

www.esahq.org www.esahq.org NON-RESPIRATORY FUNCTIONS OF THE

www.esahq.org NON-RESPIRATORY FUNCTIONS OF THE RESPIRATORY SYSTEM

• Protective functions of respiratory tract • Non-respiratory functions of • Metabolic functions of the lung

www.esahq.org • Protective functions of respiratory tract

• Warming Raises incoming air to 37 Celsius

• Humidification Raises incoming air to 100% humidity • Filtration ------> • Removal of filtered particles • (cough, cilia) • Defense mechanisms of terminal respiratory units (macrophages and other relevant cells) • Olfaction

www.esahq.org NON-RESPIRATORY FUNCTIONS OF THE RESPIRATORY SYSTEM

• Non-respiratory functions of pulmonary circulation

• Reservoir for left ventricle (contains about 500 ml blood)

• Fluid and electrolyte exchange

• Filter to protect the systemic circulation including: small fibrin or blood clots, fat cells, bone marrow, detached cancer cells, gas bubbles, agglutinated RBC's, masses of platelets or WBC's, debris in stored blood, particles in i.v. solutions

www.esahq.org NON-RESPIRATORY FUNCTIONS OF THE RESPIRATORY SYSTEM • Metabolic functions of the lung • Uptake or conversion of chemical substances by lungs (conversion of angiotensin I to angiotensin II) • Formation of chemical substances • Pulmonary surfactant • Release into blood of substances stored in pulmonary tissues • Bradykinin • Histamine • Serotonin

• PGE2, PGF2 • Heparin

www.esahq.org Thank you for attention

Manuel Otero Lopez [email protected]

Many tanks to : Dr. Armen Varosyan Department of Anaesthesiology and Intensive Care Yerevan State Medical University, Yerevan, Armenia

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