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Applied Physiology & Chemistry. RT 210 Unit B. Mechanics of Ventilation: Ventilation & Respiration. Ventilation is air movement in and out of the lungs to allow external respiration to occur Respiration is gas exchange across a permeable cellular membrane

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Applied physiology chemistry

Applied Physiology & Chemistry

RT 210

Unit B

Mechanics of ventilation ventilation respiration

Mechanics of Ventilation: Ventilation & Respiration

  • Ventilation is air movement in and out of the lungs to allow external respiration to occur

  • Respiration is gas exchange across a permeable cellular membrane

  • External respiration is gas exchange between alveolar gas (air) and capillaries (blood)

  • Internal respiration is gas exchange between capillaries and the tissues

The lung thorax relationship

The Lung - Thorax Relationship

  • Two opposing forces

    • Lungs tend to collapse due to elasticity

    • Chest wall tends to spring out

    • Linked together by the pleura

      • Negative pressure -4 to -5 cm H2O

      • Parietal pleura lines chest wall

      • Visceral pleura covers lung

      • Potential space between with small amount of lubricant/pleural fluid between layers

Normal ventilation pressures

Normal ventilation pressures

  • Inspiration, (intrapleural = -10 cm H2O, intrapulmonary -3 cm H2O)

    • Diaphragm contracts and flattens

    • Chest cavity expands

    • Negative intrapulmonary pressure

    • Negative transairway pressure

    • Gas flows in through the mouth

Normal ventilation pressures1

Normal ventilation pressures

  • Expiration, (intrapleural = -5 cm H2O, intrapulmonary = +3 cm H2O)

    • Diaphragm relaxes

    • Chest cavity recoils and decreases in size

    • Slight positive intrapulmonary pressure

    • Gas flows out through the mouth

Physics of ventilation

Physics of Ventilation

  • Law of Laplace

    • P = 2 ST/r

    • surface tension tends to collapse alveoli

    • Surfactant allows different sized alveoli to be connected without smaller emptying into the larger alveoli and collapsing

      • Phospholipid

      • Decreases surface tension of the alveoli

      • Allows critical volume to be variable from alveoli to alveoli

Compliance measures dispensability of the lung

Compliance-measures dispensability of the lung

  • Compliance of the Lung = change in volume divided by change in pressure

Compliance measures dispensability of the lung1

Compliance-measures dispensability of the lung

  • Total compliance = lung and thorax (lung is not measured out of thorax)

    • Pulmonary compliance = 0.2L/cm H2O

    • Thoracic compliance = 0.2L/cm H2O

    • Total compliance = 0.1 L/cm H2O

Compliance measures dispensability of the lung2

Compliance-measures dispensability of the lung

  • Pressure is peak pressure during gas flow

Compliance measures dispensability of the lung3

Compliance-measures dispensability of the lung

  • Decreased or less compliance seen in:

    • Pulmonary consolidation

    • Pulmonary edema

    • Pneumothorax

    • Abdominal distension

    • ARDS

    • Pulmonary fibrosis

    • Thoracic deformities

    • Complete airway obstruction

Compliance measures dispensability of the lung4

Compliance-measures dispensability of the lung

  • Compliance increases

    • Alveolar distension

    • Alveolar septal defect

    • Obstructive disorders-CBABE

      • C = Cystic Fibrosis

      • B = Bronchitis

      • A = Asthma

      • B = Bronchiectasis

      • E = Emphysema

    • Compliance is inversely related to elastance

      • Elastance is the property of resisting deformation



  • Resistance =



  • Laminar

    • Poiseuille’s Law states that flow rate varies directly with radius of a tube

    • Small changes in airway radius will dramatically affect flow and resistance

      • ½ decrease in diameter increases resistance by 16 times

    • Turbulent (non laminar or eddy flow)

      • The higher the flow the more resistance

      • Resistance is also directly proportional to gas density



  • Transitional

    • Tracheobronchial tree has both laminar and turbulent flow caused in part by the directional changes in the conductive airway

    • Reynold’s number

      • Less than 2000 is laminar flow

      • 2000-4000 is laminar and turbulent or mixed flow

      • Greater than 4000 is turbulent flow



  • Viscosity

  • Pressure Gradient

  • Bernoulli’s Principle

  • Coanda Effect

Lung volumes

Lung Volumes

  • Relate to lung/thorax relationship, compliance and surface tension

  • Four volumes and four capacities

    • IRV - Inspiratory Reserve Volume

      • Maximum inhalation following quiet inhalation

      • Normally 3.1 L

    • VT - Tidal Volume

      • Volume inspired or expired during quiet breathing

      • Normally 0.5L

Lung volumes1

Lung Volumes

  • Four volumes and four capacities (cont)

    • ERV - Expiratory Reserve Volume

      • Maximum exhalation following quiet exhalation

      • Normally 1.2L

    • RV - Residual Volume

      • Gas remaining in lung after maximum exhalation

      • Normally 1.2L

Lung volumes2

Lung Volumes

  • Capacities - consist of 2 or more volumes or capacities

    • IC - Inspiratory Capacity

      • Made of IRV and VT

      • Maximum inhalation following quiet exhalation

      • Normally 3.6L

    • FRC - Functional Residual Capacity

      • Made of ERV and RV

      • Gas in lung following quiet exhalation

      • Normally 2.4L

Lung volumes3

Lung Volumes

  • Capacity (cont)

    • VC - Vital Capacity

      • Made of IRV, VT, and ERV

      • Maximum exhalation following a maximum inspiration

      • Normally 4.8L

    • TLC - Total Lung Capacity

      • Made of IRV, VT, ERV and RV

      • Gas in the lung following maximum inhalation

      • Normally 6L

Frc and lung compliance

FRC and Lung Compliance

  • FRC is most consistent volume - diaphragm at rest

    • At FRC, equalization of opposing forces of pulmonary and thoracic elasticity

    • As elasticity changes, FRC changes

    • At FRC, intrapleural pressure is normal -5 cm H2O

    • At FRC, intrapulmonary pressure equals ambient pressure

    • With an increase in compliance, (decrease elasticity), an increase in ease of inspiration but difficulty in expiration

    • Decrease in compliance, decrease the ease of inspiration

Classification of ventilation

Classification of Ventilation

  • VE = Minute Ventilation

    • The amount of gas moved in 1 minute

    • Calculated by VT times (*) f

    • Can be measured by a respirometer

      • Vane- Draeger, Wright

      • Volume bellows spirometer

      • Venticomp bag

      • Vortex principle- Boum’s LS 75

      • Use a respirometer with a filter attached to demonstrate measuring VE

Classification of ventilation1

Classification of Ventilation

  • VD= Dead space

    • Part of min. ventilation is "wasted", does not reach alveoli where external respiration occurs

    • Anatomical (VDanat)

      • Fills space in the conductive airways

    • Alveolar (VDalv)

      • Alveoli that are not perfusion

    • Physiologic (VDphys)

      • All dead space combination of VDanat and VDalv

Classification of ventilation2

Classification of Ventilation

  • Dead space (cont)

    • Mechanical

      • Added dead space

    • Normally 1 cc per pound ideal weight (approx. 150cc)

    • Volume rebreathed

Classification of ventilation3

Classification of Ventilation

  • VA = Alveolar ventilation

    • Gas in perfused alveoli

    • Participates in external respiration

    • VA= (VT - VD)

Classification of ventilation4

Classification of Ventilation

  • Terms relating to dead space

    • Normal ventilation

      • Adequate ventilation to meet metabolic needs

    • Hypoventilation

      • Decreased alveolar ventilation

      • Can be caused by increased VD or decreased VT

      • Ventilation less than that necessary to meet metabolic needs; signified by a PCO2 greater than 45 mmHg in the arterial blood

    • Hyperventilation

      • Increased alveolar ventilation

      • Caused by decreased VD or increased VT

      • Ventilation more than necessary to meet metabolic needs, signified by a PCO2 less than 35 mmHg in the arterial blood

Ventilation and perfusion

Ventilation and Perfusion

  • Ventilation = alveolar minute ventilation

    • VA = (VT - VD)* f

    • Perfusion = blood flow to the tissues

Ventilation and perfusion1

Ventilation and Perfusion

  • External respiration = gas exchange between the alveoli and capillaries

    • Carbon dioxide leaves blood

    • Oxygen enters the blood

    • Respiratory Quotient -unequal exchange of CO2 produced vs. oxygen uptake or utilization

      • 200 ml CO2 produced by 250 ml O2 used due to normal metabolism in the Kreb’s cycle (CARC page 154 & 389).

Gas exchange unit

Gas exchange unit

  • Normal unit

    • Alveoli with capillary—relationship between ventilation and gas flow are relatively equal

  • Dead space unit

    • ventilation without or in excess of perfusion

  • Shunt

    • Perfusion without or in excess of ventilation

  • Silent unit

    • No perfusion, no ventilation

Regional differences in ventilation perfusion

Regional Differences in Ventilation & Perfusion

  • More ventilation to the bases

    • 4 times more ventilation to bases than apices

      • Due to gravity’s effect on pleural pressures

      • On inspiration the transpulmonary pressure is greater at the bases

  • More perfusion to bases

    • Due to gravity

    • 20 times more perfusion to bases than apices

  • Ventilation/Perfusion ratio (V/Q)

    • V/Q = 4L alveolar minute volume 5L minute cardiac output

    • Overall for the lung is 4:5 or 0.8

Regional differences in ventilation perfusion1

Regional Differences in Ventilation & Perfusion

  • Diffusion

    • Whole Body Diffuision Gradients

    • Determinants of Alveolar Gas Tensions

    • Mechanism of Diffusion

    • Systemic Diffusion Gradients

    • Abnormalities

      • Impaired oxygen Delivery

      • Impaired Carbon Dioxide Removal



  • Unoxygenated blood entering the left side of the heart

  • Anatomical shunt

    • Normally 2-5% of cardiac output

      • Bronchial veins drains bronchial circulation

      • Pleural veins drains pleural circulation

        • Thebesian veins drains heart circulation

  • Absolute capillary shunt

    • Alveoli perfused but not ventilated

    • “True Shunt”

    • Refractory to O2 therapy



  • Relative capillary shunt

    • V/Q mismatch

    • Areas where perfusion is in excess of ventilation

    • Physiological shunt

      • Sum of anatomical, absolute and relative shunts

  • Causes

    • Decrease in ventilation

    • An increase in perfusion (increased CO)

Dead space

Dead Space

  • "Wasted" ventilation

  • Types

    • Anatomical

      • Conducting airways in tracheobronchial tree

    • Alveolar: Alveoli that have decreased perfusion

    • Physiological: Sum of anatomical and alveolar

    • Mechanical – added dead space

    • Causes

      • An increase in ventilation

      • A decrease in perfusion (decreased CO)

    • Effect

      • Increased VD will decrease VA if VE remains constant

Effects of exercise of high pressure environs

Effects of exercise & of high pressure environs

  • Exercise

    • Increases CO2 production and O2 consumption

    • Aerobic versus anaerobic

      • Oxygen consumption correlates to alveolar ventilation

      • At rest 250ml rises to 3500ml/minute (untrained) to 5000ml/minute (trained athlete)

      • PaO2, PaCO2 and pH remain constant

Effects of exercise of high pressure environs1

Effects of exercise & of high pressure environs

  • Exercise (cont)

    • Circulation

      • Increased sympathetic impulses stimulates heart rate and perfusion to working muscles

      • Frank-Starling mechanism

      • Maximal heart rate

    • Muscle Work, Oxygen Consumption, and Cardiac Output Interrelationships

    • The Training Influence

    • Body Temperature: Cutaneous Blood Flow Relationship

Effects of exercise of high pressure environs2

Effects of exercise & of high pressure environs

  • High altitude

    • Acclimatization

    • Major cardiopulmonary responses

      • increased alveolar ventilation via peripheral chemoreceptor stimulation

      • Secondary polycythemia, increased RBC production due to low oxygen levels

      • Development of respiratory alkalemia, due to the increased alveolar ventilation and carbon dioxide elimination

      • Increased oxygen diffusion capacity in native high dwellers, due to increased lung size

Effects of exercise of high pressure environs3

Effects of exercise & of high pressure environs

  • Major cardiopulmonary responses (cont)

    • Increased alveolar arterial oxygen difference

    • Improved ventilation perfusion ratio

    • Increased cardiac output of non-acclimatized individuals

    • Increased pulmonary hypertension as a result of hypoxic vasoconstriction



  • Definition

  • Concentration

  • Osmotic pressure

  • Quantifying solute content and activity

  • Calculating solute content

  • Quantitative classification of solutions

Electrolytic activity and acid base balance

Electrolytic Activity and Acid Base Balance

  • Characteristics of acids, bases, and salts

  • Designation of acidity and alkalinity

Body fluids and electrolytes

Body Fluids and Electrolytes

  • Fluids

  • Electrolytes

Blood gases

Blood Gases

  • Define

  • Kreb’s [TCA] Cycle

Oxygen transport

Oxygen Transport

  • Dissolved

    • Henry's Law - weight of gas dissolving in liquid is proportional to the partial pressure of a gas

      • Bunsen solubility coefficient for O2

        • 0.023ml of O2 can be dissolved in 1ml of plasma at 37°C and 760mmHg PO2

        • This allows us to determine the amount of O2 (expressed in ml) dissolved in 1ml of plasma using the formula: 0.003 * PaO2

        • (ex: PaO2 of 100 mmHg = 0.3ml of dissolved O2 in plasma)

Oxygen transport1

Oxygen Transport

  • Graham's Law – rate of diffusion of a gas is directly proportional to its solubility coefficient and inversely proportional to the square root of its density

    • CO2 is 20 times more diffusible than O2

    • CO is 200 times more diffusible than O2

    • Hemoglobin’s affinity for CO is 200 times more than for oxygen.

Oxygen transport2

Oxygen Transport

  • Combined with hemoglobin

    • Carries the most oxygen to the tissues

    • Doesn't exert a gas pressure

    • Calculate 1.34 * Hb * SaO2

    • Total oxygen content is sum of dissolved and combined

Oxygen transport3

Oxygen Transport

  • Oxyhemoglobin dissociation curve

    • Curve is sigmoidal due to Hb affinity for O2 at each of 4 binding sites

      • Last site has less affinity than 2nd & 3rd

      • In the steep portion minimal changes in PO2 will cause drastic changes in saturation and total O2 content

      • P50 is where Hb is 50% saturated with O2 and is normally a PaO2 of 27mm/Hg

Oxygen transport4

Oxygen Transport

  • Oxyhemoglobin dissociation curve (cont)

    • A shift to right causes a decreased affinity for O2, resulting in decreased saturation but increased O2 to tissues

      • Factors causing shift to the right

      • Increased PCO2

      • Increased H+ (decreased pH)

      • Increased 2, 3 DPG

      • Increased temperature

Oxygen transport5

Oxygen Transport

  • Oxyhemoglobin dissociation curve (cont)

    • A shift to the left causes increased affinity for O2, resulting in increased saturation but decreased O2 to the tissues

      • Factors causing shift to the left

      • Decreased PCO2

      • Decreased H+ (increased pH)

      • Decreased temperature

      • Decreased 2, 3, DPG

Oxygen transport6

Oxygen Transport

  • Oxyhemoglobin dissociation curve (cont)

    • Bohr effect – the effect of H+ or CO2 on Hb affinity for O2

      • At lungs – PCO2 is low

        • Shifts curve to left

        • Increased affinity for O2

        • pH increased in lungs causing shift to the left with an uptake of oxygen into the blood

      • At tissues - PCO2 is high

        • Shifts curve to the right

        • Decreases affinity for O2

        • pH decreased in tissue causing shift to right releasing oxygen to the tissue

Oxygen transport7

Oxygen Transport

  • Total O2 content is determined by adding the combined oxygen content with the dissolved oxygen content

    • CaO2 = (0.003 * PaO2) + (1.34 * Hb * SaO2)



  • Deficiency of oxygen in the arterial blood

  • Causes of hypoxemia

    • Decreased alveolar oxygen tension

      • Alveolar air equation



  • Causes of hypoxemia

    • Alveolar hypoventilation

    • Decreased hemoglobin saturation

    • Alveolar hypoventilation due to V/Q abnormalities

      • Intrapulmonary shunting: blood going from right to left heart without oxygenation



  • Responses to hypoxemia

    • Increased ventilation

    • Increased cardiac output

    • Types

      • Hypoxic

      • Anemic

      • Stagnant

      • Histotoxic



  • Decreased oxygen to the tissues

  • Hypoxemic Hypoxia or Ambient Hypoxia

    • PaO2 decreased

  • Anemic Hypoxia or Hemic Hypoxia

    • Hb decreased

    • inability to accept O2 (CO poisoning)

      • Hb has 200 times more affinity for CO than O2

      • Normal HbCO is 0.5%

      • HbCO of 5-10% occurs after smoking

      • HbCO of 40-60% can cause death



  • Stagnant Hypoxia or Circulatory Hypoxia

    • Heart unable to deliver oxygenated blood to tissues (low CO)

  • Histotoxic Hypoxia

    • cells unable to accept or use oxygen (cyanide poisoning)

  • Results

    • Anaerobic metabolism

    • Production of lactic acids is a by product of CO2 metabolism

Alveolar arterial oxygen difference p a a o2

Alveolar-Arterial Oxygen Difference P(A-a)O2

  • Measurement of the pressure difference between the alveoli and the arterial blood

    • In normal lungs O2 is readily transferred from alveoli to blood and only a small PO2 difference is present

    • Diseased lungs often have larger P(A-a)O2 because of diffusion defects

    • Has been used to estimate the percent intrapulmonary shunt

      • On 100% O2, every 50 mmHg difference in P(A-a)O2 approximates a 2% shunt

Alveolar arterial oxygen difference p a a o21

Alveolar-Arterial Oxygen Difference P(A-a)O2

  • An increase in P(A-a)O2 is strictly an indication of respiratory defects in oxygenation abilities

    • Most respiratory dysfunctions that produce hypoxemia are accompanied by an increase in P(A-a)O2

  • Normal value on room air is 10 to 15 mmHg

  • Co2 transport

    CO2 Transport

    • Carbon Dioxide

      • Produced from normal metabolism

      • The burning of glucose with O2 is carried in plasma and in red blood cells

    Co2 transport1

    CO2 Transport

    • In plasma

      • Dissolved: approximately 8% of CO2

      • As Bicarbonate (HCO3):

        • CO2 + H2O form carbonic acid (H2CO3)

        • dissociates into bicarbonate and hydrogen ions

        • Equation

        • H2O + CO2 = H2CO3H+ + HCO3¯

    • about 80% of C02 is transported as bicarbonate

    • Attached to plasma proteins about 12%

    Co2 transport2

    CO2 Transport

    • In the red blood cells

      • Dissolved

      • As HCO3¯

        • HCO3¯ produced by hydrolysis of CO2

        • HCO3¯ diffuses out of cell

        • creates an electrical imbalance

        • Cl¯ enters the cell to bring balance

        • called the chloride shift or Hamburger phenomenon

      • Attached to the Hb molecule

    Co2 transport3

    CO2 Transport

    • Haldane Effect

      • The effect of O2 on CO2 transport

        • At the lungs, PO2 is increased & CO2 is unloaded off Hb

        • At the tissues, PO2 is decreased & CO2 is loaded on Hb

    Co2 transport4

    CO2 Transport

    • Terms relating to PaCO2

      • Hypocapnia or hyporcarbia

        • CO2 below 35 mmHg

      • Hypercapnia or hypercarbia

        • CO2 above 45 mmHg

      • Eucapnea

        • Normal CO2 (35-45 mmHg)

    Buffer systems acid base balance

    Buffer Systems (Acid Base Balance)

    • Purpose is to maintain the pH

      • Prevent rapid changes

    • Buffer systems

      • Open/Bicarbonate

        • Mainly the HCO3/H2CO3

          • Ventilatory

          • About 60%

        • Hb

          • Renal

          • About 30%

    Buffer systems acid base balance1

    Buffer Systems (Acid Base Balance)

    • Closed/Noncarbonate

      • Blood

        • Intracellular

        • Phosphates, proteins, sulfates and ammonia groups

      • Physiological roles of buffer systems

        • Bicarbonate

        • Noncarbonate

    Henderson hasselbalch equation

    Henderson-Hasselbalch Equation

    • pH = pk + log

      • pk = 6.10

      • normally HCO3¯= 24 mEq/L

      • normally H2CO3 = 1.2 mEq/L

      • log of 20 = 1.3

      • 6.1 + 1.3 = 7.4 normal pH

      • 10/1 = acidemia

      • 30/1 = alkalemia

    Normal values arterial

    Normal Values (Arterial)


    • pH7.47.35-7.45

    • PaCO2 40 mmHg35-45

    • PaO2100 mmHg80-100

    • HCO324 mEq/L22-26

    • Base00+ or – 2

    • Hb14 gm %12-15

    • O2 Sat97.5 %95 - 100%

    • O2 content20 volume %18-20 volume %

    Normal values venous

    Normal Values (Venous)


    • pH7.36

    • PvCO246

    • PvO240

    • HCO324

    • Base0

    • Hb14

    • O2 Sat75

    • O2 content15 volume %

    Acid base effects

    Acid Base Effects

    • Increased CO2 causes a decreased pH

    • Decreased CO2 causes an increased pH

    • Increased HCO3 causes an increased pH

    • Decreased HCO3 causes a decreased pH



    • Kidneys

      • Excrete H+ which increase HCO3 to compensate for an increased CO2

      • Excrete less H+ and more HCO3 to compensate for decreased PCO2

      • May take 3 days to compensate

      • Excess Hydrogen Ion excretion & role of urinary buffers



    • Lungs

      • Increases CO2 to compensate for an increased HCO3 (short term only)

    • Pharmacologically

      • Administer sodium bicarbonate (NaHCO3) to increase pH

      • Administer ammonium chloride (NH3Cl) to decrease pH



    • Method for interpretation

      • Categorize pH

      • Determine Respiratory Involvement

      • Determine Metabolic Involvement

      • Assess for Compensation





    • States

      • Respiratory Acidosis

        • Causes

        • Compensation

        • Correction

      • Respiratory Alkalosis

        • Causes

        • Clinical Signs

        • Compensation

        • Correction

        • Alveolar Hyperventilation Superimposed on Compensated Respiratory Acidosis





    • Respiratory Acidosis

      • Uncompensated -+N N

      • Partially Compensated-+++

      • CompensatedN+++

  • Respiratory Alkalosis

    • Uncompensated+-NN

    • Partially Compensated+---

    • CompensatedN---

  • Metabolic Acidosis

    • Uncompensated-N--

    • Partially Compensated----

    • CompensatedN ---

  • Metabolic Alkalosis

    • Uncompensated+N++

    • Partially Compensated++++

    • CompensatedN+++

  • Interpretation4


    • Metabolic Acidosis

      • Causes

      • Anion Gap

      • Compensation

      • Symptoms

      • Correction

    • Metabolic Alkalosis

      • Causes

      • Compensation

      • Correction

    • Metabolic Acid-Base Indicators

      • Standard Bicarbonate

      • Base Excess

    Assessment of hypoxemia

    Assessment of Hypoxemia

    • On room air with normal Hb and under 60 years old (PaO2 above 80mmHg = no hypoxemia)

      • Normal = 80-100mmhg

      • Mild hypoxemia = PaO2 = 60-79mmHg

      • Moderate hypoxemia = PaO2 = 40-59mmHg

      • Severe hypoxemia PaO2 = less than 40mmHg

    Assessment of hypoxemia1

    Assessment of Hypoxemia

    • O2 content

      • Mild hypoxemia 15-17 volume % (17)

      • Moderate hypoxemia = 12-14 volume % (15)

      • Severe hypoxemia = 12 volume % (12)

    • Over 60 years old

      • Subtract 1 mmHg for every year over 60

      • Severe hypoxemia is still PaO2 <40mmHg

        *Review Table 7-2 CARC p122 “Relationship between Age and Normal Predicted PaCO2

    Assessment of hypoxemia2

    Assessment of Hypoxemia

    • Patients with abnormal Hb

      • Calculate total O2 content

        • (Hb * 1.34 * SaO2) + (0. 003 * PaO2)

      • Mild hypoxemia = CaO2 17 volume %

      • Moderate hypoxemia = CaO2 15 volume %

      • Severe hypoxemia = CaO2 12 volume %

    Other oxygenation assessments

    Other Oxygenation Assessments

    • Oxygen Saturation (SaO2)

    • Arterial Oxygen Content (CaO2)

    • Alveolar-Arterial Oxygen Difference [P(A-a)O2]

    • Partial Pressure of Oxygen in Mixed Venous Blood (PvO2)

    • Arteriovenous Oxygen Content Difference C(a-v)O2

    • Carboxyhemoglobin (HbCO)

    Assessment of acid base balance

    Assessment of Acid Base Balance

    • Hydrogen Ion Concentration (pH)

    • Partial Pressure of Arterial Carbon Dioxide (PaCO2)

    • Arterial Blood Bicarbonate (HCO3-)

    • Base Excess & Base Deficit

    Control of ventilation

    Control of Ventilation

    • Ventilation

      • Under control of autonomic or involuntary nervous system

      • Is controlled by central and peripheral chemoreceptors

    • Central chemoreceptors

      • Influenced by contents of the cerebrospinal fluid (CSF)

      • CO2 diffuses freely in CSF

      • Increased CO2 in CSF will cause increased H+

      • Causes a stimulation of the inspiratory center

    Control of ventilation1

    Control of Ventilation

    • Central chemoreceptors (cont)

      • Areas of the medullary center

        • Apneustic or pontine center

          • Allows deep inspiration

        • Pneumontaxic center

          • Limits inspiration from inspiration center

          • Causes decreased rate of time

          • Hering-Breuer (stretch receptors)

            • Inflation reflex message carried to brain via Vagus nerve

            • Located in smooth muscle of both large and small airways

            • Limits inspiration

    Peripheral chemoreceptors

    Peripheral Chemoreceptors

    • Carotid bodies

      • Responds to hypoxemia

      • Increases ventilation

      • Located in the bifurcations of the common carotid arteries

    • Aortic bodies

      • Responds to hypoxemia

      • Usually effects heart more than ventilation

      • Located in the aortic arch

    Applied physiology chemistry

    Handle Gas Cylinders With Care

    States of matter

    States of Matter

    • Energy

      • Potential

      • Kinetic

      • Temperature

        • Absolute Zero

        • Scales

      • Heat Transfer

    States of matter1

    States of Matter

    • Forms

      • Solid

      • Liquid (Properties)

        • Pressure

        • Buoyancy

        • Viscosity

        • Cohesion & Adhesion

        • Surface Tension

        • Capillary Action

      • Gas

    States of matter2

    States of Matter

    • Changes

      • Liquid to Solid

        • Melting

        • Freezing

      • Liquid to Gas (Vapor)

        • Evaporation

        • Vapor Pressure

        • Humidity

      • Water

        • How its behavior is different from other compounds when it freezes or melts



    • Molecules continuously moving

    • Avogadro’s law

      • 1 gram atomic weight of any substance 6.02 * 1023 atoms

      • This is known as 1 mole.

      • 1 mole of a gas at STPD occupies 22.4 L



    • PB= barometric pressure

    • Normal barometric pressure is

      • 760mmHg

      • 14.7 PSI

      • 1034cm H2O

      • 33ft of water

    • Water vapor (or humidity) exerts pressure

      • Partial pressure of H2O (PH2O) at 100% RH at 37 degrees C = 47mmHg



    • Dalton's law

      • The sum total of the individual partial pressures of gases in the atmosphere are equal to the barometric (PB = PN2 + PO2 +PTrace gases)

      • The pressure of each gas will be exerted when separated from a mixture (PN2 = PB * %N2)

    Concentrations of atmospheric gases

    Concentrations of Atmospheric Gases

    • Oxygen 20.95%

    • Nitrogen 78.08%

    • Argon 0.93%

    • Carbon Dioxide 0.03%

    • Trace Gases 0.01 %

    Application of dalton s law to the lung

    Application of Dalton's Law To The Lung

    • Partial pressure of a gas equals Pbar * concentration (example: 760mmHg * 0.21 = 159mmHg for O2)

    • In the lung the water vapor exerts a pressure of 47mmHg thus it changes the pressure of the atmospheric gases in the alveoli (example: Pbar= 760mmHg – 47mmHg = 713mmHg)

    • Because of the change in the barometric pressure in the alveoli the partial pressure of O2 also changes (example: PO2 = 713mmHg * 0.21 = 149mmHg)

    Application of dalton s law to the lung1

    Application of Dalton's Law To The Lung

    • In the lungs the CO2 is higher than in the atmosphere and affected by the respiratory quotient (the unequal exchange of O2 for CO2)

    • Example: 149mmHg – 50mmHg = 99mmHg (99mmHg is alveolar partial pressure of oxygen)

    Application of dalton s law to the lung2

    Application of Dalton's Law To The Lung

    • Ideal Alveolar Gas Equation

      • In addition to the effects of PH2O on partial pressure of gases in the alveoli, the carbon dioxide diffusing from the bloodstream into the alveoli will further decrease alveolar PO2

      • Since carbon dioxide is leaving the bloodstream, (a closed system), and entering the respiratory tract, (an open system), there is an indirect relationship between the pressures of carbon dioxide and oxygen

    Application of dalton s law to the lung3

    Application of Dalton's Law To The Lung

    • Ideal Alveolar Gas Equation (cont)

      • Increases in PACO2 result in decreases in PAO2

      • This indirect relationship basically involves only carbon dioxide and oxygen because they are the only metabolically active gases

      • Dalton's Law must be modified to account for incoming carbon dioxide when applied to alveolar

    Application of dalton s law to the lung4

    Application of Dalton's Law To The Lung

    • Ideal alveolar gas equation

      PAO2 = FIO2 * (Pb - PH2O) - PCO2 / RQ

      • PAO2 = pressure of O2 in the alveoli

      • Pb = barometric pressure

      • PH2O = water pressure

      • FIO2 = fraction of inspired oxygen

      • PACO2 = pressure of CO2 in the alveoli

      • RQ = respiratory quotient

    Application of dalton s law to the lung5

    Application of Dalton's Law To The Lung

    • A modification of the above equation maybe used with reasonably accurate results

      PAO2 = (PB - PH2O)(FIO2) - PACO2

    • In both equations, PaCO2 is always considered equal to PACO2 because of the rapid equilibration of carbon dioxide (20 * faster or easier than O2)

    Gas laws

    Gas Laws

    • Ideal Gas Law

      • If mass is constant then

    Gas laws1

    Gas Laws

    • Boyle's Law

      • If temperature and mass are constant then volume and pressure are inversely proportional

    P1V1 = P2V2

    Gas laws2

    Gas Laws

    • Charles' Law

      • If pressure and mass are constant then temperature and volume are directly proportional

    Gas laws3

    Gas Laws

    • Gay-Lussac's Law

      • If volume and mass remain constant, pressure and temperature are directly proportional

      • The triangle demonstrates the relationship

    Gas laws4

    Gas Laws

    • All gas laws use temperature in Kelvin (absolute temperature scale)

    • C + 273 = Kelvin

    Applied physiology chemistry

    Relationships of Gas Laws











    • Ideal Gas Equation

      • A gas system has volume, moles, and temperature of 9160ml, 0.523 moles & 324K, respectively. What is the pressure in torr?

        P = x

        V = 9160ml = 9.16L

        n = 0.523 moles

        T = 324K

        (0.523 * 62.4 * 324) ÷ 9.16 = 1160 torr

    • How many moles of gas are contained in 890 ml at 21°C and 750 mmHg pressure?

      n = PV/RT

      (750 mmHg ÷ 760mmHg atm-1)(0.89L) ÷ (0.08206L at mol-1K-1)(294K)

      (0.9868) * (0.89) ÷ (24.12564)

      0.878252 ÷ 24.12564

      n = 0.0364

    • *Division of 750 by 760 is to convert mmHg to atm



    • Boyle’s Law

      • A gas system has initial pressure and volume of 3.69 atm and 5440ml. If the pressure changes to 2.38 atm, what will the resultant volume be in ml?

        P1(V1) = P2 (V2)

        3.69 * 5440 = 2.38x

        20073.6 = 2.38x

        x = 8434.29



    • Boyle’s Law (cont)

      • A gas occupies 12.3L at a pressure of 40.0 mmHg. What is the volume when the pressure is increased to 60mmHg?

        40 * 12.3 = 60x

        x = 8.2L

      • If a gas at 25°C occupies 3.6L at a pressure of 1atm, what will be its volume at a pressure of 2.5atm?

        1atm * 3.6L = 2.5x

        x = 1.44L



    • Charles’ Law

      • A gas system has an initial temperature of 308.9K with the volume unknown. When the temperature changes to -230.4°C the volume is found to be 1.67L. What was the initial volume in L?

      • -230.4°C =>42.6K



    • Charles’ Law (cont)

      • Calculate the decrease in temperature when 2L at 20°C is compressed to 1L.

        2L * 293 = 1x

        x = 146.5

      • A 600ml sample of nitrogen is warmed from 77°C to 86°C. Find its new volume if the pressure remains constant.

        600ml ÷ 350 = 359K



    • Guy-Lussac’s Law

      • A container is initially at 47mmHg and 77K (liquid nitrogen temperature). What will the pressure be when the container warms up to room temperature of 25°C?

        Ans: 180mmHg

      • A gas thermometer measures temperature by measuring the pressure of a gas inside the fixed volume container. A thermometer reads a pressure of 248 torr at 0°C. What is the temperature when the thermometer reads a pressure of 345 torr?

        Ans: 107°C



    • Guy-Lussac’s Law (cont)

      • A vessel has a pressure of 18.9 lb/in2 at 20°C. What temperature is necessary to lower the pressure to 14.2 lb/in2?

        Ans: -53°C

    Review characteristics of medical gases

    Review Characteristics of Medical Gases

    • Oxygen

    • Air

    • Carbon Dioxide

    • Helium

    • Nitrous Oxide

    • Nitric Oxide

    Agencies regulating gas administration

    Agencies Regulating Gas Administration

    • DOT - Department of Transportation

      • Before 1970, was called ICC – Interstate Commission

      • Regulates construction, transport and testing of cylinders

    • HHS - Department. of Health & Human Services

      • Formerly called HEW - Department. of Health, Education and Welfare

      • FDA - Food & Drug Administration - is part of HHS - regulates the purity of gases

    • OSHA Occupational Safety & Health Administration - responsible for occupational safety

    Recommending bodies

    Recommending Bodies

    • CGA - Compressed Gas Association - created safety systems

    • NFPA - National Fire Protection Assn.

      • Fire prevention

      • Governs storage

    • Z-79 – Committee of American National Standards for Anesthetic Equipment, which includes

      • Ventilator devices

      • Reservoir bags

      • Trachea tubes and their connectors

      • Humidifiers

      • Other related equipment

    Safety systems for cylinders

    Safety Systems for Cylinders

    • Color coding for E cylinders (not mandatory for larger cylinders)

      • Oxygen – green (white internationally)

      • Carbon dioxide – grey

      • Nitrous oxide – blue

      • Cyclopropane – orange

      • Helium – brown

      • Ethylene – red

      • Air – yellow

      • Nitrogen – black

    Safety systems for cylinders1

    Safety Systems for Cylinders

    • Pin Index Safety System

      • E cylinders and smaller

      • High pressure (greater than 200psi)

      • Yoke & pin connections

      • Oxygen 2-5 position

      • Air 1-5 position

      • CO2 1-6 position

    Safety systems for cylinders2

    Safety Systems for Cylinders

    • American Standard Safety System

      • Larger than E cylinders

      • High pressure

      • Nipple & threaded nut

    Safety systems for cylinders3

    Safety Systems for Cylinders

    • Diameter Index Safety System

      • Low pressures (less than 200 PSI)

      • All connections after the regulator

      • Threaded nut & nipple

    Qualities of cylinder gases

    Qualities of cylinder gases

    • Flammable Gases

      • Ethylene

      • Cyclopropane

    • Nonflammable Gases

      • Nitrogen

      • Carbon dioxide

      • Helium

    Qualities of cylinder gases1

    Qualities of cylinder gases

    • Gases that support combustion

      • Oxygen

      • Oxygen mixtures

        • Helium/oxygen – heliox

        • Oxygen/carbon dioxide – carbogen

        • Oxygen/nitrogen

        • Oxygen/nitrous oxide

      • Nitrous oxide

    Qualities of oxygen

    Qualities of oxygen

    • Colorless

    • Odorless

    • Tasteless

    • Atomic weight = 16gms

    • Molecular weight = 32gms

    • Critical temperature

    • -118.8ºC or -181.1ºF at 49.7 atm

    • Above this temperature it cannot remain a liquid

    • Fractional distillation

    Cylinder marking and testing

    Cylinder marking and testing

    • Front

      • DOT-3AA 2015 PSI– these are DOT specifications and service pressure

      • Serial number

      • Ownership markings

      • Manufacturers mark

    Cylinder marking and testing1

    Cylinder marking and testing

    • Back

      • Original hydrostatic testing

      • Specifications

      • Retest dates

      • Inspectors mark and specifications

    • Cylinders are filled to 5/3 maximum pressure every 5-10 years (hydrostatic testing)

    Cylinder filling and duration

    Cylinder Filling and Duration

    • Can be overfilled by 10% to hold 2200 PSI

    • Duration of flow in minutes =

    Cylinder filling and duration1

    Cylinder Filling and Duration

    • Tank factors for O2 duration of flow

      • E = 0.28

      • G = 2.41

      • H = 3.14

        • These factors are used to calculate absolute duration times; however, in practice a safety factor must be utilized to insure no interruptions in gas therapy to the patient

      • Cylinder capacities

        • E = 22 ft3 or 616 liters @ 2200 psig

        • G = 187 ft3 or 5308 liters @ 2200 psig

        • H = 244 ft3 or 6908 liters @ 2200 psig

    Cylinder handling

    Cylinder Handling

    • Keep in carrier or stand

    • No flames/smoking

    • Proper technique in attaching regulators

      • Remove cap

      • Turn on gas momentarily (away from people) “cracking”

      • Place and tighten regulator

      • Turn on gas

      • Adjust flow

      • Bleed off pressure when not in use

    Cylinder handling1

    Cylinder Handling

    • Store with cap on to prevent breaking stem

    • Cylinder testing

      • Every 5- 10 years

      • Water displacement measured to check for expansion with 5/3 maximum pressure

    Gaseous bulk systems three general types

    Gaseous bulk systems three general types

    • Standard

      • Large H or K size cylinders banked into a manifold system

      • Primary bank

      • Reserve bank (automatically switches to this when primary system drops to a preset lower pressure limit

      • Six or more cylinders manifolded together. Alarms are activated when reserve switches on or malfunction occur. Cylinders are replaced as needed.

    Gaseous bulk systems three general types1

    Gaseous bulk systems three general types

    • Fixed cylinders

      • Large bank of permanently fixed cylinders (up to 75)

      • Refilled on site by a liquid O2 truck that converts the liquid into gas to fill tanks

    • Trailer units (2200 PSI)

      • Very large cylinders mounted on trailers towed to a central location for connection

      • When low or in need of maintenance replaced with fresh trailer

    Gaseous bulk systems three general types2

    Gaseous bulk systems three general types

    • Liquid Oxygen Systems

      • Liquid O2 is stored at -183°C or -297°F in thermos bottle type storage vessels (inner and outer steel shells separated by a vacuum)

      • Pressure readings do not indicate remainder of O2 because the liquid O2 doesn't exert gas pressure

        • Weight will indicate remainder of O2

        • Pressures not to exceed 250 PSI in containers in LOX containers

      • Specifications for bulk systems by NFPA

      • Piping systems

        • Locate zone valves in hospital

        • Do not turn off unless directed by fire chief

    Gaseous bulk systems three general types3

    Gaseous bulk systems three general types

    • Liquid Oxygen Systems (cont)

      • Most economical

        1 ft3 of liquid O2 = 860 ft3 of gaseous O2 @ ambient temperature

        • Liquid O2 cylinders are used when usage too large for and not large enough for a permanently liquid vessel (come in various sizes see textbook)

        • Fixed station (stand tanks) are large spherical with gaseous equivalents up to 130,000 cubic feet. Refilled by service tank trucks.

        • All liquid O2 tank containers are equipped with 50 PSI reducing valves.

        • Liquid O2 duration (in minutes)

          Pounds of liquid O2 * 344 =

          Liters per minute

    Gaseous bulk systems three general types4

    Gaseous bulk systems three general types

    • Safety precautions for bulk O2

      • Must have 24 hour reserve or back-up supply

      • Procedure for total system failure should be known

    • Oxygen Concentrators

      • Membrane

        • Thin membrane-1 µm thick

        • Oxygen and H2O pass through membrane faster than nitrogen

        • Delivers an FIO2 of about 40%

      • Molecular Sieve

        • Uses a sieve filled with sodium-aluminum silicate

        • Air is forced through the sieve

        • The nitrogen is scrubbed from the air

        • Delivers an FIO2 of about 90% at 2 LPM

        • At higher flows the FIO2 decreases



    • Reduce high tank pressure to low working pressure

      • Usually 50 PSI

    • Single stage regulator

      • Reduces tank pressure to 50 PSI in 1 step

      • Has one pressure relief valve (about 200 PSI)



    • Multi-stage regulator

      • Reduces tank pressure to working pressure in 2 or more steps

      • Each stage has a pressure relief valve

      • The more stages the less fluctuation of working pressure

    • Preset regulator

      • Single or multi-stage regulator that is set to have pressure reduced to set working pressure (usually 50 PSI)

      • Has no way to adjust working pressure



    • Adjustable regulator

      • Single or multi-stage regulator in which working pressure may be set variably



    • Control and indicate flow

    • Thorpe Tube

      • Vertical funnel shape tube with float

        • Must be kept vertical to be accurate



    • Compensated Thorpe Tube Flowmeter

      • Needle valve adjustment is distal (after or downstream) to the float

      • Indicated flow is accurate in the presence of back pressure to check for compensation:

      • Label calibrated at 70ºF, 50 PSI

        • Visualize needle valve placement

        • Turn unit off and plug into pressure

        • Float will rise, then fall



    • Uncompensated Thorpe Tube Flowmeter

      • Needle is proximal (upstream or before) the float

      • Flow meter reading will be lower than what is delivered to the patient if back pressure is present



    • Kinetic Flowmeter

      • Has plunger instead of float

      • All other areas of Thorpe tubes apply





    • Bourdon Gauge

      • Measures pressure but reads flow

      • Flow delivered to patient is less than flow shown on the gauge if back pressure is present

      • Works in any position



    • Use of oxygen flowmeters with helium

      • Due to density of gases flow will not be accurate

      • 80% helium, 20% O2 flow will be 1.8 times the meter reading

      • 70% helium, 30% O2 flow will be 1.6 times the meter reading



    • Piston

    • Diaphragm

    • Centrifugal

    • Assembly & Troubleshooting (White p15)



    • Direct Acting

    • Diaphragm

    • Safety Features

    • Reducing

      • Single stage

      • Modified Single stage

      • Multistage

      • Safety Features

    • Regulators



    • List current manufacturer and model

    • Describe how each acts as a conservation option



    • See textbook

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