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Ventilation / Ventilation Control Tests

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Presentation on theme: "Ventilation / Ventilation Control Tests"— Presentation transcript:

1 Ventilation / Ventilation Control Tests
RET 2414 Pulmonary Function Testing Module 5.0

2 Ventilation / Ventilation Control Tests
Objectives Calculate tidal volume and minute ventilation Describe two causes of increased ventilation Identify an abnormal VD/VT ratio

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Objectives Calculate dead space and alveolar ventilation Describe one method for measuring breathing response to O2 Identify the normal breathing response to carbon dioxide (CO2)

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VT, Rate, Minute Ventilation Tidal volume (VT) is Volume of gas inspired or expired during each respiratory cycle Respiratory rate (f) Number of breaths per unit of time Minute ventilation ( ) Total volume of gas expired per minute alveolar ventilation ( ) dead space ventilation ( )

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VT, Rate, Minute Ventilation VE = f x VT Measured with volume displacement or flow-sensing spirometer .

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VT, Rate, Minute Ventilation VT decreased in: Severe restrictive patterns Neuromuscular disorders Decreased VT is usually accompanied by an increase in respiratory rate in order to maintain alveolar ventilation ( )

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VT, Rate, Minute Ventilation Decreases in both VT and respiratory rate are often associated with respiratory center depression Alveolar hypoventilation

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VT, Rate, Minute Ventilation Normal respiratory rates ranges: 10 – 20 breaths/min Increased in: Hypoxia Hypercapnia Metabolic acidosis Decrease lung compliance Exercise

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VT, Rate, Minute Ventilation Normal respiratory rates ranges: 10 – 20 breaths/min Decreased in: Central nervous system depression CO2 narcosis; a condition resulting from high levels of carbon dioxide in the blood. Confusion, tremors, convulsions, and coma may occur if blood levels of carbon dioxide are too high (>70 mm Hg or higher).

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VT, Rate, Minute Ventilation Normal minute ventilation ranges: 5 – 10 L/min When used in conjunction with arterial blood gases, indicates the adequacy of ventilation

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VT, Rate, Minute Ventilation Normal minute ventilation ranges: 5 – 10 L/min increases in response to: Hypoxia Hypercapnia Metabolic acidosis Anxiety Exercise

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Dead Space /Alveolar Ventilation Dead space is the lung volume that is ventilated but not perfused by pulmonary capillary blood flow Anatomic (conducting airways) VDan Alveolar (non-perfused alveoli) VDA VDan + VDA = VD VD (Respiratory or Physiologic Dead Space)

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Anatomic Dead Space

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Dead Space /Alveolar Ventilation The portion of ventilation wasted on the conducting airways and poorly perfused alveoli is usually expressed as a ratio: VD/VT = (PaCO2 – PECO2) X 100 PaCO2 Modification of Bohr’s equation

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Dead Space /Alveolar Ventilation For convenience VD is often estimated as equal to anatomic deadspace; VD = 1 ml/lb of ideal body weight Valid only if little or no alveolar dead space exists due to pulmonary disease

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Dead Space /Alveolar Ventilation Normal VD/VT ratio in adults: 0.3 or 30% (0.2–0.4 or 20%–40%) Increases with: Pulmonary embolism Acute pulmonary hypertension Decreased cardiac output Decreases with: Exercise (increase cardiac output and perfusion of lung apices)

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Dead Space /Alveolar Ventilation Alveolar ventilation is the volume of gas that participates in gas exchange in the lungs per minute

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Dead Space /Alveolar Ventilation Alveolar ventilation at rest is approximately 4 – 5 L/min The adequacy of can only be determined with an arterial blood gas (ABG) Hypoventilation = PCO2 >45 with a pH <7.35 Hyperventilation = PCO2 <35 with a pH >7.45

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Dead Space /Alveolar Ventilation Decreased can result from: Increases in VD Destruction/dilation airway walls >FRC (air trapping/hyperinflation) Bronchodilators Decreases in

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Ventilatory Response to CO2 Ventilatory response to CO2 is a measurement of the increase or decrease in caused by breathing various concentration of carbon dioxide while PaO2 is kept normal

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Ventilatory Response to CO2 Procedure 1-7% CO2 is breathed through either an open or closed circuit while the following are measured: PeTCO2 SaO2 P100

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Ventilatory Response to CO2 Normal response to an increased PACO2 is a linear increase in ventilation ( ) Approximately 3 L/min/mm Hg (PCO2)

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Ventilatory Response to CO2 Decreased in patients with: COPD Increased airway resistance (Raw) Lesions in the CNS Chemoreceptor dysfunction

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Ventilatory Response to Oxygen Ventilatory response to O2 is a measurement of the increase or decrease in causes by breathing various concentration of O2 while PaCO2 is kept normal

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Ventilatory Response to Oxygen Procedure 20%-12% O2 is breathed through either an open or closed circuit while the following are measured: , PaO2, P100, PetCO2 The test is repeated with decreasing concentrations of O2

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Ventilatory Response to Oxygen Normal response to a decreasing PaO2 is an exponential increase in ventilation ( ) once the PaO2 is less than 60 mm Hg (SaO2 <90%) 60 torr/90% Saturation O2

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Ventilatory Response to Oxygen Significance and Pathology Patients with obesity-hypoventilation syndrome, obstructive sleep apnea, and idiopathic hypoventilation will show a marked decrease response to hypoxemia

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Occlusion Pressure (P100 or P0.1) P100 is the pressure generated during the first 100 milliseconds of inspiratory effort against an occluded airway. It is a measurement of the neural output from the medullary centers that drive ventilation rate and volume

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Occlusion Pressure (P100 or P0.1) Normally P100 values are: 1.5 – 5.0 cm H2O Usually measured at varying PetCO2 values or levels of O2 desaturation to assess the effect of changing stimuli to ventilation

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Occlusion Pressure (P100 or P0.1) P100 is usually plotted against PetCO2

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Occlusion Pressure (P100 or P0.1) P100 values will normally increase with PaCO2 (hypercapnia) or PaO2 (hypoxemia) Healthy patients typically increase occlusion pressure 0.5 to 0.6 cm H2O/mm Hg PCO2 Patients with COPD will not increase the P100 when the PaCO2 in increased


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