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

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

Ventilation / Ventilation Control Tests 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)

Ventilation / Ventilation Control Tests 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 ( )

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

Ventilation / Ventilation Control Tests 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 ( )

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

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

Ventilation / Ventilation Control Tests 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).

Ventilation / Ventilation Control Tests 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

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

Ventilation / Ventilation Control Tests 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)

Ventilation / Ventilation Control Tests Anatomic Dead Space

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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)

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

Ventilation / Ventilation Control Tests 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

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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

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

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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests 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

Ventilation / Ventilation Control Tests Occlusion Pressure (P100 or P0.1) P100 is usually plotted against PetCO2

Ventilation / Ventilation Control Tests 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