Disoders of Ventilation Sung Chul Hwang, M.D. Dept. of Pulmonary and Critical Care Medicine Ajou University School of Medicine

Chemoreceptor Central Medulla Oblongata pH, PaCO2, PaO2 fall in pH of ECF and Carotid body Fine regulation Peripheral Aortic and Carotid body PaO2 dominant during Chronic hypoxia Coarse regulation

Alveolar Hypoventilation Increased PACO2 & PaCO2 above normal Impaired respiratory drive: brain stem, carotid body trauma Reduction in over all minute ventilation: resp. muscles, spinal cord, peripheral nerves Impaired respiratory apparatus : chest wall, airways and lung

Neuromuscular Disorders Spinal cord, peripheral nerves, respiratory muscle disease orthopnea, paradocxical movement of abdomen and diaphragm Dx : Rapid deterioration of MVV, reduced Pimax, Pemax, reduced transdisphragmatic pressures and response to phrenic nerve stimulations

Pathophysiology Increased PACO2 & PaCO2 Respiratpory Acidosis Metabolic compensation -- increase in HCO3 -- Decrease in Cl - Decrease in PAO2 & PaO2 Pulmonary vasoconstriction, Pulmonary hypertension, RV hypertrophy, CHF (Cor pulmonale)

Mechanoreceptor Stretch receptor : smooth muscle of trachea and main bronchus Irritant receptor : beneath the epithelium of larynx, trachea, bronchi J- receptor : periphery of lung C- receptor : pulmonary interstitial space near pulmonary and bronchial circulation

Clinical features Hypoxemia, cyanosis, polycythemia chronic hypoxemia, hypercapnea, pulmonary HTN, CHF ABG abnormality esp. in sleep and sleep disturbances Sx : morning headache, fatigue, daytime somnolence, mental confusion, intellectual impairment specific features of underlying diseases

Diagnosis Defect in Control System : impaired response to chemical stimuli, able to hyperventilate voluntarily Defects in N-M System : Unable to hyperventilate, abnormal static and dynamic lung measurements Defects in Chest wall, Lungs, Airways : Abnormal airway resistance and compliance, widened (A-a) DO2

Treatment Treat individual underlying disease Correction of Metabolic Alkalosis O2 supplements Respiratory Stimulants (medroxyprogesterone) Mechanical Ventilation : especially during sleep Diaphragmatic pacing

Primary Alveolar Hypoventilation (Ondine’s Curse) Chronic hypoxemia and hypercapnea without identifiable cause defect in metabolic respiratory control yrs of age males Sx and Signs of alveolar hypoventilation treatment : general supportive care for hypoventilation

Obesity-Hypoventilation SD (Pickwickian SD) Massive obesity reduced FRC Underventilation of Lung base and widening of (A-a)PO2 Chronic hypercapnia, hypoxemia, polycythemia, pulmonary HTN, Right heart failure Sx : OSA, sleep induced hypoventilation Tx : stop smoking, weight reduction, correct OSA, medroxy progesterone