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1 RSPT 1207 - CARDIOPULMONARY A&P REGULATION of VENTILATION Lecture notes Reference & Reading: Egan’s pp. 172-174, Chapter 14 I. Central Nervous System: The CNS will receive stimuli, asses and make a decision based on the data received and sends command along a motor nerve (neuron) to the muscles of ventilation. How the CNS receives stimuli: II. CHEMORECEPTORS a. Central Chemoreceptors 1. Location 2. Blood-brain barrier 3. When CO2 moves across the blood-brain barrier, it goes through the process of hydrolysis: CO2 + H2O 4. 5. 6. 7. 8. H2CO3 HCO3- + H+ The H+ ions that build in the CSF as a result of hydrolysis By increasing ventilation the PaCO2 reduces Central chemoreceptors regulate ventilation Minute Changes CO2 retention b. Peripheral Chemoreceptors 1. Location 2. This group of chemoreceptors are sensitive to Decreased PaO2 (less than 60 mmHg) Increased PaCO2 Decreased pH (acidosis) 3. Changes in pH must be as large 4. When the Central Chemoreceptors do not respond 5. CO2 retainer II. Cerebral Cortex – a. SOB 1. It is not just triggered by hypercapnia, or hypoxemia. 2. A person who is hypoxic b. Deliberate Alterations 1. The breathing pattern may be altered 2. As soon as the cerebral cortex ends How the CNS processes information: 2 There are two portions of the lower brain/brainstem that controls ventilation for a person: I. Medulla (Oblongata) On the surface of the medulla are two areas: a. Dorsal Respiratory Groups (DRG): 1. Contains 2. Vagus and glossopharyngeal nerves send sensory impulses to the DRG 3. These impulses modify the basic breathing pattern in the medulla b. Ventral Respiratory Groups (VRG): 1. Location 2. Inspiratory neurons send impulses via the vagus nerve 3. Expiratory neurons sends impulses II. Pons – the word “pon” literally means bridge. It takes commands like “I need to swim/talk/ sing” (cerebral cortex) Into “Breathe now, hold now” commands (medulla) a. There are two groups of neurons in the pons: 1. Apneustic Center: the function is ill-defined Apneustic breathing 2. Pneumotaxic Center: Works with the Apneustic Center to control the depth of inspiration. Strong signals Weak signals How the CNS sends commands: The spinal cord contain the neural pathways for nerve conduction, both sensation and motor impulses. They are along the spinal cord and lie within the protection of the spinal cord. I. Sensory Nerves a. Vagus Nerves Extends beyond head and neck b. Glossopharyngeal Nerves II. Motor Nerves a. Phrenic Nerves – Breathing commands There is a right and left phrenic nerve These nerves exit the spinal cord between C3 and C5. 3 b. Intercostal Nerves - run along the rib cage. Breathing Controlled by Reflexes I. Hering-Breur Reflex a. Generated by stretch receptors b. When lung inflation stretched these receptors II. Deflation Reflex a. deflation reflex results in hyperpnea b. Signal III. Head’s Paradoxic Reflex a. When the vagus nerve is blocked, b. Relation to Vt IV. Irritant Receptors a. Cholinergic Reflex bronchospasm 1. Larger central airways 2. Rapidly adaptive 3. Activated by tactile stimulation Inhaled irritants Mechanical factors Pulmonary congestion 4. Stimulation can result in Bronchoconstriction Hyperpnea Laryngospasm Glottis closure Coughing V. b. Vagovagal Reflex 1. When the reflex has both sensory and motor vagal components 2. Activated by physical stimulation of conducting airways Endotracheal intubation Airway suctioning Bronchoscopy 3. Stimulation can result in bradycardia coughing laryngospasm J Receptors a. Location b. Activated by Alveolar inflammatory responses Pulmonary vascular congestions Pulmonary edema c. stimulation results in rapid, shallow breathing a feeling of dyspnea 4 narrowing of the glottis on exhalation Abnormal Breathing Patterns I. Cheyne-Stokes Breathing a. Ve increases, reaches a “climax,” then decreases then apnea occurs. b. Causes c. Brain is reacting to the acidotic CSF II. Biot’s Breathing a. During regular breathing there is apnea b. Similar to Cheyne-Stokes, c. Cause III. Apneustic Breathing a. Cause b. Persistant Hyperventilation with prolonged inspiratory holds followed by short exhalations IV. Central Neurogenic Hypoventilation a. Respiratory Centers do not respond to ventilatory stimuli appropriately V. Central Neurogenic Hyperventilation a. Persistent hyperventilation because the CNS is responding to abnormal stimuli b. Related c. Associated