呼吸科呼吸系统4课件

5.4 Control of Respiration lBreathing is a critical robust homeostatic process that ensures adequate levels of oxygen in blood and provides a means to remove carbon dioxide from the body *1 Basic Requirements for Respiratory Regulation *2 lIt must be automatic lMaintenance of CO2 and O2 levels should not depend on levels of consciousness or alertness lIt must be adaptable to the needs of the organism lThere must be mechanisms to compensate for changes in oxygen uptake or CO2 production. lIt must be subject to voluntary control lThere must be mechanisms to voluntarily override the respiratory control mechanisms at least for brief periods of time Respiratory Centers and the Basic Respiratory Center lRespiratory center lBrain regions or the spinal cord that involve in the generation of rhythmic respiratory pattern and the regulation of respiratory movement; they are located in the spinal cord, brainstem, cortex, thalamus etc. lBasic respiratory center lBrain parts that are responsible for generation of basic respiration patterns lIt is located in the brainstem The Experiment Done by Lumsden in the Cat Conclusions Upper pons-pneumotaxic center; lower pons-apneustic center (not accepted); Spinal cord-Basic respiratory center; spinal cord: Cut atBreathing pattern (vagus nerve intact) Breathing pattern (vagus nerve cut off) Midbrain and the pons Nearly normalDeep and slow Mid ponsNearly normal Apneustic breathing Pons and medulla IrregularCheyne-Stokes breathing Medulla and the spinal cord No breathingNo breathing * 5 Respiratory-Related Neurons in the Basic Respiratory Center lDorsal respiratory group (DRG) lLocated in the dorsal region of the nucleus tractus solitarii lMainly contain inspiratory neurons lGenerate basic rhythm lVentral respiratory group (VRG) lA column of cells in the general region of the nucleus ambiguus. lIt houses both inspiratory and expiratory neurons lMost neurons are silent during normal quiet respiration Pneumotatic center It acts to limit inspiration. As a result, it increases the rate of breathing Is the Pre-Btzinger Complex Essential for the Generation of Basic Respiratory Pattern? Modified from Brain 2011:134; 2435 Medulla oblongata = 延髓 Pons = 脑桥 Lateral reticular nucleus (LRN) = 外侧网状 核 XII = 面神经 Obex = 栓、门 MSA = multiple system atrophy SCA3 = spinocerebellar ataxia type 3 Multiple Systems Atrophy vs. Spinocerebellar Ataxia 3 Patients with multiple systems atrophy present with central respiratory deficits but without swallowing problems Pre-Btzinger Complex neurons are reduced whereas ambigual motoneurons are preserved. Patients with spinocerebellar ataxia 3 has no central respiratory deficits but with dysphagia, Pre-Btzinger Complex neurons are preserved, whereas ambigual motoneurons are diminished. Neural Mechanisms underlying the Generation of Rhythmic Respiration Two Hypotheses Oscillatory theory or the pacemaker hypothesis (起步细胞学说) Network theory (神经网络学说) Oscillatory Theory Pacemaker neurons generate the respiratory rhythm (Smith et al., Science, 1991). Neurons in pre-Btzinger can Burst spontaneously Regular firing induced by current injection in a hippocampal granule cell Spontaneous bursting In a rat pre-Btzinger neuron Neurons in pre-Btzinger can Burst spontaneously Regular firing induced by current injection in a hippocampal granule cell Spontaneous bursting In a rat pre-Btzinger neuron * 12 Basic respiratory center (Medulla and pons) Voluntary control (Cerebrum ) Spinal motor neurons IntercostalsDiaphragm the remaining 80% from central chemoreceptors (slow). Mechanisms Underlying Hyperventilation following PaCO2 Increase Direct stimulation lStimulation of peripheral chemoreceptprs lStimulation of central chemoreceptors Indirect stimulation CO2 Arterial H+ Peripheral chemoreceptors The Effects of Lower PaO2 on Respiration lNo effect of ventilation when PaO2 is above 100 mm Hg lVentilation is up once PaO2 is below 70 mmHg and is doubled when PaO2 falls to 60 mmHg lHyperventilation following decrease in PaO2 is solely made by stimulating peripheral chemoreceptors lSevere hypoxia suppresses respiration through acting on respiratory centers of brain stem *23 The Effects of Hydrogen Ions on Respiration lAn increase in H+ concentration in arterial blood, CSF or the local tissue of brain stem stimulates respiration. lIncreased H+ stimulates both peripheral and central chemoreceptors with stimulation of the peripheral chemoreceptor playing the main role. lAs H+ cannot pass through the brain-blood barrier, increased H+ in arterial blood stimulates central chemoreceptors through CO2. lAt both peripheral and central chemoreceptors, H+ mediates increased respiration by CO2 accumulation. lCentral chemoreceptors are more sensitive to H+ than peripheral chemoreceptors. *24 How Does Increased Arterial H+ Act on the Central Chemoreceptors Significances of Hydrogen Ions on Respiration lCoordinates metabolic needs and respiration. lMaintains pH homeostasis. *26 Ondines Curse * The Oath by Ondines husband: My every waking breath shall be my pledge of love and faithfulness to you. The Curse made by Ondine (on-deen): You swore faithfulness to me with every waking breath, and I accepted your oath. So be it. As long as you are awake, you shall have your breath, but should you ever fall asleep, then that breath will be taken from you and you will die! The end: Ondines husband died. Central Alveolar Hypoventilation (Ondines Curse) lCentral alveolar hypoventilation is a rare disease in individuals who are born without ventilatory chemosensitivity lBreathing adequate when awake, but not when asleep or during sleeping lNo response to hypercapnia and hypoxia EXERCISE AND VENTILATION Exercise Is Associated with Hyperventilation Rest Maximal Exercise Intensity 6 100 Acute Respiratory Response to Graded Dynamic Exercise Exercise Intensit y Ventilati on (L/min) V/QPAO2 (mm Hg) PaO2 (mm Hg) PaCO2 (mm Hg) Arterial pH Rest51103100407.40 Walking202103100407.40 Jogging453106100367.40 Running754110100257.32 Conclusion Hyperventilation during exercise is primarily caused by mechanisms beyond chemical changes in the blood The cortex sends signals to the basic respiratory center? Is there interaction between the cardiovascular and basic respiratory centers ? MECHANICAL REFLEXES Several mechanical reflexes that arise from the chest wall and lungs affect ventilation and ventilatory patterns. Receptors Are Localized in Lung Tissue and Airways lPulmonary receptors can be divided into 3 groups: pulmonary stretch, irritant and J receptors. l Afferent fibers of all three types lie predominantly in the vagal nerves. Pulmonary Stretch Receptors lThe stretch receptors are sensory terminals of myelinated afferent fibers that lie within the smooth muscle layer of conducting airways. l The stretch receptors sense changes in lung volume. lThe stretch receptors mediate lung inflation refelx (Hering-Breuer reflex). Lung Stretch Reflexes lPulmonary inflation reflex (Hering-Breuer inspiratory- inhibitory reflex) lInflation of lungs or stretch of airways switches from inspiration to expiration. As a result, inspiration is shortened with increased breathing rate. lPulmonary deflation reflex: Deflation of lungs promotes inspiration is called pulmonary deflation reflex. lBoth are mediated by the vagal fibers; cutting of vagal nerve either unilaterally or bilaterally could deepen and prolong inspiration. More about the Hering-Breuer Inspiratory-Inhibitory Reflex lThe Hering-Breuer inspiratory-