Hypoxic respiratory drive

Respiratory Drive

1. Hypoxic Respiratory Drive O2, CO2 and H+ ??!!

2. John Scott Haldane discovered that the respiratory reflex is triggered by an excess of CO2 in the blood, rather than a lack of O2. He described in details of regulation of respiratory drive by CO2 and its effects on blood H+. And the Effect of ‘loading of oxygen in the lung facilitating unloading of carbon dioxide’ is named after him and popularly known as Haldane effect. Father of Oxygen Therapy Background

3. OVERVIEW RESPIRATORY CONTROL C ontrol of breathing is broadly divided into three categories : Neural control (voluntary and automatic control) Chemical control (PO2, PCO2 and pH) Nonchemical (reflexes from lungs and chest wall) control

4. RESPIRATORY CENTER C omposed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem, as shown in Figure 42-1 . (1) A dorsal respiratory group , located in the dorsal portion of the medulla (INSPIRATION) (2) a ventral respiratory group , located in the ventrolateral part of the medulla (EXPIRATION); and (3) the pneumotaxic center , located dorsally in the superior portion of the pons, which mainly controls rate and depth of breathing

5. The ultimate goal of respiration is to maintain proper concentrations of O2, CO2, and H+ in the tissues. Excess CO2 or excess H+ in the blood mainly act directly on the respiratory center → greatly ↑ strength of both the inspiratory and the expiratory motor signals to the respiratory muscles. Oxygen , does NOT have a major direct effect on the respiratory center of the brain in controlling respiration. Instead, it acts almost entirely on peripheral chemoreceptors located in the carotid and aortic bodies , → respiratory center for control of respiration. CHEMICAL CONTROL OF RESPIRATION

6. Chemosensitive Area of the Respiratory Center Beneath the Medulla’s Ventral Surface. A n additional neuronal area, a chemosensitive area. L ocated bilaterally, lying only 0.2 millimeter beneath the ventral surface of the medulla. This area is highly sensitive to changes in either blood Pco2 or H+ concentration → excites the other portions of the respiratory center. DIRECT CONTROL OF RESPIRATORY CENTER ACTIVITY BY CO2 AND H+

7. Excitation of the Chemosensitive Neurons by H + Is Likely the Primary Stimulus. C hemosensitive area are especially excited by H+; may be the only important direct stimulus for these neurons. However, H+ ions do not easily cross the blood–brain barrier. C hanges in H+ concentration in the blood have considerably less effect in stimulating the chemosensitive neurons than changes in blood CO2, even though CO2 is believed to stimulate these neurons secondarily

8. CO2 Indirectly Stimulates the Chemosensitive Neurons. Although CO2 has little direct effect in stimulating the neurons in the chemosensitive area, it does have a potent indirect effect. CO2 + water of the tissues → carbonic acid, which dissociates into H+ and HCO3−; the H+ then have a potent direct stimulatory effect on respiration.

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