Respiratory Control & Pathophysiology Flashcards
Where are the primary respiratory centers (dorsal and ventral respiratory groups) located? Where are the secondary respiratory centers (apneustic and pneumotaxic centers) located?
The primary respiratory centers (dorsal and ventral respiratory groups) are located in the medulla of the brainstem. Secondary respiratory centers (apneustic and pneumotaxic centers) are located in the pons of the brainstem.
Identify the anatomic site where opioids produce respiratory depression.
All opioids cause dose-dependent depression of respiration through direct mu2-receptor stimulation at the brainstem respiratory centers located superficially in the floor of the 4th ventricle (i.e., medulla and pons).
What is the single most important factor responsible for directly stimulating central chemoreceptors?
Hydrogen ions (H+) in the cerebrospinal fluid directly stimulate central chemoreceptors.
How are hydrogen ions (H+) generated in CSF?
CO2 that diffuses into the CSF is converted by carbonic anhydrase first to carbonic acid (H2CO3) and then to H+ and bicarbonate ions (HCO3-).
To what 3 physiologic parameters do peripheral (carotid and aortic) chemoreceptors respond? Which stimulates the peripheral chemoreceptors most?
Peripheral chemoreceptors (carotid body and aortic body) respond to PaO2, PaCO2, and pH. Peripheral chemoreceptors are most sensitive to PaO2, but not until Pa02 < 50 mmHg.
In addition to PaO2, PaCO2, and pH what 3 exogenous (i.e., drugs, toxins) substances also stimulate peripheral chemoreceptors?
Peripheral chemoreceptors are also stimulated by cyanide, doxapram, and nicotine.
How much of the ventilatory response to an increase in PaCO2 is mediated by the central chemoreceptors? Peripheral chemoreceptors?
The ventilatory response to an increased PaCO2 is mediated primarily by central chemoreceptors. The effect of CO2 on central chemoreceptors is seven times more powerful than it is on peripheral chemoreceptors. Point: central chemoreceptors are normally more important than peripheral chemoreceptors in controlling ventilation.
What normally drives ventilation?
C02 normally drives ventilation. CO2 is the physiological respiratory stimulant. The single most important regulator of alveolar ventilation is PaCO2.
What are pathological respiratory stimulants?
Pathological stimulants are low PaO2 or acids (hydrogen ions).
Which of the following two changes will increase ventilation the most: an increase in PaCO2 or a decrease in arterial blood pH (increase in H+)?
An increase in PaCO2 produces a far greater increase in
ventilation than does a decrease in arterial blood pH. An increase in PaCO2 from 40 to 60 or from 40 to 90 mm Hg
produces a six-fold or 10-fold increase in ventilation, respectively. In contrast, a decrease in blood pH from 7.4 to
7.0 produces a four-fold increase in ventilation.
What are four causes of hypocapnia? What is the most
common cause of hypocapnia?
Four causes of hypocapnia are:
(1) voluntary hyperventilation
(2) iatrogenic hyperventilation (mechanical ventilation)
(3) decreased C02 production (hypothermia, deep anesthesia, hypotension)
(4) decreased dead space ventilation (change from mask airway to endotracheal tube airway, decreased PEEP, decreased rebreathing)
* *By far the most common cause of hypocapnia is hyperventilation by mechanical means.
What happens if a gas mixture with 3-7% CO2 were inhaled?
The partial pressure of the inspired CO2 is 23-53 mmHg if one breathes 3-7% C02 (0.3% x 760 = 0.03 x 760 = 22.80 = 23 mmHg; 7% x 760 = 0.07 x 760 = 53.20 = 53 mmHg). Thus, hypercapnia (increased PaCO2) will occur. Ventilation will increase dramatically in an attempt to compensate.
What triggers the Hering-Breuer reflex? What happens when the Hering-Breuer reflex is triggered? What role does the Hering-Breuer reflex play in normal ventilation of the adult?
Lung inflation triggers the Hering-Breuer reflex. When the Hering-Breuer reflex is triggered by lung inflation, inspiration is inhibited. The Hering-Breuer reflex plays a minor role in normal ventilation in the adult. It is mainly a protective mechanism that is probably not activated until the tidal volume increases to greater than 1.5 liters.
Pulmonary stretch receptors within the smooth muscle of small airways involved in the Hering-Breuer reflex trigger sensory (afferent) impulses that travel along which nerve?
The vagus nerve carries sensory (afferent) impulses of the Hering-Breuer reflex.
**What are pulmonary J-receptors?
Juxtapulmonary-capillary receptors (J receptors) are located in the walls of the pulmonary capillaries or in the interstitium, hence the name. J receptors appear to be stimulated by pulmonary vascular congestion or an increase in pulmonary vascular congestion or an increase in pulmonary interstitial fluid volume, leading to tachypnea. The J receptors may also be responsible for the dyspnea encountered during pulmonary vascular congestion and edema secondary to left ventricular failure.
