Chapter 318 - Disorders of Ventilation

Question 1

What is the normal interval for arterial level of carbon dioxide (PaCO2) at the sea level?

Answer 1

37-43mmHg

Question 2

Describe the equation that represents the relantionship between CO2 production and PaCO2.

Answer 2

PaCO2=(k)(VCO2)/VA, whereas VCO2 represents CO2 production, k is a constant and VA represents fresh gas alveolar ventilattion.

Question 3

How can one calculate VA (fresh gas alveolar ventilation)?

Answer 3

VA = minute ventilation x (1 -Vd/Vt), wheares Vd/Vt represents the dead space fraction.

Question 4

What variables might explain PaCO2 disturbances?

Answer 4

“all disturbances of PaCO2 must reflect altered CO2 production, minute ventilation, or dead space fraction.”

Question 5

Define dead space fraction regarding pulmonary ventilation.

Answer 5

“dead space fraction Vd/Vt represents the portion of tidal breath that remains within the conducting airways at the conclusion of inspiration and so does not contribute to alveolar ventilation.”

Question 6

Name a lesion in a group of neurons located in the brainstem from which results complete cessation of breathing.

Answer 6

Pre-Bötzinger complex, which is responsible for the generation of avarious forms of inspiratory activity.

Question 7

Name the afferent and efferent connections related to the Dorsal Respiratory Group (DRG).

Answer 7

The DRG receives information from afferent nerves about PaO2, PaCO2, pH and blood pressure from the carotid and aortic chemoreceptors and baroreceptors. It also receives information from the vagus nerve regarding stretch receptors and juxtapulmonary-capillary receptors in the lung parenchyma and chest wall. The DRG functions as the initial site for integration and, with Ventral Respiratory Column (VRC), they send projections into the contralateral spinal cord to control the phrenic nerve, the upper airway muscle groups and spinal respiratory neurons, and innervate the intercostal and abdominal muscles that participate in normal respiration.

Question 8

What is the main function of Ventral Respiratory Column (VRC)?

Answer 8

VRC is responsible for the respiratory rythm (also dependendent on pFRG, paraFacial Respiratory Group) and it also includes the Pre-Bötzinger complex.

Question 9

Name the four categories that include the diseases that reduce minute ventilation or increase dead space.

Answer 9

“parenchymal lung and chest wall disease, sleep-disordered breathing, neuromuscular disease, and respiratory drive disorders.”

Question 10

Sleep disturbances regarding disorders of ventilation only occurs in the category of sleep-disordered breathing.
True or False?

Answer 10

False.
“Sleep disturbance and orhopnea are also described in neuromuscular disorders.”
Drive respiratory diseases also have sleep disturbances.

Question 11

How do you explain orthopnea in neuromuscular diseases?

Answer 11

“As neuromuscular weakness progresses, the respiratory muscles, including the diaphragm, are placed at a mechanical disadvantge in the supine position due to the upward movement of the abdominal contents.”

Question 12

What are the first symptoms/sign of neuromuscular disease?

Answer 12

“More commonly, however, extremity weakness or bulbar symptoms develop prior to sleep disturbance in neuromuscular diseases”

Question 13

What is the most common sleep disturbance leading to chronic hypoventilation?

Answer 13

Obesity hypoventilation syndrome.

Question 14

Name the only screening tool validated for Obstructive Sleep Apnea for outpatient primary care setting.

Answer 14

Berlin Questionnaire.

Epworth Sleepiness Scale and STOP-Bang have not been validated in this setting

Question 15

What is the sensitivity and negative predictive value for STOP-Bang Survery in the preoperative clinic?

Answer 15

93% and 90%, respectively

Question 16

In drive respiratory diseases there is as increased response to hypoxemia and hypercapnia.
True or False?

Answer 16

False.
“There is an attenuated increase in minute ventilation in response to elevated CO2 and/or low O2 in respiratory drive disorders.”

Question 17

Drive respiratory diseases are diagnosed by CT or MRI.

True or False?

Answer 17

False.
“Brain imaging (…) can sometimes identify structural abnormalities in the pons or medulla that result in hypoventilation. Chronic narcotic use or significant hypothyroidism can depress the central respiratory drive and lead to chronic hypercapnia as well.”

Question 18

In neuromuscular diseases, hypercapnia usually precedes muscle weakness.
True or False?

Answer 18

False.

Question 19

Name the ALS guidelines criteria for the use of Nocturnal noninvasive positive-pressure ventilation (NIPPV).

Answer 19

“ALS guidelines recommend consideration of nocturnal NIPPV if symptoms of hypoventilation existe and one of the following criteria is present: PaCO2 ≥45mmHg; nocturnal oximetry demonstrates oxygen saturation ≤88% for 5 consecutive min; maximal inspiratory pressure [less than] 60mmH2O; FVC [less than] 50% predicted; or snif nasal pressure [less than] 40cmH2O.”

Question 20

Explain the pH disturbances in chronic hypoventilation.

Answer 20

The retention of CO2 is responsible for respiratory acidosis, which is compensated proportionately with retention of HCO3-, leading to metabolic acidosis.

Question 21

Is there any surgical option in patients with hypoventilation due to high cervical spinal cord lesions or respiratory drive disorders?

Answer 21

“Phrenic nerve or diaphragm pacing is a potential therapy.”

“small case series suggest that effective diaphragmatic pacing can improve quality of life in these patients.”

Question 22

What is the definition of Obesity Hypoventilation Syndrome (OHS)?

Answer 22

“The diagnosis of OHS requires body mass index (BMI)≥30Kg/m2 and chronic daytime alveolar hypoventilation, defined as PaCO2≥45mmHg at sea level in the absence of other known causes of hypercapnia.”

Question 23

How do you define Obstrutive Sleep Apnea Syndrome (OSAS)? How frequent is it?

Answer 23

OSAS is the most frequent form of Obesity Hypoventilation Syndrome, although it might occur without obesity. It is define by an apnea-hypopnea index ≥5 per and daytime sleepiness (or AHI ≥15 without symptoms). It occurs in 3-4% of middle-aged men and 2% of middle-aged women.

Question 24

What are the main physiopathological mechanisms that might explain hypoventilation in patients with Obesity Hypoventilation Syndrome (OHS)?

Answer 24

“The pathogenesis of hypoventilation in these patients is the result of multiple physiologic variables and conditions including Obstrutive Sleep Apnea, increased work of breathing, respiratory muscle impairment, ventilation-perfusion mismatching, and depressed central ventilatory responsiveness to hypoxemia and hypercapnia.”

Question 25

Continuous Positive Airway Pressure (CPAP) improves daytime hypercapnia and hypoxemia in more than half of the patients with Obesity Hypopnea Syndrome with concomitant Obstrutive Sleep Apnea Syndrome.
True or False?

Answer 25

True.

Question 26

When would you start BiPAP on a patient with a hypoventilation syndrome?

Answer 26

“Bilevel positive airway pressure (BiPAP) should be reserved for patients not able to tolerate high levels of CPAP support or patients who remain hypoxemic despite resolution of obstructive respiratory events. NIPPV with BiPAP should be strongly considered if hypercapnia persists after several weeks of CPAP (Continuous positive airway pressure) therapy with objectively proven adherence. Patients with OHS (Obesity Hypoventilation Syndrome) and no evidence of OSA (Obstructive Sleep Apnea) are tipically started on BiPAP, as are patients presenting with acute decompensated OHS.”

Question 27

What gene might be implicated in Ondine’s curse (congenital central hypoventilation syndrome)?

Answer 27

PHOX2b.

Question 28

What laboratory measures do you expect to find in a patient with central hypoventilation syndrome?

Answer 28

“Regardless of the age of onset, these patients have absent respiratory response to hypoxia or hypercapnia, mildly elevated PACO2 while awake, and markedly elevated PaCO2 during non-REM sleep. Interestingly, these patients are able to augment their ventilation and “normalize” PaCO2 during exercise and during REM sleep.”

Question 29

How does one define hyperventilation?

Answer 29

“Hyperventilation is defined as ventilation in excess of metabolic requirements (CO2 production) leading to a reduction in PaCO2.”

Question 30

What symptoms might occur in hyperventilation?

Answer 30

“there is no typical clinical presentation. Symptoms can include dyspnea, paresthesias, tetany, headache, dizziness, visual disturbances, and atypical chest pain.”

Question 31

Anxiety disorders and panic attacks are synonymous with hyperventilation.
True or False?

Answer 31

False.
“Anxiety disorders can be both an initiating and sustaining factor in the pathogenesis of chronic hyperventilation, but these are not necessary for the development of chronic hypocapnia.”

Question 32

How much is the increase in chronic hyperventilation to perpetuate hypocapnia?

Answer 32

“a sustained 10% increase in alveolar ventilation is enough to perpetuate hypocapnia. This increase can be accomplished with subtle changes in the respiratiry pattern, such as occasional sigh breaths or yawning two to three times per minute.”