2013-09-18 Disorders of Respiratory Control

Question 1

What are the chemorecptors?

Answer 1

peripheral = carotid body

• measures PaO2, PaCO2 and pH

central = dispersed within the brainstem (and hypothalamus)

• measures PCO2, and pH

Question 2

Where in the brainstem is breathing controlled?

Answer 2

breathing involves three clusters of neurons called:

1. the pontine respiratory group (PRG) in the parabrachial and Kolliker-Fuse nuclei of the rostral dorso-lateral pons
2. dorsal respiratory group (DRG) in the NTS,
3. and the ventral respiratory group (VRG) including the nucleus ambiguous and the pre-Bötzinger complex, which is a putative site of rhythm generation)

Question 3

What nerve/muscle combo controls upper airway resistance?

Answer 3

C.N. XII and genioglossus m.

Question 4

carpopedal spasm

Answer 4

a form of tetany in hands caused by hyperventilation

Question 5

What happens to upper airway during expiration?

Answer 5

coordinated constriction of upper airways during expiriation to prevent you from exhaling too quickly which would decrease the efficiency of gas exchange

Question 6

Which affarents provide feedback about size and frequency of breaths?

Answer 6

The size and frequency of breaths is modulated by afferent input from stretch receptors in the lung with vagal afferents and in the chest wall with somatic afferents

Question 7

Alveolar Ventilation equation

What’s the big point?

Answer 7

V_A = V_CO2/Pa_CO2

alveolar ventilation is inversely related to PaCO2

Question 8

define hypoventilation

Answer 8

The PaCO2 is elevated above the normal value of 40 mmHg. VA is reduced.

Question 9

What are causes of central alveolar hypoventilation?

Answer 9

1. Drugs
   
   1. e.g. barbiturates, opiods
2. Neuro problems
   
   1. polio
   2. Ondine’s curse (hypovent at night b/c
   3. Congenital Central Hypoventilation Syndrome (CCHS) kids dx in early life w/ virtually no CO2 sensitivity, severe hypovent in sleep, and abnormal vent responses to hypoxia and exercise. require ventilatory support during sleep. [Case example from DHMC]

Question 10

Consequences of nocturnal hypoxia

Answer 10

increases pulmonary vasoconstriction —> RHF

Question 11

Obestity-hypoventilation syndrome

Answer 11

the Pickwickian syndrome (Figure 8 shows The Fat Boy of the Pickwick Papers) consists of obesity, hypoventilation, somnolence, cyanosis, polycythemia, and pulmonary hypertension leading to cor pulmonale.

Some, but not all, obese patients hypoventilate. The 2° hypoxemia and hypercapnia result in pulm vasoconstriction, an incr in right heart afterload, and in right sided heart failure, i.e., cor pulmonale. Hypoxemia —> stimulate erythropoietin —> cause polycythemia.

Question 12

Why do patients with obstructive dz present w/ hypoxemia?

Answer 12

hypoxemia results largely from abnormalities of V

Question 13

Why do patients with obstructive dz present w/ CO2 retentoin (hypercapnia)?

Answer 13

not quite clear. Possible factors include:

a. Genetically determined low CO2 sensitivity
b. Abnormal ventilatory muscle response to increased resistance c. Respiratory muscle weakness or fatigue d. Decreased ventilatory response to CO2 e. Decreased ventilatory sensitivity to hypoxia

Question 14

oxygen apnea

Answer 14

In many patients with CO2 retention and hypoxemia due to
chronic lung disease, a large part of the total respiratory drive is due to the carotid body. Use of increased FIO2 can remove this stimulus and result in severe CO2
retention or, in some cases, apnea.

Question 15

Expected blood gases during asthma attack? Why?

Answer 15

Asthmatics in acute attack are hypoxemic, but until the obstruction is very, very severe, they have decreased PaCO2 values (Table 1)

Question 16

DDx for hyperventilation

Answer 16

A. Psychogenic or hysterical hyperventilation: associated with symptoms due predominantly to respiratory alkalosis, including carpopedal spasm and tetany

B. Pontine infarcts: loss of a source of inhibitory input to brainstem

C. Pregnancy: related to elevated progesterone levels

D. Hepatic encephalopathy: cause unknown, but most likely metabolic

E. Drugs

F. Asthma (See above.)

Question 17

Types of periodic breathing?

Answer 17

post-hyperventilation apnea

Chyne-Stokes respiration

Question 18

post-hyperventilation apnea

Answer 18

In situations when CNS is depressed, e.g., drugs, coma, or anesthesia, patients will become apneic if their normal PCO2 is decreased by
hyperventilation

Question 19

Chyne-Stokes Breathing

Answer 19

repetitive pattern of breathing usu. seen in sleep in which respirations gradually increase, then decrease, followed by apnea. Seen in patients with bilateral cerebral dysfunction (incr ICP per First Aid), congestive heart failure, and/or hypoxia.