Week 4 Objectives/ Lecture

Question 1

51. What is the difference between a physiologic shunt and an anatomic shunt?

Answer 1

physiologic shunt includes the sum anatomical and intrapulmonary shunts (areas that are either not ventilated or not perfused); an anatomic shunt is an area where there is no ventilation

Question 2

51. What is the shunt fraction and how can it be calculated?

Answer 2

shunt fraction is the comparison of shunted flow over the total flow which is calculated by comparing the ventilation rate and the composition of CO2 (alveoli that are ventilated and perfused will give of CO2)

Question 3

How is pulmonary shunt measured in a clinical setting?

Answer 3

it is estimated by the A-a gradient at high FlO2; if the PaO2 &laquo_space;PAO2 at high FlO2 suggests large shunt– if there is a high concentration of oxygen in air into lungs but a low oxygen concentration in arterial blood, there is a large shunt

Question 4

What is FlO2?

Answer 4

fraction of oxygen in inspired air

Question 5

52. The final common pathway for rhythmic activation of the respiratory muscles is located where?

Answer 5

in the medulla below the cerebellar peduncle and above C1

Question 6

53. What afferent input information does this system use to control the rate and depth of breathing?

Answer 6

Reflexes from lungs (stretch receptors on vagal afferents), airways, CV system, muscles and joints as well as reflexes from arterial chemoreceptors and central chemoreceptors

Question 7

Where is the pneumotaxic and modulating integration of breathing located in the brainstem?

Answer 7

pneumotaxic center (regular breathing) in pons, integration center in the medulla

Question 8

Name the two respiratory centers in the medulla and their function

Answer 8

dorsal respiratory group is responsible for basic respiratory rhythm (nucleus tracts solitaries), ventral respiratory group is responsible for modulating basic respiratory rhythm (nucleus retroambiguous)

Question 9

54. Name some examples of activities that can override the respiratory controller to affect breathing.

Answer 9

during exercise or even speech, respiratory control can be overridden

Question 10

55. What nerves conduct efferent signals to the respiratory muscles of the diagphragm

Answer 10

phrenic nerve which is acted upon by the nucleus of the tracts solitarius

Question 11

What do peripheral chemoreceptors sense?

Answer 11

O2 and H+ concentrations in arterial blood; aortic bodies are less important in the manipulation of breathing BONUS: carotid bodies sensing O2 is not affected by anemia or CO because it measured dissolved O2 and requires a large amount of blood to do this

Question 12

57. Transection of the brainstem at what level causes breathing to cease?

Answer 12

transection of the medulla causes breathing to cease completely

Question 13

56. Voluntary suppression of breathing ends at the so-called break point. What stimuli are responsible for this

Answer 13

rising CO2 partial pressure is detected by arterial baroreceptors

Question 14

58 What nerves conduct afferent lung stretch receptor info to the respiratory control center?

Answer 14

large myelinated fibers in the vagus nerve, which enter the brainstem and project to DRG, the apneustic center and the pontine respiratory groups

Question 15

59. What physiological purpose are served by occasional, involuntary sighs?

Answer 15

help to prevent atelectasis

Question 16

60. What is the diving reflex and what is its function?

Answer 16

produced by the immersion of face in liquid which is sensed by receptors in the nose and face and carried via the trigeminal nerve causing respiratory apnea along with decreased heart rate and vasoconstriction

Question 17

Hypoxia does not stimulate breathing until PaO2 falls to what partial pressure

Answer 17

PaO2 falls below 60 mmHg (normal 100 mmHg) found on the “shoulder” of the oxyhemoglobin dissociation curve (note changes in breathing are only a short-term adjustment)

Question 18

What is meant by the fact that hypoxia potentates ventilatory response to CO2?

Answer 18

a hypoxic patient is more sensitive to changes in CO2, ventilatory response to CO2 is also potentiated by pH

Question 19

61. What its the single most important input to the ventilatory control system in establishing breath to breath levels of tidal volume and ventilatory frequency?

Answer 19

arterial and cerebrospinal fluid partial pressures of carbon dioxide are the most important inputs to the ventilator control system

Question 20

63. How do narcotics affect the ventilatory response to CO2 and what is the most common cause of death in opiate/barbituarate overdose?

Answer 20

narcotics and anesthetics may profoundly depress the ventilatory response to carbon dioxide, ventilatory depression is the most common cause of death in opiate/barbiturate overdose (sleep depresses the response to a much lesser degree)

Question 21

64. What is sensed by the central chemoreceptor that allows it to control the arterial PCO2 via changes in ventilation?

Answer 21

The Pco2, pH and PO2 are the principle controlled variables in the respiratory control system

Question 22

65. Why does an acidemia stimulate the peripheral chemorecptors, and not the central chemoreceptors?

Answer 22

Central chemoreceptors are exposed to cerebral spinal fluid (ventral lateral medulla), central receptors are on the brain-side of the blood-brain barrier, carbon dioxide diffuses across the blood brain barrier where as H+ and bicarbonate do not. Changes in arterial pH that are not caused by changes in PCO2 take much longer to influence the cerebrospinal fluid

Question 23

66. Which chemoreceptors are responsible for the ventilatory response to hypoxia?

Answer 23

Ventilatory response to hypoxia arises solely from the peripheral chemoreceptors, with the carotid bodies much more important than aortic bodies. When peripheral chemoreceptors are intact their excitatory influence on central respiratory controller must offset the direct depressant effect of hypoxia

Question 24

Which has a greater affect on the central chemoreceptors in the brain: H+ in the blood or CO2 in the blood?

Answer 24

only CO2 can cross the blood brain barrier, and therefore affects the central chemo receptors to a greater degree (BONUS H+ will have a direct affect on the carotid bodies)

Question 25

What affect does pCO2 have on the respiratory center's response to low pO2?

Answer 25

pCO2 potentiates a response to low O2 which requires integration between peripheral and central chemoreceptors (ventilation will respond more quickly to low O2 if there is also high pCO2)

Question 26

1. Kidneys control extracellular pH by controlling extracellular ______ concentration while lungs control pH by control the _______.

Answer 26

HCO-3 concentration v. PaCO2

Question 27

What is the normal concentration of extracellular HCO3- in arterial blood?

Answer 27

normal is 24 mEq/L in arterial blood

Question 28

2. What is the ratio of the HCO3- and CO2 concentrations in extracellular fluid?

Answer 28

HCO3- and CO2 concentrations must be 20/1 for the pH to be normal

Question 29

3. Describe a normal blood buffer line.

Answer 29

normal blood buffer line shows how blood pH and bicarbonate concentrations would change if PaCO2 was increased or decreased.

Question 30

Why is the blood buffer line steeper than bicarbonate lines?

Answer 30

blood is more strongly buffered than a HCO3- solution due to the buffering ability of hemoglobin in blood

Question 31

4. What can cause a metabolic acidosis? How does the body respond?

Answer 31

by addition of endogenous (ketoacidosis or circulatory failure that lead to a build up of lactic acid ie.) or exogenous acids (aspirin ie.); the fall in arterial pH stimulates the peripheral chemoreceptors directly causing ventilation to rise and lowing PaCO2

Question 32

5. What can cause a metabolic alkalosis? How does the body naturally respond to this?

Answer 32

any excess HCO3- added to the extracellular fluid will lead to metabolic alkalosis including excessive consumption of bicarbonate containing antacids; the rise in arterial pH inhibits breathing via peripheral chemoreceptors which cause the PaCO2 to rise

Question 33

6. What can cause a respiratory acidosis? How does the body naturally respond to this?

Answer 33

respiratory acidosis is caused by lung disease that prevents the body from adequately ridding itself of CO2 (ie. emphysema); the body responds by the kidneys making additional bicarbonate and raise the bicarbonate concentration

Question 34

7. What can cause a respiratory alkalosis? How does the body naturally respond to this?

Answer 34

respiratory alkalosis is associated with a change in environment, not with lung disease, a trip to high altitude can increase respiration and cause a corresponding drop in PaCO2; the body responds by having the kidneys excrete additional HCO3- into the urine (change is not immediate, 1-2 days)

Question 35

Hypercapnia and hypocapnia deal with what kind of acid-base disturbance?

Answer 35

respiratory acidemia v. respiratory alkalosis

Question 36

Base excess and deficit relate to what kind of acid base disturbance?

Answer 36

metabolic alkalosis and metabolic acidemia

Question 37

9. Explain the difference between an anion gap and a non-anion gap metabolic acidosis.

Answer 37

in a anion gap metabolic acidosis, anions displace Cl- into cells and widen the anion gap whereas if you loose H+ of HCO3- through vomitting or diarrhea the anion gap remains unchanged but you still produce a acid-base disturbance

Question 38

Describe a situation of hypoxemia in which the alveolar- arterial oxygen pressure difference (gradient) is unchanged.

Answer 38

when a patient goes to altitudes, the partial pressure in their alveoli due to atmospheric pressure and the partial pressure in their arterioles are decreasing to the same degree

Question 39

Describe a situation where hypoxemia is not improved by administration of supplemental oxygen.

Answer 39

if a patient has any type of R-L or L-R shunt their lungs are not being perfused adequately and increasing the oxygen to these alveoli will not change the hypoxia status

Question 40

Describe cases of hypoxia that are improved with supplemental oxygen that are brought on by acute v. chronic illnesses.

Answer 40

acute: edema/ARDS or pneumonia chronic: fibrosis due to mesothelioma

Question 41

How does emphysema affect the Va/Q ratio

Answer 41

causes a high Va/Q

Question 42

What distinguishes a diffusion abnormality v. a Va/Q mismatch

Answer 42

with a diffusion abnormality you can still have proper ventilation without corresponding diffusion

Question 43

How does altitude effect PvO2 differently than A-a gradient?

Answer 43

amount of O2 extracted from blood will increase so the pO2 in the venous return will be less, but the decrease will be delayed in comparison with the A-a gradient parallel decrease

Question 44

Describe the difference in end pCO2 difference between respiratory and metabolic alkalosis/acidosis.

Answer 44

with metabolic disturbances you can return to a relatively normal pCO2 where in respiratory disturbances you see a return to normal pH with compensation but still a mismatch in pCO2

Question 45

When you sample pCO2 and pO2 where should you sample blood from to assess the acid/base balance

Answer 45

sample arterial blood because that is the blood conditioned from the lung and heading to the body