Respiratory Quiz #5

Question 1

Describe how a weak acid behaves in a solution such as blood.

Answer 1

• Weak acids (HA-carbonic acid), such as H2CO3 reversibly donate H+ • When HA is in solution, it can ACT AS AN ACID by donating an H+ • All body fluids have acid-base buffer systems that instantly combine with any acid or alkali to prevent changes in [H+]

Question 2

Describe how a weak base behaves in solution such as blood.

Answer 2

• Its conjugate base, (A-), can ACT AS A BASE by rapidly and reversibly taking up H+ • Weak bases (A-), such as HCO3 - REVERSIBLY BIND H+ • All body fluids have acid-base buffer systems that instantly combine with any acid or alkali to prevent changes in [H+]

Question 3

Compare the three mechanisms responsible for H+ regulation.

Answer 3

• Buffer systems (rapid but incomplete) • Ventilatory responses (less rapid) • Renal responses (slow, but produces almost nearly complete correction of pH)

Question 4

Identify four buffering systems the body incorporates in regulating acid-base balance

Answer 4

HHb H+ + Hb- Hprot H+ + Prot- H2PO4- H+ + HPO42 H2CO3 H+ + HCO3 -

Question 5

Describe the effect of oxygen saturation on hemoglobin’s buffering capacity.

Answer 5

Hemoglobin Buffering Systems • Effective because of its high concentration • Buffering capacity varies with oxygenation (reduced hemoglobin is a weaker acid) • In its reduced form (carrying less oxygen), more base is available to combine with H+ produced by the dissociation of carbonic acid in the tissues

Question 6

Discuss rationale for why the bicarbonate system is the most important buffering system in the body

Answer 6

Bicarbonate Buffering System • HCO3 - accounts for > 50% of total buffering capacity of the blood (extracellular) • HCO3 - DIFFUSES EASILY INTO RBC’S SO THAT 1/3 OF ALL BICARBONATE BUFFERING OCCURS HERE • pKa is 6.1 (blood pH 7.4), so that it is a weak buffer (20:1 ratio HCO3 - to CO2 )

Question 7

Describe the role of ventilation in regulating H+ concentration

Answer 7

Role of Ventilation in Bicarbonate Buffering System • The main importance of this buffering system is that its element can be regulated by both the kidneys and the lungs • The CO2 produced by the reaction of H+ and HCO3- is easily removed by the body • Ability to maintain pH 7.4 depends on the free movement of CO2 out of the body (need ventilation and renal function) • H2O + CO2 H2CO3 H+ + HCO3 • Ventilatory responses occur within 1-5 minutes of a change in hydrogen ion concentration • Doubling alveolar ventilation eliminates sufficient CO2 to increase pH to 7.6 • Decreasing alveolar ventilation to one-fourth of normal decreases pH to 7.0 -

Question 8

Describe renal regulation of H+ concentration

Answer 8

Renal Responses • Renal responses that regulate [H+] do so by acidification or alkalinization of urine • Incomplete titration of H+ and HCO3-occurs, allowing either to enter urine and be excreted • IN THE PRESENCE OF ACIDOSIS H+ IS EXCRETED AND HCO3- IS EXCRETED IN ALKALOSIS

Question 9

Describe how pH may be calculated by the Henderson-Hasselbach equation using bicarbonate and CO2 concentrations in the blood

Answer 9

Acid-Base Status of the Blood • In the blood, the three components of the Henderson-Hasselbach equation are pH, HCO3, and CO2 (0.03 mmol H2CO3 for each mmHg PCO2) • pH results from [HCO3] and CO2 in blood: • pH=pKA + log (HCO3)/0.03 (PaCO2) • pH=6.1 + log (24)/0.03 (40) • pH=6.1 + log 20 • pH=6.1 + 1.3, or pH =7.4 • Therefore, as long as the ratio of HCO3 to (PaCO2 x 0.03) remains 20, pH will remain 7.4 • FROM THIS EQUATION IT IS APPARENT THAT THE PH IS RELATED TO THE RATIO OF CONJUGATE BASE TO THE UNDISSOCIATED ACID IMPLICATIONS OF THE HENDERSON-HASSELBACH EQUATION • PH IS A FUNCTION OF THE RATIO OF BICARBONATE AND CO2 CONCENTRATIONS IN THE BLOOD • IF RATIO IS GREATER THAN 20, RELATIVE DEGREES OF ALKALOSIS RESULT • IF RATIO IS LESS THAN 20, RELATIVE DEGREES OF ACIDOSIS RESULT • CALCULATION IS MADE USING PKA OF CARBONIC ACID, SERUM BICARBONATE AND ARTERIAL PCO2

Question 10

Compare and contrast ventilatory and renal response to acidosis in regard to efficacy and speed

Answer 10

VENTILATORY RESPONSE TO ACID-BASE STATUS • Lungs have a profound effect on acid-base status of blood • Lungs excrete over 10,000 mEq of carbonic acid/day as compared with 50-500 mEq by the kidneys • By altering alveolar ventilation and elimination of CO2, the body compensates for pH change within 1-5 minutes • Able to buffer up to twice the amount of acid or base as all other buffers combined RENAL RESPONSE TO ACID-BASE STATUS • Regulation of acid-base occurs by allowing either H+ or HCO3 - to be removed from extracellular fluid (slow, but completely neutralizes) • Ordinarily the kidneys can excrete up to 500 mEq of acid or alkali each day (urine pH 6.4) • Higher concentrations of CO2 cause excretion of H+ while hyperventilation causes retention

Question 11

List five anesthetic considerations with acidosis

Answer 11

• Potentiation of depressant effects of sedatives and anesthetic agents on CNS and circulatory system (increased nonionized fraction and increased penetration into brain) • Decreased sympathetic tone • Increased arryhthmogenicity of volatile agents • Increased K+ with succinylcholine • Augmentation of neuromuscular blockade

Question 12

Categorize a provided arterial blood gas as either compensated/uncompensated and either primarily metabolic or respiratory

Answer 12

I know this

Question 13

Identify the role of the medulla in regulating respiration

Answer 13

Medullary respiratory centers • Regulate initiation of inspiration (dorsal) • Regulate forced expiration (ventral)

Question 14

pH PaCO2 [HCO3-] 1. 7.56 28 mmHg 24mM 2. 7.58 20 mmHg 18 mM 3. 7.43 22 mmHg 14 mM 4. 7.34 50 mmHg 26 mM 5. 7.29 65 mmHg 30 mM 6. 7.36 55 mmHg 30 mM 7. 7.56 38 mmHg 33 mM 8. 7.69 50 mmHg 35 mM 9. 7.24 43 mmHg 18 mM 10.7.30 25 mmHg 12 mM

Answer 14

1. Uncompensated respiratory alkalosis 2. Partially compensated respiratory alkalosis 3. Completely compensated respiratory alkalosis 4. Uncompensated respiratory acidosis 5. Partially compensated respiratory acidosis 6. Completely compensated respiratory acidosis 7. Uncompensated metabolic alkalosis 8. Partially compensated metabolic alkalosis 9. Uncompensated metabolic acidosis 10. Partially compensated metabolic acidosis

Question 15

Identify the role of the pons in regulating respiration

Answer 15

Pons respiratory centers • Apneustic center prolongs respiration • Pneumotaxic center regulates respiratory rate

Question 16

Describe how the Apneustic and Pneumotaxic Center regulate rate and depth of respiration

Answer 16

PNEUMOTAXIC CENTER(INHIBITORY) • Pneumotaxic area is located in upper pons • Transmits inhibitory signals to DRG to avoid overinflation • Affects respiratory rate indirectly by inhibition of overinflation APNEUSTIC CENTER(STIMULATORY) • Apneustic center is located in lower pons • Promotes deep and prolonged inspiration (excitatory) • Works with pneumotaxic center to control rate and depth of respiration

Question 17

Describe the effect on respiration of pCO2, pO2 and pH on respiration

Answer 17

• Regulation occurs by concentrations of CO2, O2 and H+ • Receptors detect changes in one or more chemicals and relays the information to the medullary respiratory center • Some receptors are located peripherally, while others are located centrally • Each receptor is stimulated by a particular chemical or mechanical event

Question 18

Identify the location of the central chemoreceptors and the primary regulatory element

Answer 18

CENTRAL CHEMORECEPTORS • Region on the anterolateral surface of the medulla that is sensitive to chemical changes (CO2) • CO2 readily crosses blood-brain barrier and forms carbonic acid, which dissociates into H+ ions • CSF is poorly buffered (pH changes rapidly) • 75-80% of the ventilatory response to CO2 is due to central chemoreceptor activity

Question 19

Identify the two peripheral chemoreceptors and the primary regulatory element(s)

Answer 19

• Important peripheral chemoreceptors are those of the carotid bodies and aortic bodies • Respond to changes in PaO2, PaCO2, blood pressure and pH • Responds mainly to low PaO2 but not high PaO2 • Activation does not occur until PaO2 is less than 50 mmHg • Not stimulated by oxygen saturation abnormalities such as carbon monoxide poisoning

Question 20

Discuss the process with occurs in the medulla(central chemoreceptor) that occurs in the presence of chronic high pCO2.

Answer 20

• Increased PaCO2 affects alveolar ventilation within one minute • After several hours, the effect wanes due to active transport (ion pump) of HCO3- • HCO3- combine with H+ ions to return CSF to normal pH (7.32) • Raising PaCO2 may increase PO2 response curve from 50 mmHg to 100 mmHg • In patients with chronically elevated PaCO2 hypoxic drive becomes very important

Question 21

Discuss the effects of pO2 on the carotid body chemoreceptor

Answer 21

• Decreases in PO2 increase sensitivity to PCO2 • Lowering PO2 from 110 mmHg to 47 mmHg produces a higher ventilatory response to PCO2 • Lowering PO2 to 37 mmHg increases both response and slope of response curve

Question 22

Identify the location and innervation of the pulmonary stretch receptors and how they are stimulated

Answer 22

• Located in walls of bronchi and bronchioles • Activated when stretched, tend to inhibit inspiration (Hering-Breuer Reflex active when VT >1.5 L) and causes shortening of exhalation when the lung is deflated • Inhibitory signals are carried centrally by the vagus nerve and protects against overinflation

Question 23

Identify the location and innervation of the irritant receptors and how they are stimulated

Answer 23

• Lie between airway epithelial cells • Stimulated by noxious gases (smoke, dust, cold air) • Impulses travel up vagus, reflex effects include bronchoconstriction and hyperpnea • May play a role in bronchoconstriction during asthma attacks as a result of their response to released histamine

Question 24

Identify the location and innervation of the J receptors and how they are stimulated.

Answer 24

• “Juxtacapillary” or J receptors named as they are in alveolar walls close to capillaries • Impulses pass up vagus nerve and result in rapid shallow breathing • Engorgement of pulmonary capillaries and increased interstitial fluid volume of the alveolar wall activate these receptors • May play a role in rapid shallow breathing and sensation of dyspnea associated with CHF and interstitial lung disease

Question 25

Describe the effect of pH on respiration

Answer 25

• Reduction in arterial blood pH stimulates ventilation • It may be difficult to separate high PaCO2 from low pH, but in patients with compensated metabolic acidosis increased ventilation occurs in response to lower pH • Effect usually mediated by peripheral chemoreceptors with contribution from central chemoreceptors

Question 26

Describe the integrative effect of pCO2, pO2 and pH on respiration

Answer 26

• pH, PO2 and PCO2 are all integrated • Low pH shifts response curves to the left • Exercise enhances the response to hypoxia even if PaCO2 is not raised, possibly due to lactic acidosis, afferents from muscle, or catecholamine secretion

Question 27

Describe the effects of different anesthetic agents on the pCO2 response curve

Answer 27

• Opioids shift PCO2 response curve to the right (less sensitive to CO2) • Barbiturates produce dose-dependent depression of medullary and pontine ventilatory centers • Benzodiazepines produce a dose-dependent decrease in response to PCO2 • Ketamine does not produce significant depression of ventilation, with PCO2 unlikely to increase > 3 mmHg

Question 28

Describe the effects of different anesthetic agents on the pO2 response curve

Answer 28

Question 29

Describe the effects of inhaled anesthetics on the control of ventilation

Answer 29

• All volatile anesthetics depress minute ventilation, which is compensated to a degree by increased respiratory rate • Inhalation anesthetics inhibit pulmonary irritant receptor and increase laryngeal irritant receptors • All inhalation agents depress the ventilatory response to PaCO2 and PaO2

Question 30

Compare the effects of inhalation anesthetics on genioslossus, intercostals and diaphragm

Answer 30

Question 31

Describe the effect of the cortex and limbic system on the control of ventilation

Answer 31

• Cortex may exert voluntary control to increase or decrease tidal volume and/or respiratory rate • Limbic system and hypothalamus may exert control through various emotional states