Resp Exam 2 Valley Questions Flashcards
Liters of alveolar ventilation and liters of pulmonary blood flow
What is average VQ ratio?
**Healthy adult
Alveolar vent: 4L/min
Pulmonary blood flow: 5L/min
VQ ratio: 0.8
V/Q ratio between 0 and unity indicates what?
0 < VQ < 1
Relative shunt
V/Q ratio that is greater than one?
VQ > 1
Dead space
Importance of maintaining normal ventilation-to-perfusion relationship
Keep PaCO2 and PaO2 in normal range
Lung unit that exhibits absolute shunt, what is the V/Q ratio?
What about ventilation and perfusion?
Absolute shunt = VQ 0
V= 0, perfusion (variable)
HPV can decrease perfusion
What is the V/Q ratio in a lung unit that is ventilated but completely nonperfused?
Ie: PE
VQ = infinity
V= (variable)
Q= 0
**O can NEVER be a denominator (answer will always be infinity)
Numeric values for absolute dead space and absolute shunt:
Dead space= infinity
Shunt= 0
Compared w/ apex of lung, the base of the lung exhibits (when individual is awake and upright) higher or lower VQ ratio?
Lower
Max PaO2 achievable in young healthy adult breathing RA
104mmHg
Normal PaO2 in adult breathing RA
80-100mmHg
If oxygen saturation is 90% (SaO2), what will the PO2 be?
Where is the blood with PO2 found?
SaO2 = 90%
PO2 = 60mmHg
This is arterial blood
What is PO2 if O2 sat of hgb is 70%?
Where in circulation is blood with this PO2 found?
SaO2 = 70%
PO2 = 40mmHg
This would be mixed venous blood
Normal arteriovenous oxygen content difference
5mL/ O2/ 100 mL blood
How can you calculate how much oxygen is dissolved in blood?
What law applies?
PO2 x 0.003
Units are mL/O2/ 100 mL blood
Henry’s Law
Two factors that determine the amount of oxygen carried by hemoglobin
PO2
Amount of hemoglobin
How much O2 is carried by each gram of hemoglobin when saturated?
1.36 (Nagelhout) of O2 is carried by each gram of saturated hgb
Significance of flat portion of oxyhemoglobin dissociation curve
Flat = loading of oxygen
** Large changes in pp of PaO2 produce small changes in SaO2
Significance of steep portion of oxyhemoglobin dissociation curve
Steep = unloading of oxygen
** Large amounts of oxygen are unloaded from hgb = large decrease in SaO2 in response to small change in pp of O2
P50 is
O2 pp where hgb is 50% saturated
Normal P50 is
27mmHg
What happens to P50 when oxyhemoglobin dissociation curve shifts right?
Increases
** > 28mmHg
What happens to P50 when oxyhemoglobin dissociation curve shifts left?
Decreases
** < 26mmHg
5 conditions that cause right shift
Increased temp
Increased pp of CO2
Increased 2, 3 DPG (DBG is interchangeable)
Increased H ions (decreased pH)
Sickle cell
7 conditions that cause left shift
Decreased temp
Decreased pp of CO2
Decreased H ions (increased pH)
Decreased 2, 3 DPG
Fetal hgb
CO poisoning
Methemoglobin
Increased CO2, which way does curve shift?
Where in circulation does this occur?
Right
Occurs as blood flows through caps of tissues
**important bc more O2 IS released from hgb
Decreased CO2, which way does curve shift?
Where in circulation does this occur?
Left (think left in lung)
Occurs in pulmonary capillaries as CO2 is being blown off– O2 LOADING
Bohr effect
Caused by CO2 entering or leaving blood
Increased PCO2 –> shifts right –> unloads oxygen from hgb
Decreased PCO2 in pulm capillaries –> shifts left –> loading of oxygen onto hgb
How many grams of hgb must be in reduced form to produce cyanosis?
5 grams of hgb per 100 mL of blood must be in reduced form (without O2)
Which direction do inhalational agents or IV general anesthetics shift the curve?
To the right
Total quantity of O2 delivered to and used by tissues each min:
250 mL/min of O2
During monitoring of mixed venous: suddenly goes from 74% to 40%. What are the most likely causes?
Decrease in CO
Hypovolemia
Venous blood oxygen saturation provides what information
Relationship between oxygen delivery and oxygen consumption
What are 3 ways CO2 is transported in blood (give percentages)
Dissolved 5-10%
Bicarbonate ions 80-90%
Bound to hgb 5-10% (carbamino)
What is CO2 in vol % in RA? What is the partial pressure of CO2 in RA?
0.03%
0.3mmHg
Solubilities of O2 and CO2 in the blood
O2 - 0.003
CO2 - 0.067
Diffusion coefficients of O2 and CO2 in the blood
O2 - 1 (reference point)
CO2 - 20
When PO2 decreases, does the blood CO2 curve shifts left or right?
Where in circulation does this occur?
PO2 decreases, CO2 shifts left (more CO2 is carried by blood)
This occurs as oxygen diffuses out of capillaries of systemic tissues
**LOADING of CO2 in blood
When PO2 increases, does the blood CO2 curve shift left or right?
Where in circulation does this occur?
PO2 increases, CO2 shifts right (less CO2 is carried by blood)
Occurs as blood flows through pulmonary capillaries in lungs
*UNLOADING OF CO2
Haldane effect
Changes in PO2 alter the amount of CO2 in blood
IN THE LUNGS- increase in PO2 causes CO2 to shift right and unload CO2
IN THE TISSUES- decrease in PO2 causes CO2 to shift left and load CO2
Role of carbonic anhydrase in RBC
Catalyzes (accelerates) conversion of H2O and CO2 to carbonic acid and then to bicarb ions
After it is formed, bicarbonate moves out of RBC into plasma in exchange for what?
What is this called?
Exchanges Cl- ions
Chloride shift called Hamburger shift
Primary respiratory centers and where they are located:
VRG
DRG
Located in medulla
Secondary respiratory centers and where are they located:
Apneustic
Pneumotaxic
Located in pons
Single most important factor responsible for directly stimulating central chemoreceptors
Hydrogen ions in CSF
How are hydrogen ions generated in CSF?
CO2 diffuses into CSF
Converted by carbonic anhydrase
Yielded to bicarbonate ions and H ions
To what 3 physiologic parameters do peripheral chemoreceptors (carotid and aortic) respond?
Which stimulates them most?
PaO2, PaCO2, and pH
Most stimulated by PaO2, but not until < 60
Peak effect with peripheral chemoreceptor @ which PaO2 level?
30 mmHg
What 3 exogenous substances stimulate peripheral chemoreceptors?
Nicotine, Doxapram and cyanide
How much of the ventilatory response to an increase in PaCO2 is mediated by central or peripheral chemoreceptors?
Vent response to increased PaCO2 is central chemoreceptors
(7x more powerful than peripheral)
What normally drives ventilation?
CO2
Physiologic respiratory stimulant
** S I N G L E most important regulator of alveolar ventilation = PaCO2
When are peripheral chemoreceptors stimulated?
Decreased arterial O2, especially from 60-80
Peak at 30
Which two changes will increase ventilation most: increase in PaCO2 or decrease in pH?
Increase in PaCO2
What triggers Hering-Breuer reflex?
Lung inflation triggers reflex
Inspiration is inhibited (minor role in ventilation)
**Not activated until TV is > 1.5 L
Pulmonary stretch receptors within smooth muscle of small airways involved in Hering-Breuer reflex trigger sensory (afferent) impulses that travel along which nerve?
Vagus nerve carries afferent (sensory) impulses of Hering-Breuer
