Respiratory3 Flashcards
Dead space equation
How do you determine physiological dead space (VD)?
VD = VT x [(PaCO2 - PECO2)/PaCO2]
VT = tidal volume PaCO2 = arterial PCO2 PECO2 = expired air PCO2
“Taco Paco, PEco, Paco - refers to order of variables in equation)”
What is physiologic dead space?
Anatomic dead space of conducting airways PLUS function dead space in alveoli
*Volume of inspired air that does not take part in gas exchange
What region of the lung is the Largest contributor to functional dead space?
Apex (healthy lung)
Tendency for lungs to collapse ______ and chest wall to spring _______.
Lungs - Inward
Chest wall - Outward
At Functional Residual Capacity (FRC) what are airway and alveolar pressures?
ZERO
*Intrapleural pressure is negative – Prevents pneumothorax
What is lung Compliance?
Change in lung volume for a given change in pressure
What pathologies cause a DEcrease in lung compliance?
Pulmonary Fibrosis
Pneumonia
Pulmonary Edema
What pathologies cause an INcrease in lung compliance?
Emphysema
Normal aging
What makes up Hemoglobin?
4 polypeptide subunits
- 2 alpha
- 2 beta
What are the 2 forms of hemoglobin? What are their relative affinities for O2?
T (taut) – Low affinity for O2 – Tissues
R (relaxed) – High affinity for O2 – Lungs
What molecules favor T (taut) form over R (relaxed) form?
INcreased:
- Cl-
- H+
- CO2
- 2,3-BPG
- Temperature
*Shifts dissociation curve to right – leading to INcreased O2 unloading
Describe fetal hemoglobin.
- 2 alpha & 2 gamma subunits
- Lower affinity for 2,3-BPG than adult Hb
- Higher affinity for O2 than adult Hb
What are the 2 forms of modified hemoglobin?
What does it lead to?
Methemoglobin
Carboxyhemoglobin
Leads to tissue Hypoxia:
- DEcreased O2 saturation
- DEcreased O2 content
Define Methemoglobin.
Oxidized form of hemoglobin (ferric, Fe3+)
Does NOT bind O2 as readily
INcreased affinity for Cyanide
How do you treat cyanide poisening?
Use Nitrates to oxidize Hb to methemoglobin
This binds Cyanide
Allowing cytochorome oxidase to function
Use Thiosulfate to bind this Cyanide
Forming thiocyanate –> Renally excreted
How do you treat Methoglobinemia?
Methylene blue
Define Carboxyhemoglobin.
Form of Hb bound to CO (carbon monoxide) in place of O2
*CO has a 200X greater affinity for O2 for Hb
What does CO poisening cause?
DEcreased oxygen-binding capacity
-Left shift in the O2-Hb dissociation curve
DEcreased oxygen unloading in tissues
What happens when the O2-Hb dissociation curve shifts to the Right?
DEcreased affinity of Hb for O2
- Facilitates unloading of O2 to tissue
What does Fetal O2-Hb dissociation curve look like compared to adult O2-Hb curve?
It is shifted to the Left
*Hb has higher affinity for O2 than adult
What are the causes of a Right Shift in the O2-Hb dissociation curve?
“C-BEAT”
CO2 BPG (2,3-BPG) Exercise Acid/Altitude Temperature
