Resp Cycle & Lung Volumes Flashcards
Residual Volume (RV)
Volume of air that cannot be forced out, no matter how hard you try
Tidal Volume (VT)
Amount of air inspired/expired in a single breath. Varies under circumstances, normal resting is 500mL
Inspiratory Reserve Volume (IRV)
Volume of air you breathe above tidal volume (VT)
Expiratory Reserve Volume (ERV)
Volume of air that can be forced out, in addition to VT. Does not include residual volume. Requires activation of expiratory muscles.
Vital Capacity (VC)
The amount of air that can be maximally inspired following maximal expiration.
VC = IRV + VT + ERV
VC can be influenced by posture, ability of diaphragm to contract/expand, strength of respiratory muscles, lung elasticity, etc.
Inspiratory Capacity (IC)
Capacity of air that can be maximally inspired following a NORMAL exhale.
IC = VT + IRV
Functional Residual Capacity (FRC)
Amount of air that remains in the lungs following a normal exhalation.
FRC = ERV + RV
Helps prevent lung collapse, reduces workload, dilutes toxic inhaled gases
Total Lung Capacity (TLC)
Maximal volume to which lungs can be expanded with greatest effort.
TLC = IC + FRC = VC + RV = IRV + VT + ERV + RV
What does a low Forced Vital Capacity (FVC) value indicate?
Indicates a restrictive pattern
Forced Expiratory Reserve Volume (FEV)
The amount of air exhaled during the first second of the FVC maneuver via spirometry (tends to be lower in diseases that obstruct the airway, such as asthma)
What does a low FEV/FVC ratio indicate?
Indicates an obstructive pattern, whereas a normal value indicates a normal pattern
What does pseudorestriction due to air trapping look like on a graph compared to normal TLC?
TLC overall is increased, with a larger RV and a smaller FVC. The smaller FVC is due to air trapping resulting in an increased residual volume
What are 4 extra-parenchymal causes of restriction?
Obesity, neuromuscular disease, chest wall deformities, large pleural effusions
What do anemia, pulmonary arterial hypertension and chronic thomboemboic disease have in common?
They can all potentially reduce the diffusing capacity in the lungs, leading to progressive dyspnea, even though FVC and TLC are normal
Minute ventilation equation
V(dot) = Vt x freq (respiratory rate)
Alveolar ventilation equation
Valv = Vt - Vds (dead space)
Minute alveolar ventilation equation
V(dot)A = Valv x freq
Airway resistance equation
R = 8nL / r^4
n = viscosity L = tube length r = radius
Alveolar diffusion rate equation
J = (SA) x (D) x (P1-P2) / d
J = diffusion rate SA = surface area D = diffusion coefficient P1-P2 = pressure gradient across alveolar membrane d = diffusion distance (thickness of barrier)
What are the normal J values for O2 and CO2?
J (O2) = 250 mL/min
J (CO2) = 200 mL/min
What are normal PAO2 and PACO2 levels?
PAO2 = 100 mmHg PACO2 = 40 mmHg
What are normal PvO2 and PvCO2 levels?
PvO2 = 40 mmHg PvCO2 = 45 mmHg
What are normal PaO2 and PaCO2 levels?
PaO2 = 60 mmHg PaCO2 = -5 mmHg
What is the diffusion capacity of the lung for O2?
DlO2 = 21 mL O2/min/mmHg
What is the diffusion capacity of carbon monoxide?
DlO2 = 1.23 x DlCO
What is LaPlace’s Law?
Pressure = 2T / r
T = tension r = radius
Respiratory quotient equation
RQ = V(dot) CO2 / V (dot) O2
Alveolar gas equation
PAO2 = PiO2 - V(dot)O2
= PiO2 - PaCO2 / RQ
= O2 inspired - O2 consumed
Oxygen inspired equation
PiO2 = [P(atm) - P(h2o)] FiO2
P(atm) = 760 mmHg P(h20) = 47 mmHg FiO2 = 21%
Oxygen consumed equation
V(dot)O2 = PaCO2 / RQ
RQ will either be 0.8 (mixed fuel), 1 (glucose), 0.7 (fatty acids-hypoglycemia, diabetic starvation, etc)
