Flashcards in Respiratory Physiology Deck (72)
How does oxygen consumption and CO2 production change with GA?
Decreases both by ~15%
What is the RQ for carbohydrates? Proteins? Lipids?
How would a hemi-diaphragmatic paralysis decrease pulmonary function?
~25% (diaphragm accounts for 75% of chest volume change)
What is the end-expiration intrapleural pressure in a healthy patient?
-5 cm H2O (while alveolar pressure is 0 since there is no air flow): this keeps the alveoli open
What is Laplace's law?
Alveolar pressure = 2 * (surface tension / radius)
How does surfactant affect smaller alveoli compared to larger ones?
Surfactant is more concentrated in smaller alveoli so it decreases surface tension to a greater extent than in large radii alveoli
What makes up FRC?
Expiratory reserve volume + residual volume
Factors that decrease FRC?
Restrictive lung disease, obesity, pregnancy, posture (standing>sitting>supine>prone), height (taller people have more FRC), gender (men have more FRC than women)
What patient postures have the most reduced FRC?
Supine > prone > sitting > standing (least reduction in FRC)
What is closing capacity?
Volume at which small airways begin to close; Residual volume + closing volume
How does closing capacity change with obesity?
It does not change; however, ERV decreases and so FRC decreases causing tidal volumes to shift towards residual volume; since closing volume has not changed, the tidal volumes are not less than closing capacity
How does closing capacity change with age?
Increases with age (or any disease states within the lungh like COPD, etc that increase airway obstruction)
How does closing capacity change with GA?
Decreases under general anesthesia (bronchodilation of volatile anesthetics so you decrease airway obstruction leading to decreased closing capacity)
What is the formula for airway resistance for laminar flow?
Resistance = (8 * length * viscosity) / (pi * radius^4)
What is the major determinant for turbulent flow?
Formula for Reynold's number
R = (velocity * diameter * density) / viscosity
What Reynold's number indicates turbulent flow?
What happens to FRC under GA?
Decreases (ribcage moves inward in supine position + abdominal contents fall into thorax)
Would positive-pressure ventilation increase or decrease dead-space?
Increase by ~50%; higher alveolar pressure = West zones moved downward: alveoli at apex that were barely being perfused due to low arteriolar pressures will be totally occluded = ventilation without perfusion (dead space)
In a normal, sitting patient, where is ventilation and perfusion at its maximum?
Both are maximal near the base
Non-cardiac causes of acute pulmonary HTN?
Hypoxia, hypercarbia, acidosis, autonomic system
What does hypocarbia do to pulmonary vasculature?
Pulmonary vasodilator and causes bronchoconstriction
How does the effects of hypoxia, acidosis, and hypercarbia differ between pulmonary and systemic vasculature?
What anesthetic inhibits hypoxic pulmonary vasoconstriction?
N2O and volatile agents (2 MAC), inhaled nitric oxide, nitrates
What is the alveolar gas equation?
PAO2 = FiO2 ( Pbarometric - PH2O) - PaCO2/RQ
How does an increase in cardiac output change the A-a gradient?
1. increased CO = increased mixed venous PO2, and more left over oxygen
2. Intrapulmonary shunting decreases
You get a decrease in the A-a gradient
What is responsible for the ventilatory response to hypercarbia?
Chemoreceptors in contact with the 4th ventricular CSF on the anterolateral surface of the medulla; BBB permeable to CO2 which reacts with H20 forming H+ ions = lowering pH = stimulates chemoreceptor
What region of the brain coordinates inspiration?
Dorsal & ventral medullary center
What region of the brain coordinates expiration?
Ventral medullary center