Flashcards in Pulmonary Mechanics II Deck (18)
What is the duration of inspiration and expiration compared to a complete breath cycle?
1/3 time spent inspiring and 2/3 time spent expiring.
The functional residual capacity (FRC) is the lung volume when what value is equal to 0?
When the lung is expanded to the mechanical resting position of the chest wall (when ______ = 0?) what force opposes inspiration?
Pc=0. The elastic force of the lung opposes inspiration.
What forces exist at larger lung volumes where Pc>0
The elastic recoil of both the lungs and the chest wall provide the passive driving force for expiration.
During forced expiration (at volumes below FRC) what provides the dominant driving force for the return of the lungs to FRC?
The expansive force of the chest wall.
What does static compliance determine?
It determines what particular volume the lung and chest wall will assume for a given transmural pressure when the elastic vessels are at mechanical equilibrium with no air moving.
What does a decrease in dynamic compliance indicate about the airway? What causes it?
It indicates increased airways resistance ( Q = ∆P/R). Dynamic compliance falls due to increased resistance with small airway disease associated with mucous plugs or inflammatory swelling.
In small airway disease what happens to Tidal volume (TV) as respiration rate increases? Why is the compliance lower?
TV decreases as RR increases. In small airway disease the changes in intrapleural pressure are normal but the TV is decreased at increases RR because of increased airway resistance. Hence, the dynamic compliance is decreased because ∆V is decreased.
What percent of resistance to breathing comes from the tissue and what comes form the airway?
20% due to tissue resistance and 80% due to airway resistance. Tissue resistance is due to the motion of the tissues (lung and chest wall). Tissue resistance increases in fibrotic disease and will not be described by Poiseuille's law. Airway resistance is due to the motion of the aril this R is the R in Ohm's and Poiseuille's laws.
What does Epi do to Airway resistance in flight or fight? Describe the mechanism of action.
It decreases airway resistance. It binds to high affinity B2 receptors, increases cAMP which stimulates protein Kinase A. PKA phosphorylates MLCK, which decreases sensitivity for MLCK for Ca-Calmodulin, inhibits binding of myosin cross bridges to actin, dilates bronchi and bronchioles reducing resistance and enhancing breathing.
What autonomic function affect airway resistance (R_aw) and in which direction do they shift it?
Sympathetic dilation reduce R. Parasympathetic constriction through vagus nerve (cholinergic) on muscarinic receptors increase R.
What are factors (non ANS) that affect airway resistant and in which way do they shift it?
Histamine is a potent bronchoconstrictor but vasodilator (H1 receptor) it increases Raw. Inflammatory swelling of bronchial mucosa increases Raw in asthma. Positive end-expiratory pressure (PEEP) decreases Raw in patients on respirators. Reflex constriction to; smoke particles, noxious gases, extreme cold.
What do the Isovolume Pressure-Flow (IVPF) curves show at low lung volumes?
Increasing the driving pressures leads to a maximal flow rate, and that the maximal flow rate increases with increasing lung volumes.
On an IVPF curve the increase in resistance with increasing Palv is due to what?
Dynamic compression of the airways. Flow no longer follows Ohm's law with greater expiratory efforts, and the deviation from Ohm's law is greater at low lung volumes.
What does dynamic compression do to airways? What shift is seen in equal pressure point (pep)?
Dynamic compression partially collapses airways and pep moves closer to alveoli with greater expiratory efforts.
In patients with emphysema who have elevated compliance, how does dynamic compression during expiration compare?
They experience greater dynamic compression during expiration.
What is the equal pressure point?
It is the point where the pressure inside the airway equals Ppl.