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Phys2 Vent & Diffus

QuestionAnswer
What is the purpose of ventilation? Maintaining PO2 and PCO2 **by maintaining diffusion of CO2, it slso helps regulate H+ levels in the BL
Vetnilation rate at which air is brough into and out of the lungs per minute.
Total ventilation depends on what 2 things? 1.tidal volume (volume of air brought in with each breath). 2.Frequency of respiration
What are the typical values of total ventilation? tidal volume? respiratory frequency? Are they energetically advantageous? Total Vent: 7500ml/min. Tidal Volume: 500ml. Resp Rate: 15/min. **Body chooses the Vt and RR b/c it produces 7500ml/min with the LEAST total work expended (VERY ENERGETICALLY ADVANTAGEOUS).
What all contributes to the total work (energy expended) the lungs exert maintaining total ventilation? 1.Elastic Work (work needed to expand the lungs). 2.Frictional work (work required to bring in air through the airways because of airway resistance).
Dead space The conducting zones. air trapped here will not experience any gas exchange due to no perfusion here. **Makes up 150ml of the 500ml tidal volume (the rest makes it to the alveoli)
Calculating Alveolar ventilation Va=(Vt-Vd) x RR. **Must subtract the dead space volume from the tidal volume before multiplying by the RR.
What two things affect alveolar ventilation? 1.Vt (tidal volume). 2.RR. **Increasing the tidal volume is more effective b/c it increases the proportion of tidal gas reaching the alveoli. (RR would just increase amt wasted due to dead space)
How is HYPOventilation determined? PCO2. If a patient has high PCO2 levels, they aren't breathing as fast as they need to eliminate CO2. RR may not be a good enough indactor.
Who is hypoventilating: A) PCO2 of 40 and RR of 9/min. B) PCO2 of 50 and RR of 12/min B
How are PCO2 and Alveolar ventilation related? INVERSELY PROPORTIONAL. **One way to measure Alveolar ventilation (Va) is by the rate of CO2 removal
Arterial PCO2 with HYPOventilation? HYPERventilation? HYPO: Increased PCO2. HYPER: Decreased PCO2 **this makes sense since Va and PCO2 are inversely related.
Hypoxemia Dec PO2. If it is accompanied by Inc PCO2 Then the patient is experiencing Hypoventilation.
3 different types of Dead Space 1.Anatomic (volume in conducting airways all the way until terminal bronchioles). 2.Alveolar (any ventilated alveoli that are NOT perfused). 3.Physiologic (volume of air NOT involved with gas exchange include both 1 & 2).
Anatomic and physiologic Dead Space in a healthy patient? Lung diseased patient? Healthy: Equal. Lung Disease: Physiologic > Anatomic b/c of Alveolar dead space, which indicates enhanced ventilation-perfusion inequality
In an area of physiologic Dead Space, the alveolar gas composition would be? PaCO2: 0mmHg. PaO2:150mmHg. **No O2 has been subtracted or CO2 added b/c there is NO PERFUSION so it is equal to composition of inspired air
If alveolar dead space exists, will P(alveolar)CO2 differ from P(expired)CO2? YES. the air from the dead space will have 0mmHg PCO2 which will dilute the PCO2 air from the perfused area.
Physiologic dead space equation (Bohr) (Vd/Vt)=[(PaCO2-PeCO2)/PaCO2]. Normal values: 1.PaCO2:40mmHg. 2.PeCO2:30mmHg. 3.Vd/Vt: 0.2-0.35 at rest
Normal PaCO2 (alveolar)? 40mmHg
Normal PeCO2 (expired)? 30mmHg
Normal Vt (tidal volume)? 500ml
Normal Vd (Dead space volume)? 125ml
is ventilation uniform in the upright lung? NO. **Ventilation is higher at the lung base than at the lung apex, so ventilation increases down the lung from apex to base.
Why is ventilation higher at the base of the lungs? Due to increased compliance: there is less expansion at the base, which means less negative intrapleural pressure. This puts the base on a steeper slope meaning more volume change with a given intrapleural change than the apex.
What is the reason that the base experiences less expansion than the apex? due to gravity pull on the apex, but not the base (base sits on the diaphragm so there is less negative change in intrapleural pressure)
Fick's law of diffusion? the greater the concentration gradient, SA for diffusion, and thiness of membrane means the FASTER the diffusion.
Normal equilibration time for PO2? At Rest: 1.time spent in pulmonary capillaries: 3/4sec. 2.%of capillary needed to reach equilibration: 1/3. Exercise: 1.time spent in pulmonary capillaries: 1/4sec. 2.% of capillary needed to reach equilibration: Whole length.
Is diffusion impairment problematic at rest? NO. (b/c of the reserve capacity for diffusion). **Only causes problems during exercise and Alveolar hypoxia (Reduced PaO2 at high altitudes). Will see low PO2 levels in the BL
Is CO2 as affected as O2 by a thickening in the BL-gas barrier? NO, it has greater solubility and diffuses much quicker.
Created by: WeeG
 

 



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