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Phys2 Vent & Diffus
| Question | Answer |
|---|---|
| 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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