Page 709 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat
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RespiRatoRy ` RESPIRATORY—PhYSIOlOgY RespiRatoRy ` RESPIRATORY—PhYSIOlOgY seCtioN iii 665
Lung and chest wall Inspiration Expiration
0.5 V T
Elastic recoil Tendency for lungs to collapse inward and chest Lung
wall to spring outward. volume (L)
At FRC, airway and alveolar pressures equal 0.0 FRC
+2
atmospheric pressure (called zero), and Alveolar
intrapleural pressure is negative (preventing pressure 0
atelectasis). The inward pull of the lung is (cm H O) -2
balanced by the outward pull of the chest wall. -4
System pressure is atmospheric. Pulmonary Intrapleural -6
-8
vascular resistance (PVR) is at a minimum. pressure -10
(cm H O)
Compliance Change in lung volume for a change in pressure
(ΔV/ΔP). Inversely proportional to wall stiffness Chest wall (compliance)
and increased by surfactant. 6 TLC
compliance = lung easier to fill (eg, Lung-chest
emphysema, aging) wall system
compliance = lung harder to fill (eg, 4 (net compliance)
pulmonary fibrosis, pneumonia, ARDS, Volume (L) TV
pulmonary edema) FRC
2
Hysteresis Lung inflation follows a different pressure-
volume curve than lung deflation due to need Lung (compliance)
to overcome surface tension forces in inflation.
0
−20 −10 0 10 20 30 40
Transpulmonary static pressure (cm H O)
2
Respiratory system Aging is associated with progressive in lung function. TLC remains the same.
changes in the elderly INCREASED DECREASED
Lung compliance (loss of elastic recoil) Chest wall compliance ( chest wall stiffness)
RV FVC and FEV
1
˙ ˙
V/Q mismatch Respiratory muscle strength (can impair cough)
A-a gradient Ventilatory response to hypoxia/hypercapnia
Hemoglobin Normal adult hemoglobin (Hb) is composed of Hemoglobin acts as buffer for H ions.
+
4 polypeptide subunits (2 α and 2 β) and exists Myoglobin is composed of a single polypeptide
in 2 forms: chain associated with one heme moiety.
β β
Deoxygenated form has low affinity for O , Higher affinity for oxygen than Hb.
2 1
2
thus promoting release/unloading of O .
2
Oxygenated form has high affinity for O
Heme 2
(300×). Hb exhibits positive cooperativity
α α and positive allostery.
2 1
FAS1_2019_16-Respiratory.indd 665 11/8/19 7:34 AM
