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MP - Lecture 24
Mechanics of Breathing II
| Question | Answer |
|---|---|
| Medical Physiology – Lecture 24 | Mechanics of Breathing II |
| 5 Critical Variables in Respiratory Mechanics | Flow, volume, compliance, pressure, and resistance |
| Pressure = | Pressure = (V/C) + (Q x R) |
| Alveolar pressure is always more ___ than pleural pressure. | Positive |
| Slope of pressure (x-axis) vs. volume (y-axis) curve represents: | Compliance |
| Compliance is high at what volumes and pressures? | Low volumes and pressures |
| Compliance is low at what volumes and pressures? | High volumes and pressures |
| Hysteresis | Forward path is different than reverse path |
| Main hysteresis is observed in lungs at: | First breaths, with collapsed lungs |
| Compliance is always: | Positive |
| In a column of water, pressure is ___ at the surface. | Atmospheric |
| Gravity makes pleural pressure ___ at base than at apex. | Less negative (Ppl = -10 cm H2O vs. +2 cm H2O) |
| Local compliance at apex is ___ than local compliance at base. | Lower |
| Apex has lower compliance because: | Inspiration causes greater expansion in base than apex |
| Typical compliance of lung is: | 200 mL/cm H2O |
| Specific Compliance | Compliance divided by initial volume (value independent of size) |
| When compliance is low, elastic recoil is: | High (i.e. high lung volumes, fibrotic conditions) |
| When compliance is high, elastic recoil is: | Low (i.e. low lung volumes, emphysema) |
| If no lungs present and atmospheric pressure at airway opening: | Thorax is at relaxed volume, which is greater than FRC |
| If no lungs present, what pressure must be applied to bring thorax volume back to FRC? | -5 cm H2O (counteract thorax elastic recoil in absence Ppl = -5 cm H2O) |
| FRC of lungs is caused by: | Balance between inward lung recoil and outward thorax recoil |
| Passive elastic properties of thorax: | FRC (3 L) @ -5 cm H2O, resting volume at P = 0 cm H2O |
| Passive elastic properties of lungs: | FRC (3 L) @ +5 cm H2O |
| Passive elastic properties of thorax and lungs: | FRC (3 L) @ 0 cm H2O |
| Slope of combined passive elastic properties compared to individual curves is: | always less |
| Pressure required to inflate both chest wall and lungs is: | The sum of the respective pressures required to inflate individually |
| Compliance of lung and chest wall combined: | (1/CT) = (1/CL) + (1/CCW) |
| If either CL or CCW are very small, than total compliance is: | Very small |
| Low compliance of either lung or chest wall causes: | Restrictive breathing (low total compliance) |
| Typical compliance values: | CL = 200, CCW = 200, CT = 100 |
| Increase in pressure at airway by +10 cm H2O yields only a +5 cm H2O transpulmonary pressure because: | Combined compliance is less than individual compliances |
| Pressure needed to increase FRC by +1 with normal compliance is: | P = 10 cm H2O (P = V/CT = 1000/100) |
| Pressure needed to increase FRC by +1 with low compliance is: | P > 10 cm H2O |
| Obese people often sleep with thorax higher than abdomen because: | Reduced thorax compliance |
| During inspiration (VL, PA, Ppl): | VL increases, PA becomes negative, Ppl becomes more negative |
| At the end of inspiration (PA, Ppl): | PA = 0 cm H2O, Ppl = -10 cm H2O |
| During expiration (VL, PA, Ppl): | VL decrease, PA becomes positive, Ppl becomes less negative |
| At the end of expiration (PA, Ppl): | PA = 0 cm H2O, Ppl = -5 cm H2O |
| Airflow = | (Pmouth – Palveolus) / R (R = airway resistance) |
| Laminar lung flow: | Unidirectional flow with fastest flow in the middle |
| Turbulent lung flow: | Forward net direction flow, but many local eddy currents |
| Causes of turbulent flow: | Large radius, high flow velocity, high fluid density, and low fluid viscosity |
| Main sites of airway resistance are: | Nose and large/medium bronchi(oles) |
| Disease in small airway is difficult to detect early because: | minor contribution to airway resistance |
| If lung volume increase, resistance: | Decreases |
| Bronchial smooth muscle relaxers: | B2 adrenergic and nitric oxide |
| Bronchial smooth muscle contractors: | Acetylcholine, histamine, and prostaglandin F2a |
| If resistance increases, work: | increases |
| If compliance increases, work: | decreases |
| Resistance work is increased by | Obstructive diseases |
| Resistance work is minimized by: | Slow breathing (difficult with dyspnea) |
| Compliance work is increased by | Restrictive diseases (prevent volume increase) |
| Compliance work is minimized by: | Shallow breathing |
| Work of breathing can be increased by: | Increased airway resistance, reduced lung compliance, and reduced thorax compliance |
Created by:
emyang
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