"Medical Physiology Ventilation & Lung Volumes Amit S. Dhamoon" MARY

Question 1

What is the volume of air you breathe out after maximal inspiration in first the second of expiration?

Answer 1

FEV1 (forced expired volume in one sec)

Question 2

What is the optimal ratio of FEV1/FVC?

Answer 2

>80% for healthy lungs ~50% for COPD

Question 3

What are physical exam findings from a chronic smoker?

Answer 3

Dyspnea on exertion Chronic productive cough Barrel chest Prolonged expiration Hypoxemia (low O2 saturation in blood) Elevated hematocrit due to chronic hypoxemia —increased eurethropoietin production due to detection of low O2 by kidneys Larger lung volumes on chest X-ray, flattened diaphragm. More radiolucent lungs

Question 4

What’s the difference between obstructive vs restrictive lung disease?

Answer 4

Obstructive: high capacitance, difficult to exhale, low FEV1, low FEV1/FVC ratio, high total lung capacity. Restrictive: low lung capacitance difficult to inhale, low FEV1, normal FEV1/FVC ratio, normal to low total lung capacity

Question 5

What’s another name for emphysema? Is it a restrictive or obstructive lung disease? How about asthma? Which direction would the compliance curve shift with an obstructive/restrictive lung disease?

Answer 5

COPD - obstructive, so is asthma Pulmonary edema and fibrosis is restrictive For obstructive curve shifts to right For restrictive curve shifts left

Question 6

What is forced vital capacity?

Answer 6

The change between total lung capacity (deeeeep breath in) to residual lung capacity (what’s left after deeeep expiration)

Question 7

What is normal volume for Forced vital capacity? How about COPD?

Answer 7

Normal: 4.5L COPD: 3L

Question 8

Give the equation for minute volume (MV).

Answer 8

MV = VT x RR Minute volume = tidal volume x resp rate

Question 9

What are normal values for pH, pO2 and PCO2?

Answer 9

pH about 7.4 pO2 about 90 pCOs about 40 *If pCO2 > 40 –> hypoventilation

Question 10

What is anatomic dead space?

Answer 10

The volume of air that does not participate in gas exchange (ie in the conducting system)

Question 11

Give the 5 lung volumes and their definitions and/or relative values.

Answer 11

1. Total Lung capacity, about 6-7L 2. Tidal volume - volume of gas in and out in 1 breath, about 500-600 mL, can increase with exercise 3. Inspiratory reserve volume - extra volume you can breathe in after the peak of tidal inspiration 4. Expiratory reserve volume - extra volume you can breathe out at the nadir of tidal expiration 5. Residual volume - cannot be exhaled, extra volume that’s always there in the lung even after ERV.

Question 12

What is this: the maximum volume of gas that can be exhaled after a maximal inspiration.

Answer 12

Vital capacity VC = IRV + VT + IRV = TLC - RV

Question 13

Explain the equation: VT + IRV = TLC - FRC

Answer 13

These are two equations for inspiratory reserve capacity (IRC). The maximum volume of gas that can be inhaled from the resting expiratory position. One big deep breath…

Question 14

At what point in a volume/time graph would you find the functional residual capacity?

Answer 14

At the bottom (exhalation) of a normal breath, when diaphragm and chest muscles are relaxed, and lungs and chest wall at at mechanical equilibrium.

Question 15

Why should you not use spirometry to measure the FRC?

Answer 15

FRC includes the residual lung volume (RV). **TLC can also not be measured by spirometry for the same reason.

Question 16

__________ is characteristic of emphysema.

Answer 16

Hyperinflation (and trouble exhaling)

Question 17

Compliance and FRC are related characteristics of the lung. How does FRC change with compliance?

Answer 17

1. Increased lung compliance increases FRC, and vice versa 2. Lung compliance and FRC both increase with aging.

Question 18

FRC is an important measure to monitor when considering both obstructive and restrictive lung diseases, but spirometry is not an effective measure of FRC. One method is open-circuit nitrogen washout, but this method requires a correction calculation. Why?

Answer 18

Some N2 inhaled may diffuse into the blood, and therefore the FRC will be underestimated.

Question 19

Why is the use of helium effective at measuring FRC?

Answer 19

Because it is an inert gas with low blood solubility. However if there are bullae in the lung, using He can underestimate the FRC.

Question 20

Explain how a plethysmograph works.

Answer 20

Gas tight chamber, close to environment at FRC, breathing changes pressure and volume measurements in the chamber. FRC is calculated from the pressure and compressibility of the gas.

Question 21

T/F: The body plethysmograph measures the total amount of gas in the lung, whereas the open-circuit nitrogen washout and closed-circuit helium dilution only measure exchangeable air.

Answer 21

True. Best to use both a plethysmograph and a gas exchange method to get the full picture.

Question 22

Hypoventilation results in __1__ (increased pCO2) and __2__ (decreaed pO2).

Answer 22

1. alveolar hypercapnea
2. hypoxia

Question 23

________ results in alveolar hypocapnea and hyperoxia.

Answer 23

Hyperventilation / increased alveolar ventilation

Question 24

Give the alveolar gas equation for CO2. What does it mean?

Answer 24

P_ACO₂ = V_CO2P_T/V_A

P_ACO₂ varies inversely with alveolar ventilation (V_A)

Increasing CO₂ production increases steady state P_ACO₂

Question 25

In a steady state, influx = ? w/r/t pulmonary physiology

Answer 25

Efflux, meaning that the amount of oxygen being inhaled is the same as the rate of its consumption.

The equation for this is:

P_AO₂ = P_IO₂ - P_ACO₂/R

Question 26

What is one way to increase alveolar oxygen?

Answer 26

Increase PpO2.

Question 27

Tidal volume is about what % of TLC?

Answer 27

About 10%

Question 28

Talk to me about CO2, expiration and anatomic dead space.

Answer 28

This is the Fowler method. Presumably, when you inhale, you inhale very little CO2, and when you exhale, the first air to come out will also have little or no CO2, as it is coming from the conducting zones. As you exhale, the CO2 from the alveolar space will mis with the rest of the air and the amount will rise and plateau. These values can be used to estimate the alveolar ventilation.