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Physiology: Respiratory

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148 Questions

What is the volume that remains in the lungs after a maximal expiration?

Residual volume

What is the functional measurement that is defined as the volume of the lungs that does not participate in gas exchange?

Physiologic dead space

What is the volume that can be inspired over and above the tidal volume?

Inspiratory reserve volume

What is the volume of the conducting airways?

Anatomic dead space

What is the equation used to calculate physiologic dead space?

Vn = VT X PAco2 - PEco2

What is the normal approximate value of anatomic dead space?

150 mL

What is the volume that can be expired after the expiration of a tidal volume?

Expiratory reserve volume

What is the term for the difference between the volume of air that can be inspired and the tidal volume?

Inspiratory capacity

What happens to the abdominal contents when the diaphragm contracts?

They are pushed downward

During normal quiet breathing, which muscles are NOT used for inspiration?

External intercostals

What is the process of expiration normally?

Passive

What is the role of abdominal muscles during forced expiration?

They compress the abdominal cavity and push the diaphragm up

What is the equation for compliance of the respiratory system?

C = VIP

What is the relationship between compliance and elastance?

They are inversely related

What is the units of compliance in the respiratory system?

mL/mm Hg

What is the slope of the pressure-volume curve?

Compliance

What is the sum of all four lung volumes?

Total lung capacity (TLC)

What is the ratio of FEV1 to FVC in normal subjects?

FEV1/FVC = 0.8

What is the most important muscle for inspiration?

Diaphragm

In restrictive lung disease, such as fibrosis, what is the effect on FEV1 and FVC?

FEV1 is reduced less than FVC

What is the volume of air that can be forcibly expired after a maximal inspiration?

Forced vital capacity (FVC)

What is the effect on FEV1/FVC in obstructive lung disease, such as asthma and COPD?

FEV1/FVC is decreased

What is the unit of measurement for time in the figure illustrates FVC and FEV1?

Seconds

In which type of lung disease is FEV1 reduced more than FVC?

Obstructive lung disease

What is the difference in pressure that determines lung volume?

Alveolar pressure minus intrapleural pressure

What occurs when the pressure outside of the lungs is negative?

Lung volume increases

What is the term for the difference between the inflation and deflation curves of the lung?

Hysteresis

At what range of pressures is lung compliance greatest?

Middle range of pressures

What is the result of high expanding pressures on lung compliance?

Compliance decreases

What is the relationship between the compliance of the lungs and chest wall separately and together?

Compliance of the lung-chest wall system is less than that of the lungs alone or the chest wall alone

What is the shape of the pressure-volume curve at high expanding pressures?

Flat

Why does the lung follow a different curve during inspiration and expiration?

Due to the need to overcome surface tension forces at the air-liquid interface

What happens to the intrapleural pressure when air is introduced into the intrapleural space?

It becomes equal to atmospheric pressure

What is the result of increased lung compliance in a patient with emphysema?

A higher FRC

What is the tendency of the lungs in a patient with fibrosis?

To collapse more

What is the relationship between the collapsing force on the lungs and the expanding force on the chest wall at FRC?

The two forces are equal and opposite

What is the effect of decreased lung compliance in a patient with fibrosis?

The tendency of the lungs to collapse is increased

What happens to the chest wall in a patient with emphysema?

It becomes barrel-shaped

What is the result of the opposing forces at FRC?

The combined lung-chest wall system is in equilibrium

What is the relationship between elastic recoil and lung compliance?

As elastic recoil increases, lung compliance decreases

What is the relationship between surface tension and collapsing pressure in an alveolus?

Surface tension is directly proportional to collapsing pressure.

What is the effect of surfactant on the collapsing pressure of small alveoli?

Surfactant reduces the collapsing pressure of small alveoli.

What is the difference in collapsing pressure between large and small alveoli?

Small alveoli have a higher collapsing pressure than large alveoli.

What is the role of surfactant in preventing alveolar collapse?

Surfactant reduces the surface tension of alveoli.

What is the equation that relates collapsing pressure, surface tension, and alveolar radius?

P = 2T/r

Why do small alveoli have a tendency to collapse?

Because of their high collapsing pressure.

What is the effect of surfactant on alveolar compliance?

Surfactant increases alveolar compliance.

What is the relationship between alveolar radius and collapsing pressure?

Collapsing pressure is inversely proportional to alveolar radius.

What is the relationship between the radius of the airway and the resistance to airflow?

Inverse fourth-power

What is the primary site of airway resistance in the respiratory system?

Medium-sized bronchi

What is the effect of parasympathetic stimulation on airway resistance?

Decreases airway radius and increases resistance

What is the effect of high lung volumes on airway resistance?

Decreases airway resistance

What is the effect of sympathetic stimulation on airway resistance?

Decreases airway resistance

What is the relationship between airway radius and airflow?

Directly proportional

What is the effect of a 4-fold decrease in airway radius on resistance?

Increases resistance by a factor of 256

What is the mechanism by which lung volume affects airway resistance?

Radial traction on airways by surrounding lung tissue

What is the reason why patients with COPD learn to expire slowly with 'pursed lips'?

To create a resistance at the mouth, increasing airway pressure and preventing airway collapse

What is the characteristic of lung disease in patients with 'pink puffers'?

Mild hypoxemia and nonnocapnia

What is the effect of increased lung compliance in a patient with COPD?

Increased air trapping and increased FRC

What is the characteristic of lung disease in patients with fibrosis?

Restrictive lung disease with decreased lung compliance

What is the effect of air trapping in patients with COPD?

Increased FRC

What is the characteristic of patients with 'blue bloaters'?

Severe hypoxemia with cyanosis and hypercapnia

What is the effect of COPD on FEV1, FVC, and FEV1/FVC?

Decreased FEV1, decreased FVC, and decreased FEV1/FVC

What is the shape of the chest in a patient with COPD?

Barrel-shaped

What is the main reason for the increase in FEV1/FVC in restrictive lung disease?

Decreased FVC

What is the partial pressure of oxygen in humidified tracheal air at 37°C?

150 mm Hg

What is the effect of physiologic shunt on the Po2 of arterial blood?

Decreases the Po2 of arterial blood

What is the relationship between the amount of gas dissolved in a solution and its partial pressure?

The amount of gas dissolved is directly proportional to its partial pressure

What is the characteristic of FEV1/FVC in obstructive lung disease, such as asthma and COPD?

Decreased FEV1/FVC ratio

What is the correction factor for calculating the partial pressure of oxygen in humidified tracheal air?

47 mm Hg

What is the effect of restrictive lung disease, such as fibrosis, on FEV1 and FVC?

Decreased FEV1, decreased FVC

What is the equation for calculating the partial pressure of a gas?

Partial pressure = Total pressure x Fractional gas concentration

What is the concentration of dissolved oxygen in blood when the partial pressure of oxygen is 100 mmHg?

0.3 mL O2/100 mL blood

What is the partial pressure of oxygen in humidified tracheal air?

100 mmHg

What is the partial pressure of carbon dioxide in alveolar air after equilibration with pulmonary capillary blood?

46 mmHg

What is the effect of oxygen diffusion from alveolar air into pulmonary capillary blood on the partial pressure of oxygen?

It decreases the partial pressure of oxygen

What is the reason for the difference in partial pressure of oxygen between arterial and mixed venous blood?

Oxygen diffusion from arterial blood into tissues

What is the effect of the addition of water to inspired air on the partial pressure of oxygen?

It decreases the partial pressure of oxygen

What is the primary factor that determines the diffusion rate of oxygen and carbon dioxide across the alveolar-pulmonary capillary membrane?

Partial pressure difference of the gases

What is the equation that describes the diffusion of gases across the alveolar-pulmonary capillary membrane?

V = DL/AP

What happens to the lung diffusing capacity (DL) during exercise?

It increases due to increased surface area for diffusion

What type of gas exchange is illustrated by N2O and by O2 under normal conditions?

Perfusion-limited exchange

What is the effect of emphysema on the lung diffusing capacity (DL)?

It decreases due to decreased surface area for diffusion

What is the effect of fibrosis on the lung diffusing capacity (DL)?

It decreases due to increased diffusion distance

What is the relationship between the lung diffusing capacity (DL) and the diffusion coefficient of the gas?

DL is directly proportional to the diffusion coefficient of the gas

What is the equivalent of permeability of the alveolar-pulmonary capillary barrier?

Lung diffusing capacity (DL)

What is the primary limiting factor in perfusion-limited gas exchange?

Blood flow

In which type of gas exchange does the partial pressure difference between alveolar air and pulmonary capillary blood remain throughout the length of the capillary?

Diffusion-limited

What is the effect of thickening of the alveolar membrane on oxygen diffusion?

Decreases diffusion rate

Which of the following is an example of a diffusion-limited gas?

Oxygen during strenuous exercise

What is the primary function of hemoglobin in oxygen transport?

Increasing oxygen-carrying capacity

What is the result of decreased surface area for gas exchange in emphysema?

Decreased oxygen diffusion

In diffusion-limited exchange, what happens to the partial pressure of the gas as blood flows through the pulmonary capillary?

It remains different from the partial pressure in alveolar air

What is the primary mechanism of oxygen transport in the blood?

Oxygen bound to hemoglobin

Which of the following is an example of a perfusion-limited gas?

Oxygen during normal conditions

What is the primary cause of a high A-a gradient in a patient with fibrosis?

Decreased diffusion capacity

What is the value of the respiratory exchange ratio (R) used in the alveolar gas equation?

0.8

What is the normal range of the A-a gradient?

0-10 mm Hg

What is the equation used to calculate the A-a gradient?

PAo2 - Pao2

What is the primary factor that determines the A-a gradient?

Diffusion capacity

What is the effect of a right-to-left shunt on the A-a gradient?

Increased A-a gradient

What is the primary cause of increased A-a gradient?

Right-to-left shunt

What is the effect of decreased hemoglobin concentration on oxygen delivery?

Decreases oxygen delivery

What is the mechanism by which hypoxia-inducible factor 1a is produced in response to hypoxia?

Decreased oxygen delivery to the kidneys

What is the effect of cyanide poisoning on oxygen delivery?

Decreases oxygen delivery

What is the role of erythropoietin in response to hypoxia?

Increases hemoglobin synthesis

What is the equation that describes oxygen delivery?

O2 delivery = Cardiac output x O2 content of blood

What is the enzyme that facilitates the reaction between CO2 and H2O to form H2CO3 in the red blood cells?

Carbonic anhydrase

What is the major form in which CO2 is transported to the lungs?

HCO3-

What is the purpose of the chloride shift in red blood cells?

To exchange Cl- for HCO3-

Why is deoxyhemoglobin a better buffer for H+ ions than oxyhemoglobin?

Deoxyhemoglobin has a higher buffering capacity

What is the significance of the deoxygenation of hemoglobin by the time blood reaches the venous end of the capillaries?

It allows for more efficient transportation of CO2

What is the purpose of the hydration reaction of CO2 in the red blood cells?

To convert CO2 to H2CO3

What is the percentage of cardiac output that bypasses the lungs in right-to-left shunts under normal conditions?

2%

What happens to the arterial P~ when a right-to-left shunt occurs?

It decreases

What is the direction of blood flow in a left-to-right shunt?

From the right side of the heart to the left side of the heart

What is the approximate V/Q ratio in a normal individual?

0.8

What is the effect of a left-to-right shunt on arterial P~?

It increases

What is the purpose of having the patient breathe 100% O2 to estimate the magnitude of a right-to-left shunt?

To estimate the degree of dilution of oxygenated arterial blood by non-oxygenated shunted blood

What is the effect of gravitational forces on arterial pressure in the upright lung?

It decreases arterial pressure at the apex and increases it at the base

Which of the following statements is true about the V/Q ratio in the lung?

It is lowest at the base and highest at the apex

What is the effect of a complete airway blockage on the V/Q ratio?

It makes the V/Q ratio zero

What is the relationship between Po2 and Pco2 at the apex and base of the lung?

Po2 is highest at the apex and Pco2 is lowest at the base

What is the primary reason for the regional differences in ventilation in the upright lung?

Gravitational forces

What is the effect of the regional differences in V/Q ratio on gas exchange?

It increases the efficiency of gas exchange at the apex and decreases it at the base

Which nerve relays information from peripheral chemoreceptors and mechanoreceptors in the lung?

Vagus nerve

What is the effect of airway obstruction on the composition of systemic arterial blood?

It approaches the composition of mixed venous blood.

What is the primary function of the dorsal respiratory group?

Generation of the basic rhythm for breathing

Where is the pneumotaxic center located?

Upper pons

What is the condition where blood flow to a lung is completely blocked, leading to zero blood flow, but ventilation is normal?

Dead space.

What is the location of the medullary respiratory center?

Reticular formation.

What is the role of central chemoreceptors in the medulla?

Detection of CO2 levels

What is the primary function of the apneustic center?

Stimulation of inspiration

What is the effect of a pulmonary embolus on the composition of alveolar gas?

It approaches the composition of inspired air.

What is the term for the situation where ventilation is normal, but blood flow is zero?

Dead space.

What is the role of the ventral respiratory group?

Regulation of expiration

What is the effect of a ventilation-perfusion defect on gas exchange?

It decreases gas exchange.

What is the effect of hyperventilation on breath-holding?

It increases the duration of breath-holding

What is the coordinating center for sensory information in the brain?

Brainstem.

What is the effect of a decrease in pH of the cerebrospinal fluid (CSF) on breathing rate?

Hyperventilation

Why does CO2 diffuse from arterial blood into the CSF?

Because CO2 is lipid soluble

What happens when CO2 combines with H2O in the CSF?

H+ and HCO3- are produced

What is the effect of an increase in Pco2 and [H+] on breathing rate?

Stimulate breathing

What is the response of peripheral chemoreceptors to a decrease in arterial Pco2?

Stimulate breathing

Where are the carotid bodies located?

At the bifurcation of the common carotid arteries

What is the effect of hyperventilation or hypoventilation on arterial Pco2?

Return Pco2 to normal

Why do decreases in pH of the CSF produce increases in breathing rate?

Because H+ acts directly on the central chemoreceptors

What is the role of the central chemoreceptors in regulating breathing?

Respond to changes in CSF pH

Study Notes

Here are the study notes:

  • Respiratory Physiology*

Lung Volumes and Capacities

  • Tidal volume (VT): volume inspired or expired with each normal breath
  • Inspiratory reserve volume (IRV): volume that can be inspired over and above the tidal volume, used during exercise
  • Expiratory reserve volume (ERV): volume that can be expired after the expiration of a tidal volume
  • Residual volume (RV): volume that remains in the lungs after a maximal expiration, cannot be measured by spirometry
  • Dead space: volume of the lungs that does not participate in gas exchange
    • Anatomic dead space: volume of the conducting airways (approximately 150 mL)
    • Physiologic dead space: functional measurement of the volume of the lungs that does not participate in gas exchange (approximately equal to anatomic dead space in normal lungs, but may be greater in lung diseases with ventilation/perfusion defects)

Compliance of the Respiratory System

  • Compliance: describes the distensibility of the lungs and chest wall
  • Equation: C = ΔV / ΔP
  • Describes the change in volume for a given change in pressure
  • Inversely related to elastance and stiffness

Muscles of Inspiration and Expiration

  • Muscles of inspiration:
    • Diaphragm: most important muscle for inspiration
    • External intercostal muscles: not used for inspiration during normal quiet breathing, but used during exercise and in respiratory distress
  • Muscles of expiration:
    • Abdominal muscles: compress the abdominal cavity, push the diaphragm up, and push air out of the lungs
    • Internal intercostal muscles: pull the ribs downward and inward

Lung Disease

  • Asthma: obstructive disease, expiration is impaired, characterized by decreased FVC, FEV1, and FEV1/FVC
  • Chronic Obstructive Pulmonary Disease (COPD): obstructive disease with increased lung compliance, expiration is impaired, characterized by decreased FVC, FEV1, and FEV1/FVC
    • Emphysema: "pink puffers" (mild hypoxemia, normal PCO2)
    • Chronic bronchitis: "blue bloaters" (severe hypoxemia with cyanosis, hypercapnia, and right ventricular failure)
  • Fibrosis: restrictive disease, inspiration is impaired, characterized by a decrease in all lung volumes

Gas Exchange

  • Dalton's law of partial pressures: P = PT x F
  • Partial pressure of O2 and CO2 in inspired air, alveolar air, and blood
  • Dissolved gases: amount of gas dissolved in a solution is proportional to its partial pressure
  • Diffusion of gases: rates depend on partial pressure differences across the membrane and the area available for diffusion
  • Lung diffusing capacity (DL): equivalent to permeability of the alveolar-pulmonary capillary barrier

Oxygen Transport

  • Oxygen is carried in blood in two forms: dissolved or bound to hemoglobin

  • Hemoglobin increases the O2-carrying capacity of blood 70-fold

  • A-a gradient: difference in PO2 between alveolar gas and arterial blood

  • Causes of hypoxemia:

    • High altitude
    • Hypoventilation
    • Diffusion defect
    • V/Q defect
    • Right-to-left shunt
  • Erythropoietin (EPO): a growth factor that is synthesized in the kidneys in response to hypoxia### Hypoxia-Inducible Factor and EPO

  • Hypoxia-inducible factor 1α directs the synthesis of mRNA for EPO, which promotes the development of mature red blood cells.

CO2 Transport

  • CO2 is transported in three forms: dissolved CO2, carbaminohemoglobin, and HCO3- (the major form, accounting for 90%)
  • In the RBCs, CO2 combines with H2O to form H2CO3, which dissociates into H+ and HCO3-
  • HCO3- leaves the RBCs in exchange for Cl- (chloride shift) and is transported to the lungs in the plasma
  • H+ is buffered inside the RBCs by deoxyhemoglobin, which is a better buffer for H+ than oxyhemoglobin

Shunts

  • Right-to-left shunts occur when 2% of the cardiac output bypasses the lungs, resulting in a decrease in arterial P02
  • May be as great as 50% of cardiac output in certain congenital abnormalities, such as tetralogy of Fallot
  • Left-to-right shunts are more common, caused by congenital abnormalities or traumatic injury, and do not result in a decrease in arterial P02

V/Q Defects

  • V/Q ratio is the ratio of alveolar ventilation (V) to pulmonary blood flow (Q)
  • Ventilation and perfusion (blood flow) matching is important for achieving the ideal exchange of O2 and CO2
  • Normal V/Q ratio is approximately 0.8, resulting in an arterial P02 of 100 mm Hg and an arterial Pco2 of 40 mm Hg
  • Regional variations in the lung of perfusion, ventilation, V/Q, P02, and Pco2 occur due to gravitational effects
  • V/Q ratio is higher at the apex and lower at the base of the lung
  • As a result, gas exchange is more efficient at the apex and less efficient at the base

Changes in V/Q Ratio

  • V/Q ratio in airway obstruction: If airways are completely blocked, then ventilation is zero, resulting in a V/Q ratio of 0
  • V/Q ratio in pulmonary embolism: If blood flow to a lung is completely blocked, then blood flow to that lung is zero, resulting in a V/Q ratio of infinity (dead space)

Control of Breathing

  • Central control of breathing involves the brainstem and cerebral cortex
  • Medullary respiratory center is located in the reticular formation and responds to changes in pH of the CSF
  • Peripheral chemoreceptors in the carotid and aortic bodies respond to changes in arterial P02

This quiz covers the concept of forced vital capacity, FEV1, and spirometry in normal subjects and patients with lung diseases such as asthma, COPD, and fibrosis.

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