Spirometry Flashcards
What is recoil?
Ability to return resting volume once stretched
- lung recoil- inward force produced by the elastic properties of the alveoli; acts to collapse the lung
- Chest wall recoil (PCWR)- outward force produced by the chest wall
What is intrapleural pressure?
- The pressure within the pleural cavity
- The opposing recoil forces of the chest wall and the lung creates a negative (subatmospheric) PIP
What causes a negative intrapleural pressure?
A negative pleural pressure results from the elastic recoil of the lungs and chest wall pulling in opposite directions. The stretched lung (at the end of a normal expiration) tends to recoil inwardly, and the chest waLL tends to recoil outwardly, but in equal and opposite directions. Consequently, pleural pressure (PpI) b3comes negative (I.e., less than atmospheric pressure). Rupture or puncture of the lung or chest wall results in a pneumothorax, during which the trans pulmonary pressure becomes zero and elastic recoil causes the lung to collapse. The mediastinal membrane prevents the other lung from collapsing
What is pneumothorax?
The presence of air or gas in the pleural cavity
Tension pneumothorax- cause a shift of the mediastinum and compromise hemodynamic stability
Causes:
Spontaneous
Traumatic
What does spirometry do?
Measures lung volume
What is tidal volume?
The volume of air inhaled or exhaled with each normal breath
What is inspiratory reserve volume (IRV)?
The volume of air that can be inhaled at the end of a normal tidal inspiration
What is expiratory reserve volume (ERV)?
The volume of air that can be exhaled after the end of a tidal exhalation
What is residual volume?
The air remaining in the lungs after a maximal expiration (this volume of gas cannot be expelled, and cannot be measured by spirotremy)
What is functional residual capacity (FRC)?
The total volume of air remaining in the lungs at the end of a tidal exhalation
What is the total lung capacity?
The volume of air in the lungs at the end of a maximal inspiration
What is the vital capacity?
The volume of air exhaled from maximal inspiration to maximal exhalation; maximum expiration. When done with force this volume is termed the forced vital capacity (FVC)
What is forced expiratory volume in 1 second(FEV1)?
The volume of air exhaled in the first second of a FVC test
What is the purpose of FEV and FVC1?
From total lung capacity there is forceful exhalation into the spirometer
Measurements of FVC, FEV1 and FEV1/FVC ratio are obtained and restrictive disorders
What is an obstructive disorder?
expiratory flow rate is significantly decreased resulting in decreased FEV1 and FVC
-The FEV1/FVC ratio is low
What is a restrictive disorder?
Lung inflation is decreased resulting in decreased FEV1 and FVC
The FEV1/FVC ratio is normal or increased
W(at is a normal FEV1/FVC ratio?
4.5/5.5L*100= about 80%
Explain the use of FEF25-75
Forced expiratory flow(FEF)
Represents the expiratory flow rate over the middle half of the FVC (between 25% and 75%)
Small airway obstruction may be present even when the FEV1/FVC is above the lower limit of normal
FEF25-75 has the greatest sensitivity for the deduction of early airflow obstruction
What happens in FEV1/FVC in restrictive lung disease?
Both FEV1 & FVC is reduced
The FEV1/FVC ratio remains normal or may be increased
What happens in FEV1/FVC obstructive lung disease?
FEV1 is reduced significantly
FVC is reduced
FEV1/FVC ratio is below 0.8
Summarize obstructive disease
Expiratory flow rate decreased
Airway occlusion, air trapping
Examples:
- Chronic bronchitis
- Emphysema
- Asthma
Summarize restrictive lung diseases
Lung inflation is decreased
Intrinsic- lung tissue
Extrinsic - chest wall, pleura or neuromuscular
Examples:
- Pulmonary fibrosis
- IRDS
- Scoliosis
What is emphysema ?
Disintegration of the lungs elastic framework and destruction of alveolar
Enlargement of air spaces distal to the terminal bronchioles
Signs of air trapping- prolonged expiratory phase, barrel chest, flat diaphragm
Commonly caused by cigarette smoking
Genetic risk factor- alpha-1-antitrypsin (AAT) deficiency
Contrast main difference in flow volume loops in restrictive and obstructive lung diseases
Obstructive lung volumes> normal (increased TLC, FRC, RV); restrictive lung volumes < normal. In obstructive, FEV1 is more dramatically reduced compared with FVC —> decreased FEV1/FVC ratio. In restrictive, FVC is more reduced or close to same compared with FEV1–> increased or normal FEV1/FVC ratio
What is independent effort portion of the flow volume loop?
Despite varying effort of exhalation the latter parts of the curves all merge
Explain effort dependence/independence
The curve is effort dependent until PEF is achieved
Regardless of effort the flow after PEF is limited due to compressed airways (effort independence)
Dynamic Compression of Airways increases resistance to airflow
This effect is magnified in lungs with low elastic recoil (high compliance)- airways are floppy and the lung recoil does little to augment airway pressures above +ve intrapleural pressure during forced expiration
What is COPD?
Combination of chronic bronchitis, emphysema and asthma
The most common chronic lung disease in the US
Commonly caused by cigarette smoking
The classical feature is decreased airflow due to chronic obstruction of the small airways
Results in a decrease in FVC, FEV1 and FEV1/FVC ratio
In severe cases air is trapped in the lungs during forced expiration
What is a peak flow device?
Used for monitoring lung disease
Provides information about exacerbations
Objective data is collected the practitioner
What is Helium dilution technique?
Useful in healthy individuals with no lung obstruction
Helium doesn’t get beyond obstruction, thus yielding a false FRC
Body plethysmography
Known concentration of helium in a known volume of gas (oxygen) in spirometer
Person is asked to breathe until the gas equilibrates between the spirometer & the lungs
C1 x C2= C2 x (V1 + V2)
From this
V2= FRC/RV/TLC (depending on starting time)
What is a Body Plethysmograph?
Body box
Airtight box that measures changes in pressure and volume on inspiration and expiration
Boyles law is used to estimate lung volume
What does Body Plethysmograph measure?
Measures functional residual capacity. The subject sits in an airtight box and breathes air through a mouthpiece. The mouthpiece is closed at the end of a normal expiration, and the subject continues to try to breathe against a closed mouthpiece. P1 is the lung pressure at the end of expiration and P2 at the end inspiration. 🔼V is the volume change accompanying inspiration and expiration; It results from changes in thoracic volume against a closed mouthpiece. The body plethysmograph is used clinically for measuring FRC in patients in patients with airway obstruction
Contrast patient demographic for COPD and Asyhma
Age of onset: COPD- above 35, asthma- any age
Onset of dyspnea: COPD- gradual asthma- sudden
Productive cough: COPD- years asthma- with attack
Childhood wheeze: COPD- uncommon. asthma- common
Family history: COPD- uncommon asthma- common
Smoking history: COPD- yes Asthma- variable
Contrast FEV1 and FVC stats in COPD and asthma
FEV1 & FVC: COPD- reduced asthma- reduced during an attack
FEV1:FVC: COPD- reduced asthma- reduced during an attack
VC: COPD- reduced asthma- nearly normal
Response to steroids and bronchodilator: COPD- minimal asthma- strong
