RT 3005 CardioPulmonary Chapter 3 Pulmonary Function Measurements

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These notes will cover chapter 3 objectives from the textbook and lecture.

Define tidal volume (Vt)

The amount of air inhaled and exhaled with each breath during quiet breathing.

Define inspiratory reserve volume (IRV)

The amount of air that can be forcibly inhaled beyond the Vt

Define expiratory reserve volume (ERV)

The amount of air that can be forcibly exhaled after a normal Vt

Define residual volume (RV)

The amount of air still in the lungs after a forced ERV

Define vital capacity (VC)

The maximum volume of air that can be exhaled after a maximal inspiration VC = IRV + Vt + ERV

Define inspiratory capacity (IC)

The volume air that can be inhaled after a normal exhalation IC = Vt + IRV

Define functional residual capacity (FRC)

The volume of air remaining in the lungs after a normal exhalation FRC = ERV + RV

Define total lung capacities (TLC)

The maximum amount of air that the lungs can accommondate TLC = Vt +IRV+ ERV + RV

Identify the approximate lung volumes and capacities in milliliters in the average healthy man between 20-30 years of age

Vt 500mL
IRV 3100mL
ERV 1200mL
RV 1200mL
VC 4800mL
IC 3600mL
FRC 2400mL
TLC 6000mL

Identify the approximate lung volumes and capacities in milliliters in the average healthy woman between 20-30 years of age

Vt 400-500mL
IRV 1900mL
ERV 800mL
RV 1000mL
VC 3200mL
IC 2400mL
FRC 1800mL
TLC 4200mL

Identify the lung volumes and lung capacities changes that occur in obstruction and restrictive lung disorders

In an obstructive lung disorder, theTLC, RV,Vt, and FRC are increased and the VC, IRV, IC,and ERV are decreased.

In an restrictive lung disorder, the RV,Vt,FRC,VC,IRV,IC and TLC are all decreased.

both disorders disrupt the exchange of oxygen and carbon dioxide between the alveoli and pulmonary capillary blood.

Discuss the clinical connections associated with obstructive lung disorders

characterized by a variety of abnormal conditions of the tracheobronchial tree- bronchial secretions, mucus plugging, bronchospasm, and distal airway weaking that cause a reduction of gas flow out of the lungs and air trapping. The flow of gas is especially reduced during a force exhalation. The FEV1 / FVC ratio is the best indicator of an obstructive lung disorder. The common list of OLD are:
C-cystic fibrosis
B-bronchitis
A-asthma
B-bronchiectasis
E-emphysema
Epiglottitis
Croup

*when chronic bronchitis and emphysema appear together as one disease complex, the patient is said to have chronic obstructive pulmonary disease (COPD)

Discuss the clinical connections associated with restrictive disorders

characterized by any pathologic condition that causes a restriction of the lungs or chest wall--causes a decrease in lung volumes and capacities. Common list of RLD are:
pneumonia
pulmonary edema
flail chest
pneumothorax
pleural effusion
chronic interstitial lung disease
lung cance
acute respiratory distress syndrome
postoperative alveolar collapse (altelectasis)

Compare and contrast how the following methods indirectly measure the residual volume and the capacities containing the residual volume:
Closed circuit helium dilution test

requires the patient to rebreathe from a spirometer that contains a known volume of gas V1 and a know concentration C1 of helium (He), usually 10%. The patient is "switched -in" to the closed-circuit system at the end of a normal Vt breath where only FRC is left in the lungs. A helium analyzer continuously monitors the He concentration. Exhaled CO2 is chemically removed from the system. The FRC, that initially contains no He, mixes with the gas in the spirometer. The test lasts for 7 mins. When the He changes by less than 0.2% of a period of 1sec, the test is terminated. The He concentration at this point is C2. To calculate the V2
V2 = V1C1/ C2

FRC = V2-V1
The RV = FRC-REV
TLC = RV + VC

Compare and contrast how the following methods indirectly measure the residual volume and the capacities containing the residual volume:
Open circuit nitrogen washout test

the patient breathes 100% O2 through aa one way valve for up to 7 mins. The patient is "switched-In" to the system at the end of a normal Vt. At beginning of test nitrogen N2 concentration in the alveoli is 79% C1. During each breath, oxygen is inhaled and N2 from the FRC is exhaled. Over several minutes, the N2 in the patient's FRC is effectively washed out.
In normal lungs this occurs in 3 mins or less. A patient OLD may not wash out completely even after 7 minutes.

During the washout period, the exhaled gas volume is measured and the concentration of N2 is determined by a nitrogen analyzer. Test is complete when N2 concentration drops from 79%-1.5% or less.

The FRC (V1) can be calculated by taking the intial concentration of N2 in the FRC gas (C1), the total volume of gas exhaled during the washout period (V2) and the average concentration of N2 in the exhaled gas (C2).
V1 = C2V2 / C1
FRC= V1-Vbc + Vtis
Vbc Known volume of the breathing circuit
Vtis the volume of N2 excreted into the lungs from the plasma and body tissue during test.

Compare and contrast how the following methods indirectly measure the residual volume and the capacities containing the residual volume:
Body plethysmography test

measures the gas volume within the lungs (thoracic gas volume [Vtg]). The patient sits in an airtight chamber called a body box. The patient is permitted to breathe quietly through an open valve (shutter). Once relaxed, the test begins at the precise moment the patient exhales to the end tidal volume level FRC. The shutter is closed and the Pt is instructed to pant against the closed shutter. Pressure and volume changes are monitored during this period. (Δ Alveolar pressure from compression and decompression of the lungs are estimated by mouth)
there is no airflow during this period, the temperature is constant, the pressure and volume changes can be used to determine the trapped volume (FRC) by using Boyle's Law. This test is considered the most accurate for measuring the RV.

Compare and contrast the following expiratory flow rate measurements:
Forced vital capacity (FVC)

the maximum volume of gas that can be exhaled as forcefully and rapidly as possible after a maximal inspiration. most commonly used pulmonary function measurement.
In the normal individual, the total expiratory time (TET) required to completely exhale the FVC is 4 to 6 sec.
The FVC and the slow vital capacity (SVC) are usually equal.

In the OLD individual, the TETs increases. TETs greater than 10 sec. In Pt with OLD, the SVC is often normal and the FVC is usually decreased because of air trapping.

In the RLD individuals the FVC decreases. The TET needed to exhale the FVC in a RLD, is usually normal or even lower than normal because the wlastticity of the lung is high (low compliance).

Compare and contrast the following expiratory flow rate measurements:
Forced expiratory volume timed

the maximum volume of gas that can be exhaled within a specific time period. measurement obtained from FVC. The most frequently used time period is 1sec.

Normally the % of the total FVC exhaled during these time periods is as follows: FEV0.5 60%, FEV1 83%, and FEV2 94%

OLD patients, have a decreased FEVt
RLD patients, have a decreased FEVt due to the low vital capacity associated with the disorder.
FEVt decreases with age.

Compare and contrast the following expiratory flow rate measurements:
Forced expiratory volume 1 sec / forced vital capacity ratio

the comparison of the amount of air exhaled in 1 sec to the total amount exhaled during an FVC maneuver. Usually expressed in % and commonly referred as a Forced expiratory volume in 1 sec % FEV1%.

In normal adult exhales 83% or more of the FVC in 1 sec FEV1.
An FEV1% of 65% or more is often used as an acceptable value in older patients.

Compare and contrast the following expiratory flow rate measurements:
Forced expiratory flow 25%-75%

is the average flow rate that occurs during the middle 50% of an FVC measurement. This average measurement reflects the condition of medium- to small-sized airways.

In normal healthy men aged 20-30 years is about 4.5 L/sec (270 L/min)
In normal healthy women aged 20-30 years is about 3.5 L/sec (210 L/min).
In OLD, flow rates as low as 0.3 L/sec (18L/min) have been reported.
In RLD, FEF is also decreased in patients because of the low vital capacity.

The FEF 25-75% is similar to measuring,and averaging the flow rate from a water faucet when 25 to 75% of a specific volume of water have accumulated in a measuring container.

Compare and contrast the following expiratory flow rate measurements:
Forced expiratory flow 200-1200

the average flow rate that occurs between 200 and 1200 mL of the FVC. The 1st 200mL of the FVC is usually exhaled more slowly than the average flow rate because of inertia involved in the respiratory maneuver and the unreliability of response time of the equipment.
FEF200-1200 measures exxpiratory flows at high lung volumes, it is a good index of the integrity of large airway function (above the bronchioles).

Flow rates that originate from large airways are referred to as effort-dependent portion of the FVC. The greater the effort the higher the value.

The average FEF200-1200 for healthy men ages 20-30 yrs is about 8 L/sec (480 L/min)
The average FEF 200-1200 for healthy women ages 20-30 is about 5.5L/sec ((330 L/min)

In OLD patients, FEF 200-1200 decreases with age. Flow rates as low as 1 L/sec (60 L/min) have been reported.

In RLD patients, FEF200-1200 decreases due to low vital capacity .
It too, is similar in measuring & averaging the flow rate from a water faucet 200-1200mL has been accumulated in a measuring container.

Compare and contrast the following expiratory flow rate measurements:
Peak expiratory flow rate (FEF Max)

also know as the peak flow rate is the maximum flow rate that can be achieved during an FVC maneuver. The PEFR is commonly measured using a small handheld flow-sensing device called a peak flow meter. The PEFR reflects initial flows originating from large airways during the first part of an FVC maneuver (the effort-dependent portion of the FVC).

In normal healthy men ages 20-30 years is about 10 L/sec (600 L/min)
In normal healthy women ages 20-30 years is about 7.5 L/sec (450 L/min).

PEFR decreases with age and in OLD patients. Used to evaluate gross changes in airway function and to assess the patient's response to bronchodilator therapy.

Compare and contrast the following expiratory flow rate measurements:
Maximum voluntary ventilation

The largest volume of gas that can be breathed voluntarily in and out of the lungs in 1 min. The patient actually performs the test for only 12 sec or a minimum of 6 secs; known as maximum breathing capacity (MBC). A general test that evaluates the performance of the respiratory muscles' strength, the compliance of the lung and thorax, airway resistance, and neural control mechanisms.

In normal healthy men ages 20-30 years is about 170 L/ min
In normal healthy women ages 20-30 years is about 110 L/min.

decreases with age and chronic OLD.
is relatively normal in RLD

Compare and contrast the following expiratory flow rate measurements:
Flow-volume curves

is a graphic presentation of a forced vital capacity (FVC) maneuver followed by a forced inspiratory volume (FIV) maneuver. When the FVCc and FIV are plotted together, the illustration produced by the two curves is called a flow-volume loop. The loop campares both the flow rates and volume changes produced at ddifferent points of an FVC and FIV maneuver. It does not measure the FEF200-1200 and FEF25-75% it does show the max flows(Vmax) at any point of the FVC.

In healthy individuals, the FEF50% (Vmax50) is a straight line because the expiratory flow decreases linearly with volume throughout most of the FVC range.

In OLD, the flow rate deccreases at low lung volumes, causing the FEF50% to decrease. This causes a cuplike or scooped out effect on the flow volume loop.

The following measurements can be obtained from the flow volume loop.
PEFR PIFR FVC FEVT
FEF25% FEF75% FEF50% FEV1/
(VMAX50) FVC RATIO
(FEV1%)

Identify the following average dynamic flow rate measurements for the healthy man and woman between 20 and 30 years of age:
Forced expiratory volume timed for periods of 0.5, 1.0,2.0, and 3.0

men
FEV0.5 60%
FEV1.0 83%
FEV2.0 94%
FEV3.0 97%
women
FEV0.5 60%
FEV1.0 83%
FEV2.0 94%
FEV3.0 97%

Identify the following average dynamic flow rate measurements for the healthy man and woman between 20 and 30 years of age:
Forced expiratory flow 200-1200

men
8 L/ sec (480L/min)
women
5.5 L/sec (330L/min)

Identify the following average dynamic flow rate measurements for the healthy man and woman between 20 and 30 years of age:
Forced expiratory flow 25-75%

men
4.5 L/sec (270L/min)
women
3.5 L/sec (210L/min)

Identify the following average dynamic flow rate measurements for the healthy man and woman between 20 and 30 years of age:
Peak expiratory flow rate

men
10 L/sec (600L/min)
women
7.5 L/sec (450L/min)

Identify the following average dynamic flow rate measurements for the healthy man and woman between 20 and 30 years of age:
Maximum voluntary ventilation

men
170 L/min
women
110 L/min

The best predictor for OLD

FEV1

The best predictor for RLD

FVC

The three most commonly used pulmonary function measurements to
1. differentiate between OLD and RLD
2. determine the severity of a pt pulmonary disorder.

FVC,FEV and FEV1 /FEV Ratio

In RLD patients...

can only inhale smaller volumes of air. As a result, only smaller volumes of air can be exhaled-a smaller FVC and FEV1. The FEV1% is normal or increased.

In OLD patients...

the FEV1 is reduced because of early airway closure and air trapping. (the trapped air is blocked from being available for the FVC measurement) The FEV1% is decreased. a normal FEV1% is 83% or greater. OLD pt will exhale less than 70% of the FVC in 1 sec.

Describe the clinical connection associated with FEV1 / FVC ratio and FEV1 in the assessment and management of chronic obstructive pulmonary disease (COPD)

The Global Initiative flro Chronic Obstructive Lung Disease (GOLD) provides an excellent framework using the FEV1 / FVC ratio commonly written as: FEV1% and FEV1 values to categorize a patient's COPD as Stage 1 (mild), Stage 2 (moderate), Stage 3 (severe) and sstage 4 (very severe).

Example: COPD patient with ans FEV1 / FVC ratio of 65% of predicted and an FEV1 of 45% of predicted, the severity of the patient's COPD would be classified as Stage 3. The following chart will show the actions required in this case.

MANAGEMENT OF COPD AT EACH STAGE

Stage 1 (mild)
*FEV1 / FVC < 70%
*FEV1 > 80% predicted
-Aggressively work to reduce all risk factors
-Influenza vaccination
-Administer short-acting (reliever agents) bronchodilators when needed

Stage 2 (moderate)
*FEV1 / FVC < 70%
*FEV1 between 80% and 50% of predicted
-Aggressively work to reduce all risk factors
-Influenza vaccination
-Administer short-acting (reliever agents) bronchodilators when needed
-Administer one or more long-acting (controller agents) bronchodilators as needed
-Pulmonary rehabilitation

Stage 3 (severe)

*FEV1 / FVC < 70%
*FEV1 between 50% and 30% of predicted
-Aggressively work to reduce all risk factors
-Influenza vaccination
-Administer short-acting (reliever agents) bronchodilators when needed
-Administer one or more long-acting (controller agents) bronchodilators as needed
-Pulmonary rehabilitation
-Administer inhaled glucocorticosteroids for repeated exacerbation

Stage 4 (very severe)
*FEV1 / FVC < 70%
*FEV1 < 30% predicted or FEV1 <50% predicted plus chronic ventilator failure
-Aggressively work to reduce all risk factors
-Influenza vaccination
-Administer short-acting (reliever agents) bronchodilators when needed
-Administer one or more long-acting (controller agents) bronchodilators as needed
-Pulmonary rehabilitation
-Administer inhaled glucocorticosteroids for repeated exacerbation
-Add long term Oxygen Therapy Protocol (e.g., low F1O2 via nasal cannula)

Describe the clinical connection associated with differentiating between an obstructive and restrictive lung disorder

The FVC, FEV, and FEV1% are commonly used to determine ifia patient is suffering from either an obstructive lung disorder or a restrictive lung disorder. After performing a bedside spirometry test on a patient if the following pulmonary function values read:

PFT Measurement Predicted Actual % of Predicted
FVC 4.5L 3.4L 75%
FEV1 3.6L 2.1 58%
FEV1%
(FEV1/ FVC ratio) >83% 62% -----


An FEV1% lower than predicted means the patient is demonstrating an obstructive lung problem. Only a patient with an obstructive lung disorder has a reduced FEV1%. When a patient has a restrictive lung problem, the FEV1% is either normal or increased.

Describe the clinical connection associated with an asthma action plan--green,yellow, and red zones.

a guide to help monitor the asthma and determine what to do in response to specific symtoms. A patient is given a peak flow meter and taught to perform the measurement. The peak flow meter is a very important diagnostic tool to help monitor a patient with moderate to severe asthma. Over the course of days and weeks, the patient records his or her personal best peak flow. The patient can actually identify when an asthmatic epidsode is getting worse--even before they feel the symptoms.

A common asthma action plan is divided into 3 zones--green, yellow and red.

The green zone is 80% or better of the personal best peak flow. This is where the patient should be on the daily basis.

The yellow zone is a peak flow that falls between 80% and 50% of the personal best peak flow. The yellow is a warning that the asthma is getting worse and action is needed to prevent an asthmatic attack.

The red zone is less than 50% of the patients personal best peak flow. The red is means the patient is in immediate DANGER and emergency action must be taken right AWAY!

Describe the clinical connection associated with both an obstructive and restrictive lung disorder

A patient (no history of pulmonary disease) enters a hospital and complains of frequent coughs and shortness of breath. The patient further informs the RT that the symptoms developed shortly after breathing paint fumes while working in a small and confined area. Because of the FEVT adn PEFR) all were decreased. In addition, because of the mucus plugging ans subsequent alveolar collapse, the patient's lung volumes and capacities (RV,FRC, and VC) all decrease. This is an example of a patient with an acute obstructive and restrictive lung disorder. With appropriate treatment, the acute pulmonary problems often resolve without long term injury. Chronic OLD and RLD will not resolve.

Describe the effort-dependent portion of a forced expiratory maneuver

the first 30% of an FVC maneuver, the maximum peak flow rate is dependent ont he amount of muscular effort exerted by the individual.

Describe the effort-independent portion of a forced expiratory maneuver

the flow rate during the last 70% of an FVC maneuver. after a maximum flow rate has been attained, the flow rate cannot be increased by further muscular effort.

As lung volumes decline, flow also declines.

Explain how the dynamic compression mechanism limits the flow rate during the last 70% of a forced vital capacity and define the equal pressure point.

The limitation of the flow rate that occurs during the last 70% of an FVC maneuver is due to the dynamic compression of the walls of the airways. As gas flows through the airways from the alveoli to the atmosphere during passive expiration, the pressure within the airways diminishes to 0.

During a forced expiratory maneuver, however,as the airway pressure decreases from the alveoli to the atmosphere, there is a point at which the pressure within the lumen of the airways equals the pleural pressure surrounding the airways. This point is called the equal pressure point.

Downstream from the equal pressure point, the lateral pressure within the airway becomes less than the surrounding pleural pressure. Consequently, the airways are compressed. As muscular effort and pleural pressure increase during a forced expiratory maneuver, the equal pressure point moves upstream. Ultimately, the equal pressure point becomes fixed where the individual's flow rate has achieved maximum.

Describe the clinical connection associated with how spirometry can confirm dynamic compression

Based on Case 1 on page 174.
Brief Info:
16 year old with a long history of asthma was rushed to the emergency room. The patient had used her rescue inhaler prior to ER admittance but her condition worsened. CC & c/o of SOB. Signs of Cyanosis, BP 180/110 mm Hg, HR 130 bpm,RR 36bpm, and temp 37 degree C. Patient was placed on 4 L/min O2 via nasal cannula, Pulse Ox 83%. Chest X-ray showed hyperinflation and her diaphragm was depressed.
1st good effort
Bedside Spirometry
Parameter
FVC
Predicted
2800mL
Actual
1220 mL
Parameter
FEV1
Predicted
> 83%
Actual
44%
Parameter
PEFR
Predicted
400 L/min
Actual
160 L/min
The mother of the 16 yr old stated that her daughter's personal best (PEFR) at home was 360 L/min. RT increased flow to 6 L/min, given continuous bronchodilator therapy by nebulizer and started on an intravenous infusion. a mechanical ventilator was on standby.
2nd good effort (1 hour later)
Bedside Spirometry
Parameter
FVC
Predicted
2800mL
Actual
2375 mL
Parameter
FEV1
Predicted
> 83%
Actual
84%
Parameter
PEFR
Predicted
400 L/min
Actual
345 L/min
Vitals within normal range.
The case demonstrated hw the measurement of a patient's pulmonary mechanics can serve as an important clinical monitor.
The effects of the effort-independent portion of an FVC, dynamic compression, and the equal pressure point. This case shows that even when the patient makes a strong muscular effort on a FVC test, the closure of her airways--caused by equal pressure point changes and dynamic compression moves closer to her alveoli. This action, in turn further increases airway resistance and offsets any improvements in the FVC.

Describe the clinical connection associated with pursed-lip breathing.

commonly seen in COPD patients. It is a technique many patients learn without formal training. Pursed-lip breathing is characterized by a deep inhalation followed by prolonged expiration through pursed lips--similar to that used for whistling, kissing or blowing through a flute. This technique increases the airway pressure during exhalation and works to offset the adverse effects of dynamic compression--which causes early airway collapse,air trapping and alveolar overinflation.

This method creates a natural continuous positive airway pressure (CPAP) to hold the airways open from the inside. This technique has been shown to decrease the patient's breathing rate and yield a ventilatory pattern that is more effective in alveolar gas mixing.

Describe the diffusion capacity of carbon monoxide study

The DLCO study measures the amount of carbon monoxide (CO) that moves across the alveolar-capillary membrane. CO has an affinity for hemoglobin that is about 210X greater than that of oxygen. In individuals who have normal amounts of hemoglobin and normal ventilatory function, the only limiting factor to the diffusion of CO is the thickness of the alveolar capillary membrane.

This study measures the physiologic status of the various anatomic structures that compose the alveolar capillary membrane.

The CO single breath technique is commonly used for this measurement.

In normal individuals the average DLCO value for the resting male is 25mL/min / mm Hg (Standard temperature and pressure, dry (STPD)). In females the number is slightly smaller because of their smaller normal lung volumes.
Exercise increases the DLCO 3X and decrease with individuals with lung disorders.
The following disorders will decrease the DLCO:
emphysema, chronic interstitial lung disease, pneumonia (alveolar consolidation), pulmonary edema, and acute respiratory distress syndrome.

Describe how the following are used to evaluate the patient's ability to maintain spontaneous, unassisted ventilation:
Maximum imspiratory pressure (MIP)

is directly related to muscle strength. MIP is used to evaluate the patient's ability to maintain spontaneous unassisted ventilation. MIP is measured while the patient inhales and exhales through an endotracheal tube that is attached to a pressure gauge. MIP should be measured at the patient's residual volume. The patient is ready for a trial of spontaneous or unassisted ventilation when the MIP is greater than -25 cm H2O.

In healthy males :
MIP -125 cm H2O
In healthy females:
MIP -90 cm H2O

Describe how the following are used to evaluate the patient's ability to maintain spontaneous, unassisted ventilation:
Maximum expiratory pressure (MEP)

is directly related to muscle strength. MEP is used to evaluate the patient's ability to maintain spontaneous unassisted ventilation. MEP is measured while the patient inhales and exhales through an endotracheal tube that is attached to a pressure gauge. MEP should be measured at the patient's total lung capacity. The patient is ready for a trial of spontaneous or unassisted ventilation when the MEP is greater than 50 cm H2O.

In healthy males:
MEP 230 cm H2O
In healthy females:
150 cm H2O

Describe how the following are used to evaluate the patient's ability to maintain spontaneous, unassisted ventilation:
Rapid shallow breathing index (RSBI) ratio

is commonly used to help determine if a mechanically ventilated patient can be successfully weaned of the ventilator. The RSBI is the ratio of the patient's spontaneous breathing rate(bpm) to the tidal volume (liters) also referred to as the frequency to tidal volume (f/Vt) ratio. The RSBI is considered an excellent clinical predictor of weaning success in mechanically ventilated patients. RSBI is an easy test to perform and is independent of the patients effort and cooperation.

The RSBI measurement is taken 1 minute after disconnecting the spontaneously breathing patient from the ventilator. When the RSBI is below 105 (normal range is 60-105) it is considered successful.

>105 idicates that the patient will likely fail a weaning trail.
Ex. a patient demonstrates a spontaneous ventilatory rate of 28 bpm and an average Vt of 0.35liter, the patient's RSBI would be calculated

RSBI = 28bpm / 0.35 L = 80
this patient is clearly below the threshold criteria of 105, and assuming all other weaning criteria are acceptable, the patient will likely be successfully weaned off the ventilator. See # 48

Describe the clinical connection associated with the ventilatory mechanics used to predict mechanical ventilation weaning success.

RT uses a number of pulmonary function measurements to evaluate the patient's readiness to be successfully weaned off a mechanical ventilator.

Common Pulmonary Function Measurements Used to Determine Readiness for Weaning and Ventilator Discontinuation

Measurements
Spontaneous breathing trial
Criteria
Tolerates 12-30 min
Measurements
Respiratory rate (f)
Criteria
< 30 bpm
Measurements
Tidal Volume (Vt)
Criteria
> 5-8 mL/kg
Measurements
Vital Capacity (VC)
Criteria
> 10-15 mL/kg
Measurements
Minute Ventilation (Ve)
Criteria
< 10-15 L/min
Measurements
Maximum inspiratory pressure (MIP)
Criteria
> -20 to -30 cm H2O in 20 sec
Measurements
Dead space to tidal volume ratio (VD/Vt)
Criteria
< 0.6
Measurements
Static lung compliance (CL)
Criteria
> 25 mL/cm H2O
Measurements
Rapid shallow breathing index (RSBI) ratio or (f/Vt)
Criteria
<100 (spontaneous breathing pattern)

Additional pulmonary measurements used to help determine the possible success of weaning a patient off of a mechanical ventilator include:
1. acid-base evaluations
2. oxygenation assessments,
3. work of breathing measurements (dynamic or static compliance).

Factors affecting predicted normal values

A number of factors affects the normal predicted lung volumes and capacities, include height, weight, age , gender and race.

height is the most important factor that affects pulmonary function. Taller patients have higher pulmonary values. ** an individual's height is not as significant in expiratory flow rate measurements (FVC,FEV1, or PEFR). In kids pulmonary function values are directly related to height than age until they reach 60 in.

weight is sometimes taken into account along with height. As weight increases beyond a patient's normal, lung volumes decrease.

age can affect a patient's normal lung volumes and capacity values. After 25, lusng volumes, expiratory flow rates and diffusing capacity decreases.

gender of the patient affects the predicted normal pulmonary function values. Male subjects have higher lung volumes, expiratory flow rates and diffusing capacities than females of the same age and height.

Simple Interpretation (Obstructive)

Decreased flow
FEV1
FEV1%
FEF 200-1200
FEF 25%-75%
FEF Max (PEFR)
Increased lung vol

Simple Interpretation (Restrictive)

Decreased vol
FVC
FEV1% increased
Reduced lung vol

note***

When we trap more air in the lungs, the vital capacity shrinks and the peak flow decreases.

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