Pulmonary function and medical diagnostics

Medical diagnostics

-chest x-ray

-MRI

-CT scan

-V/Q scans (ventilation/perfusion)

-Bronchoscopy

-PFT and ABGs

-Oximetry

Pulmonary function testing provides info about

-integrity of airways

-function of respiratory musculature

-condition of lung tissues

Most common pulmonary function tests

-spirometry

-diffusing capacity of the lung for CO (DLCO)

-helium lung volumes

spriometry

-max inhalation followed by max exhalation

-measures volume of air and time

-data obtained: FVC, FEV1, FEV1/FVC,VC

Diffusing capacity of the lung for CO

-inhalation of fixed concentration of CO and helium, breath holding for 10 sec, then expiration with measurement of end-tidal CO and helium

-data obtained: uptake and diffusing capacity of CO

Helium lung volumes

-Maximal expiration, then inhalation of a known concentration of helium until steady state is reached

-data obtained: RV, ERV, IRV, TV with calculation of TLC, VC, FRC, IC

Lung volumes and capacities

Inspiratory Reserve Volume (IRV)

-amount of air that can be forcefully inhaled after a normal tidal volume inspiration

Functional Residual Capacity (FRC)

-volume of air remaining in the lungs after a normal tidal volume expiration

-ERV+RV

Vital capacity

-The total volume of air that can be exhaled after maximal inhalation.

-ERV+IC

Tidal volume

-Amount of air that moves in and out of the lungs during a normal breath

-~500 mL

Expiratory reserve volume

-Amount of air that can be forcefully exhaled after a normal tidal volume exhalation

Residual volume

-Amount of air remaining in the lungs after a forced exhalation

Total lung capacity

-vital capacity + residual volume

Normal IRV

-1.9-2.5 L

Normal TV

-0.4-0.5L

Normal ERV

-1.1-1.5L

Normal RV

-1.5-1.9L

Normal TLC

4.9-6.4L

Normal IC

-2.3-3.0L

Normal FRC

-2.6-3.4L

Normal VC

-3.4-4.5L

Spirogram

-graphic tracing related to lung function

-performed using spirometers

-often conducted at bedside using simple equipment

Body Plethysmography (Body Box)

-Measures gas volume within the lungs indirectly by using a modification of Boyle's law

-pt sits in airtight chamber

-determines how much air is in lungs after taking a deep breath

-also measure air left in lungs after max exhale

Test of gas flow rates (PFT)

-measure of airflow rates during forced breathing maneuvers

PFT provide info on

-lung function

-degree of impairment

-general location of problem

Forced Vital Capacity (FVC)

-max volume of gas exhaled as forcefully and quicklyb as possible

Normal FVC is

- ~4L

Forced expiratory volume in 1 second (FEV1)

-volume of air exhaled during first second of the FVC

FEV1 reflects airflow in _______ airways.

-large

Peak expiratory flow (PEF)

-max flow that occurs at any point in time during FVC

Normal PEF

-9-10 L/sec

DLCO assess what?

-lungs ability to transfer gas from inspired air to the blood stream

What does DLCO measure?

-uptake of CO per unit time per mm of driving pressure of CO

DLCO is used to evaluate _________ and _________ lung disease

-parenchymal

-non-parenchymal

Abnormal values of DLCO are attributed to what 3 factors

-decreased qty of hemoglobin per unit vol of blood

-increased thickness of the alveolar-capillary membrane

-decreased functional surface area avail for diffusion*** main reason

Flow volume loop

-Graphic presentation of FVC maneuver followed by forced inspiratory volume (FIV) maneuver

Normal flow volume loop

-Upsidedown ice cream cone

Flow volume loop of obstructive lung disease

-graph B

Flow volume loop of restrictive lung disease

-Graph C

Flow volume loop of tracheal stenosis

Another flow-volume loop

GOLD

-Global initiative for chronic obstructive lung disease

Mild COPD (I)

-FEV1/FVC <0.7

-FEV1 >/= 80% predicted

-pt may not be aware that their lung function is abnormal

Moderate COPD (II)

-FEV1/FVC <0.7

-50%

Severe COPD (III)

-FEV1/FVC <0.7

-30%/= FEV1<50% predicted (btwn 30-50%)

-SOB worsens and limits ADLs.

-Exacerbations begin in this stage

Very severe COPD (IV)

-FEV1/FVC <0.7

-FEV1 <30% predicted

-QOL very impaired

-exacerbations may be life-threatening

Interpretation of basic PFTs

-determine if results are normal

-determine whether results indicate OLD or RLD

-if OLD, determine reversibility

-consider hx and phys exam along with PFTs to determine disease progression

-be cautious of results if poor pt effort existed

OLD is considered reversible if

-there is a 12% increase in post-bronchodilator values in at least 2 parameters (FEV1, FVC or FEF 25-75%)

OLD value recap

-FEV1 decrease

-FVC normal/low

-FEV1/FVC < 0.7

-RV increase

-TLC increase

-DLCO decrease

RLD recap

-FEV1 decreased or normal

-FVC decrease

-FEV1/FVC normal

-RV decrease

-TLC decrease

-DLCO decrease

Blood gas analysis

-assesses problems related to acid-base balance, ventilation and oxygenation

Typical arterial blood gas (ABG) report has

-arterial pH

-PaCO2

-PaO2

-SaO2

-HCO3- (bicarb) concntration

-base excess

ABG chart

-PaO2 normal 80-100 mmHg (hypoxemia/hyperoxemia)

-PaCO2 normal 35-45 mmHg (hypo/hypercapnia)

-H+ concentration (pH) normal 7.35-7.45 (acid/alkalosis)

-SaO2 normal >95% (hypo/hyperoxemia)

-bicarb level (HCO3-) normal 22-26 mEq/L

-Base excess normal-2 to +2 mEq/L-1 (abnormal suggests metabolic process)

base excess measures

-availability of bicarb

- (-) is a base deficit

- (+) is a base excess

- >2 -->alkalosis

- <-2-->acidosis

oxyhemoglobin dissociation curve

-increase in temp will cause downward/right shift

hypoxemia (PaO2)

-mild 60-79 mmHg

-moderate 40-59 mmHg

-severe < 40 mmHg

Hyperventilation

- PaCO2<30mmHg

Hypoventilation

-PaCO2 btwn 30-50 mmHg

Ventilatory failure

-PaCO2>50 mmHg

Lung and kidneys regulate 2 types of acids

-volatile: carbonic acid (lung)

-non-volatile: lactic acid (kidney)

Normal human blood pH

-7.4

pH <7.4

-acidic

-low HCO3- lead to metabolic acidosis

-high PaCO2: respiratory acidosis

pH of >7.4

-alkaline

-High HCO3- metabolic alkalosis

-Low PaCO2 respiratory alkalosis

Metabolic acidosis

Metabolic alkalosis

Respiratory acidosis

Respiratory alkalosis

Fully compensated

-pH normal

-PaCO2 & HCO3 abnormal

Partially compensated

-All 3 values will be abnormal (pH, PaCO2, HCO3)

Uncompensated

-pH and one other value is abnormal (PaCO2, HCO3)

Pulse oximetry based on 2 physical principles

-presence of pulsatile signal generated by arterial blood

-fact that oxyhemoglobin and reduced Hb have different absorption spectra

Pulse ox is most reliable

-in 90's