Pulmonary Function Testing&

ARDS

IM Residency Lecture Series

1/26/05

Evan T. Lukow D.O.

Goal: To understand how to interpret Pulmonary

Function Tests and how they relate to certain disease states.

• The Resident will:• Understand the basic physiology behind PFT’s and how they

relate to lung function.

• Understand what the specific components of PFT’s are.

• Learn to recognized specific pulmonary disease by what PFT values are obtained.

• Recognized patterns of flow-loop diagrams as they relate to respiratory pathology.

• Develop a basic understanding of Acute Respiratory Distress Syndrome and its current treatment.

Basic Lung Physiology:

• Pulmonary Function Testing evaluates the concepts of normal lung function:• Mechanics (airflows and lung volumes).

• Ventilation-Perfusion relationships.• Ventilation – the process of generating the forces required to move

the needed volumes of air from the atmosphere to the alveoli to meet the overall needs of the body.

• Perfusion – the amount of blood that is oxygenated at the alveoli and transported to the tissues to meet the metabolic demands of the body.

• Diffusion/Gas exchange.

• Respiratory muscle (bellows) strength.

Lung Volumes:

Why PFT’s?• Screening for obstructive or restrictive lung disease.

• Pre-op evaluation of a patient:• Patients older than 65

• Known pulmonary disease

• Obesity

• History of smoking, cough, or wheeze

• Large anesthesia requirements (time)

• Extensive abdominal of thoracic procedures

• When weaning a patient from the ventilator:• Vital capacity of 10-15 mL/Kg is sufficient reserve to extubate.

• Monitoring progression and treatment of pulmonary disease.

What are PFT’s?• Four main components:

• Spirometry

• Bronchoprovocation

• Flow-Volume Loops

• Diffusing Capacity

What do PFT’s give us?

Obstructive vs. Restrictive

Common Obstructive Lung Diseases

Common Restrictive Lung Diseases

•Asthma •Asthmatic bronchitis •Chronic obstructive bronchitis •Chronic obstructive pulmonary disease (COPD includes asthmatic bronchitis, chronic bronchitis, emphysema and the overlap between them). •Cystic fibrosis •Emphysema

•Idiopathic pulmonary fibrosis •Interstitial pneumonitis •Infectious inflammation (eg, histoplasmosis, mycobacterium infection) •Sarcoidosis/beryllium disease •Thoracic deformities •Congestive heart failure •Neuromuscular diseases

 

Spirometry:

Normal Spirogram

Obstructive Spirogram

RV, FRC, and TLC are increased

VC is decreased

Expiration is prolonged FEV1/FVC less than 75%

Restrictive Spirogram

ALL lung volumes are reduced

Tidal volume is rapid and shallow

FEV1/FVC is normal, because both values are decreased

RULE of THUMB:

•Normal PFT Outcomes - > 85 % of predicted values

•Mild Disease - > 65 % but < 85 % of predicted values

•Moderate Disease - > 50 % but < 65 % of predicted values

•Severe Disease - < 50 % of predicted values

Flow-Volume Profile:

In a simplistic way, respiratory disease can be classified as obstructive or restrictive processes. Obstructive disorders, such as emphysema or asthma, are characterized by airflow limitation, have increased lung volumes with air trapping, and have normal or increased compliance (based on pressure volume profile). In contrast, restrictive disorders such as pulmonary fibrosis are characterized by reduced lung volumes and an increase in overall stiffness of the lungs (with reduced compliance)

Bronchoprovocation:• Used to define whether airway hyper-reactivity cause

pulmonary complaints.

• Inhalational challenge tests, histamine and methacholine, are used along with standard spirometry to determine if pulmonary function is affected after administration of these airway irritants.

• If there is a 20% decrease in FEV1, the test is considered positive for airway hyper-reactivity.• Sensitive for Bronchial Asthma.

• False positives with COPD, URI, Allergic rhinitis, CHF.

Flow-Volume Loops:• The flow-volume loop is generated by continuously

recording flow and volume with an electronic spirometer during a forced inspiratory and expiratory VC maneuver.

• The shape of the loop reflects the status of the lung volumes and airways throughout the respiratory cycle.

• Characteristic changes occur in restrictive and in obstructive disorders.

• The loop is especially helpful in detecting laryngeal and tracheal lesions.

NORMAL RESTRICTIVE

(i.e. Sarcoidosis, Kyphoscoliosis)

OBSTRUCTIVE

(i.e. COPD, Asthma)

FIXED UPPER AIRWAY

OBSTRUCTION

(i.e. Tracheal Stenosis, Goiter, B/L Vocal Cord

Paralysis)

Variable Extra-Thoracic

Obstruction

(i.e. Vocal Cord Paralysis)

Variable Intra-Thoracic

Obstruction

(i.e. Tracheomalacia)

Diffusing Capacity:DLCO

• Used in conjunction with spirometry to evaluate the amount of damage at the cellular level.

• Take Home Points:

• DLCO is decreased with decreased surface area, decreased hemoglobin, interstitial lung disease, and pulmonary vascular disease.

• Please reference handout for more specific breakdowns.

ARDS: Acute Respiratory Distress Syndrome

Basics of ARDS:

• ARDS is respiratory failure with various acute pulmonary injury.

• Characterized by the triad of:• Hypoxemia

• Respiratory Distress

• Non-Cardiogenic Pulmonary Edema

Etiology:

• Airway• (Drowning)

• Circulation • (Sepsis) – MOST COMMON

• Neurogenic • (Head Trauma)

                           

              

Anteroposterior chest radiograph of a 50-year-old patient with acute respiratory distress syndrome 12 hours after intubation. Bilateral, diffuse alveolar infiltrates are consistent with pulmonary edema. Note the absence of cardiomegaly and pleural effusions, which are often seen in patients with cardiogenic pulmonary edema.

Pathophysiology:

• The initial insult is at the alveolar capillary membranes.

• These membranes become leaky resulting in alveolar pulmonary edema.

• This edema results in:• Reduced lung compliance

• V/Q shunt formation

• Hypoxemia

• Pulmonary hypertension

Clinical Presentation:The FOUR phases of ARDS

• Phase 1: Hyperventilation, cyanosis, respiratory alkalosis, and normal CXR

• Beginning at time of initial insult, lasting several hours.

• Phase 2: Tachypnea, respiratory distress, marked hypoxemia, alkalosis, interstitial edema on CXR.

• Phase 3: Hypoxemic Respiratory Failure

• Phase 4: Cardiac Arrest

• Phases 2-4 all have variable timeframes, can progress over hours to days.

Treatment:

• TREAT the underlying disorder!!!• Sepsis – Broad Spectrum Antibiotics

• Support Gas Exchange – Mechanical Ventilation with PEEP

• Maintain Organ Perfusion – use lowest intravascular volume possible while still maintaining organ perfusion

• Inotropic Therapy if needed

• Numerous studies have focused on the use of multiple ventilation approaches and pharmacologic treatments with little success.

Mortality/Prognosis:

• Mortality – 50%• Infection is the #1 cause

• If patient survives, recovery of near-complete lung function is expected.

References:

• American Thoracic Society: Standardization of Spirometry, 1994 Update. Am J Respir Crit Care Med 1995 Sep; 152(3): 1107-36

• American Thoracic Society: Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis 1991 Nov; 144(5): 1202-18

• Crapo, R.O., Morris, A.H., and Gardner, R.M. 1981. Reference Spirometric Values Using Techniques and Equipment that Meet ATS Recommendations. Am. Rev. Respir. Dis., 123:659-664

• Kollef MH, Schuster DP. The acute respiratory distress syndrome. N Engl J Med 1995;332:27-37.

• Ware LB, Matthay MA. The acute respiratory distress syndrome. N Engl J Med 2000;342:1334-1349.

Core Competencies

Oh what Fun!!!

• Case # 1. 59 yo white male with a 40 pack year smoking history presents to the ER with increasing dyspnea over the last several months, and cough productive of brown sputum. PFT values are shown below.

• Obstructive or Restrictive or Normal (circle one)

• Case # 1. 59 yo white male with a 40 pack year smoking history presents to the ER with increasing dyspnea over the last several months, and cough productive of brown sputum. PFT values are shown below.

• Obstructive or Restrictive or Normal (circle one)

• Why?

• Case # 2. 62 yo African American female presents to the office with increasing SOB over the last year. Patient is a non-smoker and has a history of HTN. PFT values are shown below.

• Obstructive or Restrictive or Normal (circle one)

• Case # 2. 62 yo African American female presents to the office with increasing SOB over the last year. Patient is a non-smoker and has a history of HTN. PFT values are shown below.

• Obstructive or Restrictive or Normal (circle one)

• Why?

• Case # 3. 45 yo white male is seen in the office for follow-up for a recent ER visit. Patient was out with buddies playing football and suddenly became short of breath. He was treated with nebulizers, steroids, and referred to you for follow-up. PFT values are shown below.

• Obstructive or Restrictive or Normal (circle one)

• Case # 3. 45 yo white male is seen in the office for follow-up for a recent ER visit. Patient was out with buddies playing football and suddenly became short of breath. He was treated with nebulizers, steroids, and referred to you for follow-up.

• Obstructive or Restrictive or Normal (circle one)

• Why?

The End

?Questions?