Varying respiratory rate and IOS

Researchers from NYU / Bellevue hospitals in NYC found that elevated levels of breathing did, in fact, alter the IOS values and doctors and technicians must pay careful attention to this when looking at their data.

COPD. 2009 Jun;6(3):162-70. Distal airway function assessed by oscillometry at varying respiratory rate: comparison with dynamic compliance. Oppenheimer BW, Goldring RM, Berger KI. Division of Pulmonary and Critical Care Medicine, Department of Medicine, New York University School of Medicine/Bellevue Medical Center, New York, NY, USA. beno.oppenheimer@nyumc.org Elevated respiratory rate influences oscillometric parameters and must be considered when interpreting oscillometric data. IOS provides a non-invasive tool for assessment of distal airway function when spirometry is normal, which can be applied to various clinical settings including early diagnosis of COPD (GOLD stage 0), asthma in clinical remission and occupational/ environmental irritant exposure.

PMID: 19811371 [PubMed - in process]

More IOS Reactance

AX, or the area of reactance, is the area from X5 to Fres to 0.0

Fres, or resonant frequency

In many disease states that affect lung “stiffness” or resistance, the reactance worsens. Graphically you will see the X5 become more negative.

Both AX and Fres tend to increase in disease and decrease with bronchodilator response

IOS Reactance = Elastic Qualities of the Lung

In IOS, the elastic properties of the lung periphery are looked at in terms of Capacitance.

Capacitance can be defined as the ability to store energy.

Reactance (X) is measured and reported across the same frequencies as resistance (5-30Hz).

X5 = Lung reactance at 5Hz

Elasticity of lung & thorax

Dimensions of ventilated airways

Indirect indication of peripheral airway

obstruction

IOS Resistance Components

Airway Resistance (R) is both measured and reported in multiple frequencies.

The x-axis shows the different frequencies, with 5-20 being the most relevant for the airway.

Resistance at 20Hz:
Central Resistance (Rc)

Resistance at 5 Hz:

Total Resistance (Rc +Rp)

R (5Hz)- R(20Hz):

Peripheral resistance

When FEV1 fails to improve!

Forced oscillation using impulse oscillometry provides objective responses to corticosteroids in asthmatic patients when FEV1 fails to improve. Conclusions: As forced oscillation technique is automatic and can measure multiple breaths over long periods, it is suitable for monitoring expiratory flow limitation continuously and identifying patients’ breathing close to the onset of expiratory flow limitation, where intermittent sampling may be unrepresentative.

Dellacà RL, Duffy N, Pompilio PP, Aliverti A, Koulouris NG, Pedotti A, Calverley PM. E Resp J. 2007 Feb;29(2):363-74. Dipartimento di Bioingegneria, Politecnico di Milano University, Milan, Italy.

INCREASE PATIENT COMPLIANCE TO TESTING

Testing patients using the impulse technology requires only quiet breathing and not the maximal forced maneuvers that often result in patients quitting in the middle of the test. Data is only useful if it truly represents the patient’s best efforts, and IOS helps achieve that.

✔ QUIET BREATHING

✔ NO FORCED MANEUVERS

✔ INCREASES PATIENT COMPLIANCE

IOS: NORMAL PATIENT VS COPD PATIENT

NORMAL: The top graph depicts the results from a subject with normal lungs. It shows no frequency dependence of resistance, and both R5 and R20 follow the predicted line (dashed line) and are smaller than the upper limit of normal (indicated by the lightly shaded area).

COPD Patient: The bottom graph is representative of a COPD patient, showing a frequency dependence of resistance where R5>R20.

WHAT IOS MEASURES

IOS measures impedance (Z). As the pt. breathes on the unit, pressure and flow is measured at the mouth and then recorded at each frequency by the computer. This provides us with the individuals respiratory impedance. It is sum of all the forces opposing the pressure impulses (oscillations) and is made up primarily of 2 components:

Resistance (R)= “Forward” Pressure, Information about the conducting airways.

Reactance (X)= Echo = “Rebound Resistance” Information about the distensible airways and lung.

WORLD TRADE CENTER IRON WORKERS TESTED USING IOS

Conclusions: Respiratory symptoms occurred in the majority of ironworkers at the WTC disaster site and were not attributable to smoking. Exposure on September 11 was associated with a greater prevalence of cough. Objective evidence of lung disease was less common. Spirometry underestimated the prevalence of lung function abnormalities in comparison to FO. Continuing evaluation of symptoms, chest radiographs, and airway dysfunction should determine whether long-term clinical sequelae will exist. (CHEST 2004; 125:1248–1255)

The online version of this article, along with updated information and services can be found online on the World Wide Web at: http://www.chestjournal.org/content/125/4/1248.full.html

IOS IS BETTER THAN SPIROMETRY ALONE

Flow limitation detected by spirometry may be the result of many things:Instability of the airways, Central airways obstruction, Peripheral airways obstruction, Abnormal elasticity of the thorax, Abnormal lung volumes, Extrathoracic upper airway obstructions, Weakness or respiratory muscles.

Even if technically good results can be obtained spirometry still leaves many questions to be answered! Look to IOS!

SPIROMETRY FAILS THIS DIAGNOSIS. IOS DOES NOT.

Asthma patients may be asymptomatic and still show levels of increased airways resistance. In this example, IOS shows elevated resistance in both 5 Hz and 20 Hz indicating some central obstruction that clearly responds to a bronchodilator. Spirometry is normal and no significant changes with bronchodilator. Clearly IOS is the better! Click on the report below and it will expand.

IOS IS EASY TO PERFORM

Data is only useful if it truly represents the patient’s best efforts.

If you are a healthy person, then performing 3 Flow Volume Loops at your maximal effort may be easy. But those who suffer from asthma, COPD and other breathing disorders, this is very difficult. Patients often quit in the middle of these tests, and the results become suspect.

IOS helps change that. The IOS allows doctors to still perform traditional spirometry, but adds impulse technology to the instrument- quiet breathing, no forced maneuvers, with normals for most patient populations.

ABOUT IOS

IOS allows you to determine the respiratory system impedance and reliably measures central and peripheral airways resistance in 30 seconds of quiet breathing. The Impulse Spirometer, or IOS for short, not only provides more objective patient data than any ‘traditional’ spirometer, it is also significantly easier for patients to perform the test. IOS is about testing more patients with less effort