Jen's final study tips review (11/23)

What cannot be measured with direct spirometry?

RV, FRC, TLC

What PFT techniques are considered “indirect” spirometry? And what can they measure?

1. Gas dilution techniques (N2 washout, He dilution)

2. Body plethysmography

RV and FRC

Body Plethysmography: theory

Boyle’s law. Person pants against a closed shutter inside a box to calculate FRC.

Body Plethysmography: what is measured at the mouth and by the box?

Air pressure changes @ mouth = associate w/ alveolar pressure.

P or V changes in box = changes in thoracic volume

Box also measures 2 known values such as the pressure measured by the manometer and volume of the box calculated through the system.

Body Plethysmography: purpose of shutter?

Creates an enclosed environment. Pressure is evenly distributed throughout a closed system; hence, pressure at the mouth is pressure at the alveoli.

Raw relationship is expressed as what

PRESSURE / FLOW

How is Raw determined anatomically?

Raw is determined by the pressure difference across airways over flow. As resp. muscles generate pressure differences, these gradients result in airflow from the airway opening into the alveoli.

What does Raw depend on physiologically?

1. Size of airways (smaller = greater Raw)

2. # of airways (more = greater Raw)

3. Elasticity (more = lower Raw)

Raw is healthy physiology

As airways shrink in size in the LA, they are compensated with the increased # of airways, causing an increased cross-sectional area. This caused majority of Raw to be in the trachea + UA.

Normal Raw

>2.5cmH2O/L/sec is high

Advantages and disadvantages b/w R/Gaw and FVC

R/Gaw assess bronchodilator response, central airway obstruction and obviously airway conduction and resistance; however, it does not measure as much as FVC does.

FVC is not sensitive to central airway obstruction and can appear normal early on, but it helps provide more detail on volumes and flows for general lung fxn assessment.

FOT and interrupter technique

Both help measure Raw but rely very little pt. effort, generally used on kids. FOT provides forced flow to measure pressure, and interruptor is like a body box by placing a total face mask but baby version on to estimate alveolar pressure through the mouth pressure.

What does diffusion in and out of lungs depend on? Describe the four components of the diffusion or transfer of carbon monoxide (CO) from the alveoli to hemoglobin (Hb

1. SA + integrity of AC membrane

2. rate of BF through capillaries

3. Hb concentration in blood

4. Pb

Diffusing capacity testing: What does it assess?

Measures ability of lungs to transport inhaled gas from alveoli to capillaries, testing how EFFICIENTLY O2 goes into BF. Can also assess integrity + size of membrane.

Describe the inspired gases used in the single-breath DLCO test. Why do diffusing capacity tests use Carbon Monoxide?

Uses either helium, neon or methane because they do NOT participate in gas exchange. Used to obtain a measure of the alveolar volume.

Capacity tests use CO to trace the diffusion because it is a ONE WAY TRANSFER across AC membrane for combination w/ Hb.

What affects a DLCO value? And why? (5)

1. Hb (low = low DLCO)

2. COHb (high = lower DLCO)

3. pulmonary capillary blood volume (increased = increased DLCO)

4. Pb above sea level (high = increased DLCO)

5. Poor inspiratory effort during testing (<85% = decreased DLCO)

Describe the conditions that can result in an increased DLCO value.

1. increased pulmonary capillary blood volume

2. exercise

3. L→R shunt

4. LHF

5. supine

6. polycythemia

7. asthma

Describe the conditions that can result in a decreased DLCO value.

1. small lung volumes

2. pulmonary fibrosis

3. emphysema

4. pulmonary vascular and cardiovascular disease

5. anemia

6. renal failure

7. marijuana/cigarette smoking

Difference b/w volume + flow changes?

Obstruction = obstructive of flow = look at measurements of flow on the PFT results

Restrictive = restrictive to stretch = look at measurements of VOLUME on PFT results

Mixed? issues of both flow and volumes.

Obstruction

1. FEV1/FVC <70%

2. FEV1 (want to see where problem is coming from, follow mild moderate severe % reqs)

3. Reversibility (do bronchodilator study if FEV1 is low if they +12%/200mL)

4. RV (if increased, air trapping)

5. DLCO (if increased, parenchymal damage)

Mixed values being abnormal and normal it IS an obstructive process. High TLC can mean emphysema due to big and baggy

Restrictive

1. FEV1/FVC normal

2. FEV1 and FVC low

3. TLC or FVC <80%

4. DLCO (if abnormal DLCO, tell if its an alveoli problem, if normal, will tell its an external problem (scoliosis).

5. MIP/MEP (help confirm if normal DLCO is truly an external problem)

If ONE volume is low but others are normal, it is NOT a restrictive process.

Values in mixed diseases?

1. FEV1/FVC low

2. TLC low

Isolated DLCO

PE