MEASURING LUNG IN INFANTS

AND PRESCHOOLERS

Peter D. Sly MBBS, MD, FRACP, DSc

TECHNIQUES FOR MEASURING LUNG FUNCTION IN

INFANTS AND PRE-SCHOOLERS

Infants Preschoolers

RVRTC Pleth FOT MBW FOT Spiro Rint sRaw MBW

Commercial

Equip

Yes Yes No Yes Yes Yes Yes Yes Yes

SOP Yes Yes No Yes Yes Yes Yes No Yes

Sedation Yes Yes No No

Tidal breathing No No Yes Yes Yes No Yes No Yes

Feasible* No No Yes Yes Yes Yes Yes Yes Yes

Adeq ref data No No No No Yes Yes Yes No Yes

Clinical utility No No No No Yes Yes Yes ? Yes

*without specialist lab and extensive training

Modified from: Rosenfeld Ann Thorac Soc 2013

LUNG FUNCTION IN SA INFANTS

Median 25-75%

Age (w) 7.4 6.6 - 8.1

Weight (z-score) -0.32 -0.97 - 5.4

Height (z-score) -0.66 -1.7 - 0.2

BW (z-score) -0.7 -1.4 - -0.1

Mbekweni

(n=176)

N(%)

TC Newman

(n=187)

N(%)

Total

(n=363)

N(%)

Male 81 (46) 100 (54) 181 (50)

Maternal HIV+ 61 (35) 8 (4) 69 (19)

Maternal smoking

active

Passive

26 (15)

84 (49)

95 (52)

67 (36)

121 (34)

151 (42)

African

Mixed race

174 (99)

2 (1)

2 (1)

185 (99)

176 (48)

187 (51)

LUNG FUNCTION IN SA INFANTS

Mean (sd) Median (25-75%) CoV Median (25-75%)

MBW (n=345)

FRC (ml) 78.0 (17) 75.1 (66.1-86.6) 5.4 (3.3-7.8)

LCI (turnovers) 7.2 (0.4) 7.2 (6.9-7.5) 4.0 (2.4-5.8)

Tidal breathing (n-356)

Vt (ml) 34.9 (6.3) 34.5 (30.8-39.0) 7.7 (6.3-9.9)

Rate (BPM) 48.1 (11.9) 46.4 (40.1-54.3) 8.0 (6.7-10.2)

Tptef/Te (%) 39.8 (12.1) 39.9 (31.6-46.7) 20.1 (16.8-25.2)

eNO (n=352)

eNO (ppb) 10.1 (6.8) 9.0 (5.0-13.7) 4.3 (3.4-6.5)

NO output (nL/min) 8.9 (4.5) 8.0 (6.6-10.2) 2.4 (1.4-3.4)

FOT (n=293)

R (cmH2O/L/s) 48.6 (15.7) 45.6 (38.1-57.2) 4.9 (3.0-8.0)

C (mL/cmH2O) 0.95 (0.44) 0.87 (0.68-1.15) 11.0 (6.1-17.9)

EUROPEAN EQUATIONS NOT APPROPRIATE

FOR SA INFANTS

SA Observed

Mean (std error)

European Refs

Mean (std error)

FRC (mL) 78.0 (0.92) 107.2 (0.47)

Vt (mL) 34.9 (0.34) 33.4 (0.19)

Rate (BPM) 48.1 (0.63) 45.9 (0.31)

eNO (ppb) 10.1 (0.36) 13.1 (0.15)

NO output 8.9 (0.24) 3.7 (0.03)

FORCED OSCILLATION TECHNIQUE

No active patient cooperation

Infants measured supine via face mask

Preschoolers measured seated via mouthpiece

Zrs at single or multiple frequencies

single sine wave

pseudorandom noise, NIM, NSND

Impulse (IOS)

Frequency range depends on circumstance

LF-FOT: 0.5-20.75 Hz

Spontaneous breathing: 4-48 (5-25 for IOS)

Input impedance (Zrs), P & V’ at airway opening

FOURIER TRANSFORMATION

Complex signal represented by series of

sinusoids, varying magnitude and phase

sinusoids transformed to frequency domain

simple calculation by computer gives magnitude

(resistance) and phase (reactance) relations

between P and V’

FORCED OSCILLATION TECHNIQUE

Real part = resistance

Imaginary part = reactance

Tissue Airway

LFFOT in infant measured during Hering-Breuer reflex induced apnea

FITTING THE CONSTANT PHASE MODEL

1 10 0

20

40

60

80

100

120

140

160

180

200

Frequency (Hz)

1 10

-500

-400

-300

-200

-100

0

100

RL

(cm

H2O

.s/L

)

XL

(cm

H2O

.s/L

)

input impedence

airway resistance

tissue resistance

Zrs = Raw + jIaw + (G - jH)/

FOT IN SPONTANEOUSLY BREATHING INFANTS

Infant studied during natural sleep breathing through face mask and filter

FOT IN SPONTANEOUSLY BREATHING INFANTS

Conventional RLC model fit to Zrs to give R, C and I

Nasal passages make major contribution to R & I

DRAKESTEIN CHILD LUNG HEALTH STUDY

Boys

n=104

Girls

n=94

p

R 55.7±19.6 48.3±15.6 0.004

C 0.77±0.35 0.91±0.46 0.02

Stiffer lungs (↑Xrs) in “smoked”

infants at 6w

Non-smoking

mother

Smoking

mother

Non-smoker

n=114

Smoker

N=83

p

R 52.5±16.2 51.5±20.7 0.8

C 0.074±0.03 0.067±0.05 0.03

Lung function in 6w old infants during natural sleep, tidal breathing, non-

commercial equipment

FOT IN PRESCHOOLERS

Child seated with arms at the side

Cheeks supported by technician

Nose-clip

Data collected during gentle tidal

breathing

Forcing function 4-24 Hz

4 year old measured seated through mouthpiece and filter

Reference data are available

[Hall GL, Thorax 2007;62:521-526; Calogero Ped Pulm 2013;48:707-15]

Age (years)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

R (

hP

a.s

/L)

0

2

4

6

8

10

12

14

16

Age (years)

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5

C (

L/h

Pa)

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0.020

0.022

R= 0.389

p= <0.0001

R= 0.283p = 0.008

C = 0.00100 + (0.00144 * Age (years))

R= 12.657 - (0.967 * Age (years))

Height (cm)

85 90 95 100 105 110 115 120 125

R (

hP

a.s

/L)

0

2

4

6

8

10

12

14

16

Height (cm)

85 90 95 100 105 110 115 120 125

C (

L/h

Pa)

0.000

0.005

0.010

0.015

0.020

0.025

Rrs mean = 24.088 - (0.148 * Height (cm)) R= 0.565p= <0.001

C = -0.0129 + (0.000191 * Height (cm)) R= 0.358p= <0.001

Interpretation of R & C more simple

Clinical Report

MEASURING LUNG FUNCTION IN

CLINICAL PRACTICE

Aid in diagnosis

Bronchodilator response

Following progress or treatment response

Challenge tests?

More different for groups than for individuals

FOT IN POST-NEONATAL CLD

Height (cm)

9095100105110115120125130

Resistance (8 Hz) hPa.s/L

2

4

6

8

10

12

14

16

18

Height (cm)

9095100105110115120125130

Reactance 8 Hz (hPa.s/L)-10

-8

-6

-4

-2

0

2

4

FOT was feasible in young children with nCLD with

- baseline data obtained in 80% of children [n= 35 of 44],

- post BD data in 34 of 35 children [97%]

FOT BDR in children with neonatal CLD

Altered baseline FOT normalises following inhaled BD

Baseline

Post bronchodilator

-3

R6

2

1

0

-1

-2

R8 X6 X8

P < 0.001 P < 0.001

P < 0.001

P < 0.001

P < 0.001

P >0.2 P >0.2 P >0.2

P < 0.001 P < 0.001 P < 0.001 P < 0.001

FOT IN CF

Rrs6 0.677 ± 1.02 Xrs6 -0.759 ± 1.16

Asymptomatic Symptomatic Uninfected Infected

FOT in CF reflects lung disease in groups

FOT tracks lung

disease in children

with CF –

individual data

BRONCHODILATOR RESPONSE

What constitutes a BDR?

Absolute

change

% change Δ Z-score

R8 3.16hPa.s.L-1 34% 1.88

X8 2.25hPa.s.L-1 61% 2.48

Rint 0.26 kPa. L-1 32% 1.25

Note: this is based on limited data and more studies are required

BRONCHODILATOR RESPONSE

BDR – are we measuring the right thing?

Dynamic mechanics shows a different picture

p=0.023

Dynamic airway mechanics: ↓ distensibility with wheeze

BDR EXAMPLE 1

frequency (Hz)

4 8 12 16 20 24 28

Zrs

(hPa

.s/L

)

-15

-10

-5

0

5

10

15

20

BDR EXAMPLE 2

volume (L)

-0.1 0.0 0.1 0.2 0.3 0.4 0.5

Z 1

0 (h

Pa.

s/L)

-6

-4

-2

0

2

4

6

8

10

12

14

flow (L/s)

-0.4 -0.2 0.0 0.2 0.4 0.6

MEASURING LUNG IN INFANTS AND

PRESCHOOLERS

Conclusions

Lung function can be measures in infants and

preschoolers using a variety of techniques

Infants

No current place in clinical measurement

Preschoolers

Can be used in clinical practices as in older children

Dynamic mechanics may provide new information