The mean age of the 6 infants was 10 months (7 to 13 months) and mean weight was 7.1 kg (5.5 to 9.1 kg). Because of the selection of the infants, there was ventilatory failure present for the first recording of each subject. The magnitude of the CWD varied directly with the clinical severity of the disease, as illustrated in Figure 2, although there were three general patterns of chest wall motion in all subjects corresponding to different stages of illness. Firstly, the mildest abnormality, delayed expansion of the chest wall at the beginning of inspiration, was usually seen late in the recovery phase (Fig 1, left panel). This minimal distortion of the normal synchrony of movement of the two compartments was associated with the clinical resolution of the illness. The anticlockwise pattern of the Lissajous loop, and a phase angle (0m) of <30°, suggested that the ribcage did expand during inspiration, but was temporally delayed behind the excursion of the abdomen.
Secondly, with more severe CWD, there was early paradoxic inward displacement at the beginning of inspiration, but outward displacement of the chest wall prior to the onset of abdominal expiration (Fig 1, center panel). This stage of illness was associated with an anticlockwise Lissajous figure, and a phase angle ranging between 30° and 90°.
Finally, the most severe impairment was associated with marked CWD with inward motion of the chest wall throughout the entire inspiratory phase of the abdomen, although late minimal expansion of the chest wall occurred during abdominal expiration (Fig 1, right panel). In this case, the Lissajous figure was associated with a phase angle (0m) greater than 90°.
In all cases, increasing severity of the disease process was associated with the increasing measured phase angle. There was a direct relationship between the measured phase angle and the severity of disease, as determined by the tcPco2, and it is expressed in Figure 3 (r2 0.982, p<0.005). This change in measured phase angle did not differ significantly from the calculated phase angle by regression techniques (r2 0.991, p<0.005), as illustrated in Table 1 and Figure 4, but there was a systematic bias between the measurements with the 0c being greater than the 0m (95 percent confidence intervals —11.55 to —6.51) by the method of Bland and Altman.
Figure 2. The changes in Ve (bottom panel), Vt (middle panel), and frequency (upper panel) that occurred with changes in transcutaneous carbon dioxide tension throughout the clinical course of recovery from severe laryngotracheobronchitis. Each point represents the mean and standard deviation of 20 consecutive breaths. All regressions were significant at p<0.05.
Figure 3. The changes in the inductance of the chest wall (Irc) (upper panel), and the phase angle (lower panel), observed with changes in transcutaneous carbon dioxide tension tcPcoJ. Each point represents the mean ± SD of 20 consecutive breaths, and was significant at p<0.05 by linear regression.
Figure 4. The progressive fall in rib cage inductance (Irc) with increasing phase angle is illustrated in the upper panel. The lower panel represented the relationship between the measured (planar) phase angle, and the calculated (scalar) phase angle, with the heavy line representing the line of identity. Each point represents the mean ± SD of 20 consecutive breaths, and was significant at p<0.05 by linear regression.
Table 1—Data of the Six Infants at the Beginning of the Study
|PatientNo.||Age, mo||Weight, kg||tcPco2, mm Hg||Vt,ml*kg_l||Ve,LTnin^’kg“||Phase Angle, Measured||Phase Angle, Calculated||Irc, mV|
|1||7.0||5.5||52||5.8 ±0.7||0.37 ±0.06||110 ±12.2||90±11.6||15 ±8|
|49||8.4±1.1||0.52 ±0.09||90 ±7.7||80 ±8.8||26± 11|
|2||9.0||7.6||52||6.0 ±0.4||0.36 ±0.09||100 ±7.9||90 ±13.6||15 ±6|
|41||7.1±0.8||0.46±0.08||75 ±7.3||60 ± 12.1||23±9|
|28||15.7 ±0.4||0.63 ±0.09||20±3.8||20±4.5||75± 12|
|3||9.5||8.4||55||5.8±0.7||0.34 ±0.07||110 ±10.3||100 ±13.5||9±5|
|42||6.9 ±0.8||0.45±0.12||70 ±5.6||60 ±8.8||23 ±7|
|29||11.6±0.5||0.64 ±0.14||25 ±5.5||30 ±6.4||57 ±13|
|4||10.0||8.8||60||4.8±0.5||0.29 ±0.08||120 ±10.2||110±11.6||— 8±2|
|46||6.5±0.8||0.44 ±0.10||80 ±5.8||70 ±7.4||21 ±6|
|32||10.3 ±1.0||0.57 ±0.09||40±5.1||30±6.9||51 ±12|
|5||11.5||9.0||62||5.4 ±0.3||0.27 ±0.09||120 ±15.3||100 ±10.9||— 8±4|
|52||7.6± 1.3||0.44 ±0.09||100 ±7.6||90 ±8.4||26±8|
|33||13.5 ±0.9||0.54±0.11||45 ±5.4||35 ±8.4||65± 14|
|6||13.0||9.1||64||5.6±0.6||0.28 ±0.06||120 ±7.5||110 ±8.6||—14 ±9|
|48||7.1 ±0.8||0.40±0.09||90 ±5.4||80 ±6.1||23±5|
|36||11.8± 1.2||0.54 ±0.13||45 ±4.2||40 ±7.3||63 ±22|