CHANGES IN RESPIRATORY MECHANICS MEASURED BY IOS DURING
THE FIRST DAY OF LIFE IN CALVES
CH. UYSTEPRUYST, P. REINHOLD *, J. COGHE, F. BUREAU, T. DORTS AND P. LEKEUX.
Laboratory for Functional Investigation, Department of Large Animal Clinical Sciences, Faculty of
Veterinary Medicine, University of Liège, Belgium, *Federal Institute for Health Protection of Consumers
and Veterinary Medicine, Jena Branch, Germany
Introduction
To reduce perinatal calf mortality (6-8%) (Randall, 1978; Mee, 1999), it is
necessary to understand the rapid changes that the cardiopulmonary system
undergoes during successful transition to extrauterine life (Adams et al 1991,
1992). Indeed, around 60 % of these deaths occur during the first 24 hours
post parturition (Vestweber 1997). Knowledge of the physiological
mechanisms underlying the normal neonatal respiration is a prerequisite for
evaluation of the failing mechanisms and for all rational therapeutic measures.
Arterial blood gas analysis and pulmonary function tests are considered to be
the reference methods to evaluate pulmonary function efficiency in cattle
(Lekeux et al 1984, Gustin et al 1988). The impulse oscillometry system
(IOS) is a newly developed forced oscillation technique which has been used
for non-invasive respiratory function testing in children (Bisgaard and Klug
1995, Klug and Bisgaard 1998), in horses (van Erck et al 1997), in pigs (Klein
and Reinhold 1997) and in calves (Strie et al 1997, Reinhold et al 1996,
1998a, 1998b).
In the present study, arterial blood gas analyses and IOS were used to assess
the physiological respiratory modifications occurring during the first 24 hours
of life in healthy newborn calves.
Material & Methods
Calves
Forty clinically healthy newborn calves (8 Holstein-Friesian weighing 41 (6.2)
kg, 25 Blue Belgian weighing 51.0 (7.0) kg and 7 crossbred weighing 47.0
(4.4) kg) were investigated during their first 24 hours of life. Each calf was
investigated 1, 2, 3, 6, 12, 18 and 24 hours after birth.
Arterial blood gas analyses
Arterial blood samples were withdrawn anaerobically from the Art. subclavia
with a 2 ml heparinised syringe and were analysed within 2 minutes by a
blood gas analyser (AVL 995, VEL, Leuven, Belgium) for blood gas tensions
as well as for acid-base balance.
Impulse oscillometry measurements
In this study, the complex respiratory impedance (Zrs) was measured by use
of an IOS device (MasterScreen IOS, E. Jaeger GmbH, Würzburg, Germany).
The IOS measured the complex Zrs which is derived from the ratio of spectral
pressure and flow variations (Zrs = P/V’) after fast fourier transformation
(FFT) of pressure and flow from the time domain. The IOS calculated the
following parameters: resistance at 5, 10, 15, 20, 25, 35 Hz (R 5Hz,…R35Hz),
and reactance at 5, 10, 15, 20, 25, 35 Hz (X5Hz,…X35Hz).
Results
Changes in arterial blood
ANOVA revealed a highly significant effect of the age of the calf (p < 0.001)
on arterial blood parameters. From 1 to 24 hours old, PaO 2, SatO2, pHa and
BEa increased significantly (p < 0.01) while PaCO2 and A-aDO2 decreased
significantly (p < 0.01).
Changes in respiratory mechanics
ANOVA showed that the respiratory mechanical parameters measured with
the IOS were significantly influenced by the age of the calf (p < 0.01). This
analysis also demonstrated that the body position of the calf influences
significantly R5Hz (p < 0.001), R10Hz (p < 0.05) and X5Hz,…X35Hz (p < 0.001).
Since there was no significant change within the first 3 hours of life (1, 2, 3 h)
and between 18 and 24 hours, R and X values of these time periods were
pooled and directly compared in Fig. 1a for the lying position and in Fig. 1b for
the standing position. Fig. 1a and Fig. 1b show that R was negatively
dependent on frequency (R decreased when frequency increased). R was
more negative dependent on the frequency in the lying position compared to
the standing position. Furthermore, a negative dependency of R on frequency
observed at 1-3 hours was still present at 18-24 hours of age but was slighter.
Between the two time periods (1-3 hours and 18-24 hours), R5Hz,…R35Hz
decreased significantly (p < 0.05) and X5Hz,…X35Hz increased significantly
(p < 0.05) as shown in Fig. 1a and Fig. 1b. A Dunnett t test showed that the
absolute changes in R and X with time (between 1 and 24 hours old) were
significantly higher at 5 Hz than at 15, 20, 25 and 35 Hz for R (p < 0.05) and
significantly higher at 5 Hz than at 20, 25 and 35 Hz for X (p < 0.05).
Intra-subject variability of the respiratory impedance
Between 1-3 hours and 18-24 hours, the intra-subject variability in R
(represented by the DiffR values, i.e. the difference between the maximal and
the minimal values within 3 consecutive IOS-measurements) did not change
significantly. In contrast, the intra-subject variability in X (represented by the
DiffX values) decreased significantly for 10 Hz, 15 Hz, 20 Hz and 25 Hz
(Fig 2). Furthermore, the lower the frequency the higher the absolute value of
DiffX (Fig 2).
1.0
1.0
a
b
1-3 hours
18-24 hours
0.8
0.6
R
0.4
*
*
*
*
*
*
*
*
*
*
0.2
*
*
0.4
KPa.l-1.s
KPa.l-1.s
0.6
0.0
1-3 hours
18-24 hours
0.8
R
*
*
*
*
*
*
*
*
*
*
*
0.2
0.0
*
X
X
-0.2
-0.2
-0.4
-0.4
5
10
15
Frequency
20
(Hz)
25
35
5
10
15
Frequency
20
(Hz)
25
35
1-3
18 - 24
0.25
*
+
0.20
0.15
hours
hours
p < 0.01
p < 0.05
*
*
0.10
*
+
0.05
0.00
DiffX
5Hz
DiffX
10Hz
DiffX
15Hz
DiffX 20Hz
DiffX 25Hz
DiffX
35Hz
KPa.l-1.s
FIG. 1a and 1b : Resistance at 5,…35 Hz (R5Hz,…R35Hz) and reactance at 5,…35 Hz (X5Hz,…X35Hz)
changes with time in calves in the lying (a) and in the standing (b) positions (mean (SD)).
FIG. 2 : Changes in the intra-subject variability in reactance at 5,…35 Hz (DiffX(5Hz,….35Hz) ) between 1-3
hours and 18-24 hours in 40 newborn calves (mean (SD)).
Discussion
This study shows that, during the first 24 hours of life of healthy newborn
calves, gas exchange improves and the mixed respiratory-metabolic acidosis
present at birth is corrected as demonstrated by significant changes in arterial
blood gases and acid-base balance. These changes were accompanied by
concomitant changes in pulmonary mechanics. The first 6 hours of life
represent the most critical adaptive period, major changes occurring during
this period. From birth to 1 day old, pulmonary function tests measured by the
IOS revealed significant decrease in R and increase in X with time, reflecting
the clearance of both upper and lower airways, the increase in lung volume
and the improvement of the lung tissue elasticity and/or the improved
distribution of the ventilation occurring during this adaptive period. The IOS
spectral analysis (from 5 to 35 Hz) offered refined information concerning the
location of mechanical changes within the respiratory system: indeed,
greatest changes in R and X with time were observed at lower frequencies,
suggesting that major mechanical changes occur within peripheral airways
where foetal lung fluid is removed. The negative frequency dependence of R
may be related to a normal spectral behaviour of R for a small size lung
system with an additional negative dependency due to a peripheral airway
obstruction. This negative dependency still present at 1 day old suggests that
the removal of foetal lung fluid takes longer than 24 hours. The significant
decrease with time in the intra-subject variability of X-values within the range
10 - 25 Hz suggests a decreased variability of the respiratory system during
the first day of life. Since no significant change in DiffR was detected, it seems
to be related more to the central and peripheral airway system and/or the
elasticity of the lung tissue than to the upper or larger airways. This study also
demonstrates the effect of body posture on respiratory mechanics and
particularly on mechanical properties of the distal respiratory system and/or
chest wall. At 1 day old, both mechanical parameters and arterial blood gases
remain lower (higher R values, lower X values, relative hypoxaemia due to
right-to-left shunting mainly through areas of the lung with a low ventilationperfusion ratio,…) than predicted values of older healthy calves of the same
body weight, meaning that the pulmonary adaptation to extrauterine life takes
longer than 24 hours.
The present results provide data concerning a successful transition to
extrauterine life in calves. They might be valuable when investigation of
calves presenting an adaptation failure or delay will be required.
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