Reference values of diaphragmatic dimensions in healthy children aged 0-8 years

doi:10.21203/rs.3.rs-2231073/v1

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Research Article

Reference values of diaphragmatic dimensions in healthy children aged 0-8 years

https://doi.org/10.21203/rs.3.rs-2231073/v1

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Journal Publication

published 20 Mar, 2023

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Purpose

Diaphragmatic thickness (Tdi) and diaphragm thickening fraction (dTF) are widely used parameters in ultrasound studies of the diaphragm in mechanically ventilated children, but normal values for healthy children are scarce. We determined reference values of Tdi and dTF using ultrasound in healthy children aged 0–8 years old, and assessed their reproducibility.

Method

In a prospective, observational cohort, Tdi and dTF were measured on ultrasound images across four age groups compromising at least 30 children per group: group 1 (0–6 months); group 2 (7 months-1 year); group 3 (2–4 years); group 4 (5–8 years).

Results

Ultrasound images of 137 healthy children were included. Mean Tdi at inspiration was 2.07 (SD 0.39), 2.09 (SD 0.38), 1.73 (SD 0.33) and 1.70 (SD 0.30) mm for group 1, 2, 3 and 4 respectively. Mean Tdi at expiration was 1.63 (SD 0.33), 1.67 (SD 0.27), 1.40 (SD 0.23) and 1.40 (SD 0.24) mm for group 1, 2, 3 and 4 respectively. Mean Tdi at inspiration and mean Tdi at expiration for groups 1 and 2 were significantly greater than those for groups 3 and 4 (p < 0.001 respectively). Median dTF was 27.1% (SD 12.5), 24.7% (SD 8.6), 24.1% (SD 10.4) and 21.2% (SD 6.8) for group 1, 2, 3 and 4 respectively. The intraclass correlation coefficients for intra-rater and inter-rater reliability were 0.995 (95% CI 0.983–0.999) and 0.989 (95% CI 0.983–0.995), respectively.

Conclusion

Ultrasound measurements of Tdi and dTF were highly reproducible in healthy children aged 0–8 years.

ClinicalTrials.gov identifier (NCT number): NCT04589910

Ultrasound

Diaphragm

Thickening Fraction

Pediatric

Weaning

Extubation

What is known?

Diaphragmatic thickness and diaphragm thickening fraction are widely used parameters in ultrasound studies of the diaphragm in mechanically ventilated children, but normal values for healthy children to compare these with are scarce

What is new?

We determined normal values of diaphragmatic thickness and diaphragm thickening fraction using ultrasound in 137 healthy children aged 0-8 years old. The diaphragmatic thickness of infants up to 1 year old was significantly greater than that of children from 2 to 8 years old. Diaphragmatic thickness decreased with an increase in body surface area. These normal values in healthy children can be used to assess changes in respiratory muscle thickness in mechanically ventilated children.

The main driver of inspiration, the diaphragm muscle, is a musculo-fibrous membrane separating the thoracic and abdominal cavities. It consists of a non-contractile central fibrous portion (centrum tendineum diaphragmatis) and a peripheral muscular section that is partitioned into the sternal, costal and lumbar muscular groups. The diaphragm has a role in both the low-intensity, perpetual cycle of breathing and in more rapid and strenuous settings, such as talking, singing, sneezing and in situations of acutely increased ventilation. [1; 2] Studies in mechanically ventilated adults have demonstrated rapid development of diaphragm weakness, or: critical illness-associated diaphragmatic weakness. [3–7] This condition reflects the inability of the diaphragm to generate normal levels of maximal force. [8–11]. Diaphragmatic thickness (Tdi) and diaphragm thickening fraction (dTF) measured on ultrasound images are widely used to evaluate diaphragm function in patients with suspected diaphragm weakness [4; 11–16], including critically ill children. [16–20] For the sake of comparison, however, limited data is available about normal Tdi and dTF values in healthy children. [21–23]

In children, the chest wall musculature is still immature, with fewer type-1 muscle fibers (slow fibers for quiet breathing) than in adults. Although the proportion of type-1 muscle fibers increases from 9% at 27 weeks gestational age to 25% at term age and already reaches the adult level during the second postnatal year, a child has to develop muscle mass and greater contraction strength during childhood and puberty. [24–26] Studies in ventilated children with a median age between 3 months and 5 years old found evidence of decreases in Tdi during the course of mechanical ventilation compared to baseline values. [17; 18; 20; 27; 28] Decrease in thickness is associated with atrophy, which in turn is associated with diaphragm weakness and worse outcome in adults. [29] Smaller diaphragm thickness is also found at initiation of mechanical ventilation in sick adult patients. [3; 30] The lack of normal values in children makes it hard to establish whether even critical illness already influences changes in respiratory muscle thickness in children.

We performed a study to determine Tdi at end-inspiration, Tdi at end-expiration, and dTF with the use of ultrasound in children aged 0–8 years, and assessed the intra-rater and inter-rater reproducibility. This age group represents the largest patient group in pediatric intensive care units around the world.

We performed a prospective cohort study from September 1, 2020 until March 1, 2021.

Study population:

Healthy children aged 0–8 years old were eligible for inclusion. We created four age subgroups for analysis: 0–6 months; 7 months-1 year; 2–4 years; and 5–8 years. Participants were recruited through healthcare professionals working at the Erasmus MC-Sophia Children’s Hospital as well as through the research team members’ families, friends and neighbours. In addition, brochures were placed in waiting rooms and elevators in the Erasmus MC-Sophia Children’s hospital in which parents were invited to have their healthy children participate in this study.

Children who met any of the following criteria could not participate: neuromuscular disease, chronic lung disease, abdominal or thoracic surgery less than 3 months ago, known abnormalities of the diaphragm, and having been mechanically ventilated in the past 6 months.

Informed consent from the parents of each participant was obtained.

Diaphragm measurement

After having received thorough training from an experienced ultrasound technician (JM), two researchers (JS and AD) performed ultrasound measurements at the children’s homes, supported by a written protocol. Parents were present to keep the child as calm as possible. If necessary, the child was distracted with a video on the phone, a picture book or other toy, and a pacifier. The procedure did not start until the child was breathing quietly, lying either on a sofa, a bed or on the lap of a parent.

Ultrasound measurement of the diaphragm was performed with a Lumify L 12 − 4 linear array transducer (Philips Medical Systems B.V., Best, Netherlands) in B mode with the child in a 30-degree supine position, with the head on a pillow. The diaphragm thickness was measured on the right side, with the transducer placed perpendicular to the ribs in the ninth or tenth intercostal space between the anterior and mid axillary lines, in the zone of apposition between lung and liver. In this area, the diaphragm is observed as a three-layered structure: a non-echogenic central layer bordered by two echogenic layers: the peritoneum and the diaphragmatic pleurae (Fig. 1). [12; 13; 15; 31; 32].

Tdi in this position was defined as the vertical distance in millimeters between the midpoint of the diaphragmatic pleura and the midpoint of the parietal peritoneum. dTF was quantified by the percentage change in the right hemi-diaphragm thickness from end-expiration to end-inspiration during tidal breathing. dTF was calculated with the formula: end-inspiratory thickness of diaphragm (Tdi-insp) minus end-expiratory thickness of diaphragm (Tdi-exp) divided by end-expiratory thickness x 100. This index is widely used in various studies and is well applicable. [15; 31; 33]

Per ultrasound moment, three measurements were made when the optimum position was reached with the clearest view. The mean of the three values was used in the analyses. Short axis Digital Imaging and Communications in Medicine (Dicom) videos were recorded for offline B-mode analysis, and calculations were made with dedicated software (RadiAnt DICOM viewer from Medixant).

Outcome measures

Primary outcomes were Tdi at end-inspiration (Tdi insp), Tdi at end-expiration (Tdi exp), and dTF in healthy children up to 8 years of age, divided across four age groups: group 1 (0–6 months); group 2 (7 months − 1 year); group 3 (2–4 years); group 4 (5–8 years).

Intra-rater and inter-rater reliability of the two observers (AD, JS) were assessed using the intraclass correlation coefficient (ICC). Intra-rater reliability was measured from ultrasounds performed by each twice in five patients, with a five to ten minutes’ interval between the two measurements. AD and JS were blinded for each other’s measurements. The inter-rater reliability was calculated from measuring Tdi of eleven randomly selected ultrasound images.

Parameters

Each child’s age, sex, height, and weight were noted, and Tdi insp, Tdi exp (in millimeters) and dTF (as a percentage) were measured during tidal breathing.

Sample size

The desired sample size was determined based on the precision of the reference intervals. From previous research, we assumed that Tdi is normally distributed. [22; 34] To achieve sufficient precision, thirty children per age group (120 children in total) was considered a sufficient number.

Data analysis

Data are presented as mean (standard deviation, SD) for normally distributed data and median (Interquartile range, IQR) for non-parametric data. Differences in patients’ characteristics between the four age groups were tested with the one-way ANOVA test for normally distributed variables and Kruskal-Wallis test for continuous variables that were not normally distributed.

Inter-rater and intra-rater reliability were assessed using an intraclass correlation coefficient (ICC) for average measures with a two-way random effects model for continuous data. An ICC value below 0.5 is considered to indicate poor reliability, between 0.5 and 0.75 moderate reliability, between 0.75 and 0.9 good reliability, and any value above 0.9 excellent reliability. [35]

Correlations between body surface area, age, weight and length with Tdi and dTF were assessed using Pearson correlation coefficients (r_p) with 95% confidence interval.

Ethical considerations

The Medical Ethics Review board at Erasmus MC Rotterdam approved the study (METC No. NL70476.078.19). The study was performed in accordance with the ethical standards of the Declaration of Helsinki.

From 1 September 2020 to 1 March 2021, 137 healthy children were enrolled. In 13 of them, only two measurements instead of three could be performed because of movement artefacts. These two measurements are included in the data analysis. Age groups 1 and 2 included 30 subjects in each; age group 3 included 29 subjects because we lost the ultrasound image of one. Age group 4 was the largest group, with 48 inclusions. Baseline characteristics are shown in Table 1.

Table 1

Participants’ characteristics and diaphragm measures
Characteristics	Group 1 (0–6 months) n = 30	Group 2 (7 months-1 year) n = 30	Group 3 (2 years − 4 years) n = 29	Group 4 (5 years- 8 years) n = 48	p-value ^a
Sex, F/M (n)	14/16	17/13	13/16	27/21	0.769
Age in years*	0.5 (0.5)	1.0 (0.4)	3.0 (0.8)	6.4 (1.2)	< 0.001
Weight (kg)	5.9 (1.5)	10.0 (1.7)	15.4 (2.5)	23.6 (5.2)	< 0.001
Body surface area (m²)*	0.30 (0.06)	0.45 (0.06)	0.65 (0.07)	0.89 (0.13)	< 0.001
Height (cm)*	61.1 (7.1)	76.9 (7.0)	100.3 (7.2)	123.6 (9.5)	< 0.001
Tdi-insp (mm) *	2.07 (0.39)	2.09 (0.38)	1.73 (0.33)	1.70 (0.30)	< 0.001
Tdi-exp (mm)*	1.63 (0.33)	1.67 (0.27)	1.40 (0.23)	1.40 (0.24)	< 0.001
dTF (%)*	27.1 (12.5)	24.7 (8.6)	24.1 (10.4)	21.2 (6.8)	0.167
^a One way ANOVA; * mean (SD); Tdi-insp, thickness of diaphragm at inspiration; Tdi-exp, thickness of diaphragm at expiration; dTF, thickening fraction

Primary outcome

The mean Tdi insp ranged from 2.07 (SD = 0.39) to 1.70 mm (SD = 0.30); the mean Tdi exp ranged from 1.63 mm (SD = 0.33) to 1.40 mm (SD = 0.24) across groups. Mean dTF ranged from 27.1% (SD = 12.5) in the two youngest age groups to 21.2% (SD = 6.8) in the oldest age group. Tdi at end-inspiration and at end-expiration differed significantly between groups, with higher values observed in groups 1 and 2 than in groups 3 and 4. dTF did not significantly differ between age groups. (Table 1, Figs. 2a and 2b, Fig. 3).

The intra-rater reliability between the observers was 0.995 (95% CI 0.983–0.999). The ICC of the inter-rater reliability between the observers in 11 paired assessments was 0.989 (95% CI 0.983–0.995).

Weak to moderate negative correlations between age, body surface, weight and height on the one hand, and dTF, Tdi insp and Tdi exp on the other hand were demonstrated (Table 2). For example, the correlation coefficient between Tdi insp and body surface was − 0.400 (-0.532, -0.246) and the correlation coefficient between Tdi exp and body surface was − 0.351 (-0.490, -0.193) (Fig. 4)

Table 2

Pearson correlations between age, body surface, weight, length and Tdi and dTF
	dTF n = 135	Tdi-insp n = 135	Tdi-exp n = 135
Age in years*	-0.180 (-0.338, -0.011)	-0.422 (-0.550, -0.271)	-0.375 (-0.511, -0.219)
Body surface*	-0.161 (-0.321, 0.009)	-0.400 (-0.532, -0.246)	-0.351 (-0.490, -0.193)
Weight*	-0.148 (-0.309, -0.022)	-0.379 (-0.514, -0.223)	-0.336 (-0.477, -0.176)
Height *	-0.177 (-0.335, -0.008)	-0.424 (-0.552, -0.273)	-0.370 (-0.506, -0.213)
r_p= Pearson product correlation coefficient; CI – confidence interval; *r_p (95%CI)

To determine normal values of diaphragm thickness and thickening fraction in young children, we performed measurements in healthy children aged 0 to 8 years old. To our knowledge, this is the biggest study in this age group collecting normal values during spontaneous breathing for thickness of the diaphragm at end-inspiration and at end-expiration in combination with thickening fraction. Establishing normal values is important, for example, to be able to judge whether critical illness induces changes in respiratory muscle thickness.

Both the Tdi at end-inspiration and at end-expiration in infants from 0–1 year old were thicker than those of the children from 2–8 years old, a finding we did not expected in advance.

To relate our findings to those of other studies, it is important to know how the diaphragm muscle measurements were made. It must be taken into account that the membranes are biologically active, and that mechanical forces related to ventilation can lead to inflammation with remodeling and thickening of the tissue. [36] We measured the diaphragm thickness as the vertical distance in millimeters between the midpoint of the diaphragmatic pleura and midpoint of the peritoneal membrane, but other studies measured between the inner lines or outer lines of both membranes. Therefore, thicknesses may differ slightly from each other. (see Table 3). [36; 37]

Normal diaphragm values in relation to other publications in healthy children

The diaphragm thickness for children aged 2 to 8 years established in the present study compares well with that found by Vishwanath et al. in healthy children aged 8 to 10 years, while the mean dTF was smaller (Table 3). [34]. Of note, however, Vishwanath and colleagues did not describe how dTF and Tdi were exacly measured concerning the membranes.

Rehan et al. measured Tdi at end-expiration in 15 newborns (appropriate for gestational age, and one or two days old) and found greater thickness than we found in our youngest age group, which had a much higher mean age of 5 months. (Table 3). This finding may tentatively suggest that the thickness is greatest at birth and decreases with the lengthwise growth of the diaphragm. Van Doorn et al. found the same values for Tdi at expiration in 12 children from 0–10 years old (mean age 6.2 years) as in our oldest age group. Tdi at inspiration was higher, because they had measured maximal end-inspiration. [21] Alonso et al. and recently Yeung et al. found in term newborns diaphragm thickness values comparable with our values for the youngest age group. [23; 38]

Normal diaphragm values (dTF) in relation to publications in ventilated children

Six studies in ventilated children, with a median age between 3 months and 5 years old, found either a decrease or an increase in Tdi during the ventilation period. [17–20; 28; 39] (Table 3). Montoro et al. studied ventilated children between 0 and 18 years old with a median age of 3 months, comparable with that of our youngest age group. [17] The median dTF at baseline was comparable with our finding, but was higher before extubation. The effect of the supporting ventilation mode or the breathing work during spontaneous breathing through an endotracheal tube before extubation could have played a role here. Lee et al. studied 31 ventilated children between one month and 18 years old (median age 3 years). [19] The dTF at baseline in Lee et al. was comparable with our findings, but during the course of ventilation became lower than the values we established, both in the success group and in the three patients who failed extubation. After extubation, dTF in the successfully extubated group was higher and comparable with values in our cohort of children from 2 years to 4 years old. The dTF in the ones who failed extubation was less than 17%, lower than the 24.1% we established for this age group in healthy children. Glau et al. found a linear correlation of an decreasing dTF with less spontaneous breathing via a support ventilation mode in 56 ventilated children between 0 and 18 years old (median age 17 months) (Beta coefficient 9.4, 95% CI 4.2, 14.7, p = 0.001). [18] The dTF was very low at baseline and still low before extubation. Notable in that study is the use of neuromuscular blockade infusion (NMB) in one third of the patients, which may have led to this low dTF. The use of NMB in patients in the study of Montoro et al. led to a greater decrease in thickness and increased the daily atrophy rate in the ventilated patients. The dTF values established by IJland et al. at baseline and before extubation in ventilated children with a median age of 4 months were comparable with those of Glau et al. Three children in whom extubation had failed had a very low dTF under 5%. None of the studies in ventilated children had standardized the dTF before extubation for level of sedation or level of ventilation support, so it is difficult to compare all studies. Xue et al. found in 50 ventilated children between 0 and 18 years old, with a mean age of 3 years that a cut-off value for dTF greater or equal to 21% was associated with successful weaning, defined as passing a spontaneous breathing trial of pressure support 8 cmH₂O above PEEP 5 cmH₂O. This cut-off value of 21% is comparable with the normal dTF we found in healthy children in the same age group. [28] Abdel Rahman et al. established a cut-off value of dTF of 23.2% for predicting weaning failure in 106 ventilated children. They did not measure dTF per age group, but per failed weaning group or successful weaning group. [39] Thus, it seems plausible to aim for a normal physiological dTF to estimate the success of extubation. Before we can conclude this, more research is needed assessing the diaphragm and respiratory muscle effort from the initiation of ventilation till extubation in children and aim for diaphragm-protective mechanical ventilation. [40]

We found that the diaphragm of children from newborn age up to the age of one year was thicker than that of older children, which suggests that the diaphragm has already largely been constructed at birth – and becomes notably longer rather than thicker as the child grows. This seems to make sense from the “survival perspective”, because the young child has to assure full alveolar ventilation from the first breath onward, but does not need to be able to walk. This scenario is different from growth of the other skeletal muscles in children. [41] The need of a strong diaphragm in newborns is confirmed by the above-mentioned study of Rehan et al. in 15 healthy infants, in which diaphragm thickness was positively associated with body size. [22] The authors stated that thickness has implications for diaphragm strength and found that predicted maximal trans-diaphragmatic pressures were independent of body size and length and were greater than those predicted for adults. [22] In addition, the authors suggested that sufficient transdiaphragmatic pressure is necessary to allow the infant to generate sufficient pressure to overcome substantial elastic and resistive loads at the first breath after birth. [22]

The strength of our study is that this is the biggest study that established normal values of the thickness of the diaphragm in combination with the thickness fraction of the diaphragm of healthy children aged 0–8 years. Some limitations can be identified. First, thirteen of the 137 measurements were based on two ultrasounds of the diaphragm instead of three, which might have given less accurate results. Second, the oldest age group included more participants than did the younger age groups, mainly caused by the fact that older siblings of the younger ones wished to undergo ultrasound examination as well. We found it unethical to discard their results. Third, the method of diaphragm measurement may not have been the optimal one. The current general consensus is to measure just the muscle within the lines of the fascia, which was not yet available at the beginning of our study. [36; 37] On the other hand, we measured healthy children where membranes are not expected to be affected by disease or mechanical forces related to ventilation as in ventilated children.

This study provides normal values of diaphragm thickness and thickening fraction in healthy children aged 0 to 8 years. The diaphragm thickness of infants up to 1 year old was significantly greater than that of children from 2 to 8 years old. With an increase in body surface area, the diaphragm thickness decreased. These normal values in healthy children can be used to assess changes in respiratory muscle thickness in ventilated children.

Table 3

Results ultrasound measurements of Tdi and dTF in studies of healthy and ventilated children
Studies	Age groups					Measurement Tdi/dTF***
	0–6 months	7 months-1 year	2–4 years	5–8 years	8–10 years
Healthy children/ Spontaneous breathing
Tdi-insp (mm)
Duyndam et al 2022*	2.07 (0.39), n = 30	2.09 (0.38), n = 30	1.73 (0.33), n = 29	1.70 (0.30), n = 48		midpoint
Vishwanath et al 2016, n = 24*					1.88 (0.23)	NA
Alonso-Ojembarena et al 2020, n = 33**	2.6 (2.2–3.2), n = 33					innerpoint
Ventilated children
Montoro et al 2020, n = 47** At baseline (PS) Before extubation (PS)	2.20 (1.8–2.5) 1.95 (1.7–2.4					midpoint
Lee et al 2017, n = 31* Before extubation (SIMV + PS)			1.92 (0.48)			midpoint
Glau et al 2018, n = 56** Before extubation (Ventilation mode: NA)		2.2 (2.0-2.7)				outerpoint
Tdi-exp (mm)
Healthy children/ Spontaneous breathing
Duyndam et al 2022*	1.63 (0.33), n = 30	1.67 (0.27), n = 30	1.40 (0.23), n = 29	1.40 (0.24), n = 48		midpoint
Rehan et al 2003, n = 15*	1.90 (0.33)					midpoint
Vishwanath et al 2016, n = 24*					1.41 (0.20)	NA
Van Doorn et al 2022, n = 12*				1.4 (0.4)		innerpoint
Alonso-Ojembarena et al 2020, n = 33**	1.9 (1.6–2.4), n = 33					innerpoint
Yeung et al 2022, n = 55	1.5 (0.4)					innerpoint
Ventilated children
Montoro et al 2020, n = 47* At baseline (PS) Before extubation (PS)	1.80 (1.5-2.0) 1.40 (1.3–1.7)					midpoint
Lee et al 2017, n = 31* Before extubation (SIMV + PS)			1.52 (0.38)			midpoint
Glau et al 2018, n = 56** Before extubation (Ventilation mode NA)		2.0 (1.8–2.5)				outerpoint
IJland et al 2020, n = 34** Before extubation (PS) Successful extubation group Failed extubation group	1.4 (1.0-1.6) 1.6 (1.0-1.6)					innerpoint
Thickening fraction (%)
Healthy children/ Spontaneous breathing
Duyndam et al 2022*	27.1 (12.5), n = 30	24.7 (8.6), n = 30	24.1 (10.4), n = 29	21.2 (6.8), n = 48		midpoint
Vishwanath et al 2016, n = 24*					34.0 (SD NA)	NA
Ventilated children
Montoro et al 2020 n = 47** At baseline (PS) Before extubation (PS or SB)	24.0 (8.0–36.0) 30.0 (23.0–46.0)					midpoint
Lee at al 2017, n = 31* At baseline (SIMV + PS) Before extubation (SIMV + PS) After extubation (SB)			25.8 (3.3) 15.6 (2.7) 24.7 (8.6)			midpoint
Glau et al 2018, n = 56** At baseline (NA) Before extubation (NA)		9.7 (6.5–16.4) 14.8 (10.9–26.8)				outerpoint
IJland et al 2020, n = 34** At baseline (PRVC) Before extubation (PS)	10.7 (9.5–14.4) 15.2 (9.6–19.1)					innerpoint
Xue et al 2019, n = 50* Successful weaning (PS) Failure of weaning (PS) Cut off value			30.9 (11.2) 15.9 (6.7) 21			innerpoint

*= mean (SD); ** = median( IQR); Measurement Tdi/ dTF*** between midpoint of diaphragmatic pleura and peritoneal membrane or between inner edges of both layers or between outer edges of both layers; NA = not available; PS = Pressure Support; PRVC = pressure controlled, volume controlled ventilation; SB = spontaneous breathing (through the tube); SIMV = synchronized intermittent mandatory ventilation

Author contributions (CRediT Statement)

Anita Duyndam: Conceptualisation, methodology, investigation, writing-original draft, project administration, formal analysis, data curation, visualization, software, validation

Joke Smit: Methodology, investigation and review&editing

Leo Heunks: Review&editing

Jeroen Molinger: Conceptualisation, methodology, review&editing

Marloes IJland: Review&editing

Joost van Rosmalen: Methodology, formal analysis, review&editing

Dick Tibboel: Conceptualization, resources, review&editing

Monique van Dijk: Conceptualization, review&editing

Erwin Ista: Conceptualisation, methodology, validation, review & editing, supervision

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Ethical Approval

The Medical Ethics Review board at Erasmus MC Rotterdam approved the study (METC No. NL70476.078.19). The study was performed in accordance with the ethical standards of the Declaration of Helsinki.

Consent to Participate

Written informed consent was obtained from the parents.

Conflict of Interest

The authors have no competing interests to declare that are relevant to the content of this article.
All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.

The authors have no financial or proprietary interests in any material discussed in this article.

Acknowledgement: The authors thanks Ko Hagoort for text reviewing.

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No competing interests reported.

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Reference values of diaphragmatic dimensions in healthy children aged 0-8 years

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Journal Publication

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Abstract

Purpose

Method

Results

Conclusion

Figures

Author’s Summary

Introduction

Method

Study population:

Diaphragm measurement

Outcome measures

Parameters

Sample size

Data analysis

Ethical considerations

Results

Discussion

Normal diaphragm values in relation to other publications in healthy children

Normal diaphragm values (dTF) in relation to publications in ventilated children

Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1