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Keywords:

  • diaphragm;
  • hepatic veins;
  • liver;
  • reproducibility of results;
  • ultrasound

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

The aim of this study was to assess the reproducibility of the ultrasound (US) measurement of craniocaudal displacement of the left branch of the portal vein as an indirect method of measuring right hemidiaphragm mobility in healthy young adults. Forty-one healthy participants were selected, ranging from 20 to 30 years of age. The US tests were conducted and interpreted by two observers (A and B) on two separate occasions (Test 1 and Test 2). Intra-observer and interobserver reproducibility and repeatability of US measurements were determined by the intraclass correlation coefficient (ICC[2,1]) using a 95% confidence interval (CI). Interobserver reproducibility assessment showed ‘high correlation’ for Test 1 and Test 2 (ICC[2,1] = 0·83, 95% CI = 0·70–0·91, and ICC[2,1]  = 0·79, 95% CI = 0·61–0·89, respectively). Intra-observer reproducibility assessment showed ‘moderate correlation’ for observer A (ICC[2,1]  = 0·69, 95% CI = 0·45–0·84) and for observer B (ICC[2,1]  = 0·65, 95% CI = 0·39–0·81). Repeatability assessment showed ‘high correlation’ for all tests performed (ICC[2,1]  = 0·86, 0·80, 0·74, 0·79, P<0·001). In conclusion, US measurement of craniocaudal displacement of the left branch of the portal vein is a reproducible method of measuring right hemidiaphragm mobility in healthy young adults.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

The diaphragm is the primary inspiratory muscle and it is responsible for 70–80% of pulmonary ventilation. During its contraction, the craniocaudal excursion of the dome of the diaphragm occurs and the thoracic cavity expands, generating enough negative intrapleural pressure to allow air intake into the lungs (Reid & Dechman, 1995; Poole et al., 1997; Anraku & Shargall, 2009). To achieve optimal pulmonary mechanics, however, it is essential to have full movement of the diaphragm, which requires an ideal length–tension relationship and efficient interaction between the abdominal muscles and the diaphragm (Reid & Dechman, 1995).

Various imaging methods have been used to assess diaphragm mobility, including fluoroscopy, computerized axial tomography, nuclear magnetic resonance, thoracic radiography and ultrasound (US) (Houston et al., 1992, 1995; Gottesman & McCool, 1997; Gierada et al., 1998; Toledo et al., 2003; Bih et al., 2004; Scott et al., 2006; Boussuges et al., 2009; Roberts, 2009; Saltiél et al., 2013). Fluoroscopy has been considered the most reliable method for quantitative measurement of the diaphragm's craniocaudal movement during spontaneous respiration. But despite being considered the gold standard, this method has some limitations, that is, single view of the diaphragm, calculation for correction and patient exposure to ionizing radiation (Gierada et al., 1998).

Computerized axial tomography and nuclear magnetic resonance allow the detailed anatomical study of different parts of the diaphragm and the assessment of muscle position similarly to thoracic radiography. However, the slow speed of imaging can hinder the analysis of diaphragm motion. Furthermore, accessibility, the size and cost of the equipment, and the length of the tests make the frequent use of these methods unviable in clinical practice (Gierada et al., 1998; Roberts, 2009).

An alternative and interesting method of measuring diaphragm mobility is US. Over the last decades, researchers have used this method to directly measure diaphragm mobility and consider it an accurate tool to determine dysfunctions of this muscle. Compared to fluoroscopy, US has the advantage of being quick, portable and free of ionizing radiation (Houston et al., 1992, 1995, 1995; Gottesman & McCool, 1997; Toledo et al., 2003; Bih et al., 2004; Scott et al., 2006; Boussuges et al., 2009). However, the direct measurement of diaphragm mobility using US has some limitations. Direct visualization of the diaphragm is difficult and not always possible (Toledo et al., 2003; Bih et al., 2004; Scott et al., 2006; Boussuges et al., 2009), and the method also presents methodological difficulties that depend on transducer positioning (Toledo et al., 2003). When the US transducer is placed between the intercostal spaces, viewing of the dome of the diaphragm can be hindered during deep inspiration by the interposition of the lung and by the movement of the subjacent ribs. However, when it is positioned cranially over the subcostal abdominal window, the direction of the craniocaudal excursion is oblique to the angle of incidence of the US beam, which compromises the accuracy of diaphragm mobility measurement (Toledo et al., 2003).

In an attempt to overcome the limitations of the direct US method, Toledo et al. (2003) developed and validated a simple and practical method of indirect US to measure right hemidiaphragm mobility via craniocaudal displacement of the left branch of the intrahepatic portal vein. This method takes into consideration that the liver is a parenchymal organ that undergoes subtle changes in shape and has similar mobility to the right hemidiaphragm during respiration (Päivansölo & Myllylä, 1984; Korin et al., 1992; Davies et al., 1994). However, there are currently no studies that investigate the reproducibility of this method. The performance of this type of study is justified by the need to verify the reliability of the test in both research and clinical practice.

Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

Population and sample

The sample for this study was comprised of volunteers recruited among young adults. The following inclusion criteria were used: individuals aged from 20 to 30 years, non-smokers, non-obese (BMI < 30 Kg m−2), with no diagnosis of cardio respiratory or hepatic diseases and with proven normal pulmonary function. All subjects were previously informed of the study methods and objectives and signed an informed consent form.

Research procedures

The research was carried out at the Physical Therapy Clinic of Universidade do Estado de Santa Catarina (UDESC) and at the Radiology Sector of the University Hospital of Universidade Federal de Santa Catarina (HU/UFSC) after approval from the Human Research Ethics Committee (protocol 153/2010). At the Physical Therapy Clinic, the participants underwent a physical examination and were submitted to a pulmonary function test and a respiratory muscle strength testing. All tests were conducted on the same day by a single observer. At the Radiology Sector, each participant made an appointment to measure right hemidiaphragm mobility via US measurement of craniocaudal displacement of the left branch of the hepatic portal vein. The participants were instructed not to eat for 2 h prior to the test and to refrain from intense physical activity, and they could not have a cold.

US testing and interpretation were carried out by two radiology and diagnostic imaging residents (observers A and B) independently on two separate occasions (Test 1 and Test 2) and at least 1 week apart (Fig. 1). The observers had over 1 year of experience in abdominal US testing and underwent specific training to assess diaphragm mobility using the proposed method.

image

Figure 1. Process of assessment of the reproducibility of the ultrasound measurement of craniocaudal displacement of the left branch of the portal vein.

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Physical examination

Body mass was measured with a previously calibrated scale (model W200/5, Welmy). Height was measured with a stadiometer (model W200/5, Welmy). After the anthropometric values (body mass and height) were obtained, the body mass index (BMI) was calculated using the following equation: body mass height−2 (kg m−2).

Pulmonary function test

A pulmonary function test was performed with a portable digital spirometer (model EasyOne TM Diagnostic Spirometerl; ndd Medical Technologies, Andover, MA, USA), previously calibrated according to the methods and criteria of the American Thoracic Society (Miller et al., 2005). Forced vital capacity (FVC), forced expiratory volume in the first second (FEV1) and FEV1/FVC ratio were measured. At least three acceptable and two repeatable manoeuvres were performed, that is, the difference between the two highest FVC and FEV1 values should be <0·15 l. We considered the highest values obtained for each of the spirometric variables, expressed as absolute values and percentage values of the expected normal values, as set forth by Pereira et al. (2007). Normal pulmonary test criteria were FVC and FEV1 ≥ 80% of predicted and FEV1/FVC ≥ 0·7.

Respiratory muscle strength testing

Respiratory muscle strength was measured using a digital manual vacuum metre (model MVD500; Microhard, Porto Alegre, Rio Grande do Sul, Brazil) attached to a mouthpiece with a 2-mm diameter air-leak opening. Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) were measured as indicators of inspiratory and expiratory muscle strength, respectively, following the guidelines of the Brazilian Society of Pulmonology and Phthisiology (Souza, 2002). MIP was measured from the volume closest to residual volume by asking the participants to perform maximal expiration followed by maximal inspiration. MEP was measured at the volume closest to total lung capacity by asking the participants to perform maximal inspiration followed by maximal expiration. The participants performed three to five manoeuvres to obtain three acceptable manoeuvres (without leaks and lasting at least 2 s) including at least two repeatable manoeuvres (i.e. with difference between values of no more than 10% of the highest value). The value considered for the study was the highest among the reproducible manoeuvres. If the highest value was measured in the last manoeuvre, the test was repeated until a lower value was obtained, thus minimizing the learning effect. MIP and MEP were expressed as absolute and percentage values of the expected normal values according to Neder et al. (1999).

Right hemidiaphragm mobility measurement

Right hemidiaphragm mobility was measured using US imaging of the craniocaudal displacement of the left branch of the portal vein (model Voluson 730 Pro V; GE Healthcare, Amersham, Buckinghamshire, UK) in B-mode as described by Toledo et al. (2003). The participants were tested in the dorsal decubitus position by two physicians (observer A and observer B) independently and one immediately following the other. A 3·5 MHz convex transducer was placed over the right subcostal region in the sagittal plane, with the incidence angle perpendicular to the craniocaudal axis towards the inferior vena cava. Initially, the observers identified the intrahepatic portal vein in the field of vision, and then the left branch. Next, with the transducer over the right subcostal region, the position of this branch was marked with the cursor at the end of maximal expiration and inspiration. The craniocaudal displacement of these points was considered the measurement of right hemidiaphragm mobility (Fig. 2).

image

Figure 2. Ultrasound measurement (B-Mode) of craniocaudal displacement of the left branch of the intrahepatic portal vein. The right arrow marks the initial position of the blood vessel during maximal inspiration and the left arrow marks the position during maximal expiration.

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After a minimum period of 1 week, the participants underwent a second US test performed by the same observers. During each test, the observers obtained three consecutive measurements from each participant, which were recorded by a physical therapist. To analyse inter- and intra-observer reproducibility, the maximum value measured was considered. To assess the repeatability of the measurements obtained during each US, the first and the last measurements of each participant were considered (1st Measurement and 3rd Measurement).

It is worth noting that the participants were previously instructed by a physical therapist to perform diaphragm respiration in all US tests; however, the verbal command for maximal expiration and inspiration during the test was given by observer A and observer B. If the participant failed to use diaphragm respiration or if observers noticed that they were not using maximal inspiratory and expiratory strength, the measure was disregarded and then repeated.

Statistical analysis

Data were analysed using SPSS for Windows, version 17·0 (IBM SPSS Statistics, IBM, Armonk, NY, USA) and treated as descriptive analysis (means and standard deviation) and inferential analysis. The Shapiro–Wilk test was used to check data normality and homogeneity of variance.

The intra-observer and interobserver reproducibility of the US measurements of craniocaudal displacement of the left branch of the portal vein was determined by the intraclass correlation coefficient (ICC[2,1] - two-way random effects model with absolute agreement) and a 95% confidence interval (CI). To determine interobserver reproducibility, ICC[2,1] was calculated for each US test (Test 1 and Test 2) using the highest measurement obtained from each participant by each observer. To determine intra-observer reproducibility, each participant's ICC[2,1] was also calculated considering the highest measurement obtained from each participant in each of the tests. Repeatability was determined for each observer by calculating the ICC[2,1] considering the first and the last measurements obtained from each participant. ICC[2,1] was interpreted using the classification system by Munro (1997): 0·0 to 0·25 being ‘little if any’; 0·26 to 0·49, ‘low’; 0·50 to 0·69, ‘moderate’, 0·70 to 0·89, ‘high’; 0·90 to 1·00, ‘very high’. The significance level was set at 5% (P<0·05).

Bland–Altman plots were also used to assess inter- and intra-observer reproducibility because they provide better visualization of agreement between measurements. The Bland–Altman repeatability coefficient, defined as twice the standard deviation of the mean difference between the initial and final measurement of each assessment, was calculated for the US measurements obtained by observers A and B in each test (Bland & Altman, 1986).

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

Initially, 43 male and female participants were selected; however, two of them were not included in the study due to changes in pulmonary function. Hence, 41 participants were assessed: 27 women (66%) and 14 men (34%), with a mean age of 24·8 ± 2·7. Of the 41 participants, only 31 showed up for Test 2. Anthropometric characteristics, pulmonary function and respiratory muscle strength are shown in Table 1.

Table 1. Anthropometric characteristics, pulmonary function and respiratory muscle strength variables of study subjects
VariablesMeans ± Standard deviation (variation) (= 41)
  1. Variation, minimum value – maximum value; n, number of individuals; kg, kilograms; m,metres; BMI, body mass index. FVC, forced vital capacity (L, litre); FVC (estim%), forced vital capacity of estimated percentage; FEV1, forced expiratory volume in the first second; FEV1 (estim%), estimated percentage of forced expiratory volume in the first second; MIP, maximal inspiratory pressure; MIP (estim%), estimated percentage of maximal inspiratory pressure; MEP, maximal expiratory pressure; MEP (estim%), estimated percentage for maximal expiratory pressure.

Age (years)24·8 ± 2·7 (20–30)
Body mass (kg)69·2 ± 16·6 (49·8–104·8)
Height (m)1·72 ± 0·11 (1·54–1·90)
BMI (kg m²)23·0 ± 3·5 (17·8–29·89)
Pulmonary function
FVC (L)4·37 ± 1·11 (3·04–7·24)
(estim%)94·8 ± 10·2 (80–122)
FEV1 (L)3·68 ± 0·89 (2·52–5·67)
(estim%)95·2 ± 9·2 (80–113)
FEV1/FVC0·84 ± 0·05 (0·70–95·5)
(estim%)99·7 ± 7·7 (83–113)
Respiratory muscle force
MIP (cmH2O)−107·0 ± 32·2 (−50–−171)
(estim%)96·2 ± 23·7 (50–150)
MEP (cmH2O)137·9 ± 42·0 (69–260)
(estim%)119·3 ± 28·8 (68–206)

The mean values for right hemidiaphragm mobility obtained by each observer (observer A and observer B) on two separate occasions (Test 1 and Test 2) are shown in Table 2.

Table 2. Right hemidiaphragm mobility value for study subjects
 Right hemidiaphragm mobility (mm) Means ± Standard deviation (variation)
  1. Variation, minimum value – maximum value; n, number of individuals; mm, millimetres.

Test 1

(= 41)

Observer A62. 03 ± 10·78 (38·9–93·3)
Observer B63·66 ± 11·34 (46·2–89·1)

2 Test

(= 31)

Observer A63·36 ± 9·65 (44·8–85·5)
Observer B62·55 ± 11·24 (40·1–85·5)

In the interobserver reproducibility assessment, the ICC[2,1] was high for Test 1 and Test 2 (ICC[2,1] = 0·83 and ICC[2,1] = 0·79, respectively, P<0·001). In the intra-observer reproducibility assessment, the ICC[2,1] was moderate for observer A (ICC[2,1] = 0·69, P<0·001) and observer B (ICC[2,1] = 0·65, P<0·001). In the US measurement repeatability assessment, the ICC[2,1] was high for all tests (ICC[2,1] = 0·86; 0·80; 0·74; 0·79, P<0·001). Interobserver and intra-observer reproducibility and US measurement repeatability obtained in each US test are shown in Table 3.

Table 3. Interobserver and intra-observer reproducibility and ultrasound repeatability measurement of craniocaudal displacement of left branches of the portal vein
 ICC[2,1]CI 95% P
  1. n, number of individuals; ICC[2,1], intraclass correlation coefficient (two-way random effects model, with absolute agreement); CI 95%, 95% confidence interval; P, level of significance.

Interobserver ReproducibilityTest 1 (= 41)0·830·70–0·91<0·001
Test 2 (n = 31)0·790·61–0·89<0·001
Intra-observer ReproducibilityObserver A (n = 31)0·690·45–0·84<0·001
Observer B (n = 31)0·650·39–0·81<0·001
RepeatabilityTest 1 Observer A (n = 41)0·860·78–0·92<0·001
Test 1 Observer B (n = 41)0·800·69–0·88<0·001
Test 2 Observer A (n = 31)0·740·59–0·86<0·001
Test 2 Observer B (n = 31)0·790·65–0·88<0·001

The Bland–Altman plots (Fig. 3) show the agreement between the measurements for right hemidiaphragm mobility obtained by observer A and Observer B in both tests (interobserver agreement).

image

Figure 3. Bland–Altman plots of the agreement between the measurements of right hemidiaphragm mobility obtained by observers A and B (interobserver agreement) – Test 1 and Test 2. X axis: Average of diaphragm mobility measurements obtained by observers A and B for each participant (Measurement by observer A + Measurement by observer B/2). Y axis: Difference between diaphragm mobility measurements obtained by observers A and B for each participant (Measurement by observer B – Measurement by observer A). UL: Upper limit. LL: Lower limit.

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The Bland–Altman plots (Fig. 4) also show measurement agreement between the measurements of right hemidiaphragm mobility obtained by each observer on two separate occasions (intra-observer agreement).

image

Figure 4. Bland–Altman plots of the agreement between the measurements of right hemidiaphragm mobility obtained by observer A and by observer B during Test 1 and Test 2 (intra-observer A agreement and intra-observer B agreement). X axis: Average of diaphragm mobility measurements obtained by observer A or B for each participant in Test 1 and Test 2 (Measurement by observer A or B in Test 1 + Measurement by Observer A or B in Test 2/2). Y axis: Difference between diaphragm mobility measurements obtained by observer A or B for each participant in Test 1 and Test 2 (Measurement by observer A or B in Test 2 - Measurement by Observer A or B in Test 1). UL: Upper limit. LL: Lower limit.

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The repeatability coefficient of the measurements obtained by observer A was 11·5 mm in Test 1 and 15·3 mm in Test 2. The repeatability coefficient of measurements obtained by observer B was 16·3 mm in Test 1 and 16·4 mm in Test 2. Plots for US measurement repeatability by each observer in each test are shown in Figs 5 and 6.

image

Figure 5. Bland–Altman plots for the agreement between the measurements of right hemidiaphragm mobility obtained by observer A in Test 1 and Test 2. X axis: Average between the 1st and 3rd diaphragm mobility measurements obtained by observer A for each participant (1st Measurement + 3rd Measurement/2). Y axis: Difference between the 3rd and 1st diaphragm mobility measurements obtained by observer A for each participant (3rd Measurement – 1st Measurement).

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image

Figure 6. Bland–Altman plots for the agreement between the measurements of right hemidiaphragm mobility obtained by observer B in Test 1 and Test 2. X axis: Average between the 1st and 3rd diaphragm mobility measurements obtained by observer B for each participant (1st Measurement + 3rd Measurement/2). Y axis: Difference between the 3rd and 1st diaphragm mobility measurements obtained by observer B for each participant (3rd Measurement – 1st Measurement).

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Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

This study shows that US measurement of the craniocaudal displacement of the left branch of the portal vein is reproducible as a method of measuring right hemidiaphragm mobility in healthy young adults. Furthermore, the mean value of right hemidiaphragm mobility in healthy participants (62·89 ± 10·72 mm) was similar to values reported in former studies. Boussuges et al. (2009) found a mean value of 66 ± 13 mm, and Cohen et al. (1994) found a mean value of 60 ± 7 mm. Regarding the maximal and minimal values obtained for right hemidiaphragm mobility, there was a wide range of variation (38·9 to 93·3 mm) as found in other studies. Boussuges et al. (2009) found values between 36 and 92 mm. Kantarci et al. (2004) assessed 64 healthy participants and found a variation of 25 to 84 mm. Houston et al. (1992) also found a wide range of variation (23 to 97 mm in 55 patients without respiratory diseases) and established that normal diaphragmatic mobility is above 20 mm. Fedullo et al. (1992) and Gerscovich et al. (2001) had similar findings to those presented by Houston et al. (1992).

It is crucial to measure diaphragm mobility because the dysfunction of this muscle is commonly observed in muscular dystrophies; phrenic nerve injury; patients who received prolonged mechanical ventilation; patients with upper spinal cord injury; cardiac, thoracic and abdominal surgery patients; and patients with sequelae from poliomyelitis, malnutrition and chronic obstructive pulmonary disease (Efthimiou et al., 1991; Lemons & Wagner, 1994; Ayoub et al., 2001; Paulin et al., 2007; Yamaguti et al., 2008, 2012; Fernandes et al., 2011; Kodric et al., 2013). Therefore, it is necessary to test diaphragm function in different clinical situations to diagnose the dysfunction and to evaluate the results of therapeutic measures.

Regarding the method's reproducibility, the ICC[2,1] was high between the measurements obtained by the observers (interobserver reproducibility) when the method was applied under the same conditions. The Bland–Altman plots also show good agreement between measurements given that the average difference between measurements obtained by the observers was close to zero.

With respect to the limits of agreement in the Bland–Altman plots, the difference between measurements obtained by both observers was <14·5 mm. This difference cannot be attributed solely to the method employed because diaphragm mobility is a voluntary activity subject to interference by individual and environmental factors. Therefore, it is possible that the verbal command from the observers requesting maximal inspiration and expiration from the participants interfered in their performance as the command was not standardized. It is also noteworthy that the perception that the participants actually used their maximum capacity in every respiratory manoeuvre was only visually controlled. Air flow volume during respiratory manoeuvres could have been monitored using a ventilometer, for example, to ensure that the participants actually performed maximal efforts.

Factors such as learning effect may also have interfered in the results as repetition of the manoeuvre favours progressive improvement in diaphragm mobility measurements. In the present study, as described by Toledo et al. (2003), three successive measurements were obtained from each participant by each observer in each test, with the highest value being considered for reproducibility analysis. However, we recommend that future studies use a greater number of repetitions when the last measurement is higher than the rest to minimize the learning effect.

Another factor that can influence the variability of diaphragmatic excursion is the measurement procedure. For this reason, we followed the standardization described by Toledo et al. (2003), which prevents or limits known sources of error in US measurements. It is worth noting that the movements observed in US correspond to the displacement of structures in relation to the transducer; therefore, the device must remain static as any shifts will generate measurement artefacts. Consequently, the observers tried to stabilize the transducer on the participant's skin to avoid or minimize potential sources of error. Regarding transducer frequency and US mode, we chose 3·5 Hz because it is the ideal frequency for the abdominal cavity and B-Mode because it is the most commonly used in clinical practice and allows visualization of the shape of the object being studied (Cerri & Rocha, 1996).

Intra-observer reproducibility was also assessed in the study, and the ICC[2,1] was moderate between measurements obtained by the same observer on two separate occasions at least 1 week apart and under similar conditions. The Bland–Altman plots also show the dispersion of differences between measurements, with limits of agreement <19·8 mm. The present research attempted to create the same conditions for both Test 1 and Test 2. However, intra-individual variation factors, such as motivation or changes in the capacity to perform respiratory manoeuvres during the day of the test may have interfered with the results.

US measurement of right hemidiaphragm mobility via craniocaudal displacement of the left branch of the portal vein is a validated indirect method that proved to be reproducible and enabled the assessment of all participants. Recently, Boussuges et al. (2009) also showed the reproducibility of the direct measurement of diaphragm mobility using US testing. These authors observed that the direct method allowed the measurement of right hemidiaphragm mobility during basal respiration of the total sample (210 participants) and deep respiration in 93% of the cases. Nevertheless, the authors stress that the high rate of success during the measurement could have been lower if the study had included patients with respiratory diseases. In the case of patients with dyspnoea, increased respiratory effort could result in greater movement of the thoracic cavity and might obscure images because of the interposition of the lungs and ribs. In the measurement of left hemidiaphragm mobility during deep respiration, the direct method was more complex and only 45 participants were tested. According to the authors, the visualization of the left hemidiaphragm was frequently obscured by the expansion of the lungs during deep respiration.

Other authors reported difficulty in measuring diaphragmatic mobility using the direct method. In patients referred for pulmonary function tests, Scott et al. (2006) found 28% failure in the measurements. Gerscovich et al. (2001) were unsuccessful in measuring right hemidiaphragm mobility in 15 of 23 volunteers (65%). In contrast, the indirect measurement of diaphragm mobility using US imaging of craniocaudal displacement of the left branch of the portal vein allowed measurement of all participants of the present study, proving to be a successful alternative to the direct method.

This study also assessed the repeatability of the indirect method to determine the variation between repeated measurements obtained by a single observer in the same individual using the same instrument under identical conditions over a short period of time (Bland & Altman, 1986). In this assessment, the ICC[2,1] was calculated for each observer in Test 1 and Test 2 and showed strong agreement between measurements in each situation described. The repeatability coefficient for observer A was calculated, and the values were 11·5 mm and 15·3 mm in Test 1 and Test 2, meaning that the difference between the paired measures was 11·5 mm and 15·3 mm. For observer B, the repeatability coefficient between measurements was even greater, with 16·3 mm in Test 1 and 16·4 mm in Test 2. Toledo et al. (2003), who developed and validated the indirect method of measuring diaphragm mobility, found a repeatability coefficient of <9·6 mm.

It should be pointed out that the differences between the two paired measures and the differences between the coefficients of the present study and those of Toledo et al. (2003) cannot be attributed solely to the method, given that diaphragm mobility is susceptible to intra-individual variations and external influences. Factors such as learning effect may have contributed to progressively better results. In contrast, fatigue can have the opposite effect. Furthermore, it is possible that the verbal command given by each observer to request maximal inspiration and expiration may have interfered in the participants' performance. Thus, the conditions of the three repeated measurements of each participant by each observer in each test may not have been constant despite the short interval between them.

It is also important to point out that, in the present study, the participants were healthy and mostly active young adults (24·8 ± 2·7 years of age) with mean diaphragm mobility of 62·89 ± 10·72 mm, whereas in the study by Toledo et al. (2003), the mean diaphragm mobility was 35·2 ± 10·7 mm and the sample included liver transplant patients with a mean age of 46·8 ± 12·6. Therefore, the repeatability coefficients in this study may have been greater than those found by Toledo et al. (2003) given the higher probability of variability of data.

In view of these findings, we verified that the indirect method of measuring diaphragmatic mobility using US measurement of craniocaudal displacement of the left branch of the portal vein allowed testing of all participants and proved to be a reproducible and reliable method that can be used to determine dysfunctions of the diaphragm muscle. Furthermore, this method proved to be quick, practical and easily performed in hospitals, clinical practice and research protocols. Despite being an indirect measurement of diaphragm mobility, this method can measure diaphragm movement without the use of radiation, allowing short- to long-term follow-up of patients undergoing physical therapy and/or clinical treatment.

Conclusion

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References

US measurement of craniocaudal displacement of the left branch of the portal vein proved to be a reliable indirect method of quantifying right hemidiaphragm mobility in healthy young adults.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusion
  8. Conflict of interest
  9. References
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