Sonoelastographic evaluation of diaphragmatic thickness and stiffness in dialysis patients

Abstract

Objectives

This study aimed to quantitatively and noninvasively assess diaphragmatic alterations in patients with end-stage renal disease undergoing hemodialysis (HD) or peritoneal dialysis (PD) using ultrasonography (US) and shear wave elastography (SWE).

Methods

This prospective cross-sectional study included 69 dialysis patients (HD, n = 37; PD, n = 32) and 60 demographically matched healthy controls. Right hemidiaphragm was evaluated using greyscale US and SWE through the 8th–10th intercostal spaces in the mid-axillary line. Thickness and stiffness were measured at end-expiration and peak inspiration phases. Clinical data, laboratory parameters, and dialysis-related metrics were recorded. Comparative and correlational analyses were performed using appropriate statistical methods.

Results

At peak inspiration, the measurements were 2.24 ± 0.25 mm and 25.61 ± 6.15 kPa for the HD group, 2.53 ± 0.23 mm and 32.79 ± 5.31 kPa for the PD group, and 2.86 ± 0.29 mm and 47.68 ± 6.67 kPa for the control group. Significant differences were observed between the groups for both parameters (p < 0.001). At end expiration, diaphragm thickness and stiffness were 1.69 ± 0.20 mm/19.46 ± 4.37 kPa, 1.75 ± 0.19 mm/22.62 ± 4.84 kPa, and 2.00 ± 0.19 mm/33.26 ± 4.62 kPa in the HD, PD, and control groups, respectively. There were significant differences between the groups (p < 0.05). ROC analysis indicated excellent diagnostic performance of these parameters for distinguishing dialysis patients from controls (AUC 0.806–0.987). Furthermore, diaphragm parameters correlated significantly with dialysis duration, adequacy, comorbidity, and serum albumin levels.

Conclusion

Diaphragm thickness and stiffness are reduced in dialysis patients, especially those on hemodialysis. US and SWE may serve as early imaging biomarkers for respiratory sarcopenia.

Introduction

Chronic kidney disease (CKD) increases the risk of developing sarcopenia, which is characterised by significant losses in muscle mass and function. This is due to multifactorial mechanisms, including systemic inflammation, hormonal irregularities, metabolic acidosis, protein-energy deficiency and physical inactivity [1, 2]. Sarcopenia is becoming increasingly prevalent, particularly among dialysis-dependent patients, and is associated with decreased functional capacity, falls, hospitalisations, and mortality [3]. Sarcopenia causes atrophy in the muscles of the extremities and respiratory muscles, bringing the concept of ‘respiratory sarcopenia’ to the fore [4, 5]. Respiratory sarcopenia is defined as a condition in which low respiratory muscle strength and low respiratory muscle mass are both present [5]. Increased oxidative stress, inflammation, and muscle protein breakdown in dialysis patients lead to respiratory muscle weakness and significant respiratory function impairment. In this context, respiratory muscle dysfunction has been shown to be one of the systemic effects of sarcopenia in CKD patients [6, 7].

The diaphragm is the primary respiratory muscle, undertaking most of the work of inspiration, and it is directly affected by sarcopenic processes due to its skeletal muscle structure [8, 9]. Dysfunction of the diaphragm may lead to significant clinical outcomes, including dyspnoea, decreased exercise capacity, and impaired quality of life, in patients with CKD and dialysis [10, 11]. In recent years, it has become possible to evaluate the structure and functional properties of the diaphragm using non-invasive methods such as ultrasonography (US) and shear wave elastography (SWE) [12–14]. Diaphragm muscle thickness can be measured using US grey-scale, and muscle motility in respiratory phases can be monitored. SWE is an ultrasound-based imaging technique that can quantitatively measure stiffness values, which provide indirect information about the muscle’s biomechanical properties [14, 15].

Evaluating the diaphragm musculature is important for the early detection of respiratory sarcopenia in dialysis patients. This study aims to analyse the structure of the diaphragm muscle in peritoneal dialysis (PD) and haemodialysis (HD) patients using US and SWE, and to compare it with that of healthy individuals. The study also aims to investigate the relationship between structural changes and clinical outcomes.

Materials and methods

Study design and patient population

This single-centre, prospective cross-sectional study was conducted with the approval of the institutional ethics committee (2024/47). Written informed consent was obtained from all participants. Between March 2024 and January 2025, consecutive and random inclusion of patients was performed for those being followed up in the nephrology clinic, diagnosed with end-stage renal failure and receiving dialysis treatment, and aged between 18 and 65.

The following individuals were excluded from the study: those with acute or chronic respiratory diseases (e.g. asthma or COPD), decompensated heart failure, a smoking history of 20 packs or more per year, neuromuscular diseases, a history of cerebrovascular disease or thoracic surgery, the presence of pulmonary malignancy, moderate or advanced dementia, or who were non-cooperative. The control group consisted of healthy volunteers who were matched for age and gender. Demographic and clinical data, as well as laboratory results, were obtained from the hospital information management system for all participants and recorded.

Ultrasonography and shear wave elastography examination

Ultrasonographic evaluations were performed using a single device (Resona I14, Mindray, Shenzhen, China) fitted with a high-frequency linear probe (SC2-9 MHz). US grey scale and SWE imaging were performed on the right hemidiaphragm only. Participants were assessed in the supine position with their right arm placed overhead. The ultrasound probe was positioned between the anterior and mid-axillary lines at the level of the ninth or tenth intercostal space. The right hemidiaphragm was identified as hypoechoic muscle tissue located between two hyperechoic lines (the pleura and the peritoneum) just above the liver, and its three-layered structure was visualised. Care was taken to position the probe perpendicular to the chest wall without applying pressure. Once the diaphragm had been clearly defined using grey-scale imaging, at least three consecutive respiratory cycles were monitored, and diaphragm thickness and elasticity measurements were taken during both the inspiration and expiration phases. The elasticity of the diaphragm was measured at three different sites using consecutive regions of interest (ROIs), with the results recorded in kilopascals (kPa). The size of each ROI was adjusted to between 1 and 3 mm according to the anatomical boundaries of the diaphragm. The mean value obtained from the three measurements was considered the stiffness value of the diaphragm. SWE measurements were repeated three times for each participant, with the median value being used in the analysis. Advanced technologies provided by the manufacturer supported the accuracy and stability of the measurements. The ‘Motion Stability’ (M-STB) function enabled real-time monitoring of motion stability in the target area, with measurements taken only when 4–5 stars and a green indicator were present. Additionally, image quality was evaluated using the ‘Reliability Map’ (RLB MAP) feature, with measurements taken only in areas displaying a reliability index of 90% or above. The measurements were performed by a radiologist (N.D.) with ten years’ experience in musculoskeletal imaging and a radiology resident (A.G.U.) in their final training year. Figure 1 shows an example of a diaphragm US grey scale and SWE measurement.

Fig. 1.

Diaphragm thickness (A) is measured by the hypoechoic muscle tissue located between two hyperechoic lines (the pleura and the peritoneum), Diaphragm elasticity (B) measurement was taken in regions of interest (ROI), with the ROI dimensions adjusted between 1 and 3 mm according to the anatomical boundaries of the diaphragm. The ‘Motion Stability’ (M-STB) function was only measured at a 4–5 star level and in the presence of a green indicator. ‘Reliability Map’ (RLB MAP) measurements were taken from areas with a RLB index of 90% or above

Statistical analyses

The data from the study were analysed using SPSS software (IBM Corp., Armonk, NY, USA). Descriptive statistics were presented as the mean ± standard deviation (or the median and interquartile range if the distribution was not normal) for continuous variables, and as a frequency and percentage for categorical variables. The distribution of continuous variables was evaluated using the Kolmogorov–Smirnov test. Comparisons between two independent groups were made using an independent samples t-test for normally distributed data and a Mann–Whitney U-test for non-normally distributed data. Pearson correlation analysis was used to evaluate the relationship between variables. Receiver operating characteristic (ROC) analyses were performed to evaluate the ability of diaphragm thickness and stiffness measurements to distinguish between dialysis patients and the control group. ROC curves were generated for each measurement and the area under the curve (AUC) was calculated and presented with 95% confidence intervals. The optimal cut-off points were determined using the Youden index (J = sensitivity + specificity – 1), which provides the highest sensitivity and specificity. The positive and negative predictive values for the cut-off points are also reported. A p-value of less than 0.05 was considered statistically significant in all tests.

Results

Participant characteristics

The mean age of the 69 patients included in the study was 49.7 ± 13.6 years, of whom 55% (n = 38) were female. Of these patients, 54% underwent HD (n = 37) and 46% PD (n = 32). The control group consisted of 60 individuals with a mean age of 46.6 ± 6.6 years, of whom 52% were female. There was no statistically significant difference between the patient and control groups in terms of age and gender (p > 0.05). The demographic data of the participants are presented in Table 1.

Table 1.

The demographic data of the participants

Variables	Patient (n = 69)	Control (n = 60)	P
Age (years)	49.7 ± 13.6 (20–65)	46.6 ± 6.6 (23–65)	0.112
Sex (female/male)	38/31	31/29	0.702
Weight (kg)	63.3 ± 13.4 (44–98)	67.7 ± 10.3 (47–92)	0.161
Height (cm)	166.9 ± 7.9 (150–186)	169.1 ± 7.5 (158–190)	0.144
BMI	22.8 ± 4.3 (16–36)	23.2 ± 3.1 (17–31)	0.606

No significant differences were found between the HD and PD subgroups in terms of age or gender distribution (p > 0.05). However, the HD group had significantly higher heights and BMIs than the PD group (p < 0.05). The mean dialysis duration was 4.5 ± 4.4 years in the HD group and 7.0 ± 5.2 years in the PD group, with a statistically significant difference (p < 0.05). Dialysis adequacy was significantly higher in the PD group than in the HD group (p < 0.05). Comorbidities were present in 81% of HD patients and 59% of PD patients. The detailed demographic and laboratory findings of the patient subgroups are presented in Table 2.

Table 2.

The detailed demographic and laboratory findings of the patient subgroups

Variables	Hemodialysis (n = 37)	Peritoneal dialysis (n = 32)	P
Age (years)	51.7 ± 14.2 (24–65)	47.5 ± 12.8 (20–65)	0.205
Sex (F/M)	17/20	21/11	0.104
Height (kg)	67.1 ± 13.6 (47–98)	58.8 ± 11.9 (44–87)	0.010
Weight (cm)	167.1 ± 8.1 (150–186)	166.7 ± 7.8 (150–185)	0.808
BMI	24.0 ± 4.5 (17–36)	21.5 ± 3.7 (16–35)	0.017
Dialysis time (years)	4.5 ± 4.4 (0.5–22)	7.0 ± 5.2 (1–19)	0.024
Dialysis adequacy	1.7 ± 0.7 (0.9–4.7)	2.2 ± 0.6 (1.2–3.7)	0.006
Comorbidities n (%)	30 (81%)	19 (59%)	0.040
Hb (gm/dL)	10.8 ± 2.6 (6.1–19.2)	10.0 ± 1.6 (6.8–13.3)	0.175
WBCs (× 103/mL)	6.2 ± 1.9 (4–11)	6.0 ± 2.1 (3.9–10.8)	0.577
Platelets (× 103/mL)	241.2 ± 81.3 (60–411)	250.2 ± 102.3 (56–434)	0.684
Urea (mg/dL)	48.5 ± 19.5 (8–94)	53.5 ± 34.6 (13–225)	0.454
Creatinine (mg/dL)	6.3 ± 2.9 (1.8–12.2)	8.3 ± 2.7 (3.6–13.6)	0.006
Uric acid (mg/dL)	5.3 ± 2.0 (1.3–9.3)	5.6 ± 1.5 (1.2–8.2)	0.415
Albumin (gm/dL)	3.8 ± 0.4 (2.5–4.5)	3.6 ± 0.4 (2.7–4.5)	0.200
Cholesterol (mg/dL)	180.0 ± 36.5 (130–258)	187.5 ± 36.0 (100–243)	0.397
Triglycerides (mg/dL)	135 (100–147)	145 (99–189)	0.364
Calcium (mg/dL)	8.6 ± 0.8 (6.9–10.4)	8.8 ± 0.9 (7.3–11)	0.202
Phosphorus (mg/dL)	4.8 ± 2.0 (1.2–8.9)	4.6 ± 1.1 (2.2-7)	0.680
Sodium (mEq/L)	135.8 ± 3.9 (127–145)	136.5 ± 3.6 (130–145)	0.467
Potassium (mEq/L)	4.4 ± 0.7 (3.8-5.0)	4.3 (3.8–4.75)	0.130
CRP (mg/L)	2.0 (1.4–2.7)	2.0 (1.1–4.7)	0.547

mean ± SD (min-max)/median (IQR)

Diaphragm thickness and stiffness measurements

In the US grey-scale evaluation, the mean diaphragm thickness measured at peak inspiration was 2.86 ± 0.29 mm in the control group, 2.53 ± 0.23 mm in the PD group, and 2.24 ± 0.25 mm in the HD group. There was a significant difference between groups (p < 0.001). The mean diaphragm thicknesses measured at the end of expiration were 2.00 ± 0.19 mm, 1.75 ± 0.19 mm, and 1.69 ± 0.20 mm in the control, PD, and HD groups, respectively. There was also a significant difference between the groups (p < 0.05). Diaphragm thickness data are presented in Table 3.

Table 3.

Diaphragm measurements across study groups

Variables	Hemodialysis (n = 37)	Peritoneal dialysis (n = 32)	Control (n = 60)	P
Inspiration diaphragm thickness (mm)	2.24 ± 0.25	2.53 ± 0.23	2.86 ± 0.29	< 0.001
Expiration diaphragm thickness (mm)	1.69 ± 0.20	1.75 ± 0.19	2.00 ± 0.19	< 0.05
Inspiration diaphragm stiffness (kPa)	25.61 ± 6.15	32.79 ± 5.31	47.68 ± 6.67	< 0.001
Expiration diaphragm stiffness (kPa)	19.46 ± 4.37	22.62 ± 4.84	33.26 ± 4.62	< 0.05

The mean diaphragm stiffness at peak inspiration was 47.68 ± 6.67 kPa in the control group, 32.79 ± 5.31 kPa in the PD group, and 25.61 ± 6.15 kPa in the HD group. This difference was statistically significant (p < 0.001). The mean diaphragm stiffness values at end-expiration were 33.26 ± 4.62 kPa, 22.62 ± 4.84 kPa and 19.46 ± 4.37 kPa in the control, PD and HD groups, respectively. There were significant differences between the groups (p < 0.05). Diaphragm elasticity data are presented in Table 3.

ROC analysis of diaphragm thickness and stiffness

It was found that the diaphragm thickness and stiffness values of HD and PD patients exhibited excellent diagnostic performance in distinguishing them from the healthy control group. According to the results of the ROC analysis, the AUC values of the determined parameters ranged from 0.806 to 0.987. These results suggest that diaphragm thickness and stiffness measurements are highly effective in diagnosing diaphragm dysfunction in dialysis patients. The diagnostic performance of diaphragm thickness and stiffness values during inspiratory and expiratory phases of breathing in both dialysis groups is presented in detail in Table 4, alongside the results of the corresponding ROC analysis.

Table 4.

The diagnostic performance of diaphragm thickness and stiffness values in both Dialysis groups

	Group	Cut-off	Area under the curve	95% CI	Sensivity	Specificity	PPV	NPV	P
Inspiration diaphragm thickness (mm)	HD	0.25	0.914	0.891–0.986	0.891	0.817	75.0	92.5	< 0.05
	PD	0.27	0.806	0.710–0.881	0.906	0.667	59.2	93.0	< 0.05
Expiration diaphragm thickness (mm)	HD	0.18	0.907	0.868–0.976	0.937	0.794	72.9	95.5	< 0.05
	PD	0.19	0.882	0.798–0.940	0.843	0.783	67.5	90.4	< 0.05
Inspiration diaphragm stiffness (kPa)	HD	37	0.980	0.951–0.997	0.970	0.933	90.0	98.2	< 0.05
	PD	40	0.958	0.895–0.989	0.935	0.816	73.2	96.0	< 0.05
Expiration diaphragm stiffness (kPa)	HD	25.5	0.987	0.945–0.998	0.945	0.983	97.2	96.7	< 0.05
	PD	29	0.951	0.881–0.985	0.937	0.823	74.0	93.6	< 0.05

Correlation of diaphragm parameters with clinical variables

Statistically significant correlations were found between diaphragm thickness and stiffness values, and dialysis duration, dialysis adequacy, comorbidity, and serum albumin levels (p < 0.05). Diaphragm thickness and stiffness decreased with increasing dialysis duration and comorbidity. However, significant increases in diaphragm thickness and stiffness were observed with increasing dialysis adequacy and serum albumin levels (Table 5).

Table 5.

Diaphragm thickness and stiffness values statistically significant correlations with clinical and laboratory parameters

Variables	Dialysis time	Dialysis adequacy	Comorbidities	Albumin
Inspiration diaphragm thickness	r:-412, P:0.040	r:501, P:0.034	r: -412, P:0.042	r:651, P:0.009
Expiration diaphragm thickness	r:-515, P:0.024	r:423, P:0.045	r: -379, P:0.064	r:534, P:0.032
Inspiration diaphragm stiffness	r:-487, P:0.003	r:583, P:0.002	r: -550, P:0.022	r:677, P:0.003
Expiration diaphragm stiffness	r:-420, P:0.005	r:551, P:0.006	r: -509, P:0.039	r:649, P:0.009

Discussion

This study evaluated morphologic and elasticity changes in the diaphragm muscles of dialysis patients using US and SWE methods. According to our findings, the thickness and elasticity of the diaphragm muscle were significantly lower in dialysis patients than in the healthy control group. Furthermore, this effect was found to be more pronounced in HD patients than in PD patients. Our results provide information on diaphragm muscle mass, strength, and quality. In this context, US and SWE are potentially useful, non-invasive tools for diagnosing and monitoring respiratory sarcopenia in dialysis patients.

Sarcopenia is a common finding in patients with end-stage renal disease [1]. This is primarily due to an accelerated rate of protein breakdown, caused by the pathological process of the disease and the catabolic effects of dialysis procedures [1, 2]. CKD-associated sarcopenia can occur in adulthood and may develop rapidly in the presence of a uremic environment and malnutrition, exacerbated by the catabolic effects of dialysis procedures. Beyond the physical disability observed in elderly individuals, sarcopenia in CKD has been associated with various adverse outcomes, including reduced quality of life, depression, protein-energy loss, increased fracture risk, cardiovascular complications, and elevated hospitalisation and mortality rates [16, 17]. Notably, sarcopenia is more prevalent in HD patients than in PD or CKD patients without dialysis [1].

The diaphragm muscle may be affected by sarcopenia, given that it contains fibre types similar to those found in other skeletal muscles. Studies conducted on animals have shown that sarcopenic rats have thinner diaphragms and weaker respiratory muscle strength. Atrophy and a reduction in fast-twitch fibres in the diaphragm have also been reported in ageing sarcopenic mice [18, 19]. Studies conducted in humans also support these findings. It was found that the thickness of the diaphragm was significantly reduced in sarcopenic elderly individuals compared to non-sarcopenic individuals [8, 9, 20]. As the diaphragm is the primary muscle responsible for respiratory movement, it is a key factor in evaluating respiratory sarcopenia [21]. The results of our study were consistent with previous research, revealing that diaphragm thickness decreases in dialysis patients compared to the general population. This decrease was more pronounced in HD patients than in PD patients. This may be because PD patients are relatively young and in good physical condition, have higher dialysis efficiency and fewer comorbidities. US measurement of diaphragm thickness is simple, non-invasive, and reproducible, and may provide useful information regarding muscle mass for the diagnosis of respiratory sarcopenia.

Shear wave elastography is a promising method for diagnosis and follow-up, as it objectively measures muscle tissue elasticity [22–24]. This technique provides important data on the biomechanical properties of muscle, particularly muscle quality and endurance [25]. This information provides a more comprehensive understanding of the structural and functional aspects of sarcopenia. SWE has been shown to detect early changes in muscle function with high sensitivity and specificity. Furthermore, its non-invasive nature, portability, and reproducible measurements make it ideal for clinical use [26].

Sinanoğlu et al. [13] reported that the thickness and elasticity of the diaphragm muscle decreased in children with primary malnutrition. These findings revealed that evaluating the diaphragm muscle using US and SWE could provide important information for detecting sarcopenia-like conditions in children. Although our study included adults and different patient groups, similar results were obtained. This supports the idea that evaluating the diaphragm muscle using SWE and ultrasonography is a valuable approach for diagnosing sarcopenia. However, further studies examining the relationship between sarcopenia and the diaphragm muscle in adults are needed.

In this study, the identification of statistically significant correlations between diaphragm thickness and stiffness with dialysis duration, comorbidities, dialysis adequacy, and serum albumin levels provides important insights into the impact of CKD progression and dialysis treatment on diaphragm muscle health. Hypoalbuminemia is frequently indicative of the malnutrition–inflammation complex and protein–energy wasting, both of which are highly prevalent among patients undergoing long-term dialysis. Moreover, inadequate dialysis and the chronic uremic milieu may exacerbate systemic inflammation and metabolic disturbances, thereby impairing diaphragmatic structure and function. The observed decline in diaphragm thickness and stiffness with increasing dialysis duration and comorbidity burden aligns with previous reports suggesting that chronic uremia and associated systemic diseases contribute to diaphragmatic muscle atrophy and functional deterioration [10, 27]. This finding supports the notion that key mechanisms implicated in sarcopenia—such as enhanced protein catabolism, accumulation of uremic toxins, persistent inflammation, and nutritional deficiencies—may also compromise diaphragmatic muscle fibers [4, 28]. Conversely, the significant increase in diaphragm thickness and stiffness associated with improved dialysis adequacy and higher serum albumin levels underscores the potential protective effects of optimal dialysis therapy and preserved nutritional status on muscle health. Consistent with our findings, prior studies have demonstrated that malnutrition is associated with reduced diaphragmatic thickness and impaired function [13, 28, 29].

Recently, SWE has gained significant traction in the diagnosis and monitoring of various musculoskeletal conditions. The quantitative data provided by this technique enables an objective evaluation of changes in tissue stiffness, thereby supporting clinical decision-making and offering valuable insights for tracking treatment efficacy [30–32]. Studies have also contributed important information regarding the correct application of SWE [33].

This study has some limitations. Firstly, maximal intraoral pressure measurements, which would have allowed for a more comprehensive evaluation of respiratory muscle function, were not performed. Consequently, diaphragmatic function could only be evaluated using US and SWE parameters. Although there was insufficient data in this study to definitively diagnose sarcopenia and respiratory sarcopenia, matched comparisons with the healthy control group revealed significant findings. It is therefore thought that US and SWE measurements could serve as potential sarcopenia biomarkers. Another important limitation is the single-centre design and limited sample size, which reduces the generalisability of the results. Another important limitation is the single-centre design and limited sample size, which reduces the generalisability of the results. Furthermore, intra- and interobserver variation analyses were not performed to assess the reliability of the measurements. Although all US and SWE examinations were performed performed under the supervision of an experienced operator to minimise variability, the absence of reproducibility testing limits the methodological robustness. Additionally, the assessment was limited to the right hemidiaphragm to optimise patient compliance and minimise examination time. In light of these limitations, it is recommended that the findings are confirmed in larger, multicentre studies with a more comprehensive methodology.

Conclusion

Respiratory sarcopenia is closely associated with increased mortality and a deteriorating quality of life in dialysis patients. Given the central role of the diaphragm muscle in respiratory sarcopenia development, evaluating the diaphragm with US and SWE provides valuable information for this patient group and may be a potential biomarker.

Abbreviations

HD

Hemodialysis

PD

Peritoneal dialysis

US

Ultrasonography

SWE

Shear wave elastography

CKD

Chronic kidney disease

ROI

Regions of interest

kPa

Kilopascals

M-STB

Motion Stability

RLB MAP

Reliability map

ROC

Receiver operating characteristic

AUC

Area under the curve

Author contributions

ND, HBB and VB designed the study. ND, HBB and AGU analyzed the data and did the statistical analyses. ND and AGU drafted the initial manuscript. All authors reviewed the drafted manuscript and approved the final version. All authors have accessed and verified the data reported in the manuscript.

Funding

The study was supported by the Inonu University Scientific Research Projects Coordination Unit (Project No: 4041). The funding body played no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.

Data availability

The data underlying this article will be shared on reasonable request to the corresponding author.

Declarations

Ethics approval and consent to participate

This study was conducted in accordance with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Inonu University Ethics Committee (decision number: 2024/47), and informed consent was secured from all participants.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.