Evaluation of computed tomography in the diagnosis of ultrasound-proven diaphragm dysfunction.

INTRODUCTION: Computed tomography (CT) is routinely employed on the evaluation of dyspnea, yet limited data exist on its assessment of diaphragmatic muscle. This study aimed to determine the capability of CT in identifying structural changes in the diaphragm among patients with ultrasound-confirmed diaphragmatic dysfunction. METHODS: Diaphragmatic ultrasounds conducted between 2018 and 2021 at our center in Marseille, France, were retrospectively collected. Diaphragmatic pillars were measured on CT scans at the L1 level and the celiac artery. Additionally, the difference in height between the two diaphragmatic domes in both diaphragmatic dysfunction cases and controls was measured and compared. RESULTS: A total of 65 patients were included, comprising 24 with diaphragmatic paralysis, 13 with diaphragmatic weakness, and 28 controls. In the case group (paralysis and weakness) with left dysfunctions (n = 24), the CT thickness of the pillars at the level of L1 and the celiac artery was significantly thinner compared with controls (2.0 mm vs. 7.4 mm and 1.8 mm vs. 3.1 mm, p < 0.001 respectively). Significantly different values were observed for paralysis (but not weakness) in the right dysfunction subgroup (n = 15) (2.6 mm vs. 7.4 mm and 2.2 mm vs. 3.8 mm, p < 0.001 respectively, for paralysis vs. controls). Regardless of the side of dysfunction, a significant difference in diaphragmatic height was observed between cases and controls (7.70 cm vs. 1.16 cm and 5.51 cm vs. 1.16 cm, p < 0.001 for right and left dysfunctions, respectively). Threshold values determined through ROC curve analyses for height differences between the two diaphragmatic domes, indicative of paralysis or weakness in the right dysfunctions, were 4.44 cm and 3.51 cm, respectively. Similarly for left dysfunctions, the thresholds were 2.70 cm and 2.48 cm, respectively, demonstrating good performance (aera under the curve of 1.00, 1.00, 0.98, and 0.79, respectively). CONCLUSION: In cases of left diaphragmatic dysfunction, as well as in paralysis associated with right diaphragmatic dysfunction, CT revealed thinner pillars. Additionally, a notable increase in the difference in diaphragmatic height demonstrated a strong potential to identify diaphragmatic dysfunction, with specific threshold values.

[Correlation between diaphragmatic-rapid shallow breathing index and lung ultrasound score in elderly patients with mechanical ventilation and its predictive value for weaning results].

OBJECTIVE: To investigate the correlation between diaphragmatic-rapid shallow breathing index (D-RSBI) and lung ultrasound score (LUS) in elderly patients with mechanical ventilation and its predictive value for weaning results. METHODS: A retrospective study was conducted. The clinical data of elderly patients (age > 60 years old) with invasive positive pressure ventilation (IPPV) admitted to the department of intensive care unit (ICU) of the First Affiliated Hospital of Jinzhou Medical University from January 2021 to June 2022 were enrolled. According to the outcome of withdrawal, the patients were divided into successful and failed groups. The differences in gender, age, acute physiology and chronic health evaluation II (APACHE II), D-RSBI and LUS before weaning and extubation were compared between the two groups. Pearson correlation was used to analyze the correlation between D-RSBI and LUS. The predictive value of D-RSBI and LUS on weaning results of elderly patients with IPPV was analyzed by receiver operator characteristic curve (ROC curve). RESULTS: A total of 398 elderly patients with IPPV were enrolled, including 300 successful weaning patients and 98 failed weaning patients. There were no significant differences in gender and age between the failed group and successful group [male: 55.1% (54/98) vs. 59.0% (177/300), age (years old): 67.02±5.03 vs. 66.96±4.99, both P > 0.05]. APACHE II score in the failed group was significantly higher than that in the successful group (17.09±3.30 vs. 16.06±3.81, P < 0.05), and the D-RSBI and LUS score before extubation were significantly higher than those in the successful group [D-RSBI (time×min-1×mm-1): 2.19±0.33 vs. 1.60±0.22, LUS: 17.30±3.04 vs. 11.97±3.20, both P < 0.01]. All patients showed a significant positive correlation between D-RSBI and LUS score (r = 0.406, P = 0.000). ROC curve analysis showed that the area under the curve (AUC) of D-RSBI for predicting weaning outcomes in elderly IPPV patients was 0.920, with a 95% confidence interval (95%CI) of 0.881-0.958 and P = 0.000. When the cut-off value was 1.85 times×min-1×mm-1, the sensitivity was 88.7% and the specificity was 86.7%. The AUC of LUS score for predicting weaning outcome in elderly IPPV patients was 0.875, with a 95%CI of 0.839-0.912 and P = 0.000. When the cut-off value was 14.50, the sensitivity was 75.7% and the specificity was 84.7%. CONCLUSIONS: There is a significant correlation between D-RSBI and LUS score in elderly mechanically ventilated patients, both of them can predict weaning outcome in elderly patients with mechanical ventilation.

Relationship Between Diaphragm Thickness, Thickening Fraction, Dome Excursion, and Respiratory Pressures in Healthy Subjects: An Ultrasound Study.

PURPOSE: Diaphragm ultrasonography is used to identify causes of diaphragm dysfunction. However, its correlation with pulmonary function tests, including maximal inspiratory (MIP) and expiratory pressures (MEP), remains unclear. This study investigated this relationship by measuring diaphragm thickness, thickening fraction (TF), and excursion (DE) using ultrasonography, and their relationship to MIP and MEP. It also examined the influence of age, sex, height, and BMI on these measures. METHODS: We recruited healthy Japanese volunteers and conducted pulmonary function tests and diaphragm ultrasonography in a seated position. Diaphragm ultrasonography was performed during quiet breathing (QB) and deep breathing (DB) to measure the diaphragm thickness, TF, and DE. A multivariate analysis was conducted, adjusting for age, sex, height, and BMI. RESULTS: Between March 2022 and January 2023, 109 individuals (56 males) were included from three facilities. The mean (standard deviation) MIP and MEP [cmH2O] were 72.2 (24.6) and 96.9 (35.8), respectively. Thickness [mm] at the end of expiration was 1.7 (0.4), TF [%] was 50.0 (25.9) during QB and 110.7 (44.3) during DB, and DE [cm] was 1.7 (0.6) during QB and 4.4 (1.4) during DB. Multivariate analysis revealed that only DE (DB) had a statistically significant relationship with MIP and MEP (p = 0.021, p = 0.008). Sex, age, and BMI had a statistically significant influence on relationships between DE (DB) and MIP (p = 0.008, 0.048, and < 0.001, respectively). CONCLUSION: In healthy adults, DE (DB) has a relationship with MIP and MEP. Sex, age, and BMI, but not height, are influencing factors on this relationship.

A rare variant of scimitar syndrome characterised by right pulmonary vein drainage to portal vein with eventeration of diaphragm.

While infradiaphragmatic total anomalous pulmonary venous drainage to portal vein is well described, hemianomalous drainage of right pulmonary veins to portal vein in Scimitar syndrome has not yet been reported.

Inspiratory Muscle Dysfunction Mediates and Predicts a Disease Continuum of Hypercapnic Failure in Chronic Obstructive Pulmonary Disease.

INTRODUCTION: Advanced chronic obstructive pulmonary disease (COPD) is associated with chronic hypercapnic failure. The present work aimed to comprehensively investigate inspiratory muscle function as a potential key determinant of hypercapnic respiratory failure in patients with COPD. METHODS: Prospective patient recruitment encompassed 61 stable subjects with COPD across different stages of respiratory failure, ranging from normocapnia to isolated nighttime hypercapnia and daytime hypercapnia. Arterialized blood gas analyses and overnight transcutaneous capnometry were used for patient stratification. Assessment of respiratory muscle function encompassed body plethysmography, maximum inspiratory pressure (MIP), diaphragm ultrasound, and transdiaphragmatic pressure recordings following cervical magnetic stimulation of the phrenic nerves (twPdi) and a maximum sniff manoeuvre (Sniff Pdi). RESULTS: Twenty patients showed no hypercapnia, 10 had isolated nocturnal hypercapnia, and 31 had daytime hypercapnia. Body plethysmography clearly distinguished patients with and without hypercapnia but did not discriminate patients with isolated nocturnal hypercapnia from those with daytime hypercapnia. In contrast to ultrasound parameters and transdiaphragmatic pressures, only MIP reflected the extent of hypercapnia across all three stages. MIP values below -48 cmH2O predicted nocturnal hypercapnia (area under the curve = 0.733, p = 0.052). CONCLUSION: In COPD, inspiratory muscle dysfunction contributes to progressive hypercapnic failure. In contrast to invasive tests of diaphragm strength only MIP fully reflects the pathophysiological continuum of hypercapnic failure and predicts isolated nocturnal hypercapnia.

Diaphragm atrophy during invasive mechanical ventilation is related to extubation failure in preterm infants: An ultrasound study.

BACKGROUND: Diaphragm dysfunction is associated with poor outcomes in critically ill patients. Ventilator-induced diaphragmatic dysfunction (VIDD), including diaphragm atrophy (DA), is poorly studied in newborns. We aimed to assess VIDD and its associations in newborns. METHODS: Single-center prospective study. Diaphragm thickness was measured at end-inspiration (TDI) and end-expiration (TDE) on the right midaxillary line. DA was defined as decrease in TDE ≥ 10%. Daily measurements were recorded in preterm newborns on invasive mechanical ventilation (IMV) for ≥2 days. Clinical characteristics of patients and extubation failure were recorded. Univariate analysis, logistic regression, and mixed models were performed to describe VIDD and associated factors. RESULTS: We studied 17 patients (median gestational age 270/7 weeks) and 22 IMV cycles (median duration 9 days). Median TDE decreased from 0.118 cm (interquartile range [IQR] 0.094-0.165) on the first IMV day to 0.104 cm (IQR 0.083-0.120) on the last IMV day (p = .092). DA occurred in 11 IMV cycles (50%) from 10 infants early during IMV (median: second IMV day). Mean airway pressure (MAP) and lung ultrasound score (LUS) on the first IMV day were significantly higher in patients who developed DA. DA was more frequent in patients with extubation failure than in those with extubation success within 7 days (83.3 vs. 33.3%, p = .038). CONCLUSIONS: DA, significantly associated with extubation failure, occurred in 58.8% of the study infants on IMV. Higher MAP and LUS at IMV start were associated with DA. Our results suggest a potential role of diaphragm ultrasound to assess DA and predict extubation failure in clinical practice.

Maximum abdominal excursion assessment using an abdominal excursion measuring device: Reliability and validity of a new device for simple and quantitative assessment of respiratory function.

This study aimed to verify the reliability and validity of abdominal expansion and respiratory function measurements. Forty healthy adult males underwent lung capacity, effort lung capacity, respiratory muscle strength, cough strength, diaphragm ultrasound, and abdominal expansion measurements. Abdominal expansion was measured using a device developed to accurately evaluate abdominal movements and calculate maximum abdominal expansion on the ventral side (AE-max: the difference between maximal abdominal contraction at the same time as maximal-effort expiration and maximal abdominal expansion at the same time as maximal-effort inspiration). Intra- and inter-rater reliabilities of the AE-max measurements were examined, the paired t-test was used for assessing the ratios of the expansion and contraction displacement components in AE-max, and regression analysis was used to obtain equations for predicting maximum inspiratory pressure (MIP) based on AE-max. Both intra- and inter-rater reliabilities were high. Criterion-related validity showed that AE-max was associated with all respiratory function parameters, especially MIP, and a high percentage of expansion displacement. Regression analysis showed that AE-max was significantly associated with MIP. Based on its association with MIP, the large proportion of expansion displacement in AE-max, and the results of the multiple regression analysis, we conclude that AE-max is a helpful measure for estimating MIP.

Deep learning radiomics on shear wave elastography and b-mode ultrasound videos of diaphragm for weaning outcome prediction.

PURPOSE: We proposed an automatic method based on deep learning radiomics (DLR) on shear wave elastography (SWE) and B-mode ultrasound videos of diaphragm for two classification tasks, one for differentiation between the control and patient groups, and the other for weaning outcome prediction. MATERIALS AND METHODS: We included a total of 581 SWE and B-mode ultrasound videos, of which 466 were from the control group of 179 normal subjects, and 115 were from the patient group of 35 mechanically ventilated subjects in the intensive care unit (ICU). Among the patient group, 17 subjects successfully weaned and 18 failed. The deep neural network of U-Net was utilized to automatically segment diaphragm regions in dual-modal videos of SWE and B-mode. High-throughput radiomics features were then extracted, the statistical test and least absolute shrinkage and selection operator (LASSO) were applied for feature dimension reduction. The optimal classification models for the two tasks were established using the support vector machine (SVM). RESULTS: The automatic segmentation model achieved Dice score of 87.89 %. A total of 4524 radiomics features were extracted, 10 and 20 important features were left after feature dimension reduction for constructing the two classification models. The best areas under receiver operating characteristic curves of the two models reached 84.01 % and 94.37 %, respectively. CONCLUSIONS: Our proposed DLR methods are innovative for automatic segmentation of diaphragm regions in SWE and B-mode videos and deep mining of high-throughput radiomics features from dual-modal images. The approaches have been proved to be effective for prediction of weaning outcomes.

Initial validation of a diaphragm tracking system for multiple breath-hold volumetric modulated arc therapy of abdominal tumors: A phantom study.

BACKGROUND: The breath-hold radiotherapy has been increasingly used to mitigate interfractional and intrafractional breathing impact on treatment planning and beam delivery. Previous techniques include body surface measurements or radiopaque metal markers, each having known disadvantages. PURPOSE: We recently proposed a new markerless technique without the disadvantages, where diaphragm was registered between DRR and fluoroscopic x-ray projection images every 180 ms during VMAT delivery. An initial validation of the proposed diaphragm tracking system (DiaTrak) was performed using a chest phantom to evaluate its characteristics. METHODS: Diaphragm registration was performed between DRR and projection streaming kV x-ray images of a chest phantom during VMAT delivery. Streaming data including the projection images and the beam angles were transferred from a linac system to an external PC, where the diaphragm registration accuracy and beam-off latency were measured based on image cross correlation between the DRR and the projection images every 180 ms. RESULTS: It was shown that the average of the beam-off latency was 249.5 ms and the average of the diaphragm registration error was 0.84 mm CONCLUSIONS: Initial validation of the proposed DiaTrak system for multiple breath-hold VMAT of abdominal tumors has been successfully completed with a chest phantom. The resulting beam-off latency and the diaphragm registration error were regarded clinically acceptable.

Lung, Pleura, and Diaphragm Point-of-Care Ultrasound.

Thoracic Ultrasonography involves the ultrasonographic examination of the lungs, pleura, and diaphragm. This provides a plethora of clinical information during the point of care assessment of patients. The air filled lungs create consistent artifacts and careful examination and understanding of these artefactual signs can provide useful information on underlying clinicopathologic states. This review aims to provide a review of the ultrasound signs and features that can be seen in horacic ultrasonography and summarize the clinical evidence to support its use.

The effect of respiratory muscle training on respiratory muscle strength, diaphragm thickness/mobility, and exercise capacity in patients with systemic lupus erythematosus and associated shrinking lung syndrome.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder that can impact any organ in the body. The pathophysiology of shrinking lung syndrome (SLS), a rare pulmonary complication of SLE, remains unknown. The objective of the current case series was to investigate the effects of inspiratory muscle training (IMT) on diaphragm thickness/mobility, respiratory muscle strength, peripheral muscle thickness/strength, and functional exercise capacity in patients with SLE and associated SLS. Three patients with SLE were included in the case series. Respiratory muscle strength, peripheral muscle strength, peripheral muscle thickness, diaphragm muscle thickness, diaphragm muscle mobility, functional exercise capacity, and pulmonary function test were assessed. A significant improvement has been determined in respiratory muscle strength, functional exercise capacity, peripheral muscle strength, peripheral muscle thickness, diaphragm muscle thickness, and diaphragm muscle mobility. This is the first case series showing the beneficial effects of IMT on respiratory muscle strength, diaphragm thickness/mobility, peripheral muscle thickness/strength, and exercise capacity in patients with SLE.

Computed tomography features and prevalence of focal diaphragmatic mineralization in 300 dogs.

A focal area of mineral attenuation is commonly observed in the diaphragmatic crura of canine patients undergoing a thoracic CT. There is no mention of this finding in either the human or veterinary medicine literature. This retrospective study evaluates 300 canine thoracic CT studies with the aim of describing the CT appearance of this finding and establishing a prevalence in a large cohort of dogs. The presence of the mineral focus and its CT characteristics, including length, attenuation, and appearance, were recorded and correlated with the patient's signalments and anamnesis. The focus was observed in 43 of 300 studies (14.3%). The most common appearance was a thin, millimetric, toothpick-like mineral attenuating structure in the confluence of the diaphragmatic crura, just ventral to the aorta. There was no association with adjacent potentially pathological changes. A significant correlation was found between the presence of the focus and the patient's body weight (P = .03), as well as with a brachycephalic conformation (P = .03). This focus of mineralization represents a relatively common incidental finding in the canine diaphragm and has no evident association with pathology.

Orthopnea secondary to brachial plexitis with bilateral diaphragmatic paralysis.

BACKGROUND: Diaphragmatic paralysis can present with orthopnea. We report a unique presentation of bilateral diaphragmatic paralysis, an uncommon diagnosis secondary to an unusual cause, brachial plexitis. This report thoroughly describes the patient's presentation, workup, management, and outcome. It also reviews the literature on diaphragmatic paralysis and Parsonage-Turner syndrome. CASE PRESENTATION: A 50-year-old male patient developed insidious orthopnea associated with left shoulder and neck pain over three months with no associated symptoms. On examination, marked dyspnea was observed when the patient was asked to lie down; breath sounds were present and symmetrical, and the neurological examination was normal. The chest radiograph showed an elevated right hemidiaphragm. Echocardiogram was normal. There was a 63% positional reduction in Forced Vital Capacity and maximal inspiratory and expiratory pressures on pulmonary function testing. The electromyogram was consistent with neuromuscular weakness involving both brachial plexus and diaphragmatic muscle (Parsonage and Turner syndrome). CONCLUSIONS: Compared to unilateral, bilateral diaphragmatic paralysis may be more challenging to diagnose. On PFT, reduced maximal respiratory pressures, especially the maximal inspiratory pressure, are suggestive. Parsonage-Turner syndrome is rare, usually with unilateral diaphragmatic paralysis, but bilateral cases have been reported.

Ultrasonography to Access Diaphragm Dysfunction and Predict the Success of Mechanical Ventilation Weaning in Critical Care: A Narrative Review.

INTRODUCTION: Weaning failure is common in mechanically ventilated patients, and whether ultrasound (US) can predict weaning outcome remains controversial. This review aims to evaluate the diaphragmatic function measured by US as a predictor of weaning outcome. METHODS: PubMed was searched to identify original articles about the use of diaphragmatic US in ICU patients. A total of 61 citations were retrieved initially; available data of 26 studies were included in this review. RESULTS: To assess diaphragmatic dysfunction in adults, six studies evaluated excursion, five evaluated thickening fraction, and both in nine. Despite heterogeneity in the diagnostic accuracy of diaphragm US among the studies, the sonographic indices showed good diagnostic performance for predicting weaning outcome. CONCLUSIONS: Diaphragmatic US can be a useful and accurate tool to detect diaphragmatic dysfunction in critically ill patients and predict weaning outcome.

Ultrasound assessment of diaphragm thickness, contractility, and strain in healthy pediatric patients.

BACKGROUND: Ultrasound-based diaphragmatic assessments are becoming more common in pediatric acute care, but baseline pediatric diaphragm thickness and contractility values remain unknown. METHODS: We conducted a prospective, observational study of healthy children aged <18 years undergoing elective surgery. Diaphragm thickness at end-expiration (Tdi-exp), thickening fraction (DTF) and excursion were measured by ultrasound during spontaneous breathing and during mechanical ventilation. Diaphragm strain and peak strain rate were ascertained post hoc. Measurements were compared across a priori specified age groups (<1 year, 1 to <3, 3 to <6, 6 to <12, and 12 to <18 years) and with versus without mechanical ventilation. RESULTS: Fifty subjects were evaluated (n = 10 per age group). Baseline mean Tdi-exp was 0.19 ± 0.04 cm, DTF 0.19 ± 0.09, excursion 1.69 ± 0.97 cm, strain -10.3 ± 4.9, peak strain rate -0.48 ± 0.21 s-1 . No significant difference in Tdi-exp or DTF was observed across age groups (p > .05). Diaphragm excursion increased with age (p < .0001). Diaphragm strain was significantly greater in the 12-17-year age group (-14.3 ± 6.4), p = .048, but there were no age-related differences in peak strain rate (p = .08). During mechanical ventilation, there were significant decreases in DTF 0.12 ± 0.04 (p < .0001), excursion 1.08 ± 0.31 cm (p < .0001), strain -4.60 ± 1.93 (p < .0001), and peak strain rate -0.20 ± 0.10 s-1 (p < .0001) while there was no change in Tdi-exp 0.18 ± 0.03 cm (p = .25) when compared to baseline values. CONCLUSION: Pediatric Tdi-exp, DTF, and diaphragm peak strain rate were similar across age groups. Diaphragm excursion and strain varied across age groups. All measures of diaphragm contractility were diminished during mechanical ventilation.

[Diaphragmatic ultrasonography for the pulmonologist: Technique and clinical use]. / L'échographie diaphragmatique pour le pneumologue : méthodologie et intérêt clinique.

INTRODUCTION: Ultrasonography is an emerging tool that helps to assess diaphragmatic function. It is now widely used in ICUs to predict weaning from mechanical ventilation. Ultrasonography is readily available, harmless (no radiation), and repeatable with good interoperator reproducibility. Over the past few years, ultrasonography has seen increasing use in patients with chronic pulmonary pathologies. STATE OF THE ART: The aim of this review is (1) to describe the ultrasound techniques used to assess diaphragmatic excursion and thickening, (2) to indicate the expected, normal values in healthy patients, and (3) to summarize the main findings and clinical applications in treatment of chronic respiratory disorders. CONCLUSIONS: Chronic pulmonary diseases are associated with diaphragmatic dysfunction that can be assessed with ultrasound. Diaphragmatic dysfunction is primary in neuromuscular disorders and secondary to respiratory disease in other chronic pulmonary conditions (COPD, ILD). Ultrasound is correlated with the severity of the underlying disease (functional and clinical parameters). PERSPECTIVES: The prognostic interest of diaphragm ultrasonography remains to be established, after which its utilization should become routine.

The use of diaphragm and lung ultrasound in acute respiratory physiotherapy practice and the impact on clinical decision-making: A systematic review and meta-analysis.

OBJECTIVES: Diaphragm and lung ultrasound (DLUS) is emerging as an important point-of-care respiratory assessment tool and is being used in clinical care by trained respiratory physiotherapists, both in Australia and internationally. However, the impact of DLUS on physiotherapists' clinical decision-making remains largely unknown. This systematic review aims to review the evidence for implementing DLUS in acute respiratory physiotherapy management. REVIEW METHOD USED: We conducted a systematic review. DATA SOURCES: We searched PubMed, Embase, CINAHL, CENTRAL, and Scopus from inception to 18th April 2023 for all original clinical studies reporting on the physiotherapy clinical decision-making, following a DLUS examination and/or where DLUS was used to evaluate the effect of respiratory physiotherapy, in adults over 18 years of age. REVIEW METHODS: Two authors independently performed study selection and data extraction. Individual study risk of bias was assessed using the Newcastle-Ottawa Scale, and certainty in outcomes was assessed using the Grading of Recommendations, Assessment, Development, and Evaluations framework. RESULTS: A total of seven observational studies (n = 299) were included, all of which were in the intensive care setting. DLUS changed physiotherapy diagnosis, management, and treatment in 63.9% (50-64%), 16.8% (15-50%), and 48.4% (25-50%) of patients, respectively. There was a significant improvement in the lung ultrasound score post respiratory physiotherapy treatment (mean difference -2.31, 95% Confidence Interval (95% CI) -4.42 to -0.21; very low certainty) compared to before respiratory physiotherapy treatment. Moderate risk of bias was present in six studies, and there was variance in the DLUS methodology across included studies. CONCLUSIONS: The findings of this review suggest DLUS influences physiotherapy clinical decision-making and can be used to evaluate the effects of acute respiratory physiotherapy treatment. However, the available data is limited, and further high-quality studies are needed. TRIAL REGISTRATION: This study is registered with the International Prospective Register of Systematic Reviews; CRD42023418312.

Diaphragm Ultrasonography: Reference Values and Influencing Factors for Thickness, Thickening Fraction, and Excursion in the Seated Position.

INTRODUCTION: Measurements of diaphragm function by ultrasonography are affected by body position, but reference values in the seated position have not been established for an Asian population. This study aimed to determine reference values for diaphragm thickness, thickening fraction, and dome excursion by ultrasonography and to investigate the effects of sex, height, and body mass index. METHODS: Diaphragm ultrasonography was performed on 109 seated Japanese volunteers with normal respiratory function who were enrolled between March 2022 and January 2023. Thickness, thickening fraction, and excursion were measured. Reference values and the measurement success rate were calculated. Multivariate analysis adjusted for sex, height, and body mass index was performed. RESULTS: The measurement success rate was better for thickness than for excursion. The mean (lower limit of normal) values on the right/left sides were as follows. During quiet breathing, thickness at end expiration(mm) was 1.7 (0.9)/1.6 (0.80), thickening fraction(%) was 50 (0.0)/52 (0.0), and excursion(cm) was 1.7 (0.5)/1.9 (0.5). During deep breathing, the thickening fraction was 111 (24)/107 (22), and the excursion was 4.4 (1.7)/4.1 (2.0). In multivariate analysis, body mass index was positively associated with thickness but not with the thickening fraction. CONCLUSION: The reference values in this study were smaller than those in previous reports from Europe. Considering that thickness is influenced by body mass index, using Western reference values in Asia, where the average body mass index is lower, might not be appropriate. The thickening fraction in deep breathing is unaffected by other items and can be used more universally.