Multidimensional outcome assessment of pulmonary rehabilitation in traits-based clusters of COPD patients.

BACKGROUND: Clusters of COPD patients have been reported in order to individualize the treatment program. Neither co-morbidity clusters, nor integrated respiratory physiomics clusters contributed to a better prediction of outcomes. Based on a thoroughly assessed set of pulmonary and extra-pulmonary traits at the start of a pulmonary rehabilitation (PR) program, we recently described seven clusters of COPD patients. The aims of this study are to confirm multidimensional differential response and to assess the potential of pulmonary and extra-pulmonary traits-based clusters to predict this multidimensional response to PR pulmonary in COPD patients. METHODS: Outcomes of a 40-session PR program for COPD patients, referred by a chest physician, were evaluated based on the minimal clinically important difference (MCID) for 6-minute walk distance (6MWD), cycle endurance time, Canadian Occupational Performance Measure performance and satisfaction scores, Hospital Anxiety and Depression Scale anxiety and depression scores, MRC dyspnea grade and St George's Respiratory Questionnaire. The aforementioned response indicators were used to calculate the overall multidimensional response and patients were grouped in very good, good, moderate and poor responders. In the same way, responses to pulmonary rehabilitation were compared based on seven previously identified pulmonary and extra-pulmonary traits-based clusters. RESULTS: Of the whole sample, drop out was 19% and 419 patients (55.4% males, age: 64.3 ± 8.8, FEV1% of predicted: 48.9 ± 20) completed the pulmonary rehabilitation program. Very good responders had significantly worse baseline characteristics with a higher burden of disease, a higher proportion of rollator-users, higher body mass index (BMI), more limitations of activities in daily life, emotional dysfunction, higher symptoms of dyspnea and worse quality of life. Of the seven pre-identified clusters, 'the overall best functioning cluster' and 'the low disease burden cluster' both including the best 6MWD, the lowest dyspnea score and the overall best health status, demonstrated attenuated outcomes, while in 'the cluster of disabled patients', 76% of the patients improved health status with at least 2 times MCID. This 'cluster of disabled patients' as well as 'the multimorbid cluster', 'the emotionally dysfunctioning cluster', 'the overall worst-functioning cluster' and 'the physically dysfunctioning cluster' all demonstrated improvements in performance and satisfaction for occupational activities (more than 65% of patients improved with > 1MCID), emotional functioning (more than 50% of patients improved with > 1 MCID) and overall health status (more than 58%). CONCLUSION: The current study confirms the differential response to pulmonary rehabilitation based on multidimensional response profiling. Cluster analysis of baseline traits illustrates that non-linear, clinically important differences can be achieved in the most functionally and emotionally impaired clusters and that 'the overall best functional cluster' as well as 'the low disease burden cluster' had an attenuated outcome.

Elasticity of neck muscles in cervicogenic headache.

AIM: To compare the elasticity of the sternocleidomastoid and trapezius muscles in patients with cervicogenic headache and in healthy volunteers. METHODS: The medical history of 23 patients with cervicogenic headache was taken with a focus on pain characteristics. Elasticity of the sternocleidomastoid and trapezius muscles was measured by using shear wave elastography. Results were then compared with 23 healthy volunteers. RESULTS: The sternocleidomastoid muscle was significantly stiffer in patients with cervicogenic headache compared to healthy volunteers. The stiffness increased gradually from the parasternal area, where it was negligible, to the area near the mastoid process where it reached over 20 kPa. There was no difference in the stiffness of the trapezius muscle. The stiffness of the sternocleidomastoid muscle does show a significant dependence on headache characteristics (e.g., laterality, severity, or frequency). CONCLUSION: The results of this pilot study show that patients with cervicogenic headache have a higher stiffness of the sternocleidomastoid muscle than healthy volunteers. These findings suggest that elastography could be used as a diagnostic tool in cervicogenic headache.

Delayed-Onset Neuropathological Complications From a Foramen Magnum and Occipital Crest-Focused Traumatic Brain Injury of the Vietnam War and Other Conflicts: Part II, Research Analysis.

INTRODUCTION: Much of the research impacting diagnosis, outcome, and treatment of traumatic brain injuries (TBIs) has favored time of consciousness criteria indicative of hemispheric blast focus alone. However, recent animal-based research has widely expanded the diagnostic knowledge base and potential treatment options. METHODS: Recent animal-based research findings of foramen magnum and occipital crest-focused blast injuries in laboratory rats were reviewed and compared to the Part I human case report. RESULTS: Comparing the human case report (Part I) to that of animal research studies found very similar neuropathological outcomes, many deep and delayed, and supports why non-cerebral-focused TBIs have gone unrecognized. The overpressure wave is funneled through skull openings of the foramen magnum, with the possibility of a rebound secondary contrecoup injury impacting the orbits, oral-nasal cavity, and ears resulting in additional occult axonal and white matter injury. CONCLUSIONS: Research analysis prompted by a human case report (Part I) has helped identify mechanisms that assist in recognizing and defining non-cerebral hemispheric-focused TBI injuries. Position of the head in relationship to the blast wave, the setting in which the blast occurs, and close diagnostic follow-up are critical to the recognition, diagnosis, and treatment of injuries that have otherwise gone unrecognized and unstudied in humans since the Vietnam War.

Delayed-Onset Neuropathological Complications From a Foramen Magnum and Occipital Crest Focused Traumatic Brain Injury of the Vietnam War and Other Conflicts: Part I, Case Report.

INTRODUCTION: The diagnosis of traumatic brain injuries is typically based on hemispheric blasts resulting in degrees of unconsciousness and associated cerebral injuries. This case report describes a Vietnam War era setting in which a traumatic blast wave struck the posterior cranium in the region of the foramen magnum, occipital crest, and other skull openings (orbit, oronasal, and ear) and the unique secondary clinical signs and symptoms experienced over time. MATERIALS AND METHODS: This case report describes secondary delayed-onset clinical signs and symptoms consistent with progressive decades-long physical and functional complications. The traumatic blast resulted in brief unconsciousness, decreased vision in left eye, confusion, right sided hemotympanum, deafness, severe tinnitus, severe nasopharynx pain and difficulty swallowing, pain in right posterior and occipital area of the head, and loss of dental amalgams. Subsequent exams revealed progressive hyperacusis, sea sickness, dysdiadochokinesis, diagnosis of 9th and 10th cranial nerve traumatic schwannomas, hyperdense changes to the frontal lobe white matter, progressive tinnitus, chronic vertigo, right-sided high-frequency hearing loss, progressive oculo-gyric crisis of Tumarkin-like seizures, left-sided chronic vitreous hemorrhage, and diminished right hemisphere performance of the brain based on neurophysiological assessment. No post-traumatic stress, depression, or other emotional or psychiatric difficulties were claimed. CONCLUSION: This case report, unique to the English language scientific literature, discusses in detail the secondary signs and symptoms of a foramen magnum and occipital crest focused-associated blast injury.

Delayed-Onset Neuropathological Complications From a Foramen Magnum and Occipital Crest Focused TBI of the Vietnam War and Other Conflicts: Part III, Critique of Existing TBI Criteria and Their Operational Controversies.

INTRODUCTION: In this report, we discuss the controversy of the diverse traumatic brain injury (TBI) categorization and taxonomy and the need to develop a new multidimensional and multidisciplinary categorization system that can be an aid in improved diagnostic and prognostic outcomes. Of interest, the heterogeneity of TBI marks the major obstacle to develop effective therapeutic interventions. Currently, the Glasgow Coma Scale has been utilized to guide in the prognosis and clinical management of TBI; it does not encompass the pathophysiological mechanisms leading to neurological deficits that can impede therapeutic interventions and consequently the failure of clinical trials. An unfortunate gap exists between advances in TBI research and existing U.S. Department of Defense (DoD) definitions, categorization, and management. Part I illustrates a unique posterior-focused TBI case report that does not fit any existing TBI definitions. Part II summarizes new animal-based TBI research that supports the case report as a legitimate TBI category. Part III critiques existing TBI criteria and their controversies. METHODS: Current DoD definitions and decision-making protocols based on concussion time alone are reviewed and compared to the myriad of additional TBI definitions that further illustrate the marked differences in definitions, especially in mild TBIs. RESULTS: The DoD definitions are not consistent with what academic research and science bring to the debate. With increasing world conflicts and wars, evaluators are not prepared to accept, evaluate, and properly manage those TBIs that are not associated with immediate levels of unconsciousness alone as the prime determinant of diagnosis and long-term severity. Despite comprehensive research, current understanding among decision-makers of progressive pathology of non-hemispheric TBIs remains limited, inconsistent, and confusing. CONCLUSIONS: This dilemma requires a multidisciplinary, science/medicine-led panel to actively reassess TBI criteria that take into consideration the latest research including non-cerebral hemispheric injuries. We recommend that DoD/Veterans Affairs establish a commission to regularly review the academic-related scientific evidence and incorporate these findings in a timely fashion into their operational definitions. This would guarantee that recognition, diagnosis, and follow-up of all TBIs are properly understood, managed, and documented.

In Vivo Measurements of Middle Ear Temperature During Transcanal Endoscopic Ear Surgery.

OBJECTIVE: The light emitted from the endoscope during transcanal endoscopic ear surgery (TEES) heats the intratympanic space. This heat may potentially be dangerous to nearby important structures, as documented by in vitro and by animal and cadaveric studies. The aim of our work was to monitor middle ear temperatures during TEES in vivo. STUDY DESIGN: Cohort study. SETTING: Tertiary referral hospital. PATIENTS: Four patients (15-69 yrs old) underwent transcanal endoscopic tympanoplasties for chronic perforation or retraction. INTERVENTION: After elevating the tympanomeatal flap, a thermocouple was placed in the middle ear to measure the heat generated by a 30° Hopkins rod telescope (11 cm long, 2.7 mm wide) and fiberoptic light emitting diode light source. MAIN OUTCOME MEASURES: Middle ear temperature in the retrotympanum was monitored under these conditions: at 50 and 100% light intensity, after removing and wiping the endoscope tip, during suctioning and following middle ear irrigation. RESULTS: Maximum middle ear temperature ranged from 36.26-37.30°C. Pulling out and wiping the endoscope caused no change or minimal decrease of 0.16°C. Middle ear irrigation caused a temperature drop of 2.05°C to 5.11°C. Suctioning was associated with a drop from 0.24°C to 3.91°C that was dependent on the depth of the endoscopic tip. CONCLUSION: Middle ear temperatures during TEES using a Hopkins rod telescope and light-emitting diode light source reach values corresponding to physiological body temperature, and do not reach dangerous levels.

Shear wave elastography in diffuse thyroid disease.

AIM: Our aim was to examine the contribution of shear wave elastography to ultrasonographic assessment in diffuse thyroid disease, specifically to evaluate the stiffness of the thyroid gland in diffuse thyroid disease and compare it with healthy controls. METHODS: A total of 46 patients with diffuse thyroid disease were examined clinically, by conventional ultrasound, and shear wave elastography. The conventional ultrasound parameters followed were: volume, margin quality, presence of nodules, and vascularisation. We measured the mean, minimum, and maximum stiffnesses by shear wave elastography. Results were correlated with values in 128 healthy subjects. RESULTS: Patients with diffuse thyroid disease had significantly higher mean and maximal stiffnesses of the thyroid gland: 12.5 ± 5 kPa and 35.3 ± 12.8 kPa, respectively, and lower minimal stiffness: 0.5 ± 0.6 kPa than the healthy control group with mean, maximal, and minimal values of 9.5 ± 3.6 kPa, 22.5 ± 7.3 kPa, and 2.2 ± 2.1 kPa (P<0.001). Stiffness values were positively correlated with BMI and volume of the thyroid; they did not correlate with margin quality, presence of nodules nor vascularisation. Compared with healthy volunteers, thyroid glands of patients with diffuse thyroid disease had a blurred margin more frequently and the amount of nodules and vascularisation were higher. Patients with Graves-Basedow disease did not have significantly different mean, maximal, nor minimal stiffnesses than those with thyroiditis. CONCLUSION: Both mean and maximal stiffness of the thyroid gland are significantly higher in diffuse thyroid disease than in the healthy population, while minimal stiffness is lower.

Coexistent neck enteric cyst and intraspinal neurenteric cyst: Embryopathogenetic implications.

INTRODUCTION: Enteric cysts are very rare conditions, occurring mainly in the posterior mediastinum and posterior neck. Their pathomorphology corresponds with that of intraspinal neurenteric cysts. Both formations are derivatives of the posterior foregut. However, their embryopathogenesis has not been elucidated satisfactorily as yet. For those associated with vertebral anomalies, the split notochord theory has been widely accepted. However, this is be hardly conceivable for cases free of these anomalies. CASE REPORT: Here, a patient with concurrent separated enteric and neurenteric cysts and cervical spine dysmorphism is presented. DISCUSSION: The review of the relevant literature revealed sporadic analogical cases in which a transvertebral communication between the two cysts was present or absent. The latter was associated with a minimal abnormality of the vertebral body. CONCLUSION: The authors suggest that normal vertebrae may be formed in patients with enteric cysts, which would make the notochord-split theory plausible also for those free of spinal malformations.

Plantar vein thrombosis provoked by mechanical strain to the foot: a rare cause of plantar heel pain.

A 61-year-old mountain hiker presented with acute pain of the medial-plantar aspect of the right foot. As the location, intensity and acute onset of the pain were atypical for fasciitis plantaris, an ultrasound was performed. This demonstrated a segmental plantar vein thrombosis (PVT), which was confirmed on consequent MRI. Patient was a non-smoker, without a medical or family history of coagulopathies. Four months previously, he suffered from metatarsalgia of the left, thus contralateral, foot, which prompted treatment with bilateral orthoses. In addition to metatarsal padding, medial-arch support was prescribed due to the presence of flexible flatfeet. Following internal medicine consultation, treatment consisted of discontinuing the use of orthoses, rest and non-steroidal anti-inflammatory drugs (NSAIDs). At 2-week follow-up, the patient was pain-free. In this case report, PVT, a rare cause for plantar heel pain, is discussed. In addition, a summary of the diagnosis and treatment of PVT is outlined.

The Role of Ultrasound and Shear-Wave Elastography in Evaluation of Cervical Lymph Nodes.

AIM: To evaluate the prognostic value of ultrasound and shear-wave elastography (SWE) in diagnosing malignant cervical lymph nodes. METHODS: A total of 99 patients with enlarged lymph nodes (99 lymph nodes presenting as a neck mass) were examined clinically with conventional ultrasound including Doppler examination and shear-wave elastography. The results of the examinations were compared with the final diagnosis. RESULTS: There were 43 benign and 56 malignant lymph nodes in our cohort. Age and sex were significant predictors of malignancy. The standard ultrasound parameters-node size, long/short axis ratio, hilum, vascularization, and the presence of microcalcifications-were also statistically significant. Lymph node volume combined with age showed the best predictive power. The maximum stiffness found on SWE was also a significant predictor of malignancy. The combination of epidemiologic, classic ultrasound, and elastographic parameters yielded the highest sensitivity and specificity in the prediction of malignancy; however, the additional impact of elastographic parameters was low. CONCLUSION: A combination of epidemiologic and classic ultrasound parameters can discriminate between malignant and benign lymph nodes with satisfactory sensitivity and specificity. Examining the stiffness of lymph nodes by means of SWE does not add much new predictive power.

Cluster-randomised trial of a nurse-led advance care planning session in patients with COPD and their loved ones.

RATIONALE: Advance care planning (ACP) is uncommon in patients with chronic obstructive pulmonary disease (COPD). OBJECTIVES: To assess whether a nurse-led ACP-intervention can improve quality of patient-physician end-of-life care communication in patients with COPD. Furthermore, the influence of an ACP-intervention on symptoms of anxiety and depression in patients and loved ones was studied. Finally, quality of death and dying was assessed in patients who died during 2-year follow-up. METHODS: A multicentre cluster randomised-controlled trial in patients with advanced COPD was performed. The intervention group received an 1.5 hours structured nurse-led ACP-session. Outcomes were: quality of patient-physician end-of-life care communication, prevalence of ACP-discussions 6 months after baseline, symptoms of anxiety and depression in patients and loved ones and quality of death and dying. RESULTS: 165 patients were enrolled (89 intervention; 76 control). The improvement of quality of patient-physician end-of-life care communication was significantly higher in the intervention group compared with the control group (p<0.001). The ACP-intervention was significantly associated with the occurrence of an ACP-discussion with physicians within 6 months (p=0.003). At follow-up, symptoms of anxiety were significantly lower in loved ones in the intervention group compared with the control group (p=0.02). Symptoms of anxiety in patients and symptoms of depression in both patients and loved ones were comparable at follow-up (p>0.05). The quality of death and dying was comparable between both groups (p=0.17). CONCLUSION: One nurse-led ACP-intervention session improves patient-physician end-of-life care communication without causing psychosocial distress in both patients and loved ones.

Evaluation of the Effect of Tissue Compression on the Results of Shear Wave Elastography Measurements.

Shear wave imaging is considered to be more precise and less operator dependent when compared with strain imaging. It enables quantitative and reproducible data (Young's modulus of the imaged tissue). However, results of shear wave imaging can be affected by a variety of different factors. The aim of this study is to evaluate the effect of the pressure applied by the ultrasound probe during examination on the measured values of Young's modulus. The effect of the tissue compression on the results of the real-time shear wave elastography was evaluated via the gelatine phantom measurements, via the ex vivo experiments with pig liver, and via the in vivo measurements of the thyroid gland stiffness on healthy volunteers. The results of our measurements confirmed that the measured value of Young's modulus increases with the increasing pressure applied on the imaged object. The highest increase was observed during the ex vivo experiments (400%), and the lowest increase was detected in the case of the phantom measurements (8%). A two- to threefold increase in Young's modulus was observed between the minimum and maximum pressure in the case of the in vivo elastography measurements of thyroid gland. The Veronda-Westman theoretical model was used for the description of the tissue nonlinearity. We conclude that tissue compression by the force exerted on the probe can significantly affect the results of the real-time shear wave elastography measurements. Minimum pressure should be used when measuring the absolute value of Young's modulus of superficial organs.

Effectiveness of Pulmonary Rehabilitation in Patients With Chronic Obstructive Pulmonary Disease With Different Degrees of Static Lung Hyperinflation.

OBJECTIVE: To evaluate the effect of pulmonary rehabilitation (PR) on exercise performance and quality of life in patients with chronic obstructive pulmonary disease (COPD) with different degrees of static lung hyperinflation (LH). DESIGN: Retrospective cohort study. SETTING: PR network. PARTICIPANTS: A cohort of 1981 patients with COPD (55% men; age: 66.8±9.3y; forced expiratory volume in the first second%: 50.7±19.5; residual volume [RV]%: 163.0±49.7). INTERVENTION: An interdisciplinary PR program for patients with COPD consisting of 40 sessions. MAIN OUTCOME MEASURES: Participants were stratified into 5 quintiles according to baseline RV and were evaluated on the basis of pre- and post-PR 6-minute walk distance (6MWD), constant work rate test (CWRT), and Saint George's Respiratory Questionnaire (SGRQ), among other clinical parameters. RESULTS: With increasing RV quintile, patients were younger, more frequently women, had lower forced expiratory volume in the first second%, lower body mass index and fat-free mass index, shorter 6MWD, shorter CWRT, and worse SGRQ scores (P<.01). All RV strata improved after PR in all 3 outcomes (P<.001). Nevertheless, higher, compared to lower RV categories, had lower ΔCWRT (P<.01) but similar Δ6MWD (P=.948) and ΔSGRQ (P=.086) after PR. CONCLUSIONS: LH in COPD is related to younger age, female sex, lower body weight, worse exercise capacity and health status, but did not prevent patients from benefitting from PR. LH, however, influences walking and cycling response after PR differently.

Differential Diagnosis of Parotid Gland Tumors: Role of Shear Wave Elastography.

AIM: To create a predictive score for the discrimination between benign and malignant parotid tumors using elastographic parameters and to compare its sensitivity and specificity with standard ultrasound. METHODS: A total of 124 patients with parotid gland lesions for whom surgery was planned were examined using conventional ultrasound, Doppler examination, and shear wave elastography. Results of the examinations were compared with those ones of histology. RESULTS: There were 96 benign and 28 malignant lesions in our cohort. Blurred tumor margin alone proved to be an excellent predictor of malignancy with the sensitivity of 79% and specificity of 97%. Enlarged cervical lymph nodes, tumor vascularisation, microcalcifications presence, homogeneous echogenicity, and bilateral occurrence also discriminated between benign and malignant tumors. However, their inclusion in a predictive model did not improve its performance. Elastographic parameters (the stiffness maxima and minima ratio being the best) also exhibited significant differences between benign and malignant tumors, but again, their inclusion did not significantly improve the predictive power of the blurred margin classifier. CONCLUSION: Even though elastography satisfactorily distinguishes benign from malignant lesions on its own, it hardly provides any additional value in evaluation of biological character of parotid gland tumors when used as an adjunct to regular ultrasound examination.

Shear wave elastography parameters of normal soft tissues of the neck.

BACKGROUND: Shear wave elastography is a relatively new method of quantitative measurement of tissue elasticity. Assuming that malignant lesions are stiffer than benign ones, elastography may provide supplementary information for their discrimination. However, potential confounding factors impacting tissue stiffness should be investigated first. AIMS: The objective of this study was to measure the stiffness of selected tissues of the head and neck in a normal population and to evaluate its relationship to age, sex, and body mass index. METHODS: Stiffness of the thyroid, submandibular and parotid glands, masseter and sternocleidomastoid muscles, and cervical lymph nodes was measured bilaterally in 128 healthy volunteers (83 female and 45 male). At least 20 subjects in each decade of life (20-29, 30-39‥, 70+) were enrolled. Shear wave elastography was performed by a single radiologist in all the subjects. The stiffnesses obtained were correlated with age, sex, and body mass index. RESULTS: The mean stiffness was 9.5 ± 3.6 kPa for the thyroid, 9.5 ± 4.6 kPa for the lymph node, 11.0 ± 3.4 kPa for the submandibular gland, 9.0 ± 3.5 kPa for the parotid gland, 9.9 ± 4.1 kPa for the sternocleidomastoid, and 10.0 ± 4.3 kPa for the masseter muscle. A slight general decrease in stiffness with increasing age was found. BMI and weight had a small impact on the minimum and maximum stiffness values. The sex of the subject did not affect elasticity. CONCLUSION: The mean stiffness of healthy head and neck organs has a relatively narrow distribution around 11 kPa. The changes of stiffness with age, BMI, and weight that were identified are too small to have clinical impact.

[Ultrasound elastography and its use in the head and neck imaging]. / Ultrazvuková elastografie a její vyuzití v oblasti hlavy a krku.

Ultrasound elastography (sonoelastography, USE) is a relatively new, rapidly evolving area of imaging that measures elasticity of tissues. Its development started in the last decade of the 20th century and was accelerated after devices allowing real-time imaging and quantification (shear wave elastography, SWE) became broadly available for clinical practise. First results suggest that combination of sonoelastography and conventional ultrasound gives more precise results than ultrasound alone in certain areas. In head and neck imaging, just a few mostly pilot studies have been published till January 2014. This article summarizes available information about sonoelastography and current view on USE imaging in otorhinolaryngology.

Differential response to pulmonary rehabilitation in COPD: multidimensional profiling.

The aim of the present study was to profile a multidimensional response to pulmonary rehabilitation in patients with chronic obstructive pulmonary disease (COPD).Dyspnoea, exercise performance, health status, mood status and problematic activities of daily life were assessed before and after a 40-session pulmonary rehabilitation programme in 2068 patients with COPD (mean forced expiratory volume in 1 s of 49% predicted). Patients were ordered by their overall similarity concerning their multidimensional response profile, which comprises the overall response on MRC dyspnoea grade, 6MWD, cycle endurance time, Canadian Occupational Performance Measure performance and satisfaction scores, Hospital Anxiety and Depression Scale anxiety and depression, and St George's Respiratory Questionnaire total score, using a novel non-parametric regression technique.Patients were clustered into four groups with distinct multidimensional response profiles: n=378 (18.3%; "very good responder"), n=742 (35.9%; "good responder"), n=731 (35.4%; "moderate responder"), and n=217 (10.5%; "poor responder"). Patients in the "very good responder" cluster had higher symptoms of dyspnoea, number of hospitalisations <12 months, worse exercise performance, worse performance and satisfaction scores for problematic activities of daily life, more symptoms of anxiety and depression, worse health status, and a higher proportion of patients following an inpatient PR programme compared to the other three clusters.A multidimensional response outcome needs to be considered to study the efficacy of pulmonary rehabilitation services in patients with COPD, as responses to regular outcomes are differential within patients with COPD.

Six-minute walk distance in patients with chronic obstructive pulmonary disease: Which reference equations should we use?

The use of different 6-min walk distance (6MWD) reference equations probably results in different predicted 6MWD reference values. We wished to investigate the impact of several 6MWD reference equations for adults in patients with chronic obstructive pulmonary disease (COPD) and factors accountable for different 6MWD% predicted values. Twenty-two 6MWD reference equations were applied to a data set of 2757 patients with COPD. The predicted 6MWD reference value of Troosters and colleagues was used as the point of reference. Four out of 21 remaining equations resulted in comparable 6MWD% predicted, 16 equations resulted in significantly higher 6MWD% predicted and 1 equation resulted in a significantly lower 6MWD% predicted. Similar differences in 6MWD% predicted were observed after stratification by sex. Body mass index and global initiative for chronic obstructive lung disease (GOLD) stage classification demonstrated varying results within and between the groups; 9 out of 21 equations resulted in comparable 6MWD% predicted in underweight patients but only 1 equation demonstrated comparable result in obese. Eight equations in GOLD I, whilst 5 out of 21 equations in GOLD IV resulted in comparable 6MWD% predicted. Existing 6MWD reference equations will give varying results. The choice of 6MWD reference equation should consider the consistency of 6-min walk test operating procedures and at least be specific for the country/region of origin.