Type 2 diabetes and cardiac autonomic neuropathy screening using dynamic pupillometry

Basics, benefits, and pitfalls of pupillometers assessing visual function

Numerous commercially and non-commercially available pupillometers are nowadays able to assess various biological functions in humans, by evaluating pupils' dynamics in response to specific stimuli. However, the use of pupillometers for ophthalmic afferent evaluations (i.e., photoreceptoral responses) in real-world settings is relatively limited. Recent scientific and technological advances, coupled with artificial intelligence methods have improved the performance of such devices to objectively detect, quantify, and classify functional disturbances of the retina and the optic nerve. This review aims to summarize the scientific principles, indications, outcomes, and current limitations of pupillometry used for evaluation of afferent pathways in ophthalmic clinical settings.

Quantitative Pupillometry: Clinical Applications for the Internist

From the time of Galen, examining of the pupillary light reflex has been a standard of care across the continuum of healthcare. The growing body of evidence overwhelmingly supports the use of quantitative pupillometry over subject examination with flashlight or penlight. At current time, pupillometers have become standard-of-care in many hospitals across six continents. This review paper provides an overview and rationale for pupillometer use and highlights literature supporting pupillometer derived measures of the pupillary light reflex in both neurological and non-neurological patients across the healthcare continuum.

The impact of Alzheimer's disease risk factors on the pupillary light response

Alzheimer's disease (AD) is the leading cause of dementia, and its prevalence is increasing and is expected to continue to increase over the next few decades. Because of this, there is an urgent requirement to determine a way to diagnose the disease, and to target interventions to delay and ideally stop the onset of symptoms, specifically those impacting cognition and daily livelihood. The pupillary light response (PLR) is controlled by the sympathetic and parasympathetic branches of the autonomic nervous system, and impairments to the pupillary light response (PLR) have been related to AD. However, most of these studies that assess the PLR occur in patients who have already been diagnosed with AD, rather than those who are at a higher risk for the disease but without a diagnosis. Determining whether the PLR is similarly impaired in subjects before an AD diagnosis is made and before cognitive symptoms of the disease begin, is an important step before using the PLR as a diagnostic tool. Specifically, identifying whether the PLR is impaired in specific at-risk groups, considering both genetic and non-genetic risk factors, is imperative. It is possible that the PLR may be impaired in association with some risk factors but not others, potentially indicating different pathways to neurodegeneration that could be distinguished using PLR. In this work, we review the most common genetic and lifestyle-based risk factors for AD and identify established relationships between these risk factors and the PLR. The evidence here shows that many AD risk factors, including traumatic brain injury, ocular and intracranial hypertension, alcohol consumption, depression, and diabetes, are directly related to changes in the PLR. Other risk factors currently lack sufficient literature to make any conclusions relating directly to the PLR but have shown links to impairments in the parasympathetic nervous system; further research should be conducted in these risk factors and their relation to the PLR.

Detecting and treating the protean manifestations of diabetic autonomic neuropathy

The manifestations of diabetic autonomic neuropathy (DAN) are protean and clinically involve multiple systems, including the cardiovascular system, the gastrointestinal system, the genitourinary system as well as the sweat glands (sudomotor dysfunction) and the gallbladder. In addition, cardiac autonomic neuropathy (CAN) is associated with a correctible inability to appreciate and correct hypoglycaemia. While not a clinical problem, pupillary involvement should be the clue and the catalyst to investigate for other manifestations of DAN. This review outlines a practical approach to detecting and investigating the manifestations of DAN. Of particular importance is early detection of cardiovascular involvement where prompt therapy through glycaemic control can decrease the severity of CAN and decelerate the frequency and severity of retinopathy and nephropathy in addition to decreasing cardiovascular events and mortality. CAN also plays a role in accelerating other diabetic complications such as acute ischaemic stroke, heart failure, medial artery calcinosis, foot ulcers, peripheral artery disease and Charcot joints. Many therapies of DAN are available, which should not only decrease morbidity and mortality from DAN, but also improve the patient's quality of life. However, the therapies available are largely symptomatic.

Pupil maximum constriction velocity predicts post-induction hypotension in patients with lower ASA status: a prospective observational study

Background

Individuals affected by autonomic dysfunction are at a higher risk of developing hypotension following anesthesia induction. Dynamic pupillometry has previously been employed as a means of assessing autonomic function. This prospective observational study was developed to determine whether pupillary light reflex (PLR) parameters can reliably predict post-induction hypotension (PIH).

Methods

This study enrolled patients with lower ASA status (I-II) undergoing elective surgery. PLR recordings for these patients prior to anesthesia induction were made with an infrared pupil camcorder, with a computer being used to assess Average Constriction Velocity (ACV), Maximum Constriction Velocity (MCV), and Constriction Ratio (CR). PIH was defined by a > 30% reduction in mean arterial pressure (MAP) or any MAP recording < 65 mmHg for at least 1 min from the time of induction until 10 minutes following intubation. Patients were stratified into PIH and non-PIH groups based on whether or not they developed hypotension.

Results

This study enrolled 61 total patients, of whom 31 (50.8%) exhibited one or more hypotensive episodes. Patients in the PIH group exhibited significantly smaller ACV (P = 0.003) and MCV values (P < 0.001), as well as a higher CR (P = 0.003). Following adjustment for certain factors (Model 2), MCV was identified as a protective factor for PIH (Odds Ratio: 0.369). Receiver operating characteristic (ROC) analyses revealed that relative to CR (AUC: 0.695, 95% CI: 0.563–0.806; P = 0.004), the reciprocal of MCV (1/MCV) offered greater value as a predictor of PIH (AUC: 0.803,95%CI: 0.681–0.894; P < 0.001).

Conclusion

These results indicate that pupil maximum constriction velocity is a reliable predictor of post-induction hypotension in individuals of ASA I-II status undergoing elective surgery.

Trial registration

This study was registered with the Chinese Clinical Trial Registry (registration number: ChiCTR2200057164, registration date: 01/03/2022).

Instrumental Evaluation of COVID-19 Related Dysautonomia in Non-Critically-Ill Patients: An Observational, Cross-Sectional Study

Coronavirus disease-19 (COVID-19) is a predominantly respiratory syndrome. Growing reports about a SARS-CoV-2 neurological involvement, including autonomic dysfunction (AD), have been reported, mostly in critically-ill patients, or in the long-COVID syndrome. In this observational, cross-sectional study, we investigated the prevalence of AD in 20 non-critically-ill COVID-19 patients (COVID+ group) in the acute phase of the disease through a composite instrumental evaluation consisting of Sudoscan, automated pupillometry, heart rate variability (HRV), and pulse transit time (PTT). All the parameters were compared to a control group of 20 healthy volunteers (COVID− group). COVID+ group presented higher values of pupillary dilatation velocities, and baseline pupil diameter than COVID− subjects. Moreover, COVID+ patients presented a higher incidence of feet sudomotor dysfunction than COVID− group. No significant differences emerged in HRV and PTT parameters between groups. In this study we observed the occurrence of autonomic dysfunction in the early stage of the disease.

Pupil responses in patients with COVID-19

Aim

To compare pupillary responses in patients with Coronavirus disease-2019 (COVID-19) during active infection and at 3rd months post-infection.

Methods

This study included 58 COVID-19 cases (mean age 47.23 ± 1.1 years). The scotopic, mesopic and photopic diameters were noted. Pupil diameters were noted at the 0, 1st, 2nd, 4th, 6th, 8th, and 10th seconds in reflex pupil dilation after the termination of a light. The average dilation speed was calculated at the 1st, 2nd, 4th, 6th, 8th, and 10th seconds. Pupil responses measured during COVID-19 infection and 3 months later were compared.

Results

The mean scotopic and mesopic pupil diameter value of during COVID-19 infection was found lower than the 3rd month post-infection. (p = 0.001, p = 0.023; respectively). No statistically significant difference was found in the mean photopic pupil diameter and the mean pupil diameter at 0 s between measurements (p > 0.05, p = 0.734; respectively). The mean pupil diameter was significantly lower during COVID-19 infection at the 1st, 2nd, 4th, 6th, 8th and 10th seconds (p < 0.01, for each). The average dilation speed measurements at every second measured were lower in during COVID-19 infection than the 3rd months later (p = 0.001; p < 0.01 for each).

Conclusions

Pupil responses were found significantly different in COVID-19 cases when compared with the measurements taken three months later.

Using System Identification to Construct an Inherent Model of Pupillary Light Reflex to Explore Diabetic Neuropathy

This study proposed a pupillary light reflex (PLR) inherent model based on the system identification method to demonstrate the dynamic physiological mechanism of the PLR, in which pupillary constriction and dilation are controlled by the sympathetic and parasympathetic nervous system. This model was constructed and verified by comparing the simulated and predicted PLR response with that of healthy participants. The least root-mean-square error (RMSE) of simulated PLR response was less than 0.7% when stimulus duration was under 3 ms. The RMSE of predicted PLR response increased by approximately 6.76%/s from the stimulus duration of 1 ms to 3 s, when the model directly used the parameters extracted from the PLR at the stimulus duration of 10 ms. When model parameters were derived from the regression by the measured PLR response, the RMSE kept under 8.5%. The model was applied to explore the PLR abnormalities of the people with Diabetic Mellitus (DM) by extracting the model parameters from 42 people with DM and comparing these parameters with those of 42 healthy participants. The parameter in the first-order term of the elastic force of the participants with DM was significantly lower than that of the healthy participants (p < 0.05). The sympathetic force and sympathetic action delay of the participants with DM were significantly larger (p < 0.05) and longer (p < 0.0001) than that of the healthy ones, respectively. The reason might be that the sympathetic nervous system, which controls the dilator muscle, degenerated in diabetic patients.

Diabetes care quality according to facility setting: A cross-sectional analysis in six Peruvian regions

OBJECTIVE

To characterize diabetes care across healthcare facilities in six Peruvian regions.

METHODS

Cross-sectional study of patients with type 2 diabetes mellitus (T2DM), ranging from primary care facilities to hospital-based facilities, in six Peruvian regions. Data was collected by health staff trained between 2012 and 2016. We studied six diabetes care outcomes and four adequate diabetes care outcomes considering the healthcare facility as the exposure of interest. We estimated prevalence ratios (PR) and their 95% confidence intervals (95% CI) using Poisson regression with robust variance.

RESULTS

Data from 8879 patients with T2DM, mean age 59.1 years (SD ± 12.2), 53.6% males, was analyzed. Of these, 8096 (91.2%) were treated at primary care facilities. The proportions of patients who had HbA1c, LDL-c, and creatinine/microalbumin test performed increased with the setting of the healthcare facility. Overall, 39%-56% of patients had an adequate HbA1c control, being higher in hospital-based facilities with specialists in comparison to primary care facilities.

CONCLUSIONS

We observed that the higher the setting of the facility, the higher the rate of the assessed diabetes care outcomes and adequate diabetes care for four of the six targets (fasting glucose, HbA1c, LDL-c and creatinine or microalbumin) and for three of the four targets (glucose≤130 mg/dL, HbA1c ≤7%(53 mmol/mol) and LDL-c <100 mg/dL), respectively. Substantial gaps were observed at the primary care facilities, calling for the strengthening of diabetes care.

Altered pupillary light responses are associated with the severity of autonomic symptoms in patients with Fabry disease

Symptoms of autonomic dysfunction are common in Fabry disease. In this study we aimed to evaluate alterations in the pupillary response to white light stimulation in patients with Fabry disease and their association with the severity of autonomic symptoms. Fourteen consecutive patients with Fabry disease and 14 healthy control participants were enrolled in this cross-sectional study. The Mainz Severity Score Index (MSSI) was used to measure the severity of Fabry disease and the Composite Autonomic Symptom Scale 31 (COMPASS 31) questionnaire was used to evaluate the severity of autonomic symptoms. The pupil light responses were assessed with an infrared dynamic pupillometry unit. There were significant reductions in the amplitude (P = 0.048) and duration (P = 0.048) of pupil contraction, and the latency of pupil dilation (P = 0.048) in patients with Fabry disease compared to control subjects. The total weighted COMPASS 31 score correlated with MSSI (r = 0.592; P = 0.026) and the duration of pupil dilation (ρ = 0.561; P = 0.037). The pupillomotor weighted sub-score of the COMPASS 31 correlated inversely with the duration of pupil contraction (r = − 0.600; P = 0.023) and latency of pupil dilation (ρ = − 0.541; P = 0.046), and directly with the duration of pupil dilation (ρ = 0.877; P < 0.001) and MSSI (r = 0.533; P = 0.049). In conclusion, abnormal pupillary function is demonstrated in patients with Fabry disease, which is associated with the severity of autonomic symptoms.

Pupillary light reflex as a diagnostic aid from computational viewpoint: A systematic literature review

This work presents a detailed and complete review of publications on pupillary light reflex (PLR) used to aid diagnoses. These are computational techniques used in the evaluation of pupillometry, as well as their application in computer-aided diagnoses (CAD) of pathologies or physiological conditions that can be studied by observing the movements of miosis and mydriasis of the human pupil. A careful survey was carried out of all studies published over the last 10 years which investigated, electronic devices, recording protocols, image treatment, computational algorithms and the pathologies related to PLR. We present the frontier of existing knowledge regarding methods and techniques used in this field of knowledge, which has been expanding due to the possibility of performing diagnoses with high precision, at a low cost and with a non-invasive method.

Quantitative examination of early diabetes by light-emitting diodes light-induced pupillary light reflex

This study investigated the abnormal pupillary light reflex in patients with early diabetes mellitus (DM) without retinopathy by using a custom-made noninvasive portable pupilometer. The pupilometer recorded and analyzed the pupillary light reflex. Two light intensities, 0.2 cd and 1.2 cd, and four wavelengths of stimulus light-white (400 nm-800 nm), red (640 ± 5 nm), green (534 ± 5 nm), and blue (470 ± 5 nm)-were used to stimulate the pupil for 10 ms. The pupillary response was recorded for 15 s. A total of 40 healthy people and 40 people with DM without retinopathy participated in the experiment at the National Taiwan University Hospital. The mean and standard deviation of DM duration were 4.5 years and 3.9 years. Of the 16 indices, the duration that pupil restores from its minimum size to half of its resting size (DRP), maximum pupil restoration velocity (MRV), and average restoration velocity (ARV) exhibited the most significant differences between the healthy people and those with DM. Compared with healthy participants, DRP was 16.33% higher, and MRV and ARV were 17.45% and 4.58% lower, respectively, in those with DM. This might be attributable to the sympathetic nervous system (SNS) controlling the dilator muscle during the dark-adapted period and relaxing the pupil; the SNS had few degenerated nerve endings in people with DM. The three aforementioned indices might be used to evaluate the severity of autonomic neuropathy in early DM.

Static and Dynamic Pupillary Responses in Patients with Different Stages of Diabetic Retinopathy

This study aimed to investigate pupillary involvement in patients with type 2 diabetes mellitus (DM) and to evaluate whether there is a relationship between severity of diabetic retinopathy (DR) and pupillary responses. The study included 133 individuals in four groups: proliferative DR, non-proliferative DR, DM group without retinal involvement and a control group. Static pupillometry measurements including scotopic pupil diameter (PD), mesopic PD, low photopic PD, high photopic PD, and dynamic pupillometry measurements, including resting diameter, amplitude, latency, velocity, duration of pupil contraction and latency, duration, and velocity of pupil dilatation were taken using an automated quantitative pupillometry system. The correlations between glycosylated haemoglobin values and duration of DM with these parameters were also investigated. The study showed that patients with DR may also have diabetic autonomic neuropathy and pupillometry can be a useful screening tool for detecting diabetic autonomic neuropathy.

Association of pupil responses with severity of erectile dysfunction in diabetes mellitus

Purpose:

To investigate the relation between erectile dysfunction (ED) severity and pupillary functions in patients with diabetes mellitus (DM).

Methods:

This prospective and observational study included 90 patients with type 2 DM and ED. Patients divided into three subgroups according to severity of ED: (i) Mild ED, (ii) Moderate ED and (iii) Severe ED groups. Thirty age-matched healthy subjects formed the control group. Main outcome measures were pupil diameter and average speed of pupil dilation. Static and dynamic pupillometry analysis was performed using the Sirius Topographer (CSO, Firenze, Italy).

Results:

Mean pupil diameter during static and dynamic pupillometry analysis were significantly greater in the control group than in the all study groups (P < 0.05). Mean pupil diameter in static pupillometry analysis was significantly different in each study group and pupil was more miotic in the Severe ED group than in the both Moderate and Mild ED groups (P < 0.05 for each). Dynamic pupillometry analysis revealed that mean pupil diameter and mean average dilation speed were significantly different in each study group throughout measurement period and the highest speed was observed in the Mild ED group and the lowest speed was observed in the severe ED group (P < 0.005 for each).

Conclusion:

Our study results suggest that abnormal pupil functions due to diabetic autonomic neuropathy may indicate the associated ED in patients with DM.

Additive Effect of Topical Nepafenac on Mydriasis in Patients With Diabetes Mellitus

OBJECTIVES

To evaluate the additive effect of topical nepafenac on pupil diameter (PD) in patients with diabetes mellitus (DM) and cataract.

METHODS

This prospective comparative study included the patients having cataract surgery with and without DM. Two consecutive PD measurements were taken using an automatic quantitative pupillometry system (MonPack One, Metrovision). A baseline measurement was taken, then one drop of nepafenac % 0.1 (Nevanac; Alcon, Fort Worth, TX) was instilled only to the eye that will be operated on (study eye). Cyclopentolate 1.0% (Sikloplejin; Abdi İbrahim, İstanbul, Turkey) was instilled to both eyes (study eye/fellow eye) 5 minutes later. The second measurement was taken at 1 hour after this application.

RESULTS

The DM group consisted of 43 patients, and the control group consisted of 39 participants. The baseline PDs of both eyes were similar in the DM group (P=0.070) and the control group (P=0.345). The change in pupil size from baseline to mydriasis was statistically significantly greater in the study eyes (2.69±0.53) than fellow eyes (2.54±0.61) in the DM group (P=0.009), but there was no statistically significant difference in the control group (2.94±0.63 vs. 2.86±0.58). When the groups were compared, the PD changes were similar in the study eyes between groups (P=0.065), while the PD changes in the fellow eyes were lower in the DM group (P=0.017).

CONCLUSIONS

Nepafenac has been shown additive effect on pupil dilation in diabetic patients before cataract surgery.

Standards in Pupillography

The number of research groups studying the pupil is increasing, as is the number of publications. Consequently, new standards in pupillography are needed to formalize the methodology including recording conditions, stimulus characteristics, as well as suitable parameters of evaluation. Since the description of intrinsically photosensitive retinal ganglion cells (ipRGCs) there has been an increased interest and broader application of pupillography in ophthalmology as well as other fields including psychology and chronobiology. Color pupillography plays an important role not only in research but also in clinical observational and therapy studies like gene therapy of hereditary retinal degenerations and psychopathology. Stimuli can vary in size, brightness, duration, and wavelength. Stimulus paradigms determine whether rhodopsin-driven rod responses, opsin-driven cone responses, or melanopsin-driven ipRGC responses are primarily elicited. Background illumination, adaptation state, and instruction for the participants will furthermore influence the results. This standard recommends a minimum set of variables to be used for pupillography and specified in the publication methodologies. Initiated at the 32nd International Pupil Colloquium 2017 in Morges, Switzerland, the aim of this manuscript is to outline standards in pupillography based on current knowledge and experience of pupil experts in order to achieve greater comparability of pupillographic studies. Such standards will particularly facilitate the proper application of pupillography by researchers new to the field. First we describe general standards, followed by specific suggestions concerning the demands of different targets of pupil research: the afferent and efferent reflex arc, pharmacology, psychology, sleepiness-related research and animal studies.

Autonomic nervous system assessment by pupillary response as a potential biomarker for cardiovascular risk: A pilot study

BACKGROUND

Cardiovascular risk (CVR) biomarkers are of increasing interest because of their potential utility in management of cardiovascular diseases. The activity of the autonomic nervous system (ANS) is known to be highly correlated with CVR and therefore, is a putative biomarker. Common ANS measurement tools have several technological limitations and high-variance signals. The pupillary responses (PR) is controlled by both components of the ANS, and recent advances in pupillometry are making this measurement, easy and reliable. Thus, PR assessment could become a useful clinical tool to measure the ANS modulation and its relation to CVR. Here, we aimed to evaluate differences in PR between low CVR and moderate/high CVR individuals.

METHODS

We performed a cross-sectional study. We recruited voluntaries with low CVR (group 1, n = 12) and patients with moderate/high CVR (group 2, n = 7). An eye tracker was used to measure PR to different visual stimulus that included colors (white, black, gray) and images with known emotional valence (pleasant, unpleasant and neutrals), which were intercalated by pink "noise" images. Differences in PR between both CVR groups were assessed by Mann Whitney U test of different epochs of the PR.

RESULTS

PR was significantly different between both CVR groups (p-value < 0,05) when the observed images were unpleasant, neutral, and pink noise, for different epochs of the PR.

CONCLUSIONS

This is the first study that demonstrates that PR is different according to CVR. Thus, PR could be considered as a novel biomarker of CVR to be tested in prospective studies.

Diabetes Mellitus in Peru

BACKGROUND

Peru is an upper medium-income developing country with an increasing prevalence of chronic diseases, including diabetes.

OBJECTIVE

To review and describe the epidemiology, drivers, and diabetes care plan in Peru.

METHODS

The medical literature was reviewed based on systematic searching of PubMed, Scielo, and various gray literature from the International Diabetes Federation, World Health Organization, and local Peruvian agencies.

FINDINGS

In Peru, diabetes affects 7% of the population. Type 2 diabetes accounts for 96.8% of outpatients visits with this condition. Type 1 diabetes has an incidence of 0.4/100,000 per year, and gestational diabetes affects 16% of pregnancies. The prevalence of glucose intolerance is 8.11% and that of impaired fasting glucose 22.4%. The prevalence of overweight, obesity, and metabolic syndrome in adults is 34.7%, 17.5%, and 25%, respectively. Metabolic syndrome prevalence is greater in women and the elderly and at urban and low-altitude locations. Diabetes is the eighth cause of death, the sixth cause of blindness, and the leading cause of end-stage kidney disease and nontraumatic lower limb amputation. In Peru, diabetes accounts for 31.5% of acute myocardial infarctions and 25% of strokes. Infections, diabetic emergencies, and cardiovascular disorders are the main causes for admissions, with a mortality rate < 10%, mainly as a result of infections, chronic kidney disease, and stroke. Sixty-two percent of the population has health insurance coverage, with inequities in the distribution of health care personnel across the country. Less than 30% of treated patients have a hemoglobin A1c < 7%.

CONCLUSIONS

Diabetes is a major health care issue in Peru that exposes difficult challenges and shortcomings. The national strategy for tackling diabetes includes promotion of healthy lifestyles; training primary care physicians and providing them with evidence-based clinical practice guidelines, safe and effective medications, and tools for monitoring treatment; and, finally, construction of a comprehensive health care network for early referral in order to prevent, detect, and treat diabetic complications.

Cardiac autonomic neuropathy in patients with diabetes mellitus: current perspectives

Cardiac autonomic neuropathy (CAN) is a common and often-underdiagnosed complication of diabetes mellitus (DM). CAN is associated with increased mortality, cardiovascular disease, chronic kidney disease, and morbidity in patients with DM, but despite these significant consequences CAN often remains undiagnosed for a prolonged period. This is commonly due to the disease being asymptomatic until the later stages, as well as a lack of easily available screening strategies. In this article, we review the latest developments in the epidemiology, pathogenesis, diagnosis, consequences, and treatments of CAN in patients with DM.

Can a simple test of functional capacity add to the clinical assessment of diabetes?

AIM

To identify impairment in functional capacity associated with complicated and non-complicated diabetes using the 6-min walk distance test.

METHODS

We enrolled 111 adults, aged ≥40 years, with Type 2 diabetes from a hospital facility and 150 healthy control subjects of similar age and sex from a community site in Lima, Peru. All participants completed a 6-min walk test.

RESULTS

The mean age of the 261 participants was 58.3 years, and 43.3% were male. Among those with diabetes, 67 (60%) had non-complicated diabetes and 44 (40%) had complications such as peripheral neuropathy, retinopathy or nephropathy. The mean unadjusted 6-min walk distances were 376 m and 394 m in adults with and without diabetes complications, respectively, vs 469 m in control subjects (P<0.001). In multivariable regression, the subjects with diabetes complications walked 84 m less far (95% CI -104 to -63 m) and those without complications walked 60 m less far (-77 to -42 m) than did control subjects. When using HbA1c level as a covariate in multivariable regression, participants walked 13 m less far (-16.9 to -9.9 m) for each % increase in HbA1c .

CONCLUSIONS

The subjects with diabetes had lower functional capacity compared with healthy control subjects with similar characteristics. Differences in 6-min walk distance were even apparent in the subjects without diabetes complications. Potential mechanisms that could explain this finding are early cardiovascular disease or deconditioning.