Detecting subclinical diabetic cardiac autonomic neuropathy by analyzing ventricular repolarization dynamics

In this study, a linear parametric modeling technique was applied to model ventricular repolarization (VR) dynamics. Three features were selected from the surface ECG recordings to investigate the changes in VR dynamics in healthy and cardiac autonomic neuropathy (CAN) participants with diabetes including heart rate variability (calculated from RR intervals), repolarization variability (calculated from QT intervals), and respiration [calculated by ECG-derived respiration (EDR)]. Surface ECGs were recorded in a supine resting position from 80 age-matched participants (40 with no cardiac autonomic neuropathy (NCAN) and 40 with CAN). In the CAN group, 25 participants had early/subclinical CAN (ECAN) and 15 participants were identified with definite/clinical CAN (DCAN). Detecting subclinical CAN is crucial for designing an effective treatment plan to prevent further cardiovascular complications. For CAN diagnosis, VR dynamics was analyzed using linear parametric autoregressive bivariate (ARXAR) and trivariate (ARXXAR) models, which were estimated using 250 beats of derived QT, RR, and EDR time series extracted from the first 5 min of the recorded ECG signal. Results showed that the EDR-based models gave a significantly higher fitting value (p < 0.0001) than models without EDR, which indicates that QT-RR dynamics is better explained by respiratory-information-based models. Moreover, the QT-RR-EDR model fitting values gradually decreased from the NCAN group to ECAN and DCAN groups, which indicate a decoupling of QT from RR and the respiration signal with the increase in severity of CAN. In this study, only the EDR-based model significantly distinguished ECAN and DCAN groups from the NCAN group (p < 0.05) with large effect sizes (Cohen's d > 0.75) showing the effectiveness of this modeling technique in detecting subclinical CAN. In conclusion, the EDR-based trivariate QT-RR-EDR model was found to be better in detecting the presence and severity of CAN than the bivariate QT-RR model. This finding also establishes the importance of adding respiratory information for analyzing the gradual deterioration of normal VR dynamics in pathological conditions, such as diabetic CAN.

Quantifying the physical demands of a musical performance and their effects on performance quality

This study investigated the effects of fatigue on performance quality induced by a prolonged musical performance. Ten participants prepared 10 min of repertoire for their chosen wind instrument that they played three times consecutively. Prior to the performance and within short breaks between performances, researchers collected heart rate, respiratory rate, blood pressure, blood lactate concentration, rating of perceived exertion (RPE), and rating of anxiety. All performances were audio recorded and later analysed for performance errors. Reliability in assessing performance errors was assessed by typical error of measure (TEM) of 15 repeat performances. Results indicate all markers of physical stress significantly increased by a moderate to large amount (4.6 to 62.2%; d = 0.50 to 1.54) once the performance began, while heart rate, respirations, and RPE continued to rise by a small to large amount (4.9 to 23.5%; d = 0.28 to 0.93) with each performance. Observed changes in performance between performances were well in excess of the TEM of 7.4%. There was a significant small (21%, d = 0.43) decrease in errors after the first performance; after the second performance, there was a significant large increase (70.4%, d = 1.14). The initial increase in physiological stress with corresponding decrease in errors after the first performance likely indicates "warming up," while the continued increase in markers of physical stress with dramatic decrement in performance quality likely indicates fatigue. Musicians may consider the relevance of physical fitness to maintaining performance quality over the duration of a performance.

Multi-lag HRV analysis discriminates disease progression of post-infarct people with no diabetes versus diabetes

Diabetes mellitus is associated with multi-organ system dysfunction including the cardiovascular and autonomic nervous system. Although it is well documented that post-infarct patients are at higher risk of sudden cardiac death, diabetes adds an additional risk associated with autonomic neuropathy. However it is not known how the presence of diabetes in post-infarct patients affects cardiac rhythm. The majority of HRV algorithms for determining cardiac inter-beat interval changes describe only beat-to-beat variation determined over the whole heart rate recording and therefore do not consider the ability of a heart beat to influence a train of succeeding beats nor whether or how the temporal dynamics of the inter-beat intervals changes. This study used Poincaré Plot derived features and incorporated increased lag intervals to compare post-infarct patients with no history of prior infarct with or without diabetes and found that for the nondiabetic post-infarct patients only increased lag of short term correlation (SD1) predicted mortality, whereas in the diabetic post-infarct group only long-term correlations (SD2) significantly predicted mortality at a follow-up period of eight years. Temporal dynamics measured as a complex correlation measure (CCM) was also a significant predictor of mortality only in the diabetic post-infarct cohort. This study highlights the different pathophysiological progression and risk profile associated with presence of diabetes in a post-infarct patient population at eight year follow-up.

Effects of cold water immersion and active recovery on hemodynamics and recovery of muscle strength following resistance exercise

Cold water immersion (CWI) and active recovery (ACT) are frequently used as postexercise recovery strategies. However, the physiological effects of CWI and ACT after resistance exercise are not well characterized. We examined the effects of CWI and ACT on cardiac output (Q̇), muscle oxygenation (SmO2), blood volume (tHb), muscle temperature (Tmuscle), and isometric strength after resistance exercise. On separate days, 10 men performed resistance exercise, followed by 10 min CWI at 10°C or 10 min ACT (low-intensity cycling). Q̇ (7.9 ± 2.7 l) and Tmuscle (2.2 ± 0.8°C) increased, whereas SmO2 (-21.5 ± 8.8%) and tHb (-10.1 ± 7.7 μM) decreased after exercise (P < 0.05). During CWI, Q̇ (-1.1 ± 0.7 l) and Tmuscle (-6.6 ± 5.3°C) decreased, while tHb (121 ± 77 μM) increased (P < 0.05). In the hour after CWI, Q̇ and Tmuscle remained low, while tHb also decreased (P < 0.05). By contrast, during ACT, Q̇ (3.9 ± 2.3 l), Tmuscle (2.2 ± 0.5°C), SmO2 (17.1 ± 5.7%), and tHb (91 ± 66 μM) all increased (P < 0.05). In the hour after ACT, Tmuscle, and tHb remained high (P < 0.05). Peak isometric strength during 10-s maximum voluntary contractions (MVCs) did not change significantly after CWI, whereas it decreased after ACT (-30 to -45 Nm; P < 0.05). Muscle deoxygenation time during MVCs increased after ACT (P < 0.05), but not after CWI. Muscle reoxygenation time after MVCs tended to increase after CWI (P = 0.052). These findings suggest first that hemodynamics and muscle temperature after resistance exercise are dependent on ambient temperature and metabolic demands with skeletal muscle, and second, that recovery of strength after resistance exercise is independent of changes in hemodynamics and muscle temperature.

Review : regular brisk walking improves cardiovascular risk factors in healthy sedentary adults

QUESTION In healthy sedentary adults, does regular brisk walking improve cardiovascular risk factors?

METHODS Data sources: Medline and Web of Science (1971 to September 2004) and reference lists.Study selection and assessment:English-language, randomised controlled trials (RCTs) with duration ⩾4 weeks that assessed the effects of walking as the only intervention on changes in cardiovascular risk factors in sedentary, but otherwise healthy, adults. 24 RCTs (n = 1128, mean age 52 y, 83% women) met the selection criteria. The mean length of the walking programmes was 35 weeks (range 8–104 wk). On average, walking was done 4.4 days/week for 38 minutes per session. The mean intensity of the walking interventions was 70% of predicted maximum heart rate or 56% of VO2 max. Quality of individual studies was assessed based on allocation concealment. Outcomes: cardiovascular fitness (VO2 max), body weight, percent body fat, body mass index, and systolic and diastolic blood pressure (BP).

MAIN RESULTS Brisk walking increased cardiovascular fitness and reduced body weight, body mass index, body fat composition, and diastolic BP more than the control condition (table). No effect on systolic BP was observed (table).

CONCLUSION In healthy sedentary adults, regular brisk walking improves cardiovascular fitness, body composition, and diastolic blood pressure.

The metabolic and cognitive energy costs of stabilising a high-energy interlimb coordination task

Kinematic (relative phase error), metabolic (oxygen consumption, heart rate) and attentional (baseline and cycling reaction times) variables were measured while participants practised a high energy-demanding, intrinsically unstable 90° relative phase coordination pattern on independent bicycle ergometers. The variables were found to be strongly inter-correlated, suggesting a link between emerging performance stability with practice and minimal metabolic and attentional cost. The effects of practice of 90° relative phase coordination on the performance of in-phase (0°-phase) and antiphase (180°-phase) coordination were investigated by measuring the relative phase attractor layouts and recording the metabolic and attentional cost of the three coordination patterns before and after practice. The attentional variables did not differ significantly between coordination patterns and did not change with practice. Before practice, the coordination performance was most accurate and stable for in-phase cycling, with antiphase next and 90°-phase the poorest. However, metabolic cost was lower for antiphase than either in-phase or 90°-phase cycling, and the pre-practice attractor layout deviated from that predicted on the basis of dynamic stability as an attractor state, revealing an attraction to antiphase cycling. After practice of 90°-phase cycling, in-phase cycling remained the most accurate and stable, with 90°-phase next and antiphase the poorest, but antiphase retained the lowest metabolic energy cost. The attractor layout had changed, with new attractors formed at the practised 90°-phase pattern and its symmetrical partner of 270°-phase. Considering both the pre- and post-practice results, attractors were formed at either a low metabolic energy cost but less stable (antiphase) pattern or at a more stable but higher metabolic energy cost (90°-phase) pattern, but in neither case at the most stable and accurate (in-phase) pattern. The results suggest that energetic factors affect coordination dynamics and that coordination modes lower in metabolic energy expenditure may compete with dynamically stable modes.

Aging effects on the metabolic and cognitive energy cost of interlimb coordination

Many everyday motor tasks have high metabolic energy demands, and some require extended practice to learn the required coordination between limbs. Eight older (73.1 6 4.4 years) and 8 younger (23.3 6 5.9) men practiced a  high-energy two-hand coordination task with both 1808 and 908 target  relative phase. The older group showed greater performance error in both conditions, and performance at 908 was strongly attracted to antiphase coordination (1808). In a retention test one week following the acquisition trials, the older group had learned the 1808 condition but did not learn the 908 condition. Metabolic energy cost was not different between groups, but the older men showed higher heart rate and both conditions imposed  greater cognitive demands as revealed in auditory probe reaction time. Older adults’ motor learning may be inhibited by elevated heart rate at the same  oxygen cost, increased cognitive cost, and an attraction toward more  established low-energy in-phase or antiphase coordination.