Aims As a part of the Finnish Cardiovascular Study, we tested the hypothesis that T-wave alternans (TWA) predicts mortality in a general population of patients referred for a clinical exercise test. Methods and results A total of 1037 consecutive patients (mean age ± SD of 58 ± 13 years, 673 men and 364 women) with a clinically indicated exercise test and with technically successful electrocardiographic (ECG) data during a bicycle ergometer test were included in the study. Digital ECGs were recorded and TWA was analysed continuously with the time-domain modified moving average method. The maximum TWA value at heart rate (HR) <125 b.p.m. was derived and its capacity to stratify risk for all-cause death, cardiovascular death, and sudden cardiac death (SCD) was tested. During a follow-up of 44 ± 7 months (mean ± SD), 59 patients died; 34 were due to cardiovascular causes and 20 were due to SCD. In multivariate analysis after adjustment for age, sex, use of β-blockers, functional class, maximal HR during exercise, previous myocardial infarction, and other common coronary risk factors, the relative risk of TWA ≥65 µV for SCD was 7.4 (95% CI, 2.8–19.4; P < 0.001), for cardiovascular mortality 6.0 (95% CI, 2.8–12.8; P < 0.001), and for all-cause mortality 3.3 (95% CI, 1.8–6.3; P = 0.001). Conclusion Time-domain TWA analysis powerfully predicts mortality in a general population undergoing a clinical exercise test.

In this study perceived mental stress during occupational work was compared to heart rate variability (HRV) using a traditional questionnaire and a novel wristop heart rate monitor with related software. The aim was to find HRV parameters useful for mental stress detection. We found the highest correlation between perceived mental stress with the differences between the values of triangular interpolation of rythm-to-rythm (RR) interval histogram (TINN) and the root mean square of differences of successive RR intervals (RMSSD) obtained in the morning and during the workday(r = -.73 andr = -.60, respectively). The analysis shows that as the RMSSD and TINN value differences increase from night to morning, the stress decreases.

Background. Enhanced sympathetic activity at the ventricular myocardium can destabilize repolarization, increasing the risk of death. Sympathetic activity is known to cluster in low-frequency bursts; therefore, we hypothesized that sympathetic activity induces periodic low-frequency changes of repolarization. We developed a technique to assess the sympathetic effect on repolarization and identified periodic components in the low-frequency spectral range (≤0.1 Hz), which we termed periodic repolarization dynamics (PRD). Methods. We investigated the physiological properties of PRD in multiple experimental studies, including a swine model of steady-state ventilation (n = 7) and human studies involving fixed atrial pacing (n = 10), passive head-up tilt testing (n = 11), low-intensity exercise testing (n = 11), and beta blockade (n = 10). We tested the prognostic power of PRD in 908 survivors of acute myocardial infarction (MI). Finally, we tested the predictive values of PRD and T-wave alternans (TWA) in 2,965 patients undergoing clinically indicated exercise testing. Results. PRD was not related to underlying respiratory activity (P < 0.001) or heart-rate variability (P = 0.002). Furthermore, PRD was enhanced by activation of the sympathetic nervous system, and pharmacological blockade of sympathetic nervous system activity suppressed PRD (P ≤ 0.005 for both). Increased PRD was the strongest single risk predictor of 5-year total mortality (hazard ratio 4.75, 95% CI 2.94–7.66; P < 0.001) after acute MI. In patients undergoing exercise testing, the predictive value of PRD was strong and complementary to that of TWA. Conclusion. We have described and identified low-frequency rhythmic modulations of repolarization that are associated with sympathetic activity. Increased PRD can be used as a predictor of mortality in survivors of acute MI and patients undergoing exercise testing. Trial registration. ClinicalTrials.gov NCT00196274. Funding. This study was funded by Angewandte Klinische Forschung, University of Tübingen (252-1-0).

There is a lack of noninvasive pulmonary function measurement techniques suitable for continuous long-term measurement of tidal breathing in mobile subjects, although tidal breathing analysis has been shown to contain information that relates to the level airway obstruction. This paper is the first to assess the suitability of impedance pneumography (IP) for measurement of continuous pulmonary flow and volume signals instead of only the respiration rate (RR) or tidal volume (VT). We measured pneumotachograph (PNT) and IP signals simultaneously from 20 healthy male subjects in erect, dorsal supine, and lateral supine positions while voluntarily varying VT. IP was measured using five different impedance lead configurations with electrodes integrated into a textile chest belt. The IP signals were compared with PNT signals to assess agreement of IP with a more well-established measurement method. The pulmonary flow signal waveform agreement was assessed with standard error of measurement (SEM) between the time-differentiated IP signal and the PNT signal as ρ = 1-SEM. Additionally, we assessed the agreement of IP and PNT in VT estimation and the magnitude of the cardiogenic oscillation present in the impedance signal. The agreement in the pulmonary flow signal waveform shapes was found excellent at all tidal volumes and postures (mean ρ > 0.90). The agreement between the PNT-derived and the IP-derived VT estimates was very high when IP values were calibrated per subject and posture (mean difference <;3%). The main source of error in visual inspection of the IP signal was the cardiogenic distortion. From the five novel electrode configurations tested, the lateral ones were found clearly better than the anteroposterior ones. IP potentially enables the development of a noninvasive ambulatory measurement device for long-term studies of certain tidal breathing parameters in mobile subjects.

Objective: If the body fails to acclimatize at high altitude, acute mountain sickness (AMS) may result. For the early detection of AMS, changes in cardiac autonomic function measured by heart rate variability (HRV) may be more sensitive than clinical symptoms alone. The purpose of this study was to ascertain if the changes in HRV during ascent are related to AMS. Methods: We followed Lake Louise Score (LLS), arterial oxygen saturation at rest (R-SpO₂) and exercise (Ex-SpO₂) and HRV parameters daily in 36 different healthy climbers ascending from 2400 m to 6300 m altitudes during five different expeditions. Results: After an ascent to 2400 m, root mean square successive differences, high-frequency power (HF_{2 min}) of HRV were 17–51% and Ex-SpO₂ was 3% lower in those climbers who suffered from AMS at 3000 to 4300 m than in those only developing AMS later (≥5000 m) or not at all (all p < 0.01). At the altitude of 2400 m RMSSD_{2 min} ≤ 30 ms and Ex-SpO₂ ≤ 91% both had 92% sensitivity for AMS if ascent continued without extra acclimatization days. Conclusions: Changes in supine HRV parameters at 2400 m were related to AMS at 3000–4300 m Thus, analyses of HRV could offer potential markers for identifying the climbers at risk for AMS.

Chronic wounds impose a significant financial burden for the healthcare system. Currently, assessment and monitoring of hard-to-heal wounds are often based on visual means and measuring the size of the wound. The primary wound dressings must be removed before assessment can be done. We have developed a quasi-monopolar bioimpedance-measurement-based method and a measurement system to determine the status of wound healing. The objective of this study was to demonstrate that with an appropriate setup, long-term monitoring of wound healing from beneath the primary dressings is feasible. The developed multielectrode sensor array was applied on the wound area and left under the primary dressings for 142 h. The impedance of the wounds and the surrounding intact skin area was measured regularly during the study at 150 Hz, 300 Hz, 1 kHz, and 5 kHz frequencies. At the end of the follow-up period, the wound impedance had reached the impedance of the intact skin at the higher frequencies and increased significantly at the lowest frequencies. The measurement frequency affected the measurement sensitivity in wound monitoring. The skin impedance remained stable over the measurement period. The sensor array also enabled the administration of periodical low-intensity direct current (LIDC) stimulation in order to create an antimicrobial environment across the wound area via the controlled formation of hydrogen peroxide (H₂O₂).