Fine particulate matter and sleep-disordered breathing severity in a large Italian cohort.

BACKGROUND: Air pollution and obstructive sleep apnea (OSA) are both linked with cardiovascular co-morbidities and share similar pathophysiological mechanisms. A causal association between the two has been postulated. However, the results of the studies on this topic are conflicting mainly because of the lack of adjustment for important confounders such as seasonality and temperature. We aimed to evaluate if such an association exists in a highly polluted area like Lombardy region (Italy) when accounting for all confounders. METHODS: Data of adult patients seen at the Sleep Disorder Centre in Milan from 2010 to 2020 were analysed and the main polygraphic data were retrieved. Air pollutant concentrations of the following pollutants NO2, O3, PM2.5, and PM10 were collected through monitoring stations. RESULTS: A total of 3493 patients were included: males (2358, 67.5%) mean age 60.1 (SD = 14.3) years, BMI 29.2 (6.2) kg/m2, mean AHI 16.5 (18.1) events/h. After adjusting for all confounders, in the multivariable analysis, the only associations that remained significant were long-term exposure to O3 with indexes of OSA severity (AHI and ODI) but only in spring. Furthermore, a positive association was seen between long-term exposure to PM10 and ODI but in springtime only. CONCLUSION: The findings of the current study does not support an association between fine particulate matter and OSA severity.

Differential actigraphy for monitoring asymmetry in upper limb motor activities.

Most applications of accelerometry-based actigraphy require a single sensor, properly located onto the body, to estimate, for example, the level of activity or the energy expenditure. Some approaches adopt a multi-sensor setup to improve those analyses or to classify different types of activity. The specific case of two symmetrically placed actigraphs allowing, by some kind of differential analysis, for the assessment of asymmetric motor behaviors, has been considered in relatively few studies. This article presents a novel method for differential actigraphy, which requires the synchronized measurements of two triaxial accelerometers (programmable eZ430-Chronos, Texas Instruments, USA) placed symmetrically on both wrists. The method involved the definition of a robust epoch-related activity index and its implementation on-board the adopted programmable platform. Finally, the activity recordings from both sensors allowed us to define a novel asymmetry index AR24 h ranging from -100% (only the left arm moves) to +100% (only the right arm moves) with null value marking a perfect symmetrical behavior. The accuracy of the AR24 h index was 1.3%. Round-the-clock monitoring on 31 healthy participants (20-79 years old, 10 left handed) provided for the AR24 h reference data (range -5% to 21%) and a fairly good correlation to the clinical handedness index (r = 0.66, p < 0.001). A subset of 20 participants repeated the monitoring one week apart evidencing an excellent test-retest reliability (r = 0.70, p < 0.001). Such figures support future applications of the methodology for the study of pathologies involving motor asymmetries, such as in patients with motor hemisyndromes and, in general, for those subjects for whom a quantification of the asymmetry in daily motor performances is required to complement laboratory tests.

Wearable seismocardiography: towards a beat-by-beat assessment of cardiac mechanics in ambulant subjects.

Seismocardiogram (SCG) is the measure of the micro-vibrations produced by the heart contraction and blood ejection into the vascular tree. Over time, a large body of evidence has been collected on the ability of SCG to reflect cardiac mechanical events such as opening and closure of mitral and aortic valves, atrial filling and point of maximal aortic blood ejection. We recently developed a smart garment, named MagIC-SCG, that allows the monitoring of SCG, electrocardiogram (ECG) and respiration out of the laboratory setting in ambulant subjects. The present pilot study illustrates the results of two different experiments performed to obtain a first evaluation on whether a dynamical assessment of indexes of cardiac mechanics can be obtained from SCG recordings obtained by MagIC-SCG. In the first experiment, we evaluated the consistency of the estimates of two indexes of cardiac contractility, the pre-ejection period, PEP, and the left ventricular ejection time, LVET. This was done in the lab, by reproducing an experimental protocol well known in literature, so that our measures derived from SCG could have been compared with PEP and LVET reference values obtained by traditional techniques. Six healthy subjects worn MagIC-SCG while assuming two different postures (supine and standing); PEP was estimated as the time interval between the Q wave in ECG and the SCG wave corresponding to the opening of aortic valve; LVET was the time interval between the SCG waves corresponding to the opening and closure of the aortic valve. The shift from supine to standing posture produced a significant increase in PEP and PEP/LVET ratio, a reduction in LVET and a concomitant rise in the LF/HF ratio in the RR interval (RRI) power spectrum. These results are in line with data available in literature thus providing a first support to the validity of our estimates. In the second experiment, we evaluated in one subject the feasibility of the beat-by-beat assessment of LVET during spontaneous behavior. The subject was continuously monitored by the smart garment from 8 am to 8 pm during a workday. From the whole recording, three data segments were selected: while the subject was traveling to work (M1), during work in the office (O) and while traveling back home (M2). LVET was estimated on a beat-by-beat basis from SCG and the RRI influence was removed by regression analysis. The LVET series displayed marked beat-by-beat fluctuations at the respiratory frequency. The amplitude of these fluctuations changed in the three periods and was lower when the LF/HF RRI power ratio was higher, at O, thus suggesting a possible influence of the autonomic nervous system on LVET short-term variability. To the best of our knowledge this case report provides for the first time a representation of the beat-by-beat dynamics of a systolic time interval during daily activity. The statistical characterization of these findings remains to be explored on a larger population.

24h seismocardiogram monitoring in ambulant subjects.

Sternal seismocardiogram (SCG) is the assessment of microvibrations produced by the beating heart as detected by an accelerometer positioned on the sternum. This signal reflects mechanical events of the heart contraction, including the opening and closure of mitral and aortic valves and maximal blood flow acceleration. Traditionally, SCG has been detected in a laboratory setting with the subject lying at rest in supine position. Aims of this study were 1) to investigate the feasibility of a SCG monitoring over the 24 hours in ambulant subjects, and 2) to calculate number and time distribution of the SCG estimates obtainable over the 24 hours. In 5 healthy subjects ECG, respiration, body accelerations and sternal SCG were recorded for 24 hours in a workday by a smart garment recently developed in our laboratory, the MagIC-SCG system. Each recording was split into a series of contiguous 5-s data segments and SCG was estimated in each segment where the magnitude of the acceleration vector was < 4 milli-g (this condition indicates that the subject was not moving).All the 24-h recordings were found of good quality and could be entirely analyzed. A large number of SCG estimates could be obtained over the 24 hours. In particular, more than 100 estimates per hour were available during the day; at night this rate was three times higher.Thus our study indicates that not only the 24h SCG monitoring in daily life is feasible but also that possible changes over time in SCG and its derived parameters may be tracked with an extreme temporal detail.

Linear and fractal heart rate dynamics during sleep at high altitude. Investigation with textile technology.

OBJECTIVES: To investigate the effects of hypoxia during sleep on linear and self-similar components of heart rate variability (HRV) in eight healthy subjects at high altitude on Mount Everest. METHODS: ECG was monitored by using an innovative textile-based device, the MagIC system. For each subject three night recordings were performed at sea level (SL), at 3500 m and 5400 m above SL. RR Interval (RRI) was derived on a beat-by-beat basis from the ECG and the VLF, LF and HF spectral components and the LF/HF ratio were estimated. Short- (α1) and long-term (α2) scale exponents as well as the recently proposed spectrum of self-similarity coefficients, α(n) were estimated by detrended fluctuation analysis (DFA). RESULTS: With respect to SL, all HRV parameters but one (α2) were significantly modified at 3500 m. However, at 5400 m they tended to return to the SL values and this was in contrast with the increase in the hypobaric hypoxia and in the number of central sleep apneas occurring at higher altitude. The only HRV index that displayed changes at 5400 m was the DFA α(n) spectrum, with α(n) values significantly lower than at SL for 20 < n <50 and higher for 200 < n <400, being n the box size. CONCLUSIONS: While the biological interpretation of these results is still in progress, our data indicates that the cardiac response to high altitude hypoxia during sleep can hardly be fully explored by traditional HRV estimators only, and requires the additional support of more sophisticated indexes exploring also nonlinear and fractal features of cardiac variability.

Heart rate monitoring and control in altered gravity conditions.

On the basis of indirect evidences it has been hypothesized that during space missions the almost complete absence of gravity might impair the baroreflex control of circulation. In the first part of this paper we report results obtained from a series of experiments carried out to directly verify this hypothesis during the 16-day STS 107 Shuttle flight. Spontaneous baroreflex sensitivity was assessed in four astronauts before flight (baseline) and at days 0-1, 6-7 and 12-13 during flight, both at rest and while performing moderate exercise. Our results indicate that at rest the baroreflex sensitivity significantly increased in the early flight phase, as compared to pre-flight values and tended to return to baseline in the mid-late phase of flight. During exercise, baroreflex sensitivity was lower than at rest, without any difference among pre-flight and in-flight values. These findings seem to exclude the hypothesis of an impairment of the baroreflex control of heart rate during exposure to microgravity, at least over a time window of 16 days. In the second part of the paper we propose a novel textile-based methodology for heart rate and other vital signs monitoring during gravity stress. The positive results obtained from its use during parachute jumps support the use of smart garments for the unobtrusive assessment of physiological parameters in extreme environments.