Comparison of systolic time interval measurement modalities for portable devices.

Systolic time intervals (STI) have shown significant diagnostic and prognostic value to assess the global cardiac function. Their value has been largely established in hospital settings. Currently, STI are considered a promising tool for long-term patient follow-up with chronic cardiovascular diseases. Several technologies exist that enable beat-by-beat assessment of STI in personal health application scenarios. A comparative study is presented using the echocardiographic gold standard synchronized with impedance cardiography (ICG), phonocardiography (PCG) and photoplethysmography (PPG). The ability of these competing technologies in assessing the pre ejection period (PEP) and the left ventricle ejection time (LVET) is given a general overview with comparative results.

Assessing systolic time-intervals from heart sound: a feasibility study.

Systolic time intervals are highly correlated to fundamental cardiac functions. In this paper we investigate the feasibility of using heart sound (HS) to accurately measure the opening and closing moments of the aortic valve, since these are crucial moments to define the main systolic timings of the heart cycle, i.e. the pre-ejection period (PEP) and the left ventricular ejection time (LVET). We introduce a HS model, which is applied to define several features that provide clear markers to identify these moments in the HS. Using these features and a comparative analysis with registered echocardiographies from 17 subjects, the results achieved in this study suggest that HS can be used to accurately estimate LVET and PEP.

Assessing PEP and LVET from heart sounds: algorithms and evaluation.

This paper addresses the estimation of systolic time intervals, namely the pre-ejection period (PEP) and the left ventricular ejection time (LVET), using heart sound. PEP is estimated with a Bayesian approach resorting to the signal's instantaneous amplitude and typical time intervals between atrio-ventricular valve closure and aortic valve opening. As for LVET, aortic valve closure is determined through the analysis of a high-frequency signature of S2. Additionally, LVET has also been estimated from a PPG signal at a peripheral site, for the sake of comparison over a subset of data. We evaluated our algorithms on a set of 658 heartbeats and achieved 10.32 msec average absolute PEP estimation error with 7.3 msec standard deviation and for LVET, 15.8 msec average estimation error with 13.6 msec standard deviation. Current results support our assumption that heart sounds can be applied to detect the onset of the aortic valve movement processes.

Continuous cuff-less blood pressure monitoring based on the pulse arrival time approach: the impact of posture.

There is an unmet need for cuff-less blood pressure (BP) monitoring especially, in personal healthcare applications. The pulse arrival time (PAT) approach might offer a suitable solution to enable comfortable BP monitoring even at beat-level. However, the methodology is based on hemodynamic surrogate measures, which are sensitive to patient activities such as posture changes, not necessarily related to blood pressure variations. In this paper, we analyze the impact of posture on the PAT measure and related hemodynamic parameters such as the pre-ejection period in well-defined procedures. Additionally, the PAT of a monitored subject is investigated in an unsupervised scenario illustrating the complexity of such a measurement. Our results show the failure of blood pressure inference based on simple calibration strategies using the PAT measure only. We discuss opportunities to compensate for the observed effects towards the realization of wearable cuff-less blood pressure monitoring. These findings emphasize the importance of accessing context information in personal healthcare applications, where vital sign monitoring is typically unsupervised.

Cuffless estimation of systolic blood pressure for short effort bicycle tests: the prominent role of the pre-ejection period.

This paper investigates the specific contributions of the pre-ejection period (PEP) and pulse transit time (PTT) for blood pressure estimation based on the pulse wave methodology. We show that in short-term physical stress tests, PEP dominates PTT variations raising the question of a suitable blood pressure calibration. A model using a generalized pulse wave velocity achieves acceptable accuracy for systolic blood pressure estimation, given our experimental conditions.

Variation in the isometric maintenance heat rate with muscle length near that of maximum tension in frog striated muscle.

1. Tension and heat rate were measured as a function of muscle length in the range 0.75--1.25 lO in 10-sec isometric tetani in frog striated muscle at 0 degrees C in seven experiments. lO was defined as the length at which maximal tension was developed. 2. The length at which the stable maintenance heat rate (hB) was maximal was 7--16% lO shorter than the length at which tension was maximal (Pmax). 3. The range of hB at the length at which tension was maximal was 0.82-0.97 times the maximum value of hB. 4. For equal values of tension of 0.9 Pmax on each side of lO, hB was almost 40% greater at the shorter muscle length. 5. The results show that h(B) varies considerably with muscle length near lO, where tension varies little, and imply that tension is not the sole determinant of energy liberation in this little region.

The heat of shortening during the plateau of tetanic contraction and at the end of relaxation.

1. The net thermal effect of shortening on the heat production of the sartorius muscle of Rana temporaria has been studied at 0 degrees C in tetanic contractions of either 1.2 or 2.0 sec analysed up to the end of relaxation.2. Three types of contractions have been compared: isometric at the standard length (l(o)); isometric at a shorter length (l(o) minus 4.27 mm); and rapid shortening at constant velocity between those two lengths during the plateau of tetanic activity, the work being collected by an ergometer of the Levin-Wyman type. After the end of the shortening, stimulation was continued long enough to allow a complete recovery of tension before relaxation started.3. In those conditions, shortening heat appears clearly by comparison with the isometric contractions, and most of its effect persists up to the end of relaxation. However, a reduction of the net thermal effect, of the order of 15-25%, is observed during relaxation.4. The net supplement of heat is the same whether the shortening occurs in the beginning (0.4 sec) or towards the end (1.2 sec) of the contraction period; the reduction of the effect during relaxation is more important in the pelvic part than in the tibial part of the muscle.5. This small reduction of the thermal effect of the shortening is fully accounted for by the fact that the tension redeveloped after the end of the movement remains always below the tension developed in a tetanus at the same final length, but isometric from the start.6. As the greater part of the net thermal effect of the shortening persists at the end of relaxation, shortening heat cannot be part of a cyclic process reversed during relaxation; it must derive from some chemical source of energy.