Systolic peak detection in acceleration photoplethysmograms measured from emergency responders in tropical conditions

Photoplethysmogram (PPG) monitoring is not only essential for critically ill patients in hospitals or at home, but also for those undergoing exercise testing. However, processing PPG signals measured after exercise is challenging, especially if the environment is hot and humid. In this paper, we propose a novel algorithm that can detect systolic peaks under challenging conditions, as in the case of emergency responders in tropical conditions. Accurate systolic-peak detection is an important first step for the analysis of heart rate variability. Algorithms based on local maxima-minima, first-derivative, and slope sum are evaluated, and a new algorithm is introduced to improve the detection rate. With 40 healthy subjects, the new algorithm demonstrates the highest overall detection accuracy (99.84% sensitivity, 99.89% positive predictivity). Existing algorithms, such as Billauer's, Li's and Zong's, have comparable although lower accuracy. However, the proposed algorithm presents an advantage for real-time applications by avoiding human intervention in threshold determination. For best performance, we show that a combination of two event-related moving averages with an offset threshold has an advantage in detecting systolic peaks, even in heat-stressed PPG signals.Mohamed Elgendi, Ian Norton, Matt Brearley, Derek Abbott, Dale Schuurman

Na+ pump inhibition and non-selective cation channel activation by cyanide and anoxia in guinea-pig chromaffin cells

Hypoxia and metabolic inhibition with cyanide (CN) evoke catecholamine secretion in adrenal chromaffin cells through depolarization. We elucidated mechanisms for a CN- or anoxia-induced inward (depolarization) current, using the perforated patch method.Bath application of Ba2+ induced a dose-dependent inhibition of a muscarine-induced current (IMUS) and part of the CN-induced current (ICN) with an IC50 (concentration responsible for 50 % inhibition) of 1.3 mM. The Ba2+-sensitive component was estimated to comprise 58 % of the total ICN.The Ba2+-resistant component of ICN tended to increase with shifts of membrane potential from -40 to 40 mV and was markedly suppressed by exposure to a K+-free solution or 200 μm ouabain, indicating that the majority of the Ba2+-resistant component of ICN is due to suppression of the Na+ pump current (Ipump).The non-Ipump component of ICN diminished progressively in K+-free solution. Substitution of glucose for sucrose in a K+-free CN solution further diminished the CN potency to produce the non-Ipump component.The I-V relationship for the non-Ipump component of ICN had a reversal potential of -3 and -47 mV at 147 and 5.5 mM Na+, respectively, and showed an outward rectification, indicating that the non-Ipump component of ICN is due to activation of non-selective cation channels.Exposure to anoxia induced a current with an amplitude comparable to that of ICN, and the anoxia-induced current apparently occluded development of ICN. The anoxia-induced current diminished by ca 60 % in the absence of K+ and reversed polarity at 5 mV under K+-free conditions.It is concluded that exposure to CN and to anoxia induces suppression of the Na+ pump and activation of non-selective cation channels, probably due to an ATP decrease resulting mainly from consumption by the Na+ pump

Rectification of rabbit cardiac ryanodine receptor current by endogenous polyamines.

The actions of three endogenous polyamines (spermine, spermidine, and putrescine) were defined on Ca2+ release channels (ryanodine receptors, RyRs) isolated from rabbit cardiac sarcoplasmic reticulum. The current-voltage relationship of the RyR channel was N-shaped in the presence of polyamine (1-5 mM). Polyamine blocked conduction near 0 mV, but the blockade was relieved at large potentials. Polyamines acted (blocked) from both sides of the channel. Polyamine efficacy was dependent on current direction and was inversely related to the ion selectivity of the RyR pore. This suggests that polyamine interacts with current-carrying ions in the permeation pathway. The apparent half-block concentration of spermine at 0 mV was < 0.1 mM. The features of polyamine blockade suggest that the polyamines are permeable cationic blockers of the RyR channel. Further, the levels of polyamines found in muscle cells are sufficient to block single RyR channels and thus may alter the sarcoplasmic reticulum Ca2+ release process in situ