Blood pressure variability over 24 hours: its different components and its relationship to the arterial baroreflex

SUMMARY  This paper describes several different methods for the analysis of blood pressure and heart rate variability over the 24 hours, both in the time and in the frequency domain. The mechanisms possibly involved in the genesis of the variations in blood pressure and heart rate which occur over a 24-hour period are also discussed. Finally, new approaches to the dynamic evaluation of the sensitivity of baroreflex control of heart rate and of its changes over the 24 hours in daily life conditions, based on computer analysis of the interaction between fluctuations in blood pressure and heart rate, are described. Data obtained by applying these methods in different clinical conditions (normotensive vs. hypertensive subjects, young vs. elderly individuals and pure autonomic failure patients) are presented.     

Cross-bridge kinetics studied with staircase shortening in single fibres from frog skeletal muscle

The kinetics of actin-myosin interaction has been studied in single active muscle fibres by repetitively eliciting tension transients with staircase shortening, consisting in a sequence of step releases of identical size (1--5 nm per half-sarcomere) imposed at regular time intervals (3--11 ms). Under sarcomere length-clamp conditions, the quick phase of tension recovery following each step in the staircase is the manifestation of the working stroke by synchronized cross-bridges. Different average shortening velocities are obtained by varying both the size of the step and the time interval between steps. Ti, the tension just before each step in the sequence, and T2, the tension attained at the end of the quick phase of tension recovery, decrease with the number of steps, reaching a steady state value, which is lower the larger the shortening velocity. In agreement with previous results on tension response to steady shortening, the overall shortening necessary to approach the steady state values of Ti and T2 is about 15 nm. The normalized amplitude of quick tension recovery (T2r), which is measured by the ratio of the amount of tension recovered at the end of the quick phase (T2--T1) over the tension drop simultaneous with the step (Ti--T1), has been used to measure the extent of the working stroke elicited by each step in the staircase. The steady state value of T2r decreases progressively with the increase of shortening velocity. At velocities higher than 0.5 μm s−1 per half-sarcomere the steady state value of T2r is attained after a transitory depression, which reaches a maximum for an amount of overall shortening increasing from about 8 nm up to about 13 nm with increase in shortening velocity from 0.5 to 1.4 μm s−1 per half-sarcomere. The velocity-dependent transitory depression of T2r can be explained with the mechanical-kinetic model described previously. In the model cross-bridges cycle through two pathways distinct for the kinetics of the detachment/reattachment process. Shortening promotes are distribution of cross-bridges interacting in the isometric conditions among the various states of the force-generating process. Shortening at high speed, preventing most of cross-bridges from undergoing the relatively fast (100 s−1) detachment/reattachment process, uncovers a rate limiting step in the cycle at the end of the 12 nm working stroke. Under these conditions, the finding that the fraction of the working stroke elicited by each step is transitorily depressed with respect to the steady state value reveals that in the original isometric state a large fraction of interacting cross-bridges was accumulated near the beginning of the working stroke This revised version was published online in July 2006 with corrections to the Cover Date.     

Induction Ovens and Electromagnetic Interference:

Electromagnetic fields may interfere with normal pacemaker function. Despite the introduction of modern pacemakers and bipolar lead systems, electromagnetic interference (EMI) still remains to be a concern during daily lives when patients are exposed to cellular phones, electronic security systems, and several household appliances. The aim of this study was to evaluate potential EMI risk of induction ovens, which are increasingly used in private households. The study included 40 consecutive patients (22 men, 18 women; age   73 ± 11  years   ) with implanted DDD, VVI, VDD, and AAI pacemaker systems. The pacemakers were programmed to unipolar sensing and pacing. Sensitivity remained unchanged, if the measured sensing threshold was more than twice the programmed value; otherwise, it was set at half of the measured sensing threshold. Patients were placed in a sitting position at the closest possible distance of about 20 cm between two cooking pots and pacemaker bending the upper part of the body slightly over the induction oven. The energy was increased stepwise to the maximum. One pot was removed and placed again at the highest oven level. Potential interference was monitored continuously. The study showed no incidence of pacemaker malfunction during the entire test while the patients with intrinsic cardiac rhythms were exposed to the induction oven at varying energy strengths. Likewise, there was no external interference when the patients were paced at heart rates of 10–15 beats/min above their heart rates. The programmed parameters remained unchanged after the study. In conclusion, this study shows no EMI risk of an induction oven in patients with bipolar or right-sided unipolar pacemakers. (PACE 2003; 26[Pt. I]:1494–1497)     

N-terminal sequence of some ribosome-inactivating proteins

The N-terminal portion of some type 1 ribosome-inactivating proteins (RIPs) isolated from the seeds of Gelonium multifiorum, Momordica charantia, Bryonia dioica, Saponaria oficinalis and from the leaves of Saponaria oficinalis are reported in the present paper. Their relationship with other RIPS is discussed.     

Leaving work to smoke

Work-place smoking bans have not only reduced work-day cigarette consumption but also been associated with going outside to smoke during working hours. We examined the extent of "exiled smoking", estimated how much work-day cigarette consumption can be attributed to it, and examined proximal predictors of both these two variables. Some 794 smokers from 42 medium-sized work-places were surveyed as the baseline for an intervention study. A self-completed questionnaire assessed smoking behaviour on work and non-working days, leaving work to smoke, and beliefs and opinions about smoking and smoking bans. Multiple regressions were used to examine predictors of leaving work to smoke, and of the amount smoked when doing so. Smokers reported consuming an average of 5.4 cigarettes during work breaks, 3.5 of which were associated with deliberately seeking opportunities to smoke; 39% reported leaving work to smoke one or more times per day during non-break periods. Indices of addiction were significant predictors of both leaving work to smoke and of cigarette consumption while doing so. Leaving work to smoke is in part an activity of addicted smokers, presumably to maintain blood nicotine levels. There is the potential to further reduce rates of cigarette consumption associated with work-place smoking bans if this "exiled smoking" can be reduced. This may be easier to achieve in light smokers.     

Comparative Analysis of the Vascular Actions of Diterpenes Isolated from Euphorbia canariensis

We have analysed the effects of 2,3-diepiingol 7,12-diacetate-8-isobutyrate (compound 1 ), ingenol-3-angelate-17-benzoate (compound 2 ), ingenol-3-angelate-17-benzoate-20-acetate (compound 3 ) and 3,5,7,8,9,15-hexahydroxyjatropha-6(17),11-dien-14-one-5,8-bis(2-methylbutyrate)-7-(2-methylpropionate) (compound 4 ), four diterpenes isolated from E. canariensis, on the isometric tension developed by isolated rabbit basilar and carotid arteries. Concentration-response curves to these compounds were obtained cumulatively in both arteries at resting tension and active tone (KCl, 50 mM). At resting tension a concentration-dependent contraction was induced by the four compounds. In the basilar artery the order of potency was 3 = 1 > 2 = 4 , without significant differences between E_max values. In the carotid artery the order of potency was 3 > 2 = 1 = 4 and there were no significant differences between the E_max (maximum effect) values of compounds 1–3 , all of which were higher than that of compound 4 . In pre-contracted basilar artery compounds 1–3 induced concentration-dependent relaxation and compound 4 was almost ineffective; the order of potency was 3 > 2 = 1 without significant differences between E_max values. In the carotid artery with active tone the four compounds tested induced further contractions; the order of potency was 3 > 2 = 4 > 1 without significant differences between E_max values. These results show that the four diterpenes are potent active substances in rabbit basilar and carotid arteries and that there are regional differences between their action. The four compounds tested contract basilar and carotid arteries at resting tension. Compounds 1–3 relax pre-contracted basilar artery but not carotid artery.