1,721,272 research outputs found
Mechanism of influence of PR interval on loudness of first heart sound
No full textThe mechanism is described of the influence of PR interval on loudness of first heart sound
The time factor in the treatment of hypertension
No full textTime is a relevant factor for the treatment of hypertension
Consistency and accuracy of the Medical Subject Headings® thesaurus for electronic indexing and retrieval of chronobiologic references
No full textThe aim of this study was to investigate the reliability of the National Library of Medicine (NLM)'s Medical Subject Headings((R)) (MeSH) thesaurus for electronic indexing and retrieval of published chronobiologic papers. A sample set of 228 recent chronobiologic references was downloaded from the MEDLINE((R))'s database together with all MeSH entries associated with them. The following descriptors were analyzed among the headings of obvious chronobiologic relevance: chronobiology, chronobiology disorders, biological clocks, circadian rhythm, chronotherapy, drug administration schedule, periodicity, seasons, sleep disorders/circadian rhythm, and time factors. A comparison was made between the number of references identified by each heading and the number of articles actually pertinent to the same heading (as ascertained after reading each article of the sample set). This made possible an assessment of consistency (retrieved number not less than actual number) and accuracy (retrieved number not greater than actual number) of the usage of each MeSH entry. By reading each article, it was also possible to identify common chronobiologic concepts not yet associated with specific MeSH headings. In the preselected set of chronobiologic references, seasons identified all articles pertinent to seasonal variations and rhythms. However, chronobiology disorders missed 97.6% of its pertinent articles; periodicity, 95.2%; chronobiology, 87.7%; chronotherapy, 70%; time factors, 62.3%; and sleep disorders/circadian rhythm, 47.4%. Drug administration schedule missed 40% of the chronotherapeutic articles and identified 15% of the chronopharmacologic articles; biological clocks missed 24.1% of its pertinent articles and wrongly identified 8.3% of the retrieved articles; and circadian rhythm missed 2.7% of all circadian studies and wrongly identified 8.2% of the articles it retrieved. When used to search chronobiologic articles in the entire MEDLINE database, drug administration schedule, seasons, and time factors appeared to lack sufficient specificity to produce accurate results. Some common chronobiologic concepts were found not to be associated with any specific MeSH heading, namely, chronoepidemiology, chronopharmacology, chronotoxicology, chronotype, entrainment, and masking. For common chronobiologic concepts and definitions, the use of available MeSH headings appears to often yield inconsistent and inaccurate results; moreover, the MeSH thesaurus remains incomplete
The circadian organization of the cardiovascular system in health and disease
No full text395-398 In normal conditions, the temporal organization
of blood pressure (BP) is mainly controlled by neuroendocrine mechanisms. Above
all, the monoaminergic systems (including variations in activity of the
autonomous nervous system,
and in secretion of biogenic amines) appear to integrate the major driving
factors of temporal variability, but
evidence is available also for a role of the hypothalamic-pituitary-adrenal,
hypothalamic-pituitary-thyroid, opioid,
renin-angiotensin-aldosterone, and endothelial systems, as well as other
vasoactive peptides. Many hormones with established actions on the
cardiovascular system (arginine vasopressin, vasoactive intestinal peptide,
melatonin, somatotropin, insulin, steroids, serotonin, CRF, ACTH, TRH,
endogenous opioids, and prostaglandin E2) are also involved in sleep induction
or arousal, which in turn affects BP regulation. Hence, physical, mental, and
pathological stimuli which may drive activation or inhibition of these
neuroendocrine effectors of biological rhythmicity, may also interfere with the
temporal BP structure. On the other hand, the immediate adaptation of the
exogenous components of BP rhythms to the demands of the environment are
modulated by the circadian-time-dependent responsiveness of the biological
oscillators and their neuroendocrine effectors.
These notions may contribute to a
better understanding of the pathophysiology and therapeutics of hypertension,
myocardial ischemia and infarction, cardiac arrhythmias and all kind of acute
cardiovascular accidents. For instance, the normal temporal balance between
external stimuli and neurohumoral influences with endogenous rhythmicity is
preserved in uncomplicated, essential hypertension, whereas it is frequently
lost in complicated and secondary forms of hypertension where gross alterations
are found in the circadian profile of BP.
When all the
gates of the critical physiologic functions are aligned at the same time, the
susceptibility, and thus risk, of adverse events becomes extremely high, even
in the presence of minor environmental stimuli that could be usually harmless,
and circadian rhythms of cardiovascular events are observed. This implies that one
cannot afford to miss what happens during day but also night. Moreover, the
requirement for preventive and therapeutic interventions varies predictably
during the 24 h, suggesting that the delivery of protective or preventive
medications should be synchronized in time in proportion to need, as determined
by established rhythmic patterns in cardiovascular function as well as risk, in
a manner that will avert or minimize their undesired side effects
Loss of nocturnal blood pressure fall in patients with renal impairment
No full textDavidson et al reported an excellent study correlating a blunted nocturnal fall in BP with the subsequent decline in renal function. I would like to mention that the loss or reversal of the physiologic nocturnal fall in BP was demonstrated many years ago in chronic kidney disease, independently from external interfering factors. Patients with chronic nephropathies and patients with essential hypertension were matched by age, sex, and mean 24-hour BP values. Ambulatory BP monitoring was performed in an open hospital ward for 48 hours at 15-minute sampling intervals after standardization of diet, meal times, sleep times, and activity schedules. In essential hypertension, the nocturnal fall in BP was preserved as in normal conditions, whereas patients with renal impairment displayed blunted or reversed nocturnal BP and heart rate patterns. Hence, it appeared that casual measurements of BP confined to daytime may underestimate a hypertensive condition associated with chronic kidney disease. Increased sympathetic tone related to renal impairment was proposed to play a role in such a finding.
Some years later, however, a polysomnographic study using continuous BP monitoring with a Finapres device (Finapres Medical Systems BV, Amsterdam, the Netherland) showed that nondipping status is also present in a minority (15%) of essential hypertensive patients and is strictly associated with undiagnosed sleep-related breathing disorder characterized by apneic snoring. Furthermore, only continuous BP recording during the night allowed the proper identification of the nondipping condition, since a notable proportion of cases were miscategorized as nondipping by ambulatory BP monitoring. It appeared that polysomnography is necessary to differentiate sleep apnea from other possible underlying mechanisms.
In view of the higher amount of target organ damage, which is to be expected in patients with nondipping status (including the renal function deterioration reported by Davidson et al), and the high prevalence of undiagnosed sleep-related breathing disorder in the adult population, the recommendation that one should incorporate an assessment of the subject’s sleep history into the routine diagnostic screening of any type of hypertension seems justified
Non-invasive blood pressure monitoring in man
No full textNon-invasive, ambulatory, blood pressure monitoring is now widely used for research and clinical purpose. Its main advantages over the traditional sphygmomanometric method pertain to its ability in providing measures of centrality, but also variability, 24-h profile, and excess over selected limits (load) of BP in the individual subject. Placebo and 'white-coat' effects are much less evident when this monitoring technique is used. However, standardization of the procedures, choice of methods of data analysis, definition of normalcy, and particularly prognostic value are still a matter of discussion. Hence, blood pressure monitoring cannot be used as a routine diagnostic technique, except in selected clinical situation of proven advantage over the traditional sphygmomanometric method
Neurohumoral control of the sleep-wake cycle and the circadian organization of the cardiovascular function
No full text
- …
