Human head exposure to a 37 Hz electromagnetic field: effects on blood pressure, somatosensory perception, and related parameters.

Previous studies have shown that exposure to an electromagnetic field (EMF) of 37 Hz at a flux density of 80 microT peak enhances nociceptive sensitivity in mice. Here we examined the effects on pain sensitivity and some indexes of cardiovascular regulation mechanisms in humans by measuring electrical cutaneous thresholds, arterial blood pressure, heart rate and its variability, and stress hormones. Pain and tolerance thresholds remained unchanged after sham exposure but significantly decreased after electromagnetic exposure. Systolic blood pressure was significantly higher during electromagnetic exposure and heart rate significantly decreased, both during sham and electromagnetic exposure, while the high frequency (150-400 mHz) component of heart rate variability, which is an index of parasympathetic activity, increased as expected during sham exposure but remained unchanged during electromagnetic exposure. Cortisol significantly decreased during sham exposure only. These results show that exposure to an EMF of 37 Hz also alters pain sensitivity in humans and suggest that these effects may be associated with abnormalities in cardiovascular regulation.

Do geomagnetic disturbances of solar origin affect arterial blood pressure?

OBJECTIVE: Episodic reports suggest that geomagnetic disturbances of solar origin are associated with biological and clinical events, including increased arterial blood pressure (BP). We reassessed this aspect by relating solar activity levels to ambulatory BP measured in our out-patient population. PATIENTS AND METHODS: The ambulatory BP measurements of 447 consecutive untreated patients attending a hypertension out-patient clinic who did a monitoring for diagnostic purposes over 5 years were retrieved. The mean daytime, night-time and 24-h BP and heart rate values were related to the temporally corresponding geomagnetic index k-sum obtained by the nearest observatory. K-sum is a local measurement of the irregular disturbances of the geomagnetic field caused by solar particle radiation. RESULTS: Significant to highly significant positive correlations were observed for k-sum with systolic (daytime and 24 h) and diastolic BP (daytime, night-time and 24 h), but not with heart rate. No correlations were found with the k-sum of 1 or 2 days before the monitorings. Multiple correlations which also included other potential confounding factors (date, age) confirmed a significant effect of k-sum on BP. Comparison made in season-matched subgroups of quiet and disturbed days (using three different criteria of definition), always showed significantly higher values in the disturbed days for all BP parameters except systolic night-time pressure. The difference between the quietest and the most disturbed days was of about 6 to 8 mm Hg for 24-h systolic and diastolic BP. CONCLUSION: These results are unlikely to be due to unrelated secular trends, but seem to reflect a real relation between magnetic field disturbances and BP.

On the contribution of biomedical engineering and technology to the understanding and the management of arterial hypertension.

There are several reasons why arterial blood pressure, i.e. the pressure within the large arterial vessels, is out of the physical parameters of the human body, one of the most frequently measured. Firstly, arterial blood pressure is a physiologically meaningful parameter, since it represents the driving pressure generated by the heart which maintains blood perfusion in the periphery. Secondly, it is a clinically important parameter: a decline of arterial blood pressure (e.g. in shock) may represent a life-threatening emergency which requires prompt recognition and correction; elevated blood pressure (hypertension) on the other hand is a very common condition, which bears a high risk of cardiovascular mortality and morbidity and can be controlled with appropriate pharmacological means. Thirdly, but not lastly, arterial blood pressure is easily measurable with a fair degree of accuracy by the standard manual sphygmomanometric method and, more recently, by non-invasive automatic techniques. This paper discusses some of the aspects related to arterial blood pressure measurement, in which, in the author's opinion, medical engineering and technology are expected to provide useful advancements. Two major areas will be considered. The first regards the methodologies for arterial blood pressure assessment; the second the identification and acquisition of information additional to blood pressure which would be helpful for a better understanding of blood pressure measurements and/or of risk profiling. For the purpose of this brief paper, we shall mainly use examples and reasonings from our own experience.

Captopril radionuclide test in renovascular hypertension: a European multicentre study. European Multicentre Study Group.

The diagnostic work-up of renovascular hypertension is still controversial. The efficacy of renal scintigraphy with technetium-99m diethylene triamine pentaacetate (DTPA) before and after captopril (scintigraphic captopril test) was evaluated in a multicentre study. All 380 hypertensive patients in the study underwent renal arteriography; 125 had renal arterial stenosis > or = 70%, and 54 had a technically successful intervention to correct the stenosis. The post-captopril study had a sensitivity of 93% and a specificity of 100% for predicting blood pressure response to intervention, if renal function was normal and a combination of quantitative parameters was applied (individual kidney uptake index < 40%, time to peak activity < 2 min or > 10 min). In the entire population renal artery stenosis > or = 70% was detected with a sensitivity of 83% and a specificity of 93% if renal function was normal. In patients with abnormal renal function the performance of the test was worse, owing to a lower specificity which could be increased by using only time parameters. The performance of the test was optimal when the post-captopril findings were examined; no improvement was achieved by evaluation of the changes induced by captopril from the baseline. The test can thus be simplified by performing only a post-captopril study for routine use: a negative test would exclude a curable form of renovascular hypertension in > 80% and a positive test would predict it in > 90% of the patients selected for suspicion of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)

European Captopril Radionuclide Test Multicenter Study. Preliminary results. Inspective renographic analysis. The European Captopril Radionuclide Test Multicenter Study Group.

Captopril radionuclide test (CRT) has been introduced in clinical practice as a screening test for renovascular hypertension, since it allows the detection of the decrease of glomerular filtration rate that may be induced by angiotensin converting enzyme inhibition (25 mg oral captopril) in kidneys ipsilateral to a renal artery stenosis. However, due to the low prevalence of the disease, experiences in single centers may hardly satisfy the need for representative series of patients to validate the test. Nineteen centers participated in a collaborative study (CRT European Multicenter Study) that collected data from 424 patients. Here we report on the first results obtained by inspective renographic analysis. The captopril radionuclide test greatly potentiated the diagnostic performance of conventional renography and the accuracy was maximal when relying simply on postcaptopril findings alone. Specificity was 84.1% in the overall population and 91.8% in uncomplicated patients without nephropathy and renal insufficiency. Taking into account the sole arteriographic diagnosis, sensitivity was 73.2% or 90.7% for the subjects with unilateral or bilateral stenosis and an angiographic degree of stenosis greater than or equal to 70%. On the other hand, when a successful outcome of blood pressure after revascularization or nephrectomy was considered as the gold standard for the diagnosis of renovascular hypertension, a high sensitivity was obtained (92.7%). Moreover, the test became negative after intervention in the great majority (88%) of patients who had a positive preintervention CRT and a normalization of blood pressure after revascularization.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular mass in borderline hypertension, assessed by echocardiography. Relationships with resting and stress blood pressure.

The relationship between clinical measurement of blood pressure (BP) and left ventricular hypertrophy in arterial hypertension appears to be weak in most studies. On the contrary, stronger correlations with target organ damage in general, and left ventricular hypertrophy in particular, have been reported for blood pressure measurements obtained by ambulatory monitoring; this finding may indicate a possible role for blood pressure response to naturally occurring stresses in determining left ventricular hypertrophy. Aim of this study was to investigate, in 18 patients with borderline arterial hypertension, the relationships between echocardiographically assessed left ventricular mass and, respectively, casual BP and BP responses to some standardized stress tests. Only three patients had a diastolic wall thickness of the interventricular septum and of the posterior wall greater than or equal to 1.2 cm and none had a pathologically increased left ventricular mass index. The following statistically significant correlations were found: casual diastolic BP vs. left ventricular mass index (r = 0.53, p less than 0.02), systolic BP response to bicycle exercise test vs. left ventricular mass index (r = 0.55, p less than 0.05). Multiple regression analysis showed that almost fifty percent of the variability of left ventricular mass index could be predicted by these two BP measurements. These findings suggest that besides the chronically increased afterload, also the transient hypertensive responses to naturally occurring physical stresses may have a role in determining the extent of cardiac structural changes in borderline hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial hypertension is associated with hypalgesia in humans.

An association between increased blood pressure and hypalgesia has been reported in several studies in animals and in a few reports in humans. We investigated the relationship between hypertension and pain perception by comparing the response to graded electrical stimulation of the tooth pulp, which is thought to represent an exclusively nociceptive system. The test was performed with a commercial tooth pulp tester in a large series of subjects with borderline or established hypertension and in three groups of normotensive controls: volunteers, nonhypertensive patients, and medical students with a well-established or no family history of hypertension. Subjects had to report when they started to feel pulp stimulation (sensory threshold) and when this became painful (pain threshold). Sensory and pain thresholds were obtained as means of the measurements on four healthy, unfilled teeth. Sensory thresholds were significantly higher in subjects with borderline or established hypertension than in two of the three normotensive groups (volunteers and normotensive patients), whereas no significant difference was observed between the two hypertensive groups. The results for the pain threshold were qualitatively similar but less clear and less amenable to statistical analysis because this parameter could not be determined with accuracy in a number of subjects in whom the subjective pain threshold was above the upper range of stimulation of the instrument. The association between blood pressure levels and pain perception was further confirmed by the highly significant correlation found for the overall data between mean arterial blood pressure and both thresholds.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between pain sensitivity, cardiovascular reactivity to cold pressor test and indexes of activity of the adrenergic and opioid system.

An association between increased blood pressure levels and hypoalgesia has been reported in the experimental animal and in man. The relation between pain perception and cardiovascular function is however still obscure. In order to gain some insight into this aspect, normotensive subjects with low and high tolerance to pain, as assessed by tooth pulp stimulation, were compared for blood pressure and heart rate during cold pressor test, 24 hr urinary catecholamines, supine and upright PRA and plasma beta-endorphin levels. No significant difference was observed between the two groups for casual blood pressure, heart rate and PRA. Compared to subjects with low tolerance to pain, those with high tolerance to pain were significantly older and had: 1) significantly higher levels of diastolic blood pressure and of beta endorphin levels during cold pressor test; 2) significantly higher beta-endorphin levels after cold pressor test; 3) a significantly higher excretion of noradrenaline (but not of adrenaline and dopamine).

Medium-term reproducibility of stress tests in borderline arterial hypertension.

Stress tests are commonly used for an evaluation of blood pressure reactivity, but few data exist in the literature about interindividual variability and intraindividual medium-term reproducibility of blood pressure responses to these tests in borderline hypertension. To this aim we have studied 20 borderline hypertensive patients (age range, 33-59, mean 45). Our data suggest that borderline hypertensive patients cannot be considered a homogeneous group with regard to blood pressure reactivity because they tend to have widely different blood pressure responses to various stress tests. For each test (except for orthostatic stimulation), a fairly good intraindividual reproducibility was found. Considering the poor correlations existing between blood pressure responses to tests for each patient, one test may not be sufficient to characterize blood pressure reactivity to stress in borderline hypertension.

Long-term hypotensive treatment with nitrendipine in mild to moderate essential hypertension: preliminary results of a placebo-controlled study versus atenolol.

Nitrendipine is a dihydropyridine calcium antagonist suggested to be a new drug for first-line antihypertensive therapy, possibly active in once-daily administration. In the present study the acute and long-term hypotensive effects of nitrendipine have been evaluated in comparison with those of atenolol in a randomized, double-blind, clinical trial. Twenty-four patients have been studied, and the effects of treatment have been evaluated both at rest and during psychological and physiological stresses. Hemodynamic noninvasive parameters have also been obtained, at rest and during mental arithmetic tests, by a continuous-wave Doppler technique. Preliminary results about the first 13 consecutive patients are reported here. Nitrendipine induced a highly significant acute hypotensive effect (2 h after drug administration), whereas no effect was observed for atenolol except for heart rate. During chronic treatment (5 weeks), nitrendipine showed less hypotensive effect than atenolol when BP values 24 h after the last administration were analyzed, but significantly more effect when values obtained 2 h after drug administration were evaluated. These findings confirm that nitrendipine is effective in decreasing blood pressure, but the once-daily administration may not bring about the maximum effect in all patients. Interesting aspects of this drug, which make the clinical use of this compound safe, are represented by apparent lack in tolerance and rebound, and by the moderate increase in cardiac output associated with the treatment.

Comparison of pain perception in normotensives and borderline hypertensives by means of a tooth pulp-stimulation test.

Recent studies indicate a reduced sensitivity to pain in genetically and experimentally hypertensive rats. A similar finding is also reported for human established hypertension. However, to our knowledge, no data have been reported in borderline hypertension. The aim of this study was to assess in subjects with borderline hypertension the sensory and pain thresholds by a noninvasive pulp-stimulation test performed with a commercial pulp tester that delivered stepwise increased electrical stimuli to four healthy teeth. The data reported are the means of measurements. In order to assess the possible importance of differences in the selection of the controls, two distinct groups of normotensives were chosen, one of volunteers and the other of outpatients. Significantly higher values for the pain and sensory thresholds were observed in borderline hypertensives compared with pooled normotensives. No significant effect on pain perception could be observed for sex, whereas a significant tendency toward higher threshold levels was found for younger subjects. In two normotensive groups, the sensory and pain thresholds were significantly higher in volunteers than in patients. These results suggest that changes in pain perception are present not only in established hypertension but also in borderline hypertension and, moreover, that differences in the selection of normotensive controls can have important influences on the results.

Correlations between digoxin-like immunoreactivity and electrolyte values in urinary samples of newborns.

Elevated levels of a group of substances with digoxin-like immunoreactivity (DLIS) are present in biological fluids of newborns. These endogenous substances could also have the biological properties of cardiac glycosides, such as natriuretic and vasoconstrictor activity. Therefore, DLIS could be involved in electrolyte and volume regulation in infants. We measured DLIS, electrolyte (Na+, K+, Cl-) and creatinine concentrations in 157 urine samples collected from full-term and preterm infants, with the aim to establish if a correlation exists between the urinary DLIS levels and the respective values of these electrolytes. Significant and positive correlations were found between the urinary concentrations of DLIS and electrolytes. In addition, electrolyte values correlated significantly between themselves. DLIS, K+ and Cl- values correlated positively with urinary creatinine concentrations (n = 142). A significant multiple correlation was found among DLIS concentrations and creatinine and Cl- values. We also studied the DLIS concentrations in serum samples collected at birth in peripheral blood of the mothers and in umbilical cord and gastric aspirate of 5 full-term infants. We observed that DLIS values in newborns are significantly higher than the respective values of the mothers. In conclusion, our data do not demonstrate a clear relationship between DLIS and electrolyte concentrations in urine samples of newborns. Further investigations are necessary to elucidate the biochemical and physiological properties of DLIS.

Comparison of sensory and pain threshold in tooth pulp stimulation in normotensive man and essential hypertension.

Recent studies indicate a diminished responsiveness to noxious stimuli in arterial hypertension in the experimental animal. A similar finding is also reported in the only study published to our knowledge on this subject in man. The aim of the study was to assess in humans the sensory and pain threshold by a non-invasive tooth pulp stimulation test (stepwise increased electrical stimuli delivered by a commercial pulp tester). Subjects had to report when they started to feel pulp stimulation and when this became painful. The data reported are the means of the measurements on four healthy teeth in each subject. Significantly higher values (expressed as relative units [RU]) were found in 28 non-treated essential hypertensives compared with 33 normotensive controls for sensory threshold (40.64 +/- 8.07 versus 29.96 +/- 6.82 RU, P < 0.0001) and for pain threshold (55.67 +/- 12.74 versus 42.08 +/- 12.58 RU, P < 0.001). Multivariate analysis of variance showed that this difference was apparently not related to age and sex. These data lend further support to the view that pain modulation may be altered in the hypertensive state in man.