Orthostatic tests after a 4-day confinement or simulated weightlessness

Besides microgravity, inactivity is likely to play a role in the cardiovascular deconditioning after space flights and weightlessness simulations. The aim of the study was to compare the effects of a 4-day head-down bed rest (HDBR) (?68) and a 4-day confinement (C) on cardiovascular responses to orthostatic stress. Eight male subjects underwent head-up tilt (HUT) (+60°) and lower-body negative pressure (LBNP) (?20, ?30, ?40 and ?50 mmHg) before (D?1) and at the end (R1) of each situation. Blood pressure, heart rate variability (HRV) and spontaneous baroreflex slope (SBS) were determined. The HDBR reduced orthostatic tolerance, as five subjects presented orthostatic hypotension during the HUT at R1, compared with two subjects at D?1. These same two subjects presented orthostatic hypotension after confinement. The main findings, after HDBR, included reductions in RR interval and total spectral power and a decrease in the parasympathetic indicator (PNS) in favour of a decrease in vagal tone; the increase in the sympathetic indicator (SNS) was not significant. After confinement, the RR interval was also significantly reduced and PNS decreased, but not significantly. RR interval and PNS were further reduced during HUT and LBNP, reflecting a withdrawal of parasympathetic activity. SBS was reduced after HDBR (P<0·05) and confinement (P=0·05), with a further reduction during HUT and LBNP without difference between D?1 and R1. This experiment showed that a 4-day HDBR leads to impaired baroreflex function and changes in autonomic balance, which may contribute to orthostatic intolerance. Although less significant, similar patterns of changes in the autonomic nervous system were observed after confinement, suggesting an influence of the inactivity in cardiovascular deconditioning.     

Using 100% oxygen does not alter the cardiovascular autonomic regulation during non-invasively simulated haemorrhage in healthy volunteers

We tested the effect of 100% oxygen on heart rate (HR), arterial blood pressure (ABP), cardiac output (CO), stroke volume (SV), total peripheral resistance (TPR), HR variability (HRV), systolic blood pressure variability (SBPV) and baroreflex sensitivity (BRS) in 20 healthy volunteers during simulated haemorrhage induced by -40 mmHg lower body negative pressure (LBNP). HRV in the high frequency region (HRV HF), BRS, ABP and TPR were significantly increased, SBPV in the low frequency region (SBPV LF), CO and SV were unchanged, and HR was significantly decreased by 100% oxygen administration during normovolaemia. HRV HF, BRS, CO and SV were significantly decreased, SBPV LF and ABP were unchanged, and HR and TPR were significantly increased by LBNP during 21% or 100% oxygen administration. There were no significant differences in cardiovascular autonomic and haemodynamic responses to LBNP during 21% or 100% oxygen administration, suggesting that 100% oxygen does not alter normal cardiovascular autonomic responses during simulated haemorrhage.     

Frequency-domain analysis of heart rate variability during positive and negative head-up tilt test: importance of age

The study of autonomic behavior during a head-up tilt test (HUT) has been deemed important to understand the loss of consciousness mechanism. Though HRV in patients with HUT(+) and HUT(-) has been compared, few trials emphasized the importance of age. HRV in frequency domain was analyzed based on 5-minute samples in the supine position, and between 5 and 10 minutes during early tilt test (R1) in 102 patients with one or more episodes of syncope (mean age 44.3 +/- 20.8, range 15-85 years, 55 women). Two subgroups were selected afterwards: (1) young patients between 15 and 35 years of age (41 patients) and (2) elderly patients aged 60 or more (36 patients). The following parameters were taken into account: the sum of low (LF) and high frequency (HF) (LF and HF in absolute values and in normalized units), the LF/HF ratio (L/H ratio), and the percentage of change between baseline and R1 values. The HRV behavior in young and elderly patients with positive and negative HUT was established. We then analyzed the correlation between HRV and age and HUT outcome. A multiple regression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was performed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and R1. The L/H ratio increases from baseline to R1. Conversely, these differences were not significant in the elderly. No differences between HUT(+) and HUT(-) within the same age group were observed. Age related significantly to practically all HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during R1, and the L/H ratio changes between baseline and R1. By means of a multivariate analysis, only age shows a significant correlation with the HRV values. Despite an all age triggering of vasovagal syncope during HUT, the young and elderly patients' autonomic behavior differs. The young considerably increase their sympathovagal balance during HUT, whereas the elderly have a mitigated autonomic response. No significant differences were observed during the first minutes of the test between those with a HUT(+) and those with a HUT(-) within the same age group. Age, and not the HUT response, is the major determinant of the autonomic behavior during early HUT.     

Cardiac sympathovagal balance during sleep apnea episodes

Summary. The main acute cardiovascular effects of obstructive sleep apnea syndrome (OSAS) are elevation of blood pressure and reflectory bradycardia, which are followed by an abrupt tachycardia on resumption of breathing. This haemodynamic instability is related to hypoxemia and arousal, and may lead to increased risk from cardiac arrhythmias and sudden cardiac death, as well as to the development of chronic arterial hypertension, in these patients. The aim of this study was to apply frequency domain analysis of heart rate variability (HRV) measured from continuous electrocardiogram (ECG) recordings to evaluate how cardiac autonomic function, and especially cardiac sympathovagal tone, changes during sleep apnea episodes. We identified 41 apneas leading to more than 4%-unit arterial oxygen desaturation in 12 patients (11 men, 1 women, age range 27–67 years). Frequency domain analysis of HRV was performed from ECG recordings using 4 min epochs starting 20 min before apnea began and lasting 20 min after the beginning of apnea. The mean (± SEM) fall in oxygen saturation during the apnea was 6.8±0.6%-units. While high frequency band (HF, reflects cardiac vagal activity) remained unchanged, low frequency band (LF, mainly sympathetic activity) showed a constant increase, leading to significant change in the sympathovagal balance (LF/HF ratio). In conclusion, concordantly with previous peripheral sympathetic-nerve recordings, frequency domain analysis of HRV is able to detect sympathetic activation during sleep apnea episodes, leading to marked change in the sympathovagal balance.     

The sauna and pregnancy

Sauna bathing does not appear to affect fertility in men. Nor is the sauna teratogenic. The haemodynamic changes brought about by the sauna are similar in non-pregnant and pregnant women, regardless of the duration of pregnancy. There are, however, differences in the hormonal responses. Pregnant women adapt well to the thermal stress of the sauna, which is also true of the fetus, provided that it is healthy. Although the fetal heart rate rises during maternal hyperthermia, cardiotocographic tracings remain normal during and after maternal thermal stress. Healthy pregnant women may safely have sauna baths throughout their pregnancy.     

Changes in baroreceptor sensitivity for heart rate during normotensive pregnancy and the puerperium

Normal pregnancy is associated with marked changes in cardiovascular haemodynamics, which in part may be due to changes in autonomic control mechanisms. Baroreflex sensitivity for heart rate (BRS) was calculated in the supine and standing positions using power spectral analysis of pulse interval (PI) and systolic blood pressure (SBP) in 16 normotensive pregnant women and 10 normotensive non-pregnant controls. The pregnant women were studied on three occasions during their pregnancy (early, mid- and late gestation) and once during the puerperium. Supine total SBP variability increased between early and late pregnancy by 79% [95% confidence intervals (CI) 30%, 145%; P<0. 001], and supine high-frequency PI variability decreased by 75% (CI 51%, 88%; P<0.001). Supine BRS fell by 50% (P<0.001), with values returning to early-pregnancy levels in the puerperium, which were similar to those recorded in the control group. Standing SBP variability and BRS values were unchanged during pregnancy and post partum. The low/high frequency ratio of PI variability, taken as a surrogate measure of sympathovagal balance, increased by 137% (CI 42%, 296%; P<0.01) in the supine but not the standing position from early to late pregnancy. This was due to a decrease in high-frequency variability rather than to an increase in low-frequency variability, suggesting that these changes may have been due to vagal withdrawal rather than increased sympathetic activity. Normotensive pregnancy is associated with a marked decrease in supine BRS, although the exact mechanisms for these changes remain unclear. Further studies are required to define whether changes in BRS and sympathovagal tone in early pregnancy can be used to predict the onset of pregnancy-induced hypertension.     

Impaired cardiac autonomic function in women with prior gestational diabetes mellitus

BACKGROUND: Cardiac autonomic neuropathy is a common dysfunction in manifest diabetes mellitus and is associated with duration of diabetes and/or an inadequate glycaemic control. Heart rate variability (HRV) reflects autonomic heart function. The aim of the present study was to investigate whether in women with prior gestational diabetes (GD; pre-type 2 diabetes) alterations of cardiac autonomic function can be observed after delivery in relation to insulin sensitivity and glycaemic control. MATERIALS AND METHODS: Forty-eight healthy women with prior GD were consecutively admitted to the study. HRV was analysed by both time, as well as frequency, domain methods using 24-h Holter monitoring. In addition, 20 women with normal glucose tolerance during and after pregnancy were investigated as control subjects. All women underwent a frequently sampled intravenous glucose tolerance test (FSIGT) for measurement of insulin sensitivity. RESULTS: Time domain analysis (standard deviation of normal RR intervals; SDNN) showed a reduced HRV in 25 out of the 48 (52%) women with prior GD. Frequency domain analysis revealed that in these 25 subjects both low and high frequency components of power spectral density (reflecting mainly sympathetic respectively parasympathetic activity) were reduced, indicating that sympathetic as well as parasympathetic functional impairment may be assumed. However, a relative predominance of the sympathetic over parasympathetic cardiac function was observed. The impairment of cardiac autonomic function (reduced SDNN) was correlated with HbA1c values and the 2-h blood glucose concentration (oral glucose tolerance test) but not with insulin sensitivity. CONCLUSION: The present results demonstrate that in 52% of the women examined who had prior GD, an impairment of cardiac sympathetic as well as parasympathetic function was present, which related to glycaemic control, but not to insulin sensitivity. This infers that functional autonomic changes could be an early prognostic indicator in pre-type 2 diabetes.     

Assessment of autonomic activity during daily life of patients with head-up tilt-induced prolonged asystole

Autonomic activity is important in the pathophysiology of neurally mediated syncope (NMS) patients diagnosed by the head-up tilt (HUT) test, and prolonged systole induced by HUT is associated with a malignant vasovagal syndrome. This study investigated whether or not daily autonomic activity evaluated by heart rate variability (HRV) assessed through 24-hour ambulatory ECG monitoring was augumented in HUT-induced asystole (AS; >30 s) and whether or not HRV differed between NMS patients with and without AS. Ambulatory ECG monitoring was performed in 176 patients with suspected NMS and in 62 age-matched healthy control subjects (C group, age: 36±13 yr), with HRV time and frequency domain indices measured within 48 hours of HUT. Six patients displayed prolonged AS (PAS group, age: 33±12 yr), and 109 patients had positive HUT (P group, age: 29±17 yr), while 61 patients had negative HUT (N group, age: 40±18 yr). Several HRV indices in the P group were higher than those in the N and C groups. However, HRV indices did not differ between the P group and the PAS group. It is concluded that impairment of autonomic activity specifically related to orthostatic stress could be important in the pathophysiology of HUT-induced prolonged asystole, while impairment of autonomic activity in daily life is not as important in NMS patients with HUT-induced prolonged asystole.     

Continuous enteral and parenteral feeding each reduces heart rate variability but differentially influences monocyte gene expression in humans

ABSTRACT: Enteral (EN) or parenteral (PN) nutrition is used to support critically ill patients until oral feeding resumes. Enteral nutrition is assumed preferable to PN, but the differential influence on immune function is not well defined. Autonomic nervous activity is known to influence innate immune responses, and we hypothesized that EN and PN could influence both autonomic signaling and gene activation in peripheral blood monocytes (PBMs). Ten subjects (aged 18-36 years) received continuous EN or PN for 72 h. Peripheral blood monocytes were isolated from whole blood before and after continuous feeding and were analyzed for gene expression using a microarray platform. Gene expression after feeding was compared from baseline and between groups. To measure autonomic outflow, subjects also underwent heart rate variability (HRV) monitoring during feeding. Time and frequency domain HRV data were compared between groups and five orally fed subjects for changes from baseline and changes over time. During continuous EN and PN, subjects exhibited declines in both time and frequency domain HRV parameters compared with baseline and with PO subjects, indicating a loss of vagal/parasympathetic tone. However, PN feeding had a much greater influence on PBM gene expression compared with baseline than EN, including genes important to innate immunity. Continuous EN and PN are both associated with decreasing vagal tone over time, yet contribute differently to PBM gene expression, in humans. These preliminary findings support assumptions that PN imposes a systemic inflammatory risk but also imply that continuous feeding, independent of route, may impart additional risk through different mechanisms.     

Effects of age on autonomic cardiovascular responsiveness in healthy men and women

Blood pressure and heart rate responses to the Valsalva maneuver (straining) were used to quantify the effects of age on autonomic cardiovascular responsiveness in 110 healthy men and women, 30 to 76 years. In general, aging was associated with diminished sympathetic responsiveness during strain. In women, however, the predominant age effect was a significant reduction in bradycardic response to systolic blood pressure overshoot following release of strain. When present, age-related differences in cardiovascular responses to the Valsalva maneuver were manifest by age 45. These findings are consistent with an age-related diminution of autonomic cardiovascular responsiveness in healthy adults. Moreover, they suggest that interventions to reduce the frequency and intensity of straining may be especially important in older adults in order to minimize health risks associated with rapid, abrupt changes in blood pressure.     

Short- and long-term reproducibility of autonomic measures in supine and standing positions

Autonomic nervous tests and heart rate variability (HRV) have been used to assess cardiac autonomic function and to evaluate long-term prognosis. The aim of this study was to evaluate the short- and long-term reproducibility of HRV parameters and autonomic nervous tests according to body position (supine or standing). The study group consisted of 26 healthy subjects. Autonomic nervous tests and HRV were performed twice during the day and the results were averaged. The protocol was then repeated 3 days after each examination and also after 6 and 24 months. Autonomic nervous tests included deep breathing, Valsalva manoeuvre and isometric muscle exercise (handgrip), as well as blood pressure and heart rate in response to standing. ECG recordings were taken for 10 min during spontaneous breathing for HRV analysis. We found that the reproducibility of some parameters of the autonomic nervous test were independent of body position [E/I ratio (heart rate response to deep breathing)], whereas other parameters were dependent on body position (Valsalva manoeuvre and blood pressure response to sustained handgrip). In addition, within-day measurements of those parameters varied from non-reproducible (Valsalva ratio, handgrip and blood pressure response to standing) to moderately reproducible [E/I ratio and 30/15 ratio (heart rate response to standing)]. Among the HRV parameters, we found that total power (TP), low (LF)- and high (HF)-frequency were reproducible not only for measurements made within the same day, but also during short- and long-term observations, and only the LF/HF ratio was dependent on body position. We conclude that only a few autonomic nervous tests are reproducible in the short- and long-term. Because HRV parameters obtained during spontaneous respiration showed high reproducibility for measurements made within the same day as well as in the short- and long-term, they should be used instead of autonomic nervous tests when long-term observations are carried out in a healthy population.     

The effect of orthostatic stress on multiscale entropy of heart rate and blood pressure

Cardiovascular control acts over multiple time scales, which introduces a significant amount of complexity to heart rate and blood pressure time series. Multiscale entropy (MSE) analysis has been developed to quantify the complexity of a time series over multiple time scales. In previous studies, MSE analyses identified impaired cardiovascular control and increased cardiovascular risk in various pathological conditions. Despite the increasing acceptance of the MSE technique in clinical research, information underpinning the involvement of the autonomic nervous system in the MSE of heart rate and blood pressure is lacking. The objective of this study is to investigate the effect of orthostatic challenge on the MSE of heart rate and blood pressure variability (HRV, BPV) and the correlation between MSE (complexity measures) and traditional linear (time and frequency domain) measures. MSE analysis of HRV and BPV was performed in 28 healthy young subjects on 1000 consecutive heart beats in the supine and standing positions. Sample entropy values were assessed on scales of 1-10. We found that MSE of heart rate and blood pressure signals is sensitive to changes in autonomic balance caused by postural change from the supine to the standing position. The effect of orthostatic challenge on heart rate and blood pressure complexity depended on the time scale under investigation. Entropy values did not correlate with the mean values of heart rate and blood pressure and showed only weak correlations with linear HRV and BPV measures. In conclusion, the MSE analysis of heart rate and blood pressure provides a sensitive tool to detect changes in autonomic balance as induced by postural change.     

Recovery from sauna bathing favorably modulates cardiac autonomic nervous system

ObjectiveSauna bathing is becoming a common activity in many countries and it has been linked to favorable health outcomes. However, there is limited data on the heart rate (HR) and heart rate variability (HRV) responses to an acute sauna exposure.DesignWe conducted a single-group, longitudinal study utilizing a pre-post design to examine acute effects of sauna bathing on the autonomic nervous system as reflected by HRV. A total of 93 participants (mean [SD] age: 52.0 [8.8] years, 53.8% males) with cardiovascular risk factors were exposed to a single sauna session (duration: 30 min; temperature: 73 °C; humidity: 10–20%) and data on HRV variables were collected before, during and after sauna.ResultsTime and frequency-domain HRV variables were significantly modified (p < 0.001) by the single sauna session, with most of HRV variables tending to return near to baseline values after 30 min recovery. Resting HR was lower at the end of recovery (68/min) compared to pre-sauna (77/min). A sauna session transiently diminished the vagal component, whereas the cooling down period after sauna decreased low frequency power (p < 0.001) and increased high frequency power in HRV (p < 0.001), favorably modulating the autonomic nervous system balance.ConclusionsThis study demonstrates that a session of sauna bathing induces an increase in HR. During the cooling down period from sauna bathing, HRV increased which indicates the dominant role of parasympathetic activity and decreased sympathetic activity of cardiac autonomic nervous system. Future randomized controlled studies are needed to show if HR and HRV changes underpins the long-term cardiovascular effects induced by regular sauna bathing.     

Women with metabolic syndrome present different autonomic modulation and blood pressure response to an acute resistance exercise session compared with women without metabolic syndrome

Metabolic syndrome (MetS) is a cluster of risk factors in individuals with high risk of diabetes and heart disease. Resistance training (RT) has been proposed to be a safe, effective and worthwhile method for the prevention and treatment of metabolic and cardiovascular diseases. However, no study has analysed the acute response of blood pressure (BP) and autonomic control of heart rate (HR) after a RT session in female patients with MetS. The aim of the present study was to analyse the response of laboratory assessed and ambulatory BP and cardiac autonomic modulation after a RT session in women with MetS. Nine women without MetS (35·0 ± 6·7 years) and 10 women with MetS (34·1 ± 9·4 years) completed one experimental exercise session and a control session. Laboratory BP, heart rate variability (HRV) and ambulatory BP of each subject were measured at rest, over 60 min, and for 24 h after the end of the sessions, respectively. There was a significant reduction in systolic blood pressure (SBP), night time diastolic blood pressure (DBP) and mean blood pressure (MBP) only for women with MetS, for all periods after the RT session when compared with the control session (P<0·05). Significantly lower laboratory values of SBP and DBP (10, 30 and 40 min postexercise) and MBP (10, 40 and 50 min postexercise) were observed in women with MetS (P<0·05). Patients with MetS exhibited significant lower basal HRV and a lower autonomic responsiveness during the 60 min of acute recovery. These results confirmed that an acute session of resistance exercise induced a lower BP during day time and sleeping hours in women with MetS that may offer a cardio‐protective effect. Women with MetS exhibited an impaired autonomic modulation at rest and a lower acute autonomic responsiveness to a RT session. The dissociation between BP and HRV responses suggests that other factors than autonomic control could be involved in the hypotensive effect of a RT session in MetS patients.     

Power spectral analysis of heart rate variability during the 100-g oral glucose tolerance test in pregnant women

OBJECTIVE: The aims of the present study were to 1) evaluate autonomic function during the oral glucose tolerance test (OGTT) in pregnant women and 2) investigate whether gestational diabetes mellitus (GDM) modifies autonomic control of heart rate variability. RESEARCH DESIGN AND METHODS: We prospectively studied 27 pregnant women (15 without GDM, 12 with GDM) during a 100-g OGTT. The maternal electrocardiogram was recorded before and 60 min after glucose ingestion, when peak glucose levels are expected. The time and frequency domains of maternal cardiac intervals were analyzed. RESULTS: There was a significant decrease in the high-frequency (HF) band in both groups after the ingestion of glucose. The normalized low-frequency (LF) band significantly increased and the normalized HF band significantly decreased after glucose ingestion. The LF-to-HF ratio was significantly higher in the group with GDM at baseline and significantly increased in both groups after glucose ingestion. A regression analysis revealed a significant decrease in the HF band with increasing blood glucose levels. CONCLUSIONS: Acute elevation of blood glucose levels during the OGTT caused substantial autonomic alterations, including sympathetic activation and parasympathetic withdrawal. Both arms of the autonomic system were affected during the test, thus lending support to the concept that these changes are centrally integrated. The autonomic changes were less pronounced in women with GDM compared with in normal control subjects, suggesting that chronic hyperglycemia and hyperinsulinemia may alter modulation of the autonomic nervous system.     

Hormone Replacement Therapy Does Not Affect the 24-Hour Heart Rate Variability in Postmenopausal Women:

Postmenopausal women are at greater risk of coronary heart disease. The results of previous studies of the effects of hormone replacement therapy (HRT) on cardiac autonomic modulation in postmenopausal women have been contradictory. This study examined whether continuous treatment for 3 months with estradiol alone (ERT) or with estradiol plus norethisterone (HRT), increases 24-hour heart rate variability (HRV) in postmenopausal women. In this double-blind, placebo-controlled trial, 40 healthy postmenopausal women, 46–63 years of age, were randomly assigned to (1) continuous 2 mg of estradiol plus 1 mg of norethisterone acetate daily (HRT, n = 13), or (2) 2 mg of estradiol daily (ERT, n = 14), or (3) placebo (n = 13). Before and after 3 months of therapy, blood estradiol concentrations were measured and 24-hour electrocardiograms recorded for evaluation of 24-hour time-domain indices of HRV, and indices derived from the three-dimensional return map. Both hormone replacement regimens significantly increased blood estradiol concentrations, while no change occurred in the placebo group. In the three treatment groups, multiple 24-hour time-domain indices of HRV and indices derived from the three-dimensional return map remained unchanged. In healthy postmenopausal women, HRT with estradiol or estradiol and norethisterone for 3 months did not modify cardiac autonomic activity evaluated by 24-hour indices of HRV. These findings are consistent with a lack of protective cardiovascular effect of HRT described in recent large randomized trials.     

Effects of mental state on heart rate and blood pressure variability in men and women

Summary. The effect of different mental states on autonomic modulation of the cardiovascular system was assessed in healthy, normotensive men (n=18) and women (n=12). Heart rate variability (HRV), systolic blood pressure variability (BPV) and arterial baroreflex function were assessed during 4 tests at rest ((10 min+5 min recovery)×4):

• 1 Control (spontaneous breathing, (SB)
• 2 Mental distraction (SB+word puzzle)
• 3 Conscious control of breathing (paced at SB rate) and
• 4 Mental stress (SB+computer quiz).

There were no significant gender differences in the responses to the interventions in terms of arterial (spontaneous) baroreflex (SPBX) control of HR, and indices of time and frequency domains of HRV and BPV, with the exception of the sympathetic indicator of HRV (low frequency power/total power; P<0.01) which was lower in women during control and mental stress tests. Conscious control of breathing at SB did not alter HRV, BPV or SPBX in either men or women. Mental distraction and mental stress led to decreases in indices of time and frequency domains of HRV and BPV in all subjects, as well as increases in HR during distraction and in systolic BP during stress. These findings suggest that in studies of cardiovascular control:

• 1 Paced breathing at SB can be used for individuals with irregular breathing patterns
• 2 The extent of mental stress achieved is intervention-specific and for the most part, independent of gender and
• 3 Resting assessment of HRV, BPV and SPBX can be made by having subjects sit quietly without interventions in a controlled laboratory setting.

     

Impact of body fat mass extent on cardiac autonomic alterations in women

Background  Obesity has been associated with significant abnormalities of the cardiac autonomic regulation. However, the precise impact of increasing body weight on cardiac autonomic function and the metabolic and hormonal contributors to these changes are presently unclear. The aim of our study was to explore in subjects with increasing values of body mass index (BMI) the alterations of cardiac autonomic function and to establish the potential role of various metabolic and hormonal contributors to these alterations.
Materials and methods  We investigated time and frequency domain heart rate variability (HRV) parameters taken from 24-h Holter recordings, and several anthropometric, metabolic and hormonal parameters (plasma glucose, insulin, triglycerides, free fatty acids, leptin and adiponectin) in 68 normoglycaemic and normotensive women (mean age of 40 ± 3 years), subdivided according to their BMI into 15 normal body weight (controls), 15 overweight, 18 obese and 20 morbidly obese.
Results  Heart rate was increased and HRV was decreased in the morbidly obese group as compared with controls. In overall population, a negative association linked body fat mass (FM) to HRV indices. None of the metabolic and hormonal parameters were significantly related to the HRV indices, after they were adjusted for the body FM.
Conclusions  Morbidly obese, normoglycaemic and normotensive young women have increased HR and low HRV, indicating an abnormal cardiac autonomic function and representing a risk factor for adverse cardiovascular events. A decrease of HRV parameters is associated with a progressive increase of body FM. Other metabolic and hormonal factors, characterising obesity, do not show an independent influence on these HRV alterations.     

Haemodynamic response to moderate thermal stress in pregnancy

The effect of a moderate heat stress on cardiovascular responses was studied: group I consisted of 15 healthy non-pregnant women, group II of 23 women 13-14 weeks pregnant and group III of 23 women 36-37 weeks pregnant. Heart rate, stroke volume, cardiac output, arterial blood pressure and peripheral vascular resistance were recorded every 5-10 minutes during a resting period (20 min, 21-23 degrees C) followed by heat stress (20 min, 70 degrees C, 15% relative humidity) and a recovery period (45 min, 21--23 degrees C). The rectal temperature increased 0.3-0.4 degrees C in each group during thermal stress. The heart rate before stress was highest in the advanced pregnancy group but increased almost identically in each group by 36--37 beats per minute during stress and approached starting values during recovery. There were no major changes in stroke volume during the experiment in any group nor were there any differences between the three groups. Arterial blood pressure did not change significantly in any group during the experiment; the differences between the groups were minimal. Peripheral vascular resistance began to fall at the start of the thermal stress and returned to prestress levels at the end of the recovery period. There were no differences between the groups in proportional changes of peripheral resistance. We conclude that pregnancy does not alter the cardiovascular responses to moderate thermal stress.     

糖尿病自主神经病变患者直立倾斜试验特点

目的探讨糖尿病自主神经病变患者直立倾斜试验的特点及其对阳性结果的影响。方法对72例因晕厥就诊的糖尿病自主神经病变患者在安静环境下进行直立倾斜试验,观察其心率、血压变化。结果试验阳性率为87.5%,其中血管抑制型9例,心脏抑制型51例,混合型3例,阴性9例。实验开始后各型心率均呈现逐渐上升的趋势,但心脏抑制型的峰值提前出现,在晕厥前各型心率均明显上升而后在晕厥时快速回落。结论糖尿病自主神经病变患者晕厥主要为心脏抑制型,晕厥前心率变化可以作为直立倾斜试验阳性的预测指标。