Cardiovascular responses to various autonomic tests in males and females

The results of cardiovascular autonomic reflex tests on 224 healthy, randomly selected subjects were analysed to study possible sex differences in the autonomic responses. The heart rate response to the Valsalva manoeuvre (Valsalva ratio) was greater in females over 50 years than in males of the same age (1.58 ± 0.34 vs. 1.44 ± 0.30,p < 0.05). The heart rate response to deep breathing (E/I ratio) was higher in females under 50 years than in males under 50 years (1.37 ± 0.17 vs. 1.34 ± 0.18,p < 0.001). The diastolic blood pressure response to isometric handgrip was higher in males under 50 years than in females of the same age (p < 0.05). Although there were sex differences in the magnitude of the responses, the effect of age was similar in males and females and accelerated attenuation of the autonomic responses could not be demonstrated with increasing age. It can be concluded that significant sex differences exist in cardiovascular autonomic responses. The implication of such differences need consideration.     

Autonomic nervous system function in patients with primary obstructive sleep apnoea syndrome

Ten patients with obstructive sleep apnoea syndrome cured by uvulopalatopharyngoplasty were compared to nine patients considered as surgical failures, using cardiovascular reflex tests—Valsalva manoeuvre, respiratory sinus arrhythmia, isometric handgrip and head-up tilt. Two patients had signs of moderate vagal dysfunction, but no case of definite autonomic nervous dysfunction was diagnosed. The overall results indicated sympathetic overreactivity, positively correlated to oxygen desaturation indices and remaining after successful treatment. Four patients did not exhibit bradycardia during sleep apnoea. Two of them had decreased respiratory sinus arrhythmia when awake, but two had normal values. This implies a difference in vagal responsiveness between the awake and sleeping states, or that other factors besides vagus function influence the bradycardia response to apnoea. The group mean values were all within normal limits. There was no significant difference between the two groups in any test. Autonomic nervous dysfunction therefore does not seem to contribute to surgical failure, nor to occur with increased incidence among patients with primary obstructive sleep apnoea syndrome.     

Is there a relationship between supine systemic blood pressure and orthostatic hypotension in the elderly?

The relationship between blood pressure and orthostatic hypotension was studied in 48 elderly patients with orthostatic hypotension and 29 healthy age-matched controls. Individuals were designated as hypertensive (systolic > 160 and or diastolic > 90 mmHg) or normotensive on the basis of supine blood pressure levels. Systolic, diastolic and mean blood pressures, heart rate, stroke volume, cardiac output, cardiac index and total peripheral resistance were measured every 5 min before, during and after 10 min head-up tilt to 70°.Eighteen orthostatic hypotension subjects and six controls were hypertensive, while 30 orthostatic hypotension subjects and 23 controls were normotensive. There were no differences between hypertensive and normotensive patients in mean age, weight, height or body surface area. Mean systolic blood pressure in orthostatic hypotension subjects was higher than in controls (148.8 ± 3.6 vs. 137.5 ± 3.34 mmHg). Mean diastolic pressure was not different (79.1 ± 2.0 vs. 79.0 ± 2.0 mmHg). There were no differences between patients with or without hypertension in the haemodynamic changes produced by head-up tilt. Heart rates in orthostatic hypotension subjects with hypertension were significantly lower throughout the study when compared with normotensive orthostatic hypotension patients. Further, the increases in heart rate on tilting were significantly smaller (8.4 ± 1.9 vs. 14.5 ± 1.8 beats/min). Control hypertensive subjects had significantly higher mean cardiac output and cardiac index compared with non-hypertensives from before and during tilt. We conclude that hypertension is not related to the development or the degree of orthostatic hypotension in the elderly. Elderly patients with orthostatic hypotension who had supine hypertension were unable to accelerate heart rate as much on tilt as normotensive patients. This may suggest cardiac impairment, failure to respond to increased sympathetic drive or a combination of these factors.     

Sleep apnoea syndrome: states of sleep and autonomic dysfunction.

Eleven patients with upper airway apnoea during sleep (one with SHY-Drager syndrome) were monitored polygraphically for wakefulness, sleep, and cardiovascular variables. Systemic hypertension and most of the severe arrhythmias recorded during sleep were secondary to repetitive obstructive apnonea and were mediated through the autonomic nervous system. Sleep related elevations of pulmonary arterial pressure were not influenced by atropine or impaired autonomic functions. Upper airway sleep apnoea is sleep related; the type of sleep (REM or NREM) is critical in the appearance of abnormalities. The distinction between two patient subgroups (total sleep dependent and NREM sleep dependent) has haemodynamic, and possibly long-term, implications. Sleep apnoea syndrome should be looked for in pateints with the Shy-Drager syndrome.     

Atrial natriuretic peptide response to postural change and medication in familial dysautonomia

Circulating atrial natriuretic peptide (ANP) was assayed before and after postural change and exercise in 54 patients with familial dysautonomia (FD) and 20 controls. ANP levels were compared with blood pressure, heart rate, plasma catecholamines and parameters of renal function. Compared with controls supine FD subjects had elevated blood pressures, heart rates and ANP levels (39 ± 4 pg/ml vs. 23 ± 3 pg/ml,p < 0.01). With the erect posture and exercise in FD subjects, blood pressure fell below control values, with ANP lowered. In FD subjects, blood pressure was correlated with ANP levels when supine and when erect and with heart rate post exercise. In controls, ANP levels did not correlate with other parameters. In FD patients on metoclopramide, supine and erect blood pressure and ANP levels were higher. FD subjects treated with fludrocortisone, had elevated supine and erect noradrenaline (p < 0.05 andp = 0.06); and those on diazepam had lower erect and post exercise noradrenaline (p < 0.05), but ANP levels were similar. In conclusion, sympathetic denervation may increase FD patients' responsiveness to other regulators of cardiovascular integrity, such as ANP. In addition, circulating ANP and catecholamines in FD subjects appear to be influenced by commonly used medications, such as metoclopramide.     

Ambulatory blood pressure in patients with Parkinson's disease without and with orthostatic hypotension

Non-invasive ambulatory recordings of blood pressure and heart rate were performed using a Spacelabs device during day and night periods in patients with Parkinson's disease with (n = 19) or without orthostatic hypotension (n = 19). In patients with orthostatic hypotension, the average systolic and diastolic blood pressure during the night (137 ± 5/80 ± 3 mmHg) was higher (p < 0.05) than during the day period (121 ± 3/76 ± 2 mmHg). In patients without orthostatic hypotension, a decrease in blood pressure was recorded during the nocturnal period. In patients with orthostatic hypotension, the blood pressure variability was higher (p < 0.05) during the day (systolic: 14.6 ± 1.3%; diastolic: 16.5 ± 1.0%) than during the night (systolic: 9.1 ± 0.8%; diastolic: 10.8 ± 1.1%). The blood pressure load (percentage of values above 140/90 mmHg) during the night was significantly higher than during the day for both systolic (41.2 ± 8.1 vs. 19.6 ± 4.7%) and diastolic blood pressure (24.9 ± 6.9 vs. 16.3 ± 4.9%). There was a decrease in heart rate in both groups during the night. A fall of 25 mmHg or more in systolic blood pressure after meals occurred in ten patients with orthostatic hypotension and in one patient without orthostatic hypotension. These results indicate that orthostatic hypotension in Parkinson's disease is associated with specific modifications of ambulatory blood pressure including loss of circadian rhythm of blood pressure, increased diurnal blood pressure variability and post-prandial hypotension.     

Parasympathetic hyperresponsiveness and bradyarrhythmias during apnoea in hypertension

Voluntary end-expiratory apnoea in a 23-year-old asymptomatic mild hypertensive patient consistently elicited bradyarrhythmias (complete heart block and sinus pause) and sympathetic activation to muscle blood vessels, indicating simultaneous sympathetic and parasympathetic activation during apnoea. The sympathetic bradyarrhythmic response to apnoea was potentiated by hypoxia and eliminated by atropine. Baroreflex activation also attenuated the bradycardic response to apnoea.A 43-year-old hypertensive patient with sleep apnoea also exhibited bradyarrhythmias (sinus arrest for up to 10 s) and a fall in perfusion pressure to <50 mmHg during episodes of sleep apnoea. These cardiovascular changes were associated with a reduction in oxygen saturation to levels as low as 35%. Neither patient was on any medication.Simultaneous sympathetic and parasympathetic activation during episodes of apnoea may predispose to cardiovascular catastrophe. These chemoreflex mediated autonomic changes are inhibited by baroreflex activation. We propose that patients with impaired baroreflexes (patients with hypertension or heart failure and premature infants) may be especially susceptible to excessive autonomic responses to chemoreflex stimulation during periods of apnoea. In these patient groups, brady-arrhythmias, hypoxia, hypoperfusion and sympathetic activation during apnoea may predispose to sudden death.     

Muscle sympathetic nerve activity during postural change in healthy young and older adults

Recent evidence suggests that during orthostatic stress the reflex increase in muscle sympathetic nerve activity may be diminished in older adults. To test this hypothesis, we measured muscle sympathetic nerve activity, plasma noradrenaline concentrations, heart rate, and arterial blood pressure in twelve young (mean, 25 years; range, 19–29 years) adults and 14 older (mean 64 years; range, 60–74 years) healthy adults, while supine and during upright sitting. Supine control levels of muscle sympathetic nerve activity were higher in the older subjects (35 ± 1 vs. 25 ± 1 bursts/min,p < 0.05), but there were no differences in plasma noradrenaline concentrations, heart rate or arterial pressure. Despite higher supine control levels in the older group, the absolute unit increases in muscle sympathetic nerve activity in response to upright sitting (p < 0.05 vs. control) were not different in the two groups (7 ± 1 vs. 7 ± 1 bursts/min), nor were the increases in plasma noradrenaline concentrations. Heart rate did not increase above supine control in response to sitting in either group. Arterial pressure increased slightly (p < 0.05, supine vs. control), but there were no age-related differences. These results indicate that, contrary to recent findings, the reflex increases in muscle sympathetic nerve activity and plasma noradrenaline concentrations and regulation of arterial pressure during this natural orthostatic stress are well preserved in older healthy men and women.     

Positive pressure on neck reduces baroreflex response to apnoea

This study was designed to evaluate the arterial blood pressure and heart rate responses to positive pressure applied to the neck during repetitive inspiratory apnoea. Twenty-five subjects (aged 20–40 years) were trained to exert a positive pressure on the neck by actively contracting the neck muscles and pressing the chin in the jugular notch. Blood pressure and heart rate were evaluated during 5-min long periods at rest, at the beginning and end of a 25-min period of apnoea with and without positive pressure and after a second period of rest. Positive pressure diminished the initial hypotensive and bradycardiac reactions to apnoea and augmented the heart rate and blood pressure increase towards the end of apnoea. Both systolic and diastolic pressures and heart rate were significantly elevated during both apnoeic sequences, and also remained significantly elevated after the release of pressure. Spectral analysis (FFT) and autoregressive model showed the entrainment of the slow 0.03Hz oscillations by repetitive apnoea and the occurrence of 0.1 Hz and respiratory 0.2 Hz components in the heart rate and blood pressure in both types of apnoea. It is suggested, since the positive pressure decreases the baroreflex and the increased sympathetic tone persists after apnoea, that such effects may contribute to the development of cardiac complications in prediposed individuals with obstructive apnoea syndrome.     

Evaluation of non-invasive blood pressure measurement by the Finapres method at rest and during dynamic exercise in subjects with cardiovascular insufficiency

The accuracy and precision of the Finapres in recording rest and exercise blood pressure compared with the intra-arterial (aortic and brachial) and random-zero sphygmomanometer methods was assessed in 84 ischaemic patients in three different studies. Firstly, comparison at rest with the aortic intraarterial pressure in 50 ischaemic patients demonstrated that the Finapres systolic (136.5 ± 21.1 vs. 129.3 ± 19.0 mmHg;p < 0.001) and mean (92.4 ± 13.4 vs. 90.7 ± 11.4 mmHg;p < 0.001) arterial pressures were higher and diastolic pressures lower (70.4 ± 11.5 vs. 71.5 ± 9.8 mmHg;p < 0.001). The reproducibility of the Finapres and invasive method was similar for systolic (4.6% vs. 4.0%), diastolic (2.8% vs. 2.7%) and mean (3.3% vs. 3.0%) blood pressures. Second, in seven subjects studied twice at rest and during 4 min supine bicycle exercise, the exercise increase in blood pressure was greater on the Finapres compared with the brachial intra-arterial pressure (systolic +10.2 ± 6.3 vs. +3.6 ± 9.8 mmHg; diastolic +9.6 ± 11.1 vs. +0.2 ± 2.1 mmHg;p = 0.02 for each); however, at steady-state the peak/trough differences in pressure between the methods were similar. Thirdly, compared under rest conditions, to random zero sphygmomanometer (RZO), the Finapres systolic pressure was higher (6.8 ± 3.5 mmHg) and diastolic pressure lower (–6.0 ± 1.9 mmHg). During upright bicycle exercise, the difference between the Finapres and RZO in systolic blood pressure increased at each level of exercise (+14.3 ± 4.2, +17.9 ± 4.0 and +22.2 ± 4.1 mmHg respectively at each exercise stage:p < 0.01). For RZO, diastolic blood pressure fell as exercise workload increased whereas Finapres diastolic blood pressure increased on exercise (3.1 ± 2.6, 7.0 ± 2.1 and 8.1 ± 2.0 mmHg respectively:p < 0.01). Thus there were systematic differences between the values recorded by the Finapres and proximal blood pressure methods and limited agreement in the rest to exercise increments related to light exercise. Calibration of the Finapres values in terms of the other methods is limited by the variable relationship to these related changes in arterial distensibility.     

Effect of recombinant erythropoietin on anemia and orthostatic hypotension in primary autonomic failure

Anemia is a common complication of autonomic failure and reduced red blood cell mass may contribute to the orthostatic hypotension of these patients. We investigated whether treatment with recombinant erythropoietin improves anemia and increases blood pressure in patients with primary autonomic failure. Three patients with multiple system atrophy and autonomic failure and one with pure autonomic failure were studied. All patients had normocytic normochromic anemia and low (n = 2) or normal (n = 2) serum levels of erythropoietin. Treatment with erythropoietin, 4000 U subcutaneously biweekly for 6 weeks, increased hematocrit and blood pressure in all patients. Hematocrit increased from 33.9 ± 0.7 to 44.3 ± 1.4%, blood pressure in supine position increased from 150 ± 8/87 ± 8 (systolic/diastolic; mean ± SD) to 166 ± 25/92 ± 12 mmHg, and after 3 min in the head-up tilt position from 86 ± 21/47 ± 15 to 102 ± 23/63 ± 12 mmHg, (p < 0.05). All patients reported improvement in orthostatic symptoms and increased tolerance to standing. The study shows that treatment with erythropoietin improves anemia, increases blood pressure and ameliorates orthostatic hypotension in patients with primary autonomic failure.     

Association between plasma homocysteine levels and obstructive sleep apnoea in patients with ischaemic stroke

We aimed to investigate the association between plasma homocysteine and obstructive sleep apnoea (OSA) syndrome in patients with ischaemic stroke. A total of 102 patients with ischaemic stroke were classified into four OSA groups based on their apnoea–hypopnoea index (AHI): absent (AHI < 5/hour); mild (5–14/hour); moderate (15–30/hour); and severe (>30/hour). The mean (±standard deviation) homocysteine levels in the four OSA groups were: absent, 8.98 ± 3.74 μmol/L; mild, 11.46 ± 3.31 μmol/L; moderate, 14.18 ± 4.36 μmol/L; and severe, 18.57 ± 4.56 μmol/L; and these differences were statistically significant (p < 0.001). The Pearson correlation analysis revealed a positive correlation between homocysteine levels and the severity of AHI (r = 0.482, p < 0.001). Multiple linear regression analysis showed that AHI and folate were independent predictors of homocysteine levels (R² = 0.539, p < 0.001, β for AHI = 0.259, β for folate = –0.400). In conclusion, the severity of OSA is significantly associated with elevated homocysteine levels in patients with ischaemic stroke, and this association is independent of other factors that cause elevation in homocysteine.     

Sleep architecture and attenuated heart rate response to arousal from sleep in patients with autonomic failure

ObjectiveTo determine if patients with autonomic failure have increased sleep disturbances and if multiple system atrophy (MSA) and pure autonomic failure (PAF) patients have frequent arousals from sleep associated with an attenuated heart rate (HR) response compared to healthy volunteers.MethodsWith informed consent, 10 autonomic failure patients and 10 healthy volunteers were studied. Sleep disturbances were scored using standard criteria. Arousals were identified from stage 2 sleep and differences in the R–R interval between groups were tested using a mixed-model regression analysis.ResultsThree MSA and one PAF patient had obstructive sleep apnoea compared to one volunteer. One MSA and three PAF patients had periodic limb movements. One MSA patient had REM behaviour disorder. The autonomic patients had significantly reduced total sleep time (p = 0.007) and sleep efficiency (p = 0.003). The HR response to arousal was smaller in autonomic failure patients compared to volunteers during the early phase of the arousal (p = 0.047), but not the later phase (p = 0.67).ConclusionAutonomic failure patients have increased sleep disturbances compared to healthy volunteers. The smaller HR response in autonomic failure patients suggests that an intact sympathetic nervous system is a key component of the HR response associated with arousal from sleep.     

The effect of indomethacin on the circulatory and plasma noradrenaline responses to cold pressor testing in normal subjects

Prostaglandins may alter neuronal noradrenaline release or vascular responsiveness to sympathoexcitation. The purpose of this study was to determine if indomethacin, a prostaglandin synthesis inhibitor, influences the sympathetic and circulatory adjustments to a commonly utilized laboratory stressor in the clinical assessment of autonomic function, the cold pressor test. Venous plasma noradrenaline levels (n = 8), mean arterial pressure and heart rate (n = 10) were measured in healthy male subjects during immersion of the non-dominant hand in cold water (1°C) for 90 s. The subjects were given either placebo or indomethacin (100 mg) in a double-blind manner. The order of administration was counterbalanced and a 1 week period was given for systemic clearance of the drug. The absolute level of mean arterial pressure was elevated during the resting control period after indomethacin treatment (88 in placebo vs. 92 mmHg in indomethacin). Both heart rate and venous plasma noradrenaline levels were similar between trials during the resting control period. Mean arterial pressure and heart rate increased similarly during cold pressor testing in both indomethacin and placebo. Venous plasma noradrenaline levels increased during cold pressor testing 162 ± 39 vs. 200 ± 69 pg/ml in indomethacin vs. placebo (p > 0.05), respectively. In addition, perceived pain (peak level = 7 ± 1 vs. 6 ± 1 units; indomethacin vs. placebo, respectively) was not different between the trials. These results suggest that administration of indomethacin in a maximal single therapeutic dose, does not affect the sympathetic nervous system or circulatory responsiveness to cold pressor testing. It may not be necessary to discontinue indomethacin prior to autonomic function testing.     

The effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in spinal muscular atrophy

In patients with spinal muscular atrophy (SMA), obstructive sleep apnea syndrome (OSAS) constitutes an important cause of cardiovascular morbidity and mortality. We investigated heart rate variability (HRV) to evaluate the effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in patients with SMA and OSAS. Six patients with SMA (type 1 and 2) and six age- and sex-matched healthy children were consecutively enrolled. A whole-night diagnostic polysomnography was performed, and SMA patients with OSAS were given non-invasive mechanical ventilation therapy. HRV analysis was performed on the basis of whole-night electrocardiography recordings via a computer-base program. Apnea-hypopnea index (AHI) was 9.2 ± 6.2/hr in SMA patients, while it was 0.4 ± 0.5/hr in controls (p = 0.036). All SMA patients had OSAS, while none of the controls had OSAS (p = 0.012). Mean percentage of successive R wave of QRS complex (R-R) intervals>50 ms was significantly lower in SMA patients than those in controls (p = 0.031). Significant correlations were found between AHI and high-frequency power, low/high-frequency ratio in wakefulness and in sleep (p<0.05). Repeated HRV analysis in SMA patients following OSAS therapy showed significant reductions in average R-R duration (p = 0.028) and percentage of successive R-R intervals>50 ms (p = 0.043). Our study demonstrates the beneficial effects of non-invasive mechanical ventilation on cardiac autonomic dysfunction in SMA patients with OSAS.     

Cerebral haemodynamics in obstructive sleep apnoea and Cheyne-Stokes respiration

Obstructive sleep apnoeas are common among stroke patients and, as different from central apnoeas, they do not decline during stroke rehabilitation. Cerebral and cardiovascular changes display a different pattern during central and obstructive sleep apnoeas. The cerebral blood flow velocity according to transcranial Doppler increases during an obstructive apnoea and decreases after apnoea termination concomitant with changes in arterial pressure. The changes in cerebral circulation during obstructive apnoeas could be an immediate effect of rapid changes in blood pressure because cerebral autoregulation is overridden. Low cerebral blood flow, low arterial pressure and hypoxemia after apnoea termination may predispose to nocturnal cerebral ischaemia. The opposite pattern is seen during a central apnoea, with a decrease in cerebral blood flow velocity during apnoea and an increase after apnoea termination. Changes during obstructive apnoeas are probably hazardous, with adverse cardiovascular effects including stroke. This may not be the case during central apnoeas, as Cheyne-Stokes respiration with central apnoeas is a result of an underlying disorder such as heart failure and stroke and is not a disease entity in itself. It is suggested that obstructive sleep apnoea is a risk factor for stroke as it is common among stroke victims and cerebral hypoperfusion occurs after an obstructive apnoea. The treatment of sleep apnoea should also be taken into account among stroke patients. Large cohort studies, treatment studies and further studies of possible mechanisms for apnoea-induced stroke are, however, essential in order to evaluate whether obstructive sleep apnoea is an independent risk factor for stroke.     

Abnormal heart rate and blood pressure responses to baroreflex stimulation in multiple sclerosis patients

Abstract Cardiovascular autonomic neuropathy has been previously reported in patients with multiple sclerosis (MS) using standard reflex tests. However, no study has separately evaluated both parasympathetic and sympathetic cardiovascular autonomic regulation. We therefore assessed the baroreflex-mediated vagal and sympathetic control of the heart rate and sympathetic control of the blood vessels in MS patients using sinusoidal neck stimulation.We studied 13 multiple sclerosis patients aged 28–58 years and 18 healthy controls aged 26–58 years. The carotid baroreflex was stimulated by sinusoidal neck suction (0 to –30 mmHg) at 0.1 Hz to assess the autonomic control of the heart and blood vessels, and at 0.2 Hz to assess the vagal control of the heart. Continuous recordings were made of blood pressure, electrocardiographic RR-interval and respiration, with breathing paced at 0.25 Hz. Spectral analysis was used to evaluate the magnitude of the low frequency (LF, 0.03–0.14 Hz) and high frequency (HF, 0.15–0.50 Hz) oscillations in RR-interval and blood pressure in response to the sinusoidal baroreceptor stimulation. Responses to the applied stimulus were assessed as the change in the spectral power of the RR-interval and blood pressure fluctuations at the stimulating frequency from the baseline values.The increase in the power of 0.1 Hz RR-interval oscillations during the 0.1 Hz neck suction was significantly smaller (p<0.01) in the MS patients (4.47±0.27 to 5.62±0.25 ln ms²) than in the controls (4.12±0.37 to 6.82±0.33 ln ms²). The increase in the power of 0.1 Hz systolic BP oscillations during 0.1 Hz neck suction was also significantly smaller (p<0.01) in the MS patients (0.99±0.19 to 1.96±0.39mmHg²) than in the healthy controls (1.27±0.34 to 9.01±4.10mmHg²). Neck suction at 0.2 Hz induced RR-interval oscillations at 0.2 Hz that were significantly smaller (p<0.05) in the patients (3.22±0.45 ln ms²) than in the controls (5.27±0.29 ln ms²). These results indicate that in MS patients, baroreflex dysfunction is not only restricted to the cardiovagal limb of the baroreflex, but that the sympathetic modulation of the blood vessels is also affected.     

Autonomic reflexes in patients with cardioinhibitory carotid sinus syncope

Autonomic reflexes were investigated in patients with the cardioinhibitory carodid sinus syndrome. Heart rate, blood pressure and forearm blood flow responses were recorded during prolonged head-up tilt, the Valsalva manoeuvre, lower body negative pressure and sequential respiratory cycles in ten patients and nine age-matched controls.The mean maximum R—R interval prolongation during carotid sinus massage was 4.4 s. Three patients had syncope during prolonged head-up tilt. Heart rate and blood pressure responses were similar for patients and controls who completed tilt. Responses to lower body negative pressure and Valsalva manoeuvre were similar for both groups. Respiratory sinus arrhythmia was significantly less marked in patients, 7 bpm (0 to 20 bpm) versus 15 bpm (6 to 35 bpm;p = 0.05). Therefore, neck massage and deep breathing produce abnormal cardiac vagal responses, whereas other reflexes, including response to lower body negative pressure and the Valsalva manoeuvre are within the normal range in cardioinhibitory carotid sinus syndrome.     

Sciatic nerve stimulation induces hypotension but not renal or lumbar sympathoinhibition in hypertensive Dahl rats

Sustained reductions in arterial pressure and sympathetic nerve activity occur after prolonged sciatic nerve stimulation in spontaneously hypertensive and pre-hypertensive Dahl salt-sensitive rats whereas these responses are not observed in renal hypertensive or Dahl resistant rats. These observations suggest that the development of poststimulation hypotension and sympathoinhibition may be related to the genetic predisposition for hypertension rather than to the increased level of arterial pressure. However, it is not known whether the magnitude of the post-stimulation blood pressure and sympathetic nerve responses are influenced by the increased level of arterial pressure in addition to the genetic predisposition to hypertension. In the present study, we sought to determine if sustained sciatic nerve stimulation induces post-stimulation hypotension in hypertensive Dahl sensitive (DS) rats. For this purpose, mean arterial pressure (MAP), heart rate (HR), renal (RSNA) and lumbar (LSNA) sympathetic nerve activity were recorded during and after sciatic nerve stimulation in hypertensive DS rats (n = 17) fed an 8.0% NaCl diet for 7–8 weeks. Sciatic nerve stimulation increased HR (control, 443 ± 10 b.p.m.; stimulation, 487 ± 8 b.p.m.;p < 0.05) and tended to increase MAP, RSNA and LSNA. Two hours after stimulation, MAP was reduced (control 145 ± 5 mmHg; recovery, 124 ± 8 mmHg;p < 0.01) from control values. In contrast, RSNA and HR remained unchanged whereas LSNA was increased (69 ± 20%;p < 0.05) from control values 120 min after stimulation. MAP, HR and RSNA were unchanged from control values during and for 2 h after sham stimulation in eight DS rats. These results demonstrate that sustained somatic afferent stimulation induces post-stimulation hypotension but not renal or lumbar sympathoinhibition in hypertensive DS rats.     

Continuous Blood Flow Velocity Measurements in Obstructive Sleep Apnea Syndrome

Mean blood flow velocity was measured by transcranial Doppler (TCD) sonography in 15 patients with obstructive sleep apnea syndrome. Relative increases of mean flow velocity in the middle cerebral artery (MCA) during apneas were seen in all patients, and were related to the severity of desaturation (p < 0.05). Additionally, a relationship between mean flow velocity and both end-tidal carbon dioxide pressure and oxyhemoglobin desaturation could be demonstrated, suggesting that cerebral blood flow is regulated by both parameters. After patients were treated with nasal continuous positive airway pressure, the mean flow velocity was normalized, demonstrating a beneficial effect of this treatment. Magnetic resonance imaging of the brain demonstrated abnormalities in 2 patients, raising the possibility that daytime neuronal dysfunction in sleep apnea patients may relate to increased mean flow velocity with secondary microvascular damage.