Sympathetic-nerve activity during sleep in normal subjects

The sympathetic nervous system and obstructive sleep apnea: implications for hypertension

Patients with obstructive sleep apnea experience repetitive apneic events during sleep, with consequent hypoxia and hypercapnia. Hypoxia and hypercapnia, acting via the chemoreflexes, elicit increases in sympathetic nerve activity. The sympathetic responses to hypoxia and hypercapnia are potentiated during apnea, when the sympathetic inhibitory influence of the thoracic afferent nerves is eliminated. As a consequence of the sympathetic vasoconstrictor response to apneic events, patients with obstructive sleep apnea manifest marked increases in blood pressure during sleep, especially evident at the end of the apnea. The increases in sympathetic activity and blood pressure during sleep in these patients appear to carry over into the daytime such that patients with sleep apnea have an increased prevalence of hypertension and high levels of sympathetic nerve activity. Although the mechanism underlying the persistent elevation in sympathetic activity during the daytime is not known, it is likely that the increased sympathetic drive is implicated in the higher daytime blood pressures in these patients. Whereas patients with sleep apnea have an increased prevalence of hypertension, in those patients with sleep apnea who do have hypertension, the sympathetic response to apneic events may be potentiated. This may be secondary to impaired baroreflex sensitivity, since the baroreflexes exert an inhibitory influence on the chemoreflex responses to hypoxia. Treatment with continuous positive airway pressure results in an acute reduction in blood pressure and sympathetic activity during sleep. Prolonged effective treatment of sleep apnea may also reduce daytime blood pressure levels. This review examines the physiology of the chemoreflex responses to hypoxia, hypercapnia and apnea, as well as the physiologic responses to sleep in normal humans. These physiologic responses are compared with the pathophysiologic sympathetic and hemodynamic responses that characterize obstructive sleep apnea. Increases in sympathetic activity and blood pressure in patients with obstructive sleep apnea may play a role in linking sleep apnea to hypertension and cardiac and vascular events.

Nonuniform nighttime distribution of acute cardiac events: a possible effect of sleep states

BACKGROUND

Although 250,000 myocardial infarctions and 38,000 sudden cardiac deaths occur at night annually, this public health problem is underappreciated and poorly understood. We examined whether the incidence of myocardial infarction, sudden cardiac death, and automatic implantable cardioverter-defibrillator (AICD) discharge was nonuniform, a result that may implicate physiological triggers such as sleep-state dependent changes in autonomic nervous system activity.

METHODS AND RESULTS

We conducted a review of the circadian pattern of the onset of myocardial infarction (n=19), sudden cardiac death (n=12), and AICD discharge (n=7). The nighttime period was chosen a priori as midnight to 5:59 AM. These reports documented 11,633 nocturnal myocardial infarctions (20% of the total myocardial infarctions), 1981 nocturnal sudden cardiac deaths (14.6% of the total sudden cardiac deaths), and 1200 nocturnal AICD discharges (15.0% of the total discharges). The distributions of myocardial infarction, sudden cardiac death, and AICD discharge were each significantly nonuniform (P<.001). The peak incidence of myocardial infarction and AICD discharge occurred between midnight and 0:59 AM, whereas the peak incidence of sudden cardiac death was between 1:00 and 1:59 AM. The trough in incidence occurred between 4:00 and 4:59 AM for sudden cardiac death and between 3:00 and 3:59 AM for myocardial infarction and AICD discharge.

CONCLUSIONS

Nocturnal myocardial infarction, sudden cardiac death, and AICD discharge exhibit nonuniform distributions. This finding is consistent with the hypothesis that sleep-state dependent fluctuations in autonomic nervous system activity may trigger the onset of major cardiovascular events and provides further impetus for more directly testing this hypothesis at population, individual, and mechanistic levels. A better understanding of nocturnal triggers may make it possible to reduce the incidence of myocardial infarction, ventricular tachyarrhythmias, and sudden cardiac death during the nocturnal period.

Low-frequency (< 1 Hz) oscillations in the human sleep electroencephalogram

Low-frequency (< 1 Hz) oscillations in intracellular recordings from cortical neurons were first reported in the anaesthetized cat and then also during natural sleep. The slow sequences of hyperpolarization and depolarization were reflected by slow oscillations in the electroencephalogram. The aim of the present study was to examine whether comparable low-frequency components are present in the human sleep electroencephalogram. All-night sleep recordings from eight healthy young men were subjected to spectral analysis in which the low-frequency attenuation of the amplifier was compensated. During sleep stages with a predominance of slow waves and in the first two episodes of non-rapid-eye-movement sleep, the mean power spectrum showed a peak at 0.7-0.8 Hz (range 0.55-0.95 Hz). The typical decline in delta activity from the first to the second non-rapid-eye-movement sleep episode was not present at frequencies below 2 Hz. To detect very low frequency components in the pattern of slow waves and sleep spindles, a new time series was computed from the mean voltage of successive 0.5 s epochs of the low-pass (< 4.5 Hz) or band-pass (12-15 Hz) filtered electroencephalogram. Spectral analysis revealed a periodicity of 20-30 s in the prevalence of slow waves and a periodicity of 4 s in the occurrence of activity in the spindle frequency range. The results demonstrate that distinct components below 1 Hz are also present in the human sleep electroencephalogram spectrum. The differences in the dynamics between the component with a mean peak value at 0.7-0.8 Hz and delta waves above 2 Hz is in accordance with results from animal experiments.

Undiagnosed sleep-disordered breathing among male nondippers with essential hypertension

OBJECTIVE

A blunting of the nocturnal fall in arterial blood pressure is found in a minority of patients (nondippers) with essential hypertension. We tested whether sleep-disordered breathing (snoring and apnea or hypopnea) might explain such a finding for male patients, among whom its prevalence is much higher.

SETTING AND PATIENTS

We studied 100 new cases of hypertension in men, observed consecutively by a local group of general practitioners and diagnosed essential hypertensives in a referral clinic. By using 24 h ambulatory blood pressure monitoring with a SpaceLabs 90207 device, 15 patients were classified initially nondippers (daytime ambulatory blood pressure > or = 136/87 mmHg; night-time decrease by < 10% of the daytime mean), but only 11 were confirmed to be nondippers by continuous blood pressure monitoring with a Finapres device. Ten dippers matched by age, body mass index and mean 24 h blood pressure were used as controls.

MAIN OUTCOME MEASURES

Parameters of nocturnal polysomnography.

RESULTS

During polysomnography, the nondippers exhibited a blunting of the sleep-related fall in blood pressure and an increased variability in blood pressure associated with sleep-disordered breathing (heavy snoring for all, with an apnea or hypopnea index > 10 in 10 cases). Six of the control patients breathed normally and four snored nonapneically. There was a normal fall in nocturnal blood pressure in all 10 cases.

CONCLUSIONS

The nondipper condition appears to be associated with undiagnosed apneic snoring for an unselected population of previously untreated male subjects with a diagnosis of essential hypertension. Ambulatory blood pressure monitoring of such patients is of limited diagnostic value.

Sleep and circadian influences on cardiac autonomic nervous system activity

To assess the separate contributions of the sleep and circadian systems to changes in cardiac autonomic nervous system (ANS) activity, 12 supine subjects participated in two 26-h constant routines, which were counterbalanced and separated by 1 wk. One routine did not permit sleep, whereas the second allowed the subjects to sleep during their normal sleep phase. Parasympathetic nervous system activity was assessed with respiratory sinus arrhythmia as measured from the spectral analysis of cardiac beat-to-beat intervals. Sympathetic nervous system activity was primarily assessed with the preejection period as estimated from impedance cardiography, although the 0.1-Hz peak from the spectral analysis of cardiac beat-to-beat intervals, the amplitude of the T wave in the electrocardiogram, and heart rate were also measured. Respiratory sinus arrhythymia showed a 24-h rhythm independent of sleep, whereas preejection period only showed a 24-h rhythm if sleep occurred. Thus the findings indicate that parasympathetic nervous system activity is mostly influenced by the circadian system, whereas sympathetic nervous system activity is mostly influenced by the sleep system.

Is the absence of a normal nocturnal fall in blood pressure (nondipping) associated with cardiovascular target organ damage?

OBJECTIVE

To determine whether the failure to decrease blood pressure normally during sleep is associated with more prominent target organ damage.

METHODS

Cardiac and vascular structure and function were characterized in 183 asymptomatic, unmedicated hypertensive patients and compared with their ambulatory blood pressures.

RESULTS

The 104 patients with a normal (> 10%) nocturnal fall in systolic blood pressure (dippers) were similar to the 79 patients with an abnormal fall (nondippers) in sex, race, body size, smoking history, and average awake ambulatory blood pressure. Nondippers tended to be older (57 versus 54 years, P = 0.06). The supine blood pressure upon completion of the ultrasound studies was higher in the nondippers (156/93 versus 146/89 mmHg, P < 0.005) as was the variability of the awake diastolic blood pressure. There were no differences between dippers and nondippers in left ventricular mass (170 versus 172 g), mass index (90 versus 91 gm/m2), prevalence of abnormal ventricular geometry, common carotid artery diameter (5.74 versus 5.75 mm), and vascular strain. Although nondippers were more likely to have carotid artery plaque (41 versus 27%, P = 0.053) and an increased intimal-medial thickness (0.84 versus 0.79 mm, P < 0.05), adjustment for age rendered the differences insignificant. There were no differences in the relation of awake and sleeping systolic pressures to the left ventricular mass (r = 0.36 and 0.35, respectively, both P < 0.005) or to the carotid wall thickness (r = 0.28 and 0.29, respectively, both P < 0.005). When the 114 men and 69 women were considered separately, similar findings were obtained. When the 109 whites and 56 blacks (African-Americans and Afro-Caribbeans) were considered separately, there were no differences in left ventricular structure in either group, and differences in vascular structure were confined to the white subgroup.

CONCLUSION

The lack of a normal nocturnal fall in blood pressure is not associated with an increase in left ventricular mass or in arterial disease independently of age. Age-related changes in carotid artery wall thickness and plaque among nondippers may reflect a contribution of an altered baroreceptor function to the lack of normal nocturnal and supine blood pressure decreases.

A controlled study of the effects of mental relaxation on autonomic excitatory responses in healthy subjects

OBJECTIVE

Circumstantial evidence indicates that, in the presence of a suitable substratum, sudden, behaviorally induced increases in sympathetic drive to the cardiovascular system might play an important physiopathological role in various conditions, ranging from arterial hypertension to sudden coronary death. Accordingly, it might be useful to study the effects of behavioral interventions, such as mental relaxation, that might be capable of blunting excitatory autonomic responses. It would also be preferable to study healthy subjects in whom autonomic control is not modified by the presence of disease, and to use noninvasive approaches to minimize the possible emotional impact produced by invasive recordings.

METHODS

We examined healthy subjects who were either subjected to relaxation training (N = 13) or sham relaxation (N = 12). An additional group, treated with beta-adrenergic blockade (N = 12), was also examined. Spectral and cross-spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided quantitative markers of sympathovagal balance modulating the sinoatrial (SA) node, of sympathetic vasomotor modulation, and of the gain of the arterial pressure/heart period baroreflex (index alpha). Subjects were studied at rest, during standing, and during mental arithmetic.

RESULTS

Data indicate that both beta-adrenergic blockade and relaxation training significantly blunted the excitatory autonomic responses to standing and to mental arithmetic. Indices of sympathetic modulation also seemed reduced by beta blockade at rest. No changes were observed with sham training.

CONCLUSIONS

Frequency domain analysis of cardiovascular variabilities, using a totally noninvasive approach, indicates that relaxation training significantly blunts the excitatory autonomic changes produced by standardized behavioral laboratory stimuli.

Diet and infant behavior

We studied 142 preterm infants (mean gestation 31 weeks, mean birthweight 1364 g) fed prospectively varied protein and energy intakes. Infants were grouped as either slow or rapid growers based on rate of weight gain. Rapid growers had increased heart rates (166 vs 160 beats/min), respiratory rates (55.7 vs 53.9 bpm), energy expenditure (64.8 vs 61.6 kcal kg(-1) day(-1)), urinary C-peptide levels (1.59 vs 0.79 ng ml(-1)) and time in active sleep (78.0 vs 75.2%), and decreased spectral edge frequency in the electroencephalogram (2.96 vs 4.45 Hz) compared to slow growers. We conclude that preterm infants growing at varying rates manifest physiological and behavioral differences, and that these patterns may reflect altered autonomic balance.

Plasma epinephrine and norepinephrine concentrations of healthy humans associated with nighttime sleep and morning arousal

We assessed the activity of the sympathetic nervous system during undisturbed nocturnal sleep and periods of wakefulness directly before and after sleep in healthy young men. Changes induced by periods of rapid eye movement and by morning awakening, both periods reported to demonstrate an enhanced risk for the onset of cardiovascular diseases, were of particular interest. In 13 healthy men (age, 18 to 35 years), blood for determination of epinephrine and norepinephrine was drawn every 7 minutes between 9:30 PM and 8:30 AM with the subjects resting in a strictly horizontal position. Lights were switched off at 11 PM until awakening at 7 AM. At 8:30 AM, subjects stood up and a final blood sample was drawn. Sleep was monitored somnopolygraphically, and heart rate and blood pressure were continuously measured. Average epinephrine but not norepinephrine concentrations were significantly lower during nocturnal sleep than during wakefulness before and after sleep. In parallel, heart rate and blood pressure declined significantly during sleep. During rapid eye movement sleep, both epinephrine and norepinephrine concentrations were significantly lower than during sleep stages 1 and 2 and slow-wave sleep. Whereas epinephrine concentrations gradually began to increase after morning awakening, norepinephrine levels were not significantly enhanced. However, standing up at the end of the experiment sharply increased norepinephrine concentrations by 180%, whereas epinephrine levels were less enhanced (46%) by the change of body position. This study suggests that the decrease in the activity of the sympathoadrenal branch of the sympathetic nervous system is probably due to an entrainment to the sleep-wake cycle, whereas the low activity of the noradrenergic branches depends mainly on horizontal body position during nocturnal sleep. The activities of the sympathoadrenal and noradrenergic branches of the sympathetic nervous system seem to be downregulated during rapid eye movement sleep. Awakening itself selectively enhances epinephrine levels. Subsequent orthostasis activates both the sympathoadrenal and, most prominently, the noradrenergic branches of the sympathetic nervous system.

Ambulatory and home blood pressure normality in the elderly: data from the PAMELA population

To determine ambulatory blood pressure (BP) means and distributions in an elderly population, we studied a random sample of 800 subjects stratified by sex and representative of residents aged 65 to 74 years of the city of Monza. Participation was 50%. Measurements consisted of clinic BP (average of three measurements with mercury sphygmomanometry), home BP (average of morning and evening measurements with a semiautomatic device), and ambulatory BP (SpaceLabs 90207). Clinic BP was obtained before and after home and ambulatory BP measurements. In normotensive and untreated hypertensive subjects (n=248), clinic, home, and ambulatory BPs were significantly related (P<.001). The means of the clinic BPs obtained on consecutive days were very similar and markedly higher than 24-hour average BP (+25 mm Hg systolic and + 10 mm Hg diastolic, P<.001). Nighttime BP was markedly less than daytime BP (-14 and -13 mm Hg, P<.001), whereas home BP values occurred approximately midway between clinic and 24-hour average BP values. Only minor differences existed between data in men and women, and the differences in clinic, home, and ambulatory BP values occurred in both normotensive and untreated hypertensive subjects. All BPs were similar in the untreated and treated hypertensive groups. Thus, as previously reported in subjects younger than 65 years, in the elderly fraction of the population, 24-hour average BP is much lower than clinic BP. The upper limit of normality for 24-hour average BP (calculated as the value corresponding to 140/90 mm Hg clinic BP) is about 120 mm Hg systolic and 76 mm Hg diastolic. At variance with data from younger subjects, home BP in the elderly is higher than 24-hour average BP. However, similar to data from younger subjects, clinic, home, and ambulatory BPs are higher in treated hypertensive than normotensive elderly subjects, indicating that in hypertensive elderly subjects, antihypertensive treatment does not commonly achieve full BP control both inside and outside the clinic environment.

Heart rate variability: sleep stage, time of night, and arousal influences

Spectral analysis was used to assess heart rate variability in consecutive 5-min epochs during the night in 12 normal adults. Simultaneous time coding of EEG and digitized EKG allowed examination of heart rate variability as a function of sleep stage, time of night and presence of EEG arousal. The results replicated previous studies in showing increases in high frequency components and decreases in low frequency components of heart rate variability across NREM sleep stages and opposite changes in REM sleep and wake. These results are consistent with sympathetic nervous system activation during REM sleep and wake periods. The shift in heart rate variability seen during REM sleep began in NREM sleep several minutes prior to standardly scored REM and often continued beyond the end of REM sleep. EEG arousals during Stage 2 and to some extent REM sleep were also associated with changes in heart rate variability which were consistent with sympathetic activation. An examination of beat to beat intervals in proximity to EEG arousals showed heart rate acceleration at least 10 beats prior to the EEG arousal. The arousal data along with Stage 2 sleep transition data support the contention that increases in central nervous system sympathetic activity precede and possibly play a role in the initiation of REM sleep and arousals during sleep.

Autonomic function in narcolepsy: power spectrum analysis of heart rate variability

Ten narcoleptic patients that had never been treated previously and ten healthy volunteers of comparable age underwent 48-h polygraphic recording to assess the effects of wakefulness and sleep on beat-to-beat heart rate variability by means of power spectrum analysis. The study revealed decreased power in the low frequencies (LF) during sleep (whereby an increase of the power in this band is associated with sympathetic activation) compared with wakefulness, with minimal values during stage 3-4 non-REM sleep and higher levels during REM sleep, both in patients and controls. Significantly reduced power in high frequencies (HF; mainly expression of parasympathetic control) and a significantly increased LF/HF ratio during wakefulness before sleep in narcoleptics compared with controls were found. Our study excludes a primary disturbance of cardiac autonomic nervous system in narcoleptics but suggests an altered circadian autonomic function in these patients.

Cardiac autonomic function during sleep in several neuropsychiatric disorders

Cardiac autonomic activity during sleep is only very slightly influenced by the emotional state of the patient and, unlike some of the traditional tests of autonomic function, may be studied in all patients. In an attempt to evaluate autonomic function in patients with different neuropsychiatric disorders, two different methods of quantifying the changes in sympathetic and parasympathetic cardiac control during sleep were used: (1) the ratios of consecutive R-wave (R-R) intervals before and after spontaneous body movements; (2) spectral analysis of R-R intervals. It was found that more than one third of patients with presenile Alzheimer's disease had defective cardiac sympathetic control. Untreated parkinsonian patients showed predominantly defective parasympathetic, and to a lesser extent sympathetic, function during sleep. In these patients, as well as in patients with multiple sclerosis, autonomic evaluation during sleep led to earlier detection of impairment than the traditional tests during wakefulness. Narcoleptic patients and patients with panic disorder showed normal autonomic function during sleep, but had altered control levels during the wakeful period before sleep. The findings in these narcoleptic patients were probably related to the impairment of their sleep-wake cycle. The sympathetic overactivity found in patients with panic disorder was probably a result of cognitive activity, as the nocturnal data excluded an intrinsic defect in autonomic regulation.

Effect of a westward transmeridian flight on ambulatory blood pressure monitoring in normotensive subjects

OBJECTIVE

To evaluate the effects of a westward transmeridian flight over six time zones (from Milan to New York) on ambulatory blood pressure monitoring (ABPM) in normotensive individuals.

METHODS

Eighteen normotensive subjects (blood pressure < 140/90 mmHg), 11 men and seven women, of mean age 38.3 years, were studied. On the day of travel they underwent 26 h noninvasive ABPM (started at 1100 h); the take-off time was 1200 h and the landing time was 8 h later, at 1400 h New York time (2000 h Italian time). Subjects were requested not to sleep until 2300 h and to get up at 0700 h the following morning. The results were compared with those of a 26 h ABPM performed in Italy the week before during which they slept from 2300 h to 0700 h.

RESULTS

During the flight blood pressure and heart rate did not change compared with values during the corresponding time interval of the control day. After the landing, during the New York afternoon and evening (corresponding to the Italian sleeping time), blood pressure and heart rate remained unchanged, whereas during the night they decreased significantly, although their drop was less pronounced than that during the control day.

CONCLUSION

The results of this study indicate that the decrease in blood pressure during sleep is the result of sleep itself rather than of the actual time of day.

Traumatic intrusive imagery as an emotional memory phenomenon: a review of research and explanatory information processing theories

Intrusive imagery is both a common response to trauma and a hallmark of Posttraumatic Stress Disorder. However, its features and underlying mechanisms have not been reviewed systematically. This paper delineates the characteristics of intrusions and critically reviews the literature, conceptualizing intrusive imagery as an emotional memory phenomenon. This approach integrates otherwise separate research arenas in emotion and memory, psychobiology, pharmacology, and physiology, which converge to suggest that intrusive imagery is driven primarily by affective arousal and sympathetic nervous system reactivity. These basic and applied research findings are addressed directly by three information processing theories, which are reviewed and critiqued for their heuristic value in accounting for intrusions. Directions for research, treatment, and assessment are presented.

Paradoxical failure of QT prolongation during cardioinhibitory neurocardiogenic syncope

QT modulation was explored in 31 patients with cardioinhibitory neurocardiogenic syncope. Despite a marked in increase in RR intervals, the QT interval remained stable.

Short-term variability of blood pressure during sleep in snorers with or without apnea

In normal subjects, the level and variability of blood pressure decrease during non-rapid eye movement (non-REM) sleep. In contrast, sleep apnea is associated with large swings in nocturnal pressure. In this study, we evaluated a computer-derived index of all-night blood pressure variability in normotensive snorers with or without sleep apnea. We also examined this index in snorers receiving medical treatment for coexistent ischemic heart disease. Beat-to-beat blood pressure was recorded with a photoplethysmographic device (Finapres) throughout polysomnography. Subjects were categorized into four groups: those without cardiovascular disease without or with sleep apnea (> or = 15 apnea plus hypopnea per hour of sleep), and those with ischemic heart disease without or with sleep apnea. A frequency distribution histogram of all increases and decreases of blood pressure according to their amplitudes was drawn and the SD of the distribution used as an estimation of variability. Mean systolic and diastolic pressures during the total sleep time were not different among the four groups. In contrast, the SD of the distribution of systolic and diastolic pressure variations that were higher in the apneic than in the nonapneic groups (P < .05) correlated with apnea plus hypopnea (P < .0001) and transient electroencephalographic arousal number per hour of sleep (P < .0001). In both apneic and nonapneic subjects, blood pressure variability as assessed by SD decreased during stages 3 and 4 of non-REM sleep compared with stages 1 and 2 and REM sleep (P < .001). Blood pressure variability was similarly increased in apneic subjects with or without ischemic heart disease. We speculate that in apneic individuals with coexistent ischemic heart disease, pressure variability that is increased despite treatment with beta-blockers or calcium antagonists may be a risk factor for acute coronary events.

Assessment of depth of midazolam sedation using objective parameters

OBJECTIVE

To determine the relationship between the clinically evaluated depth of midazolam-induced sedation and the cardiac beat-to-beat variability (RR variability) in ICU patients in the intensive care unit (ICU).

DESIGN

Prospective study.

SETTING

ICU of a university hospital.

PATIENTS

20 consecutive patients studied during weaning from mechanical ventilation and withdrawal of midazolam-induced sedation.

MEASUREMENTS AND RESULTS

After clinical evaluation of depth of sedation according to the Ramsay sedation score, the RR variability over 512 RR intervals and predominant respiratory rate were measured. The power spectrum of RR variability was calculated by a fast Fourier transformation and the resulting total frequency band (0.016-0.35 Hz) was subdivided into a very low, a low, and a high frequency band. Stepwise multiple regression analysis in the first 10 patients (group 1) showed a significant relationship between depth of sedation and measures of RR variability combined with respiratory rate (r2 = 0.59; F = 12.1; p < 0.001). The more effective sedation was, the more depressed were both RR variability and predominant respiratory rate. Mean heart rate, mean respiratory rate, median deviation of RR intervals from the mean, and the ratio between spectral power density in the high and the low frequency bands proved to be the most important predictors of the Ramsay score (+/-1 level accuracy: 87%, p < 0.001). Using this regression equation, the Ramsay score was predicted in the remaining 10 patients (group 2) with a +/-1 level of accuracy of 81% (p < 0.001).

CONCLUSION

In ICU patients, a significant correlation is found between the depth of midazolam-induced sedation as assessed by the Ramsay sedation score and RR variability, with a clinically sufficient prediction accuracy. RR variability can serve as an objective, continuously available, and non-invasive measurement to monitor midazolam-induced sedation in intubated and mechanically ventilated patients.

Sleep-related erectile activity

Sleep-related erections occur in all healthy, potent men in close temporal association with REM sleep. These erections are naturally occurring and can be assessed quantitatively. The nocturnal tumescence cycle seems unaffected by behavioral factors. Furthermore, sleep-related erections are present across the life span with only a slight decline in older healthy people. Analogous phenomena are present in women. The function of sleep-related erections is not known; however, they clearly involve vascular, neurologic, and hormonal mechanisms. Sleep-related erection testing provides a physiologic, objective, diagnostically useful technique for evaluating erectile capacity. Laboratory-based studies with comprehensive polysomnography offer the most complete diagnostic picture of erectile function available. Nonlaboratory procedures require further validation. The sleep-related tumescence pattern contains a wealth of information about the physiology and pathophysiology of erection. The coordination between REM sleep and erection, the differential expansion at the penile base and upper shaft, and the rate of circumference increase and decrease are meaningful indicators for determining if erectile dysfunction exists. Sleep-related erection testing indexes the magnitude and nature of organic involvement and takes the differential diagnosis of impotence beyond a simplistic psychogenic-organic dichotomy.

Autonomic changes associated with spontaneous coronary spasm in patients with variant angina

OBJECTIVES

This study sought to investigate whether changes in nervous autonomic tone may have a role in the mechanisms triggering spontaneous coronary spasm in variant angina.

BACKGROUND

Previous studies have suggested that both sympathetic and vagal activation may act as a trigger of epicardial artery spasm in patients with variant angina, but the actual role of autonomic changes in spontaneous coronary spasm remains unknown.

METHODS

We analyzed the changes in heart rate variability associated with episodes of ST segment elevation detected on Holter monitoring in 23 patients with variant angina (18 men, 5 women; mean [+/-SD] age 59 +/- 12 years). For study purposes, episodes of transmural ischemia lasting > or = 3 min and without any ST segment changes in the previous 40 min were selected for analysis. Heart rate variability indexes were calculated at 2-min intervals, at 30,15,5 and 1 min before ST elevation and at peak ST segment elevation. Ninety-three of 239 total ischemic episodes (39%) fulfilled the inclusion criteria.

RESULTS

The results showed that 1) high frequency (HF) (0.04 to 0.15 Hz), a heart rate variability index specific for vagal activity, decreased in the 2 min preceding ST segment elevation (p < 0.001) and returned to basal levels at peak ST segment elevation; 2) heart rate and low frequency (0.04 to 0.15 Hz), which are partially correlated with sympathetic activity, showed a significant increase at peak ST segment elevation (p < 0.001 for both); 3) the pattern of the HF reduction before ST segment elevation was consistently confirmed in several subgroups of ischemic episodes, including those of patients with or without coronary stenoses, those of patients with anterior or inferior ST segment elevation, those occurring during daily or nightly hours and silent episodes. There were no significant variations in heart rate variability in control periods selected from Holter tapes of patients and before ST segment elevation induced by balloon inflation in 20 patients undergoing coronary angioplasty.

CONCLUSIONS

Our data show that changes in autonomic tone are likely to contribute to trigger or predispose to epicardial spasm. In particular, although not excluding an active role for adrenergic mechanisms, our data suggest that a vagal withdrawal may often be a component of the mechanisms leading to spontaneous coronary vasospasm.

Pathophysiologic and therapeutic implications of sleep apnea in congestive heart failure

Obstructive and central sleep apnea are common in patients with congestive heart failure (CHF). These sleep-related breathing disorders are characterized by two pathophysiologic features that could have important implications for disease progression in CHF: sympathetic nervous system activation, and adverse changes in cardiac loading conditions. In patients with obstructive sleep apnea, blood pressure is frequently elevated as a result of excessive sympathetic nervous system activity elicited by the combination of apnea, hypoxia, and arousals from sleep. The generation of exaggerated negative intrathoracic pressure during obstructive apneas further increases left ventricular afterload, reduces cardiac output, and may promote the progression of pump failure. Increased afterload and hypoxia can also predispose such patients to myocardial ischemia and arrhythmias. In patients with CHF, abolition of coexisting obstructive sleep apnea by nasal continuous positive airway pressure improves left ventricular function. Central sleep apnea (i.e., Cheyne-Stokes respiration) is also characterized by apnea, hypoxia, and increased sympathetic nervous system activity and, when present in CHF, is associated with increased risk of death. Recent medium-term trials involving small numbers of patients have demonstrated that nocturnally applied continuous positive airway pressure in patients with CHF and central sleep apnea alleviates central sleep apnea, improves left ventricular function, reduces sympathetic nervous system activity and improves symptoms of CHF. These studies emphasize the importance of considering obstructive and central sleep apnea in the differential diagnosis of conditions that could contribute to the development or progression of CHF. They also suggest that continuous positive airway pressure is a promising nonpharmacologic adjunctive therapy for patients with CHF and coexisting sleep-related breathing disturbances that warrants further investigation.

Endocrine mechanisms of blood pressure rhythms

The temporal organization of blood pressure is mainly controlled by neuroendocrine mechanisms. The monoaminergic systems appear to integrate the major driving factors of temporal variability, but evidence also indicates a role of the hypothalamic-pituitary-adrenal, hypothalamic-pituitary-thyroid, opioid, renin-angiotensin-aldosterone, and endothelial systems as well as other vasoactive peptides. Although their hormonal secretions are typically episodic, the probability of secretory episodes is "gated" by mechanisms that are coupled either to sleep or to an endogenous pacemaker which usually is predominantly (though not only) circadian. 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. Hence, physical, mental, and pathologic stimuli, which may drive activation or inhibition of these neuroendocrine effectors of biologic rhythmicity, may also interfere with the temporal blood pressure structure. On the other hand, the immediate adaptation of the exogenous components of blood pressure rhythms to the demands of the environment are modulated by the circadian-time-dependent responsiveness of the biologic oscillators and their neuroendocrine effectors. These notions may contribute to a better understanding of the pathophysiology and therapeutics of changes in blood pressure.

Relationships of the circadian rhythms of thrombotic, ischemic, hemorrhagic, and arrhythmic events to blood pressure rhythms

Convincing evidence has recently accumulated that several unfavorable cardiovascular events show a well defined pattern in their occurrence throughout the day. Myocardial angina and infarction, sudden cardiac death, arrhythmias, fatal pulmonary thromboembolism, and ischemic and hemorrhagic cerebrovascular accidents occur more frequently in the morning, after awaking, until noon. Diurnal variations in multiple biologic functions, such as assumption of an upright posture associated with increased platelet aggregability, changes in blood clotting, fibrinolysis, and vascular tone and resistance, may be potentially active triggering factors. Moreover, variations in sympathetic tone, catecholamine secretion, and blood pressure have to be considered. The role of triggering factors and their relationships with blood pressure patterns is discussed in view of an optimized pharmacologic treatment.

Circadian rhythm of arterial blood pressure and albuminuria in diabetic nephropathy

The aim of our study was to evaluate the diurnal relationship between arterial blood pressure and albuminuria, and some potential mechanisms responsible for impaired nocturnal blood pressure reduction (non-dippers, groups I and II) in diabetic nephropathy (DN). Twenty-four-hour ambulatory blood pressure, heart rate (HR) variation (autonomic nervous function) and extracellular fluid volume (ECV) were measured, and urine samples were collected three times during the corresponding day- and nighttimes in 47 insulin-dependent diabetic (IDDM) patients with DN. Mean arterial blood pressure (MABP) during the daytime [mm Hg, median (range)] was identical in group I [105 (96-137)], group II [109 (86-124)] and group III [dippers; average blood pressure reduction from day to night > 10%, 107 (93-132), P = NS], while the nighttime MABP differed [group I, 106 (95-144); group II, 100 (78-118); group III, 91 (76-118); P < 0.001]. No significant difference between the groups concerning the daytime or nighttime albuminuria [microgram/min; median (range)] was observed; [Day: group I, 1467 (235-3933); group II, 695 (170-6719); group III, 875 (228-3173). Night: group I, 1079 (279-4665); group II, 572 (113-3807); group III, 659 (81-2493)]. A significant correlation between MABP and albuminuria was demonstrated during day- (rho = 0.50, P < 0.0005) and nighttime (rho = 0.46, P < 0.005), while neither the absolute nor the relative changes in MABP from day to night correlated significantly with absolute or relative changes in albuminuria from day to night. The night/day ratio of HR was higher in group I [0.93 (0.76-1.09), median (range)] compared to group III [0.83 (0.74-1.02), P < 0.005] and a significant correlation between this ratio and the night/day ratio of MABP was found (rho = 0.54, P < 0.0005). ECV was about the same in the three groups. Our study indicated an association between blood pressure and albuminuria, but the mechanisms involved in the reduction of albuminuria from day to night was not unraveled. A relative lack of sympathetic withdrawal during sleep seems to be an important feature of nocturnal hypertension in diabetic nephropathy.

Relationship of ventricular tachycardia to sleep/wakefulness in a model of sudden cardiac death

Death from some childhood disorders such as sudden infant death syndrome and the congenital long QT syndrome are associated with specific behaviors such as sleep or emotional stress. We studied young German shepherd dogs that die suddenly during presumed sleep. These dogs have inherited ventricular tachycardia (VT) which is most frequent during sinus bradycardia and sinus arrhythmia. We hypothesized that the number of VT complexes (three or more consecutive ectopic complexes) would be greatest during sleep. Moreover, we hypothesized that pauses in the sinus rhythm of greater than 1000 ms would be greatest in the behavior with the most frequent VT. Behavioral states [excited, ambulatory, sitting, lying, rapid eye movement (REM) sleep] were quantified from 24-h video recordings of seven dogs. VT and pauses were quantified for each behavior using simultaneously recorded ECGs. A multivariate model was used to analyze the results. After controlling for time of day, lying, and REM sleep were significantly (p < 0.02) associated with VT, whereas more active behaviors were not. Time of day also independently affected the number of VT complexes. However, behavior and time of day did not account for all of the variability in the number of VT complexes. Pauses were significantly associated with behavior, with the highest number of pauses occurring during lying and REM sleep. However, pauses were not always associated with VT, indicating that a pause was a necessary, but not sufficient, condition for the development of VT. These results suggest that modulation of VT incidence in these animals is multifactorial and that the highest number of VT complexes is associated with the bradycardia that accompanies REM sleep.

Periodic limb movements during sleep in patients with congestive heart failure

The prevalence of periodic limb movements (PLM) during sleep and their effect on sleep and daytime alertness were determined in 23 men with severe, stable congestive heart failure (CHF) and 9 healthy control subjects. Each subject had overnight polysomnography and the following day completed a subjective assessment of daytime sleepiness (Epworth Sleepiness Scale [ESS]) and a multiple sleep latency test (MSLT). The proportion of CHF patients with moderately severe PLM (>25/h) was significantly higher (52%) than control subjects (11%). CHF patients were subdivided into two groups, those with more than 10 PLM per hour (group 1, n=15) and those with less than 10 PLM per hour (group 2, n=8). Group 1 had a significantly higher frequency of PLM (group 1, 73 +/- 50; group 2, 4 +/- 4; control, 11 +/- 12/h) and associated arousals from sleep (group 1, 14 +/- 13; group 2, 2 +/- 3; control subjects, 1 +/- 1/h) than group 2 and the control group, and had more stage 1 and 2 nonrapid eye movement sleep than the control group (group 1, 77 +/- 11; group 2, 71 +/- 11; control, 63 +/- 9% total sleep time). Mean sleep latency on the MSLT was significantly shorter in group 1 than the control group (group 1, 6.1 +/- 2.9; group 2, 9 +/- 6.7; control subjects, 12.4 +/- 1.9 min). Although the ESS score was highest in group 1, this did not reach statistical significance. We conclude that PLM are more prevalent in patients with CHF and may contribute to their sleep/wake complaints.

Improvement of exercise capacity with treatment of Cheyne-Stokes respiration in patients with congestive heart failure

OBJECTIVES

The aim of this study was to determine the impact of nasal nocturnal oxygen therapy on respiration, sleep, exercise capacity, cognitive function and daytime symptoms in patients with congestive heart failure and Cheyne-Stokes respiration.

BACKGROUND

Cheyne-Stokes respiration is common in patients with congestive heart failure and is associated with significant nocturnal oxygen desaturation and sleep disruption with arousals. Oxygen desaturations and arousals cause an increase in pulmonary artery pressure and sympathoneural activity and therefore may reduce exercise capacity. Oxygen is an effective treatment of Cheyne-Stokes respiration and should improve exercise capacity in these patients.

METHODS

The study was designed as a randomized crossover, double-blind, placebo-controlled trial: 22 patients were assigned to 1 week each of nocturnal oxygen and room air. After each week, polysomnography, maximal bicycle exercise with expiratory gas analysis and trail-making test were performed, and a health assessment chart was completed.

RESULTS

Nocturnal oxygen significantly reduced the duration of Cheyne-Stokes respiration (162 +/- 142 vs. 88 +/- 105 min [mean +/- SD]; p < 0.005). Sleep improved as evidenced by less stage 1 sleep and fewer arousals (20 +/- 13 vs. 15 +/- 9/h total sleep time; p < 0.05) as well as more stage 2 and slow-wave sleep; nocturnal oxygen saturation also improved. Peak oxygen consumption during exercise testing increased after oxygen treatment (835 +/- 395 vs. 960 +/- 389 ml/min; p < 0.05). Cognitive function evaluated by the trail-making test improved, but daytime symptoms in the health assessment chart did not improve significantly.

CONCLUSIONS

Successful treatment of Cheyne-Stokes respiration with nocturnal nasal oxygen improves not only sleep, but also exercise tolerance and cognitive function in patients with congestive heart failure.

Life-threatening cardiovascular consequences of anger in patients with coronary heart disease

Anger is the affective state most commonly associated with myocardial ischemia and life-threatening arrhythmias. The scope of the problem is sizeable-at least 36,000 (2.4% of 1.5 million) heart attacks are precipitated annually in the United States by anger. The lethal cardiovascular consequences in ischemic heart disease are attributable to the unique physiology of this state, which activates high-gain central neurocircuitry and the sympathetic nervous system, leading to acute sinus tachycardia, hypertension, impaired myocardial perfusion, and a high degree of cardiac electrical instability. Exciting new tools have emerged from the fields of epidemiology, behavioral medicine, and cardiovascular physiology that offer considerable promise in accelerating our understanding of the pathophysiology of anger and in developing means to sever the link between anger and its life-threatening consequences.

Overnight heart rate and cardiac function in patients with dual chamber pacemakers

Animal data indicate that chronic, overnight pacing at normal evening heart rates impairs cardiac function. We examined the relationship of pacing rate and cardiac function in nine patients with dual-chamber pacemakers. We investigated two, 3-week pacing regimens (80 and 50 ppm: DDD mode) in a cross-over design. Doppler echocardiograms were performed at 1700 hours (PM) and 0600 hours (AM) at the end of each regimen. Ventricular function and preload decreased overnight (PM vs AM) with both pacing regimens. Compared to the morning values, the ratio of preejection to ejection time (PEP/ET) rose (0.43 vs 0.46), while the mean velocity of circumferential fiber shortening (Vcf) fell (1.16 cm/s vs 1.11 cm/s). Stroke volume (SV) (61 mL vs 53 mL) and ejection fraction (EF) also fell (0.56 vs 0.53) in the morning. End-diastolic volume (EDV) (94 mL vs 88 mL) decreased in the morning, as did the ratio of passive to active filling (E/A) (1.06 vs 0.96). Isovolumic relaxation time (91 ms vs 101 ms) increased overnight at both pacing rates. Systolic function decreased at 80 ppm relative to 50 ppm at both times of day. SV fell (54 mL vs 61 mL), while both EDV (92 mL vs 90 mL) end-systolic volume (ESV) increased (43 mL vs 40 mL). Contractility measured by Vcf (1.09 cm/s vs 1.18 cm/s) and PEP/ET (0.49 vs 0.41) was reduced at 80 ppm. The heart needs to rest at night by slowing its rate of contraction. Pacing at 80 ppm impairs systolic and diastolic ventricular function compared to 50 ppm. Longer term consequences of ostensibly physiological pacing rates merit inquiry, particularly in those with preexisting cardiac dysfunction.

Hemodynamic changes as triggers of cardiovascular events

Although a large number of clinical studies during the past decade have documented that myocardial ischemia, acute myocardial infarction, and sudden cardiac death have definite circadian patterns, recently published work suggests that it is not necessarily a specific time of the day but the sleep/wake cycle and postural changes as well as the balance between triggers and protective factors that determine the onset of cardiovascular events. A clear understanding of the pathophysiologic processes responsible for ischemic events and the specific roles played by various triggers would be helpful in better defining the therapeutic strategies designed for the prevention and treatment of acute cardiac events. Because changes in hemodynamic parameters are of paramount importance in initiating an ischemic event, it is critical to review their role and relationship in the pathogenesis of acute coronary events.

Cardiac sympathovagal balance during sleep apnea episodes

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 woman (correction for 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.

Sleep fragmentation as a risk factor for hypertension in middle-aged nonapneic snorers

Although a high prevalence of hypertension has been observed in snorers, whether there is a direct link between hypertension and snoring remains controversial. It has recently been demonstrated that an abnormal amount of breathing effort during snoring is responsible for sleep fragmentation even in the absence of sleep apnea syndrome criteria. We hypothesized that sleep fragmentation during snoring may be a direct risk factor for the development of hypertension. On the basis of polysomnographic data, 105 nonapneic patients between 40 and 65 years of age referred for snoring with social impairment were selected and categorized as snorers with (n=55) or without sleep fragmentation (n=50) based on whether the arousals index was 10 or greater or less than 10/h of sleep, respectively. Sleep distribution did not differ between the two groups, except for a longer duration of wake after sleep onset (58 +/- 43 min vs 42 +/- 38 min) and a shorter duration of slow-wave sleep in the group with sleep fragmentation (72 +/- 34 min vs 97 +/- 34 min). Although there were no statistically significant differences between the snorers with and without sleep disruption in terms of age (51.3 +/- 7.7 vs 48.6 +/- 6.0 years), body mass index (26.9 +/- 4.0 vs 27.2 +/- 5.5 kg/m2), sex ratio, respiratory indexes during sleep, daytime sleepiness, and daytime tiredness, prevalence of systemic hypertension was significantly higher in the sleep-fragmented group (20/55 vs 7/50). This significant difference persisted (16/51 vs 6/49) when patients using antihypertensive drugs with possible effects on the CNS were excluded. Our data suggest that sleep fragmentation is common in patients who seek medical help for snoring with social impairment and may play a role in the development of hypertension.

Phenylephrine-induced ventricular arrhythmias in dogs with inherited sudden death

INTRODUCTION

Dogs with an inherited predisposition to sudden death display ventricular arrhythmias having certain characteristics, such as pause dependence, that are suggestive of early afterdepolarization-induced triggered activity. We hypothesized that alpha-adrenergic stimulation may facilitate the development of these arrhythmias by inducing a reflex bradycardia and by exerting a direct myocardial effect.

METHODS AND RESULTS

Twenty affected dogs and 7 unaffected dogs were studied. The incidence and severity of ventricular arrhythmias were determined after administration of phenylephrine (0.01 mg/kg IV), with or without pretreatment with propranolol (0.1 to 0.3 mg/kg IV), atropine (0.04 mg/kg IV), or prazosin (0.5 mg/kg IV). Third-degree heart block was induced by AV nodal ablation in 4 affected dogs. Phenylephrine increased ventricular arrhythmias in affected dogs, with or without pretreatment with propranolol, but did not induce ventricular arrhythmias in unaffected dogs. In dogs with intact AV nodal conduction, atropine increased sinus rate, which suppressed baseline and phenylephrine-induced arrhythmias. In dogs with heart block, arrhythmias were increased during baseline and after phenylephrine, with or without pretreatment with atropine. Prazosin and overdrive ventricular pacing suppressed phenylephrine-induced arrhythmias.

CONCLUSION

Phenylephrine increases ventricular arrhythmias in dogs with inherited sudden death via both an induction of reflex bradycardia and a direct myocardial effect. Superimposition of heightened alpha-adrenergic and vagal tone may facilitate the development of sudden death in these animals.

Investigating the relationship between stroke and obstructive sleep apnea

BACKGROUND AND PURPOSE

We aimed to prospectively determine whether the incidence of obstructive sleep apnea in patients with recent stroke was significantly different from that of a sex- and age-matched control group with no major medical problems.

METHODS

We prospectively performed overnight polysomnography in 24 patients with a recent stroke (13 men and 11 women; mean age [+/- SD], 64.6 +/- 10.4 years) and 27 subjects without stroke (13 men and 14 women; mean age, 61.6 +/- 8.8 years). Patients with either ischemic or hemorrhagic stroke were entered into this study. Polysomnographic evaluations were performed within approximately 2 to 5 weeks after each patient's stroke.

RESULTS

Obstructive sleep apnea was found in 10 of 13 men with stroke (77%) and in only 3 of 13 male subjects without stroke (23%) (P=.0169). Seven of 11 women with stroke (64%) had obstructive sleep apnea, while only 2 of 14 female subjects without stroke (14%) had obstructive sleep apnea (P=.0168). For men with stroke, the mean apnea/hypopnea index (+/- SE) was 21.5 +/- 4.2 events per hour, while for male subjects without stroke it was 4.8 +/- 1.8 events per hour (P=.0014). For women with stroke the mean apnea/hypopnea index was 31.6 +/- 8.8 events per hour, while for female subjects without stroke it was 2.9 +/- 1.6 events per hour (P=.0024). The 4-year mortality for patients with stroke was 20.8%. All patients with stroke who died had obstructive sleep apnea.

CONCLUSIONS

Patients with stroke have an increased incidence of obstructive sleep apnea compared with normal sex- and age-matched control subjects. Hypoxia and hemodynamic responses to obstructive sleep apnea may have predisposed these patients to stroke.

Sleep and depression in combat-related PTSD inpatients

The sleep of 27 unmedicated Vietnam combat-related posttraumatic stress disorder (PTSD) inpatients was monitored for 3 nights. Depressive comorbidity was considered both as a diagnostic category using DMS-III-R criteria, and as a continuous variable using the Beck Depression Inventory (BDI). Data collected included sleep architecture features that have discriminated unipolar depressives from controls in many prior studies, rapid eye movement (REM) sleep latency, and slow-wave sleep time, as well as two additional indices that have sometimes discriminated depressives from controls in waking studies-baseline heart rate and facial electromyography. Structured Clinical Interview for the DSM-III-R (SCID)-diagnosed PTSD+major depressive disorder (MDD) patients failed to exhibit shorter REM latencies, greater REM percents of sleep, or greater REM densities than PTSD-MDD patients, but did exhibit less slow wave sleep. PTSD+MDD patients also exhibited less facial (mentalis) electromyographic activity. REM densities and baseline heart rates were equivocal. REM density, baseline heart rate, and mentalis electromyography all correlated with the BDI, the former two positively, the last, negatively. In summary, SCID-diagnosed PTSD+MDD patients failed to exhibit the classic REM sleep architectural modifications associated with unipolar depression, despite the fact that several other psychophysiologic indices of dysphoria were detectable in their sleep.

Role of hypoxemia in sleep apnea-induced sympathoexcitation

The importance of hypoxemia in determining sympathoexcitation during obstructive sleep apnea was examined by comparing changes in efferent sympathetic nerve activity (SNA) during spontaneous obstructive apneas with hypoxemia alone of similar magnitude and duration induced by 1-4 breaths of 100% nitrogen in six patients with obstructive sleep apnea and with spontaneous apneas while breathing 100% oxygen (apnea without hypoxemia) in three patients. In addition, eight control subjects were studied during induced hypoxemia. The magnitude of sympathoexcitation during spontaneous apneas (103 +/- 15%) was more than twice that observed during induced hypoxemia (47 +/- 14%) during episodes in which the nadir of oxygen desaturation (78 +/- 2 and 75 +/- 2%, respectively) and duration of hypoxemia (27 +/- 3 and 33 +/- 3 s, respectively) were the same (P > 0.20). Similarly, in three patients SNA increased 115% during normoxic spontaneous obstructive apneas, but increased only 43% during hyperoxic spontaneous obstructive apneas in which oxygen saturation did not decrease significantly. Sympathetic neural responses to induced hypoxemia in control subjects (17 +/- 7%) were significantly less than that of the sleep apnea patients. We conclude that hypoxemia contributes importantly, but is not the sole determinant of the sympathoexcitation provoked during episodes of obstructive sleep apnea.

Possible involvement of an endogenous benzodiazepine receptor ligand of the inverse agonist type in the regulation of rapid-eye movement (REM) sleep: an hypothesis

1. Rapid-eye movement (REM) sleep is a complex behavioral state characterized by desynchronized electroencephalographic (EEG) activity, postural atonia, rapid, saccadic movements of the eyes, and vivid dreaming. 2. A recently developed class of drugs, the inverse agonist beta-carboline-3-carboxylates, elicits a number of effects similar to the properties of REM sleep, such as desynchronized cortical EEG and penile erections. 3. The hypothesis is put forth that an endogenous beta-carboline-3-carboxylate exists which may initiate many aspects of REM sleep. 4. Clinical relevance of this hypothesis is discussed with regard to REM anxiety dreams, night terrors, narcolepsy, and depression.

Postganglionic sympathetic discharge in neonatal swine

We hypothesized that cardiac and respiratory modulation of postganglionic peroneal activity appeared in an age-related manner. In anesthetized, paralyzed and artificially ventilated piglets, simultaneous recordings of efferent phrenic and peroneal discharges were obtained during hyperoxia (fraction of inspired oxygen, FiO2 = 1.0) and hypoxia (FiO2 = 0.1). Spectral analyses of peroneal and aortic blood pressure signals revealed peaks at the cardiac frequency (3.25-5.0 Hz). Coherence analysis showed that these two signals were highly correlated at those frequencies, providing evidence for baroreceptor entrainment. Statistically significant (p < 0.05) increases of coherence values were observed during hypoxic stimulation. Such results were observed in most animals despite age, and provided evidence of a potent mechanism for insuring vasomotor tone even in newborn animals. In contrast, spontaneous respiration-related peroneal discharges were observed only in animals > or = 20 d old. In animals < 20 d old, hypoxic stimulation elicited respiration-related discharges in peroneal activity. In many cases, peroneal hypoxic discharges exhibited an immature biphasic response pattern despite the presence of a mature response pattern of phrenic activity. Such findings suggest a developmental lag in the linkages of respiratory and sympathetic controlling networks.

Effects of aging on glucose regulation during wakefulness and sleep

Glucose intolerance, reduced sleep efficiency, and disturbed circadian rhythmicity occur in aging. In normal young subjects, glucose regulation is modulated by sleep and circadian rhythmicity. To examine age-related alterations in the temporal pattern of glucose tolerance and insulin secretion, eight modestly overweight healthy older men, eight weight-matched young men, and six young lean men were studied during constant glucose infusion for 53 h. Levels of glucose, insulin, C-peptide, and growth hormone (GH) were measured every 20 min. Rates of insulin and GH secretion were calculated by deconvolution. In older volunteers, sleep ws shallow and more fragmented than in young subjects but was nevertheless associated with robust glucose elevations. However, postsleep increases of insulin secretion were markedly dampened. During wakefulness, the normal morning-to-evening increase in glucose was preserved in the elderly, but insulin secretion failed to increase proportionately. Thus decreased glucose tolerance in aging is associated with insulin resistance and also with a relative insensitivity of the beta-cell to the modulation of glucose regulation by sleep and circadian rhythmicity.

Effects of beta adrenergic receptor blockade on hemodynamic changes associated with obstructive sleep apnea

To study the effects of airway obstruction (AWO) and arousal on coronary blood flow, mean arterial pressure (MAP) and heart rate (HR), pigs were chronically instrumented with arterial catheters, Doppler flow probes on the left circumflex coronary artery, and electrodes for determination of sleep stages. A modified balloon catheter was placed in the trachea to obstruct the upper airway during sleep. Following control studies, the role of beta adrenergic receptors in hemodynamic responses to AWO was assessed by administering propranolol, a beta adrenoreceptor blocking agent. In control studies, during nonrapid eye movement sleep (NREM), MAP was 85 +/- 2 mmHg before AWO and increased by 8 +/- 2 mmHg upon arousal. Mean arterial pressure was lower during rapid eye movement (REM) sleep (64 +/- 2 mmHg) and the increase upon arousal was threefold greater (22 +/- 2 mmHg). Heart rate was similar in both sleep stages (NREM 123 +/- 5 bpm; REM 125 +/- 6 bpm) and increased significantly upon arousal (NREM, 11 +/- 2 bpm; REM, 18 +/- 3 bpm increase). Coronary blood flow was similar during both stages (NREM 44 +/- 5 ml/min; REM 44 +/- 6 ml/min) and increased by 13% (NREM) and 22% (REM) during arousal. Coronary vascular resistance increased significantly by 17% during arousal from AWO during REM sleep. All changes were significant at p < 0.05. Following beta adrenergic receptor blockade studies using propranolol, baseline HR was reduced in NREM sleep and HR and coronary blood flow increases during arousal from apnea were eliminated. Adrenoreceptor blockade studies suggest that these effects were mediated by the beta adrenergic component of the sympathetic nervous system.

Independent autonomic modulation of the human sinus and AV nodes: evidence from beat-to-beat measurements of PR and PP intervals during sleep

INTRODUCTION

Evidence from animal experiments indicates that the autonomic nervous system may influence the sinus (SA) and atrioventricular (AV) nodes differently. We investigated, therefore, whether there are spontaneous functional differences in the innervation of the SA and AV nodes in man.

METHODS AND RESULTS

This study was performed in 10 healthy males (ages 21 to 26 years) during strict bed rest from 10 pm to 6 am. Three ECG leads were digitized on-line. PR and PP intervals were determined on a beat-to-beat basis off-line using a correlation algorithm with an accuracy of +/- 2 msec and were verified visually. During major body movements, there were sudden decreases in PP intervals of 36 to 827 msec (mean 335) for periods of 6 to 265 seconds (mean 24). During these phases of heart rate (HR) acceleration, PR intervals showed either concomitant shortening (9 to 30 msec), no change, or lengthening (6 to 25 msec). Furthermore, tonic changes in the PR interval occurred over 15-minute periods during which the range of PP intervals was constant. Additionally, recovery-adjusted PR interval (PR-b2/RP) and cycle length were negatively correlated for some periods, which confirmed independent autonomic effects on SA node and AV node.

CONCLUSION

Beat-to-beat measurement of PR intervals allows for evaluation of autonomic effects on the human AV node. The different patterns in PR intervals during sudden spontaneous increases in HR and the tonic changes in PR interval indicate that the autonomic inputs to the SA and AV nodes are, in principle, independent of each other.

Slow wave electroencephalic activity parallels renin oscillations during sleep in humans

Previous studies have demonstrated that the nocturnal oscillations of plasma renin activity (PRA) exactly reflect rapid eye movement (REM) non-REM (NREM) sleep alternation with levels of PRA that increase during NREM sleep and decrease during REM sleep. These studies were based exclusively on conventional scoring of sleep stages. In the present study, we used spectral analysis of the sleep EEG to determine the variations in the different EEG frequency bands, together with PRA profiles. Eight male volunteers participated in a 1 night study. They were subjected to 8 h polysomnography including spectral analysis of the EEG, and to blood sampling every 10 min. Delta relative power and Sleep Intensity Index and PRA oscillations ran parallel in all individuals. An increase in slow waves was associated with an increase in PRA, whereas a decrease was associated with a decrease in PRA. Cross-correlation coefficients were significant and ranged between 0.34 and 0.74. Conversely, theta, alpha and beta bands and the EEG mean frequency were inversely proportional to PRA, with lower cross-correlation coefficients. These results may give further support to the hypothesis of a common mechanism controlling both SWA and renin release from the kidney.

Sympathetic neural mechanisms in obstructive sleep apnea

Blood pressure, heart rate, sympathetic nerve activity, and polysomnography were recorded during wakefulness and sleep in 10 patients with obstructive sleep apnea. Measurements were also obtained after treatment with continuous positive airway pressure (CPAP) in four patients. Awake sympathetic activity was also measured in 10 age- and sex-matched control subjects and in 5 obese subjects without a history of sleep apnea. Patients with sleep apnea had high levels of nerve activity even when awake (P < 0.001). Blood pressure and sympathetic nerve activity did not fall during any stage of sleep. Mean blood pressure was 92 +/- 4.5 mmHg when awake and reached peak levels of 116 +/- 5 and 127 +/- 7 mmHg during stage II sleep (n = 10) and rapid eye movement (REM) sleep (n = 5), respectively (P < 0.001). Sympathetic activity increased during sleep (P = 0.01) especially during stage II (133 +/- 9% above wakefulness; P = 0.006) and REM (141 +/- 13%; P = 0.007). Peak sympathetic activity (measured over the last 10 s of each apneic event) increased to 299 +/- 96% during stage II sleep and to 246 +/- 36% during REM sleep (both P < 0.001). CPAP decreased sympathetic activity and blood pressure during sleep (P < 0.03). We conclude that patients with obstructive sleep apnea have high sympathetic activity when awake, with further increases in blood pressure and sympathetic activity during sleep. These increases are attenuated by treatment with CPAP.

Cardiovascular autonomic control is disturbed in nocturnal teethgrinders

To examine the hypothesis of disturbed autonomic function, non-invasive cardiovascular reflex tests were performed on 11 sleep bruxists in the waking state. The tests included the Valsalva manoeuvre, a deep-breathing test, and an orthostatic test (standing up). The R-R intervals were monitored continuously, and blood pressure was measured non-invasively and continuously using the Finapres method. In total, 64% of bruxists showed abnormalities in at least two variables reflecting the cardiovascular autonomic function. Abnormalities were found in blood pressure regulation during the Valsalva strain, and in the immediate biphasic heart rate response during standing up, but not in the vagally mediated deep-breathing difference. These findings suggest that bruxism is accompanied by abnormalities in autonomic function, particularly in sympathetic vasoconstrictor function.

Circadian profile of systemic hemodynamics

We determined the continuous 24-hour profile of mean arterial pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance in eight healthy ambulatory volunteers. Beat-to-beat intra-arterial blood pressure was recorded with the Oxford system; subjects were ambulant during daytime and slept at night. Beat-to-beat stroke volume was determined by the pulse contour method from the arterial pulse wave. During the nighttime, compared with the daytime average, there was a decrease in blood pressure (9 mm Hg), heart rate (18 beats per minute), and cardiac output (29%); stroke volume showed a small decrease (7%), and total peripheral resistance increased unexpectedly by 22%. When subjects arose in the morning a steep increase in cardiac output and decrease in total peripheral resistance were found. Comparable changes were seen during a period of supine resting in the afternoon, whereas physical exercise caused opposite changes in hemodynamics. This pattern was observed in all subjects. We conclude that the circadian pattern of cardiac output and total peripheral resistance originates from the day-night pattern in physical activity: during the nighttime, blood flow to the skeletal muscles is decreased through local autoregulation, which increases total peripheral resistance and decreases cardiac output compared with the daytime.