Comparison of standard autonomic tests and power spectral analysis in normal adults

Haemodynamic effects of hyperventilation on healthy men with different levels of autonomic tone

The topicality of the research is stipulated by insufficient study of the correlation between the functional state of the cardiorespiratory system and autonomic tone. The goal of the research was to analyze the changes of central haemodynamics with 10-minute regulated breathing at the rate of 30 cycles per minute and within 40 minutes of recovery after the test in healthy young men with different levels of autonomic tone. Records of the chest rheoplethysmogram were recorded on a rheograph KhAI-medica standard (KhAI-medica, Kharkiv, Ukraine), a capnogram - in a lateral flow on a infrared capnograph (Datex, Finland), and the duration of R-R intervals was determined by a Polar WIND Link in the program of Polar Protrainer 5.0 (Polar Electro OY, Finland). Systolic and diastolic blood pressure were measured by Korotkov’s auscultatory method by mercury tonometer (Riester, Germany). The indicator of the normalized power of the spectrum in the range of 0.15–0.40 Hz was evaluated by 5-minute records; three groups of persons were distinguished according to its distribution at rest by the method of signal deviation, namely, sympathicotonic, normotonic and parasympathicotonic. The initial level of autonomic tone was found to impact the dynamics of СО2 level in alveolar air during hyperventilation and during recovery thereafter. Thus, PetCО2 was higher (41.3 mm Hg) in parasympathicotonic than in sympathicotonic (39.3 mm Hg) and normotonic (39.5 mm Hg) persons. During the test, R-R interval duration decreased being more expressed in normotonic persons. At the same time, the heart index was found to increase in three groups, and general peripheral resistance – to decrease mostly in normo- and parasympathicotonic persons. In addition, the reliable increase of stroke index and heart index was found in these groups. In the recovery period after hyperventilation, the decrease of tension index and ejection speed was found in normo- and, particularly, parasympathicotonic compared with sympathicotonic men and the increase of tension phase and ejection phase duration.

Abnormal small bowel motility in patients with hereditary transthyretin amyloidosis

BACKGROUND

Gastrointestinal complications are common in hereditary transthyretin amyloid (ATTRm) amyloidosis. The underlying mechanisms have not been fully elucidated, and the patients' small bowel function remains largely unexplored. The aim of the present study was to compare the small bowel motility in ATTRm amyloidosis patients with that in non-amyloidosis patient controls.

METHODS

ATTRm amyloidosis patients undergoing evaluation for liver transplantation were consecutively investigated with 24-hour duodenojejunal manometry (n = 19). The somatostatin analogue octreotide was used to induce fasting motility. Patients with age at onset of ≥50 years were defined as late-onset cases. For each patient, three age- and sex-matched patient controls (n = 57) were selected from the total pool of investigated patients.

KEY RESULTS

Manometry was judged as abnormal in 58% of the patients and in 26% of the patient controls (P = .01). Patients displayed significantly more daytime phase III migrating motor complexes than patient controls (median 4 vs 2, P < .01), and had a higher frequency of low-amplitude complexes (16% vs 4%; however, this difference did not reach statistical significance, P = .10). Furthermore, late-onset patients showed a delay in octreotide response (5.4 vs 3.8 minutes, P < .01), but this was not observed for early-onset patients or within the control group.

CONCLUSIONS AND INFERENCES

Patients with ATTRm amyloidosis displayed abnormalities in their small bowel motility more frequently than non-amyloidosis patient controls, and the manometric pattern was probably best consistent with a combined neuromyopathic disorder. The delayed octreotide response in late-onset patients warrants further investigation.

Gastric emptying in hereditary transthyretin amyloidosis: the impact of autonomic neuropathy

BACKGROUND

Gastrointestinal (GI) complications are common in hereditary transthyretin amyloidosis and an autonomic dysfunction has been considered to explain these symptoms. The aim of this study was to investigate the impact of autonomic neuropathy on gastric emptying in hereditary transthyretin amyloidosis and to relate these findings to nutritional status, GI symptoms, gender, and age at disease onset.

METHODS

Gastric emptying was evaluated with gastric emptying scintigraphy. Spectral analysis of the heart rate variability and cardiovascular responses after tilt test were used to assess the autonomic function. The nutritional status was evaluated with the modified body mass index (s-albumine × BMI).

KEY RESULTS

Gastric retention was found in about one-third of the patients. A weak correlation was found between the scintigraphic gastric emptying rate and both the sympathetic (rs = -0.397, P < 0.001) and parasympathetic function (rs = -0.282, P = 0.002). The gastric emptying rate was slower in those with lower or both upper and lower GI symptoms compared with those without symptoms (median T(50) 123 vs 113 min, P = 0.042 and 192 vs 113 min, P = 0.003, respectively). Multiple logistic regression analysis showed that age of onset (OR 0.10, CI 0.02-0.52) and sympathetic dysfunction (OR 0.23, CI 0.10-0.51), but not gender (OR 0.76, CI 0.31-1.84) and parasympathetic dysfunction (OR 1.81, CI 0.72-4.56), contributed to gastric retention.

CONCLUSIONS AND INFERENCES

Gastric retention is common in hereditary transthyretin amyloidosis early after onset. Autonomic neuropathy only weakly correlates with gastric retention and therefore additional factors must be involved.

Autonomic nervous system laboratories: a European survey

We present a questionnaire-based survey on methods adopted in European autonomic nervous system (ANS) laboratories in the year 2002. Seventy-nine laboratories from 16 countries in Western and Eastern Europe provided information on test methods, equipment, staff, educational programme and research activities. The results confirmed the anticipated heterogeneity of techniques used to investigate ANS disorders. However, cardiovascular (84.8%) and sudomotor (43.0%) tests were the most common. There were no standards regarding equipment, but devices used varied widely, in part commercially available, in part self-developed. Some ANS laboratories performed cardiovascular tests using standard EMG devices with implemented routines to measure heart rate variability. Many investigators used published normative data (75.4%). Most of the responders were involved in scientific work, half were active in education of trainees. A wide variation was found in number and profession of staff members. As more than 60% of questionnaires were returned by neurologists our results may be limited to neurological ANS laboratories. Given the wide variation of methods and equipment used in European ANS laboratories, minimal standards for routine ANS testing are desirable. Standards may help to compare results of diagnostic tests, evaluate equipment and test laboratory methods and commercial devices and set-up educational programmes.

Cardiovascular autonomic nervous system tests: reference values in young people (15-19 years) and influence of age and gender

OBJECTIVE

The aim of this study was to determine values of the deep breathing test (DB), orthostatic test (OT) and Valsalva manoeuvre (VM) parameters in young people and influence of age and gender.

METHODS

A total of 206 healthy subjects (100 girls, 106 boys) at the age of 15-19 years, BMI 21.3+/-2.3 (mean +/- SD) were examined by system Varia Pulse TF3.

RESULTS

Reference values of DB, OT, VM parameters are presented as arithmetic mean +/- SD and percentiles (P90, P75, P50, P25, P10). In the whole group HRrest was lower in 19-year-old group, in OT this difference was significant already in 18-year-old group compared with 15-year-old group. DB: I/E was significantly increased in 19-year-old group compared with 15-year-old group. HRrest was higher in girls compared with boys in the whole group. DB: I/E was significantly lower in girls compared with boys. OT: 30:15 and HRmax/HRrest were significantly decreased in girls compared with boys.

CONCLUSION

Reference values of DB, OT, VM parameters were determined in young people at the age of 15-19 years. The most sensitive test for ascertainment of developmental changes was test of deep breathing. I/E was increased in the 19-year-old group compared with 15-year-old group indicating an increase of vagal activity. Girls had decreased some parameters of deep breathing and orthostatic test compared with boys in the same group (15-19 years).

[Autonomic hyperreflexia induced by sacral root stimulation is detected by spectral analysis of the EEG]

PURPOSE

To compare spectral analysis of the electrocardiogram (ECG) with mean arterial pressure (MAP) and heart rate (HR) monitoring in the detection of autonomic hyperreflexia (AHR) induced by sacral root stimulation.

METHODS

Ten spinal cord injured patients scheduled for implantation of a sacral root stimulator for bladder retention were included. Under target controlled anesthesia with propofol 4 micro g*mL(-1) and remifentanil 4 ng*mL(-1), the patients were placed in the knee chest position. The sacral roots were exposed by laminectomy (L2-S1) and their function assessed by electrostimulation under urodynamic and cardiovascular monitoring. Online power spectrum densities were calculated from the ECG R-R interval by the MemCalc(TM) software using the maximum entropy method. Low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.4 Hz) spectra were associated with sympathetic and parasympathetic activities respectively. The most extreme value of each variable was noted before and during each stimulation. A difference ( triangle up ) of more than 10% signified AHR. The comparison ( triangle up LF vs triangle up MAP and triangle up HF vs triangle up HR) was done by a concordance test with a kappa coefficient (k): -1 = total discordance to 1 = total concordance.

RESULTS

AHR was detected in six patients as an increase in LF and MAP (n = 4); an increase in LF, HF, MAP with a decrease in HR (n = 2). The detection delay was 5.3 +/- 1 sec (LF, HF) and 10.4 +/- 1.2 sec (MAP and HR). Concordance was 85% (LF vs MAP: k = 0.7) and 90% (HF vs HR: k = 0.8).

CONCLUSION

AHR induced by sacral root stimulation is detected by spectral analysis of the ECG earlier than MAP and HR. Other studies are needed to confirm these results.

Comparison of heart rate variability analysis methods in patients with Parkinson's disease

The aim of the present study was to evaluate different analysis methods for revealing heart rate variability (HRV) differences between untreated patients with Parkinson's disease and healthy controls. HRV in standard cardiovascular reflex tests and during a 10 min rest period were measured by time- and frequency-domain and geometrical and non-linear analysis methods. Both frequency- and time-domain measures revealed abnormal HRV in the patients, whereas non-linear and geometrical measures did not. The absolute high-frequency spectral power of HRV was the strongest independent predictor to separate the patients from the controls (p = 0.001), when the main time-domain and absolute frequency-domain measures were compared with each other. When the corresponding normalised spectral units, instead of the absolute units, were used in the comparison, the two best single measures for separating the groups were the 30/15 ratio of the tilting test (p = 0.003) and the max/min ratio during deep breathing (p = 0.024). When the correlations between the different measures were estimated, the time-domain measures, fractal dimension and absolute spectral powers correlated with each other. The frequency- and time-domain analysis techniques of stationary short-term HRV recordings revealed significant differences in cardiovascular regulation between untreated patients with Parkinson's disease and the controls. This confirms cardiovascular regulation failure before treatment in the early stages of Parkinson's disease. The HRV spectral powers, in absolute units, were the most effective single parameters in segregating the two groups, emphasising the role of spectral analysis in the evaluation of HRV in Parkinson's disease.

A comparative study of tests of cardiac parasympathetic nervous activity in healthy human subjects

Conventional tests of cardiac parasympathetic nervous system (PNS) activity were compared with the high frequency component of the heart rate power spectrum in a heterogenous group of normal subjects encompassing a wide age range. The data suggest that the linear associations between the various conventional tests of parasympathetic nervous activity even when statistically significant, were relatively modest, with r values ranging from 0.23 to 0.53. Three of the five conventional tests of parasympathetic nervous activity were significantly correlated (r = 0.33 to 0.46) with the absolute high frequency power of RR variability. However, these relationships were poorer and non-significant when the high frequency power spectrum was normalized for total power (r = 0.06 to 0.19, NS). An evaluation of the heart rate responses to cough and a single maximal hand grip indicated that the responses were repeatable but that the extent to which these manoeuvres induced vagally mediated cardioacceleration was significantly lesser than the other conventional tests of PNS activity. Taken together, the data suggest that despite the advent of heart rate variability measures, it is advisable to use multiple tests of parasympathetic nervous activity while evaluating autonomic dysfunction, since, despite the specificity of the tests, there is a variable correlation between them.

Electrodiagnosis of polyneuropathy

Electrodiagnostic studies comprising electromyography (EMG) and nerve conduction studies (NCS) are well-established objective methods for the diagnosis, quantification and classification of polyneuropathies (PNP). This paper reviews examination techniques, their pathophysiological interpretation, examination strategies and diagnostic criteria for the diagnosis and classification of a PNP. The routine electrodiagnostic evaluation includes sensory NCSs performed with surface or needle electrodes, motor NCSs, F-wave studies and EMG by qualitative or quantitative techniques. Sensory NCSs and F-wave studies have a high sensitivity in PNPs and the different techniques complement each other. The distinction between a PNP with predominantly axonal loss and a PNP with predominantly demyelination is one of the major aims of the electrophysiological examination. There are, however, large variation in suggested criteria for predominantly demyelination. The degree of slowing in conduction taken to indicate demyelination varies between a decrease of 50 to 30% from mean of controls, distal latency prolongation criteria vary from 35% to 70% of mean of controls, F-wave latency prolongation criteria vary from 120% to 150% of upper limit of controls, and criteria for partial motor conduction block vary from 11 to 50% reduction of CMAP amplitude and/or area between proximal and distal stimulation. Needle EMG studies may be valuable in order to detect and quantify denervation activity, to assess chronicity by an evaluation of the extent of reinnervation, and to evaluate the topographical distribution of changes. It is concluded that electrodiagnostic studies are valuable in patients with suspected PNP and the results may have consequences for prognosis and therapy of individual patients. Large variation in examination techniques, strategies, interpretations and diagnostic criteria have been found among electromyographers and it is suggested that the value of electrodiagnostic studies may be further improved by international standardisation.

Neurophysiological studies of thin myelinated (A delta) and unmyelinated (C) fibers: application to peripheral neuropathies

Dysfunction of small fibers may appear in isolation or associated with large fiber lesions. In some acute neuropathies, such as pandysautonomia, small-fiber impairment is relatively pure but it may also appear in disorders with prominent somatic damage, such as Guillain-Barré syndrome, in which autonomic failure worsens the prognosis. At the present time, chronic idiopathic distal small-fiber neuropathy is diagnosed more frequently, and in some prevalent disorders, such as diabetic or amyloidotic polyneuropathies, small-fiber dysfunction is very noticeable. In pure autonomic failure, a peripheral autonomic failure exists, distinguishing it from multiple-system atrophy. Complex regional pain syndrome is a severe condition in which small fibers are responsible for disabling signs and symptoms, and only instrumental recordings lead to the proper treatment. Standard neurophysiological techniques evaluate large myelinated fibers exclusively. Small-fiber polyneuropathy has been considered as a type of somatic neuropathy, but thin myelinated and unmyelinated fibers are responsible not only for temperature and pain perception but also autonomic function. For instance, full autonomic evaluation is needed in some clinical situations such as autonomic failure in the elderly or orthostatic intolerance syndrome. To evaluate small-fiber impairment we need a battery of sensitive, reproducible, specific and noninvasive tests covering somatic and autonomic systems. In this review, we describe and analyze a number of neurophysiological techniques used to diagnose and characterize small-fiber dysfunction in humans. These include cardiovascular monitoring, sudomotor testing, pupillary responses and quantitative sensory tests, and also to some extent thermography and laser evoked potentials. The use of such techniques has proven useful not only for diagnosis, but also to guide adequate therapy and optimize follow-up.

Spectral analysis of arterial blood pressure and cerebral blood flow velocity during supine rest and orthostasis

This study evaluates the effect of orthostasis on the low frequency (LF, 0.04 to 0.15 Hz) fluctuations in the blood flow velocity of the middle cerebral artery (MCAFV) in relation to its arterial blood pressure (ABP) equivalent to further define and quantify this relationship in cerebrovascular regulation. Spectral analysis was performed on 22 healthy subjects during supine rest and head-up tilt. The power in the LF range can be used to quantify the LF fluctuations, and four types of LF power data could be obtained for each individual: LF power of supine MCAFV, LF power of supine ABP, LF power of tilt MCAFV, and LF power of tilt ABP. By comparing LF power of MCAFV with LF power of ABP, two power ratios could be generated to describe the flow-pressure relationship during supine rest and head-up tilt, respectively, supine power ratio (LF power of supine MCAFV/ LF power of supine ABP) and tilt power ratio (LF power of tilt MCAFV/ LF power of tilt ABP). In addition, an index for dynamic autoregulation in response to orthostasis can be calculated from these two power ratios (tilt power ratio/supine power ratio). The authors found that this index was dependent on the extent of orthostatic MCAFV changes, and the dependency could be mathematically expressed (r = 0.61, P = .0001), suggesting its involvement in cerebrovascular regulation. Moreover, these data further support the previous observation that the LF fluctuations of MCAFV might result from modulation of its ABP equivalent, and the modulation effect could be quantified as the power ratio (LF power of MCAFV/ LF power of ABP). These observations could be an important step toward further insight into cerebrovascular regulation, which warrants more research in the future.

Cerebrovascular mechanisms in neurocardiogenic syncope with and without postural tachycardia syndrome

BACKGROUND AND PURPOSE

Recent transcranial Doppler studies in patients with neurocardiogenic syncopes (NCS) have demonstrated that the cerebrovascular response to sudden systemic hypotension is vasoconstriction instead of compensatory vasodilation (autoregulation). We tried to characterize the conditions leading to this unexpected response in NCS patients further by continuously monitoring autoregulation and autonomic parameters during a standardized tilt-table test (TTT).

METHODS

Sixteen patients below the age of 50 years with a history of at least three syncopes of undetermined cause and tilt-table verified NCS and 20 normal controls were studied. Arterial blood pressure (ABP) and heart rate (HR) were monitored by Finapres and cerebral blood flow velocity (CBFV) of the left middle cerebral artery by transcranial Doppler. Baroreflex sensitivity and autoregulation parameters were measured continuously, using cross-spectral analysis of Mayer waves (3-9 cycles per minute oscillations) in ABP, HR and CBFV, respectively. Pulsatility indices (PI) of CBFV and ABP were determined continuously. Measurements were taken during 5 min in supine and during 5 min in tilted position. In patients, tilting was continued for a maximum of 45 min until the onset of syncope or presyncope.

RESULTS

According to the maximum increase in heart rate (deltaHR) during the first 5 min of standing, heart rate responses were classified as postural tachycardia syndrome (POTS) (deltaHR > 35/min) or as normal. Only one out of 20 control subjects showed a POTS (5%) in contrast to seven patients (44%). Patients with a POTS had significantly lower PI values in ABP and higher ratios between the PI of CBFV and the PI of ABP both in supine and in tilted positions. Baroreflex sensitivity during standing decreased significantly in POTS patients when compared to controls. Although autoregulation remained intact during standing, mean CBFV decreased significantly and continuously. The nine patients without a POTS showed almost the same cardiovascular and cerebrovascular responses as the control subjects. All 16 patients showed similar circulatory responses during syncope (sudden hypotension, relative or absolute bradycardia, reduced CBFV and increased PI in CBFV).

CONCLUSIONS

The development of a POTS during tilting indicates a high risk for fainting. The characteristic hemodynamic features in the initial phase of standing in these patients can be interpreted in terms of central hypovolemia (low PI of ABP) with sufficient ABP regulation and increased cerebrovascular resistance (defined as the ratio between PI of CBFV and ABP). Cerebral autoregulation seems not to be affected in patients suffering from NCS.

Reduced baroreflex sensitivity and cardiorespiratory transfer in amyotrophic lateral sclerosis

INTRODUCTION

Clinically relevant autonomic disturbances have been reported for respirator-dependent ALS patients while subclinical involvement may be present in the early course.

METHODS

Eighteen patients with early-stage ALS and 18 age-matched controls were studied by means of standard autonomic tests (heart off + response to deep breathing and tilt-table testing), and spectral analysis of heart rate (HR) and arterial blood pressure (ABP), using the associated transfer function as a measure of baroreflex sensitivity for the mid-frequency band (MF band, 0.05-0.15 Hz) and as a measure of cardiorespiratory transfer for the high-frequency band (HF band, 0.15-0.33 Hz).

RESULTS

Mean HR and ABP were increased in ALS, while results of standard autonomic tests were similar for ALS and controls. Transfer function analysis revealed reduced baroreflex sensitivity and diminished cardiorespiratory transfer during normal breathing.

CONCLUSIONS

Cardiovascular autonomic functions are intact in patients with ALS. There is evidence of sympathetic enhancement and vagal withdrawal, accompanied by reduced baroreflex sensitivity. These findings are similar to those reported for essential hypertension and may point to a common central autonomic derangement in both disorders.

Spontaneous blood pressure oscillations and cerebral autoregulation

The relationship between spontaneous oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) was analysed in normal subjects in order to evaluate whether these relationships provide information about cerebral autoregulation. CBFV was measured using transcranial Doppler sonography and continuous ABP and heart rate using Finapres in 50 volunteers. Measurements were made over 5 min in a supine position and 6 min in a tilted position. Coefficients of variation were calculated using power- and cross-spectral analysis in order to quantify amplitudes within two frequency ranges: 3-9 cycles per min (cpm) (M-waves); and 9-20 cpm (R-waves). Correlations, coherence values, phase angle shifts and gains were also computed between corresponding waves in CBFV and in ABP. A clear correlation was seen for M-waves and R-waves between CBFV and ABP and coherence values were large enough to calculate phase angle shifts and gains. Phase angles for M-waves were larger and gains lower than was the case for R-waves, either tilted or supine. These data are consistent with a highpass filter model of cerebral autoregulation. Relatively high CBFV/ABP gain values (between 1.4 and 2.0) suggest that the principle of frequency-dependent vascular input impedances has to be considered in addition to autoregulatory feedback mechanisms. Spontaneous ABP oscillations in the M-wave and R-wave ranges may serve as a basis for continuous autoregulation monitoring.

Sympathetic cardiovascular dysfunction in long-standing idiopathic Parkinson's disease

Standard autonomic tests (heart rate response to deep breathing--HRDB, heart rate and systolic blood pressure response to tilt--delta HR and delta SBP) and spectral analysis of heart rate and arterial blood pressure and their transfer function (for the mid-frequency band a measure of baroreflex sensitivity) were performed in 20 patients with idiopathic Parkinson's disease (IPD) and 20 age-matched controls. Patients showed significantly diminished delta SBP, and reduced sympathetic vasomotor and cardiomotor outflow (diminished Mayer waves), consistent with an alteration of the efferent arc of the baroreflex. These results were only significant in long-standing IPD (IPD-l, > 5 years), whereas patients with short disease duration (IPD-s, < 5 years) showed values comparable to controls. Respiratory-related heart rate variability was slightly reduced in IPD-1 but this was mainly due to diminished respiratory effort, indicated by low respiratory-related blood pressure variability. We conclude that autonomic abnormalities are only present in long-standing IPD and consist in reduced sympathetic vasomotor and cardiomotor outflow.

AAEM minimonograph #48: autonomic nervous system testing

The autonomic nervous system maintains internal homeostasis by regulating cardiovascular, thermoregulatory, gastrointestinal, genitourinary, exocrine, and pupillary function. Testing and quantifying autonomic nervous system function is an important but difficult area of clinical neurophysiology. Tests of parasympathetic cardiovagal regulation include heart rate analysis during standing (the 30:15 ratio), heart rate variation with deep breathing, and the Valsalva ratio. Tests of sympathetic adrenergic vascular regulation include blood pressure analysis while standing, the Valsalva maneuver, sustained handgrip, mental stress, and cold water immersion. Tests of sympathetic cholinergic sudomotor function include the sympathetic skin response, quantitative sudomotor axon reflex test, sweat box testing, and quantification of sweat imprints. Pupil function is tested pharmacologically and with pupiilographic techniques. Tests of gastrointestinal and genitourinary function do not satisfactorily isolate autonomic regulation from their other functions. The available tests have various sensitivities and ease of administration. They are typically administered in a battery of multiple tests, which improves sensitivity and reliability, and allows probing of various autonomic functions.

Autonomic evaluation by means of standard tests and power spectral analysis in multiple sclerosis

Standard autonomic tests [heart rate response to deep breathing (HRDB), change in systolic blood pressure due to tilt], and spectral analysis of heart rate (HR), arterial blood pressure (ABP), and the associated transfer function analysis (gains and phases) were performed in 20 patients with multiple sclerosis to determine their diagnostic value. Transfer function analysis suggested impairment of baroreflex function in 7 patients and an alteration of cardiorespiratory coupling on a brain stem level in 4 patients. In addition, sympathetic vasomotor outflow was reduced in 2 patients (spectral ABP measures in the mid frequency band) and a decrease of vagal outflow was suggested by abnormal respiratory HR parameters in another 2 patients. An abnormal HRDB was present in 5 patients and was probably due to a central alteration (cardiorespiratory coupling) in 2 patients and due to diminished respiratory effort in 1 patient. Spectral analysis of both HR and ABP oscillations and their transfer function may considerably improve the pathophysiological interpretation of cardiovascular autonomic dysfunction in patients with central nervous system disease.

Determinants of heart rate variability during deep breathing: basic findings and clinical applications

The measurement of heart rate variation during forced breathing (HRDB) is a well-known clinical test of parasympathetic function. It is known that normal values of HRDB are strongly dependent on age. However, little is known about other physiological factors that may lead to reduced HRDB values that may mimic parasympathetic failure. Thirty-two normal subjects (age 56.7 +/- 12.4 years) and 32 neurological patients with pathological autonomic test findings (age 57.9 +/- 10.2) were studied. Oscillations in heart rate and in mean arterial blood pressure were recorded in the supine position during forced breathing (6 cycles/min) using the Finapres monitor. Amplitudes of heart rate and blood pressure waves at 6 cycles/min (HR6 and ABP6) as well as gain values (Gain6 = HR6/ABP6) and phase differences (delta phi 6) between HR and ABP waves were calculated by means of spectral analysis. The mean (+/-SD) HR6 in normal subjects was 6.34 +/- 3.36 cycles/min with a mean ABP6 of 5.11 +/- 2.49 mmHg. HR6 correlated significantly with age (r = -0.426) and with ABP6 (r = 0.602). No significant correlation was found between HR6 and mean blood pressure, mean heart rate or sex. From 24 patients with pathological findings in the classical HRDB value, only nine could be classified as pathological when the effect of ABP6 was considered. In conclusion, ABP variations significantly influence the amplitude of heart rate variations during forced breathing. We interpret these findings in terms of a baroreflex mechanism of HRDB including both vagal and sympathetic efferents. Normal reference value tables for clinical HRDB studies should not only consider age but also the amplitude of blood pressure variations.