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Biomedical subjects

C Passino

Publications and source records attributed to C Passino.

At least 19 recordsLinked to original sources
PubMed2001

Hyperthyroidism is associated with lengthening of ventricular repolarization.

OBJECTIVE: Lengthened ventricular repolarization, as assessed by the QT interval on electrocardiogram (ECG), can predispose to an increased risk of cardiac dysrhythmias; no data are available on QT corrected for heart rate (QTc) in hyperthyroidism in vivo. DESIGN: QT and RR intervals from 24 h ambulatory ECG Holter recording were measured in patients with hyperthyroidism and again following pharmacological achievement of stable euthyroidism for at least 2 months. PATIENTS: We enrolled a total of 16 hyperthyroid patients with Graves' disease, six males and 10 females (mean age 47 +/- 4 years, mean +/- SEM); 13 healthy age- and sex-matched subjects were utilized as a control group. MEASUREMENTS: The QT analysis was carried out by a computerized algorithm (QTc was corrected by the heart rate by Bazett's formula). Serum total T4, total T3, free T4, free T3 and TSH concentrations were measured by a fully automated immunoenzymometric assay; plasma norepinephrine by automatized high-pressure liquid chromatography, potassium and chloride by a potentiometric method, magnesium and calcium by a colourimetric method. RESULTS: The 24-h average QTc in the hyperthyroid patients was significantly prolonged compared to controls (458 +/- 7 vs. 431 +/- 6 ms, P = 0.01) and it returned to normal after treatment of thyrotoxicosis (432 +/- 6 ms, P < 0.05 vs. time H, NS vs. controls). QTc positively correlated with FT3 (r = 0.63, P < 0.001) and with FT4 (r = 0.481, P < 0.02). Conversely, QTc did not correlate with plasma basal norepinephrine levels, nor with electrolytes. CONCLUSIONS: Hyperthyroidism is associated with prolonged QTc that normalizes once the patient becomes euthyroid. The strong positive correlation between FT3 and QTc supports the hypothesis of an important role of thyroid hormone on modulation of QTc lengthening.

Adrenergic beta-Antagonists↗
PubMed2001

Respiratory and cardiovascular adaptations to progressive hypoxia; effect of interval hypoxic training.

AIM: Interval hypoxic training was proposed as a technique for adapting hypoxia of various origins. Its effects on the hypoxic ventilatory response and on cardiovascular autonomic control are unknown. METHODS AND RESULTS: We recorded ventilation, end-tidal oxygen (PETO2) and carbon dioxide partial pressures, RR interval and blood pressure during progressive isocapnic hypoxia, before and after 14 days of: (a) interval hypoxic training (three to four periods of 7 min progressive hypoxia in 1 h, each day) in 12 healthy men (training group); (b) breathing into a spirometer by six age-matched male controls. The hypoxic ventilatory response was estimated by the hyperbolic relationship between PETO2 and ventilation (shape factor A). Spectral analysis was used to characterize low- (mainly sympathetic) and high-frequency (vagal) cardiovascular fluctuations. Shape factor A was increased in the interval hypoxic training group from 268+/-59 to 984+/-196 l x mmHg(-1)(P<0.003), but not in the control group (from 525+/-180 to 808+/-245 l x mmHg(-1), P=ns). Before interval hypoxic training, progressive hypoxia decreased, to a similar extent in both groups, mean RR, RR variability and high-frequency power. After interval hypoxic training, RR still decreased significantly, but the decrease in RR variability and high-frequency power was no longer significant in the training group. No significant changes were observed in blood pressure fluctuations. No changes were observed in the control group. CONCLUSIONS: Two weeks of interval hypoxic training increased the hypoxic ventilatory response, in association with reduced vagal withdrawal during progressive hypoxia.

Adult↗
PubMed2001

Prognostic value of serum gamma-glutamyl transferase activity after myocardial infarction.

AIMS: Serum gamma-glutamyl transferase activity (gamma-GT) is able to catalyse low-density lipoprotein oxidation and has been detected in coronary atherosclerotic plaques. gamma-GT has been documented as an independent risk factor for cardiac mortality in middle-aged men. The purpose of this study is to determine the prognostic value of gamma-GT in patients with coronary artery disease. METHODS AND RESULTS: In a prospective study, gamma-GT and other cardiac risk factors were evaluated in 469 consecutive subjects with angiographically documented coronary artery disease, using mortality and mortality plus non-fatal myocardial infarction as end-points. gamma-GT showed an independent prognostic value beyond known established risk factors in the subgroup of 262 patients with previous myocardial infarction. At a 6-year follow-up, cardiac mortality was 25.2% in patients with gamma-GT >40 U x l(-1)vs 13.9% in those with gamma-GT <40 U x l(-1)(P=0.038). When both cardiac mortality and non-fatal myocardial infarction were considered as end-points, these events were recorded in 32.7% of patients with gamma-GT >40 U x l(-1)and in 20.4% of those with levels <40 U x l(-1)(P=0.031). Excess mortality and non-fatal infarction in patients with high gamma-GT levels were concentrated in the first 2 years of follow-up (P=0.014). The association of gamma-GT values >40 U x l(-1), previous myocardial infarction, and multiple vessel disease identified a subgroup of 168 patients with the highest risk of cardiac events at 6 years (P=0.024). The relationship between gamma-GT levels and cardiac events remained significant after adjustment for cardiac risk factors, and possible confounders, including alcohol consumption. gamma-GT did not show significant prognostic value in the 207 patients without previous myocardial infarction. CONCLUSION: gamma-GT is an independent cardiac risk factor in ischaemic patients with established coronary atherosclerosis and previous myocardial infarction.

Adult↗
PubMed2001

Peripheral arterial vascular function at altitude: sea-level natives versus Himalayan high-altitude natives.

OBJECTIVES: Regulation of the vascular system may limit physical performance and contribute to adaptation to high altitude. We evaluated vascular function in 10 Himalayan high-altitude natives and 10 recently acclimatized sea-level natives at an altitude of 5,050 m. METHODS: We registered electrocardiogram, blood flow velocity in the common femoral artery, and blood pressure in the radial artery using non-invasive methods under baseline conditions, and during maximal vasodilation after 2 min leg occlusion. Vascular mechanics were characterized by estimating pulse wave velocity and input impedance. RESULTS: Pulse wave velocity and parameters of input impedance did not differ between groups under baseline conditions. In the post-ischemic period, the ratio between maximal hyperemic and baseline blood flow velocity was significantly higher in the high-altitude than in the sea-level natives (5.7 +/- 2.5 versus 3.8 +/- 1.2, P < 0.05). The leg vascular resistance decreased in the post-occlusive period without differences between groups. Characteristic impedance decreased in the post-ischemic period by about one third of the baseline level without differences between groups. The post-ischemic decrease of input impedance modulus was more marked in the high-altitude than in the sea-level natives at low frequencies (28 +/- 12 versus 6.4 +/- 20% at 2 Hz, P < 0.01). CONCLUSIONS: Our results demonstrate a superior ability to increase blood flow velocity as a response to muscular ischemia in high-altitude natives compared to sea-level natives. This phenomenon may be associated with a more effective coupling between blood pressure and blood flow which is probably caused by differences in conduit vessel function.

Adolescent↗
PubMed2001

Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.

OBJECTIVE: To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia. DESIGN: We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO2), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5,000 m, in a hypobaric chamber). METHODS: We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during 'complete yogic breathing' (slow diaphragmatic + thoracic breathing, approximately 5 breaths/min) in yoga trainees, or simple slow breathing in controls. RESULTS: At baseline %SaO2, VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO2 decreased in all subjects (P< 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P< 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 +/- 45 to 770 +/- 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 +/- 0.5 to 3.2 +/- 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 +/- 0.31 to 3.07 +/- 0.24 In-mmHg2, P< 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing. No effect of altitude was seen on stimulation of carotid baroreceptors in both groups. CONCLUSIONS: Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia.

Adult↗
PubMed2000

Effects of breathing control on cardiocirculatory modulation in Caucasian lowlanders and Himalayan Sherpas.

This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude in adapted and non-adapted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on synchronized 15 min periods of R-R intervals and the oxygen saturation of arterial blood (SaO2). Despite mean SaO2 being similar in lowlanders and Himalayan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], fluctuations in SaO2 were significantly increased in lowlanders compared to Sherpas, thus indicating an unstable regulation of respiration control in lowlanders. Regression analysis demonstrated a significant relationship between spectrum power of SaO2 and the relative power of R-R intervals in the frequency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas. Our results demonstrate differences in respiratory and autonomic cardiac control between non-adapted lowlanders and Himalayan high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated with the autonomic cardiocirculatory regulation.

Acclimatization↗
PubMed2000

Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability.

OBJECTIVES: To assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted. BACKGROUND: Sympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded without measuring respiration; slow breaths might artefactually increase low frequency power in RR interval (RR) and falsely mimic sympathetic activation. METHODS: In 12 healthy volunteers we evaluated the effect of free talking and reading, silently and aloud, on respiration, RR and blood pressure (BP). We also compared spontaneous breathing to controlled breathing and mental arithmetic, silent or aloud. The power in the so called low- (LF) and high-frequency (HF) bands in RR and BP was obtained from autoregressive power spectrum analysis. RESULTS: Compared with spontaneous breathing, reading silently increased the speed of breathing (p < 0.05), decreased mean RR and RR variability and increased BP. Reading aloud, free talking and mental arithmetic aloud shifted the respiratory frequency into the LF band, thus increasing LF% and decreasing HF% to a similar degree in both RR and respiration, with decrease in mean RR but with minor differences in crude RR variability. CONCLUSIONS: Simple mental and verbal activities markedly affect HRV through changes in respiratory frequency. This possibility should be taken into account when analyzing HRV without simultaneous acquisition and analysis of respiration.

Arousal↗
PubMed2000

Cardiocirculatory coupling during sinusoidal baroreceptor stimulation and fixed-frequency breathing.

The question of whether respiratory sinus arrhythmia (RSA) originates mainly from a central coupling between respiration and heart rate, or from baroreflex mechanisms, is a subject of controversy. If there is a major contribution of baroreflexes to RSA, cardiocirculatory coupling during breathing and during cyclic baroreflex stimulation should show similarities. We applied a sinusoidal stimulus to the carotid baroreceptors and generated heart rate fluctuations of the same magnitude as RSA with a frequency similar to, but different from, the breathing frequency (0.2 Hz, compared with 0.25 Hz), and at 0.1 Hz, in 17 supine healthy subjects (age 28-39 years). The data were analysed using discrete Fourier-transform and transfer function analysis. Respiratory fluctuations in systolic blood pressure preceded RSA with a time lag equal to that between baroreceptor stimulation and oscillations in RR interval (0.62+/-0.18 s compared with 0.57+/-0.28 s at 0.2 Hz neck suction). The response of systolic blood pressure to neck suction at 0.2 Hz was 5 times less than the respiratory blood pressure fluctuations. Neck suction at 0.1 Hz largely increased fluctuations in blood pressure and RR interval, whereas the spontaneous phase relationship between blood pressure and RR interval remained unchanged. Our results are not consistent with the hypothesis that the origin of RSA is predominantly a central phenomenon which secondarily generates fluctuations in blood pressure, but suggest that, under the condition of fixed-frequency breathing at 0.25 Hz, baroreflex mechanisms contribute to respiratory fluctuations in RR interval.

Adult↗
PubMed1998

Influence of type of surgery on the occurrence of parasympathetic reinnervation after cardiac transplantation.

BACKGROUND: Cardiac autonomic reinnervation after human cardiac transplantation has been demonstrated frequently but to date only for sympathetic efferents. Standard surgical techniques leave many parasympathetic branches intact in the original atria and thus with less stimulus to reinnervate the donor atria. METHODS AND RESULTS: We used changes in the RR-interval power spectrum induced by sinusoidal modulation of arterial baroreceptors by neck suction at different frequencies to detect both parasympathetic and sympathetic reinnervation in 79 subjects with "standard" and 10 "bicaval" heart transplants. In 24 subjects (17 standard and 7 bicaval), the protocol was repeated 6 and 11 months after transplantation. Neck suction at 0.20 Hz produced a component at 0.20 Hz in the RR-interval spectrum not due to respiration (fixed at 0.25 Hz), which suggested parasympathetic reinnervation, in 4 of 10 bicaval but in only 2 of 79 standard transplant subjects (whose recipient atria underwent >50% resection to remove scars of previous interventions), P<.001. In only 1 (bicaval) transplant subject was parasympathetic reinnervation present 6 months after transplantation (confirmed 3 months later); in 4 subjects, it was absent at 6 months but appeared after 11 months after transplantation. Atropine (0.04 mg/kg i.v.) abolished the response to fast (0.20 Hz) and reduced that to slow stimulation, confirming the presence of parasympathetic reinnervation (4 subjects). CONCLUSIONS: Parasympathetic reinnervation depends on the surgical technique: because bicaval surgery cuts all sympathetic and parasympathetic nerves, regeneration might be stimulated similarly in both branches. Standard surgery cuts only approximately 50% of sympathetic fibers; most recipient parasympathetic axons remain intact, hence their regeneration might not be stimulated.

Atropine↗
PubMed1998

Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude.

1. To assess the effects of acute exposure to high altitude on baroreceptor function in man we evaluated the effects of baroreceptor activation on R-R interval and blood pressure control at high altitude. We measured the low-frequency (LF) and high-frequency (HF) components in R-R, non-invasive blood pressure and skin blood flow, and the effect of baroreceptor modulation by 0. 1-Hz sinusoidal neck suction. Ten healthy sea-level natives and three high-altitude native, long-term sea-level residents were evaluated at sea level, upon arrival at 4970 m and 1 week later.2. Compared with sea level, acute high altitude decreased R-R and increased blood pressure in all subjects [sea-level natives: R-R from 1002+/-45 to 775+/-57 ms, systolic blood pressure from 130+/-3 to 150+/-8 mmHg; high-altitude natives: R-R from 809+/-116 to 749+/-47 ms, systolic blood pressure from 110+/-12 to 125+/-11 mmHg (P<0.05 for all)]. One week later systolic blood pressure was similar to values at sea level in all subjects, whereas R-R remained elevated in sea-level natives. The low-frequency power in R-R and systolic blood pressure increased in sea-level natives [R-R-LF from 47+/-8 to 65+/-10% (P<0.05), systolic blood pressure-LF from 1.7+/-0. 3 to 2.6+/-0.4 ln-mmHg2 (P<0.05)], but not in high-altitude natives (R-R-LF from 32+/-13 to 38+/-19%, systolic blood pressure-LF from 1. 9+/-0.5 to 1.7+/-0.8 ln-mmHg2). The R-R-HF decreased in sea-level natives but not in high-altitude natives, and no changes occurred in systolic blood pressure-HF. These changes remained evident 1 week later. Skin blood flow variability and its spectral components decreased markedly at high altitude in sea-level natives but showed no changes in high-altitude natives. Neck suction significantly increased the R-R- and systolic blood pressure-LF in all subjects at both sea level and high altitude.3. High altitude induces sympathetic activation in sea-level natives which is partially counteracted by active baroreflex. Despite long-term acclimatization at sea level, high-altitude natives also maintain active baroreflex at high altitude but with lower sympathetic activation, indicating a persisting high-altitude adaptation which may be genetic or due to baroreflex activity not completely lost by at least 1 year's sea-level residence.

Adult↗
PubMed1998

Hypoxic ventilatory responses and gas exchange in patients with Parkinson's disease.

Ventilatory responses to isocapnic, progressive hypoxic rebreathing (HVR), in supine and sitting positions, lung ventilation and gas exchange while breathing air and during 5 min of breathing 11% O2 in N2 were studied in 12 healthy young (20-28 years), 5 old (57-73 years) male subjects, and in 7 male patients with Parkinson's disease (PD) aged 55-67 years. The piecewise linear approximation technique was used for evaluation of the ventilatory response curves, which allowed a separate analysis of slopes during minor and severe hypoxia. It has been shown that body position affected HVR. In the range of PETO2 from 60 to 35 mm Hg, the ventilatory response in the sitting position was higher than supine: in young persons by 43%, in healthy old persons by 76%, and in the PD patients by 211%. No significant differences in HVR to minor hypoxia (PETO2 from 100 to 60 mm Hg) were found in the 3 groups. During severe hypoxia (PETO2 from 60 to 35 mm Hg) the slope of minute ventilation versus O2 was 4.6 (supine) and 2.6 (sitting) times greater in healthy old men than PD patients' slopes. PD patients compared to old controls had 32% lower alveolar ventilation, 10% lower PETO2 and 15% elevation of PETCO2 while breathing air; similar differences were found while the patients were breathing 11% O2. The reduced alveolar ventilation under severe hypoxia in patients with PD could not be attributed to mechanical restriction of lung function. We suggest that the discrepancy in HVR under minor and severe hypoxia results from dysfunction in chemoreception associated with Parkinsonism.

Adaptation, Physiological↗
PubMed1997

Origin of respiratory sinus arrhythmia in conscious humans. An important role for arterial carotid baroreceptors.

BACKGROUND: We investigated whether respiratory sinus arrhythmia (RSA) in healthy humans originated from central neuronal oscillations or from peripheral baroreceptors responding to respiratory changes in venous return. METHODS AND RESULTS: During subjects' controlled breathing we used sinusoidal neck suction to influence RSA (spectral analysis of RR interval). In 11 subjects, 20-second apnea greatly reduced RSA, which was restored by neck suction at the frequency of respiration. Counteracting the respiration-induced cycles of carotid blood pressure decreased RSA in 13 subjects (from 2136 +/- 682 to 1372 +/- 561 ms2, P < .01). The critical phase of this neck suction was constant for each subject at around the phase shift (with regard to respiration-related fluctuations of blood pressure) best for smoothing respiratory (mechanical) changes in blood pressure. Suction of a non-baroreceptor area (the thigh) did not affect RSA. In 4 subjects, to separate the effects of peripheral baroreceptor afferents from respiration-entrained central oscillation (15 breaths/min), we cycled the neck suction at 12 cycles/min. Increasing neck suction from -7 to -30 mm Hg increased the ratio of the power of the 12 cycles compared with the 15-cycle RSA oscillation in RR interval spectral analysis from 0.26 to 2.57. A 12-cycle/min suction of an area other than the neck had little effect on the RR interval spectrum. CONCLUSIONS: RSA can be mimicked or reduced by stimulation of arterial baroreceptors with cycles of appropriately phased neck suction at the frequency of respiration. This suggests an important influence of the arterial baroreceptors in the generation of RSA in conscious humans.

Adult↗
PubMed1997

Acute and persistent effects of a 46-kilometer wilderness trail run at altitude: cardiovascular autonomic modulation and baroreflexes.

OBJECTIVE: To test the hypothesis that prolonged physical exercise induces long-lasting effects on blood pressure and heart rate we studied 17 endurance runners before and after the 1995 Sandia Wilderness Crossing Research Run (46 km of rocky trails, average altitude 2500 m). METHODS: We evaluated the response of the cardiovascular system to sympathetic stimulation by orthostatism and to sympathetic and parasympathetic carotid baroreceptor stimulations by sinusoidal neck suction at different frequencies (sympathetic activity on blood pressure by low-frequency stimulation, parasympathetic activity on RR interval by high-frequency stimulation). We used power spectral analysis of beat-to-beat RR interval, systolic and diastolic non-invasive blood pressure, in order to quantify the respiratory fluctuations (depending on vagal activity on the RR interval) and the slower non-respiratory fluctuations, depending on sympathetic activity on the blood pressure. Recordings were performed 24 h before, and 30 min, 24 h and 48 h after the run. RESULTS: Thirty minutes after the race we found reduced blood pressure, signs of relative sympathetic predominance (increased RR interval low-frequency/high-frequency ratio from 0.65 +/- 0.15 to 1.63 +/- 0.37, P < 0.05), reduced effect of parasympathetic baroreceptor stimulation (decrease in RR interval high-frequency neck-suction synchronous oscillations, from 5.33 +/- 0.34 to 3.55 +/- 0.37 ln-ms2, P < 0.005), unchanged blood pressure responses to sympathetic stimulations; 24 h after the race, the response to parasympathetic stimulation was increased (to 6.44 +/- 0.32 ln-ms2, P < 0.0005) compared to baseline (24 h before the race), whereas sympathetic stimulation by neck suction had no longer an effect on blood pressure. CONCLUSION: The acute effects of prolonged exertion are associated with a relative increase in sympathetic activity. Twenty-four hours after this race an increased sensitivity to vagal and reduced sensitivity to sympathetic baroreflex stimulation was found. In this field study at altitude we found long-lasting effects on cardiovascular autonomic modulation after physical exertion.

Adult↗
PubMed1997

Lack of peripheral modulation of cardiovascular central oscillatory autonomic activity during apnea in humans.

Respiratory sinus arrhythmia (RSA) high-frequency oscillations (HF) and slow fluctuations in heart rate (LF) are thought to result from entrainment of a medullary oscillator, from the baroreflex, or from a combination of both central and baroreflex mechanisms. We sought to distinguish between the alternatives by examining with spectral analysis the behavior of heart rate (R-R interval) and blood pressure in 10 healthy subjects (mean age 27 +/- 1 yr) during apnea, altering the rate of preapnea entrainment stimuli by changing the frequency either of respiration (controlled at 0.1 or 0.25 Hz) or of baroreceptor stimulation by sinusoidal neck suction (0 to -30 mmHg, 0.1 or 0.2 Hz). During apnea the RSA-EF power decreased (from 6.73 +/- 0.15 to 3.67 +/- 0.10 In ms2: P < 0.0001), regardless of preapnea conditions, whereas LF power was reduced only if preceded by 0.1-Hz respiration or neck suction [from 8.71 +/- 0.18 to 6.52 +/- 0.11 In ms2 (P < 0.001) and from 8.31 +/- 0.23 to 6.90 +/- 0.38 In ms2 (P < 0.01), respectively]. The LF frequency seen in the R-R interval during apnea was slower than the spontaneous LF during 0.25-Hz breathing (0.082 +/- 0.01 vs. 0.112 +/- 0.001 Hz, P < 0.001), but the maneuvers during preapnea had no influence on the observed frequency or other characteristics of the slow oscillations during apnea. Moreover, we found no evidence of a progressive decrease in the power of the oscillation during apnea. The same behavior was observed on the mean blood pressure signal. In conclusion, a slow rhythm is present during apnea. In healthy subjects at rest the characteristics of this oscillation indicate that it could be generated by a central oscillator this may thus contribute to the origin of LF present during normal respiration, in addition to the baroreflex.

Administration, Inhalation↗
PubMed1997

Synchronous and baroceptor-sensitive oscillations in skin microcirculation: evidence for central autonomic control.

To determine whether skin blood flow is local or takes part in general regulatory mechanisms, we recorded laser-Doppler flowmetry (LDF; left and right index fingers), blood pressure, muscle sympathetic nerve activity (MSNA), R-R interval, and respiration in 10 healthy volunteers and 3 subjects after sympathectomy. We evaluated 1) the synchronism of LDF fluctuations in two index fingers, 2) the relationship with autonomically mediated fluctuations in other signals, and 3) the LDF ability to respond to arterial baroreflex stimulation (by neck suction at frequencies from 0.02 to 0.20 Hz), using spectral analysis (autoregressive uni- and bivariate, time-variant algorithms). Synchronous LDF fluctuations were observed in the index fingers of healthy subjects but not in sympathectomized patients. LDF fluctuations were coherent with those obtained for blood pressure, MSNA, and R-R interval. LDF fluctuations were leading blood pressure in the low-frequency (LF; 0.1 Hz) band and lagging in the respiratory, high-frequency (HF; approximately 0.25 Hz) band, suggesting passive "downstream" transmission only for HF and "upstream" transmission for LF from the microvessels. LDF fluctuations were responsive to sinusoidal neck suction up to 0.1 Hz, indicating response to sympathetic modulation. Skin blood flow thus reflects modifications determined by autonomic activity, detectable by frequency analysis of spontaneous fluctuations.

Adult↗
PubMed1996

Effect of different interventions on heart rate variability after heart transplantation: non-autonomic vs autonomic factors.

1. The human transplanted heart is initially denervated, hence any fluctuation present in the RR interval variability can be either due to reacquired innervation, or to the effect of some non autonomic activity, such as a direct effect of respiration on atrial (sinus node) stretch. 2. In order to distinguish between sympathetic, vagal and non autonomic factors we examined the effects of various physical and pharmacologic manoeuvres on the respiratory and non-respiratory components of heart rate variability. 3. We found that sinusoidal neck suction appears a useful, noninvasive tool to characterise the relative importance of the different factors, which can influence heart rate variability in the transplanted heart.

Autonomic Nervous System↗
PubMed1996

Progressive withdrawal of muscle nerve sympathetic activity preceding vaso-vagal syncope during lower-body negative pressure.

We report the observation of a vaso-vagal syncope (VVS) occurring during lower body negative pressure in a young male volunteer. Recording of the peripheral blood flow, blood pressure and muscular sympathetic nerve activity revealed first a progressive withdrawal of muscle nerve sympathetic activity with redistribution of blood flow before the onset of the VVS.

Adult↗