Biomedical subjects

C Passino

Publications and source records attributed to C Passino.

28 records · Page 2Linked to original sources

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↗

PubMed1996

Autonomic regulation of heart rate and peripheral circulation: comparison of high altitude and sea level residents.

1. To evaluate the activity of the autonomic nervous system on the heart and peripheral circulation in native high-altitude residents, during a Himalayan expedition we studied 12 men (age: 48 +/- 4, mean +/- SEM), life-long resident in a village at 4800 m (Sumdo village, Zanskar, India) and 7 healthy sea-level residents (age: 37 +/- 4) after 7 days of acclimatization (acclimatized lowlanders) at the same altitude. Furthermore 25 sea level residents (age: 46 +/- 2) underwent the same protocol at sea level. 2. R-R interval (RR), respiratory signal, non-invasive blood pressure, and skin arteriolar blood flow were evaluated in three different conditions: during free breathing in supine position and during controlled breathing (at 0.15 Hz), in supine and upright position, and analysed by autoregressive spectral analysis [low- (around 0.1 Hz) and high-frequency (respiratory) fluctuations, LF and HF, markers of sympathetic and vagal activity, respectively]. 3. High-altitude residents showed in supine position a higher RR than acclimatized lowlanders, similar to sea-level residents. RR variability was reduced in acclimatized lowlanders compared to both high-altitude residents and sea level residents. Systolic blood pressure (SBP) did not show significant differences between the three groups. High altitude residents showed in supine lower LF in RR signal compared to sea-level residents, and, compared to acclimatized lowlanders, higher HF and lower LF/HF ratio; high-altitude residents showed a reduction in skin microcirculation variability compared to sea-level residents, but this was eight fold greater than in acclimatized lowlander, thus indicating a much greater vasoconstriction in acclimatized lowlanders than in high-altitude residents. 4. In upright position, high-altitude residents showed the same behaviour as sea-level residents, with increase in LF-RR, and decrease in HF and LF-SBP. Acclimatized lowlanders showed similar directional trends though not significant changes for RR-LF. 5. After one week of acclimatization, lowlanders still manifested sympathetic activation and skin vasoconstriction; high-altitude residents did not show reduced vagal tone compared to sea-level residents, but a mild vasoconstriction appeared to be present. In conclusion, normal or enhanced vagal tone and preserved vasomotion are probably evidence of adaptation at high altitude hypoxia.

Adaptation, Physiological↗

PubMed1995

Demonstrable cardiac reinnervation after human heart transplantation by carotid baroreflex modulation of RR interval.

BACKGROUND: After heart transplantation, respiration-synchronous fluctuations (0.18 to 0.35 Hz, high frequency [HF]) in RR interval may result from atrial stretch caused by changes in venous return, but slower fluctuations (0.03 to 0.15 Hz, low frequency [LF]) not due to respiration suggest reinnervation. In normal subjects, sinusoidal neck suction selectively stimulates carotid baroreceptors and causes reflex oscillations of RR interval. METHODS AND RESULTS: To evaluate the presence of reinnervation, we measured the power of RR-LF and RR-HF in 26 heart transplant recipients and 16 control subjects before and during sinusoidal neck suction at 0.1 Hz and 0.20 Hz (similar to but distinct from that of controlled respiration, 0.25 Hz) and before and during administration of atropine or beta-blocker (esmolol hydrochloride) by spectral analysis. All transplant recipients showed small respiratory HF fluctuations. Nonrespiratory LF fluctuations were present in 13 of 26 transplant recipients and increased with months since transplantation (r = .53, P < .01). HF neck suction induced a 0.20-Hz component in all 16 control subjects and none of the 26 transplant subjects. LF neck suction increased RR-LF (from 0.73 +/- 0.20 to 1.30 +/- 0.26 ln ms2, P < .001), similar to but less than in control subjects (from 6.12 +/- 0.21 to 8.27 +/- 0.21 ln ms2, P < .001). Atropine reduced all fluctuations in control subjects and blocked the HF increase caused by 0.20-Hz neck suction but not the LF increase during 0.10-Hz stimulation. Neck suction-induced changes in LF fluctuations persisted after administration of atropine in transplant recipients but were attenuated by esmolol hydrochloride, suggesting sympathetic rather than vagal reinnervation. CONCLUSIONS: The presence of baroreceptor-induced RR oscillations is evidence of functional, although incomplete, autonomic reinnervation.

Adrenergic beta-Antagonists↗

PubMed1995

Flow-diameter phase shift. A potential indicator of conduit artery function.

This study assesses (1) the relation of the very-low-frequency vasomotion (< 0.02 Hz) of the radial artery of young healthy volunteers to regional blood flow and (2) its distribution in the upper extremities. Radial artery diameters from comparable sites were measured on contralateral extremities in 18 young healthy volunteers by an echo tracking system simultaneously with blood flow velocity determined by continuous wave Doppler and blood pressure acquired by photoplethysmography in the middle finger. A synchronous global pattern of vasomotion was detected on contralateral radial arteries, suggesting the presence of either a centrally located pacemaker or a humoral system. Modulation of sympathovagal balance in 8 subjects did not significantly alter either the frequency or amplitude of the very-low-frequency vasomotor waves. Matching patterns of diameter and flow oscillations of the very-low-frequency type recorded at the same site were obtained in 10 strictly nonsmoking volunteers for given periods of time. A consistent phase lag was observed between flow and diameter signals. Flow always preceded the diameter fluctuations by a mean (+/- SEM) course of 20.8 +/- 1.56 seconds. Although the physiological basis for oscillatory behavior remains for the moment highly speculative, these results suggest that the very-low-frequency vasomotion pattern in this conduit vessel might be a flow- or shear stress-dependent phenomenon. Shear stress changes at the endothelium modulate vascular tone through the release of vasodilators. The noninvasive assessment of the diameter-flow relation may thus offer a new way of addressing vascular wall function in medium-sized and large arteries in subjects with cardiovascular risk factors.

Adult↗

PubMed1994

Low-frequency spontaneous fluctuations of R-R interval and blood pressure in conscious humans: a baroreceptor or central phenomenon?

1. We have tested the hypothesis that the non-respiratory, low-frequency (around 0.1 Hz) fluctuations of heart rate variability are generated by the baroreflexes, but with a delay caused by the slower response of the efferent sympathetic arm, (compared with the vagus), in 11 healthy subjects (mean age +/- SD 27 +/- 5 years). 2. In random order, at the onset of 20 s of apnoea starting at end expiration, we applied either 600 ms neck suction (-40 mmHg) to the carotid sinus region, or no stimulus (anticipation control), or a loud whistle (alerting control), every 60 s, for 30 min. (i.e. 10 of each 'stimulus'). We recorded neck pressure, blood pressure (Finapres), R-R interval (ECG), infra-red plethysmographic skin blood flow and respiration (impedance). By subtracting the alerting response from the neck suction response we obtained the responses caused purely by baroreceptor stimulation. 3. The initial reflex bradycardia and hypotension was followed by arteriolar vasoconstriction, presumably due to recompensation by the baroreflex, and then by a further reflex bradycardia-producing a decaying oscillation of the R-R interval about the control R-R. The period of this damped oscillation was 0.103 +/- 0.024 Hz, similar to the frequency of the low-frequency peak obtained by power spectral analysis of heart rate variability (0.093 +/- 0.016 Hz, not significant) at rest. These two values were significantly correlated in individual subjects (r = 0.715, P < 0.025). 4. These findings support the hypothesis that the low-frequency waves of heart rate variability can be generated from baroreceptor sensed blood pressure fluctuations.

Adult↗

PubMed1994

[The noninvasive demonstration of functional reinnervation after heart transplantation].

Although RR interval variability appears to be an ideal method for assessing reinnervation after heart transplantation, it has been shown that respiratory sinus arrhythmia is caused by the mechanical effect of respiration on the right atrium. The neck-suction induces heart rate changes only by means of nervous reflex and its hemodynamic effect is local and hence appears as a useful method for assessing reinnervation. We tested the presence of autonomic reinnervation in 18 heart transplant recipients, compared to 12 donor-age-matched controls. We measured the power of RR interval low- (LF, around 0.1 Hz) and respiratory fluctuations (HF) before and during rhythmic neck-suction stimulation at 0.1 Hz and at a frequency (0.20 Hz) similar to, but distinct from, that of respiration (controlled at 0.25 Hz), before and during 0.04 mg/kg atropine infusion, using autoregressive spectral analysis of RR interval, respiration and neck pressure signals. The relationship between pairs of signals at each frequency was quantitatively assessed by bivariate coherence function. All transplanted subjects showed low-amplitude HF, related to respiration. Detectable LF (whose power was lower than in controls: 1.15 +/- 0.39 versus 6.08 +/- 0.27 1n-ms2, p < 0.001), non coherent with respiration, were present in 11/18 transplanted subjects, and correlated with months since transplantation (r = +0.59, p < 0.05). HF neck suction induced the presence of a 0.20 Hz fluctuation in 12/12 controls, distinct from and greater than the 0.25 Hz respiratory component (7.28 +/- 0.26 versus 6.69 +/- 0.74 1n-ms2, p < 0.01); this was not seen in any of the transplanted subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

[Vasovagal syncope].

The nature of most syncopal episodes, previously unknown, was recently elucidated by new diagnostic techniques such as the use of the tilt test. The vasovagal syncope can be clinically diagnosed by means of the tilt test. The transitory loss of consciousness during prolonged orthostasis is typically associated with sudden hypotension and bradycardia, which are commonly preceded by relative tachycardia and by premonitory symptoms such as pallor, nausea, asthenia, yawns, hyperventilation, mydriasis, humming, lasting several minutes. The nature of the vasovagal reflex is now better understood: in subjects with vasovagal syncope, during prolonged orthostasis, it was observed a fall in the venous return, inducing an increased sympathetic drive to the heart (with positive inotropic and chronotropic effect) and a lower ventricular filling. The powerful contraction around an almost empty cardiac chamber induces the activation of ventricular mechanoreceptors, and through a reflex mechanism, a sudden increase in the vagal and a sudden reduction in the sympathetic drive. These autonomic changes are responsible for a sudden hypotension and bradycardia. The discussion is still open about the origin of the reduced venous return: it probably originates from a redistribution in the blood volume, due to a venous pooling in the lower limbs or from a reduced muscle tone, because many subjects with vasovagal syncope are slender and with less developed muscle apparatus. Others suggest that a reduction in the sympathetic drive to the vessels, responsible for a progressive hypotension in the minutes preceding syncopal episodes, is the origin of the reduced venous return. In this review a diagnostic pattern for the assessment of the vasovagal syncope is suggested. The medical history, clinical examination, electro- and echocardiogram, chest x-ray identify two main groups of patients (with or without cardiopathy) who will follow different diagnostic protocols. The therapy of vasovagal syncope, which is based on beta-blockers, scopolamine, dysopiramide and plasma expanders, is reviewed.

Hemodynamics↗

PubMedDate not supplied

[Natriuretic peptides in heart failure].

The recent discovery of cardiac endocrine function, together with the development of accurate and feasible assay methods for cardiac natriuretic hormone evaluation, i.e. for B-type natriuretic peptide (BNP) and inactive peptide NT-proBNP have confirmed their pathophysiological and clinical significance for cardiovascular disease assessment. Concerning heart failure, their value is for diagnostic screening in selected/unselected populations, for differential diagnosis of dyspnea and for prognostic stratification, and as a guide for follow-up and treatment of patients. Recent Italian recommendations pointed out that BNP/NT-proBNP has a role in ruling-out the diagnosis of heart failure in patients with dubious signs/symptoms: plasma BNP/NT-proBNP concentrations help in the clinical evaluation of chronic heart failure patients when risk stratification is needed, whereas the routine BNP/NT-proBNP assay is still not recommended to guide therapeutic decision-making.

Heart Failure↗