Biomedical subjects

J Jalonen

Publications and source records attributed to J Jalonen.

At least 37 records · Page 2Linked to original sources

PubMed1997

Dexmedetomidine as an anesthetic adjunct in coronary artery bypass grafting.

BACKGROUND: Alpha 2-adrenergic agonists decrease sympathetic tone with ensuing attenuation of neuroendocrine and hemodynamic responses to anesthesia and surgery. The effects of dexmedetomidine, a highly specific alpha 2-adrenergic agonist, on these responses have not been reported in patients undergoing coronary artery bypass grafting. METHODS: Eighty patients scheduled for elective coronary artery bypass grafting received, in a double-blind manner, either a saline placebo or a dexmedetomidine infusion, initially 50 ng.kg-1.min-1 for 30 min before induction of anesthesia with fentanyl, and then 7 ng.kg-1.min-1 unit the end of surgery. Filling pressures, blood pressure, and heart rate were controlled by intravenous fluid and by supplemental anesthetics and vasoactive drugs. RESULTS: Compared with placebo, dexmedetomidine decreased plasma norepinephrine concentrations by 90%, attenuated the increase of blood pressure during anesthesia (3 vs. 24 mmHg) and surgery (2 vs. 14 mmHg), but increased slightly the need for intravenous fluid challenge (29 vs. 20 patients) and induced more hypotension during cardiopulmonary bypass (9 vs. 0 patients). Dexmedetomidine decreased the incidence of intraoperative (2 vs. 13 patients) and postoperative (5 vs. 16 patients) tachycardia. Dexmedetomidine also decreased the need for additional doses of fentanyl (3.1 vs. 5.4), the increments of enflurane (4.4 vs. 5.6), the need for beta blockers (3 vs. 11 patients), and the incidence of fentanyl-induced muscle rigidity (15 vs. 33 patients) and postoperative shivering (13 vs. 23 patients). CONCLUSIONS: Intraoperative intravenous infusion of dexmedetomidine to patients undergoing coronary artery revascularization decreased intraoperative sympathetic tone and attenuated hyperdynamic responses to anesthesia and surgery but increased the propensity toward hypotension.

Adjuvants, Anesthesia↗

PubMed1997

Invasive haemodynamic monitoring: concepts and practical approaches.

The goal of haemodynamic care is to ensure adequate organ blood flow and oxygen supply. Clinical signs of organ perfusion have limited value in estimation of tissue perfusion, but invasive haemodynamic monitoring is needed to gain information of the underlying pathological condition and to guide oxygen delivery and haemodynamic therapy. Many of the available haemodynamic measurements involve pulmonary artery (PA) catheterization. Pressure measurements from PA catheters require meticulous attention to the dynamic properties of the transducer-pressure line system and appreciation of pressure variation owing to respiration. New techniques of continuous measurement of mixed venous oxygen saturation and cardiac output provide valuable trend data, allowing immediate diagnosis and treatment of pathological changes. Fast-response thermistor PA catheters are useful tools for estimating right ventricular function. Although clinicians generally regard PA-catheter data as a valuable therapy guide, few studies showing the beneficial influence on overall outcome have been carried out, and some studies have reported suboptimal understanding and utilization of these data. Transoesophageal echocardiography (TEE) is also a valuable monitor of left ventricular systolic and diastolic function and myocardial ischaemia in anaesthetized patients and in intensive care settings, but it requires a trained operator and is time-consuming. Continuously displayed TEE data, obtainable with automatic border detection, will make TEE even more useful in the near future. More effective monitors of perfusion and oxygenation of individual organs are needed. Less invasive techniques are also constantly sought. Combining data from several noninvasive monitors, including measurements of pulse oximetric O2 saturation, transthoracic impedance cardiac output and transcutaneous oxygen tension, has been reported to reflect closely changes obtained with more invasive monitoring.

Carbon Dioxide↗

PubMed1996

The effects of midazolam and ephedrine on post-exercise autonomic chronotropic control of the heart in normal subjects.

Benzodiazepines may induce hypotension by inhibiting the pressor response. Ephedrine has adrenergic effects on the circulation. After exercise, changes in cardiovascular control impair orthostatic tolerance. The impaired pressure response can be compensated for by chronotropic control of the heart. We studied the effect of midazolam and ephedrine on post-exercise cardiac autonomic chronotropic control in six 21-year-old female volunteers, who received single doses of 15 mg midazolam, 50 mg ephedrine, or placebo orally according to a placebo-controlled, double-blind, crossover design. After exercise, the subjects assumed the supine position for rest, then a -10 degrees head-down position followed by a 70 degrees head-up position. Power spectral analysis of heart rate variability for 7 min and steady-state brachial arterial blood pressure were measured in each position. After administration of midazolam, three subjects had an abnormal fall in their arterial blood pressure (with one presyncope) as a response to head-up tilt. Changes in heart rate variability exceeded those seen during placebo treatment (p < 0.01) and involved oscillations, suggesting activation of both sympathetic and parasympathetic dynamics. After ephedrine administration, arterial blood pressure increased during head-down tilt, but parasympathetic dynamics to the heart were dampened. Head-up tilt induced increased sympathetic stimulation of the heart and a sympathicotonic cardiovascular response (p < 0.01). In conclusion, midazolam induced unexpectedly great changes in dynamic cardiac control during cardiovascular stimulation. Ephedrine increased tonic sympathetic activity and stabilized the neural circulatory control of the heart by immobilizing dynamic parasympathetic activation.

Adrenergic Agonists↗

PubMed1996

Static-charge-sensitive bed ballistocardiography in cardiovascular monitoring.

We evaluated the autonomic influence on balistocardiograms recorded by a static-charge-sensitive bed for cardiovascular monitoring in nine healthy males (20-44 years) and its clinical use in 11 patients who underwent coronary bypass surgery (51-59 years). The ballistocardiogram displayed a distorted low amplitude from the empty beating heart during bypass surgery, impaired by a reduced effective transmural filling pressure of the heart, and returned to its pre-bypass level when the preload to the heart and its pumping was restored. Submaximal dynamic exercise and isoprenaline caused the heart rate to rise to 90-114 beats min-1, and increased the ballistocardiographic amplitude threefold, while at the same time shortening the interval between the R-wave of the electrocardiogram and the peak of the ballistocardiographic waveform (P < 0.01). In contrast, atropine accelerated the heart rate to 96 beats min-1, but did not significantly change the amplitude or temporal pattern of the ballistocardiogram. Thus, the ballistocardiogram reflects sympathetic and parasympathetic influence on the contractility of the myocardium and the effect of cardiac filling (e.g. during bypass surgery).

Adult↗

PubMed1996

Reactivity of skin blood flow and heart rate to thermal stimulation in infants during the first postnatal days and after a two-month follow-up.

The reactivity of skin blood flow and heart rate to periodic thermal stimulation was studied in 10 term small-for-gestational age (SGA) infants, in 9 preterm and 8 term normal-sized infants during the first two postnatal months. During the first postnatal days, the increase in thermally stimulated skin blood flow oscillations was absent in SGA infants but was clearly present in both preterm (p < 0.01) and term (p < 0.01) normal-sized infants. The responsiveness of SGA infants improved during the follow-up (p < 0.05). The response of the periodic heart rate variability of SGA and preterm infants was inferior to term normal-sized infants until the age of 2 months. The cardiovascular responsiveness of growth-retarded infants seems abnormal during the first days of life, and may impair their ability to meet stress, e.g. changes of ambient temperature.

Age Factors↗

PubMed1995

Skin blood flow oscillations respond more effectively to rhythmic thermal stimulation than to continuous or periodic breathing in newborn infants.

Effect of continuous (n = 30) and periodic (n = 5) breathing on forehead skin blood flow (SBF) oscillations was studied in healthy 3-day-old preterm and term infants. Femoral SBF was measured in 10 of the term infants during continuous breathing. Respiratory and SBF signals were analysed by power spectrum during the control period. The signal analysis was repeated during rhythmic thermal stimulation which was applied to the skin of each infant in order to synchronise spontaneous SBF oscillations. During the control period, the forehead and femoral SBF of all the studied infants oscillated at frequencies corresponding to the frequency of regular continuous breathing. External thermal stimulation decreased these high-frequency oscillations of forehead SBF in both preterm and term infants. Oscillations in femoral SBF of term infants remained unchanged. During periodic breathing, the spontaneous forehead SBF oscillation was synchronised to the frequency of respiratory amplitude variation. Despite periodic breathing, thermal stimulation was able to resynchronise the SBF oscillation to the stimulation frequency in 4/5 infants. Forehead SBF oscillates at the frequency of both continuous and periodic breathing in preterm as well as in term infants on postnatal day 3. Rhythmic thermal stimulation synchronises SBF and affects SBF more effectively than continuous or periodic breathing. These results suggest functional neural control of cutaneous vasculature at birth.

Blood Flow Velocity↗

PubMed1995

Cerebral circulation assessed by transcephalic electrical impedance during the first day of life--a potential predictor of outcome?

Pulsatile changes in intracranial blood volume (transcephalic electrical impedance, delta Z), arterial blood pressure (aBP) and respiration were studied during the first day after birth in 42 neonates with a birth weight of 1040-3850 g and gestational age of 26-36 weeks. The neurological outcome was assessed at 1 year of age to study the predictive ability of delta Z. delta Z, ECG, respirogram and direct aBP were recorded at 8-h intervals. Outcome was adverse in seven infants of whom two died from severe peri-intraventricular haemorrhage. PCO2 was higher (6.2 kPa) in the infants with adverse outcome than in those infants with favourable outcome (5.0 kPa) (P = 0.004). Blood glucose (4.5 vs. 3.3 mmol/l, P = 0.030) and first day administration of fluid (80 vs. 63 ml/kg/day, P = 0.003) behaved, respectively. Of the infants receiving dopamine therapy, 60% had adverse outcome while only 11% of those not receiving dopamine had adverse outcome (P = 0.016). Of the infants with high diastolic blood pressure levels, 32% had adverse outcome, while none with low diastolic blood pressure levels had adverse outcome (P = 0.031). Spectral analysis was used to examine signal variabilities in the frequency domain. During the first 24 h of life, the variabilities of aBP and respiration were equal in all the infants. The high-frequency delta Z signal variability (1.50-4.00 Hz, heart rate level) was found to be lower in the infants with adverse outcome (330 units) than in the infants with favourable outcome (1280 units, P = 0.017). The low delta Z variability allowed us to assume that there is a decrease of pulsatile cerebral blood flow (CBF) in the infants with adverse outcome. We speculate that this may result from the 'no reflow phenomenon', increased tissue pressure due to ischaemia and/or PIVH, the 'brain sparing effect' or constriction of main cerebral arteries due to increased pressure support or metabolic factors (PCO2, glucose). We believe that transcephalic impedance provides a potential cot-side method for monitoring cerebral circulation in the neonatal period with an ability to predict outcome.

Blood Glucose↗

PubMed1995

Multivariate autoregressive modelling combined with transcephalic electrical impedance: method to relate neonatal systemic circulation and respiration to cerebral circulation.

We studied the pulsatile component of cerebral circulation with transcephalic electrical impedance (delta Z) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance delta Z signal, ECG, arterial blood pressure, (aBP) and respirogram were recorded on analogue magnetic tape for 30 min. Artefact-free stationary segments (lasting for 2 min) of the four signals were digitised. A digital multivariate autoregressive (MAR) model was used to study frequency-specific variability in the signals and to quantify interrelations between the variabilities of delta Z, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of delta Z was lower and the influences of respiration and aBP on delta Z significantly greater in infants with severe PIVH than in controls. These changes were observed at high frequencies corresponding to respiration and heart rate. This may be interpreted as a marker of pressure passivism in the cerebral circulation following PIVH. We conclude that in preterm babies the application of MAR modelling, together with transcephalic impedance, may be a new, helpful and quantitative method for the study of simultaneous interrelations between variables of cerebral and systemic circulations and respiration.

Cerebral Hemorrhage↗

PubMed1995

Effects of dexmedetomidine on coronary hemodynamics and myocardial oxygen balance.

OBJECTIVE: alpha 2-adrenergic agonists decrease central sympathetic outflow and maintain normal transmural myocardial blood flow distribution, but intravenous bolus doses of these agents can also induce excessive coronary vasoconstriction and myocardial ischemia. The hypothesis of the present study was that a rapid intravenous bolus of dexmedetomidine, a specific alpha 2-adrenergic agonist, will cause coronary vasoconstriction and accompanying myocardial ischemia in young pigs. DESIGN: Prospective, controlled study on experimental animals. SETTING: Animal laboratory of a university cardiorespiratory research center. PARTICIPANTS: Twelve domestic 8-week-old open-chest pigs, anesthetized with high-dose fentanyl. Another six pigs served as controls. INTERVENTIONS: Sequential intravenous dexmedetomidine boluses of 3, 10, and 30 mg/kg were administered, and responses were measured during peak changes (2 minutes after injection) and during recovery after each dose. MEASUREMENTS AND MAIN RESULTS: Left anterior descending coronary artery blood flow, calculated regional coronary vascular resistance, myocardial extraction of oxygen and lactate, plasma catecholamine levels, and conventional central hemodynamic parameters were measured. The two higher doses of dexmedetomidine induced 21% and 29% immediate increases in left anterior descending coronary artery blood flow. At the same time mean systemic blood pressure and pulmonary capillary wedge pressure increased, and calculated regional coronary vascular resistance increased. Myocardial extraction of oxygen and lactate remained unchanged. CONCLUSIONS: Large intravenous doses of dexmedetomidine caused moderate regional coronary vasoconstriction without metabolic signs of myocardial ischemia in young domestic pigs at the same time as a marked vasoconstrictive response in the systemic circulation.

Adrenergic alpha-Agonists↗

PubMed1995

Myocardial reperfusion after coronary bypass surgery. Suture of only distal or all anastomoses with the aorta cross-clamped?

Sixty patients undergoing elective coronary artery bypass grafting were randomly allocated into two groups, each of 30 patients and similar as regards age, sex, number of coronary artery bypasses and left ventricular ejection fraction. In group A the proximal anastomoses of vein grafts were sutured after aortic declamping during partial occlusion of the aorta, and in group B these anastomoses were done during aortic cross-clamping. The aortic cross-clamp time was significantly longer in group B than in group A (72 vs 57 min, p < 0.0001). Myocardial cooling and rewarming and the number of sustained or possible perioperative myocardial infarctions were equal in both groups. Central haemodynamics showed no intergroup difference, before or after induction of anaesthesia or at the end of surgery. Conduction disturbances were more common in group A than in group B (12 vs 3, p = 0.0246), and transient external pacing was more often required in group A (9 vs 2, p = 0.0534). Myocardial reperfusion via native coronary arteries and bypass grafts gives better protection against conduction disturbances than does reperfusion via only native arteries, despite longer aortic cross-clamping time.

Anastomosis, Surgical↗

PubMed1994

Post-prandial effects in reactivity of forehead and mid-femoral skin blood flow and heart rate in neonates.

The effect of post-prandial period on the cutaneous vascular reactivity was studied in twelve full-term infants on their 3rd postnatal day. The differences in vasomotor reactions between the forehead and femoral skin were also investigated. Two 10-min control registrations about 30 and 90 min after feeding were followed by a registration of equal duration during thermal stimulation of the skin. The lower extremity of each infant was stimulated by warm and cool air currents (5 cycles/min) to induce periodic vasomotor changes. The fast Fourier transform was used to compute variability spectra for the recorded skin blood flow, heart rate and respiratory wave form signals. The skin blood flow became synchronised to the thermal stimulation in both skin regions. Neither the spontaneous nor synchronised oscillations of the skin blood flow differed significantly between femoral skin and forehead. The post-prandial time did not have any influence on this synchronisation. Heart rate variability was synchronised to the periodicity of thermal stimulation more 1.5 h after feeding than 0.5 h after feeding. Respiration was not affected. The results show that increasing post-prandial time has no influence on the synchronised oscillations of skin blood flow. However, it potentiates reactivity of heart rate to perturbations in the peripheral vasculature.

Body Temperature↗

PubMed1994

Elevated arterial blood pressure is associated with peri-intraventricular haemorrhage.

UNLABELLED: In a prospective study, brain ultrasound scans were performed in 42 newborns (median birth weight 1700 g, range 1020-3720 g; gestational age 32 weeks, 26-36) to reveal peri-intraventricular haemorrhage (PIVH) (grades I-IV) as well as echodensities (ED) and/or periventricular leucomalacia (PVL). ECG and arterial blood pressure were recorded on magnetic tape at 8-h intervals during the first 24 h of life for further computer analysis. Heart rate (HR) and its variability (HRV) indices RMSM (long-term variability) and RMSSD (short-term variability), together with their coefficients of variation, were computed. Systolic (SBP), diastolic (DBP), and mean blood pressures (MBP) were detected as average values for 2-min stationary segments together with the respective minima and maxima. The indices of variability and their coefficients of variation were computed for the arterial pressure. PIVH was found in 12 newborns and ED in 8 (of whom two developed PVL). The remaining 22 served as controls. Neither HR, HRV nor BP variability differed between the groups. DBP was higher in the group with PIVH (39 mmHg) when compared to both the controls (33 mmHg, P < 0.05) and the ED group (32 mmHg, P < 0.01). MBP behaved respectively (45 mmHg, 38 mmHg, 37 mmHg, P < 0.01). SBP behaved also similarly when gestational age and birth weight were used as covariates (57 mmHg, 48 mmHg, 47 mmHg, P < 0.01). CONCLUSION: Our results suggest that elevated diastolic, mean and systolic blood pressure are significantly associated with peri-intraventricular haemorrhage in preterm newborn infants.

Blood Pressure↗

PubMed1994

Effects of cardiopulmonary bypass on lymphocytes and their subset counts with or without use of autotransfusion devices.

Lymphocytes and their subset counts were determined in 30 cardiac surgery patients during cardiopulmonary bypass (CPB) with or without use of an autotransfusion device. In the autotransfusion group, centrifuged and washed autologous red blood cells (median 400 mL [range 200-770 mL]) and in the control group corresponding amounts of homologous packed red blood cells (median 500 mL [range 250-750 mL]) were transfused after declamping the aorta. The percentages of T lymphocytes (CD3) and T cytotoxic cells (CD8) increased in both groups (CD3 up to 5%, P < 0.05 and CD8 up to 35%, P < 0.01), but the percentage of T helper cells (CD4) did not change. The ratio of CD4/CD8 cells decreased (up to 34%, P < 0.01). The percentage of naive resting T cells (CD45RA) increased slightly (up to 8%, P < 0.05) whereas the percentages of memory T cells (CD45RO), T cells with IL-2 receptor (CD25), and natural killer cells (CD16) remained unaltered. The percentage of HLA-DR positive lymphocytes increased during CPB (up to 18%, P < 0.05), but it was decreased thereafter (up to 16%, P < 0.05). The percentage of monocytes (CD14) decreased first during CPB in both groups (up to 32%, P < 0.01), but it was higher in the autotransfusion device group (decreased 29% from initial value) than in the control group (decreased 65% from initial value) at the end of CPB (P < 0.05). This study shows that extracorporeal circulation has an effect on lymphocytes and their subset counts. The changes were slightly immunosuppressive. By contrast, use of autotransfusion devices had only minor effects.

Blood Transfusion↗

PubMed1994

Combined cardioplegia delivery offers no advantage over antegrade cardioplegia administration in coronary surgical patients with a preserved left ventricular function.

The effects of antegrade and of combined antegrade and retrograde cardioplegia were compared in 101 patients undergoing elective coronary artery surgery. The patients were randomly allocated to two groups: antegrade cardioplegia was administered in 53 patients and combined cardioplegia in 43 patients. The patients of the two groups were similar in age, sex and left ventricular ejection fraction. Aortic clamping time and the number of coronary bypasses were equal in the groups. The ventricular septal temperature was measured continuously during cardioplegia administration, after each distal anastomosis accomplished, and continuously after aortic declamping. Serum CK-MB activities were serially measured for up to 3 days postoperatively. Electrocardiograms (ECG) were taken preoperatively, as well as on the first, second and eighth postoperative days. The left ventricular function was evaluated with a volume load test preoperatively and on the first postoperative morning. The two groups were similar with respect to myocardial cooling, response to volume loading, the number of patients with perioperative myocardial infarctions, cardiac arrhythmias or atrioventricular conduction blocks and clinical outcome. However, the CK-MB activities were lower in the antegrade group suggesting better myocardial protection in an unselected group of patients undergoing coronary artery bypass grafting.

Analysis of Variance↗

PubMed1993

Dynamics of vasomotor thermoregulation of the skin in term and preterm neonates.

Eighteen fullterm infants and 17 preterm infants were studied on their 3rd day of life to investigate the reactivity of skin blood flow to thermal stimulation. The infants were studied during quiet sleep. After a 10-min control period a constant air current was used to synchronise the external cutaneous stimulus to the distal lower extremity of each infant: the heating element of an air blower was automatically switched on and off to generate successive warm and cool periods of equal duration (5 cycles/min). Heart rate (HR), skin blood flow (SBF) and respiratory waveform signals were recorded and their variability was analysed using the fast Fourier transform and spectral analysis. Fullterm infants showed a clear response to external thermal stimulation: both HR and SBF were synchronised to the stimulation frequency. A response of preterm infants was present but it was markedly attenuated in comparison to term infants. The effect of stimulation did not seem to be dependent on postnatal age. The results suggest that the vasomotor control is immature in preterm infants.

Body Temperature Regulation↗

PubMed1991

Clinical testing of thermally stimulated cardiovascular oscillations in man.

STUDY OBJECTIVE: The study assessed the physiological validity of an automatic thermal stimulation method to induce synchronised oscillations in the neural cardiovascular control system. DESIGN: Automatic alternating rhythmic warm and cool immersion of different skin areas of 18 males was done at different frequencies and water temperatures. The neurally mediated responses to the periodic thermal stimulation were measured from skin blood flow and heart rate and compared to those of a sham stimulation. Respiration was monitored for control purposes. The reproducibility of the stimulation and responses was examined. SUBJECTS: 18 young males volunteered for the study. MEASUREMENTS AND MAIN RESULTS: The water bath method produced reproducible thermal stimulation and responses of skin blood flow and heart rate. Rhythmic thermal stimulation at 0.013-0.096 Hz synchronised the oscillations of the forearm skin blood flow when the thermal stimulus amplitude exceeded 10 degrees C. The increase in the stimulus amplitude or enlargement of the stimulus area did not further increase the oscillatory response of skin blood flow. Sham stimulation or mean temperature of the periodic thermal stimulation in the range 23-33 degrees C did not influence the oscillations of skin blood flow. Local cooling of the stimulated lower legs attenuated the response of skin blood flow. Both thermal stimulation and sham stimulation affected heart rate, but no stable synchronisation of the periodic heart rate variability was found at supine rest. Thermal stimulation of the sitting subjects' forearm instead of legs increased the synchronisation of the periodic heart rate variability. CONCLUSIONS: The response of skin blood flow agreed with the theory of the thermal entrainment. In a supine man, both thermal stimulation and non-specific central nervous influences induced significant and reproducible interactions with periodic heart rate variability and respiration.

Adult↗

PubMed1991

Post-transfusion hepatitis after open-heart surgery in Finland--a prospective study.

A countrywide prospective study on open-heart surgery patients was performed between 1987 and 1989 to determine the prevalence and nature of post-transfusion hepatitis in Finland. Altogether 685 coronary by-pass operation patients, who received on average 12.3 units of blood products, were postoperatively followed for 6 months. Ten blood samples were drawn from each patient. Hepatitis was diagnosed when the alanine aminotransferase values exceeded the upper normal value 2.5 times in one sample and twice in another, and non-viral causes could reasonably be excluded. Eleven hepatitis cases (1.6%) were recorded with a mean incubation period of 8.4 weeks; all represented the non-A, non-B type. The majority had mild symptoms or were asymptomatic but two became icteric. Six patients (55%) had abnormal alanine aminotransferase values for at least 6 months, which indicates possible chronicity. These 685 open-heart surgery patients received a total of 8,436 units of blood products; thus the rate of NANBH cases per 1000 units was as low as 1.3. This is less than recently reported in six other prospective studies.

Adult↗

PubMed1990

Effect of posture on spontaneous and thermally stimulated cardiovascular oscillations.

STUDY OBJECTIVE: The aim of the study was to investigate the effect of posture on thermally stimulated cardiovascular oscillations. DESIGN: The effect of increased gravitational stress (rising from sitting to standing position) on the thermally stimulated cardiovascular oscillations was measured in young male volunteers. Extensive cardiovascular function data were obtained using a cardiovascular investigation protocol. SUBJECTS: The volunteers were five fit young men, aged 20-21 years. EXPERIMENTS AND MAIN RESULTS: Cardiovascular changes from sitting to standing indicated increased sympathetic and decreased parasympathetic influence on heart and skin blood vessels; mean heart rate increased, beat to beat heart rate variability diminished, high frequency periodic heart rate variability decreased, low frequency heart rate oscillations and ratio of low frequency to high frequency heart rate variability increased, mean skin blood flow and oscillations of skin blood flow decreased (all p less than 0.05). Thermal skin stimulation at 0.01-0.10 Hz frequency increased both sitting and standing 0.10 Hz periodic heart rate variability (p less than 0.05), and 0.10 Hz thermal stimulation entrained the heart rate oscillations in sitting and standing subjects (p less than 0.05). In contrast, skin blood flow oscillations in sitting subjects decreased, while in standing subjects it increased during 0.10 Hz thermal stimulation compared to the corresponding prestimulus values (p less than 0.04). CONCLUSIONS: On the basis of previous physiological experiments, these results suggest coupling between thermoregulatory and 0.10 Hz reflex activities.

Adult↗