Biomedical subjects

Pekka Talke

Publications and source records attributed to Pekka Talke.

8 recordsLinked to original sources

PubMed2006

Effect of peripheral vasoconstriction on pulse oximetry.

OBJECTIVE: We tested the hypothesis that peripheral vasodilation has an effect on arterial oxygen saturation measurements by pulse oximetry, independent of temperature. METHODS: Study 1 compared finger arterial oxygen saturation values (SpO(2)), before and after peripheral vasoconstriction while temperature was kept constant. This was achieved by administering dexmedetomidine (peripheral vasoconstrictor) to 16 volunteers given general anesthesia. Study 2 compared SpO(2) before and after peripheral vasodilation (brachial plexus block) in a neurally denervated left hand and a neurally innervated right hand in ten awake volunteers. In both studies measurements were also made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmission through a finger (LTF), finger temperature and of hemodynamic variables. RESULTS: In Study 1, systolic blood pressure, SpO(2) and LTF values increased (vasoconstriction) during dexmedetomidine infusion, (P<0.0001 for all) while there were no changes in finger temperature. In Study 2, in the left hand (axillary block), temperature increased by 1.9 +/- 1.6 degrees C (P=0.004), SpO(2) decreased by 2.5 +/- 1.0 % (P<0.0001) and LTF values decreased (vasodilation) by 42 +/- 8 % (P<0.0001) after axillary block. Simultaneously, the axillary block did not induce any changes in temperature, SpO(2) or LTF values in the neurally innervated right hand. CONCLUSIONS: Our results demonstrate that finger pulse oximeter SpO(2) measurements can be affected by peripheral vascular tone independent of temperature. The mechanism for this effect remains speculative and unproven.

Adult↗

PubMed2005

Placement of deep brain stimulator electrodes using real-time high-field interventional magnetic resonance imaging.

A methodology is presented for placing deep brain stimulator electrodes under direct MR image guidance. The technique utilized a small, skull-mounted trajectory guide that is optimized for accurate alignment under MR fluoroscopy. Iterative confirmation scans are used to monitor device alignment and brain penetration. The methodology was initially tested in a human skull phantom and proved capable of achieving submillimeter accuracy over a set of 16 separate targets that were accessed. The maximum error that was obtained in this preliminary test was 2 mm, motivating use of the technique in a clinical study. Subsequently, a total of eight deep brain stimulation electrodes were placed in five patients. Satisfactory placement was achieved on the first pass in seven of eight electrodes, while two passes were required with one electrode. Mean error from the intended target on the first pass was 1.0 +/- 0.8 mm (range = 0.1-1.9 mm). All procedures were considered technical successes and there were no intraoperative complications; however, one patient did develop a postoperative infection.

Brain↗

PubMed2005

Effect of alpha2B-adrenoceptor polymorphism on peripheral vasoconstriction in healthy volunteers.

BACKGROUND: Alpha-2B adrenoceptor is the vasoconstrictive subtype in the mouse. Human alpha2B-AR deletion (D) allele has been associated with loss of short-term agonist-promoted receptor desensitization, which may lead to increased vasoconstriction on alpha2 activation. The goal of this study was to test the hypothesis that alpha2B-adrenoceptor activation induces enhanced vasoconstriction in carriers of the DD genotype, compared with carriers of the insertion/insertion (II) genotype. METHODS: The authors administered increasing doses of dexmedetomidine (targeting plasma concentrations of 0.15, 0.3, 0.6, and 1.2 ng/ml) to 16 healthy young volunteers (8 carrying the alpha2B DD genotype, 8 carrying the II genotype) in whom sympatholytic effects of the drug were attenuated by general anesthesia. Measurements were made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmitted through a finger, finger blood flow by venous occlusion plethysmography, and hemodynamic variables. RESULTS: All concentration of dexmedetomidine increased light transmitted through the finger (vasoconstriction) and systolic blood pressure and decreased heart rate in both groups (P < 0.001 for all). Dexmedetomidine reduced finger arterial inflow only in the DD group (P < 0.001). Dexmedetomidine had no effect on finger venous outflow or venous capacitance. There were no significant differences between the II and DD groups in any of the variables. CONCLUSIONS: The results of this study confirm the alpha2 agonist induced vasomotor and hemodynamic effects in peripheral vasculature. However, the results do not support the hypothesis that alpha2B-adrenoceptor polymorphism has an effect on peripheral vasoconstriction in humans.

Adrenergic alpha-Agonists↗

PubMed2005

Alpha-2B adrenoceptor polymorphism and peripheral vasoconstriction.

OBJECTIVES: Alpha-2B adrenoceptors (AR) mediate vasoconstriction in the mice. A human alpha-2B AR deletion (D) variant has been associated with loss of short-term agonist-promoted receptor desensitization, which may lead to increased vasoconstriction upon alpha-2 AR activation. This study tested the hypothesis that alpha-2 AR activation will induce enhanced vasoconstriction in carriers of the alpha-2B AR DD genotype, compared to carriers of the II or the DI genotypes. METHODS: We administered 1 microg/kg dexmedetomidine (an alpha-2 agonist) intravenously to 80 surgical patients in whom sympatholytic effects of the drug were attenuated by general anesthesia. Measurements were made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmission through a finger (LTF) and of hemodynamic variables. RESULTS: Dexmedetomidine increased LTF (vasoconstriction), induced an initial increase in systolic blood pressure and decreased heart rate in all genotype groups (P<0.0001 for all). Three min after the start of dexmedetomidine infusion, the increase in LTF was more pronounced (P=0.014) in the DD group compared to the DI and II groups. There were no significant differences in LTF values between the groups at the end of or 5 min after dexmedetomidine infusion. There were no differences in systolic blood pressure or heart rate values between the groups during or after the dexmedetomidine infusion. CONCLUSIONS: The results of this study confirm that the alpha-2 agonist dexmedetomidine induced marked peripheral vasoconstriction. Subjects with the alpha 2B DD genotype had an enhanced vasoconstrictive response at the beginning of dexmedetomidine infusion. However, this enhanced vasoconstrictive response was not sustained throughout or after the 15-min dexmedetomidine infusion.

Adrenergic alpha-2 Receptor Agonists↗

PubMed2004

Intracranial vascular surgery.

PURPOSE OF REVIEW: To review the recent literature on intracranial vascular surgery, to summarize the main findings, and to discuss the impact of these findings on clinical practice. RECENT FINDINGS: Three areas of vascular neurosurgery literature have recently generated significant interest, controversy and heated debate: (1) The International Study of Unruptured Intracranial Aneurysms studied the natural history and treatment options of unruptured aneurysms, and reported surprisingly low aneurysm rupture rates for small asymptomatic aneurysms. The study also reported favorable morbidity rates for endovascular treatment compared with surgical treatment of unruptured aneurysms. (2) The International Subarachnoid Aneurysm Trial compared endovascular and surgical treatments for ruptured intracranial aneurysms. The study concluded that the outcome in terms of survival free of disability at one year was significantly better with endovascular coiling. (3) The Intraoperative Hypothermia for Aneurysm Surgery Trial compared intraoperative hypothermia and normothermia for potential neuroprotection during neurovascular procedures. Preliminary results suggest no difference between the treatments. SUMMARY: The International Study of Unruptured Intracranial Aneurysms and the International Subarachnoid Aneurysm Trial have provided data on the natural history of unruptured intracranial aneurysms and on the morbidity and mortality of surgical and endovascular treatments for intracranial aneurysms. Although morbidity rates of endovascular therapy compare favorably with those of surgery, long-term data on the efficacy of endovascular coiling of aneurysms are needed to assess the overall risk-benefit ratio of these therapies.

Journal Article↗

PubMed2003

Systemically administered alpha2-agonist-induced peripheral vasoconstriction in humans.

BACKGROUND: alpha(2)-Adrenoceptors mediate both sympatholytic and vasoconstrictive hemodynamic effects. The goal of this study was to profile the peripheral vasoconstrictive effects of a selective alpha(2)-adrenoceptor agonist in isolation from the sympatholytic effects it also induces. METHODS: The authors administered increasing plasma target concentrations of dexmedetomidine (0.075, 0.15, 0.3, and 0.6 ng/mL) or saline placebo to healthy young volunteers in whom the sympatholytic effects of the drug were attenuated in one of two ways: general anesthesia (propofol-alfentanil-nitrous oxide) or axillary brachial plexus block. Measurements were made of finger blood volume (an indicator of vasoconstriction) by photoplethysmographic determination of light transmitted through a finger (LTF) and hemodynamic variables. Measurements made before and during the four steps of infusion were compared by repeated-measures ANOVA. RESULTS: In anesthetized volunteers, all concentrations of dexmedetomidine increased LTF (vasoconstriction) and systolic blood pressure (P < 0.001 for both), whereas placebo did not. In awake volunteers, all concentrations decreased systolic blood pressure (P < 0.001). Concentrations of 0.15, 0.3, and 0.6 ng/mL decreased LTF (vasodilation) in the neurally intact hand; in contrast, the same concentrations increased LTF (vasoconstriction) in the sympathectomized hand (P < 0.001 for both). CONCLUSIONS: The results of this study are the first to characterize the lower end of the dose-response curve for vasoconstriction induced by dexmedetomidine. By denervating the vascular bed of interest or by decreasing sympathetic nervous system activity, the authors were able to observe vasoconstriction induced by a systemically administered alpha(2)-agonist with minimal interference from the sympatholytic effects of the drug.

Adrenergic alpha-2 Receptor Agonists↗

PubMed2002

A comparison of three anesthetic techniques in patients undergoing craniotomy for supratentorial intracranial surgery.

UNLABELLED: Several anesthetic techniques have been used successfully to provide anesthesia for resection of intracranial supratentorial mass lesions. One technique used to enhance recovery involves changing anesthesia from vapor-based to propofol-based for cranial closure. However, there are no data to support a beneficial effect of this approach in the immediate postoperative period after craniotomy. We evaluated 3 anesthetic techniques in 60 patients undergoing elective surgery for supratentorial mass lesions. Patients were randomly assigned to three anesthesia study groups: propofol infusion, isoflurane inhalation, and these two techniques combined. In the combination group, once the dura was closed, isoflurane was discontinued and propofol infusion simultaneously started. We studied intra- and postoperative hemodynamics and several recovery variables for 2 h after the end of anesthesia. Baseline and average intraoperative blood pressure and heart rate values did not differ among the groups. Heart rate and blood pressure increased similarly in all groups in response to intubation and pin placement and postoperatively. None of the recovery event times (open eyes, extubation, follow commands, oriented, Aldrete score) or psychomotor test performance differed significantly. We conclude that the sequential administration of isoflurane and propofol did not provide earlier recovery and cognition than the intraoperative use of isoflurane alone. IMPLICATIONS: We evaluated three anesthetic techniques with and without propofol in patients undergoing elective surgery for supratentorial mass lesions by using a prospective, randomized clinical study design and found that the three anesthetics did not differ in intra- or postoperative hemodynamic stability or early postoperative recovery variables.

Adult↗

PubMed2002

Autonomic nervous system responses during sedative infusions of dexmedetomidine.

BACKGROUND: The purpose of this study was to determine the effects of dexmedetomidine on systemic and cardiac autonomic reflex responses during rest and during thermal stress. METHODS: Volunteers received either placebo or low- or high-dose dexmedetomidine (target plasma concentrations 0.3 or 0.6 ng/ml, respectively) infusions in a prospectively randomized, double-blinded crossover study design. After 1 h, baroreflex sensitivity was assessed, and then core body temperature was raised to the sweating threshold and then lowered to the shivering threshold. Plasma catecholamines and blood pressure were measured, and cardiac autonomic responses were assessed by analysis of heart rate variability. RESULTS: Compared with placebo, plasma norepinephrine concentrations, blood pressure, heart rate, and some heart rate variability measures were lower after 1-h infusion of dexmedetomidine, but baroreflex responses did not differ significantly. Dexmedetomidine blunted the systemic and cardiac sympathetic effects of sweating observed during placebo infusion but had no effect on parasympathetic measures. Increases in blood pressure, and systemic catecholamines due to shivering were observed during placebo and dexmedetomidine, but these responses were less with dexmedetomidine. During shivering, dexmedetomidine infusion was associated with higher low-frequency and high-frequency heart rate variability power but lower heart rate compared with the sweating threshold and with the control period, suggesting nonreciprocal cardiac autonomic responses. CONCLUSIONS: Infusion of dexmedetomidine results in compensated reductions in systemic sympathetic tone without changes in baroreflex sensitivity. Dexmedetomidine blunts heart rate and the systemic sympathetic activation due to sweating, but it is less effective in blunting cardiac sympathetic responses to shivering. During dexmedetomidine infusion, cardiac sympathetic and parasympathetic tone may have nonreciprocal changes during shivering.

Adult↗