Martin Štrucl

Effect of Regular Physical Training on Cutaneous Microvascular Reactivity

PURPOSE To investigate whether regular intense physical training induces changes in microvascular reactivity of human glabrous and nonglabrous skin. METHODS Subjects were physically trained competitive cyclists (N = 19) and age-matched sedentary controls (N = 20). We measured cutaneous microvascular blood flow on the dorsum of the hand (nonglabrous skin) and on the finger pulp (glabrous skin) using the laser-Doppler (LD) method. Endothelium-dependent vasodilation was assessed by an iontophoretic application of acetylcholine (ACh) on the dorsum of the hand and by an induction of postocclusive reactive hyperemia (PRH) on the finger pulp. Endothelium-independent vasodilation was assessed on the dorsum of the hand by iontophoretically applied sodium-nitroprusside (SNP). RESULTS The ACh-evoked increase in LD flux (LDF) was significantly greater in the group of cyclists (7.5-fold +/- 0.5 increase) as compared with controls (5.9-fold +/- 0.5). We found no differences in the peak LDF during PRH, whereas the recovery time of PRH was significantly longer (241.5 +/- 21.6 s in trained vs 154.6 +/- 9.3 s in sedentary group) and the area under the PRH curve significantly larger in the group of trained subjects (19,066 +/- 2,653 PU x s in trained vs 12,168 +/- 864 PU x s in sedentary). In contrast, we found a significantly smaller response to SNP in the group of cyclists (6.2-fold +/- 0.5 increase) as compared with sedentary subjects (7.8-fold +/- 0.5 increase). CONCLUSION The results of our study point to a greater vasodilator capacity of endothelium in glabrous as well as in nonglabrous skin in the group of physically trained subjects. In addition, our results indicate that regular physical activity also modifies the reactivity of vascular smooth muscle cells.

Autonomic nervous system and microvascular alterations in normotensives with a family history of hypertension

Autonomic nervous system and microvascular alterations at pre‐hypertensive stage of hypertension have still not been fully elucidated. We aimed at addressing central and local influences on microvascular reactivity at pre‐hypertensive stage of hypertension. To that end, we studied microvascular reactivity in 59 normotensives with a family history of hypertension and 46 controls. We measured laser‐Doppler flow on the finger nailfold skin in the resting condition, after an 8‐min occlusion of digital arteries and during local nitroglycerin application. Finger pressure, pulse and ECG were monitored by a Finapres device. Heart rate power spectral analysis was performed using Fast Fourier transformation. Baroreflex sensitivity was estimated by the sequence method. Normotensives with a family history of hypertension showed higher systolic pressure, decreased high‐frequency power of the heart rate variability spectrum and reduced baroreflex sensitivity in the resting condition as well as decreased fundamental frequency of laser‐Doppler flow oscillations during nitroglycerin application. We conclude that normotensives with a family history of hypertension exhibit altered sympathovagal balance with decreased parasympathetic activity at the cardiac level as well as increased myogenic microvascular reactivity.

Autonomic nervous system activity in normotensive subjects with a family history of hypertension.

This study was designed to address alterations in autonomic nervous system activity in normotensive subjects with a family history of hypertension. We compared the autonomic nervous system activity in 59 normotensives with a family history of hypertension and 46 normotensives with no family history of hypertension. Skin blood flow was measured using laser-Doppler method on the nailfold skin in the resting condition, during systemic cooling and during upright tilting. Finger blood pressure, pulse and ECG were monitored by a finapres device. Heart rate, systolic pressure and microvascular flow power spectral analyses were performed using fast Fourier transformation. Baroreflex sensitivity was estimated with the sequence method. Compared to the control group, normotensives with a family history of hypertension showed significantly higher systolic pressure, decreased proportion and area of the high-frequency band of the heart rate variability power spectrum and reduced baroreflex sensitivity in the resting condition as well as a decreased proportion and area of the high-frequency band of the heart rate variability power spectrum during systemic cooling. We also proved a different time course of baroreflex sensitivity during upright tilting in the two groups. In contrast, we did not find any significant differences in the parameters of systolic pressure and microvascular variability power spectra between the two groups. Our results indicate that even normotensives with a family history of hypertension exhibit an increased ratio of sympathetic to parasympathetic activity at the cardiac level; however, they do not show any alteration of the vascular sympathetic reactivity.

Coupling between visual evoked cerebral blood flow velocity responses and visual evoked potentials in migraneurs

Neurovascular coupling may be altered in migraneurs. Therefore, visual evoked potentials (VEP) and visually evoked cerebral blood flow velocity responses (VEFR) were simultaneously recorded in 30 healthy controls and 30 migraneurs interictally using a checkerboard stimulus with visual contrasts of 1%, 10% and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler and VEP were recorded from occipital leads. We found an increase in VEFR and VEP in both the healthy and migraneur groups (P < 0.01). VEFR were significantly higher in migraneurs (P < 0.01), while VEP did not significantly differ between the groups (P > 0.05). Regression showed a significant association between VEP and VEFR in both healthy controls (r = 0.66, P < 0.01) and migraneurs (r = 0.63, P < 0.01). The regression coefficient of migraneurs (b = 0.88, SE = 0.08) was significantly higher than that of healthy controls (b = 0.55, SE = 0.07) (P = 0.04). We conclude that neurovascular coupling is increased in migraneurs interictally.

The relationship between visually evoked cerebral blood flow velocity responses and visual-evoked potentials.

A noninvasive assessment of neurovascular coupling would be of great importance. For this reason, we simultaneously studied graded responses of visually evoked cerebral blood flow (CBF) velocity responses (VEFR) and visual-evoked potentials (VEP) to visual contrasts. The records were made from 30 healthy volunteers aged 38.0 +/- 9.6 years. The stimulus was a black-and-white checkerboard with visual contrasts (VC) of 1%, 10%, and 100%. The VEFR were measured in the posterior cerebral artery using transcranial Doppler, and the VEP were recoded from the scalp from occipital leads. To test the relationship between the VEFR and the VEP, a linear regression analysis was performed. We found that the VEFR at 100% VC were 36% higher than those at 10% VC (P < 0.01). The VEFR at 10% VC were 81% higher than those at 1% VC (P < 0.01). The VEP at 100% VC were 76% higher than those at 10% VC (P < 0.01). The VEP at 10% VC were 184% higher than those at 1% VC (P < 0.01). The linear regression showed a significant, moderate association between the VEP and the VEFR (r = 0.66, P < 0.01). The analysis of the regression slopes (b = 0.48 in older subjects vs. b = 0.58 in younger subjects) between two different age subgroups (P < 0.01) did not show any significant difference (P = 0.035). We concluded that a simultaneous recording of VEFR and VEP to graded visual contrasts could allow an assessment of neurovascular coupling.

Regular physical activity alters the postocclusive reactive hyperemia of the cutaneous microcirculation

Regular physical activity leads to increased endothelium-dependent vasodilatation. Postocclusive reactive hyperemia (PRH) is a transient increase of blood flow after the release of an arterial occlusion and has been used as a clinical tool to estimate endothelial function. The aim of our study was to assess the potential effect of regular physical training on PRH of skin microcirculation. Skin blood flux was estimated by laser-Doppler fluxmetry (LDF) in two groups of subjects: 12 highly trained athletes and 12 age-matched sedentary controls. LDF was measured on two specific skin sites: volar aspect of the forearm (nonglabrous area) and finger pulp of the middle finger (glabrous area). After the release of a 3-min occlusion of the brachial artery, we determined the following indices of PRH: the time to peak (tpeak), the maximal LDF (LDFpeak), the recovery time (trec), the area under the PRH curve (AUC). Baseline LDF did not differ between the trained and sedentary subjects in either site. On the forearm, we found no significant differences in either PRH parameter. On the contrary, on the finger pulp, there were statistically significant differences in the tpeak and the AUC (p < or = 0.05). The results show an altered PRH response of skin microcirculation in the finger pulp in the trained subjects. We may speculate that this could be the result of an increased endothelial vasodilator capacity. Further, the potential adaptations of the endothelium differ between the glabrous and nonglabrous skin sites.

Do visual neurophysiological tests reflect magnocellular deficit in dyslexic children

To address the question of a possible magnocellular visual deficit in children with reading problems (dyslexia), we examined pattern ERG and VEP responses to stimulation with checks of 24′, 49′ and 180′ in size and of 5%, 42% and 100% contrast level. Neurophysiological difference between children with reading problems and those without them was found confined to VEP which showed a significant prolongation of P100 wave in dyslexic children at highest contrast (100%) and smallest checks (24′). Pattern ERG was normal. These results support the assumption of a visual deficit in dyslexic children. However, they are not consistent with an isolated deficit of the magnocellular function, which, theoretically, would cause VEP changes to lower contrast and largest check stimuli.

The effect of glibenclamide on acetylcholine and sodium nitroprusside induced vasodilatation in human cutaneous microcirculation.

Objective:  KATP channels have an important regulatory role in resting vascular tone and during hypoxia. Their role in endothelium dependent and independent vasodilatation in human skin microcirculation is less known.

Central fiber contribution to W-shaped visual evoked potentials in patients with optic neuritis.

We studied W-shaped waveforms that occurred in full-field responses to pattern large-field stimulation in patients who had optic neuritis. Affected eyes showed no absolute scotomata; visual acuity was normal at the time of recording. To evaluate the contribution of macular- and paramacular-derived components to the development of the W-shaped waveforms in the patients, half-field and central full-field stimulation was used. The responses were compared with those obtained with the use of experimental scotomata in healthy subjects.The W-shaped waveforms recorded in the patients closely resembled the responses observed in healthy subjects after the introduction of experimental scotomata. In all affected eyes, half-field stimulation showed absence of the ipsilateral P100 component or its interaction with the P135 component. Enhanced paramacular N105 and P135 components were seen over the contralateral hemisphere. Responses to central full-field stimulation were an attenuated and prolonged P100 in the majority of affected eyes.Results of our study showed that W-shaped waveforms in response to large full-field stimulation may reflect impaired function of macular fibers. These electrophysiologic findings, however, were not always associated with evidence of a central field defect demonstrated by Friedmann perimetry.

The effect of α-adrenoceptor agonists and L-NMMA on cutaneous postocclusive reactive hyperemia

Postocclusive reactive hyperemia (PRH) is considered to be a locally mediated vascular reaction independent of sympathetic activity. However, experiments on animal vascular preparations have shown that alpha(2)-adrenoceptor activity interferes with the production of endothelium-derived nitric oxide (NO) that has been found to play an important role in the PRH response. We attempted to elucidate the role of endothelium-derived NO in the cutaneous PRH response. Especially, we aimed to clarify the interference of the alpha-adrenoceptor activity with NO mechanism in cutaneous microcirculation. We studied the effect of intradermal microinjection of the NO synthase inhibitor L-NMMA alone, alpha(1)-agonist phenylephrine alone, alpha(2)-agonist clonidine alone and L-NMMA in combination with each alpha-agonist. The effect of the saline solution injection was used as a reference value. Laser-Doppler flux was monitored in 11 healthy volunteers before and after a 4-minute and an 8-minute occlusion of digital arteries. The application of L-NMMA significantly reduced resting LD-flux (p<0.05) only in combination with alpha(2)-agonist but not alpha(1)-agonist. The application of L-NMMA alone changed the time in which LD flux reached half of the preocclusive value during the PRH response (T/2) only after 4-minute (p<0.05) but not after an 8-minute occlusion. Phenylephrine (alpha(1)-agonist) alone shortened (p<0.05), while clonidine (alpha(2)-agonist) alone prolonged T/2 (p<0.05) of 8-minute PRH. The combined application of L-NMMA and clonidine abolished the effect of clonidine alone on 8-minute PRH. In contrast, the combination of L-NMMA and phenylephrine did not cause any change of the PRH response when compared to the injection of phenylephrine alone. Our finding is consistent with the hypothesis that alpha(2)-adrenoceptor activity (in the condition of maximal agonist stimulation) could interfere with NO mechanisms in cutaneous microcirculation, probably by increasing NO production.