Effects of different frequencies of transcutaneous electrical nerve stimulation on venous vascular reactivity

Transcutaneous electrical nerve stimulation (TENS) is a type of therapy used primarily for analgesia, but also presents changes in the cardiovascular system responses; its effects are dependent upon application parameters. Alterations to the cardiovascular system suggest that TENS may modify venous vascular response. The objective of this study was to evaluate the effects of TENS at different frequencies (10 and 100 Hz) on venous vascular reactivity in healthy subjects. Twenty-nine healthy male volunteers were randomized into three groups: placebo (n=10), low-frequency TENS (10 Hz, n=9) and high-frequency TENS (100 Hz, n=10). TENS was applied for 30 min in the nervous plexus trajectory from the superior member (from cervical to dorsal region of the fist) at low (10 Hz/200 μs) and high frequency (100 Hz/200 μs) with its intensity adjusted below the motor threshold and intensified every 5 min, intending to avoid accommodation. Venous vascular reactivity in response to phenylephrine, acetylcholine (endothelium-dependent) and sodium nitroprusside (endothelium-independent) was assessed by the dorsal hand vein technique. The phenylephrine effective dose to achieve 70% vasoconstriction was reduced 53% (P<0.01) using low-frequency TENS (10 Hz), while in high-frequency stimulation (100 Hz), a 47% increased dose was needed (P<0.01). The endothelium-dependent (acetylcholine) and independent (sodium nitroprusside) responses were not modified by TENS, which modifies venous responsiveness, and increases the low-frequency sensitivity of α1-adrenergic receptors and shows high-frequency opposite effects. These changes represent an important vascular effect caused by TENS with implications for hemodynamics, inflammation and analgesia.

Alterações hematológicas provocadas pelo ultra-som de 1MHz na forma contínua aplicadas no tratamento da fase aguda de lesão muscular iatrogênica em ratos / Hematological changes produced by 1MHz continuous ultrasound, applied during the acute phase of iatrogenic muscle injury in rats

CONTEXTUALIZAÇÃO: A literatura demonstra o efeito benéfico da terapia ultra-sônica de baixa intensidade sobre o processo de cicatrização de vários tecidos. OBJETIVO: Avaliar o efeito do ultra-som contínuo (USC) sobre a dinâmica hematológica do processo inflamatório agudo de lesão muscular iatrogênica. MÉTODOS: Foram utilizados 16 ratos da raça Wistar (350 a 400g), divididos em grupo controle (GC=8) e grupo experimental (G1=8), submetidos à incisão cirúrgica na face lateral do membro posterior direito, onde o músculo bíceps femoral foi lesionado transversalmente. O USC (1MHz) foi aplicado sobre o local da lesão a uma intensidade de 0,4W/cm², durante três minutos, na 1ª, 8ª e 24ª hora após a lesão. Nestes períodos, foram realizadas as coletas de sangue por punção venosa do plexo retroorbital para as análises sangüíneas das séries brancas e vermelhas. RESULTADOS: O USC diminui 8 por cento dos eritrócitos na primeira coleta (9,9±0,1 versus 7,8±0,1; x10(5)/mm³, p<0,001); dobrou os neutrófilos segmentados na segunda coleta (3.166,8±161,4 versus 6.426,2±306,0; x10³/mm³ p=0,008) e os eosinófilos na terceira coleta (2.883,6±99,0 versus 4.714,4±275,2; x10³/mm³ p=0,011) em relação ao GC. Não se observaram diferenças entre os grupos no hematócrito, leucócitos totais, neutrófilos bastonetes, monócitos e linfócitos, nos três momentos estudados. CONCLUSÕES: A aplicação do USC no tratamento agudo de lesão muscular é contra-indicada nesta condição, pois promove a redução dos eritrócitos, aumento dos neutrófilos segmentados e dos eosinófilos, favorecendo a hemorragia e o aumento do processo inflamatório.

BACKGROUND: The literature shows the beneficial effects of low-intensity ultrasound therapy on the healing process of several biological tissues. OBJECTIVE: To evaluate the effects of continuous ultrasound (CUS) on the hematological dynamics of an acute inflammatory process in iatrogenic muscle injuries. METHODS: Sixteen Wistar rats (350 to 400g) were divided into a control group (CG=8) and an experimental group (G1=8). The rats were submitted to a surgical incision on the lateral aspect of the right hind limb, in which the biceps femoris muscle was transversally injured. The CUS (1MHz) was applied to the injury site at an intensity of 0.4W/cm², for three minutes, in 1, 8 and 24 hour after the injury. At these times, blood was drawn by venipuncture of the retroorbital plexus, for analysis of red and white blood cells. RESULTS: The CUS reduced erythrocytes in 8 percent at the first blood collection (9.9±0.1 versus 7.8±0.1; x10(5)/mm³; p<0.001); it doubled the number of segmented neutrophils at the second collection (3,166.8±161.4 versus 6,426.2±306.0; x10³/mm³; p=0.008) and the eosinophils at the third collection (2,883.6±99.0 versus 4,714.4±275.2; x10³/mm³; p=0.011), in relation to the CG. No differences between the groups were seen with regard to hematocrit, total leukocytes, rod neutrophils, monocytes or lymphocytes at the three times studied. CONCLUSIONS: Application of CUS for acute treatment of muscle injuries is contraindicated under this condition, because it promotes reductions in erythrocytes and increases in segmented neutrophils and eosinophils, thus favoring hemorrhage and increasing inflammatory process.

Hemodialysis improves endothelial venous function in end-stage renal disease

The objective of the present study was to determine the acute effect of hemodialysis on endothelial venous function and oxidative stress. We studied 9 patients with end-stage renal disease (ESRD), 36.8 ± 3.0 years old, arterial pressure 133.8 ± 6.8/80.0 ± 5.0 mmHg, time on dialysis 55.0 ± 16.6 months, immediately before and after a hemodialysis session, and 10 healthy controls matched for age and gender. Endothelial function was assessed by the dorsal hand vein technique using graded local infusion of acetylcholine (endothelium-dependent venodilation, EDV) and sodium nitroprusside (endothelium-independent venodilation). Oxidative stress was evaluated by measuring protein oxidative damage (carbonyls) and antioxidant defense (total radical trapping antioxidant potential - TRAP) in blood samples. All patients were receiving recombinant human erythropoietin for at least 3 months and were not taking nitrates or a-receptor antagonists. EDV was significantly lower in ESRD patients before hemodialysis (65.6 ± 10.5) vs controls (109.6 ± 10.8; P = 0.010) and after hemodialysis (106.6 ± 15.7; P = 0.045). Endothelium-independent venodilation was similar in all comparisons performed. The hemodialysis session significantly decreased TRAP (402.0 ± 53.5 vs 157.1 ± 28.3 U Trolox/µL plasma; P = 0.001). There was no difference in protein damage comparing ESRD patients before and after hemodialysis. The magnitude of change in the EDV was correlated negatively with the magnitude of change in TRAP (r = -0.70; P = 0.037). These results suggest that a hemodialysis session improves endothelial venous function, in association with an antioxidant effect.