93 research outputs found
Forearm training attenuates sympathetic responses to prolonged rhythmic forearm exercise
No full text Sinoway, Lawrence, Jeffrey Shenberger, Gretchen Leaman, Robert Zelis, Kristen Gray, Robert Baily, and Urs Leuenberger.Forearm training attenuates sympathetic responses to prolonged rhythmic forearm exercise. J. Appl. Physiol. 81(4): 1778–1784, 1996.—We previously demonstrated that nonfatiguing rhythmic forearm exercise at 25% maximal voluntary contraction (12 2-s contractions/min) evokes sympathoexcitation without significant engagement of metabolite-sensitive muscle afferents (B. A. Batman, J. C. Hardy, U. A. Leuenberger, M. B. Smith, Q. X. Yang, and L. I. Sinoway. J. Appl. Physiol. 76: 1077–1081, 1994). This is in contrast to the sympathetic nervous system responses observed during fatiguing static forearm exercise where metabolite-sensitive afferents are the key determinants of sympathetic activation. In this report we examined whether forearm exercise training would attenuate sympathetic nervous system responses to rhythmic forearm exercise. We measured heart rate, mean arterial blood pressure (MAP), muscle sympathetic nerve activity (microneurography), plasma norepinephrine (NE), and NE spillover and clearance (tritiated NE kinetics) during nonfatiguing rhythmic forearm exercise before and after a 4-wk unilateral forearm training paradigm. Training had no effect on forearm mass, maximal voluntary contraction, or heart rate but did attenuate the increase in MAP (increase in MAP: from 15.2 ± 1.8 before training to 11.4 ± 1.4 mmHg after training; P < 0.017), muscle sympathetic nerve activity (increase in bursts: from 10.8 ± 1.4 before training to 6.2 ± 1.1 bursts/min after training; P < 0.030), and the NE spillover (increase in arterial spillover: from 1.3 ± 0.2 before training to 0.6 ± 0.2 nmol ⋅ min−1 ⋅ m−2after training, P < 0.014; increase in venous spillover: from 2.0 ± 0.6 before training to 1.0 ± 0.5 nmol ⋅ min−1 ⋅ m−2after training, P < 0.037) seen in response to exercise performed by the trained forearm. Thus forearm training reduces sympathetic responses during a nonfatiguing rhythmic handgrip paradigm that does not engage muscle metaboreceptors. We speculate that this effect is due to a conditioning-induced reduction in mechanically sensitive muscle afferent discharge. </jats:p
Forearm training reduces the exercise pressor reflex during ischemic rhythmic handgrip
No full text Mostoufi-Moab, Sogol, Eric J. Widmaier, Jacob A. Cornett, Kristen Gray, and Lawrence I. Sinoway. Forearm training reduces the exercise pressor reflex during ischemic rhythmic handgrip. J. Appl. Physiol. 84(1): 277–283, 1998.—We examined the effects of unilateral, nondominant forearm training (4 wk) on blood pressure and forearm metabolites during ischemic and nonischemic rhythmic handgrip (30 1-s contractions/min at 25% maximal voluntary contraction). Contractions were performed by 10 subjects with the forearm enclosed in a pressurized Plexiglas tank to induce ischemic conditions. Training increased the endurance time in the nondominant arm by 102% ( protocol 1). In protocol 2, tank pressure was increased in increments of 10 mmHg/min to +50 mmHg. Training raised the positive-pressure threshold necessary to engage the pressor response. In protocol 3, handgrip was performed at +50 mmHg and venous blood samples were analyzed. Training attenuated mean arterial pressure (109 ± 5 and 98 ± 4 mmHg pre- and posttraining, respectively, P < 0.01), venous lactate (2.9 ± 0.4 and 1.8 ± 0.3 mmol/l pre- and posttraining, respectively, P < 0.01), and the pH response (7.21 ± 0.02 and 7.25 ± 0.01, pre- and posttraining, respectively, P < 0.01). However, deep venous O2 saturation was unchanged. Training increased the positive-pressure threshold for metaboreceptor engagement, reduced metabolite concentrations, and reduced mean arterial pressure during ischemic exercise. </jats:p
Sympathetic discharge and vascular resistance after bed rest
No full text Shoemaker, J. Kevin, Cynthia S. Hogeman, Urs A. Leuenberger, Michael D. Herr, Kristen Gray, David H. Silber, and Lawrence I. Sinoway. Sympathetic discharge and vascular resistance after bed rest. J. Appl. Physiol. 84(2): 612–617, 1998.—The effect of −6° head-down-tilt bed rest (HDBR) for 14 days on supine sympathetic discharge and cardiovascular hemodynamics at rest was assessed. Mean arterial pressure, heart rate ( n = 25), muscle sympathetic nerve activity (MSNA; n = 16) burst frequency, and forearm blood flow ( n = 14) were measured, and forearm vascular resistance (FVR) was calculated. Stroke distance, our index of stroke volume, was derived from measurements of aortic mean blood velocity (Doppler) and R-R interval ( n = 7). With these data, an index of total peripheral resistance was determined. Heart rate at rest was greater in the post (71 ± 2 beats/min)- compared with the pre-HDBR test (66 ± 2 beats/min; P < 0.003), but mean arterial pressure was unchanged. Aortic stroke distance during post-HDBR (15.5 ± 1.1 cm/beat) was reduced from pre-HDBR levels (20.0 ± 1.5 cm/beat) ( P < 0.03). Also, MSNA burst frequency was reduced in the post (16.7 ± 2.8 beats/min)- compared with the pre (25.2 ± 2.6 beats/min)-HDBR condition ( P < 0.01). Bed rest did not alter forearm blood flow, FVR, or total peripheral resistance. Thus reductions in MSNA with HDBR were not associated with a decrease in FVR. </jats:p
Revisiting the Role of Oxygen Therapy in Cardiac Patients
No full textOver the past century, multiple studies lacking the precision of today's advanced technology provided conflicting data on the effects of oxygen therapy in normoxic cardiac patients. More importantly, no randomized, blinded, controlled studies have shown a benefit of such treatment. Yet the use of supplemental oxygen is widespread in cardiac patients. In these conditions, inadvertent hyperoxia commonly occurs because of concerns to ensure sufficient oxygenation and because hyperoxia is not perceived to be detrimental. In recent years, there has been mounting evidence demonstrating the potential adverse effects of hyperoxia on the cardiovascular system. In this report, we review data examining the effects of supplemental oxygen in normoxic patients with acute presentations of coronary artery disease. It is also the aim of this report to emphasize the point that oxygen therapy might have major adverse physiologic effects that must be considered when it is employed
Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis
No full text Shoemaker, J. Kevin, Prasant Pandey, Michael D. Herr, David H. Silber, Qing X. Yang, Michael B. Smith, Kristen Gray, and Lawrence I. Sinoway. Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis. J. Appl. Physiol. 82(6): 1932–1938, 1997.—It is unclear whether sympathetic tone opposes dilator influences in exercising skeletal muscle. We examined high levels of sympathetic tone, evoked by lower body negative pressure (LBNP, −60 mmHg) on intramuscular pH and phosphocreatine (PCr) levels (31P-nuclear magnetic resonance spectroscopy) during graded rhythmic handgrip (30 contractions/min; ∼17, 34, 52 and 69% maximal voluntary contraction). Exercise was performed with LBNP and without LBNP (Control). At the end of exercise, LBNP caused lower levels of muscle pH (6.59 ± 0.09) compared with Control (6.78 ± 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was less during the recovery phase of the LBNP trial. Exercise mean arterial pressure was not altered by LBNP. The protocols were repeated with measurements of forearm blood flow velocity and deep venous samples (active forearm) of hemoglobin (Hb) saturation, pH, and lactate. With LBNP, mean blood velocity was reduced at rest, during exercise, and during recovery compared with Control ( P < 0.05). Also, venous Hb saturation and pH levels during exercise and recovery were lower with LBNP and lactate was higher compared with Control ( P < 0.05). We conclude that LBNP enhanced sympathetic tone and reduced oxygen transport. At high workloads, there was a greater reliance on nonoxidative metabolism. In other words, sympatholysis did not occur. </jats:p
Inventing the world grant university: Chinese international students' mobilities, literacies, and identities
No full textIncludes bibliographical references.In English with passages in Chinese with English translationCulturally responsive pedagogies developed for undergraduate Chinese international students, who have enrolled in Western institutions in increasing numbers in recent years. Focusing on the literacy practices of these students at Michigan State University and at Sinoway International Educational Summer School in China, Fraiberg.--Provided by publisher.Friction in the educational marketplace -- Geographies of difference: underground knotworks and transnational social fields -- Relationship webs in academic lives -- Learning lords and scumbags: underground literacies and learning economies -- Study abroad at home -- Assembling the cosmopolitan -- Gaming life like outlaws
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