摘要:

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean±1 SD) was 0.4 ± 0.3, 1.76 ± 0.65, 0.90 ± 0.32 and 1.06 ± 0.59 l min‐1, and mean arterial pressures (MAP) were 104±13, 140±14, 160 ± 17 and 161 ± 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation.Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3–3.5 l min‐1, which corresponded to 150 ml 100 g‐1min‐1. When both O2uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found.When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood f

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08844.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The changes in muscle content of carnitine and acetylcarnitine have been studied during incremental dynamic exercise. Six subjects exercised for 10 min on an ergometer at 40 and 75% of their maximal oxygen uptake (Vo2max) and to fatigue at 100% ofVo2max (about 4 min). Muscle samples were taken from the quadriceps femoris muscle at rest and after exercise. Muscle content of free carnitine was (x̄± SE) 15.9 ± 1.7 mmol kg‐1d. wt (dry weight) at rest and remained unchanged after exercise at low intensity but decreased to 5.9 ± 0.6 and 4.6 ± 0.5 mmol kg‐1d. wt after exercise at 75 and 100% ofVo2max respectively. Acetylcarnine content at rest was 6.9 ± 1.9 mmol kg‐1d. wt and increased during exercise in correspondence with the decrease in free carnitine. Muscle content of pyruvate and lactate was unchanged after exercise at 40% ofVo2max but increased at the higher intensities. The parallel increases in acetylcarnitine, pyruvate and lactate indicate that formation of acetylcarnitine is augmented when the availability of glycolytic three‐carbon metabolites is high and is consistent with the idea that acetylcarnitine provides a sink for pyruvate and acetyl CoA. This could be of importance for the maintenance of an adequate level of CoA and thus function of the tricarboxyl

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08845.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Healthy males (n= 14) performed three bouts of 32 unilateral, maximal voluntary concentric (CON) or eccentric (ECC) quadriceps muscle actions on separate days. Surface electromyography (EMG) of the m. vastus lateralis (VL) and m. rectus femoris (RF) and torque were measured. Integrated EMG (IEMG), mean (MPF) and median power frequencies and torque were averaged for seven separate blocks of four consecutive muscle actions. Torque was greater (P<0.05) for ECC than for CON muscle actions at the start of exercise. It did not decline throughout ECC exercise, but decreased (P<0.05) markedly for each bout and over bouts of CON exercise. Thus, torque overall was substantially greater (P<0.05) for ECC than for CON exercise. At the start of exercise IEMG of VL or RF was greater (P<0.05) for CON than for ECC muscle actions. This was also true for overall IEMG activity during exercise. The IEMG increased (P<0.05) modestly for both muscles during each bout of CON or ECC muscle actions, but did not change for the VL over bouts. The IEMG of RF decreased (P<0.05) modestly over CON but not ECC exercise bouts. At the beginning of the first bout of exercise the IEMG/torque ratio was twofold greater (P<0.05) for CON than ECC muscle actions. The ratio of IEMG/torque increased (P<0.05) markedly during CON but did not change during ECC exercise. Thus, by the end of the third bout there was a fivefold difference (P<0.05). The MPF decreased (P<0.05) substantially in each CON bout with only a partial recovery between bouts. In contrast, MPF remained the same within each bout and over bouts of ECC exercise. These results indicate that the ability to maintain force during repeated bouts of maximal voluntary muscle actions at a relatively high angular velocity is remarkably greater for eccentric than for concentric exercise. It is suggested that the factors responsible for fatigue and for changes in the EMG signal pattern during concentric exercise do not materialize during, or are different for, eccentric exercise as performed here.

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08846.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The purpose of this study was to determine in man the effect on the breathing pattern of continuous positive (CPAP), continuous negative (CNAP) and positive end‐expiratory (PEEP) airway pressure during air breathing and CO2inhalation. Six subjects were exposed to CPAP, CNAP and PEEP 0.5 kPa, while five subjects were exposed to CPAP and CNAP 0.8 kPa.End‐expiratory lung volume increased during CPAP 0.8 kPa and decreased during CNAP 0.8 kPa. CPAP induced more extensive changes in the ventilatory pattern, and the changes in each parameter were larger than observed during CNAP and PEEP at the same pressure level. In contrast to previous reports we found the effect of CO2inhalation combined with the effect of pressure breathing to be not stronger than additive. Even moderate CPAP induced alveolar hyperventilation with marked reduction in arterialPCO2(PaCO2) when breathing air. With increasing fraction of CO2in the inspiratory gas, the difference inPaCO2between CPAP and no CPAP disappeared. PEEP also affected the breathing pattern in that it induced an increase in mean inspiratory flow and mean expiratory flow and a reduction in inspiratory duration. Occurrence of ventilatory pauses depended on whether mouthpiece or facemask was used. CPAP and CNAP did not influence the occurrence of pauses, while PEEP prolonged post‐expiratory pauses.We conclude that CPAP, CNAP and PEEP induce active ventilatory responses in man and that strong mechanisms are involved during CPAP sincePaCO2is markedly re

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08847.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The contribution of different receptor subtypes in the contractile response during cooling in human hand vessels is of considerable interest in the understanding of cold‐induced peripheral vasospasm as it appears in Raynaud's phenomenon. Subcutaneous vein segments from 50 patients undergoing hand operations not related to vascular disorders were examinedin vitro.The temperature in the organ bath was initially 37 °C and was either continuously lowered to 10 °C or kept constant at 37 °C, 29 °C or 20 °C. The characteristics of the α‐adrenoceptor‐mediated motor response were elucidated with the use of the α1‐antagonist, prazosin, and the α2‐antagonist, yohimbine. A great variability between individuals in the proportions of α1‐ and α2‐adrenoceptors was found. In the majority of the vessels continuous cooling to 25 °C augmented a noradrenaline‐induced contraction. This augmentation was unaltered in the presence of prazosin but abolished by yohimbine, suggesting that it was mediated via the α2‐adrenoceptor. In the remaining vessels with a predominating α1‐adrenoceptor‐mediated response a cold‐induced relaxation was registered. This could be the result of a reduced α1‐adrenoceptor‐mediated contraction at this low temperature. These varying reactions to cooling were unaffected by the β‐antagonist, propranolol, and by endothelial denudation. The results obtained in corresponding experiments with the α1‐agonist methoxamine and α2‐agonist, oxymetazoline, were conflicting, probably due to the poor selectivity of these agonists in human tissues. The results suggest that in patients with peripheral cold‐induced vasospasm administration of an α2‐adrenoceptor antagonist might be of therapeutic int

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08848.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The influence of bilaterally narrow, medial forebrain lesions on the increase in plasma Cortisol concentration normally seen in response to intravenous angiotensin II was studied in five goats. For comparison, the pre‐ and post‐lesion Cortisol responses to intravenous endotoxin were also evaluated. The Cortisol response to angiotensin was extinguished in two goats, whereas a slightly attenuated response to endotoxin was still obtained post‐lesioning. In these animals the lesions embraced the subfornical organ (SFO), the organum vasculosum of the lamina terminals (OVLT) and the interjacent anterior wall of the third ventricle. In two other goats, in which the SFO was completely destroyed but the OVLT remained largely intact, the lesions caused about 50% reduction of the Cortisol response to angiotensin without any concomitant reduction of the response to endotoxin.It is concluded that ACTH‐cortisol release in response to systemic angiotensin II is not mediated exclusively by receptors for the octapeptide confined to the SFO. Angiotensin receptors in the OVLT seem to be equally important in this

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08849.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The influence of cerebrospinal fluid (CSF) NaCl concentration upon the Cortisol release induced by intracerebroventricular (i. c.v.) and intravenous (i. v.) infusions of angiotensin II (All) was studied in conscious goats. A first series of experiments involved i. c.v. infusion (20 min; 20 μl min‐1) of simply hypertonic (0.5 M) NaCl, or of All (2 pmol kg‐1min‐1) dissolved in 0.5 M or isotonic (0.15 M) NaCl or in isotonic glucose. The most pronounced rise in plasma Cortisol concentration (PC) was elicited by All in 0.5 M NaCl, but responses of nearly the same size were obtained by merely 0.5 M NaCl and by All in isotonic NaCl, whereas All in glucose induced a smaller PC rise. An urge to drink developed during all infusions, except during the All/glucose infusion. Here, however, thirst became apparent 2–6 min post‐infusion. When, in a second series, the hypertonicity of the NaCl was reduced to 0.3 M, and the dose of All to 0.5 pmol kg‐1min‐1, only the infusion of All in 0.3 M NaCl elicited any appreciable rise in PC. The response was approximately the same size as that earlier obtained as the effect of the larger dose of All dissolved in isotonic saline. In a third series of experiments, a 30‐min i. c.v. infusion of isotonic glucose, preceding and out‐lasting a 10‐min i. v. infusion of AN (40 pmol kg‐1min‐1), was found to extinguish the rise in PC obtained as the effect of a separate i. v. infusion of AIL The results suggest that the potency of i. c.v. as well as of systemic angiotensin in stimulating the pituitary‐adrenocortical axis is positively correlated to the N

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08850.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

It has recently been demonstrated in the rat that the majority of cerebrovascular pain fibres containing immunoreactive substance P and calcitonin gene‐related peptide reach the vessels via the nasociliary nerve, a branch of the ophthalmic trigeminal division. In order to elucidate the effect of these nerves on blood flowin vivo, the relative changes in cortical microvascular flow were continuously monitored by a laser‐Doppler flowmeter system during electrical nerve stimulation, with the central nerve connection cut and after removal of neighbouring dilatory parasympathetic nerves. The nasociliary nerve on one side was stimulated proximal to the ethmoidal foramen by a bipolar platinum electrode. Activation at different frequencies, continuously or as bursts with a constant voltage, impulse duration and total stimulus length, revealed that a maximum increase in blood flow amounting to 16.7% after 36 s was obtained with continuous stimulation at 10 Hz. Flow markedly declined during the following i‐min stimulation period. No changes in contralateral cortical blood flow, mean arterial blood pressure or blood gases were observed during or after stimulation. The present study demonstrates for the first time that direct and selective electrical activation of trigeminal cerebrovascular nerves induces an increase, albeit small and transient, in blood flow within the

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08851.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The contractile response to endothelin has been examined in cerebral arteries from rats subjected to a prior subarachnoid haemorrhage (SAH) and compared with saline‐injected controls. Endothelin elicited concentration‐dependent contractions of rat basilar artery segments. The endothelin‐induced contractions were much stronger in the SAH compared to control animals, which suggests a role in the pathophysiology of cerebral vaso

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08852.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The present study examined whether α‐adrenergic stimulation causes a change in splanchnic intravascular volume in the anaesthetized animal with an intact circulation, which region(s) mediate the volume change, and whether the splanchnic volume change influences cardiac output. In order to ascertain that a radionuclide imaging technique could be used to assess total splanchnic volume changes, drugs known to increase or decrease splanchnic volume were infused on 21 occasions in eight dogs studied under conditions of selective perfusion and drainage of the splanchnic vasculature with erythrocytes labelled with99Tcmand a gamma camera placed over the abdomen. For these 21 infusions, volume and radionuclide count changes were related:r≥ 0.90 (n= 20),r= 0.76 (n= 1). After ascertaining tissue attenuation and blood radioactivity in four of the animals, the standard error for a single estimate of the absolute volume change using the radionuclide technique was determined to be 75 ml. In six animals with intact circulations, phenylephrine (40–80 μg min‐1) for 20 min was associated with an increase in cardiac output of 12 ± 2% (P<0.001) and a decrease in total splanchnic volume estimated to be 431 ± 95 ml (P<0.001). The splanchnic volume decrease was due entirely to decreases in splenic and intestinal volume. In eight eviscerated animals, cardiac output decreased by 30 ± 2% (P<0.001) during phenylephrine. With 40–160 μg phenylephrine boluses in the splenic artery in three dogs, splenic volume decreased by 11 ± 2% (P<0.001)and cardiac output increased by 18 ± 4% (P<0.01), but neither parameter changed with left atrial boluses. Thus, a‐adrenergic stimulation is associated with a decrease in splanchnic volume in the animal with an intact circulation, and this decrease acts to incr

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08853.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY