The work of walking: a calorimetric study

Experiments were designed to test the traditional assumption that during level walking all of the energy from oxidation of fuel appears as heat and no work is done. Work is force expressed through distance, or energy transferred from a man to the environment, but not as heat. While wearing a suit calorimeter in a respiration chamber, five women and five men walked for 70 to 90 min on a level treadmill at 2.5, 4.6, and 6.7 km.h-1 and pedalled a cycle ergometer for 70 to 90 min against 53 and 92 W loads. They also walked with a weighted backpack and against a horizontal load. During cycling, energy from fuel matched heat loss plus the power measured by the ergometer. During walking, however, energy from fuel exceeded that which appeared as heat, meaning that work was done. The power increased with walking speed; values were 14, 29, and 63 W, which represented 11, 12, and 13% of the incremental cost of fuel above the resting level. Vertical and horizontal loads increased the fuel cost and heat loss of walking but did not alter the power output. This work energy did not re-appear as thermal energy during 18 h of recovery. The most likely explanation of the work done is in the inter-action between the foot and the ground, such as compressing the heel of the shoe and bending the sole. We conclude that work is done in level walking.     

Effects of alterations in left ventricular filling, contractility, and systemic vascular resistance on the ascending aortic blood velocity waveform of normal subjects.

OBJECTIVES: To confirm the consistent effects on Doppler-measured aortic blood flow velocity waveform variables of alterations in left ventricular preload, afterload, and inotropy using pharmacologic and physiologic maneuvers. SETTING: Medical school laboratory. SUBJECTS: Healthy volunteers. INTERVENTIONS: Increasing infusion rates of dobutamine (1.25 to 5 micrograms/kg.min), esmolol (1.25 to 5 mg/min), phentolamine (1.25 to 5 mg/min), methoxamine (1.25 to 5 mg/min), metaraminol (1.25 to 5 mg/min), and placebo (1.25 to 5 mL of 0.9% saline/min) and increasing plasma removal (0.5 to 1 L) in awake, rested, supine subjects. MEASUREMENTS AND MAIN RESULTS: Ascending aortic blood flow was measured by the suprasternal Doppler approach allowing calculation of waveform variables of stroke distance and minute distance (linear measures of stroke volume and cardiac output), peak velocity, mean acceleration and flow time corrected for heart rate. An index of systemic vascular resistance was obtained by dividing mean systemic BP by the minute distance. Inotropic changes predominantly affected peak velocity and mean acceleration. Changes in preload mainly affected the flow time corrected for heart rate, whereas afterload changes had an intermediate effect. Unsuspected but subsequently confirmed hemodynamic effects were seen with esmolol and metaraminol. CONCLUSIONS: Aortic blood flow velocity waveform variables measured by Doppler ultrasound can be used to noninvasively follow changes in left ventricular preload, afterload, and inotropy.     

Changes in alpha 2-adrenoceptors on vascular smooth muscle and neural membranes following hypertension induced by renal ischemia.

alpha 2-Adrenoceptors were characterized on neural and vascular membranes from 2-kidney-1-clip renal hypertensive (RHT) and normotensive (NT) rats. Rats were sacrificed 6 weeks after induction of renal ischemia, and the specific binding of 3H-clonidine to smooth muscle membranes form tail arteries and neural membranes from various brain regions was examined. Additionally, isometric contractions of helically cut tail artery strips produced by various alpha-adrenoceptor agonists were measured. Scatchard analysis indicated an increased number of high-affinity binding sites on the smooth muscle membranes from RHT rats (Bmax = 43.5 +/- 1.4 fmol/mg protein) compared to that from the NT rats (25.4 +/- 3.8 fmol/mg protein). An increased contractile sensitivity to clonidine was also observed in tail artery strips from RHT rats (EC50 for RHT = 3.04 x 10(-8) M; NT = 1.52 x 10(-7) M). In neural tissue, the number of alpha 2-adrenoceptor-binding sites was significantly increased in the locus coeruleus from RHT rats, but not in the amygdala, hypothalamus, parietal cortex, hippocampus or lower brain stem. These results demonstrate that renal ischemia produces changes in both peripheral and neural alpha 2-adrenoceptor density. The increase in smooth muscle alpha 2-adrenoceptors might also provide a partial explanation for the supersensitivity to adrenergic agonists in this model of hypertension.     

Reversible and irreversible effects of chemical fixation on the NMR properties of single cells.

The effects of chemical fixation are known to alter MR parameters, such as relaxation times and the apparent diffusion coefficient (ADC) of water. It is often assumed that such changes are reversible after samples have been reimmersed in a buffer solution for a sufficient period of time. In this study we characterize the changes associated with fixation of single Xenopus laevis oocytes and their subsequent reimmersion in buffer. Substantial reductions in both T(1) and T(2) values were measured for all compartments of the cell after fixation, with the cytoplasm showing larger changes than the nucleus. After reimmersion in buffer, there were small but statistically significant differences in MR parameters between fresh and reimmersed cells. Experiments with a gadolinium (Gd) contrast agent showed evidence of irreversible changes in the permeability of cellular membranes to small molecules.     

The Association of Different Measures of Insulinaemia with Vascular Risk Factors in Healthy Normoglycaemic Normotensive Non-obese Men and Women

Hyperinsulinaemia is said to be a risk factor for cardiovasculardisease, but the extent to which different insulinaemic measuresare associated with vascular risk factors in ostensibly healthyindividuals, and whether they operate independently in men andwomen, remains uncertain. The association between risk factors and various insulinaemicmeasures was examined in 148 men and 118 women who were normoglycaemic,normotensive, and non-obese (body mass index in men <27,in women <25). A 75 g glucose tolerance test was administeredafter blood sampling for fibrinogen, lipids, lipoproteins andinsulin. Insulin was also measured after 1 and 2 hours. Significantunivariate correlations (p<0.01) were most consistently recordedbetween insulinaemic measures and fasting serum triglyceridesin men and women, whilst systolic blood pressure only correlatedwith insulinaemia in women, and diastolic blood pressure correlatedwith fasting and 2 hour insulinaemic measures in men and women.Inconsistent associations were noted with total serum cholesterolin men and women, with high density lipoprotein cholesterol,body mass index, apoprotein B and A1 in men, and with fibrinogenin women. Age was not correlated with any insulinaemic measurein men or women. Differences in vascular risk factors between quintiles of theinsulinaemic measures were examined, after correction for bodymass index. The dominant association with fasting and post-glucoseload insulinaemic measures was with triglycerides, especiallyin women, with less frequent graded differences between quintilesobserved for total cholesterol, and diastolic and systolic bloodpressures in men and women. The incidence of other risk factors often only differed in thelowest or highest quintile in comparison to other quintiles,suggesting a threshold rather than a graded effect. Furthermore,differences in HDL cholesterol and apoprotein B were only recordedfor top quintiles of post-glucose challenge/integrated insulinaemicmeasures in men, whilst serum fibrinogen concentrations onlydiffered significantly in women in the top insulinaemic areaunder the curve quintile. In the absence of additional risk factors such as diabetes,hypertension and obesity, insulinaemic measures are not consistentlyrelated to blood pressure and measures of lipid metabolism andcoagulation, and are thus a weak predictor of other cardiovascularrisk factors. The vascular risk profile associated with insulinappears somewhat different in apparently healthy men and women.     

SRTR Center-Specific Reporting Tools: Posttransplant Outcomes

Measuring and monitoring performance—be it waiting list and posttransplant outcomes by a transplant center, or organ donation success by an organ procurement organization and its partnering hospitals—is an important component of ensuring good care for people with end-stage organ failure. Many parties have an interest in examining these outcomes, from patients and their families to payers such as insurance companies or the Centers for Medicare and Medicaid Services; from primary caregivers providing patient counseling to government agencies charged with protecting patients.
The Scientific Registry of Transplant Recipients produces regular, public reports on the performance of transplant centers and organ procurement organizations. This article explains the statistical tools used to prepare these reports, with a focus on graft survival and patient survival rates of transplant centers—especially the methods used to fairly and usefully compare outcomes of centers that serve different populations. The article concludes with a practical application of these statistics—their use in screening transplant center performance to identify centers that may need remedial action by the OPTN/UNOS Membership and Professional Standards Committee.     

Long-term results of dietary fenbendazole to eradicate Syphacia muris from rat colonies.

The pinworm Syphacia muris was eradicated from rats after treatment with fenbendazole-medicated chow (150 ppm) and without environmental decontamination for > 54 months. However, this regimen was successful only when the treatment was delivered and efficacy monitoring was done by personnel of the institutional animal resources program. The same pinworm elimination program failed 7 to 24 months after the cessation of treatment in a satellite colony in which animal care, including provision of medicated diet and sample collection for efficacy monitoring, was provided by research personnel. A failure to uniformly deliver adequate therapeutic doses or reinoculation of rats with pinworm eggs from the contaminated environment could not be excluded as causes of the failure. However, there were risk factors, and animal care practices unique to the satellite colony that may have facilitated the re-emergence of pinworms. These risk factors included hand-washing of cages, storage of contact bedding in areas that were not vermin-proof, and animal care provided by personnel having contact with rodents of pet-store origin.