Muscle power after glucose-potassium loading in undernourished patients

Isometric thermogenesis at rest and during movement: a neglected variable in energy expenditure and obesity predisposition

Isometric thermogenesis as applied to human energy expenditure refers to heat production resulting from increased muscle tension. While most physical activities consist of both dynamic and static (isometric) muscle actions, the isometric component is very often essential for the optimal performance of dynamic work given its role in coordinating posture during standing, walking and most physical activities of everyday life. Over the past 75 years, there has been sporadic interest into the relevance of isometric work to thermoregulatory thermogenesis and to adaptive thermogenesis pertaining to body-weight regulation. This has been in relation to (i) a role for skeletal muscle minor tremor or microvibration - nowadays referred to as 'resting muscle mechanical activity' - in maintaining body temperature in response to mild cooling; (ii) a role for slowed skeletal muscle isometric contraction-relaxation cycle as a mechanism for energy conservation in response to caloric restriction and weight loss and (iii) a role for spontaneous physical activity (which is contributed importantly by isometric work for posture maintenance and fidgeting behaviours) in adaptive thermogenesis pertaining to weight regulation. This paper reviews the evidence underlying these proposed roles for isometric work in adaptive thermogenesis and highlights the contention that variability in this neglected component of energy expenditure could contribute to human predisposition to obesity.

Caloric restriction induces energy-sparing alterations in skeletal muscle contraction, fiber composition and local thyroid hormone metabolism that persist during catch-up fat upon refeeding

Weight regain after caloric restriction results in accelerated fat storage in adipose tissue. This catch-up fat phenomenon is postulated to result partly from suppressed skeletal muscle thermogenesis, but the underlying mechanisms are elusive. We investigated whether the reduced rate of skeletal muscle contraction-relaxation cycle that occurs after caloric restriction persists during weight recovery and could contribute to catch-up fat. Using a rat model of semistarvation-refeeding, in which fat recovery is driven by suppressed thermogenesis, we show that contraction and relaxation of leg muscles are slower after both semistarvation and refeeding. These effects are associated with (i) higher expression of muscle deiodinase type 3 (DIO3), which inactivates tri-iodothyronine (T₃), and lower expression of T₃-activating enzyme, deiodinase type 2 (DIO2), (ii) slower net formation of T₃ from its T₄ precursor in muscles, and (iii) accumulation of slow fibers at the expense of fast fibers. These semistarvation-induced changes persisted during recovery and correlated with impaired expression of transcription factors involved in slow-twitch muscle development. We conclude that diminished muscle thermogenesis following caloric restriction results from reduced muscle T₃ levels, alteration in muscle-specific transcription factors, and fast-to-slow fiber shift causing slower contractility. These energy-sparing effects persist during weight recovery and contribute to catch-up fat.

Neuromuscular disorders in critical illness

Neuromuscular disorders in the background of critical illness are under diagnosed. Standardized screening for weakness in the intensive care unit (ICU) setting is uncommon and persistent weakness as a sequel of critical illness is usually not recognized by physicians in the ICU for whom survival from acute illness is the primary outcome. The spectrum of illness ranges from isolated nerve entrapment with focal pain or weakness, to disuse muscle atrophy with mild weakness, and to severe myopathy or neuropathy with associated severe, prolonged weakness. This update focuses on neuromuscular disorders occurring in the critical care set up associated with diffuse and severe weakness.

Noninvasive measurement of the maximum relaxation rate of inspiratory muscles in patients with neuromuscular disorders

BACKGROUND

Slowing of inspiratory muscle relaxation has been used as an index for inspiratory muscle fatigue. However, maximum relaxation rate measured from oesophageal pressure traces after maximum sniff (P(oes) MRR) has limited clinical usefulness because it requires an oesophageal balloon catheter system.

OBJECTIVES

It was the aim of this study to establish whether, in neuromuscular patients, maximum relaxation rate assessed from sniff nasal pressure (P(nasal) MRR) reflects oesophageal MRR and the tension-time index of the diaphragm (TT(di)).

METHODS

Twenty patients with neuromuscular disease and 10 healthy subjects were studied. P(oes) and transdiaphragmatic pressure were measured while P(nasal) was recorded with a balloon advanced through the nose into the nasopharynx. Maximum P(oes), transdiaphragmatic pressure and P(nasal) were simultaneously measured while the patients performed maximal sniffs. The MRR (% pressure fall/10 ms) for each sniff, the TT(di) and the tension-time index of respiratory muscles were determined.

RESULTS

Neuromuscular patients showed higher TT(di), lower P(oes) MRR and lower P(nasal) MRR than the control group. In patients with neuromuscular disease, the correlation coefficient of P(nasal) MRR and P(oes) MRR was 0.985 (p < 0.001). Regression analysis showed that P(oes) MRR = -1.101 + 1.113.P(nasal) MRR (r(2) = 0.929, standard error of the estimate = 0.208). Indeed, P(nasal) MRR was negatively correlated with TT(di) (r = -0.914, p < 0.001) and the tension-time index of respiratory muscles (r = -0.732, p < 0.001). In the neuromuscular group, the mean difference between P(nasal) MRR and P(oes) MRR was 0.286 +/- 0.217%/10 ms.

CONCLUSIONS

P(nasal) MRR obtained from a maximal sniff accurately reflects P(oes) MRR and TT(di) in patients with neuromuscular disorders.

Quadriceps muscle weakness following acute hemiplegic stroke

OBJECTIVE

To determine whether quadriceps muscle weakness develops on the side ipsilateral to the brain lesion in the first week following acute ischaemic hemiplegic stroke.

DESIGN

A prospective study of muscle strength.

SETTING

Acute stroke unit (ASU) in a teaching hospital.

SUBJECTS

Ten patients admitted within 48 hours of stroke onset, and 10 healthy age-matched controls.

INTERVENTIONS

Repeat nonvolitional measurements of quadriceps muscle strength of the unaffected limb in patients and the right leg in normal subjects using magnetic femoral nerve stimulation (MS), prospectively one week apart. In addition the level of voluntary activation was assessed during a maximum voluntary contraction (MVC) manoeuvre. The Trunk Control Test (TCT) was measured in the patients.

RESULTS

The median (95% confidence interval, (CI)) baseline quadriceps twitch tension (Tw Q) and MVC in the control group were 9.4 kg (6.1-12.5 kg) and 37.2 kg (23.8-54.6 kg), and in the stroke group were 7.6 kg (4.4-9.9 kg) and 12.15 kg (7.9-30.8 kg). The median (95% CI) change in Tw Q and MVC respectively between baseline and one week later were 1.75% (-9.8 to 8%) and 5.45% (-15.1 to 22.7%) (NS) in the control group and -16.2% (-6 to -25.9%) and -30.45% (0 to -78.6%) (p < 0.01) in the stroke patients. There was a significant correlation between the percentage fall in Tw Q and both change in TCT (rs = 0.83, p < 0.01) and percentage change in body weight (rs = 0.83, p < 0.01).

CONCLUSION

In the first week after acute hemiplegic stroke, weakness develops in the unaffected leg.

Assessing the efficacy of nutritional support

This review outlines the conventional methods of assessing nutritional status and their limitations in the presence of acute trauma and sepsis. It also discusses the problems of attempting to improve or at least maintain nutritional status in the presence of an inflammatory stimulus. Most of the conventional markers of nutritional status are altered in trauma and sepsis with decreases in plasma protein concentrations and muscle strength, an apparent depression of immune function and an increase in extracellular fluid volume. It also appears to be impossible to improve nutritional status in the presence of a severe inflammatory stimulus, and the most one can hope for is to attenuate the rate of decline. The evidence for these observations is discussed.

Assessment of involuntary muscle function in patients after critical injury or severe sepsis

BACKGROUND

Study of involuntary skeletal muscle function (MFA) has been well accepted in the area of nutrition assessment and potentially offers a means for following progress of the critically ill patient. We report on the application of this technique to intensive care patients.

METHODS

MFA was performed by study of the contraction/relaxation characteristics of the adductor pollicis muscle of the thumb after ulnar nerve stimulation. Serial measurements were made in 16 critically injured patients and 28 patients with severe sepsis and were compared with those obtained from 26 control subjects. Extent of loss of total body protein (TBP) was quantified with in vivo neutron activation.

RESULTS

Significant difficulties exist in applying this technique to intensive care patients. In the critically injured, only five acceptable traces could be obtained from a possible 58 measurements. For patients with severe sepsis it was possible to obtain an acceptable trace on 12 of 56 occasions. Neuromuscular blockade and lack of patient cooperation were significant impediments to MFA study. Although frequently perceived as unpleasant by these patients, there was no long-term morbidity associated with MFA. No significant differences were seen in maximal relaxation rate at 30 Hz (MMR30) or force frequency ratios (F10/50 and F30/ 50) between trauma patients and controls. In the sepsis patient group, a significantly higher F10/50 was measured (52% +/- 3% severe sepsis vs 40% +/- 1% control subjects, p < .01). Six patients had MFA measured approximately 21 days after the illness, by which stage they had lost 11% of their initial TBP. Compared with control subjects, no significant differences were observed in MRR30 or F30/50, whereas a higher value for F10/50 was measured (48% +/- 1% critical illness vs 40% +/- 1% control subjects, p < .01).

CONCLUSIONS

The MFA technique is difficult to apply to intensive care patients. No significant disturbance to MFA is seen after critical injury. Severe sepsis results in an elevation of F10/ 50 only. When able to be obtained, MFA results do not reflect the extent of proteolysis but are indicative of the state of cellular energetics.

Quadriceps strength and fatigue assessed by magnetic stimulation of the femoral nerve in man

There is no nonvolitional method of assessing quadriceps strength which both supramaximally activates the muscle and is acceptable to subjects. In 10 normal subjects and 10 patients with suspected muscle weakness we used magnetic stimulation of the femoral nerve to elicit an isometric twitch and measured twitch tension (TwQ), surface electromyogram in addition to the maximum voluntary contraction force (MVC). Supramaximality was achieved in all subjects at a mean of 83% of maximum stimulator output. When supramaximal, TwQ was reproducible (mean coefficient of variation 3.6%, range 0.7-10.9) and correlated well with MVC (r2 = 0.83, P<0.001). In 7 normal subjects we measured TwQ before and after a fatiguing protocol; after 20 min TwQ was a mean of 55% (range 29-77%) of baseline and remained substantially reduced at 90 min. Magnetic femoral nerve stimulation is a painless, supramaximal method of assessing quadriceps strength and fatigue which is likely to be of value in clinical and physiological studies.

Impaired recovery of strength in older patients after major abdominal surgery

OBJECTIVE

This study compared changes in muscle strength after major elective abdominal surgery in young and old patients, and related these changes to body composition and nitrogen balance.

SUMMARY BACKGROUND DATA

The breakdown of muscle protein, erosion of lean tissue, and negative nitrogen balance are characteristic metabolic responses to surgical illness. With a substantial loss of muscle mass typical of advancing age, the authors postulated that older patients would be weaker during acute surgical illness and less able to maintain muscle function and meet metabolic demands.

METHODS

Active, community-dwelling individuals undergoing major abdominal procedures who were 70 years of age or older or 50 years of age or younger were studied. Total body water (TBW) was determined preoperatively by deuterium oxide dilution. Maximal voluntary handgrip, respiratory muscle strength, and visual analog pain scores were measured preoperatively and on postoperative days 2, 4, and 6. All urine was collected postoperatively for 7 days for determination of total nitrogen, creatinine, and cortisol.

RESULTS

The young (age, 36 +/- 9 years [mean +/- standard deviation]; n = 20) and old groups (age, 77 +/- 5 years; n = 20) were similar regarding weight, sex distribution, nutritional status, surgical procedures and anesthesia, and postoperative urine cortisol values. Age group, time after operation, and interaction effects were significant for each strength variable (all p < 0.005 by analysis of variance). Older patients had lower preoperative strength (29% to 41%) and mean 24-hour urine creatinine (27%). Postoperative strength was decreased most markedly on postoperative day 2, with similar proportional changes in the two age groups but lower absolute levels in the older patients. The rate of recovery of strength was substantially less rapid and complete in older patients. Older patients had less postoperative pain and received much less parenteral narcotic than younger patients. Postoperative urine nitrogen was similar in each group. Recovery of strength was not related to malignancy, preoperative strength, muscle mass (urine creatinine), lean body mass (TBW), sex, malignancy, pain, or narcotic administration.

CONCLUSIONS

Older patients are weaker preoperatively than younger patients; their strength falls to lower levels after surgery and their postoperative recovery of strength is impaired. The lesser preoperative strength of older patients is due in large part but not totally to diminished muscle mass. Their impaired postoperative recovery appears to be related to more acute factors, such as muscle energetics or substrate availability.

Can protein-calorie malnutrition cause dysphagia?

Nutrient deprivation has previously been shown to cause alterations in muscle and nerve function. Although an effect has never been studied in the neuromusculature of deglutition, the authors argue that an effect is likely. The proposed result is an increase in swallowing impairment in dysphagic individuals and associated risk of aspiration. Research studying the relationship between malnutrition and dysphagia is needed to verify clinical significance. Until controlled studies are completed, the authors suggest alternative alimentation in repleting severely malnourished dysphagic patients prior to attempting oral diet. A review of nutritional status indices is included to aid in identifying dysphagic patients at nutritional risk. Early identification of nutritional compromise and intervention can prevent malnutrition and its deleterious effects.

Effect of malnutrition on aerobic and anaerobic performance of fast- and slow-twitch muscles of rats

The effect of malnutrition on the functional properties of fast- and slow-twitch muscles from rats was studied using aerobic and anaerobic preparations. A 2-day fast and hypocaloric feeding to a weight loss of 25% were used as models of malnutrition. Soleus (slow-twitch) and extensor digitorum longus (EDL) (fast-twitch) muscles were studied using an in situ preparation with the blood supply intact and an in vitro preparation to which cyanide had been added to render the muscles anaerobic. We found that a 2-day fast had little effect on the function of muscles stimulated in situ, whereas anaerobic stimulation produced a decrease in force per gram of muscle weight in the soleus, but not in the EDL, compared with control values. Hypocaloric feeding resulted in a slowed relaxation rate, an increased Fs/Fmax ratio, and an upward shift of the force-frequency curve relative to controls when studied in situ. Under anaerobic conditions, soleus muscles from hypocaloric rats continued to show a slow relaxation rate and demonstrated a loss of force per gram of muscle weight compared with controls, particularly at low stimulation frequencies. EDL muscles from hypocaloric rats had an increased relaxation rate and were able to maintain force with anaerobic stimulation. Soleus and EDL muscles from the fasted and hypocaloric groups had lower activities of phosphofructokinase. We conclude that slow-twitch muscles from malnourished rats are at a disadvantage when required to function under anaerobic conditions. These findings suggest that muscle performance may be impaired in malnourished patients subjected to hypoxia.

Maximal relaxation rate of inspiratory muscle can be effort-dependent and reflect the activation of fast-twitch fibers

We have measured the normalized maximal relaxation rate (MRR, % pressure loss/10 ms) of esophageal and transdiaphragmatic pressures in five normal subjects who performed unoccluded shifts from FRC, with the peak pressure varying between 10 and 100% of each subject's maximum. MRR was computed as the maximal rate of decay of pressure divided by the peak pressure, with units of %pressure loss/10 ms. We observed that MRR became progressively faster as sniff peak pressure increased in amplitude above 10% maximum. In four subjects this trend was most marked for sniffs of less than 40% maximal pressure, with little change as peak pressure increased further. In a fifth subject this trend continued across the full range of pressure. Thus, MRR may be an effort-dependent variable during voluntary inspiratory maneuvers. We postulate that sniff MRR becomes faster with increasing peak pressure because of progressive activation of fast-twitch type II muscle fibers. The findings of this study suggest that erroneous conclusions about the significance of slowing of sniff MRR with fatigue may be made if MRR is determined from voluntary efforts with a peak pressure of less than 60% of control maximum, as may occur with fatigue.

Functional and metabolic changes during feeding in gastrointestinal cancer

The impact of feeding a hypercaloric parenteral solution on N balance, energy metabolism, and muscle strength has been investigated in cachectic patients with gastrointestinal cancer and in malnourished patients without evidence of cancer (controls). Patients were examined during 5% dextrose administration (D5W) for 2 days, followed by an infusion of a carbohydrate-based (53% carbohydrate, CB) or fat-based (55% fat, FB) diet with a constant protein intake. Diets were administered for 1 week each, in a randomized crossover design. During D5W, cancerous patients demonstrated a similar energy expenditure, but significantly lower N balance (p less than 0.005) than controls. Compared to control patients, N balance in cancerous patients was similar on the CB diet and significantly lower during the FB diet (p less than 0.025). Unlike the control patients, muscle strength and endurance tests did not improve after 2 weeks of feeding in cancerous patients. The cancerous patients differ from controls because they are hypercatabolic (especially during D5W administration), and they showed no improvement in muscle strength with 2 weeks of feeding.

Effect of dietary manipulations (fasting, hypocaloric feeding, and subsequent refeeding) on rat muscle energetics as assessed by nuclear magnetic resonance spectroscopy

31P nuclear magnetic resonance (NMR) spectroscopy in vivo and fluorometry were used to measure muscle ATP, total creatine, pH, and Mg2+ in vivo; and to calculate creatine phosphate (CrP), the ratios of CrP/inorganic phosphate (Pi), CrP/ATP, free ADP levels, and the free-energy change in ATP hydrolysis so nutritional effects could be ascertained. These parameters were determined in vivo in resting control, 2-d-fasted, and hypocalorically fed rats and in animals similarly hypocalorically fed and then refed. The ATP, Pi, and intracellular Mg2+ levels were comparable in the four groups. When the fasted and underfed animals were compared with the control and refed animals, there were falls in the ratios of CrP/Pi and CrP/ATP, in the calculated CrP, and the free-energy change of ATP hydrolysis, but a rise in the calculated free ADP. In the hypocaloric group, intracellular pH fell significantly and a large peak was noted in the phosphodiester region. The data are consistent with the hypothesis that ATP levels are maintained at the cost of CrP, suggesting that ATP production is disturbed by aerobic and anaerobic mechanisms.

Pre-operative assessment of fitness score

Death within 30 days or survival after a major operation depends on three things: the severity of the disease and the operation, the technical proficiency of the surgeon and the ability of the patient to withstand both disease and operation. The first of these can be estimated by reference to published figures, the second can only be guessed at and the third has in the past been a matter of subjective judgement. With the aim of producing an objective assessment of the likelihood of survival, we have constructed a score system comprising 26 items including age, chronic disease and acute presenting disease. These items are each given a weight of 1 to 4 and the total fitness score for any patient ranges from 0 (fit) to 10 (unlikely to survive). We have validated this score prospectively in 1517 consecutive patients undergoing emergency or elective major abdominal operations (excluding appendicectomies and hernia repairs). In 492 operations in which the patient scored 0 or 1, one patient died (0.2 per cent); in 290 with scores of 2 or 3, one died (0.3 per cent); in 313 with scores of 4 or 5, five died (1.6 per cent). It was when the score rose to 6 or over that the chances of survival progressively declined: 16 died of the 105 patients who scored 6 (15.2 per cent) as did 74 of the 191 who scored 7 or 8 (38.7 per cent) and 70 of the 126 who scored 9 or 10 (55.6 per cent). We now use the score as part of our audit and enquire particularly closely into the death of any patient with a pre-operative score of less than 6.