Lean Mass Loss and Altered Muscular Aerobic Capacity after Bariatric Surgery.

INTRODUCTION: Patients undergoing weight loss surgery do not improve their aerobic capacity or peak oxygen uptake (VO2peak) after bariatric surgery and some still complain about asthenia and/or breathlessness. We investigated the hypothesis that a post-surgery muscular limitation could impact the ventilatory response to exercise by evaluating the post-surgery changes in muscle mass, strength, and muscular aerobic capacity, measured by the first ventilatory threshold (VT). METHODS: Thirteen patients with obesity were referred to our university exercise laboratory before and 6 months after bariatric surgery and were matched by sex, age, and height to healthy subjects with normal weight. All subjects underwent a clinical examination, blood sampling, and body composition assessment by dual-energy X-ray absorptiometry, respiratory and limb muscle strength assessments, and cardiopulmonary exercise testing on a cyclo-ergometer. RESULTS: Bariatric surgery resulted in a loss of 34% fat mass, 43% visceral adipose tissue, and 12% lean mass (LM) (p < 0.001). Absolute handgrip, quadriceps, or respiratory muscle strength remained unaffected, while quadriceps/handgrip strength relative to LM increased (p < 0.05). Absolute VO2peak or VO2peak/LM did not improve and the first VT was decreased after surgery (1.4 ± 0.3 vs. 1.1 ± 0.4 L min-1, p < 0.05) and correlated to the exercising LM (LM legs) (R = 0.84, p < 0.001). CONCLUSIONS: Although bariatric surgery has numerous beneficial effects, absolute VO2peak does not improve and the weight loss-induced LM reduction is associated to an altered muscular aerobic capacity, as reflected by an early VT triggering early exercise hyperventilation.

Near-Infrared Fluorescence Lymphatic Imaging to Reconsider Occlusion Pressure of Superficial Lymphatic Collectors in Upper Extremities of Healthy Volunteers.

BACKGROUND: There are very little scientific data on occlusion pressure for superficial lymphatic collectors. Given its importance in determining the transport capacity of lymphatic vessels, it is crucial to know its value. The novel method of near-infrared fluorescence lymphatic imaging (NIRFLI) can be used to visualize lymphatic flow in real time. The goal of this study was to see if this method could be used to measure the lymphatic occlusion pressure. METHODS: We observed and recorded lymph flow in the upper limb of healthy volunteers through a transparent cuff using near-infrared fluorescence lymphatic imaging. After obtaining a baseline of the lymph flow without pressure inside the cuff, the cuff was inflated by increments of 10 mm Hg starting at 30 mm Hg. A NIRFLI guided manual lymphatic drainage technique named "Fill & Flush Drainage Method" was performed during the measurement to promote lymph flow. Lymphatic occlusion pressure was determined by observing when lymph flow stopped under the cuff. RESULTS: We measured the lymphatic occlusion pressure on 30 healthy volunteers (11 men and 19 women). Mean lymphatic occlusion pressure in the upper limb was 86 mm Hg (CI ±3.7 mm Hg, α = 0.5%). No significant differences were found between age groups (p = 0.18), gender (p = 0.12), or limb side (p = 0.85). CONCLUSIONS: NIRFLI, a transparent sphygmomanometer cuff and the "Fill and Flush" manual lymphatic drainage method were used to measure the lymphatic occlusion pressure in 30 healthy humans. That combination of these techniques allows the visualization of the lymph flow in real time, while ensuring the continuous filling of the lymph collectors during the measurement session, reducing false negative observations. The measured occlusion pressures are much higher than previously described in the medical literature.

Placement of the nebulizer before the humidifier during mechanical ventilation: Effect on aerosol delivery.

BACKGROUND: Therapeutic aerosols are commonly used in mechanically ventilated patients. The position of the nebulizer in the ventilator circuit and the humidification of inhaled gases can influence the efficiency of aerosol delivery. We evaluated the effect of nebulizer position on the pulmonary bioavailability of nebulized ipratropium in ventilated patients without known preexisting respiratory disease. METHODS: The study included 38 mechanically ventilated and sedated patients after open heart surgery. Ipratropium (500 microg) was delivered by an ultrasonic nebulizer. Patients were randomized into 2 groups: the nebulizer positioned before the heat humidification system (group 1, n = 19) or at the end of the inspiratory limb before the Y-piece (group 2, n = 19). The amount of ipratropium in the urine collected during the 4 hours after drug administration was measured by mass spectrometry. RESULTS: There were no statistically significant differences in tidal volume or respiratory rate between groups. There were no significant differences between the 2 groups in the amount of drug excreted (group 1 vs 2: 13,237 +/- 2313 pg/mL vs 15,529 +/- 3204 pg/mL) or in pulmonary bioavailability (.9% +/- .1% vs 1.1% +/- .2%). CONCLUSION: The position of the nebulizer in the ventilatory circuit had no effect on the pulmonary bioavailability of ipratropium.

Effects of acetazolamide on aerobic exercise capacity and pulmonary hemodynamics at high altitudes.

Aerobic exercise capacity is decreased at altitude because of combined decreases in arterial oxygenation and in cardiac output. Hypoxic pulmonary vasoconstriction could limit cardiac output in hypoxia. We tested the hypothesis that acetazolamide could improve exercise capacity at altitude by an increased arterial oxygenation and an inhibition of hypoxic pulmonary vasoconstriction. Resting and exercise pulmonary artery pressure (Ppa) and flow (Q) (Doppler echocardiography) and exercise capacity (cardiopulmonary exercise test) were determined at sea level, 10 days after arrival on the Bolivian altiplano, at Huayna Potosi (4,700 m), and again after the intake of 250 mg acetazolamide vs. a placebo three times a day for 24 h. Acetazolamide and placebo were administered double-blind and in a random sequence. Altitude shifted Ppa/Q plots to higher pressures and decreased maximum O(2) consumption ((.)Vo(2max)). Acetazolamide had no effect on Ppa/Q plots but increased arterial O(2) saturation at rest from 84 +/- 5 to 90 +/- 3% (P < 0.05) and at exercise from 79 +/- 6 to 83 +/- 4% (P < 0.05), and O(2) consumption at the anaerobic threshold (V-slope method) from 21 +/- 5 to 25 +/- 5 ml.min(-1).kg(-1) (P < 0.01). However, acetazolamide did not affect (.)Vo(2max) (from 31 +/- 6 to 29 +/- 7 ml.kg(-1).min(-1)), and the maximum respiratory exchange ratio decreased from 1.2 +/- 0.06 to 1.05 +/- 0.03 (P < 0.001). We conclude that acetazolamide does not affect maximum exercise capacity or pulmonary hemodynamics at high altitudes. Associated changes in the respiratory exchange ratio may be due to altered CO(2) production kinetics.

Respiratory muscle strength may explain hypoxia-induced decrease in vital capacity.

PURPOSE: High altitude exposure has consistently been reported to decrease forced vital capacity (FVC), but the mechanisms accounting for this observation remain incompletely understood. We investigated the possible contribution of a hypoxia-related decrease in respiratory muscle strength. METHODS: Maximal inspiratory and expiratory pressures (MIP and MEP), sniff nasal inspiratory pressure (SNIP), FVC, peak expiratory flow rate (PEF), and forced expiratory volume in 1 s (FEV1) were measured in 15 healthy subjects before and after 1, 6, and 12 h of exposure to an equivalent altitude of 4267 m in a hypobaric chamber. RESULTS: Hypoxia was associated with a progressive decrease in FVC (5.59 +/- 0.24 to 5.24 +/- 0.26 L, mean +/- SEM, P < 0.001), MIP (130 +/- 10 to 114 +/- 8 cm H2O, P < 0.01), MEP (201 +/- 12 to 171 +/- 11 cm H2O, P < 0.001), and SNIP (125 +/- 7 to 98 +/- 7 cm H2O, P < 0.001). MIP, MEP, and SNIP were strongly correlated to FVC (r ranging from 0.77 to 0.92). FEV1 didn't change, and PEF increased less than predicted by the reduction in air density (11-20% of sea-level value compared with 32% predicted). CONCLUSION: We conclude that a decrease in respiratory muscle strength may contribute to the decrease in FVC observed at high altitude.

Effects of high altitude exposure on cerebral hemodynamics in normal subjects.

BACKGROUND AND PURPOSE: Acute mountain sickness (AMS) may be an early stage of high altitude cerebral edema. If so, AMS could result from an alteration of dynamic autoregulation of cerebral blood flow resulting in overperfusion of capillaries and vasogenic cerebral edema. METHODS: We measured middle cerebral artery blood flow velocity (Vmca) by transcranial Doppler and arterial blood pressure by finger plethysmography at 490 m and 20 hours after arrival at 4559 m in 35 volunteers who had been randomized to tadalafil, dexamethasone, or placebo in a study on the pharmacological prevention of high altitude pulmonary edema. A dynamic cerebral autoregulation index (ARI) was calculated from continuous recordings of Vmca and blood pressure during transiently induced hypotension. RESULTS: Altitude was associated with an increase in a cerebral-sensible AMS (AMS-C) score (P<0.001) and with a decrease in arterial oxygen saturation (Sao2), whereas average Vmca or ARI did not change. However, at altitude, the subjects with the lowest ARI combined with the lowest Sao2 presented with the highest AMS-C score (P<0.03). In addition, a stepwise multiple linear regression analysis on arterial Pco2, Sao2, and baseline or altitude ARI identified altitude ARI as the only significant predictor of the AMS-C score (P=0.01). The AMS-C score was lower in dexamethasone-treated subjects compared with high altitude pulmonary edema-susceptible untreated subjects. Neither tadalafil nor dexamethasone had any significant effect on Vmca or ARI. CONCLUSIONS: High altitude hypoxia is associated with impairment in the regulation of the cerebral circulation that might play a role in AMS pathogenesis.

Estimation of total-body skeletal muscle mass in children and adolescents.

PURPOSE: The estimation of total-body skeletal muscle mass (SMM) has been predicted in healthy adults using anthropometric measurements and urine creatinine excretion. SMM measurement is compulsory to evaluate exercise performance and the influence of physical training on muscle mass. However, there is a lack of information on children and adolescents when quantifying appendicular skeletal muscle mass. METHODS: Thirty-nine Caucasian children and adolescents (male and female, 7-16 yr old) and 20 adults (men and women, 20-24 yr old) were tested for total-body SMM using dual-energy x-ray absorptiometry measurement (DEXA), anthropometric measurements (ANTHR), and urine creatinine (UCrn) determination. Skinfold thickness and circumference were measured at mid-arm (CAG), mid-thigh (CTG), and mid-calf (CCG) and the skin-corrected circumferences (cm), together with height (Ht; m), age (yr), and sex (0 for female, 1 for male). The UCrn excretion (g.24 h(-1)) was also determined in all subjects. The ANTHR and UCrn measurements were then compared with DEXA as reference value. RESULTS: The multiple linear regression from anthropometric measurements gave the following equation to evaluate the total-body skeletal muscle mass (SMM) in children and adolescents: SMM (kg) = Ht x [(0.0064 x CAG) + (0.0032 x CTG) + (0.0015 x CCG)(2)] + (2.56 x sex) + (0.136 x age). The prediction of SMM from a 24-h urine collection was obtained with the following equation: SMM (kg) = (10.62 x Crn) + 6.63. The correlation coefficient (r(2)) was 0.966 and 0.710 for the anthropometric and creatinine methods, respectively (P < 0.001). CONCLUSION: Besides DEXA technique, the determination of total-body skeletal muscle mass in children and adolescents can be highly validated with satisfactory confidence by simple anthropometric measurements or 24-h urine creatinine excretion.

The cuff leak test to predict failure of tracheal extubation for laryngeal edema.

OBJECTIVE: Laryngeal edema secondary to endotracheal intubation may require early re-intubation. Prior to extubation the absence of leak around an endotracheal tube may predict laryngeal edema after extubation. We evaluated the usefulness of a quantitative assessment of such a leak to identify the patients who will require early re-intubation for laryngeal edema. METHODS: This prospective study included 76 patients with endotracheal intubation for more than 12 h. The leak, in percent, was defined as the difference between expired tidal volume measured just before extubation, in volume-controlled mode, with the cuff inflated and then deflated. The best cut-off value to predict the need for re-intubation for significant laryngeal edema was determined and the patients were divided into two groups, according to this cut-off value. RESULTS: Eight of the 76 patients (11%) needed re-intubation for laryngeal edema. Patients requiring re-intubation had a smaller leak than the other patients [9 (3-18) vs 35 (13-53)%, p<0.01]. The best cut-off value for gas leak was 15.5%. The high leak group included 51 patients, of whom only two patients (3%) required re-intubation. The low leak group included 25 patients, among whom six patients (24%) required re-intubation ( p<0.01). The sensitivity of this test was 75%, the specificity 72.1%, the positive predictive value 25%, the negative predictive value 96.1% and the percent of correct classification 72.4%. CONCLUSIONS: A gas leak around the endotracheal tube greater than 15.5% can be used as a screening test to limit the risk of re-intubation for laryngeal edema.

Prone positioning in acute respiratory failure: survey of Belgian ICU nurses.

OBJECTIVE: To determine the frequency of use and attitudes towards prone positioning in patients with acute respiratory failure. DESIGN AND SETTING: Verbal questionnaire survey in all 79 intensive care units in French-speaking Belgium. METHODS: Of the 79 ICUs 29 performed prone-positioning, and 25 agreed to participate in the questionnaire. MEASUREMENTS AND RESULTS: Nurses at 9 of the 25 hospitals expressed reluctance to use prone positioning. The time schedules associated with prone positioning varied among the units surveyed, with no consensus. Units used two to six members of staff to turn a patient, with three most commonly being employed. Patients were most commonly positioned with both arms above the head and cushions under the chest, head, and legs, but there was considerable variation among units. The complications most commonly reported were facial edema and decubitus ulcers, with only three of the units reporting accidental extubation. Only two of the units had an established protocol for prone positioning although nurses from 14 of the units felt this would be useful. CONCLUSIONS: Prone positioning is approached with some reluctance by ICU staff. If the use of prone positioning in patients with acute respiratory distress syndrome is deemed worthwhile, discussion and development of departmental protocols may facilitate its use.