Biomedical subjects

M Johnson

Publications and source records attributed to M Johnson.

At least 37 records · Page 2Linked to original sources

PubMed2000

Factors associated with long-term progression or stability in primary open-angle glaucoma.

PURPOSE: To evaluate long-term risk factors for progression or stability in patients with primary open-angle glaucoma. METHOD: We retrospectively included consecutively reviewed patients who had primary open-angle glaucoma for at least 5 years in this multicenter trial. Historical and clinical factors in these patients were evaluated for their association with stability or progression of the glaucoma. RESULTS: We included 218 patients in this study; of these, 34 progressed over an average length of follow-up of 45.5 +/- 30.0 months, and 184 were stable over an average of 72.8 +/- 18.3 months. The mean intraocular pressure over the follow-up period for the progressed group was 19.5 +/- 3.8 mm Hg and for the stable group 17. 2 +/- 3.1 mm Hg (P =.001). The average standard deviation of individual intraocular pressures was greater in the progressed group (5.1 mm Hg) than the stable group (3.9 mm Hg, P =.012). Baseline characteristics indicating a greater potential to progress were a larger cup-to-disk ratio (P <.001), a greater number of medications (P =.02), older age (P.007), and worse visual acuity (P =.003). However, no difference was observed in pressure levels that prevented progression in these subpopulations compared with the total sample size. CONCLUSIONS: This study suggests that lowering the intraocular pressure is important in the treatment of primary open-angle glaucoma to help prevent long-term progression. Lowering the pressure, however, is not uniformly effective in preventing progression. Additionally, risk factors for progression do not further help identify pressure levels that prevent worsening of glaucoma.

Aged↗

PubMed2000

Isolation of differentially expressed aldose reductase in ovaries after estrogen withdrawal from hypophysectomized diethylstilbestrol treated rats: increased expression during apoptosis.

More than 99% of the follicles are eliminated by apoptosis before reaching ovulation. Several growth factors and hormones inhibit apoptosis in the ovary, including estrogen. Using differential display of mRNA, aldose reductase was shown to increase in the ovary of diethylstilbestrol treated hypophysectomized rats after estrogen withdrawal, inducing apoptosis. The aldose reductase mRNA expression was confirmed to be 2.2 +/- 0.2-fold higher after estrogen withdrawal using northern blot analysis. In addition, untreated immature rats showed a 1.7 +/- 0.3-fold higher expression of ovarian aldose reductase mRNA compared to ovaries 24 h after pregnant mare's serum gonadotropin treatment, decreasing apoptosis in the ovary. In the prostate, the level of aldose reductase was increased 3.1 +/- 1.1-fold 2 days after castration induced apoptosis. Although the physiological role of aldose reductase in the ovary is not known, these data suggest that aldose reductase may be part of a hormonally regulated apoptotic pathway in the ovary and prostate.

Aldehyde Reductase↗

PubMed2000

Cancer pain education: the use of a structured clinical instruction module to enhance learning among medical students.

The Structured Clinical Instruction Module (SCIM) is an educational format developed for the teaching of clinical and interpersonal skills. The purpose of this study was to develop and pilot-test a SCIM to enhance medical students' learning and understanding about cancer pain assessment and management. The Cancer Pain SCIM was presented to 34 third-year medical students. Eight instructors and six standardized patients (five cancer patients) participated in the course. All participants evaluated the course using a five-point Likert scale (1 = strongly disagree; 5 = strongly agree). Students self-assessed their clinical skills before and after the course using a five-point scale (1 = not competent; 5 = very competent). Students agreed [mean (S.D.)] very strongly that the SCIM was a valuable educational experience [4.4 (0.56)] and that it was beneficial to use actual cancer patients in the SCIM [4.5 (0.63)]. Students believed their skills in the assessment and management of cancer pain significantly improved after the course. The SCIM is a valuable and novel instructional format to teach essential skills in the assessment and management of cancer pain to medical students.

Clinical Competence↗

PubMed2000

Evaluation of BioStar FLU OIA assay for rapid detection of influenza A and B viruses in respiratory specimens.

BACKGROUND: Demand for the rapid diagnosis of influenza infections has increased with the advent of the availability of neuraminidase antiviral therapy for influenza A and B. Several rapid assays that detect both influenza A and B are now available. OBJECTIVES: In this study we compared the performance of the BioStar FLU OIA assay to Bartels Viral Respiratory Screening and Identification Kit (Bartels Inc., Issaquah, WA), and cell culture. STUDY DESIGN: A total of 145 patient specimens for influenza virus detection submitted in either viral transport medium or in sterile containers were evaluated by the three methods. Specimen types included nasal washings, nasal swabs, sputum, throat swabs, and bronchial alveolar lavage (BAL) fluids. RESULTS: Fifty six positive specimens were identified based on culture and/or DFA. Of these, 30 specimens were positive by the OIA assay for an overall sensitivity of 54%. The OIA assay detected 48% (n = 21) of the 44 culture positive specimens and 81% (n = 29) of the 36 DFA positive specimens. Eighty six of the 89 culture/DFA negative samples were negative by the OIA assay (97% specificity). Analysis of the OIA assay sensitivity from samples submitted in M4 transport medium or in sterile containers revealed that M4 transport medium does not reduce the sensitivity of the OIA assay. Fifteen of the 27 positive samples submitted in M4 transport medium were positive by the OIA assay (56% sensitivity) compared to 15 of 29 positive samples transported in sterile containers (52% sensitivity). Twelve specimens were either culture and/or DFA positive for viruses other than influenza, but negative by the OIA assay, suggesting that there was no cross reactivity of the OIA assay with the other virus types recovered in this study. CONCLUSIONS: The overall excellent specificity of the BioStar FLU OIA allows for treatment of positive patients for influenza, however, a negative result should be confirmed by DFA and culture.

Animals↗

PubMed2000

Gene expression analysis by massively parallel signature sequencing (MPSS) on microbead arrays.

We describe a novel sequencing approach that combines non-gel-based signature sequencing with in vitro cloning of millions of templates on separate 5 microm diameter microbeads. After constructing a microbead library of DNA templates by in vitro cloning, we assembled a planar array of a million template-containing microbeads in a flow cell at a density greater than 3x10(6) microbeads/cm2. Sequences of the free ends of the cloned templates on each microbead were then simultaneously analyzed using a fluorescence-based signature sequencing method that does not require DNA fragment separation. Signature sequences of 16-20 bases were obtained by repeated cycles of enzymatic cleavage with a type IIs restriction endonuclease, adaptor ligation, and sequence interrogation by encoded hybridization probes. The approach was validated by sequencing over 269,000 signatures from two cDNA libraries constructed from a fully sequenced strain of Saccharomyces cerevisiae, and by measuring gene expression levels in the human cell line THP-1. The approach provides an unprecedented depth of analysis permitting application of powerful statistical techniques for discovery of functional relationships among genes, whether known or unknown beforehand, or whether expressed at high or very low levels.

Cell Line↗

PubMed2000

Donor leukocyte infusions in acute lymphocytic leukemia.

Donor leukocyte infusion (DLI) has well-documented activity in CML but the role of DLI in other diseases is less well defined. To evaluate the strategy in acute lymphocytic leukemia (ALL) we evaluated 44 ALL patients from 27 centers who were treated with DLI. Patients with persistent or recurrent disease received DLI from the original marrow donor (30 matched related, four mismatched family, and 10 matched unrelated). Chemotherapy was given before DLI to 28 patients. Of 15 patients who received no pre-DLI chemotherapy, two achieved complete remissions, lasting 1112 and 764+ days. In four patients who received DLI as consolidation of remission induced by chemotherapy or immunosuppression-withdrawal, duration of remission post DLI was 65, 99, 195 and 672+ days. Of 25 patients who received DLI in the nadir after chemotherapy, 13 survived > or =30 days post DLI but did not achieve remission, seven died within less than 30 days post DLI, and five entered remissions that lasted 42, 68, 83, 90, 193 days. Seven patients who did not respond to the initial DLI received a second DLI; none of these patients attained durable remission. Eighteen of 37 evaluable patients developed acute GVHD and five of 20 evaluable patients developed chronic GVHD. Overall actuarial survival is 13% at 3 years. In conclusion, DLI has limited benefit in ALL. New approaches are needed in this group of patients.

Actuarial Analysis↗

PubMed2000

On the assessment of stability and patterning of speech movements.

Speech requires the control of complex movements of orofacial structures to produce dynamic variations in the vocal tract transfer function. The nature of the underlying motor control processes has traditionally been investigated by employing measures of articulatory movements, including movement amplitude, velocity, and duration, at selected points in time. An alternative approach, first used in the study of limb motion, is to examine the entire movement trajectory over time. A new approach to speech movement trajectory analysis was introduced in earlier work from this laboratory. In this method, trajectories from multiple movement sequences are time- and amplitude-normalized, and the STI (spatiotemporal index) is computed to capture the degree of convergence of a set of trajectories onto a single, underlying movement template. This research note describes the rationale for this analysis and provides a detailed description of the signal processing involved. Alternative interpolation procedures for time-normalization of kinematic data are also considered.

Adult↗

PubMed2000

Men's lived experiences following transurethral prostatectomy for benign prostatic hypertrophy.

The aim of this study was to illuminate the lived experience of prostatectomy recovery by means of semi-structured interviews. Despite the commonality of prostatic enlargement and the corrective transurethral procedure, surprisingly little is known of the impact upon the men's social and psychological well-being. The interviews have produced very rich data, which illustrate the extent to which the men are initially very reluctant to identify 'problems' either with their hospital experience or their subsequent recovery period. However, once respondents appeared to feel more comfortable, we began to learn of their very substantial difficulties both before and after the operation.

Aftercare↗

PubMed2000

Early detection of viral resistance by determination of hepatitis B virus polymerase mutations in patients treated by lamivudine for chronic hepatitis B.

We have analyzed the molecular dynamics of emergence of drug-resistant strains in patients receiving lamivudine therapy for chronic hepatitis B. Twenty consecutive patients with lamivudine resistance were studied (13 hepatitis B e antigen [HBeAg]-positive patients and 7 HBe antibody [anti-HBe]-positive patients). Determination of viral genotype, precore mutants, and polymerase gene mutants (L528M, M552V, M552I) was performed using the research version of Lipa-HBV. Quantitative analysis of HBV DNA was performed using both branched DNA (bDNA) and polymerase chain reaction (PCR) assays. Polymerase mutants (genotypic resistance) were found in 16 of 20 patients. Genotypic resistance was detected earlier than the phenotypic resistance (P =.004). Quantitative PCR allowed detection of viral DNA throughout the entire study period in 16 of 20 patients. Analysis of pretreatment variables showed that high alanine transaminase (ALT) levels (>3 x the upper limit of normal [ULN]) was associated with a more rapid selection of drug-resistant mutants (P =.027) and a high hepatitis B virus (HBV) DNA level (>1,497 Meq/mL, bDNA) with a more rapid occurrence of phenotypic resistance (P =.04). At the time of viral breakthrough, the mean serum HBV-DNA values were not different from the pretreatment values (P =.37). ALT levels were higher in anti-HBe-positive patients compared with pretreatment values and to HBeAg-positive patients (P =.01). In 8 patients, antiviral therapy was modified after viral breakthrough, with the introduction of famciclovir and/or interferon alfa. Viral DNA became undetectable by bDNA in 3 patients who received interferon. Our results suggest that genotypic assays for polymerase mutant detection and quantitative determination of viremia with highly sensitive assay are warranted for an optimal monitoring of antiviral therapy of chronic hepatitis B.

2-Aminopurine↗

PubMed2000

Low-dose inhaled fluticasone propionate versus oral zafirlukast in the treatment of persistent asthma.

BACKGROUND: Few studies have compared the efficacy of inhaled corticosteroids and leukotriene modifiers for the treatment of persistent asthma. OBJECTIVE: Our purpose was to compare the efficacy of a low dose of inhaled fluticasone propionate (FP) with that of oral zafirlukast in the treatment of persistent asthma previously treated with short-acting beta(2)-agonists alone. METHODS: A 12-week, randomized, double-blind, double-dummy, multicenter study was conducted in 451 patients aged 12 years and older with asthma who were symptomatic on short-acting beta(2)-agonists alone. After an 8- to 14-day run-in period, patients were randomized to treatment with FP 88 microg twice daily or zafirlukast 20 mg twice daily. RESULTS: Treatment with FP was more effective than treatment with zafirlukast in increasing morning FEV(1) (by 0.42 L vs 0.20 L over baseline, P <.001), morning peak expiratory flow (by 49.94 L/min vs 11.68 L/min over baseline, P <. 001), and evening PEF (by 38.91 L/min vs 10.50 L/min over baseline, P <.001). Statistically significant differences between the two treatments in FEV(1) were noted after the first observation (week 4) and in morning and evening peak expiratory flow by week 2. Mean change in percentage of symptom-free days was greater with FP than with zafirlukast (28.5% of days vs 15.6% of days, P <.001) and FP significantly increased the percentage of rescue-free days by 40.4% of days compared with 24.2% of days with zafirlukast (P <.001). Treatment with FP significantly reduced albuterol use by 2.39 puffs per day compared with 1.45 puffs per day (P <.001) and increased the percentage of nights with no awakenings by 21.2% of nights compared with 8.0% of nights with zafirlukast (P <.001). CONCLUSION: The clinical effectiveness of a low dose of FP as first-line therapy in patients with persistent asthma who are symptomatic on beta(2)-agonists alone is superior to that of zafirlukast.

Administration, Inhalation↗

PubMed2000

The indigenous fisherman divers of Thailand: diving-related mortality and morbidity.

The Urak Lawoi are indigenous fishermen on Thailand's west coast. The population includes an estimated 400 divers who dive using surface-supplied compressed air. In a cross-sectional survey conducted among the 6 major communities of Urak Lawoi, questionnaire-based interviews were administered to active divers, ex-divers, and families or colleagues of divers who had died in the previous 5 years. Six deaths resulting from diving-related accidents were identified, indicating a diving-related mortality rate of approximately 300 per 100,000 person-years, while in the same 5-year period 11 divers had been disabled owing to diving-related events, indicating a diving-related disabling event rate of approximately 550 per 100,000 person-years. Among 342 active divers interviewed, one third reported having suffered from decompression illness, although based on reported current symptoms over 50% were classified as suffering from recurring non-disabling decompression illness. Physical examination conducted on a subset of 98 active divers revealed the presence of spinal injury (clonus, raised muscle tone, and heightened reflexes) and of joint damage (pain in one or more joint, crepitus, or restricted movement) in 24 and 30% respectively. Improved primary prevention and medical treatment are needed to reduce mortality and morbidity among this population.

Accidents, Occupational↗

PubMed2000

An instrument to measure symptom experience. Symptom occurrence and symptom distress.

This article describes the development of an instrument that measures symptom experience (symptom occurrence and symptom distress). The Adapted Symptom Distress Scale-2 (ASDS-2), adapted from the McCorkle and Young Distress Scale, is a 31-item, 5-point, self-report paper-and-pencil instrument that measures patients' perception of the occurrence and distress of 14 symptoms: nausea, vomiting, pain, eating, sleep, fatigue, bowel elimination, breathing, coughing, concentration, lacrimation, changes in body temperature, appearance, and restlessness. Use of the instrument yields a total score for symptom experience, scores for symptom occurrence, scores for symptom distress, and subscale scores for six symptom categories: gastrointestinal, fatigue/restlessness, concentration, pain/discomfort, respiratory, and appearance. Reliability and validity were determined with well adults (n = 97), medical-surgical patients (n = 82), and oncology patients (n = 175). Findings revealed a Cronbach's alpha of 0.91 for symptom experience, 0.90 for symptom occurrence, and 0.76 for symptom distress. Cronbach's alpha for the subscales ranged from 0.38 for appearance symptoms to 0.83 for gastrointestinal symptoms. Inclusion of symptoms reported by patients with cancer strengthened content validity. A contrasted groups approach was used to demonstrate construct validity.

Adolescent↗

PubMed2000

Osteosarcoma in preadolescent patients.

The medical records of boys younger than 11 years and girls younger than 10 years of age with osteosarcoma of the pelvis or extremity were reviewed. Thirty patients were identified who were newly diagnosed but untreated for osteosarcoma. None of these patients had pulmonary metastases. The same four protocols were used to treat the patients in the current study as were used to treat adolescents. The event-free and overall survival was calculated and prognostic factors were assessed. The median followup time was 8 years (range, 6-14 years). The results were compared with the results of older patients treated with the same protocols and with published results. Fourteen patients had pulmonary metastases (47%); among these patients, four also had skeletal metastases (in two of the latter, skeletal metastases appeared before the pulmonary metastases). Event-free survival was 53% and overall survival was 57%. This result is comparable with current survival results in adolescent and older patients. Serum alkaline phosphatase and serum lactic dehydrogenase levels before treatment, height percentile greater than 50%, chemotherapy-induced tumor necrosis, surgical procedure, tumor site, tumor histologic features, and patient gender were not prognostic indicators. The prognosis for prepubertal patients with osteosarcoma is similar to the prognosis of their adolescent and older counterparts. There does not seem to be any indication to treat preadolescent patients with osteosarcoma using alternate therapies.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2000

A dose ranging study of the pharmacokinetics, safety, and preliminary efficacy of lamivudine in children and adolescents with chronic hepatitis B.

Fifty-three patients with chronic hepatitis B and active viral replication were studied for 4 weeks while on treatment and for 12 weeks after treatment with the oral nucleoside analogue lamivudine. Children aged 2 to 12 years were randomized to receive twice-daily doses of 0.35, 1.5, or 4 mg of lamivudine solution per kg of body weight or once-daily doses of 3 mg of lamivudine solution per kg. Adolescents aged 13 to 17 years received lamivudine at 100 mg (as tablets). Blood samples for pharmacokinetic assay were taken on days 1 and 28. Lamivudine was rapidly absorbed following oral administration, with the maximum concentration in serum being reached 0.5 to 1 h postdosing. Apparent oral clearance (CL/F) was higher in younger children and decreased with age, with CL/F values for adolescents reaching those seen for adults by the age of 12. All doses produced a dramatic fall in serum hepatitis B virus (HBV) DNA levels, with a median reduction of >/=99.5% after 4 weeks of treatment and with the levels returning to the baseline levels posttreatment. The correlation of dose, area under the concentration-time curve (AUC), and changes in HBV DNA levels, as measured by the Chiron Quantiplex assay, showed maximal antiviral effects (99.9% inhibition and a reduction of the amount of HBV DNA of approximately 3 log(10)) at 3 mg/kg/day, with no discernible increase in effect seen whether the drug was given at 4 mg/kg twice daily or whether it was given once daily or twice daily. The limit of detection of the assay (2.5 pg/ml) was reached for some but not all patients across the dose ranges, with the smallest number (n = 2) of those having values negative by the Chiron Quantiplex assay being in the lowest-dose group. The 13- to 17-year-olds showed a similar overall response in terms of the HBV DNA level reduction compared to that for patients younger than age 13. Analysis of the same samples by PCR, which has a lower limit of sensitivity than the Chiron Quantiplex assay, also showed average drops in HBV DNA levels of about 3 log(10) at 4 weeks for patients for which the AUC was >/=4,000 ng. h/ml, confirming the conclusions given above. Lamivudine treatment was well tolerated at all doses, with no significant adverse events or laboratory data changes. On the basis of pharmacokinetic and pharmacodynamic data, a 3-mg/kg/day dose in children (ages 2 to 12 years) with chronic hepatitis B provides levels of exposure and trough concentrations similar to those seen in adults following the receipt of doses of 100 mg. The 100-mg dose is being evaluated in a large phase III study with HBV-infected pediatric patients.

Adolescent↗

PubMed2000

Pharmacokinetics and tolerability of gemifloxacin (SB-265805) after administration of single oral doses to healthy volunteers.

Gemifloxacin (known as SB-265805 or LB-20304) is a potent, novel fluoroquinolone compound with a broad spectrum of antibacterial activity. The pharmacokinetics and tolerability of oral gemifloxacin were characterized in healthy male volunteers after a single dose of 20, 40, 80, 160, 320, 600, or 800 mg. Multiple serum and urine samples were collected and analyzed for gemifloxacin using high-performance liquid chromatography with fluorescence detection. Safety assessments included vital signs, 12-lead electrocardiogram readings, hematology, clinical chemistry, urinalysis, and adverse-experience monitoring. Gemifloxacin was rapidly absorbed after all doses. Maximum concentrations of gemifloxacin in serum (C(max)) were achieved approximately 1 h after dosing, after which concentrations in serum declined in a biexponential manner. Values of C(max) and the area under the concentration-time curve in serum from 0 h to infinity (serum AUC(0-infinity)) increased linearly with dose. Serum AUC(0-infinity) values (mean +/- standard deviation) were 0.65+/-0.01, 1.28+/-0.22, 2.54+/-0.31, 5.48+/-1.24, 9.82+/-2.70, 24.4+/-7.1, and 31.4+/-7.6 microg. h/ml following 20-, 40-, 80-, 160-, 320-, 600-, and 800-mg doses, respectively. The terminal phase elimination half-life was independent of dose, with an overall mean of 7.4+/-2.0 h. The profiles indicated that the pharmacokinetic profile is suitable for a once-daily dosing regimen. Approximately 25 to 40% of the administered dose was excreted unchanged in the urine, and renal clearance (ca. 150 ml/min) was independent of dose. There were no significant changes in clinical chemistry, hematology, or urinalysis parameters, vital signs, or 12-lead electrocardiogram readings in subjects, irrespective of dose. The results of these studies support the further investigation of once-daily administration of gemifloxacin.

Administration, Oral↗

PubMed2000

Automated measurement of unsaturated iron binding capacity is an effective screening strategy for C282Y homozygous haemochromatosis.

BACKGROUND: C282Y hereditary haemochromatosis is an appropriate condition for population screening. Transferrin saturation, the best screening test to date, is relatively expensive, labour intensive, and cannot be automated. Unsaturated iron binding capacity is a surrogate marker of transferrin saturation and its measurement can be automated. AIMS: To evaluate a screening strategy for C282Y hereditary haemochromatosis in a tertiary hospital environment based on unsaturated iron binding capacity as the initial screening test. METHODS: Measurement of unsaturated iron binding capacity was adapted to the main laboratory analyser. An unsaturated iron binding capacity of less than 30 micromol/l was identified as an appropriate decision point and 5182 consecutive subjects were screened over 28 consecutive days. RESULTS: Of those screened, 697 had an unsaturated iron binding capacity less than 30 micromol/l. Of these, transferrin saturation was greater than 40% in 294. A total of 227 were able to be genotyped for the C282Y mutation. Nine subjects homozygous for C282Y were identified. Based on full cost recovery, affected persons were identified at a cost of Aus$2268.77 per case (approximately US$1496). CONCLUSION: Automated measurement of unsaturated iron binding capacity enables a cost effective, large scale population screening programme for C282Y hereditary haemochromatosis to be developed.

Adult↗

PubMed2000

Human skeletal muscle exercise metabolism following an expedition to mount denali.

Chronic exposure to high altitude is known to result in changes in the mechanisms regulating O(2) delivery to the contracting muscle. However, the effects of acclimatization on metabolism in the contracting muscle cell remain unclear. In this study, we have investigated the hypothesis that acclimatization would result in a closer coupling between ATP utilization and ATP production and that the improved energy state would be accompanied by a reorganization of the metabolic pathways consisting of an increased oxidative and decreased glycolytic potential. Five men, mean age of 28 +/- 2 (SE) yr, performed a standardized, two-stage submaximal cycling task in normoxia for 20 min at each of 59 and 74% peak O(2) consumption before and 3-4 days after returning from a 21-day expedition to Mount Denali (6,194 m). Acclimatization was without effect in altering the resting values of the adenine nucleotides (ATP, ADP, AMP), inosine monophosphate (IMP), or phosphocreatine (PCr) in the vastus lateralis. During exercise (40 min) after acclimatization compared with preacclimatization, PCr was not as depressed (33.2 +/- 7.1 vs. 40.6 +/- 5.4 mmol/kg dry wt) and IMP (0.289 +/- 0.11 vs. 0. 131 +/- 0.03 mmol/kg dry wt) and lactate (26.1 +/- 6.2 vs. 18.6 +/- 8.8 mmol/kg dry wt) in contracting muscle were not as elevated (P < 0.05). Although no effect of acclimatization was observed for the maximal activity (mol. kg protein(-1). h(-1)) of citrate synthase (4. 76 +/- 0.44 vs. 4.94 +/- 0.45), lactate dehydrogenase was increased by 13% (36.5 +/- 2.6 vs. 41.2 +/- 3.1, P < 0.05). It is concluded that acclimatization results in an improved energy state in the contracting muscle when tested under normoxic conditions; however, these effects are not associated with a higher oxidative potential or a lower glycolytic potential as hypothesized.

Acclimatization↗

PubMed2000

Increases in submaximal cycling efficiency mediated by altitude acclimatization.

To investigate the hypothesis that respiratory gas exchange and, in particular, the O(2) consumption (VO(2)) response to exercise is altered after a 21-day expedition to 6,194 m, five male climbers (age 28.2 +/- 2 yr; weight 76.9 +/- 4.3 kg; means +/- SE) performed a progressive and prolonged two-step cycle test both before and 3-4 days after return to sea level. During both exercise tests, a depression (P < 0.05) in VO(2) (l/min) and an increase (P < 0.05) in minute ventilation (VE BTPS; l/min) and respiratory exchange ratio were observed after the expedition. These changes occurred in the absence of changes in CO(2) production (l/min). During steady-state submaximal exercise, net efficiency, calculated from the rates of the mechanical power output to the energy expended (VO(2)) above that measured at rest, increased (P < 0.05) from 25.9 +/- 1.6 to 31. 3 +/- 1.3% at the lighter power output and from 24.4 +/- 1.3 to 29.5 +/- 1.5% at the heavy power output. These changes were accompanied by a 4.5% reduction (P < 0.05) in peak VO(2) (3.99 +/- 0.17 vs. 3.81 +/- 0.18 l/min). After the expedition, an increase (P < 0.05) in hemoglobin concentration (15.0 +/- 0.49 vs. 15.8 +/- 0.41 g/100 ml) was found. It is concluded that, because resting VO(2) was unchanged, net efficiency is enhanced during submaximal exercise after a mountaineering expedition when the exercise is performed soon after return to sea level conditions.

Acclimatization↗