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Biomedical subjects

C S Houston

Publications and source records attributed to C S Houston.

At least 37 records · Page 2Linked to original sources
PubMed1993

The cloning and sequencing of the genes encoding phytase (phy) and pH 2.5-optimum acid phosphatase (aph) from Aspergillus niger var. awamori.

The genes encoding phytase (EC 3.1.3.8) and pH 2.5-optimum acid phosphatase (EC 3.1.3.2) have been cloned and sequenced from Aspergillus niger var. awamori. The translated nucleotide sequences yielded polypeptides of 467 and 479 amino acids (aa) for phytase and acid phosphatase, respectively. The genes were isolated using oligodeoxyribonucleotide probes based on the aa sequences of the purified proteins. Recombinant A. niger var. awamori strains carrying additional copies of the gene sequences demonstrated elevated enzyme activities.

6-Phytase↗
PubMed1993

Nazi medicine.

Explore the source record for details and available documents.

Attitude of Health Personnel↗
PubMed1993

Acute mountain sickness in children at 2835 meters.

OBJECTIVE: Acute mountain sickness has been described in adults but little is known concerning its occurrence in children. Our objective was to determine the incidence of acute mountain sickness in children. METHODS: A survey questionnaire was completed by 558 children (aged 9 to 14 years) after they ascended from 1600 to 2835 m and from 405 similarly aged children after travel at sea level. RESULTS: Three or more of the following symptoms in the high-altitude setting were considered as the case definition of acute mountain sickness: headache, loss of appetite, vomiting, fatigue, insomnia, shortness of breath, and dizziness. One hundred fifty-six (28%) of the children at 2835 m developed acute mountain sickness. Three or more symptoms developed in a smaller, but nonetheless considerable, number (86 [21%]) of children at sea level. Headache, shortness of breath, and dizziness were reported more frequently at high altitude than at low altitude, whereas the other symptoms occurred with equal frequency at the two locations. CONCLUSIONS: More than one fourth of the children visiting high altitude developed acute mountain sickness. A high proportion (21%) of children at sea level developed similar symptoms, suggesting that an appreciable portion of the symptoms present were due to factors other than altitude, such as travel, anxiety, or disruption of daily routine.

Adolescent↗
PubMed1993

Operation Everest II: an indication of deterministic chaos in human heart rate variability at simulated extreme altitude.

It has been shown that fluctuation of human heartbeat intervals (heart rate variability, HRV) reflects variations in autonomic nervous system activity. We studied HRV at simulated altitudes of over 6000 m from Holter electrocardiograms recorded during the Operation Everest II study (Houston et al. 1987). Stationary, approximately 30-min segments of HRV data from six subjects at sea level and over 6000 m were supplied to (1) spectral analysis to evaluate sympathetic and parasympathetic nervous system (SNS, PNS) activity, (2) the analysis of Poincaré section of the phase space trajectory reconstructed on a delayed coordinate system to evaluate whether there was fluctuation with deterministic dynamics, (3) the estimation of the correlation dimension to evaluate a static property of putative attractors, and (4) the analysis of nonlinear predictability of HRV time series which could reflect a dynamic property of the attractor. Unlike HRV at sea level, the recordings at over 6000 m showed a strong periodicity (period of about 20 s) with small cycle-to-cycle perturbation. When this perturbation was expressed on a Poincaré section, it seemed to be likely that the perturbation itself obeyed a deterministic law. The correlation dimensions of these recordings showed low dimensional values (3.5 +/- 0.4, mean +/- SD), whereas those of the isospectral surrogates showed significantly (P < 0.05) higher values (5.3 +/- 0.5) with embedding dimensions of 5.6 +/- 0.9.(ABSTRACT TRUNCATED AT 250 WORDS)

Altitude↗
PubMed1993

Regional and total body bone mineral content, bone mineral density, and total body tissue composition in children 8-16 years of age.

Normative values for total body bone mineral content (TBBM) and total body bone mineral density (TBMD) were derived from measurements on 234 children 8-16 years of age. In addition, bone mineral content (BMC) and bone mineral density (BMD) values for selected regions of interest and soft tissue (bone free lean and fat) for the total body are presented. Bone mineral and soft tissue values were determined by dual energy X-ray absorptiometry (DXA) using a Hologic QDR-2000 in the array mode. Results of a stepwise multiple regression analysis revealed a significant correlation between bone-free lean tissue (BFLT) and BMD (r2 = 0.80) in girls. Adding age to the equation accounted for an additional 2% of the variance (P < 0.05) and height accounted for another 1% of the variance (P < 0.05). Body weight and fat tissue (FT) did not account for any additional variance. In boys BFLT correlated significantly with BMD (r2 = 0.75; P < 0.05); none of the other predictor variables accounted for additional variance. No significant differences were found in TBBM or TBMD between boys and girls at any age. There was a significant overall gender effect for only three regions of interest. Boys had greater BMC in the head region and had greater BMD in the upper limbs, but post hoc analysis revealed no significant differences for any specific age groups. Girls had greater overall BMD in the pelvis, but this difference was only significant at the 15-16-year age group. The changes in BFLT and FT over the age ranges were consistent with the growth literature.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1993

Operation Everest. II: Spirometric and radiographic changes in acclimatized humans at simulated high altitudes.

We report spirometry and radiographic data on eight normal male human subjects during prolonged graded altitude exposure to as high as 8,848 m above sea level in a hypobaric chamber. We found a significant and progressive drop in FVC by 14 +/- 3% over 40 days, which resolved slowly during the first 48 h after descent. With altitude, midrange forced expiratory flow (FEF25-75) increased by 82 +/- 3%, probably because of reduced air density. FEV1, however, did not change. Chest radiographs on subjects taken 2 h after descent to sea level showed a pattern of pulmonary artery enlargement and interstitial edema. These data suggest that increased pulmonary blood volume and edema may be causes of the restricted pulmonary function pattern.

Acclimatization↗
PubMed1993

Abnormal ossification of the hyoid bone in cleidocranial dysplasia.

Radiographs of the hyoid region of 13 patients with cleidocranial dysplasia were reviewed. In all but one the hyoid bone was less ossified than normal. Delayed ossification, affecting the skull, the teeth, the pelvis and the extremities, is a known, frequent manifestation of this abnormality.

Adolescent↗
PubMed1993

Operation Everest II: gas tensions in expired air and arterial blood at extreme altitude.

Measurements in alveolar gas have suggested extreme hypocapnia and alkalosis on the summit of Mt. Everest. However, tensions in both expired gas and arterial blood have not been reported for the summit of Mt. Everest (PIO2 = 43 mm Hg). To approach the problem, we examined alveolar (and end-tidal) and arterial gas tensions in 6 healthy men who completed a 40-d chamber study to the simulated "summit," with 20 d above 6,400 m and 9 d above 8,000 m. In 27 simultaneous samples of alveolar air and arterial blood for inspired oxygen tensions ranging from PIO2 of 55 mm Hg (7,380 m) to 43 mm Hg, the mean alveolar-arterial difference was negligible for PO2 (-0.8 +/- 2.4 (S.D.) mm Hg) and PCO2 (0.5 +/- 1.4 mm Hg). For all 6 subjects at the summit, PACO2 was 12.0 +/- 1.8 and PACO2 was 11.4 +/- 1.6 mm Hg, and for the two with the lowest values, alveolar and arterial PCO2, respectively, were 9.5 and 9.8 mm Hg. Arterial pH averaged 7.53 units. We conclude that while acclimatization to severe hypoxia results in extreme hypocapnia, alkalosis is more moderate than previously reported. Alveolar gas tensions reflect well the values obtained in arterial blood.

Acclimatization↗
PubMed1992

Mountain sickness.

The varied and subtle symptoms of this potentially lethal disorder humble many who scale the summits. But the problem is often preventable.

Acclimatization↗
PubMed1992

From the mountains to the labs. A brief summary of the people and their studies on which rests most of what we know today.

The science of mountain medicine is less than 150 years old, partly because mountaineering became popular only in the middle of the 19th century. In the last 30 years there has been an explosion of activity on very high mountains, in laboratories, and in simulated high altitude environments. Our knowledge and understanding of high altitude hypoxia has been built slowly and painfully over many centuries. First came recognition that pure air was essential to health. Then the physical properties of the atmosphere were demonstrated 300 years ago. Slowly the vital ingredient in air was identified, and even more recently the relationship between barometric pressure, oxygen, and the sicknesses that affect men at altitude was appreciated. In this paper, will be described how some of the most important advances were made, and where the explorers sometimes went astray. I will mention some of the people whose major contributions have been forgotten, to remind us that fame or fortune does not necessarily go to those who deserve it most. Remember that not until the middle of the 18th century did men climb high mountains. The intrepid prehistoric hunter (Otzi) who was lost on a high mountain 5000 years ago and found last year was certainly an exception. Only recently have mountaineer-scientists begun to study in the laboratory what they observed on the summits. By knowing how we came to know what we believe to be true today, perhaps we may understand better how knowledge grows, not only in a steady flow but now and then by brilliant leaps.(ABSTRACT TRUNCATED AT 250 WORDS)

Europe↗
PubMed1992

Oxygen transport and cardiovascular function at extreme altitude: lessons from Operation Everest II.

Operation Everest II was designed to examine the physiological responses to gradual decompression simulating an ascent of Mt Everest (8,848 m) to an inspired PO2 of 43 mmHg. The principal studies conducted were cardiovascular, respiratory, muscular-skeletal and metabolic responses to exercise. Eight healthy males aged 21-31 years began the "ascent" and six successfully reached the "summit", where their resting arterial blood gases were PO2 = 30 mmHg and PCO2 = 11 mmHg, pH = 7.56. Their maximal oxygen uptake decreased from 3.98 +/- 0.2 L/min at sea level to 1.17 +/- 0.08 L/min at PIO2 43 mmHg. The principal factors responsible for oxygen transport from the atmosphere to tissues were (1) Alveolar ventilation--a four fold increase. (2) Diffusion from the alveolus to end capillary blood--unchanged. (3) Cardiac function (assessed by hemodynamics, echocardiography and electrocardiography)--normal--although maximum cardiac output and heart rate were reduced. (4) Oxygen extraction--maximal with PvO2 14.8 +/- 1 mmHg. With increasing altitude maximal blood and muscle lactate progressively declined although at any submaximal intensity blood and muscle lactate was higher at higher altitudes.

Adult↗
PubMed1992

Operation Everest II: metabolic and hormonal responses to incremental exercise to exhaustion.

The reasons for the reduced exercise capacities observed at high altitudes are not completely known. Substrate availability or accumulations of lactate and ammonium could have significant roles. As part of Operation Everest II, peak oxygen uptakes were determined in five normal male volunteers with use of progressively increasing cycling work loads at ambient barometric pressures of 760, 380, and 282 Torr. Decrements from sea level (SL) to 380 and 282 Torr occurred in peak power output (19 and 47%), time to exhaustion (19 and 48%), and oxygen uptake (41 and 61%), respectively. Arterial saturations after exhaustive exercise were decreased to 63% at 380 Torr and 39% at 282 Torr. At 380 and 282 Torr, postexercise plasma concentrations of glucose and free fatty acids were not increased, whereas plasma glycerol concentrations were decreased relative to SL (145 +/- 24 microM at 380 Torr and 77 +/- 10 microM at 282 Torr vs. 213 +/- 24 microM at SL). Preexercise plasma insulin concentrations were elevated at both 380 and 282 Torr (87 +/- 16 pM at 380 Torr and 85 +/- 18 pM at 282 Torr vs. 41 +/- 30 pM at SL). In general, postexercise concentrations of plasma catecholamines were decreased at altitude compared with SL. Preexercise lactate and ammonium concentrations were not different at any simulated altitude. From these data neither substrate availability nor metabolic product accumulation limited exercise capacity at extreme simulated altitude.

Adult↗
PubMed1992

Operation Everest II: arterial oxygen saturation and sleep at extreme simulated altitude.

Frequent sleep disturbances and desaturation during sleep are common at high altitude, but few data are available from the highest altitudes at which humans are known to sleep. Because sleep fragmentation at low altitude may impair mental function and oxygen deprivation produces lasting central nervous system abnormalities, a better understanding of the severity of sleep disturbances and oxygen desaturation at extreme altitudes is important. The purpose of this study was to determine the severity of sleep disturbance and the extent of arterial oxygen desaturation at extreme simulated altitude. Out of eight healthy male subject volunteers who started, five aged 27.2 +/- 1.5 yr completed the study during 6 weeks of progressive hypobaric hypoxia in a decompression chamber. The men were studied at barometric pressures of 760, 429, 347, 282 mm Hg and following return to 760 mm Hg. All demonstrated frequent nighttime awakenings (37.2 awakenings per subject per night at 282 mm Hg, decreasing significantly to 14.8 on return to sea level, p less than 0.05). Total sleep time decreased from 337 +/- 30 min at 760 mm Hg to 167 +/- 44 min at 282 mm Hg (p less than 0.01). Rapid eye movement (REM) sleep decreased from 17.9% +/- 6.0% of sleep time at sea level to 4.0% +/- 3.3% at 282 mm Hg (p less than 0.01). Sleep continuity as reflected by brief arousals increased from 22 +/- 6 arousals per hour of sleep at sea level to 161 +/- 66 arousals per hour at 282 mm Hg (p less than 0.01). All subjects showed arterial oxygen desaturation proportional to the altitude. The average oxygen saturation (SaO2) was 79% +/- 3% at 429 mm Hg, 66% +/- 6% at 347 mm Hg, and 52% +/- 2% at 282 mm Hg. Sleep stage had only a minimal effect on SaO2 at any altitude. SaO2 was negatively correlated with brief sleep arousals, r = -0.72, p less than 0.01. All subjects demonstrated periodic breathing with apneas throughout much of the night at 347 and 282 mm Hg. These data indicate that sleep quality progressively worsens as SaO2 decreases despite lack of progressive changes in sleep stages at altitude. This study extends previous information on the severity of desaturation during sleep, and suggests that improvements in oxygenation might prove beneficial in restoring consolidated sleep, possibly even improving daytime performance.

Adult↗
PubMed1991

Operation Everest II: structural adaptations in skeletal muscle in response to extreme simulated altitude.

Alterations in skeletal muscle structure were investigated in 6 male subjects who underwent 40 days of progressive decompression in a hypobaric chamber simulating an ascent to the summit of Mount Everest. Needle biopsies were obtained from vastus lateralis of 5 subjects before and immediately after confinement in the chamber, and were examined for various structural and ultrastructural parameters. In addition, total muscle area was calculated in 6 subjects from CT scans of the thighs and upper arms. Muscle area at these sites was found to decrease significantly (by 13 and 15%) as a result of the hypobaric confinement. This was substantiated by significant (25%) decreases in cross sectional fibre areas of the Type I fibres and 26% decreases (non significant) in Type II fibre area. Capillary to fibre ratios remained unchanged following hypoxia as did capillary density although there was a trend (non significant) towards an increase in capillary density. There were no significant increases in mitochondrial volume density or other morphometric parameters. These data indicate that chronic, severe hypoxia on its own does not result in an increase in absolute muscle capillary number or a de novo synthesis of mitochondria. The trends toward an increase in capillary density and mitochondrial volume density were interpreted as being secondary occurrences in response to the pronounced muscle atrophy which occurred.

Acclimatization↗
PubMed1991

Minor anatomic abnormalities of the hip joint persisting from childhood and their possible relationship to idiopathic osteoarthrosis.

A retrospective review was made of roentgenograms from 30 patients with idiopathic osteoarthrosis of the hip. The roentgenograms were taken before the onset or very early in the course of the disease. Nine measurements were made on the anteroposterior and cross-table lateral roentgenograms. These were compared to 54 hips from normal patients. Twenty-nine of 30 patients had abnormal measurements, with as many as seven in a single individual, when compared to normal patients. There were no abnormalities in the control group. The availability of lateral views allowed an additional dimension to be added to previous studies in the literature. This study lends further support to the biomechanical theory of the etiology of idiopathic osteoarthrosis of the hip.

Adolescent↗