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Biomedical subjects

C M Chow

Publications and source records attributed to C M Chow.

At least 19 recordsLinked to original sources
PubMed2006

Interspersed normoxia during live high, train low interventions reverses an early reduction in muscle Na+, K +ATPase activity in well-trained athletes.

Hypoxia and exercise each modulate muscle Na(+), K(+)ATPase activity. We investigated the effects on muscle Na(+), K(+)ATPase activity of only 5 nights of live high, train low hypoxia (LHTL), 20 nights consecutive (LHTLc) versus intermittent LHTL (LHTLi), and acute sprint exercise. Thirty-three athletes were assigned to control (CON, n = 11), 20-nights LHTLc (n = 12) or 20-nights LHTLi (4 x 5-nights LHTL interspersed with 2-nights CON, n = 10) groups. LHTLc and LHTLi slept at a simulated altitude of 2,650 m (F(I)O(2) 0.1627) and lived and trained by day under normoxic conditions; CON lived, trained, and slept in normoxia. A quadriceps muscle biopsy was taken at rest and immediately after standardised sprint exercise, before (Pre) and after 5-nights (d5) and 20-nights (Post) LHTL interventions and analysed for Na(+), K(+)ATPase maximal activity (3-O-MFPase) and content ([(3)H]-ouabain binding). After only 5-nights LHTLc, muscle 3-O-MFPase activity declined by 2% (P < 0.05). In LHTLc, 3-O-MFPase activity remained below Pre after 20 nights. In contrast, in LHTLi, this small initial decrease was reversed after 20 nights, with restoration of 3-O-MFPase activity to Pre-intervention levels. Plasma [K(+)] was unaltered by any LHTL. After acute sprint exercise 3-O-MFPase activity was reduced (12.9 +/- 4.0%, P < 0.05), but [(3)H]-ouabain binding was unchanged. In conclusion, maximal Na(+), K(+)ATPase activity declined after only 5-nights LHTL, but the inclusion of additional interspersed normoxic nights reversed this effect, despite athletes receiving the same amount of hypoxic exposure. There were no effects of consecutive or intermittent nightly LHTL on the acute decrease in Na(+), K(+)ATPase activity with sprint exercise effects or on plasma [K(+)] during exercise.

Adult↗
PubMed2005

Snakebite in a child: could we avoid the anaphylaxis or the fasciotomies?

INTRODUCTION: We report the unusual presentation and complications of a case of snakebite, involving a child and his mother, who were bitten by the same snake. CLINICAL PICTURE: The mother was well but the child developed worsening local pain and swelling. TREATMENT AND OUTCOME: Test doses of antivenom were administered but he developed anaphylactic shock. Subsequently, he developed compartment syndrome and fasciotomies were performed. CONCLUSIONS: This report serves to alert the public to a few of the avoidable risk factors associated with snakebites (such as avoiding areas known to harbour snakes in the evening in summer and autumn, and wearing protective footwear), and the clinician of the important management issues in snakebites. Precautions for anaphylaxis must be taken when antivenom is administered. If a bitten patient with rapid extension of local injury does not receive any antivenom, compartment syndrome complicating local injury can occur.

Anaphylaxis↗
PubMed2004

Effect of temperature and duration of hyperthermia on HSP72 induction in rat tissues.

The aim of the present study was to determine whether heat shock protein 72 (HSP72) is induced in a heated rat model at rectal temperatures below 42 degrees C. Rats were divided into a control group and six groups (n = 6) heated to different rectal temperatures: 39 degrees C for 1 h (39), 40.0 degrees C for either 15 min (40S) or 1 h (40L), 41.0 degrees C for either 15 min (41S) or 1 h (41L) and 42.0 degrees C for 15 min (42). Tissues were sampled 4 h after heating. Following 1 h at 40.0 degrees C, HSP72 was significantly elevated in heart (p < 0.005), but not in gut or liver tissue. In all three tissues, HSP72 was significantly elevated under the conditions 41L and 42 compared to control tissue (p < 0.005). Marked differences were found in the amount of HSP72 induced in different tissues in response to the same heat stress. Duration of heating was important in modulating HSP72 induction, with a significantly greater induction of HSP72 following 1 h compared to 15 min at 41 degrees C in all three tissues (p < 0.02). A correlation was found between thermal load and HSP72 content in liver, heart (both p < 0.01) and gut (p < 0.001) for the rats heated to 41 and 42 degrees C. These data show that HSP72 is induced at temperatures below 42 degrees C, with striking differences between tissues.

Animals↗
PubMed2003

Sleep quality responses to atmospheric variation: case studies of two elite female cyclists.

Strategies applied during sleep to potentially enhance athlete performance use different atmospheric conditions. High altitude conditions are known to affect sleep adversely but the effects of mild-moderate altitude and O2 enrichment at mild altitude are uncertain. We performed case studies using two elite female road cyclists (mass and maximal aerobic power of 62 kg, 65.8 ml x kg(-1) x min(-1); 57 kg, 62.7 ml x kg(-1) x min(-1)) to examine changes in sleep for different atmospheric conditions applied throughout the preparation for, and during, an International Stage race. Conditions were: i) normoxia (600 m), ii) simulated moderate altitude (2650 m), iii) natural mild altitude (1380 m) and iv) O2 enrichment at mild altitude (30% O2@ 1300-1500 m). We measured respiratory disturbances, arousals, number of awakenings, blood oxygen saturation (SpO2), heart rate (HR), rapid eye movement sleep (REM) and deep sleep. Respiratory disturbances, SpO2 and HR responses were similar for both cyclists for all conditions. Compared with normoxia, both cyclists had somewhat reduced REM at natural mild altitude and moderate simulated altitude but differed in their REM and deep sleep responses to O2 enrichment. Compared with mild altitude, both showed increased awakenings and deep sleep with O2 enrichment. Only one cyclist clearly increased her REM sleep with O2 enrichment compared to mild altitude. Our data highlight two different sleep quality responses to atmospheric variation.

Altitude↗
PubMed2003

Pulmonary arteriovenous malformation: a rare, treatable cause of stroke in young adults.

Pulmonary arteriovenous malformation (PAVM) predisposes affected patients to a significantly increased risk of stroke. Most commonly, PAVM is seen in patients with hereditary haemorrhagic telangiectasia (HHT), an inherited disorder that can be difficult to diagnose in young people because of variable age-related penetrance. As such, stroke in the young adult may be the presenting feature of underlying PAVM in a previously undiagnosed patient. The importance of considering this diagnosis in the evaluation of young adults with cryptogenic stroke is underscored by the availability of both sensitive screening and effective treatment for PAVM, from which this at-risk population can greatly benefit.

Adult↗
PubMed2001

Vascular endothelial function in cyclosporine and tacrolimus treated renal transplant recipients.

BACKGROUND: Endothelial dysfunction is an early key event in the development of arteriosclerotic cardiovascular disease (ASCVD), thus an early marker of subclinical ASCVD. Endothelial function is impaired in renal transplant recipients (RTR) treated with cyclosporine (CyA). Tacrolimus is associated with less hyperlipidemia and hypertension than CyA, however, there are no data on endothelial function in tacrolimus-treated RTR. METHODS: High-resolution brachial ultrasonography was used to assess endothelium-dependent dilatation (EDD), and endothelium-independent dilatation (EID) in 20 stable RTR and a control group of 10 healthy subjects without clinical evidence of ASCVD. The RTR group included patients receiving CyA (n=10) and tacrolimus (n=10). EDD and EID were measured as percent increase in brachial artery diameter in response to reactive hyperemia and nitroglycerin, respectively. RESULTS AND CONCLUSIONS: EDD was significantly lower in RTR versus controls (1.7+/-0.7 vs. 7.3+/-0.7%, P<0.0001), whereas EID was similar in the two groups. No significant differences were found in EDD or in EID between CyA- and tacrolimus-treated RTR. Glomerular filtration rate, plasma homocysteine, blood pressure, and lipid profiles were similar in CyA- and tacrolimus-treated RTR.

Adult↗
PubMed2001

Paradoxic decrease in ischemic mitral regurgitation with papillary muscle dysfunction: insights from three-dimensional and contrast echocardiography with strain rate measurement.

BACKGROUND: Ischemic mitral regurgitation (MR) was first ascribed to papillary muscle (PM) contractile dysfunction. Current theories include apical leaflet tethering caused by left ventricular (LV) distortion, but PM dysfunction is still postulated and commonly diagnosed. PM contraction, however, parallels apical tethering, suggesting the hypothesis that PM contractile dysfunction can actually diminish MR due to ischemic distortion of the inferior base alone. METHODS AND RESULTS: We therefore occluded the proximal circumflex circulation in 7 sheep while maintaining PM perfusion, confirmed by contrast echocardiography. By 3D echocardiography, we measured the tethering distance between the ischemic medial PM tip and anterior annulus and LV ejection volume to give MR (by subtracting flowmeter LV outflow). In 6 sheep without initial MR, inferior ischemia alone produced PM tip retraction with restricted leaflet closure and mild-to-moderate MR (regurgitant fraction, 25.2+/-2.8%). Adding PM ischemia consistently decreased MR and tethering distance (5.2+/-0.3 to 1.4+/-0.3 mL; +3.8+/-0.5 mm to -2.2+/-0.7 mm axially relative to baseline; P<0.001) as PM strain rate decreased from +0.78+/-0.07 per second (contraction) to -0.42+/-0.06 per second (elongation, P<0.001) and leaflet tenting decreased. In one sheep, prolapse and MR resolved with inferior ischemia and recurred with PM ischemia. CONCLUSIONS: PM contractile dysfunction can paradoxically decrease MR from inferobasal ischemia by reducing leaflet tethering to improve coaptation. This emphasizes the role of geometric factors in ischemic MR mechanism and potential therapy.

Animals↗
PubMed2001

Chordal cutting: a new therapeutic approach for ischemic mitral regurgitation.

BACKGROUND: Mitral regurgitation (MR) conveys adverse prognosis in ischemic heart disease. Because such MR is related to increased leaflet tethering by displaced attachments to the papillary muscles (PMs), it is incompletely treated by annular reduction. We therefore addressed the hypothesis that such MR can be reduced by cutting a limited number of critically positioned chordae to the leaflet base that most restrict closure but are not required to prevent prolapse. This was tested in 8 mitral valves: a porcine in vitro pilot with PM displacement and 7 sheep with acute inferobasal infarcts studied in vivo with three-dimensional (3D) echo to quantify MR in relation to 3D valve geometry. METHODS AND RESULTS: In all 8 valves, PM displacement restricted leaflet closure, with anterior leaflet angulation at the basal chord insertion, and mild-to-moderate MR. Cutting the 2 central basal chordae reversed this without prolapse. In vivo, MR increased from 0.8+/-0.2 to 7.1+/-0.5 mL/beat after infarction and then decreased to 0.9+/-0.1 mL/beat with chordal cutting (P<0.0001); this paralleled changes in the 3D leaflet area required to cover the orifice as dictated by chordal tethering (r(2)=0.76). CONCLUSIONS: Cutting a minimum number of basal chordae can improve coaptation and reduce ischemic MR. Such an approach also suggests the potential for future minimally invasive implementation.

Animals↗
PubMed2001

Assault by burning--a reappraisal.

Assault by burning is a serious form of trauma that often results in higher incidence of inhalation injury, longer intensive care unit (ICU) and hospital stay, and higher mortality rate than is observed in the general burn population. We evaluated the epidemiology and outcome of assault burn victims treated in a tertiary burn center over a 6-year period. Among the 1063 acute burn patients who had been admitted to the Burns Unit between March 1993 and February 1999, 28 (2.6%) had assault burn injuries either by scald, chemical or fire. The mean extent of burn was 21.9%+/-20.8% (range 2-90%) total body surface area and the mean length of hospital stay was 65.2+/-107.3 days (range 1-565). Nineteen out of 25 patients (67.9%) underwent 76 operations. Nine patients had inhalation injuries requiring intubation and ICU admission. Three patients died in the series, which yielded a mortality rate of 10.7%. Compared to the general burn population, the assault burn group had significantly larger burn size (P<0.001), higher incidence of inhalation injury (P<0.001), longer ICU and hospital stay (P<0.001), and higher mortality rate (P<0.005). When these 28 victims were grouped according to the type of assault burn injury into a fire group, chemical group and scald group, all the 9 ICU admission and the 3 mortalities belonged to the fire group. Assault by fire resulted in larger burn size (P=0.03), more inhalation injury (P<0.001) and longer ICU stay (P=0.02). Although the fire group had a longer hospital stay and higher mortality rate, this was statistically insignificant.

Adolescent↗
PubMed2001

Relationship between the size of neopharynx after laryngectomy and long-term swallowing function: an assessment by scintigraphy.

OBJECTIVES: To study the relationship between the size of neopharynx after total laryngectomy and long-term swallowing function by means of scintigraphy. STUDY DESIGN: The width of pharyngeal remnant was measured during surgery in 11 patients. Their swallowing function was assessed by scintigraphy 8 to 10 years after surgery. METHODS: The width of pharyngeal remnant at its narrowest point in both relaxed and stretched state was measured during surgery. Postoperative scintigraphy data on swallowing were obtained and computed along 3 lines, (1) transit time through neopharynx, (2) percentage of bolus transferred, and (3) swallowing efficiency. The relationship between the 2 sets of data was analyzed by linear regression analysis. RESULTS: (1) No statistically significant relationship was found between the size of neopharynx and swallowing function. (2) All patients are clinically asymptomatic. CONCLUSIONS: The swallowing function is not affected by the size of the neopharynx in 11 patients with pharyngeal remnant width ranging from 3 to 8 cm (stretched).

Aged↗
PubMed2001

Expectant treatment of ectopic pregnancies: clinical and sonographic predictors.

OBJECTIVE: We identified the potential clinical and sonographic predictors of the spontaneous resolution of ectopic pregnancies. SUBJECTS AND METHODS: We performed a prospective study of 78 consecutive patients with a transvaginal sonographic diagnosis of ectopic pregnancy who had either two consecutive quantitative measurements of their beta subunit of human chorionic gonadotropin (beta-hCG) more than 24 hrs apart or an embryo with a heart beat. We evaluated the patient's age, time from the last menstrual period, beta-hCG level, size of ectopic pregnancy, presence of a gestational sac or embryonic elements, vascularity on color Doppler sonography, peak systolic velocity, and resistive index of ectopic pregnancy at the time of presentation as potential independent predictors of the final outcome. Logistic regression was performed to identify the independent predictors. RESULTS: Forty-six patients had declining beta-hCG levels, and 32 ectopic pregnancies showed an embryo with a heart beat or had steady or rising beta-hCG levels. Univariate analysis indicated that a longer time from the last menstrual period (older ectopic pregnancies), lower beta-hCG levels, and the absence of gestational sac are statistically more significantly seen in ectopic pregnancies with declining beta-hCG levels (p < 0.05). Resistive index of ectopic pregnancy reached borderline significance (p = 0.05). In a multiple logistic model, the same variables were independent predictors of outcome (p < 0.05). Resistive index was also a predictor (p = 0.09). CONCLUSION: Longer times from the last menstrual period, lower beta-hCG levels, absence of gestational sacs, and higher resistive indexes of ectopic pregnancy at the time of presentation appear to be independent predictors of the spontaneous resolution of ectopic pregnancy.

Adult↗
PubMed2000

Transcription factor dosage affects changes in higher order chromatin structure associated with activation of a heterochromatic gene.

The mechanisms of transcriptional activation in heterochromatin were investigated by using FISH to directly visualize changes in chromatin organization during activation of a heterochromatic lambda5 transgene. A DNase I hypersensitive site was shown to relocate the transgene to the outside of the pericentromeric heterochromatin complex in the absence of transcription. Activation of transcription, which is dependent on the transcription factor EBF, occurs in a stochastic manner that resembles telomeric silencing in yeast, with the transcribed gene remaining closely associated with the heterochromatin complex. Reducing the dosage of EBF results in a reduced frequency of localization of the transgene to the outside of the heterochromatin complex and lower levels of transcription. These data provide evidence that transcription factors can initiate changes in higher order chromatin structure during the earliest stages of gene activation.

Animals↗
PubMed2000

Transmitral Doppler: a new transthoracic contrast method for patent foramen ovale detection and quantification.

OBJECTIVES: This study compared a new transthoracic echocardiographic (TTE) method for detection of right to left bubble passage, transmitral Doppler (TMD), against two-dimensional (2D) TTE contrast study and the gold standard, of transesophageal echocardiography (TEE), and assessed its utility in quantitative assessment of patent foramen ovales (PFO). BACKGROUND: Current TTE methods are relatively insensitive in PFO detection and do not allow quantitative assessment of right to left shunt. METHODS: In 44 patients (59 years, range 34 to 76 years) saline contrast and color Doppler studies were performed in three conditions--TTE TMD, TTE 2D and TEE. Bubble transit on the TMD was measured semiquantitatively by a visual bubble score and objectively by integrating the acoustic power within the mitral velocity envelope. RESULTS: By TEE it was determined that 17 patients (39%) had PFOs; 16 had right to left contrast passage, and only 1 had left to right flow by color Doppler. Against TEE contrast study, the sensitivity of TMD and 2D contrast studies were 100% and 75%, respectively, with specificity of 96% and 100%. Greater than 10 bubbles on a single beat of the resting contrast TMD identified patients with a maximum resting TEE PFO opening diameter >2 mm with 78% sensitivity and 100% specificity. There was a strong correlation (r2 = 0.72, p<0.01) between the TMD acoustic power and PFO opening diameter. CONCLUSIONS: Transmitral Doppler is a sensitive and specific method for TTE PFO detection that allows quantification of right to left bubble passage and may obviate the need for TEE in many patients after stroke.

Adult↗
PubMed2000

Conservation of heterochromatin protein 1 function.

Heterochromatin represents a cytologically visible state of heritable gene repression. In the yeast, Schizosaccharomyces pombe, the swi6 gene encodes a heterochromatin protein 1 (HP1)-like chromodomain protein that localizes to heterochromatin domains, including the centromeres, telomeres, and the donor mating-type loci, and is involved in silencing at these loci. We identify here the functional domains of swi6p and demonstrate that the chromodomain from a mammalian HP1-like protein, M31, can functionally replace that of swi6p, showing that chromodomain function is conserved from yeasts to humans. Site-directed mutagenesis, based on a modeled three-dimensional structure of the swi6p chromodomain, shows that the hydrophobic amino acids which lie in the core of the structure are critical for biological function. Gel filtration, gel overlay experiments, and mass spectroscopy show that HP1 proteins can self-associate, and we suggest that it is as oligomers that HP1 proteins are incorporated into heterochromatin complexes that silence gene activity.

Amino Acid Sequence↗
PubMed1998

Transesophageal echocardiography for ascending aortic dissection: is it enough for surgical intervention?

BACKGROUND: Acute ascending aortic dissection is a surgical emergency that requires expeditious diagnosis and prompt surgical intervention. In many centers, transesophageal echocardiography (TEE) is the test of choice on which surgical decisions are based. Echocardiographic false-positive diagnoses are rare but can occur with potentially severe consequences. CASE REPORT: Two clinical cases where ascending aortic dissections were falsely diagnosed by TEE are presented. DISCUSSION: Recent literature comparing the diagnostic accuracy of TEE and other imaging techniques are reviewed. Anatomical limitations of TEE and potential causes of false-positive results are discussed. Multiplane probe reduces, but does not eliminate, the occurrence of false-positive findings. To improve diagnostic specificity without undue delays in the course of clinical decision making, we recommend dividing positive TEE findings into "definite" and "probable" categories. Such subclassification is helpful in identifying cases where additional confirmatory tests are desirable in situations of uncertain diagnosis.

Adult↗
PubMed1996

Correlation of exons with functional domains and folding regions in a cellulase from Agaricus bisporus.

The cellulase gene cel3 has been isolated from Agaricus bisporus and sequenced. The 5'-end of the cel3 transcript was determined by primer extension and S1 nuclease protection. Putative regulatory elements have been identified in the cel3 promoter and 3'-untranslated regions. The cel3 coding region is interrupted by six short introns, two of which separate the coding regions for the three modules in the CEL3 protein: cellulose-binding domain, linker region, and catalytic domain. Three of the remaining four introns are positioned in regions coding for loops between structural moieties. Intron positions are conserved between cel3 and other related cellulases.

Agaricus↗
PubMed1995

Sequence of the met-10+ locus of Neurospora crassa: homology to a sequence of unknown function in Saccharomyces cerevisiae chromosome 8.

We have determined the sequence of the Neurospora crassa met-10+ gene and its flanking regions, and have isolated and analyzed cDNA clones for this region. We have identified two closely linked genes transcribed in the same orientation. The met-10+ gene is the downstream gene; an open reading frame (ORF) derived from five exons encodes a 475-amino-acid protein. The deduced protein lacks similarity to other characterized proteins. However, it exhibits a strong similarity to the product of an ORF of unknown function on Saccharomyces cerevisiae chromosome 8. This sequence similarity suggests functional equivalence and should facilitate identification of the function of met-10+ using gene disruptions in S. cerevisiae.

Amino Acid Sequence↗