Biomedical subjects

Christopher M Ryan

Publications and source records attributed to Christopher M Ryan.

21 records · Page 2Linked to original sources

PubMed2002

Effects of six anti-hypertensive medications on cognitive performance.

OBJECTIVE: To describe and compare the effects of six different antihypertensive medications on cognitive performance. DESIGN: Prospective, randomized, and double-blind with treatment cross-over. SETTING: University hypertension clinic and neuropsychology laboratory. PARTICIPANTS: Ninety-eight Caucasian men between 25 and 55 years of age with mild-to-moderate essential hypertension (88 of whom completed the study), and 32 normotensive men with similar socio-demographic characteristics. INTERVENTIONS: Six-week treatment periods with atenolol, metoprolol, hydrochlorothiazide, methyldopa, enalapril and verapamil, and 2-week placebo baseline and wash-out periods. MAIN OUTCOME MEASURES: In-depth neuropsychological assessments and several mood questionnaires were completed during placebo (baseline) periods and active treatment periods. Practice effects due to repeated neuropsychological testing were estimated from data collected concurrently in the normotensive participants. RESULTS: The antihypertensive treatments lowered blood pressure comparably and did not affect mood or anxiety. Small treatment effects were noted in four of seven domains of cognitive performance. Irrespective of medication type, treatment reduced the simple motor speed (P < 0.001), and slowed completion of two tests measuring perceptuo-motor speed and mental flexibility (P </= 0.05). Manual dexterity declined somewhat with metoprolol and methyldopa (P = 0.01). In contrast, all antihypertensive agents favorably affected performance on several tests that require working memory (P < 0.01). Performance on other tests assessing grip strength, learning and memory, attention and executive function was not affected. CONCLUSION: Short-term treatment with standard antihypertensive medications was associated with some small decrements in psychomotor performance and small improvements in working memory, without notable drug-class differences. Long-term effects await further study.

Adult↗

PubMed2002

Experienced, recreational scuba divers in Australia continue to dive despite medical contraindications.

OBJECTIVE: In Australia, a medical examination is required before undertaking a scuba diving course in order to screen for contraindications to diving. No further medical screening is required, and yet divers may develop diseases during their diving careers. This study aimed to survey experienced recreational scuba divers to determine the prevalence of diseases contraindicated in diving. METHODS: A cross-sectional, postal survey was taken of divers belonging to scuba diving clubs across Australia. RESULTS: Three hundred forty-six divers returned completed questionnaires. Two hundred fifty-four (73.4%) were male, and 258 (74.6%) were aged 31 to 60 years. The mean years of diving equaled 10.6 +/- 9.18 years, and the mean number of dives undertaken was 414 +/- 740 dives. One hundred sixty-two (46.8%) divers were overweight, 45 (13.0%) divers required regular medication, and 39 (11.3%) divers smoked. Thirty-six (10.4%) divers reported a past or present history of asthma, and the same number reported hypertension or coronary heart disease. Eighty-six (24.9%) divers reported past or present psychological symptoms. Forty-two (12.1%) divers reported hearing difficulties, and 81 (23.4%) divers reported past or present tinnitus. Two divers had a past history of epilepsy, 2 had a history of pneumothorax, and I was diabetic. CONCLUSIONS: Experienced, recreational scuba divers continue to dive despite medical contraindications. This raises the questions: Did the divers fail to disclose these conditions at the initial examination, or did these conditions develop subsequently? Is the risk associated with these conditions clinically significant, and should screening examinations be undertaken at regular intervals? The high prevalence of hearing difficulties and tinnitus may be the result of aural barotrauma and requires further research.

Adult↗

PubMed2002

Detection of symptoms by adolescents and young adults with type 1 diabetes during experimental induction of mild hypoglycemia: role of hormonal and psychological variables.

OBJECTIVE: To identify hormonal, psychological, and demographic predictors of symptom detection and accuracy of blood glucose estimation during mild hypoglycemia in adolescents and young adults with type 1 diabetes. RESEARCH DESIGN AND METHODS: During an insulin-glucose clamp study, 53 adolescents and 19 young adults estimated blood glucose levels and reported symptoms at euglycemia and after 30 min of mild hypoglycemia (3.3 mmol/l). Epinephrine and pancreatic polypeptide were measured, and both change in anxiety level during hypoglycemia and baseline level of anxiety were measured with the Spielberger Anxiety Inventory. Elevated levels of anxiety during euglycemia were used as an indicator of the psychological trait "negative affectivity." Previous studies have suggested that individuals with higher negative affectivity are more internally focused and, therefore, more likely to report somatic and visceral changes. RESULTS: During mild hypoglycemia, 42% of the sample subjects reported an increase in autonomic symptoms; 29% reported an increase in neuroglycopenic symptoms, and 28% estimated blood glucose levels accurately (within 10% of actual). Hormonal excursions did not predict any outcome, but higher anxiety levels during the euglycemic baseline were associated with better detection of hypoglycemic symptoms and more accurate estimation of blood glucose values after controlling for change in anxiety level during hypoglycemia. CONCLUSIONS: Psychological factors such as elevated anxiety levels ("negative affectivity") can influence blood glucose estimation and symptom detection in adolescents and young adults and may explain why some individuals are more adept than others at reducing their risk of severe hypoglycemia after participation in a formal blood glucose awareness training program.

Adolescent↗