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Biomedical subjects

David Hillman

Publications and source records attributed to David Hillman.

6 recordsLinked to original sources
PubMed2006

Metabolic risk factors for vascular disease in obstructive sleep apnea: a matched controlled study.

RATIONALE: Obstructive sleep apnea (OSA) is reported to have a metabolic profile predisposing to cardiovascular disease. However, previous case-control studies have not adequately controlled for confounders. OBJECTIVES: To determine whether OSA is associated with increased insulin resistance and related metabolic risk factors. METHODS: We performed a matched case-control study (n = 42) examining putative metabolic risks among men with OSA attending a sleep clinic (apnea-hypopnea index [AHI] > 15] compared with no OSA (AHI < 5). Participants were matched for age +/- 5 yr, body mass index +/- 10%, and current smoking status. They were free of diabetes, clinically demonstrable cardiovascular disease, marked hypertension, and dyslipidemia. MEASUREMENTS AND MAIN RESULTS: Mean +/- SD AHI was higher in patients with OSA (40 +/- 27) than in control subjects (3 +/- 1.3, p = 0.02), and median (interquartile range) nocturnal oxygen saturation was lower (OSA, 83 [76-88]; control, 91 [90-93]%; p < 0.001). Patients with OSA had a higher median (interquartile range) homeostasis model assessment score for insulin resistance (OSA, 1.7 [0.8-4.1]; control, 1.0 [0.7-1.8] mU.mmol/L(2); p = 0.02), total cholesterol (OSA, 5.6 [4.8-6.2]; control, 4.8 [4.3-5.4] mmol/L; p = 0.049), and low-density-lipoprotein cholesterol (OSA, 3.8 [2.9-4.2]; control, 3.1 [2.6-3.6] mmol/L; p = 0.04). Patients with OSA had higher 24-h and nocturnal (12-h) urinary norepinephrine excretion and plasma leptin levels, and lower insulin-like growth factor (IGF)-1 levels (all, p < or = 0.02). Multiple linear regression, adjusting for central obesity, age, and alcohol consumption, confirmed an independent association between OSA and metabolic risks (all, p < 0.05), with a trend for IGF-1 (p = 0.053). CONCLUSIONS: In a sleep clinic population, men with OSA and no identifiable cardiovascular disease have increased insulin resistance and other metabolic changes that act to increase the risk of vascular disease, compared with age- and body mass index-matched attendees without OSA.

Body Mass Index↗
PubMed2003

Feasibility of high-intensity, interval-based respiratory muscle training in COPD.

BACKGROUND: Specific respiratory muscle training can improve respiratory muscle function in patients with COPD, but the magnitude of improvement appears dependent on the magnitude of the training load. High training loads are difficult to achieve using conventional, constant loading techniques, but may be possible using interval-based training techniques. METHODS: To assess the feasibility of high-intensity respiratory muscle training, nine subjects with moderate-to-severe COPD (FEV(1) 34 +/- 12% predicted [mean +/- SD]) completed 8 weeks of interval-based respiratory muscle training combined with a general exercise program. This involved three 20-min sessions per week, each session comprising seven 2-min bouts of breathing against a constant inspiratory threshold load, each bout separated by 1 min of unloaded recovery. Inspiratory load was progressively incremented. Respiratory muscle strength (maximum inspiratory pressure generated against an occluded airway [PImax]) and endurance (maximum pressure generated against a progressively increasing inspiratory threshold load [Pthmax]) were measured before and immediately after the 8-week training period. RESULTS: By the third training session (week 1), subjects breathed against a threshold that required generation of pressures equivalent to 68 +/- 5% of the pretraining PImax. By week 8, this had increased to 95 +/- 12% of the pretraining PImax. On completion of training, PImax had increased by 32 +/- 27% (p < 0.05), Pthmax had increased by 56 +/- 33% (p < 0.05), and Pthmax/PImax had increased by 20 +/- 20% (p < 0.05). CONCLUSIONS: This study has demonstrated that high-intensity, interval-based respiratory muscle training is feasible in patients with moderate-to-severe COPD, resulting in significant improvements in respiratory muscle strength and endurance when performed three times a week for 8 weeks.

Aged↗
PubMed2002

Respiratory function changes in a wilderness multisport endurance competition: a prospective case study.

OBJECTIVE: To document serially and in detail the changes in respiratory function during competition in a typical wilderness multisport endurance athlete. METHODS: Prospective observational case study over two years during a 105 km wilderness multisport endurance competition consisting of cross country skiing, cross country running, cycling, and whitewater canoeing. Nedocromil prophylaxis was used during the second year of the study only. FEV1, FVC, flow volume loops, and oxygen saturation were measured serially during the race. RESULTS: Baseline spirometry and histamine bronchial provocation tests were normal. SaO2% decreased to a minimum of 92%. Decreases in both FEV1 (up to 25%) and FVC (up to 22%) were observed at race finish in both years. Although FEV1/FVC ratios only decreased marginally, the pattern of change in maximum expiratory flow rates was most consistent with evolving airflow obstruction. The changes were not prevented by nedocromil. The subject did not develop symptomatic wheezing or abnormal breathlessness and finished the event without incident. CONCLUSIONS: Ultra endurance multisport competition may induce substantial changes in respiratory function. These appear to be attributable to evolving airflow obstruction.

Adult↗