Breath hydrogen reflects canine intestinal ischemia

The relationship between breath hydrogen excretion and intestinal ischemia was investigated in nine mechanically ventilated dogs under pentobarbital anesthesia. An ileal segment was isolated in situ, ligated at each end, and insufflated with hydrogen. Expired air was collected at intervals. Blood volume was reduced 30% by three successive equivalent hemorrhages 10 min apart. Local bowel ischemia was produced by clamping the blood supply to the isolated segment for 10 min. Graded hemorrhage produced step-wise reductions in breath hydrogen concentration, to 77 +/- 13, 66 +/- 15, and 35 +/- 8% (mean +/- S.E.) of baseline after the first, second, and third hemorrhages, respectively. These reductions correlated highly (r = 0.84; P less than 0.01) with declines in mean aortic blood pressure. Occlusion of blood supply caused a significant (P less than 0.025) decrease in breath hydrogen concentration and excretion to 39 +/- 14% of baseline. Termination of occlusion was followed within 2 min by a 7-fold increase in breath H2 concentration above the original baseline, probably reflecting reactive hyperemia. Breath hydrogen measurements appear to reflect functional (hemorrhagic shock-induced) and mechanical (vascular occlusion induced) enteric ischemia in dogs.

Characteristics of control group participants who increased their physical activity in a cluster-randomized lifestyle intervention trial

BACKGROUND

Meaningful improvement in physical activity among control group participants in lifestyle intervention trials is not an uncommon finding, and may be partly explained by participant characteristics. This study investigated which baseline demographic, health and behavioural characteristics were predictive of successful improvement in physical activity in usual care group participants recruited into a telephone-delivered physical activity and diet intervention trial, and descriptively compared these characteristics with those that were predictive of improvement among intervention group participants.

METHODS

Data come from the Logan Healthy Living Program, a primary care-based, cluster-randomized controlled trial of a physical activity and diet intervention. Multivariable logistic regression models examined variables predictive of an improvement of at least 60 minutes per week of moderate-to-vigorous intensity physical activity among usual care (n = 166) and intervention group (n = 175) participants.

RESULTS

Baseline variables predictive of a meaningful change in physical activity were different for the usual care and intervention groups. Being retired and completing secondary school (but no further education) were predictive of physical activity improvement for usual care group participants, whereas only baseline level of physical activity was predictive of improvement for intervention group participants. Higher body mass index and being unmarried may also be predictors of physical activity improvement for usual care participants.

CONCLUSION

This is the first study to examine differences in predictors of physical activity improvement between intervention group and control group participants enrolled in a physical activity intervention trial. While further empirical research is necessary to confirm findings, results suggest that participants with certain socio-demographic characteristics may respond favourably to minimal intensity interventions akin to the treatment delivered to participants in a usual care group. In future physical activity intervention trials, it may be possible to screen participants for baseline characteristics in order to target minimal-intensity interventions to those most likely to benefit. (Australian Clinical Trials Registry, http://www.anzctr.org.au/default.aspx, ACTRN012607000195459).

The impact of behavioural screening on intervention outcomes in a randomised, controlled multiple behaviour intervention trial

BACKGROUND

With an increasing research focus on multiple health behaviour change interventions, a methodological issue requiring further investigation is whether or not to employ pre-trial behavioural screening to exclude participants who are achieving a pre-specified level of one or more behaviours. Behavioural screening can be used to direct limited resources to participants most in need of a behaviour change intervention; but may reduce the representativeness of the sample and limit comparability with trials that do not employ pre-trial behavioural screening. Furthermore, the impact of this type of screening on intervention participation and intervention effects is unknown.

METHODS

Data for this study come from the Logan Healthy Living Program, a randomised, controlled telephone counselling lifestyle intervention trial which did not employ behavioural screening prior to randomisation. Screening for physical activity, diet or the combination was simulated using baseline trial data. To examine the impact of behavioural screening on intervention participation (in terms of participant characteristics, intervention dose received and retention), characteristics of participants included an excluded under the various screening scenarios were compared. To examine the impact of behavioural screening on intervention effects, results from the main trial analysis were compared with results obtained from the same analyses performed separately for each of the screened groups.

RESULTS

Simulated pre-trial behavioural screening impacted minimally on intervention dose received and trial retention rate. Beyond the anticipated effect of reducing baseline levels of the behaviours being screened for, behavioural screening affected baseline levels of behaviours not targeted by screening, and participants' demographic and health-related characteristics. Behavioural screening impacted on intervention effects in ways that were anticipated and positive, but also unexpected and detrimental. Physical activity screening (alone or in combination with diet) resulted in improved intervention effects for physical activity, while fruit and vegetable screening had no impact on intervention effects for these outcomes. All three types of screening impacted detrimentally on intervention effects for behaviours not being targeted by screening.

CONCLUSIONS

Behavioural screening may have desirable and undesirable consequences in the context of multiple behaviour intervention trials, and thus its potential merits and pitfalls should be carefully considered.

Effects of gastric inhibitory polypeptide on leucine- and arginine-stimulated insulin release

Insulin release stimulated by single amino acids, with and without gastric inhibitory polypeptide (GIP), was studied in vivo in anesthetized rats and in vitro in collagenase-digested isolated rat pancreatic islets. Insulin release in vivo during a 15-min intravenous infusion of leucine (0.97 mM) or arginine (0.97 mM) with GIP (17 ng/min) was greater than with infusion of either amino acid or GIP alone. Serum immunoreactive GIP was in the physiological range, and serum glucose showed no significant change in these studies. In contrast, insulin release did not occur with valine infused alone or with GIP. Insulin release in vitro by isolated islets was greater during a 45-min incubation period with leucine (5-20 mM) or arginine (20 mM) plus GIP (10 ng to 10 micrograms/ml) than with either amino acid alone. This effect that occurred in the absence of glucose could not be demonstrated with low concentrations of leucine (1.5 mM) or with 20 mM valine. In vitro insulin release during paired perfusion studies of isolated islets was greater with leucine (20 mM) plus GIP (50 ng/min) than with leucine alone, and augmentation of insulin release by GIP was demonstrable in both the early and late phases of insulin release. From these results it is concluded that insulin release is greater, both in vivo and in vitro, after leucine or arginine plus GIP than with either amino acid or GIP alone. This effect appears to be specific for the insulinotropic amino acids tested, does not appear to be glucose dependent, and can be demonstrated in both the early and late phases of insulin release.