UBC-Nepal Expedition: Haemoconcentration underlies the reductions in cerebralblood flow observed during acclimatization to high-altitude

At high‐altitude, increases in haematocrit (Hct) are achieved through altitude‐induced diuresis and erythropoiesis, both of which result in increased arterial oxygen content (CaO2). Given the impact alterations in Hct have on CaO2, haemoconcentration has been hypothesized to partly mediate the attenuation of the initial elevation in cerebral blood flow (CBF) at high‐altitude. To test this hypothesis, healthy males (n = 13) ascended to 5050 m over nine days without the aid of prophylactic acclimatization medications. Following one‐week of acclimatization at 5050 m, participants were haemodiluted by rapid saline infusion (2.10 ± 0.28 L) to return Hct towards pre‐acclimatized levels. Arterial blood gases, Hct, global CBF (duplex ultrasound), and haemodynamic variables were measured following initial arrival to 5050 m, and after one‐week of acclimatization at high‐altitude, prior to and following the haemodilution protocol. Following one‐week at 5050 m, Hct increased from 42.5 ± 2.5 to 49.6 ± 2.5% (P < 0.001), and was subsequently reduced to 45.6 ± 2.3% (P < 0.001) following haemodilution. Global CBF decreased from 844 ± 160 to 619 ± 136 ml mi−1 n (P = 0.033) following one‐week of acclimatization and increased to 714 ± 204 ml mi−1n (P = 0.045) following haemodilution. Despite the significant changes in Hct, and thus CaO2, cerebral oxygen delivery was unchanged at all time points. Furthermore, these observations occurred in the absence of any changes in mean arterial blood pressure, cardiac output, arterial blood pH, or oxygen saturation pre‐ and post‐haemodilution. These data highlight the influence of Hct in the regulation of CBF and are the first to demonstrate experimentally that haemoconcentration contributes to the reduction in CBF during acclimatization to altitude

Resting-State Brain Connectivity After Surgical and Behavioral Weight Loss

Objective: Changes in food-cue neural reactivity associated with behavioral and surgical weight loss interventions have been reported. Resting functional connectivity represents tonic neural activity that may contribute to weight loss success. This study explores whether intervention type is associated with differences in functional connectivity after weight loss. Methods: Fifteen participants with obesity were recruited prior to adjustable gastric banding surgery. Thirteen demographically matched participants with obesity were selected from a separate behavioral diet intervention. Resting-state functional magnetic resonance imaging was collected 3 months after surgery/ behavioral intervention. ANOVA was used to examine post-weight loss differences between the two groups in connectivity to seed regions previously identified as showing differential cue-reactivity after weight loss. Results: Following weight loss, behavioral dieters exhibited increased connectivity between left precuneus/ superior parietal lobule (SPL) and bilateral insula pre- to postmeal and bariatric patients exhibited decreased connectivity between these regions pre- to postmeal (Pcorrecte