A native of the Peruvian Andes (4,250 m) was studied before and after isovolemic hemodilution of the hematocrit from 62 to 42%. O2 transport was studied with newly developed catheters in the radial and pulmonary arteries. These catheters allowed continuous measurement of arteriovenous O2 content and intermittent cardiac output by thermodilution. During exercise tests, breath-by-breath gas exchange measurements also allowed cardiac output to be calculated by the O2-Fick technique. A complex series of interrelated physiological changes occurred in response to hemodilution. These included increased ventilation, increased arterial and mixed venous PO2, increased cardiac output (both heart rate and stroke volume), and improved ventilation-flow match. The general improvement in symptoms that followed hemodilution correlated well with increased anaerobic threshold and mixed venous PO2 during exercise.

Background Intracellular tenofovir diphosphate (TFV-DP) concentration measured in dried blood spots (DBS) is used to monitor cumulative adherence to pre-exposure prophylaxis (PrEP). We evaluated TFV-DP in DBS following daily oral PrEP (emtricitabine 200mg/tenofovir diphosphate 300mg) among pregnant and postpartum adolescent girls and young women (AGYW). Methods Directly observed PrEP was administered for 12 weeks in a pregnancy group (14-24 weeks gestation, n=20) and a postpartum group (6-12 weeks postpartum, n=20) of AGYW aged 16-24 years in sub-Saharan Africa. Weekly DBS TFV-DP was measured by validated liquid chromatography-tandem mass spectrometry assay. Week 12 TFV-DP distributions were compared between groups with the Wilcoxon test. Population pharmacokinetic models were fit to estimate steady-state concentrations and create benchmarks for adherence categories. Baseline correlates of TFV-DP were evaluated. Results Participant median age was 20 years (IQR:19,22). Of 3360 doses, 3352 (>99%) were directly observed. TFV-DP median half-life was ten days (IQR:7, 12) in pregnancy and 17 days (IQR:14, 21) postpartum, with steady-state achieved by five and eight weeks, respectively. Observed median steady-state TFV-DP was 965 fmol/punch (IQR:691, 1166) in pregnancy vs 1406 fmol/punch (IQR:1053, 1859) postpartum (p=0.006). Modelled median steady-state TFV-DP was 881 fmol/punch (IQR: 667,1105) in pregnancy vs 1438 fmol/punch (IQR: 1178,1919) postpartum. In pooled analysis, baseline creatinine clearance was associated with observed TFV-DP concentrations. Conclusion TFV-DP in African AGYW was approximately one-third lower in pregnancy than postpartum. Population-specific benchmarks provided by this study can be used to guide PrEP adherence support in pregnant/postpartum African women.

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