Reasons for an increase in maximal O2 consumption (VO2max) following blood reinfusion remain unclear; thus the present investigation was undertaken to examine the arterial and femoral venous blood gases during submaximal and maximal exercise. Four untrained males (22-25 yr) performed modified Balke work capacity tests under control conditions (Hct = 42.4 +/- 0.8%; Hb = 14.7 +/- 0.5 g X 100 ml-1) and following autologous blood reinfusion (Hct = 46.2 +/- 1.3%; Hb = 16.4 +/- 0.9 g X 100 ml-1). VO2 was determined by open-circuit spirometry and cardiac output by the N2O method; radial arterial and deep femoral venous blood were sampled at each work load throughout the incremental work tests. Following blood reinfusion, subjects' VO2max increased (P less than 0.05) from 4.0 (in control) to 4.5 1 X min-1. Throughout submaximal exercise arterial PO2 remained relatively constant (between 80.1 +/- 4.4 and 89.1 +/- 5.0 Torr) and cardiac output unchanged, comparing the two experimental conditions. Femoral venous PO2 values were almost identical throughout the work capacity tests, declining at exhaustion to 15.7 +/- 1.5 Torr in control and to 13.8 +/- 3.3 Torr postreinfusion. It appeared that the subjects' increase in VO2max postreinfusion was due to an increased O2 supplied to the tissue [i.e., cardiac output (Q) X arterial O2 content (CaO2)] by the central circulation. This resulted from a small (10%) increase in Q and a constant elevation in CaO2 of 1.7-2.2 ml X 100 ml-1, since virtually no changes were observed in the femoral venous blood postreinfusion and the acid-base status and temperature, important determinant of O2 dissociation, were (almost) identical, comparing the two experimental conditions.
In healthy human sojourners to 3,100 m we studied exercise-induced shifts in HbO2 dissociation: their regulation in femoral venous blood and their net effect on estimated capillary PO2 (PC-O2) in working skeletal muscle. Prolonged heavy work effected an increase of 10.3 plus or minus 0.9 mmHg in in vivo P50 (7.30 PH-v, 41 degrees C-v, and 45 Pv-CO2); due entirely to the additive effects of increased venous temperature and [H+]. The rightward curve shift during work at 3,000 m, compared to that at 250 m, produced a similar increase in in vivo P50 but a reduced net effect on PC-O2, because Cv-02 at 3,100 m was reduced similar to 2 ml/100 ml to the lower converging portions of the curve. The lower Cv-O2 (and Pv-O2) at 3,100 M was attributable to a small decrease in total systemic blood flow. The net effect of the rightward curve shift during exercise on mean to end-capillary PO2 was positive in most cases (+1 to +8 mmHg PCO2). However, it was shown that the levels of mean to end-capillary PO2 (28-13 mmHg), which would have been obtained during exercise in the absence of any rightward curve shift, were more than adequate to sustain a steady state of aerobic energy production in working skeletal muscle. These data do not support the concept of a significant contribution to oxygen delivery to working skeletal muscle from in vivo shifts in HbO2 dissociation, during either acclimatization to high altitude or during prolonged muscular work.
Aim/BackgroundThe aim of this study was to describe the clinical impact of management of coarctation of the aorta by transcatheter stent placement in the context of longer term management of systemic hypertension. In the long term, poor outlook associated with untreated coarctation of the aorta is likely to relate to uncontrolled systemic hypertension.Transcatheter stent placement to treat native and recurrent coarctation of the aorta is an established therapy in adolescents and adults. There remains confusion about longer term outcomes, particularly the relation between procedural success and improvement in blood pressure (BP) control. Improvement in lifelong systemic BP control after transcatheter stent placement remains unproved.Abstract P17 Figure 1The age distribution of patients undergoing transcatheter stent placement.Abstract P17 Figure 2The variation in underlying pathology of patients undergoing transcatheter stent placement.Results89 patients underwent transcatheter stent placement over a 14-year period (2001 to 2015) at the Yorkshire Heart Centre. The average age at the time of procedure was 29.3 years (range 6 to 59). Figure 1 shows the ages of the patients undergoing treatment divided into 3 age groups. Figure 2 demonstrates that native coarctations formed the majority of the cases seen, followed by recurrent coarctations, and it shows that only a minority were as part of complex congenital heart disease.We found there was a reduction in peak systolic gradient across the narrowed segment from mean of 27.7 to <5 mm Hg in 84 patients. Figure 3 shows the differences in peak systolic gradient before and after intervention. After stent placement, there was a significant improvement in systolic BP control at early and later follow-up (mean 156.2 mmHg before the procedure and 129.6 mmHg at 3.51-year follow-up, p < 0.0001), as shown in Figure 4.Abstract P17 Figure 3Box and whisker plots of the peak systolic gradient across the lesion in 84 patients before and after intervention.Abstract P17 Figure 4Box and whisker plots demonstrating the systolic blood pressure in 55 patients before and after intervention. ConclusionTranscatheter stent placement for the management of aortic coarctation is associated with a reduction in systolic BP that is maintained over the medium term. A significant minority of patients remain significantly hypertensive, and the best management strategy for this group of patients remains unclear.
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