1. We studied cardiovascular variability, baroreflex and blood volume regulating hormones to determine the relative roles of autonomic regulation and hormones during blood donation.2. The sympathetic response was studied by measuring the R-R interval and systolic blood pressure variability using coarse graining spectral analysis in eight blood donors. Beat-by-beat R-R intervals and blood pressure were recorded for 20 min before and 5 min after a whole-blood donation of 480+/-10 ml (about 7 ml/kg of blood volume, over 4 min). Plasma catecholamines, vasopressin, atrial natriuretic peptide, endothelin, active renin, osmolality, Na+, K+, haemoglobin and haematocrit were measured just before and after blood withdrawal.3. Blood donation led to increases in the plasma catecholamines (adrenaline, 21+/-2 versus 35+/-3 pg/ml; noradrenaline, 229+/-26 versus 323+/-37 pg/ml; dopamine, 34+/-3 versus 66+/-9 pg/ml) and in systolic blood pressure (130+/-6 versus 140+/-5 mmHg). These changes were independent of ionic or slow endocrine mechanisms. Heart rate, cardiovascular variability and the spontaneous baroreflex sensitivity did not change despite the increase in blood pressure and catecholamines. Thus the peripheral vascular control was probably involved.4. We conclude that the absence of any change in heart rate usually observed during non-hypotensive hypovolaemic stress is probably due to the sympathetic activation being counterbalanced by the high supine vagal tone at the heart and not to the heterogeneous nature of the sympathetic neural response or to changes in sympathetic and parasympathetic activity without any change in autonomic balance.

Background and Objectives: An unusual serological pattern of HIV‐1 seroconversion in a blood donor is described. The seroconversion panel was used to investigate the sensitivity of existing screening assays. Materials and Methods: A volunteer blood donor who had given blood 79 times was diagnosed anti‐HIV‐1‐antibody‐positive. The heteroduplex mobility assay identified a subtype B HIV‐1 strain. The frozen plasmas from the last four blood donations had been kept at −30°C. They were thawed and aliquoted for subsequent testing. Results: The last two blood donations contained HIV‐1 RNA, 2,800 copies/ml (October 26) and 170 copies/ml (November 23). Weak anti‐p24 antibodies were detected by Western blot in the October 26 sample, and a clear p24 reactivity along with a faint gp 160 reactivity was oberved on November 23. HIV p24 antigen was undetectable in both samples. Out of 13 screening assays, only 6 gave positive results on the November sample and 7 negative results which were obtained by 1 competitive enzyme immunoassay (EIA) and 6 of the 9 sandwich EIAs. Conclusion: Most sandwich EIAs gave prolonged false‐negative results in the present case. p24 antigen testing was negative and would not have reduced the risk of HIV transmission.

Background and Objectives: An unusual serological pattern of HIV–1 seroconversion in a blood donor is described. The seroconversion panel was used to investigate the sensitivity of existing screening assays. Materials and Methods: A volunteer blood donor who had given blood 79 times was diagnosed anti–HIV–1–antibody–positive. The heteroduplex mobility assay identified a subtype B HIV–1 strain. The frozen plasmas from the last four blood donations had been kept at –30°C. They were thawed and aliquoted for subsequent testing. Results: The last two blood donations contained HIV–1 RNA, 2,800 copies/ml (October 26) and 170 copies/ml (November 23). Weak anti–p24 antibodies were detected by Western blot in the October 26 sample, and a clear p24 reactivity along with a faint gp160 reactivity was observed on November 23. HIV p24 antigen was undetectable in both samples. Out of 13 screening assays, only 6 gave positive results on the November sample and 7 negative results which were obtained by 1 competitive enzyme immunoassay (EIA) and 6 of the 9 sandwich EIAs. Conclusion: Most sandwich EIAs gave prolonged false–negative results in the present case. p24 antigen testing was negative and would not have reduced the risk of HIV transmission.

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