Microvascular responses to hemodilution with Hb vesicles as red blood cell substitutes: influence of O 2 affinity

• Published in: American journal of physiology. Heart and circulatory physiology Vol. 276; no. 2; pp. H553 - H562
• Main Authors: Sakai, Hiromi, Tsai, Amy G, Rohlfs, Ronald J, Hara, Hiroyuki, Takeoka, Shinji, Tsuchida, Eishun, Intaglietta, Marcos
• Format: Journal Article
• Language: English
• Published: United States 01.02.1999
• Subjects: oxygen carrier; autoregulation; microcirculation; liposome; oxygen dissociation curve
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.1999.276.2.H553

Phospholipid vesicles encapsulating purified hemoglobin (HbV) were developed to provide O -carrying capacity to plasma expanders. Microvascular perfusion was determined for HbV with different O affinity (P = 9, 16, and 30 mmHg) prepared by coencapsulating pyridoxal 5'-phosphate (PLP) at the molar ratios of [PLP]/[Hb] = 0, 0.5, and 3, respectively (cf. hamster blood, P : 28 mmHg), and suspended in 8 g/dl human serum albumin (HSA). Eighty percent of the red blood cell (RBC) mass of conscious Syrian golden hamsters fitted with dorsal skinfold windows was substituted with either of the HbV-HSA suspensions, washed hamster RBC suspended in HSA (RBC-HSA), and HSA alone. All three HbV-HSA groups and RBC-HSA groups showed stable blood pressure and heart rate, which could not be sustained with HSA alone. Only the HbV (P = 9)-HSA group showed an increase in arterial O tension (89.8 ± 14.7 mmHg, baseline 58.4 ± 4.0 mmHg) because of hyperventilation, and microvascular perfusion was decreased, indicating that facilitated O unloading of HbV by decreasing the O affinity (increasing P ) with PLP as an allosteric effector is important. Microvascular perfusion and microvascular and interstitial O tensions in the HbV (P = 16 and 30)-HSA groups were significantly higher than those in the HSA group. The O release rate from the HbV was 18-32 s vs. 4.4 s for RBC. Functional capillary density was improved from 17 to 41% on average by decreasing P from 30 to 16 mmHg, which appears to be an optimal value for the P in this system.