The effect of propofol on haemodynamics: cardiac output, venous return, mean systemic filling pressure, and vascular resistances

BACKGROUND

Although arterial hypotension occurs frequently with propofol use in humans, its effects on intravascular volume and vascular capacitance are uncertain. We hypothesized that propofol decreases vascular capacitance and therefore decreases stressed volume.

METHODS

Cardiac output (CO) was measured using Modelflow(®) in 17 adult subjects after upper abdominal surgery. Mean systemic filling pressure (MSFP) and vascular resistances were calculated using venous return curves constructed by measuring steady-state arterial and venous pressures and CO during inspiratory hold manoeuvres at increasing plateau pressures. Measurements were performed at three incremental levels of targeted blood propofol concentrations.

RESULTS

Mean blood propofol concentrations for the three targeted levels were 3.0, 4.5, and 6.5 µg ml(-1). Mean arterial pressure, central venous pressure, MSFP, venous return pressure, Rv, systemic arterial resistance, and resistance of the systemic circulation decreased, stroke volume variation increased, and CO was not significantly different as propofol concentration increased.

CONCLUSIONS

An increase in propofol concentration within the therapeutic range causes a decrease in vascular stressed volume without a change in CO. The absence of an effect of propofol on CO can be explained by the balance between the decrease in effective, or stressed, volume (as determined by MSFP), the decrease in resistance for venous return, and slightly improved heart function.

CLINICAL TRIAL REGISTRATION

Netherlands Trial Register: NTR2486.

A single amino acid substitution in the transmembrane envelope glycoprotein of feline immunodeficiency virus alters cellular tropism

The cellular tropism of the feline immunodeficiency virus (FIV) is affected by changes in variable region 3 (V3) of the surface (SU) envelope glycoprotein (Verschoor, E. J., et al., J. Virol. 69:4752-4757, 1995). By using high-dose DNA transfection, an FIV molecular clone with a non-CRFK-tropic V3 acquired the ability to replicate in CRFK cells. A single point mutation from a methionine to a threonine in the ectodomain of its transmembrane (TM) envelope glycoprotein was responsible for this change in viral tropism. This substitution is located in the putative SU interactive region, between the fusion peptide and the membrane-spanning region. Our results show that this region of the TM envelope glycoprotein constitutes an additional determinant for cell tropism.

Evaluation of subunit vaccines against feline immunodeficiency virus infection

Subunit vaccines prepared against feline immunodeficiency virus (FIV) infection were evaluated in two trials. First, cats were immunized with bacterial expression products of an envelope fragment that contained the V3 neutralization domain of the FIV surface protein fused to either galactokinase (K-SU3) or glutathione-S-transferase (G-SU3). Quantitative and qualitative differences in the humoral immune response were observed with three adjuvants of which Quil A was the best in terms of total and virus neutralizing antibody. Notwithstanding the responses induced, 19 of 20 immunized cats did not resist challenge and became infected. To determine whether priming with a live viral vector would confer protection, cats were inoculated oronasally and subcutaneously with a feline herpesvirus (FHV) mutant expressing the FIV env gene; two booster immunizations followed using the K-SU3 product in either Quil A or a mineral oill Al(OH)3 adjuvant. FIV-specific antibody responses were only weak, and the vaccinates did not withstand challenge with a low dose of homologous virus.

A single mutation within the V3 envelope neutralization domain of feline immunodeficiency virus determines its tropism for CRFK cells

Feline immunodeficiency virus (FIV) isolates differ in the ability to replicate in Crandell feline kidney (CRFK) cells. The difference in tropism between two variants of the Dutch isolate FIV-UT113 was studied by using molecular clones which contained the envelope genes of the variants in a background of the FIV-14 Petaluma sequence. Virus produced from clone pPET-113Th replicated in thymocytes, whereas virus from pPET-113Cr propagated in both thymocytes and CRFK cells, thereby reflecting the phenotypes of the parental variants. Exchange of envelope gene fragments showed that a 464-bp surface protein (SU)-encoding fragment encompassing the third variable region (V3) determines CRFK cell tropism. Sequence analysis of the exchanged fragments demonstrated two amino acid changes that led to an increase of the overall charge of the V3 domain: a G-->R transition at position 397 and a E-->K change at position 407. Mutational analysis of these residues revealed that the E-->K shift was responsible for the change in tropism, while the G-->R mutation improved the replication kinetics in CRFK cells. Mapping of a tropism determinant for FIV to a region which is also a major neutralization domain is reminiscent of human immunodeficiency virus type 1, in which a similar colocation was found.

Vaccination against feline immunodeficiency virus using fixed infected cells

Crandell feline kidney cells and feline thymocytes, either feline immunodeficiency virus (FIV) infected or uninfected, were fixed with paraformaldehyde and used to vaccinate cats. The cells were mixed with a 30:70 water/mineral oil emulsion containing 250 micrograms ml-1 N-acetyl-D-glucosaminyl-beta-(1-4)-N-acetyl-muramyl-L-alanyl-D-isoglutam ine. Eighteen specific pathogen-free cats were vaccinated three times with 3-week intervals and challenged 21 days after the final boost with a low dose of the homologous FIV-UT113 strain. Eight out of ten cats that had received FIV-infected cell vaccines developed significant anti-FIV antibody titres to the envelope and core antigens. Neutralizing antibodies were detectable at the moment of challenge in the sera of these animals. Within 5 weeks after challenge 15 out of 18 cats became viraemic. Three animals, two that had been vaccinated with FIV-infected thymocytes and did not develop antibody, and one that had received an uninfected thymocyte preparation, remained uninfected for 6 months. Upon rechallenge of the three animals, two again resisted infection; these cats had been immunized with the infected and the uninfected thymocyte preparations, respectively.

Expression of feline immunodeficiency virus gag and env precursor proteins in Spodoptera frugiperda cells and their use in immunodiagnosis

The gag and env genes of the feline immunodeficiency virus strain UT113 were cloned into a baculovirus transfer vector. The recombinant plasmids were used to create recombinant baculoviruses that expressed either the gag or the env precursor protein in insect cells (Sf9 cells). Leader sequence cleavage occurred in Sf9 cells expressing the envelope precursor, but further processing was not observed. Crude lysates of insect cells infected with the wild-type baculovirus or with the recombinant viruses were used to develop an enzyme-linked immunosorbent assay for the detection of feline immunodeficiency virus-specific antibodies in cat sera. The assay showed a higher sensitivity and specificity than immunofluorescence and Western blotting (immunoblotting).