Biomedical subjects

J Lofthouse

Publications and source records attributed to J Lofthouse.

10 recordsLinked to original sources

PubMed2000

Nurses' perceptions of the nature and frequency of aggression in general ward settings and high dependency areas.

Studies on aggression in healthcare settings have reported increased frequency of this behaviour in both psychiatric and accident and emergency areas; however, to date, very few studies have addressed this issue in general ward settings in Australia. This descriptive study was conducted to determine nurses' perceptions of the nature and frequency of aggressive behaviours in general wards and high dependency areas and thereby address the gap in the literature. Two hundred and nine nurses in one Australian hospital completed a 23-item questionnaire on aggression in the workplace. The findings revealed that the majority (89.5%) of nurses defined aggressive behaviour as including verbal aggression, physical aggression and intimidation. Ninety-five per cent of respondents had encountered at least several episodes of verbal aggression within the last 12 months. Patients were found to be the main perpetrators of aggressive acts, followed by relatives. After experiencing either verbal or physical aggression nurses most frequently reported feeling angry or emotionally hurt. These findings confirm that acts of aggression are experienced frequently in the general medical and surgical ward areas of the study hospital. Consequently, there is a need to provide staff with education and support in order to deal with this issue and minimize the impact of increasing levels of aggression in the workplace.

Adaptation, Psychological↗

PubMed2000

Effect of intraperitoneal pressures on tissue water of the abdominal muscle.

A major factor that affects solute and water transport through tissue is the state of tissue hydration. The amount of interstitial water directly affects the transport coefficients for both diffusion and convection. To investigate the effect of simultaneous exposure of tissue to hydrostatic and osmotic pressures on the state of tissue hydration and the pattern of distribution of tissue water, we dialyzed rats with isotonic (290 mosmol/kg) or hypertonic (510 mosmol/kg) solution at intraperitoneal pressures (P(ip)) between 0 and 6 mmHg, and we infused isotopic markers intravenously and determined their equilibrium distribution volumes (V(D)) in the anterior abdominal muscle (AAM) by quantitative autoradiography. Total tissue water volume (theta(TW)) was determined from dry-to-wet weight ratios. theta(urea), the V(D) of [(14)C]urea, equals the sum of the extracellular water volume (theta(EC), V(D) of [(14)C]mannitol) and intracellular water volume (theta(IC) = theta(urea) - theta(EC)). If theta(if) = interstitial water volume and theta(IV) = vascular water volume (V(D) of (131)I-labeled IgG), then theta(EC) = theta(if) + theta(IV). AAM hydrostatic pressure profiles were measured by a micropipette/servo-null system and demonstrated that elevation of P(ip) above 3 mmHg significantly (P < 0.05) increases mean tissue pressure (P(T)) to the same level regardless of intraperitoneal osmolality. The increase in P(T) resulted in a nonlinear tissue expansion primarily in the interstitium regardless of osmolality. From 0 to 6 mmHg, theta(if) (in ml/g dry tissue) increased from 0.59 +/- 0.02 to 1.7 +/- 0.05 and to 1.5 +/- 0.05 after isotonic and hypertonic dialysis, respectively, whereas theta(IC) increased from 2.8 +/- 0.08 to 3.0 +/- 0.1 after isotonic dialysis and decreased to 2.6 +/- 0.1 after hypertonic dialysis. After dialysis at 6 mmHg with isotonic or hypertonic solutions, theta(IV) increased from 0.034 +/- 0.001 to 0. 049 +/- 0.001 and 0.042 +/- 0.002, respectively. theta(urea) during hypertonic dialysis at P(ip) between 0 and 6 mmHg increased in a nonlinear fashion (F = 26.3, P < 0.001), whereas theta(IC) invariably decreased (F = 11.1, P < 0.001) and theta(if) doubled from its control value at low P(ip). In conclusion, elevation of intraperitoneal hydrostatic pressure causes tissue expansion, primarily in interstitium, irrespective of osmolality of the bathing solution. Tissue hydrostatic pressure is therefore the primary determinant of tissue properties with respect to hydration, which in turn affects diffusive and convective transport.

Abdominal Muscles↗

PubMed1999

In vivo effects of hydrostatic pressure on interstitium of abdominal wall muscle.

Fluid loss from the peritoneal cavity to surrounding tissue varies directly with intraperitoneal hydrostatic pressure (Pip). According to Darcy's law [Q = -KA(dPif/dx)], fluid flux (Q) across a cross-sectional area (A) of tissue will increase with an increase in either hydraulic conductivity (K) or the interstitial fluid hydrostatic pressure gradient (dPif/dx, where x is distance). Previously, we demonstrated that in the anterior abdominal muscle (AAM) of rats, dPif/dx increases by only 40%, whereas K rises fivefold between Pip of 1.5 and 8 mmHg. Because K is a function of interstitial volume (thetaif), we hypothesized that perturbations of Pip would change Pif and expand the interstitium, increasing thetaif. To test this hypothesis, we used dual-label quantitative autoradiography (QAR) to measure extracellular fluid volume (thetaec) and intravascular volume (thetaiv) in the AAM of rats within the Pip range from -2.8 to +8 mmHg. thetaif was obtained by subtraction (thetaec - thetaiv). dPif/dx was measured with a micropipette and a servo-null system. Local thetaiv did not vary with Pip and averaged 0.010 +/- 0.002 ml/g, and thetaif averaged 0. 19 +/- 0.01 ml/g at Pif </=1.2 mmHg. However, thetaif doubled between Pif of 1.2 and 4.2 mmHg (from 0.20 +/- 0.00 to 0.39 +/- 0.01 ml/g, respectively) but did not increase with further increases in Pif. This nonlinear pressure-volume relationship does not explain the fivefold increase in K with Pip. Because the interstitial matrix contributes to the interstitial resistance to fluid flow, and because hyaluronan (HA) is the only component of the matrix that is not anchored to the tissue, we hypothesized that the loss of interstitial HA was responsible for the continued decrease in interstitial resistance to fluid flow. We determined HA concentration in the rat AAM and adjacent subcutaneous tissue (SC) at Pip = 0 mmHg and after 2 h of dialysis at constant Pip = 6 mmHg. The HA content (normalized to dry weight) in the AAM was reduced from 487 +/- 16 to 360 +/- 27 micrograms/g dry tissue (n = 4, P < 0.05) and increased from 528 +/- 72 to 1,050 +/- 136 mg/g dry tissue (n = 4, P > 0.001) in the SC. We conclude that the mechanisms responsible for the increase in K with Pip include expansion of the interstitium, dilution of interstitial macromolecules, and washout from the AAM to SC of interstitial macromolecules responsible for resistance to fluid flow.

Abdominal Muscles↗

PubMed1999

Tissue sources and blood flow limitations of osmotic water transport across the peritoneum.

Despite the daily use of hypertonic solutions to remove fluid from patients throughout the world who are undergoing peritoneal dialysis, the tissue sources of this water flow are unknown. To study this phenomenon in specific tissues, small plastic chambers were affixed to parietal and visceral surfaces of the peritoneum and were filled with either an isotonic or hypertonic solution. The volume changes over 60 to 90 min were determined and divided by the chamber area to yield the volume flux. The hypertonic solution produced a positive flux into the chamber of 0.6 to 1.1 microl/min per cm2 in all tissues tested. In contrast, the isotonic solution resulted in a net loss or an insignificant change in the chamber volume. Additional experiments tested the influence of blood flow on the hypertonic water flux during periods of control, reduced (50 to 80%), or postmortem (no) blood flow, as determined by laser Doppler flowmetry. With the exception of the liver, small but insignificant changes in the flux into the chamber were observed during the period of reduced flow; all water fluxes were markedly depressed during the postmortem period. It is concluded that both parietal and visceral tissues are sources of osmotically induced water flow into the cavity. Except for the liver, marked blood flow reductions have small but insignificant effects on osmotic water transport.

Animals↗

PubMed1999

Blood flow does not limit peritoneal transport.

OBJECTIVE: We investigated the assumption that blood flow to the microvessels underlying the peritoneum does not limit solute or water exchange between the blood and the dialysis fluid. DESIGN: Small plastic chambers were affixed to the serosal side of the liver, cecum, stomach, and abdominal wall of anesthetized rats. Solutions that contained labeled solutes or that were made hypertonic were placed into the chambers, which restricted the area of transfer across the tissue to the base of the chamber and which permitted calculation of mass or water transfer rates on the basis of area. The local blood flow was monitored continuously with a laser Doppler flowmeter during three periods of observation: control, after 50%-70% reduction of the blood flow, and postmortem. RESULTS: Urea transfer across all serosa, except for the liver, showed no difference in mean mass transfer coefficient (cm/min) between control (0.0038-0.0046) and after 70% flow reduction (0.0037-0.0040), but demonstrated a significant decrease with blood flow equal to zero (0.0020). These tissues demonstrated small but insignificant decreases in osmotic water flow into the chamber (0.7-0.9 microL/min/cm2 under control conditions versus 0.4-0.7 microL/min/cm2 with reduced blood flow). The liver demonstrated limitations in water and solute transport with a 70% decrease in blood flow. CONCLUSION: Because the liver makes up a small part of the peritoneal area, we conclude that large drops in blood flow do not limit overall solute or water transfer across the peritoneum during dialysis, and therefore acute peritoneal dialysis may be an appropriate modality for ICU patients in shock and renal failure.

Animals↗

PubMed1999

Hydrostatic and osmotic pressures modulate partitioning of tissue water in abdominal muscle during dialysis.

OBJECTIVES: To investigate the effect of simultaneous exposure of anterior abdominal muscle (AAM) to changes in intraperitoneal hydrostatic pressure (Pip) and to osmolality of peritoneal fluid on total tissue water (TTW) and on the pattern of distribution of TTW in the AAM. DESIGN: A pilot study of single 60-min dwells in anesthetized Sprague-Dawley (SD) rats, dialyzed with either isotonic (290 mOsm/kg) or hypertonic (510 mOsm/kg) dialysis solutions at nominal Pip of 0 mmHg or 6 mmHg. MEASUREMENTS: TTW (from dry-weight-to-wet-weight ratios) can be divided into the extracellular volume [theta(ec), from quantitative autoradiography (QAR) with 14C-mannitol] and intracellular volume (theta(ic) = TTW - theta(ec)). Theta(ec) = theta(if) + theta(iv), where theta(if) = interstitial volume and theta(iv) = vascular volume [from QAR with 131I-immunoglobulin G (IgG)]. All measured parameters are standardized to tissue dry weight and expressed as mean +/- standard error. RESULTS: Regardless of the osmolality of the dialysis solution, elevation of Pip to 6 mmHg results in tissue expansion, primarily in theta(if), which is doubled to 1.71+/-0.11 mL/g dry weight and 1.60+/-0.17 mL/g dry weight with isotonic and hypertonic dialysis, respectively, as compared to controls (0.64+/-0.04 mL/g dry weight). The local theta(iv) was not affected by Pip or osmolality of the bathing solution. The overall theta(iv) is 0.046+/-0.006 mL/g dry weight. A two-way analysis of variance (ANOVA) to access the effect of osmolality and Pip on theta(ic) demonstrated no significant change in theta(ic) (F = 1.2, p > 0.1) as calculated for controls (3.13+/-0.19 mL/g dry weight), after isotonic dialysis (3.13+/-0.20 mL/g dry weight), or after hypertonic dialysis (2.77+/-0.30 mL/g dry weight). CONCLUSION: Elevation of Pip to 6 mmHg significantly increased TTW and expanded the tissue. Tissue expansion is primarily in interstitium (theta(if)), which is doubled from control value regardless of dialysis fluid osmolality.

Abdominal Muscles↗

PubMed1997

In vivo hydraulic conductivity of muscle: effects of hydrostatic pressure.

We and others have shown that the loss of fluid and macromolecules from the peritoneal cavity is directly dependent on intraperitoneal hydrostatic pressure (Pip). Measurements of the interstitial pressure gradient in the abdominal wall demonstrated minimal change when Pip was increased from 0 to 8 mmHg. Because flow through tissue is governed by both interstitial pressure gradient and hydraulic conductivity (K), we hypothesized that K of these tissues varies with Pip. To test this hypothesis, we dialyzed rats with Krebs-Ringer solution at constant Pip of 0.7, 1.5, 2.2, 3, 4.4, 6, or 8 mmHg. Tracer amounts of 125I-labeled immunoglobulin G were added to the dialysis fluid as a marker of fluid movement into the abdominal wall. Tracer deposition was corrected for adsorption to the tissue surface and for local loss into lymphatics. The hydrostatic pressure gradient in the wall was measured using a micropipette and a servo-null system. The technique requires immobilization of the tissue by a porous Plexiglas plate, and therefore a portion of the tissue is supported. In agreement with previous results, fluid flux into the unrestrained abdominal wall was directly related to the overall hydrostatic pressure difference across the abdominal wall (Pip = 0), but the interstitial pressure gradient near the peritoneum increased only approximately 40% over the range of Pip = 1.5-8 mmHg (20-28 mmHg/cm). K of the abdominal wall varied from 0.90 +/- 0.1 x 10(-5) cm2.min-1.mmHg-1 at Pip = 1.5 mmHg to 4.7 +/- 0.43 x 10(-5) cm2.min-1.mmHg-1 on elevation of Pip to 8 mmHg. In contrast, for the same change in Pip, abdominal muscle supported on the skin side had a significantly lower range of fluid flux (0.89-1.7 x 10(-4) vs. 1.9-10.1 x 10(-4) ml.min-1.cm-2 in unsupported tissue). The differences between supported and unsupported tissues are likely explained in part by a reduced pressure gradient across the supported tissue. In conclusion, the in vivo hydraulic conductivity of the unsupported abdominal wall muscle in anesthetized rats varies with the superimposed hydrostatic pressure within the peritoneal cavity.

Abdominal Muscles↗

PubMed1997

In vivo diffusion of immunoglobulin G in muscle: effects of binding, solute exclusion, and lymphatic removal.

Previously, we demonstrated that immunoglobulin G (IgG), dissolved in an isotonic solution in the peritoneal cavity, transported rapidly into the abdominal wall when the intraperitoneal (ip) pressure was > 2 cmH2O. We hypothesized that this was chiefly caused by convection and that diffusion of IgG was negligible. To investigate the role of diffusion, we dialyzed rats with no pressure gradient across the abdominal wall muscle for 2 or 6 h with an ip isotonic solution containing 125I-labeled IgG. At the end of the experiment, the animal was euthanized and frozen and abdominal wall tissue was processed to produce cross-sectional autoradiograms. Quantitative densitometric analysis resulted in IgG concentration profiles with far lower magnitude than profiles from experiments in which convection dominated. In other in vivo experiments, we determined the lymph flow rate to be 0.8 x 10(-4) ml.min-1.g-1 and the fraction of extravascular tissue (theta s) available to the IgG to be 0.041 +/- 0.001. An in vitro binding assay was used to determine the time-dependent, nonsaturable binding constant: 0.0065 min-1 x duration of exposure. A non-steady-state diffusion model that included effects of theta s, time-dependent binding, and lymph flow was fitted to the diffusion profile data, and the IgG diffusivity within the tissue void was estimated to be 2 x 10(-7) cm2/s, a value much higher than that published by other groups. We also demonstrate from our previous data that convection of IgG through tissue dominates over diffusion at ip pressures > 2 cmH2O, but diffusion may not be negligible. Furthermore, nonsaturable binding must be accounted for in the interpretation of tissue protein concentration profiles.

Abdominal Muscles↗

PubMed1997

Blood flow limitations of solute transport across the visceral peritoneum.

In a previous study, no limitations to urea transfer across the parietal peritoneum were demonstrated with decreases in local blood flow of 70%. It was hypothesized that the visceral peritoneum would have similar characteristics. To address this problem at the tissue level, diffusion chambers were affixed to the serosal side of the stomach, cecum, or liver of anesthetized rats (n = 6 each tissue), and solutions containing 14C urea were placed in the chamber. During each experiment, the local chamber blood flow was measured with laser Doppler flowmetry, and, simultaneously, the disappearance of the tracer versus time was determined under three conditions: control, after 60 to 70% blood flow reduction, and postmortem (flow = 0). The results showed no difference in the urea mass transfer coefficient (MTC; mean +/- SEM; cm/min x 10[3]) between control and blood flow reduction for the stomach (4.0 +/- 0.4 versus 3.6 +/- 0.3) or for the cecum (4.6 +/- 0.3 versus 4.0 +/- 0.3). However, the MTC was significantly decreased by local blood flow reduction in the liver (5.4 +/- 0.2 versus 2.6 +/- 0.2). Postmortem data demonstrated significant reductions in the MTC with blood flow equal to zero. It is concluded that a 60 to 70% blood flow reduction from control values does not limit solute transperitoneal transfer in the hollow viscera but causes significant changes in the mass transfer across the liver surface. Because the liver makes up only a small portion of the effective exchange area, overall transperitoneal solute transfer should not be greatly affected by significant decreases in blood flow.

Animals↗

PubMed1997

A method to test blood flow limitation of peritoneal-blood solute transport.

Current transperitoneal transport models assume that effective blood flow to the microcirculation does not limit solute exchange with dialysate in the cavity. Despite evidence that gas transfer across the peritoneum (assumed to equal the effective blood flow) occurs at rates that exceed maximum urea transfer rates by a factor of two to three, the assumption has been strongly challenged. To address this problem at the tissue level, a technique to determine the effect of local blood flow on small-solute transport was developed in this study. Diffusion chambers were affixed to the serosal side of the anterior abdominal wall of rats, and solutions containing radiolabeled urea or mannitol were placed in the chambers. During each experiment, the local blood flow beneath the chamber was monitored with laser Doppler flowmetry and the disappearance of the tracer versus time was simultaneously measured under three conditions of blood flow: control, 30% of control, and zero blood flow. The results demonstrated no significant differences for either solute between control and the condition in which blood flow was reduced by 70%. However, there was a significant reduction in the rate of mass transfer with no blood flow. It was concluded that blood flow at > or = 30% of control values does not limit solute transfer across the abdominal wall peritoneum during dialysis.

Abdominal Muscles↗