Biomedical subjects

C P Winlove

Publications and source records attributed to C P Winlove.

At least 19 recordsLinked to original sources

PubMed2005

Viscoelastic properties of insoluble amphiphiles at the air/water interface.

The effects of the presence of a molecular monolayer on the dilatational properties of the air/water interface have been investigated. Two water insoluble amphiphiles, dipalmitoyl phosphatidyl choline and quercetin 3-O-palmitate, were spread onto a pendant drop and the dynamic surface pressure was measured by means of drop shape analysis. The surface dilatational elasticity and viscosity of the spread monolayers were also determined by the oscillating drop technique. Constraints on the range of measuring conditions were investigated and we demonstrated that the pressure-area isotherms derived from oscillatory dynamic measurements display phase behaviour similar to that found in equilibrium measurements, albeit at reduced resolution. Both the amphiphiles formed purely elastic films that were characterised by a dilatational modulus that depended on the surface concentration and obeyed a power scaling law. The exponent of the relationship could be related to the thermodynamic conditions prevailing at the interface. The phospholipid monolayer scaling exponent was 2.8 in a temperature range of 20-26 degrees C indicates a favourable solvency of molecules in the bidimensional matrix. A very high scaling exponent (11.8 at 7 degrees C) for quercetin palmitate was interpreted assuming that molecules self-organise in fibre-like structures. This interface structure and the phase behaviour was found consistent with observations of the surface film obtained by Brewster angle microscopy. The structured quercetin 3-O-palmitate monolayers are disrupted by temperature increase or by adding a 0.2 molar fraction of the immiscible dipalmitoyl phosphatidyl choline.

Journal Article↗

PubMed2003

Oxygen partial pressure in outer layers of skin of human finger nail folds.

To gain insight into oxygen transport by the cutaneous microcirculation, we have developed oxygen-sensitive microelectrodes (tip diameter approximately 5 micro m) to measure the distribution of PO2 in dermal papillae of the finger nail folds of healthy human subjects. Oxygen entry into the tissue was minimised by covering the skin with a layer of paraffin oil. The finger was held under a dissecting microscope and microelectrodes were guided into position. PO2 varied from 5-25 % of its atmospheric value, Pair (approximately 160 mmHg), depending on the location within the papilla. Along the axis of a papillary loop, PO2 decreased from 40.0 +/- 4.8 mmHg (mean +/- S.E.M., n = 6) at the base to 30.4 +/- 5.2 mmHg (n = 6) at the tip. The lowest values of PO2, in the range of 5 % of Pair, were measured in the epidermis where the metabolism of cells was highest and the steepest PO2 gradients were recorded in the vicinity of the epidermal-dermal boundary. When the local circulation was abruptly reduced or stopped, PO2 fell exponentially with time, with a time constant of 8.4 +/- 1.5 s (n = 7). When flow was reinstated, PO2 rose exponentially to a new value with a time constant of 4.8 +/- 0.8 s (n = 6). The steady state PO2 following reperfusion was approximately 23 % higher than the pre-occlusion value (P < 0.05, ANOVA and two-tailed Student's t test) indicating localised reactive hyperaemia.

Adult↗

PubMed2002

Effects of perfusion rate on permeability of frog and rat mesenteric microvessels to sodium fluorescein.

The permeability, P(S), to sodium fluorescein (Stokes-Einstein radius = 0.45 nm) has been measured in single mesenteric capillaries of pithed frogs and anaesthetised rats as perfusion velocity, U, was varied over a range from 400 up to 2000-10,000 microm s(-1). P(S) increased linearly with U. In 20 frog capillaries, mean (+/- S.E.M.) P(S) (in microm s(-1)) = 9.35 (+/- 1.55)U x 10(-5) + 0.244 (+/- 0.0291). Similarly, in nine rat venules, mean P(S) = 1.62 (+/- 0.385)U x 10(-4) + 0.375 (+/- 0.025). The flow-dependent component of permeability could be reversibly abolished in frog capillaries by superfusing with 100 microM noradrenaline and by superfusing rat venules with the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (20 microM). It was shown that changes in microvascular pressure accompanying changes in U during free perfusion could account for only 15 % of the changes in P(S), i.e. 85 % of the changes in P(S) were changes in the permeability coefficient itself. A comparison between the changes in P(S) with U and the previously described changes in microvascular permeability to K(+) with U, suggest that if the flow-dependent component of permeability is modelled as a population of pores of constant size, these have radii of 0.8 nm. Such a pathway would limit flow-dependent permeability to small hydrophilic molecules and have minimal effect on net fluid exchange.

Animals↗

PubMed2001

High resolution imaging of the distribution and permeability of methyl viologen dication in bovine articular cartilage using scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM) has been used in the induced transfer (SECMIT) mode to image the permeability of a probe cation, methyl viologen (MV(2+)), in samples of articular cartilage. An ultramicroelectrode (UME), scanned just above the surface of a sample, is used to amperometrically detect the probe solute. The resulting depletion of MV(2+) in solution induces the transfer of this cation from the sample into the solution for detection at the UME. The current provides quantitative information on local permeability, provided that the sample-UME distance is known. It is shown that the necessary topographical information can be obtained using the amperometric response for the oxidation of Ru(CN)(4-)(6), which does not permeate into the cartilage matrix. This procedure was validated by marking samples in situ, after electrochemical imaging, with subsequent examination by ex situ interferometry and optical microscopy. Wide variations in the permeability of MV(2+) have been detected by SECMIT. These observations represent the first demonstration of the inhomogeneous permeability of a cation in cartilage on a micrometre scale. The permeability maps show similar features to the proteoglycan distribution, identified by toluidine blue staining, and it is likely that proteoglycans are the main determinant of MV(2+) permeability in articular cartilage.

Animals↗

PubMed2001

Electrochemical measurement of transport into scoliotic intervertebral discs in vivo using nitrous oxide as a tracer.

STUDY DESIGN: An in vivo study measuring nitrous oxide concentrations in scoliotic intervertebral discs during surgery. OBJECTIVES: To determine pathways for nutrient transport into scoliotic human discs in vivo. SUMMARY OF BACKGROUND DATA: The intervertebral disc is the largest avascular structure in the body. Disc cells in the nucleus rely on the blood supply from the vertebral bodies for supply of nutrients and removal of waste. Loss of nutrient supply is thought to lead to disc degeneration, but solute transport has not been measured in vivo in humans. METHODS: We measured solute transport into the disc using N2O as a tracer, in 19 human discs from five patients with neuromuscular scoliosis (6-19 years of age) during surgery for correction of scoliotic deformities. During anesthesia N2O diffuses into the disc at a rate governed by effective permeability of the vertebral body-disc interface. Intradiscal N2O concentrations were measured amperometrically using silver needle microelectrodes, which were inserted into the discs once they were exposed by an anterior approach. RESULTS: For all spines N2O concentrations were very low in the disc at the curve apex (6% those expected from unimpeded diffusion) and, although still low, were significantly higher 2 discs below or above the apex. CONCLUSIONS: Because flux into the apical disc is most restricted, the decrease in solute transport is possibly induced by changes in mechanical stress on the disc; microfocal radiographs of a scoliotic spine suggest that increased endplate calcification could be partly responsible for limiting solute diffusion.

Adolescent↗

PubMed2001

Combination of preconditioning and delayed flap elevation: evidence for improved perfusion and oxygenation of the latissimus dorsi muscle for cardiomyoplasty.

BACKGROUND: Atrophy and fibrosis of the distal part of the latissimus dorsi muscle (LDM) wrap is a recognized complication of cardiomyoplasty that has been attributed to ischemia. Failure of the muscle wrap contributes to the late attrition seen in clinical cardiomyoplasty. In this study we examined the role of two-staged mobilization and of preconditioning by electrical stimulation on the regional perfusion and oxygenation of the LDM. METHODS: In a rabbit model (n = 36) the LDM was preconditioned as follows: group A muscles received preconditioning in situ; group B muscles were partially mobilized by dividing the intercostal perforators and then preconditioned; and group C muscles were completely mobilized and wrapped around a silicone-rubber mandrel before conditioning. Controls received no conditioning. The preconditioning regimen consisted of 2 weeks of continuous stimulation at 2.5 Hz. At completion of preconditioning the muscles were fully mobilized and mounted on a muscle-testing apparatus. Purpose-built microelectrodes measured regional PO2 and perfusion using a diffusible gas tracer technique. Muscles were weighed and processed for fiber typing and capillary counting. RESULTS: All preconditioned muscles demonstrated fiber transformation, with increased fatigue resistance. Perfusion of preconditioned muscles both at rest and during contraction was higher than control in the proximal part of the muscle. Distal regions of group B muscles had higher perfusion and capillary density than any other group (p < 0.05). Distal regions of group C had the lowest perfusion and capillary density, and showed muscle atrophy and histologic evidence of necrosis. During fatigue testing there was a decrease in the PO2 in the distal regions of the control and group C muscles (p < 0.05), whereas it was maintained at resting levels in both group A and B muscles. CONCLUSIONS: Conditioning in situ improves perfusion of the distal LDM and prevents a fall in tissue PO2 during contraction. Two-stage mobilization further improves distal perfusion and capillary density. In contrast, shortterm elevation followed by conditioning produces impaired distal perfusion, decrease in PO2, and fiber necrosis in the distal muscle. The present study suggests that partial mobilization of the LDM performed at the same time as placement of electrodes for preconditioning may prepare the LDM better for the demands of cardiomyoplasty.

Animals↗

PubMed2001

Scapular insertion of the rabbit latissimus dorsi muscle: gross anatomy and fibre-type composition.

This paper defines the characteristics and significance of the scapular insertion of the latissimus dorsi muscle (LDM) of the rabbit. In a study of the New Zealand White species (n = 10) the scapular insertion was found to be a consistent anatomical feature of the LDM that made up 12.3% (+/-2.3) of the total muscle weight. The fibres arise from the medial aspect of the body of the LDM and run in a caudocranial direction to be inserted into a broad, thin tendon beneath the scapula ridge. This is morphologically different from the scapular component of the human LDM which is a well-recognized but inconsistent feature and consists of no more than a small leash of fibres running around the lower pole of the scapula. The scapular insertion was deeper red in colour than the body of the muscle and fibre-typing demonstrated a mean slow-fibre composition of 49% (+/-2.6) compared to 16% (+/-1.7) for the body of the muscle (p < 0.01). Mapping of the fibre types throughout the remainder of the LDM confirmed that the body of the muscle was of fast phenotype but with significantly more slow fibres in the superomedial segment of the muscle than elsewhere. This region of the muscle contributes mainly to the scapular insertion and it is proposed that this part of the muscle takes on a predominantly postural role in stabilising the scapula during movement of the forelimb.

Adenosine Triphosphatases↗

PubMed2001

Regional transcapillary albumin exchange in rodent endotoxaemia: effects of fluid resuscitation and inhibition of nitric oxide synthase.

Sepsis is characterized by increased microvascular permeability and regional variations in capillary perfusion, which may be modulated by nitric oxide (NO) and reversed by fluid resuscitation (FR). The effects of saline FR and NO synthase blockade [by N(G)-nitro-L-arginine methyl ester (L-NAME)] on microvascular albumin transport and perfused capillary density were assessed in anaesthetized Wistar rats with acute normodynamic endotoxaemia. Separate dual-isotope techniques were employed to measure the permeability index (PI(A)) and the permeabilityxsurface area product index (PI(B)), which provide different and complementary information regarding blood-tissue albumin exchange. PI(A) represents the tissue/blood distribution volume ratio of albumin. PI(B) is a composite measure of endothelial permeability and the vascular surface area available for albumin exchange, and therefore takes into account the effect of altered blood volume. Capillary density was quantified by fluorescence microscopy following circulation of Evans Blue-labelled albumin. Compared with controls, PI(A) was reduced significantly in lipopolysaccharide (LPS)-treated animals in skeletal muscle and skin, probably due to blood volume redistribution rather than to changes in permeability. PI(B) was increased significantly in LPS-treated animals in the kidney, mesentery, skeletal muscle, skin and lung, and in the small bowel following FR. FR also improved the LPS-induced metabolic base deficit, but did not alter capillary density. L-NAME significantly attenuated the LPS-induced rise in PI(B) in the lung. In conclusion, acute endotoxaemia induces tissue-dependent variations in microvascular albumin exchange. FR improves acid-base disturbance in endotoxaemia, through mechanisms other than microvascular recruitment. NO appears to increase microvascular permeability in endotoxaemia, an effect that may be attenuated by L-NAME, particularly in the lung.

Acute Disease↗

PubMed2000

Scanning electrochemical microscopy as a local probe of oxygen permeability in cartilage.

The use of scanning electrochemical microscopy, a high-resolution chemical imaging technique, to probe the distribution and mobility of solutes in articular cartilage is described. In this application, a mobile ultramicroelectrode is positioned close ( approximately 1 microm) to the cartilage sample surface, which has been equilibrated in a bathing solution containing the solute of interest. The solute is electrolyzed at a diffusion-limited rate, and the current response measured as the ultramicroelectrode is scanned across the sample surface. The topography of the samples was determined using Ru(CN)(6)(4-), a solute to which the cartilage matrix was impermeable. This revealed a number of pit-like depressions corresponding to the distribution of chondrocytes, which were also observed by atomic force and light microscopy. Subsequent imaging of the same area of the cartilage sample for the diffusion-limited reduction of oxygen indicated enhanced, but heterogeneous, permeability of oxygen across the cartilage surface. In particular, areas of high permeability were observed in the cellular and pericellular regions. This is the first time that inhomogeneities in the permeability of cartilage toward simple solutes, such as oxygen, have been observed on a micrometer scale.

Animals↗

PubMed2000

Oxygenation and perfusion of rabbit tibialis anterior muscle subjected to different patterns of electrical stimulation.

Dual amperometric microelectrodes were used to measure local pO2 and perfusion at multiple sites in the fast-twitch tibialis anterior muscles of anaesthetized rabbits. Six muscles were stimulated continuously at 10, 5, or 2.5 Hz. For all three frequencies, perfusion declined to about 50% of resting levels and recovered after stimulation. These changes corresponded to a rise followed by a fall in extracellular pO2. The highest levels of pO2 were reached during stimulation at 10 Hz. Eight muscles were stimulated tetanically at 100 Hz for 200 ms with duty cycles that were varied between 1.3 and 20.0%. Perfusion rose to 8.7 +/- 2.0 ml s(-1) 100 g(-1) at a duty cycle of 5% and declined with further increases in duty cycle. pO2 was depressed for duty cycles less than 10% but rose above resting levels at higher duty cycles. It is suggested that the paradoxical combination of elevated pO2 and depressed perfusion is attributable to stimulation conditions that exceed the oxygen transport capacity of a fast muscle.

Animals↗

PubMed2000

Myocardial tissue oxygen supply and utilization during coronary artery bypass surgery: evidence of microvascular no-reflow.

The supply and utilization of oxygen by the myocardium reflect the dynamic efficiency of the microcirculation. The present study examines these parameters during coronary artery bypass surgery. We used a voltammetric microelectrode technique to assess regional variations in myocardial tissue partial pressure of oxygen (PO(2)) and myocardial tissue perfusion (MTP) in patients undergoing coronary artery bypass surgery. A total of 29 myocardial regions were studied in 17 patients to assay tissue PO(2), and 13 regions in 10 patients to measure MTP. There was an increase in MTP from 53+/-9 ml.min(-1).100 g(-1) before cardiopulmonary bypass to 72+/-13 ml. min(-1).100 g(-1) after (means+/-S.E.M.; P=0.05). Tissue PO(2) showed an overall increase from a baseline level of 45+/-8 mmHg to a final level of 88+/-10 mmHg (P<0.0001). Following release of the aortic cross-clamp there was a variable time delay before a change in tissue PO(2) was observed. There was an immediate response in five regions, whereas in 20 regions the response was delayed by between 0.5 and 32 min. In the remaining four regions there was no change in tissue PO(2). The duration of the delay in response was correlated positively with the cross-clamp time (r=0.45, P<0.05) and negatively with the final tissue PO(2) (r=-0.5, P<0.05). Voltammetric methods for monitoring changes in oxygen supply and utilization offer new insights into the changes that occur during ischaemia and reperfusion. A delay in the delivery of oxygen to the myocardium occurs in many patients following coronary artery bypass surgery.

Aged↗

PubMed1999

Physicochemical properties of arterial elastin and its associated glycoproteins.

Microfibrillar glycoproteins are a significant component of vascular elastic tissue, but little is known about their contribution to vascular physiology and pathology. We have investigated some physicochemical properties of the glycoproteins that may be pertinent to these roles. Because of the difficulty in isolating intact glycoproteins in a form and quantity suitable for physicochemical examination, we based our analysis on a comparison of the properties of porcine thoracic aorta and pulmonary artery extracted with GuHCl and collagenase (preparation GC) and after further treatment with dithioerythritol to remove glycoproteins (preparation GC/DTE). Amino acid analysis showed that GC/DTE had the amino acid composition of pure elastin while GC contained a higher proportion of polar amino acids, particularly in the aortic preparation. GC stained with alcian blue, particularly in the intimal region, but GC/DTE did not. GC had a higher water content and a slower viscoelastic response and the circumferential elastic modulus was approximately 50% lower (whether expressed in terms of sample weight or elastin content). Clearly, therefore, the microfibrils do not stiffen the network and may prevent the alignment of elastin fibers in the circumferential direction. Their effect on hydration may arise either because they impose mechanical constraints on the geometry of the network or because they modify the inter- and intramolecular hydrophobic or electrostatic interactions that influence the tissue organization and hydration. Molecular probe measurements of the intrafibrillar pore structure using radiolabeled and fluorescent probes showed that removal of the microfibrils caused a slight decrease in the extrafibrillar water space and a larger decrease in the intrafibrillar water space. Sucrose, a small probe molecule, was able to penetrate most of the intrafibrillar water space when microfibrils were present but was virtually excluded when they were not. Potentiometric titration and radiotracer assays of ion binding both showed that the microfibrils contribute a considerable negative charge (-9 mumoles/g wet tissue in the aortic preparation and -16 mumoles/g wet weight in the pulmonary artery) and increase calcium binding by approximately 30%.

Animals↗

PubMed1999

The deformation of spherical vesicles with permeable, constant-area membranes: application to the red blood cell.

The deformation of an initially spherical vesicle of radius a with a permeable membrane under extensive forces applied at its poles is calculated as a function of the in-plane shear modulus, H, and the out-of-plane bending modulus, B, using an axisymmetric theory that is valid for large deformations. Suitably nondimensionalized, the results depend upon a single nondimensional parameter, C identical with a(2)H/B. For small deformations, the calculated force-polar strain curves are linear and, under these conditions, the slope of the curve determines only C, not the values of H and B separately. Independent determination of H and B from experimental measurements require deformations that are large enough to produce nonlinear behavior. Simple approximations for large and small C are given, which are applied to experimental measurements on red blood cell ghosts that have been made permeable by treatment with saponin.

Biomechanical Phenomena↗

PubMed1999

Abnormal tissue oxygenation and cardiovascular changes in endotoxemia.

Experimental sepsis induces disturbances in microcirculatory flow and nutrient exchange that may result in impaired tissue oxygenation. Volume resuscitation is a principal clinical intervention in patients with sepsis. Nitric oxide (NO) has been implicated in the pathophysiology of endotoxemia, but few data exist concerning the effects of either NO synthase inhibition (NOSi) or volume resuscitation on microvascular regulation and tissue oxygenation. Amperometric measurements were made of skeletal muscle (tissue) oxygen tension (PtO2) and its response to changes in fraction of inspired oxygen (FIO2) in rats rendered endotoxemic. Simultaneous measurements were made of systemic hemodynamic indices and arterial blood gas tensions. At normal PaO2, PtO2 in endotoxemic animals was significantly lower than in control animals, with marked attenuation of the response to increasing FIO2. These changes were associated with significant metabolic acidemia. In volume-resuscitated endotoxemic rats, PtO2 and blood pH were unchanged. A significant reduction in the PtO2 response to hyperoxia was observed in animals treated with the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), an effect not reversed by fluid resuscitation. These data suggest that significant tissue hypoxia and abnormal microvascular control occur in endotoxemia. Volume resuscitation can reverse the changes in PtO2, whereas nitric oxide synthase (NOS) inhibition has deleterious effects on muscle PtO2 in both control and endotoxemic animals.

Animals↗

PubMed1998

Oxygen and lactate concentrations measured in vivo in the intervertebral discs of patients with scoliosis and back pain.

STUDY DESIGN: Oxygen concentrations in intervertebral discs were measured in 10 patients during discography and in 13 patients with scoliosis and 11 patients with back pain during spinal surgery. Lactate concentration profiles were measured in 12 of these discs. The discs were graded for degeneration by magnetic resonance imaging and histology where possible. OBJECTIVES: To determine if oxygen and lactate levels in human discs vary with degree of degeneration. Failure of nutrient transport is thought to lead to disc degeneration. SUMMARY OF BACKGROUND DATA: The disc is avascular. Oxygen is used by the disc cells, and lactate is produced. Low oxygen and high lactate concentrations have been measured in the center of healthy animal discs. METHODS: Oxygen concentrations were measured amprometrically. The sterilized gold-needle electrode was introduced into the disc during discography or after the disc was exposed surgically via an anterior approach. Concentration profiles of each disc took approximately 5 minutes to measure. Lactate concentrations were measured biochemically on the excised disc segment. RESULTS: Oxygen concentrations were highest at the disc surface and fell toward the center. Lactate concentrations showed the reverse profile. Oxygen levels were very variable, ranging from 5-150 mm Hg in the center of the nucleus. No correlation was seen with age, pathology, or degree of degeneration. Lactate concentrations ranged for the most part from 2 mmol/L to 6 mmol/L. CONCLUSIONS: Concentrations of metabolites depend on cellular activity and on transport of the metabolite between the blood supply and the cell. The correlation between degeneration and nutrition cannot be determined only from metabolite concentrations; measurements of metabolic activity and nutrient transport rates also are required.

Adolescent↗

PubMed1998

Measurement of the charge properties of articular cartilage by an electrokinetic method.

The charge structure of the surface of articular cartilage determines its interactions with the macromolecules and cells of synovial fluid. It may thereby be important to the physiological function and pathological degeneration of the tissue. To determine whether the electrokinetic properties of the surface differ from those of the bulk tissue, we measured the streaming potential generated by the flow of electrolyte over the surface of a cartilage plug mounted in a chamber built for that purpose. We then calculated the effective surface charge density. In nonfibrillated cartilage from the human femoral head, the surface charge density, 0.037+/-0.004 Cm(-2) (mean+/-SD), was approximately half that measured at the surface of slices cut from the middle and deep zones. In addition, the surface charge density fell relatively little at low pH; this is consistent with a higher proportion of strongly acidic groups. The variations in surface charge density were found to be similar to those in total fixed charge density in the slices by the tracer cation method. Therefore, no evidence exists that the actual surface differs in composition from the immediately underlying matrix. The addition of synovial fluid (0.0025 ml/ml) to the superfusing solution reduced the surface charge density by 25+/-9% (n=5), and we attributed this to the binding of synovial-fluid macromolecules.

Animals↗

PubMed1998

Solute exchange in the rabbit myocardium: ischaemia, reflow, and myocardial necrosis.

OBJECTIVE: Coronary occlusion in the rabbit reduces the delivery of particulate tracers to close to zero, but exchange of diffusible solutes, derived from non-arterial sources, continues at a significant level. We investigated the relationships between the exchange of diffusible solutes during coronary occlusion and the extent of myocardial necrosis and between duration of ischaemia and the extent of recovery of solute exchange during reflow. METHODS: In an anaesthetised rabbit model of regional ischaemia and reflow, solute exchange is measured using the voltammetric hydrogen clearance technique. The area at risk and infarct size are determined ex vivo with monastral blue and nitroblue tetrazolium staining, respectively. Three groups are studied: control perfusion for 130 minutes (group A); 30 minutes coronary ligation followed by 90 minutes reflow (group B) and 40 minutes coronary ligation followed by 90 minutes reflow (group C). RESULTS: There was no significant difference in area at risk between the groups B and C (50 +/- 2% and 45 +/- 5%; p = ns) or in infarct size when expressed relative to the area at risk (42 +/- 7% and 55 +/- 5%; p = ns). During coronary ligation hydrogen clearance remained constant at 22 +/- 4% of the control region in group B and 32 +/- 4% in group C, at the same time period in group A it was 87 +/- 2% (ANOVA = p < 0.05, with a significant non-linear trend). Although the duration of ischaemia and the level of solute exchange during ischaemia did not correlate individually with the extent of myocardial necrosis, together they showed a significant correlation (ANOVA; p < 0.05). Following coronary occlusion, hydrogen clearance recovered to 72 +/- 9% after 30 minutes ischaemia but only to 57 +/- 5% following 40 minutes ischaemia and was 95 +/- 2% in the control group (ANOVA between the three groups p < 0.05 with a significant linear trend). Myocardial hydration fell in the apical region following coronary ligation by 27 +/- 5% in group B and by 25 +/- 5% in group C, and rose on reperfusion but only to 80 +/- 3% in group B and 83 +/- 3% in group C of their preligation values. CONCLUSION: In collateral deficient myocardium, the extent of myocardial necrosis is dependent on the level of solute exchange occurring during ischaemia. The level of solute exchange during reflow is dependent on the duration of ischaemia.

Animals↗

PubMed1998

Muscle transformation in cardiomyoplasty: the effect of conditioning and mobilisation on perfusion, oxygenation and fatigue resistance in the latissimus dorsi muscle.

BACKGROUND: In the clinical application of transformed skeletal muscle to cardiac assistance there is evidence that the latissimus dorsi muscle (LDM) wrap can undergo atrophy, which would prevent it from providing a sustained functional improvement. Possible causes are ischaemia and degeneration related to the conditioning process. We studied the nutritional and structural changes occurring under different stimulation regimes with the aim of improving the conditioning protocol. METHODS: Microelectrodes were used to measure regional perfusion and oxygenation in the rabbit LDM during mobilisation and subsequent repeated contraction. Group A muscles (n = 10) were conditioned for 6 weeks at 10 Hz, Group B muscles (n = 10) for 2 weeks at 2.5 Hz. Each muscle was then mobilised and tested in a hydraulic apparatus which recorded the pressure generated in a closed circuit. RESULTS: Muscles of Group A and Group B demonstrated transformation of fibre type, with a predominance of type I (62 +/- 4%) fibres in Group A and type IIa (68 +/- 9%) fibres in Group B. There was no evidence of muscle degeneration. After 10 min of fatigue testing the pressure produced was 53 +/- 5% of initial values in Group A and 51 +/- 8% in Group B, compared to 8 +/- 1% in the control group (P < 0.001). Maximum rate of relaxation was faster in Group B than in Group A (46 +/- 3% vs. 36 +/- 3% of control muscle, P < 0.05). Mobilisation resulted in a decrease in the distal perfusion of the control muscles (P < 0.05) and PO2 decreased by 8.7 +/- 1.7 mmHg during a fatigue test, which resulted in rapid loss of contractile function to 46 +/- 1% of the initial value within 1 min. In both Groups A and B the perfusion of all regions of the muscles both before and after mobilisation was greater than that of controls. During the same fatigue test, the PO2 of the distal regions was maintained and the contractile function fell more slowly to between 70 and 80% of initial values within 1 min. CONCLUSION: We showed that ischaemia in the distal region of the control LDM could result from mobilisation and repeated contraction. Muscle transformation improved perfusion and prevented a fall in tissue PO2 during a sustained series of contractions. Muscles that were conditioned at 2.5 Hz shared the improved perfusion of the fully transformed muscle, but had faster relaxation characteristics. Short periods of in situ conditioning prior to mobilisation may help to avoid ischaemic changes in distal parts of the LDM while achieving fatigue resistance in the grafted muscle at an earlier postoperative stage.

Animals↗