Changes In Blood Flow Distribution Research Articles

Blood flow distribution in embryonic common snapping turtles Chelydra serpentina (Reptilia; Chelonia) during acute hypoxia and α-adrenergic regulation

Embryonic turtles have four distinct vascular beds that separately perfuse the developing embryo's body and the extra-embryonic yolk sac, amnion and chorioallantoic membrane (CAM). The mechanisms enabling differential regulation of blood flow through these separate beds, in order to meet the varying demands of the embryo during development, is of current interest. The present investigation followed the changes in blood flow distribution during an acute exposure to hypoxia and after α-adrenergic blockade. We monitored heart rate (fH), mean arterial pressure (Pm), and determined relative blood flow distribution (%Q̇sys) using colored microspheres. At 70% and 90% of the incubation period hypoxia elicited a bradycardia without changing Pm while %Q̇sys was altered only at 70%, increasing to the CAM and liver. Blockade of α-adrenergic responses with phentolamine did not change fH or Pm but increased %Q̇sys to the shell. These results show the capacity of embryos to redistribute cardiac output during acute hypoxia, however α-adrenergic receptors seemed to play a relatively small role in embryonic cardiovascular regulation.

Changes in blood flow distribution after hypogastric artery embolization and the ischaemic tolerance of the pelvic circulation.

This study aimed to compare the pelvic cavity vasculature before and after the interventional occlusion of a hypogastric artery (IOHA) and to reveal the protective mechanism of the collateral vessels against pelvic ischaemia.Sixty-nine patients with abdominal aortic or aortoiliac aneurysms who underwent endovascular aneurysm repair accompanied with IOHA were retrospectively analysed. Patients were divided into those who complained of buttock claudication (BC) group and asymptomatic patients (non-BC group).Two analyses were performed. In Study 1, the factors associated with postoperative BC were evaluated in patients who underwent IOHA using only 0.035 Tornade embolization coils. In Study 2, the pelvic arterial volume (PAV) was assessed in patients with both pre- and postoperative multidetector computed tomography images. PAV was calculated by subtracting the aortoiliac artery volume from the total PAV. The PAV ratio was defined as the postoperative PAV divided by preoperative PAV and represented collateral development in the pelvis.In Study 1, BC occurred in 16 patients (BC group) and did not occur in 25 patients (non-BC group). Significantly more coils were used in the BC group than in the non-BC group (8.6 ± 1.0 vs 5.6 ± 0.83, P = .013). Study 2 had 24 patients in the BC group and 31 patients in the non-BC group. The PAV ratio was significantly higher in the BC group than in the non-BC group (0.93 ± 0.05 vs 0.62 ± 0.04, P<.0001).The use of more coils in IOHA is associated with BC. In addition, volumetric analysis revealed that less collateral vessel development occurred in the non-BC group than in the BC group, which might reflect a potential reservation capacity of non-BC patients for acute pelvic ischaemia.

Bladder Distension Increases Blood Flow in Pain Related Brain Structures in Subjects with Interstitial Cystitis

In healthy control subjects certain brain regions of interest demonstrate increased regional cerebral blood flow in response to painful stimuli. We examined the effect of bladder distension on arterial spin label functional magnetic resonance imaging measures of regional cerebral blood flow in regions of interest in subjects with interstitial cystitis. A total of 11 female subjects with interstitial cystitisand 11 healthy controls underwent 3 brain perfusion scan studies using arterial spin label functional magnetic resonance imaging, including 1) with a full bladder, 2) with an empty bladder and 3) while experiencing heat pain. Regional cerebral blood flow was calculated using custom software and individual scans were spatially normalized to the MNI (Montreal Neurological Institute) template. Region of interest based, absolute regional cerebral blood flowwas determined for each condition and for the within group/within subjectregional cerebral blood flow distribution changes induced by each condition. Bladder distension was associated with robust increases in regional cerebral blood flow in subjects with interstitial cystitis. The increases were greater than those in healthy controls in multiple regions of interest, including the supplemental motor area (mainly Brodmann area 6), the motor and sensory cortex, the insula bilaterally, the hippocampal structures bilaterally, and the middle and posterior cingulate areas bilaterally. During heat pain healthy controls had more robust regional cerebral blood flow increases in the amygdala bilaterally. At baseline with an empty bladder there was lower regional cerebral blood flow in the insula, and the mid and posterior cingulate cortex bilaterally in subjects with interstitial cystitis. Compared to healthy controls, subjects with interstitial cystitis have limited differences in regional cerebral blood flow in baseline (empty bladder) conditions as well as during heat pain. However, they had robust regional cerebral blood flow increases in the full bladder state in regions of interest typically associated with pain, emotion and/or motor control, indicating altered processing of bladder related sensations.

In situ cardiac perfusion reveals interspecific variation of intraventricular flow separation in reptiles.

The ventricles of non-crocodilian reptiles are incompletely divided and provide an opportunity for mixing of oxygen-poor blood and oxygen-rich blood (intracardiac shunting). However, both cardiac morphology and in vivo shunting patterns exhibit considerable interspecific variation within reptiles. In the present study, we develop an in situ double-perfused heart approach to characterise the propensity and capacity for shunting in five reptile species: the turtle Trachemys scripta, the rock python Python sebae, the yellow anaconda Eunectes notaeus, the varanid lizard Varanus exanthematicus and the bearded dragon Pogona vitticeps To simulate changes in vascular bed resistance, pulmonary and systemic afterloads were independently manipulated and changes in blood flow distribution amongst the central outflow tracts were monitored. As previously demonstrated in Burmese pythons, rock pythons and varanid lizards exhibited pronounced intraventricular flow separation. As pulmonary or systemic afterload was raised, flow in the respective circulation decreased. However, flow in the other circulation, where afterload was constant, remained stable. This correlates with the convergent evolution of intraventricular pressure separation and the large intraventricular muscular ridge, which compartmentalises the ventricle, in these species. Conversely, in the three other species, the pulmonary and systemic flows were strongly mutually dependent, such that the decrease in pulmonary flow in response to elevated pulmonary afterload resulted in redistribution of perfusate to the systemic circuit (and vice versa). Thus, in these species, the muscular ridge appeared labile and blood could readily transverse the intraventricular cava. We conclude that relatively minor structural differences between non-crocodilian reptiles result in the fundamental changes in cardiac function. Further, our study emphasises that functionally similar intracardiac flow separation evolved independently in lizards (varanids) and snakes (pythons) from an ancestor endowed with the capacity for large intracardiac shunts.

Heterogeneous ageing of skeletal muscle microvascular function.

The distribution of blood flow to skeletal muscle during exercise is altered with advancing age. Changes in arteriolar function that are muscle specific underlie age-induced changes in blood flow distribution. With advancing age, functional adaptations that occur in resistance arterioles from oxidative muscles differ from those that occur in glycolytic muscles. Age-related adaptations of morphology, as well as changes in both endothelial and vascular smooth muscle signalling, differ in muscle of diverse fibre type. Age-induced endothelial dysfunction has been reported in most skeletal muscle arterioles; however, unique alterations in signalling contribute to the dysfunction in arterioles from oxidative muscles as compared with those from glycolytic muscles. In resistance arterioles from oxidative muscle, loss of nitric oxide signalling contributes significantly to endothelial dysfunction, whereas in resistance arterioles from glycolytic muscle, alterations in both nitric oxide and prostanoid signalling underlie endothelial dysfunction. Similarly, adaptations of the vascular smooth muscle that occur with advancing age are heterogeneous between arterioles from oxidative and glycolytic muscles. In both oxidative and glycolytic muscle, late-life exercise training reverses age-related microvascular dysfunction, and exercise training appears to be particularly effective in reversing endothelial dysfunction. Patterns of microvascular ageing that develop among muscles of diverse fibre type and function may be attributable to changing patterns of physical activity with ageing. Importantly, aerobic exercise training, initiated even at an advanced age, restores muscle blood flow distribution patterns and vascular function in old animals to those seen in their young counterparts.

Evolution of the in‐series circulation in tetrapods: form follows function

The ancestral in‐parallel circulation of tetrapods combines a single ventricle and two systemic aortae, which allow central vascular shunting. Loss of the shunt and evolution of the in‐series circulatory design, as exemplified by extant mammals and birds, involved independent acquisition of two anatomic features: a complete interventricular septum, and a single aorta. Extent and location of the interventricular septum is dictated by the expression gradient of Tbx transcription factors in the myocardium. Loss of an aorta, however, has yet to be addressed by developmental studies. Our experimental work on the American alligator suggests that the heart's outflow tract is remodelled by changes in blood flow distribution in response to environmental stressors. Flow capacity of the left aorta (a conduit for the pulmonary bypass shunt) was significantly reduced (−27%) in alligator hatchlings chronically exposed for three months to atmospheric hypoxia (12%O2), when compared to conspecifics reared in normoxia (21%O2) or hyperoxia (30%O2). In contrast, outflow tract capacities did not differ in juvenile alligators subject to 15 months of different exercise regimina (sedentary, running or swimming). We suggest that a global hypoxic episode, rather than increased activity, may have been the driving pressure behind loss of the shunt and origin of the in‐series circulation. Funded by NSF IOB0445680 and IOS922756 to JWH.

Evaluation of the effects of dorsal versus lateral recumbency on the cardiopulmonary system during anesthesia with isoflurane in red-tailed hawks (Buteo jamaicensis)

To evaluate the effects of dorsal versus lateral recumbency on the cardiopulmonary system during isoflurane anesthesia in red-tailed hawks (Buteo jamaicensis). 6 adult 1.1- to 1.6-kg red-tailed hawks. A randomized, crossover study was used to evaluate changes in respiratory rate, tidal volume, minute ventilation, heart rate, mean arterial and indirect blood pressures, and end-tidal Pco(2) measured every 5 minutes plus Paco(2) and Pao(2) and arterial pH measured every 15 minutes throughout a 75-minute study period. Respiratory rate was higher, tidal volume lower, and minute ventilation not different in lateral versus dorsal recumbency. Position did not affect heart rate, mean arterial blood pressure, or indirect blood pressure, although heart rate decreased during the anesthetic period. Birds hypoventilated in both positions and Paco(2) differed with time and position × time interaction. The Petco(2) position × time interaction was significant and Petco(2) was a mean of 7 Torr higher than Paco(2). The Paco(2) in dorsal recumbency was a mean of 32 Torr higher than in lateral recumbency. Birds in both positions developed respiratory acidosis. Differences in tidal volume with similar minute ventilation suggested red-tailed hawks in dorsal recumbency might have lower dead space ventilation. Despite similar minute ventilation in both positions, birds in dorsal recumbency hypoventilated more yet maintained higher Pao(2), suggesting parabronchial ventilatory or pulmonary blood flow distribution changes with position. The results refute the hypothesis that dorsal recumbency compromises ventilation and O(2) transport more than lateral recumbency in red-tailed hawks.

Impact of acute hypobaric hypoxia on blood flow distribution in brain

Acute hypobaric hypoxia is well known to alter brain circulation and to cause neuropsychological impairment. However, very few studies have examined the regional changes occurring in the brain during acute exposure to extreme hypoxic conditions. Regional cerebral blood flow (rCBF) response to hypoxia was investigated in six healthy subjects exposed to either normobaric normoxia or hypobaric hypoxia with ambient pressure/inspired oxygen pressure of 101/21 kPa and 50/11 kPa respectively. After 40 min at the desired pressure they were injected (99m)Tc-HMPAO and subsequently underwent single photon emission computed tomography. Regional cerebral blood flow distribution changes in the whole brain were assessed by Statistical Parametric Mapping, a well established voxel-based analysis method. Hypobaric hypoxia increased rCBF distribution in sensorymotor and prefrontal cortices and in central structures. PCO(2) correlated positively and SatO(2) negatively with rCBF in several temporal, parahippocampal, parietal and central structures. These findings underscore the specific sensitivity of the frontal lobe to acute hypobaric hypoxia and of limbic and central structures to blood gas changes emphasizing the involvement of these brain areas in acute hypoxia.

Evaluation of Influence of Acupuncture and Electro‐Acupuncture for Blood Perfusion of Stomach by Laser Doppler Blood Perfusion Imaging

The objective of this study is to observe effects of acupuncture and electro-acupuncture (EA) on blood perfusion in the stomach, and probe into the application of laser Doppler blood perfusion imaging technique in the study of the effect of acupuncture and moxibustion on the entrails. In the acupuncture group of 20 rats, acupuncture was given at “Zusanli” (ST 36) and in EA group of 18 rats, EA was applied at “Zusanli” (ST 36), with 18 rats without acupuncture used as control group. Changes of blood perfusion and microcirculation distribution in the stomach were investigated with laser Doppler blood perfusion imager (LDPI). The laser Doppler blood perfusion image could clearly display changes of blood flow distribution in the stomach before and after acupuncture. After acupuncture or EA was given at “Zusanli” (ST 36), the blood perfusion in the stomach increased significantly, the blood perfusion in the blood vessels and microcirculation of other parts significantly increased, and the maximum increase of the blood perfusion was found at 10 min after acupuncture or EA, with increases of 0.50 _ 0.11 (PU) and 0.66 _ 0.16 (PU), respectively, and the blood perfusion still kept at a higher degree within 10 min after ceasing of the acupuncture or EA. While the blood perfusion in the stomach in the rat of the control group tended to gradual decrease. It has been concluded that both acupuncture and EA can increase blood perfusion in the stomach, the EA having stronger action, and LDPI can display the regulative action of acupuncture on the blood vessel of the stomach by using an image.

Changes in hepatic blood flow during whole body hyperthermia

Purpose: Changes in blood flow distribution are important for heat dispersion and for supportive therapeutic strategies such as simultaneous whole body hyperthermia (WBH) and administration of chemotherapy. The aim of this clinical study was to determine changes in hepatic blood flow during WBH for the treatment of metastatic cancer.Materials and methods: This observational clinical study was part of a phase I/II feasibility study of WBH. WBH was induced using a radiant heat device. Hepatic blood flow was estimated using indocyanine green clearance measurements. The plasma disappearance rate of indocyanine green (PDR-ICG) was recorded in percent/min. We used an invasive thermo-dye-dilution technique to estimate hepatic blood flow, cardiac output, and volume status. Mean arterial blood pressure was also measured invasively. To determine the effects of hyperthermia the measurements were performed at defined temperature points.Results: In 10 of 22 treatments the PDR-ICG fell below normal values during hyperthermia, which represented a significant fall in hepatic blood flow. Cardiac output, volume status, and mean arterial blood pressure did not differ between patients whose liver blood flow was reduced and those whose liver blood flow remained unchanged.Conclusions: We observed distinct reductions in hepatic blood flow during WBH, which suggested a significant redistribution of blood flow away from the core during WBH. This was not mirrored by global circulatory parameters.

Comparison of exogenous adenosine and voluntary exercise on human skeletal muscle perfusion and perfusion heterogeneity

Adenosine is a widely used pharmacological agent to induce a "high-flow" control condition to study the mechanisms of exercise hyperemia, but it is not known how well an adenosine infusion depicts exercise-induced hyperemia, especially in terms of blood flow distribution at the capillary level in human muscle. Additionally, it remains to be determined what proportion of the adenosine-induced flow elevation is specifically directed to muscle only. In the present study, we measured thigh muscle capillary nutritive blood flow in nine healthy young men using PET at rest and during the femoral artery infusion of adenosine (1 mg min(-1) l thigh volume(-1)), which has previously been shown to induce a maximal whole thigh blood flow of approximately 8 l/min. This response was compared with the blood flow induced by moderate- to high-intensity one-leg dynamic knee extension exercise. Adenosine increased muscle blood flow on average to 40 +/- 7 ml x min(-1) x 100 g muscle(-1) with an aggregate value of 2.3 +/- 0.6 l/min for the whole thigh musculature. Adenosine also induced a substantial change in blood flow distribution within individuals. Muscle blood flow during the adenosine infusion was comparable with blood flow in moderate- to high-intensity exercise (36 +/- 9 ml x min(-1) x 100 g muscle(-1)), but flow heterogeneity was significantly higher during the adenosine infusion than during voluntary exercise. In conclusion, a substantial part of the flow increase in the whole limb blood flow induced by a high-dose adenosine infusion is conducted through the physiological non-nutritive shunt in muscle and/or also through tissues of the limb other than muscle. Additionally, an intra-arterial adenosine infusion does not mimic exercise hyperemia, especially in terms of muscle capillary flow heterogeneity, while the often-observed exercise-induced changes in capillary blood flow heterogeneity likely reflect true changes in nutritive flow linked to muscle fiber and vascular unit recruitment.

Rebuttal from Drs. Thijssen and Hopman

POINT-COUNTERPOINTRebuttal from Drs. Thijssen and HopmanPublished Online:01 Sep 2008https://doi.org/10.1152/japplphysiol.90570.2008cMoreSectionsPDF (33 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Reading through Drs. Green, Maiorana, and Cable's argument, we hit on another of Oscar Wilde's wisdoms: “The truth is rarely pure and never simple.”In a series of experiments, Dr. Green and colleagues demonstrated that typical changes in shear pattern, characterized by an increase in retrograde flow, are linked with endothelial NO release in the nonactive regions (4). Although it might be tempting to relate vascular adaptation in inactive regions to alterations in shear pattern, we believe that the truth is not that simple. In nonactive vascular beds during exercise, an enhanced release of vasoconstrictors is present, such as endothelin-1 (5), angiotensin II (7), and vasopressin (8). The actions of these local vasoconstrictors, combined with enhanced activity of the sympathetic nervous system (2), likely outweigh the beneficial effects of NO.The role for shear rate in exercise-induced vascular adaptations is well recognized, but shear rate is not the only factor involved; unfortunately the truth is never simple. Hypoxia, through release of growth factors such as VEGF, importantly contributes to exercise-induced vascular adaptations (6). Notably, hypoxia and VEGF also contribute to the release and homing of circulating bone marrow-derived endothelial progenitor cells (1). These progenitor cells predict the occurrence of cardiovascular events and death (9), possibly through their capability for endothelial repair, arteriogenesis, and angiogenesis. Appreciating a key role for hypoxia in exercise-induced vascular adaptations casts doubt on vascular adaptations in nonactive muscles during exercise where this essential physiological stimulus is absent (3).Interestingly, blood flow and related shear patterns vary markedly among different locations and sizes of arteries at rest and during exercise. The prominent retrograde component in the nonactive brachial artery blood flow pattern is hypothesized to result from an increased downstream vasoconstriction (4). In contrast, arteries supplying highly metabolic tissues (i.e., heart and legs) have marked vasodilation and will therefore not demonstrate this blood flow pattern. Therefore, one may question whether findings in the brachial artery during leg exercise can be extrapolated to the coronary vascular bed, since shear rate as well as other physiological stimuli will be markedly different.Taken together, the central question in this discussion is which stimuli are obligatory, either alone or in combination with others, to result in exercise-induced vascular adaptations in the active and nonactive regions. We enjoyed discussing this topic and hope we presented our arguments in line with Oscar Wilde's “One should always play fairly when one has the winning cards.”REFERENCES1 Asahara T, Murohara T, Sullivan A, Silver M, van der Zee R, Li T, Witzenbichler B, Schatteman G, Isner JM. Isolation of putative progenitor endothelial cells for angiogenesis. Science 275: 964–967, 1997.Crossref | PubMed | ISI | Google Scholar2 Buckwalter JB, Clifford PS. The paradox of sympathetic vasoconstriction in exercising skeletal muscle. Exerc Sport Sci Rev 29: 159–163, 2001.Crossref | PubMed | Google Scholar3 Calbet JA, Gonzalez-Alonso J, Helge JW, Sondergaard H, Munch-Andersen T, Boushel R, Saltin B. Cardiac output and leg and arm blood flow during incremental exercise to exhaustion on the cycle ergometer. J Appl Physiol 103: 969–978, 2007.Link | ISI | Google Scholar4 Green DJ, Bilsborough W, Naylor LH, Reed C, Wright J, O'Driscoll G, Walsh JH. Comparison of forearm blood flow responses to incremental handgrip and cycle ergometer exercise: relative contribution of nitric oxide. J Physiol 562: 617–628, 2005.Crossref | PubMed | ISI | Google Scholar5 Maeda S, Miyauchi T, Sakane M, Saito M, Maki S, Goto K, Matsuda M. Does endothelin-1 participate in the exercise-induced changes of blood flow distribution of muscles in humans? J Appl Physiol 82: 1107–1111, 1997.Link | ISI | Google Scholar6 Prior BM, Yang HT, Terjung RL. What makes vessels grow with exercise training? J Appl Physiol 97: 1119–1128, 2004.Link | ISI | Google Scholar7 Stebbins CL, Symons JD. Role of angiotensin II in hemodynamic responses to dynamic exercise in miniswine. J Appl Physiol 78: 185–190, 1995.Link | ISI | Google Scholar8 Stebbins CL, Symons JD. Vasopressin contributes to the cardiovascular response to dynamic exercise. Am J Physiol Heart Circ Physiol 264: H1701–H1707, 1993.Link | ISI | Google Scholar9 Werner N, Kosiol S, Schiegl T, Ahlers P, Walenta K, Link A, Bohm M, Nickenig G. Circulating endothelial progenitor cells and cardiovascular outcomes. New Engl J Med 353: 999–1007, 2005.Crossref | PubMed | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 105Issue 3September 2008Pages 1007-1007 Copyright & PermissionsCopyright © 2008 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.90570.2008cHistory Published online 1 September 2008 Published in print 1 September 2008 Metrics

1.1. How important are changes in blood flow distribution for thermoregulation in a reptile (Crocodylus porosus)?

1.1. How important are changes in blood flow distribution for thermoregulation in a reptile (Crocodylus porosus)?

Nitric Oxide and Fetal Organ Blood Flow During Normoxia and Hypoxemia in Endotoxin-Treated Fetal Sheep

To investigate the role of nitric oxide in the process of circulatory decentralization during fetal hypoxemia. Fifteen sheep with singleton pregnancies were chronically instrumented at 107 days of gestation (term is 147 days). Three days later, 8 of the fetuses received nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis. Fifteen minutes after L-NAME administration, all 15 fetuses received lipopolysaccharides (LPS) from a strain of Escherichia coli. The 7 fetuses that received LPS only were used as controls. Sixty minutes after LPS was administered, the maternal aorta was occluded for 2 minutes in all fetuses. Organ blood flow and physiological variables were measured at 75 minutes before the start of occlusion (ie, at the time of L-NAME administration to the experimental group), at 1 minute before the start of occlusion, and at 2, 4, and 30 minutes after the start of occlusion. Arterial pH was lower in the L-NAME group than in the control group at 1 minute before and 2 minutes after occlusion. Mean arterial pressure was higher in the L-NAME group than in the control group at 2 and 4 minutes after occlusion. Cardiac output fell in the L-NAME group and was lower than in the control group; the percentage of cardiac output to the cerebrum in the L-NAME group was 35% lower than that in the control group. Throughout the study, placental blood flow decreased by more than 80% in both groups and remained low. Blood flow to the fetal body decreased by 65% in the L-NAME group and was lower than in the control group. Blood flow to the carcass also decreased in the L-NAME group and was 36% of that in the control group. Inhibition of nitric oxide synthesis causes a general vasoconstriction in practically all organs and leads to a reduction in LPS-induced circulatory decentralization. The changes in blood flow distribution in endotoxin-treated fetal sheep seem to be mediated in part by nitric oxide.

Effects of Exercise Training on Cardiovascular Function and Structure in Elite Athletes

2282 BACKGROUND: Chronic exercise training is associated with “athletes' heart”, characterised by enhanced left ventricular (LV) mass and dimensions. It is not known whether these structural adaptations alter cardiac diastolic function or if there are simultaneous changes in structure and function of the vasculature. METHODS: High resolution vascular and cardiac ultrasonography was performed in 35 elite level athletes from WA Institute of Sport and 12 matched untrained controls. Measures were repeated following 3 month intensive training in the athletes. RESULTS AND DISCUSSION: Compared to controls, the athletes possessed higher SV, due to increased diastolic LV dimensions (P<0.01). Athletes also displayed increased LV thickness (P<0.02) and mass (291 ± 9.4 v 222 ± 18.1g;P<0.01), whilst ejection fraction (EF) did not differ between the groups. LV structural changes in the athletes were associated with a reduction in diastolic function (colour M-mode Propagation, deceleration time and atrial reversal; P<0.02), relative to controls, at baseline. The athletes displayed larger conduit and resistance vessel structure than controls (P<0.01), both at rest and during exercise. Following intensive training in the athletes, there was a further increase in cardiac structure, associated with enhanced systolic (P<0.01) and diastolic (P<0.05) function, conduit vessel enlargement (4.49 ± 0.1 v 4.91 ± 0.8mm;P<0.01) and changes in blood flow distribution during exercise (P<0.05). CONCLUSION: These data indicate for the first time in humans that exercise training is associated with changes in cardiac structure with corresponding improvements in cardiac function. In addition, these cardiac changes occur in concert with changes in peripheral vascular structure, and function during exercise.

Pathophysiology of cardiovascular damage in the early renal population.

In renal disease, mechanisms available to compensate for the reduced haemoglobin levels associated with anaemia include increased oxygen extraction from peripheral tissues and, primarily, increased blood flow and changes in blood flow distribution. Haemodynamic changes induced by anaemia include decreases in blood viscosity, peripheral vascular resistance and oxygen delivery, and an increase in sympathetic activity. The overall effect of anaemia is a chronic increase in cardiac output and cardiac work. Under normal conditions, the increased cardiac work and blood flow associated with anaemia results in adaptive left ventricular hypertrophy (LVH)/remodelling and adaptive arterial hypertrophy/remodelling. However, under uraemic conditions these changes lead to maladaptive hypertrophy and arteriosclerosis. In end-stage renal disease (ESRD) patients, increases in both left ventricular end-diastolic volume and mass are related to decreases in haemoglobin. Therefore, LVH progresses in parallel with changes in haemoglobin level and is associated with decreased survival in ESRD patients receiving renal replacement therapy. In conclusion, anaemia is a contributory factor to LVH in renal disease and cardiovascular damage starts at an early stage. Therefore, early intervention to treat anaemia in these patients can prevent or delay this damage.

EFFECTS OF RESPIRATORY MUSCLE LOADING AND UNLOADING ON TIME TO EXHAUSTION DURING CYCLE ERGOMETRY

1077 During maximal exercise with respiratory muscle unloading (RMU), leg blood flow and leg VO2 are increased (Harms et al. JAP 82(5), 1997), while pulmonary VO2 and cardiac output are reduced. In addition, although respiratory muscle loading (RML) had no effect on pulmonary VO2 or cardiac output, leg vascular resistance increased while leg blood flow and leg VO2 decreased. We sought to determine if these cardiovascular and blood flow distribution changes seen at max exercise were associated with performance. Six competitive male cyclists (VO2 max: 65±4 ml/kg/min) each completed 11 randomized trials on a cycle ergometer at 90% of their VO2 max workload. In each trial, respiratory muscle work was either decreased using a proportional assist ventilator (RMU), increased by adding an inspiratory load (RML), or unchanged (control). Time to exhaustion increased significantly (P<0.05) with RMU and decreased significantly with RML compared to control trials (mean time to exhaustion was-10% longer and -20% shorter with RMU and RML, respectively). Perceived exertion and dyspnea ratings were taken throughout each trial. Ratings during the first half of all trials were negatively correlated with time to exhaustion. We conclude that reducing the work of the respiratory muscles improves performance, possibly as a result of blood redistribution from respiratory to working leg muscles.

Changes in muscle blood flow distribution during hyperthermia

Blood flow is a critical parameter for obtaining satisfactory temperature distributions during clinical hyperthermia. This study examines the changes in blood flow distribution in normal porcine skeletal muscle before, during and after a period of regional microwave hyperthermia. The baseline blood flow distribution during general anaesthesia and after the insertion of the thermal probes was established independently in order to isolate the changes due to hyperthermia. General anaesthesia alone and thermocouple insertion during anesthesia had no significant effect on the muscle blood flow distribution. Regional microwave heating generated a non-uniform blood flow distribution which was a function of the tissue temperature distribution. Blood flow was greater in those tissues samples in which higher temperatures were recorded and less in those sampled further from the applicators peak SAR (Specific Absorption Rate). The increase in blood flow appears to be primarily a local phenomenon. Although muscle blood flow may be considered to be uniform prior to heating, this does not hold during hyperthermia treatment. Therefore, the non-uniform nature of the blood distribution during heating should be incorporated into any practical bioheat transfer model.

Adverse effects of hyperoxemia during cardiopulmonary bypass

Objective: Aiming at elucidating the effects on capillary blood flow and tissue oxygenation of hyperoxemia during cardiopulmonary bypass, we studied skeletal muscle surface oxygen tensions in 10 patients undergoing elective cardiac operations. Methods: In a prospective investigation each patient was exposed to normoxemia (arterial oxygen tension 75 to 115 mm Hg) and hyperoxemia (arterial oxygen tension > 185 mm Hg, inspired oxygen fraction = 1.00) during normal anesthetized conditions before and after cardiopulmonary bypass, as well as during normothermic and hypothermic continuous-flow bypass. In each state hemodynamic variables and arterial and mixed venous blood gas and acid base values were measured. From these data oxygen transport variables were calculated. Tissue oxygenation was studied with the use of a multiple-point polarographic oxygen microelectrode, known to provide measures of oxygen tensions at the capillary level. The oxygen distribution profile of such a sample is also indicative of capillary blood flow distribution changes. Results: In all patients and at each occasion of the investigation markedly low mean surface oxygen tensions in skeletal muscle were registered. When hyperoxemia was instituted, a significant decrease in these surface oxygen tensions together with an increase in distribution heterogeneity was seen during all stages. Contrary to prebypass, postbypass, and hypothermic bypass, where vascular resistance, oxygen delivery, and oxygen consumption remained similar during hyperoxemia and normoxemia, a significant ( p < 0.05) increase in vascular resistance together with a decline in oxygen consumption was seen during hyperoxemic normothermic (35° to 36°C) cardiopulmonary bypass. Conclusion: These findings show that the microcirculatory response to hyperoxemia, seen under other circumstances, persists during continuous-flow cardiopulmonary bypass, normothermic as well as hypothermic. If these adverse effects on tissue oxygenation by hyperoxemia can be further verified and shown to be valid for other organs than skeletal muscle, we would suggest that hyperoxemia should be avoided, especially during normothermic cardiopulmonary bypass. (J T HORAC C ARDIOVASC S URG 1996;112:812-9)

Changes in blood flow distribution and capillary function after deep hypothermia in rat

The present experiments were carried out in the rat to investigate the peripheral vascular function prior to the development of posthypothermic circulatory collapse. In the first study, mean arterial blood pressure, heart rate, cardiac output, regional blood flow, and plasma volume of hypothermic (4 h, 15-13 degrees C) and rewarmed rats were compared with normothermic controls. In response to hypothermia, arterial blood pressure, heart rate, and cardiac output declined markedly. After rewarming, arterial blood pressure and heart rate recovered fully, whereas cardiac output was only 33 +/- 7% of the control value (p < 0.025). Tissue blood flow was markedly depressed during hypothermia (p < 0.025), except for the abdominal skin. After rewarming, blood flow in skeletal muscle returned to within control levels, whereas blood flow in internal organs remained low (p < 0.025 vs. control). Posthypothermic plasma volume was 77 +/- 3% of control (p < 0.05). In the second study, the transcapillary colloid osmotic pressure gradient (COPp-COPi) was calculated following measurement of colloid osmotic pressure in plasma (COPp) and interstitium (COPi) in prehypothermic, hypothermic, and posthypothermic rats. The posthypothermic value of COPp-COPi was 76 +/- 4% of the prehypothermic value (p < 0.05). In conclusion this study demonstrates that the reduced cardiac output in rewarmed rats is associated with an altered regional blood flow distribution compared with that of normal rats. Capillary integrity also seemed perturbed. Thus, changes in both control and function of the peripheral vasculature are important mechanisms in the development of a posthypothermic circulatory collapse.