Author + information
- Received June 15, 2004
- Revision received September 13, 2004
- Accepted September 14, 2004
- Published online December 21, 2004.
- Jason M.R. Gill, PhD*,* (, )
- Ali Al-Mamari, MD†,
- William R. Ferrell, MD, PhD†,
- Stephen J. Cleland, MD, PhD‡,
- Chris J. Packard, DSc*,
- Naveed Sattar, MD, PhD*,
- John R. Petrie, MD, PhD† and
- Muriel J. Caslake, PhD*
- ↵*Reprint requests and correspondence:
Dr. Jason M. R. Gill, Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, West Medical Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
Objectives We investigated whether a session of prior exercise could ameliorate postprandial endothelial dysfunction.
Background Endothelial function is impaired after fat ingestion, and this may be related to rises in triglyceride concentrations. Exercise reduces postprandial triglyceride concentrations.
Methods Ten lean (waist <90 cm) and 10 centrally obese (waist >100 cm) middle-aged men each underwent two oral fat tolerance tests (blood taken fasting and for 8 h after a high-fat meal containing 80 g fat and 70 g carbohydrate). On the afternoon before one test, subjects performed a 90-min treadmill walk (exercise); no exercise was performed before the control test. Endothelium-dependent and -independent microvascular function was assessed using laser Doppler imaging in the fasted state and at two hourly intervals during the 8-h postprandial period.
Results Exercise reduced both fasting and postprandial triglyceride concentrations by 25% in both the lean and centrally obese groups (p < 0.0005). For all subjects taken together, exercise improved fasting endothelium-dependent function by 25% (p < 0.05), and, although there was a significant postprandial decrease in both endothelium-dependent and -independent function in both the control and exercise trials (p < 0.01), postprandial endothelium-dependent and -independent function were 15% and 20% higher, respectively, in the exercise trial than the control trial (both p < 0.05).
Conclusions A session of prior exercise improves fasting and postprandial vascular function in middle-aged men. This may be one mechanism by which exercise influences cardiovascular risk.
Free-living humans spend the majority of their lives in the postprandial state, and the changes to metabolism seen during the hours after meal ingestion are likely to play an important role in the atherosclerotic disease process. It has been postulated that postprandial lipoproteins and their remnants directly infiltrate the arterial wall and accumulate in atheromatous plaques (1). Furthermore, high concentrations of postprandial lipoproteins facilitate the exchange of neutral lipids between triglyceride (TG)-rich and cholesterol-rich lipoproteins, promoting the atherogenic lipoprotein phenotype of small, dense, low-density lipoprotein (LDL) and low high-density lipoprotein (HDL) (1).
More recent study has focused on nonlipid disturbances occurring in the postprandial state. It is now evident that systemic inflammation is increased (2,3) and that endothelial function is impaired (4,5) postprandially, with some studies reporting that the postprandial decrement in endothelial function is proportional to the postprandial TG increase (4,5). As endothelial dysfunction and inflammation are central to atherogenic progression (6), it is likely that these transient postprandial changes, repeated on a daily basis, have implications for long-term risk of vascular disease. There is now a large body of evidence indicating that a single session of moderate exercise can reduce subsequent postprandial lipemia by ∼20% to 25% (7). Thus, given the reported relationship between postprandial lipemia and endothelial dysfunction (4,5), we hypothesized that exercise of this nature could attenuate the postprandial decrement in endothelial function.
We chose to study centrally obese middle-aged men, a typical population at which exercise for health guidelines are targeted. We also included a comparative group of lean men. These two groups differ in insulin sensitivity (8) and exhibit marked differences in insulin-regulated postprandial glucose and lipid metabolism (9). A secondary aim of this study was to investigate whether the magnitude of exercise-induced changes to postprandial metabolism would differ between these two subject groups with differing metabolic profiles.
Ten lean men (waist circumference <90 cm) and 10 age-matched centrally obese (waist circumference >100 cm) men participated in this study. Their physical characteristics are shown in Table 1.All were apparently healthy normoglycemic nonsmokers who displayed no symptoms of coronary artery disease during a clinical exercise stress test. None was taking any drugs thought to affect lipid or carbohydrate metabolism or vascular function. The study was conducted with the approval of North Glasgow University Hospitals National Health Service Trust Ethics Committee, and subjects gave written informed consent before participation.
Subjects participated in two oral fat tolerance tests in a randomized, balanced design with an interval of 7 to 14 days and different preconditions. In one trial, subjects walked on a treadmill for 90 min at an intensity of ∼50% of maximal oxygen uptake (VO2max) (determined from a preliminary submaximal incremental treadmill test ) on the day before the oral fat tolerance test (exercise trial). In the other trial, subjects performed no exercise on the day preceding the oral fat tolerance test (control trial).
Subjects weighed and recorded their dietary intake and abstained from alcohol for the two days before the first oral fat tolerance test and replicated this before the second fat tolerance test. In addition, subjects were instructed to perform no exercise, other than the treadmill walk in the exercise trial, during the three days preceding each oral fat tolerance test.
The walk in the exercise trial was performed on the afternoon before the oral fat tolerance test and completed ∼16 to 18 h before ingestion of the test meal. Oxygen uptake and carbon dioxide production were measured using an online gas analysis system (CPX/D BreezeEx v3.0, MedGraphics Cardiorespiratory Diagnostic Systems, St. Paul, Minnesota), heart rate was measured by short-range telemetry (Polar Electroky, Kempele, Finland), and ratings of perceived exertion (11) were obtained at 15-min intervals during the walk.
Oral fat tolerance tests
On the morning of the oral fat tolerance tests, subjects reported to the laboratory after a 12-h fast. Forearm microvascular function was assessed using laser Doppler imaging with iontophoresis (see the following text for description). A venous cannula was then inserted, and, after an interval of 10 min, a baseline blood sample was withdrawn. Subjects then consumed a high-fat test meal composed of whipping cream, fruit, cereal, nuts, and chocolate, which provided 80 g fat, 70 g carbohydrate, 12 g protein, and 4.3 MJ energy. Further blood samples were obtained 20, 40, 60, 90, 120, 240, 360, and 480 min postprandially. Microvascular function was assessed again after the 120-, 240-, 360-, and 480-min blood samples. Subjects rested throughout this day and consumed only water. This was provided ad libitum during the first fat tolerance test, and the volume and pattern of water intake was replicated during the second test.
Assessment of microvascular function
Peripheral microvascular function was assessed using a validated technique to quantify vasodilator responses to iontophoresis of 1% acetylcholine (ACh) (endothelium-dependent) and 1% sodium nitroprusside (SNP) (endothelium-independent), which has been described in detail elsewhere (12,13). Subjects lay in a semirecumbent position in a temperature-controlled room with their noncannulated forearm supported by an armrest. Iontophoresis chambers were attached to the volar aspect of the forearm with ACh and SNP introduced into the anodal and cathodal chambers, respectively. Drug iontophoresis was by a constant-current controller (MIC-1ev; Moor Instruments Ltd., Axminster, United Kingdom), incremented from 5 μA to 20 μA (8 mC total charge). Noninvasive measurement of skin perfusion was by a laser Doppler imager (Moor Instruments Ltd.). Twenty repetitive scans were performed, including a control scan (no current). For each scan, median flux values within each chamber were determined, corrected for variation in skin resistance (12), and the area under the corrected flux versus time curve defined the overall microvascular response. The within-day and between-day coefficients of variation for this method are both <10% (12).
Blood samples were collected into potassium EDTA tubes and lithium heparin tubes and placed on ice. Plasma was separated within 15 min of collection. Plasma for lipoprotein analyses was stored at 4°C; the remainder was divided into aliquots and stored at −70°C. In the fasted state and 8 h postprandially, a small sample of whole blood was retained for the determination of white blood cell count.
Plasma very low-density lipoprotein (VLDL) cholesterol, LDL cholesterol, and HDL cholesterol concentrations were determined in the fasted state according to the Lipid Research Clinics Program Manual of Laboratory Operations (14). Triglyceride, glucose, and non-esterified fatty acid (NEFA) concentrations were determined by enzymatic colorimetric methods using commercially available kits (Roche Diagnostics GmbH, Mannheim, Germany, and Wako Chemicals Inc., Richmond, Virginia). Insulin was determined using a commercially available enzyme-linked immunoassay (ELISA) with <0.01% cross-reactivity with proinsulin (Mercodia AB, Uppsala, Sweden). Interleukin (IL)-6 concentrations were determined using a commercially available high-sensitivity ELISA (R&D Systems Inc., Oxon, United Kingdom). White blood cell count was measured in a Coulter counter in the routine hospital hematology laboratory. Other than lipoprotein analyses and white blood cell count, which were performed on fresh samples, all samples for each subject were analyzed in the same run. Coefficients of variation were <5% for all non-ELISA assays and <10% for all ELISA assays.
Calculations and statistics
Energy expenditure during the 90-min treadmill walk was calculated using indirect calorimetry assuming no protein oxidation (15).
Where appropriate, the time-averaged postprandial concentration—defined as the trapezium rule-derived area under the plasma concentration versus time curve, divided by the duration of postprandial observation period (8 h)—was used as a summary measure of the postprandial responses. The postprandial rise in concentration was defined as the time-averaged postprandial concentration minus the fasting concentration (i.e., the incremental area under the concentration vs. time curve, divided by 8 h).
Statistical analyses were performed using Statistica (version 6.0, StatSoft Inc., Tulsa, Oklahoma) and Minitab (version 13.1, Minitab Inc., State College, Pennsylvania). Data sets were tested for normality using Anderson-Darling normality tests, and, where necessary, data were logarithmically transformed before statistical analysis. Comparisons of fasting values and summary postprandial responses were made using two-way analysis of variance (group × trial) with repeated measures on the trial (exercise or control) factor. Where it was necessary to determine changes over the postprandial period, three-way analysis of variance (group × trial × time) were performed with repeated measures on the trial and time factors. Post-hoc Fisher least significant difference tests were used to identify exactly where any differences lay. A priori power calculations, based on our data for intrasubject reproducibility of ACh vasodilator responses (within-day and between-day coefficients of variation both <10% ) and postprandial TG responses (between-day coefficient of variation 10.1%, unpublished data) indicated that 10 subjects per group would enable detection of exercise-induced changes of ∼10% in either response. Significance was accepted at the p < 0.05 level, and data are presented as mean values ± SEM unless otherwise stated.
For the 90-min treadmill walk, the lean men walked at a speed of 6.0 ± 0.2 km·h−1up a 4.3 ± 0.6% gradient, and the centrally obese men walked at 5.8 ± 0.1 km·h−1up a 3.6 ± 0.5% gradient. Mean VO2and heart rate were 22.1 ± 0.9 ml·kg−1(50.6 ± 0.9% VO2max) and 119 ± 3 beat·min−1for the lean men and 20.5 ± 0.7 ml·kg−1(51.1 ± 1.1% VO2max) and 126 ± 3 beat·min−1for the centrally obese men. The lean and centrally obese subjects rated the intensity of the walk as 11.8 ± 0.5 (between “fairly light” and “somewhat hard”) and 12.9 ± 0.5 (“somewhat hard”), respectively, on the Borg scale of 6 to 20 (11). There were no significant differences between the lean and centrally obese men in any of the previously mentioned factors. However, as a consequence of their greater body mass, the overall gross energy expenditure of the walk was higher in the centrally obese men (3.7 ± 0.1 MJ) than the lean men (2.9 ± 0.2 MJ) (p = 0.003).
Plasma concentrations in the fasted state
Plasma concentrations in the fasted state are shown in Table 2.Concentrations of TG, glucose, insulin, and IL-6 were all significantly higher and the concentration of HDL cholesterol was significantly lower in the centrally obese than the lean men (all p < 0.05). Exercise reduced fasting TG concentrations to the same degree in the lean and centrally obese men (25% reduction for both, p = 0.001). Concentrations of NEFA were significantly higher in the exercise trial than the control trial.
Metabolic responses to the test meal
Figure 1shows the metabolic responses to the test meal with summary measures of these responses shown in Table 3.As expected, the centrally obese men exhibited greater postprandial metabolic perturbations than the lean men with significantly higher postprandial plasma TG, insulin, glucose and NEFA responses. Exercise significantly reduced postprandial TG concentrations (and postprandial rises in TG concentration) by ∼25% in both the lean and centrally obese groups (p < 0.0005 for both). Analysis of variance main effects indicated that the postprandial insulin response was significantly reduced by exercise (p = 0.037), but post-hoc analysis revealed that this was only evident in the centrally obese group (11% reduction, p = 0.015), with no significant reduction occurring in the lean subjects (3% reduction, p = 0.63). Postprandial NEFA (p = 0.006) concentrations were both significantly higher in the exercise trial than the control trial, but postprandial glucose concentrations did not differ significantly between the two trials.
Microvascular responses to ACh and SNP in the fasted and postprandial states
Microvascular responses to ACh and SNP did not differ significantly between the lean and centrally obese groups. Data from the two groups were, therefore, combined for further statistical analyses. These combined responses are shown in Figure 2.The fasting ACh response was 25% higher in the exercise trial than the control trial (p = 0.02). In both trials, the ACh responses at 2, 4, 6, and 8 h postprandially were significantly lower than the responses in the fasted state (p < 0.01), but the average ACh response over the postprandial observation period (mean of 2-, 4-, 6-, and 8-h responses) was 15% higher in the exercise trial than the control trial (10,745 ± 986 flux U vs. 9,349 ± 857 flux U, p = 0.048). In contrast with the ACh responses, SNP responses did not differ significantly between the control and exercise trials in the fasted state (p = 0.98). In the control trial, SNP responses at 2, 4, 6, and 8 h postprandially were significantly lower than the responses in the fasted state (p < 0.01), and, in the exercise SNP responses, 4, 6, and 8 h postprandially were significantly lower than fasting values (p < 0.05). However, the average SNP response over the postprandial observation period was 20% higher in the exercise trial than the control trial (11,111 ± 847 flux U vs. 9,230 ± 790 flux U, p = 0.036).
Inflammatory responses to the test meal
The inflammatory responses to the test meal are shown in Figure 3.In all trials, IL-6 concentrations rose significantly after ingestion of the test meal and were significantly higher than concentrations in the fasted state at the late postprandial time points. The time-averaged postprandial IL-6 concentration did not differ significantly between control and exercise trials or between the lean and centrally obese groups, and there was no significant group × trial interaction. White blood cell counts were significantly higher at 8 h postprandially than in the fasted state in both the control and exercise trials for both the lean and centrally obese subject groups (all p < 0.01). There were no significant differences between the control and exercise trials or between the lean and centrally obese subjects, nor were there any significant interactions.
The major novel finding in this study is that a single session of moderate exercise significantly improved small vessel vasodilator function in both the fasted and postprandial states in a group of middle-aged men. Prior exercise increased the ACh response in the fasted state by 25%, with no change in the SNP response, indicating that this improvement in vascular function was endothelium-dependent. This is likely to be clinically important, as endothelial function measures predict future cardiovascular events and do so independently of conventional risk factors (6). Moreover, although it has been demonstrated that endothelial function can be improved after a number of weeks of exercise training (16), we believe that this is the first study to demonstrate a sustained improvement in endothelial function which was evident on the day after a single exercise session. Thus, in common with changes in TG metabolism (7) and insulin sensitivity (17), exercise training-induced improvements to endothelial function may, at least in part, be a consequence of relatively short-term changes in response to recent exercise.
We assessed microvascular function using the relatively novel method of laser Doppler imaging with iontophoresis. This noninvasive in vivo method, which assesses the cutaneous microcirculation, provides a robust surrogate marker of vascular function in other vascular beds. Reduced cutaneous responsiveness to iontophoresis of ACh has been observed in hypercholesterolemia (18) and diabetes (19), and in these conditions there is a parallel reduction of the ACh response in the forearm circulation (predominantly a skeletal muscle vascular bed) assessed by venous occlusion plethysmography (20–22). The iontophoresis method has also revealed an inverse relationship between blood pressure and the ACh response (23), and ACh-induced vasodilation of both forearm skin and muscle is reduced in essential hypertension (24). Moreover, attenuated cutaneous responses to ACh iontophoresis of heart transplant patients (25) are paralleled by reduced responsiveness of coronary blood vessels to ACh in this group (26). Thus, many conditions affecting the cardiovascular system appear to result in global endothelial dysfunction, affecting cutaneous vessels as well as vascular beds more directly involved in the pathogenesis of vascular disease.
We found no significant correlations between the exercise-induced change in fasting TG, insulin, glucose, NEFA, IL-6, or white blood cell count and the exercise-induced change in the fasting ACh response (data not shown). This is in accord with a recent report that found that changes to endothelial function elicited by longer-term exercise programs were not significantly related to the exercise-induced changes in a number of cardiovascular risk factors (16), suggesting that exercise may improve endothelial function via other mechanisms. The improvement in the fasting ACh response after exercise may be due to increased blood flow augmenting shear stress on the endothelium, thereby stimulating nitric oxide release. Indeed, recent evidence suggests that this is evident in vascular beds which are not actively exercising as well as in the exercising tissues (27). Furthermore, the effects of moderate exercise on blood flow persist for a number of hours after exercise cessation; it has been reported that leg blood flow is almost 40% higher during the day after a 2-h moderate-intensity exercise session than after a day with no exercise (28) and that subcutaneous adipose tissue blood flow is elevated for a number of hours after exercise (29). This prolonged increase in blood flow during recovery from exercise may enable augmented endothelial function to persist for a number of hours after exercise, in line with the present findings.
In both the control and the exercise trials, the ACh response declined significantly postprandially, in agreement with other reports (4,5). However, postprandial ACh responses were significantly higher in the exercise trial than the control trial, indicating that prior exercise acted to oppose the postprandial decrement. Interestingly, there was a postprandial decline in the SNP response, which tracked the decrease in the ACh response, indicating that the postprandial decrement in microvascular function cannot be attributed with certainty to endothelial as opposed to smooth muscle vascular structures. However, as postprandial SNP responses were higher in the exercise than the control trial, it seems likely that prior exercise also ameliorated any postprandial decline in vascular smooth muscle vasoactivity. These findings mirror the effects of fenofibrate on vasodilator function in hypertriglyceridemic patients (30), in which fibrate treatment reduced TG concentrations and improved resistance vessel vasodilator responses to both ACh and SNP to a similar degree. Thus, it is possible that the TG-mediated impairment of resistance vascular function may, to some extent, be mediated by endothelium-independent mechanisms, and this may differ somewhat from the effects of TG on conduit vessel vascular function, where it appears that that the postprandial decrement in vasodilator response is mediated by endothelium-dependent mechanisms (4,5). Certainly, in vitro studies have demonstrated that remnants and fatty acids derived from the hydrolysis of TG-rich lipoproteins are cytotoxic to vascular smooth muscle cells (31,32). Moreover, cardiovascular risk factors such as hypercholesterolemia (33), hypertension (34), and type 2 diabetes (20) have been linked to the perturbance of both endothelium-dependent and -independent vasodilation (however measured), and their treatments often improve both responses (22,33).
Because ingestion of high-fat meals blunts vasodilator function (4,5), but ingestion of a low-fat meal does not (4), it seems likely that the postprandial decrement in vascular function is a consequence of fat ingestion per se. However, as yet, the mechanisms responsible have not been fully elucidated. Some studies have reported that the postprandial decrement in vasodilator function correlates with the postprandial rise in TG (4,5), but this is not a universal finding (35), and, in the present study, we found no significant relationships between postprandial TG concentrations or rises in concentration and postprandial ACh responses in either the control or exercise trial (data not shown). We similarly found no significant relationships between exercise-induced changes in postprandial TG concentrations or rises in concentration and exercise-induced changes in postprandial ACh responses (data not shown), suggesting that differences in TG may not explain the changes in ACh response observed in the present study. Alternatively, postprandial increases in systemic inflammation may contribute to endothelial dysfunction (3); in the present study, there was clear evidence of a postprandial increase in inflammation with rises in IL-6 concentrations and white blood cell counts. However, we observed similar postprandial inflammatory responses in the control and exercise trials, suggesting that either differences in these inflammatory markers were not a major mediator in the exercise-induced improvements to postprandial vasodilator responses or that the study had insufficient power to detect a clear effect of exercise on these inflammatory responses. A further possibility is that prior exercise influenced endothelial function through effects on postprandial oxidative stress or antioxidant mechanisms. It has been reported that co-ingestion of antioxidant vitamins with fat abolishes the postprandial decrement in endothelial function (36) and moderate exercise may act through a similar mechanism, as it has been demonstrated that moderate exercise training increases plasma antioxidant defenses (37). Whether this occurs in response to a single exercise session warrants further investigation. Alternatively, it is possible that the higher postprandial ACh responses seen after exercise were a direct consequence of the higher ACh baseline response, rather than a specific effect of exercise on postprandial metabolism.
We did not observe significant differences in microvascular function between the lean and the centrally obese subjects in this study; however, ACh responses were, overall, ∼10% lower in the centrally obese than the lean subjects. This difference between groups was substantially smaller than that observed for the postprandial TG response (control trial response 79% higher in the centrally obese subjects, p < 0.01) (Table 3) or the postprandial insulin response (106% higher, p < 0.01) and suggests that the effects of obesity on microvascular function may be more subtle than their effects on TG metabolism and insulin sensitivity. The present study, with 10 subjects in each group, had insufficient power to determine whether this small difference in microvascular function between the groups was real, and further investigation in a larger study is warranted to address this issue.
The results from this study demonstrate that a session of prior moderate exercise effectively reduces postprandial TG concentrations in both lean and centrally obese middle-aged men. The percentage reductions in TG were remarkably similar in the two groups—∼25% for each—but the centrally obese subjects, by virtue of their higher TG concentrations, experienced a greater absolute TG decrease. The percentage TG reductions observed are comparable with those found in other reports (7). However, these earlier reports have generally studied subjects with lower TG concentrations than those of the centrally obese subjects in the present study, and, thus, our findings extend the evidence base, demonstrating the efficacy of moderate exercise in reducing postprandial lipemia in a range of study populations. Importantly, despite many of the men being unused to walking long distances, all managed to complete the 90-min treadmill walk without difficulty, and none complained of undue tiredness or muscle soreness, indicating that, although this goes beyond the current “30 min per day” exercise recommendation (38), walks of this intensity and duration are not beyond the capability of inactive centrally obese middle-aged men.
In conclusion, this study has demonstrated that a single session of moderate-intensity exercise, which was well tolerated by the study participants, improved fasting and postprandial resistance vessel vasodilator function in a group of middle-aged men. Furthermore, prior exercise reduced postprandial lipemia to the same degree in lean and centrally obese men and reduced postprandial insulin concentrations in the centrally obese men. These findings indicate that moderate exercise is effective in attenuating many of the adverse metabolic and vascular changes occurring during the hours after ingestion of dietary fat and, thus, contribute to our understanding of the mechanisms by which exercise can reduce cardiovascular risk.
The authors would like to thank Ms. Pamela Doherty, Mr. Stephen Day, and Mr. Boyd Sigerson for technical assistance with sample processing and analysis.
Supported by a grant from the British Heart Foundation, London, United Kingdom (PG/2001018).
- Abbreviations and acronyms
- enzyme-linked immunoassay
- high-density lipoprotein
- low-density lipoprotein
- non-esterified fatty acid
- sodium nitroprusside
- very low-density lipoprotein
- maximal oxygen uptake
- Received June 15, 2004.
- Revision received September 13, 2004.
- Accepted September 14, 2004.
- American College of Cardiology Foundation
- Nappo F.,
- Esposito K.,
- Cioffi M.,
- et al.
- Van Oostrom A.J.,
- Sijmonsma T.P.,
- Verseyden C.,
- et al.
- Gaenzer H.,
- Sturm W.,
- Neumayr G.,
- et al.
- Bonetti P.O.,
- Lerman L.O.,
- Lerman A.
- Abbasi F.,
- Brown B.W. Jr.,
- Lamendola C.,
- McLaughlin T.,
- Reaven G.M.
- Potts J.L.,
- Coppack S.W.,
- Fisher R.M.,
- Humphreys S.M.,
- Gibbons G.F.,
- Frayn K.N.
- American College of Sports Medicine
- ↵Lipid Research Clinics Program Manual of Laboratory Operations. DHEW Publication No. (NIM) 75, 1975.
- Frayn K.N.,
- Macdonald I.A.
- Green D.J.,
- Walsh J.H.,
- Maiorana A.,
- Best M.J.,
- Taylor R.R.,
- O'Driscoll J.G.
- Khan F.,
- Litchfield S.J.,
- Stonebridge P.A.,
- Belch J.J.
- Vehkavaara S.,
- Yki-Jarvinen H.
- Serne E.H.,
- Stehouwer C.D.,
- ter Maaten J.C.,
- et al.
- Treasure C.B.,
- Vita J.A.,
- Ganz P.,
- et al.
- Green D.,
- Cheetham C.,
- Mavaddat L.,
- et al.
- Malkova D.,
- Evans R.D.,
- Frayn K.N.,
- Humphreys S.M.,
- Jones P.R.,
- Hardman A.E.
- Capell W.H.,
- DeSouza C.A.,
- Poirier P.,
- et al.
- Goode G.K.,
- Heagerty A.M.