An adaptation of central and peripheral ...

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using a combination of two methods, iontophoresis and Laser Doppler Perfusion Imaging. (LDPI) (PeriScan, PIM II Laser Doppler, Perimed AB, Sweden) in both ...
The proceeding of the XXVIIth International Symposium of the European Group of Paediatric Work Physiology 2011. Routledge, New York, 233-236.

CHAPTER 34

An adaptation of central and peripheral cardiovascular responses to exercise in children as a determinant of microvascular function M. N. Jawis1, A.R. Middlebrooke2, A.V. Rowland2, N. Armstrong2. 1

Sports Science Unit, School of Medical Sciences, Universiti Sains Malaysia, Malaysia. 2 Children’s Health and Exercise Research Centre (CHERC), School of Sport and Health Sciences, University of Exeter, UK. 1.1 INTRODUCTION

The vascular endothelium has an influence on the progression of atherosclerosis via anticoagulant, anti - inflammatory, and vascular remodeling properties (Ross 1999). Studies have indicated that subjects with cardiovascular disease or risk factors for cardiovascular disease may exhibit impaired endothelium-dependent vasomotor responses (Al Suwaidi et al. 2001) and attenuated vascular nitric oxide (NO) activity. The relevance of endothelial dysfunction has been highlighted by many studies indicating that endothelial dysfunction is an independent predictor of cardiac events (Vita and Keaney 2002). Regular physical exercise is believed to improve endothelium-dependent vasodilation in a number of populations (Walsh et al. 2003) including those of heart failure (Maiorana et al. 2000), type 2 diabetes (Middlebrooke et al. 2005) and hypertension (Higashi et al. 1999). The cardiovascular system plays a major role in the body’s ability to respond to increased demands of physical activity and exercise. Cardiac variables may be important determinants of microvascular function in the adult population. Studies have demonstrated that the level of aerobic fitness might relate to the maximal performance of

The proceeding of the XXVIIth International Symposium of the European Group of Paediatric Work Physiology 2011. Routledge, New York, 233-236.

the skin microcirculation (Colberg et al. 2005; Middlebrooke et al. 2005). To date, there is no published data on the adaptation of both central and peripheral cardiovascular responses to exercise in children as a determinant of microvascular function or whether aerobic fitness is reflected in the skin microvascular function. Therefore, the aim of this study was to investigate the adaptations of the cardiovascular system in relation to skin blood flow of the microvascular function. 1.2 METHODS 1.2.1

Experimental Design

Sixteen boys, aged 9 - 10 years, were recruited from a local school at Exeter. No participant had a personal history of any cardiovascular disease risk factors such as hypertension, diabetes, high blood pressure and atherosclerosis. Each participant was requested to attend the testing on two occasions. Skin blood flow responses were tested using a combination of two methods, iontophoresis and Laser Doppler Perfusion Imaging (LDPI) (PeriScan, PIM II Laser Doppler, Perimed AB, Sweden) in both occasions. On the second visit, the children completed an incremental cycle ergometer protocol for the determination of maximum peak VO2 followed by 30 - minutes post-maximal exercise microvascular function test. All exercise testing took place in the morning at approximately the same time for each child.

The proceeding of the XXVIIth International Symposium of the European Group of Paediatric Work Physiology 2011. Routledge, New York, 233-236.

Figure 1 The positioning of the full complement of electrodes placed onto the subject 1.2.2

Determination of cardiac output (Q), stroke volume (SV) and peak oxygen uptake (VO2 peak)

Cardiac output (Q) was attained using Physioflow, (Manatec Biomedical, France) a thoracic electrical bioimpedance method (Figure 1). Physioflow is a non-invasive Q measurement system that can be used on subjects at rest and during exercise. Changes in thoracic impedance during cardiac ejection were used to calculate stroke volume (SV). A high frequency current was used to eliminate the risk of interference with the heart and brain bioelectrical activity. Maximal exercise testing on a cycle ergometer was performed by measuring the peak oxygen uptake (VO2 peak) achieved during a graded maximal exercise test to exhaustion. The test was performed on an electronically braked cycle ergometer (Lode, Gronigen, Netherland). 1.2.3

Determination of microvascular function of iontophoresis and LDPI

Following the termination of the maximal exercise, the participant was taken immediately into the microvascular laboratory for post – maximal microvascular function test. The participant was required to rest down in supine position for about 30 minutes to get acclimatized to the temperature-controlled room (21.5 ± 0.5º C) to ensure the blood pressure and heart rate return to resting values. Skin microvascular perfusion was measured at the drug delivery site using LDPI (PeriScan, PIM II Laser Doppler, Perimed AB, Sweden). LDPI was used to map skin perfusion. A 1-mW Helium Neon laser beam (wavelength 633 nm) sequentially scans an area of tissue. 1.2.4

Statistical analysis

The paired Student’s t-test was used to compare HR, peak VO2, Q, SV and skin blood flow of the microvascular function before and after acute maximal exercise. A P-value of ≤ 0.05 was considered as statistically significant. Data were expressed as mean ± (SD).

The proceeding of the XXVIIth International Symposium of the European Group of Paediatric Work Physiology 2011. Routledge, New York, 233-236.

1.3 RESULTS There was a significant difference on the peak sodium nitroprusside (SNP) response between pre and post maximal exercise (p = 0.04). Similarly, the peak percentage change of SNP response was greater at post maximal exercise relative to baseline (p = 0.03). Heart rate increased significantly with exercise intensity from rest to maximal (74 ± 7 vs 194 ± 18 bpm). On the other hand, SV rose significantly at the onset of exercise (45.6 ± 6.9 vs 55.5 ±7.6 mL). Peak SNP was significantly correlated with maximum Q (p = 0.02) at post maximal exercise.

1.4. CONCLUSION The main findings from the current study are: 1) acute exercise is reflected in the skin microvascular function; 2) the iontophoresis of acetylcholine (ACh) could not last longer when compared to SNP at post peak VO2 test; and 3) when Q and SV were related to the ACh, microvascular function, no significant difference was obtained either at rest or post maximal exercise. Overall, the iontophoresis of ACh and SNP caused vasodilation of the microvascular blood vessels and smooth muscle cells at the forearm location at both pre and post maximal exercise. However, the perfusion of SNP causes greater vasodilation of the blood vessel in the system, than the perfusion of ACh. An explanation for this finding may relate to the importance of the endothelium, which the ACh binds to endothelial cells in producing nitric oxide (Vallance and Collier 1994). This mechanism delays the relaxation of smooth muscle cell, resulting in the lethargic behaviour of the vasodilation of blood vessels (Higashi and Yoshizumi 2004). 1.5 REFERENCES Al Suwaidi, J., S. T. Higano, et al. 2001. Association between obesity and coronary atherosclerosis and vascular remodeling. The American Journal of Cardiology. 88(11): 1300-3. Colberg, S. R., H. K. Parson, et al. 2005. Change in cutaneous perfusion following 10 weeks of aerobic training in Type 2 diabetes. Journal of Diabetes Complications 19(5): 276-83. Higashi, Y., S. Sasaki, et al. 1999. Regular aerobic exercise augments endothelium-dependent vascular relaxation in normotensive as well as hypertensive subjects: role of endothelium-derived nitric oxide. Circulation 100(11): 1194-202.

The proceeding of the XXVIIth International Symposium of the European Group of Paediatric Work Physiology 2011. Routledge, New York, 233-236.

Higashi, Y. and M. Yoshizumi 2004. Exercise and endothelial function: role of endotheliumderived nitric oxide and oxidative stress in healthy subjects and hypertensive patients. Journal of Pharmacology Theraphy 102(1): 87-96. Maiorana, A., G. O'Driscoll, et al. 2000. Effect of aerobic and resistance exercise training on vascular function in heart failure. American Journal of Physiology. Heart and circulatory physiology. 279(4): H1999-2005. Middlebrooke, A. R., N. Armstrong, et al. 2005. Does aerobic fitness influence microvascular function in healthy adults at risk of developing Type 2 diabetes? Diabetic Medicine 22(4): 483-9. Ross, R. 1999. Atherosclerosis is an inflammatory disease. American Heart Journal 138(5 Pt 2): S419-20. Vallance, P. and J. Collier 1994. Biology and clinical relevance of nitric oxide. BMJ 309(6952): 453-7. Vita, J. A. and J. F. Keaney, Jr. 2002. Endothelial function: a barometer for cardiovascular risk? Circulation 106(6): 640-2. Walsh, J. H., W. Bilsborough, et al. 2003. Exercise training improves conduit vessel function in patients with coronary artery disease. Journal of Applied Physiology. 95(1): 20-5.