Cardiovascular (CV) disease is one of the leading causes of mortality and disability and remains a major concern despite improved clinical outcomes with evidence-based treatment.^{1 , 2} Platelets are essential for primary hemostasis and repair of the endothelium, but they also play a key role in the pathogenesis of atherosclerosis and arterial thrombosis.¹ Platelet activation is associated with CV events.³ Monitoring the function of platelets may help to evaluate the prognosis of patients with coronary artery disease (CAD).⁴

However, because platelet function testing is a time-consuming, costly, and technically challenging process, it is not widely used.⁴ Compared with smaller platelets, larger platelets contain dense granules, express more adhesion receptors, and induce higher thrombotic activity, which can reflect the degree of platelet activation.⁵ Mean platelet volume (MPV) is a major parameter of platelet size that has been proposed as an indicator of platelet reactivity and is routinely determined by complete count analyzers at a relatively low cost.⁶ Increased MPV levels have been reported to be associated with CAD, myocardial infarction, peripheral arterial disease, cerebrovascular disease, and poor outcome.⁷

Exercise-based cardiac rehabilitation (CR) is a comprehensive intervention that includes medically supervised exercise training, risk factor management, patient education, and psychosocial counseling.⁸ CR has been proven effective in improving exertional ischemic symptoms, exercise tolerance, and coronary risk factors in patients with CAD. Also, it was shown to also reduce all-cause and CV mortality in 20% to 32% among patients with CAD.⁹

Studies on the effects of exercise on platelet activation have yielded conflicting results.² The purpose of this study was to determine the effect of an exercise-based CR program on MPV in patients with stable CAD.

The study population (300 patients) was divided into two groups according to their ingression in the CR program. Two hundred three patients participated in the CR program (CR group), and 97 patients did not (non-CR group). Demographic and clinical characteristics, as well as laboratory findings of the population, as listed in Table 1 . History of acute coronary syndrome, CABG, and PCI was similar in both groups ( Table 1 ).

Table 1

Variables	non-CR group (n=97)	CR group (n=203)	p value
Age (year)	57.9±7.4	56.2±7.8	0.072
Gender (Male %)	74(76.3%)	159(78.3%)	0.399
Hypertension (n, %)	82(84.5%)	184(90.6%)	0.088
Diabetes mellitus (n, %)	20(20.6%)	55(27.1%)	0.142
Current smoker (n, %)	11(11.3%)	27(13.3%)	0.391
BMI (kg/m2)	28.2±3.1	28.3±3.9	0.885
PCI history (n, %)	61(62.9%)	117(57.6%)	0.230
ACS history (n, %)	28(28.9%)	50(24.6%)	0.259
CABG history (n, %)	19(19.6%)	37(18.2%)	0.446
LVEF %	57.1±5.3	58.3±5.6	0.086
CAD severity
1 vessel	35(36.1%)	89(44.1%)
2 vessels	58(59.8%)	98(48.5%)
>2 vessels	4(4.1%)	15(7.4%)	0.155
Gensini Score	54.1±28	50.1±28.2	0.266
ASA (n, %)	95(97.9%)	200(98.5%)	0.745
P2Y12 inhibitors (n, %)	60(61.5%)	115(56.6%)	0.493
Beta-blockers (n, %)	82(84.5%)	158(77.8%)	0.113
Calcium-channel-blockers (n, %)	42(43.3%)	91(44.8%)	0.451
RAAS inhibitors (n, %)	80(82.5%)	165(81.3%)	0.469
Statin (n, %)	92(94.8%)	197(97.5%)	0.377
Fasting plasma glucose (pre) (mg/dL)	102.6±27.1	106.2±33.7	0.307
Creatinine (pre) (mg/dl)	0.9±0.21	0.87±0.21	0.374
Hemoglobin (pre) (g/dL)	13.4±1.02	13.6±1.07	0.135
MPV (pre)	8.7±0.98	9.1±1.02	0.010
MPV (post)	8.6±0.98	7.9±0.82	<0.001
ΔMPV*	-0.10 (-2.00-0.00)	-1.10(-1.40-[-0.90])	<0.001*
ΔMPV %*	-1.15 (-2.37-0.00)	-12.63(-14.46-[-10.11])	<0.001*
ΔLDL-c (mg/dL)*	-2.00 (-1.00-0.00)	-20.00 (-36.00-[-10.00])	<0.001*
ΔTG (mg/dL)*	-9.00 (-10.50-[-1.00])	-21.00 (-49.00-[-10.00])	<0.001*
ΔHDL-c (mg/dL)*	1.00 (0.00-1.00)	4.00 (3.00-6.00)	<0.001*
ΔWBC (103/µ3)*	0.10 (-0.25-0.30)	-0.70(-1.20-[-0.35])	<0.001*
ΔNeutrophil (103/µ3) *	-0.10 (-0.50-0.03)	-0.80 (-1.50-[-0.39])	<0.001*
ΔCRP (mg/dL) *	-0.10 (-0.10-0.10)	-0.80 (-1.80-[-0.40])	<0.001*

Data are presented as mean ± standard deviation or number of patients and percentage of patients. CR: cardiac rehabilitation; Δ: delta; BMI: body mass index; PCI: percutaneous coronary intervention; ACS; acute coronary syndrome; CABG: coronary artery bypass graft; LVEF: left ventricular ejection fraction; CAD: coronary artery disease; ASA: acetylsalicylic acid; RAAS: rennin-angiotensin-aldosterone; MPV: mean platelet volume; LDL: low density lipoprotein; TG: Triglycerides; HDL: high density lipoprotein; WBC: white blood cell; CRP: C-reactive protein; pre: before CR. *Comparison by Mann-Whitney U test at p<0.05. Values were described as medians with inter-quartile range (25^th and 75^th percentile).

The decrease in MPV was greater in the CR group than in the non-CR group [((-1.10(-1.40-(-0.90)) vs. (-0.10 (-2.00-0.00)) vs.; p<0.001, Table 1 ]. The correlation between ΔMPV and variables is shown in Table 2 . As shown in Figure 1 , the ΔMPV had a strong positive correlation with CR (r = 0.750, p < 0.001).

Table 2

	ΔMPV
	r	p value
Δneutrophil	0.326	<0.001
ΔLDL-c	0.478	<0.001
ΔWBC	0.412	<0.001
ΔCRP	0.572	<0.001
ΔTG	0.439	<0.001
LVEF	-0.133	0.021
hemoglobin (pre)	-0.139	0.019
fasting plasma glucose (pre)	-0.129	0.026
ΔHDL-c	-0.537	<0.001
CR	0.750	<0.001
age	0.034	0.563
BMI	-0.022	0.727

Δ: delta; MPV: mean platelet volume; LDL: low density lipoprotein; TG: Triglycerides; LVEF: left ventricular ejection fraction; HDL: high density lipoprotein; WBC: white blood cell; CRP: C-reactive protein; CR: cardiac rehabilitation; BMI: body mass index; pre: before CR.

Figure 1

This study showed that exercise-based CR has a strong relationship with MPV reduction in patients with CAD.

Studies on the effect of exercise on platelet activation have yielded conflicting results so far. In agreement with our study, Yazıcıet al.⁷ reported that a lifestyle change that includes at least 180 minutes/week of moderate-intensity physical activities decreased MPV in pre-hypertensive patients. Also, Rauramaa et al.¹² showed that low to moderate intensity exercise training was associated with diminished platelet aggregation. Contrary to these results, it was shown that exercise stress test increased MPV in patients with CAD.^{11 , 13} Also, it has been shown that graded resistance exercises increase MPV.^{12 , 14}

Exercise training can bring beneficial effects on platelets via different mechanisms. With exercise training, the pulsatile flow in the aorta increases, and this might induce an acute release and upregulation of nitric oxide (NO), which is a potent mediator of antiplatelet effects and suppression of platelet reactivity.^{7 , 15} It is known that CR increases HDL cholesterol, which can stimulate platelet production and thereby decrease platelet activation.⁹ In our study, ΔHDL-cholesterol was found to be independently correlated with a decrease in MPV.

MPV has been recognized as an inflammatory marker in cardiovascular, cerebrovascular, rheumatologic, and gastroenterological diseases.¹⁶ Recently, it was shown that the presence of activated megakaryocytes in bone marrow correlates with increased circulating levels of IL-6 in patients with atherosclerosis.¹⁷ Previous research provided evidence that a physically active lifestyle is associated with lower whole-body inflammatory biomarkers, and the anti-inflammatory actions of chronic exercise training are evident after as little as 2 to 12 weeks of supervised exercise training.¹⁸ In our study, we demonstrated that ΔCRP was one of the independent predictors of ΔMPV. Reduction in MPV after CR might be explained by the anti-inflammatory effect of exercise-based CR programs.

The contradictions in the results of studies can be explained by various aspects of exercise affecting platelet functions such as different exercise intensity, duration, and various fitness levels of the subjects.⁷ Acute intense exercise is proven to increase plasma pro-inflammatory cytokines.¹⁸ MPV can reflect the changes in platelet stimulation and the rate of platelet production level.¹³ An increase in MPV after exercise may be attributed to the fresh release of young large platelets, particularly from the splenic pool, into the circulation.⁷ In this study, we implemented the CR program five days per week for a total of six weeks with a gradually increasing density, according to the individual’s exercise capacity.

Atherosclerosis itself can stimulate bone marrow megakaryocytes, which was shown to be associated with acute coronary syndrome, by causing circulating platelet consumption during athereogenesis.^{17 - 19} One of the mechanisms of exercise-based CR potentially involved in the reduction of infarction and re-infarction may be related with reduction of MPV.^{9 , 20}

Reticulated platelets are larger and possibly more active than non-reticulated platelets.¹ Moreover, reticulated or large platelets exhibit increased reactivity despite anti-platelet therapy.^{21 , 22} Since it has been shown that high MPV is an independent risk factor for future myocardial infarction (MI) and recurrent MI, being associated with acute coronary syndrome or cardiovascular risk factors,^{1 , 19 , 23} the questioning on how to decrease MPV has already been raised.^{17 , 23} Although it was previously shown that statin treatment decreases MPV,²¹ in our study most of the patients were already on statins, so we showed the additive effect of CR on MPV reduction.

This study showed that exercise-based CR has a strong relationship with MPV reduction in patients with CAD. We consider that decreased platelet activation with exercise-based CR might play an important role in reducing thrombotic risk in patients with stable CAD.