Heart rate variability and hematological parameters in pregnant women

Abstract Background There are few researches on hematological parameters (hemoglobin, red cell distribution width [RDW], white blood cells [WBCs], mean platelets volume [MPV], and heart rate variability [HRV]). There are no published data on this concept (HRV and hematological parameters) during pregnancy. Methods A cross‐sectional study was conducted at Saad Abul Ela hospital in Khartoum, Sudan during the period of July to August 2018. Pregnant women with singleton, a live baby, were enrolled in this study. Clinical history and examination were performed. HRV (autonomic modulation) was assessed using time and frequency domain HRV indices. Results One hundred and five pregnant women were enrolled. The median (quartile) of the age, parity, and gestational age was 30.0 (25.0‐35.0) years, 1.0 (0‐3.0), and 38.0 (32.0‐39.0) weeks, respectively. While there were positive correlations between hemoglobin and low frequency (LF), RDW and high frequency (HF), WBCs and HF Norm, WBCs and LF/HF, MPV and HF Norm, LF Norm and LF/HF, there was no significant correlation between the hematological (hemoglobin, WBCs, RDW, and MPV) and HRV parameters. Linear regression analysis showed no significant association between age, parity, gestational age, body mass index, hemoglobin, RDW, and HRV variables. The Log10 WBCs were negatively associated with Log10 HF (ms2/Hz). MPV was positively associated with LF Norm and negatively associated with HF Norm. Conclusion The study failed to show significant associations between age, parity, gestational age, hemoglobin, RDW, and HRV variables. The WBCs were negatively associated with HF. MPV was positively associated with LF Norm, and it was negatively associated with HF Norm.


| INTRODUC TI ON
Heart rate variability (HRV) is an informative tool in assessing cardiac autonomic modulations; it has a prognostic value in cardiac diseases, and it is widely used to assess the impact of autonomic imbalance on various diseases such as type 2 diabetes mellitus and obesity, 1,2 coronary heart disease, 3 and inflammatory conditions. 4 Previous studies have shown altered sympathovagal balance (autonomic modulations) during pregnancy and labor. [5][6][7][8][9] There are previous publications of blood parameters, for example, hemoglobin, 10 iron deficiency anemia (IDA), 11 red cell distribution width (RDW), 12 mean platelets volume (MPV), 13 folate and vitamin B 12 deficiencies, 14 and white blood cells (WBCs). 15,16 However, there are no published data on this concept (HRV and hematological parameters) during pregnancy. Previously, performing complete blood count (CBC) was a hectic procedure and its results might not be accurate; however, now, CBC can be performed using the automated procedures within few minutes and reasonable cost. 17 We have recently observed a high level of anemia (57.7%), an IDA (12.1%) folate and vitamin B 12 deficiency among pregnant Sudanese women. 18,19 Moreover, we reported different HRV and autonomic modulations in pregnant Sudanese women. 20,21 The current study was conducted to investigate the associations between HRV, autonomic modulations, and hematological parameters (hemoglobin, WBCs, RDW, and MPV) in normal pregnant Sudanese women.

| ME THODS
A cross-sectional study was conducted at Saad Abul Ela tertiary maternity hospital in Khartoum, Sudan during the period of July -August 2018.
An inclusion criterion was any Sudanese pregnant women with singleton, a live baby. Participants who were in labor had any disease, such as hypertension, diabetes, heart disease or any other medical condition complicating pregnancy, or taking any medication (except supplements) were excluded.
After signing an informed consent form each woman, all the women were examined and personal, medical, and obstetrics history were taken. Then, weight and height measurements were taken, and body mass index (BMI) was computed using the equation The details of the HRV recordings were mentioned in our previous work. 20,21 In summary, after taking a complete bed rest for 10 minutes, systolic and diastolic blood pressures were recorded using sphygmomanometer. Then, a 5 minutes HRV recording was obtained using biocom 3000 recorder (heart rhythm scanner-version 2.0-biocom technologies) as recently described. 2 HRV and the autonomic modulation of the heart were examined using both time and frequency domains analysis. HRV parameters include the following: the NN intervals (SDNN), the square root of the mean squared differences of successive NN intervals (RMSSD), total power (TP), very low frequency (VLF), low frequency (LF), and high frequency (HF). Meanwhile, the sympathetic and parasympathetic autonomic modulations were evaluated via normalized low frequency (LF Norm) and high frequency (HF Norm),

respectively.
Because HRV has a circadian rhythm, 22 all measurements of HRV were done in the morning between 8 and 12 AM Then, 2 mL of blood was withdrawn from every participant in an ethylene diamine tetra acetic acid and analyzed for a complete blood count using an automated hematology analyzer and following the manufacturers' instructions (Sysmex KX-21) previously described. 17,23 Guided by Bujang and Baharum findings, 24 a sample size of 105 pregnant women was calculated to give the significant minimum difference in the correlations (r = .27) between HRV and hematological parameters. The calculated sample size was set to give the study 80% power and a difference of 5% at α = .05.

| Statistics
Data were entered in computer using SPSS (version 20.0) software (SPSS Inc). The Shapiro-Wilk test was used to assess if the continuous variables were normally distributed. Mean (SD) and median (interquartile) were used to express the normally and non-normally distributed, respectively. Data (hematological and HRV parameters) which were not normally distributed were log-transformed to allow using the parametric statistical tests. The Pearson's correlation coefficients were used to assess the associations between two continuous variables. Stepwise multivariate linear regression analyses were performed where (Log) HRV parameters (one by one) as the dependent variable and the other clinical and hematological parameters were the independent variables.
Log-transformed variables were entered when appropriate. A twosided P-value <.05 was considered statistically significant.

| RE SULTS
One hundred and five pregnant women were enrolled in the study.
The clinical and obstetrical characteristics were shown in Table 1.
The median (quartile) of the age, parity, and gestational age was 30 Table 2.

| D ISCUSS I ON
Our results showed a significant association between HRV and WBCs (Log 10 WBCs was negatively associated with Log 10 HF). A similar finding demonstrating an association between HRV and WBCs was recently reported. 15 Independent relationships of 24-hours HRV (measured by SDNN) with WBCs were recently reported in a large population-based study. 16 WBCs which are marker for a lowgrade inflammatory process were observed to be an independent predictor of cardiovascular disease. 25 The association between HRV and WBCs could be explained by epinephrine (the main sympathetic neurotransmitter), which was reported to be negatively associated with HRV and positively associated with inflammatory parameters. 26 Moreover, previous researches reported expression of adrenoceptors on immune cells. 27,28 A medical induced sympathectomy was reported to reduce inflammatory process. 29 An anti-inflammatory process seems to be associated with vagal activity. 30 In the current study, MPV was positively associated with LF Norm and was negatively associated with HF Norm. Our finding (MPV was positively associated with LF) points to increased cardiac sympathetic modulations in association with MPV. A significant association between MPV and increased sympathetic activity was previously reported in patients with vasovagal syncope. 13 An increased MPV (which are large-sized metabolically and enzymatically more active compared with the normal-sized platelets) was associated with increased cardiovascular risk factor. 31 The reported prognostic role of increased MPV in patients with acute myocardial infarction could be explained by increased sympathetic activity and decreased HR variability. 32 Peripheral activation, splenic release of platelets, and increased thrombocytopoiesis might explain the impact of sympathetic activity on MPV. 33 High adrenaline concentration can cause changes in the shape and size of platelets through adrenoreceptor activation and thereby, influence MPV. 32 Nearly one third of platelets sequestered in the spleen through the activation of sympathetic system. 34 However, to our knowledge, there is no published work investigating the effect of increased sympathetic activity on platelet turnover during pregnancy.

VLF (ms 2 /Hz) LF(ms 2 /Hz) HF(ms 2 /Hz) LF Norm(nu) HF Norm(nu) LF/ HF
In the current study, hemoglobin and RDW were not associated with HRV. Previous studies have reported significant associations between hemoglobin, 10 IDA, 11 RDW, 12 and HRV. To the best of our knowledge, this is first work of homological parameters and HRV.
However, the hematological values such as hemoglobin, RBC, WBCs, and platelets are expected to change due to increase plasma volume during pregnancy expansion. 35,36 Moreover, it is worth to be mentioned that HRV parameters during pregnancy are shifted toward sympathetic dominance. 5

| CON CLUS ION
The study failed to show significant associations between age, parity, gestational age, BMI, hemoglobin, RDW, and HRV variables. The WBCs negatively associated with HF. MPV was positively associated with LF Norm and negatively associated with HF Norm.

| Limitations of the study
There was no case of severe anemia in this study. Other markers for inflammation such high C-reactive protein were not investigated. HRV is a good method, but it is not the only one to the analysis of cardiovascular autonomic control. Further research taking into account the development of other approaches such as chronotropic competence indices in graded exercise testing and baroreflex sensitivity to the analysis of cardiovascular autonomic control is needed. 37,38

ACK N OWLED G M ENTS
We would like to thank the patients for participating in this study.

CO N FLI C T O F I NTE R E S T S
The authors declare that they have no competing interests.